Lipid Matters - Archive of Older Blogs - 2016

This Blog is an occasional series of notes on publications or other items dealing with lipid science that seem to be of particular interest to the editor Bill Christie. Inevitably, the selection is highly personal and subjective. In this web page, the blogs for 2016 are archived, while those for other years can be accessed from the foot of the current blog page.

December 28^th, 2016

Scottish thistle Like many of my readers, I have been enjoying a relatively lazy time over the holiday period with too much food and television and too little exercise. This web site has been largely but not entirely neglected, and I have found one open access article that those of you with an interest in the fat-soluble vitamins and vitamin A especially will want to read (Chelstowska, S. et al. Molecular basis for vitamin A uptake and storage in vertebrates. Nutrients, 8, 676 (2016); DOI).

I have also found an analysis paper of interest in that it demonstrates a separation that has always been rather difficult if not impossible, i.e., of monogalactosyl- and monoglucosyl-diacylglycerols. Advances in analytical methodology often lead to advances in other areas, so this should enable better opportunities for metabolic studies of these lipids (Shan, Y.B. et al. Lipid profiling of cyanobacteria Synechococcus sp PCC 7002 using two-dimensional liquid chromatography with quadrupole time-of-flight mass spectrometry. J. Sep. Sci., 39, 3745-3753 (2016); DOI).

December 21^st, 2016

While innumerable benefits of fatty acids to aspects of human health have been demonstrated over the years, it is also true that many studies have shown the importance of fatty acid biosynthesis for cancer cell growth and survival. Rapidly growing tissues, such as cancer cells, have a high demand for fatty acids for membrane biogenesis and as a source of energy. They are also required for the synthesis of key lipids in mitochondrial oxidation such as cardiolipin, for protein acylation and for the production of lipid mediators. In consequence, there are ongoing attempts to target the fatty acid synthase and its regulatory elements with the hope of therapeutic benefits, so far without success, in part because of uptake of these metabolites from other tissues. Another important enzyme in this context is stearoyl-CoA desaturase, which introduces a double bond with formation of oleate. A fascinating new review, which happily is open access, describes all these factors together with the opportunities for influencing them by pharmaceutical intervention (Röhrig, F. and Schulze, A. The multifaceted roles of fatty acid synthesis in cancer. Nature Rev. Cancer, 16, 732-749 (2016); DOI).

The fertility regulator in the UK has decided to allow the birth of babies from embryos modified to contain the DNA of three people in “certain, specific cases” making us the first country to explicitly permit the therapy. Their press statement says “Today’s historic decision means that parents at very high risk of having a child with a life-threatening mitochondrial disease may soon have the chance of a healthy, genetically related child. This is life-changing for those families.” I hope that we will never again see a brave boy suffering from the debilitating symptoms of Barth syndrome or a girl worrying that she may be a carrier.

I wish all my readers a very happy Christmas and a healthy and happy New Year.

December 14^th, 2016

The November issue of the journal Biochimie (Volume 130, Pages 1-194) is devoted to the topic of 'Lipidomics and Functional Lipid Biology' and is edited by Hubert Schaller and Nicolas Vitale. There is a good mix of review articles including some on analysis, sphingolipids and many more. Having recommended a lipidomics review that dealt primarily with animal lipids last week, I must now redress the balance by citing a comparable review on the subject of plant lipids (Tenenboim, H. et al. Using lipidomics for expanding the knowledge on lipid metabolism in plants. Biochimie, 130, 91-96 (2016); DOI).

All lipids are subject to autoxidation, although as they tend to lack polyunsaturated fatty acid constituents I would not have expected this to be a serious problem. A quick perusal of my personal data base of references to analytical methodology picked up five publications only on the subject over the last 15 years. What caused me to look was a new paper on the oxidation of gangliosides, which drew my attention to the fact that carbohydrate moieties are also susceptible to oxidation (Couto, D. et al. New insights on non-enzymatic oxidation of ganglioside GM1 using mass spectrometry. J. Am. Soc. Mass Spectrom., 27, 1965-1978 (2016); DOI). The authors found that the ganglioside GM1 underwent oxidative cleavages in the carbohydrate chain with formation of other gangliosides GM2, GM3, asialo-gangliosides, smaller glycolipids and various oxygenated gangliosides and ceramides. These products could contribute to an imbalance of gangliosides metabolism in vivo and play some role in neurodegenerative processes.

The Cyberlipid website is a wonderful source of information on lipid structures, biochemistry and functions, which I check regularly when updating these pages, or which I simply browse through from time to time for my own satisfaction. This week I came across a record of a lipid class that was new to me at least although it has been known to others for more than 30 years - Lipo-chitooligosaccharides or nodulation factors (Nod factors), i.e., a class of signalling molecules produced by rhizobia that are essential for establishment of the nitrogen-fixing root nodule symbiosis with legume plants. In brief, they consist of a carbohydrate backbone with an amide linkage from glucosamine to an unusual fatty acid, such as 2E,9Z-hexadecadienoate. Suffice it to say, that it encouraged me to find a recent review and to add a few paragraphs on the subject in the Lipid Essentials section of this web site here.. While they should be classified as lipopolysaccharides, I have been unable to find them listed anywhere under this heading.

December 7^th, 2016

There is a strong body of evidence, some derived from lipid studies, that during evolution the mitochondria in eukaryotes originated by symbiosis with a prokaryotic organism. For example, cardiolipin is found almost exclusively in certain membranes of bacteria (plasma membrane and hydrogenosomes), a few species of Archaea (haloarchaea) and mitochondria of eukaryotes, i.e., those membranes whose function is to generate an electrochemical potential for substrate transport and ATP synthesis. Further evidence comes from the findings that mitochondria in animals, including humans, and in yeasts contain type II fatty acid synthases, related to those in prokaryotes and entirely distinct from those of type I found in the cytoplasm. Indeed, the components of this enzyme, such as malonyl-CoA:ACP transferase, β-ketoacyl synthase and 2-enoyl-ACP reductase, were first identified by their similarity to the corresponding bacterial and yeast proteins and can be regarded as orthologs. A new review discusses the properties and function of this mitochondrial enzyme, which is known to be essential for cellular respiration and mitochondrial biogenesis and may be involved in many aspects of the coordination of intermediary metabolism in eukaryotic cells (Kastaniotis, A.J. et al. Mitochondrial fatty acid synthesis, fatty acids and mitochondrial physiology. Biochim. Biophys. Acta, 1862, 39-48 (2017); DOI).

This article is part of a Special Issue of the journal Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids (Volume 1862, Issue 1, January 2017), which is entitled "Lipids of Mitochondria" (edited by Guenther Daum) and includes a number of other fascinating reviews.

As an armchair scientist, I find it hard to keep up with the modern mass spectrometric techniques that are applied to lipidomics. Puzzling new acronyms for variations in the methods seem to appear every month. There has been no shortage of reviews on this subject in the current year, but it is impossible to read them all. What can I recommend then? I like a new review from Xianlin Han, the co-author of the most recent edition of my book 'Lipid Analysis'. It is well written, authoritative, up-to-date and has a useful glossary to remind me of the definitions of many of the technical terms. I was intrigued to learn that the methodology is now sufficiently sensitive to analyse the lipids of single cells - it seems that the main problem now is how to handle single cells! (Yang, K. and Han, X. Lipidomics: techniques, applications, and outcomes related to biomedical sciences. Trends Biochem. Sci., 41, 954-969 (2016); DOI).

November 30^th, 2016

Scottish thistle Chiral chromatography has long been recognized as an invaluable tool for the isolation and characterization of eicosanoids and related oxylipins. It has also been used to separate chiral di- and monoacyl-sn-glycerol derivatives produced as part of procedures for stereospecific analysis of triacyl-sn-glycerols. However, applications to intact lipids are relatively scarce. A new publication demonstrates some remarkable separations of triacyl-sn-glycerols containing polyunsaturated fatty acids, including synthetic standards and natural algal samples (Rezanka, T. et al. Enantiomeric separation of triacylglycerols containing polyunsaturated fatty acids with 18 carbon atoms. J. Chromatogr. A, 1467, 261-269 (2016); DOI).

A second new paper demonstrates separations of intact phosphatidylcholines containing chiral hydroperoxides derived from linoleate that are just as notable. If these are formed by autoxidation, two enantiomers are formed in equal amounts, which can now be resolved by chiral chromatography, but if they are formed enzymatically, only a single enantiomer is seen. It is therefore possible to distinguish between enzymatic and auto-oxidation (Ito, J. et al. A novel chiral stationary phase HPLC-MS/MS method to discriminate between enzymatic oxidation and auto-oxidation of phosphatidylcholine. Anal. Bioanal. Chem., 408, 7785-7793 (2016); DOI). As it now appears that phospholipids containing oxylipins may have some biological activity in their own right, I can foresee further useful applications of this methodology.

November 23^rd, 2016

The must-read publication of the week is happily open access and is an autobiographical account of his career and research by Professor Edward Dennis (Dennis, E.A. Liberating chiral lipid mediators, inflammatory enzymes, and LIPID MAPS from biological grease. J. Biol. Chem., 291, 24431-24448 (2016); DOI). It covers a fascinating period in lipid science, when it first became apparent that chiral lipid molecules were just as capable of encoding specific and unique biological information as other natural organic molecules. Stemming from his work on phospholipases, which release so many of the oxylipin precursors, he was among the first to recognize that lipids have a central role in cell signalling. With the creation of the LIPID MAPS initiative in 2003, he was at the forefront of establishing the importance of lipidomics to so many aspects of human metabolism. I am always fascinated by personal accounts of this kind that describe what stimulated particular research directions as well as telling a very human story.

One of the important aspects of the WOW is the ease with which articles can be updated, and I do my best to ensure that my articles in the Lipid Essentials section are kept as current as possible. I keep a simple list of my improvements to each article, and from time to time I check the literature to see whether anything of importance has been omitted. Last week I noted that only one page had not been updated at all this year, i.e., that on the glycosyldiacylglycerols of animal as opposed to plant origin. With that in mind, I did a citation search using some key references but found no new publications that were relevant to my account of the topic. For example, an important paper on the structure of the digalactosyldiacylglycerols of animal tissues from 2001 had been cited only 6 times since. A key paper on seminolipid of a similar vintage had been cited more often, but I found nothing new to explain the functional properties of this lipid at a cellular level. One problem with the analysis of neutral galactosyldiacylglycerols is that they occur at low levels in tissues relative to sphingolipids, which are often concentrated prior to analysis by a mild transesterification process that removes glycerolipids. I'll keep hoping for more.

I recently had a fascinating correspondence with someone with concerns about the use of potentially hazardous solvents in lipid analysis. There is no single solution, but increasing use of sealed instrumental methods and robotics may be one way forward. Aided by the sensitivity of modern mass spectrometric methods, another approach is to miniaturize such procedures as lipid extraction as proposed in a new publication (Panchal, S. et al. Ionic liquid based microextraction of targeted lipids from serum using UPLC-MS/MS with a chemometric approach: a pilot study. RSC Adv., 6, 91629-91640 (2016); DOI). As an arm-chair warrior these days, I cannot follow up such studies myself.

November 16^th, 2016

Three weeks ago in this blog, I discussed the bacterial isoprenoid lipid II. This molecule is probably of little interest to main-stream lipid scientists, but its biosynthesis is considered a potential target for the development of novel antibiotics. I make no claims to clairvoyance, but a new publication demonstrates that this is indeed a realistic possibility (Cochrane, S.A. et al. Antimicrobial lipopeptide tridecaptin A₁ selectively binds to Gram-negative lipid II. Proc. Natl. Acad. Sci. USA, 113, 11561-11566 (2016); DOI). The tridecaptins, isolated from strains of Paenbacillus polymyxa, are linear cationic tridecapeptides with a combination of L- and D-amino acids that are acylated with β-hydroxy fatty acids. They show strong activity against Gram-negative bacteria, exerting their bactericidal effect by binding to the cell-wall precursor lipid II on the inner membrane, disrupting the proton motive force. As their toxicity is relatively low and preliminary experiments show that bacteria do not appear to develop resistance, they are considered strong candidates for therapeutic use.

The open access journal Nature Communications has recently published two papers of particular interest to lipid scientists. In the first, N-docosahexaenoylethanolamide or 'synaptamide' has been found to have its own receptor, i.e., the orphan G-protein-coupled receptor GPR110 (ADGRF1). It binds specifically to this and triggers cAMP production and signalling with low nM potency, with the effect of inducing neurogenesis, neuritogenesis and synaptogenesis in developing neurons. It is a further mechanism by which DHA promotes brain development and function (Lee, J.W. et al. Orphan GPR110 (ADGRF1) targeted by N-docosahexaenoylethanolamine in development of neurons and cognitive function. Nature Commun., 7, 13123 (2016); DOI). It is intriguing how this and the arachidonoyl, palmitoyl, oleoyl and stearoyl ethanolamides have such diverse biological functions (see our web page on simple amides). The second paper also relates to a metabolite of DHA. In relation to atherosclerotic plaques, it is reported that the deleterious effects of leukotriene LTB₄ resulting from an excessive inflammatory response are countered by the presence of specialized proresolving mediators, especially resolvin D1 (RvD1), which are derived from DHA, suggesting a new therapeutic approach to promote plaque stability (Fredman, G. et al. An imbalance between specialized pro-resolving lipid mediators and pro-inflammatory leukotrienes promotes instability of atherosclerotic plaques. Nature Commun., 7, 12859 (2016); DOI).

I have just come across a new definition - 'ectopic lipids', which appears to be another name for the lipids in the small fat droplets found in tissues other than adipocytes (Loher, H. et al. The flexibility of ectopic lipids. Int. J. Mol. Sci., 17, 9 (2016); DOI; open access).

November 9^th, 2016

In my Lipid Essentials section, I have discussed the effects of oxidized phospholipids in a number of different web pages. For example, the oxidatively truncated phospholipids are treated under platelet-activating factor, while others are dealt with under the headings Isoprostanes and Bioactive aldehydes. However, it can be useful to see the various aspects of the biochemistry of these important lipid molecules, which can have pro- or anti-inflammatory activities depending on their chemical structures and cellular location, reviewed together in a single coherent account. A recent review that is open access does just that (Freigang, S. The regulation of inflammation by oxidized phospholipids. Eur. J. Immun., 46, 1818-1825 (2016); DOI).

Last week, I discussed the potential therapeutic importance of synthetic lipids such as edelfosine. I have just encountered a review describing how it may function in lipid rafts, i.e., highly ordered membrane domains that are enriched in cholesterol and sphingolipids and act as sorting platforms for molecules involved in signal transduction. Among other aspects, it is suggested that "edelfosine shows a high affinity for cholesterol and accumulates in lipid rafts in a number of malignant hematological cells, leading to an efficient in vitro and in vivo antitumor activity by inducing translocation of death receptors and downstream signaling molecules to these membrane domains." This may be a mechanism for its anti-cancer activities (Mollinedo, F. and Gajate, C. Lipid rafts as major platforms for signaling regulation in cancer. Adv. Biol. Reg., 57, 130-146(2015); DOI).

November 2^nd, 2016

I have changed the title of this website from "LipidHome" to the "LipidWeb", as unfortunately the name "LipidHome" was already in use for a lipidomics software package. My aim in setting up this site was to demonstrate to AOCS how easy it was to change the structure of a website in a relatively short period - three weeks in fact. It was intended simply as a demonstration as AOCS had already spend two years, consultant costs and a huge amount of staff time to redesign the Lipid Library with no end in sight. I checked that the URL was available but did not check sufficiently for any other uses of my chosen title. As this site was not originally intended to last, this did not bother me to begin with. However, it now seems likely that the "LipidWeb" is going to last as long as I do - hopefully a few years yet. Hence the change of name. Unfortunately, changing the URL of the site is much more difficult, so I plan to leave it as it is for the moment. My sincere apologies to the original users of "Lipidhome".

In these pages, I tend to concentrate on naturally occurring lipids, their occurrence, chemistry, biochemistry and especially - function. However, there are occasons when natural lipids have inspired the design of synthetic compounds with valuable therapeutic properties so cannot be ignored. One such is 'edelfosine' (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine) illustrated, which has obvious structural similarities to platelet activating factor. Other related molecules have the glycerol ether moiety attached to a carbohydrate, such as 'ohmline' (1-O-hexadecyl-2-O-methyl-rac-glycero-3β-lactose). These are proving to have valuable anti-cancer properties "that target cell membranes to induce apoptosis and to decrease cell migration/invasion, leading to the inhibition of tumor and metastasis development". Unfortunately, edelfosine per se seems to be too toxic for use in humans, but the new carbohydrate-containing analogues do not appear to have such problems. A new review discusses their potential clinical applications to prevent or treat tumor development and metastasis (Jaffres, P.A. et al. Alkyl ether lipids, ion channels and lipid raft reorganization in cancer therapy. Pharm. Ther., 165, 114-131 (2016); DOI).

Formula of edelfosine

I have been writing this blog here and in the AOCS LipidLibrary for more than 10 years, and I have highlighted the plight of young researchers on many occasions. A new article in Nature News seems like deja vu - Young, talented and fed-up: scientists tell their stories. Why is nothing done about it? I suspect that Nature will be carrying similar stories 10 years from now.

October 26^th, 2016

Scottish thistle Few lipid scientists, other than those concerned with microbial lipids, will have heard of lipid II or undecaprenyl diphosphate-MurNAc-pentapeptide-GlcNAc; it is more liked to be discussed in text books dealing with carbohydrates or proteins than with lipids. Yet, it is the last significant lipid intermediate in the construction of the peptidoglycan cell wall in bacteria with the important function of transferring the MurNAc-pentapeptide-GlcNAc monomer across the cell wall to form the complex peptidoglycan polymer that provides strength and shape to bacteria. The turnover rate is very high so the lipid II cycle is considered to be the rate-limiting step in peptidoglycan biosynthesis. Because of its highly conserved structure and accessibility on the surface membrane, synthesis and transport of lipid II is an important target for the development of novel antibiotics. As a new review points out, appreciable progress is being made towards this goal (Ng, V. and Chan, W.C. New found hope for antibiotic discovery: lipid II inhibitors. Chem. Eur. J., 22, 12606-12616 (2016); DOI).

It was rather unexpected to find a publication describing a completely new mechanism for targeting otherwise soluble proteins to membranes. Bacteria of the genus Mycoplasma are already unusual in that they have a very small genome, they lack a cell wall and they are obligate parasites that must obtain all their lipids from the host. Now, it has been demonstrated that in M. pulmonis an otherwise cytoplasmic protein, lacking signal peptides, is tethered to the outer membrane by a link from glutamine near the C-terminus of the protein to rhamnose and thence to a phospholipid, presumed for the moment to be phosphatidic acid. Whether other bacteria have a similar mechanism has yet to be determined (Daubenspeck, J.M. Rhamnose links moonlighting proteins to membrane phospholipid in Mycoplasmas. PLOS One, 11, e0162505 (2016); DOI; open access).

October 19^th, 2016

Two years ago, I discussed here a fascinating finding that fatty acids with a centrally located hydroxyl group to which a further fatty acid was linked as an estolide or 'FAHFA' (Fatty Acid Hydroxy Fatty Acid), such as the palmitoyl ester of 9-hydroxy-stearic acid, had been found in the adipose tissue of mice. They were reported to have anti-diabetic and anti-inflammatory effects, even when administered orally. Now, a new publication from the same group describes how branched fatty acid esters of hydroxy fatty acids protect against colitis by regulating gut innate and adaptive immune responses (Lee, J. et al. J. Biol. Chem., 291, 22207-22217 (2016); DOI). While it appears that little is yet known of their biosynthesis, it has been established that they are produced endogenously. Whatever their origin, they are an important addition to the range of lipids with therapeutic potential.

I have been enjoying the Thematic Review Series: Living History of Lipids, which is being published at intervals in the Journal of Lipid Research. The latest installment dealing with lipoproteins is no exception (Siri-Tarino, P.W. and Krauss, R.M. The early years of lipoprotein research: from discovery to clinical application. J. Lipid Res., 57, 1771-1777 (2016); DOI). Amongst other fascinating personal insights, it seems that after obtaining a medical degree John Gofman (together with his first graduate student Frank Lindgren, who I recall meeting 50 years ago) called upon his war-time experience of uranium isotope characterization to use ultracentrifuges for the first successful separation of serum lipoprotein classes. Their first publication on the subject was at first rejected summarily by the Journal of Biological Chemistry, before being accepted on appeal.

I have finally obtained a copy of the book by Gurr et al., mentioned in my last blog, via Amazon. I must say that it is superbly produced and the senior author must be congratulated on producing such a vital and uniform text from the contributions of multiple authors. So far, I have only dipped into it, but sufficiently for me to make some minor adjustments to some of my pages here already. Over the next few weeks, I expect to spend some time with it partly to check the accuracy of my own work, but mainly because it is always of interest to see how others with very different backgrounds approach the subject of lipid science.

October 12^th, 2016

For the last week, I have been relaxing and enjoying the sunshine of the Canary Islands. No doubt the world of lipids is continuing to turn, and I hope soon to catch up with it. On my return from holiday, I found an email informing me that a long awaited book "Lipids: Biochemistry, Biotechnology and Health, 6^th Edition" (by Michael I. Gurr, John L. Harwood, Keith N. Frayn, Denis J. Murphy and Robert H. Michell, ISBN: 978-1-118-50113-9, 448 pages, Wiley-Blackwell) is now available. I ordered a digital copy initially - my small contribution to saving the planet - but the publisher's website was so opaque and put so many impediments in my way that I will have to settle for the paper edition.

October 5^th, 2016

From time to time, I come across a review publication that contains fascinating data on lipid functionality, although I am not clear how I can easily relate these to the documents in my Lipid Essential pages here. One such deals with CD1 molecules, i.e., a family of antigen-presenting glycosylated proteins that bind structurally diverse lipids and lipopeptides for the immune interaction with T cells (Zajonc, D.M. The CD1 family: serving lipid antigens to T cells since the Mesozoic era. Immunogenetics, 68, 561-576 (2016); DOI). These proteins exist in a large number of isoforms in which the shape and volume of the lipid binding groove can vary to suit different lipid antigens and how the CD1-lipid complexes are recognized by antigen receptors on T cells. The lipid antigens are often glycolipids of various kinds where the nature of the head group is of particular relevance. However, it also appears that the binding pocket can confer specificity according to the nature of the acyl groups, as monoacylated lipids or lipopeptides to tetra-acylated lipids are recognized with variable chain lengths and alkyl chain substitutions (double bonds, methylation, hydroxylation, cyclization). In part, this may explain the importance of particular molecular species of lipids.

In a visit to my local garden centre, I found that they already had set out a large Christmas display. It is not quite the same but as another sign of the times in my monthly literature survey, I have already one publication listed for 2017! Of course, this is due to online publication now, but presumably the relevant journal will not be sent out in print form until next year.

September 28^th, 2016

Scottish thistle Nature News section has just published an article under the heading "Mass production of review articles is cause for concern", suggesting that "a torrent of low-quality meta-analyses and systematic reviews in biomedicine might be hiding valuable research and misleading scientists - that much of the overall increase stems from articles intended mainly to increase citations and publications - or to serve as marketing tools for industry groups". Nowadays, I do not consider myself a specialist in any one area, but rather as a populariser of most aspects of lipid science or as a generalist. There is absolutely no way that I can keep abreast of the primary literature in such a wide field, so I am dependent on review articles to update these web pages. On the other hand, I have indeed had a vague sense that I was seeing a large number of reviews on similar topics, and to test this I have quickly checked the data base behind my literature survey pages for the Lipid Essentials section of this web site for the year 2015. I found 31 reviews on phosphoinositides, 5 on endocannabinoids, 11 on lysophospholipids, 15 on sphingosine-1-phosphate and 8 on ceramides. These are all dynamic areas, but 31 in one subject area does seem a bit excessive, even if this does encompass phosphatidylphosphoinositides, the water-soluble inositol phosphates, GPI-anchors for proteins, and animals versus plant metabolites (in fairness, there was a special journal issue on the topic that boosts the numbers). So far this year, there are a further 22 in this one area! The next problem is to decide which are the most useful, and I must have taken such a decision as I have cited just 7 of these in my document on phosphoinositides here - please don't ask why these and not any of the remaining 46.

That said, I am now going to recommend that you check out a new review - on phosphoinositides! This is now available ahead of formal publication in manuscript form and therefore open access (Irvine, R.F. A short history of inositol lipids. J. Lipid Res., in press; DOI). I find the history of such scientific topics both illuminating and entertaining, especially as I have lived and worked through the period without always recognizing the key milestones. The author's personal insights concerning the many scientists involved add greatly to the story.

My attention has been drawn to a new web site produced by John Ohlrogge of Michigan State University (USA), apparently as a post-retirement project: PhyloFAdb - "phylogenetic relationships between hundreds of fatty acids synthesized by thousands of plants". It contains a vast amount of data that will prove invaluable to all those with an interest in plant lipids. The data are easy to access via an elegant interface.

September 21^st, 2016

Marine invertebrates contain a wide range of prostaglandins of the conventional type in addition to many novel prostanoids that differ in stereochemistry from the typical forms, or contain acetyl groups, or are substituted with halogen atoms, such as chlorine or bromine. They are presumed to perform similar functions as in mammals, but why should one species of coral (Plexaura homomalla) contains up to 8% of its dry mass as prostanoid esters? (For many years, this was a primary source of material for experimental work). It is perhaps more surprising that some red algae, better known as seaweeds, such as Gracilaria species contain prostaglandins (PGE₂ and PGF_2α) and are known to have a cyclooxygenase gene, although the function of these oxylipins in the organisms is unknown. As far as I am aware this is the only source of prostanoids from outwith the animal kingdom.

I was interested to see a new study of the molecular species composition of the glycerolipids from one species of this genus, i.e., mono- and digalactosyldiacylglycerols, sulfoquinovosyldiacylglycerol and phosphatidylcholine. The content of arachidonic acid in each lipid is remarkably high - up to 64%, so the source of the precursor to the prostaglandins is explained if not their function (Honda, M. Lipid classes, fatty acid composition, and glycerolipid molecular species of the red alga Gracilaria vermiculophylla, a prostaglandin-producing seaweed. J. Oleo Sci., 65, 723-732 (2016); DOI; open access). I suppose the best guess is that they operate in a similar manner to jasmonates in higher plants.

Monoenoic fatty acids with double bonds in even numbered positions are relatively rare in nature, with petroselinic acid (6-18:1) from seed oils of the Umbelliferae family and sapienic acid (6-16:1) from sebum being the obvious exceptions. A correspondent has now drawn my attention to the fact that 10-18:1 and 8-16:1 are considered specific for methane-oxidizing bacteria.

September 14^th, 2016

A recent issue of the European Journal of Pharmacology (Volume 785, Pages 1-214, 15 August 2016) is devoted to the topic of "Immunopharmacology of fatty acids" (guest editors Philip C. Calder and Linette Willemsen). It deals largely with the biochemistry and functions of eicosanoids and docosanoids in health and disease. So far, I have only had the opportunity to browse rapidly through the contents, but I was pleased to see that some of the less obvious oxylipins were discussed at length, including those derived from linoleate, eicosapentaenoate and docosapentaenoate in addition to the better known resolvins and protectins derived from docosahexaenoic acid. I have a lot of reading to do!

The physical chemistry of lipids in membranes is an important topic that goes into scientific realms where I am soon left far behind, and that is especially true of a recent issue of Biochimica et Biophysica Acta (BBA) - Biomembranes (Volume 1858, Issue 10, October 2016) on the topic of "Biosimulations of lipid membranes coupled to experiments". However, I did find one short gem that I can recommend to a general lipid audience that discusses the molecular complexity of natural membranes and the experimental challenges ahead, where the tools of lipidomics will be especially relevant (Simons, K. Cell membranes: A subjective perspective. Biochim. Biophys. Acta, Biomembranes, 1858, 2569-2972 (2016); DOI).

The role of glycerol in the structure of plant cutins has been unclear, but a new study involving careful quantitative analysis has demonstrated that the molar ratio of glycerol to total dicarboxylic acids (DCA) in Arabidopsis cutins is 2:1, suggesting that glycerol-DCA-glycerol is the dominant structural motif (Yang, W. et al. Quantitative analysis of glycerol in dicarboxylic acid-rich cutins provides insights into Arabidopsis cutin structure. Phytochemistry, 130, 159-169 (2016); DOI). The key methodology was a stable isotope-dilution assay for the quantitative determination of glycerol by GC-MS of triacetin, together with simultaneous determination of the aliphatic monomers

September 7^th, 2016

Further to my comment last week on links between the metabolism of sphingolipids and glycerolipids, I have been reminded that ceramide 1-phosphate (with phosphatidylinositol 4,5-bisphosphate) binds to the specific phospholipase A₂ (cPLA₂α) responsible for the hydrolysis of phosphatidylinositol to release arachidonic acid for eicosanoid production. It has stimulated me to add a new section to my web page Introduction to Sphingolipids, which I can update when new information becomes available.

Last week, the biological properties of 18:1 isomers came to the fore, and this week it is the turn of 16:1. Thus, 9-cis-hexadecenoic acid (palmitoleic acid, 9-16:1 or 16:1(n-7)) is a ubiquitous but normally minor component of animal lipids, and it has been found to have a distinctive function in mice as a lipokine - a newly coined word to define a lipid hormone, i.e., it is an adipose tissue-derived molecule, which amongst other effects stimulates the action of insulin in muscle. It is also an essential covalent modifier of Wtn proteins. Now an isomer cis-7-hexadecenoic acid (7-16:1 or 16:1(n-9)) is reported to be enriched in the lipids of foamy monocytes and to show significant anti-inflammatory activity; it may be a biomarker for early detection of cardiovascular disease (Guijas, C. et al. Foamy monocytes are enriched in cis-7-hexadecenoic fatty acid (16:1n-9), a possible biomarker for early detection of cardiovascular disease. Cell Chem. Biol., 23, 689-699 (2016); DOI). It is one of those minor fatty acids that is often ignored, overlooked or misidentified by analysts. I don't have access to this journal, but I was able to get a copy of the paper courtesy of the ResearchGate website.

Can we really consider formic acid to be truly a fatty acid, albeit the simplest of all? By some definitions, it is not even a lipid, but it is occasionally reported in esterified form in lipids. The latest is as a component of wax esters in an acarid mite (Shimizu, N. et al. Identification and synthesis of (Z,Z)-8,11-heptadecadienyl formate and (Z)-8-heptadecenyl formate: unsaturated aliphatic formates found in the unidentified astigmatid mite, Sancassania sp. Sasagawa (Acari: Acaridae). Molecules, 21, 619 (2016); DOI). The paper is open access.

August 31^st, 2016

Scottish thistle A new publication demonstrates that N-cis-vaccenoylethanolamide (i.e., of 11-18:1) is the most abundant 18:1 fatty acylethanolamide in rat plasma and the second most abundant in human plasma (Rohrig, W. et al. Identification of the oleic acid ethanolamide (OEA) isomer cis-vaccenic acid ethanolamide (VEA) as a highly abundant 18:1 fatty acid ethanolamide in blood plasma from rats and humans. Anal. Bioanal. Chem., 408, 6141-6151 (2016); DOI). Its biological properties are as yet unknown, but hopefully will soon be explored. As there has been potential for confusion in some studies with the isomeric N-oleoylethanolamide, which is well-known for its effects as an endogenous regulator of food intake, some re-appraisal of the latter may also be required.

At the end of my presentation to the Scottish Lipid Group meeting last week, a questioner asked whether I knew of any links between glycerolipid and sphingolipid metabolism, other than sphingosine kinase 2 binding to phosphoinositides (which may facilitate its location to different membranes) and the provision of phosphorylethanolamine from sphingosine-1-phosphate catabolism for phosphatidylethanolamine biosynthesis. The obvious simple answer was that phosphatidylcholine is the precursor of sphingomyelin, but I was sure that there were other examples that I could not call to mind immediately. Having had time to check, I now have been reminded that the CERT protein involved in ceramide transport has a binding site for phosphatidylinositol 4-phosphate, while the ceramide kinase responsible for the biosynthesis of ceramide-1-phosphate requires phosphatidylinositol 4,5-bisphosphate to function. Of course, if there are other examples of which I am not aware, I would be grateful for enlightenment.

Stereospecific analysis of triacyl-sn-glycerols, i.e., the determination of the fatty acid compositions of each of positions sn-1, sn-2 and sn-3 of the glycerol moiety, can be a daunting task technically. There have been relatively few publications in recent years, possibly because of the concentration on modern mass spectrometric methodology for lipid analysis. However, regiospecific analysis only is possible by this means so positions sn-1 and sn-3 cannot be distinguished. There are two general approaches to full stereospecific analysis, both starting with the generation of random diacylglycerol species from triacylglycerols. The first uses enzymatic means to generate sn-1,2-diacylphosphatides as the basis for the reaction, while the second uses some form of chiral chromatography to separate the various enantiomeric diacylglycerol species. A good example of the first approach has now been published, in which the enzyme diacylglycerol acyl transferase from E. coli is used to generate an sn-1,2-diacylglycerophosphatide. Although the method was first described some years ago, it does not appear to have been used other than by the Italian originators. As the paper is open access and the method is illustrated rather well, I am happy to publicise it here (Cossignani, L. et al. Authentication of Coffea arabica according to triacylglycerol stereospecific composition. J. Anal. Chem., 7482620 (2016); DOI).

August 24^th, 2016

Volume 199 (September 2016) of Chemistry and Physics of Lipids (pp. 1-186) is a substantial special issue dealing with "The Properties and Function of Cholesterol" (edited by Richard M. Epand and Amitabha Chattopadhyay). Much of it deals with the chemistry and physical chemistry of cholesterol in membranes, a topic which I have difficulties in digesting. However, there are two sections with a number of papers more relevant to my interests - "Cholesterol in biological membranes" and "Cholesterol and whole organism". I have only had time to read two of the papers in the latter, but I am sure they will be helpful in updating the sterol pages in my Lipid Essential section here.

It can be hard to determine when any scientific topic first became established, and this is certainly true of work on phosphoinositides. Was in the pioneering work on brain lipids by Folch in the 1940s, that of Mabel and Lowell Hokin in the 1950s, that of Bernard Agranoff in the 1960s, or that of several scientists in the 70s whose work could be cited for the discoveries on phosphoinosite signalling? Those interested in the early history of the subject will appreciate an autobiographical review published a few years ago by Agranoff (Turtles all the way: reflections on myo-inositol. J. Biol. Chem., 284, 21121-21126 (2009); DOI). Judging by the number of times I have updated my article on phosphoinositides on this site, work in this area is just as dynamic as ever. While plant scientists have lagged a little behind, they are catching up rapidly. A new paper demonstrates that phosphatidylinositol-4-phosphate is an important constituent of the plasma membrane in plant cells, where it controls the electrostatic state and is involved in cell division. It may control the location and function of many membrane proteins, including those required for development, reproduction, immunity, nutrition and signalling (Simon, M.L.A. et al. A PtdIns(4)P-driven electrostatic field controls cell membrane identity and signalling in plants. Nature Plants, 2, 16089 (2016); DOI).

August 17^th, 2016

There has been enormous interest in the biologically active fatty acid amides and lipoamino acids in recent years, especially the endocannabinoids such as anandamide. However, I have only seen a few papers dealing with the N-acyl-taurine conjugates. A new publication may lead to renewed interest (Sasso, O. et al. Endogenous N-acyl taurines regulate skin wound healing. Proc. Natl. Acad. Sci. USA, 113, E4397-E4406 (2016); DOI). Potential receptors have been identified, and as the title suggests "an unprecedented lipid-based mechanism of wound-healing control in mammalian skin, which might be targeted for chronic wound therapy", especially when consequent to aging, diabetes, and immunosuppression, has been identified. The process is controlled by the fatty acid amide hydrolase, and in mouse skin two long-chain saturated N-acyl taurines, N-tetracosanoyl-taurine and N-eicosanoyl-taurine, are the primary substrates.

Formula of acyl-taurine

Transferring the results of animal studies to a clinical situation can be fraught with difficulties, but hopefully if the treatment can be applied directly to the skin this may not be a problem with acyl taurines. Clinical interventions with other potential lipid 'drugs' have not always proved successful. In my blog of three weeks ago, I discussed recent findings that α-galactosylceramides were potent endogenous stimulators of mammalian immune systems, and this is the topic of a new open access review (Carreño, L.J. et al. Synthetic glycolipid activators of natural killer T cells as immunotherapeutic agents. Clin. Translat. Immunol., 5, e69 (2016); DOI). The aim is to use these lipids or synthetic analogues to modulate the responses of natural killer T cell to improve immunity against infections and cancer. Unfortunately, this has not yet been achieved in humans, but it is hoped that improvements to the delivery systems may be the answer.

August 10^th, 2016

Cardiolipin is a fascinating lipid for any number of reasons, but especially as a key component that binds to and activates three of the four enzymes involved in oxidative phosphorylation and the generation of ATP. It is a common constituent of bacterial membranes, but in animal tissues, it is in essence found only in mitochondria. This is often cited as confirmatory evidence for the evolutionary origin of mitochondria as bacterial cells engulfed by a eukaryotic organism. The picture was complicated relatively recently when this lipid was found in one group of the Archaea (haloarchaea). The biosynthetic mechanism differs between eukaryotes and bacteria, but this is now believed to be the result of convergent evolution. Now a publication has just come to my attention that suggests from protein domain analyses that the relevant biosynthetic enzymes in Eukarya arose by a chimeric event between the bacterial and archaeal pathways (Luévano-Martínez, L.A. The chimeric origin of the cardiolipin biosynthetic pathway in the Eukarya domain. Biochim. Biophys. Acta-Bioenergetics, 1847, 599-606 (2015); DOI).

Formula of cardiolipin

The structure is distinctive in that in essence it consists of two phosphatidic acid units linked by glycerol, i.e., it has four fatty acid components. In heart mitochondria, a high proportion of the fatty acids consists of linoleic acid so the molecule is relatively symmetrical, a feature that appears to be essential for its biological activity. This composition is attained post-synthesis largely by the action of a transacylase known as tafazzin. From a mathematical model based on the assumption that different molecular species have different free energies, it has been concluded that specific acyl-distributions in cardiolipin could arise from phospholipid transacylations in the tafazzin domain, even if tafazzin itself does not have substrate specificity. On the other hand, a new publication argues that the specificity is inherent in tafazzin per se in the model yeast Saccharomyces cerevisiae at least (Abe, M. et al. Mechanism for remodeling of the acyl chain composition of cardiolipin catalyzed by Saccharomyces cerevisiae tafazzin. J. Biol. Chem., 291, 15491-15502 (2016); DOI). Incidentally, a new study of the molecular species composition of cardiolipin in plants, shows that it contains mostly linoleic and linolenic acids (Zhou, Y.H. et al. Molecular species composition of plant cardiolipin determined by liquid chromatography mass spectrometry. J. Lipid Res., 57, 1308-1321 (2016); DOI).

August 3^rd, 2016

Those with an interest in plant lipids will want to take note of a substantial review volume - Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, Volume 1861, Issue 9, Part B, Pages 1205-1422 (September 2016) - devoted to the topic of "Plant Lipid Biology" and edited by Kent D. Chapman and Ivo Feussner. The various articles are grouped into three sections - "Lipid Synthesis and Turnover - Structural Lipids - Lipid Signalling".

I have only had a brief look at these myself so far, but I was intrigued by an article on pollen lipids (Ischebeck, T. Lipids in pollen - They are different. Biochim. Biophys. Acta, 1861, 1315-1328 (2016); DOI). To deliver the sperm cells from the stigma through the style to the ovule, a pollen tube must be produced rapidly that can be many centimeters in length and so requires vast amounts of lipid for membrane synthesis. These lipids include extraplastidial galactolipids and triacylglycerols stored in lipid droplets, together with special sterol and sphingolipid moieties that might together form raft-like domains in the membranes. Just last week, I came across another review dealing with a different aspect of lipid metabolism in pollen (Heilmann, I. and Ischebeck, T. Male functions and malfunctions: the impact of phosphoinositides on pollen development and pollen tube growth. Plant Reproduction, 29, 3-20 (2016); DOI). In this instance, the phosphoinositides have a critical regulatory function, controlling key steps in trafficking and polarization.

July 27^th, 2016

Scottish thistle It is apparent that increasing numbers of pathogenic bacteria are becoming resistant to antibiotics, and the search for replacements is a major task for the pharmaceutical industry and academia world wide. I suspect that it may become a recurring task for each generation of scientists. One area that looks promising and of relevance to lipid science is the field of antimicrobial lipopeptides. Some of these, such as the polymixins i.e., 7-membered cyclic peptides attached to a short linear peptide and thence to a fatty acid, are already being employed for the purpose. They are produced by Paenibacillus species and are effective against Gram-negative bacteria as they bind to the lipid A on the bacterial surface and render it innocuous. Unfortunately they are also somewhat toxic to humans, so can only be used for topical treatment of infections or as a last-line therapy against multi-drug-resistant Gram-negative bacilli. To counter these drawbacks, molecular biological methods and chemical synthesis are being used to create analogues with differing amino acid and fatty acid constituents as a new review explains (Velkov, T. et al. Polymyxins: a new hope in combating Gram-negative superbugs? Future Med. Chem., 8, 1017-1025 (2016); DOI - open access). So far, it appears that no new products have reached a commercial stage, but there is hope for the future.

Until relatively recently, galactosylceramides were though to possess only a β-D-galactosyl unit linked to ceramides, so it was somewhat of a surprise when epimeric α-galactosylceramides were found in a sponge and then in human gut microflora. Subsequently it was demonstrated that these were potent stimulators of mammalian immune systems by activating invariant natural killer T cells, one of the first pieces of evidence to show that glycolipids, like glycoproteins, could invoke an immune response. I have just been catching up on some elegant publications demonstrating that α-glycosylceramides are in fact produced endogenously in mammalian cells. Although they only amount to 0.02% of the total galactosylceramides, they are in fact the natural ligand for NKT cells in the thymus and the periphery (Kain, L. et al. Endogenous ligands of natural killer T cells are alpha-linked glycosylceramides. Mol. Immunol., 68, 94-97 (2015); DOI). How they are synthesised in animal tissues has still to be determined.

July 20^th, 2016

I was delighted to learn that the Lipid Maps website (www.lipidmaps.org) is to move to the UK. The Wellcome Trust is providing more than £1M over 5 years to Cardiff University, Babraham Institute and UCSD to enable the transfer from the USA and presumably for the development of the site. The level of funding should permit the employment of permanent staff to work on the site, and I hope that this means more editorial content and news as occurred during the brief period when there was an involvement with Nature. It should also be a boost to the science of lipidomics in the UK. As it stands, the site is an invaluable font of information but not one I would visit for casual browsing; I hope this will change. Of course I am not envious, but I receive no salary for this website and the running costs of £50 per annum come out of my own pocket.

Two news items in Nature caught my eye this week. First, the Wellcome Trust is to establish a new open access journal to enable grantees to publish their research more quickly and free of cost. I will not duplicate the news item here but the new journal will have a novel peer review policy. Incidentally the Wellcome Trust already insists that grantees publish in open access journals.

The second news item concerns the sale of the Web of Science to a private equity company. The fear in such circumstances is that asset stripping will occur and prices will rise, though the article suggests that there may already be a buyer in the wings, such as the Nature-Springer conglomerate. I depend on this for my monthly literature updates, so I hope that the transfer will be seamless.

Normally you will not find anything on these pages dealing with politics, although in the aftermath of the Brexit decision in the UK it is hard to avoid. Like the majority of Scots, I voted to remain, although I have some sympathy with the alternative view. Scientists in particular have cause for concern because of uncertainty about access to EU funding, and I have doubts as to whether this will be resolved quickly. In my final years of employment at the James Hutton Institute, I had a share in three successive EU projects, which carried out some excellent science and allowed me to make some lasting international friendships. I was not cut out to organize such proposals, so I must pay tribute to the coordinator of these, Jean-Louis Sébédio of INRA, Clermont-Ferrand, France, for his dedicated professional work. The main projects lead to many publications, but the friendships formed enabled many other incidental and fruitful collaborations. It would be a great pity of scientists in the UK were no longer to contribute to international science in this way.

July 13^th, 2016

Nowadays, I more interested in what lipids do in nature, i.e., their biological functions, than in other aspects of their chemistry and biochemistry. I have just found a paper describing what appears to be a completely new function for lipids. The swordfish can swim faster than any other living creature, and it is now reported that it may achieve its high speeds in part thanks to an organ that produces a wax from oil-excreting pores in the skin of the head. It is hypothesized that it "creates a super-hydrophobic layer that reduces streamwise friction drag and increases swimming efficiency" (Videler, J.J. et al. Lubricating the swordfish head. J. Exp. Biol., 219, 1953-1956 (2016); DOI). I have to wait six months until access is opened fully to the paper, but from the abstract the wax consists of methyl esters.

The essential fatty acids of the omega-6 and omega-3 families are "essential" because they cannot be synthesized de novo in animal tissues where they have innumerable functions, not least as precursors of the eicosanoid, docosanoids, and so forth. However, there are many other fatty acids that are not essential in this sense but for which there is an absolute requirement in animals. For want of a better term, I have been calling them "vital" fatty acids here and elsewhere. Those that fall into this category may be surprising to some of you as they are mainly saturated and monoenoic. For example, N-linked myristic acid is required to ensure 150 different proteins take their proper station in membranes in humans. Similarly, 500 proteins require S-acylated fatty acids, most of which is palmitic acid. The peptide hormone ghrelin has an absolute requirement for O-acyl linked octanoic acid to function. Oleic acid linked to ammonia is a hormone in the brain that induces sleep, while linked to ethanolamine it is produced to indicate satiety in the gut. Wnt proteins are central mediators of animal development, influencing cell proliferation, differentiation and migration - they are N-palmitoylated on a conserved cysteine residue and have a second unusual O-acyl modification with palmitoleic acid; the latter is essential to bind the protein to both a transporter and its receptor in cells. Multi-methyl-branched fatty acids, such as pristanic and phytanic acids, are reported to affect cellular metabolism through regulating gene expression. Arguably the most important of all is palmitic acid, which is the precursor of sphingoid bases and thence of all sphingolipids. There may be many more vital fatty acids that might be added to this list.

July 6^th, 2016

In view of the commercial importance of seed oils for the human diet, most plant biochemists will be familiar with the biosynthesis and metabolism of triacylglycerols in seeds. However, until recently, little attention has been given to triacylglycerols in the vegetative tissue of plants. They are important for pollen function, but there has been little interest in the low amounts present in leaves and stems. This is changing in the era of genetic engineering as it is evident that increasing the energy level in green tissues through increasing the concentration of triacylglycerols would increase the energy available for nutritional purposes and for biomass production. A new review discusses what has been achieved and what may be possible (Xu, C.C. and Shanklin, J. Triacylglycerol metabolism, function, and accumulation in plant vegetative tissues. Annu. Rev. Plant Biol., 67, 179-206 (2016); DOI). As an example, the authors point out that increasing the oil content of sugar cane biomass to 1.5% could produce a similar oil yield per acre as canola.

It is always fascinating to read a paper describing a major new advance in lipid science, but sometimes a publication that may appear more prosaic can be of great value. Of course, it is always difficult to decide on first reading what may come into this category, but I suspect that one such will prove to be an invaluable compilation of data on retention properties of lipids in reversed-phase HPLC systems (Ovčačiková, M. et al. Retention behavior of lipids in reversed-phase ultrahigh-performance liquid chromatography-electrospray ionization mass spectrometry. J. Chromatogr. A, 1450, 76-85 (2016); DOI).

Incidentally, the ISI web of Science, which I used to compile my reference lists, omits the accents on letters in the names of scientists from European countries. When I become aware of them (as with the last), I try to insert them here, but inevitably I miss very many for which I apologize. One of the reasons I stopped working with AOCS on the web was that they insisted on moving from the international html standard to a proprietary US system, which made the introduction of accented letters and symbols of all kinds a tedious task that was fraught with errors.

June 29^th, 2016

Scottish thistle The journal Biochimie (Volume 125) contains a special issue section on the topic of 'Lipids, Signaling and Pathophysiology', guest edited by Professor Hugues Chap. The editor has contributed a fascinating autobiographical review describing his research career, and especially how he and his colleagues studied and used phospholipases to solve biochemical problems (Chap, H. Forty five years with membrane phospholipids, phospholipases and lipid mediators: A historical perspective. Biochimie, 125, 234-249 (2016); DOI). The early work explored phospholipid structure and metabolism in relation to membrane organization, followed by pioneering work on lysophosphatidic acid, the biochemistry of platelet-activating factor and the role of phosphoinositides in cell signaling. In recent years, novel digestive (phospho)lipases have been discovered and novel data on lipid mediators is promised. I was intrigued by his interaction with Jacques Beneviste, one of the discoverers of platelet-activating factor, who later published more controversial and irreproducible work.

There appears to be little doubt of the general health benefits of the omega-3 series of fatty acids, although there is no uniformity of opinion on some aspects. A new review discusses the availability of these fatty acids in a wide variety of natural ecosystems and the potential limitations for the food web, especially for human consumers (Twining, C.W. et al. Highly unsaturated fatty acids in nature: what we know and what we need to learn. Oikos, 125, 749-760 (2016); DOI). The paper is open access.

Formula of dioxolane A3 (DXA3) More than fifty years after the discovery of prostaglandins, new eicosanoid structures and classes continue to be found. The latest is 8-hydroxy-9,11-dioxolane eicosatrienoic acid (dioxolane A₃, DXA₃), which is a platelet-derived lipid generated by cyclooxygenase-1 that can activate or prime human neutrophils. It is characterized by a unique five-membered endoperoxide ring, and is presumed to have a role in innate immunity and acute inflammation (Hinz, H. et al. Human platelets utilize cycloxygenase-1 to generate dioxolane A₃, a neutrophil-activating eicosanoid. J. Biol. Chem., 291, 13448-13464 (2016); DOI). The paper is open access.

June 22^nd, 2016

Regular readers will know that I tend to avoid nutritional comment here, because present conclusions rarely seem to pass the test of time. However, some items seem to be worth a few words on occasion. Some years ago I found a few papers suggesting that omega-3 fatty acids were beneficial towards peridontal disease and I passed on the information to a friend who was troubled by gum disease. The data has now been reviewed in a new publication and while most studies appear to have small sample sizes, the early conclusions appear to be sound (Chee, B. et al. Omega-3 fatty acids as an adjunct for periodontal therapy-a review. Clin. Oral Invest., 20, 879-894 (2016); DOI). My friend is a group of one with no control for comparison but claims some success.

I had thought that the assertion of the European Food Safety Authority that arachidonic acid was not required in the infant diet when docosahexaenoic acid was present had been quashed years ago, but apparently not. Their assumption seems to be that as long as sufficient linoleic acid is available in the diet, there is no need for arachidonic. The failings in this argument have been pointed out by Professor Brenna before, and are repeated in a new publication (Brenna, J.T. Arachidonic acid needed in infant formula when docosahexaenoic acid is present. Nutr. Rev., 74, 329-336 (2016); DOI). All breastfed term infants of adequately nourished mothers consume both DHA and ARA, and I agree with the author that a very good reason indeed is needed before anyone can recommend deviation from the natural intakes. No attention appears to have been paid to vascular or immune function or to cognitive benefits.

June 15^th, 2016

I have just been acquainting myself with ion mobility spectroscopy, which I have not encountered before in relation to lipid analysis and is a technique that separates ions from small molecules up to protein complexes based on their differential mobility through a buffer gas. Coupled with mass spectrometry, it acts as a tool to separate complex mixtures and resolve ions that may be indistinguishable by mass spectrometry alone with high sensitivity and a low signal to noise ratio. It came to my attention from a paper in an ACS publication, though because of the publisher's restricted access policy I have only been able to read the abstract (Sarbu, M. et al. Electrospray ionization ion mobility mass spectrometry of human brain gangliosides. Anal. Chem., 88, 5166-5178 (2016); DOI). In addition to confirming much of what is known of ganglioside composition in such a seemingly well-studied organ, the authors found several novel gangliosides including a remarkable series of mono- up to octasialylated molecules.

It has long been known that phosphatidylethanolamine reacts with glucose and other sugars to form first unstable Schiff bases, which then rearrange to produce Amadori products, especially under hyperglycemic conditions. These can undergo further reactions, for example with reactive oxygen species to form carboxymethyl- and carboxyethyl-adducts. There are brief notes on this web site here on this subject. However, I have to confess that to date I have not paid too much attention to the biological consequences of these reactions. It now appears that Amadori-phosphatidylethanolamine may be a useful predictive marker for hyperglycemia in the early stages of diabetes, and that the various products also have the potential to trigger pathological processes including the neuropathy and retinopathy associated with diabetic complications. They induce the production of pro-inflammatory cytokines and that they have a role in apoptotic cell signaling. Unsurprisingly, such changes to the phospholipid head group change the biophysical properties of membrane bilayers appreciably and can lead ultimately to the disintegration of cell membranes. A new publication on the topic has improved my perception of these biological consequences (Annibal, A. et al. Structural, biological and biophysical properties of glycated and glycoxidized phosphatidylethanolamines. Free Rad. Biol. Med., 95, 293-307 (2016); DOI).

June 8^th, 2016

While I have been enjoying the sunshine of the Canary Islands over the last week, the world of lipids has continued to turn. A colleague has brought an article in the Guardian newspaper to my attention that discusses an EU proposal to make all scientific papers open access by 2020. To quote the article - "The changes are part of a broader set of recommendations in support of Open Science, a concept that also includes improved storage of and access to research data". Obviously this will change the economics of scientific publication substantially, and I can't see print copies of journals continuing for much longer - the increasing cost of postage alone will see to that. Personally, I find it frustrating that I can't access digital copies of my own early publications, which I would like to have simply for record purposes. In fairness, many publishers are making more articles, especially reviews, freely available nowadays, and for example I have obtained a number on line in recent weeks from the Nature Publishing Group, formerly a closed book.

A new publication from Serhan's laboratory shows that human milk possesses a suite of proresolving specialized proresolving mediators, including resolvins, protectins, maresins and lipoxins at bioactive levels (pico-nanomolar concentrations) (Arnardottir, H. et al. Human milk proresolving mediators stimulate resolution of acute inflammation. Mucosal Immunol., 9, 757-766 (2016); DOI). The authors demonstrate that these lipid constituents have beneficial effects in the resolution of inflammation and bacterial infection, and they suggest that they "educate the innate immune system in early life". The paper is open access.

I would be interested in learning whether such lipids are present in cow's milk and survive pasteurization, as this is a major component of the human diet through much of life.

The Journal of Bioenergetics and Biomembranes has a special issue (Volume 48, Issue 2, April 2016) devoted to the topic of "Essential Roles of Lipids in Mitochondrial Function and Pathology" (Issue Editor: Binks W. Wattenberg).

May 25^th, 2016

Scottish thistle In developing the Lipid Essentials section of this website, I believe that I have now included all the major lipid classes (please point out any omissions if I am wrong). The last piece of the jigsaw was a document dealing with bioactive aldehydes. I had put this topic off for years, partly because it did not really interest me but mainly because too much of the formation and biological activity appeared to be uncontrolled. On the other hand, I had included a section on the reaction of aldehydes with phosphatidylethanolamine some time ago, so I felt that I had to see if I could write something on the wider picture. In fact, once I got into it, the subject was much more interesting than I anticipated. True there are an incredible number of possible aldehyde products formed in cells, most of which don't do very much, while others simply add arbitrarily to form covalent bonds with what appear to be random proteins to inhibit their activities. At high concentrations, these are cytotoxic and can lead to cell death. On the other hand, some of the aldehydes, and especially 4-hydroxy-trans-2-nonenal derived from the n-6 family of polyunsaturated fatty acids is an endogenous activating ligand of peroxisome proliferator-activated receptor gamma (PPARγ) at low and noncytotoxic concentrations. It is believed to have beneficial effects in that it regulates genes that control the oxidative capacity of the mitochondrion, stimulates detoxification mechanisms and represses inflammation. My new web page is online, but I regard it as a work in progress that I must return to soon. This is one of the advantages of the web - changes can be made when new information comes to light or the author has second thoughts on any topic.

Formula of 4-hydroxy-trans-2-nonenal

In science, it can be dangerous to make too many assumptions. When a natural analogue of the long-chain base sphingosine was discovered that lacked the hydroxyl group in position 1, it was termed 'deoxysphingosine', and it was assumed that the double bond would be in position 4 and of the trans configuration as in sphingosine per se. Now, a study just accepted for the Journal of Lipid Research shows that the double bond is in position 14 and is of the cis configuration (Steiner, R. et al. Elucidating the chemical structure of native 1-deoxysphingosine. J. Lipid Res., DOI). It appears that an as yet unknown Δ14-desaturase is responsible.

May 18^th, 2016

Arsenic-containing lipids ('arsenolipids') were first detected in marine samples in the 1970s, but there was no sustained interest until relatively recently when modern mass spectrometry methods greatly facilitated their detection and characterization. An additional stimulus to research is that the arseno-hydrocarbon are now known to be highly toxic. Initially, the arsinoyl-fatty acids were thought to be present only in unesterified (free) form, until they were detected in triacylglycerols of whiting. Now, a new study has found arsinoyl fatty acids in the phospholipids of fish roe, including a novel C₃₀ fatty acid of this type with eight double bonds (Viczek, S.A. et al. Arsenic-containing phosphatidylcholines: a new group of arsenolipids discovered in herring caviar. Angew. Chem.-Int. Ed., 55, 5259-5262 (2016); DOI). It raises that possibility that these unusual lipids may have some as yet undefined metabolic role in fish.

The role of lipids as signalling molecules in plants is very different from that in animals. Phosphatidic acid is especially important in this connection in plants, but it seems that we know very little about any putative role for lysophosphatidic acid. Phosphoinositides are important signalling molecules in plants, but a very different group of molecular forms is involved from those in animals. On the other hand, diacylglycerols derived from phosphoinositides appear to have no signalling function in plants. Then there are the oxylipins, which are derived primarily from linolenic acid in plants as opposed to arachidonic acid in animals. A new review is available on this topic (Hou, Q.C. et al. Lipid signalling in plant responses to abiotic stress. Plant Cell Environ., 39, 1029-1048 (2016); DOI).

For those who have a subscription or are sufficiently patient to wait until access is opened, there is and interesting symposium - "More Signalling 2015: Cellular Functions of Phosphoinositides and Inositol Phosphates" in Biochemical Society Transactions

May 11^th, 2016

The Journal of Lipid Research has the enlightened policy of putting accepted papers online in manuscript form ahead of publication. As I don't have direct access to the journal, it enables me to keep the pages here up-to-date, as well as satisfying my general interest in lipid science. Currently, a fascinating historical review is now available in this format (Martin, S.A. et al. The discovery and early structural studies of arachidonic acid. J. Lipid Res. DOI). Arachidonic acid was first discovered in 1907 and named in 1913, but in the absence of all the chromatographic and spectroscopic techniques we now take for granted, it was 1940 before the positions for the four double bonds was determined. The stereochemistry of these was confirmed by total synthesis in 1961. If this is of interest to you, I can also recommend an article by Frank Gunstone on "Fatty acid analysis before gas chromatography" in the AOCS Lipid Library.

In my days as a book and journal editor, it was very frustrating to find that in producing a review volume on a specific topic the publication date was decided by the slowest author, by which time the more prompt authors feared that their contributions might be already out of date. The Journal of Lipid Research has got around this problem by publishing review series over several months as papers become available, rather than as a single volume. The latest topic concerns lipoprotein(a) with the first papers now formally published and with others just appearing in final manuscript form. This is an LDL-like particle containing a specific highly polymorphic glycoprotein named apolipoprotein(a) (apo(a)), which is covalently bound via a disulfide bond to the apoprotein B100. There is a strong correlation between the concentration of this and cardiovascular disease, but from what I have read so far it appears that the mechanism for this effect is not at all clear. I imagine that I was not alone in being confused by the terminology apo(a) versus apo A, as the two have nothing in common. The reason is that apo(a) was characterized and named well before the apo A, B, C, etc. nomenclature was developed. The Introduction to the series is worth reading even if the topic is of marginal interest to you.

May 4^th, 2016

I believe it is especially important to keep up-to-date with the literature on specialized pro-resolvin mediators (protectins, resolvins and maresins) as these metabolites of the (n-3) series of essential fatty acids are proving to have such important biological activities with considerable therapeutic potential. Each new publication from the laboratory of Professor Charles N. Serhan seems to have a fascinating new story to tell. Over the last two years, there has been the important discovery of sulfido-peptide conjugated mediators with some structural similarity to the cysteinyl-leukotrienes. Those derived from maresins were the first to be found but the 17-series protectins derived from docosahexaenoic acid were then shown to be produced by human leukocytes and were highly abundant in lymphatic tissue. Now, a new publication demonstrates that among many other related metabolites macrophages produce a protectin analogue PCTR1, via the intermediate 16S,17S-epoxy-protectin, which enhances resolution of bacterial infections (Ramon, S. et al. The protectin PCTR1 Is produced by human M2 macrophages and enhances resolution of infectious inflammation. Am. J. Pathol., 186, 962-973 (2016); DOI). The paper is open access.

Formula of protectin PCTR1

April 27^th, 2016

Scottish thistle I have written extensively on most classes of lipids in the Lipid Essentials section of this website, but I consider myself as a populariser of lipid science and certainly not an expert in any one area. While I try to keep abreast of new research findings, I am dependent on the latest review articles by real experts to put new information into a proper perspective. Hence my frequent reference to new reviews in this blog. I run into problems where there are no relevant review articles and I have most difficulty with protein-containing lipids, such as lipoproteins and lipopeptides, which I suppose can be considered outwith the lipid mainstream. A new publication on the analysis of lipopeptides of cyanobacteria lead me to a number of interesting research publications, which I have tried to pull together some salient facts for these pages (Urajová, P. et al. A liquid chromatography-mass spectrometric method for the detection of cyclic β-amino fatty acid lipopeptides. J. Chromatogr. A, 1438, 76-83 (2016); DOI). I was most struck by the fact that many of these contained what were to me novel fatty acids with amine groups in position 3, together with hydroxyls in position 2, and often long saturated alkyl chains together with at least one C₁₈ fatty acid with two groups of three conjugated double bonds. As many of the papers were written by protein chemists, these are often described as 'novel amino acids' not 'amine-containing fatty acids' so it is not surprising that they might be missed in my regular computerized searches.

Cutins and suberins are distinct layers on the surface of higher plants with similar but highly unusual lipid compositions (simplistically, suberins form the external layer or bark on woody plants). They contain complex polyesters of polyhydroxy, epoxy and dibasic acids, together with aromatic polymers and glycerol in suberins, compositions that are very different from those of any other living tissues. Recent reviews in open access journals have clarified the distinctions between the two layers for me (Fernández, V. et al. Cuticle structure in relation to chemical composition: re-assessing the prevailing model. Front. Plant Sci., 7, 427 (2016); DOI. Graça, J. Suberin: the biopolyester at the frontier of plants. Front. Chem., 3, 62 (2015); DOI).

April 20^th, 2016

Did you know that when you cough, prostaglandins play a major part in the cough reflex? Prostaglandin PGE₂ in particular mediates the action via a specific receptor, with a further involvement from PGD₂. This is a minor but interesting fact from a new review, which I have been reading to update my web page on prostanoids here (Rumzhum, N.N. and Ammit, A.J. Cyclooxygenase 2: its regulation, role and impact in airway inflammation. Clin. Exp. Allergy, 46, 397-410 (2016); DOI).

It is now recognized that an enormous number of proteins are subjected to covalent lipid modifications of various kinds in order to target them to those membrane locations where they are required to carry out their specific functions. Various linkages are involved and often very specific fatty acids. For example, I have never been clear on how or why nature has selected myristic acid, which is such a minor component of tissues, for the irreversible N-acylation of proteins. This is especially puzzling in that this modification alone is not sufficient to hold the protein in a membrane and further S-palmitoylations are required for stable anchorage. This particular question is not answered in a substantial new review of the topic, but this does not hinder me from recommending it, especially as it is open access (Hentschel, A. et al. Protein lipid modifications - more than just a greasy ballast. Proteomics, 16, 759-782 (2016); DOI).

I have never been fond of the term 'hydrophilic interaction liquid chromatography or HILIC', or to be more accurate I don't like the way it is promoted as a new technique by manufacturers. Only the name is new as such columns have been in use for more than 30 years. Also, many analysts simply say they are using HILIC chromatography without specifying details of the column chemistry, which can often be difficult to find in the manufacturer's literature. I have no complaints, however, about a new publication that is quite clear about the chemistry of the columns the authors tried out for a particularly difficult lipid analytical problem (Cífková, E. et al. Hydrophilic interaction liquid chromatography-mass spectrometry of (lyso)phosphatidic acids, (lyso)phosphatidylserines and other lipid classes. J. Chromatogr. A, 1439, 65-73 (2016); DOI). The best separations were obtained with one new to me with a silicon hydride surface chemistry.

April 13^th, 2016

It has long been evident that aberrations in innumerable aspects of lipid metabolism can have serious consequences for human diseases. However, it is also true that certain lipids have considerable pharmacological and therapeutic potential. Gangliosides are highly complex sphingolipids and their biochemistry is equally complex, although they tend to be neglected by main-stream lipid scientists because they are lost during extraction by most common extraction procedures in the aqueous 'waste'. Ganglioside GM1 is one of the simplest gangliosides and the easiest to obtain on a relatively large scale, and its chemical and biological properties are described in a new review (Aureli, M. et al. GM1 ganglioside: past studies and future potential. Mol. Neurobiol., 53, 1824-1842 (2016); DOI). In the 1990s, gangliosides were tested in various therapeutic situations with variable results. Eventually, trials were stopped because they appeared to show that some patients were developing antibodies that promoted peripheral neuropathies like the Guillain-Barré syndrome. Now, these results are being re-evaluated and new methods of ganglioside delivery are being developed in the hope of eliminating the potential problems.

A second lipid class with more immediate therapeutic potential is the nitro fatty acids, which have "revealed clinically relevant protection from inflammatory injury in a number of cardiovascular, renal and metabolic experimental models" according to a new review (Villacorta, L. et al. Nitro-fatty acids in cardiovascular regulation and diseases: characteristics and molecular mechanisms. Front. Biosci.-Landmark, 21, 873-889 (2016); DOI). Indeed, Phase II clinical trials are already underway in patients with chronic kidney diseases.

Incidentally, I do not have direct access to either of these publications, but received digital copies courtesy of the authors and ResearchGate. In my early career, I must have spent a very considerable sum on postage for reprint requests and in turn on reprints and postage to send to others. I hope that such new online systems do not make it too easy to forget to show our gratitude to authors.

April 6^th, 2016

I have to confess that when I saw the first papers on the beneficial effects of conjugated linoleic acid (CLA) from Michael Pariza's lab in Wisconsin back in 1987 I was highly sceptical. In my defence, at that time it seemed a novel concept to find C₁₈ fatty acids, especially those that were 'non-natural', with any kind of biological function, and I soon came round to a correct view. We now realize that many different fatty acids, including those that are saturated or with branched-chains or with only one double bond, can have profound effects on animal metabolism. Recent research suggests that many more conjugated fatty acids other than those derived from linoleate, including those produced from α-linolenic acid, nonadecadienoic acid and eicosapentaenoic acid by incubation with microorganisms, may have pharmacological value. For example, they have been found to have "anti-carcinogenic, anti-adipogenic, anti-inflammatory and immune modulating properties". These are discussed in a fascinating new review, which also points out how much is still to be learned of the mechanisms behind their actions (Hennessy, A.A. et al. Sources and bioactive properties of conjugated dietary fatty acids. Lipids, 51, 377-397 (2016); DOI).

My own first brush with CLA came more than 40 years ago in a short study of the phosphatidylcholine of sheep bile, which had been reported to contain high concentrations of α-linolenic acid. In fact, I showed that half of what was thought to be 18:3(n-3) was 9c,11t-18:2 with which it co-chromatographed on the packed GC columns then in use (Christie, W.W. The structure of bile phosphatidylcholines. Biochim. Biophys. Acta, 316, 204-211 (1973); DOI). This is still a unique phospholipid composition for a mammalian tissue, and I have never come up with a convincing biological explanation.

March 30^th, 2016

Formula of 3-pyridylcarbinol tetradecanoate 3-Pyridylcarbinol esters, formerly termed 'picolinyl esters' incorrectly, appear to have fallen out of favour for mass spectrometric identification of fatty acids in recent years. While they are arguably the best of the nitrogen-containing derivatives in mass spectrometric terms, their chromatographic properties are less desirable in that they require rather high GC column temperatures for separation, which often means that non-polar phases with poorer resolution may be needed. Also, the preparation procedures are tedious in comparison to the simple one-pot method used for DMOX derivatives, for example. A seemingly simple method involving base-catalysed transesterification with potassium tert-butoxide was described some years ago, but I have never obtained good yields with it - I suspect because it is difficult to remove traces of moisture from the reagents. Now two alternative transesterification methods for preparation of 3-pyridylcarbinol esters have appeared that look promising.

The first involves simply heating the fatty acid methyl esters with 3-pyridylcarbinol in the presence of a molecular sieve that acts both as a reaction catalyst and to sequester the methanol released. The reaction is carried out in toluene under reflux overnight so that minimal work-up conditions are required (Sieben, D. et al. Preparation of the even-numbered 3-oxo fatty acid nicotinyl esters from C6:0 to C18:0. Tetrahedron Letts., 57, 808-810 (2016); DOI). I have yet to get hold of the second paper, but according to the abstract it uses a commercial immobilized enzyme from Candida antartica in toluene at 50°C for 1 hour as transesterification catalyst to derivatize fatty acids in the form of triacylglycerols (Kim, C.S. et al. Lipase-catalyzed synthesis of fatty acid pyridylcarbinol ester for the analysis of seed lipids. J. Am. Oil Chem. Soc., 93, 339-346 (2016); DOI). I suspect that the latter would also work with methyl esters. As the real test of all new procedures is how well they work in other labs, I will look forward to seeing further publications on their use.

March 23^rd, 2016

Scottish thistle A new publication poses an interesting question (Tsikas, D. Quantitative analysis of eicosanoids in biological samples by LC-MS/MS: Mission accomplished? J. Chromatogr. B, 1012, 211-214 (2016); DOI). In essence, the author is discussing the gradual replacement in the eicosanoid literature of GC-MS/MS techniques with LC-MS/MS. In his opinion, GC-MS methods have the advantage that the methodology has been established over nearly 40 years for what is an enormously challenging task to analyse metabolites in such low natural abundances. LC-MS obviously has great potential, but demands considerable knowledge of classical chemistry, so it is easy to over estimate the capabilities of the technique. While LC-MS no longer requires the use of derivatization techniques, Tsikas believes that this "is absolutely necessary for all eicosanoids". He also suggests that the desire to analyse as many different classes of compounds in a single analytical run is doomed to failure because of the need to make compromises that may favour one class of compounds over others, and he cites examples to prove his point.

I have never worked in this area myself, so my knowledge is entirely academic and I won't comment further. Nor do I need to as the journal editors have provided a rebuttal of many of the points raised in the following paper (Gachet, M.S. and Gertsch, J. Quantitative analysis of arachidonic acid, endocannabinoids, N-acylethanolamines and steroids in biological samples by LCMS/MS: Fit to purpose. J. Chromatogr. B, 1012, 215-221 (2016); DOI). I have simplified the debate here, and I encourage you to decide for yourself.

The journal Experimental Cell Research (Volume 340, Issue 2, Pages 171-328, January 2016) contains a special section on the topic of "The Biology of Lipid Droplets" (edited by Marlon Schneider).

March 16^th, 2016

The new mass spectrometry procedures that have revolutionized the approach to lipid analysis have done more than just simplify the task. They have also changed the way we think about molecular species of each lipid class, as these are the primary data produced which have to be collated to obtain the amounts of lipid classes. One obvious problem is that so much data are produced that it is almost impossible to summarize it or present it in such as way that inter-laboratory comparisons are feasible. I certainly can't attempt it and I am grateful when other seek out salient points for me. A new review does just this and draws attention to a number of examples where single molecular species of particular lipids participate in biological processes while related molecules have no influence (Kimura, T. et al. Roles of specific lipid species in the cell and their molecular mechanism. Prog. Lipid Res., 62, 75-92 (2016); DOI). It is perhaps not surprising that arachidonic acid is so often involved.

One methodology that ought to be better known to lipid analysts is the use of ³¹P NMR for the identification of phospholipids. It enables identification and accurate quantification of total diacyl, alkylacyl and alkenylacyl forms of each phospholipid class. The data obtained are manageable and often sufficient for many biological purposes. A new automated approach to this methodology utilizes ¹H chemical shifts for assignment and ³¹P intensities for quantification enabling "20 different lipids to be automatically and unambiguously assigned and quantified" (Balsgart, N.M. et al. High throughput identification and quantification of phospholipids in complex mixtures. Anal. Chem., 88, 2170-2176 (2016); DOI).

The open access journal Translational Cancer Research (Vol 4, No 5, October 2015) is largely devoted to the topic of "Lysophospholipids on Immunity and Cancer" (edited by Hsinyu Lee and Markus H. Gräler). As might be expected, many of the review articles are concerned with the biochemistry and function of sphingosine-1-phosphate. There appears to be no diminution in the interest in this fascinating lipid.

March 9^th, 2016

A large part of the impetus for setting up a website when I reached retirement age at the Scottish Crop (or James Hutton) Research Institute was the realization that I was sitting on a wealth of mass spectrometry data, especially of various fatty acid derivatives, which could potentially be lost to the wider scientific community. Many journals do not allow full mass spectra to be published, restricting authors to a list of key ions; all journals restrict the number of mass spectra that can be illustrated in any publication. Similarly, most commercial libraries inevitably have a finite number of spectra available to them, and then they can only show a select number of the more abundant ions. A complete spectrum can be so much more meaningful.

One important feature that I have come to understand better with experience is that the general pattern or fingerprint of a spectrum can give useful information, even if it does not lead to a definitive identification or lend itself to a ready mechanistic explanation. For example, back in 1967 I published a paper on my post-doc work with Prof. Ralph Holman of the Hormel Institute in which I synthesised the methylene-interrupted C₁₈ dienoic fatty acids from the 2,5-, 3,6,- through to the 14,17-isomer. Our conclusion on the mass spectra of the methyl ester derivatives was that only the first of these was different from the rest and interpretable in terms of the double bond positions. However, I have come to realize that in fact the 3,6-, 4,7- and 5,8-isomers each have distinct and consistent spectra, that differ in significant ways from that of methyl linoleate (see web page). I cannot explain these in mechanistic terms, but if analysts come across a spectrum of a C₁₈ diene that differs in the pattern of ions from that of linoleate they should consider further work to establish the identity. Similarly, it is usually considered that the methyl esters of positional isomers of C₁₈ monoenes all have identical spectra, other than that of 2-18:1. This not so, and in particular I recognized the distinctive fingerprint of 3-18:1 at first glance when I was presented with mass spectra from a new seed oil recently. In the Archive page, there are spectra of 11 different positional isomers of C₁₈-trienes as the methyl esters - all with significantly different fingerprints, even if only a few of these are immediately interpretable in terms of double bond positions.

Incidentally, I was once approached by a commercial library who wished to buy my mass spectrometry files. After much debate I named a price, and was inadvertently sent an internal memo obviously not intended for me that stated that they would never get a cheaper price and to jump at the offer! However, I can assure you that I honoured my initial price - don't believe all you hear about thrifty Scots.

My first mass spectrometer was a small HP bench-top, and now I have access to a more recent Agilent/HP model of this type, though I was able to use other HP/Agilent models in between. While my first instrument had an HP computer attached with a 20Mb hard disk and its own proprietary operating system (then the most powerful computer in my Institute), HP/Agilent should be commended in that the file structure is still the same and my modern Windows system can read the 30 year-old files. Indeed, many of the spectra added over the last few years have come from a re-analysis of the old files, though many more have come from new samples or from old samples with alternative derivatization.

Back in 1999, I only had about a thousand spectra available, but now I have more than double this number on line, and I continue to add to them though more slowly nowadays. My hope is that my readers will continue to find these spectra and the attendant tutorials useful for some years to come. I have acknowledged many collaborators or those who have send me samples to add to the spectra on this website here... Also, I am always grateful for loans of HP/Agilent files that have enabled me to abstract spectra to add to those already online, and again I always acknowledge the source.

March 2^nd, 2016

Following their discovery and structural characterization in the laboratory of H.E. Carter in the 1960s, glycosylinositol phosphoceramides (GIPCs) were the forgotten plant lipids for 40 years. It is only recently with the resurgence of interest in sphingolipids in general together with the development of modern mass spectrometry methods that their true importance has been realized. In studies with tobacco plants, it has now been demonstrated that a large part of the lipid component of the outer leaflet (apoplastic side) of the plasma membrane comprises bulky GIPCs together with sterols (free and glycosylated), while the inner leaflet (cytoplasmic side) contains digalactosyldiacylglycerols, phosphatidylserine and phosphatidylinositol-4,5-bisphosphate, amongst other lipids (Cacas, J.L. and 19 others. Revisiting plant plasma membrane lipids in tobacco: a focus on sphingolipids. Plant Physiol., 170, 367-384 (2016); DOI). Raft-like microdomains are believed to exist in both leaflets. The high concentration of GIPCs in the apoplastic leaflet is presumed to present a physical barrier involved in the maintenance of thermal tolerance, cell integrity and the responses to pathogens.

It has become evident in recent years that nitro fatty acids have important signalling functions in animal tissues, especially as anti-inflammatory agents. A new publication (open access) now suggests that they also have signalling functions in plants with nitro-linolenic acid being the key metabolite (Mata-Pérez, C. et al. Nitro-fatty acids in plant signaling: nitro-linolenic acid induces the molecular chaperone network in Arabidopsis. Plant Physiol., 170, 686-701 (2016); DOI)). There seems to be a single isomer in vivo as only a single peak is seen on GC analysis, but the precise structure does not appear to have been determined. It is involved in plant defence responses against different abiotic-stress conditions, mainly by inducing heat shock proteins. For example, it reacts to oxidative stress conditions by inducing high levels of ascorbate peroxidase. Its concentration rose also in response to wounding or exposure to salinity, cadmium, and low temperature. I have still to get hold of a new review relating nitro fatty acids to human disease conditions (Villacorta, L. et al. Nitro-fatty acids in cardiovascular regulation and diseases: characteristics and molecular mechanisms. Front. Biosci.-Landmark, 21, 873-889 (2016); DOI).

Following my notes on furanoid fatty acids in my last blog, a short review of their occurrence and function in plants has just appeared (Mawlong, I. et al. Furan fatty acids: their role in plant systems. Phytochem. Rev., 15, 121-127 (2016); DOI). The only function suggested is that they act as antioxidants, although I would still put my money on some as yet undefined signalling mechanism.

For those who have access, the latest issue of the journal Current Opinion in Clinical Nutrition and Metabolic Care (Vol 19, Issue 2) has a number of review articles on the theme of "Lipid Metabolism and Therapy" (edited by Philip C. Calder and Richard J. Deckelbaum).

February 26^th, 2016

Scottish thistle Furanoid fatty acids are intriguing molecules, which occur at trace levels in plants, but via the food chain are concentrated in the tissues of fish and especially the cholesterol ester fraction. There are innumerable suggestions about their function and nutritional significance, but as far as I am aware little hard evidence. They are usually depicted as linear molecules with a central protuberance for the ring, which simplifies discussion of the mass spectrometric fragmentations, but equally they could be drawn as I have shown here. The shape then bears a passing resemblance to a prostaglandin - could this be a clue as to function?

Formula of a furanoid fatty acid

Although they are usually present at low concentrations, they have highly distinctive mass spectra in the form of the methyl esters and they are easy to spot if you know what you are looking for. I have to confess that I did not know what to look for so overlooked them for many years when analysing marine samples. Now that I have been suitaby enlightened I believe that I have encountered 8 natural isomers (see our Mass spectrometry pages), but a new study reports the occurrence of 23 different forms in fish with one or two methyl groups attached to the ring, and with zero, one or two double bonds in the chain (Wendlinger, C. et al. Detailed study of furan fatty acids in total lipids and the cholesteryl ester fraction of fish liver. Food Anal. Methods, 9, 459-468 (2016); DOI).

A second publication (open access) from the same laboratory reports the existence of non-methylated furanoid fatty acids in fish in aquaculture (Vetter, W. et al. Novel non-methylated furan fatty acids in fish from a zero discharge aquaculture system. NFS J., 2, 8-14 (2016); DOI). The main one is 8-(5-hexylfuran-2-yl)-octanoic acid, which incidentally is readily formed during autoxidation of conjugated linoleic acid, and as far as I am aware is the only furanoid fatty acid available commercially (Matreya Inc.). Here, it appears to be derived from the fish feed.

February 17^th, 2016

I don't recall having seen the open-access journal JOVE-Journal of Visual Experiments before, but it has a fascinating novel feature. In addition to formal written publications with detailed experimental protocols, it has short videos demonstrating the analytical procedures. I was particularly taken by a recent contribution on the analysis of the complex oxygenated fatty acids in plant cuticles (Jenkin, S. and Molina, I. Isolation and compositional analysis of plant cuticle lipid polyester monomers. JOVE-J. Vis. Exp., 105, e53386 (2015); DOI). The 10 minute online video accompanying the paper was clear and informative. We use related methodology in the commercial lab, where I am an occasional consultant (www.lipid.co.uk), but it is always possible to learn from the approach of others.

A second publication on lipid analytical methodology in a subsequent issue is a bit outside my range of interests but I am sure many of my readers will wish to take a look (Ho, C.Y. et al. Radiolabeling and quantification of cellular levels of phosphoinositides by high performance liquid chromatography-coupled flow scintillation. JOVE-J. Vis. Exp., 107, e53529 (2016); DOI). Also, I have only had time for a brief glance at back issues, but there does seem to be a number of further publications on lipid analytical topics that should be of interest.

Lipid A is a glycolipid present in the outer membrane of Gram-negative bacteria, including those of many human pathogens. It is an indispensable macromolecule for the growth and survival of the organisms, and its function is to anchor complex lipopolysaccharides to the outer membrane. The latter are of particular scientific interest in that they are toxins and stimulate strongly the innate immune system in eukaryotic host species. However, the lipid component is more than just an inert anchor as a new publication has shown that lipid A from invasive strains of Neisseria meningitides, which can cause meningococcal infections, has six fatty acid constituents, whereas that from strains that are merely carriers has five (John, C.M. et al. Lipooligosaccharide structures of invasive and carrier isolates of Neisseria meningitidis are correlated with pathogenicity and carriage. J. Biol. Chem., 291, 3224-3238 (2016); DOI). Why one fatty acid constituent makes such a difference has still to be determined.

February 10^th, 2016

It tends to be assumed that the long-chain iso- and anteiso-methyl-branched fatty acids that occur in minor amounts in animal tissues are derived from microorganisms in the food chain. However, this cannot be entirely so as 18-methyleicosanoic acid is a major component of hair fibres in all mammalian species studied, and it is known to be synthesised de novo. It has also been known for some years that iso-methyl-branched fatty acids are synthesised by the nematode Caenorhabditis elegans, widely used as a model organism, and that these appear to be essential for its development. A new study has demonstrated that a deficiency in these fatty acids caused by inhibiting a branched-chain α-ketoacid dehydrogenase, which is responsible for synthesis of the primer molecules from amino acids, is embryonically lethal. However, the deficiency can be corrected by administering pre-formed branched fatty acids (Jia et al. Developmental defects of Caenorhabditis elegans lacking branched-chain α-ketoacid dehydrogenase are mainly caused by monomethyl branched-chain fatty acid deficiency. J. Biol. Chem., 291, 2967-2973 (2016); DOI). There is a suggestion that a deficiency in this enzyme can also cause health problems in animals including humans.

Lipid II or undecaprenyl diphosphate-MurNAc-pentapeptide-GlcNAc is not your average lipid, but it is vitally important to bacteria as it transports essential components across the cellular membrane to manufacture the main structural peptidoglycans of cell walls. Because of its highly conserved structure and accessibility on the surface membrane, synthesis and transport of lipid II is considered an important target for the development of novel antibiotics, as a new open access review explains (Scheffers, D.J. and Tol, M.B. LipidII: just another brick in the wall? PLOS Pathogens, 11, e1005213 (2015); DOI).

The journal Biochimie (Volume 120, January 2016) is a special issue devoted to the topic of "Lipids: from (bio)synthesis to function" and edited by Frédéric Carrière. At first glance, it covers a wide range of topics and disciplines.

February 3^rd, 2016

Happily, we can abbreviate the title of the French journal Oilseeds & Fats, Corps and Lipids to OCL, which makes it one of the shortest journal names so easy to transcribe. It is a matter of regret to me that it is not abstracted in the Web of Science, which I use for my weekly literature updates, as it means that I have to check it regularly on its own. It really ought to be read more widely as it is open access, most of the articles are in English, and the standard is high. The nature of the content is variable, spanning agricultural topics to pure science, but always of high quality. The latest issue is a good example, as it contains 18 substantial reviews or original research publications on the topic of 'Lipids and Brain', with eminent authors from around the world including Bill Lands and Bob Gibson, as well as many well-known French scholars.

When I came to the James Hutton Institute (then the Scottish Crop Research Institute) to head the Department of Chemistry many years ago, the director gave me the task of setting up a quality control system. Initially, it was to apply to my Department only, but eventually to cover the whole Institute. We decided to go for the one of the ISO9000 standards (currently ISO9001:2008) as this seemed to be the most appropriate for our situation. As guinea pigs, we encountered a number of problems but nothing insurmountable. In extending the system to the rest of the Institute, the first step was to set up a system of formal note-keeping using specially designed notebooks, which were the property of the Institute, an important consideration when you have many scientists who are visiting or on short-term contracts. However, I was not prepared for the storm of criticism and outrage that this seemingly innocuous proposal provoked. Scientists claimed to have perfectly good systems using their own personal computers and felt there was no need to change. Even when we pointed out that proper note taking was essential if patents were to be applied for, they proved difficult to convince. I was grateful that our Director fully supported my colleagues and I and while it took a number of years, we eventually had a full formal accreditation scheme in place. I was reminded of our travails by a new article in Nature entitled "How quality control could save your science".

The real virtues of the system became apparent when we set up a commercial analysis unit - Mylnefield Lipid Analysis. Then we found that rigid quality control was absolutely essential, and our early experience stood us in good stead in upgrading to obtain FDA Approval (GMP), where regular inspection is mandatory.

Chloroform-methanol as part of the well-known Folch procedure is the standard solvent extraction combination against which all other are judged. However, chloroform use is taboo in many countries because of toxicity problems, and many other alternative solvents have been suggested over the years. The most recent is 1-butanol:methanol (1:1 v/v), and it appears to have several virtues. The paper is open access so I will leave you to decide (Alshehry, Z.H. et al. An efficient single phase method for the extraction of plasma lipids. Metabolites, 5, 389-403 (2015); DOI).

January 27^th, 2016

Scottish thistle The relatively new journal Redox Biology is open access for the moment, and there are two important review articles for lipid biologists in recent issues. The first in the August issue deals with protein lipoxidation - an exceedingly complex subject. Any number of oxidized lipid species are involved but especially those that are reactive and electrophilic because they contain carbonyl groups (aldehydes or ketones) or α,β-unsaturated moieties. These include relatively simple molecules such as acrolein and complex prostanoids such as 15d-PGJ₂. The range of proteins that can react and be modified by these agents is enormous, so the analytical task alone is daunting but very important in view of the potential pathophysiological effects of lipid-protein adducts. The review by an international consortium will be required reading for those with an interest in this area (Aldini et al. Protein lipoxidation: detection strategies and challenges. Redox Biol., 5, 253-266 (2015); DOI). The second review deals with lipoxygenases, a topic that is in general well covered in the literature. However, I found that this publication clarified a number of issues for me and enabled me to update my web page here... (Mashima, R. and Okuyama, T. The role of lipoxygenases in pathophysiology; new insights and future perspectives. Redox Biol., 6, 297-310 (2015); DOI).

The popular press regularly contains articles expounding the virtues of this food or that because they contain antioxidants, with little concern as to whether these are absorbed efficiently when consumed or whether they are active in vivo. As Redox Biology was new to me, I scanned back issues quickly to see if there was anything else of interest that my computerized searches might have missed. There were a number, and in particular the April issue contains a salutary review on why clinical trials of antioxidants can show opposite effects from those expected with cautionary notes for future studies (Vrolijk, M.F. et al. The shifting perception on antioxidants: The case of vitamin E and β-carotene. Redox Biol., 4, 272-278 (2015); DOI).

January 20^th, 2016

It has been known for 50 years that most methods or the preparation of long-chain bases from sphingolipids by acid or basic catalysis are flawed in that they give poor yields of products that are often isomerized. Little seems to have been done to improve this methodology in the intervening years, in spite of the increasing recognition of the importance of sphingolipids in the metabolism of animals and plants. Now a new publication promises a substantial improvement by using microwave-enhanced butanolysis of glucosylceramides and an almond β-glucosidase (Gowda, S.G.B et al. Highly efficient preparation of sphingoid bases from glucosylceramides by chemoenzymatic method. J. Lipid Res., in press (2016); DOI). Having successfully prepared the sphingoid bases, an improved derivatization technique with deuterated methyl iodide (CD₃I) to produce trimethylated derivatives having a positively charged quaternary amine group is claimed to enable sensitive and quantitative profiling (Ejsing, C.S. et al. Quantitative profiling of long-chain bases by mass tagging and parallel reaction monitoring. PLOS One, 10, e0144817 (2015); DOI). Both publication are open access, the first in manuscript form.

Spiders are not my favourite creatures, and it appears that the venom from some species can do unpleasant things to our lipids. That from one group can convert sphingomyelin to ceramide-1-phosphate, while a those from a second react with lysophosphatidylcholine and sphingomyelin to produce cyclic phosphates. A new publication demonstrates that the two phospholipase D forms responsible for this activity from the second group (sicariid spiders) share distant homology with toxins from pathogenic actinobacteria and ascomycete fungi with interesting evolutionary implications (Lajoie, D.M. and Cordes, M.H.J. Spider, bacterial and fungal phospholipase D toxins make cyclic phosphate products. Toxicon, 108, 176-180 (2015); DOI).

January 13^th, 2016

There seems to be an increasing push from European governments to make more journals open access, as discussed in a recent article in Nature. The main problem is to make sure that this does not drive commercial publishers of scientific journals out of business, although there is a view that their profits have been excessive in some cases in recent years. Personally, I would be happy if all papers were open access after a fixed period, say 1-2 years, as is already the case with many journals published by societies. I cannot believe that many scientists pay the quoted commercial rates for older publications that may now only be of historic value. I like to keep up with the literature as far as possible to update my pages here, but my philosophy these days is that if what looks like a useful review article is not accessible to me another will come along soon if I am patient. If I cannot access a publication, I am unlikely to cite it in these web pages.

In 2012, I highlighted a publication in my blog that showed that conjugated linoleic acid (CLA) might be the preferred substrate for the formation of nitro metabolites. A further study from the same laboratory reports that healthy humans consuming ¹⁵N-labeled nitrate or nitrite, with and without CLA supplementation, produce labelled CLA-NO₂ metabolites that are detected in plasma and urine (Delmastro-Greenwood, M. et al. Nitrite and nitrate-dependent generation of anti-inflammatory fatty acid nitroalkenes. Free Rad. Biol. Med., 89, 333-341 (2015); DOI). In my first blog, I commented that scientists with an interest in CLA per se should take note, as this might explain some of the observed effects. However, I have just done a citation search on the original publication and I could not see any obvious interest from this fraternity.

My interest in modern mass spectrometric methods is largely academic these days, and I find it hard enough just to keep up to date with the jargon surrounding the subject. Direct infusion-based 'shotgun' lipidomics is an approach that permits high through-put of samples to enable more comprehensive studies. I can recommend a new review on the topic (Wang, M. et al. Novel advances in shotgun lipidomics for biology and medicine. Prog. Lipid Res., 61, 83-108 (2016); DOI).

January 6^th, 2016

It is well known that phosphatidylinositol (PI) in animal tissues consists largely of a single molecular species with stearic acid in position 1 and arachidonic acid in position 2; there is virtually no ether component. Indeed, this is the source of much of the ararachidonic used for oxylipin biosynthesis. Yet in the glycosylphosphatidylinositol anchors for proteins, the PI part of the molecule has in the main a C₁₈ ether-linked moiety in position 1 and stearic acid in position 2. How does this happen? A new review has greatly aided my understanding and has helped me update the appropriate web page here. Synthesis is a complex process that does indeed start with the abundant PI species, which undergoes a series of transformations involving transport across and between membranes during which the lipid changes occur as the polar head group is also transformed via specific additions and modifications of various carbohydrate units and ethanolaminephosphate (incidentally derived from another lipid phosphatidylethanolamine) and eventually a protein (Kinoshita, T. and Fujita, M. Biosynthesis of GPI-anchored proteins: special emphasis on GPI lipid remodelling. J. Lipid Res.,, 57, 6-24 (2016); DOI). The various steps in the process are known, but it appears that in relation to the lipid component at least, much remains to be learned of the enzymology. We probably understand why the lipid changes are necessary, as the saturated form of the lipid component facilitates the formation of raft micro-domains with sphingomyelin in membranes

I don't have access to this journal, but they have the enlightened policy of allowing us to view papers when they are still in manuscript form. I also like the policy of having a review series spread over several issues, as when I edited books in days gone by it was frustrating to have to wait for the tardiest author before publication was possible. Four reviews on the topic of GPI-anchored proteins are planned apparently, of which I have seen the manuscript version of the second.

Some of the more basic steps in lipid analysis barely rate a footnote in many published studies and they are often neglected in review articles. A new review is therefore particularly welcome (Metherel, A.H. and Stark, K.D. The stability of blood fatty acids during storage and potential mechanisms of degradation: A review. PLEFA, 104, 33-43 (2016); DOI). In particular, lipid peroxidation and strategies employed to prevent or minimize it during storage and analysis are described.

Blogs for the previous year (2015) can be located here..

© Bill Christie
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