A LIPID BLOG
An occasional series of notes on publications or other items dealing with lipid science that seem to be of particular interest to the Technical Editor, Bill Christie. Inevitably, the selection is highly personal and subjective.
December 4th, 2013
I am used to articles extolling the virtues of fish oils in the diet, so it was something of a surprise to find an article with a very different view point (Fenton, J.I. et al. Immunomodulation by dietary long chain omega-3 fatty acids and the potential for adverse health outcomes. Prostaglandins, Leukotrienes and Essential Fatty Acids, 89, 379–390 (2013); DOI: 10.1016/j.plefa.2013.09.011). The suggestion is that “Recent studies of bacterial, viral, and fungal infections in animal models of infectious disease demonstrate that long-chain ω-3PUFA intake dampens immunity and alters pathogen clearance and can result in reduced survival.” It seems that the properties of these fatty acids that lead to the resolution of inflammation can impair the clearance of pathogens during serious infections. On the other hand, a sister journal carries a useful review on the beneficial properties of the resolvins (derived from DHA) in which it is stated that “Lipoxins and resolvins are safe and efficacious in treating human diseases” (Recchiuti, A. Resolvin D1 and its GPCRs in resolution circuits of inflammation. Prostaglandins Other Lipid Mediators, 107, 64–76 (2013); DOI: 10.1016/j.prostaglandins.2013.02.004). Perhaps the answer lies in the general nutritional advice – a little of what you fancy does you good. Taking extra may not confer additional benefits.
The latter article is published as part of conference proceedings, including several reviews that caught my eye. For example, a great deal of fascinating information is now being published on lysophospholipids, especially lysophosphatidic acid, which is an important lipid mediator and signalling molecule. On the other hand, I was less aware of important data on the biological activity of lysophosphatidylinositol (LPI). It seems that 2-arachidonoyl-LPI in particular interacts with a very specific receptor and may even be an endocannabinoid (Yamashita, A. et al. The actions and metabolism of lysophosphatidylinositol, an endogenous agonist for GPR55. Prostaglandins Other Lipid Mediators, 107, 103–116 (2013); DOI: 10.1016/j.prostaglandins.2013.05.004). Also, it is potentially a precursor for the endocannabinoid 2-arachidonoylglycerol.
November 27th, 2013
A paper with the technique “ultra-performance convergence chromatography” in the title sent me to the internet to discover what this was. It turns out that that this is simply supercritical fluid chromatography under a new name, albeit with significant technical improvements (Zhou, Q. et al. Chemical profiling of triacylglycerols and diacylglycerols in cow milk fat by ultra-performance convergence chromatography combined with a quadrupole time-of-flight mass spectrometry. Food Chem., 143, 199-204 (2014) – yes we are in 2014 already it seems; DOI: 10.1016/j.foodchem.2013.07.114). The separations described are indeed very good, but I suppose the re-naming of the technique is simply for commercial purposes. Supercritical fluid chromatography never really caught on for the analysis of lipids in spite of the potential advantages of being able to use carbon dioxide as the mobile phase. The methodology was at its best with triacylglycerols and I understand that it was used routinely in process control of infant formulations in industry, for example. However, with most other lipids it was necessary to add other solvents to the mobile phase, negating the benefits of the volatility of carbon dioxide. It will be interesting to see whether sufficient improvements have been made with the new instrumentation to influence lipid analysts to attempt other separations.
November 20th, 2013
You might think that it is self-evident that lipid oxidation in tissues is a ‘bad thing’. However, a new review of the process in plants suggests that this may not be so, and that both lipid peroxidation and generation of reactive electrophile species can be of benefit to cells. It is suggested that these metabolites or 'phytoprostanes' reprogram gene expression and are involved in a number of signalling pathways. In particular they stimulate ‘the expression of genes encoding detoxification functions, cell cycle regulators, and chaperones’. It seems that these reactions are on a par with the functions of the jasmonates (see our webpage on plant oxylipins) (Farmer, E.E. and Mueller, M.J. ROS-mediated lipid peroxidation and RES-activated signalling. Annu. Rev. Plant Biol., 64, 429–450 (2013); DOI: 10.1146/annurev-arplant-050312-120132).
This should not be entirely surprising as the isoprostanes, i.e. prostanoids formed non-enzymically in animal tissues, are now believed to have distinct biological functions in normal physiology. Indeed, it has been proposed that during evolution in primitive cells, isoprostanes formed in the increasing aerobic conditions became a means of signalling the redox state of the cells and may have been retained as a back-up system to enzymic production.
November 13th, 2013
Non-scientists may cringe at the thought of working on the components of urine, but it should be evident that it is in fact an invaluable biofluid that is easy to obtain in quantity. It is relatively sterile and lacks interfering proteins or bulk lipids. On the other hand, it does contain a number of lipids that can be useful diagnostic markers, including acylcarnitines, which can be an indicator of metabolic problems in the newborn, and isoprostanes, which are considered to be a marker for oxidative stress. A new open-access publication gives as comprehensive account of the constituents ’metabolome’) of urine as we are likely to get (Bouatra, S. and 18 others. The human urine metabolome. PLOS One, 8, e73076 (2013); DOI: 10.1371/journal.pone.0073076). The authors used a combination of chromatographic and spectroscopic techniques to identify 445 distinct metabolites in urine. However, an accompanying literature survey lists a further 2206 compounds.
As a service to the scientific community, the data have been assembled into an online database containing all known metabolites in human urine, their structures and concentrations, together with references to key publications. They are freely available at www.urinemetabolome.ca.
November 6th, 2013
Cardiolipin is a unique lipid in many ways. For example, it is located only in mitochondria, where it is a key component of the oxidative phosphorylation system, and it has twice as many phosphate and fatty acid moieties as the conventional phospholipids. Also, depending on tissue, it has a restricted range of fatty acid components, resulting in a few relatively symmetrical molecular species. It has been accepted up till now that the two phosphate groups have very different acidities, with pK1 = 2.8 and pK2 = 7.5-9.5. A new study has come up with very different results, i.e. pK1 = 2.15, similar to that of phosphoric acid, with pK2 about one unit greater. The paper is open access (Olofsson, G. and Sparr, E. Ionization constants pK(a) of cardiolipin. PLOS One, 8, e73040 (2013); DOI: 10.1371/journal.pone.0073040). The data are important for understanding how cardiolipin interacts with enzymes and proteins in membranes to affect their biological functions.
The mechanism by which free fatty acids cross membranes into animal cells has long been a matter for debate, i.e. whether it is a simple diffusion process or whether an active transport system is involved. The evidence for the former is strengthened by a paper demonstrating that a candidate for an active transporter, a protein designate ‘CD36’, in fact promotes esterification, thereby reducing the cellular concentration of unesterified fatty acids and indirectly increasing flux across the plasma membrane by a passive process (Xu, S. et al. CD36 enhances fatty acid uptake by increasing the rate of intracellular esterification but not transport across the plasma membrane. Biochemistry, 52, 7254-7261 2013; DOI: 10.1021/bi400914c).
All biochemists will recognise the qualities of the Journal of Biological Chemistry. I have just noticed that they have a specific webpage – “Lipids at the JBC”, edited by George Carman - lipids.jbc.org/. Please note that you can find links to this and many other lipid-related web sites from our own ‘Links’ page.
October 30th, 2013
When I was a post-doctoral fellow at the Hormel Institute nearly 50 years ago, one laboratory was filled by a counter-current distribution apparatus. It was an awesome sight in operation using large quantities of solvents to enable separations of fractions enriched in specific fatty acids on a scale suitable for nutritional experiments. I have never seen modern equipment in action, but I understand that it can sit handily on a bench top. Amongst numerous applications, it seems to be a mild and convenient method to obtain enrichment of minor fatty acids for further analysis by GC-MS, while operating on a greater scale than is possible with conventional HPLC equipment. A number of interesting papers in which this apparatus has been utilized for detailed analyses of fatty acids have been published from the laboratory of Professor Walter Vetter in Germany, e.g. the most recent (Hammann, S. et al. Profiling the fatty acids from a strain of the microalgae Alexandrium tamarense by means of high-speed counter-current chromatography and gas chromatography coupled with mass spectrometry. J. Chromatogr. A, 1312, 93-103 (2013); DOI: 10.1016/j.chroma.2013.08.090).
Last week in the UK, an eminent cardiologist wrote an piece in the British Medical Journal, which was widely publicized in our national press, to "bust the myth of the role of saturated fat in heart disease". Two days later the major food manufacturers gave a pledge to reduce the saturated fat content of their products, as part of a voluntary "responsibility deal" between industry and government (the sugar and salt contents are not affected). Should we care?
I would like to congratulate my colleague, friend and mentor, Professor Frank Gunstone, on the occasion of his 90th birthday. He is still actively writing and editing, although he is threatening to really retire this year.
October 23rd, 2013
After the Lipid Library, my favourite lipid-oriented website is Cyberlipid) maintained by Claude Leray in France. In particular, I frequently consult the section of the site titled ‘Descriptions’, where there is a wealth of basic information especially on the structures of unusual lipids.
One review to catch my eye this week is one dealing with ‘lipidic nanoparticles’ as carriers for anti-cancer drugs. These have low toxicity and enable controlled release of the drugs incorporated into the matrix (Mussi, S.V. and Torchilin, V.P. Recent trends in the use of lipidic nanoparticles as pharmaceutical carriers for cancer therapy and diagnostics. J. Materials Chem. B, 1, 5201-5209 (2013); DOI: 10.1039/C3TB20990C). By coincidence, I also came across an article in Science Daily News on the use of liposomes as a safe and effective way to introduce one specific anticancer drug that is otherwise toxic.
I suppose few of us have access to all the journals we would wish. My former employer permits me to access their library where they have contracts with the bigger publishers, but there are innumerable journals out of my reach. When a new review appears in any of these that might be of interest, I always have a quick look as many journals have an enlightened attitude of making some of these open access. One such is a recent review in the Journal of Biochemistry on polyphosphoinositides (Takasuga, S. and Sasaki, T. Phosphatidylinositol-3,5-bisphosphate: metabolism and physiological functions. J. Biochem., 154, 211-218 (2013); DOI: 10.1093/jb/mvt064).
October 16th, 2013
We are getting used to seeing fascinating papers on the lipidomics of human tissues, and these are providing important new approaches to health or disease issues. There is also a great deal of fascinating, if less heralded, work on plant lipidomics. A new study on the lipidome of maize leaf has found innumerable associations with the genome as well as strong connections with agronomic traits (Riedelsheimer, C. et al. The maize leaf lipidome shows multilevel genetic control and high predictive value for agronomic traits. Scientific Rep., 3, 2479 (2013): DOI: 10.1038/srep02479). The paper is open access.
I have just come across a paper dealing with the application of a new variant on the evaporative light-scattering detector to lipid analysis, the Nano Quantity Analyte Detector (NQAD™) (Beppu, F. et al. Quantification of triacylglycerol molecular species in cocoa butter using high-performance liquid chromatography equipped with nano quantity analyte detector. J. Oleo Sci., 62, 789-794 (2013); DOI: 10.5650/jos.62.789). This employs a similar nebulization and evaporation phase to other ELSD, but the dry aerosol passes into a chamber where water vapour is condensed onto the particles so they increase in size to the point where individual particles can be counted. Thus, rather than measuring a cloud of particles, the instrument counts separate droplets. It is claimed that the sensitivity and linearity of the response are apparently greatly improved, and this paper (open access) appears to confirm this for one analytical problem at least.
A fascinating review on the biochemistry and function of lipids in mitochondria has just been published online first (Horvath, S.E. and Daum, G. Lipids of mitochondria. Prog. Lipid Res., 52, 590-614 (2013); DOI: 10.1016/j.plipres.2013.07.002). Some of the key lipids, including phosphatidylglycerol and cardiolipin, can be synthesized in the organelle, while others such as phosphatidylcholine and phosphatidylserine have to be imported. In addition, their precise location in the inner and outer membranes are essential to their function. Cardiolipin is of course of crucial importance to the respiratory function of mitochondria.
October 9th, 2013
Two reviews of analytical methodology from the journal Biomedical Chromatography have caught my eye this week. The first deals with the analysis of sterols other than cholesterol in plasma, including cholesterol precursors and metabolites and plant sterols (Andrade, I. et al. Advances in analytical methods to study cholesterol metabolism: the determination of serum noncholesterol sterols. Biomed. Chromatogr., 27, 1234-1242 (2013): DOI: 10.1002/bmc.2840). I am not aware of an online source of mass spectra of sterols similar to the one we have on this website for fatty acids derivatives. We do have a few spectra of sterols here for reference, but it would be useful if a much more comprehensive selection were available somewhere.
The second review deals with the analysis of acylcarnitines (Mansour, F.R. et al. Separation of carnitine and acylcarnitines in biological samples: a review. Biomed. Chromatogr., 27, 1339-1353 (2013); DOI: 10.1002/bmc.2995). The concentrations of these in biological fluids are invaluable markers for many metabolic disorders, including those of the brain and heart, together with diabetes. I had an interest in the analysis of these lipids many years ago before LC-MS techniques became available, but had little success mainly because of the zwitterionic nature of the molecules. They tended to co-elute with choline-containing lipids in many chromatographic systems. Modern mass spectrometric techniques appear to have solved the problem
October 2nd, 2013
I have been getting a little hot under the collar recently over simple nomenclature errors in publications, often in the titles. For example in my literature search this week, I found the term ‘sphingosine, which refers to a very specific sphingoid base, used as a generic term for a sphingolipid. In another paper, I found the term ‘stereospecific’ used in the title instead of ‘regiospecific’, when the two primary positions of triacylglycerols were not distinguished, and in yet another (in the body of the paper) the fatty acids of the ‘sn-1’ position were analysed when in fact it was again the combined sn-1/3 positions. Finally, I found a paper in which each of the terms ‘triacylglycerols, triacylglycerides and triglycerides’ were used in different parts of the abstract to denote the single lipid class.
While I am on my hobby horse, I may as well have another go at the use of the term HILIC or Hydrophilic Interaction Liquid Chromatography. Aside from the fact that such usage as ‘HILIC chromatography’ is redundant, the technique is used in many different ways with quite distinct chromatographic mechanisms. For example, I have seen it used for conventional silicic acid columns and with bonded diol or nitrile phases (‘adsorption chromatography’). It is also used with amide, amine and zwitterionic phases, where the mechanism of the separation is partly adsorption and partly ion-exchange. However, my main concern is reserved for manufacturers who simply label their columns as HILIC without giving any information on the chemical nature of the phase. Incidentally, amine-bonded phases are not new – I published my first paper using one such more than 30 years ago, and I was not the first. I can accept a term such as a ‘HILIC amide’ phase, also seen this week, if reluctantly.
I feel much better now I have all of this off my chest and I am ready for another short vacation!
September 25th, 2013
I admire the Journal of Lipid Research for making new articles available in manuscript form up to the date of publication and then fully open access after a year. Also, I like how they have thematic review series that appear over months, rather than as a special issue. For an editor, it means that timely contributions are not held back by tardy authors (I speak from bitter experience). A new series “Thematic Reviews on the Living History of Lipids” edited by A.H. Merrill is now promised, and this is one that I am sure I will enjoy. The manuscript of the editorial page lists “Lipid Hypothesis of Atherosclerosis”, phospholipids, eicosanoids, endocannabinoids, bile acids and sphingosines as the initial topics. There may be more to come later.
A new class of lipids has been found in animal tissues – a steroidal alkaloid, formed by enzymatic conjugation of 5,6α-epoxy-cholesterol and histamine. As this has anticancer activities, I am sure we will be hearing more about it in years to come (de Medina, P. et al. Dendrogenin A arises from cholesterol and histamine metabolism and shows cell differentiation and anti-tumour properties. Nature Commun., 4, 1840 (2013); DOI: 10.1038/ncomms2835). Happily, the paper is open access.
September 18th, 2013
The November issue of the journal Biochimica et Biophysica Acta - Molecular Cell Research is devoted to the topic of “Functional and structural diversity of endoplasmic reticulum” (edited by Maya Schuldiner and Blanche Schwappach). It contains several papers of direct interest to lipid biochemists, including reviews dealing with phospholipids, sphingolipids and glycosylphosphatidylinositol-anchored proteins.
The October issue of the journal Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids is concerned with the topic of “Lipid Metabolism in Cancer” (edited by B.F. Cravatt and D.K. Nomura). I will not be delving deeply into this as it is more the realm of the specialist, but a brief perusal of the abstracts has been sufficient to show that lipids are involved in a host of different ways in the progression of cancer. Often it appears that disturbances in lipid metabolism are merely a symptom of the disease, but there are other examples where lipids have a more direct role sometimes in promoting and in other instances in inhibiting the proliferation of cancer cells.
The phosphatidylinositol phosphates have a key role in the functioning of all eukaryotic cells. However, there is a major divergence between plants and animals in which pathways are present and how they operate pathways. A new review demonstrates this for plant systems (Heilmann, M. and Heilmann, I. Arranged marriage in lipid signalling? The limited choices of PtdIns(4,5)P-2 in finding the right partner. Plant Biol., 15, 789-797 (2013); DOI: 10.1111/plb.12025). There is a more general article by the senior author on this topic in this website here....
Past items are archived for about a year here..
James Hutton Institute (and Mylnefield Lipid Analysis), Invergowrie, Dundee (DD2 5DA), Scotland.
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