A LIPID BLOG
An occasional series of notes on publications or other items dealing with lipid science that seem to be of particular interest by the Editor-in-Chief, Bill Christie. Inevitably, the selection is highly personal and subjective.
August 31st, 2010
In this blog, I seem to swing from the good to the bad news regarding the biological properties of lipids. Definitely one of the good guys is daptomycin, a natural bacterial lipopeptide, the biosynthesis and properties of which have just been reviewed (Robbel, L. and Marahiel, M.A. Daptomycin, a bacterial lipopeptide synthesized by a nonribosomal machinery. J. Biol. Chem., 285, 27501-27508 (2010) – DOI: 10.1074/jbc.R110.128181). This is a peptide of 13 amino acids, ten of which are in a ring structure, and with a fatty acid attached to the N-terminal amino acid. It was approved in 2003 by the Food and Drug Administration in the USA “for the nontopical treatment of skin structure infections caused by Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus”. It is hoped that a detailed knowledge of the biosynthetic mechanism will lead to the production of related compounds that will keep ahead of any organisms that might develop resistance to the existing compound
August 27th, 2010
The members of the Lipid Maps consortium have just published the results of detailed analyses of the molecular species of lipids in some of the main subcellular membranes in macrophages (Andreyev, A.Y. and 18 others. Subcellular organelle lipidomics in TLR-4-activated macrophages. J. Lipid Res., 51, 2785-2797 (2010). - DOI: 10.1194/jlr.M008748). In the process, they identified “229 individual/isobaric species, including 163 glycerophospholipids, 48 sphingolipids, 13 sterols, and 5 prenols”. This is a major achievement upon which the authors should be congratulated, and I expect it to become a classic, much cited paper. My only caveat, and one that I have raised before here, is that so much data have been acquired that it is impossible to reproduce it other than in simple graphical form. If I were working in another laboratory on a different cell type, it would be impossible to compare results in a meaningful way. It may be that we have to look at alternatives or additions to publication in traditional journals to make such data available. Elsewhere on this website, I have attempted to compare lipid compositional data for animal and plant tissues in a tabulated form. I would very much like to add some of this new information but it is simply not possible technically.
August 24th, 2010
As it is unethical and possibly illegal to use squalene from shark oils in cosmetic formulations, there has been a need to differentiate this from the costlier material derived from the vegetable oils. It seems that this can be accomplished by stable-isotope determination by means of mass spectrometry (Camin, F. et al. Stable isotope ratios of carbon and hydrogen to distinguish olive oil from shark squalene-squalane. Rapid Comm. Mass Spectrom., 24, 1810–1816 (2020) - DOI: 10.1002/rcm.4581
August 20th, 2010
I have been away from the bench for some years and have only just noticed an increasing use of the term ‘hydrophilic interaction liquid chromatography (HILIC)’ as a branch of HPLC. As I am always keen to learn about new techniques, I turned to the manufacturer’s literature to find out more. It was disappointing to read that there is nothing new about the technique whatsoever – it simply appears to be a generic term to describe the use of various functional groups, other than those for reversed-phase chromatography, bonded chemically to silica. It apparently encompasses amine, nitrile, diol and numerous other disparate phases. As these interact with lipids by different mechanisms, it seems to me to be confusing to lump them together. They are certainly not new - I was the author of a paper on the use of amine bonded phases for phospholipid separations as long ago as 1984, and I was certainly not the first. Indeed, there is an old article on this topic on this website here.. Perhaps, I am a cynic but it seems to me to be simply an attempt by chromatography suppliers to create a new market amongst those who do not know the older literature, that is pre-1995 when many institutions do not have online subscriptions. As I may have said before, the only virtue of growing older is that one remembers older publications.
That said, there are some interesting new phases on the market, and I have recently come across a paper describing phospholipid separations on one that contains both sulfonic acid and quaternary ammonium groups, so in theory should approximate to neutrality (Zheng, LA. et al. Profiling of lipids in Leishmania donovani using hydrophilic interaction chromatography in combination with Fourier transform mass spectrometry. Rapid Commun. Mass Spectrom., 24, 2074-2082 (2010) - DOI: 10.1002/rcm.4618). It has the virtue that acidic lipids, such as phosphatidylinositol, which are normally difficult to separate by HPLC, elute as sharp peaks ahead of the zwitterionic phospholipids. Whether it is any better than with a phase containing bonded sulfonic acid residues alone as demonstrated 30 years ago (and seemingly forgotten by everyone but myself) is a moot point (Gross, R.W. and Sobel, B.E. Isocratic high-performance liquid chromatography separation of phosphoglycerides and lysophosphoglycerides. J. Chromatogr., 197, 79-85 (1980)).
August 17th, 2010
There is an interesting new paper in which anandamide metabolism has been studied with substrates labelled with stable isotopes and with liquid chromatography linked to electrospray mass spectrometry as the main analytical tool. The authors showed that “arachidonic acid-derived metabolites were primarily comprised of the eicosanoid lipid class, whereas anandamide-derived arachidonic acid, in addition to eicosanoids, was metabolized into diradylglycerols, fatty acid amides, sterols, and glycerophospholipids”. This seems a powerful demonstration of the value of these techniques that goes beyond simple analysis (Placzek, E.A. et al. Lipidomic metabolism analysis of the endogenous cannabinoid anandamide (N-arachidonylethanolamide). J. Pharm. Biomed. Anal., 533, 567-575 (2010) – DOI: 10.1016/j.jpba.2010.03.035).
August 13th, 2010
In my literature search this week, I could not escape some of the less pleasant biological aspects of lipids. A new review in an open access journal highlights the role of glycosphingolipids in binding of viruses to cell surfaces. For example, binding to gangliosides determines how viruses, such as the polyomaviruses, enter cells (Taube, S. et al. Glycosphingolipids as receptors for non-enveloped viruses. Viruses-Basel, 2, 1011-1049 (2010) - DOI: 10.3390/v2041011). Unfortunately, we can put all the blame on the carbohydrate component, although this is indeed the primary recognition site. It seems that particular combinations of fatty acid and sphingoid base in the ceramide component of glycosphingolipids are involved in membrane organization and cellular signalling and thence in the susceptibility to toxins (Hoffmann, P. et al. On the structural diversity of Shiga toxin glycosphingolipid receptors in lymphoid and myeloid cells determined by nanoelectrospray ionization tandem mass spectrometry. Rapid Commun. Mass Spectrom., 24, 2295-2304 (2010) – DOI: 10.1002/rcm.4636).
I am solely responsible for the choice of papers listed in the Literature review section of this website that deals with analytical methodology. I try to select papers that cover novel aspects of methodology or novel types of sample, and inevitably this cannot be entirely objective. Papers that use tried and tested methods are rarely included, however good they may be technically. There seems to be less innovation in methods that only use chromatography nowadays. In consequence, there has been an increasing concentration on ‘high-tech’ methodology in recent years, especially mass spectrometry, and the word ‘lipidomics’ appears increasingly in the titles or abstracts of papers. At one time, the simple fact that these techniques had been employed guaranteed that publications would be included in my listings. As such methods become more routine, I suspect that in future I will have to take awkward decisions on whether to include some papers in this category in my monthly lists, if I am to keep the numbers within manageable bounds.
August 9th, 2010
Leukotrienes are a family of powerful inflammatory eicosanoids and they seem to be the lipid in vogue this week. There have been two reviews of their properties. The first (Singh, R.K. et al. Cysteinyl leukotrienes and their receptors: molecular and functional characteristics. Pharmacology, 85, 336-349 (2010) – DOI: DOI: 10.1159/000312669). The journal is subscription only in general, but we can be grateful that this article is open access. The second review deals with the first steps in leukotriene biosynthesis via the action of 5-lipoxygenase, which catalyses the conversion of arachidonic acid to leukotriene LTA4 in two steps. (Newcomer, M.E. and Gilbert, N.C. Location, location, location: compartmentalization of early events in leukotriene biosynthesis. J. Biol. Chem., 285, 25109-25114 (2010) – DOI: 10.1074/jbc.R110.125880).
August 6th, 2010
I have had difficulty in understanding how certain species have become the models for studies of lipid metabolism. I know that Arabidopsis has a compact genome, and it is easy to grow in the laboratory, reaching maturity at a relatively early age, but how was such an insignificant looking plant noticed in the first place. Similarly, the tiny zebra fish, which I kept in an aquarium tank as a boy, has become a model for vertebrate metabolism. A new review has enlightened me on why it has become so popular (Holtta-Vuori, M. et al. Zebrafish: gaining popularity in lipid research. Biochem. J., 429, 235-242 (2010) – DOI: 10.1042/BJ20100293). It seems that among the reasons are “relatively low cost, rapid development and ease of genetic manipulation”. However, it is also a good model for study of lipid metabolism in a number of disease states that affect humans, including atherosclerosis, obesity and diabetes.
In contrast, a paper in press in the Journal of Lipid Research casts doubt on the use of Drosophila as a model species in that it does not contain any C20 or C22 polyunsaturated fatty acids (Shen, L.R. et al. Drosophila lacks C20 and C22 polyunsaturated fatty acids. DOI: 10.1194/jlr.M008524). I am rather puzzled as to why it has taken so long to discover this fact.
August 2nd, 2010
It
has been encouraging to see how the scientific world in general has embraced the concept of lipidomics
and with it the importance of lipids in biology. With this has come recognition that for many purposes,
it is no longer sufficient simply to determine the fatty acid composition of a tissue or the concentrations of the bulk components.
It is now evident that specific molecular species of individual lipids may be key modulators of biological activity in tissues.
Of course, the recognition of lipidomics as a science has been driven by developments in mass spectrometry
and there have been any number of useful reviews in recent years that have discussed this methodology.
However, I have enjoyed reading a new review that discusses what we can learn in biochemical terms
from applying the techniques of lipidomics, from cellular architecture, through raft formation and function,
protein-lipid interactions to effects on health and disease
(Shevchenko, A. and Simons, K. Lipidomics: coming to grips with lipid diversity.
Nature Rev. Mol. Cell Biol., 11, 593-598 (2010) -
DOI: 10.1038/nrm2934).
July 28th, 2010
Non-invasive methods for the analysis of metabolites produced in human tissues are obviously to be preferred when they are available. Good examples in the lipid field are the analysis of acylcarnitines and isoprostanoids in urine. The sensitivity of modern mass spectrometric methods is making possible analyses that would not have been considered feasible only a few years ago. A new paper shows that it is possible to measure eicosanoids in the moisture condensed from exhaled breath (Sanak, M. et al. Targeted eicosanoids lipidomics of exhaled breath condensate in healthy subjects. J. Chromatogr. B, 878, 1796-1800 (2010) - DOI: 10.1016/j.jchromb.2010.05.012). Significant differences between smokers and non-smokers were found, and is there is obviously the potential to investigate eicosanoid metabolism in inflammatory lung diseases.
July 23rd, 2010
In one of my blogs in September last year, I mentioned the use of a term that was new to me, i.e. an “orphan lipid”, defined then as lipids that occur naturally but as yet have no known function. I have just come across the term again, but this time applied to geologically modified lipids from peat bogs for which the true biological origin is not known. In this case, the lipids are branched glycerol dialkyl glycerol tetraethers with glucuronosyl or glucosyl units attached. Such lipids with octacosane alkyl units with either 13,16-dimethyl- or 5,13,16-trimethyl substituents have been known as soil constituents for about ten years. Forms with 4 to 6 methyl groups (non-isoprenoid) attached to the n-alkyl chains and 0 to 2 cyclopentyl moieties within the alkyl chain have also been identified. While they are superficially similar to the ether lipids of Archaea, they have a 1,2-di-O-alkyl-sn-glycerol rather than a 2,3-di-O-alkyl-sn-glycerol configuration typical of the latter. They may therefore arise from some unidentified group of anaerobic bacteria in soils (Liu, X.L. et al. Identification of polar lipid precursors of the ubiquitous branched GDGT orphan lipids in a peat bog in Northern Germany. Org. Geochem., 41, 653-660 (2010) - DOI: 10.1016/j.orggeochem.2010.04.004). It appears that there are research groups hot on the trail of these bacteria, so hopefully we will have an answer soon.
July 21st, 2010
The apparent demise of the online SOFA and Peoria data bases of fatty acid compositions of seed oils was a great loss to science. There have been rumours for some time that the online SOFA data base was going to be resurrected, and I was pleased to see that these were confirmed in a news article in the European Journal of Lipid Science and Technology (DOI: 10.1002/ejlt.201000302). It is expected to be restored later this year.
July 16th, 2010
Analysis of phospholipids by means of 31P nuclear magnetic resonance spectroscopy is a long-established technique, which in my opinion does not receive as much attention as it deserves. It permits analysis of all the phospholipids in a sample, and is capable of distinguishing between and quantifying diacyl-, alkylacyl- and alkenylacyl-forms. Of course, it is only suitable for phosphorus-containing lipids, and it does not distinguish the fatty acid constituents. On the other hand, the sample is not destroyed and the simplicity of the methodology is a considerable advantage. Two new papers in Analytical Chemistry should stimulate interest in the technique (Lutz, N.W. and Cozzone, P.J. Multiparametric optimization of 31P NMR spectroscopic analysis of phospholipids in crude tissue extracts. 1. Chemical shift and signal separation. Anal. Chem., 82, 5433-5440 (2010) - DOI: 10.1021/ac100514n; ditto. 2. Line width and spectral resolution. Anal. Chem., 82, 5441-5446 (2010) - DOI: 10.1021/ac100515y).
July 10th, 2010
It has been assumed for many years that the primary route for loss of cholesterol from the body was via the production of bile acids and secretion from the bile. A proportion of this was not re-absorbed and was lost in the faeces. Now a study in which mice were genetically modified to inhibit biliary cholesterol secretion has shown that fecal sterol loss still occurs at normal rates. It appears that there is some as yet undefined mechanism whereby the intestine has a direct role in reverse cholesterol transport that is independent of hepatobiliary secretion (Temel, R.E. et al. Biliary sterol secretion is not required for macrophage reverse cholesterol transport. Cell Metabolism, 12, 96-102 (2010) - doi:10.1016/j.cmet.2010.05.011.
This has been a popular month for special journal issues dealing with biochemistry of lipids. Thus the journal Experimental Neurology has a special issue (Volume 224, Issue 1, pages 1-330) on the subject of ‘Endocannabinoids signalling in healthy and diseased brain’ (edited by Mauro Maccarrone). The journal Biochimie has an issue devoted to the subject of ‘Phospholipases A2 and lipid mediators’ (Volume 92, Issue 6, pages 561-728; edited by Gerard Lambeau and Makoto Murakami), while Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids has an issue dealing with ‘Lipids and Alzheimer's Disease’ (Volume 1801, Issue 8, pages 747-982; edited by B. Garner).
July 8th, 2010
I have just been catching up on what is new in relation to lipids in the Annual Review series of books. Three reviews in particular have caught my eye. For example, I will have to devote some time to one on mass spectrometry of lipids (Blanksby, S.J. and Mitchell, T.W. Advances in mass spectrometry for lipidomics. Ann. Rev. Anal. Chem., 3, 433-465 (2010) - DOI: 10.1146/annurev.anchem.111808.073705). Incidentally, we will soon be adding a new section on lipidomics to this website.
The remaining two reviews deal with biochemical topics. The first describes the function of phosphatidylserine in its membrane environment (Leventis, P.A. and Grinstein, S. The distribution and function of phosphatidylserine in cellular membranes. Ann. Rev. Biophys., 39, 407-427 (2010) – DOI: 10.1146/annurev.biophys.093008.131234), while the second reviews chylomicron formation in enterocytes (Mansbach, C.M. and Siddiqi, S.A. The biogenesis of chylomicrons. Ann. Rev. Physiol., 72, 315-333 (2010) – DOI: 10.1146/annurev-physiol-021909-135801).
July 1st, 2010
What is the difference between a glycophospholipid and a phosphoglycolipid?
Go to our web page on glycero-glycophospholipids to find out.
An interesting new phosphoglycolipid has just been described from the anaerobic bacterium Clostridium tetani,
the causative agent of tetanus. It is a glycosyldiacylglycerol, with N-acetyl glucosamine as the sugar component,
to which a phosphoethanolamine unit is attached (Johnston, N.C.
et al. A phosphoethanolamine-modified glycosyl diradylglycerol in the polar lipids of
Clostridium tetani. J. Lipid Res., 51, 1953-1961 (2010) –
DOI: 10.1194/jlr.M004788).
June 29th, 2010
I have often seen the analysis of isoprostanes in urine described as the ‘gold standard’ for measuring oxidative stress (a term that is rarely if ever defined). However, a recent paper suggests that there is still a need for caution in interpreting the results (Halliwell, B. and Lee, C.Y.J. Using isoprostanes as biomarkers of oxidative stress: some rarely considered issues. Antiox. Redox Signaling, 13, 145-156 (2010) - DOI: 10.1089/ars.2009.2934).
The term ‘stereospecific analysis’ in relation to triacyl-sn-glycerols implies the determination of the fatty acid compositions of each of positions sn-1, sn-2 and sn-3 by appropriate methods. The term ‘regiospecific analysis’ should be used for determination of position sn-2 alone. I was therefore surprised to find a recent paper in a highly regarded journal published by the American Chemical Society with the title ‘Stereospecific analysis of triacylglycerols, etc’ in which neither of these types of analyses was performed, but rather simple molecular species determinations by reversed-phase HPLC. To spare the blushes of the editors, I will not give the citation in full.
June 21st, 2010
The journal Molecular Nutrition and Food Research has devoted a special issue (Volume 54, Issue 5) to the topic of ‘Widened Horizon of Vitamin E Research’ with guest editor Regina Brigelius-Flohé. There appears to be a special emphasis on the role of tocopherols other than as antioxidants in tissues.
N-Myristoylated proteins make up about 0.5% of the total proteins in eukaryotic cells, where the lipid modification is necessary for anchoring of proteins to membranes. However, there is increasing evidence that this also facilitates protein-protein interactions as part of signalling mechanisms, and a recent article reviews this aspect (Hayashi, N. and Titani, K. N-myristoylated proteins, key components in intracellular signal transduction systems enabling rapid and flexible cell responses. Proc. Japan Acad. B, 86, 494-508 (2010) – DOI: 10.2183/pjab.86.494 (open access)).
Fatty acid amides appear to have a number of beneficial functions, but it has recently been shown that they are elevated in plasma of patients suffering from strokes. It remains to be discovered whether as cause or symptom (Naccarato, M. et al. Possible anandamide and palmitoylethanolamide involvement in human stroke. Lipids Health Disease, 9, 47 (2010) - DOI: 10.1186/1476-511X-9-47 (open access)).
June 18th, 2010
The presence of phosphatidylthreonine in animal tissues as a minor lipid component has been known for more than 50 years, but it is only rarely encountered in the literature, possibly because of difficulties of analysis or simply because analysts don’t know when or where to look for it. It has now been located in several types of macrophage by a combination of liquid chromatography and electrospray mass spectrometry. No quantitative data are recorded for the 30 molecular species found, but mass spectral characteristics are given, and these should aid further study (Ivanova, PT. et al. Identification of atypical ether-linked glycerophospholipid species in macrophages by mass spectrometry. J. Lipid Res., 51, 1581-1590 (2010) - DOI: 10.1194/jlr.D003715).
It is known that phosphatidylthreonine is synthesised in brain by the same base-exchange enzyme involved in phosphatidylserine synthesis but with much lower activity. Whether the former has any distinctive function has yet to be determined. It is decarboxylated in mitochondria in vitro to phosphatidylisopropanolamine.
Past items are archived for about a year here..
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Scottish Crop Research Institute (and MRS Lipid Analysis Unit), Invergowrie, Dundee (DD2 5DA), Scotland. |
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| © AOCS | Updated: August 31st, 2010 |
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