Biochemist India

Tuesday, November 8, 2011

Overview of Quantitative Lipid Analysis by Mass Spectrometry (png) (PDF) - Flow chart outlining the procedure for lipid analysis of various lipid classes, from extraction to laboratory analysis to bioinformatics.

Methods in Enzymology Volume 432, LIPID MAPS chapters - (PDF) For the complete Methods in Enzymology volumes, including LIPID MAPS chapters in Volumes 432, 433, and 434, please see http://www.sciencedirect.com/science/bookseries/00766879..
References to individual chapters from these volumes can also be found on our LIPID MAPS Publications: 2007 page.
- Qualitative Analysis and Quantitative Assessment of Changes in Neutral Glycerol Lipid Molecular Species Within Cells
- Glycerophospholipid Identification and Qualitation by Electrospray Ionization Mass Spectrometry
- Detection and Quantitation of Eicosanoids via High Performance Liquid Chromotography-Electrospray Ionization-Mass Spectrometry
- Structure-Specific, Quantitative Methods for Analysis of Sphingolipids by Liquid Chromotography-Tandem Mass Spectrometry: "Inside-Out" Sphingolipidomics
- Analysis of Ubiquinones, Dolichols, and Dolichol Diphosphate-Oligosaccharides by Liquid Chromatography-Electrospray Ionization-Mass Spectrometry
- Extraction and Analysis of Sterols in Biological Matrices by High Performance Liquid Chromatography Electrospray Ionization Mass Spectrometry
- The Lipid Maps Initiative in Lipidomics
- Bioinformatics for Lipidomics
- Quantitation and Standardization of Lipid Internal Standards for Mass Spectrometry

Lipidomics workshop at EB2009 - (PDFs) The LIPID MAPS Consortium presented a workshop on lipidomics techniques at EB2009 under the auspices of the ASBMB. The slides from each of these presentations contain references to most of the methodoligies described .

Lipidomics workshop at EB2007 - (PDFs) The LIPID MAPS Consortium conducted a workshop on lipidomics at Experimental Biology 2007 under the auspices of the American Society for Nutrition. A panel of eight experts discussed methods for analysis of various lipids by mass spectrometry, plus related issues such as sample extraction, internal standards, bioinformatics, and nomenclature.

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Lipid of the week : Sphingomyelin

Not merely membrane building blocks, sphingomyelin species carry out important signaling roles as precursor molecules and by providing localized platforms.

Sphingomyelin species comprise a ceramide unit and a phosphorylcholine or phosphoethanolamine polar headgroup. Typically, sphingosine is the long-chain base component of ceramide, although other long-chain bases can be present; differences in the sphingoid base and the fatty acid components (which are very-long-chain saturated and monounsaturated) confer great variability on the composition of sphingomyelins¹.

As a major constituent of cell membranes, sphingomyelin is found at particularly high concentrations in the membranes of nerve cells (in the myelin sheaths) and red blood cells. It was previously thought to have a purely structural role, similar to the function of phosphatidylcholine, through intermolecular interactions mediated by the 2-amide group, the 3-hydroxy group and the 4,5-trans double bond of the sphingoid base. However, it is now appreciated that sphingomyelin has a high affinity for cholesterol and that these two lipids pack tightly into liquid-ordered domains among a liquid-disordered phase to form lipid rafts¹². These membrane microdomains are thought to function as signaling platforms that regulate the localization and interactions of proteins. But sphingomyelin does not just influence signaling as a component of lipid rafts — it is also a precursor to ceramides and other sphingolipid metabolites that comprise the sphingomyelin cycle or sphingolipid network.

Sphingomyelin biosynthesis begins in the Golgi but continues in the plasma membrane. Sphingomyelin synthase catalyzes the transfer of phosphorylcholine from phosphatidylcholine to ceramide. The consequent decrease in ceramide levels is accompanied by an increase in the levels of sphingomyelin and the release of the well-known signaling molecule diacylglycerol. Alternatively, ceramide can also first be converted to ethanolamine phosphorylceramide through the transfer of the head group from phosphatidylethanolamine followed by sequential methylation of the ethanolamine moiety to a choline group, although whether this pathway is physiologically relevant is unknown¹.

Conversely, sphingomyelin can be metabolized to ceramide (and further, to other biologically active sphingolipids such as sphingosine and sphingosine-1-phosphate) by sphingomyelinases. The function of ceramide as a proapoptotic molecule is well known, although the exact mechanism through which this lipid induces cell death is not fully understood. By contrast, a decrease in ceramide levels accompanies the accumulation of sphingomyelin in cells of the brain, spleen and liver that occurs as a consequence of a deficiency in sphingomyelinase in Niemann–Pick disease types A and B¹. Notably, levels of cholesterol are also elevated in Niemann–Pick disease, which is consistent with reports suggesting that the metabolism, as well as the distribution, of these two lipids is linked, which has clear implications for several other diseases.

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Tuesday, November 8, 2011

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