Lipid Diversity Revealed in Human Plasma

A large range of lipids have been identified and quantified in human plasma obtained from 100 individuals between 40 and 50 years of age who have undergone overnight fasting prior to the blood draw.

The classes of lipids found included free fatty acids that were extracted and analyzed by gas chromatography mass spectrometry (GC/MS). Other classes were glycerolipid and cholesteryl esters, glycerophospholipids, sphingolipids, sterols, cardiolipin, dolichol and ubiquinone, which were identified by modifications of various standard methods.

In a collaborative study lead by a team of scientists at the University of California (UCSD; San Diego, CA, USA), the lipidome of human plasma was analyzed. The totality of lipids in cells is called the lipidome and the study of lipids is known as lipidomics. The most number of lipid molecular species analyzed was for the sphingolipid category, but the sterols, including cholesterol and its esters, were the most abundant of the lipids on a molar basis (nmol/mL) followed by triglycerides, glycerophospholipids, free fatty acyls, sphingolipids, diacylglycerols, and prenols, though on a weight basis (mg/dL) the glycerophospholipids were the most abundant.

The new lipidome establishes benchmark levels for 588 lipid species, based on a new human plasma standard reference material.

In recent years, scientists have begun to appreciate the greater, more complex roles of lipids in human biology and among these is the emergence of vitamin D related diseases. The utility of lipids in building cell membranes is well known, as is their function as repositories of stored energy. Less well understood, however, is their role as signaling molecules. The upper limit of lipid species, from fatty acyls and glycerophospholipids to sterols and prenols, has yet to be determined and it may reach into the tens of thousands.

Oswald Quehenberger, Ph.D., professor of medicine at UCSD, said, "Fatty acids, which are common, are turning out to be very important communication conduits in some diseases. For example, adipocytes use specific fatty molecules to communicate with distant tissues, a process that has been linked to insulin resistance and diabetes and may also involve inflammatory networks."

The study was published on line in the November 2010, issue of the Journal of Lipid Research.

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