Abstract
In the current studies, we examined the molecular species of lysophosphatidic acids (lysoPAs) and their precursors in human plasma. We first examined the extraction of phospholipids under highly acidic conditions, which have been reported to allow high recovery of lysoPAs. Capillary liquid chromatography/electrospray ionization mass spectrometry (LC/ESIMS) revealed a variety of phospholipids, including lysophosphatidylethanolamines (lysoPEs), lysoPAs, and lysophosphatidylmethanols (lysoPMEs). However, we found that most of lysoPMEs and part of lysophosphatidylcholines (lysoPCs), lysoPEs, and lysoPAs were artifacts generated by hydrolysis under acidic extraction conditions. In contrast, a solid phase method was effective for the extraction of lysophospholipids, including lysoPAs. Analysis of the solid phase-extracted lipids obtained from plasma by LC/ESIMS (C18 column), followed by neutral loss scanning and product ion scanning, indicated that acyl 16 : 0, 18 : 0, 18 : 1, 18 : 2, 20 : 4, and 22 : 6 lysoPEs are present in human plasma. Furthermore, following incubation of plasma at 37°C, there was an increase in lysoPAs. On the other hand, the levels of some molecular species of lysoPCs and lysoPEs were reduced, indicating that lysoPCs and lysoPEs are precursors of lysoPAs in human plasma.
