Sphingolipid profiling of human plasma and FPLC-separated lipoprotein fractions by hydrophilic interaction...

Sphingolipids comprise bioactive molecules which are known to play important roles both as intracellular and extracellular signalling molecules. Here we used a previously developed hydrophilic interaction chromatography tandem mass spectrometry (HILIC-MS/MS) method to profile plasma sphingolipids. Method validation showed sufficient precision and sensitivity for application in large clinical studies. Sample stability testing demonstrated that immediate plasma separation is important to achieve reliable results. Analysis of plasma from 25 healthy blood donors revealed a comprehensive overview of free sphingoid base, sphingosylphosphorylcholine (SPC), hexosylceramide (HexCer), lactosylceramide (LacCer), and ceramide-1-phosphate (Cer1P) species level. Besides the major sphingoid base sphingosine (d18:1), we found d16:1 and d18:2 species in most of these lipid classes. Interestingly, pronounced differences were detected in the species profiles of HexCer and LacCer. Additionally, sphingolipids were quantified in lipoprotein fractions prepared by fast performance liquid chromatography (FPLC). HexCer and LacCer showed similar distributions with about 50% in LDL, 40% in HDL and less than 10% in the VLDL fraction. More than 90% of sphingoid base phosphates were found in HDL and albumin containing fractions. In summary, HILIC-MS/MS provides a valuable tool to profile minor sphingolipid species in plasma and in lipoprotein fractions. Comparing profiles from tissues or blood cells, these species profiles may help to address the origin of plasma sphingolipids.