Measurement of Ether Phospholipids in Human Plasma with HPLC–ELSD and LC/ESI–MS After Hydrolysis of Plasma with Phospholipase A1

Ethanolamine ether phospholipid (eEtnGpl) and choline ether phospholipid (eChoGpl) are present in human plasma or serum, but the relative concentration of the ether phospholipids in plasma is very low as compared to those in other tissues. Nowadays, measurement of ether phospholipids in plasma depends on tandem mass spectrometry (LC/MS/MS), but a system for LC/MS/MS is generally too expensive for usual clinical laboratories. Treatment of plasma with phospholipase A1 (PLA1) causes complete hydrolysis of diacylphospholipids, but ether phospholipids remain intact. After the treatment of plasma with PLA1, both eEtnGpl and eChoGpl are detected as independent peaks by high-performance liquid chromatography with evaporative light scattering detection (HPLC-ELSD). The same sample used for HPLC-ELSD can be applied to detect eEtnGpl and eChoGpl with electrospray ionization mass spectrometry. Presence of alkylacylphospholipids in both eChoGpl and eEtnGpl in human plasma was indicated by sequential hydrolysis of plasma with PLA1 and hydrochloric acid.