Analysis of plasmenylethanolamines using electrospray tandem mass spectrometry and its application in screening for peroxisomal disorders.

Abstract

Ether phospholipids are major membrane constituents in mammalian cells and can be divided into two subgroups, namely alkenyl-acyl phospholipids and alkyl-acyl phospholipids. The alkenyl-acyl phospholipids are predominantly present in the phosphatidylethanolamine fraction (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphatidylethanolamine), whereas the alkyl-acyl phospholipids are predominantly found in the phosphatidylcholine fraction (l-alkyl-2-acyl-sn-glycero-3-phosphatidylcholine) (Lee 1998). The glycerolipids with alk-1-enyl groups at the sn-1 position are also referred to as plasmalogens. Two essential steps in the biosynthesis of ether phospholipids take place in peroxisomes and are catalysed by acyl-CoA: dihydroxyacetone-phosphate acyltransferase (DHAP-AT, EC 2.3.1.42) and alkyldihydroxyacetone-phosphate synthase (alkyl-DHAP synthase, EC 2.5.1.26) (Lee 1998). In a number of peroxisomal disorders (e.g. peroxisomal biogenesis defects, rhizomelic chondrodysplasia punctata (RCDP) and isolated DHAP-AT or alkyl-DHAP synthase deficiency), ether phospholipid biosynthesis is (partially) deficient (Van den Bosch et al 1993; Wanders et al 1992; Wanders et al 1994). For diagnostic purposes, erythrocyte plasmalogens are usually measured indirectly after transmethylation, which converts the plasmalogens to their corresponding dimethyl acetals (DMAs), followed by gas chromatographic (GC) analysis (Bjorkhem et al 1986; Dacremont and Vincent 1995). The relative plasmalogen content is then calculated as a ratio of DMA versus the corresponding fatty acid methyl ester.