Characterization of omega-3-docosahexaenoic acid-containing molecular species of phospholipids in rainbow trout liver

Four major phospholipids from rainbow trout liver were purified by chromatography, and the phospholipid classes and their molecular species were quantitatively and qualitatively determined by P-31 nuclear magnetic resonance, gas chromatography, liquid secondary ion mass spectrometry, and liquid secondary ion mass spectrometry combined with tandem mass spectrometry. Trout liver phospholipids consist mainly of glycerophosphatidylcholine (GPC; 67%), glycerophosphatidylethanolamine (GPE; 22%), glycerophosphatidylserine (GPS; 10%), and glycerophosphatidylinositol (GPI; 1.6%); the contents of 22:6 omega-3 fatty acid in the first three phospholipid classes were 34% (GPC), 31% (GPE), and 27% (GPS), respectively, and abundant molecular species were 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (GPC 16:0-22:6) (see Table 2 for phospholipid molecular species designations), 1-eicosaenoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (GPE 20: 1-22:6), 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (GPE 18:0-22:6), 1-oleoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (GPE 18:1-22:6), 1-linoleoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (GPE 18:2-22:6), 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (GPE 16:0-22:6), 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphoserine (GPS 16:0-22:6), and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphoserine (GPS 18:0-22:6). GPI in trout liver lacks molecular species containing 22:6 omega-3 fatty acid. The study clearly indicates that a very high content of 22:6 omega-3 fatty acid-containing molecular species within phospholipids, mainly within GPC and GPE, is characteristic of rainbow trout liver.