Oxidation of 5,8,11,14,17-eicosapentaenoic acid by hepatic and renal microsomes

Liver and kidney microsomes were isolated from rats raised on high-fat diets. In terms of energy, the high-fat diets contained 4% vegetable and 40% fish, vegetable or coconut oils. Each microsomal preparation was fortified with 1 mM NADPH and incubated with 5,8,11,14,17-eicosapentaenoic acid (20:5(n-3]. The number of metabolites formed was assessed by reverse-phase high-performance liquid chromatography (HPLC). To identify the major metabolites, large-scale incubations were done with 20:5(n-3) and microsomes from phenobarbital-treated rats. After extracts from the phenobarbital and dietary studies were combined, individual products were isolated by reverse- and normal-phase HPLC. The metabolites were identified by mass spectrometry, by chromatographic properties, and by comparing their retention times and mass spectra with those of chemically synthesized standards. For liver microsomes, the major metabolites were: 17,18-, 14,15-, 11,12- and 8,9-dihydroxyeicosatetraenoic acids, 20-hydroxyeicosapentaenoic acid, and 19-hydroxyeicosatetraenoic acid. For renal microsomes, the major metabolites were 20-hydroxyeicosapentaenoic and 19-hydroxypentaenoic acids. Because formation of these metabolites required NADPH and was enhanced by phenobarbital pretreatment, 20:5(n-3) appears to be oxidized by cytochrome P-450 monooxygenases. Based on reverse-phase high performance liquid chromatograms, all three high-fat diets may produce the same types of monooxygenase metabolites from 20:5(n-3). It remains unknown whether fish-oil diets induce the synthesis of monooxygenases to oxidize n-3 fatty acids, because these preliminary studies involved only two animals per dietary group.