Unusual isomeric polyunsaturated fatty acids in liver phospholipids of rats fed hydrogenated oil

Abstract

Linoleic acid (18:2 omega 6) and linolenic acid (18:3 omega 3) are precursors of two series of essential fatty acids (EFA) formed by alternate desaturations and elongations. In EFA deficiency (EFAD), oleic acid (18:1 omega 9) and palmitoleic acid (16:1 omega 7) undergo the same reactions to form polyunsaturated fatty acids (PUFA) of other structures. Partially hydrogenated soybean oil (PHSO) contains isomeric 18:1 acids that can be converted to unusual isomers of 18:2 by liver microsomes. To test whether 18:2, 20:3, and 20:4 of unusual structure occur in phospholipids as a consequence of EFAD or ingestion of PHSO, rats were fed corn oil, an EFA-deficient diet, or PHSO to provide isomeric 18:1 acids. At 2.5 months the phospholipids were isolated from livers and converted to methyl esters, and the 18:2, 20:2, 20:3, and 20:4 fractions were isolated. The 18:2 and 20:2 fractions were ozonized, and, by using a computer solution of simultaneous equations, the structures and proportions of each isomer were calculated. The 20:3 and 20:4 fractions were analyzed by ozonolysis and capillary gas chromatography. When corn oil was fed, the major isomer in each group was 9,12-18:2, 11,14-20:2, 8,11,14-20:3, and 5,8,11,14-20:4. Patterns in EFAD- and PHSO-fed groups were more diverse, with large proportions of unusual isomers. Feeding EFA-deficient diet and PHSO induced measurable amounts of unusual PUFA at each step of the cascade, and these PUFA may compete in metabolism of normal PUFA and are substrates for oxidative formation of autacoids of unknown structures and function.