OCCURRENCE OF 5C,8C,11C,15T-EICOSATETRAENOIC ACID AND OTHER UNUSUAL POLYUNSATURATED FATTY-ACIDS IN RATS FED PARTIALLY HYDROGENATED CANOLA OIL

Uncommon cis and trans fatty acids can be desaturated and elongated to produce unusual C-18 and C-20 polyunsaturated fatty acids in animal tissues. In the present study we examined the formation of such metabolites derived from cis and trans isomers of oleic and linoleic acids of partially hydrogenated vegetable oil origin in rats. For two months, adult male rats were fed a partially hydrogenated canola oil diet containing moderately high levels of trans fatty acids (9.6 energy%) and an adequate level of linoleic acid (1.46 energy%). Analysis of the phospholipid (PL) fatty acids of liver, heart, serum and brain showed no new C-18 polyunsaturated fatty acids, except for those uncommon 18:2 isomers originating from the diet. However, minor levels (each <0.3% PL fatty acids) of six unusual C-20 polyunsaturated fatty acids were detected in the tissues examined, except in brain PL. Identification of their structures indicated that the dietary 9c,13t-18:2 isomer, which is the major trans polyunsaturated fatty acid in partially hydrogenated vegetable oils, was desaturated and elongated to 5c,8c,11c,15t-20:4, possibly by the same pathway that is operative for linoleic acid. Furthermore, dietary 12c-18:1 was converted to 8c,14c-20:2 and 5c,8c,14c-20:3; dietary 9c,12t-18:2 metabolized to 11c,14t-20:2 and 5c,8c,11c,14t-20:4, and dietary 9t,12c to 11t,14c-20:2. These results suggested that of all the possible isomers of oleic and linoleic acids in partially hydrogenated vegetable oils, 12c-18:1, 9c,13t-18:2, 9c,12t-18:2 and 9t,12c-18:2 are the preferred substrates for desaturation and elongation in rats. However, their conversions to C-20 metabolites were not as efficient as that of oleic or linoleic acids.