-linolenic acids in perfused rat liver

Trans polyunsaturated fatty acids are produced during heat treatment of oils, such as deodorization and frying. The detailed metabolic pathways of these trans isomers are not fully understood. In the present work, the desaturation and chain elongation of [114 C]linoleic acid, 9 cis ,12 trans -18:2, 9 trans ,12 cis -18:2, a -linolenic acid, 9 cis , 12 cis ,15 trans -18:3 and 9 trans ,12 cis ,15 cis -18:3 were studied using a perfused rat liver model. After perfusion with both trans isomers of 18:2n–6, the 14 C was equally distributed between phospholipids and triacylglycerols, compared to the 70:30 distribution (phospholipids:triacylglycerols) observed after infusing linoleic acid. The corresponding distribution of 14 C after perfusion with both trans isomers of 18:3n–3 was comparable to what was obtained for a -linolenic acid. The products of conversion were analyzed by combination of different radio chromatographic methods. 9 cis ,12 trans 18:2 was 16 times more converted into a C18:3n–6 fatty acid than linoleic acid into g -linolenic acid. Trans -18:2 isomers were more elongated into “dead-end products” when compared to the conversion of linoleic acid into 20:2n–6 (from 2to 5-times more). 9 cis ,12 cis ,15 trans -18:3 and 9 trans ,12 cis , 15 cis -18:3 were 2and 10-times less converted to trans -20:5, respectively, than a -linolenic acid into eicosapentaenoic acid. Moreover, 9 cis ,12 cis ,15 trans -18:3 and 9 trans ,12 cis , 15 cis -18:3 were equally and 2.5-times more elongated into “dead-end products”, respectively, than a -linolenic acid into 20:3n–3. The partitioning of the conversion between formation of desaturated and chain elongated products on the one hand and production of “dead-end products” on the other was also calculated. Compared to their cis analogs, 9 trans ,12 cis -18:2 and 9 trans ,12 cis ,15 cis -18:3 were elongated into trans “dead-end products” rather than being converted to desaturated and chain elongated trans -metabolites. On the other hand 9 cis ,12 cis ,15 trans -18:3 was more desaturated and chain elongated into 17 trans 20:5 rather than elongated into 17 trans -20:3.— Bretillon, L., J-M. Chardigny, J-P. Noël, and J-L. Sébédio. Desaturation and chain elongation of [114 C]monotrans isomers of linoleic and a -linolenic acids in perfused rat liver. J. Lipid Res. 1998. 39: 2228–2236. Supplementary key words trans polyunsaturated fatty acids • desaturation • elongation Heat treatment of oils leads to the formation of trans isomers of both linoleic and a -linolenic acids. 9 Cis , 12 trans -18:2, 9 trans ,12 cis -18:2, 9 cis ,12 cis ,15 trans -18:3, and 9 trans ,12 cis ,15 cis -18:3 are the major isomers produced by isomerization of linoleic and a -linolenic acids, respec-