Abstract
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 [1-14C]linoleic acid, 9cis,12trans-18:2, 9trans,12cis-18:2, α-linolenic acid, 9cis, 12cis,15trans-18:3 and 9trans,12cis,15cis-18:3 were studied using a perfused rat liver model. After perfusion with both trans isomers of 18:2n–6, the 14C was equally distributed between phospholipids and triacylglycerols, compared to the 70:30 distribution (phospholipids:triacylglycerols) observed after infusing linoleic acid. The corresponding distribution of 14C after perfusion with both trans isomers of 18:3n–3 was comparable to what was obtained for α-linolenic acid. The products of conversion were analyzed by combination of different radio chromatographic methods. 9cis,12trans-18:2 was 16 times more converted into a C18:3n–6 fatty acid than linoleic acid into γ-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 2- to 5-times more). 9cis,12cis,15trans-18:3 and 9trans,12cis, 15cis-18:3 were 2- and 10-times less converted to trans-20:5, respectively, than α-linolenic acid into eicosapentaenoic acid. Moreover, 9cis,12cis,15trans-18:3 and 9trans,12cis, 15cis-18:3 were equally and 2.5-times more elongated into “dead-end products”, respectively, than α-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, 9trans,12cis-18:2 and 9trans,12cis,15cis-18:3 were elongated into trans “dead-end products” rather than being converted to desaturated and chain elongated trans-metabolites. On the other hand 9cis,12cis,15trans-18:3 was more desaturated and chain elongated into 17trans 20:5 rather than elongated into 17trans-20:3. —Bretillon, L., J-M. Chardigny, J-P. Noël, and J-L. Sébédio. Desaturation and chain elongation of [1-14C]mono-trans isomers of linoleic and α-linolenic acids in perfused rat liver. J. Lipid Res. 1998. 39: 2228–2236.
Highlights
Trans polyunsaturated fatty acids are produced during heat treatment of oils, such as deodorization and frying
About 30% of the radioactivity in the liver was recovered in the triacylglycerols after infusing linoleic acid, whereas this value was higher than 50% after perfusion with its trans isomers (P ϭ 0.0033)
We showed that the geometry of the double bonds greatly affected the conversion of the fatty acids, as has already been reported for the 18:2 fatty acids [11, 14, 18, 19]
Summary
Trans polyunsaturated fatty acids are produced during heat treatment of oils, such as deodorization and frying. Trans-18:2 isomers were more elongated into “dead-end products” when compared to the conversion of linoleic acid into 20:2n–6 (from 2- to 5-times more). 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 calculated. Desaturation and chain elongation of [1-14C]mono-trans isomers of linoleic and ␣-linolenic acids in perfused rat liver. Essential fatty acids are desaturated and elongated, leading to the formation of arachidonic acid from 18:2n–6 and eicosapentaenoic and docosahexaenoic acids from 18:3n–3, and elongated to “dead-end products” (20:2n–6 from linoleic acid and 20:3n–3 from ␣-linolenic acid) [6,7,8,9,10,11,12].
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