In vitro desaturation and elongation of rumenic acid by rat liver microsomes

Abstract

Various nutritional studies on CLA, a mixture of isomers of linoleic acid, have reported the occurrence of conjugated long-chain PUFA after feeding experimental animals with rumenic acid, 9c,11t-18:2, the major CLA isomer, probably as a result of successive desaturation and chain elongation. In the present work, in vitro studies were carried out to obtain information on the conversion of rumenic acid. Experiments were first focused on the in vitro delta6-desaturation of rumenic acid, the regulatory step in the biosynthesis of long-chain n-6 PUFA. The conversion of rumenic acid was compared to that of linoleic acid (9c,12c-18:2). Isolated rat liver microsomes were incubated with radiolabeled 9c,12c-18:2 and 9c,11t-18:2 under desaturation conditions. The data indicated that [1-(14)C]9c,11t-18:2 was a poorer substrate for delta6-desaturase than [1-(14)C]9c,12c-18:2. Next, in vitro elongation of 6c,9c,11t-18:3 and 6c,9c,12c-18:3 (gamma-linolenic acid) was investigated in rat liver microsomes. Under elongation conditions, [1-(14)C]6c,9c,11t-18:3 was 1.5-fold better converted into [3-(14)C]8c,11c,13t-20:3 than [1-(14)C]6c,9c,12c-18:3 into [3-(14)C]8c,11c,14c-20:3. Finally, in vitro delta5-desaturation of 8c,11c,13t-20:3 compared to 8c,11c,14c-20:3 was investigated. The conversion level of [1-(14)C]8c,11c,13t-20:3 into [1-(14)C]5c,8c,11c,13t-20:4 was 10 times lower than that of [1-(14)C]8c,11c,14c-20:3 into [1-(14)C]5c,8c,11c,14c-20:4 at low substrate concentrations and 4 times lower at the saturating substrate level, suggesting that conjugated 20:3 is a poor substrate for the delta5-desaturase.

Trans fatty acids and atopic eczema/dermatitis syndrome: The relationship with a free radical cis‐trans isomerization of membrane lipids

“…Once formed in the biological environment, TFA are active molecules known to inhibit desaturase and elongase enzymes and cause interruption of lipid pathways at different levels (25)(26)(27). The effects of trans arachidonic acid isomers are not yet fully disclosed, although some evidence for their interaction with lipid enzymes has been gathered (45)(46)(47)(48).…”

“…We hypothesized that the formation of trans phospholipids in cell membranes might occur by radical-based isomerizing species derived from chronic inflammation in AEDS, and the effects could parallel those of dietary trans lipids. Indeed, the effect of TFA on lipid enzymatic pathways is well assessed (25)(26)(27).…”

Nutritional implications of trans fatty acids during perinatal period, in French pregnant women

“…Several animal studies, in vivo [4][5][6] and in vitro experiments in animal tissues [7][8][9][10] as well as human fibroblast studies [11] have demonstrated that TFAs impair the microsomal desaturation and chain elongation of essential fatty acids linoleic acid (LA) and alpha-linolenic acid (LNA) to long chain polyunsaturated fatty acids (LC-PUFA). Among all trans isomers, 9t12t-18:2 isomer exerts the strongest impairment of delta6 desaturase activity [4,[12][13][14].…”

In vitro metabolism of rumenic acid in bovine liver slices

“…Moreover, it has been recently demonstrated in the rat that the liver is able to convert rumenic acid into a conjugated derivative identified on the basis of its retention time as the cis-6, cis-9, trans-11 C18:3 [21]. In isolated rat microsomes, this conversion was shown to result from the action of ∆6 desaturase [43]. Furthermore, Juanéda and Sébédio [44] demonstrated in the rat liver that rumenic acid is converted not only into C18:3 but also into C20:3 derivatives, the latter being identified as ∆8, 11, 13 C20:3.…”