On the mechanism of induction of the enzyme systems for peroxisomal β-oxidation of fatty acids in rat liver by diets rich in partially hydrogenated fish oil

Abstract

In this paper, we describe the early biochemical changes in liver cells that occur in rats fed a semisynthetic diet containing 20% (w/w) partially hydrogenated fish oil. Within hours the level of ornithine decarboxylase (ODC) increased, peaked at about 24 h (11-fold increase) and returned to subnormal levels within 48 h. The diet evoked a similar rapid increase in the cellular level of mRNA for the bifunctional enzyme of peroxisomal β-oxidation (enoyl-CoA hydratase: β-hydroxyacyl-CoA dehydrogenase (HD)) (12-fold), followed by increases in the specific content of HD protein (3-fold) and the capacity for β-oxidation in peroxisomes (5.3-fold). The cellular level of long-chain acyl-CoA increased 2.1-fold. By contrast, no significant changes were observed in the specific activities of ornithine decarboxylase, peroxisomal β-oxidation activity and microsomal ω-hydroxylation as well as the level of long-chain acyl-CoA in livers of rats fed (1 week) diets containing 20% (w/w) soybean oil with added 3 or 6% (w/w) of either elaidic acid (18:1(11) ( trans)), brassidic acid (22:1(13) ( trans)) or erucic acid (22:1(13) ( cis)). Expression of normal levels of mRNA for the bifunctional enzyme was also found. Morphometric analyses revealed no proliferation of peroxisomes in these fatty acid-supplemented diets, in contrast to that observed with the partially hydrogenated fish oil diet. These results are consistent with the proposal (Flatmark, T., Christiansen, E.N. and Kryvi, H. (1983) Biochim. Biohys. Acta 753, 460–466) that components in dietary oils, different from C22:1 cis and trans fatty acids, are responsible for the pleiotropic responses evoked in target cells. Thus, the pattern of response induced by partially hydrogenated fish oil mimics those induced by xenobiotic compounds collectively termed peroxisome proliferators.