Effect of dietary fish oil and corn oil on lipid metabolism and apolipoprotein gene expression by rat liver

Abstract

A 3-week fish oil diet induced in weanling rats a decrease in plasma lipids and liver triacylglycerol, and an increase in insulinemia, compared to a corn oil diet. At the same time, plasma apolipoprotein (apo) A-I was slightly lower and plasma heavy apo Bjlight apo B ratio was higher in fish-oil-fed than in corn-oil-fed rats. Hepatocytes obtained from fish-oil-fed and corn-oil-fed rats were used to examine how fish oil affects lipid and apolipoprotein synthesis and secretion. Primary culture of hepatocytes from fish-oil-fed rats displayed a lower ability to synthesize and secrete triacylglycerol than hepatocytes from corn-oil-fed rats, as measured by mass determination or [U-'4C]glycerol incorporation. Hepatocytes from fish-oil-fed rats exhibited a lower synthesis of cholesterol, measured by [I4C]acetate incorporation, than hepatocytes from corn-oil-fed rats. This impairment was associated with an increase in P-oxidation, a higher channeling of oleic acid into phospholipids, and a lower triacylglycerol/diacylglycerol ratio in hepatocytes from fish-oil-fed rats than in hepatocytes from corn-oil-fed rats. Incorporation of [3 %]methionine into secreted apoB was reduced in hepatocytes from fish-oil-fed rats, but was not paralleled by a decrease in apo B mRNA. The appearance of degradative forms of apo B suggest an increase in apo B degradation in hepatocytes from fish-oil-fed rats. Incorporation of [35S]methionine into cellular and secreted apo A-I was lower in hepatocytes from fish-oil-fed rats than in hepatocytes from corn-oil-fed rats, and was not paralleled by any difference in the apo A-I mRNA level. Finally, [35S]methionine incorporation into cellular and secreted forms of apo E and apo A-I mRNA were reduced in hepatocytes from fish-oil-fed rats, compared with hepatocytes from corn-oil-fed rats. These combined data show that fish oil diet reduces triacylglycerol synthesis and secretion and affects apo B synthesis at a post-transcriptional level, and reduces cholesterol synthesis and affects apo E and apo A-I synthesis at a transcriptional and a post-transcriptional level.Dietary fish oil has been shown to decrease plasma triacylglycerol in humans. Such an effect is related to their high content in n-3 polyunsaturated fatty acids, mainly eicosapentaenoic acid [20 : 5(3)] and docosahexaenoic acid [22:6(3)] [l, 21. The low incidence of coronary heart disease in people consuming fish oil as the main fat source has been attributed to their lowering effect on plasma triacylglycerol [3, 41. Nevertheless, humans exhibit contradictory responses to a fish oil diet with respect with plasma cholesterol, apolipoprotein (apo) B or low-density-lipoprotein (LDL) concentrations [5].In nonhuman primates, enrichment of the diet with polyunsaturated fatty acids of the n-6 series has no effect on hepatic apo B secretion and hepatic apo B mRNA levels [6]. When fish oil is substituted for the standard fat source, plasma cholesterol decreases without any significant decrease in plasma apo B level [7]. Furthermore, liver perfusion of ...

Effects of moderate fat intake with different n-3 fatty acid sources and n-6/n-3 ratios on serum and structural lipids in rats

“…The authors observed that the inhibition of the n-6 pathways occurred at low (0. (Roach ef al, 1987a (Roach et al, 1987a (Harris et al, 1983;Balasubramaniam et al, 1985;Huang et al, 1986;Roach et al, 1987a;Chautan et al, 1990;Ribeiro et al, 1991;Otto et al, 1991 It It is unlikely that the small excess of saturated fatty acids fed to the SM group could attenuate the hypotriglyceridemic effect of long-chain n-3 PUFA. Indeed saturated fatty acids accounted for only 2.4 and 1.6% of total energy in SM and SF diets, respectively.…”

Regulation of Rat Liver Apolipoprotein A‐I, Apolipoprotein A‐II and Acyl‐Coenzyme A Oxidase Gene Expression by Fibrates and Dietary Fatty Acids

“…These authors, however, did not measure apo A-I mRNA steadystate levels in whole liver. Furthermore, primary hepatocytes from fish oil and control rats were both supplemented with oleic acid in their study [49], which may up-regulate apo A-I expression [50]. It is, therefore, conceivable that the culture conditions used in their study conceal the effects of the fish oil diet on hepatic apo A-I gene expression.…”

Effects of dietary lipids and Clostridium butyricum on serum lipids and lipid-related gene expression in broiler chickens

“…There have been numerous reports on how fish oil affects fatty acid metabolism in mammals (Ribeiro et al, 1991;Kim et al, 1999;Yu et al, 2010), but few have focused on birds. Moreover, the effects of dietary C. butyricum on the expression of genes linked to fatty acid metabolism have not been examined in chickens.…”