Differential effects of geometrical isomers of octadecadienoic acids on ketogenesis and lipid secretion in the livers from rats fed a cholesterol-enriched diet

Dietary 5-Campestenone (Campest-5-en-3-one) Enhances Fatty Acid Oxidation in Perfused Rat Liver

The effect of dietary 5-campestenone (campest-5-en-3-one), a chemical modification product of a naturally-occurring plant sterol, campesterol, on lipid metabolism was examined using a rat liver perfusion system. Male Sprague-Dawley rats weighing about 140 g were fed a diet supplemented with or without 0.2% 5-campestenone for 14 d. 5-Campestenone feeding resulted in a marked reduction in the concentrations of serum lipids, such as triacylglycerol (TG), cholesterol, phospholipid, and free fatty acid, without influencing food intake or growth. Then, isolated livers from both groups were perfused for 4 h in the presence of an exogenous linoelaidic acid substrate. Dietary 5-campestenone markedly elevated hepatic ketone body production, while cumulative secretions of TG, cholesterol, and phospholipid by the livers of rats fed 5-campestenone were all significantly lowered as compared to those fed without the compound: the extent of the reduction was more prominent in the secretion of TG than other lipid components. In addition, the reduction of TG secretion was concomitantly accompanied by the reduced incorporation of both exogenous and endogenous fatty acids into this lipid molecule. These results suggest that dietary 5-campestenone exerts its hypotriglyceridemic effect, at least, in part through an enhanced metabolism of endogenous and exogenous fatty acids to oxidation at the expense of esterification in rat liver.

Trans polyunsaturated fatty acids have more adverse effects than saturated fatty acids on the concentration and composition of lipoproteins secreted by human hepatoma HepG2 cells

The objective of this study was to assess the relative long-term effects of linoleic (cis, cis 18:2), linolelaidic (trans, trans 18:2), and palmitic (16:0) acids on hepatic lipoprotein production in HepG2 cells. All fatty acids increased the mass of triglycerides (TG) in the medium and the incorporation of [(3)H]-glycerol into secreted TG; the increase was more pronounced with linoleic acid than with linolelaidic and palmitic acids. The net accumulation in the medium of apolipoprotein (apo) A-I was not affected by the fatty acids tested and moderate changes in that of apoB resulted in apoB/apoA-I mass ratios of 1.05, 1.27 and 0.86 with linoleic, linolelaidic and palmitic acids, respectively. The incorporation of [(14)C]-acetate into cellular plus secreted total sterols was 9.1%, 33.6% and 17.4% of total [(14)C]-labeled lipids with linoleic, linolelaidic and palmitic acids, respectively. Relative to linoleic acid, palmitic acid, and to a greater extent (P < 0.05) linolelaidic acid, increased the secretion and cellular accumulation of [(14)C]-labeled free cholesterol (FC) and cholesteryl esters and decreased those of TG and phospholipids (PL). Compared with linoleic acid, linolelaidic acid increased LDL-cholesterol (C) and HDL-C by 154% (P < 0.001) and 50% (P = 0.016), respectively, whereas palmitic acid increased LDL-C by 17% (P > 0.1) and did not affect HDL-C. The LDL-C to HDL-C ratios were 0.70, 1.18 and 0.96 with linoleic, linolelaidic and palmitic acids, respectively. These differences were not due to altered LDL receptor activity. The PL to C ratios of HDL particles were 1.61, 0.40 and 0.77 with linoleic acid, linolelaidic acid and palmitic acid, respectively. These results suggest that relative to cis polyunsaturated and saturated fatty acids, trans PUFA more adversely affect the concentration and composition of apoA-I- and apoB-containing lipoproteins secreted by HepG2 cells.

Metabolism of trans fatty acids by hepatocytes

The present work was undertaken to study the metabolism of fatty acids with trans double bonds by rat hepatocytes. In liver mitochondria, elaidoyl-CoA was a poorer substrate for carnitine palmitoyltransferase I (CPT-I) than oleoyl-CoA. Likewise, incubation of hepatocytes with oleic acid produced a more pronounced stimulation of CPT-I than incubation with trans fatty acids. This was not due to a differential effect of cis and trans fatty acids on acetyl-CoA carboxylase (ACC) activity and malonyl-CoA levels. Elaidic acid was metabolized by hepatocytes at a higher rate than oleic acid. Surprisingly, compared to oleic acid, elaidic acid was a better substrate for mitochondrial and, especially, peroxisomal oxidation, but a poorer substrate for cellular and very low density lipoprotein triacylglycerol synthesis. Results thus show that trans fatty acids are preferentially oxidized by hepatic peroxisomes, and that the ACC/malonyl-CoA/CPT-I system for coordinate control of fatty acid metabolism is not responsible for the distinct hepatic utilization of cis and trans fatty acids.