Distribution of dietary elaidic acid in subcellular particles of rat liver

Influence of dietary linoleic acid and trans fatty acids on the fatty acid profile of cardiolipins in rats

Cardiolipins (CL) have unique fatty acid profiles with generally high levels of polyunsaturated fatty acids, primarily 18:2n-6, and low levels of saturated fatty acids. In order to study the effect of dietary fatty acid isomers on the fatty acid composition of cardiolipins, rats were fed partially hydrogenated marine oils (HMO), rich in 16:1, 18:1, 20:1, and 22:1 isomeric fatty acids, supplemented with linoleic acid at levels ranging from 1.9% to 14.5% of total fat. Although the dietary fats contained 33% trans fatty acids, the levels of trans fatty acids in CL were below 2.5% in all organs. The fatty acid profiles of cardiolipins of liver, heart, kidney and testes showed different responses to dietary linoleic acid level. In liver, the contents of 18:2 reflected the dietary levels. In heart and kidney, the levels of 18:2 also paralleled increasing dietary levels, but in all groups fed HMO, levels of 18:2 were considerably higher than in the reference group fed palm oil. In testes, the 18:2 levels were unaffected by the dietary level of 18:2 and HMO.

Influence of fatty acids on microsomal diacylglycerol acyltransferase activity in primary cultures of hepatocytes

The regulation of triacylglycerol synthesis by various long-chain fatty acids was studied using primary cultures of hepatocytes. The activity of diacylglycerol acyltransferase was measured after 72-h incubation with various fatty acids in equimolar concentrations (0.5 mM): oleate, linoleate, linolenate, palmitate, stearate and arachidonate increased enzyme activity to 191%, 161%, 148%, 124%, 116% and 114%, respectively, compared to controls. Cellular triacylglycerol levels showed the same changes, suggesting a regulatory function of diacylglycerol acyltransferase in triacylglycerol synthesis. Elaidate lowered the enzyme activity by 57%. The addition of different fatty acids to the incubation medium did not influence the distribution of enzyme activity in the 30 000 x g pellet which was routinely discarded and the microsomal fraction (105 000 x g), where the enzyme was predominantly localized (91%). The release of lactate dehydrogenase into the culture medium of hepatocyte monolayers as well as ketone body production was not affected by any of the fatty acids.

Changes of fatty acid composition of phospholipids in liver mitochondria and microsomes of the rat during growth

The fatty acid patterns of rat liver mitochondrial and microsomal phospholipids were analyzed from term fetuses, 1 and 4 days old, and adult rats. The main fatty acids of phosphatidylethanolamine and -choline were stearic and palmitic acids, although the patterns differed slightly. The fatty acid composition of corresponding phospholipids in mitochondria and microsomes was similar. The fatty acid pattern of cardiolipin was dominated by linoleic acid. The most consistent feature of the developmental changes in the fatty acid patterns of all phospholipids studied was a decrease in the relative amount of monounsaturated fatty acids. The percentages of saturated fatty acids in phosphatidylethanolamine and -choline increased during neonatal development. It is suggested that the high levels of fetal monounsaturated fatty acids were due to low availability of polyunsaturated fatty acids.

Incorporation of cis- and trans-octadecenoic acids into the membranes of rat liver mitochondria

The incorporation of dietary isomeric fatty acids into the membranes of liver mitochondria was investigated. Three groups of rats were fed diets containing 3% sunflower seed oil plus 15%, 20%, or 25% partially hydrogenated arachis oil. A fourth group was fed 25% partially hydrogenated arachis oil, but no sunflower seed oil. All diets were given for 3, 6, or 10 weeks. After 10 weeks, the content of trans fatty acids in the lipids of the mitochondrial membranes was 15--19% of the total fatty acids. The composition of the trans- and the cis-octadecenoic acids in the lipids of the mitochondrial membranes was similar for all groups supplemented with sunflower seed oil (SO), irrespective of time and dietary level of partially hydrogenated arachis oil (HAO). The cis 18:1 (n-8), which was a major isomer of the partially hydrogenated arachis oil, was almost excluded from the mitochondrial fatty acids. Likewise, the content of trans 18:1 (n-8) was considerably lower in the mitochondrial lipids than in the diet. On the contrary, the content of trans 18:1 (n-6) was higher in the mitochondrial lipids than in the diet. In the group fed without sunflower seed oil, isomers of linoleic acid and arachidonic acid were observed in the lipids of mitochondrial membranes.

Eicosenoic and docosenoic acid incorporation in serum lipoproteins in rats fed rapeseed oil

Rats were fed rapeseed oil rich in eicosenoic (20:1) and docosenoic (22:1) acids for 7 days, and the fatty acid composition of the lipid classes of serum and serum lipoproteins was determined. Concentrations of 20:1 and 22:1 acids in the lipid classes were variable, especially among lipoproteins, and were a direct function of the alimentary state of the animal. The results suggest differences in the incorporation of the above acids among the major lipoprotein types and various lipid classes within a given lipoprotein type. The quick partial disappearance of very low density lipoproteins (VLDL) and of low density lipoproteins (LDL) containing 20:1 and 22:1 acids upon starvation and the preferential incorporation of these acids in the triacylglycerols of high density lipoproteins (HDL) are discussed.

In vitro incorporation of isomeric cis-octadecenoic acids by rat liver mitochondria

The metabolic fate of positional isomers of cis-octadecenoic acids was compared to that of oleic acid, elaidic acid and stearic acid in rat liver mitochondria. The positional isomers as well as elaidic acid and stearic acid were labelled with 3H and they were incubated in pairs with [1-14C]oleic acid. 3H/14C ratios were determined for the administered mixtures and for the isolated lipid classes. The results suggested that all isomers were readily incorporated into the membraneous structure of mitochondria. Those with the double bond in the middle of the acyl chain resembled oleic acid and they were preferentially incorporated in cholesterol esters, triacylglycerols and in the 2-position of triacylglycerols and of phosphatidylcholines. Those with the double bond away from the middle of the chain were metabolically distinct from oleic acid and behaved like trans fatty acids. They were rapidly taken up by mitochondria. They were preferentially incorporated in phospholipids and they occupied the 1-position in phosphatidylcholines and the 1- and 3-positions in triacylglycerols.

Rat testicular lipids and dietary isomeric fatty acids in essential fatty acid deficiency

Weanling rats were fed essential fatty acid-deficient diets, either completely fat-free, or with partially hydrogenated fish oil (PHFO, 28 wt %), or with fractions derived from PHFO containing primarily positional isomers of trans-eicosenoate (20:1, 3 wt %) or trans-docosenoate (22:1, 3 wt %). Control animals were fed a peanut oil-containing diet (28 wt %). After 5 or 15 weeks on the diet, the content of neutral and phosphorus-containing lipids in the testes was determined. The fatty acid distribution in major lipid classes was analyzed for animals fed the diets for 15 weeks. The testicular stage of maturation or degeneration was assessed by histology. The group fed PHFO exhibited signs of complete testicular degeneration, or lack of maturation, already after 5 weeks, whereas the animals on the diets with the very long chain monoenoic acids suffered severe degenerations only after 15 weeks. In the PHFO-fed rats, a sharp decline in the concentration of testicular triacylglycerols was observed. In all of the essential fatty acid-deficient groups, an increase in testicular sphingomyelin was observed. Cholesterol levels were fairly similar among all dietary groups. The total testicular fatty acids of the PHFO-fed animals contained somewhat more eicosadienoic acid than found in the other groups, and somewhat less (n-9)-acids. In all EFA-deficient groups, (n-6)-acids were lowered, in particular in triacylglycerols and phosphatidyl cholines. The PHFO group did not show a lower (n-6)-concentration than the other deficient groups, in spite of the more severe symptoms of deficiency. There was no evidence of a major accumulation of long chain isomeric fatty acids in the degenerated testes of the PHFO-, 20:1-, and 22:1-fed groups.