Incorporation of different fatty acids into combined lipids in rabbit atherosclerotic lesions

Lipid composition and cholesterol esterifying activity in microsomal preparations of porcine coronary arteries and heart tissue

Lipid composition and cholesterol esterifying activity were determined in microsomal preparations from coronary arteries and heart tissues of swine. There was a higher concentration of free cholesterol in coronary arteries than in the heart, whereas phospholipid was more concentrated in the heart compared to the coronary arteries. Esterified cholesterol was a minor form of cholesterol in both tissues. Individual classes of microsomal lipids possessed characteristic fatty acid spectra and a number of differences were noted between coronary arteries and heart tissue. The portion of microsomal polyunsaturated fatty acids, particularly linoleic acid, was notably higher in the cholesteryl ester, free fatty acid, and phospholipid fractions of heart tissue compared to the corresponding lipid fractions of the coronary arteries. Cholesterol esterifying activity, measured with 14C-labeled fatty acids, was fairly low in coronary arteries, but considerable activity was present in heart tissue. Oleic acid substrate esterified cholesterol most effectively, followed by linoleic and elaidic acid. Under the incubation conditions for cholesterol esterifying activity, however, the bulk of the fatty acid was actively incorporated into phospholipid rather than cholesteryl ester or triglyceride. Among the fatty acids tested, linoleic acid was the most preferential substrate for phospholipid synthesis and phospholipid synthesizing activity was much greater in heart tissue than in coronary arteries.

Removal of fatty acid labelled cholesterol ester, phospholipid and triglyceride from atherosclerotic rabbit aorta in vitro

An organ culture technique was used to investigate the removal of fatty acids incorporated into various lipid fractions in intimal segments of atherosclerotic rabbit aorta. Segments of aorta were pulse-labelled in vitro with [9,10-3H]oleic acid and [1-14C]linoleic acid for 24 h. The incubation medium was replaced with non-radioactive medium and the removal of the endogenously labelled phospholipid, triglyceride and cholesterol ester was followed for a further period of 10 days. Fatty acids incorporated into phospholipid and triglyceride were removed rapidly from the aortic intima, with fractional half-times of 4--5 days. Cholesterol ester fatty acids were removed more slowly from the aortic intima with fractional half-times of 9--12 days. When the removal rate of oleic acid incorporated into phospholipid, triglyceride and cholesterol ester was compared with that of linoleic acid incorporated into the same lipid fractions, no difference between removal of the two fatty acids could be detected with respect to any of the 3 lipid fractions.

Effect of cholesterol feeding and estrogen treatment on synthesis of fatty acids in liver

The effect of cholesterol feeding and estrogen administration on synthesis of fatty acids in liver mitochondria, microsomes and cytoplasm of male rabbits has been investigated. The synthesis was measured by the incorporation of [1(-14)C] acetyl CoA or [2(-14)C]malonyl CoA into long chain fatty acids under optimal conditions. It was found that atherogenesis markedly decreased the fatty acid synthesis in cytoplasm. The mitochondrial fatty acid synthesis was not affected by the disease. There was a small but measurable decrease in the synthesis of fatty acids in microsomes. Estrogen had no effect on the synthesis of fatty acids in mitochondria or microsomes. But if effectively counteracted, after a short lag period, the decreased synthesis of cytoplasmic fatty acids observed in atherosclerosis. It is possible that liver fatty acid synthetase is one of the enzyme systems through which estrogens exert their atherosclerosis-retarding effect. The decreased cytoplasmic fatty acid synthesis observed in atherosclerosis might account for the low levels of saturated fatty acids reported in liver and plasma lipids of atherosclerotic animals.

Uptake and metabolism of 3H-fatty acid labelled lecithin by normal and atherosclerotic intima in vivo and in vitro

Following the intravenous injection of tracer doses of 3H-fatty acid labelled lecithin into normally fed rabbits, minimal incorporation into serum cholesterol ester over a 6-hour period was observed. The labelled phospholipid was rapidly removed from the serum primarily by R.E. tissues with little uptake by the aorta. The uptake and metabolism of 3H-fatty acid labelled lecithin by explants of normal and cholesterol-fed rabbit aortas was also investigated in vitro for periods up to 8 days. Low uptake and incorporation into cholesterol ester was observed for the normal aortic explants. The labelled phospholid was taken up to a greater extent by explants from cholesterol-fed rabbit aortas and the fatty acid incorporated into both triglyceride and cholesterol ester in the explants. The incorporation of fatty acid into cholesterol ester from phospholipid was associated with hydrolysis of the phospholipid and re-incorporation of the fatty acid into cholesterol ester, rather than by the action of lecithin cholesterol acyl transferase.

Synthesis and removal of different cholesterol esters by aortic smooth muscle cells in culture

The incorporation of 3H-labelled oleic acid and of 14C-labelled linoleic acid into phospholipid, triglyceride and cholesterol ester in smooth muscle cells grown in incubation medium supplemented with either 5% normal or 5% hyperlipemic serum has been studied. Both fatty acids were incorporated into cholesterol esters to a greater extent when cells grown in incubation medium containing hyperlipemic serum. Oleic acid was incorporated into cholesterol esters in preference to linoleic acid. The addition of hyperlipemic serum to the incubation medium did not increase the incorporation fo either 3H-labelled oleic acid or of 14C-labelled linoleic acid into phospholipid or triglyceride. The removal of labelled lipid fractions has also been followed for four days in cells pulse labelled for 24 hours with 3H-labelled oleic acid and 14C-labelled linoleic acid. Both 3H- and 14C-labelled cholesterol esters were removed more rapidly when the smooth muscle cells were grown in medium containing normal serum than in medium containing hyperlipemic serum. The removal of both phospholipid and triglyceride was similar in normal and hyperlipemic serum. Comparison of the 3H/14C ratio indicated that the cholesterol oleate and cholesterol linoleate were removed at similar rates.

Effects of palm-kernel oil and sunflower-seed oil on serum lipids and atherogenesis in alloxan-diabetic rabbits

Groups of metabolically normal (controls) and alloxan-diabetic adult female rabbits were fed semi-synthetic diets containing 40 cal % palm-kernel oil (PKO) or sunflower-seed oil (SSO) for 54 weeks. In contrast to control rabbits fed PKO-diet, the alloxan-diabetic rabbits on this diet, developed no or only a negligible degree of atherosclerosis, although the serum levels of all lipid classes had increased in the diabetic rabbits above that of the controls during almost the whole experimental period. The diabetic rabbits and the controls fed SSO-diet were both free from any significant atherosclerotic involvement in spite of the fact that the SSO-diet appeared unable to suppress the very high levels of the various serum lipid classes induced by the diabetic state. On both diets, the diabetic rabbits showed a significantly higher cholesteryl linoleate/oleate ratio than the controls, which was caused by an increase in the cholesteryl linoleate level in the diabetics. No serious aorta atherosclerosis was found in rabbits with a cholesteryl linoleate/oleate ratio higher than 0.6, although no correlation was found between the atherosclerosis indices and these ratios at values lower than 0.6. Rabbits with cholesteryl linoleate/oleate ratios below 0.6 seemed to run a greater risk of developing atherosclerosis. It is suggested that insulin might be required for atherogenesis in addition to hyperlipemia and hypercholesterolemia.