Release of phagocytosed cholesterol by liver macrophages and spleen cells

Effects of delipidated serum and lipoprotein-deficient serum on sterol biosynthesis and efflux in cultured skin fibroblasts - a comparison of the behaviour of cells from a control with those from a heterozygote and homozygote for familial hypercholesterolaemia

The biosynthesis and efflux of sterols from cells into the medium were investigated in skin fibroblasts from a control, a patient with obligate heterozygous familial hypercholesterolaemia and a patient with the homozygous condition. The behaviour of the cells was studied in two lipid free media (lipoprotein deficient and delipidated serum), with and without the addition of low density lipoproteins (LDL) in order to find experimental conditions which showed maximum differences between the three cell lines. Incorporation of [14C]acetate into sterols in the presence (repression) and absence (induction) of LDL was similar in the normal and heterozygous cells, whereas the homozygous cells showed reduced repression and increased induction. In all three cell lines induction of sterol synthesis was greater with delipidated than lipoprotein deficient serum. The efflux of sterols in both the presence and absence of LDL did not differ between the three cell lines, but it was greater when LDL was added to the medium and when delipidated serum was used. Sterol biosynthesis and efflux from the cells of the heterozygote did not differ significantly from those of the control.

The effect of a putative anti-atherosclerotic agent (S 1204) on lipid metabolism in rabbit aorta

The effects of the novel fenfluramine derivative, S 1204 (meta-trifluoromethyl phenyl-1 [beta(sulfamyl-3'-chloro-4'-benzoyloxyethyl)]amino-2-propane) were studied on lipid metabolism in rabbit aorta and other tissues. Pretreatment of rabbits with S 1204 (50 mg/kg orally) for 10 days strongly inhibited the aortic incorporation of an intravenous 20 muCi tracer-dose of [4-(14)C]-cholesterol given 24 h earlier. However, incorporation of such cholesterol radioactivity into the liver, intestine, lung or plasma was not affected, in comparison with control animals. One hour after i.v. injection of a 100 muCi tracer-dose of [2-(14)C]acetate, S 1204 significantly reduced the radioactivity of total lipids in the aorta and liver. Such inhibition of acetate incorporation into arterial lipids was observed with all lipid fractions (that is, free fatty acids, esterified cholesterol, especially phospholipids, glycerides and free cholesterol). Incorporation of acetate into intestinal triglyceride fractions was also significantly decreased. The results indicate that S 1204 may have anti-atherogenic properties, which could be valuable in the clinical treatment of atherosclerosis.

The effects of serum albumin and phospholipid on sterol excretion in tissue culture cells

Serum albumin was as effective as whole serum or alpha-globulins in facilitating sterol release from strain L mouse fibroblasts. Commercial bovine serum albumin preparations, however, had markedly different absolute effects in this regard. These differences were attributable to the variation in phospholipid content of these products. All but one of these albumins enhanced sterol release when supplemented with phospholipid. The exception was fatty acid-poor albumin which contained an adequate amount of phospholipid. Among the phospholipids examined, lecithin proved to be most effective, while phosphatidylethanolamine had little potentiating influence. As the unsaturation of the test lecithins increased, enhancement of sterol release decreased. The potentiating effect of the phospholipid was in turn dependent on the protein used, since the phenomenon was not observed with non-serum proteins like ovalbumin or with non-transport serum proteins such as gamma-globulins. The results of these studies raise the possibility that serum albumin together with phospholipid can play an important role in sterol release in tissue culture cells.

Effect of metformin on lipid metabolism in the rabbit aortic wall

The aim of the present study was to investigate whether metformin was capable of altering aortic lipid metabolism. Pretreatment of rabbits for 8 days with 120 mg/kg per os metformin reduced by 50--70% the incorporation of a 20 muCi tracer doseof [4(-14)C]cholesterol (given orally 24 h before) into various segments of aorta, plasma, liver, intestine and lung, as compared with control animals. However, as intestinal absorption of cholesterol was also diminished in the same proportion, it was then decided to inject the labelled cholesterol directly into the blood. Under these conditions, metformin induced the same reduction in [4(-14)C]cholesterol specific activity in the aorta, but not in other tissues. Three hours after intravenous injection of a 200 muCi tracer dose of [2(-14)C]-acetate, metformin strongly diminished the radioactivity of total lipids of the aorta, both in fed-rabbits and in rabbits on a 24 h fast, independently of the plasma radioactivity level. The inhibition of acetate incorporation into arterial lipids was observed in all lipid fractions (i.e. free and esterified cholesterol, free fatty acids, phospholipids and especially triglycerides) and the effect persisted unaltered over periods of increasing length after the injection of precursor (1/4, 1/2, 1, 3, 5, 8, 12 h). Metformin also significantly inhibited lipid biosynthesis in the liver and intestine. These properties, added to others previously described, can to a large extent explain the preventive effect of metformin on experimental atherosclerosis.

Effects of 780 SE on lipid metabolism in rabbit aorta

Pretreatment of rabbits with Benfouorex (780 SE) 50 mg/kg p.o. for 10 days strongly inhibited the incorporation of a 20 muCi tracer dose of 4-14C-cholesterol (given i.v. 24 h earlier) into various segments of the aorta. Incorporation of specific activity into the liver, intestine, lung or plasma was not affected. 1 h after i.v. injection of a 100 muCi tracer dose of 2-14C-acetate, a significant reduction in the radioactivity of total lipids of the aorta and liver was seen in rabbits pretreated with 780 SE. The inhibition of acetate incorporation into arterial lipids was observed in all lipid fractions (i.e. free fatty acids, free and esterfied cholesterol, phospholipids and especially triglycerides). Incorporation of acetate into triglyceride fractions of liver and intestine and into hepatic cholesterol was also significantly decreased. The results indicate that 780 SE may have anti-atherogenic properties which could be valuable in the clinical treatment of atherosclerosis.

Mechanisms of cholesterol accumulation in the arterial wall

The rate of cholesterol accumulation is a function of three separate processes: the transfer of lipid or lipoprotein from blood plasma to the artery, the binding and sequestering of lipids in the arterial wall and the solubilization and removal of lipid from the artery. These processes have been studied with lipids or lipoproteins labeled with radioisotopes by autoradiographic and quantitative chemical procedures. More recently immunochemical procedures have been applied to this problem. Studies have been performed with intact animals, isolated organs and cell cultures. In addition, homogenates have been used successfully to study intraarterial transformations of lipids, (for example, cholesterol esterification). Although epidemiologic and clinical studies, as well as animal experiments, have provided evidence that the concentration of plasma low or very low density lipoproteins parallels the rate of atherogenesis, the nature of the causal chain linking plasma lipoproteins to atherosclerosis is as yet unclear. A possible link between plasma lipoproteins, arterial liproprotein lipase and atherogenesis has been postulated.