Biomedical subjects

Y Stein

Publications and source records attributed to Y Stein.

280 records · Page 16Linked to original sources

PubMedDate not supplied

Cholesteryl ester efflux from extracellular and cellular elements of the arterial wall. Model systems in culture with cholesteryl linoleyl ether.

Cholesteryl ester (CE) accretion in human atheroma is a slow process during which lipoproteins infiltrate the arterial extracellular space and then gain entry into the cellular components. The present aim was to simulate this process in model systems in culture to learn whether cholesteryl ester transfer protein (CETP) may promote CE efflux at different stages of atheroma formation. To simulate CE efflux from arterial interstitium, cationized LDL labeled with 3H-cholesteryl linoleyl ether (3H-CLE) was added to fixed aortic smooth muscle cells (SMC) or to extracellular matrix. To study efflux of 3H-CLE taken up by cells via receptor-mediated endocytosis of LDL, the SMC cultures were fixed and permeabilized prior to the determination of CE efflux. The cellular model included macrophages, which had ingested acetylated LDL labeled with 3H-CLE. Efflux of 3H-CLE and 14C-CE was studied during postincubation of the labeled cultures with human lipoprotein deficient serum (LPDS) or partially purified CETP. As controls, we used SMC cultures incubated with albumin. In all systems, a 3- to 12-fold increase of 3H-CLE or 14C-CE efflux was found in the postincubation medium containing human LPDS or partially purified CETP when compared to controls. Permeabilization of the cells with saponin enhanced cellular 3H-CLE and 14C-CE efflux in the presence of human LPDS. The findings indicate that CETP may promote CE efflux from aortic interstitium or disintegrating cells. We propose that CETP may play an important role in aortic CE homeostasis under physiological and pathological conditions.

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PubMedDate not supplied

Effect of verapamil on cholesteryl ester hydrolysis and reesterification in macrophages.

The macrophage-like cell line, J774, and its variant, CT2, were used to study the effect of verapamil on metabolism of esterified cholesterol. The cells had been labelled with 3H-cholesterol for 24 hours and thereafter acetylated low density lipoprotein (LDL) or d less than 1.019 g/ml fraction of hypercholesterolemic rabbit plasma was added. After an additional 24 hours, 60% or 40% of the label, respectively, was recovered in esterified cholesterol in control dishes, but only 2% to 15%, in the presence of 50 microM verapamil. Enhancement of esterification of cellular 3H-cholesterol was also obtained by addition of liposomes with a cholesterol/phosphatidylcholine molar ratio of 2:1. This reaction was almost completely inhibited by compound 58-035, an acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, while addition of verapamil resulted in a dose-dependent partial inhibition which was evident after 4 hours. To determine whether the reduction in cholesterol esterification was due to a direct inhibition of ACAT or to an effect of verapamil on the transport of cholesterol to the site of ACAT activity, the cells were incubated with acetylated LDL labelled with 3H-cholesteryl ester, and the amount of uptake, lysosomal hydrolysis, and cytoplasmic reesterification was determined. In control cells and in cells exposed to the ACAT inhibitor, more than 98% of the 3H-cholesteryl ester taken up had been hydrolyzed. Reesterification of 3H-cholesterol was negligible in the presence of the ACAT inhibitor and amounted to 37.1% in control cells. When verapamil was present, reesterification of 3H-cholesterol to cholesteryl ester was only 4%, while the amount of 3H-cholesteryl ester hydrolyzed was 58% of that taken up.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMedDate not supplied

Long-term effects of verapamil on aortic smooth muscle cells cultured in the presence of hypercholesterolemic serum.

Smooth muscle cells derived from rabbit and bovine aorta were cultured for up to 5 weeks in the presence of d less than 1.019 g/ml fraction of hypercholesterolemic rabbit serum. When this fraction was added to serum containing culture medium, there was a significant increase in DNA, protein, and cholesteryl ester per dish. Addition of 50 microM verapamil markedly reduced the stimulatory effect of the d less than 1.019 g/ml fraction on both DNA and protein content per dish. The effect of verapamil on cholesteryl ester content was more complex: there was an increase within the first week, but later the net accumulation of cholesteryl ester per dish was lower than in untreated dishes. The recovery of less DNA in verapamil-treated dishes was not due to increased cell loss, as evidenced by retention of a residualizing marker, 3H-cholesteryl linoleyl ether. Moreover, verapamil did reduce incorporation of 3H-thymidine into DNA. In verapamil-treated dishes, there was flattening and a cobblestone appearance of the cells. A hypothesis is proposed to explain the inhibitory effect of verapamil on the development of atheroma formation in cholesterol-fed rabbits: Assuming that macrophages play an active role in cholesteryl ester removal from atheroma, verapamil, which reduces lysosomal cholesteryl ester hydrolysis in macrophages, would permit the lipid-laden macrophage to remove more cholesteryl ester per cell from the arterial wall. In addition, the presently reported results support the possibility that verapamil may impede the development of atheroma formation by reduction of smooth muscle cell proliferation.

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PubMedDate not supplied

Use of 3H-cholesteryl linoleyl ether as a quantitative marker for loss of cholesteryl ester during regression of cholesterol-induced aortic atheromas in rabbits.

In this study, use was made of 3H-cholesteryl linoleyl ether (3H-CLE) to follow regression of aortic atheromatosis induced by feeding cholesterol to rabbits. After a 3-month induction period, the rabbits were divided into two groups with an attempt to match them by plasma cholesterol levels. They were injected with rabbit plasma labeled with 3H-CLE, and the baseline group rabbits were killed 10 to 12 days after injection. The experimental (regression) group rabbits were given rabbit chow containing 3% cholestyramine and were killed up to 330 days thereafter. Aortic 3H-CLE of both the baseline and the regression groups correlated highly with the plasma cholesterol levels at the time of injection of label. The radioactivity recovered in the aortas of the baseline and regression groups was not significantly different, indicating retention of label between day 12 and 330 days after injection. During that time, the mean aortic cholesteryl ester content decreased from 7.6 +/- 1.3 mg to 3.1 +/- 0.7 mg (p less than 0.01). The specific activity of 3H-CLE/cholesteryl ester determined in the aortic arch and the thoracic and abdominal aorta was significantly increased in all three regions examined in the regression group as compared to the baseline group. The present data show that 3H-CLE is retained in the atheromatous aorta for at least 330 days and that its use may add another dimension to the quantitative evaluation of regression of atherosclerotic lesions.

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PubMedDate not supplied

The effect of acute and chronic administration of nicotine on lipoprotein lipase activity.

Nicotine was injected intraperitoneally to rats and 2 h later lipoprotein lipase was determined in isolated perfused hearts. There was a significant increase in heparin releasable lipoprotein lipase activity which represents the functional pool without increase in total enzyme activity. When 1 microliter/h of a solution of nicotine (120 mg/ml) was delivered for 3 days from subcutaneously implanted miniosmotic pumps, total lipoprotein lipase activity in the heart increased 1.5-3.0 fold. Endogenous lipoprotein lipase activity in plasma doubled and there was a significant fall in plasma triglyceride levels. The effect of nicotine on heart lipoprotein lipase activity was evident also after 6 days of continuous delivery and was accompanied by a fall in adipose tissue lipoprotein lipase activity. No effect was seen when the dose of nicotine was halved. A positive correlation was seen between plasma nicotine levels and heart lipoprotein lipase activity, while adipose tissue lipoprotein lipase correlated negatively with plasma nicotine levels. Chronic administration of nicotine was accompanied by either weight loss or diminished weight gain. It is concluded that in the rat the acute effect of nicotine on the shift of lipoprotein lipase to the functional pool could be related to enhanced beta-adrenergic stimulation. The chronic effect of nicotine could have been mediated by the loss in body weight, due to reduced caloric intake.

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PubMedDate not supplied