Retention Of Low-density Lipoprotein Research Articles

Interaction of arterial cells. I. Endothelial cells alter cholesterol metabolism in co-cultured smooth muscle cells.

Results of previous in vivo experiments indicated that the presence of arterial endothelium modifies cholesteryl ester (CE) metabolism and the retention of low density lipoproteins (LDL) in injured arteries. We describe herein the effects of bovine arterial endothelial cells (ENDO) on the CE cycle, fluid phase endocytosis, and cell proliferation in co-cultured bovine arterial smooth muscle cells (SMC). Following several days of cultivation on confluent SMC, ENDO were removed from SMC by treatment of the co-cultures with 1.0% collagenase (type II). Removal of only ENDO from the co-culture dishes was confirmed by immunofluorescent staining for Factor VIII antigen, hemotoxylin-eosin staining, and biochemical analyses. We observed that ENDO grown to 75% confluency on confluent SMC induced: 1) a reduction of CE hydrolysis as a result of decreased lysosomal CE hydrolytic activity in SMC as compared to SMC cultured alone; and 2) an increase in the rate of incorporation of labeled oleate into CE as a result of increased acyl CoA:cholesterol O-acyltransferase activity in SMC as compared to SMC cultured alone. Neither endothelial cell-derived culture media (ECDM) nor fibroblasts modulated CE metabolism in co-cultured SMC. Additional experiments showed that the presence of endothelial cells or ECDM decreased the proliferation of co-cultured SMC by 50%, but enhanced the endocytotic rate of labeled sucrose into SMC threefold. Results of experiments described herein demonstrate that, in addition to providing a thrombo-resistant surface and regulating permeability, endothelial cells may also serve to modulate cholesteryl ester metabolism in smooth muscle cells derived from the arterial wall.

Distribution of plasma proteins across the human aortic wall Barrier functions of endothelium and internal elastic lamina

The concentrations of plasma proteins of different molecular weights were measured in layers across the human aortic wall. On a volumetric basis the concentration of low density lipoprotein (LDL) in inner intima, adjacent to the endothelium, was almost twice the concentration in the patient's plasma. With the exception of transferrin, which behaved anomalously, the concentration of each protein was a linear function of its plasma concentration and molecular weight, so that the relative retention of albumin was only 15% of LDL retention and its concentration in inner intima less than one-quarter of the plasma concentration. Between the inner (luminal) and outer layers of intima the concentration of all proteins decreased by about 40%. In aortas in which the internal elastic lamina (IEL) appeared to be intact it provided an almost total barrier to LDL, but for smaller proteins the concentrations in the layer immediately outside it were inversely related to molecular weight; the concentration of LDL was only 0.3% of the intimal concentration whereas albumin was 26% of the intimal concentration. However, in aortas in which the IEL appeared morphologically frayed, fragmented or discontinuous there was an 80% increase in albumin, and a 25-fold increase in LDL in this layer. The differential barrier functions of endothelium and IEL produce bizarrely different macromolecular environments for smooth muscle cells in intima and media.

Modulation by sodium ascorbate of the effect of chloroquine on low density lipoprotein retention and degradation in cultured human skin fibroblasts

Human skin fibroblasts in culture were incubated for 48 h with 125I-labelled low density lipoprotein and chloroquine in the presence and absence of sodium ascorbate. Pretreatment of the cells for 3 days with sodium ascorbate and addition of the vitamin during incubation resulted in a decrease in cellular retention and an increase in degradation of the labelled low density lipoprotein. Similar results were obtained when the cells were pretreated for 3 days but the vitamin was not added during the final 48 h of incubation. Pretreatment of the cells with dithiothreitol, butylated hydroxy-toluene, β-mercaptoethanol and D-α-toco-pherol had a similar effect to that of ascorbate, i.e. reduction in low density lipoprotein retention and increase in degradation. Neither ascorbate nor the other reducing agents affected low density lipoprotein catabolism in control cells not treated with chloroquine. Sodium ascorbate pretreatment resulted also in a slight but significant alleviation of the chloroquine-induced inhibition of hydrolysis of cholesterol linoleate. It is proposed that sodium ascorbate by virtue of its reducing properties provides some protection to the intralysosomal hydrolases against the inhibitory action of chloroquine. If cholesterol accumulation in human and experimental atheroma is caused by partial inhibition of lysosomal enzymes, sodium ascorbate could play a role in the alleviation of such an inhibition.