Dynamics of lipoprotein-glycosaminoglycan interactions in the atherosclerotic rabbit aorta in vivo

Dynamics of lipoprotein-glycosaminoglycan interactions in aortas were studied in vivo using the atherosclerotic rabbit model. Severe hypercholesterolemia and atherosclerosis were produced by relatively long-term feeding of a high cholesterol diet. [35S]Sulfate uptake by aorta was measured to assess the sulfated glycosaminoglycan metabolism while the plasma and aorta distribution of 125I-labeled LDL after intravascular injection was determined to monitor aortic LDL uptake and complex formation with glycosaminoglycans. The retention and distribution of LDL as lipoprotein-glycosaminoglycan complexes in different extracellular connective tissue elements were evaluated by extracting the tissues with saline, collagenase and elastase. Hypercholesterolemia with atherosclerosis resulted in a several-fold increase in the uptake of LDL by aorta despite a marked reduction of 125I-labeled LDL in the plasma compartment and in a significant increase in glycosaminoglycan content of aorta coupled with an increased 35S incorporation into glycosaminoglycans. Elastase-solubilized fractions from normal aortas and collagenase-solubilized fractions from atherosclerotic aortas contained maximum labeled and nonlabeled glycosaminoglycan, suggesting alterations in the make-up of fibrous structures of connective tissue matrix in atherosclerosis. Saline extraction and collagenase and elastase digestions solubilized varied proportions of lipoprotein-cholesterol and 125I-labeled LDL, thereby representing different pools of extracellular matrixbound lipoproteins. A tendency for 125I-labeled LDL to increase in collagenase- and elastase-solubilized fractions with time (4 h vs. 24 h) was noted. The occurrence of both lipoproteins and glycosaminoglycan (labeled and nonlabeled) in the ultracentrifugal floating fraction at solvent density 1.063 g/ml demonstrated that the lipoproteins solubilized by different extraction procedures occur in part as lipoprotein-glycosaminoglycan complexes. The specific activities of glycosaminoglycan in the complexes obtained by different extraction procedures differed markedly (elastase greater than collagenase greater than saline), emphasizing the presence of different pools of complexes. Thus, besides arterial cell-mediated processes, extracellular matrix components are important in affecting the retention and accumulation of LDL in atherosclerosis.

Long-term effect of hyperlipidemic serum on the synthesis of glycosaminoglycans and on the rate of growth of rabbit aortic smooth muscle cells in culture

Rabbit aortic smooth muscle cells (SMCs) were successfully subcultured in 10% hyperlipidemic rabbit serum (HLS) for at least 9 passages. SMCs grown in HLS grew into higher cell densities than SMCs cultured in normolipidemic rabbit serum (NLS) for at least 4-5 passages in NLS and HLS, respectively. However, cells cultured in NLS and HLS for up to 7 passages had similar growth characteristics when they were trypsinised and seeded to grow in 10% fetal calf serum (FCS). Incorporation of [3H]glucosamine into GAGs was taken to represent their rate of synthesis. As compared with cultures incubated in 10% NLS, incubation of rabbit aortic SMCs in the presence of 10% HLS increased the synthesis of sulphated GAGs secreted into the pericellular space by 35% during the first 24 h of contact with HLS. After preincubation for one week in the presence of HLS the synthesis of sulphated GAGs secreted into the incubation medium and into the pericellular space was stimulated by 95% and 34%, respectively. The stimulation of the synthesis of sulphated GAGs by HLS continued for up to 4 weeks at least if the contact of the cells with HLS was maintained. When the cells were subcultured in the presence of NLS and HLS and seeded to grow in FCS after the 1st, 3rd and 7th trypsinisations, the synthesis of sulphated GAGs in cultures of cells from both sources was similar.

The effect of various dietary regimens and cholestyramine on aortic glycosaminoglycans during regression of atherosclerotic lesions in rhesus monkeys

The effect of various diets on the aortic glycosaminoglycan (GAG) composition was studied in rhesus monkeys. Aortas were obtained from monkeys fed diets containing cholesterol and comparative fats including coconut oil--butter and peanut oil and with and without cholestyramine. Additional groups in each experiment were placed on regression diets of low-fat, low-cholesterol with and without cholestyramine. Further, an atherogenic diet of coconut oil--butter was alternated every 2 months with a diet enriched with corn oil. GAG isolated from intima and media--adventitia indicated slight variations in the concentration of total GAG among different dietary groups but major differences in the concentration of individual GAG. The concentrations of hyaluronic acid and heparan sulfate were generally greater in aortas of monkeys fed corn oil diets than in those fed coconut oil--butter or peanut oil diets. The concentration of dermatan suulfate generally decreased during regression of lesions induced by the saturated fat--cholesterol diet. Furthermore, the aortas of monkeys with lesions from feeding peanut oil showed higher levels of dermatan sulfate and lower levels of chondroitin 4-sulfate than the saturated fat-fed groups. The addition of cholestyramine enhanced the effects of regression. These observations show that the composition of GAG of the arterial wall can be influenced by various dietary programs and that GAG play a role in induction and regression of experimental atherosclerotic lesions.