Proteoglycans in human coronary arteriosclerotic lesions.

Proteoglycans in human coronary arteries were characterized immunohistochemically, using specific monoclonal antibodies to distinct proteoglycan types. In addition, apoB, macrophage, and arterial smooth muscle cell alpha-actin markers were localized. The expression of chondroitin sulfate proteoglycans and apoB was observed in healthy areas (operationally defined by morphology) as well as in lesions in the intima, but with greater expression in the atheromatous lesions. In healthy intima heparan sulfate proteoglycan was cell associated, but in lesions it was found also in the extracellular space. A dermatan sulfate proteoglycan of decorin type was not observed in the healthy intima but was observed in the intima with adaptive thickening especially in zones with reduced staining for smooth muscle cell alpha-actin. In atheroma (fibrous plaque with necrotic core) decorin along with alpha-actin and macrophage marker stained brightly in the extracellular regions in fibrous cap (actively progressing lesion) but was sparse in fibrous base (quiescent lesion). The observations suggest that decorin along with extracellular alpha-actin and macrophage marker may be useful for differentiating lesions that tend to progress with disease.

Racial (black-white) differences in insulin secretion and clearance in adolescents: the Bogalusa heart study.

OBJECTIVE: Earlier we found black-white contrast in insulin levels in adolescents. The purpose of this study is to assess whether this difference is attributable to alterations in insulin secretion and/or clearance. METHODS: Fasting circulating insulin and C-peptide concentrations were examined in 1157 adolescents aged 11 to 18 years from a biracial community. Fasting plasma C-peptide, C-peptide to insulin ratio, and glucose to insulin ratio were used as indices of insulin secretion, hepatic insulin clearance, and insulin sensitivity, respectively. RESULTS: After adjusting several covariates (age, sexual maturation, and obesity), black adolescents had higher insulin levels (14.99 vs 12.66 microU/mL in girls). However, they had lower C-peptide levels than their white counterparts, indicating lower insulin secretion by pancreatic beta cells in black adolescents. Moreover, black adolescents had lower levels of C-peptide to insulin ratio than white adolescents (0.14 vs 0.17), suggesting reduced hepatic insulin clearance in black adolescents. In addition, significantly lower levels of glucose to insulin ratio in black girls suggest a reduced insulin sensitivity in this group. Further, differences in insulin levels between white and black girls disappeared after adjusting for differences in C-peptide to insulin ratio. CONCLUSION: These data suggest that elevated insulin levels observed in black adolescents, especially in black girls, may be attributed to their decreased hepatic insulin clearance, not hypersecretion of insulin.

Urinary N-acetyl-beta-D-glucosaminidase changes in relation to age, sex, race, and diastolic and systolic blood pressure in a young adult biracial population. The Bogalusa Heart Study.

Increased urinary activity of N-acetyl-beta-D-glucosaminidase (NAG) has been reported in many clinical conditions, including essential hypertension. Since hypertension is increasingly recognized as beginning in childhood, we hypothesized that urinary NAG changes with increasing blood pressure may start early in life and may also be the evidence of the existence of early hypertensive disease. We analyzed the urinary NAG changes in 980 young adults, ages between 18 to 32, in relation to age, race, sex, and systolic and diastolic blood pressure. We observed that black women had the highest level of NAG, with or without adjustment for creatinine. With aging, urinary NAG significantly increased in men. As blood pressure increased, urinary NAG excretion appeared to increase, and this was more apparent in black women (P < .05). Significant correlations between NAG excretion and systolic (r = 0.12, P = .04) and diastolic (r = 0.18, P = .003) blood pressures existed in the oldest age group, 28 to 32 years old. These findings show that a significant association between urinary NAG and blood pressure exists in normal young adults and changes in urinary NAG may be evidence of early hypertensive disease.

Rationale to study the early natural history of heart disease: the Bogalusa Heart Study.

The Bogalusa Heart Study now establishes that precursors of adult cardiovascular diseases begin in childhood. The clearest evidence comes from autopsy studies that show coronary atherosclerotic lesions occur in early life and are strongly associated with very-low-density lipoprotein cholesterol, systolic and diastolic blood pressure, and obesity, and have an inverse relationship with high-density lipoprotein cholesterol. Observations of cardiovascular risk factors span a period of life from birth to 31 years of age, and longitudinal studies span a 15-year period. Risk factor variables tend to persist over time, "track." Although tracking is best for height and weight, low-density lipoprotein cholesterol and serum total cholesterol track at a high order; blood pressure tends to track at a lower order. Obesity and body fatness have an adverse influence on risk factors in children, just as noted in adults, with central obesity becoming more obvious after puberty, and having a greater adverse effect on risk factors. The emergence of abnormal levels of risk factors by adult criteria begins to occur in young adults, and is not evident in childhood. Retrospective studies, interestingly, for obesity, higher blood pressure, and dyslipidemia reveal evidence of their presence already in childhood. These findings have strong implications for undertaking prevention in early life.

Does adult-onset diabetes mellitus begin in childhood?: the Bogalusa Heart Study.

Children and young adults (N = 52, age 7-31, average 15.3 years) from parents with or without a history of onset of diabetes mellitus after the age of 30 years were studied for anthropometric and metabolic parameters related to diabetes. An oral glucose tolerance test was performed and blood samples were collected fasting and 15, 30, and 60 minutes after a standard glucose load. Offspring of diabetic parents were significantly heavier and more obese, although not uniformly overweight. Blood pressure, fasting insulin, glucagon, and triglycerides were significantly higher in offspring of diabetic parents. Approximately one-half of the offspring and siblings of diabetic parents had 30-minute blood glucose levels greater than 161 mg/dL, whereas none of the controls exceeded this level. These observations suggest abnormalities consistent with diabetes mellitus are already present in children and young adults, and may be detected by a response to glucose load.

Primary structure of bovine aorta biglycan core protein deduced from cloned CDNA.

Two overlapping cDNA clones for core protein of a biglycan of bovine aorta were isolated from a pSPORT bovine aorta tissue cDNA library. The 2043-bp cDNA contains a 114-bp 5' untranslated region, a 1224-bp cDNA open reading frame and a 705-bp 3' untranslated region. The encoded core preproprotein contains a prepeptide (residues no. -37 to -19) and a propeptide (residues no. -18 to -1), with 369 amino acid residues corresponding to a molecular mass of 41.6 kDa. The deduced amino acid sequence revealed a striking homology to rat vascular smooth muscle cell, human bone and bovine articular cartilage biglycans from cell culture.

Low-density lipoprotein binding affinity of arterial chondroitin sulfate proteoglycan variants modulates cholesteryl ester accumulation in macrophages.

Proteoglycans are considered to facilitate lipid accumulation in the arterial wall, as part of the injury and repair process in atherogenesis. The present study determined (1) characteristics of arterial tissue chondroitin sulfate proteoglycan (CS-PG) monomers of versican type that vary in binding affinity to low-density lipoproteins (LDL), and (2) the ability of these variants to modulate LDL metabolism by macrophages. A large CS-PG devoid of dermatan sulfate (DS) was isolated and purified from bovine aorta intima-media under dissociative conditions. The proteoglycan was further subfractionated by LDL affinity chromatography into CS-PGI and CS-PGII variants, the former eluting at 0.1 M NaCl and the latter at 1.0 M NaCl. The core protein of both variants had a similar molecular mass (1.7 x 10(5). However, CS-PGII contained more glycosaminoglycan (GAG) chains (30 vs. 25) with higher average molecular mass (4.2 x 10(4) vs. 3.8 x 10(4)) than CS-PGI. Furthermore, CS-PGII contained a relatively higher proportion of CS6-sulfate to CS4-sulfate (65: 35 vs. 52: 48). Sulfate-to-hexosamine molar ratio of GAG measured approximately 1 in both variants. In terms of metabolism by macrophages, when compared to complex of LDL and CS-PGI, complex of LDL and CS-PGII produced consistent increase in degradation (10.3-fold vs. 8.4-fold over native LDL) and cell association (16.3-fold vs. 10.2-fold over native LDL) of the ligand, and stimulation of cholesteryl ester synthesis (8.4-fold vs. 6.4-fold over native LDL). CS-PGII was as potent as native CS/DS-PG aggregate, which is a complex made of proteoglycan monomers, hyaluronate, and link protein(s), in stimulating the above activities in macrophages. Thus, variations in LDL-binding affinity of CS-PG can potentially modulate the lipid accumulation in atherogenesis.

N-terminal sequence of a core protein from a biglycan isolated from bovine aorta.

A biglycan was isolated from bovine aorta intima media by 4M guanidine HCl extraction of the tissue; the material was fractionated and purified by using isopycnic ultracentrifugation and DEAE Sephacel ion-exchange chromatography. Core proteins, resulting from digestion of the proteoglycan preparation with chondroitinase ABC, were resolved by SDS-polyacrylamide gel electrophoresis into three bands. The apparent molecular weight of the fast migrating major protein band was 47 kDa and the other slow-moving minor protein bands were 90 and 105 kDa. These proteins were recognized by a monoclonal anti-proteoglycan deltaDi-6S (MAb 3-B-3/Cl). The amino acid composition of 47 kDa core protein revealed a high content of aspartic acid, glutamic acid and leucine, similar to those found for biglycans isolated from bovine cartilage, rat vascular smooth muscle cell culture and human bone. The N-terminal sequence of 47 kDa core protein was determined as Asp-Glu-Glu-Ala-X-Gly-Ala-Glu-Thr-Thr-X-Gly-Ile-Pro-Asp which is identical to the sequence of bovine articular cartilage biglycan. The proteoglycan had two glycosaminoglycan chains.

Consequences of prolonged inhalation of ozone on F344/N rats: collaborative studies. Part III: Effects on complex carbohydrates of lung connective tissue.

Glycosaminoglycans are constituents of proteoglycans, which are integral components of lung connective tissue. Glycosaminoglycans not only provide structural support to organs, but also influence extracellular matrix assembly, cell adhesion, and cell proliferation. Changes in the metabolism of glycosaminoglycans have been noted in several pulmonary diseases, for example, pulmonary fibrosis and emphysema. We studied quantitative and qualitative changes of glycosaminoglycans in the lungs of rats exposed to a range of ozone levels (0, 0.12, 0.5, 1.0 parts per million) for 20 months. Glycosaminoglycans were isolated from dry-defatted lung tissues through successive digestions by pronase, papain, and 2 M sodium hydroxide. The glycosaminoglycans then were fractionated into individual components using high-performance liquid chromatography. The concentration of total glycosaminoglycans in the tissues varied from 1.5 to 4.2 micrograms of uronate/mg of dry-defatted tissue. Although wide variations in total glycosaminoglycan concentrations exist among individual animals within each exposure group, regression analyses of data indicate a monotonic and statistically significant decrease of total glycosaminoglycans after ozone exposure (p = 0.02). Among individual glycosaminoglycans, hyaluronan, chondroitin 4-sulfate, and chondroitin 6-sulfate levels decreased significantly (p < 0.001, p < 0.05, and p < 0.01, respectively) in animals exposed to ozone when compared with control animals. Heparan sulfate concentration exhibited a significant (p < 0.05) trend toward increase with increasing doses of ozone, but the difference in heparan sulfate concentration between ozone-exposed animals and control animals was not significant. Gel filtration studies of glycosaminoglycans in pooled samples indicated that the molecular size of hyaluronan in animals exposed to ozone was lower than it was in control animals. We noted differences in heparan sulfate's chemical properties and affinity to antithrombin III in ozone-exposed animals and control animals. Although these studies do not provide the mechanism responsible for the observed changes in the lung glycosaminoglycans in ozone-exposed animals, the observations indicate that inhalation of ozone for 20 months affects normal cellular metabolism of proteoglycans, which may contribute to the functional impairment of the lung.

Microalbuminuria in young adults related to blood pressure in a biracial (black-white) population. The Bogalusa Heart Study.

The association between microalbuminuria and blood pressure levels was examined in young white and black adults (n = 1131) aged 19 to 32 years. Urinary ratio of albumin (mg/L) to creatinine (mmol/L) was used as an estimation of urinary albumin excretion. Black men and women compared with their white counterparts had higher levels of blood pressure. Significantly positive correlations between urinary albumin excretion and systolic and diastolic blood pressures were observed in black men (r = 0.20 and r = 0.24, P < .01) and black women (r = 0.15 and r = 0.14, P < .05). Similar correlations of significance were not seen in the white counterparts. Systolic and diastolic blood pressure levels were significantly higher in normotensive black subjects (< 140/90 mm Hg) with increased urinary albumin excretion (> or = 90th percentile) than in those without increased urinary albumin excretion. After accounting for potential confounding by age, sex, and body mass index, blacks in the uppermost systolic and diastolic blood pressure group were 7.1 times (95% CI, 2.0 to 25.8) and 4.8 times (1.3 to 18.3), respectively, as likely to have elevated albumin/creatinine excretion as those in the lowest group. In contrast, the likelihood for elevated albumin/creatinine excretion were 0.9 times (95% CI, 0.5 to 2.2) and 1.1 times (0.5 to 2.3), respectively, in whites, which were not significant. These data suggest that a stronger association between blood pressure levels and urinary albumin excretion exists in young blacks than in whites, which supports the notion that blacks may be more susceptible to renal damage from relatively low levels of blood pressure increases.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibronectin synthesis by aorta explants from rabbits fed high cholesterol diets.

Fibronectin synthesis was studied in aorta explants in culture from rabbits fed a high fat-high cholesterol diet. [3H]Mannose and [14C]leucine were used to label oligosaccharide side chains and the protein core, respectively. The synthesis was followed by monitoring immunoprecipitable fibronectin from the culture medium using polyclonal goat anti-rabbit fibronectin antibody. Synthesis of fibronectin increased by [14C]leucine (81%) and [3H]mannose (29%) incorporation over controls. On gel filtration, fibronectin synthesized by controls and cholesterol-fed rabbit resolved into four fractions. Pulse-chase experiment with [3H]glucosamine or [3H]leucine showed that fibronectin secreted by the aorta explants from rabbits fed high fat-high cholesterol diets incorporated an increased amount of radioactivity. Pulsing with [3H]mannose showed decreased incorporation of the label. During the chase period, the rate of secretion of fibronectin into the media by the hypercholesterolemic rabbit aorta explants was increased. The fibronectin that bound to the gelatin or heparin columns from cholesterol-fed rabbit aorta media had lower levels of [3H]mannose incorporated into the glycoprotein than the control. These results indicate that there is an alteration in carbohydrate composition of the fibronectin synthesized by the aorta explants from rabbits fed a high cholesterol diet. High fat-cholesterol intake could play a causative role in matrix dysfunction during atherogenesis by altering glycoprotein synthesis.

Injury to the arterial wall of rabbits produces proteoglycan variants with enhanced low-density lipoprotein-binding property.

The effect of arterial injury on proteoglycans (PG) and their ability to bind low-density lipoprotein (LDL) were studied in rabbits 12 weeks after balloon injury. Following biosynthetic labeling in an organ culture system, PG were isolated under dissociative conditions from deendothelialized areas (DEA), reendothelialized areas (REA), and uninjured areas (control) of the aortic tissue. DEA and REA tissues yielded 42-52% more PG and incorporated 39-67% more 35S-label into proteoglycans than control tissues. Ion-exchange chromatography of PG from DEA and REA tissues yielded PG-I, PG-II, and PG-III, while from control tissue only PG-I and PG-II. PG-II formed major portion (74-84%) of the isolated PG in all three tissue types. PGI preparations comprised entirely of heparan sulfate (HS)-PG of similar hydrodynamic size (Kav = 0.45-0.47). PG-II from DEA and REA tissues consisted of PGII-A (Kav = 0.02-0.04) and PGII-B (Kav = 0.32), while PG-II from control tissue contained only PGII-B with relatively smaller hydrodynamic size (Kav = 0.40). PGII-A preparations contained predominantly chondroitin sulfate (CS)-PG with no dermatan sulfate (DS); whereas PGII-B consisted mainly of CS/DS-PG, with relatively high proportion of DS in DEA and REA tissues vs. control tissue (50-54% vs. 43%). Further, the glycosaminoglycan chains of CS/DS-PG from DEA and REA tissues were 1.7-fold longer than those from control tissue. PG-III contained about 80% CS/DS-PG and 20% HS-PG; CS/DS-PG was similar to those found in PGII-B from DEA and REA tissues. HS-PG from PG-II and PG-III, unlike those from PG-I, was enriched with N-sulfated residues. PGI from all the three tissue types bound poorly to LDL. On the other hand, PGII-A, PGII-B, and PG-III from DEA and REA tissues showed enhanced ability to bind LDL, in that order. For example, the LDL-binding ability of PGII-B from DEA and REA was 2.9- to 3.1-fold above that from control tissue. Thus, arterial injury with or without regenerated endothelium produces proteoglycan variants with altered characteristics and enhanced LDL-binding ability.

Lipoprotein-proteoglycan complexes induce continued cholesteryl ester accumulation in foam cells from rabbit atherosclerotic lesions.

We studied the metabolism of lipoprotein-proteoglycan complexes by macrophage-derived foam cells. Foam cells were isolated from atherosclerotic rabbit aortas. ApoB-lipoprotein-proteoglycan complex was isolated from human aorta fibrous plaque lesions and LDL-proteoglycan complex was formed in vitro. Both in vitro and in vivo complexes stimulated cholesteryl ester synthesis in foam cells by a dose-dependent, saturable process that resulted in the intracellular accumulation of cholesteryl ester. Stimulation of cholesteryl ester synthesis was linear with time over a 32-h period. Polyinosinic acid inhibited the stimulation of cholesteryl ester synthesis by the complexes by 32-37%, whereas cytochalasin D only produced a 6-16% inhibition. Foam cells degraded 125I-LDL-proteoglycan complex and 125I-acetyl LDL in a saturable, dose-dependent manner. Excess unlabeled acetyl-LDL inhibited the degradation of 125I-LDL-proteoglycan complex by 52%, while LDL had no effect. Similarly, excess unlabeled complex suppressed the degradation of 125I-acetyl-LDL by 48%. Foam cells degraded 125I-methyl-LDL-proteoglycan complex to the same extent as 125I-LDL-proteoglycan complex. These results show that foam cells from atherosclerotic lesions metabolize lipoprotein-proteoglycan complexes predominantly via receptor-mediated endocytosis and consequently continue to accumulate intracellular cholesteryl ester.

Human monocyte-derived macrophages bind low-density-lipoprotein-proteoglycan complexes by a receptor different from the low-density-lipoprotein receptor.

We have shown recently that lipoprotein-proteoglycan complexes isolated from human atherosclerotic lesions stimulated cholesteryl ester synthesis in human monocyte-derived macrophages [Vijayagopal, Srinivasan, Radhakrishnamurthy and Berenson (1992) Arterioscler. Thromb. 12, 237-249]. The present study was conducted to determine the mechanism of cellular uptake of the complexes. A chondroitin sulphate-dermatan sulphate proteoglycan was isolated from normal human aorta and complexed to 125I-labelled human low-density lipoprotein (LDL). The binding and degradation of 125I-LDL-proteoglycan complex were then studied in human monocyte-derived macrophages. The specific binding and degradation of the complex showed saturability and concentration-dependency. The Kd for binding was 1.5 x 10(-8) M, which was greater than that reported for LDL in monocyte-derived macrophages. Binding of the complex was not subject to down-regulation. Chloroquine inhibited degradation of the complex and the resultant stimulation of cholesteryl ester synthesis. Limited treatment of macrophages with proteolytic enzymes abolished binding and degradation of the complex significantly. Macrophages bound 125I-methyl-LDL-proteoglycan complex to the same extent as 125I-LDL-proteoglycan complex. Excess LDL and proteoglycan did not compete against the binding of the complex; however, excess acetyl-LDL competed for 61% of the binding. Likewise, excess LDL-proteoglycan complex inhibited the binding of 125I-acetyl-LDL by 64%. Polyinosinic acid and cytochalasin D inhibited the binding of 125I-LDL-proteoglycan complex by 60% and 36% respectively. Compared with that of acetyl-LDL, the degradation of LDL-proteoglycan complex was retarded in human macrophages. The results indicate that the uptake of LDL-proteoglycan complex in human monocyte-derived macrophages is not mediated through binding to the LDL receptor; but occurs predominantly via the scavenger receptor, with phagocytosis playing a minor role in the process.

A monoclonal antibody that recognizes hyaluronic acid binding region of aorta proteoglycans.

A chondroitin sulfate-dermatan sulfate proteoglycan was isolated from bovine aorta intima by extraction of the tissue with 4 M guanidine hydrochloride. The proteoglycan was purified by CsCl isopycnic centrifugation followed by gel filtration and ion exchange chromatography. A monoclonal antibody C8F4 was developed to this core protein. The characteristics and specificity of the antibody were studied by an enzyme-linked immunosorbent assay (ELISA) using an alkaline phosphatase conjugated antibody (goat anti-mouse IgG). The antibody binding to the core protein was found specific and optimal at pH 7.0. The antibody recognizes either intact chondroitin sulfate-dermatan sulfate proteoglycan monomer, chondroitinase ABC digested monomer or chemically deglycosylated proteoglycan. Free chondroitin sulfates, keratan sulfate and hyaluronic acid did not compete for the antigenic sites in ELISA. Limited hydrolysis of the core protein by trypsin resulted in three peptides and only the peptide with a molecular weight M(r) = 40,000 was found capable of binding to hyaluronic acid. The antibody C8F4 recognized this hyaluronic acid binding peptide but did not recognize the other two peptides suggesting that the epitope(s) for this antibody is in the hyaluronic acid-binding region of the core protein. The antibody recognized the core proteins from bovine nasal cartilage proteoglycan and human aorta proteoglycan but did not recognize bovine aorta link protein, bovine serum albumin, human serum albumin, human transferrin, collagen Type I and fibronectin. The antibody was found useful to localize proteoglycans in atherosclerotic lesions in human aorta by immunohistochemical techniques.

Heparin stimulates proteoglycan synthesis by vascular smooth muscle cells while suppressing cellular proliferation.

We studied the effect of heparin on proteoglycan synthesis by bovine aortic smooth muscle cells in culture. Confluent, growth-arrested cells were incubated with [35S]sulfate, [3H]glucosamine or [3]serine in the presence of 0-600 micrograms/ml heparin. Metabolically labeled proteoglycans secreted into the culture medium and associated with the cell layer were analyzed. In cultures treated with heparin there was a dose-dependent increase in [35S]sulfate incorporation into secreted proteoglycans which reached a maximum (35% above controls) at 100 micrograms/ml heparin. At higher concentrations of heparin, the stimulatory activity declined and finally disappeared. Radioactivity in cell-associated proteoglycans increased significantly (16% above controls) only in cultures treated with 100 micrograms/ml heparin. Heparin also produced similar increases in the incorporation of [3H]glucosamine and [3H]serine into secreted and cell-associated proteoglycans. While chondroitin sulfate, dermatan sulfate and heparan sulfate were elevated in the media, only chondroitin sulfate and heparan sulfate were increased in the cell layer. Heparin did not alter the degradation of proteoglycans. Heparin, while inhibiting the proliferation of subconfluent smooth muscle cells, also stimulated to a greater extent the incorporation of [35S]sulfate into proteoglycans. Other glycosaminoglycans, such as heparan sulfate, dermatan sulfate, heparin hexasaccharide and Sulodexide caused a significant but lesser stimulation of proteoglycan synthesis, while chondroitin sulfates and hyaluronic acid had no effect. Gel filtration chromatography of proteoglycans and their constituent glycosaminoglycans from heparin-treated and untreated cultures showed no differences in their molecular size. The results indicate that heparin can stimulate proteoglycan synthesis by vascular smooth muscle cells irrespective of their state of proliferation. This might have implications in vessel wall repair and arterial wall lipid deposition.

Lipoprotein-proteoglycan complexes from atherosclerotic lesions promote cholesteryl ester accumulation in human monocytes/macrophages.

Lipoprotein-proteoglycan complexes from human atherosclerotic lesions were studied to determine their ability to stimulate cholesteryl ester accumulation in human monocytes/macrophages. Complexes containing apolipoprotein (apo) B lipoproteins and proteoglycans were extracted from fatty streaks and fibrous plaque lesions of human aortas by extraction with 0.15 M NaCl. Fractionation of the complex with Bio-Gel A-50m yielded a single fraction from fatty streaks and two fractions from fibrous plaques. The complexes were further purified by anti-apo B affinity chromatography and analyzed for apolipoproteins, lipids, and glycosaminoglycans Apo B was the only apolipoprotein present in the complexes. Although the complexes from fatty streaks and fibrous plaques contained varying proportions of hyaluronic acid, chondroitin 6-sulfate, and dermatan sulfate, heparin was present in only the fibrous plaque complexes. All three lipoprotein-proteoglycan complexes increased the rate of incorporation of [14C]oleate into cholesteryl [14C]oleate and stimulated cholesteryl ester accumulation in monocytes/macrophages. However, the complexes from fibrous plaques were more potent than those from fatty streaks in this regard. Cholesteryl ester synthesis that is mediated by the uptake of the complexes was dose dependent and showed apparent saturation, suggesting that cell surface binding may be required. Chloroquine, a lysosomotropic agent, inhibited cholesteryl ester synthesis that is induced by the complexes, indicating that lysosomal hydrolysis was essential. Cholesteryl ester synthesis that is mediated by the complexes was inhibited 70-79% by polyinosinic acid. Furthermore, excess unlabeled fibrous plaque complexes significantly inhibited the binding and internalization of in vitro 125I-low density lipoprotein (LDL)-proteoglycan complexes and 125I-acetylated-LDL and not 125I-LDL. These results suggest the involvement of the scavenger receptor in the uptake of the complexes. Phagocytosis played a minor role in the metabolism of these ligands because cytochalasin D inhibited cholesteryl ester synthesis, which is mediated by fibrous plaque complexes, by 7.5-25%. Cholesteryl ester synthesis increased linearly over 32 hours in macrophages incubated with the complexes, indicating an apparent lack of downregulation of binding sites. This resulted in the appearance of intracellular oil red O-positive lipid droplets. These studies show for the first time that apo B lipoprotein-proteoglycan complexes isolated from human atherosclerotic lesions can induce cholesteryl ester accumulation in monocytes/macrophages.

Studies on the mechanism of uptake of low density lipoprotein-proteoglycan complex in macrophages.

Earlier, we (Vijayagopal, P. et al. (1988) Biochim. Biophys. Acta 960, 210) showed that mouse peritoneal macrophages metabolize low density lipoprotein (LDL)-proteoglycan complex by a receptor pathway distinct from the acetyl-LDL receptor. Further studies were conducted to probe further into the mechanism of LDL-proteoglycan complex uptake by macrophages. Both 125I-methyl-LDL-proteoglycan complex and 125I-LDL-proteoglycan complex were taken up and degraded by the cells to the same extent. Similarly, the ability of these ligands to stimulate cholesteryl ester synthesis was also indistinguishable. These results rule out the possibility of apoB,E receptor involvement in the uptake of LDL-proteoglycan complex in macrophages. Sodium fluoride, cytochalasin D and aggregated LDL inhibited degradation of the complex by 24%, 26% and 28%, respectively, indicating that phagocytosis is only a minor pathway for the uptake. Both binding and degradation of the complex were not inhibited by excess hyaluronic acid suggesting that ligand recognition was not through hyaluronic acid binding sites. As compared to acetyl-LDL, the cellular degradation of LDL-proteoglycan complex was retarded. Macrophages exhibited a rapid stimulation of [3H]inositol trisphosphate (IP3) release and diacylglycerol production when incubated with LDL-proteoglycan complex. Furthermore, pertussis toxin produced a 62% inhibition of LDL-proteoglycan complex mediated IP3 release, suggesting that LDL-proteoglycan complex metabolism in macrophages is dependent upon the G-protein coupled signal transduction mechanism. These results show that receptor mediated endocytosis plays a major role in the metabolism of LDL-proteoglycan complex in macrophages.