Isolation of lipoprotein-acid mucopolysaccharide complexes from fatty streaks of human aortas

ADAMTS-5: A difficult teenager turning 20

A Disintegrin And Metalloproteinase with ThromboSpondin motif (ADAMTS)-5 was identified in 1999 as one of the enzymes responsible for cleaving aggrecan, the major proteoglycan in articular cartilage. Studies in vitro, ex vivo and in vivo have validated ADAMTS-5 as a target in osteoarthritis (OA), a disease characterized by extensive degradation of aggrecan. For this reason, it attracted the interest of many research groups aiming to develop a therapeutic treatment for OA patients. However, ADAMTS-5 proteoglycanase activity is not only involved in the dysregulated aggrecan proteolysis, which occurs in OA, but also in the physiological turnover of other related proteoglycans. In particular, versican, a major ADAMTS-5 substrate, plays an important structural role in heart and blood vessels and its proteolytic processing by ADAMTS-5 must be tightly regulated. On the occasion of the 20th anniversary of the discovery of ADAMTS-5, this review looks at the evidence for its detrimental role in OA, as well as its physiological turnover of cardiovascular proteoglycans. Moreover, the other potential functions of this enzyme are highlighted. Finally, challenges and emerging trends in ADAMTS-5 research are discussed.

Arterial heparan sulfate is negatively associated with hyperglycemia and atherosclerosis in diabetic monkeys

Background

Arterial proteoglycans are implicated in the pathogenesis of atherosclerosis by their ability to trap plasma lipoproteins in the arterial wall and by their influence on cellular migration, adhesion and proliferation. In addition, data have suggested an anti-atherogenic role for heparan sulfate proteoglycans and a pro-atherogenic role for dermatan sulfate proteoglycans. Using a non-human primate model for human diabetes, studies examined diabetes-induced changes in arterial proteoglycans that may increase susceptibility to atherosclerosis.

Methods

Control (n = 7) and streptozotocin-induced diabetic (n = 8) cynomolgous monkeys were assessed for hyperglycemia by measurement of plasma glycated hemoglobin (GHb). Thoracic aortas obtained at necropsy, were extracted with 4 M guanidine HCL and proteoglycans were measured as hexuronic acid. Atherosclerosis was measured by enzymatic analysis of extracted tissue cholesterol. Glycosaminoglycan chains of arterial proteoglycans were released with papain, separated by agarose electrophoresis and analysed by scanning densitometry.

Results

Tissue cholesterol was positively associated with hexuronic acid content in diabetic arteries (r = .82, p < .025) but not in control arteries. Glycosaminoglycan chain analysis demonstrated that dermatan sulfate was associated with increased tissue cholesterol in both control (r = .8, p < 0.05) and diabetic (r = .8, p < .025) arteries, whereas a negative relationship was observed between heparan sulfate and tissue cholesterol in diabetic arteries only (r = -.7, p < .05). GHb, which was significantly higher in diabetic animals (8.2 ± 0.9 vs 3.8 ± 0.2%, p < .0005) was negatively associated with heparan sulfate in diabetic arteries (r = -.7, p < .05).

Conclusions

These data implicate hyperglycemia induced modifications in arterial proteoglycans that may promote atherosclerosis.

Sphingomyelinase activity associated with human plasma low density lipoprotein

Isolated human plasma low density lipoprotein (LDL) was observed to possess sphingomyelinase activity. Accordingly, the formation of ceramide was catalyzed by LDL at 37 degrees C using tertiary liposomes composed of sphingomyelin (mole fraction (x) = 0.2), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (x = 0.7), 1, 2-dimyristoyl-sn-glycero-3-phospho-rac-glycerol (x = 0.1), and either the fluorescent sphingomyelin analog Bodipy-sphingomyelin or [(14)C]sphingomyelin as substrates. However, this activity was not present in either very low density lipoprotein or the high density lipoprotein subfractions HDL(2) and HDL(3). Oxidation of LDL abrogated its sphingomyelinase activity. Aggregation of the liposomes upon incubation with LDL was evident from the light scattering measurements. Microinjection of LDL to the surface of giant liposomes composed of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), N-palmitoyl-d-sphingomyelin (C16:0-sphingomyelin), and Bodipy-sphingomyelin as a fluorescent tracer (0.75:- 0.20:0.05, respectively) revealed the induction of vectorial budding of vesicles, resembling endocytosis.

Glycation of plasma low density lipoproteins increases interaction with arterial proteoglycans

The increased susceptibility to atherosclerosis of diabetic individuals, may result from diabetes-associated modification in plasma low density lipoproteins (LDL) which enhance their interaction with arterial extracellular matrix proteoglycans. Using a nonhuman primate model for human diabetes, studies were conducted to examine diabetes-induced changes in LDL. Plasma LDL were isolated from control (n = 4) and streptozotocin-induced diabetic (n = 3) cynomolgus macaques by differential ultracentrifugation. An in vitro binding assay was used to measure LDL interaction with arterial proteoglycans. Significantly more diabetic LDL bound to proteoglycans than control LDL (12.9+/-0.7 microg LDL cholesterol/microg proteoglycan versus 8.9+/-0.5 microg LDL cholesterol/microg proteoglycan (mean +/- S.E.M.), P < 0.005). Glycation of LDL, determined by fructosamine content, was significantly enhanced in diabetic versus control animals (37+/-3.1 versus 20+/-1.5 micromol/l (mean +/- S.E.M.) P < 0.005). The correlation coefficient between fructosamine content of LDL and its binding to arterial proteoglycans was 0.95. No LDL compositional variables other than glycation correlated with proteoglycan binding. Removal of the glycated portion of LDL from diabetic animals returned LDL proteoglycan binding to normal. These data demonstrate that the diabetes induced glycation of LDL increases its proteoglycan binding properties: thus, a critical mechanism in atherosclerosis, enhanced LDL interaction with arterial proteoglycans, may be accelerated by the diabetic state.

Aggregation of dimyristoylphosphatidylglycerol liposomes by human plasma low density lipoprotein

Turbidity (absorbance at 470 nm) measurements revealed human serum low density lipoprotein (LDL) to cause, within a few minutes and at physiological pH and [NaCl], the aggregation of liquid crystalline large unilamellar liposomes (LUVs) of dimyristoylphosphatidylglycerol (DMPG). No evidence for concomitant lipid or aqueous contents mixing was obtained with fluorescent assays for these processes, in keeping with the lack of fusion of LUVs. Involvement of apoB is implicated by the finding that tryptic digestion of LDL abrogates its ability to cause aggregation. Aggregation is not caused by VLDL, HDL2, or HDL3. Interestingly, also oxidised LDL failed to aggregate DMPG vesicles. Aggregation of DMPG LUVs by LDL did depend on the ionic strength of the medium as well as on the phase state of the lipid. More specifically, below the main transition temperature Tm maximal aggregation was seen in the presence of 25-100 mM NaCl, whereas slightly higher (up to 150 mM) [NaCl] were required when T>Tm. Aggregation due to LDL was also observed for dimyristoylphosphatidylserine as well as for dipalmitoylphosphatidylglycerol LUVs, whereas liposomes composed of either unsaturated acidic phospholipids or different phosphatidylcholines were not aggregated. Involvement of electrostatic attraction between the acidic phosphate of DMPG and cationic residues in apoB is suggested by the finding that increasing the content of dimyristoylphosphatidylcholine (DMPC) in DMPG liposomes reduced their aggregation and at XDMPC=0.50 no response was evident. Notably, increasing the mole fraction of 1-palmitoyl-2-oleyl-PG (POPG) in DMPG LUVs progressively reduced their aggregation by LDL and at XPOPG=0.50 there was complete inhibition. The latter effect of POPG is likely to be due to augmented hydration of the unsaturated lipid constituting a barrier for the contact between apoB and the vesicle surface. In keeping with this view, the presence of the strongly hygroscopic polymer, poly(ethylene glycol) at 1% (by weight) enhanced the aggregation and could partly reverse the inhibition by POPG.

Divalent cation-dependent interaction of sulfated polysaccharides with phosphatidylcholine and mixed phosphatidylcholine/phosphatidylglycerol liposomes

The Ca(2+)-dependent interaction of various polyanionic polysaccharides (chondroitin sulfate, heparin, dextran sulfate, beta-cyclodextrin sulfate, hyaluronic acid and carboxymethyldextran) with multilamellar dimyristoyl phosphatidylcholine (DMPC) liposomes was investigated by calorimetric and fluorescence spectroscopic measurements. It was found that an observed polysaccharide-induced phospholipid phase separation depends on the density of the sulfate groups along the polysaccharide chain independent of the presence of additional carboxyl groups. The phase separation resulting from the drastic dehydration of the covered membrane regions is monitored by the upward shift of the lipid phase transition and by the blue shift of the emission spectrum of a headgroup-dansylated phosphatidylethanolamine (DPE). This shift is only observable if the required polysaccharide chain length contains at least three glycosyl units. The Ca(2+)-mediated interaction of dextran sulfate with various phosphatidylcholines, differing in their compressibility, showed the maximal difference between the phase transition temperatures of the lipid phase covered by the polysaccharide and the uneffected lipid domains for dielaidinoyl phosphatidylcholine (DEPC), the most compressible phospholipid investigated here. Mixed negatively charged DMPC/dimyristoyl phosphatidylglycerol (DMPG) liposomes were found to compete with the likewise negatively charged dextran sulfate for the binding of Ca2+. At excess Ca2+ concentrations, the binding of the polysaccharide was strengthened, compared to pure DMPC liposomes. The monovalent cation sodium, was able to inhibit the interaction between the membrane surface and dextran sulfate. Various divalent cations were found to mediate the interaction, depending on their ionic radii and electron configuration. Within the second group of the periodic system Ca2+ is the most effective ion. However, within the horizontal forth period the ability to bind sulfated dextran to membrane surfaces decreases from Ca2+ to Ni2+, but then increases again if Cu2+ or Zn2+ was used as the mediating ion.

Alteration of glycosaminoglycans induced by cadmium in cultured vascular smooth muscle cells

Alteration of glycosaminoglycans (GAGs) in cultured bovine aortic smooth muscle cells after exposure to cadmium was investigated. It was revealed that cadmium increased the accumulation of GAGs metabolically labeled with [3H]glucosamine but decreased that with [35S]sulfate in the cell fraction, the cell surface fraction and the medium fraction. This suggested that cadmium stimulated the biosynthesis of GAGs but inhibited their sulfation in the cells. A similar alteration was observed in cadmium-treated human aortic smooth muscle cell layer. Of tested cations including cadmium, bismuth, cobalt, copper, lead, manganese, nickel and zinc, only cadmium stimulated [3H]glucosamine incorporation, with a strong inhibition of the [35S]sulfate incorporation in the bovine cells. Characterization of bovine smooth muscle GAGs showed that the cadmium-induced increase in the [3H]glucosamine incorporation was mainly observed in heparan sulfate; the inhibition of the [35S]sulfate incorporation occurred non-selectively. Cadmium accumulated in bovine vascular smooth muscle cells in a dose-dependent manner with an increase in the leakage of lactate dehydrogenase into the medium. The present data suggest that vascular smooth muscle cells respond to the cytotoxicity of cadmium and promote the GAG synthesis with a reduction of their sulfation. It is postulated that this response may be a defensive one to the damage of the vascular tissue caused by cadmium but would be a component of the metal-induced atherosclerosis.

Isolation of lipoprotein-proteoglycan complexes from balloon catheter deendothelialized aortas and the uptake of these complexes by blood monocyte-derived macrophages

Lipoprotein-Proteoglycan (LP-PG) complexes from the neointima, developed in response to injury, were studied to examine their ability to stimulate lipid accumulation in blood monocyte-derived macrophages (BMDM). LP-PG complexes were extracted from intimal-medial tissues from normal and balloon catheter deendothelialized aortas of normocholesterolemic rabbits, in 0.16 M NaCl for 24 h at 4 degrees C. The extract was purified through an anti-apo-B affinity column. Adsorbed material dissociated with 4 M Gu-HCI buffer was analyzed for lipoproteins (LP) and glycosaminoglycans (GAG). Results demonstrated that LP-PG complexes consisted of apo-B associated with chondroitin sulfate and hyaluronic acid. BMDM were incubated with 125I-LP, 125I-LP-NPG (from normal aortas) or 125I-LP-IPG (from injured aortas) for 20 h at 37 degrees C. LP binding, internalization and degradation was markedly increased for LP-NPG and LP-IPG over native LP. Phagocytosis appeared to be the primary route of uptake of LP-PG complexes. Competition experiments indicated that about 40% of the uptake of LP-PG complexes is mediated by the apo-B/E receptor pathway. The scavenger receptor played a minor part in the uptake of LP-PG complexes. Data from this study indicate that LP-PG complexes are present in normal and injured aortas of normocholesterolemic rabbits and these complexes accelerate LP uptake by BMDM more than native LP. Therefore, LP-PG complexes may contribute to lipid accumulation by BMDM, thus generating foam cells. Furthermore, LP-PG complexes prepared from PG of injured aortas are more effective in lipid accumulation than LP-PG complexes from PG of normal aortas.

The role of cholesterol accumulation in prosthetic vascular graft anastomotic intimal hyperplasia

PURPOSE

To demonstrate that modulation of plasma cholesterol concentrations affects prosthetic vascular graft anastomotic intimal hyperplasia (AIH), aortic grafts were examined histologically and biochemically in 41 rabbits.

METHODS

Twenty-seven rabbits were fed standard rabbit diet, whereas 14 were fed cholesterol-supplemented diet to induce hypercholesterolemia.

RESULTS

A smooth muscle cell proliferative response, similar to AIH in humans, was seen equally at the proximal and distal anastomoses. However, surface area and thickness of AIH were significantly greater in rabbits with hypercholesterolemia. Anastomotic tissue cholesterol concentrations were fifteenfold higher in rabbits with hypercholesterolemia than in rabbits with normal cholesterol concentrations and anastomotic cholesterol concentrations were fivefold higher than in the aorta away from the graft in rabbits with hypercholesterolemia. Preferential deposition of radioiodinated dilactitol tyramine coupled to low-density lipoproteins, but not albumin, was demonstrated in anastomotic areas and grafts of rabbits with normal cholesterol concentrations as well. Surface area and thickness of AIH correlated closely with plasma and tissue cholesterol concentrations.

CONCLUSIONS

Oxidized products of lipoproteins have been shown to stimulate production of growth factors that cause smooth muscle cell proliferation, migration, and synthetic function. It is likely they play an important part in prosthetic vascular graft AIH, similar to their role in atherogenesis.

Tumor necrosis factor alpha-induced alteration of glycosaminoglycans in cultured vascular smooth-muscle cells

We studied alteration of glycosaminoglycans (GAGs) induced by recombinant human tumor necrosis factor alpha (rhTNF alpha) in vascular smooth-muscle cells from bovine aorta in a culture system. It was found that rhTNF alpha at 10 ng/ml and below significantly increased the incorporation of [35S]sulfate (35S) but conversely decreased that of [3H]glucosamine (3H) into GAGs in the trypsinate fraction of the cell layer after a 24-h incubation. These results suggested that rhTNF alpha reduced the formation and/or the anchorage of sugar chains in the cell layer but enhanced their sulfation in whole GAG synthesis by the cells. In results, the ratio of 35S to 3H in the GAGs was markedly increased. This increase occurred after 24 h and longer when the cells were treated with 1.0 ng/ml rhTNF alpha. The TNF alpha-induced alteration of the incorporation of both 35S and 3H was completely blocked by anti-rhTNF alpha antibody. Other cytokines including recombinant human interleukin-1 beta and -6, and platelet-derived growth factor failed to alter the ratio of 35S to 3H in the GAGs of the trypsinate fraction of the cell layer. In cultured vascular endothelial cells from bovine aorta, however, rhTNF alpha at 1.0 ng/ml significantly decreased the incorporation of both 35S and 3H into GAGs of both the trypsinate fraction and the medium; the ratio of 35S to 3H was not changed. Characterization of GAGs in vascular smooth muscle cell trypsinate fraction revealed that rhTNF alpha at 10 ng/ml induced (i) no change of the incorporation of 3H in the hyaluronate fraction, (ii) a marked increase in the incorporation of 35S and no change of that of 3H in chondroitin sulfates (A plus C) fraction, (iii) a significant decrease in the incorporation of both 35S and 3H in the heparan sulfate fraction, and (iv) no change of the incorporation of 35S and a marked decrease in that of 3H in the dermatan sulfate fraction. In the medium, rhTNF alpha also induced various changes of GAGs. It was therefore concluded that TNF alpha may have a capacity of inducing a qualitative change of vascular smooth-muscle cell GAGs, which may be involved in the vascular pathology such as atherosclerosis.

Metabolism of LDL in mast cells recovering from degranulation. Description of a novel intracellular pathway leading to proteolytic modification of the lipoprotein

Rat serosal mast cells contain cytoplasmic secretory granules composed of a proteoglycan matrix in which histamine and neutral proteases are embedded. On stimulation, these granules are exocytosed, but some of them remain in the degranulation channels where on exposure to the extracellular fluid, they lose their histamine and a fraction of their proteoglycans. In vitro, such granule remnants efficiently bind low density lipoprotein (LDL) present in the incubation medium. After a lag period of about 10 minutes, the granule remnants, still within the channels and coated with LDL particles, are internalized by the parent mast cells. During subsequent recovery from degranulation, the apolipoprotein B of the intracellularly located remnant-bound LDL becomes efficiently (up to 70%) degraded by the proteolytic enzymes of the granule remnants. Since the granule remnants lack cholesteryl esterase activity, no LDL cholesterol is made available for cellular nutrition. Instead, selective proteolytic degradation of the bound LDL leads to formation of LDL particles enlarged by fusion on the granule remnant surface. In response to restimulation of the mast cells, about 50% of the fused LDL particles are exocytosed with the granule remnants. Of these, about one in five are expelled into the incubation medium. The granule remnants that again remain in the degranulation channels bind and internalize more LDL. This "round trip" of LDL in mast cells exposed to repeated stimulation constitutes a hitherto-unknown intracellular pathway for modification of LDL.

Altered susceptibility to in vitro oxidation of LDL in LDL complexes and LDL aggregates

Low density lipoprotein (LDL) is known to form complexes with polysulfated compounds, like heparin, dextran sulfate (DS), and chondroitin sulfate. In particular, chondroitin 6-sulfate (C6S)-rich proteoglycans of the arterial intima can associate with LDL, resulting in accumulation of LDL in atherosclerotic lesions. Besides LDL complex formation, LDL self-aggregation has been recently suggested to play a role in atherogenesis. Oxidative modification of LDL has also been implicated as a factor in the generation of the atherosclerotic plaque. Assuming that LDL self-aggregation may alter the molecule's susceptibility to oxidative modification, we have studied the sensitivity of LDL in LDL a aggregates as well as in insoluble and soluble LDL-C6S, LDL-heparin, and LDL-DS complexes to in vitro oxidation by cooper ions. Complexing the LDL with C6S and heparin resulted in an increased susceptibility of LDL to in vitro oxidation, whereas the oxidation of LDL complexed with DS was unaffected. In great contrast to the oxidation of LDL in LDL complexes, the in vitro oxidation of LDL in LDL aggregates (self-aggregation by denaturation) was strongly reduced. The results suggest that complex or aggregate formation may alter the susceptibility of the lipoprotein to oxidative modification and finally its metabolic fate or biological activity.

Interactions of LDL and modified LDL with mesangial cells and matrix

Hyperlipidemia may play a role in the progression of diabetic and other renal diseases. Low density lipoprotein (LDL) and other proteins including extracellular matrix components undergo nonenzymatic glycation in vivo. We examined the effects of glycation of LDL as occurs in diabetes (4 to 8%) on binding and uptake by mesangial cells and their proliferation. The glycation of LDL (g-LDL) significantly decreased its binding and uptake by mesangial cells by 15 to 20%, indicating that glycated LDL binds to the LDL receptor, but with lower affinity than LDL. Both LDL and g-LDL modestly stimulated [3H] thymidine incorporation into mesangial cells at 5 to 10 micrograms/ml. Native, oxidized (Ox-LDL) and glycated LDL all bound to the extracellular matrix generated by rat mesangial cells in culture. The binding of LDL, Ox-LDL and g-LDL to mesangial matrix was two to four times higher than to mesangial cells. Binding of LDL and g-LDL was significantly higher to glycolaldehyde modified matrix, which serves as an in vitro model for nonenzymatic glycation end-product cross-linking of matrix which occurs in long-standing diabetes. Based on these findings, we propose that glycation of LDL decreases its binding and uptake by the LDL receptor of mesangial cells and may slow its catabolism. Furthermore, LDL bound to extracellular mesangial matrix can undergo oxidation and generate cytotoxic LDL components. This process may be further enhanced by advanced glycation of the mesangial matrix in diabetes, contributing to glomerular pathology.

Effect of arterial proteoglycans and glycosaminoglycans on low density lipoprotein oxidation and its uptake by human macrophages and arterial smooth muscle cells

The reversible interaction of low density lipoprotein (LDL) with arterial chondroitin sulfate proteoglycans (CSPGs) or glycosaminoglycans (GAGs) selects LDL particles with a high affinity for sulfated GAGs and also induces modifications in apolipoprotein B (apo B) and the lipid organization of the lipoprotein. In the present work we studied the effect that the reversible interaction with sulfated polysaccharides has on the susceptibility of LDL to in vitro oxidation. For this purpose soluble, nonaggregated CSPG- or GAG-treated LDL was subjected to oxidation in the presence of 5 microM CuSO4 for as long as 48 hours. The rate of formation of thiobarbituric acid-reactive substances, the decrease in isoelectric point, the increase in relative electrophoretic mobility of LDL, the higher degradation rate by human macrophages, and the lower degradation rate by human arterial smooth muscle cells showed that LDLs exposed to CSPGs and GAGs were significantly more susceptible to oxidation than native LDL. Results from competition experiments indicate that C6S-treated LDL after 4 hours of oxidation is taken up via the acetylated LDL receptor in human macrophages. Coincubation of lipoproteins with human macrophages or human arterial smooth muscle cells for 24 hours also indicated that C6S-treated LDL was more susceptible to cell-induced modifications than native LDL. The occurrence in vivo of similar processes may contribute to focal retention, increased rate oxidation of LDL in the arterial intima, and foam cell formation during atherogenesis.

Molecular parameters that control the association of low density lipoprotein apo B-100 with chondroitin sulphate

The association of low density lipoprotein (LDL) with proteoglycans of the arterial intima, in particular chondroitin 6-sulphate proteoglycans, may contribute to LDL accumulation during atherogenesis. We studied the interactions of apolipoprotein B-100 (apo B-100) peptide segments and model peptides with chondroitin 6-sulphate. The ability of these peptides to inhibit complex formation between LDL and chondroitin 6-sulphate was used as a measurement of the interaction. Results from earlier studies suggest that surface located segments of apo B-100 are responsible for the interaction of LDL with heparin and chondroitin sulphate-rich arterial proteoglycans. Therefore 16 hydrophilic apo B-100 peptides were selected for studies and synthesized with a peptide synthesizer. These synthetic peptides were 7 to 26 amino acids long. Four of the peptides inhibited the association of LDL with chondroitin 6-sulphate, namely apo B segments 4230-4254, 3359-3377, 3145-3157 and 2106-2121. The 3359-3377 segment was the most efficient. A common feature between the interacting peptides was an excess of positively charged side chains and based on these results we synthesized nine model peptides that shared sequence characteristics with the interacting apo B-100 peptides. Five of these: RSGRKRSGK, RSSRKRSGK, RGGRKRGGK, RSRSRSRSR and RGRGRGRGR were shown to block the LDL-chondroitin-6-sulphate association, RSRSRSRSR being the most effective. The results suggest that the optimal association of the peptides with chondroitin 6-sulphate is obtained with a minimal chain length of nine amino acids and a minimum of five positive charges and that flexibility in the binding region is important.

Human aortic proteoglycans of subjects from districts of high and low prevalence of atherosclerosis in China

The contents of three species of proteoglycans (PGs), heparan sulfate PG(HSPG), chondroitin sulfate PG(CSPG) and dermatan sulfate chondroitin sulfate PG(DSCSPG), in human thoracic aortas of subjects from districts of high (Beijin, in North China) and low (Nanning, in South China) prevalence of atherosclerosis in China were quantitated. Higher aortic HSPG and DSCSPG (but lower DS) in samples from Nanning than those from Beijing might be implicated in the lower prevalence of atherosclerosis in the former.

Stimulation of human arterial smooth muscle cell chondroitin sulfate proteoglycan synthesis by transforming growth factor-beta

Human platelet-derived transforming growth factor-beta (TGF-beta) is a cell-type specific promotor of proteoglycan synthesis in human adult arterial cells. Cultured human adult arterial smooth muscle cells synthesized chondroitin sulfate, dermatan sulfate, and heparan sulfate proteoglycans, and the percent composition of these three proteoglycan subclasses varied to some extent from cell strain to cell strain. However, TGF-beta consistently stimulated the synthesis of chondroitin sulfate proteoglycan. Both chondroitin 4- and chondroitin 6-sulfate were stimulated by TGF-beta to the same extent. TGF-beta had no stimulatory effect on either class of [35S]sulfate-labeled proteoglycans which appeared in an approximately 1:1 and 2:1 ratio of heparan sulfate to dermatan sulfate of the medium and cell layers, respectively, of arterial endothelial cells. Human adult arterial endothelial cells synthesized little or no chondroitin sulfate proteoglycan. Pulsechase labeling revealed that the appearance of smooth muscle cell proteoglycans into the medium over a 36-h period equaled the disappearance of labeled proteoglycans from the cell layer, independent of TGF-beta. Inhibitors of RNA synthesis blocked TGF-beta-stimulated proteoglycan synthesis in the smooth muscle cells. The incorporation of [35S]methionine into chondroitin sulfate proteoglycan core proteins was stimulated by TGF-beta. Taken together, the results presented indicate that TGF-beta stimulates chondroitin sulfate proteoglycan synthesis in human adult arterial smooth muscle cells by promoting the core protein synthesis.

Insoluble complex formation between low density lipoprotein and heparin. A 31P-NMR study

31P-NMR has been used to probe the motions of the phosphate moiety of phospholipid head-groups in samples of human low density lipoprotein (LDL) in which particle tumbling has been greatly reduced by increasing the viscosity of the medium, by forming an LDL gel by ultracentrifugation, or by precipitation with heparin. The 31P-NMR spectra of LDL gel give broad "powder-like" lineshapes, with the sign and magnitude of the anisotropy characteristic of the bilayer mesophase, which narrow as the temperature is raised from 5 to 45 degrees C. This narrowing occurs over the same temperature range as the core cholesteryl ester liquid-crystalline to liquid phase transition, suggesting interactions between the surface and core. The 31P lineshapes of LDL-heparin insoluble complexes are also "powder-like", but are broader than native LDL at all temperatures studied. The spectra were simulated assuming an axially-symmetric shielding tensor motionally narrowed by Brownian isotropic diffusion [Burnell et al. (1980) Biochim. Biophys. Acta 603, 63-69], allowing determination of the lateral diffusion coefficients, DT, and the chemical shift anisotropy, delta sigma, of the monolayer phospholipids. Relative to LDL gel, the temperature-dependence of DT was reduced in the LDL-heparin insoluble complexes, and delta sigma was increased from 50 to 60 ppm. The results suggest that insoluble complex formation slows phospholipid lateral diffusion in the LDL monolayer and alters the orientation and/or order of the head-group.

Variations in the composition of arterial wall isomeric chondroitin sulfate proteoglycans among different animal species

1. Isomeric chondroitin sulfate proteoglycans were extracted from human, bovine, swine and rabbit aortas by 4 M guanidine-HCl and were fractionated and purified by CsCl isopycnic centrifugation, Sepharose CL-4B gel filtration, DEAE-Sepharose ion-exchange chromatography and octyl-Sepharose hydrophobic interaction chromatography. 2. The molecular size and the composition of isomeric chondroitin sulfate proteoglycans varied among species. Variations were also noted in the composition and molecular weight of constituent glycosaminoglycan chains. 3. Observations made on chondroitinase ABC and chondroitinase AC digests of proteoglycans indicate that dermatan sulfate is linked to the core proteins through chondroitin sulfates.

Total glycosaminoglycans in the plasma of adults: effects of age and gender, and relationship to plasma lipids: a preliminary study

Plasma glycosaminoglycans and lipids have been measured in the plasma of 92 fasted males and females. In the males, glycosaminoglycans correlated significantly with age (r = 0.39), triglycerides (r = 0.44), and cholesterol (r = 0.30). When the effect of age was allowed for, the significance of the correlation between glycosaminoglycans and triglycerides was maintained (r = 0.36). Glycosaminoglycan levels are higher in females than in males. The correlation of glycosaminoglycans with age in women was only marginally significant. In both men and women the effect of age is attributable principally to an increase in glycosaminoglycan concentration in those over 54 years. The only lipid fraction correlating with glycosaminoglycans in females was VLDL cholesterol (r = 0.34) and by stepwise linear regression allowing for the effect of age, this significance was retained (beta = 0.34).

Affinity of LDL to a human arterial proteoglycan among male survivors of myocardial infarction

In the present study, the hypothesis that the affinity of LDL to arterial proteoglycans might discriminate myocardial infarction patients from controls were tested. The patients were 52 men who had sustained a myocardial infarction at an age of 50 years or less and the controls, selected from a random population sample, were matched to the patients for age and sex. Serum cholesterol, triglycerides, LDL-cholesterol, HDL-cholesterol and apoB discriminated patients from controls. In addition, LDL reactivity with arterial proteoglycans was significantly higher in patients than in controls. In a multiple regression analysis, with patient or control as the dependent variable, apoB levels, LDL proteoglycan reactivity and serum triglycerides appeared as independent contributors to the regression. These observations indicate that LDL reactivity with arterial proteoglycans is a new, highly significant factor which discriminates between young myocardial infarction patients and controls.

Low density lipoprotein interaction with artery derived proteoglycan: the influence of LDL particle size and the relationship to atherosclerosis susceptibility

An in vitro binding system was used to determine whether increases in LDL particle size and altered LDL chemical composition accompanying increased plasma cholesterol concentrations result in greater association of LDL with artery proteoglycan (PG) and whether the binding is related to atherosclerosis. LDL isolated from hypercholesterolemic atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons was complexed to purified White Carneau pigeon aorta-derived high molecular weight PG under conditions whereby PG monomers were saturated. Using LDL of molecular weight greater than 5.0 x 10(6) daltons from both pigeon breeds, an inverse correlation between LDL size and the number of LDL particles bound per micrograms PG was demonstrated (r = 0.87, P less than 0.01). This relationship was attributed to the increased size of the LDL particle rather than any modification in chemical composition known to occur when LDL size increases, suggesting the major effect was attributed to steric hindrance. White Carneau pigeons with high molecular weight LDL had more severe atherosclerosis and the PG-LDL complexes contained excess cholesterol but no relationship was seen between atherosclerosis and number of LDL complexed. In animals with LDL between 3.6 x 10(6) and 4.8 x 10(6) daltons, considerable variability in PG binding was apparent, but this also was not related to LDL chemical composition. In this group of pigeons, which were all White Carneau, the positive relationship of PG-LDL binding and aorta cholesterol concentration was significant (r = 0.67, P less than 0.05). These results suggest that factors other than chemical composition (perhaps surface charge or apoprotein conformation changes) influence PG-LDL binding and that the assessment of PG-LDL binding is useful in predicting atherosclerosis in animals that do not respond to hypercholesterolemia by increasing LDL size.

Soluble complex formation between low-density lipoprotein and glycosaminoglycans. A 2H and 31P-NMR, and quasi-elastic light scattering study

Soluble complex formation between LDL and heparin (HEP) and chondroitin sulfate (CS) has been studied by 2H- and 31P-NMR and light scattering. The 2H-NMR linewidths of [2H]HEP and [2H]C4S increase substantially upon binding to LDL, with the [2H]HEP linewidths broader at low glycosaminoglycan (GAG)/low density lipoprotein (LDL) ratios. Preliminary analysis of the bound C2H3 group correlation times suggests that the observed linewidths are determined by the complex size, and that both [2H]GAGs have similar motions when bound to LDL. The 31P-NMR data demonstrate that large LDL-HEP complexes (diameter approx. 50 nm) are formed only over a narrow range of HEP concentrations, whereas the size of LDL-CS complexes increases continuously over the range of CS concentrations studied, reaching values of 32-35 nm for both C4S and C6S. At the lower protein concentrations studied by light scattering (less than or equal to 1 mg/ml), the same trends are observed, although the mean diameters are less than those estimated by 31P-NMR. Soluble complex formation was unaffected by the presence of 2 mM Ca2+. Dilution studies demonstrate that complex size varies with protein concentration. The binding of GAGs to LDL was also examined by HEP-CS competition studies. HEP has the higher affinity while no differences in binding could be detected between C4S and C6S.

Interaction of native and cell-modified low density lipoprotein with collagen gel

We have examined the binding of native and cell-modified low density lipoprotein (LDL) to gels of Type I collagen. Diffusion of native 125I-LDL into the collagen gel was slow, reaching equilibrium after 24 to 48 hours, while L-3H-glucose, a low molecular weight marker, equilibrated in 6 hours. Binding of 125I-LDL was measured at 48 hours as the amount associated with the collagen after extensive washing. Binding was saturable with an increasing concentration of LDL. Prior incubation with cell-free culture medium resulted in modest, but progressive, increases in electrophoretic mobility and binding to collagen. Incubation with cells produced a marked increase in electrophoretic mobility and a 5- to 10-fold increase in collagen binding; the presence of butylated hydroxytoluene during incubation prevented both effects. These changes in LDL were induced by porcine aortic endothelial cells, smooth muscle cells, human skin fibroblasts, and a variety of cell lines, as well as by acetylation. There was a curvilinear relationship between the amount of LDL protein bound and the net negative charge of the LDL; increasing net charge was associated with progressively greater increases in binding. These results suggest a potential role for collagen in trapping lipid in the extracellular matrix of arterial intima by slowing the diffusion of and by binding LDL. The data also demonstrate that binding of LDL to collagen is enhanced by modifications that increase its net negative charge.

Low density lipoprotein binding affinity of arterial wall isomeric chondroitin sulfate proteoglycans

Although the selective interaction of low density lipoproteins (LDL) with arterial proteoglycans is known, information is lacking on LDL-binding affinity of different subspecies occurring within a proteoglycan family. Isomeric chondroitin sulfate proteoglycan preparations sedimenting at densities of 1.54 g/ml (D1), 1.50 g/ml (D2) and 1.46 g/ml (D3) were isolated from bovine aorta intima-media under dissociative conditions and subjected to equilibrium binding to LDL-agarose gel. D1, D2 and D3 contained 36%, 37% and 11% dermatan sulfate, respectively. Sulfate to hexosamine ratio was low (0.73) in D1 when compared to D2 and D3 (0.94 and 1.04). Of the total proteoglycans contained in D1, D2 and D3, 41%, 52% and 66% interacted with LDL, respectively. LDL-bound proteoglycans dissociated over a wide range of ionic strengths (0.15-1.0); in comparison, LDL-bound heparin dissociated within a narrow range (0.5-0.75). Unlike other preparations, 30% of bound D3 dissociated at an ionic strength of 1.0. In D1 and D2 the proportion of dermatan sulfate increased in proteoglycan fractions that were bound firmly to LDL, whereas a high affinity fraction in D3 contained no dermatan sulfate. Thus, isomeric chondroitin sulfate proteoglycans display considerable divergence with respect to LDL binding. This may depend not only on the degree of sulfation but on other characteristics of the chondroitin sulfate isomers as well.

Identification of Apo B-100 segments mediating the interaction of low density lipoproteins with arterial proteoglycans

The interactions of low density lipoprotein (LDL) and apolipoprotein (apo) B-100 segments with chondroitin-6-SO4 rich aortic proteoglycans aggregate (CSPG) were studied by using quantitative frontal elution affinity chromatography. The affinity of the agarose-CSPG was higher for LDL than for very low density lipoprotein and high density lipoprotein was not bound. LDL from different individuals had dissociation coefficients (Kd) from 28 to 179 nM. Experiments with tryptic hydrolysates of apo B suggested that the capacity of LDL to bind with CSPG resides in the protein. Nine apo B-100 hydrophilic peptides, 12 to 26 amino acids long, were selected, and three were found to interact with the agarose-bound CSPG: apo B P-1 (LRKHKLIDVISMYRELLKDLSKEA, residues 4230 to 4254), apo B P-2 (RLTRKRGLKLATALSLSNK, residues 3359 to 3377), and apo B P-11 (RQVSHAKEKLTALTKK, residues 2106 to 2121). These peptides competed with LDL for binding to the agarose-bound and soluble CSPG; apo B P-2 was the most effective. This correlates with Kd values: 63, 86, and 82 microM for apo B P-2, P-1, and P-11, respectively. The peptides shared an excess of positive-charged side chains. Apo B P-2 belongs to the lys- and arg-rich, LDL-receptor domain. Apo E also binds to the agarose-proteoglycan. The results suggest that apo B regions with sequences and charge distributions analogous to those of residues 3359 to 3377, 4230 to 4254, and 2106 and 2121 are among those responsible for the interaction of LDL with intima-media CSPG.

Composition of proteoglycans from human atherosclerotic lesions

Proteoglycans from human atherosclerotic lesions and from uninvolved aortic intima were isolated and their composition was studied. The tissues were sequentially extracted by guanidine hydrochloride followed by hydrolysis of the tissue by elastase. Chondroitin sulfate/dermatan sulfate proteoglycans were predominant in guanidine hydrochloride extracts of the tissue. Most of the heparan sulfate proteoglycans were released from the tissue by hydrolysis with elastase. The content of proteoglycan material, measured as uronate per unit weight of wet tissue, was lower in fatty streaks and fibrous plaques than in uninvolved tissue (0.58 and 0.48 mg vs. 0.7 mg/g wet tissue). The distribution of different glycosaminoglycans in guanidine hydrochloride-extracted proteoglycans was similar among the lesions and uninvolved tissue, but varied in the elastase-hydrolyzed extracts. Gel filtration studies suggested that the major proteoglycan material, chondroitin sulfate proteoglycans, from lesions had greater molecular weight than proteoglycans from uninvolved tissue. The studies indicate that alteration in intrinsic composition and molecular size of proteoglycans occurs in atherosclerotic lesions.

Effect of arterial proteoglycans on the interaction of LDL with human monocyte-derived macrophages

The effect of human arterial proteoglycans (PG1) on the interaction of low density lipoprotein (LDL) with cultured human monocyte-derived macrophages (HMDM) was studied. LDL was insolubilized by treatment with chondroitin-6-sulfate-rich, partially purified PG1. The LDL, resolubilized in culture medium, was added to HMDM. The PG1 pretreated LDL induced lipid accumulation in the HMDM, converting them into foam cells. Mass determination of lipids by spectrophotometric and chromatographic procedures showed a 2-4-fold accumulation of triglycerides, phospholipids, unesterified cholesterol and cholesterol esters in 48 h, in the HMDM incubated with PG pretreated LDL, when compared to those incubated with native LDL. Incorporation of [14C]oleic acid into the HMDM lipid esters correlated with the accumulation. Association of 125I-labeled LDL and of fluorescent labeled LDL (3,3-octadecyl indocarbocyanine) to HMDM also indicated that the PG1-pretreatment of LDL increased its uptake. Density gradient centrifugation, isoelectric focusing and electron microscopy showed that, when added to the cells, the PG1 pretreated LDL was not aggregated or altered in its surface charge. However, controlled trypsin treatment and polypeptide pattern analysis indicate that the accessibility of apoB has been altered. The results suggest that changes in the surface of LDL, induced by the arterial PG1, lead to increased endocytosis of the lipoprotein and stimulation of lipid synthesis in the macrophages. The possibility that a similar process may cause lipid accumulation in arterial macrophages is discussed.

Effects of mesoglycan sulfate on the arterial elastic module

Ten patients with peripheral obstructive arterial disease (POAD) in stages I and II according to Leriche-Fontaine, were subjected to therapy with mesoglycan sulfate (60 mg/day for twenty days), to evaluate the effect of the drug on the elastic module of the arterial wall. The wall elasticity was deduced from some Doppler velocitographic indices (arterial dynamics index, resistance index, perfusion pressure index, tibial distensibility index); from the analysis of systolic, protodiastolic, and end diastolic velocity variations; and from computerized analysis of the Doppler sound spectrum. The results show a significant improvement of arterial wall elasticity, which suggests a rational use for the drug in the initial stages of peripheral obstructive arterial disease.

Artery wall derived proteoglycan-plasma lipoprotein interaction: lipoprotein binding properties of extracted proteoglycans

Artery proteoglycan-lipoprotein binding characteristics were determined using intact, high molecular weight chondroitin sulfate proteoglycans (CS-PG) isolated from grossly appearing normal aortas of atherosclerosis susceptible WC-2 pigeons and plasma lipoproteins from normolipemic, randomly bred White Carneau pigeons. Optimum formation of particulate proteoglycan-lipoprotein complexes occurred in 5 mM Tris, 6 mM KCl, 4 mM CaCl2, 1 mM MgSO4, pH 7.2. The binding of CS-PG was specific for low density lipoprotein (LDL) and not high density lipoprotein (HDL). The relative importance of the intact monomeric structure of the PG was suggested in studies where glycosaminoglycan chains isolated from the PG monomer possessed less than 1% of the binding reactivity of the intact PG. The core protein prepared from the CS-PG monomer formed no measurable particulate complex.

Proteoglycan composition of rabbit arterial wall under conditions of experimentally induced atherosclerosis

The concentration and composition of proteoglycans (PG) of the neointima developed following balloon catheter removal of aortic endothelium in rabbits, were assessed. PG were extracted from the aortic intimal-medial tissues with 4 M guanidinium chloride in the presence of protease inhibitors and purified subsequently by cesium chloride gradient ultracentrifugation and fractionation by high-performance liquid chromatography (HPLC). PG so obtained was analysed for its protein, cholesterol and glycosaminoglycan (GAG) content. For the characterization of the GAG moiety, an exhaustive proteolytic digestion was done. The GAG were then recovered by ethanolic precipitation and their relative distribution was determined after a selective enzymatic digestion using specific enzymes. Results show a significant increase in the amount of PG in the areas of the injured arterial wall covered by regenerated endothelium. In addition, changes in the composition of GAG were also found in the PG isolated from experimental animals when compared to PG isolated from normal aorta. A marked increase in the content of chondroitin sulfates and dermatan sulfate of injured tissue was seen. Hyaluronic acid content also changed in response to de-endothelialization and cholesterol feeding, but only moderately. The content of heparan sulfate remained unaffected in experimental tissues. Furthermore, cholesterol feeding aggravated the injury-induced increment of GAG. These findings are consistent with previously reported morphological observations, and correlate well with reports that arterial injury and cholesterol feeding act synergistically in the evolution of the atherosclerotic lesion and provide further evidence that the interaction of lipid and PG of the arterial wall may be of particular importance to our comprehension of the pathogenesis of atherosclerosis.

Hypercholesterolemia and aortic glycosaminoglycans of rabbits fed semi-purified diets containing sucrose and lactose

This study was designed to evaluate the role of dietary sucrose and lactose in a semipurified diet as initiating factors for aortic glycosaminoglycan (GAG) and lipid changes. Rabbits were fed sucrose or lactose as 40% by weight of a semi-purified, cholesterol-free diet for 10 weeks. At the end of the feeding period there was no macroscopic evidence of atherosclerosis. Sucrose-fed rabbits had significantly higher plasma cholesterol and phospholipid levels than the lactose-fed rabbits and triglyceride levels were variably elevated in the sucrose group. Analysis of plasma lipoproteins indicated that sucrose elevated VLDL and LDL when compared to lactose. Only the higher molecular weight form of apo B (apo BH) could be demonstrated when apo B components of isolated lipoproteins were analyzed. Sucrose-fed rabbits had significantly more aortic cholesterol, cholesteryl ester and phospholipid and tended to have more GAG/mg dry defatted aorta than the lactose-fed rabbits. Plasma cholesterol levels correlated with aortic lipids and in the sucrose group, aortic cholesteryl ester and cholesterol were strongly correlated with aortic GAG particularly hyaluronic acid. Results suggest that the semi-purified diet alters aortic GAG composition but in order for the initiation of cholesterol accumulation a significant increase in plasma lipoprotein cholesterol is necessary.

Increase in glycosaminoglycan synthesis in familial hypercholesterolemic fibroblasts

The enzymes of biosynthesis are usually bound to membranes and require an undisturbed lipid environment for regulated activity. In familial hypercholesterolemia, this lipid environment is disturbed and there is a low cholesterol ester level in the cellular membranes that results from impaired processing of low density lipoprotein (LDL). Thus, altered activities of various synthesizing enzymes could be expected. In this study, we found that microsomal glucuronyltransferase activity was 3.4-fold higher in homozygous familial hypercholesterolemic skin fibroblasts (n = 5) than in normal fibroblasts (n = 8). The secretion rates of glycosaminoglycans in familial hypercholesterolemia were also higher and the incorporation of radiolabeled precursor into glycosaminoglycans was enhanced. In addition to the differences in total synthesis and secretion, we found an altered pattern of individual glycosaminoglycan species with respect to the carbohydrate backbone and a different degree of sulfation in familial hypercholesterolemia. Heparan sulfate with a high degree of sulfation was secreted at a particularly high rate by hypercholesterolemic fibroblasts. Although the affinity of this glycosaminoglycan for LDL is lower than that of dermatan sulfate, it might cause formation of enhanced LDL-glycosaminoglycan complex and induce the xanthomas and atheromas of familial hypercholesterolemia.

The effect of procyanidolic oligomers on the composition of normal and hypercholesterolemic rabbit aortas

Rabbits were fed with normal (group 1 and 2) and cholesterol rich diets (group 3 and 4) concomitantly to a daily peroral administration of 50 mg/kg procyanidolic oligomers (PCO) to groups 2 and 4. After 10 weeks, the cholesterol content of the blood serum and the excised aortic intima-media were significantly higher in groups 3 and 4 than in groups 1 and 2. The DNA, hydroxyproline, uronic acid contents were similar in aortic dry weight basis in all four groups. The intima-media samples were extracted successively with 0.15 M NaCl, 0.02 M sodium phosphate pH 7.4 (NaCl extract) and with 4 M guanidinium chloride, 0.05 M sodium acetate pH 5.8 prior (G1 extract) and following (G2 extract) hydrolysis of the collagen with collagenase. The cholesterol contents of G1 extracts were higher in groups 2 and 4 than in groups 1 and 3. The cholesterol content of aortic elastin increased with cholesterol feeding (group 3). With simultaneous administration of cholesterol and PCO the cholesterol content of aortic elastin in group 4 was significantly lower than in group 3. The uronic acid contents increased in G1 extracts and in the collagenase digest with PCO treatment of both normal and hypercholesterolemic rabbits. The ratio of dermatan-sulphate to chondroitin-sulphate decreased with hypercholesterolemia (group 3) and with PCO (group 2 and 4). The parallelism between increased cholesterol and uronic acid contents and modified glycosaminoglycan composition in G1 extract, indicate that the interaction of cholesterol with macromolecules of the aorta can be modulated by PCO. This drug modifies the extractibility of aortic cholesterol and glycosaminoglycans and reduces the association of cholesterol to elastin.

Lipoprotein-heparin-fibronectin-denatured collagen complexes enhance cholesteryl ester accumulation in macrophages

The sequestration of low-density lipoprotein (LDL) by components of the vascular extracellular matrix has long been recognized as a contributing factor to lipid accumulation during atherogenesis. The effects, however, that components of the extracellular matrix might have on LDL catabolism by scavenger cells have been little investigated. For these purposes we have prepared insoluble complexes of LDL, heparin, fibronectin, and denatured collagen (gelatin) and examined their effects on lipid accumulation, LDL uptake and degradation, and cholesteryl ester synthesis in mouse peritoneal macrophages. The results of these experiments have demonstrated that the cholesteryl ester content of macrophages incubated with a particular suspension of LDL, heparin, fibronectin, and collagen complexes is four- to fivefold that of cells incubated with LDL alone. The uptake of complexes containing 125I-LDL is rapid; however, in contrast to either endocytosed 125I-LDL or 125I-acetyl LDL, the degradation of complex-derived LDL is impaired. In addition, the uptake of complex-derived LDL stimulates the incorporation of [14C]oleic acid into cholesteryl oleate, however, the stimulation was a small fraction of that observed in cells incubated with acetyl LDL. Ultrastructurally, macrophages incubated with LDL, heparin, fibronectin, and collagen complexes did not contain many lipid droplets, but rather their cytoplasm is filled with phagosomes containing material similar in appearance to LDL-matrix complexes. These results indicate that components of the extracellular matrix can alter the catabolism of LDL by scavenger cells, suggesting that they may play a role in cellular lipid accumulation in the atherosclerotic lesion.

Proteoglycans in human atherosclerotic lesions--a pilot qualitative and quantitative study by ruthenium red

A pilot study was carried out to test whether normal human aorta and aortic atherosclerotic lesions obtained at post-mortem examination were suitable for the demonstration of proteoglycans (PGs) by ruthenium red (RR) staining, and whether by this method qualitative and quantitative differences of PGs might be detectable in various types of lesions and between lesions and the normal aortic intima. The results indicate that the PGs of the above tissues obtained at post mortem were clearly visualized by electron microscopy using the RR-indicator and were thus suitable for quantitative and qualitative evaluation. Of the RR-positive granules only those 20 nm and larger were assessed. RR-granules measuring 20-50 nm were present in normal intima and media, in increased concentration in the innermost part of the mixed fatty-gelatinous lesion, and in a decreased concentration in the fibrous cap of an atherosclerotic plaque. The same RR-granules were observed in a fatty streak and in addition 50-100 nm granules were present in this type of lesion; the overall RR-granule-concentration was reduced here. Granules of both sizes were interconnected by filamentous network. The differential presence of the large (and hitherto unreported) as well as the smaller granules in the various lesions is briefly discussed in the light of the present-day knowledge of tissue-PGs, and the importance of an examination in situ of the compound PGs-complexes in their native form, is emphasized.

Partial structure of the active moiety of a lipoprotein complexing proteoglycan from human aorta

Proteoglycans and glycosaminoglycans of the intima-media extracellular matrix have been stated to play a role in lipoprotein deposition associated with atherogenesis. It is therefore important to characterize the active lipoprotein-complexing moiety of these macromolecular aggregates. We have isolated a soluble proteoglycan aggregate of approximately 5 X 10(6) molecular weight after homogenization of human aortic intima-media in an isosmotic sucrose solution, sequential differential centrifugation, dialysis, exclusion chromatography and preparative electrophoresis. This proteoglycan aggregate, labelled lipoprotein-complexing proteoglycan (LCP), has been previously shown to form specific complexes with low density lipoproteins, either isolated or in sera. Density gradient centrifugation in dissociative conditions of the LCP, cellulose acetate acetate electrophoresis of the subfractions, chondroitinases treatment and high performance liquid chromatography of the unsaturated disaccharides indicated that the glycosaminoglycan moiety was composed of 56% chondroitin-6-SO4, 26% hyaluronate and/or undersulfated chondroitin and 17% chondroitin-4-SO4. In pore-gradient polyacrylamide gel electrophoresis, the hyaluronate monomer appeared to have a molecular weight of 250000 while that of the chondroitin sulfates ranged between 50000 and 70000 after extensive treatment with protease. The fractions enriched in the chondroitin sulfate monomers were the most reactive towards LDL and their reactivity was abolished by chondroitinase AC indicating that the lipoprotein-complexing capacity of the LCP aggregate is associated to these molecules.

Proteoglycan distribution in areas of differing permeability to Evans blue dye in the aortas of young pigs. An ultrastructural study

We studied proteoglycan distribution in areas of spontaneously occurring high and low permeability by TEM examination of ruthenium red-stained sections of the aortic arch of normolipemic and hyperlipemic pigs. We noted granules of two sizes: those smaller than 20 nm contained heparan sulphate, and those from 20 to 50 nm in size contained chondroitin or dermatan sulphate. In the aortas of pigs fed a normal diet, there were significantly more granules of both types in low permeability areas than in areas permeable to Evans blue dye. This is consistent with the theory that glycosaminoglycan provides a component for the control of aortic permeability. In the aortas of pigs fed cholesterol, there was an accumulation of lipid-filled monocytes in areas of high permeability and an increase in proteoglycan granule concentration, suggesting an increase in glycosaminoglycan concentration, which may be the precursor to extracellular lipid deposition.