Glycosaminoglycan — lipoprotein interactions: 1. Effect of uronic acid composition and charge density of the glycan

Static adhesion of cancer cells to glass surfaces coated with glycosaminoglycans

Using a previously described method for the functionalization of glass substrates with glycosaminoglycans (GAGs), in vitro experimental comparison of adhesion levels of cancer cells to glycosaminoglycan-modified substrates was performed with non-treated and heparin-treated human cancer cells of different metastatic activity. For both non-treated and heparin-treated cells, our results indicate that heparan sulfate is the preferred substrate for adhesion while keratan sulfate shows anti-adhesive properties. The observed net effect of heparin is a cell-dependent reduction in the adhesion figures. Overall, our results suggest that tissues with higher composition of heparan sulfate chains may be preferential metastatic targets and indicate that the effective use of heparin as anti-metastatic or anti-inflammatory agent may also depend on glycosaminoglycan composition of the affected organs.

Reduced proteoglycan binding of low density lipoproteins from monkeys (Macaca fascicularis) fed a fish oil versus lard diet

We examined the effect of isocaloric substitution of dietary fish oil for lard on the properties of low density lipoproteins (LDL) important in binding to arterial proteoglycans (PG). Cynomolgus monkeys (n = 10) were fed atherogenic diets enriched in fish oil or lard in a crossover study consisting of two 15-week phases of atherogenic diet separated by a 6-week monkey chow "wash-out period." LDL were isolated from plasma during each dietary phase, characterized for chemical and physical properties, and assessed for their ability to interact in vitro with arterial PG. Plasma LDL cholesterol was similar during fish oil and lard consumption (356 +/- 34 and 331 +/- 17 mg/dl, mean +/- SEM), but during fish-oil feeding relative to that of lard, LDL size was smaller (4.2 +/- 0.1 versus 4.9 +/- 0.1 g/mumol) and LDL particles differed in chemical composition. When animals were fed fish oil, significantly fewer (p less than 0.05) LDL particles bound to PG in both dietary phases: 1.00 +/- 0.27 (x10(12)) versus 5.31 +/- 0.83 (x10(12)) particles/micrograms PG in phase 1 and 3.56 +/- 0.67 (x10(12)) versus 6.00 +/- 0.52 (x10(12)) in phase 2 for LDL from animals fed fish oil and lard, respectively. These studies indicate that dietary fat-induced changes in LDL particles lead to altered in vitro interactions with artery wall PG and suggest a novel mechanism for the protective effect of fish oil against atherosclerosis.

Interaction of a high-affinity heparin subfraction with low-density lipoprotein stimulates cholesteryl ester accumulation in mouse macrophages

A high-affinity heparin subfraction accounting for 8% of whole heparin from bovine lung was isolated by low-density lipoprotein (LDL)-affinity chromatography. When compared to whole heparin, the high-affinity subfraction was relatively higher in molecular weight (11,000 vs. 17,000) and contained more iduronyl sulfate as hexuronic acid (76% vs. 86%), N-sulfate ester (0.75 vs. 0.96 mol/mol hexosamine), and O-sulfate ester (1.51 vs. 1.68 mol/mol hexosamine). Although both heparin preparations formed insoluble complexes with LDL quantitatively in the presence of 30 mM Ca2+, the concentrations of NaCl required for 50% reduction in maximal insoluble complex formation was markedly higher with high-affinity subfraction (0.55 M vs. 0.04 M). When compared to complex of 125I-LDL and whole heparin (H-125I-LDL), complex of 125I-LDL and high-affinity heparin subfraction (HAH-125I-LDL) produced marked increase in the degradation of lipoproteins by macrophages (7-fold vs. 1.4-fold over native LDL, after 5 h incubation) as well as cellular cholesteryl ester synthesis (16.7-fold vs. 2.2-fold over native LDL, after 18 h incubation) and content (36-fold vs. 2.7-fold over native LDL, after 48 h incubation). After a 5 h incubation, macrophages accumulated 2.3-fold more cell-associated radioactivity from HAH-125I-LDL complex than from [125I]acetyl-LDL. While unlabeled HAH-LDL complex produced a dose-dependent inhibition of the degradation of labeled complex, native unlabeled LDL did not elicit any effect even at a 20-fold excess concentration. Unlabeled particulate LDL aggregate competed for 33% of degradation of labeled complex; however, cytochalasin D, known inhibitor of phagocytosis, did not effectively inhibit the degradation of labeled complex. Unlabeled acetyl-LDL produced a partial (33%) inhibition of the degradation of labeled complex. These results indicate that (1) the interaction of high-affinity heparin subfraction with LDL leads to scavenger receptor mediated endocytosis of the lipoprotein, and stimulation of cholesteryl ester synthesis and accumulation in the macrophages; and (2) with respect to macrophage recognition and uptake, HAH-LDL complex was similar but not identical to acetyl-LDL. These observations may have implications for atherogenesis, because both mast cells and endothelial cells can synthesize heparin in the arterial wall.

Comparative study of the precipitation of low density lipoproteins by aortic proteodermatan sulphate and heparin

The aortic proteoglycans and heparin were shown to form insoluble complexes with human low density lipoproteins (LDL). The effect of temperature, polyethylene glycol and ionic strength on the formation of complexes between porcine aortic proteodermatan sulphate (PDS) and LDL has been studied by laser nephelometry and comparisons made with heparin LDL complexes. Turbidity was a nonlinear function of the quantity of LDL precipitated by PDS. The turbidity of aggregates was constant at temperatures between 2 degrees C and 30 degrees C but increased with temperature above 30 degrees C up to 50 degrees C. The formation of insoluble complexes decreased rapidly with increasing NaCl concentration. Polyethylene glycol enhanced the turbidity at 20 degrees C but not at 37 degrees C. It also increased the resistance of complexes to dissociation by increasing ionic strength. The turbidity of heparin--LDL complexes was linearly correlated with the quantity of precipitated LDL. The heparin-LDL aggregates were less sensitive to modification of temperature and ionic strength than the PDS-LDL aggregates. These results suggest that ionic interactions are weaker in PDS-LDL complexes than in the heparin-LDL complexes. Non-coulombic interactions and/or temperature dependent conformational changes may be involved in the stabilization of supramolecular PDS-LDL aggregates. No such interactions or changes appear to be involved in complex formation between heparin and LDL.

Low-density lipoprotein binding affinity of arterial wall proteoglycans: characteristics of a chondroitin sulfate proteoglycan subfraction

The characteristics of an arterial wall chondroitin sulfate proteoglycan (CS-PG) subfraction that binds avidly to low-density lipoproteins (LDL) was studied. A large CS-PG was extracted from bovine aorta intima-media under dissociative conditions, purified by density-gradient centrifugation and gel filtration chromatography, and further subfractionated by affinity chromatography on LDL-agarose. A proteoglycan subfraction, representing 25% of the CS-PG, showed an elution profile (with dissociation from LDL-agarose occurring between 0.5 and 1.0 M NaCl) corresponding to that of heparin, heretofore considered to be the most strongly binding glycosaminoglycan with LDL. The proteoglycan subfraction which migrated as a single band on composite agarose-polyacrylamide gel electrophoresis contained chondroitin 6-sulfate, chondroitin 4-sulfate and dermatan sulfate in a proportion of 70:22:8. The core protein of the proteoglycan had an apparent molecular weight of 245,000, and contained approx. 33 glycosaminoglycan chains with an average molecular weight of 32,000. The CS-PG subfraction, like heparin, formed insoluble complexes in the presence of 30 mM Ca2+. Complexing of LDL with proteoglycan resulted in two classes of interactions with 0.1 and 0.3 proteoglycan monomer bound per LDL particle characterized by an apparent Kd of 4 and 21 nM, respectively. This indicates that multiple LDL particles bind to single proteoglycan monomers even at saturation. In contrast, LDL-heparin interactions showed a major component characterized by an apparent Kd of 151 nM and a Bmax of 9 heparin molecules per LDL particle. The occurrence of a potent LDL-binding proteoglycan subfraction within the family of arterial CS-PG may be of importance in terms of lipid accumulation in atherogenesis.

Serum lipoprotein binding by Treponema pallidum: possible role for proteoglycans

Acquisition by the syphilis spirochaete, Treponema pallidum, of radioiodinated total human plasma lipoprotein and lipoprotein subfractions was examined. Time dependent and saturation binding kinetics were observed for total lipoproteins and subfractions, including high density lipoproteins, low density lipoproteins (LDL), and very low density lipoproteins. All subfractions competed equally well in binding iodinated total lipoproteins and individual subfractions, but apoproteins common to all subfractions were ineffective in inhibiting lipoprotein acquisition. The interaction of LDL with T pallidum was studied further and, interestingly, the presence of 17% sulphated dextran sulphate (DS) in the reaction mixture containing treponemes and LDL resulted in up to 172 times more LDL being bound by live treponemes. Biological variability was observed in the extent of increased LDL bound in the presence of 17% sulphated DS by preparations of T pallidum isolated from different infected rabbits. Saturation kinetics of iodinated LDL acquisition was obtained in the presence of 17% sulphated DS but not 1% sulphated DS. Other proteoglycan molecules, such as chondroitin sulphate, hyaluronic acid and heparin, and fibronectin, the extracellular matrix protein targeted by treponemes in parasitism of host cells and tissues neither diminished nor enhanced LDL binding by live treponemes. Only 5% and 10% of associated radioactivity was released from treponemal surfaces after T pallidum was incubated with iodinated LDL and 17% sulphated-DS for 15 and 30 minutes, respectively. These data show binding and possible internalisation of host lipoproteins by T pallidum, which may be mediated by sulphated proteoglycan. Sulphated proteoglycans accumulate during T pallidum infections of host cells.

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.

Fibronectin stimulates macrophage uptake of low density lipoprotein-heparin-collagen complexes

In this study, we investigated whether fibronectin will enhance macrophage uptake of particulate complexes of low density lipoproteins (LDL), heparin, and fibrillar collagen and whether fibronectin's opsonic effect could be modulated by the heparin component in these model matrices. We isolated a heparin fraction (HepFn) based on its affinity to fibronectin. HepFn appeared more charged than unfractionated heparin, as evidenced by enhanced electrophoretic mobility and ability to effect a cathodic shift in the electrophoretic migration of fibronectin. HepFn lacked the smaller molecular weight species present in unfractionated heparin. Macrophage endocytosis of LDL-heparin-collagen complexes, as evidenced by the intracellular accumulation of LDL-derived cholesteryl esters and endogenously synthesized cholesteryl esters, was enhanced by fibronectin. When LDL matrix complexes were prepared with HepFn, fibronectin's opsonic properties were significantly enhanced. F(ab)2 fragments of anti-fibronectin, capable of inhibiting fibronectin's opsonization of gelatin-derivatized latex particles, inhibited the fibronectin-dependent stimulation of cholesteryl ester synthesis by macrophages exposed to LDL-HepFn-collagen complexes. Thus, fibronectin stimulates macrophage endocytosis of LDL matrix complexes. The affinity of the constituent glycosaminoglycan for fibronectin is important in the regulation of this phenomenon.

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.