Evidence for an interaction of lipoprotein lipase with artery wall proteoglycans

Solid phase assays in glycoconjugate research: applications to the analysis of proteoglycans, glycosaminoglycans and metalloproteinases

Glycoconjugates are a class of macromolecules consisting of different constituents, one of which is sugar moieties. Glycoconjugates comprise the majority of tissue constituents, both intracellular and extracellular. Extracellular glycoconjugates (glycoproteins and proteoglycans) participate in a wide variety of interactions, through which they maintain tissue integrity. Therefore, their analysis or the study of their possible interactions would give evidence for the state of tissues. Since the amounts of some of the extracellular glycoconjugates are usually low or the amounts of tissue to be examined come from biopsies, specific analytical systems are developed for their study, the most familiar being solid phase assays, which have the advantages of analysis of multiple samples on the same time, cheap instrumentation and high specificity.

Apolipoprotein E mediates the retention of high-density lipoproteins by mouse carotid arteries and cultured arterial smooth muscle cell extracellular matrices

Lipoprotein retention in the vascular extracellular matrix (ECM) plays a critical role in atherogenesis. Previous studies demonstrated the presence of apo A-I and E in atherosclerotic lesions, suggesting that HDL may be trapped by the artery wall. We sought to determine mechanisms by which HDL could be bound and retained by the arterial wall, and whether apo E was a principal determinant of this binding. We evaluated in situ accumulation of fluorescently labeled DiI-human HDL+/-apo E in perfused carotid arteries from apo E-null mice. Apo E was important in mediating HDL binding to the vascular wall, with a 48+/-16% increase in accumulation of DiI-labeled apo E-containing HDL (HDL3+E) compared with DiI-apo E-free HDL (HDL3-E) (P=0.003). To investigate possible mechanisms responsible for retention, we assessed binding of unlabeled HDL3-E and HDL3+E to ECM generated by cultured arterial smooth muscle cells. Similar to the in situ carotid artery data, HDL3+E bound better to the ECM than did HDL3-E (3-fold lower K(a) and 3.5-fold higher B(max) for HDL3+E versus HDL3-E). These differences were eliminated after either neutralization of arginine residues on apo E or digestion of matrix with chondroitin ABC lyase, suggesting that chondroitin and/or dermatan sulfate proteoglycans were responsible for apo E-mediated increased binding. These findings demonstrate that HDL can bind to both intact murine carotid arteries and smooth muscle cell-derived ECM, and that apo E is a principal determinant in mediating the ability of HDL to be trapped and retained via its interaction with ECM proteoglycans.

Polylysine as a vehicle for extracellular matrix-targeted local drug delivery, providing high accumulation and long-term retention within the vascular wall

We present the first steps in the elaboration of an approach of extracellular matrix-targeted local drug delivery (ECM-LDD), designed to provide a high concentration, ubiquitous distribution, and long-term retention of a drug within the vessel wall after local intravascular delivery. The approach is based on the concept of a bifunctional drug comprising a "therapeutic effector" and an "affinity vehicle," which should bind to an abundant component of the vessel wall. The aim of the present study was to select molecules suitable for the role of affinity vehicles for ECM-LDD and to study their intravascular delivery and retention ex vivo and in an animal model. By use of fluorescence microscopy, the following molecules were selected on the basis of strong binding to cross sections of human vessels: protamine, polylysine, polyarginine, a glycosaminoglycan-binding peptide from vitronectin, and a synthetic dendrimer. With polylysine as a prototypic affinity vehicle, we showed that after intravascular delivery, polylysine was concentrated throughout a luminal layer of the vascular wall to an extremely high concentration of 20 g/L and was retained therein for at least 72 hours of perfusion without noticeable losses. Low molecular weight (fluorescein) and high molecular weight (hirudin) compounds could be chemically conjugated to polylysine and were retained in the vessel wall after intravascular delivery of the conjugates. In conclusion, by use of the ECM-LDD method, an extremely high concentration and long-term retention of locally delivered drug can be reached. Polycationic molecules can be considered as potential affinity vehicles for ECM-LDD.

Lipoprotein lipase enhances the binding of native and oxidized low density lipoproteins to versican and biglycan synthesized by cultured arterial smooth muscle cells

Retention of low density lipoproteins (LDL) by vascular proteoglycans and their subsequent oxidation are important in atherogenesis. Lipoprotein lipase (LPL) can bind LDL and proteoglycans, although the effect of different proteoglycans to influence the ability of LPL to act as a bridge in the formation of LDL-proteoglycan complexes is unknown. Using an electrophoretic gel mobility shift assay, [(35)S]SO(4)-labeled versican and biglycan, two extracellular proteoglycans secreted by vascular cells, bound native LDL in a saturable fashion. The addition of bovine milk LPL dose-dependently increased the binding of native LDL to both versican and biglycan, approaching saturation at 30-40 microgram/ml LPL for versican and 20 microgram/ml LPL for biglycan. LDL was oxidized by several methods, including copper, 2, 2-azo-bis(2-amidinopropane)-2HCl and hypochlorite. Extensively copper- and hypochlorite-oxidized LDL bound poorly to versican and biglycan. Proteoglycan binding to LDL was correlated inversely with the extent of LDL; however, the addition of LPL to oxidized LDL together with biglycan or versican allowed the oxidized LDL to bind the proteoglycans in an LPL dose-dependent manner. Addition of LPL had a greater relative effect on the binding of extensively oxidized LDL to proteoglycans compared with native LDL. LPL had a slightly greater effect on increasing the binding of native and oxidized LDL to biglycan than versican. Thus, LPL in the artery wall might increase the atherogenicity of oxidized LDL, since it enables its binding to vascular biglycan and versican.

Alterations of proteoglycans in ultraviolet-irradiated skin

The effect of UVB exposure on the distribution and synthesis of dermal proteoglycans was measured in the skin of hairless mice. Two groups of mice were included: one was irradiated for 10 weeks; the other was kept as control. After intraperitoneal injection of sodium 35-S-sulfate, punch biopsies were taken for histology and proteoglycans were extracted from the remaining skin with 4 M guanidinium chloride, containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (0.5%, weight per volume). Following proteolytic digestion, the glycosaminoglycan constituents were isolated and analyzed by quantitative cellulose acetate electrophoresis and enzymatic digestibility. Under the influence of UVB radiation, newly synthesized proteoglycans measured by 35SO4 uptake increased as much as 60%. In addition, the irradiated skin had a higher average content of proteoglycan than had control skin (4981 micrograms vs 4134 micrograms/g dry weight). This could be ascribed to an increase in heparin (1400 vs 533 micrograms/g dry weight) and heparan sulfate (472 vs 367 micrograms/g dry weight), whereas no change in the concentration of hyaluronic acid (1243 vs 1372 micrograms/g dry weight) and dermatan sulfate (1866 vs 1863 micrograms/g dry weight) was observed. The irradiated animals also exhibited a marked increase in the synthesis of heparan sulfate and heparin (62% and 71%, respectively). These results demonstrate that chronic doses of UVB altered proteoglycan metabolism through both quantitative and qualitative changes.