EFFECT OF POLYSULFATED GLYCOSAMINOGLYCAN ON OSTEOARTHRITIC EQUINE ARTICULAR-CARTILAGE IN EXPLANT CULTURE

Middle carpal cartilage explants from 4 horses with mild osteoarthriti s involving that joint were maintained in tissue culture to test the e ffects of a polysulfated glycosaminoglycan (PSGAG) on proteoglycan syn thesis and degradation. Cultures were exposed to 0.025 or 25 mg of PSG AG/ml for 48 hours, after which the medium was replaced with medium co ntaining similar doses of PSGAG and S-35. Subsequently, the sulfated p roteoglycan content of the medium and extracts of the explants was mea sured. Gel filtration chromatography was used to estimate the size and to purify the principal, large proteoglycan monomer, which was furthe r characterized by digestion, using glycosidic enzymes. In a second ex periment, explants were incubated with S-35 for 48 hours, and were sub sequently exposed to the same concentrations of the PSGAG for an addit ional 48 hours. The amount of remaining labeled proteoglycan was deter mined for culture medium and cartilage extracts. Gel filtration chroma tography was used to assess the hydrodynamic size of the large proteog lycan monomer. Aliquots of proteoglycans from the second experiment we re incubated in high-molecular weight hyaluronate and chromatographed to assess reaggregation. Polysulfated glycosaminoglycan caused a signi ficant (P less-than-or-equal-to 0.04) decrease in sulfated proteoglyca n synthesis by cartilage explants. Radioactive proteoglycan content in explants labeled prior to exposure to PSGAG were similar. Large prote oglycan monomer size was similar in both experiments (median partition coefficient [K(AV)] = 0.40), and was not influenced by PSGAG treatmen t. Prelabeled explants exposed to hyaluronate and chromatographed unde r associative conditions had similar proportions of the radiolabel elu ting as proteoglycan aggregate. Enzymatic digestion of newly synthesiz ed large monomer revealed a mild dose-dependent increase in the propor tion of keratan sulfate substitution on core protein. It was concluded that PSGAG in vitro, at the dosages evaluated, caused a decrease in p roteoglycan synthesis, had little effect on labeled proteoglycan degra dation, did not influence the size of large monomer, and caused a mode st increase in the concentration of keratan sulfate in proteoglycans s ynthesized by osteoarthritic equine chondrocytes.