Effect of polysulfated glycosaminoglycan on DNA content and proteoglycan metabolism in normal and osteoarthritic canine articular cartilage explants.

Abstract

To study the effect of polysulfated glycosaminoglycan (PSGAG) on proteoglycan metabolism and DNA content of control and osteoarthritic (OA) cartilage. An in vitro study comparing the effects of PSGAG on articular cartilage explants from canine stifle joints with and without chronic OA after transection of the left cranial cruciate ligament. Five large cross-breed dogs. Cartilage explants (6 to 13 per treatment group) from the medial side of the femoral trochlea and medial femoral condyle from both stifles of each dog were incubated in a defined medium containing 0, 0.05, 0.5, or 5 mg/mL of PSGAG. After 72 hours in culture, explants were pulsed for 6 hours with sodium [35S]sulfate. Aminophenylmercuric acetate (APMA) was used to activate endogenous neutral matrix metalloproteinases (MMPs) and induce proteoglycan degradation in the radiolabeled explants. DNA content and radioactivity were measured in papain-digested explants, and radioactivity was measured in the medium by liquid scintillation counting. Proteoglycan synthesis and degradation were calculated. Cartilage was examined histologically for signs of OA. A mixed model analysis of variance and linear contrasts were used to test for significant (P < .05) effects of OA and treatment with PSGAG. Transection of the cranial cruciate ligament produced OA in operated joints. DNA content and proteoglycan synthesis of OA cartilage were significantly lower than in cartilage from control joints. For both DNA content and proteoglycan synthesis, significant interactions occurred between the concentration of PSGAG and whether the articular cartilage was from OA or control joints. The two lower concentrations of PSGAG (0.05 and 0.5 mg/mL) predominantly increased DNA content in OA cartilage (7 and 18%, respectively, compared with 0 mg/mL PSGAG) while the highest concentration (5 mg/mL) predominantly increased DNA content in control cartilage (30% compared with 0 mg/mL PSGAG). PSGAG at .05 mg/mL predominantly decreased proteoglycan synthesis in OA cartilage (19% reduction compared with 0 mg/mL PSGAG) while PSGAG at .5 and 5 mg/mL predominantly decreased proteoglycan synthesis in control cartilage (17 and 55% reduction, respectively, compared with 0 mg/mL PSGAG). Following activation of MMPs, PSGAG caused a dose-dependent decrease in degradation of radiolabeled proteoglycan in both OA and control cartilage. OA cartilage was responsive to treatment with PSGAG at 100-fold lower concentration than control cartilage. When treated with PSGAG, articular cartilage explants maintained or increased DNA content at the expense of proteoglycan synthesis. Following MMP activation, proteoglycan degradation was inhibited in OA and control explants in a dose-dependent manner. If the results of this study extend to in vivo use, treatment with PSGAG may modify the progression of OA in articular cartilage by maintaining chondrocyte viability or stimulating chondrocyte division as well as protecting against extracellular matrix degradation.