Effects of long-term exposure to glucosamine and mannosamine on aggrecan degradation in articular cartilage

Objective: To investigate the effect of long-term exposure to glucosamine or mannosamine on the catabolism of aggrecan by explant cultures of bovine articular cartilage maintained in the presence of retinoic acid. Design: The kinetics Of loss Of 35 S-labeled and total aggrecan from explant cultures of bovine articular cartilage maintained in the presence of 1 muM retinoic acid and exposed to varying concentrations of glucosamine or mannosamine was investigated over a 9-day culture period. In other experiments, the reversibility of the inhibition of aggrecan catabolism by glucosamine or mannosamine was investigated in cultures exposed to these amino sugars for the first 5 days of a 15-day culture period. The metabolism of chondrocytes exposed to these amino sugars was evaluated by measurement of lactate production or H-3-serine and S-35-sulfate incorporation into protein and glycosaminoglycans, respectively. The direct effect of these amino sugars on soluble aggrecanase activity was determined from immunoblots of aggrecan digests. Results: Glucosamine at 5 mM concentration and mannosamine at 2 mM concentration inhibited degradation of radiolabeled and chemical levels of aggrecan. At concentrations of up to 10 mM amino sugars, the metabolism of chondrocytes was not impaired, as determined by lactate production, protein synthesis and the incorporation of S-35-sulfate into proteoglycans. These amino sugars did not inhibit soluble aggrecanase activity. The exposure of articular cartilage explants to 5 mM glucosamine or mannosamine for 5 days in culture in the presence or absence of retinoic acid did not provide long-term suppression of stimulated aggrecan loss. Conclusions: This study indicates that continuous presence of amino sugars is required to protect cartilage from stimulated loss of aggrecan. (C) 2003 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.