Aurothiomalate inhibits COX-2 expression in chondrocytes and in human cartilage possibly through its effects on COX-2 mRNA stability

Abstract Cyclooxygenase-2 (COX-2) is expressed in rheumatoid and osteoarthritic cartilage and produces pro-inflammatory prostanoids in the joint. In the present study, we investigated the effects of disease modifying anti-rheumatic drugs on COX-2 expression in chondrocytes. Unlike the other tested drugs, aurothiomalate was found to inhibit COX-2 expression in chondrocytes. In the further studies, effects and mechanisms of action of aurothiomalate were investigated in more detail. Aurothiomalate inhibited IL-1β-induced COX-2 protein expression and PGE 2 production in chondrocytes in a dose-dependent manner. Because aurothiomalate did not alter IL-1β-induced mRNA levels when measured 0–3 h after addition of IL-1β, its effects on COX-2 mRNA degradation were tested by Actinomycin D assay. The half-life of COX-2 mRNA was reduced from 3 h to less than 1.5 h in aurothiomalate-treated cells. The 3′-untranslated region (3′-UTR) of COX-2 mRNA contains an ARE element which has been shown to bind mRNA stabilizing factor HuR. Interestingly, aurothiomalate inhibited HuR expression which may explain its destabilizing effect on COX-2 mRNA. Aurothiomalate reduced COX-2 expression and PGE 2 production also in human cartilage at drug concentrations which have been measured in serum and synovial fluid during treatment with aurothiomalate. The results show that aurothiomalate reduces COX-2 expression and PGE 2 production in chondrocyte cultures and in human cartilage. The action is likely mediated by enhanced COX-2 mRNA degradation possibly through a mechanism related to reduced expression of HuR. The results provide a novel mechanism of action for aurothiomalate which may be important in the treatment of arthritis.