Inhibition of the nitrosothiol production of cultured osteoarthritic chondrocytes by rhein, cortisol and diclofenac

Objective: Nitric oxide (NO degrees) is a free molecule produced by NO synt hases which acts as a mediator in inflammatory processes. NO degrees can re act with thiol groups of proteins to produce nitrosothiols. increased conce ntrations of these bioactive compounds have been found in sera and synovial fluids from patients with osteoarthritis (OA). The aim of this study was t o assess the ability of human osteoarthritic chondrocytes to synthesize nit rosothiols and to compare the in vitro effects of rhein, cortisol and diclo fenac on nitrosothiol and nitrite production. Methods: Osteoarthritic chondrocytes were incubated for 24 h with 1 ng/ml o f recombinant human interleukin-1 beta (IL-1 beta) in the presence or absen ce of rhein (1.3x10(-5) M, 6.5x10(-6) M, or 1.3x10(-6) M), cortisol (10(-5) M) or diclofenac (10(-5) M or 10(-6) M). Nitrite levels were measured in c ell supernatants by the Griess method; nitrosothiol levels were determined in supernatants and cellular lysates by fluorimetry. Results: At the basal level, nitrosothiols represented 80% of the total of nitrite and nitrosothiol production. After IL-1 beta stimulation, NO degree s production was highly increased in the supernatants (45-fold increase in nitrite, 60-fold increase in nitrosothiols) as well as in cell lysates (35- fold increase in nitrosothiols). Rhein caused a dose-dependent decrease in nitrosothiol and nitrite production. In comparison. diclofenac (10(-5) M) m oderately decreased nitrite and nitrosothiol levels in the supernatants but had no effect on lysate nitrosothiol. Cortisol had no significant effect o n NO degrees production. Conclusions: The IL-1 beta stimulation increased nitrosothiol production by osteoarthritic chondrocytes. These results demonstrate the need to measure nitrosothiol as well as nitrite production. Rhein inhibited the IL-1 degre es induced NO degrees production, and may be a suitable treatment for osteo arthritis. (C) 2001 OsteoArthritis Research Society International.