IN-VITRO EFFECTS OF DIACERHEIN AND RHEIN ON INTERLEUKIN-1 AND TUMOR-NECROSIS-FACTOR-ALPHA SYSTEMS IN HUMAN OSTEOARTHRITIC SYNOVIUM AND CHONDROCYTES

Objective. To evaluate the in vitro effects of diacerhein, a new drug for the treatment of osteoarthritis (OA), and its active metabolite, r hein, on interleukin 1 beta (IL-1 beta) and tumor necrosis factor-alph a (TNF-alpha) synthesis and expression in human OA synovial membrane, and on the IL-1 beta and TNF-alpha receptors on human OA chondrocytes. Methods. Levels of IL-1 beta and TNF-alpha were determined using spec ific ELISA in culture medium of human synovial membrane explants incub ated in the presence of 1 mu g/ml of lipopolysaccharide with or withou t therapeutic concentrations of diacerhein (1.4, 2.7, 5.4 x 10(-5) M) and rhein (1.7, 3.5, 7.0 x 10(-5) M). IL-1 beta mRNA level was quantit ated by Northern blotting. Using radioligand binding experiments, we d etermined the effects of these agents on the density and affinity of c hondrocyte IL-1 and TNF receptors. Results. IL-1 beta synthesis was si gnificantly inhibited by diacerhein and rhein, with maximum inhibition at 5.4 x 10(-5) M for diacerhein (p < 0.02) and 3.5 x 10(-5) M for rh ein (p < 0.05). The effect of both agents on IL-1 beta was found to be translational and/or post-translational, judging by the absence of ef fect on gene expression level. Both agents produced dose and time depe ndent decreases in the number of IL-1 receptors (IL-1R) on OA chondroc ytes. This effect was mediated through a reduction in the level of the type I IL-1R as shown by experiments using a blocking monoclonal anti body against this receptor type. Both agents also markedly reduced the IL-1 induced synthesis and expression of stromelysin 1. Neither diace rhein nor rhein significantly affected the level of synthesis of TNF-a lpha or the level of TNF-R. Conclusion. Diacerhein and rhein can effec tively inhibit the synthesis of IL-1 beta on human OA synovium, as wel l as the action of this cytokine at the cartilage level, by reducing t he number of chondrocyte IL-1R. The effects of these agents seemed ''s elective'' to the IL-1 system.