Objective: To evaluate the in vitro effects of diacerhein, a new drug for the treatment of osteoarthritis (OA), and its active metabolite, rhein, on the production of nitric oxide (NO), prostaglandin (PGE2), cyclooxygenase-2 (COX-2), as well as the production and expression of the inducible nitric oxide synthase (iNOS) in human OA chondrocytes. These results were compared to those of the nonsteroidal antiinflammatory drug (NSAID) naproxen.
Methods: Human OA chondrocytes were incubated in the presence or absence of 25 units/ml recombinant human interleukin-1beta (rhIL-1beta) with or without therapeutic concentrations of diacerhein and rhein at 5, 10, and 20 microg/ml and naproxen at 30 and 90 microg/ml. Effect of the drugs was also tested on both OA chondrocytes and cartilage explants on increasing IL-1beta concentration (0-100 units/ml). The NO and PGE2 levels were determined in the culture medium using the Griess reaction and a specific ELISA, respectively. Production of COX-2 and synthesis and expression of iNOS were quantitated by Western blot and Northern blot, respectively.
Results: The IL- 1beta induced NO production was inhibited by both diacerhein and rhein in a time and dose dependent fashion, with statistical significance reached at the therapeutic concentration of 20 microg/ml. A decrease over 80% was found at 24, 48, and 72 h incubation. This was consistent for both chondrocytes and cartilage explants even in the presence of high IL-1beta concentration (100 units/ml). Moreover, this effect appeared to result from iNOS transcriptional and/or post-transcriptional events as indicated by a decrease in this enzyme level for both the mRNA and protein. Naproxen, however, showed only a slight inhibition of IL-1beta induced NO production at the highest dose used, 90 microg/ml. A maximum decrease of 23% in IL-1beta induced NO production was recorded after a 72 h incubation. In contrast to naproxen, which abrogated PGE2 and had no effect on COX-2 synthesis, rhein and diacerhein at 5 and 10 microg/ml produced an enhancement in their levels.
Conclusion: Diacerhein and rhein, in contrast to an NSAID, are potent inhibitors of IL-1beta induced NO production by chondrocytes and cartilage, without reducing PGE2 production.