Abstract
Curcumin (diferuloylmethane) is a nontoxic dietary pigment in tumeric and curry and a potent inhibitor of the common transcription factor Nuclear Factor kappaB (NF-kappaB) in several cell types. It is well established that some of the catabolic effects of the proinflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha in osteoarthritis are regulated by the activation of NF-kappaB. Therefore, the aim of this study was to determine whether curcumin modifies the catabolic response of chondrocytes to IL-1beta. Human articular chondrocytes were prestimulated with 10 ng/mL IL-1beta for 0, 4, 8, 12, or 24 h and then cotreated with 50 microM curcumin for 0, 12, 24, 36, or 48 h. Synthesis of the cartilage-specific collagen type II and matrix-degrading enzyme matrix metalloproteinase-3 (MMP-3) was investigated in chondrocytes by Western blot analysis. Activation and nuclear translocation of NF-kappaB were observed by immunofluorescence microscopy. IL-1beta induced a decrease in collagen type II and upregulation of MMP-3 in a time-dependent manner. Upregulation of MMP-3 was inhibited by curcumin in a time-dependent manner. In addition, IL-1beta-induced a decrease in type II collagen, which was relieved by curcumin treatment. In response to IL-1beta, NF-kappaB translocated to the nucleus, but translocation was inhibited by curcumin, as revealed by immunofluorescence microscopy. Taken together, these results confirmed an IL-1beta-mediated upregulation of proinflammatory MMP-3 in chondrocytes via an NF-kappaB activation mechanism. Curcumin protected chondrocytes from the catabolic effects of IL-1beta, such as MMP-3 upregulation, and interestingly also relieved cytokine-induced suppression of matrix protein synthesis. Therefore, curcumin antagonizes crucial catabolic effects of IL-1beta signaling that are known to contribute to the pathogenesis of osteoarthritis.
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