To investigate the role of peroxidation end product, 4-hydroxynonenal (HNE), in osteoarthritic (OA) cartilage degradation. Total HNE/protein adducts were quantified in synovial fluids or in cellular extracts of chondrocytes using a house Elisa. The formation of HNE/type II collagen adducts was analysed by immunoprecipitation. Type II collagen synthesis was analysed by Western blotting. MMP-13 activity and synthesis as well as TIMP-1 synthesis were measured by commercial kits. Our data show that the level of HNE/protein adducts markedly increased in OA synovial fluids compared to normal subjects and in cellular extracts of OA chondrocytes treated with free radicals donors (H2O2 or SIN) compared to untreated cells. Using an immunoprecipitation approach, we demonstrated the formation of HNE/type II collagen adducts in OA cartilage and their increased level in the presence of H2O2 or SIN. Furthermore, we find that HNE induces MMP-13 synthesis and activity in a dose-dependent manner, but in contrast, inhibits type II collagen and TIMP-1 synthesis. Interestingly, HNE was proved to exert a dual effect in vitro, activating proMMP-13 at low molar ratio (MR~100:1) and inhibiting active MMP-13 at high molar ratio (MR >
1000:1). The data generated in this study support the hypothesis that HNE plays a dual role in OA cartilage degradation. At posttranslational level, HNE promotes modification of type II collagen and MMP-13 by adducts formation. At transcriptional level, HNE inhibits type II collagen and TIMP-1 synthesis and induces MMP-13 synthesis and activity. Support: This work was supported by FRSQ
