Hypoxia-induced nitric oxide protects chondrocytes from damage by hydrogen peroxide

Objective:Because articular cartilage has no vascular supply, chondrocytes are hypoxic under normal physiological conditions. Nitric oxide (NO) plays an important role in chondrocyte damage, such as apoptosis. Although oxygen stress with hydrogen peroxide was found to cause chondrocyte damage, these data were obtained under normoxic (21% O-2) conditions. We investigated the effects of hypoxia on hydrogen peroxide-induced chondrocyte damage Methods:Bovine articular chondrocytes were used in this study. Proteoglycan (PG) synthesis and the induction of apoptosis were analyzed with [S-35]-sulfate incorporation and annexin V staining, respectively. The induction of NO was examined using a fluorescent probe and RT-PCR. Results:Cells maintained at 5% O-2 had the maximum PG synthesis. Under normoxic conditions, hydrogen peroxide inhibited PG synthesis and induced annexin V positive cells in a dose-dependent fashion. However, in those cells cultured under hypoxic (5%) conditions, the hydrogen peroxide-induced annexin V expression was attenuated. Chondrocytes exposed to hypoxia showed induction of NO. When the hypoxia-induced NO was inhibited, the hypoxia-enhanced PG synthesis was abolished and hydrogen peroxide clearly induced cell damage. Conclusions:Endogenous NO induced by hypoxia protects chondrocytes from apoptosis induced by an oxidative stress.