The degenerative joint disease such as osteoarthritis (OA) is closely associated with the death of chondrocytes in
apoptosis fashion. Hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), higher expression following acute damage in OA patients, has been shown
to be up-regulated during apoptosis in a bulk of experimental models. This study was aimed to explore the mechanism of
H2O2-induced rabbit chondrocytes apoptosis. Articular cartilage was biopsied from the joints of 6 weeks old New
Zealand rabbits. Cell Counting Kit (CCK-8) assay was used to assess the inhibitory effect of H<sub>2</sub>O<sub>2</sub> on cell viability. H<sub>2</sub>O<sub>2</sub>
treatment induced a remarkable reduction of cell viability. We used flow cytometry to assess the form of cell death with
Annexin-V/PI double staining, and found that H2O2 treatment induced apoptosis in a dose-and time-dependent manner.
Exposure of chondrocytes to 1.5 mM of H<sub>2</sub>O<sub>2</sub> for 2 h induced a burst apoptosis that can be alleviated by N-acetyl
cysteine (NAC) pretreatment, an anti-oxidant amino-acid derivative. Loss of mitochondria membrane potential (▵Ψm)
was evaluated using confocal microscopy imaging and flow cytometry (FCM). H<sub>2</sub>O<sub>2</sub> treatment induced a marked
reduction of ▵Ψm, and the abrupt disappearance of ▵Ψm occurred within 5 minutes. These results indicate that H<sub>2</sub>O<sub>2</sub>
induces a rapid apoptosis via a mitochondrial pathway in rabbit chondrocytes.