4-Hydroxynonenal (HNE) modified Bcl-2/Bax protein expression and induced cytochrome c release from mitochondria. Chondrocytes were treated with 30 μM HNE for the indicated times and then Bcl-2 (a) and Bax (b) protein levels were determined by commercial kit and Western blot, respectively. (c) Chondrocytes were pre-incubated with or without 200 μM N-acetyl-cysteine (NAC) for 1 hour followed by another incubation for 16 hours in the presence of increasing concentrations of HNE (0 to 30 μM). Cytochrome c level was assessed in cytosolic fractions with a kit. *P < 0.05, **P < 0.01, ***P < 0.001.