4-Hydroxynonenal (HNE) induced DNA fragmentation, poly (ADP-ribose) polymerase (PARP) cleavage, and apoptosis-inducing factor (AIF) translocation to the nucleus. Chondrocytes were pre-incubated for 1 hour with or without 200 μM N-acetyl-cysteine (NAC) and then incubated for another 16 hours with 30 μM HNE or with increasing concentrations of HNE (0 to 30 μM). (a) The cytoplasmic histone-associated DNA fragments were quantified with a kit. (b) Chondrocytes were pre-incubated for 1 hour with or without 200 μM NAC followed by another incubation with 30 μM HNE at different incubation times. PARP cleavage and AIF translocation in nuclear fractions were analyzed by Western blot. Data are mean ± standard error of the mean and expressed as a percentage of untreated cells. Statistics: Student unpaired t test; *P < 0.05, **P < 0.01.