Induction of apoptosis by benzamide and its inhibition by aurin tricarboxylic acid (ATA) in Chinese hamster V79 cells.

To investigate the effect of benzamide and nicotinamide, well known inhibitors of poly(ADP-ribose) polymerase, in Chinese hamster V79 cells at the physiological condition of cell growth, we have tested the ability of the inhibitors to induce apoptosis. Apoptosis was detected by nuclear fragmentation, nucleosomal ladder formation, cytochrome-c release from the mitochondria and caspase-3 activation. Benzamide treatment alone increased nuclear fragmentation in dose (2.5-10 mM) and time (4-48 h)-dependent manner. Such treatment also increased nucleosomal ladders. However, 5 mM benzamide pre-treatment inhibited the nucleosomal ladders induced by gamma-irradiation indicating the role of poly(ADP-ribose) polymerase was different in irradiated cells and in un-irradiated cells. Release of cytochrome-c from the mitochondria and caspase-3 activity were also increased by such treatment. Treatment with 200 microM of aurin tricarboxylic acid (ATA), an inhibitor of DNases, inhibited the nucleosomal ladders induced by benzamide or gamma-irradiation without changing the cytochrome-c release or caspase-3 activation. This result showed that ATA inhibited the nucleosomal ladders possibly by inhibiting DNase(s) involved in apoptosis.