The role of NADPH oxidase and neuronal nitric oxide synthase in zinc-induced poly(ADP-ribose) polymerase activation and cell death in cortical culture.

In the present study, we examined the role and the mechanism of poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG) activation in zinc-induced cell death in cortical culture. After brief exposure to 400 microM zinc, cortical cells exhibited DNA fragmentation, increased poly(ADP-ribosyl)ation, and decreased levels of nicotinamide adenine dinucleotide (NAD) and ATP and subsequently underwent cell death. Inhibitors of PARP/PARG attenuated both zinc-induced NAD/ATP depletion and cell death, thereby implicating the PARP/PARG cascade in these processes. The zinc-inducible enzymes NADPH oxidase and neuronal nitric oxide synthase (nNOS) contributed to PARP activation as their inhibitors attenuated zinc-induced poly(ADP-ribosyl)ation. Levels of nitric oxide and nitrites increased following zinc exposure, consistent with NOS activation. In addition, Western blots and RT-PCR analysis revealed that protein and mRNA levels of nNOS specifically increased following zinc exposure in a manner similar to that of NADPH oxidase. The present study demonstrates that induction of NADPH oxidase and nNOS actively contributes to PARP/PARG-mediated NAD/ATP depletion and cell death induced by zinc in cortical culture.