Differential role of poly(ADP-ribose) polymerase-1 in apoptotic and necrotic neuronal death induced by mild or intense NMDA exposure in vitro

Overactivation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) plays a key role in the mechanisms responsible for neuronal death. In the present study, we examined the effects of the PARP-1 inhibitor 3,4-dihydro-5-[4-1(1-piperidinyl)buthoxy]-1(2H)-isoquinolinone (DPQ) in two models of N-methyl-d-aspartate (NMDA)-induced neurotoxicity. The exposure of mixed cultured cortical cells to 300 microM NMDA for 10 min induced a caspase-dependent type of apoptotic neuronal death. Conversely, exposure to 2 mM NMDA for 10 min led to the appearance of morphological features of necrosis, with no increase in caspase-3 activity and depletion in adenosine triphosphate (ATP) levels. DPQ (10 microM) reduced the NMDA-induced PARP activation, restored ATP to near control levels and significantly attenuated neuronal injury only in the severe NMDA exposure model. Similar results were obtained when pure neuronal cortical cultures were used. PARP-1 activation thus appears to play a preferential role in necrotic than in caspase-dependent apoptotic neuronal death.