Adenine nucleotide metabolism and cell fate after oxidant exposure of rat cortical neurons: effects of inhibition of poly(ADP-ribose) polymerase

We exposed cultured neurons prelabeled with 14C-adenine to H 2O 2 with or without the poly(ADP-ribose) polymerase (PARP) inhibitor 3,4-Dihydro-5-[4-(1-piperidinyl)butoxy]-1(2 H)-isoquinolinone (DPQ) to quantify its effects on acute ATP depletion, later ATP synthesis, cellular and nuclear morphology, extent of DNA fragmentation, and PARP cleavage. According to the extent of the acute ATP depletion, the exposures were classified as ‘mild’ (50 μM H 2O 2), ‘moderate’ (100–250 μM H 2O 2), or ‘severe’ (500 μM–1 mM H 2O 2) insults. Mild exposure had no significant effects on the parameters studied. In the ‘moderately’ exposed neurons, ATP depletion to 59±6% of control was associated with a decrease in the cell counts, apoptotic morphology, and cleavage of PARP. In this group, DPQ prevented the acute ATP (to 95±15% of control), preserved cell morphology, and improved cell survival. In the ‘severe’ group, ATP depletion to 18±4% was associated with necrosis and intact PARP. DPQ elevated ATP levels (to 44±12% of control) and post-insult ATP synthesis, improved cell counts, and altered cell morphology towards apoptosis rather than necrosis. Post-insult application of DPQ was less effective. Our results show that the extent of oxidant-induced ATP depletion and cell fate can be modified by PARP inhibition, to some extent also after the insult.