Abstract
Cell death by oxidative stress has been proposed to be based on suicidal NAD depletion, typically followed by ATP depletion, caused by the NAD-consuming enzyme poly(ADP)ribose polymerase, which becomes activated by the presence of excessive DNA-strand breaks. In this study NAD +, NADH and ATP levels as well as DNA-strand breaks (assayed by alkaline elution) were determined in Chinese hamster ovary (CHO) cells treated with either H 2O 2 or hyperoxia to a level of more than 80% clonogenic cell killing. With H 2O 2 extensive DNA damage and NAD depletion were observed, while at a higher H 2O 2 dosage ATP also became depleted. In agreement with results of others, the poly(ADP)ribose polymerase inhibitor 3-aminobenzamide completely prevented NAD depletion. However, both H 2O 2-induced ATP depletion and cell killing were unaffected by the inhibitor, suggesting that ATP depletion may be a more critical factor than NAD depletion in H 2O 2-induced killing of CHO cells. With hyperoxia, only moderate DNA damage (2 × background) and no NAD depletion were observed, whereas ATP became largely (70%) depleted. We conclude that (1) there is no direct relation between ATP and NAD depletion in CHO cells subjected to toxic doses of H 2O 2 or hyperoxia; (2) H 2O 2-induced NAD depletion is not by itself sufficient to kill CHO cells; (3) killing of CHO cells by hyperoxia is not due to NAD depletion, but may be due to depletion of ATP.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have