Poly(ADP-ribose) metabolism in X-irradiated Chinese hamster cells: its relation to repair of potentially lethal damage.

Nicotinamide-adenine dinucleotide (NAD+) is the substrate used by cells in poly(ADP-ribose) synthesis. X-irradiation of log-phase Chinese hamster cells caused a rapid decrease in NAD+ levels which was linearly dependent on radiation dose. The activity of ADP-ribosyl transferase ( ADPRT ) also increased linearly with radiation dose. The decrease of NAD+ was slower, and the increase in ADPRT activity was less pronounced, in a radiation sensitive line, V79- AL162 /S-10. An inhibitor of ADPRT , m-aminobenzamide, largely prevented the depletion of cellular NAD+ and reduced the rate at which ADPRT activity disappeared during post-irradiation incubation. Post-irradiation treatment with hypertonic buffer or with medium containing D2O--which inhibit repair of radiation-induced potentially lethal damage--enhanced the depletion of NAD+ and prevented the reduction in ADPRT activity following irradiation. The characteristics of the effects of treatment with hypertonic buffer on NAD+ metabolism were qualitatively similar to the effects that such treatment has on radiation-induced cell killing. These results suggest that poly(ADP-ribose) synthesis after irradiation plays a role in the repair of potentially lethal damage.