Effects of nicotinamide on NAD and poly(ADP-ribose) metabolism in DNA-damaged human lymphocytes.

The effect of nicotinamide on unscheduled DNA synthesis was studied in resting human lymphocytes. In cells treated with UV irradiation or with MNNG, nicotinamide caused a two-fold stimulation of unscheduled DNA synthesis and retarded the rate of NAD+ lowering caused by these treatments. Nicotinamide also reduced the burst of poly(ADP-ribose) synthesis caused by MNNG treatment. Thus under conditions that it enhances unscheduled DNA synthesis, nicotinamide causes marked effects on the metabolism of NAD+ and poly(ADP-ribose). The effect of nicotinamide on unscheduled DNA synthesis was shown to be independent of protein or polyamine synthesis.