Ethanol enhances ADP‐ribosylation of protein in rat hepatocytes

Decreases in hepatocyte NAD + produced by ethanol are only partially explained by the increased conversion of NAD + to NADH and NADP +. The purpose of this study was to determine whether a mechanism for the ethanol‐induced decrease in NAD + is its increased use in ADP‐ribosylation. Exposure of hepatocytes in culture for 2 hr to 100 mmol/L ethanol increased the incorporation of 14 C‐ribose from prelabeled NAD + into 14 C‐ribosylated proteins. Poly (ADP‐ribose) polymerase activity was increased by exposure of isolated hepatocytes to 100 mmol/L ethanol for 10 min. In hepatocyte culture, increases in poly (ADP‐ribose) polymerase were not detected after exposure to 100 mmol/L ethanol for 10 min or 2 hr but rather occurred at 24 hr. Ethanol exposure of hepatocytes in culture for 2 hr, however, decreased the K m for NAD + of poly (ADP‐ribose) polymerase. Both nicotinamide and 5‐aminobenzamide, which are inhibitors of poly (ADP‐ribose) polymerase, prevented the decrease in NAD + produced by 2‐hr exposure of hepatocytes in culture to 100 mmol/L ethanol. The effect of ethanol in decreasing DNA synthesis on days 3 and 4 of culture was not reversed by the inhibitors of poly (ADP‐ribose) polymerase. These results indicate that increased ADP‐ribosylation of hepatocyte proteins is a mechanism for the effect of ethanol in decreasing NAD + (Hepatology 1992; 15:471–476).