STUDIES ON DNA STRAND BREAK AND PROMOTION OF ITS REPAIR

研究了烟酸对人淋巴细胞NAD含量和DNA修复的影响。淋巴细胞在补充有各种浓度的烟酸或烟酰胺的培养基中孵育。用5 μ M烟酸或10 mM烟酰胺孵育淋巴细胞导致NAD含量增加2-3倍。在此条件下，用N-甲基-N-硝基-N-亚硝基胍（MNNG）处理淋巴细胞，研究烟酸对DNA修复合成的影响。有趣的是，烟酸促进DNA链断裂的重新连接，但烟酰胺抑制重新连接。在用烟酸而不是烟酰胺升高细胞中的NAD水平后，用MNNG处理淋巴细胞时观察到NAD的急剧降解。这些结果表明，聚（ADP-核糖）聚合酶的DNA修复的可能作用。

The effect of niacin on NAD content and on DNA repair in human lymphocytes was investigated. Lymphocytes were incubated in culture medium supplemented with various concentrations of nicotinic acid or nicotinamide. Incubation of lymphocytes with nicotinic acid at 5 muM or nicotinamide at 10 mM resulted 2-3 fold increase in NAD content. Under these conditions lymphocytes were treated with N-methyl-N-nitro-N-nitrosoguanidine (MNNG) to investigate the effect of niacin on DNA repair synthesis. Interestingly, the rejoining of DNA strand breaks was promoted by nicotinic acid but nicotinamide inhibited the rejoining. The dramatic degradation of NAD was observed when lymphocytes were treated with MNNG after elevating NAD level in the cells with nicotinic acid but not with nicotinamide. These results suggest the possible role of poly (ADP-ribose) polymerase to DNA repair.