Effect of norharman on DNA strand breaks and mutation of Chinese hamster V79 cells by chemical carcinogens.

The effect of norharman, which shows a comutagenic activity in the Salmonella mutation assay, was examined on the action of mutagens towards Chinese hamster V79 cells. Norharman reduced the DNA strand breaks by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), but enhanced the 4-hydroxyaminoquinoline l-oxide ( 4HAQO )-induced DNA strand breaks. Norharman also reduced the cytotoxicity and the mutagenicity of MNNG but enhanced the cytotoxicity of 4HAQO to V79 cells. In the Salmonella mutation assay, norharman showed no effect on the mutagenic activity of MNNG but reduced the mutagenic activity of 4HAQO . The effect of norharman on the action of mutagens to V79 cells appeared dependent on mutagens and did not correlate with the effect observed in Salmonella mutation assay.