Mutagenesis associated with nitric oxide production in transgenic SJL mice

We recently reported development of an experimental model for the study of nitric oxide (NO.) toxicology in vivo. SJL mice were injected with superantigen-bearing RcsX (pre-B-cell lymphoma) cells, which migrated to the spleen and lymph nodes, where their rapid growth induced activation of macrophages to produce large amounts of NO. over a period of several weeks. In the experiments described here, we used this model to investigate mutagenesis in splenocytes exposed to NO. during RcsX cell growth. Transgenic mice were produced by crossbreeding animals of the pUR288 transgenic C57BL/6 and SJL strains. RcsX cells were injected into F1 mice and NO. production was confirmed by quantification of urinary nitrate, the ultimate metabolite of NO. Mutant frequency in the lacZ gene of the pUR288 plasmid was determined in DNA isolated from spleen (target) and kidney (nontarget) tissues. A significant elevation in mutant frequency was found in the spleen, but not in the kidney, of tumor-bearing mice. Furthermore, increases in mutant frequency in the spleen as well as NO. production were abrogated by administration of N-methylarginine, a NO. inhibitor, to mice following injection of RcsX cells. These results indicate that NO. had mutagenic activity in RcsX tumor-bearing mice and thus support a possible role for its involvement in the carcinogenic process.