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Sprague-Dawley rats were exposed by inhalation to 1-nitroso-4-methylpiperazine (NMPz) vapor at 2.4 p.p.m. for 15 h/day for 74 days over a 7.5 month period. After a dose of 1.1 mg/day NMPz (total dose 340 mg/kg body wt) 10/10 animals developed tumors of the nasal cavity, mostly invasive muco-epidermoidal carcinomas; no such tumors were observed in sham-exposed controls. This high tumor yield was seen at an 80 times lower dose and a shorter latency period when compared with rat carcinogenicity studies reported earlier. The single cell microgel electrophoresis (Comet) assay was used to determine genotoxicity in target tissues. Short-term in vitro exposure of rat and human nasal epithelial tissues to NMPz caused genotoxic effects in cells of both species. Short-term in vivo exposure of rats to NMPz vapor for 1 h induced DNA damage in nasal epithelial cells. Our results revealed NMPz as a potent genotoxic nitrosamine in rat and human nasal cells, the carcinogenicity of inhaled NMPz vapor in rats being remarkably higher as compared with oral uptake.

Strong nasal carcinogenicity and genotoxicity of 1-nitroso-4-methylpiperazine after low dose inhalation in rats