In vivo and in vitro genotoxicity of several N-nitrosamines in extrahepatic tissues of the rat

Toxicological mechanisms involved in organotropism of tumor induction may include cell-specific metabolic activation of the carcinogen, in vivo distribution of active metabolites and persistance of induced DNA damage. In order to elucidate which factors are involved in the organotropic action of environmentally relevant N-nitrosamines, we have studied their genotoxic and cytotoxic effects within primary intact cells of lung and kidney. The end-points determined were cytotoxicity by trypan blue exclusion and DNA single-strand break (SSB) induction by alkaline filter elution. The assays were performed in vitro to determine organ-specific metabolic activation by incubating the cells with the test compounds. The results obtained with N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodiethanolamine (NDEIA), N-nitrosoethylvinylamine (NEVA), N-nitrosodibutylamine (NDBA), N-nitrosobutylbutanolamine (NBBOH), N-nitrosobutylcarboxypropylamine (BCPN), N-nitrosomethylbenzylamine (NMBzA) and N-nitrosodibenzylamine (NDBzA) indicate that several compounds may be activated to reactive metabolites by cells of kidney and lung, NDBzA revealing the highest degree of cytotoxicity. In contrast, genotoxicity in kidney cells was induced only by NBBOH and BCPN and at relative low levels. Primary lung cells could not be employed as indicators for genotoxic effects in vitro because the cell yield was not sufficient to perform the alkaline elution assay. To assess the distribution of NDMA in the whole rat and the persistence of the induced DNA damage in the two organs, further studies were carried out after oral application of 1, 2, 4, 10, 20, 32 and 40 mg/kg to the animals. Following 1 h exposure of rats to NDMA, the lowest effective genotoxic dose for lung and kidney was 2 mg NDMA/kg body wt. A plateau was achieved after a dose of 20 mg/kg in both organs. Furthermore, the persistence of DNA damage was studied in the lung. After 4 h exposure, DNA damage was still detectable at 32 mg NDMA/kg, but for the lower doses it was reduced nearly to control levels. After 16 h exposure the SSB rate in lung cells was reduced for all dose levels except for the highest dose of 40 mg/kg.