In-vivo nitrosation of amines in mice by inhaled nitrogen dioxide and inhibition of biosynthesis of N-nitrosamines.

Inhalation of nitrogen dioxide (NO2) by mice administered orally morpholine (MOR) or dimethylamine (DMA) resulted in the biosynthesis of N-nitrosomorpholine (NMOR) or N-nitrosodimethylamine (NDMA), respectively, as determined by the analysis of frozen whole-mouse powder, using gas chromatography with a Thermal Energy Analyzer detector. Significant levels of NMOR were detected following exposure of mice to 0.38 mg/m3 NO2 for 0.5 h (26 ng NMOR/mouse) and there was a two-fold increase when NO2 exposure was extended to 4 h. NMOR levels also increased in a time-dependent manner at 28.4 and 47.3 mg/m3 NO2 exposure levels, reaching a maximum of 450 and 725 ng NMOR/mouse, respectively, at 4 h. Oral administration of sodium ascorbate (50-250 mg), ammonium sulfamate (50-100 mg) or DL-alpha-tocopherol (67-167 mg) immediately after MOR or DMA, but prior to NO2 exposure, significantly inhibited both NMOR and NDMA biosynthesis, sulfamate being the most effective (greater than 90% NMOR and NDMA inhibition), followed by ascorbate (83-90% NMOR and 58-90% NDMA inhibition) and alpha-tocopherol (22-42% NMOR and 46-69% NDMA inhibition). Low levels of NDMA were found in untreated control mice (less than 13 ng/mouse) and in most samples of commercially obtained animal feed (10-15 micrograms/kg); NMOR, however, was not detectable or was detected in negligible amounts in these cases. Various control experiments indicated that most of the recovered nitrosamine resulted from in-vivo nitrosation in mice, with only up to 1-2% of NMOR and approximately 10% of NDMA yields being attributed to artefact formation, possibly during work-up of the mouse-powder samples.