Microsomal metabolism of the Z and E isomers of N-nitroso-N-methyl-N-n-pentylamine

Mutagenicity of isomeric alkanediazotates, precursors for ultimate alkylating species of carcinogenic N-nitroso compounds

Alkanediazohydroxides are common key intermediates in carcinogenesis and mutagenesis of N-nitroso compounds, which are widely found in human environment. Mutagenicity of (E)- and (Z)-potassium alkanediazotates, as precursors of corresponding alkanediazohydroxides were evaluated to investigate the effect of geometric isomerism and also the effect of alkyl groups on their biological activity. Mutagenicity of N-nitroso-N-alkylureas which spontaneously produce alkanediazohydroxides after non-enzymatic hydrolysis were also tested in comparison to that of the corresponding diazotates and other activated chemical species of N-nitrosamines. When the mutagenicity was assayed in three microbial strains, Salmonella typhimurium TA1535, and Escherichia coli WP2 and WP2 uvrA, the order of mutagenic potency of the compounds with the same alkyl group was as follows; (E)-diazotates > (Z)-diazotates > nitrosoureas. The effect of alkyl groups on the mutagenic potency was different in Salmonella strain and in E. coli strains, and this result could be explained by the efficiency of O6-alkylguanine-DNA alkyltransferase. In each bacterial strain, this effect of alkyl groups was similar in mutagenicity induced by (E)- and (Z)-diazotates, N-nitroso-N-alkylureas and other activated N-nitrosodialkylamines such as alpha-hydroxy nitrosamines. The geometrical isomerism affected the mutagenicity of (E)- and (Z)-potassium alkanediazotates, and the result suggested that alkanediazohydroxides react through diazonium ions in a cage rather than through free alkyldiazonium ions which have no geometrical isomerism. Our results confirmed that (E)-potassium alkanediazotates, (Z)-potassium alkanediazotates and N-nitroso-N-alkylureas all decomposed through diazohydroxides, and that alkanediazohydroxides are the active alkylating species of N-nitroso compounds, and also that the geometrical isomerism is important for carcinogenic N-nitroso compounds to show their biological activity.

Analysis of N-nitrosamines by high-performance liquid chromatography with post-column photohydrolysis and colorimetric detection

N-Nitrosamines eluted from reversed-phase HPLC were quantitatively photohydrolysed in a UV photoreactor in aqueous solution to give the nitrite ion which could be determined colorimetrically with the Griess reagent. The chromatographic behavior of N-nitroso compounds (including 19 volatile dialkyl and 7 non-volatile N-nitrosamines) was studied on three octadecylsilane columns. The capacity factor varies linearly with the number of carbons atom of the n-dialkyl chains. N-nitrosamines bearing di-n-alkyl chains with the same number of carbon atoms could be separated with a highly polar mobile phase. The yield of photohydrolysis depends upon pH and time of exposure under UV light. The response was shown to be linear in the 0-200 ng range with a limit of detection of 8 pmoles injected for N-dialkyl nitrosamines. This limit was 20 pmoles for N-nitrosamines bearing two phenyl groups. Although N-nitrosamines could be detected at 230 nm without post-column reaction, such a reaction enhances the specificity of detection in biological matrices such as gastric juice or alcoholic beverages.