Activation of N-Nitrosobis(2-oxopropyl)amine and N-Nitroso(2-hydroxypropyl)-(2-oxopropyl)amine to Mutagens for V79 Cells by Isolated Hamster and Rat Pancreatic Acinar Cells

A pancreatic acinar cell-mediated mutagenicity assay was developed as an in vitro model system to study the metabolism of N -nitrosobis(2-oxopropyl)amine (BOP) and N -nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP) into forms mutagenic for Chinese hamster V79 cells. Mutations at the hypoxanthine:guanine phosphoribosyltransferase locus and the Na/K ATPase locus were scored by resistance to 6-thioguanine and ouabain, respectively. The ability of both Syrian golden hamster and Fischer rat pancreatic acinar cells to convert BOP and HPOP to mutagens for V79 cells was investigated in order to examine the basis for species specificity. Acinar cells of both species were capable of activating BOP and HPOP to mutagens for V79 cells in a dose-dependent manner. In the 6-thioguanine resistance assay, rat acinar cells induced higher mutation frequencies than hamster acinar cells with both BOP and HPOP. In the ouabain resistance assay, both cell types induced equivalent levels of mutation with the respective nitrosamines. BOP was a considerably more potent mutagen than HPOP after activation by either cell type. This is consistent with the known in vivo specificity of BOP versus HPOP in the hamster pancreas and suggests that BOP may be activated to mutagenic metabolites by a pathway(s) independent from its enzymatic reduction to HPOP. The comparable abilities of rat and hamster acinar cells to convert BOP or HPOP to mutagenic forms imply that pancreatic metabolic activation alone cannot explain the difference in organotropism of BOP and HPOP in the two species.