Lack of enhancing effects of sodium nitrite on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mammary carcinogenesis in female Sprague–Dawley rats

A number of heterocyclic amines (HCAs) have been shown to exert enhanced carcinogenic and mutagenic potential when given simultaneously with sodium nitrite (NaNO2). In the present experiment, effects of combined treatment with NaNO2 and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), one of the most prevalent carcinogenic HCAs in the human environment, were assessed with regard to mammary tumor induction in female Sprague–Dawley (SD) rats. Animals at 6 weeks of age were given intragastric doses of 100 mg/kg body weight of PhIP twice a week for 4 weeks, during which period 0 or 0.2% NaNO2 was administered in the drinking water. Control rats received 0.2% NaNO2 alone for the 4 weeks or non-supplemented water during the entire 48 week experimental period, without carcinogen treatment. The first tumor in the PhIP+NaNO2 group appeared significantly later than with PhIP alone, and during the experimental period, the incidence, multiplicity and volume of mammary tumors in this group tended towards decreased, although values did not significantly differ at the terminal sacrifice. These results indicate that NaNO2 does not enhance PhIP-induced rat mammary carcinogenesis, rather possessing some potential for inhibition.