Dose-dependent induction of aberrant crypt foci in the colons but no neoplastic lesions in the livers of heterozygous p53-deficient mice treated withlow dose 2-amino-3-methylimidazo [4,5-f]quinoline

2-Amino-3-methylimidazo[4,5-]quinoline (IQ) is a food derived heterocyclic amine which induces aberrant crypt foci (ACF) and tumors in the livers in m ice. However, most previous studies of carcinogenicity were carried out wit h high dose treatments, so the practical risk associated with the low dose exposure is unclear. We, therefore, assessed whether low dose IQ causes ACF formation in the colons of mice constitutively hemizygous for functional p 53, Simultaneously, we screened for development of preneoplastic foci in th e liver. A total of 60 heterozygous p53-deficient mice as well as 60 wild-t ype mice were divided into five groups and administered IQ in the diet at c oncentrations of 50, 10, 2, 0.4 and 0 ppm until the end of the experiment. ACF were detected in the 50, 10 and 2 ppm-treated groups and the numbers of those comprising one aberrant crypt (AC) in p53-deficient mice treated wit h 10 or 2 ppm were significantly increased, compared to counterpart wild-ty pe values. A dose-dependent increase of ACF was also observed in transgenic mice groups but no large ACF developed. In spite of extensive examination, no preneoplastic foci could be detected in either transgenic or wild-type mice. The results suggested that germline p53 deficiency may slightly enhan ce the development of ACF in colons but not in the liver. The fact that no ACF were detected in the lowest, 0.4 ppm, treated groups may imply a practi cal non-effective level of IQ for tumor induction. (C) 1999 Elsevier Scienc e Ireland Ltd. All rights reserved.