Mutagenesis Advance Access originally published online on December 14, 2004
Mutagenesis 2005 20(1):15-22; doi:10.1093/mutage/gei001
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mutagenesis vol. 20 no. 1 © UK Environmental Mutagen Society 2005; all rights reserved.
Effects of 
-naphthyl isothiocyanate and a heterocyclic amine, PhIP, on cytochrome P-450, mutagenic activation of various carcinogens and glucuronidation in rat liver
Laboratory of Radiochemistry, Gifu Pharmaceutical University, 6-1 Mitahora-higashi 5-chome, Gifu 502-8585, Japan, 1Department of Pathology, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa 920-0293, Japan and 2Department of Tumor Pathology, Graduate School of Medicine, Gifu University, 1-1 Yanagido, Gifu 501-1194, Japan
To elucidate the mechanism underlying suppression by 
-naphthyl isothiocyanate (ANIT) of mammary carcinogenesis induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), we evaluated hepatic levels of cytochrome P-450 (CYP) enzymes, mutagenic activation of environmental carcinogens and UDP-glucuronyltransferase (UDPGT) activities in female Sprague–Dawley rats fed a high fat diet. Immunoblot analyses revealed induction of CYP1A1, newly found 51 and 53 kDa proteins and constitutive CYP1A2 and 2B2 by intragastric treatment with 85 mg/kg PhIP eight times for 11 days. Although the extents of induction were not as high as in the case of PhIP, 3 weeks feeding of 400 p.p.m. ANIT induced CYP1A1 and the 51 and 53 kDa proteins. CP1A2 level was decreased by the feeding of ANIT. The mutagenicity in strain TA98 of PhIP, four other heterocyclic amines (HCAs) and benzo[a]pyrene was greatly enhanced in the presence of liver S9 mix prepared from rats pretreated with PhIP but not with ANIT. The mutagenicities of these five HCAs were significantly decreased in the presence of liver S9 from rats pretreated with a combination of PhIP and ANIT as compared with that pretreated with PhIP alone. The level of hepatic CYP1A2, which is known to be involved in the metabolic activation of PhIP, was consistently decreased in liver microsomes from rats administered PhIP plus ANIT as compared with that from rats administered PhIP alone. On the other hand, UDPGT activity towards 4-nitrophenol (4-NP) was enhanced using liver microsomes prepared from rats pretreated with a combination of PhIP and ANIT as compared with those pretreated with PhIP or ANIT alone. These results show that chemoprevention by ANIT against PhIP-induced rat mammary carcinogenesis can be explained by a dual action mechanism, i.e. a reduction in metabolic activation by hepatic CYP1A2 and an enhancement of detoxification by 4-NP UDPGT. The role of the newly found 51 and 53 kDa proteins in activation of HCAs is also discussed.
* To whom correspondence should be addressed. Tel: +81 58 237 3931; Fax: +81 58 237 5979; Email: ymori{at}gifu-pu.ac.jp