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The cytochrome P450 (P450 or CYP) is involved in both detoxification and metabolic activation of many carcinogens. In order to identify the role of hepatic P450 in the mutagenesis of genotoxic carcinogens, we generated a novel hepatic P450 reductase null (HRN) gpt delta mouse model, which lacks functional hepatic P450 on a gpt delta mouse background. In this study, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was used to treat HRN gpt delta mice and control littermates. Gene mutations in the liver and lungs were detected, and mutation spectra were analyzed. Pharmacokinetic analyses were performed, and tissue levels of NNK and metabolite were determined. NNK-induced mutant frequencies (MFs) were equivalent to spontaneous MFs in the liver, but increased more than 3 times in the lungs of HRN gpt delta mice compared to control mice. NNK-induced mutation spectra showed no difference between HRN gpt delta mice and control littermates. Toxicokinetic studies revealed reduced clearance of NNK with elevated tissue concentrations in HRN gpt delta mice. To our knowledge, these are the first data demonstrating that NNK cannot induce mutagenesis in the liver without P450 metabolic activation, but can induce mutagenesis in lungs by a hepatic P450-independent mechanism. Moreover, our data show that hepatic P450 plays a major role in the systemic clearance of NNK, thereby protecting the lungs against NNK-induced mutagenesis. Our model will be useful in establishing the role of hepatic versus extrahepatic P450-mediated mutagenesis, and the relative contributions of P450 compared to other biotransformation enzymes in the genotoxic carcinogens' activation. [ABSTRACT FROM AUTHOR]

Triptolide (TL) is an active component of Tripterygium wilfordii Hook. F which is used to treat autoimmune and inflammatory disease. However, a high incidence of adverse effects is often observed in clinic. Previously we have demonstrated that cytochrome P450s (CYPs) are involved in the metabolism of TL and low activity of hepatic P450 reductase aggravates TL-induced toxicity. However, the underlying mechanisms of TL-induced toxicity mediated by hepatic CYPs have not been well delineated. Here, an integrated H NMR-based metabolomic analysis was performed to evaluate the global biochemical alteration in the liver-specific cytochrome P450 reductase (CPR) knockout (KO) mice and wild-type (WT) counterparts with a same dose of TL (0.5 mg/kg) administration. Dramatically different metabolic profiles indicated more severe hepatotoxicity and nephrotoxicity induced by TL in KO mice than in WT mice, which were confirmed by serum biochemistry and histopathological examination. Furthermore, the results from both multivariate statistical analysis and system statistical metabolic correlation analysis indicated that the significantly changed endogenous metabolites were primarily involved in oxidative stress, energy metabolism, amino acid metabolism, gut microflora metabolism, and choline metabolism. Our results reveal the molecular mechanisms of TL-induced toxicity in the condition of hepatic CYP inactivation. As CYP inactivation and/or inhibition are usually caused by genetic polymorphism and/or drug-drug interactions, personalized prescription according to enzyme activity of CYPs and metabolic profiling could be used to maximize therapeutic efficacy and avoid or reduce TL-induced toxicity clinically. [ABSTRACT FROM AUTHOR]

Abstract: Aristolochic acid (AA) is known to be a potent mutagen and carcinogen. Aristolochic acid I (AAI) and aristolochic acid II (AAII), the two major components of AA, differ from each other by a single methoxy group. However, their individual mutagenic characteristics in vivo are unclear. In the present study, we compared their DNA adduct formation and mutagenicities in the gpt delta transgenic mouse kidney. The dA-AAI, dG-AAI, dA-AAII and dG-AAII were identified in the kidney two days after intragastric administration of AAI or AAII at 5mg/kg. The concentration of DNA adducts formed by AAII was approximately 2.5-fold higher than that formed by AAI (p <0.05). The mutant frequency induced by AAII was nearly two-fold higher than that induced by AAI (p <0.05) following administration of 5mg/kg AAI or AAII, five times per week for six weeks. Investigation of the mutation spectra showed no statistically significant difference between AAI- and AAII-treated mice (p >0.05). A:T to T:A transversion was the predominant type of mutation in both treated groups, the GC-associated mutation rates, however, differed between the AAI and AAII treatments. The in vivo metabolic pathways of AAI and AAII are different, and this may affect their mutagenicity. In the present study, we measured the levels of AAI and AAII in the kidney and plasma of gpt delta transgenic mice at multiple time points after a single intragastric dose of 1 or 5mg/kg of either component. Our results showed that the levels of AAII in both kidney and plasma were considerably higher than those of AAI (p <0.01). The present study indicated that AAII showed more carcinogenic risk than AAI in vivo, and this may be, at least partly, the result of its increased levels in kidney and plasma. [Copyright &y& Elsevier]