ABSTRACT
The induction of phase 2 detoxifying enzymes, such as UDP-glucuronosyltransferases (UGTs), in response to an array of naturally occurring and synthetic agents, such as oltipraz (4-methyl-5-[2-pyrazinyl]-1,2-dithiole-3-thione), provides an effective means of protection against a variety of carcinogens. Transcription factor Nrf2 is an essential regulator of the inducible expression of detoxifying enzyme genes by chemopreventive agents. In this study, we investigated in Nrf2-deficient mice the susceptibility to the urinary bladder-specific carcinogen N-nitrosobutyl(4-hydroxybutyl)amine (BBN) and the chemopreventive efficacy of oltipraz. The incidence of urinary bladder carcinoma by BBN was significantly higher in Nrf2-/- mice than in wild-type mice; invasive carcinoma was found in 24.0 and 38.5% of wild-type and Nrf2-/- mice, respectively. Oltipraz induced the phase 2 enzymes responsible for BBN detoxification in the liver and urinary bladder in an Nrf2-dependent manner. As expected, therefore, oltipraz decreased the incidence of urinary bladder carcinoma by BBN in wild-type mice but had little effect in Nrf2-/- mice. In wild-type mouse liver, oltipraz significantly induced BBN glucuronidation and decreased the urinary concentration of N-nitrosobutyl(3-carboxypropyl)amine, a proximate carcinogen of BBN. Importantly, BBN was found to suppress the expression of UGT1A specifically in the urinary bladder. This suppression was counteracted by oltipraz in wild-type mice but not in Nrf2-/- mice. These results show that Nrf2 and its downstream target genes are responsible for BBN detoxification. Furthermore, oltipraz prevents carcinogenesis by BBN by enhancing detoxification of this carcinogen in the liver and urinary bladder.
Subject(s)
Anticarcinogenic Agents/pharmacology , DNA-Binding Proteins/physiology , Pyrazines/pharmacology , Trans-Activators/physiology , Urinary Bladder Neoplasms/prevention & control , Animals , Butylhydroxybutylnitrosamine/pharmacokinetics , Carcinogens/pharmacokinetics , DNA-Binding Proteins/deficiency , DNA-Binding Proteins/genetics , Enzyme Induction/drug effects , Female , Gene Expression/drug effects , Genetic Predisposition to Disease , Glucuronides/metabolism , Glucuronosyltransferase/antagonists & inhibitors , Glucuronosyltransferase/biosynthesis , Glucuronosyltransferase/genetics , Glucuronosyltransferase/metabolism , Inactivation, Metabolic , Male , Mice , Mice, Inbred C57BL , Mice, Inbred ICR , Mice, Knockout , Microsomes, Liver/drug effects , Microsomes, Liver/enzymology , Microsomes, Liver/metabolism , NF-E2-Related Factor 2 , Thiones , Thiophenes , Trans-Activators/deficiency , Trans-Activators/genetics , Urinary Bladder/drug effects , Urinary Bladder/enzymology , Urinary Bladder/metabolism , Urinary Bladder Neoplasms/chemically induced , Urinary Bladder Neoplasms/genetics , Urinary Bladder Neoplasms/metabolismABSTRACT
A time- and dose-dependent study of N-ethyl-N-(4-hydroxybutyl)nitrosamine (EHBN) bladder carcinogenesis was performed in nude mice maintained on tap water containing 0.025% EHBN for 4, 12, and 20 weeks ad libitum. A total of 13 invasive tumors, comprising 11 transitional cell carcinomas (TCCs) (84.6%) and 2 squamous cell carcinomas (SCCs) (15.4%), were found. Compared with previous results for B6C3F1 mice exposed to the same EHBN insult, the numbers of invasive carcinomas induced in nude mice, and especially of SCCs, were low. In order to ascertain whether this difference in cancer incidence between nude and B6C3F1 mice was due to variation in urinary excretion, the metabolism of EHBN was also investigated and compared with that of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). Respective total urinary excretions over 48 hr of N-ethyl-N-(3-carboxypropyl)nitrosamine (ECPN) or N-butyl-N-(3-carboxypropyl)nitrosamine (BCPN), the ultimate carcinogenic species of EHBN or BBN, were 822.4 +/- 41.4 micrograms and 530.4 +/- 81.0 micrograms, respectively, in nude mice, and 800.6 +/- 83.7 micrograms and 407.8 +/- 69.7 micrograms, respectively, in B6C3F1 mice. In conclusion, although it is apparent that nude mice have a low susceptibility to EHBN induction of urinary bladder cancer, this does not appear to be dependent on reduced metabolism to the active form.
Subject(s)
Butylhydroxybutylnitrosamine/analogs & derivatives , Carcinogens/toxicity , Carcinoma, Squamous Cell/chemically induced , Carcinoma, Transitional Cell/chemically induced , Urinary Bladder Neoplasms/chemically induced , Animals , Body Weight/drug effects , Butylhydroxybutylnitrosamine/pharmacokinetics , Butylhydroxybutylnitrosamine/toxicity , Carcinogens/pharmacokinetics , Carcinoma in Situ/chemically induced , Carcinoma in Situ/pathology , Carcinoma in Situ/physiopathology , Carcinoma, Squamous Cell/pathology , Carcinoma, Squamous Cell/physiopathology , Carcinoma, Transitional Cell/pathology , Carcinoma, Transitional Cell/physiopathology , Male , Mice , Mice, Nude , Nitrosamines/pharmacokinetics , Nitrosamines/toxicity , Urinary Bladder Neoplasms/pathology , Urinary Bladder Neoplasms/physiopathology , Urodynamics/drug effectsABSTRACT
N-Nitrosodibutylamine and its omega-hydroxylated metabolite N-nitrosobutyl(4-hydroxybutyl)amine (NB4HBA) induce tumors in the urine bladder of different animal species through their common urinary metabolite N-nitrosobutyl(3-carboxypropyl)amine (NB3CPA), resulting from the oxidation of the alcoholic group of NB4HBA to a carboxylic group. NB4HBA disappearance from blood, the formation of its main metabolites, NB3CPA and NB4HBA-glucuronide (NB4HBA-G), and their urinary excretion, were investigated in rats after an i.v. dose of 1 mg/kg (5.7 mumol/kg). NB3CPA and NB4HBA-G formation was readily detectable 2 min after treatment and levels were still measurable at 120 and 30 min, respectively. The parent compound disappeared from blood 90 min after injection. The NB4HBA blood concentration-time profile was adequately described by a one-compartmental linear model. NB4HBA half-life was 8 min, total body clearance and renal clearance were 86.1 and 0.22 ml/min/kg, respectively. The 0-96-h urinary excretion of NB4HBA was 0.3% of the administered dose. NB3CPA half-life was 15 min; NB3CPA and NB4HBA-G urinary excretion were 36 and 11.7%, respectively, urinary excretion of known compounds accounting for less than 50%. After i.v. injection of NB3CPA equimolar to the NB4HBA dose, only 50% of unchanged compound was recovered in the urine and after NB4HBA-G, 41% of the administered dose was excreted unchanged, NB3CPA accounting for 10%. Thus NB3CPA and NB4HBA-G might undergo further biotransformation, suggesting that NB3CPA may not be the ultimate carcinogen responsible for urinary bladder tumor induction.
