Experimental model for investigating bladder carcinogen metabolism using the isolated rat urinary bladder

The capacity of the isolated rat urinary bladder to metabolize chemical carcinogens was studied. Under our experimental conditions, the bladder carcinogen N-nitrosobutyl-(4-hydroxybutyl)amine (NBHBA) was oxidized to N-nitrosobutyl(3-carboxypropyl)amine (NBCPA). A time-dependent increase in the amount of NBCPA formed and a simultaneous disappearance of NBHBA indicated that the bladder can metabolize NBHBA to the metabolite considered to be responsible for tumour induction in the urinary bladder of laboratory animals. After 15, 30, 60 and 120 min, the percentages of NBCPA formed were 10%, 21%, 35% and 61%, respectively, and 59%, 49%, 36% and 25% of NBHBA remained unchanged. When N-nitrosodi-n-butylamine (NDBA) was introduced into the isolated urinary bladder and incubated for 120 min, its oxidized metabolites NBHBA and NBCPA were formed, in amounts of 0.13% and 0.06% of the substrate added.     

Development of an experimental model for studying bladder carcinogen metabolism using the isolated rat urinary bladder

The isolated rat urinary bladder was used to study this organ's capacity to metabolize chemical carcinogens. In our experimental conditions, the urinary bladder carcinogen N-nitrosobutyl(4-hydroxybutyl)amine was oxidized to N-nitrosobutyl(3-carboxypropyl)amine. A time-dependent increase was observed in the amount of N-nitrosobutyl(3-carboxypropyl)amine formed and simultaneous disappearance of N-nitrosobutyl(4-hydroxybutyl)amine added, indicating that the bladder can metabolize N-nitrosobutyl(4-hydroxybutyl)amine to the metabolite considered responsible for tumor induction in the urinary bladder of laboratory animals. At 15, 30, 60, and 120 min the percentages of N-nitrosobutyl(3-carboxypropyl)amine formed were 11, 22, 36, and 64%, respectively, and 62, 48, 37, and 26% of N-nitrosobutyl(4-hydroxybutyl)amine remained unchanged. When N-nitrosodibutylamine was introduced into the isolated urinary bladder and incubated for 120 min, its oxidized metabolites N-nitrosobutyl(4-hydroxybutyl)amine and N-nitrosobutyl(3-carboxypropyl)amine were formed, amounting to, respectively, 0.13 and 0.06% of the substrate added. The glucuronide of N-nitrosobutyl(4-hydroxybutyl)amine was incubated in the isolated rat urinary bladder both as a buffer and as a urine solution in order to detect cellular and urinary beta-glucuronidase activity. In both systems N-nitrosobutyl(4-hydroxybutyl)amine released was about 1% at 4 h and this percentage did not increase at 6 h. N-Nitrosobutyl(3-carboxypropyl)amine was detectable at 2 h and reached 0.2% of the substrate incubated at 6 h. The results indicate that the urinary bladder may play a role in activating bladder carcinogens.     

Escherichia coli infection of the urinary bladder: induction of tumours in rats receiving nitrosamine precursors and augmentation of bladder carcinogenesis by N-nitrosobutyl (4-hydroxybutyl)amine

Experimental introduction of Escherichia coli type 04 into the subserosa of the urinary bladder of female Fischer 344 rats produced chronic bacterial infection in more than 90% of animals. Groups of rats with bacterial infection were given sodium nitrate and either piperazine (Group 1) or dibutylamine (Group 2) in the drinking-water. Control, noninfected animals received nitrate and either piperazine (Group 3) or dibutylamine (Group 4). At 40 weeks, transitional-cell carcinomas of the bladder were detected in 9/30 rats in Group 1 compared to 0/34 in Group 3 (p less than 0.0005), and in 11/34 rats in Group 2 compared to 0/32 in Group 4 (p less than 0.0003). Early changes were examined by scanning and transmission electron microscopy as well as autoradiography. Preneoplastic liver foci were detected in infected groups of animals receiving amine and nitrate, indicating reabsorption of the carcinogen synthesized in situ to induce distant organ transformation. In another experiment, E. coli infection augmented bladder carcinogenesis by N-nitrosobutyl(4-hydroxybutyl)amine (NBHBA), as indicated by earlier appearance of bladder tumours (six weeks compared to nine weeks) and, after 25 weeks, higher incidences of transitional-cell carcinomas (41/46 compared to 39/53, p less than 0.05), squamous metaplasia (43% compared to 9%, p less than 0.0001), glandular metaplasia (26% compared to 13%, p less than 0.05) and muscle invasion (30% compared to 11%, p less than 0.01) in the E. coli-infected group receiving carcinogen compared to the noninfected group receiving carcinogen, respectively. These results indicate that bacterial infection of the urinary bladder may play a major role in bladder carcinogenesis, both by helping in-situ nitrosamine synthesis and by augmenting carcinogenesis by nitrosamines.     

Alpha-oxidative metabolism of the bladder carcinogens N-nitrosobutyl(4-hydroxybutyl)amine and N-nitrosobutyl(3-carboxypropyl)amine within the rat isolated bladder

The most widely accepted metabolic pathway leading to the formation of reactive intermediates from nitrosamines involves enzymatic hydroxylation at the carbon atom alpha to the nitroso moiety. All subsequent steps are non-enzymatic reactions and the final result is the stoichiometric formation of a cationic product and molecular nitrogen. Thus the amount of molecular nitrogen evolved can be used as an indicator of alpha-hydroxylation. The use of doubly 15N-labelled nitrosamines and the detection of 15N2 by MS makes it simpler to measure the extent of alpha-hydroxylation. We have studied the alpha-oxidation of doubly 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine (BBN) and its metabolite N-nitrosobutyl(3-carboxypropyl)amine (BCPN), two potent urinary bladder carcinogens in animals, within the target organ. Various amounts of 15N-labelled BBN ranging from 0.1 to 5 mumol were incubated at 37 degrees C for 4 h in the isolated rat bladder and the formation of 15N2 was measured by GC-MS. 15N2 production was linear up to 1 mumol and represented approximately 0.1% of the substrate incubated. Time-course experiments showed that 15N2 production was linear over a 6 h incubation period, ranging from 2.16 +/- 0.05 to 4.55 +/- 0.33 nmol/mg urothelial cell protein. 15N-labelled BCPN (1-5 mumol) was also incubated within the rat isolated bladder. 15N2 production from BCPN was approximately 10 times less than that from BBN. The results indicate that, though to a lower extent, the target organ activates 15N-labelled BBN and BCPN through the alpha-hydroxylation pathway.     

N-Nitrosobutyl(4-hydroxybutyl)amine alpha-hydroxylation by rat liver and urothelial cell homogenates.

Determination of molecular nitrogen formed as a consequence of nitrosamine alpha-hydroxylation provides a useful means for studying the extent of activation of these compounds in target and nontarget organs and tissues. alpha-Hydroxylation in rat liver and urothelial cells was compared using as substrate doubly 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine (15N-NBHBA), a potent bladder carcinogen in rodents. Both enzyme sources metabolized 15N-NBHBA through the alpha-hydroxylation pathway. 15N2 production was dependent on the amount of substrate incubated. Vmax values for 15N2 production by urothelial cells and by liver postmitochondrial supernatant were 4.47 and 3.21 nmol/mg protein per h, respectively.     

A comparative study of the mutagenic activation of N-nitrosopropylamines by various animal species and man: evidence for a cytochrome P-450 dependent reaction

The mutagenic potential of seven carcinogenic N-nitrosopropylamines was examined by means of Ames' preincubation assay using liver 9000 g superanatant (S9) fractions from rats, hamsters, mice, rabbits, monkeys and humans for metabolic activation. N-Nitroso(2-hydroxypropyl) (2-oxopropyl)amine (HPOP), N-nitrosobis(2-oxopropyl)amine (BOP), N-nitrosobis(2-acetoxypropyl)amine (BAP), N-nitroso-2,6-dimethylmorpholine, N-nitrosomethyl(2-hydroxypropyl)amine (MHP) and N-nitrosomethyl(2-oxopropyl)amine all showed positive mutagenicity in strain TA100 in the presence of liver S9 from each of the uninduced animals, but N-nitrosobis(2-hydroxypropyl)amine was negative. The mutagenic activity of MHP was highest with liver S9 from the hamster, but that of BAP was lowest with hamster liver S9. With regard to the activities of the other N-nitrosopropylamines, there were no significant differences among five animal species. In the presence of liver S9 from humans, HPOP, BOP and MHP showed positive mutagenicity. With the exception of HPOP and BOP, the animal or human liver S9-mediated mutagenicity of these N-nitrosopropylamines was almost completely lost upon removal of NADP+ from the assay system, preincubation in an atmosphere of carbon monoxide, or addition of cytochrome c to the S9 mixture. metyrapone decreased the activities of five compounds (except for BOP) by between 29 and 71%, whereas 7,8-benzoflavone was totally lacking in this effect. These results demonstrated that the phenobarbital-inducible major cytochrome P-450 in animal and human livers is involved in the mutagenic activation of the N-nitrosopropylamines.     

Pharmacokinetic profile and metabolism of N-nitrosobutyl-(4-hydroxybutyl)amine in rats

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.     

Participation of phenobarbital-inducible cytochrome P450 in the mutagenic activation of N-nitrosopropylamines by liver and lung 9000 g fractions from five animal species and man.

The mutagenicity of nine carcinogenic N-nitrosopropylamines was studied by the Ames preincubation assay using 9000 g supernatant (S9) fractions or alcohol dehydrogenase. Treatment of animals with polychlorinated biphenyls or phenobarbital resulted in a marked increase in the ability of liver S9 to activate N-nitrosobis(2-hydroxypropyl)amine, N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine, N-nitrosobis(2-oxopropyl)amine, N-nitrosobis(2-acetoxypropyl)amine, N-nitroso-2,6-dimethylmorpholine, N-nitroso(2-hydroxypropyl)methylamine, N-nitroso(2-oxopropyl)methylamine, N-nitroso(2,3-dihydroxypropyl)methylamine and N-nitroso(2,3-dihydroxypropyl)(2-hydroxypropyl)amine to mutagens, whereas 3-methylcholanthrene induction was not effective. All reactions required NADP as a cofactor for mutagenic activation, and nitrogen, carbon monoxide, cytochrome c and metyrapone considerably inhibited their mutagenic activities, whereas 7,8-benzoflavone did not. Five propanol derivatives were not mutagenic in the presence of NAD and alcohol dehydrogenase. We conclude that the phenobarbital-inducible major cytochrome P450 in liver S9 from five animal species tested was selectively involved in mutagenic activation. The same cytochrome in human liver S9 and in lung S9 from three rodent species also activated the mutagenicity of N-nitroso(2-hydroxypropyl)methylamine.     

Induction of bacterial mutations by aminopyrazoles, compounds which cause mammary cancer in rats

An aminopyrazole PD 71627 (5-amino-l, 3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl)methanone, and two amide derivatives, PD 108298,N-[4-(2-flurobenzyD-13-dimethyl-1H/-pyrazol-5-yl]-2-([3K2-methyl-1-piperidmyI)-propyl]amino)acetamide-(Z)-2-butanedioate (1: 2), and PD 109394, 2-(di-ethylamino)-N-(4-(2-fluorobenzoyI)-l,3-dimethyl-1H-5-pyrazol-5-yl]acetamide hydrochloride, proposedneuroleptic drugs, were found to elicit mammary adenocarcinomasin male rats after 13 weeks of treatment. These compounds wereassess-ed for their ability to induce His⁺ revertants (rev)in five strains of Salmonella typhimurium (TA98, TA100, TA1535,TA1537 and TA1538) in the presence and absence of S9 activation.All were found to be potent mutagens in TA98 and TA100 aftera 20 min pre-incubation with Aroclor 1254-induced rat liverS9. However, the activity of the aminopyrazole PD 71627 wasmuch greater than the amide derivatives, PD 108298 or PD 109394,with activity of 11 800 rev/µmol, 670 rev/µmol,and 230 rev/µmol respectively in TA100, the strain showingthe greatest response. A comparison of liver S9 fractions fromrats untreated or pretreated with phenobarbital (PB) or Aroclor1254 showed that S9 from animals pretreated with PB providedthe greatest activation capability for the aminopyrazole PD71627 (59 300 rev/µmol in TA100). Three structural analogsof the aminopyrazole PD 71627, two without the amine and onewith a methyl substi-tuent on the amine, were compared withPD 71627 for in-duction of revertants in TA100 and TA98. Thecompounds without the amine had no mutagenk activity while themethyl derivative induced 3100 rev/µmol in TA100 afterpreincuba-tion with Aroclor 1254-induced S9. This confirmedthat the amine on the pyrazole ring was required for mutagenkac-tivity. The results of these studies support the hypothesisthat these compounds cause cancer in animals as a result ofDNA damage.     

Mutagenic activation of carcinogenic N-nitrosopropylamines by rat liver: evidence for a cytochrome P-450 dependent reaction

Mutagenic potential of carcinogenic N-nitrosopropylamines wasexamined by the Ames's liquid incubation assay, using rat liver9000 g supernatant (S9) fraction for metabolic activation. N-Nitrosobis(2-hydroxypropyl)amine,N-nitroso(2-hydroxypropyl)-(2-oxopropyl)amine (HPOP), N-nitrosobis(2-oxopropyl)amine(BOP), N-nitrosobis(2-acetoxypropyl)amine, N-nitroso-2,6-dimethylmorpholine,N-nitrosomethyl-(2-hydroxypropyl)amine and N-nitrosomethyl(2-oxopropyl)amineall showed positive mutagenicity in strain TA100 in the presenceof liver S9 while being negative in strain TA98. With the exceptionof HPOP and BOP, which were also mutagenic in TA100 withoutS9 metabolic activation, these N-nitrosopropylamines requiredthe presence of microsomes as a source of enzymes as well asNADP⁺ as a cofactor for mutagenic activation. Treatment of ratswith polychlorinated biphenyls or phenobarbital (PB) resultedin a marked increase in the ability of S9 to activate the sevenN-nitrosamines tested whereas 3-methylcholanthrene (3-MC) inductionwas not effective. All the mutagenic activities were considerablydecreased by preincubation in an atmosphere of either carbonmonoxide or nitrogen gas or by adding cytochrome c to the S9mixture. Metyrapone, a specific inhibitor of PB-inducible majorcytochrome P-450, considerably inhibited mutagenicity, whereas7,8-benzoflavone, a specific inhibitor of 3-MC-inducible majorcytochrome P-448, was totally lacking this effect. These resultsdemonstrate a correlation between rat liver S9 dependent mutagenicityof six N-nitrosopropylamines and their known carcinogenicityin rat in vivo experiments, and that the PB-inducible majorcytochrome P-450 is involved in the mutagenic activation. BOPwas also shown to be activated by extrahepatic (lung, kidney,pancreas) tissue S9, blood S9 and bovine serum albumin (BSA)to the extent of 50% of that activity obtained with liver S9.A possible mechanism of BSA-mediated activation of BOP is discussed.     

Mutagenic activation of carcinogenic N-nitrosopropylamines by liver S9 fractions from mice, rats and hamsters: evidence for a cytochrome P-450-dependent reaction

The mutagenic potential of nine carcinogenic N-nitrosopropylamineswas examined by Ames preincubation assay using liver 9000 gsupernatant (S9) fractions from female rats and male hamstersand mice for metabolic activation. N-Nitrosobis(2-hydroxypropyl)amine,N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine, N-nitrosobis(2-oxopropyl)amine,N-nitrosobis(2-acetoxypropyl)amine, N-nitroso-2,6-dimethylmorpholine,N-nitrosomethyl(2-hydroxypropyl)amine, N-nitrosomethyl(2-oxopropyl)amine,N-nitroso(2,3-dihydroxypropyl)(2-hydroxypropyl)amine and N-nitrosomethyl(2,3-dihydroxypropyl)amineall showed positive mutagenicity in strain TA100 in the presenceof liver S9 from three animal species pretreated with polychlorinatedbiphenyls or phenobarbital (PB). The S9-mediated mutagenicityof these N-nitrosamines was almost completely diminished bythe removal of NADP⁺ from the assay system. All the activitieswere considerably decreased by preincubation in an atmosphereof carbon monoxide or adding cytochrome c to the S9 mixture.Metyrapone considerably inhibited mutagenicity, whereas 7,8-benzoflavonewas totally lacking this effect. These results demonstrate acorrelation between the mutagenicity of nine N-nitrosopropylaminesmediated by liver S9 from three animal species and their knowncarcinogenicity in rodent in vivo experiments, and that thePB-inducible major cytochrome P-450 is selectively involvedin the mutagenic activation. A relationship between mutagenicpotencies of the N-nitrosamines and their known carcinogenicpotencies in rats and hamsters is discussed     

Dose-response relationships for the binding of benzo(a)pyrene metabolites to DNA and protein in lung, liver, and forestomach of control and butylated hydroxyanisole-treated mice

In this study, the formation of benzo(a)pyrene (BP) metabolite:DNA adducts in lung, liver, and forestomach of control and butylated hydroxyanisole (BHA)-treated (5 mg/g diet) female A/HeJ mice was examined as a function of BP dose (p.o.), ranging from 2 to 1351 mumol/kg. The major identified adduct in each tissue at each dose was the (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDEI):deoxyguanosine adduct. A 7 beta,8 alpha-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene:deoxyguanosine adduct, a(-)-BPDEI:deoxyguanosine adduct, and an unidentified adduct were also observed. In lung and liver of untreated animals, the dose-response curves for BPDEI:DNA adduct levels were sigmoidal. In forestomach, there was no indication of saturation of DNA binding over the BP dose range examined. The dose-response curves became linear as BP dose approached zero and thus, no threshold dose existed below which binding of BPDEI to DNA did not occur, at least in lung, liver, and forestomach of these mice. In forestomach, the dose-response curve for BPDEI:DNA adducts in BHA-treated mice, 0.5% of diet for 2 weeks, was parallel to the curve for control animals and thus, the inhibition (45%) of adduct formation is independent of BP dose. In contrast, BHA treatment diminished the curvilinear nature of the dose-response curves for BPDE adducts in lung and liver. The inhibition of BPDEI:DNA adduct formation by BHA in lung and liver was dose dependent. The inhibition of lung (68%) and liver (82%) adduct formation was highest at a BP dose of 270 mumol/kg. As the BP dose approached zero, the inhibition of BPDEI:DNA adduct formation by BHA decreased with BP dose and approached values of approximately 40% (lung) and 55% (liver). The dose dependency of the binding of BP metabolites to protein was also examined. BPDEI:DNA adduct concentrations ranged from 2 to 10% of protein binding concentrations in liver of untreated animals, from 3 to 7% in forestomach, and from 5 to 7% in lung. The dose-response curves for protein binding of BP metabolites in lung and liver from BHA-treated animals were essentially parallel to those in control animals and thus, the inhibition of protein binding by BHA treatment had no dose dependency in these organs. No consistent BHA effect was observed on the amount of binding of BP metabolites to forestomach protein.     

Dose-response studies of the effect of dietary butylated hydroxyanisole on colon carcinogenesis induced by methylazoxymethanol acetate in female CF1 mice

The effect of dietary butylated hydroxyanisole (BHA) on methylazoxymethanol acetate [(MAM AC) CAS: 592-62-1; methyl-ONN-azoxy)methanol acetate]-induced intestinal carcinogenesis was studied in female CF1 mice. BHA was added at levels of 0, 0.03, 0.1, 0.3, and 0.6% to the NIH-07 open-formula diet and at 0 and 0.6% to the AIN-76 semipurified diet and fed to mice, starting at 5 weeks of age until termination of the experiment. At 7 weeks of age, all animals except the vehicle-treated controls were given ip injections of MAM AC (15 mg/kg body wt for four times in 11 days for the low-dose group: total dose, 60 mg/kg body; 15 mg/kg body wt for eight times in 22 days for the high-dose group: total dose, 120 mg/kg body wt). With a low dose of carcinogen, the lung tumor incidence was inhibited in mice fed the NIH-07 diet containing 0.03-0.6% BHA and the AIN-76 diet containing 0.6% BHA compared to lung tumor incidence in those fed the diets without BHA; with a high dose of carcinogen, the inhibition was observed in mice fed the NIH-07 diet containing 0.1-0.6% BHA. Colon tumor incidence and colon tumor multiplicity (number of tumors per animal and number of tumors per tumor-bearing animal, respectively) were lower in mice fed the NIH-07 diets with 0.03-0.6% BHA or fed the AIN-76 diet with 0.6% BHA, as well as treated with a low dose of carcinogen, than in animals fed no BHA; with a high dose of carcinogen, colon tumor multiplicity and colon tumor incidence were inhibited in animals fed the NIH-07 diet containing 0.1-0.6% BHA. Consumption of the NIH-07 diets containing 0.03-0.6% BHA resulted in increased glutathione transferase activity of liver and small intestinal and colon mucosae in a dose-related manner.     

A comparative study of the mutagenic activation of carcinogenic N-nitrosopropylamines by various animal species and man

N-Nitrosomethyl(2-hydroxypropyl)amine (NMHPA), N-nitrosomethyl(2-oxopropyl)-amine (NMOPA), N-nitrosomethyl(2,3-dihydroxypropyl)amine (NMD23HPA), N-nitrosobis(2-hydroxypropyl)amine (NDHPA), N-nitroso(2,3-dihydroxypropyl)(2-hydroxypropyl)-amine(ND23HPHPA), N-nitrosobis(2-acetoxypropyl)amine (NDAcPA) and N-nitroso-2,6-dimethylmorpholine (NDMMOR) were mutagenic in Salmonella typhimurium strain TA100 in the presence of liver 9000 X g supernatant (S9) from mice, rats, hamsters, rabbits and monkeys. N-Nitroso(2-hydroxypropyl)(2-oxopropyl)amine (NHPOPA) and N-nitrosobis(2-oxopropyl)amine (NDOPA) were mutagenic in strain TA100 without metabolic activation, and both compounds were further activated by animal liver S9. NMOPA and NMHPA were also mutagenic in the presence of lung S9 from these animals and in the presence of human lung or liver S9. Pancreatic S9 from any of the animals did not activate any of the nine N-nitrosamines to mutagens.     

Effect of butylated hydroxyanisole on the level of DNA adduction by aristolochic acid in the rat forestomach and liver

Administration of butylated hydroxyanisole (BHA) orally at either 0.5 g or 1 g/kg daily for 14 days to rats did not produce any DNA adducts in the forestomach as measured by the 32P-postlabeling method using (1) limiting concentrations of 32P-ATP; (2) nuclease P1 enhancement; or (3) butanol extraction. Experiments were conducted to establish the effects of BHA administration on aristolochic acid (AA) DNA adduct formation in the forestomach and liver, when BHA was administered prior to, together with or after AA administration. Adduct levels per 10(9) nucleotides in the liver after oral dosing daily for 5 days with 1 mg/kg AA and BHA (1 g/kg) or corn oil (5 ml/kg) for 7 days were as follows: (a) BHA and AA given simultaneously; 235 +/- 71, (b) AA + corn oil; 63 +/- 39, (c) AA followed by BHA; 57 +/- 13, (d) AA followed by corn oil; 91 +/- 38, (e) BHA followed by AA; 90 +/- 12, (f) corn oil followed by AA; 83 +/- 24. For the forestomach the values were: (a) 236 +/- 86, (b) 77 +/- 25, (c) 367 +/- 97, (d) 296 +/- 47, (e) 217 +/- 81, (f) 70 +/- 64. These data suggest that BHA could have an enhancing effect on AA-induced lesions in the forestomach if dosed together with, or prior to, AA as adduct levels are significantly higher than in controls.     

Effect of butylated hydroxyanisole on the metabolism of benzo[a]-pyrene and the binding of metabolites to DNA, in vitro and in vivo, in the forestomach, lung, and liver of mice

The effects of butyldted hydroxyanisole (BHA) administrationon the amounts of benzo[a]pyrene (BP) metabolite-DNA adductsformed in vivo in the forestomach of A/HeJ mice were investigated48 h after oral administration of BP. BP was administered tomice in amounts known to result in BPInduced neoplasia in certaintissues. Analysis of deoxyribonudeosides by h.p.l.c. showedthat several BP metabolite-DNA adducts were formed in this tissue.The major identified adduct was the (±)-7ß,8-dihydroxy-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDEI) deoxyguanosine adduct. Addition of BHA to the diet inhibitedBPDE I-DNA adduct formation in the forestomach. The inhibitionof BPDE I-DNA adduct formation by BHA occurred under the sameexperimental conditions as does inhibition of tumor formationby this compound. These results in forestomach and previousresults in lung and forestomach demonstrated that inhibitionof the formation of the BPDE I-DNA adduct in the target tissueis a possible mechanism by which BHA inhibits BP-induced neoplasia.BP metabolism and DNA binding were also studied under in vitroconditions using microsomes prepared from forestomach, lung,and liver of A/HeJ mice. The amount of BPDE-DNA adduct formedin vitro is either equal to or lower than the amount of BP phenol-oxide-DNAadduct formed. BPDE I-DNA adduct formation was not significantlydifferent in incubations containing microsomes prepared fromBHA-treated or untreated mice. These results suggest that alterationsof the microsomal monooxygenases induced by BHA feeding arenot sufficient to account for the observed decreases in BPDE-DNAadduct formation in vivo. The monooxygenases were apparentlyaltered by BHA feeding as indicated by the substantial changesin the metabolic profile of BP and the decrease in the formationof the BP phenol-oxide-DNA adducts in the forestomach. The exclusionof glutathione transferases from the in vitro incubations couldaccount for the lack of effect of BHA treatment on BPDE-DNAadduct formation. BHA enhancement of ghitathione transferaseactivity has been postulated to play a role in the anticarcinogenicaction of BHA.     

Mutagenicity of N-nitrosobis(2-hydroxypropyl)amine and its related compounds in the presence of rat lung and liver S9

The mutagenic activities of N-nitrosobis(2-hydroxypropyl)amine (BHP) and its related compounds were studied in Salmonella typhimurium TA100 and TA98 strains by Ames's liquid incubation assay in the presence or absence of lung and liver S9 of rats treated with polychlorinated biphenyl (PCB). BHP and its related compounds, N-nitroso-(2-hydroxypropyl)(2-oxopropyl)amine (HPOP), N-nitrosobis(2-oxopropyl)amine (BOP), N-nitrosobis(2-acetoxypropyl)amine (BAP), and N-nitroso-2,6-dimethylmorpholine (NDMM) showed negative mutagenicity in the absence of lung and liver S9 in TA100 and TA98 strains while those compounds showed positive in the presence of liver S9 in TA100 strain. HPOP and BOP showed positive mutagenic activity in the presence of lung S9 in TA100 strain. HPOP showed the strongest mutagenic activity in the presence of lung and liver S9.     

Co-carcinogenic Effect of Retinyl Acetate on Forestomach Carcinogenesis of Male F344 Rats Induced with Butylated Hydroxyanisole

The potential modifying effect of retinyl acetate (RA) on butylated hydroxyanisole (BHA)-induced rat forestomach tumorigenesis was examined. Male F344 rats, 5 weeks of age, were maintained on diet containing 1% or 2% BHA by weight and simultaneously on drinking water supplemented with RA at various concentrations (w/v) for 52 weeks. In groups given 2% BHA, although marked hyperplastic changes of the forestomach epithelium were observed in all animals, co-administration of 0.25% RA significantly (P<0.05) increased the incidence of forestomach tumors (squamous cell papilloma and carcinoma) to 60% (9/15, 2 rats with carcinoma) from 15% (3/20, one rat with carcinoma) in the group given RA-free water. In rats given 1% BHA, RA co-administered at a dose of 0.05, 0.1, 0.2 or 0.25% showed a dose-dependent enhancing effect on the development of the BHA-induced epithelial hyperplasia. Tumors, all papillomas, were induced in 3 rats (17%) with 0.25% RA and in one rat (10%) with 0.05% RA co-administration. RA alone did not induce hyperplastic changes in the forestomach. These findings indicate that RA acted as a co-carcinogen in the BHA forestomach carcinogenesis of the rat.