Differential effects of butylated hydroxyanisole on metabolism of aflatoxin B1 in vitro by liver and lung microsomes

Growing epidemiological evidence points out the carcinogenic hazard of inhaled aflatoxin B1 (AFB1) to the pulmonary system. Metabolism of AFB1 by lung microsomes and its binding to calf thymus DNA are reported for the first time in this paper. In addition, the ability of dietary butylated hydroxyanisole (BHA) to modulate AFB1 adduct formation with DNA was examined. Lung microsomes from BHA-treated rats unlike those from liver caused a 50% inhibition of AFB1-DNA binding. However, pulmonary cytosolic glutathione (GSH) S-transferase activity remained unaltered. The addition of BHA-treated lung cytosol failed to produce a greater inhibition of AFB1-DNA binding than control cytosol. Microsome mediated AFB1-DNA binding was markedly inhibited (30%) by the addition of GSH alone to the incubation system. Further addition of cytosol contributed much less (10%) to the inhibition of AFB1-DNA binding. These observations together with the induction of microsomal GSH S-transferase strongly implicate the role of microsomal GSH S-transferase in the modulation of AFB1-DNA binding.     

Inhibition of 7,12-dimethylbenz(a)anthracene-induced rat mammary carcinogenesis by concomitant or postcarcinogen antioxidant exposure

When administered prior to or at the time of carcinogen exposure, the phenolic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are effective inhibitors of carcinogenesis in several target organs. However, chronic, postcarcinogen administration of BHT apparently enhances tumorigenesis in certain animal models for liver and lung cancer. The present study was performed to determine the effects of BHA and BHT on mammary carcinogenesis when antioxidant exposure is limited to defined periods encompassing or following carcinogen availability. At 50 days of age (Time O), virgin female Sprague-Dawley rats (25/group) were given a single intragastric dose of 8 mg of 7,12-dimethylbenz(a) athracene . Basal diet (Wayne Lab Meal) was supplemented with 5000 or 2500 mg of BHA or BHT/kg by the following protocol: 2 weeks before until 1 week after carcinogen administration; 1 week after carcinogen administration until the end of the study; or none. The experiment was terminated 210 days after 7,12-dimethylbenz(a)anthracene administration, and all mammary tumors were confirmed histologically. When administered by the 2 weeks before to 1 week after schedule, both BHA and BHT were effective inhibitors of mammary carcinogenesis. However, the compounds also were active in chemoprevention when administered by the 1 week after to end protocol. These data indicate that the anticarcinogenic activity of antioxidants is not limited to influences on carcinogen metabolism, since both BHA and BHT inhibited mammary tumor induction when their administration was begun following clearance of the carcinogen from the mammary gland. The anticarcinogenic activity of postcarcinogen administration of BHA and BHT in the mammary gland is in contrast to the apparent tumor-enhancing activity of BHT in the liver and lung.     

Effect of antioxidants and antitoxicants of isoniazid on the formation of lung tumours in mice by isoniazid and hydrazine sulphate

The present study reports the effects of antioxidants and antitoxicants on the formation of lung tumours in Swiss mice induced by isoniazid (INH) and hydrazine sulphate (HS).Dietary administration of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) or simultaneous oral administration of antitoxicants (l-arginine, l-sodium glutamate and pyridoxine hydrochloride) failed to prevent HS-induced lung tumours. On the other hand BHA and BHT inhibited the formation of lung tumours in groups of mice receiving INH. Folic acid supplementation had marginal effect on the formation of lung tumours in groups receiving HS (P < 0.1).Higher lung tumour incidence was observed in groups maintained only on BHT diet as compared to animals maintained on standard diet.     

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.     

Inhibitory Effects of Antioxidants on N-Bis(2-hydroxypropyl)nitrosamine-induced Lung Carcinogenesis in Rats

Potential second-stage modifying effects of 8 antioxidants on lung tumorigenesis initiated by N-bis(2-hydroxypropyl)nitrosamine (DHPN) were examined in male F344 rats. After an initial 2-week treatment with DHPN (0.1% in drinking water), rats were administered one of the antioxidants supplemented in the diet for 30 weeks. Although the incidences of lung adenomas were not affected, those of carcinomas were lowered by 2% butylated hydroxyanisole (BHA, 2 rats/20 rats), 1% butylated hydroxytoluene (BHT, 1/20), 0.8% ethoxyquin (EQ, 3/20) and 1%α-tocopherol (α-TP, 2/20) treatments as compared to the control level (9/20), while 5% sodium l -ascorbate (SA), 0.8% catechol (CC), 0.8% resorcinol (RN), and 0.8% hydroquinone (HQ) did not exert any significant effect on incidence. Quantitative analysis of adenomas and carcinomas (numbers and areas of lesions per unit area of lung section) revealed obvious inhibitory effects of SA, CC, and RN as well as BHA, BHT, EQ, and α-TP. Among the antioxidants, BHT exerted the strongest inhibitory activity. In contrast, DHPN-induced thyroid tumorigenesis was significantly enhanced by BHT (14/20) and EQ (20/20) treatments (control=5/20). Thus the antioxidants showed opposite effects on lung and thyroid carcinogenesis in the rat.     

Inhibitory effects of antioxidants on N-bis(2-hydroxypropyl)nitrosamine-induced lung carcinogenesis in rats

Potential second-stage modifying effects of 8 antioxidants on lung tumorigenesis initiated by N-bis(2-hydroxypropyl)nitrosamine (DHPN) were examined in male F344 rats. After an initial 2-week treatment with DHPN (0.1% in drinking water), rats were administered one of the antioxidants supplemented in the diet for 30 weeks. Although the incidences of lung adenomas were not affected, those of carcinomas were lowered by 2% butylated hydroxyanisole (BHA, 2 rats/20 rats), 1% butylated hydroxytoluene (BHT, 1/20), 0.8% ethoxyquin (EQ, 3/20) and 1% a-tocopherol (a-TP, 2/20) treatments as compared to the control level (9/20), while 5% sodium L-ascorbate (SA), 0.8% catechol (CC), 0.8% resorcinol (RN), and 0.8% hydroquinone (HQ) did not exert any significant effect on incidence. Quantitative analysis of adenomas and carcinomas (numbers and areas of lesions per unit area of lung section) revealed obvious inhibitory effects of SA, CC, and RN as well as BHA, BHT, EQ, and a-TP. Among the antioxidants, BHT exerted the strongest inhibitory activity. In contrast, DHPN-induced thyroid tumorigenesis was significantly enhanced by BHT (14/20) and EQ (20/20) treatments (control = 5/20). Thus the antioxidants showed opposite effects on lung and thyroid carcinogenesis in the rat.     

Inhibition of promutagen activation by the antioxidants butylated hydroxyanisole and butylated hydroxytoluene.

Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) exhibited antimutagenic activity in the Salmonella typhimurium reversion test. Both BHA and BHT reduced reversion induced by chemicals requiring metabolic activation for effectiveness. However, they did not affect reversion induced by direct-acting mutagens. These results suggested that BHA and BHT may inhibit the metabolic activation processes and demonstrated that the S. typhimurium reversion test may be used to identify inhibitors of the neoplastic process.     

Effects of butylated hydroxyanisole, butylated hydroxytoluene, and NaCl on gastric carcinogenesis initiated with N-methyl-N'-nitro-N-nitrosoguanidine in F344 rats

Promoting activities of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and NaCl and of combinations of these antioxidants with NaCl on gastric carcinogenesis initiated by N-methyl-N'-nitro-N-nitrosoguanidine [(MNNG) (CAS: 70-25-7; 1-methyl-3-nitro-1-nitrosoguanidine] were investigated in male inbred F344 rats. Animals, 6-week old, were given an intragastric administration of MNNG at 150 mg/kg body weight by gastric tube and 1 week later were placed on a diet containing BHA (0.5%), BHT (1.0%), NaCl (5.0%), BHA (0.5%) plus NaCl (5%), or BHT (1.0%) plus NaCl (5.0%) for 51 weeks. Control rats received no further treatment after MNNG administration. A single intragastric application of MNNG to rats induced multiple epithelial tumors of the forestomach and a few epithelial tumors of the glandular stomach after 52 weeks. Squamous cell carcinomas of the forestomach were seen in 2 of 18 effective rats (11.1%) in the control groups, and the incidences in the groups receiving the subsequent treatment were 45.0% with BHA, 15.8% with BHT, 30% with NaCl, 70% with BHA plus NaCl, and 52.9% with BHT plus NaCl. Differences in the incidences of squamous cell carcinoma between the controls and groups given BHA, BHA plus NaCl, and BHT plus NaCl were statistically significant. NaCl given alone after MNNG administration also significantly increased the incidence of papillomas in the forestomach. Incidences of glandular stomach tumors, adenomas and carcinomas were not affected by any of the subsequent treatments. No tumors of the stomach developed in the groups given BHA, BHT, and NaCl without MNNG pretreatment. Thus the present experiment revealed that BHA and NaCl but not BHT exert promoting activity on MNNG-induced forestomach carcinogenesis in rats and that, when BHA and BHT were given with NaCl, promotion was more marked, suggesting a synergistic effect on tumor promotion.     

Dose-dependent effects of butylated hydroxyanisole, butylated hydroxytoluene and ethoxyquin for promotion of bladder carcinogenesis in N-butyl-N-(4-hydroxybutyl)nitrosamine-initiated, unilaterally ureter-ligated rats

Dose-dependent effects of 3 antioxidants, butylated hydroxyanisole (BHA, 2.0, 1.0 and 0.5%), butylated hydroxytoluene (BHT, 1, 0.5 and 0.25%) and ethoxyquin (0.5, 0.25 and 0.125%) on the development of preneoplastic lesions in the bladder of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-treated rats were investigated. Feeding of the antioxidants after pretreatment of 0.05% BBN commenced and unilateral ureteric ligation was combined at week 3 of the experiment. Surviving rats were killed at the end of week 24. BHA and BHT, but not ethoxyquin increased dose-dependently the incidence and number of preneoplastic lesions, papillary or nodular hyperplasia of the urinary bladder in rats treated with BBN. Particularly, the incidence and number of PN hyperplasia in rats treated with 2.0% BHA and 1.0% BHT were significantly higher than those of the control group. Thus, promoting activities of BHA and BHT, but not ethoxyquin for the urinary bladder were confirmed in this system of BBN-initiated, unilaterally ureter-ligated rats.     

Different modifying response of butylated hydroxyanisole, butylated hydroxytoluene, and other antioxidants in N,N-dibutylnitrosamine esophagus and forestomach carcinogenesis of rats

The modifying effects of antioxidants were examined in a carcinogenesis system after N,N-dibutylnitrosamine treatment. Male F344 rats were given 0.05% N,N-dibutylnitrosamine in their drinking water for 4 wk and then treated with basal diet containing 2% butylated hydroxyanisole (BHA), 1% butylated hydroxytoluene (BHT) with 7 ppm vitamin K, 0.8% ethoxyquin, 5% sodium L-ascorbate, 5% sodium erythorbate, or no added chemical for 32 wk. BHA enhanced forestomach carcinogenesis but did not enhance esophageal carcinogenesis. BHT enhanced esophageal carcinogenesis but did not enhance forestomach carcinogenesis. Ethoxyquin significantly enhanced esophageal tumorigenesis. Neither esophageal nor forestomach carcinogenesis was affected by the other antioxidants evaluated. BHA significantly increased DNA synthesis of the forestomach epithelium, whereas BHT tended to increase that of the esophageal epithelium. Thus, BHA and BHT showed different modifying responses in carcinogenesis of the esophagus and forestomach.     

Induction of hepatic tumors with butylated hydroxyanisole in the self-fertilizing hermaphroditic fish Rivulus ocellatus marmoratus

The three-day-old larvae of self-fertilizing hermaphroditic fish Rivulus ocellatus marmoratus were fed a diet containing the antioxidant butylated hydroxyanisole (BHA) at levels of 0.01-0.8% for 12 days. Six months after BHA administration, hepatic tumors were found in all groups of BHA-treated fish. The BHA-induced tumor incidences were clearly dose-dependent. These results show that dietary BHA is hepatocarcinogenic in Rivulus even at 0.01% dose.     

Initiating potential of 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and 3,3',4',5,7-pentahydroxyflavone (quercetin) in two-stage mouse skin carcinogenesis

Tumor initiating activity of 3,3',4',5,7-pentahydroxyflavone (quercetin), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and 2-(2-furyl)-3-(5-nitro-2-furyl) (AF-2) acrylamide) were tested in a two-stage mouse skin carcinogenesis model using 12-O-tetradecanoyl phorbol-13-acetate (TPA) as a promoter. These compounds dissolved in dimethyl sulfoxide were topically applied twice weekly for 5 weeks on the dorsal skin, and then followed by TPA for 47 weeks. The total initiating dose was 100 mg for each compound. 7,12-Dimethylbenz(a)anthracene (DMBA) at a total dose of 100 micrograms was used as a positive control compound. AF-2 induced skin tumors in 35% of the mice (average of 0.4 tumors/mouse), HBA in 15% in (0.2/mouse), BHT in 13% (0.13/mouse) and quercetin in 5% (0.1/mouse). No tumors appeared in the groups treated with either test chemicals alone or TPA alone. Statistical analysis according to either Fisher's exact test or Peto's trend test revealed significant differences for tumor appearance in the AF-2/TPA and BHA/TPA followed by TPA groups as compared to in the DMSO/TPA group. The results indicate that AF-2 and BHA have weak tumor initiating activity on mouse skin, but such effects are not apparent for BHT or quercetin.     

Inhibition of binding of 2-acetylaminofluorene to DNA by butylated hydroxytoluene and butylated hydroxyanisole in vitro

Numerous studies have shown that the food antioxidants butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), under specific exposure conditions, can inhibit hepatocarcinogenesis induced by various carcinogens. The purpose of the present work was to study the biochemical mechanisms responsible for the anticarcinogenic activity of BHA and BHT using in vitro systems. The effects of BHA and BHT on the binding of 2-acetylaminofluorene (2-AAF) to DNA was determined in a microsomal system and in primary cultures of rat hepatocytes. It was found that both antioxidants reduce the binding of 2-AAF and that of N-OH-2-acetylaminofluorene (N-OH-2-AAF) to calf thymus DNA in the presence of liver microsomes. The inhibition was however more pronounced with the parent compound. Lower levels of DNA binding were also detected in hepatocytes incubated with 2-AAF along with BHA or BHT. These results suggest that phenolic antioxidants can exert anticarcinogenic activity through modulation of carcinogen interaction with DNA which may reflect on alteration in carcinogen metabolic activation.     

Induction of Hepatic Tumors with Butylated Hydroxyanisole in the Self-fertilizing Hermaphroditic Fish Rivulus ocellatus marmoratus

The three-day-old larvae of self-fertilizing hermaphroditic fish Rivulus ocellatus marmoratus were fed a diet containing the antioxidant butylated hydroxyanisole (BHA) at levels of 0.01–0.8% for 12 days. Six months after BHA administration, hepatic tumors were found in all groups of BHA-treated fish. The BHA-induced tumor incidences were clearly dose-dependent. These results show that dietary BHA is hepatocarcinogenic in Rivulus even at 0.01% dose.     

Comparative effect of dietary butylated hydroxyanisole and {beta}-naphthoflavone on aflatoxin B1 metabolism, DNA adduct formation, and carcinogenesis in rainbow trout

Butylated hydroxyanisole (BHA) and ß-naphthoflavone(BNF), both chemicals with anti-carcinogeneic properties insome experimental animals, were compared for effects on afiatoxinB1 (AFB1) metabolism, hepatic DNA adduct formation and carcinogenesisin the rainbow trout. Dietary BHA had no effect on the hepatictumor incidence when fed at 0.03 or 0.3% 4 weeks prior to andduring a 4 week dietary exposure of 10 p.p.b. AFB1. BNF, whenfed at 0.005 or 0.05% under similar conditions, significantlyreduced tumor response, which confirms previous results in trout(Nixon et al.9 Carcinogenesis, 5, 615–619, 1984). BHAfed at either 0.03 or 0.3% for 8 weeks had no post-initiationeffect on the 52 week hepatic tumor incidence of trout exposedto a 0.5 p.p.m. AFB1 solution as embryos. A similar post-initiationexposure to 0.05% BNF significantly enhanced AFB1 tumor response.The influence of dietary BHA and BNF on AFB1 metabolism andDNA adduct formation and persistence in trout were examined.A 3 week pre-treatment with 0.3% dietary BHA had no effect onin vivo hepatic nuclear AFB1-DNA adduct formation at 0.5, 1,2 and 7 days after AFB1 i.p. injection. By contrast 0.05% dietaryBNF reduced hepatic AFB1-DNA adducts to 33–60% of controllevels at 0.5, 1, 2 and 4 days after AFB1 exposure. This wasaccompanied by significantly lower blood and liver levels ofAFB1 during the first 24 h after i.p. injection. Livers of BNFtrout also contained 4-fold more of the less carcinogenic metabolite,aflatoxin M1, and 50% less aflatoxicol (AFL), a metabolite withsimilar carcinogenicity as AFB1. Bile AFL-glucuronide levelswere significantly decreased in BNF-fed trout, but total bileglucuronides were significantly increased due to a 15-fold increasein aflatoxicol-M1 glucuronide. Freshly isolated hepatocytesfrom BHA-fed fish, when incubated with AFB1 for 1 h, showedno difference in levels of AFB1-DNA adducts or ratios of AFB1metabolites when compared to hepatocytes isolated from fishfed a control diet only. By contrast, dietary BNF has been previouslyshown to greatly enhance AFM1 production, reduce AFL production,and significantly reduce AFB1-DNA adduct formation in isolatedtrout hepatocytes (Bailey et al., Natl. Cancer Inst. Monograph,65, 379–385, 1984). These results indicate that dietaryBHA up to 0.3% does not alter AFB1 metabolism or DNA adductionin trout, nor does it inhibit or promote AFB1 hepatocarcinogenesisin this species. This is in contrast to anti-oxidant enhancementof AFB1-glutathione conjugation, reduction of AFB1-DNA binding,and consequent reduction of tumor response in rats. The nullresults in trout thus support enhanced glutathione conjugationas the major mechanism for BHA inhibition of AFB1 cardnogenesisin mammalian models. By contrast, BNF dietary pre-treatmentappears to inhibit AFB1 carcinogenicity in trout by enchancingglucuronide formation and elimination of the carcinogen, leadingto reduced DNA adduct formation in target tissue.     

Selective induction of rat urinary bladder tumors by simultaneous administration of 3,2'-dimethyl-4-aminobiphenyl (DMAB) and butylated hydroxyanisole or butylated hydroxytoluene is associated with increased DMAB-DNA adduct formation

Modification of 3,2'-dimethyl-4-aminobiphenyl (DMAB) multi-organ carcinogenesis by simultaneous treatment with butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT) was studied using young and old male F344 rats. Animals, 4 or 54 weeks old, were given DMAB (s.c. injection of 50 mg/kg body wt once a week for 10 weeks) along with BHA (2.0% in diet for 11 weeks) or BHT (1.0% in diet for 11 weeks). The experiments were terminated 55 weeks after the commencement. Combined administration of BHA or BHT with the carcinogen resulted in development of urinary bladder tumors in greater than 90% of both young and old rats thus treated, whereas no tumors were induced in animals given DMAB alone. In contrast, the appearance of preneoplastic lesions in the liver and pancreas was reduced by BHA or BHT treatment. Tumor development (less than 30% incidence) was also evident in the small and large intestines, prostate, preputial glands, skin/subcutis and ear duct, with no modification by BHA or BHT. No ageing effects were evident. The formations of DMAB-DNA adducts, evaluated by the enzyme-linked immunosorbent assay and immunohistochemical staining, correlated well with tumorigenesis in the urinary bladder, liver and pancreas. The selective enhancement of urinary bladder tumor induction by BHA and BHT appeared to be due to both increased DMAB-DNA adduct formation caused by metabolic alteration of DMAB in the liver and increased DNA synthesis in the urothelial cells.     

Modulation of benzo[a]pyrene-induced morphological transformation of Syrian hamster embryo cells by butylated hydroxytoluene and butylated hydroxyanisole

The Syrian hamster embryo cell transformation assay has been used to investigate the effect of two synthetic antioxidants on morphological transformation induced by the initiator benzo[a]pyrene (BP). A two-stage protocol was employed with an initiation phase of 2 days and a subsequent promotion phase of 5 days. When 10 microM butylated hydroxytoluene (BHT) were present in the promotion phase instead of the solvent the transformation frequency at 0.1 micrograms BP/ml increased from 0.27% to 0.55%; at 100 microM of BHT the transformation frequency was 0.77%. Butylated hydroxyanisole (BHA) also enhanced the percentage of transformed colonies from 0.40% (10 microM) to 0.49% (100 microM), respectively. No significant initiating activity was detected for both antioxidants when tested in the initiation phase instead of BP; when the antioxidants were applied simultaneously with BP (1 microgram/ml) during the initiation phase the transformation frequency was decreased from 0.64% to 0.15% (100 microM BHT) and to 0.17% (100 microM BHA), respectively. These results show that the dual action of phenolic antioxidants on chemical carcinogenesis, which depends on the administration schedule, can be imitated in an in vitro test system. In addition to their anti-initiation effect, BHT and BHA, while devoid of intrinsic initiator potency, exert a moderate promotional activity on hamster embryo cell cultures. Their ability to enhance tumorigenesis by various carcinogens in vivo is likely to be at least partially related to such promotion-like effects on cell growth and morphology.     

Modification by five antioxidants of 1,2-dimethylhydrazine-initiated colon carcinogenesis in F344 rats

The effects of antioxidants given in the post initiation phaseof colon tumor development were investigated in male F344 ratstreated with 1 ,2-dimethylhydrazine (DMH). Animals (20/group)were given s.c. injections of DMH at a dose of 20 mg/kg oncea week for four consecutive weeks. One week after the last injection,rats were fed diet containing 5% sodium L-asorbate (SA), 0.5%butylated hydroxyanisole (BHA), 0.8% ethoxyquin (EQ), 1.0% propylgallate or 0.5% butylated hydroxytoluene (BHT) for 36 weeks.A control group was fed the basal diet not containing antioxidants.The experiment was terminated 40 weeks after the first injectionof DMH and all intestinal tumors were confirmed histologically.SA significantly increased the incidence of adenomas and thenumber of tumors per rat of the colon (especially of the distalcolon). Although EQ and BHT did not affect the number of ratswith colon tumors, the number of tumors per rat occurring inthe distal colon was significantly increased by EQ while beingdecreased by BHT. No modification of tumor development was observedwith BHA or PG. Thus, modification of tumor development by SA,EQ and BHT was apparent, mainly in the distal colon.     

Modifying effects of concomitant treatment with butylated hydroxyanisole or butylated hydroxytoluene on N,N-dibutylnitrosamine-induced liver, forestomach and urinary bladder carcinogenesis in F344 male rats

The modifying effects of concomitant antioxidant treatment on N,N-dibutylnitrosamine (DBN)-induced carcinogenesis were investigated. Male F344 rats were given 0.05% DBN in their drinking water for 16 weeks, and simultaneously administered powder diet containing 2.0% butylated hydroxyanisole (BHA) or 0.7% butylated hydroxytoluene (BHT) for 16 weeks. Control animals received drinking water containing 0.05% DBN without antioxidant treatment. The final incidences of hepatocellular carcinomas were 100, 100 and 40% in the DBN plus BHA, DBN plus BHT and DBN treated groups, respectively, the difference being significant (P less than 0.001). Lung metastases were only observed in the DBN plus BHT group and DBN plus BHA group (50%, P less than 0.001; 7%, respectively). The incidence of papillary or nodular hyperplasia of the urinary bladder in the DBN plus BHA group was significantly higher than that of the control (P less than 0.05). Furthermore, esophageal carcinomas and papillomas were observed in all DBN treated groups, with no inter-group significant variation in yield. On the other hand, combination of DBN treatment with BHA or BHT significantly reduced the resultant incidences of forestomach hyperplasia. The results clearly demonstrated that concomitant administration of antioxidants, and in particular BHT, can modify DBN carcinogenesis.     

Inhibition of chemically induced mammary carcinogenesis in rats by short-term exposure to butylated hydroxytoluene (BHT): interrelationships among BHT concentration, carcinogen dose, and diet

Dietary butylated hydroxytoluene (BHT) fed 14 days before and 14 days after carcinogen administration resulted in a dose-dependent inhibition of 7, 12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumor incidence in outbred Sprague-Dawley rats. In addition, the inhibitory effects of BHT were strongly influenced by the dose of initiating carcinogen and the type of diet in which BHT was administered. In animals fed the NIH-07 diet and receiving a low dose of DMBA (5 mg/rat), the inhibitory effect of BHT was manifested at all four BHT concentrations (6,000 leads to 300 ppm). Maximal inhibition was approximately 50% in animals given 5 mg DMBA and receiving 6,000 ppm BHT. However, in the group administered a high dose of DMBA (15 mg/rat), the inhibitory effect of BHT was expressed only at 6,000 ppm, the highest concentration given. Lower concentrations (300 and 1,000 ppm) of BHT had no detectable effect on tumor incidence. In animals fed the defined, semipurified AIN-76A diet during the 4-week treatment period and initiated with 5 mg DMBA, BHT at 6,000 ppm inhibited tumor development. However, at 15 mg DMBA animals fed the AIN-76A diet differed markedly from those fed the NIH-07 diet. In the former group, BHT at 6,000 ppm was unable to elicit any inhibitory response; in the latter group, BHT inhibited tumor development by 40%. Dietary BHT also inhibited DMBA-induced adrenocortical hyperplastic nodules in a dose-dependent fashion. These results indicate that short-term exposure to dietary BHT can inhibit experimental mammary tumor development at environmentally relevant concentrations.