Comparison of lesions induced in the Syrian golden hamster by diethylnitrosamine, dimethylhydrazine, and dibutylnitrosamine: influence of subsequent butylated hydroxyanisole treatment

The target organ specificity of the carcinogens diethylnitrosamine [(DENA) CAS: 55-18-5], dimethylhydrazine [(DMH) CAS: 57-14-7], and dibutylnitrosamine [(DBN) CAS: 924-16-3] was examined in Syrian golden hamsters. Groups of male animals were given 8 weekly injections of one of these carcinogens and then were maintained on a basal diet or a diet supplemented with 1% butylated hydroxyanisole [(BHA) CAS: 25013-16-5], or they were given the respective carcinogens in the drinking water until they were sacrificed at week 34. While DENA specifically induced tracheal polyps and hepatocellular foci and nodules, DMH administration was associated with development of both hepatocellular and hemangiocellular liver lesions as well as forestomach papillomas and adenocarcinomas of the large intestine. DBN induced lesions in the urinary bladder, forestomach, and trachea, in addition to a few preneoplastic foci in the liver and lungs. In all organs studied, preneoplastic and neoplastic populations were essentially similar to those observed in other experimental animals, with colon and tracheal lesions demonstrating alteration in polysaccharide metabolism. While inhibiting the development of hepatocellular lesions, especially in the group initiated with DENA, and while itself inducing extensive papillomatous forestomach hyperplasia, BHA administration did not exert a significant modifying influence on tumorigenesis in other organs. The present results demonstrate the efficacy of Syrian golden hamster studies for investigation of comparative neoplasia. Of particular interest in this respect were differences in the degree of phenotypic instability demonstrated by glutathione S-transferase placental form-positive foci induced by the 3 carcinogens, which indicated a possible qualitative variation in "initiation."     

Differential modification of development of preneoplastic lesions in the Syrian golden hamster initiated with a single dose of 2,2'-dioxo-N-nitrosodipropylamine: influence of subsequent butylated hydroxyanisole, alpha-tocopherol, or carbazole

The effects of butylated hydroxyanisole [(BHA) CAS: 25013-16-5], alpha-tocopherol [(TC) CAS: 59-02-9], and carbazole [(CA) CAS: 86-74-8] administered subsequent to a single dose of 2,2'-dioxo-N-nitrosodipropylamine [(DOPN) CAS: 60599-38-4] on the development of putative preneoplastic lesions were investigated in Syrian golden hamsters. Whereas the 2 antioxidants BHA and TC inhibited the incidence of both liver and pancreatic lesions, CA, itself giving rise to considerable numbers of enzyme-altered foci, enhanced carcinogenesis in the liver while inhibiting carcinogenesis in the pancreas. All 3 of these agents induced hyperplastic and papillomatous lesions in the forestomachs of treated animals, independent of prior DOPN treatment; these forestomach lesions were not evident in controls. Cellular atypia and invasive growth characteristics signifying malignant change were also observed in BHA-induced forestomach lesions. The results demonstrate that hepatocarcinogenesis in the Syrian golden hamster, like that in the rat, can be inhibited by antioxidants. The similar decrease in putative preneoplastic lesion yield evident in the pancreas of BHA- or TC-treated hamsters, considered in the light of similarities in altered enzyme phenotype in carcinogen-induced lesions of both organs, suggests that common biochemical changes can be an underlying factor in the modification of neoplastic development in liver and pancreas. The present results also provide further evidence that CA has carcinogenic potential for the liver and forestomach of experimental animals.     

Dose response in butylated hydroxyanisole induction of forestomach carcinogenesis in F344 rats

Groups of 50 6-week-old male F344 rats were given a powdered diet containing 0, 0.125, 0.25, 0.5, 1, or 2% butylated hydroxyanisole [(BHA) CAS: 25013-16-5] for 104 weeks. The highest dose--2% BHA--induced significant increase in the incidence of squamous cell carcinoma of the forestomach. Papillomas of the forestomach developed in 20 and 100% of the rats given diets containing 1 and 2% BHA, respectively. The incidence of epithelial hyperplasia of the forestomach increased with the increased BHA doses, to 100% incidence at the highest dose. Thus the incidences of proliferative and neoplastic lesions of the forestomach were dose dependent.     

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.     

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.     

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.     

Regression of butylated hydroxyanisole (BHA)-induced hyperplasia but not dysplasia in the forestomach of hamsters

The reversibility of butylated hydroxyanisole (BHA)-inducedhamster forestomach hyperplasia was examined histopathologically.Groups of 10–15 male Syrian golden hamsters were treatedwith 2% BHA, for 12, 24 or 48 weeks and in each case then placedon basal diet until termination of the experiment at week 72,or treated with 2% BHA continuously for 72 weeks. Although sequentialsampling revealed that BHA-induced hyperplasia reverted aftercessation of antioxidant treatment, dysplastic lesions suchas squamous cell dysplasia and basal cell dysplasia persistedand tended to increase with time on BHA. Basal cell dysplasia,i.e. those treated with BHA for 24 weeks or more and killedup to 48 weeks later. Whereas the increase in labeling indexevident in areas of hyperplasia during treatment returned tocontrol level after cessation, this was not the case for thedysplastic lesions which continued to demonstrate elevated proliferation.The results thus suggest that basal cell dysplasia, includingregions of squamous cell dysplasia, may be of particular importanceas a precursor pre-neoplastic lesion.     

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.     

Disappearance of upward proliferation and persistence of downward basal cell proliferation in rat forestomach papillomas induced by butylated hydroxyanisole

The reversibility of forestomach lesions induced in rats by butylated hydroxyanisole (BHA) was examined. F344 rats were given BHA for 24 weeks, followed by the basal diet, and their forestomach lesions at weeks 24 and 96 were compared histopathologically. Hyperplasias and papillomas showing upward proliferation were found in week 24 but not in week 96. However, downward proliferation of basal cells persisted after the discontinuation of BHA administration. This finding suggests that downward growth of basal cells is not reversible and is important in the development of BHA-induced forestomach tumors in rats.     

Combined effects of butylated hydroxyanisole and other antioxidants in induction of forestomach lesions in rats

The possibility that changes in the forestomach of rats induced by butylated hydroxyanisole (BHA) are caused by inductions of free radicals and their reactions with macromolecules was examined. Groups of five male F344 rats were pretreated with 1% alpha-tocopherol, 1% ellagic acid, 1% propyl gallate, 0.25% ethoxyquin, 0.5% glutathione, 1% sodium L-ascorbate or 1% 3,3'-thiodipropionic acid for 1 week, then treated with the same antioxidant plus 1% BHA for 1 week, and then killed. Histological examination showed that BHA induced epithelial hyperplasia of the forestomach. This induction of hyperplasia was not inhibited, but increased by the antioxidants, particularly propyl gallate and ethoxyquin. Thus the induction of hyperplasia by BHA may not be related to a free radical reaction.     

Regression of simple hyperplasia and papillomas and persistence of basal cell hyperplasia in the forestomach of F344 rats treated with butylated hydroxyanisole

The reversibility of forestomach lesions induced in rats by butylated hydroxyanisole (BHA) was examined. F344 rats were given a 2% BHA diet for 24, 48, or 72 wk followed by a basal diet for the remainder of the 96-wk experiment. Two other groups of rats were given a 2% BHA diet or basal diet alone for 96 wk. The forestomach lesions at wk 24, 48, 72, or 96 were compared histopathologically. The results showed that exophytic epithelial proliferation (simple hyperplasia or papilloma) induced by BHA was reversible, while endophytic proliferation of basal cells (basal cell hyperplasia) persisted after withdrawal of BHA administration. This suggests that simple hyperplasia and papilloma of the forestomach induced by BHA are not autonomous and need continuous feeding of BHA to develop further.     

Induction of forestomach lesions in rats by oral administrations of naturally occurring antioxidants for 4 weeks

The effects of naturally occurring antioxidants on rat forestomach epithelium were compared with those of synthetic antioxidants, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), of which the former is a known forestomach carcinogen. Groups of five F344 male rats were given diet containing BHA, BHT, gallic acid, syringic acid, sesamol, caffeic acid, chlorogenic acid, ferulic acid, eugenol or esculin for 4 weeks at a level of 0.7% for BHT or 2% for other compounds. Histological examination of the forestomach showed that BHA induced hyperplasia mainly in the prefundic region near the esophageal orifice, caffeic acid induced pronounced hyperplasia throughout the forestomach epithelium, and sesamol induced large ulcers and hyperplasia in the central region. Thus, these naturally occurring antioxidants showed different toxicities and abilities to induce hyperplasia in the rat forestomach.     

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.     

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 less than 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.     

Effects of butylated hydroxyanisole pretreatment on low dose N-methyl-N'-nitro-N-nitrosoguanidine- or N,N-dibutylnitrosamine-induced rat forestomach or esophageal carcinogenesis

The effects of butylated hydroxyanisole (BHA) pretreatment on subsequent low dose N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N,N-dibutylnitrosamine (DBN) treatment on forestomach or esophageal carcinogenesis were investigated in male F344 rats. Groups of animals were pretreated with 2% BHA or basal diet alone for 24 weeks and then were given 20 mg/kg body wt MNNG once every 2 weeks, 0.025% DBN in drinking water continuously or basal diet alone for the subsequent 24 weeks. Further groups of rats were similarly treated with BHA or basal diet alone for 24 weeks, placed on basal diet for the next 24 weeks and then treated with MNNG, DBN or basal diet alone for the subsequent 24 weeks. Animals were killed 48 or 72 weeks after the beginning of the experiment. Histopathological examination showed that the incidence of forestomach tumors was not significantly affected by the BHA pretreatment in the MNNG-treated groups. On the other hand, the incidence of esophageal squamous cell carcinomas was lower in the group pretreated with BHA followed by DBN than in that treated with basal diet followed by DBN (48 week experiment). There was no significant difference in esophageal tumor incidence in the 72 week experiment. The results thus indicate that continuous treatment with 2% BHA for 24 weeks does not exert initiating activity on forestomach and esophageal epithelia.     

Antagonistic effect of diethylmaleate on the promotion of forestomach carcinogenesis by butylated hydroxyanisole (BHA) in rats pretreated withN-methyl-N'-nitro-N-nitrosoguanidine

The effects of diethyhaleate (DEM), previously demonstratedto inhibit butylated hydroxyanisole (BHA)-induced forestomachhyperplasia, on BHA promotion of forestomach carcinogenesisin rats pretreated with N-methyl-N'-nitro-N- nitrosoguanidine(MNNG) were examined. Groups of male 6-week-old F344 animalswere given a single i.g. administration of 150 mg/kg body weightMNNG and starting 1 week later administered powdered diet containing1% BHA plus 0.2% DEM, 1% BHA, 0.2% DEM or basal diet alone for51 weeks. Further groups of rats were treated with 1% BHA plus0.2% DEM, 1% BHA, 0.2% DEM or basal diet alone without MNNGpretreatment. Histopathological assessment of lesions at week52 revealed enhancement of MNNG-initiated papilloma (100 versus50%) and squamous cell carcinoma (100 versus 0%) developmentby BHA as compared to controls. Additional treatment with DEM,however, significantly reduced the relative incidences of carcinomain situ (0 versus 35.7%) and squamous cell carcinoma (35.7 versus100%), as well as BHA-induced forestomach hyperplasia with orwithout prior MNNG treatment. The results thus clearly demonstratethat DEM acts as a potent antagonist to BHA-promotion of ratforestomach carcinogenesis.     

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.     

Modifying effects of simultaneous treatment with butylated hydroxyanisole (BHA) on rat tumor induction by 3,2'-dimethyl-4-aminobiphenyl, 2,2'-dihydroxy-di-n-propylnitrosamine and N-methylnitrosourea

The modifying effects of concurrent treatment with high or low doses of butylated hydroxyanisole (BHA) on wide-spectrum carcinogen-induced carcinogenesis were studied in male F344 rats. Groups of 20 animals were treated with 2 or 0.04% BHA for 24 weeks. Starting 2 weeks after the commencement of BHA treatment, they were given s.c. injection of 50 mg/kg body weight 3,2'-dimethyl-4-aminobiphenyl (DMAB) once a week, i.g. administrations of 200 mg/kg body weight 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN) once every 2 weeks, or i.p. injection of 15 mg/kg body weight N-methylnitrosourea (MNU) once every 2 weeks for 22 weeks. Further groups of rats were treated with DMAB, DHPN, MNU, or 2 or 0.04% BHA alone. All surviving animals were killed 24 weeks after the beginning of the experiment and the target organs examined histopathologically. The BHA treatment dose-dependently decreased the incidence of DMAB-induced liver preneoplastic lesions but was associated with significant tumor induction in the forestomach (papillomas, 40%, P less than 0.01) and urinary bladder (papillomas, 53%, P less than 0.001; carcinomas, 80%, P less than 0.001), where no lesions were observed in the group given only DMAB. Concurrent administration of 2% BHA also significantly inhibited the development of alveolar hyperplasia (P less than 0.001) of the lung in DHPN-treated animals, while enhancing induction of forestomach papillomas (P less than 0.05) and simple hyperplasia in the urinary bladder. Neither MNU nor 2% BHA alone induced forestomach carcinoma or papillary or nodular hyperplasia (PN hyperplasia) in the urinary bladder. However, these lesions were observed in 100% (P less than 0.001) and 55% (P less than 0.001) of animals respectively, receiving the two compounds in combination. These results demonstrated that concurrent treatment with BHA not only inhibits but can also strongly enhance carcinogenesis depending on the organ, irrespective of whether the carcinogens act directly or require metabolism. The finding that BHA potently modified carcinogenesis at 0.04% in diet, 1/50 of the carcinogenic dose, suggests that actual dietary levels close to the human situation might play a significant role in tumor development in man.     

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.     

Dose-dependent effects of short-term dietary administration of the food additive butylated hydroxyanisole on cell kinetic parameters in rat gastro-intestinal tract

Groups of ten 5-week old male Wistar rats were fed a diet containing 0, 0.25, 0.50, 0.75, 1.0 or 2.0% butylated hydroxyanisole (BHA) ad libitum for 2 weeks; another group of rats served as a pair-fed control (PFC) group for the 2% BHA-fed animals. Subsequently, rats were injected i.p. with the thymidine-analogue bromodeoxyuridine (BrdU) which was incorporated into the DNA of cells during DNA synthesis. Cell kinetic parameters in gastro-intestinal tract tissues were determined by means of bivariate BrdU/DNA analysis applying flow-cytometry to randomized tissue samples or by applying immunohistology to randomized tissue sections. In the forestomach, glandular stomach, small intestine and colon/rectum, mean tissue labelling index (LI) was significantly increased in rats on a diet supplemented with 2% BHA, in comparison with rats fed the basal diet (0% BHA) ad libitum or restricted to the mean daily intake of 2% BHA-fed rats (PFC). In the oesophagus of rats fed 2% BHA, the LI was significantly higher in comparison with their PFC group, but not with the group of rats fed 0% BHA ad libitum. In rat forestomach, an apparent no observed effect level for ad libitum fed rats was found at 0.5% BHA (LI) and at 0.75% BHA (potential doubling time). Thus, the oesophagus, glandular stomach, small intestine and large bowel, in addition to the forestomach, are possible target tissues in rats for the proliferation enhancing effects of BHA. At the time of termination of the experiment, plasma BHA concentrations were dose dependently increased and were in the range that is easily attained in man after ingestion of a dose equal to the acceptable daily intake for BHA (0.5 mg/kg).