Dose-dependent effects of butylated hydroxyanisole, butylated hydroxytoluene and ethoxyquin in induction of foci of rat liver cells containing the placental form of glutathione S-transferase

The dose-dependence effects of 3 antioxidants, butylated hydroxyanisole (BHA: 2.0%, 1.0% and 0.5%), butylated hydroxytoluene (BHT: 1.0%, 0.5% and 0.25%) and ethoxyquin (EQ: 0.5%, 0.25% and 0.125%) combined with partial hepatectomy on the development of preneoplastic lesions in the liver of diethylnitrosamine (DEN, 200 mg/kg body wt)-treated rats were investigated. Feeding of the antioxidants commenced 2 weeks after the single dose of DEN used to initiate the lesions. gamma-Glutamyl transpeptidase (gamma-GT) and the placental form of glutathione S-transferase (GST-P) were used for quantitation of altered focal populations. Results with both markers demonstrated a dose-dependent decrease of foci in BHA-treated rats relative to those in control rats. Morphometric analysis of gamma-GT-positive lesions also revealed decrease in both the number and area of foci in BHT- and EQ-treated groups. The discrepancy between results of quantitation of gamma-GT- and GST-P-positive foci was attributable to the induction of a background, periportal zone staining for gamma-GT, which made differentiation of smaller foci difficult. Comparison of results with the 2 markers suggested that GST-P is the more accurate marker for quantitative studies on enzyme altered foci in rat liver.     

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.     

Promoting activities of butylated hydroxyanisole and butylated hydroxytoluene on 2-stage urinary bladder carcinogenesis and inhibition of {gamma}-glutamyl transpeptidase-positive foci development in the liver of rats

Butylated hydroxyanisole (BHA) and butylated hydroxy-toluene(BHT) were evaluated for possible promoting activity for urinarybladder carcinogenesis in male F344 rats initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine(BBN). The rats were treated with 0.01 or 0.05% BBN in the drinkingwater for 4 weeks and then administered 2% BHA or 1% BHT inthe diet for 32 weeks. Surviving rats were killed at the endof week 36 of the experiment. The incidences of cancer and papillomaand the average number of cancers, papillomas and papillaryor nodular hyperplasias (PN hyperplasias) per 10 cm of basementmembrane were significantly increased in the group receivingBHA following initiation by 0.05% BBN compared with the groupgiven BBN only. BHT also significantly increased these lesionsof the bladder, but not the average number of cancers, in ratstreated with 0.05% BBN. The ability of four antioxidants, BHA,BHT, sodium L-ascorbate (ascorbate) and ethoxyquin, to promotethe induction of -glutamyllranspeplidase (-GT)-positive fociinitiated by diethylnitrosamine (DENA) in the liver of F344rats was tested. Rats were given a single i.p. injection of200 mg/kg body weight of DENA, and 2 weeks later the animalswere exposed to 2% BRA, 1% BHT, 5% ascorbate or 1% ethoxyquin,respectively, in the diet for 6 weeks. All animals were subjectedto partial hepatectomy at the end of week 3. The number of -GT-positivefoci in the groups fed either BHA, BBT or ethoxyquin after DENAwere significantly decreased compared with the control group.These findings show that BRA and BHT are promoters for the urinarybladder carcinogenesis initiated by BBN, but that these andother antioxidants significantly inhibit the induction of -GTpositive foci in the liver.     

Structure-activity relations in promotion of rat urinary bladder carcinogenesis by phenolic antioxidants

The urinary bladder tumor-promoting potentials of the phenolic antioxidants, 2-tert-butyl-4-methylphenol (TBMP), propylparaben, catechol, resorcinol and hydroquinone, which are structurally related to butylated hydroxyanisole (BHA), were investigated in 170 male F344 rats. The animals were initially given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as an initiator in their drinking water for 4 weeks. Three days later, groups of 20 rats received diet containing 1.0% TBMP, 3% propylparaben, 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone or basal diet alone until the end of week 36. Significant increases in the incidences and average numbers of the putative preneoplastic lesions, papillary or nodular (PN) hyperplasia, and papillomas of the urinary bladder were only observed in the group given TBMP after BBN. Development of these lesions was not enhanced by diet containing the other test compounds and no induction was associated with any of the test chemicals alone. The results thus clearly showed that TBMP, which most closely resembles BHA, promoted urinary bladder carcinogenesis. The similar effects of TBMP and BHA on urinary bladder carcinogenesis suggest a direct link between chemical structure and biological potency.     

Structure-Activity Relations in Promotion of Rat Urinary Bladder Carcinogenesis by Phenolic Antioxidants

The urinary bladder tumor-promoting potentials of the phenolic antioxidants, 2- tert -butyl-4-methyl-phenol (TBMP), propylparaben, catechol, resorcinol and hydroquinone, which are structurally related to butylated hydroxyanisole (BHA), were investigated in 170 male F344 rats. The animals were initially given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as an initiator in their drinking water for 4 weeks. Three days later, groups of 20 rats received diet containing 1.0% TBMP, 3% propylparaben, 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone or basal diet alone until the end of week 36. Significant increases in the incidences and average numbers of the putative preneoplastic lesions, papillary or nodular (PN) hyperplasia, and papillomas of the urinary bladder were only observed in the group given TBMP after BBN. Development of these lesions was not enhanced by diet containing the other test compounds and no induction was associated with any of the test chemicals alone. The results thus clearly showed that TBMP, which most closely resembles BHA, promoted urinary bladder carcinogenesis. The similar effects of TBMP and BHA on urinary bladder carcinogenesis suggest a direct link between chemical structure and biological potency.     

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.     

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.     

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.     

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.     

Modification by antioxidants and p, p'-diaminodiphenylmethane of 7, 12-dimethylbenz[a]anthracene-induced carcinogenesis of the mammary gland and ear duct in CD rats

The effects of antioxidants on mammary gland carcinogenesispretreated with 7, 12-dimethylbenz[a]anthracene (DMBA) in femaleSprague-Dawley rats were examined. The antioxidants used werebutylated hydroxyanisole (BHA), butylated hydr-oxytoluene (BHT),sodium L-ascorbate, -tocopherol, ethoxy-uin and p, p’-diaminodiphenylmethane(DDPM), which is an inhibitor of carcinogenesis in the liver,kidney and urinary bladder. Female Sprague-Dawley rats of 50days old were treated with 2.5 mg/100 g body weight of DMBA,and from 1 week later were given diet supplemented with 1% BHA,0.7% BHT, 5% sodium L-ascorbate, 1.5% -tocopherol, 0.5% ethoxyquinor 0.1% DDPM for 33 weeks and then killed. The incidences ofmammary tumors, carcinomas and fibroaden-omas in DMBA-treatedanimals were reduced by diet containing BHA or ethoxyquin. Dietcontaining BHT or DDPM inhibited the induction of only fibroadenomas.The incidence of ear duct tumors in DMBA-treated animals wasreduced by diet containing BHT, -tocopherol or ethoxyquin.     

Modification by alpha-tocopherol, propyl gallate and tertiary butylhydroquinone of urinary bladder carcinogenesis in Fischer 344 rats pretreated with N-butyl-N-(4-hydroxybutyl)nitrosamine

The promoting activity of 3 antioxidants, alpha-tocopherol (alpha-TP), propyl gallate (PG) and tertiary butylhydroquinone (TBHQ) in urinary bladder carcinogenesis initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in male F344 rats was examined. Rats, 6-week-old, were treated with 0.05% BBN in the drinking water for 4 weeks and then administered 1.50, 0.75 or 0.38% alpha-TP, 1.0% PG or 2.0% TBHQ in the diet for 32 weeks. The urinary bladder of all animals was examined histologically after the total 36 experimental weeks. The incidence of papillary or nodular hyperplasia (PN hyperplasia) of the urinary bladder was significantly higher in the rats treated with BBN followed by 2.0% dietary TBHQ that in controls initiated with 0.05% BBN followed by control diet. This result indicates that TBHQ has weak promoting activity in urinary bladder carcinogenesis. alpha-TP and PG did not demonstrate a promoting effect for urinary bladder lesions.     

Histologic and autoradiographic studies on the forestomach of hamsters treated with 2-tert-butylated hydroxyanisole, 3-tert-butylated hydroxyanisole, crude butylated hydroxyanisole, or butylated hydroxytoluene

The inductions of hyperplasia and neoplastic lesions in the forestomach of Syrian golden hamsters by 2-tert-butylated hydroxyanisole [(2-tert-BHA) CAS: 121-00-6], 3-tert-butylated hydroxyanisole [(3-tert-BHA) CAS: 88-32-4], crude butylated hydroxyanisole [(BHA) CAS: 25013-16-5], and butylated hydroxytoluene [(BHT) CAS: 128-37-0] were compared histopathologically and autoradiographically. In hamsters fed the 2-tert-BHA diet, severe hyperplasia developed from week 4, reaching a maximum level in week 16 of 0.56 cm/10 cm basement membrane (bm), and papillomatous lesions appeared in week 16 (0.13 cm/10 cm bm). In hamsters fed 3-tert-BHA or crude BHA, severe hyperplasia developed from week 1, which reached a maximum level in week 4 of 3.63 cm/10 cm bm with 3-tert-BHA and 5.10 cm/10 with crude BHA; it then decreased. Papillomatous lesions were found in week 3 in hamsters fed 3-tert-BHA and in week 4 in hamsters fed crude BHA; they increased to maximum levels in week 16 of 0.50 cm/10 cm bm with 3-tert-BHA and 0.29 cm/10 cm bm with crude BHA. Mild hyperplasia occurred slightly more often in hamsters fed the BHT diet than in the control group. BHT induced no severe hyperplasia and papillomatous lesions. Changes in the labeling index of the forestomach epithelium paralleled the histologic changes, except in hamsters fed the BHT diet in which no significant increase in the labeling index was observed throughout the experiment. These data suggest that the tumorigenic action of crude BHA on hamster forestomach is largely due to 3-tert-BHA and that BHT does not induce forestomach tumors in hamsters.     

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.     

The influence of subsequent dehydroepiandrosterone,diaminopropane, phenobarbital,butylated hydroxyanisole and butylated hydroxytoluene treatment on the development of preneoplastic and neoplastic lesions in the rat initiated with di-hydroxy-di-N-propyl nitrosamine

The comparative modifying potential of dehydroepiandrosterone (DHEA), diaminopropane (DAP), phenobarbital (PB), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on the development of lesions initiated by dihydroxy-di-n-propyl nitrosamine (DHPN) in F344 rats were investigated. DHEA, BHA and BHT were all associated with significant reduction in numbers of glutathione-S-transferase P form (GST-P) positive foci in the liver whereas PB brought about their enhanced development. BHT and PB exerted promoting activity on the incidence of thyroid adenomas while DAP similarly increased lung adenoma formation. The results illustrate the advantages to be gained from two stage experiments using broad spectrum carcinogen initiation for comparative analysis of ‘modifiers’ of the neoplastic process and suggest that studies of enzyme alteration within putative preneoplastic lesions may be directly relevant to elucidation of mechanisms underlying such modification.     

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-dependent promoting effect of trisodium nitrilotriacetate monohydrate on urinary bladder carcinogenesis in Wistar rats pretreated with N-butyl-N-(4-hydroxybutyl)nitrosamine

The dose-dependent effect of trisodium nitrilotriacetate monohydrate (Na3.NTA.H2O) as a promoter in 2-stage carcinogenesis in the urinary bladder of male Wistar rats was investigated. Carcinogenesis was initiated by administration of 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in the drinking water for 4 weeks, then Na3.NTA.H2O was given at 1%, 0.5% and 0.3% in the diet for 28 weeks, and rats were killed in week 32. The incidences and numbers of preneoplastic lesions [papillary or nodular hyperplasia (PN hyperplasia)] in rats treated with 0.3% to 1% Na3.NTA.H2O increased progressively with increasing concentration of Na3.NTA.H2O. The incidences of papillomas in rats treated with 1% and 0.5% Na3.NTA.H20 in the diet and the incidence of transitional cell carcinoma (TCC) of the urinary bladder in the rats treated with 1% Na3.NTA.H2O (P less than 0.05) were significantly higher than those in rats treated with BBN only. Administration of various doses of Na3.NTA.H2O without BBN did not cause any histological changes (PN hyperplasia, papilloma or TCC) in the urinary bladder. These findings showed that Na3.NTA.H2O is a potent promoter of urinary bladder carcinogenesis initiated by BBN in rats, and that its effect is dose-dependent.     

Protective effect of butylated hydroxytoluene against induction of gastric cancer by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of butylated hydroxytoluene (BHT) on the incidence and histology of gastric cancers induced by oral administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in Wistar rats. Oral administration of 1.0% BHT in regular chow pellets during treatment with MNNG for 25 weeks significantly reduced the incidence of gastric cancers in experimental week 40. BHT had no influence on the histological type of adenocarcinomas induced in MNNG-treated rats. BHT alone induced slight glandular hyperplasia, but not moderate glandular hyperplasia or gastric cancer.     

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.     

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.     

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.