The effects of butylated hydroxytoluene on the in vitro metabolism, DNA-binding and mutagenicity of aflatoxin B1 in the rat

Final report on the safety assessment of BHT(1)

BHT is the recognized name in the cosmetics industry for butylated hydroxytoluene. BHT is used in a wide range of cosmetic formulations as an antioxidant at concentrations from 0.0002% to 0.5%. BHT does penetrate the skin, but the relatively low amount absorbed remains primarily in the skin. Oral studies demonstrate that BHT is metabolized. The major metabolites appear as the carboxylic acid of BHT and its glucuronide in urine. At acute doses of 0.5 to 1.0 g/kg, some renal and hepatic damage was seen in male rats. Short-term repeated exposure to comparable doses produced hepatic toxic effects in male and female rats. Subchronic feeding and intraperitoneal studies in rats with BHT at lower doses produced increased liver weight, and decreased activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue. BHT was not a reproductive or developmental toxin in animals. BHT has been found to enhance and to inhibit the humoral immune response in animals. BHT itself was not generally considered genotoxic, although it did modify the genotoxicity of other agents. BHT has been associated with hepatocellular and pulmonary adenomas in animals, but was not considered carcinogenic and actually was associated with a decreased incidence of neoplasms. BHT has been shown to have tumor promotion effects, to be anticarcinogenic, and to have no effect on other carcinogenic agents, depending on the target organ, exposure parameters, the carcinogen, and the animal tested. Various mechanism studies suggested that BHT toxicity is related to an electrophillic metabolite. In a predictive clinical test, 100% BHT was a mild irritant and a moderate sensitizer. In provocative skin tests, BHT (in the 1% to 2% concentration range) produced positive reactions in a small number of patients. Clinical testing did not find any depigmentation associated with dermal exposure to BHT, although a few case reports of depigmentation were found. The Cosmetic Ingredient Review Expert Panel recognized that oral exposure to BHT was associated with toxic effects in some studies and was negative in others. BHT applied to the skin, however, appears to remain in the skin or pass through only slowly and does not produce systemic exposures to BHT or its metabolites seen with oral exposures. Although there were only limited studies that evaluated the effect of BHT on the skin, the available studies, along with the case literature, demonstrate no significant irritation, sensitization, or photosensitization. Recognizing the low concentration at which this ingredient is currently used in cosmetic formulations, it was concluded that BHT is safe as used in cosmetic formulations.

Protective effect of soybean saponins and major antioxidants against aflatoxin B1-induced mutagenicity and DNA-adduct formation

Saponins from various plant sources have been suggested as possible anticarcinogens. Major dietary sources of saponins include legumes such as soybeans. This study was performed to determine the effect of soybean saponins on aflatoxin B(1)(AFB(1))-induced mutagenicity and AFB(1)-DNA adduct formation using Salmonella typhimurium and human liver hepatoma (HepG2) cells, respectively. Major antioxidants including L-ascorbic acid, alpha-tocopherol, all-trans-retinol, and butylated hydroxytoluene (BHT), previously reported to possess antimutagenic activity, were used as test materials to evaluate the relative effectiveness of saponins. Results indicated antimutagenicity was in the order of BHT > saponins > alpha-tocopherol > L-ascorbic acid. Soybean saponins exerted a significant effect, inhibiting the mutagenicity of AFB(1) by 52%, 64%, and 81% at concentrations of 600, 900, and 1,200 microg per plate, respectively. The amount of tritiated AFB(1) metabolites-DNA adducts formed in HepG2 cells was significantly reduced when cells were preincubated with 10 or 30 microg/ml of test materials. Soybean saponins inhibited AFB(1)-DNA adduct formation by 50.1% at a concentration of 30 microg/ml, whereas L-ascorbic acid and BHT reduced adduct formation by 38.4% and 32.6%, respectively, at the same concentrations. These results indicate that soybean saponins possess not only a significant antimutagenic activity but a strong inhibitory action against carcinogen-induced DNA damages. Soybean saponins possibly block the initiation stage of carcinogenesis, and further studies are required to elucidate the mechanisms of action.

Effects of co-administration of butylated hydroxytoluene, butylated hydroxyanisole and flavonoids on the activation of mutagens and drug-metabolizing enzymes in mice

Effects of co-administration of food additives and naturally occurring food components were studied on the activation of mutagens. Male mice (ddY) were given diets containing butylated hydroxytoluene (BHT) or butylated hydroxyanisole (BHA) and flavone or flavanone (2,3-dihydroflavone) for two weeks and the ability of hepatic microsomes to activate aflatoxin B1, benzo[a]pyrene and N-nitrosodimethylamine was determined by the mutagenicity test. Co-administration of an antioxidant (0.1% BHT or 0.2% BHA in diet) and a flavonoid (0.1% flavone or 0.1% flavanone) resulted in additive effects on the activation of aflatoxin B1 and benzo[a]pyrene, while the activation of N-nitrosodimethylamine was not elevated significantly by the co-administration. To understand the mechanism for the additive effects, induction of specific isozymes of cytochrome P450 involved in the activation of the mutagens was studied. Co-administration of BHT (0.1%) and flavone (0.1%) increased markedly the levels of proteins and the activities of the enzymes related to the isozymes of CYP2A and CYP2B, while co-administration of BHA (0.2%) and flavanone (0.1%) elevated those related to CYP1A. Further, the activation of aflatoxin B1 and benzo[a]pyrene in hepatic microsomes was inhibited by the antibodies against these isozymes, which suggested that the enhanced activation of the mutagens by the co-administration might be mediated by the induction of these isozymes.

Comparison of the effect of low- and high-dose dietary butylated hydroxytoluene on microsome-mediated aflatoxin B1-DNA binding

Butylated hydroxytoluene (BHT) is known to inhibit tumor formation due to several chemical carcinogens including aflatoxin B1 (AFB1). Pre-treatment of laboratory animals with high doses of BHT (0.75% for 15 days in diet) is associated with pathological effects. The mechanism of action of BHT against AFB1 carcinogenesis is by induction of liver glutathione (GSH) S-transferases. As a result, the formation of AFB1-DNA binding is effectively inhibited. In the present study, effects of low and high doses of dietary BHT on in vitro activation and inactivation of AFB1 was examined. BHT feeding to rats at a dose of 0.75% for 15 days caused a significant increase in the GSH S-transferase activity. Addition of liver cytosolic fractions prepared from the rats pre-treated with high dose BHT to the cell free system caused a 48% inhibition in AFB1-DNA binding. In contrast, low dose BHT feeding (0.06% for 6 months) had little influence on GSH S-transferase activity. This was corroborated when addition of liver cytosol from low dose BHT-treated rats failed to inhibit microsome-mediated AFB1-DNA binding as compared to that of control. It is concluded that the permitted dose of BHT, added to processed food as preservative, plays no role in the biotransformation of AFB1.

A study of the mutagenicity of some commercially canned Spanish mushrooms

The mutagenicity of two wild (Lactarius deliciosus and Boletus luteus) and two cultivated (Agaricus bisporus and Pleurotus ostreatus) mushrooms, preserved by canning and widely consumed in Spain, was studied in the Ames Salmonella/microsome test and in the CHO/HPRT assay system using mammalian cells. The mushroom extracts did not show mutagenicity in the microbial Ames test nor in the mammalian CHO-K1 cells, and this response was not modified by the presence of S-9 mix in the assay mixtures. Only the extracts from P. ostreatus showed a weak mutagenic activity in the CHO/HPRT assay in the presence of a metabolic activation system (S-9).

Lack of influence of butylated hydroxytoluene on modification of lung microsome mediated aflatoxin B1-DNA binding: role of pulmonary glutathione S-transferase

Phenolic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are known to inhibit tumor formation due to several chemical carcinogens including aflatoxin B1 (AFB1). Metabolic activation of AFB1 by lung microsomes and possible modification by dietary BHA was reported in an earlier communication (Allameh et al. (1988) Cancer Lett., 40, 49). Here we report the effect of dietary BHA at a high dose (0.75% for 15 days) and a low dose (0.06% for 180 days) on the activation and inactivation of AFB1 by subcellular preparations of lung. BHT at high dose alone induced hepatic cytosolic glutathione (GSH) S-transferases activity while the pulmonary enzyme was unaffected by BHT feeding. This observation was substantiated when the addition of lung cytosol from control and BHT-treated rats showed similar inhibition (50%) in the microsome mediated AFB1-DNA binding. Thus BHT appears to have little influence on the pulmonary metabolism of AFB1.

Effects of dietary Schizandra chinensis, brussels sprouts and Illicium verum extracts on carcinogen metabolism systems in mouse liver

Ethanol extracts of Brussels sprouts (BRX), Schizandra chinensis (SZX) or Illicium verum (IVX) were added to a semi-purified basal diet and fed to adult male and female C57B1/6 mice for 14 and 10 days, respectively. Other groups received the unsupplemented basal diet or a mouse chow. Liver fractions were prepared from these mice to investigate the effects of the diets on the enzyme systems involved in benzo[a]pyrene (BP) and aflatoxin B1 (AFB1) metabolism. The effects of the microsomal or cytosolic liver fractions on the in vitro mutagenicity of BP and AFB1 and on the DNA binding of AFB1 were also studied. There were several apparently sex-related differences in the responses of the monooxygenase system components measured. In males, cytochrome P-450 levels were significantly increased only in the chow group, while significant increases in both 7-ethoxycoumarin O-deethylase (ECD) and aryl hydrocarbon hydroxylase (AHH) activities were seen only in the SZX group. In females, cytochrome P-450 levels were significantly increased in both the BRX and SZX groups, whereas AHH activity was significantly increased only in the chow and BRX groups and ECD activity was increased in the SZX and IVX groups. Microsomal epoxide hydratase (EH) was induced in males in the SZX and IVX groups and in females only in the SZX group, while cytosolic EH was significantly increased only in IVX males. Diet-induced changes in monooxygenase activities were found to be the best indicators of changes in microsome-mediated BP mutagenesis and AFB1 mutagenesis and binding to DNA in vitro, with a direct correlation between high AHH and/or ECD activities and the levels of mutagenic response to BP or AFB1 in the Ames assay and of DNA binding of AFB1.

Biological reactive intermediates of mycotoxins

The various reactions involved in the formation and actions of biological reactive intermediates of AFB1 are undoubtedly common to the wide variety of mycotoxins. The structural diversity of mycotoxins and their widespread occurrence in nature has made them a significant class of model environmental toxicants for mode of action studies. Identification of the reactive intermediates of prototype mycotoxins and elucidation of their reactions with molecular receptors will provide information useful for the design of antidotes of other remedial measures and for a better understanding of the mechanisms of action of comparable environmental toxicants. This type of studies will also permit the more precise biochemical analyses to be applied to the assessment of health risk due to exposure to mycotoxins.

Effect of butylated hydroxytoluene pretreatment on the excretion, tissue distribution and DNA binding of [14C]aflatoxin B1 in the rat

The effect of butylated hydroxytoluene (BHT) pretreatment (0.5% in the diet for 10 days) on the excretion, tissue distribution and DNA binding of orally administered [14C]aflatoxin B1 (AFB1) was determined in male Fischer F344 rats. The amount of radioactivity excreted in the urine and faeces by 24 hr was higher in BHT-treated rats than in controls. Treatment with BHT enhanced the excretion of water-soluble metabolites in the urine and in the large intestines plus faeces at the earlier sampling times. The amount of radioactivity bound to hepatic nuclear DNA was six times less in the BHT-pretreated rats than in controls 6 hr after administration of the isotope. The half-lives of [14C]DNA in the rat liver were 30 and 46 hr for control and BHT-pretreated rats, respectively. These results indicate that BHT pretreatment may protect the animal from the carcinogenic effects of AFB1 by enhancing the detoxification and excretion of the mycotoxin.

Synthetic antioxidants: biochemical actions and interference with radiation, toxic compounds, chemical mutagens and chemical carcinogens

Biological actions of 4 commonly used synthetic antioxidants--butylated hydroxyanisole, butylated hydroxytoluene, ethoxyquin and propyl gallate--on the molecular, cellular and organ level are complied. Such actions may be divided into modulation of growth, macromolecule synthesis and differentiation, modulation of immune response, interference with oxygen activation and miscellaneous. Moreover, an overview of beneficial and adverse interactions of these antioxidants with exogenous noxae is given. Beneficial interactions include radioprotection, protection against acute toxicity of chemicals, antimutagenic activity and antitumorigenic action. Possible mechanisms of the antitumorigenic action of antioxidants are discussed. This discussion is centered around antioxidant properties which may contribute to a modulation of initiation-related events, especially their ability to interfere with carcinogen metabolism. The beneficial interactions of antioxidants with physical and chemical noxae are contrasted to those leading to unfavorable effects. These include radiosensitization, increased toxicity of other chemicals, increased mutagen activity and increased tumor yield from chemical carcinogens. At present, the latter one can most adequately be characterized as tumor promotion at least in the case of butylated hydroxytoluene. It is concluded that current information is insufficient to promote expectations as to the use of antioxidants in the prevention of human cancer.

Effect of butylated hydroxytoluene on the disposition of [14C]aflatoxin B1 in the lactating rat

The distribution and metabolism of an ip dose of [14C]aflatoxin B1 (AFB1) were studied in lactating Sprague-Dawley rats fed for the previous 13 days on a diet containing 0.5% butylated hydroxytoluene (BHT). Compared with ingestion of a BHT-free diet, treatment with BHT increased the biotransmission of AFB1 metabolites, predominantly aflatoxin M1 (AFM1), into the mammary gland and its content of milk, decreased AFB1 binding to liver nuclear DNA and enhanced the excretion of water-soluble metabolites of AFB1, all measured 6 hr after an oral dose of [14C]AFB1. These changes are related to the induction by BHT of hepatic enzymes involved in the transformation and detoxification of AFB1. The results suggest that exposure to BHT may protect the lactating animal from the carcinogenic effect of AFB1 but may increase the risk of exposure of the newborn infant to the carcinogenic metabolite AFM1.