Inhibition by butylated hydroxytoluene of excision repair synthesis and semiconservative DNA synthesis

Chemical, Physical, and Genetic Factors Interfering with DNA Repair-a Review

Because of its function as transmitter of genetic information, DNA is the most important macromolecule in need of protection from attack by chemical and physical agents, but mechanisms have evolved for repairing such damage to DNA. The presence of the adaptive response and other cellular repair systems (excision, post-replication, SOS, etc.) diminishes the toxicologic effects of low doses of toxic or muta-genic substances. Whether or not these genotoxic effects can be reduced to undetectable levels is not certain. Nonetheless, this repair-mediated diminution of damage due to chemicals constitutes one of the arguments in favor of existence of “safe” threshold levels of chemical exposure (Schendel, 1981).

In turn, the repair process itself may be affected by chemical and physical agents. To determine the mode of action of a specific compound on the process of DNA repair becomes complex when all factors are taken into consideration. There are agents which interfere with DNA repair but they are also as active or more active in suppressing replicative DNA synthesis, as well as RNA and protein synthesis. The interference with repair may arise from other major processes such as alteration of energy metabolism and effects on precursor pathways and/or enzymatic cofactors. Whether or not an agent can specifically inhibit DNA repair enzymes has not been answered. The point must be made, however, that this type of interference with essential protective mechanisms is taking place and it may change anticipated outcomes of chemical or physical exposures. The magnitude of this effect due to the exposure of people to so many chemicals should be recognized and studied for their degree of interference with all the processes of DNA repair.

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.

Safety assessment of butylated hydroxyanisole and butylated hydroxytoluene as antioxidant food additives

Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are widely used antioxidant food additives. They have been extensively studied for potential toxicities. This review details experimental studies of genotoxicity and carcinogenicity which bear on cancer hazard assessment of exposure to humans. We conclude that BHA and BHT pose no cancer hazard and, to the contrary, may be anticarcinogenic at current levels of food additive use.

Review of the mutagenicity/genotoxicity of butylated hydroxytoluene

Butylated hydroxytoluene (BHT) is an effective, widely used, low cost antioxidant. A host of studies examining the potential of BHT to cause point mutations have been published. They include in vitro studies on various bacterial species and strains and on various types of mammalian cell lines as well as in vivo studies on Drosophila melanogaster, silk worms and also the mouse specific locus test (involving long-term exposure). Together these studies convincingly show the absence of a potential for BHT to cause point mutations. A great number of studies on many cell types and species have also been carried out to examine the potential of BHT to cause chromosome aberrations. In vitro studies have been published using plant cells and the WI-38, CHL, CHO, and V79 mammalian cell lines. In vivo studies have been carried out on somatic and/or germ cells of Drosophila melanogaster, rats and mice. Nearly all studies, especially those using validated test systems, indicate that BHT lacks clastogenic potential. In vitro studies on bacterial, yeast and various mammalian cell lines including DON, CHO, CHL cells and primary hepatocytes demonstrate the absence of interactions with or damage to DNA. Taking all the existing data into account, the weight of evidence suggests that BHT does not represent a relevant mutagenic/genotoxic risk to man.

Hepatocellular tumorigenicity of butylated hydroxytoluene administered orally to B6C3F1 mice

Butylated hydroxytoluene (BHT), a preservative widely found in food as a food additive, was orally administered at concentrations of 1% and 2% of the diet to B6C3F1 mice for 104 consecutive weeks. Treated animals underwent a 16-week recovery period prior to pathological examination. In male mice administered BHT, the incidence of mice with either a hepatocellular adenoma or a focus of cellular alteration in the liver was increased in a clear dose-response relationship. The incidences of male mice with other tumors and the incidences of female mice with any tumor were not significantly increased as a consequence of BHT administration. The results of this study indicate BHT to be tumorigenic to the liver of the B6C3F1 male mouse.

Mechanism of butylated hydroxytoluene-associated modification of diethylnitrosamine-induced squamous stomach carcinoma

The metabolism of butylated hydroxytoluene (BHT) and the effect of BHT on the metabolism of diethylnitrosamine (DEN) was studied in male and female BALB/c mice to further understanding of the selective protection of BHT on the incidence of DEN-induced squamous-stomach carcinomas in female (but not in male) mice. Following intragastric administration of [14C]BHT, the antioxidant was covalently bound to tissue macromolecules. The relative distribution of this bound BHT varied with time; 8 hr after [14C]BHT administration, most of the covalently bound BHT was associated with the protein components; at 96 hr the nucleic acid components bound more BHT than did the protein components. Animals pretreated with BHT and given [14C]DEN intragastrically had lower blood levels of radioactivity and eliminated a larger percentage of DEN and/or its metabolites in the urine and as carbon dioxide than animals given [14C]DEN alone. The binding of DEN and/or its metabolites to cellular macromolecules of the squamous stomach of female animals was decreased following pretreatment with BHT. However, the BHT-associated decrease in DEN binding was also observed in the squamous stomach of male animals and in the liver of both sexes, although the tumour incidence in these target organs for DEN carcinogenesis is not modified by BHT. These results suggest that the BHT-associated decrease in the binding of DEN to DNA is of a generalized rather than a selective nature, and may be insufficient to account for the protective effect of BHT. Two parameters that were found to parallel the susceptibility of DEN target tissues to the anticarcinogenic effects of BHT were the relative degree of inhibition of DEN bound to RNA species and the relative amount of BHT bound to DNA. Thus the anticarcinogenic properties of BHT may be more complex than an induction of enzymes that detoxify the carcinogen and/or an inhibition of enzymes that activate the carcinogen with a resulting decrease in the quantity of carcinogen available for electrophilic reactions.

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.

Review: putative mutagens and carcinogens in foods. III. Butylated hydroxytoluene (BHT)

Although the average American's daily consumption of BHT can be measured in milligrams, there are numerous reports that BHT causes organ damage in laboratory animals. Only a few genotoxic effects of BHT have been reported, however, including mutagenicity in the abnormal sperm assay and ambiguous results regarding its teratogenicity. More dramatic are the modulatory effects of BHT on the actions of established mutagens and carcinogens. BHT can either enhance or inhibit mutagenic potency, depending on the substance tested. For example, in the Ames test, BHT is antimutagenic towards benzo(a)pyrene, but increases the number of Salmonella revertants induced by aflatoxin B1. BHT is one of the few compounds to have both tumor prophylactic and tumor promoting capacities. It is the temporal sequence in which BHT and carcinogens are administered to test animals which determines how BHT affects the response to these carcinogens. In common with other antioxidants, BHT inhibits the ability of carcinogens to induce tumors in various rodent organs when the animal is given BHT prior to carcinogen treatment. Unlike other antioxidants, however, the number of tumors increase when BHT is administered after carcinogen exposure. The comutagenic and cocarcinogenic properties of BHT have been demonstrated in tests ranging from the Ames test to cell transformation procedures to in vivo assays. These effects are probably mediated by metabolites of BHT, rather than by BHT itself.

Effect of membrane lipid perturbers on the temperature dependence of repair of sublethal and potentially lethal radiation damage

The repair of sublethal radiation damage (SLD) in Chinese hamster (V79) cells was investigated as a function of temperature in the presence and absence of the membrane lipid perturbers, butylated hydroxytoluene (BHT) or adamantanone, which decrease the viscosity of the membrane lipids. Addition of 0.01 mM BHT to the cells significantly increased the amount of repair of SLD over controls from 0 to 25 degrees C but not from 30 to 37 degrees C. The amount of repair of SLD decreased as a function of temperature to about 20 degrees C and remained relatively constant thereafter till about 2.5 degrees C where it began to decrease again. The change in the amount of repair at approximately 20 degrees C coincides with a membrane lipid phase transition, as seen by spin labelling, in these cells. The repair of potentially lethal damage (PLD) was not increased by BHT at the two temperatures investigated (5 and 20 degrees C). In fact, additional PLD was expressed when cells were incubated post-irradiation at these temperatures. The results imply that at least a component of the SLD repair system is membrane associated and that the SLD and PLD repair systems are independent.