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

Comparison of the standard and reduced pH Syrian hamster embryo (SHE) cell in vitro transformation assays in predicting the carcinogenic potential of chemicals

A comprehensive review of the Syrian Hamster Embryo (SHE) cell transformation literature was performed in order to catalogue the chemical/physical entities which have been evaluated for in vitro cell transformation potential. Both reduced pH (pH 6.7) and standard pH (pH 7.1-7.3) SHE cell testing protocols were considered. Based upon this analysis, over 472 individual chemical/physical agents and 182 combinations of chemical/physical agents have been tested under the standard pH conditions, while over 56 chemical/physical agents have been tested under reduced pH conditions. Of the 472 chemical/physical agents tested at the standard pH, 213 had in vivo carcinogenicity data available. Of these 213 chemical/physical agents, 177 were carcinogens while 36 were non-carcinogens. The results of testing the SHE transformability of these 213 chemical/physical agents indicates that the standard pH SHE cell transformation assay had a concordance of 80% (171/213), a sensitivity of 82% (146/177), and a specificity of 69% (25/36). Of these 213 chemical/physical agents, 53% (112/213) were tested more than once often in more than one laboratory, with a 82% (92/112) interlaboratory agreement rate, thus providing confirmatory results. Carcinogenicity data were available for 48 of the 56 chemical/physical agents tested for SHE cell transformation under the reduced pH conditions. The SHE cell transformation assay under reduced pH conditions had a concordance of 85% (41/48), a sensitivity of 87% (26/30), and a specificity of 83% (15/18). For Salmonella-negative carcinogens, the standard pH SHE assay correctly predicted carcinogenicity 75% (48/64) of the time while the reduced pH SHE assay correctly predicted carcinogenicity for Salmonella-negative carcinogens 78% (14/18) of the time. For chemical/physical agents tested under both the reduced pH and standard pH conditions, the standard pH and reduced pH SHE cell assays had a 69% (22/32) agreement rate. Under the reduced pH conditions, the SHE assay correctly predicted rodent carcinogenicity in 86% (25/29) of the chemicals tested under both reduced and standard pH conditions. Under standard pH conditions, the SHE assay correctly predicted rodent carcinogenicity in 69% (20/29) of the chemicals tested under both reduced and standard pH conditions. Collectively, these data indicate that the SHE cell transformation assay is predictive for rodent carcinogenicity under either reduced or standard pH conditions. Importantly, the assay displays better performance and appears to have improved carcinogen prediction capability under reduced pH conditions.

Cytogenetic changes in primary, immortalized and malignant mammalian cells

Some chromosomes in transformed rat cells and somatic cell hybrids fail to display the presence of kinetochore proteins as detected by antikinetochore antibodies. Such chromosomes (K- chromosomes) may constitute a novel mechanism for the genesis of aneuploidy. We have analyzed primary, immortalized and malignant mammalian cells for the presence of kinetochore proteins and micronuclei. Our results suggest a correlation of the K- chromosome and micronucleus frequency with the variability in chromosome number. Upon in situ hybridization with the minor satellite and alpha satellite sequences some K- chromosomes showed a signal. This indicates that the observed lack of kinetochores is not necessarily due to a lack of centromeric DNA. We conclude that dislocated K- chromosomes may become incorporated into micronuclei which are prone to loss. Such events would be associated with the generation of aneuploidy.

[Toxicology of the synthetic antioxidants BHA and BHT in comparison with the natural antioxidant vitamin E]

The toxicology of the food preservatives butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT) as well as the naturally occurring vitamin E (alpha-tocopherol) is described. In high dosages all three compounds induce in animals impairment of blood clotting, which can be explained by an antagonism with vitamin K. Specific toxic effects to the lung have only been observed with BHT. The other described toxic effects of BHA and BHT are less characteristic and often occur only after high dosage and long-term treatment. However, BHA induces in animals tumours of the forestomach, which are dose dependent, whereas BHT induces liver tumours in long-term experiments. Because there is no indication of genotoxicity of BHA and BHT, all published findings agree with the fact that BHA and BHT are tumour promoters. In contrast to BHA and BHT, vitamin E is not carcinogenic. On the other hand, all three antioxidants have also anticarcinogenic properties. The intake of the necessary high doses as for these effects are, however, contraindicated with BHA and BHT because of their carcinogenic effects. The present overview concludes that the concentrations of BHA and BHT nowadays used in food, drugs and cosmetics are probably harmless. In addition, vitamin E can also be used in higher doses without the occurrence of adverse effects.

Butylated hydroxyanisole in perspective

Butylated hydroxyanisole (BHA) is a synthetic food antioxidant used to prevent oils, fats and shortenings from oxidative deterioration and rancidity. This review depicts the current knowledge on BHA. The physical and chemical characteristics of BHA are summarized and its function as a food antioxidant is made clear. The toxicological characteristics of BHA and its metabolic fate in man and animal are briefly reviewed. Special emphasis is laid on the carcinogenicity of BHA in the forestomach of rodents and to related events in the forestomach and other tissues in experimental animals. At present there is sufficient evidence for carcinogenicity of BHA, but there is hardly any indication that BHA is genotoxic. Therefore risk assessment for this epigenetic carcinogen is based on non-stochastic principles. However, the mechanism underlying the tumorigenicity of BHA is not known. In the last part of this review an attempt is made to unravel the unknown mechanism of carcinogenicity. It is hypothesized that BHA gives rise to tumor formation in rodent forestomach by inducing heritable changes in DNA. Evidence is being provided that reactive oxygen species, in particular hydroxylradicals, may play a crucial role. The key question with respect to risk assessment for BHA is whether or not the underlying mechanism is thresholded, which is important for the choice of the appropriate model to assess the risk, if any, for man and to manage any potential risk.

Production of reactive oxygen species due to metabolic activation of butylated hydroxyanisole

The synthetic antioxidant butylated hydroxyanisole (BHA) stimulates superoxide formation in rat liver microsomes up to 10-fold. This stimulation is prevented by the monooxygenase inhibitor metyrapone and does not occur when NADH is consumed instead of NADPH indicating that metabolic activation is required for superoxide production. The BHA metabolite tert-butylhydroquinone (TBHQ) is much more active than BHA in stimulating superoxide production, and the amounts of TBHQ and formaldehyde formed from BHA in microsomes are sufficient to explain the effect of BHA. In buffer and in a xanthine oxidase system, superoxide production by TBHQ also takes place. TBHQ autoxidizes to tert-butylquinone (TBQ) and TBQ exceeds TBHQ by far in its capacity for superoxide production in microsomes. Thus, a 30-fold increase of basal superoxide production is induced by 5 microM TBQ. In rat forestomach, the target organ of BHA carcinogenicity in rodents, stimulation of superoxide production by BHA and more markedly by TBHQ and TBQ is also observed. Excess production of superoxide in microsomes by TBHQ is accompanied by excess production of hydrogen peroxide and of hydroxyl radicals. It is concluded that TBQ undergoes redox cycling leading to an oxidative burst in the presence of enzymes capable of one electron reduction of TBQ and that the BHA metabolite TBHQ enters the redox cycle by autoxidation. No oxygen activating properties can be ascribed to BHA itself.

Chemoprevention of cancer: phenolic antioxidants (BHT, BHA)

1. The synthetic phenolic antioxidants (e.g. BHT, BHA) added to human and animal food are able to lengthen the life of organisms and lower the incidence of cancer caused by chemical compounds. 2. On the other hand they may not be rendered completely harmless since they can cause lung damage (BHT) or promote the action of some carcinogens (BHA). 3. They could act as compounds preventing cancer either via interception of harmful free radicals, activating the detoxifying enzymes of the body, inhibiting the formation of ultimately carcinogenic metabolites and their binding to DNA, and modifying the immune response of the organism. 4. Their action is influenced by their own chemical structure, the composition of carcinogen, the strain, sex and age of experimental animals, the tissue upon which they are supposed to act and the time of their administration in relation to the time of the carcinogen insult. 5. These compounds are concentrated in adipose tissue, liver and kidney. They are excreted within tens of hours mainly in urine. 6. The acceptable daily intake of BHA is at present considered to be 0.6 mg kg-1 body wt day-1. In spite of their possible tumor-promoting properties they could not be considered overtly toxic. Their pronounced chemoprotective role against some forms of chemical carcinogenesis deserves considerable attention.