Investigation of the role of the 2',3'-epoxidation pathway in the bioactivation and genotoxicity of dietary allylbenzene analogs

The genotoxic potential of naturally occurring allylbenzene analogs, including safrole, eugenol, estragole, and others, has been examined in many studies over the past 30 years. It has been established that these compounds are subject to biotransformation in the liver, which can lead to the formation of reactive electrophilic intermediates. The major route of bioactivation is via hydroxylation of the 1′ carbon atom of the allylic side chain. We have synthesized 2′,3′- (allylic) epoxide derivatives of allylbenzene, estragole eugenol and safrole, and have used them to characterize the genotoxic potential of epoxidation at the allylic double bond for allylbenzene and its naturally occurring analogs. In order to assert that this pathway has the potential for genotoxicity, it is necessary to demonstrate (1) that epoxide metabolites of these compounds are capable of forming covalent adducts with DNA bases; and (2) that these epoxide metabolites are actually formed in vivo. We have demonstrated that allylic epoxides derived from allylbenzene and estragole are capable of forming covalent adducts with all four deoxyribonucleotides in vitro and, in the case of deoxyguanosine, form at least four different adducts. We also deduce, from evidence obtained using the isolated perfused rat liver, that formation of potentially genotoxic 2′,3′ epoxide metabolites occurs readily in vivo, but that these metabolites are rapidly further metabolized to less toxic dihydrodiol or glutathione conjugates. We conclude that 2′,3′ epoxide metabolites of allylbenzene analogs are formed in vivo and that these epoxides are sufficiently reactive to facilely form covalent bonds with DNA bases. Epoxide formation at the allylic double bond represents, therefore, a potentially genotoxic bioactivation pathway for allylbenzene analogs. However, comparison of the relative kinetics of epoxide metabolism and epoxide formation suggests that a wide margin of protection from DNA covalent adduct formation exists in the rat liver, thus preventing genotoxicity resulting from this pathway to any significant degree. In this regard, we have also observed that the general rate of epoxide hydrolysis is much greater in human liver than in rat liver. We therefore suggest that while the epoxidation pathway poses a potential genotoxic threat to humans, no actual genotoxicity occurs as a result of this metabolic pathway.     

Review of the Toxicology of Three Alkyl Diamines

Three alkyl diamines, which are by-products formed and separated during the production of hexamethylene diamine, have been tested, mostly for their acute toxicity. This paper reviews methodologies used and the results obtained from these three chemicals. All three tested [2-methyl-1,5-pentanediamine (2-MP), 1,3-diaminopentane (DAMP), and 1,2-cyclohexanediamine (DCH)] were 95% pure and were supplied by the DuPont Company. The acute toxicity of all three chemicals is relatively low with acute oral lethal levels in the rat ranging from 1000 to 2300 mg/kg. Single 4-h inhalation exposures show similarly low toxicity with lethality produced in the rat at concentrations ranging from 2.9 to 4.3 mg/L. These diamines are severe skin irritants in both the rabbit and the guinea pig and are also severe eye irritants (studied only in 2-MP). Dermal sensitization was seen in the guinea pig with DAMP and DCH but not with 2-MP. The irritant dose of these materials was shown in repeated exposure inhalation studies when 2-MP and DCH produced irritation in the upper respiratory tract (point of contact) with some lower lung involvement but no significant systemic effects. 2-MP when fed to rats produced a slight body weight effect at dose equivalents of 800 mg/kg with no other parameters affected. All three materials were inactive in Salmonella, and 2-MP did not produce chromosomal aberrations in cultured human lymphocytes. The main effects of this series of diamines appear related to their irritant properties, and attention needs to be paid to their delayed hypersensitivity potential.     

A Bacterial DNA Repair Test Evaluating the Genotoxicity of Light Sources

A DNA repair test was used in order to assess its applicability for detecting the genotoxicity of sunlight and of the light emitted by halogen lamps and fluorescent lamps. This experimental system compares the lethality of test agents in the Escherichia coli wild-type WP2 and its isogenic counterparts lacking, either individually or in combination, various DNA repair mechanisms. DNA repair-deficient strains included WP2uvrA (uvrA^-), WP67 (uvrA^- polA^-), CM561 (lexA^-), CM571 (recA^-), WP100 (uvrA^- recA^-), and CM871 (uvrA^- recA^- lexA^-). All light sources produced a substantial killing of repair-deficient strains, with a maximum activity in the triple mutant CM871, at doses that did not affect survival of the wild type. The genotoxicity of uncovered quartz halogen bulbs was particularly potent, compared to fluorescent lamps and sunlight. Moreover, the mechanisms involved in repairing the DNA damage induced by halogen lamps were similar to those of a 254 nm UV source. The spectrum of genetic damage produced by sunlight and fluorescent lamps was conversely more comparable to that of a 365 nm UV source. These data demonstrated a harmful emission of appreciable amounts of genotoxic far-UV wavelengths by halogen lamps, thereby confirming our previous results in the his^-Salmonella typhimurium mutagenicity test. Genotoxicity of halogen lamps could be easily prevented in both experimental systems by suitable glass or plastic covers. Compared to the mutagenicity end point, the differential lethality end point provided even more clear-cut results in detecting the DNA-damaging ability of all light sources. Moreover, parallel assays provided evidence that the bacterial DNA repair test was far more sensitive than the mutagenicity test in evaluating the genotoxicity of the light produced by halogen lamps. On the whole, the DNA repair test in E. coli is even simpler and faster (24 vs. 48 h) than the Salmonella mutagenicity test, and compares favorably in terms of sensitivity to genotoxic light sources.     

BC nanofibres: In vitro study of genotoxicity and cell proliferation

Nanomaterials have unusual properties not found in the bulk materials, which can be exploited in numerous applications such as biosensing, electronics, scaffolds for tissue engineering, diagnostics and drug delivery. However, research in the past few years has turned up a range of potential health hazards, which has given birth to the new discipline of nanotoxicology. Bacterial cellulose (BC) is a promising material for biomedical applications, namely due its biocompatibility. Although BC has been shown not to be cytotoxic or genotoxic, the properties of isolated BC nanofibres (NFs) on cells and tissues has never been analysed. Considering the toxicity associated to other fibre-shaped nanoparticles, it seems crucial to evaluate the toxicity associated to the BC-NFs.     

Nicotine and methyl methane sulfonate in mini organ cultures of human parotid gland tissue

The aim was to demonstrate the applicability of using mini organ cultures (MOC) of the human parotid gland for indicating DNA damage by nicotine.     

Patulin-induced genotoxicity and modulation of glutathione in HepG2 cells

Patulin (PAT), a mycotoxin produced by certain species of Penicillium, Aspergillus and Byssochlamys, is mainly found in ripe apple and apple products. In our present study, a significant increase of the micronuclei frequency induced by PAT was found in human hepatoma HepG2 cells. To elucidate the role of glutathione (GSH) in the effect, the intracellular GSH level was modulated by pre-treatment with buthionine-(S, R)-sulfoximine (BSO), a specific GSH synthesis inhibitor, and by pre-treatment with N-acetylcysteine (NAC), a GSH precursor. It was found that depletion of GSH in HepG2 cells with BSO dramatically increased the PAT-induced micronuclei frequencies and that when the intracellular GSH content was elevated by NAC, the chromosome damage induced by PAT was significantly prevented in our test concentrations (0.19-0.75 μM). These results indicate that GSH play an important role in cellular defense against PAT-induced genotoxicity.     

Thinner inhalation effects on oxidative stress and DNA repair in a rat model of abuse

Humans can come into contact with thinner by occupational exposure or by intentional inhalation abuse. Numerous studies of workers for genotoxic effects of thinner exposure have yielded conflicting results, perhaps because co‐exposure to variable other compounds cannot be avoided in workplace exposure studies. In contrast, there is no data concerning the genotoxic effects of intentional inhalation abuse. The aim of this project was to examine the genotoxic effects of thinner inhalation in an animal model of thinner abuse (rats exposed to 3000 ppm toluene, a high solvent concentration over a very short, 15 min time period, twice a day for 6 weeks). The data presented here provides evidence that thinner inhalation in our experimental conditions is able to induce weight loss, lung abnormalities and oxidative stress. This oxidative stress induces oxidative DNA damage that is not a characteristic feature of genotoxic damage. No significant difference in DNA damage and DNA repair (biomarkers of genotoxicity) in lymphocytes from thinner‐treated and control rats was found. Lead treatment was used as a positive control in these assays. Finally, bone marrow was evaluated as a biomarker of cellular alteration associated with thinner inhalation. The observed absence of hemopoietic and genetic toxicity could be explained in part by the absence of benzene, the only carcinogenic component of thinner; however, benzene is no longer a common component of thinner. In conclusion, thinner did not cause genotoxic effects in an experimental model of intentional abuse despite the fact that thinner inhalation induces oxidative stress. Copyright © 2009 John Wiley & Sons, Ltd.     

Studies on the genotoxicity of the anabolic drugs trenbolone and zeranol

The androgen trenbolone, and the mycoestrogen zeranol, both anabolic drugs, were tested for their genotoxic potential. Test systems were the SOS-chromotest, the rec-assay and the V79 sister chromatid exchange test without and with metabolic activation using rat liver homogenates and primary rat hepatocytes.It is still a matter of debate if trenbolone has carcinogenic properties, because of its cell transforming activity in vitro. Trenbolone, however, did not demonstrate any genotoxic effect in the assays performed. The results obtained for zeranol were also negative in the SOS-chromotest and V79 sister chromatid exchange test but positive in the rec-assay.     

Riscos ocupacionais,danos no material genético e estresse oxidativo frente à exposição aos resíduos de gases anestésicos

Background and objectives

The waste anesthetic gases (WAGs) present in the ambient air of operating rooms (OR), are associated with various occupational hazards. This paper intends to discuss occupational exposure to WAGs and its impact on exposed professionals, with emphasis on genetic damage and oxidative stress.

Evaluation of the genotoxic potential of single-wall carbon nanotubes by using a battery of in vitro and in vivo genotoxicity assays

The genotoxic potential of a high purity sample of single-wall carbon nanotubes (SWCNTs) was evaluated using a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse mutation test (Ames test), an in vitro chromosomal aberration test, and an in vivo mouse bone marrow micronucleus test. The SWCNTs exerted no genotoxicity in Salmonella typhimurium TA97, TA98, TA100, and TA1535, or in Escherichia coli WP2 uvrA/pKM101, whether in the absence or presence of metabolic activation and at concentrations of 12.5–500 μg/plate. In the chromosomal aberration test, at 300–1000 μg/mL, the SWCNTs did not increase the number of structural or numerical chromosomal aberrations, whether the test was conducted with or without metabolic activation. In the in vivo bone marrow micronucleus test, doses of 60 mg/kg and 200 mg/kg SWCNTs did not affect the proportions of immature and total erythrocytes, nor did it increase the number of micronuclei in the immature erythrocytes of mice. The results of these studies show that the high purity and well-dispersed sample of SWCNTs are not genotoxic under the conditions of the in vitro bacterial reverse mutation assay, chromosomal aberration assay, or in vivo bone marrow micronucleus test, and thus appear not to pose a genotoxic risk to human health in vivo.