Mutagenic Metabolites Research Articles

Modulation of the Rat Hepatic Cytochrome P4501A Subfamily Using Biotin Supplementation

Studies have found that biotin favors glucose and lipid metabolism, and medications containing biotin have been developed. Despite the use of biotin as a pharmacological agent, few studies have addressed toxicity aspects including the possible interaction with cytochrome P450 enzyme family. This study analyzed the effects of pharmacological doses of biotin on the expression and activity of the cytochrome P4501A subfamily involved in the metabolism of xenobiotics. Wistar rats were treated daily with biotin (2 mg/kg, i.p.), while the control groups were treated with saline. All of the rats were sacrificed by cervical dislocation after 1, 3, 5, or 7 days of treatment. CYP1A1 and CYP1A2 mRNAs were modified by biotin while enzyme activity and protein concentration were not affected. The lack of an effect of biotin on CYP1A activity was confirmed using other experimental strategies, including (i) cotreatment of the animals with biotin and a known CYP1A inducer; (ii) the addition of biotin to the reaction mixtures for the measurement of CYP1A1 and CYP1A2 activities; and (iii) the use of an S9 mixture that was prepared from control and biotin-treated rats to analyze the activation of benzo[a]pyrene (BaP) into mutagenic metabolites using the Ames test. The results suggest that biotin does not influence the CYP1A-mediated metabolism of xenobiotics.

Biochemical mutagens affect the preservation of fungi and biodiversity estimations

Many fungi have significant industrial applications or biosafety concerns and maintaining the original characteristics is essential. The preserved fungi have to represent the situation in nature for posterity, biodiversity estimations, and taxonomic research. However, spontaneous fungal mutations and secondary metabolites affecting producing fungi are well known. There is increasing interest in the preservation of microbes in Biological Resource Centers (BRC) to ensure that the organisms remain viable and stable genetically. It would be anathema if they contacted mutagens routinely. However, for the purpose of this discussion, there are three potential sources of biochemical mutagens when obtaining individual fungi from the environment: (a) mixtures of microorganisms are plated routinely onto growth media containing mutagenic antibiotics to control overgrowth by contaminants, (b) the microbial mixtures may contain microorganisms capable of producing mutagenic secondary metabolites, and (c) target fungi for isolation may produce "self" mutagens in pure culture. The probability that these compounds could interact with fungi undermines confidence in the preservation process and the potential effects of these biochemical mutagens are considered for the first time on strains held in BRC in this review.

Mutagenicity of 5-Hydroxymethylfurfural in V79 Cells Expressing Human SULT1A1: Identification and Mass Spectrometric Quantification of DNA Adducts Formed

5-Hydroxymethylfurfural (HMF), a heterocyclic product of the Maillard reaction, is a ubiquitous food contaminant. It has demonstrated hepatocarcinogenic activity in female mice. This effect may originate from sulfo conjugation of the benzylic alcohol yielding 5-sulfooxymethylfurfural (SMF), which is prone to react with DNA via nucleophilic substitution. Indeed, we showed that HMF induces gene mutations in Chinese hamster V79 cells engineered for the expression of human (h) sulfotransferase (SULT)1A1 but not in parental V79 cells. In order to identify potential DNA adducts, we incubated DNA samples with SMF or HMF in aqueous solution. Modified DNA was digested and surveyed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for adducts that may be formed by nucleosides either via nucleophilic substitution at the electrophilic carbon atom of SMF or via imine formation with the aldehyde group present in HMF and SMF. The most abundant adducts formed from SMF, N(6)-((2-formylfuran-5-yl)methyl)-2'-deoxyadenosine (N(6)-FFM-dAdo) and N(2)-((2-formylfuran-5-yl)methyl)-2'-deoxyguanosine (N(2)-FFM-dGuo), were synthesized, purified, and characterized by (1)H NMR. Imine adducts were only detected when DNA was incubated with very high levels of HMF following reduction of the imines to corresponding secondary amines by NaBH(3)CN. Sensitive techniques based on LC-MS/MS multiple reaction monitoring for the quantification of the adducts in DNA samples were devised using isotope-labeled [(15)N(5)]N(6)-FFM-dAdo and [(13)C(10),(15)N(5)]N(2)-FFM-dGuo as internal standards. Both 5-methylfurfuryl adducts were detected in DNA from V79-hSULT1A1 treated with HMF but not in DNA from V79 control cells. Considering the lack of other known mutagenic metabolites, we hypothesize that the hepatocarcinogenic potential of HMF originates from the formation of mutagenic SMF.

Induction of mouthpart deformities in chironomid larvae exposed to contaminated sediments

The aim of the present study was to improve the cause–effect relationship between toxicant exposure and chironomid mouthpart deformities, by linking induction of mouthpart deformities to contaminated field sediments, metal mixtures and a mutagenic polycyclic aromatic compound metabolite (acridone). Mouthpart deformities in Chironomus riparius larvae were induced by both the heavy metal mixture and by acridone. A clear correlation between metal concentrations in the sediment and deformities incidence was only observed when the contaminated field sediments were left out of the analysis, probably because these natural sediments contained other toxic compounds, which could be responsible for a higher incidence of deformities than predicted by the measured metal concentrations only. The present study clearly improved the cause–effect relationship between toxicant exposure and the induction of mouthpart deformities. It is concluded that the incidence of mouthpart deformities may better reflect the potential toxicity of contaminated sediments than chemical analysis.

Study of 5‐hydroxymethylfurfural and its metabolite 5‐sulfooxymethylfurfural on induction of colonic aberrant crypt foci in wild‐type mice and transgenic mice expressing human sulfotransferases 1A1 and 1A2

It was reported that the Maillard product 5-hydroxymethylfurfural (HMF) initiates and promotes aberrant crypt foci (ACF) in rat colon. We studied whether 5-sulfooxymethylfurfural (SMF), an electrophilic and mutagenic metabolite of HMF, is able to induce ACF in two murine models. In the first model, FVB/N mice received four intraperitoneal administrations of SMF (62.5 or 125 mg/kg) or azoxymethane (10 mg/kg). Animals were killed 4-40 weeks after the last treatment. A total of 1064 ACF and five adenocarcinomas were detected in the azoxymethane-treated groups (20 animals), but none in the negative control and SMF-treated groups (35 and 50 animals, respectively). In the second model, HMF was administered via drinking water to wild-type FVB/N mice and transgenic mice carrying several copies of human sulfotransferase (SULT) 1A1 and 1A2 genes. HMF SULT activity was clearly elevated in cytosolic fractions of colon mucosa, liver and kidney of transgenic animals compared to wild-type mice and humans. The animals (six per group) received 134 and 536 mg HMF/kg/day for 12 weeks. HMF did not induce any ACF either in wild-type or transgenic animals. We found no evidence for an induction of ACF by HMF or its metabolite SMF in extensive studies in mice.

The effect of acute and chronic exposure to acetaldehyde—a mutagenic metabolite of dietary ethanol—on prostate cancer cells: A potential source of race disparity disfavoring black men.

143 Background: We recently reported that the ADH1B*3 allele, which is specific to African Americans (AA), when combined with ethanol intake may constitute a gene-environment interaction leading to elevated prostate cancer (CaP) and potentially aggressive CaP risk among AA men possibly through intra-prostatic acetaldehyde accumulation. Indeed, studies have shown microsomes from rat ventral prostates biotransform ethanol to acetaldehyde that further metabolizes into oxidative stress-inducing acetyl radicals. In addition, acetaldehyde has been previously shown to enhance proliferation of colon cancer cells. Whether acetaldehyde has the same effect on CaP is unknown. Methods: We subjected DU-145 CaP cells to varying concentrations of acetaldehyde using acute and chronic models of exposure and measured tumor proliferation using MTS assay. Proliferation was measured over 4 days of acetaldehyde treatment in acute and after 2 weeks of treatment in chronic exposure experiments. All experiments were conducted in triplicate. Results were expressed as mean values for each treatment referenced to untreated cells. Doubling times were calculated using least squares fitting exponential regression. Results: In the acute exposure model, proliferation of DU-145 cells was inhibited by 150 uM acetaldehyde by 28% while 1,500uM and higher concentrations resulted in complete inhibition of proliferation. After chronic exposure to acetaldehyde, proliferation of DU-145 cells was inhibited by 500 uM acetaldehyde by 19%. In contrast, chronic exposure with 1,000 uM acetaldehyde resulted in increased proliferation by 9% and shortened tumor doubling time. Conclusions: Acute exposure to acetaldehyde resulted in inhibition of CaP cellular proliferation. Chronic exposure to high acetaldehyde concentrations promoted tumor proliferation likely through selection for more robust CaP cells that survive the repeated chemical insult. Our results suggest that chronic acetaldehyde exposure of existent CaP may potentially promote disease aggressiveness. Uncovering mechanisms for enhanced CaP cell proliferation by acetaldehyde are warranted.

Conjugation of Butadiene Diepoxide with Glutathione Yields DNA Adducts in Vitro and in Vivo

1,2,3,4-Diepoxybutane (DEB) is reported to be the most potent mutagenic metabolite of 1,3-butadiene, an important industrial chemical and environmental pollutant. DEB is capable of inducing the formation of monoalkylated DNA adducts and DNA-DNA and DNA-protein cross-links. We previously reported that DEB forms a conjugate with glutathione (GSH) and that the conjugate is considerably more mutagenic than several other butadiene-derived epoxides, including DEB, in the base pair tester strain Salmonella typhimurium TA1535 [Cho et al. (2010) Chem. Res. Toxicol. 23, 1544-1546]. In the present study, we determined steady-state kinetic parameters of the conjugation of the three DEB stereoisomers-R,R, S,S, and meso (all formed by butadiene oxidation)-with GSH by six GSH transferases. Only small differences (<3-fold) were found in the catalytic efficiency of conjugate formation (k(cat)/K(m)) with all three DEB stereoisomers and the six GSH transferases. The three stereochemical DEB-GSH conjugates had similar mutagenicity. Six DNA adducts (N(3)-adenyl, N(6)-adenyl, N(7)-guanyl, N(1)-guanyl, N(4)-cytidyl, and N(3)-thymidyl) were identified in the reactions of DEB-GSH conjugate with nucleosides and calf thymus DNA using LC-MS and UV and NMR spectroscopy. N(6)-Adenyl and N(7)-guanyl GSH adducts were identified and quantitated in vivo in the livers of mice and rats treated with DEB ip. These results indicate that such DNA adducts are formed from the DEB-GSH conjugate, are mutagenic regardless of sterochemistry, and are therefore expected to contribute to the carcinogenicity of DEB.

Smoking, estradiol metabolism and hormone replacement therapy.

Products for hormone replacement therapy (HRT) in the postmenopause are the second most frequently prescribed drugs in the USA. Among the women receiving this treatment many are smokers. In the Women's Health Initiative (WHI), one of the largest interventional studies on HRT to date and which recently had to be discontinued, 50% of the 8,500 women on HRT had smoked before or continued to smoke during the study. Remarkably, there is little knowledge about the impact smoking has on the efficacy and side effects of HRT. However, it has been proven that, depending on the type, duration and intensity of nicotine consumption, smoking can reduce or completely cancel the efficacy of orally administered estrogens. Not only does smoking diminish the otherwise well-established beneficial effects of estrogen on hot flashes and urogenital symptoms and its positive effects on lipid metabolism, i.e. by reducing cholesterol, but smoking also specifically reduces estrogen's ability to prevent osteoporosis. The reduction or loss of therapeutic efficacy is mainly caused by dose-dependently elevated hepatic clearance, partially in conjunction with lower estrogen levels, and has been demonstrated only with oral estrogen applications. This failure of therapeutic action should not be compensated for by increasing the dose in smokers as this might result in the production of toxic, even potentially mutagenic estrogen metabolites-compounds recently associated with a higher risk of breast cancer. The favorable effects of estrogens are not lost in smokers when they are applied transdermally. This route enables low dosage and also avoids the formation of unphysiological metabolites by bypassing the liver. Women who continue to smoke despite all warnings should therefore only be treated via the transdermal route. Oral contraceptives, but not HRT, are contraindicated in elderly smokers. However, the principal conclusion of the WHI study was that the lowest dose possible should be chosen, especially in patients with an increased cardiovascular risk, as is the case in smokers.

Safrole-2′,3′-oxide induces cytotoxic and genotoxic effects in HepG2 cells and in mice

Safrole-2′,3′-oxide (SAFO) is a reactive electrophilic metabolite of the hepatocarcinogen safrole, the main component of sassafras oil. Safrole occurs naturally in a variety of spices and herbs, including the commonly used Chinese medicine Xi xin (Asari Radix et Rhizoma) and Dong quai (Angelica sinensis). SAFO is the most mutagenic metabolite of safrole tested in the Ames test. However, little or no data are available on the genotoxicity of SAFO in mammalian systems. In this study, we investigated the cytotoxicity and genotoxicity of SAFO in human HepG2 cells and male FVB mice. Using MTT assay, SAFO exhibited a dose- and time-dependent cytotoxic effect in HepG2 cells with TC50 values of 361.9μM and 193.2μM after 24 and 48h exposure, respectively. In addition, treatment with SAFO at doses of 125μM and higher for 24h in HepG2 cells resulted in a 5.1–79.6-fold increase in mean Comet tail moment by the alkaline Comet assay and a 2.6–7.8-fold increase in the frequency of micronucleated binucleated cells by the cytokinesis-block micronucleus assay. Furthermore, repeated intraperitoneal administration of SAFO (15, 30, 45, and 60mg/kg) to mice every other day for a total of twelve doses caused a significant dose-dependent increase in mean Comet tail moment in peripheral blood leukocytes (13.3–43.4-fold) and in the frequency of micronucleated reticulocytes (1.5–5.8-fold). Repeated administration of SAFO (60mg/kg) to mice caused liver lesions manifested as a rim of ballooning degeneration of hepatocytes immediately surrounding the central vein. Our data clearly demonstrate that SAFO significantly induced cytotoxicity, DNA strand breaks, micronuclei formation both in human cells in vitro and in mice. More studies are needed to explore the role SAFO plays in safrole-induced genotoxicity.

Explanation for Main Features of Structure–Genotoxicity Relationships of Aromatic Amines by Theoretical Studies of Their Activation Pathways in CYP1A2

Aromatic and heteroaromatic amines (ArNH(2)) represent a class of potential mutagens that after being metabolically activated covalently modify DNA. Activation of ArNH(2) in many cases starts with N-hydroxylation by P450 enzymes, primarily CYP1A2. Poor understanding of structure-mutagenicity relationships of ArNH(2) limits their use in drug discovery programs. Key factors that facilitate activation of ArNH(2) are revealed by exploring their reaction intermediates in CYP1A2 using DFT calculations. On the basis of these calculations and extensive analysis of structure-mutagenicity data, we suggest that mutagenic metabolites are generated by ferric peroxo intermediate, (CYP1A2)Fe(III)-OO(-), in a three-step heterolytic mechanism. First, the distal oxygen of the oxidant abstracts proton from H-bonded ArNH(2). The subsequent proximal protonation of the resulting (CYP1A2)Fe(III)-OOH weakens both the O-O and the O-H bonds of the oxidant. Heterolytic cleavage of the O-O bond leads to N-hydroxylation of ArNH(-) via S(N)2 mechanism, whereas cleavage of the O-H bond results in release of hydroperoxy radical. Thus, our proposed reaction offers a mechanistic explanation for previous observations that metabolism of aromatic amines could cause oxidative stress. The primary drivers for mutagenic potency of ArNH(2) are (i) binding affinity of ArNH(2) in the productive binding mode within the CYP1A2 substrate cavity, (ii) resonance stabilization of the anionic forms of ArNH(2), and (iii) exothermicity of proton-assisted heterolytic cleavage of N-O bonds of hydroxylamines and their bioconjugates. This leads to a strategy for designing mutagenicity free ArNH(2): Structural alterations in ArNH(2), which disrupt geometric compatibility with CYP1A2, hinder proton abstraction, or strongly destabilize the nitrenium ion, in this order of priority, prevent genotoxicity.

Biotransformation enzyme-dependent formation of micronucleus and multinuclei in cell line V79-hCYP2E1-hSULT1A1 by 2-nitropropane and N-nitrosodimethylamine

V79-hCYP2E1-hSULT1A1, a V79-derived cell line co-expressing both human CYP2E1 and SULT1A1, has been constructed and efficiently used in detection of the mutagenic activities of a number of promutagens. 2-Nitropropane (2-NP) and N-nitrosodimethylamine (NDMA), both being hepatocarcinogenic to animals but inactive in standard genotoxicity assays in vitro, are activated to mutagenic metabolites by human SULT1A1 and CYP2E1, respectively. Nevertheless, little is known about the chromosomal effects of these two carcinogens. In the present study, we investigated the effects of 2-NP and NDMA on frequencies of micronucleated ( F mi) and multinucleated cells ( F mu) in V79-hCYP2E1-hSULT1A1 cells. The results showed induction of both F mi and F mu by 2-NP and NDMA individually, and this effect was completely suppressed by relatively specific inhibitor of SULT1A1 and CYP2E1, i.e., pentachlorophenol and 1-aminobenzotriazole, respectively. The F mu/ F mi ratio in 2-NP groups was significantly higher than NDMA groups, probably indicating an aneugenic activity of 2-NP based on proposed F mu/ F mi ratio as a simple index to discriminate aneugens from clastogens. The present study has established biotransformation enzyme-dependent formation of multinuclei and micronuclei induced by 2-NP and NDMA.

Abstract 3701: Dimethylbenzanthracene (DMBA) and DMBA dihydrodiol mutagenicity in rat epithelial and fibroblast cell lines, and its inhibition by combinations of nutraceuticals

Abstract 7,12-Dimethylbenzanthracene (DMBA) is a potent mammary carcinogen in rats. Combinations of non-toxic nutraceutical agents, administered at or near physiological levels, were investigated for their abilities to inhibit the mutagenicity of DMBA or DMBA-dihydrodiol (DMBAD, a primary metabolite and proximate mutagen of DMBA) in vitro, in rat mammary epithelial and fibroblast cells derived from a lacI (BigBlue) Fischer rat (McDiarmid, H.M., Douglas, G.R., Coomber, B.L., and Josephy, P.D. Epithelial and fibroblast cell lines cultured from the transgenic BigBlue rat: an in vitro mutagenesis assay. Mutat. Res., 497: 39-47, 2001). In the epithelial cells, DMBA was not appreciably mutagenic at concentrations up to 4 µM, but DMBAD, was significantly mutagenic at ten-fold lower concentrations. These results indicate that the epithelial cells can bioactivate the intermediate, DMBAD, but cannot effect the complete biotransformation of DMBA to its ultimate mutagenic metabolite, DMBA-dihydrodiolepoxide. In the fibroblast cell line, in contrast, DMBA was mutagenic at concentrations as low as 20 nM and DMBAD was even more potent than DMBA. Several combinations of nutraceuticals (dietary components providing health benefits) were tested for their abilities to inhibit mutagenesis in these cell lines; the concentrations tested were based on reported serum concentrations and these were used to establish 1x concentrations. The agents and their 1x concentrations were: resveratrol (Res), 2.4 μM; sulforaphane (Sul), 0.06 μM; antioxidant mix (α- and γ-tocopherol, 30 μM, plus vitamin C, 68 μM – VCE); α-lipoic acid (LA), 2 μM; epigallocatechin gallate (EGCG), 0.7 μM; and N-acetylcysteine (NAC), 12 μM. None of the agents or their combinations, tested at 1 – 3 x concentrations, showed any cytotoxicity. In both epithelial and fibroblast cells, Sul and Res alone slightly inhibited mutagenesis at 2x concentrations; no other agents had observable effects. All binary combinations of Res, LA, and Sul, at 2x concentrations, inhibited mutagenesis; the Res + Sul combination was particularly effective (ca. 50% inhibition). These results suggest a role for fibroblast cells in the bioactivation of carcinogens, implicating the microenvironment, and indicate that combinations of nutraceuticals can inhibit mutagenesis by polycyclic aromatic hydrocarbons. Supported by the Susan Komen Foundation grant # KG080836 (JBG) and NSERC Canada (PDJ). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3701. doi:10.1158/1538-7445.AM2011-3701

Role of quercetin on mitomycin C induced genotoxicity: Analysis of micronucleus and chromosome aberrations in vivo

Quercetin, a flavonol group of plant flavonoid, has generated immense interest because of its potential antioxidant, anti-proliferative, chemoprotective, anti-inflammatory and gene expression modulating properties. However, the pro-oxidant chemistry of quercetin is important as it is related to the generation of mutagenic quinone-type metabolites. In the present study, 25 mg/kg, 50 mg/kg and 100 mg/kg of quercetin given through the intra peritoneal (i.p.) route induced 2.31 ± 0.27%, 4.72 ± 0.58% and 6.38 ± 0.68% (control value = 0.67 ± 0.30%) respectively, of cells with micronucleus (MN) in polychromatic erythrocytes in bone marrow cells and 10.93 ± 0.98%, 10.00 ± 0.89% and 14.27 ± 3.94% (control 2.61 ± 0.48) of cells with chromosome aberrations (CA) following 24 h of the treatments. Higher frequencies of MN and CA were also observed after 48 h of the treatments. To verify the effect of route of treatment on the quercetin induced damage, 100 mg/kg b.w. was given through oral route which declined frequency of MN ( P < 0.001) as well as CA ( P < 0.05) as compared to the i.p. route for the same dose. Quercetin also induced higher frequency of metaphases with sticky chromosomes and C-mitosis. Pre-treatment with quercetin significantly reduced the frequency of mitomycin C (MMC) induced MN as well as CA, but no clear correlation between the dose and effect could be observed. Further studies are required to elucidate the possible interaction of quercetin with DNA as well as with other DNA damaging agents like MMC in vivo. The protective action of quercetin was not enhanced when given orally. Our findings suggest that quercetin may result in genomic instability in the tested dose range and significant reduction in MMC induced genotoxicity in the highest dose tested. These effects of quercetin are to be taken into consideration while evaluating the possible use of quercetin as a therapeutic agent.

DFT/TD-DFT investigation of optical absorption spectra, electron affinities, and ionization potentials of mono-nitrated benzanthrones

Density functional theory (DFT) method B3LYP with basis sets 6-311+G(d,p), 6-31G(d) and 6-311G(d,p) have been used to compute molecular structures, UV–vis absorption spectra, electron affinities (EAs), and ionization potentials (IPs) of benzanthrone and 1-, 2-, 3-, 9-, 10-, and 11-nitrobenzanthrones. With the use of the time-dependent TD-B3LYP/6-311G(d,p) approach, the UV/vis absorption spectral bands, vertical excitation energies and oscillator strengths was studied. The calculated vertical excitation energies lie within <0.15 eV of the observed values. In comparison to benzanthrone, calculated absorption spectra of nitrated nitrobenzanthrones show red-shifting to >383 nm, which is correlated to their relative reactivity. Detailed clarification of the singlet-singlet excited states (and energies) are made. The calculated electron affinities are ∼0.5 eV greater than in benzanthrone (BA); being in the order 3-NBA > 10-NBA > 1-NBA > 2-NBA > 9-NBA > 11-NBA > BA. Similarly, ionization potentials follow a very close order in nitro-BAs. The calculated EAs and IPs implicate both reductive and oxidative pathways on transformation to mutagenic metabolites. The implications of the results are discussed in the context of their differential mutagenic potencies.

1,3-Butadiene: Biomarkers and application to risk assessment

1,3-Butadiene (BD) is a known rodent and human carcinogen that is metabolized mainly by P450 2E1 to three epoxides, 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB) and 1,2-epoxy-3,4-butanediol (EB-diol). The individual epoxides vary up to 200-fold in their mutagenic potency, with DEB being the most mutagenic metabolite. It is important to understand the internal formation of the individual epoxides to assign the relative risk for each metabolite and to understand the molecular mechanisms responsible for major species differences in carcinogenicity. We have conducted extensive exposure-biomarker studies on mice, rats and humans. Using low exposures that range from current occupational levels to human exposures from tobacco smoke has provided evidence that mice are very different from humans, with mice forming ∼200 times more DEB than humans at exposures of 0.1–1.5 ppm BD. While no gender differences have been noted in mice and rats for globin adducts or N-7 guanine adducts, female rats and mice had 2–3-fold higher Hprt mutations and DNA–DNA cross-links, suggesting a gender difference in DNA repair. Numerous molecular epidemiology studies have evaluated globin adducts and Hprt mutations, SCEs and chromosomal abnormalities. None of the blinded studies have shown evidence of human genotoxicity at current occupational exposures and studies of globin adducts have shown similar or lower formation of adducts in females than males. If one calculates the EB dose-equivalents for the three species, mice clearly differ from rats and humans, being ∼44 and 174 times greater than rats and humans, respectively. These data provide a scientific basis for improved risk assessment of BD.

The role of oxidative stress in carcinogenesis induced by metals and xenobiotics.

In addition to a wide range of adverse effects on human health, toxic metals such as cadmium, arsenic and nickel can also promote carcinogenesis. The toxicological properties of these metals are partly related to generation of reactive oxygen species (ROS) that can induce DNA damage and trigger redox-dependent transcription factors. The precise mechanisms that induce oxidative stress are not fully understood. Further, it is not yet known whether chronic exposures to low doses of arsenic, cadmium or other metals are sufficient to induce mutations in vivo, leading to DNA repair responses and/or tumorigenesis. Oxidative stress can also be induced by environmental xenobiotics, when certain metabolites are generated that lead to the continuous release of superoxide, as long as the capacity to reduce the resulting dions (quinones) into hydroquinones is maintained. However, the specific significance of superoxide-dependent pathways to carcinogenesis is often difficult to address, because formation of DNA adducts by mutagenic metabolites can occur in parallel. Here, we will review both mechanisms and toxicological consequences of oxidative stress triggered by metals and dietary or environmental pollutants in general. Besides causing DNA damage, ROS may further induce multiple intracellular signaling pathways, notably NF-κB, JNK/SAPK/p38, as well as Erk/MAPK. These signaling routes can lead to transcriptional induction of target genes that could promote proliferation or confer apoptosis resistance to exposed cells. The significance of these additional modes depends on tissue, cell-type and is often masked by alternate oncogenic mechanisms being activated in parallel.

Antimicrobial and Genotoxicity Activities of Medicinal Plant Extracts in vitro

The effect of selected plant extracts on microbial growth and mutagenicity was evaluated in this study. The initial population of foodborne pathogens was approximately 5 log CFU/mL. The growth of selected pathogens was inhibited by the extracts in a concentration‐dependent manner. The bactericidal effect was observed against L. monocytogenes, S. aureus, and S. boydii at 100 mg/mL of the extract, showing more than 5 log reduction compared to the control. The mutagenic activity of the extracts was evaluated against frame‐shift mutants (TA98 and TA1537) and base‐pair substitution‐carrying mutants (TA100 and TA1535) of S. typhimurium with and without metabolic activation. The numbers of spontaneous revertant colonies were ranged from 16 to 110 for all test strains of TA 98, TA 100, TA 1535, and TA 1537 with and without S9, while those of mutagen‐induced revertants were ranged from 157 to 1410. No significant differences in the frequencies of revertants of S. typhimurium TA 98, TA 100, TA 1535, and TA 1537 were observed at the different concentrations of the extract when compared to the negative controls, indicating that the extract is not mutagenic against all test strains in the absence and the presence of S9. The results imply that the medicinal plant extracts was not involved in the production of mutagenic metabolites and the secondary metabolites and released substances did not caused genotoxicity in vitro. The extract used in this study can be a promising additive for functional foods.

Exposure-response of 1,2:3,4-diepoxybutane-specific N-terminal valine adducts in mice and rats after inhalation exposure to 1,3-butadiene.

1,3-Butadiene (BD) is a known rodent and human carcinogen that is metabolized mainly by P450 2E1 to three epoxides, 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB), and 1,2-epoxy-3,4-butanediol. The individual epoxides vary up to 200-fold in their mutagenic potency, with DEB being the most mutagenic metabolite. It is important to understand the internal formation of the individual epoxides to assign the relative risk for each metabolite and to understand the molecular mechanisms responsible for extensive species differences in carcinogenicity. This study presents a comprehensive exposure-response for the formation of the DEB-specific N,N-(2,3-dihydroxy-1,4-butadiyl)valine (pyr-Val) in mice and rats. Using nano-ultra high pressure liquid chromatography-tandem-mass spectrometry allowed analysis of pyr-Val in mice and rats exposed to BD as low as 0.1 and 0.5 ppm BD, respectively, and demonstrated significant differences in the amounts and exposure-response of pyr-Val formation. Mice formed 10- to 60-fold more pyr-Val compared to rats at similar exposures. The formation of pyr-Val increased with exposures, and the formation was most efficient with regard to formation per parts per million BD at low exposures. While formation at higher exposures appeared linear in mice, in rats formation saturated at exposures > or = 200 ppm for 10 days. In rats, amounts of pyr-Val were lower after 20 days than after 10 days of exposure, suggesting that the lifespan of rat erythrocytes may be shortened following exposure to BD. This research supports the hypothesis that the lower susceptibility of rats to BD-induced carcinogenesis results from greatly reduced formation of DEB following exposure to BD.

Xenobiotic metabolizing enzyme polymorphisms and survival in lung cancer patients

Event Abstract Back to Event Xenobiotic metabolizing enzyme polymorphisms and survival in lung cancer patients Mumtaz Iscan1* 1 Ankara University, Department of Toxicology, Türkiye Lung cancer is an increasing worldwide public health problem particularly in men and has two histological types, namely small cell lung carcinoma (SCLC) and non small cell lung carcinoma (NSCLC). Approximately 80 % of lung carcinomas have NSCLC histology. In the patients with NSCLC platinum based chemotherapy and chemoradiotherapy are standard treatment strategies. The response to chemotherapy particularly for patients with NSCLC has been reported to be rather poor. Thus, the investigation of the reasons behind this failure of chemotherapy, and thus possibly poorer survival in these patients is very important. It is well known that most of the lung cancer patients are cigarette smokers. Cigarette smoke has been reported to cause elevated levels of carcinogen DNA-adducts which in turn form aggressive tumors by mutating and thus inactivating tumor suppressor genes (such as p53) and thereby decrease the survival rates of patients with NSCLC . Metabolic activation of polycyclic aromatic hydrocarbons (PAHs) and nitrosamines in cigarette smoke to mutagenic and carcinogenic metabolites are mediated by CYPs namely CYP1A1, CYP1B1 and CYP2E1. In addition, these CYPs play a role in the metabolism of a number of drugs including chemotherapeutic agents and thus involve in drug resistance. These CYP genes have been found to be polymorphic and the most common alleles and polymorphisms of these CYPs have altered enzyme activities. Glutathione S-transferases (GST)s are involved in the inactivation of various carcinogenic compounds found in cigarette smoke that are activated by CYPs but on the other hand also play an important role in the resistance of lung cancer therapy especially to platinum compounds. GSTs decrease the cytotoxic impact of these chemotherapeutic drugs. However, certain polymorphisms in GSTs are associated with changes or loss in enzyme activity. Since CYPs and GSTs catalyze several chemotherapeutic agents and reactive metabolites including by-products of reactive oxygen species which damage the DNA, lung cancer patients may differ in response to therapy, depending on CYP and GST activity. Thus, CYP and GST genotypes may have influence on the response to therapy and survival of the lung cancer patients. Herein, recent findings with respect to the role of CYP and GST gene polymorphisms in response to therapy and survival in lung cancer patients will be evaluated (Supported by the Research Fund of Ankara University grants; 20060803002HPD, 20070803005 HPD, 20080803006HPD, 10A3336002). Keywords: cytochrome P450, Glutathione S-transferase, polymorphism, lung cancer, Survival, chemotherapy, cigarette smoke Conference: 8th Southeast European Congress on Xenobiotic Metabolism and Toxicity - XEMET 2010, Thessaloniki, Greece, 1 Oct - 5 Oct, 2010. Presentation Type: Invited speaker Topic: Genomics - Proteomics - Metabolomics Citation: Iscan M (2010). Xenobiotic metabolizing enzyme polymorphisms and survival in lung cancer patients. Front. Pharmacol. Conference Abstract: 8th Southeast European Congress on Xenobiotic Metabolism and Toxicity - XEMET 2010. doi: 10.3389/conf.fphar.2010.60.00131 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Mar 2011; Published Online: 04 Nov 2010. * Correspondence: Dr. Mumtaz Iscan, Ankara University, Department of Toxicology, Ankara, Türkiye, Mumtaz.Iscan@pharmacy.ankara.edu.tr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Mumtaz Iscan Google Mumtaz Iscan Google Scholar Mumtaz Iscan PubMed Mumtaz Iscan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Taxol as chemical detoxificant of aflatoxin produced by aspergillus flavus isolated from sunflower seed

Aflatoxins are the potent toxic, mutagenic, heterogenic and carcinogenic metabolites produced by species of A. flavus and A. parasiticus. In the present study, an attempt has been made to prevent aflatoxin production using an anticancerous drug taxol. Taxol (Paclitaxel) is a well known drug for its anticancerous property mainly to treat breast and ovarian cancers. It was obtained from Taxus brevifolia and it was also obtained from the endophytic fungi present in Taxus brefivolia [1]. Therefore, this drug is specifically selected to screen its activity on the control of A. flavus and AFB1 production at various concentrations. Among the 6 concentrations used, 3 μg of taxol was found to be suitable to control the growth and AFB1 production. The content of AFB1 found at this concentration was 6 ppm by TLC and 6.3 ppm by HPTLC. The complete elimination of AFB1 might require higher concentrations of taxol.