Exposure assessment of benzene in Thai workers, DNA-repair capacity and influence of genetic polymorphisms

Exposure to benzene can cause DNA damage and the subsequent development of cancer. In this study, study subjects were 31 laboratory workers at a petrochemical factory and 31 gasoline service attendants. Control subjects were 34 workers from a mail sorting service center. Occupational exposures to benzene were assessed using biomarkers of exposure in blood and urine. Induction of DNA-repair capacity was assessed as a biomarker of early effect. The effects of polymorphisms in a metabolizing gene (CYP2E1), in detoxification genes (NQO1 and GSTT1), and in a DNA-repair gene (XRCC1, codon 399) on biomarker levels were evaluated. The mean individual benzene exposure of laboratory workers (24.40+/-5.82 ppb) and that of gasoline service attendants (112.41+/-13.92 ppb) were significantly higher than in controls (1.39+/-0.17 ppb, p<0.001). Blood benzene levels of laboratory workers (169.12+/-30.60 ppt) and gasoline service attendants (483.46+/-59.62 ppt) were significantly higher than those of the controls (43.30+/-4.89 ppt, p<0.001). Trans,trans-muconic acid levels in post-shift urine samples collected from laboratory workers (0.14+/-0.02 mg/g creatinine) and gasoline service attendants (0.20+/-0.02 mg/g creatinine) were significantly higher than in urine samples of controls (0.04+/-0.01 mg/g creatinine, p<0.001). The level of benzene exposure was correlated with blood benzene levels (R2=0.65, p<0.01) and post-shift urinary trans,trans-muconic acid concentrations (R2=0.49, p<0.01). As a biomarker of early effect, DNA-repair capacity was assessed by use of the cytogenetic challenge assay, i.e., chromosomal aberrations in peripheral lymphocytes were assessed after challenging blood cultures with 1 Gy gamma radiation. A significantly lower DNA-repair capacity--determined as dicentrics in laboratory workers (0.17 per metaphase cell) and in gasoline service attendants (0.19 per metaphase cell) compared with controls (0.12 per metaphase cell, p<0.001)--was observed. The frequency of deletions in laboratory workers (0.22 per metaphase cell) and gasoline service attendants (0.39 per metaphase cell) were significantly higher than in control workers (0.16 per metaphase cell, p<0.01 and p<0.001, respectively). An increase in radiation-induced dicentrics and deletions indicate a lower DNA-repair capacity in benzene-exposed workers. The influence of genetic polymorphisms on the biomarkers was assessed. Benzene-exposed workers who carried CYP2E1*1/*5 or *5/*5 genotypes excreted slightly higher levels of trans,trans-muconic acid than workers who carried the CYP2E1*1/*1 genotype. In this study, NQO1 and GSTT1 genotypes did not have any effect on the levels of trans,trans-muconic acid. In the case of XRCC1, laboratory workers with 399Arg/Gln or Gln/Gln had a lower DNA-repair capacity--measured as radiation-induced frequency of dicentrics and deletions--than those with the 399Arg/Arg genotype (p<0.01). Our results show that biomarkers of internal dose and early biological effect in people occupationally exposed to benzene are influenced by genetic polymorphisms in susceptibility genes.     

Micronuclei in humans induced by exposure to low level of ionizing radiation: influence of polymorphisms in DNA repair genes

Understanding the risks deriving from protracted exposure to low doses of ionizing radiation has remarkable societal importance in view of the large number of work settings in which sources of IR are encountered. To address this question, we studied the frequency of micronuclei (MN), which is an indicator of DNA damage, in a population exposed to low levels of ionizing radiation and in matched controls. In both exposed population and controls, the possible influence of single nucleotide polymorphisms in XRCC1, XRCC3 and XPD genes on the frequency of micronuclei was also evaluated. We also considered the effects of confounding factors, like smoking status, age and gender. The results indicated that MN frequency was significantly higher in the exposed workers than in the controls [8.62+/-2.80 versus 6.86+/-2.65; P=0.019]. Radiological workers with variant alleles for XRCC1 or XRCC3 polymorphisms or wild-type alleles for XPD exon 23 or 10 polymorphisms showed a significantly higher MN frequency than controls with the same genotypes. Smoking status did not affect micronuclei frequency either in exposed workers or controls, while age was associated with increased MN frequency in the exposed only. In the combined population, gender but not age exerted an influence on the yield of MN, being higher in females than in males. Even though there is a limitation in this study due to the small number of subjects, these results suggest that even exposures to low level of ionizing radiation could have genotoxic effects and that XRCC3, XRCC1 and XPD polymorphisms might contribute to the increased genetic damage in susceptible individuals occupationally exposed to chronic low levels of ionizing radiation. For a clear conclusion on the induction of DNA damage caused by protracted exposure to low doses of ionizing radiation and the possible influence of genetic polymorphism in DNA repair genes larger studies are needed.     

Molecular biomonitoring of a population of nurses handling antineoplastic drugs

Many antineoplastic drugs have been found to have carcinogenic, mutagenic and teratogenic activity and so hospital personnel handling these substances are potentially exposed to health risk. Understanding this risk derived from protracted occupational exposure has great relevance even if the workers normally adopt individual and environmental protective measures. To address this question we have studied the presence of DNA and chromosome damage in a population of nurses employed in Italian oncology units and in matched controls. We used the comet assay to evidence the presence of DNA strand breaks, due to both acute and chronic exposure, and the micronucleus (MN) test, which is a measure of clastogenic and aneugenic events. Furthermore, since the individual response to the exogenous insults may be genetically determined, we studied the possible influence of single nucleotide polymorphism in XRCC1 and XRCC3 DNA repair genes on induced genetic damage. We also considered the effects of confounding factors like smoking, age and gender. The results indicated that the exposed subjects had significantly high levels of genetic damage. Age and gender were associated with increased values in MN, both in control and in exposed groups; the smoking habit affects MN frequency in controls, but not in workers. Furthermore we found that exposed subjects bearing at least one XRCC1 variant allele (399Gln) show higher values of MN. The present data provide the evidence to show that occupational exposure to antineoplastic drugs, even if in safety controlled conditions, represents a serious health risk. Furthermore we have shown that the presence of XRCC1 genetic polymorphism could contribute to increase the genetic damage in susceptible individuals who are occupationally exposed to dangerous substances.     

Polymorphisms in metabolic GSTP1 and DNA-repair XRCC1 genes with an increased risk of DNA damage in pesticide-exposed fruit growers

Pesticide exposure is associated with various neoplastic diseases and congenital malformations. Previous studies have indicated that pesticides may be metabolized by cytochrome P450 3A5 or glutathione S-transferases. DNA-repair genes, including X-ray repair cross-complementing group 1 (XRCC1) and xeroderma pigmentosum group D (XPD), may also be implicated in the process of pesticide-related carcinogenesis. Thus, we investigated whether various metabolic and DNA-repair genotypes increase the risk of DNA damage in pesticide-exposed fruit growers. Using the comet assay, the extent of DNA damage was evaluated in the peripheral blood of 135 pesticide-exposed fruit growers and 106 unexposed controls. The metabolic genotypes CYP3A5 (A(-44)G) and GSTP1 (Ile105Val) and DNA-repair genotypes XRCC1 (Arg399Gln, Arg194Trp, T(-77)C) and XPD (Asp312Asn, Lys751Gln) were identified by polymerase chain reaction. Our multiple regression model for DNA tail moment showed that age, high pesticide exposure, low pesticide exposure, GSTP1 Ile-Ile, and XRCC1 399 Arg-Arg genotype were associated with increased DNA tail moment (DNA damage). Further analysis of interaction between GSTP1 and XRCC1 genes that increase susceptibility revealed a significant difference in DNA tail moment for high pesticide-exposed subjects carrying both GSTP1 Ile-Ile with XRCC1 399 Arg-Arg genotypes (2.49+/-0.09 microm/cell; P=0.004), compared to those carrying GSTP1 Ile-Val/Val-Val with XRCC1 399 Arg-Gln/Gln-Gln genotypes (1.98+/-0.15 microm/cell). These results suggest that individuals with susceptible metabolic GSTP1 and DNA-repair XRCC1 genotypes may be at increased risk of DNA damage due to pesticide exposure.     

Effects of environmental benzene: micronucleus frequencies and haematological values in traffic police working in an urban area

Among the toxic chemicals present in the ambient air of urban centres, benzene raises particular concern due to its haematoxicity and leukaemogenic hazards, probably related to clastogenic factors. However, little is known about the health risks associated with environmental--rather than industrial--exposure to benzene. We analysed micronucleus (MN) frequencies in peripheral lymphocytes by use of the cytokinesis-block technique, and haematological parameters among 49 traffic police and 36 indoor workers (controls) in the city of Bologna. The analysis of urban air provided by a municipal air-quality monitoring station indicated that the levels of environmental benzene were often above the recommended threshold level (10 microg/m3) whereas other pollutants--nitrogen oxides, polycyclic aromatic hydrocarbon compounds, total suspended particulate matter, carbon monoxide, sulfur dioxide--did not exceed the maximum atmospheric concentration established for air-quality standards. Mean levels of individual airborne benzene exposure--as measured by personal devices worn during 4-h morning work-shifts--were six-fold higher in the traffic police than in controls (P=0.001). While no significant difference in haematological parameters was found between the two groups, MN frequency was significantly higher among the traffic police than in indoor workers (P=0.001). Among the study population, MN frequency was found to increase with age, but no influence was observed for gender or smoking. Although it cannot be excluded that the increase of MN frequency observed in traffic police could also depend, apart from benzene, on the complex mixture of pollutants encountered in urban air, our data indicate that elevated personal benzene exposure could represent a genetic risk. The analysis of biomarkers of genetic damage in subjects particularly exposed to environmental benzene deserves careful study.     

Biomonitoring of exposure to urban air pollutants: analysis of sister chromatid exchanges and DNA lesions in peripheral lymphocytes of traffic policemen

In order to elucidate the health effects of occupational exposure to traffic fumes, a few biomarkers of early genetic effect were investigated in Rome traffic policemen. One hundred and ninety healthy subjects engaged in traffic control (133 subjects) or in office work (57 subjects) participated the study. For all subjects, detailed information on smoking habits and other potential confounders were recorded by questionnaires. Average exposure of the study groups to benzene and other aromatic hydrocarbons was evaluated in a parallel exposure survey. All workers were genotyped for the following metabolic polymorphisms: CYP1A1 (m1, m2, and m4 variants), CYP2E1 (PstI and RsaI), NQO1 (Hinf1), GSTM1 and GSTT1 (null variants). In this paper, the results of the analysis of sister chromatid exchanges (SCE) in peripheral lymphocytes, and DNA damage by alkaline (pH 13) comet assay in mononuclear blood cells are reported. No statistically significant difference in the frequency of SCE or high frequency cells (HFC) was observed between traffic wardens and office workers (controls), despite the significantly higher exposure to benzene of the former (average group exposure 9.5 versus 3.8microg/m(3), 7h TWA). Conversely, both SCE per cell and HFC were highly significantly (P<0.001) increased in smokers compared to nonsmokers, showing a significant correlation (P<0.001) with the number of cigarettes per day. Multiple regression analyses of data, with metabolic polymorphisms, smoking habits, alcohol consumption, age, gender, and family history of cancer as independent variables, showed that smoking habits, and possibly the CYP2E1 variant genotypes, were the main factors explaining the variance of both SCE and HFC. Within smokers, an association of borderline significance between the CYP1A1 variant genotypes and increased SCE (P=0.050) and HFC (P=0.090) was found. This effect was mainly observed in light smokers (<15 cigarettes per day). The analysis of DNA damage by comet assay did not highlight any statistically significant difference between the exposed and control workers. Moreover, no significant model explaining tail moment variance was obtained by multiple regression analysis using the independent variables shown above. On the whole, these results indicate that exposure to moderate air pollution levels does not result in a detectable increase of genetic damage in blood cells. This evidence does not rule out any possibility of adverse effects, but strongly suggests that in urban residents life-style related factors, such as tobacco smoking, give the prevailing contribution to individual genotoxic burden.     

Assessment of the mutagenic potential of arecoline in gpt delta transgenic mice

Until recently, knowledge about the genotoxicity of roxarsone in vitro or in vivo was limited. This study assessed the genotoxicity of roxarsone in an in vitro system. Roxarsone was tested for potential genotoxicity on V79 cells by a Comet assay and a micronucleus (MN) test, exposing the cells to roxarsone (1-500 μM) and to sodium arsenite (NaAsO?, 20 μM) solutions for 3-48 h. Roxarsone was found to be cytotoxic when assessed with a commercial cell counting kit (CCK-8) used to evaluate cell viability, and moderately genotoxic in the Comet assay and micronucleus test used to assess DNA damage. The Comet metrics (percentages TDNA, TL, TM) increased significantly in a time- and concentration-dependent manner in roxarsone-treated samples compared with PBS controls (P<0.05), while the data from samples treated with 20 μM NaAsO? were comparable to those from 500 μM roxarsone-treated samples. The MN frequency of V79 cells treated with roxarsone was higher than that in the negative control but lower than the frequency in cells treated with 20 μM NaAsO?. A dose- and time-dependent response in MN induction was observed at 10, 50, 100 and 500 μM doses of roxarsone after 12-48 h exposure time. The DNA damage in V79 cells treated with 500 μM roxarsone was similar to cells exposed to 20 μM NaAsO?. The uptake of cells was correlated with the DNA damage caused by roxarsone. This investigation depicts the genotoxic potentials of roxarsone to V79 cells, which could lead to further advanced studies on the genotoxicity of roxarsone.     

Inherited susceptibility to bleomycin-induced micronuclei: correlating polymorphisms in GSTT1, GSTM1 and DNA repair genes with mutagen sensitivity

Susceptibility to DNA damage varies among individuals and sensitivity to bleomycin (BLM) may reflect the inter-individual differences. BLM sensitivity in part may be explained by inherited differences in DNA repair genes. We investigated the association between genetic polymorphisms in the GSTT1, GSTM1, XPD, XRCC1 and XRCC3 genes and the levels of spontaneous and BLM-induced DNA damage in peripheral blood lymphocytes from 200 healthy, unexposed individuals. The investigation of BLM sensitivity on cancer- or disease-free subjects and not occupationally exposed to known mutagen represents the strengths of the present study, as the detection of genetic damage is not biased by any disease- and occupational-related factor. The micronucleus (MN) assay was used to detect the spontaneous and BLM-induced genetic damage whereas, genotype analysis was carried out using methods based on polymerase chain reaction. Poisson regression analysis showed that subject's age, gender and smoking status had no effect on the spontaneous and BLM-induced MN frequencies. Genotype analysis revealed a clear association between GSTT1-null and XPD polymorphisms and both spontaneous and BLM-induced MN frequencies, whereas the effect of the XRCC1 polymorphism was marginally significant only with regard to spontaneous MN frequency. Genotype analysis did not reveal a clear association between the other studied SNPs (GSTM1 and XRCC3) and MN frequencies. Poisson regression analysis revealed no association between the score of protective alleles and the frequency of spontaneous MN. However, an increased number of protective alleles was significantly associated with a lower frequency of BLM-induced MN (P=0.0003). This finding highlights the genetic basis for BLM sensitivity, which could be a valid and useful surrogate for identifying genotypes that might increase susceptibility in population exposed to carcinogens. Further investigations in a large sample size and including more SNPs, reflecting the complexity of DNA repair machinery, might lead to the identification of a genetic profile responsible for the susceptibility to genotoxicants, with a far-reaching long-term impact on primary prevention and early detection of disease associated genes.     

Relationship between the capacity to repair 8-oxoguanine, biomarkers of genotoxicity and individual susceptibility in styrene-exposed workers

Genotoxic effects related to exposure to styrene have been a matter of investigation for many years by employing markers of exposure, effect and susceptibility. The role of individual DNA-repair capacity in response to exposure to styrene may explain the controversial results so far obtained, but it is still scarcely explored. In the present study, we measured capacity to repair oxidative DNA damage in cell extracts obtained from 24 lamination workers occupationally exposed to styrene and 15 unexposed controls. The capacity to repair oxidative DNA damage was determined by use of a modified comet assay, as follows: HeLa cells, pre-treated with photosensitizer and irradiated with a halogen lamp in order to induce 7,8-dihydroxy-8-oxoguanine, were incubated with cell extracts from mononuclear leukocytes of each subject. The level of strand breaks reflects the removal of 7,8-dihydroxy-8-oxoguanine from substrate DNA by the enzymatic extract. In styrene-exposed subjects a moderate, non-significant increase in oxidative DNA repair was observed. Stratification for sex and smoking habit showed that unexposed males (P=0.010) and unexposed smokers (P=0.037) exhibited higher DNA-repair rates. The repair capacity did not correlate with parameters of styrene exposure and biomarkers of genotoxic effects (DNA strand breaks, N1-styrene-adenine DNA adducts, chromosomal aberrations and mutant frequencies at the HPRT locus). Significantly higher levels of DNA-repair capacity were observed in carriers of GSTM1-plus, compared to those with a deletion in GSTM1. The DNA-repair capacity was significantly lower in individuals with variant Gln/Gln genotype in XRCC1 Arg399Gln than in those with heterozygous Arg/Gln and wild-type Arg/Arg genotypes. Significantly lower repair capacity was also found in individuals with the wild-type Lys/Lys genotype in XPC Lys939Gln as compared with those homozygous for the Gln/Gln variant genotype.     

Influence of DNA-repair gene variants on the micronucleus frequency in thyroid cancer patients

The role of different DNA-repair genes (OGG1, XRCC1, XRCC2 and XRCC3) on both the spontaneous and the induced frequency of micronuclei (MN) has been studied in the lymphocytes of a group of 114 patients with differentiated thyroid cancer (DTC). Induction of MN was achieved by treatment of the lymphocytes with 0.5 Gy of gamma-radiation.The selected genes are involved in base-excision repair (BER) (OGG1, Ser326Cys; XRCC1, Arg280His and Arg399Gln), and in homologous recombination repair (HRR) (XRCC2, Arg188His and XRCC3, IVS5-14G). Genotyping was carried out by use of the iPLEX (Sequenom) technique.Results indicate that only the OGG1-Ser326Cys polymorphism was able to modulate the MN frequency. This effect was only observed in the spontaneous MN frequency (P = 0.016), but not in the MN frequency induced after irradiation. In addition, a strong correlation was observed between spontaneous and induced MN frequency, which would suggest an underlying genetic background.     

XRCC1 Arg399Gln was associated with repair capacity for DNA damage induced by occupational chromium exposure

ABSTRACT: BACKGROUND: Occupational chromium exposure may induce DNA damage and lead to lung cancer and other work-related diseases. DNA repair gene polymorphisms, which may alter the efficiency of DNA repair, thus may contribute to genetic susceptibility of DNA damage. The aim of this study was to test the hypothesis that the genetic variations of 9 major DNA repair genes could modulate the hexavalent chromium (Cr (VI))-induced DNA damage. FINDINGS: The median (P25-P75) of Olive tail moment was 0.93 (0.58-1.79) for individuals carrying GG genotype of XRCC1 Arg399Gln (G/A), 0.73 (0.46-1.35) for GA heterozygote and 0.50 (0.43-0.93) for AA genotype. Significant difference was found among the subjects with three different genotypes (P = 0.048) after adjusting the confounding factors. The median of Olive tail moment of the subjects carrying A allele (the genotypes of AA and GA) was 0.66 (0.44-1.31), which was significantly lower than that of subjects with GG genotype (P = 0.043). The A allele conferred a significantly reduced risk of DNA damage with the OR of 0.39 (95% CI: 0.15-0.99, P = 0.048). No significant association was found between the XRCC1Arg194Trp, ERCC1 C8092A, ERCC5 His1104Asp, ERCC6 Gly399Asp, GSTP1 Ile105Val, OGG1 Ser326Cys, XPC Lys939Gln, XPD Lys751Gln and DNA damage. CONCLUSION: The polymorphism of Arg399Gln in XRCC1 was associated with the Cr (VI)- induced DNA damage. XRCC1 Arg399Gln may serve as a genetic biomarker of susceptibility for Cr (VI)- induced DNA damage.     

A genotoxicity study on N-acryloyl-N′-phenylpiperazine: implications of aneugenic effects in risk evaluations

Further to a previous genotoxicity study, we analyzed sister-chromatid exchange (SCE) and DNA-repair induction (V79 and EUE cells in vitro) and DNA damage (rat liver in vivo) with regard to N-acryloyl-N-phenylpiperazine (AcrNPP), a chemical proposed for biomaterial polymerization which contains an aromatic tertiary amino function in a piperazine cycle. This chemical induced SCEs in a dose-dependent fashion (up to ≈ 3.7 times the control value), while it was negative for DNA-repair induction and weakly yeat significantly positive for in vivo DNA damage (maximum increase ≈ 1.4 times the control value). Taken together with our previous genotoxicity data on AcrNPP and structurally related compounds, the present results confirm that aneuploidy is a possible major effect of aromatic tertiary amines. As regards exposure to aneugenic agents, considerations on cancer risk evaluation are presented.     

Are genetic polymorphisms in OGG1, XRCC1 and XRCC3 genes predictive for the DNA strand break repair phenotype and genotoxicity in workers exposed to low dose ionising radiations?

Identification of higher risk individuals carrying genetic polymorphisms responsible for reduced DNA repair capacity has substantial preventive implications as these individuals could be targeted for cancer prevention. We have conducted a study to assess the predictivity of the OGG1, XRCC1 and XRCC3 genotypes and the in vitro single strand break repair phenotype for the induction of genotoxic effects. At the population level, a significant contribution of the OGG1 genotypes to the in vitro DNA strand break repair capacity was found. At an individual level, the OGG1 variants Ser/Cys and Cys/Cys genotypes showed a slower in vitro DNA repair than the Ser/Ser OGG1genotype. A multivariate analysis performed with genotypes, age, cumulative dose, exposure status and smoking as independent variables indicated that in the control population, repair capacity is influenced by age and OGG1 polymorphisms. In the exposed population, DNA damage is greater in older men and in smokers. Repair capacity is slower in individuals with Ser/Cys or Cys/Cys OGG1 genotypes compared to those with the Ser/Ser OGG1 genotype. Micronuclei (MN) frequencies increased with age and the cumulative dose of gamma-rays. Analysis of the total population revealed that genetic polymorphisms in XRCC1 resulted in higher residual DNA (RDNA) values and the Met/Met variant of XRCC3 resulted in an increased frequency of micronuclei. The analysis confirms that MN frequencies are reliable biomarkers for the assessment of genetic effects in workers exposed to ionising radiation (IR). A combined analysis of the three genotypes, OGG1, XRCC1 and XRCC3 polymorphisms is advised in order to assess individual susceptibility to ionising radiation. As an alternative or complement, the in vitro DNA strand break repair phenotype which integrates several repair pathways is recommended. Smokers with OGG1 polymorphisms who are exposed to ionising radiation represent a specific population requiring closer medical surveillance because of their increased mutagenic/carcinogenic risk.     

Relationship between the capacity to repair 8-oxoguanine, biomarkers of genotoxicity and individual susceptibility in styrene-exposed workers

Genotoxic effects related to exposure to styrene have been a matter of investigation for many years by employing markers of exposure, effect and susceptibility. The role of individual DNA-repair capacity in response to exposure to styrene may explain the controversial results so far obtained, but it is still scarcely explored. In the present study, we measured capacity to repair oxidative DNA damage in cell extracts obtained from 24 lamination workers occupationally exposed to styrene and 15 unexposed controls. The capacity to repair oxidative DNA damage was determined by use of a modified comet assay, as follows: HeLa cells, pre-treated with photosensitizer and irradiated with a halogen lamp in order to induce 7,8-dihydroxy-8-oxoguanine, were incubated with cell extracts from mononuclear leukocytes of each subject. The level of strand breaks reflects the removal of 7,8-dihydroxy-8-oxoguanine from substrate DNA by the enzymatic extract.In styrene-exposed subjects a moderate, non-significant increase in oxidative DNA repair was observed. Stratification for sex and smoking habit showed that unexposed males (P = 0.010) and unexposed smokers (P = 0.037) exhibited higher DNA-repair rates. The repair capacity did not correlate with parameters of styrene exposure and biomarkers of genotoxic effects (DNA strand breaks, N1-styrene-adenine DNA adducts, chromosomal aberrations and mutant frequencies at the HPRT locus). Significantly higher levels of DNA-repair capacity were observed in carriers of GSTM1-plus, compared to those with a deletion in GSTM1. The DNA-repair capacity was significantly lower in individuals with variant Gln/Gln genotype in XRCC1 Arg399Gln than in those with heterozygous Arg/Gln and wild-type Arg/Arg genotypes. Significantly lower repair capacity was also found in individuals with the wild-type Lys/Lys genotype in XPC Lys939Gln as compared with those homozygous for the Gln/Gln variant genotype.     

Cytogenetic effects induced by Prestige oil on human populations: the role of polymorphisms in genes involved in metabolism and DNA repair

The spill from the oil tanker Prestige (NW Spain, November 2002) was perhaps the biggest ecological disaster that happened worldwide in the last decades. As a consequence of this catastrophe a general concern led to a huge mobilization of human and technical resources. Given that no information was reported in the scientific literature regarding to the chronic repercussions to human health of exposure to oil spills, a pilot study was performed by our group revealing some increased genotoxic effects in the subjects exposed to the oil during cleaning activities. Due to the seriousness of the results, we extended our study comprising a larger population and including an extensive evaluation of the main polymorphic sites in metabolizing and DNA-repair genes. General increases in micronucleus (MN) frequency and decreases in the proliferation index were observed in individuals with longer time of exposure. Age was a significant predictor of MN frequency. CYP1A1 3'-UTR, EPHX1 codons 113 and 139, GSTP1, GSTM1 and GSTT1 metabolic polymorphisms, and XRCC3 codon 241 and XPD codon 751 repair polymorphisms influenced cytogenetic damage levels. In view of these results, it seems essential to pay more attention to the chronic human health effects of exposure to oil and to focus new studies on such a relevant but overlooked public health field that involves a large number of people all over the world.     

Assessment of the genotoxicity in toad Bufo raddei exposed to petrochemical contaminants in Lanzhou Region, China

Single cell gel electrophoresis or comet assay, micronucleus (MN) test and global DNA methylation detection were used to assess the genotoxicity in toad Bufo raddei exposed to the petrochemical (mainly oil and phenol) polluted area in Lanzhou Region (LZR) comparing with a relatively unpolluted area in Liujiaxia Region (LJXR). The results from the present study indicated that DNA damage and MN frequency in toad from LZR were significantly higher than those from LJXR at the same sampling month, whereas the degree of global DNA methylation was lower, which implies that the petrochemical contaminants at environmental level in LZR were genotoxic to B. raddei. The degree of genotoxic damage was obviously related with the extent of pollution among the three sampling months in LZR. The significantly positive correlations between DNA damage and concentrations of oil and/or phenol existed in liver cells but erythrocytes, implying that liver is more suitable as a sentinel tissue for the assessment of genotoxic impact of low-level contamination. The results from both comet assay and global DNA methylation detection on liver cells showed that the genotoxicity varied significantly with oil and/or phenol concentrations, suggesting that these two methods are relatively sensitive and suitable for monitoring the genotoxicity of petrochemical pollutants on amphibians.     

Genetic polymorphisms and micronucleus formation: a review of the literature

The formation of micronuclei (MN) is extensively used in molecular epidemiology as a biomarker of chromosomal damage, genome instability, and eventually of cancer risk. The occurrence of MN represents an integrated response to chromosome-instability phenotypes and altered cellular viabilities caused by genetic defects and/or exogenous exposures to genotoxic agents. The present article reviews human population studies addressing the relationship between genetic polymorphisms and MN formation, and provides insight into how genetic variants could modulate the effect of environmental exposures to genotoxic agents, host factors (gender, age), lifestyle characteristics (smoking, alcohol, folate), and diseases (coronary artery disease, cancer). Seventy-two studies measuring MN frequency either in peripheral blood lymphocytes or exfoliated cells were retrieved after an extensive search of the MedLine/PubMed database. The effect of genetic polymorphisms on MN formation is complex, influenced to a different extent by several polymorphisms of proteins or enzymes involved in xenobiotic metabolism, DNA repair proteins, and folate-metabolism enzymes. This heterogeneity reflects the presence of multiple external and internal exposures, and the large number of chromosomal alterations eventually resulting in MN formation. Polymorphisms of EPHX, GSTT1, and GSTM1 are of special importance in modulating the frequency of chromosomal damage in individuals exposed to genotoxic agents and in unexposed populations. Variants of ALDH2 genes are consistently associated with MN formation induced by alcohol drinking. Carriers of BRCA1 and BRCA2 mutations (with or without breast cancer) show enhanced sensitivity to clastogens. Some evidence further suggests that DNA repair (XRCC1 and XRCC3) and folate-metabolism genes (MTHFR) also influence MN formation. As some of the findings are based on relatively small numbers of subjects, larger scale studies are required that include scoring of additional endpoints (e.g., MN in combination with fluorescent in situ hybridization, analysis of nucleoplasmic bridges and nuclear buds), and address gene-gene interactions.     

Correlation between base-excision repair gene polymorphisms and levels of in-vitro BPDE-induced DNA adducts in cultured peripheral blood lymphocytes

In vitro benzo[a]pyrene diol epoxide (BPDE)-induced DNA adducts in cultured peripheral lymphocytes have been shown to be a phenotypic biomarker of individual’s DNA repair phenotype that is associated with cancer risk. In this study, we explored associations between genotypes of base-excision repair genes (PARP1 Val762Ala, APEX1 Asp148Glu, and XRCC1 Arg399Gln) and in vitro BPDE-induced DNA adducts in cultured peripheral blood lymphocytes in 706 cancer-free non-Hispanic white subjects. We found that levels of BPDE-induced DNA adducts were significantly higher in ever smokers than in never smokers and that individuals with the Glu variant genotypes (i.e., Asp/Glu and Glu/Glu) exhibited lower levels of BPDE-induced DNA adducts than did individuals with the common Asp/Asp homozygous genotype (median RAL levels: 32.0 for Asp/Asp, 27.0 for Asp/Glu, and 17.0 for Glu/Glu, respectively; P _trend = 0.030). Further stratified analysis showed that compared with individuals with the common APEX1-148 homozygous Asp/Asp genotype, individuals with the APEX1-148Asp/Glu genotype or the Glu/Glu genotype had a lower risk of having higher-level adducts (adjusted OR = 0.60, 95% CI: 0.36–0.98 and adjusted OR = 0.47, 95% CI: 0.26–0.86, respectively; P _trend = 0.012) among smokers. Such an effect was not observed in non-smokers. However, there was no significant interaction between the APEX1 Asp148Glu polymorphism and smoking exposure in this study population (P = 0.512). Additional genotype-phenotype analysis found that the APEX1-148Glu allele had significantly increased expression of APEX1 mRNA in 270 Epstein-Barr virus-transformed lymphoblastoid cell lines, which is likely associated with more active repair activity. Our findings suggest that the functional APEX1-148Glu allele is associated with reduced risk of having high levels of BPDE-induced DNA adducts mediated with high levels of mRNA expression.     

Altered gene expression profiles and higher frequency of spontaneous DNA strand breaks in APEX2-null thymus

A second class II AP endonuclease, APEX2, possesses strong 3'-5' exonuclease and 3'-phosphodiesterase activities but only very weak AP-endonuclease activity. APEX2 associates with proliferating cell nuclear antigen (PCNA), and the progression of S phase of the cell cycle is accompanied by its expression. APEX2-null mice exhibit severe dyslymphopoiesis in thymus as well as moderate dyshematopoiesis and growth retardation. Comparative gene expression profiling of wild-type and APEX2-null mice using an oligonucleotide microarray revealed that APEX2-null thymus has significantly altered gene expression profiles, reflecting its altered populations of thymocytes. Beyond these altered populations, APEX2-null thymus exhibits significant alterations in expression of genes involved in DNA replication, recombination and repair, including Apex1, Exo1 and Fen1 as well as master genes for the DNA damage response, such as E2f1, Chek1, and proapoptotic genes. We therefore examined the extent of DNA strand breakage, and found that both of single-strand breaks detected as comets and double-strand breaks detected as gammaH2AX foci were significantly higher in frequency in most APEX2-null thymocytes compared to wild-type thymocytes. This higher frequency of DNA breaks was accompanied by increased expression of PCNA and increased phosphorylation of p53 at Ser23 and to a lesser extent, at Ser18. The present study clearly demonstrates that APEX2-null lymphocytes have a higher frequency of DNA breaks, indicating that APEX2 may play an important role(s) during their generation and/or repair.