Chromosomal aberrations under basal conditions and after treatment with X-ray in human lymphocytes as related to the GSTM1 genotype

Assessment of individual susceptibility to baseline DNA and cytogenetic damage in a healthy Turkish population: evaluation with lifestyle factors

BACKGROUND

Cytogenetic biomarkers are most frequently used well-established endpoints in human population studies with their sensitivity for measuring exposure to genotoxic agents. They have an important role as early predictors of cancer risk. Identification of individual genotypes of metabolic gene polymorphisms helps to understand the modulation of cancer susceptibility by environmental exposures, such as cigarette smoking and other lifestyle factors.

AIM

To evaluate individual susceptibility to chemicals, we determined individual DNA damage related to glutathione S-transferase (GST) genotypes (GSTM1, GSTT1, and GSTP1) in a Turkish population.

METHODS

Peripheral blood lymphocytes (PBL) and DNA samples of 127 subjects were analyzed for the presence of DNA damage, using single-cell gel electrophoresis (the Comet assay), and for cytogenetic parameters (chromosomal aberrations [CAs], bleomycin-induced CA, and a cytokinesis-blocked micronucleus assay), and the polymerase chain reaction/restriction fragment length polymorphism method, respectively.

RESULTS

Individuals carrying a GSTT1-null allele showed higher frequencies of CA and micronucleus (MN) (p=0.026, p=0.003, respectively), whereas the GSTM1-null and GSTP1 mutant genotypes did not show any differences in cytogenetic parameters. Our findings demonstrated that none of the lifestyle factors (smoking, alcohol drinking, dietary habits, vitamin intake, and physical activity), except for vitamin intake (p=0.002), were significantly associated with the studied cytogenetic parameters.

CONCLUSION

Our results suggest that the GSTT1 gene polymorphism may influence the baseline cytogenetic frequency in a healthy population.

Correlations between DNA polymorphism and frequencies of gamma-radiation induced and spontaneous cytogenetic damage

With the aim of developing genetic tests for elevated and reduced radiation sensitivity, the authors studied the correlations between various genotypes and frequencies of spontaneous and radiation-induced chromosome aberrations in human lymphocytes. Cytogenetic analysis and genotyping (19 sites of detoxification and DNA repair genes) were carried out for a group of cleanup workers of the Chernobyl nuclear power plant accident (83 people) and for a uniform control group of volunteers (97 people). In both cases, the frequencies of chromosome type aberrations were higher in carriers of minor alleles of gene XPD [sites T2251G (Lys751Gln) and G862A (Asp312Asn)] and the "positive" genotypes GSTM1/GSTT1. The polymorphism of these genes did not affect the frequency of aberrations induced by gamma radiation in the control group (1 Gy in vitro), which was associated with genotypes by loci OGG1, XRCC1, and CYP1A1. Thus, in the control group, spontaneous and in vitro induced cytogenetic effects are associated with different groups of polymorphic genes. In the cleanup workers group (irradiated in vivo), the elevated frequency of aberrations was observed in the carriers of those genotypes that typically have a higher level of spontaneous (but not in vitro induced) cytogenetic damage in the control. The genotype "minor XPD + insertion GST," having an estimated incidence of 64% in central Russia, was characterized and found to be strongly associated with an elevated frequency of chromosome type aberrations following irradiation in vivo (OR = 6.9; p = 0.008).

Genotoxic damage in hospital workers exposed to ionizing radiation and metabolic gene polymorphisms

Of all workers exposed globally to synthetic sources of radiation, medical personnel represent the largest group, but receive relatively low doses. Accidental or therapeutic acute radiation exposure of humans was observed to induce various forms of cytogenetic damage, including the possibility of increasing the incidence of micronuclei (MN) and chromosomal aberrations (CA). The aim of this study was to assess occupationally induced chromosomal damage in a large population of hospital workers exposed to low doses of ionizing radiation (IR). The cytokinesis-block MN and comet assays were used to examine peripheral blood lymphocytes (PBL) of 31 exposed workers to IR and 33 control subjects corresponding in gender, age, and smoking. Glutathione S-transferases (GSTM1, GSTT1, and GSTP1) are postulated to be involved in the detoxification of endogenous and exogenous genotoxicants. The association between these biomarkers and polymorphic genes of xenobiotic metabolizing enzymes was thus also assessed. MN frequency was significantly higher in the exposed subjects compared controls. Comet assay results showed a significant increase of tail length in workers exposed to IR. Data obtained suggest that GSTM1, GSTT1, and GSTP1 polymorphism do not modify significantly the genotoxic potential of IR. Therefore, the exposed medical personnel need to carefully apply radiation protection procedures and minimize, as low as possible, IR exposure to avoid possible genotoxic effects.

Patterns of persistent DNA damage associated with sun exposure and the glutathione S-transferase M1 genotype in melanoma patients

Solar radiation can lead to changes affecting DNA metabolism resulting in loss of DNA integrity. Skin specimens obtained from melanoma patients treated at the Memorial Sloan-Kettering Cancer Center were used to study patterns of DNA fragmentation using the comet assay and levels of deletions in mitochondrial DNA (mtDNA) using real-time PCR. Skin specimens were classified according to the glutathione S-transferase M1 (GSTM1) genotype (either wild type [WT] or null) and patient sunburn history. GSTM1 null individuals with a sunburn history showed increased levels of both DNA fragmentation by comet assays and mtDNA deletions relative to GSTM1 WT patients with little or no sunburn history. Microarray analyses identified a number of genes whose expression was upregulated >or=5-fold in cells from GSTM1-null patients or from those reporting histories of sunburn. These genes encoded small molecule transporters, various growth factor/chemokine receptors, transcription factors and tumor suppressors. Of 17 genes directly involved in DNA repair, three DNA ligases were highly upregulated while the RAD23 UV excision repair gene and the Growth Arrest and DNA Damage gene (GADD45) were downregulated. These findings support the idea that exposure to solar radiation early in life may induce long-term cellular changes that lead to persistent DNA damage and altered patterns of gene expression.

Polymorphism of detoxification genes and cell resistance to mutagens in patients with Ehlers-Danlos syndrome

Study of polymorphism in 3 genes of the glutathione S-transferase family (GSTM1, GSTT1, and GSTP1) in children with Ehlers-Danlos syndrome whose cells were defective in repair of gamma-induced DNA damages revealed accumulation of GSTM1(+) genotypes compared to children of the control group. Generation of reactive oxygen species by neutrophils from patients with this syndrome was higher than in healthy donors. Our results indicate that glutathione S-transferase genes are involved in the resistance to mutagenic agents and demonstrate medical and genetic peculiarities of patients with Ehlers-Danlos syndrome.

Chromosomal aberrations in tire plant workers and interaction with polymorphisms of biotransformation and DNA repair genes

We evaluated chromosomal aberrations in lymphocytes of 177 workers exposed to xenobiotics in a tire plant and in 172 controls, in relation to their genetic background. Nine polymorphisms in genes encoding biotransformation enzymes and nine polymorphisms in genes involved in main DNA repair pathways were investigated for possible modulation of chromosomal damage. Chromosomal aberration frequencies were the highest among exposed smokers and the lowest in non-smoking unexposed individuals (2.5+/-1.8% vs. 1.7+/-1.2%, respectively). The differences between groups (ANOVA) were borderline significant (F=2.6, P=0.055). Chromosomal aberrations were higher in subjects with GSTT1-null (2.4+/-1.7%) than in those with GSTT1-plus genotype (1.8+/-1.4%; F=7.2, P=0.008). Considering individual groups, this association was significant in smoking exposed workers (F=4.4, P=0.040). Individuals with low activity EPHX1 genotype exhibited significantly higher chromosomal aberrations (2.3+/-1.6%) in comparison with those bearing medium (1.7+/-1.2%) and high activity genotype (1.5+/-1.2%; F=4.7, P=0.010). Both chromatid- and chromosome-type aberration frequencies were mainly affected by exposure and smoking status. Binary logistic regression analysis revealed that frequencies of chromatid-type aberrations were modulated by NBS1 Glu185Gln (OR 4.26, 95%CI 1.38-13.14, P=0.012), and to a moderate extent, by XPD Lys751Gln (OR 0.16, 95%CI 0.02-1.25, P=0.081) polymorphisms. Chromosome-type aberrations were lowest in individuals bearing the EPHX1 genotype conferring the high activity (OR 0.38, 95%CI 0.15-0.98, P=0.045). Present results show that exposed individuals in the tire production, who smoke, exhibit higher chromosomal aberrations frequencies, and the extent of chromosomal damage may additionally be modified by relevant polymorphisms.

Acetylsalicylic acid exhibits anticlastogenic effects on cultured human lymphocytes exposed to doxorubicin

Acetylsalicylic acid (ASA) is a non-steroidal anti-inflammatory drug (NSAID) with many pharmacological properties, such as anti-inflammatory, antipyretic and analgesic. Many studies have suggested the possible efficiency of ASA and other NSAIDs in preventing cancer. ASA could also have antimutagenic and antioxidant properties. The aim of this study was to investigate the possible clastogenic and anticlastogenic effects of different concentrations of ASA on doxorubicin-induced chromosomal aberrations in human lymphocytes. Human blood samples were obtained from six healthy, non-smoking volunteers; and the chromosomal aberration assay was carried out using conventional techniques. The parameters analyzed were mitotic index, total number of chromosomal aberrations and percentage of aberrant metaphases. The concentrations of ASA (25, 50 or 100 microg/mL) tested in combination with DXR (0.2 microg/mL) were established on the basis of the results of the mitotic index. The treatment with ASA alone was neither cytotoxic nor clastogenic (p>0.01). In lymphocyte cultures treated with different combinations of ASA and DXR, a significant decrease in the total number of chromosome aberrations was observed compared with DXR alone (p<0.01). This protective effect of ASA on DXR-induced chromosomal damage was obtained for all combinations, and it was most evident when ASA was at 25.0 microg/mL. In our experiments, ASA may have acted as an antioxidant and inhibited the chromosomal damage induced by the free radicals generated by DXR. The identification of compounds that could counteract the free radicals produced by doxorubicin could be of possible benefits against the potential harmful effects of anthracyclines. The results of this study show that there is a relevant need for more investigations in order to elucidate the mechanisms underlying the anticlastogenic effect of ASA.

Basal and induced micronucleus frequencies in human lymphocytes with different GST and NAT2 genetic backgrounds

Basal and induced frequencies of genetic damage can be modulated by different host factors, including genes involved in phase II metabolism. Since polymorphic variants in the glutathione S-transferase (GST) and N-acetyl transferase (NAT) genes have been associated with cancer risk, we explored the possible links between GSTM1, GSTP1, GSTT1 and NAT2 variants and the frequency of micronuclei (MN) in human lymphocytes. This exploratory study was carried out in 30 thyroid cancer patients, before and after receiving an average dose of 109.9+/-1.3 mCi radioactive iodine as a co-adjuvant therapy. The results indicate that none of the polymorphisms studied show any kind of association with the basal level of micronuclei. When the same patients were followed after radioiodine exposure, a significant increase in the frequency of MN was observed in practically all of them (28/30), indicating the genotoxic activity of the ionising radiation exposure. The increase in MN frequency was not associated with any of the GST polymorphisms evaluated. Nevertheless, the presence of slow acetylator phenotypes and, in particular, the presence of the NAT2*7 allele was significantly associated with a lower increase of the MN frequency after radioiodine treatment.

Assessment of abnormal DNA repair responses and genotoxic effects in lead exposed workers

BACKGROUND

One of the main sources of occupational exposure to lead (Pb) in Turkey is in workers of battery industries. Genotoxic studies in human populations exposed to this metal have had conflicting results.

METHODS

Genotoxic effects of Pb were studied in blood cell samples from workers of battery manufactures exposed to Pb compounds by chromosomal aberration (CA) assay and X-ray induced challenge (XRC) assay to assess DNA damage and interference with DNA repair processes after an in vitro exposure of X-ray (1 Gy). The battery manufacturers (n=23) and 23 people who were not occupationally exposed to lead compounds were selected as a control group and classified into categories according to their blood lead levels.

RESULTS

The CA frequencies in the exposed and control group were not significantly different (P>0.05) by conventional CA (CCA) assay, however, the XRC assay demonstrated significantly elevated CAs (P<0.05). Statistically non-significant but reduced DNA repair responses have also been observed in lead exposed workers.

CONCLUSION

The results of this study showed significant increases in the CAs by XRC assay in Pb exposed workers compared to CCA assay. Our data suggests that Pb exposure may cause reduction in DNA repair capacity and these individuals will be more prone to DNA damage. Therefore, preventive measures should be improved against genotoxic risk in workplaces.

Human population studies with cytogenetic biomarkers: review of the literature and future prospectives

Cytogenetic biomarkers are by far the most frequently used endpoints in human population studies. Their sensitivity for measuring exposure to genotoxic agents and their role as early predictors of cancer risk have contributed to this success. In this article, we present an overview of the last 25 years of population studies with cytogenetic biomarkers, describing the evolution of this research and addressing the most promising innovations for the future. The evaluation has been restricted to the most popular assays, i.e., chromosomal aberrations (CAs) and micronucleus (MN), which are considered to be causally related to early stages of chronic diseases, especially cancer, and may therefore play a major role in prevention. An extensive literature search covering the period 1 January 1980 to 31 December 2003 was performed using the Medline/PubMed database. A total of 833 population studies using CAs and 434 using matched MN inclusion criteria were included in the analysis. We report the distribution of selected papers by year of publication, country, language, agents investigated, and methods employed. The state of the art and future prospects regarding cytogenetic techniques and epidemiologic and statistical methods are discussed. The role of susceptibility and its potential impact on genotoxic damage are discussed with special attention to the effect of major genetic polymorphisms on the baseline frequency of CAs and micronuclei.

Diazepam and propofol used as anesthetics during open-heart surgery do not cause chromosomal aberrations in peripheral blood lymphocytes

Diazepam is a benzodiazepine with anticonvulsant, anxiolytic, sedative and muscle-relaxing properties. Many aspects of its toxicity have been investigated, including genotoxic and carcinogenic effects in various model systems. However, it is still unclear whether diazepam is in fact a genotoxic agent. Propofol is a rapid-onset, short-acting intravenous anesthetic agent. It is used widely for the induction and maintenance of anesthesia as well as for long-term sedation in intensive care units. There is limited information in the literature on its genotoxic effects. Both drugs are commonly used as anesthetic in patients undergoing open-heart surgery. Therefore, we investigated the possible genotoxic effects of propofol and diazepam in those patients, using a chromosomal aberration (CA) assay. Peripheral blood samples were collected from 45 patients before induction of anesthesia and at the end of the anesthesia with diazepam or propofol. In Group I (n=24), anesthesia was induced with 0.2 mg kg(-1) diazepam and 10 microg kg(-1) fentanyl. In Group II (n=21), anesthesia was induced with 1 mg kg(-1) propofol and 10 microg kg(-1) fentanyl. Pancuronium bromide (0.1 mg kg(-1)) was administered for skeletal muscle relaxation in both groups. Anesthesia was maintained by diazepam administration at 5 mg kg(-1) in Group I or by continuous propofol administration at 2-4 mg (kg h)(-1) in Group II. All patients received 0.02 mg kg(-1) pancuronium and 5 microg kg(-1) fentanyl boluses at 30-40 min intervals for anesthesia maintenance. Body temperature was controlled during bypass in the two groups. We found that the mean frequency of CAs in both groups before and at the end of the anesthesia were not statistically significantly different. Our analysis also indicated that age, smoking habit and gender were not confounding factors. In conclusion, our results indicate that diazepam and propofol do not exert genotoxic effects in blood cells during open-heart surgery.

Lack of increased genetic damage in 1,3-butadiene-exposed Chinese workers studied in relation to EPHX1 and GST genotypes

1,3-Butadiene (BD) is an important industrial chemical and pollutant. Its ability to induce genetic damage and cause hematological malignancies in humans is controversial. We have examined chromosome damage by fluorescence in situ hybridization (FISH) and mutations in the HPRT gene in the blood of Chinese workers exposed to BD. Peripheral blood samples were collected and cultured from 39 workers exposed to BD (median level 2 ppm, 6 h time-weighted average) and 38 matched controls in Yanshan, China. No difference in the level of aneuploidy or structural changes in chromosomes 1, 7, 8, and 12 was detected in metaphase cells from exposed subjects in comparison with matched controls, nor was there an increase in the frequency of HPRT mutations in the BD-exposed workers. Because genetic polymorphisms in glutathione S-transferase (GST) enzymes and microsomal epoxide hydrolase (EPHX1) may affect the genotoxic effects of BD and its metabolites, we also related chromosome alterations and gene mutations to GSTT1, GSTM1 and EPHX1 genotypes. Overall, there was no effect of variants in these genotypes on numerical or structural changes in chromosomes 1, 7, 8 and 12 or on HPRT mutant frequency in relation to BD exposure, but the GST genotypes did influence background levels of both hyperdiploidy and HPRT mutant frequency. In conclusion, our data show no increase in chromosomal aberrations or HPRT mutations among workers exposed to BD, even in potentially susceptible genetic subgroups. The study is, however, quite small and the levels of BD exposure are not extremely high, but our findings in China do support those from a similar study conducted in the Czech Republic. Together, these studies suggest that low levels of occupational BD exposure do not pose a significant risk of genetic damage.

Assessment of individual sensitivity to ionizing radiation and DNA repair efficiency in a healthy population

Inter-individual variation in response to exposure to carcinogens has been ascribed to differences in carcinogen metabolism as well as to variability in DNA repair capacity (DRC). In order to investigate the role of inherited and acquired factors on individual variation in DNA repair capacity, a mutagen sensitivity assay was carried out on 31 healthy subjects. Fresh blood samples were irradiated with gamma-rays (2Gy) and the kinetics of DNA repair in leukocytes assessed by the comet assay 0, 15, and 30 min after irradiation. Whole blood cultures were set up to detect spontaneous and induced structural chromosomal aberrations in lymphocytes 48 h after irradiation. The results obtained were evaluated with respect to age, gender, smoking habits, occupational exposure to chemicals and metabolic genotype (NQO1, GSTM1 and GSTT1) of the study subjects. A higher frequency of radiation-induced aberrations was observed in GSTM1-positive individuals compared with GSTM1-null subjects (P=0.025), as well as in non-smokers compared with heavy smokers (P=0.05). Similar results were obtained by measuring residual DNA damage (RD) shortly after irradiation by means of the comet assay, with non-smokers showing a higher amount of RD compared with smokers (P=0.016). Moreover, a significant correlation (P=0.008) was observed between the amount of RD and the frequency of chromosome breaks after irradiation. The results of this pilot study suggest a modulator effect of smoking habits and GSTM1 genotype on the individual DNA repair capacity, possibly related to the higher expression of enzymes involved in the repair of oxidative DNA damage in heavy smokers and GSTM1-null subjects.