Rapid screening assay for mutagen sensitivity and DNA repair capacity in human peripheral blood lymphocytes

SOD1 is a synthetic lethal target in PPM1D-mutant leukemia cells

The DNA damage response is critical for maintaining genome integrity and is commonly disrupted in the development of cancer. PPM1D (protein phosphatase, Mg2+/Mn2+ dependent 1D) is a master negative regulator of the response; gain-of-function mutations and amplifications of PPM1D are found across several human cancers making it a relevant pharmacologic target. Here, we used CRISPR/Cas9 screening to identify synthetic-lethal dependencies of PPM1D, uncovering superoxide dismutase-1 (SOD1) as a potential target for PPM1D-mutant cells. We revealed a dysregulated redox landscape characterized by elevated levels of reactive oxygen species and a compromised response to oxidative stress in PPM1D-mutant cells. Altogether, our results demonstrate the protective role of SOD1 against oxidative stress in PPM1D-mutant leukemia cells and highlight a new potential therapeutic strategy against PPM1D-mutant cancers.

Spatial-temporal genome damaging in the blue crab Cardisoma guanhumi as ecological indicators for monitoring tropical estuaries

In this study, to better our understanding of the current state of conservation of Cardisoma guanhumi and its habitats, we evaluated the potential spatio-temporal genomic damage of this species across five estuaries in Brazil. The experiment was performed over two consecutive years, and the sampling was performed in the winter and summer seasons. Two genetic tests - micronucleus test and comet assay - were used to quantify the DNA damage. Unlike in the summers and in the winter of 2013, in the winter of 2012 a significant increase was noted in the frequency of micronucleated cells and genomic damage index. The occurrence of genomic damage coincided with the arrival of the harsh winter of 2012 as the water sourced from the coastal rivers significantly affected the estuarine species under study. Our results confirmed that this species was resilient to the atypical climatic conditions, which facilitated the generation of excessive waste.

Premature chromosome condensation assay to study influence of high-level natural radiation on the initial DNA double strand break repair in human G0 lymphocytes

The inherent capacity of individuals to efficiently repair ionizing radiation induced DNA double strand breaks (DSBs) may be inherited, however, it is influenced by several epigenetic and environmental factors. A pilot study tested whether chronic low dose natural radiation exposure influences the rejoining of initial DNA DSBs induced by a 2 Gy γ-irradiation in 22 individuals from high (>1.5 mGy/year) and normal (≤1.5 mGy/year) level natural radiation areas (H&NLNRA) of Kerala. Rejoining of DSBs (during 1 h at 37 °C, immediately after irradiation) was evaluated at the chromosome level in the presence and absence of wortmannin (a potent inhibitor of DSB repair in normal human cells) using a cell fusion-induced premature chromosome condensation (PCC) assay. The PCC assay quantitates DSBs in the form of excess chromosome fragments in human G₀ lymphocytes without the requirement for cell division. A quantitative difference was observed in the early rejoining of DNA DSBs between individuals from HLNRA and NLNRA, with HLNRA individuals showing a higher (P = 0.05) mean initial repair ratio. The results indicate an influence of chronic low dose natural radiation on initial DNA DSB repair in inhabitants of HLNRA of the Kerala coast.

Application of mutagen sensitivity assay in a glioma case-control study

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MSA is an appropriate molecular epidemiology tool in case control studies.

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Case-control status/exposure categories are not associated with the number of breaks.

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Cell lines of glioma patients did not show reduced DNA repair capacity in response to acrylamide in the MSA assay.

Few risk factors for glioma have been identified other than ionizing radiation. The alkylating agent acrylamide is a compound found in both occupational and the general environment and identified as one of the forty known or suspected neurocarcinogens in animal models. The mutagen sensitivity assay (MSA) has been used to indirectly show reduced DNA repair capacity upon exposure to ionizing radiation in those with glioma compared to controls. In this study, MSA was used to assess its applicability to a glioma case-control study and to test the hypothesis that subjects with glioma may have lower DNA repair capacity after exposure to selected potential human neurocarcinogens (i.e. acrylamide), compared to controls. Approximately 50 case and 50 control subjects were identified from a clinic-based study that investigated environmental risk factors for glioma, who completed an exposure survey, and had frozen immortalized lymphocytes available. A total of 50 metaphase spreads were read and reported for each participant. The association of case-control status with MSA for acrylamide, i.e. breaks per spread, was examined by multivariable logistic regression models. The mean number of breaks per slide was similar between hospital-based controls and cases. In addition, case-control status or exposure categories were not associated with the number of breaks per spread. Although the MSA has been shown as a useful molecular epidemiology tool for identifying individuals at higher risk for cancer, our data do not support the hypothesis that glioma patients have reduced DNA repair capacity in response to exposure to acrylamide. Further research is needed before the MSA is utilized in large-scale epidemiological investigations of alkylating agents.

Arsenic and ultraviolet radiation exposure: melanoma in a New Mexico non-Hispanic white population

Cases of cutaneous melanoma and controls were enrolled in a New Mexico population-based study; subjects were administered questionnaires concerning ultraviolet (UV) and inorganic arsenic (iAs) exposure. Historical iAs exposure was estimated. UV exposure estimates were also derived using geospatial methods. Drinking water samples were collected for iAs analysis. Blood samples were collected for DNA repair (Comet) and DNA repair gene polymorphism assays. Arsenic concentrations were determined in urine and toenail samples. UV exposures during the previous 90 days did not vary significantly between cases and controls. Mean (±SD) current home iAs drinking water was not significantly different for cases and controls [3.98 μg/L (±3.67) vs. 3.47 μg/L (±2.40)]. iAs exposure showed no effect on DNA repair or association with melanoma. Results did not corroborate a previously reported association between toenail As and melanoma risk. Arsenic biomarkers in urine and toenail were highly significantly correlated with iAs in drinking water. A UV-DNA repair interaction for UV exposure over the previous 7-90 days was shown; cases had higher DNA damage than controls at low UV values. This novel finding suggests that melanoma cases may be more sensitive to low-level UV exposure than are controls. A UV-APEX1 interaction was shown. Subjects with the homozygous rare APEX1 DNA repair gene allele had a higher risk of early melanoma diagnosis at low UV exposure compared with those with the homozygous wild type or the heterozygote. Notably, a UV-arsenic interaction on inhibition of DNA repair was not observed at iAs drinking water concentrations below 10 ppb (μg/L).

Effect of chronic low dose natural radiation in human peripheral blood mononuclear cells: Evaluation of DNA damage and repair using the alkaline comet assay

This study investigates whether peripheral blood mononuclear cells (PBMCs) from inhabitants of Kerala in southwest India, exposed to chronic low dose natural radiation in vivo (>1 mSv year(-1)), respond with a radioadaptive response to a challenging dose of gamma radiation. Toward this goal, PBMCs isolated from 77 subjects from high-level natural radiation areas (HLNRA) and 37 subjects from a nearby normal level natural radiation area (NLNRA) were challenged with 2 Gy and 4 Gy gamma radiation. Subjects from HLNRA were classified based on the mean annual effective dose received, into low dose group (LDG) and high dose group (HDG) with mean annual effective doses of 2.69 mSv (N=43, range 1.07 mSv year(-1) to 5.55 mSv year(-1)) and 9.62 mSv (N = 34, range 6.07 mSv year(-1) to 17.41 mSv year(-1)), respectively. DNA strand breaks and repair kinetics (at 7 min, 15 min and 30 min after 4 Gy) were evaluated using the alkaline single cell gel electrophoresis (comet) assay. Initial levels of DNA strand breaks observed after either a 2 Gy or a 4 Gy challenging dose were significantly lower in subjects of the HDG from HLNRA compared to subjects of NLNRA (2 Gy, P = 0.01; 4 Gy, P = 0.02) and LDG (2 Gy P = 0.01; 4 Gy, P=0.05). Subjects of HDG from HLNRA showed enhanced rejoining of DNA strand breaks (HDG/NLNRA, P = 0.06) during the early stage of repair (within 7 min). However at later times a similar rate of rejoining of strand breaks was observed across the groups (HDG, LDG and NLNRA). Preliminary results from our study suggest in vivo chronic low-level natural radiation provides an initial exposure that allows an adaptation to a subsequent higher radiation exposure, perhaps through improving DNA repair via an unknown mechanism. Therefore, further investigations would be necessary in this population to understand the biological and health effects of chronic low-level natural radiation exposures.

Exit from dormancy provokes DNA-damage-induced attrition in haematopoietic stem cells

Haematopoietic stem cells (HSCs) are responsible for the lifelong production of blood cells. The accumulation of DNA damage in HSCs is a hallmark of ageing and is probably a major contributing factor in age-related tissue degeneration and malignant transformation. A number of accelerated ageing syndromes are associated with defective DNA repair and genomic instability, including the most common inherited bone marrow failure syndrome, Fanconi anaemia. However, the physiological source of DNA damage in HSCs from both normal and diseased individuals remains unclear. Here we show in mice that DNA damage is a direct consequence of inducing HSCs to exit their homeostatic quiescent state in response to conditions that model physiological stress, such as infection or chronic blood loss. Repeated activation of HSCs out of their dormant state provoked the attrition of normal HSCs and, in the case of mice with a non-functional Fanconi anaemia DNA repair pathway, led to a complete collapse of the haematopoietic system, which phenocopied the highly penetrant bone marrow failure seen in Fanconi anaemia patients. Our findings establish a novel link between physiological stress and DNA damage in normal HSCs and provide a mechanistic explanation for the universal accumulation of DNA damage in HSCs during ageing and the accelerated failure of the haematopoietic system in Fanconi anaemia patients.

Recent physical activity in relation to DNA damage and repair using the comet assay

BACKGROUND

Limited evidence suggests that very high-intensity exercise is positively associated with DNA damage but moderate exercise may be associated with DNA repair.

METHODS

Participants were 220 healthy, Washington State 50- to 76-year-olds in the validity/biomarker substudy of the VITamins And Lifestyle (VITAL) cohort, who provided blood samples and completed questionnaires assessing recent physical activity and demographic and health factors. Measures included nested activity subsets: total activity, moderate- plus high-intensity activity, and high-intensity activity. DNA damage (n = 122) and repair (n = 99) were measured using the comet assay. Multivariate linear regression was used to estimate regression coefficients and associated 95% confidence intervals (CIs) for relationships between MET-hours per week of activity and each DNA outcome (damage, and 15- and 60-minute repair capacities).

RESULTS

DNA damage was not associated with any measure of activity. However, 60-minute DNA repair was positively associated with both total activity (β = 0.21, 95% CI: 0.0057-0.412; P = .044) and high-intensity activity (β = 0.31, 95% CI: 0.20-0.60; P = .036), adjusting for age, sex, BMI, and current multivitamin use.

CONCLUSIONS

This study is the first to assess broad ranges of activity intensity levels related to DNA damage and repair. Physical activity was unrelated to DNA damage but was associated with increased repair.

DNA repair deficiency in peripheral blood lymphocytes of endometrial cancer patients with a family history of cancer

BACKGROUND

Individual susceptibility to endogenous and/or exogenous DNA damage depends on DNA repair efficiency and can be evaluated using the comet assay with bleomycin as genotoxic agent. The aim of the study was to evaluate baseline and bleomycin-induced DNA damage and DNA repair capacity in peripheral blood lymphocytes (PBLs) of endometrial cancer (EC) patients considering a family history of cancer.

METHODS

DNA damage was analyzed in PBLs of 45 EC patients compared to a control group of 10 healthy women, using the comet assay. The level of DNA damage was determined by the% tail DNA.

RESULTS

The level of baseline DNA damage in PBLs of EC patients was significantly higher (% DNA in tail 9.31 ± 15.32) than in healthy women (% DNA in tail 3.41 ± 4.71) (P <0.01). PBLs of EC patients repaired less bleomycin-induced DNA damage (removed% DNA in tail 63.94 ± 20.92) than PBLs of healthy individuals (removed% DNA in tail 80.24 ± 3.03) (P <0.001). Efficiency of DNA repair in PBLs of EC patients depended on the family history of cancer. The amount of restored damaged DNA was significantly lower (removed% DNA in tail 36.24 ± 14.05%) in EC patients with a family history of cancer compared to patients with sporadic EC (removed% DNA in tail 64.91 ± 19.36%) (P <0.004).

CONCLUSIONS

Lymphocytes of EC patients are characterized by an increased basal level of DNA damage as well as deficiency in DNA repair. DNA repair is less efficient in PBLs of EC patients with a family history of cancer compared to patients with sporadic cancer.

LORD-Q: a long-run real-time PCR-based DNA-damage quantification method for nuclear and mitochondrial genome analysis

DNA damage is tightly associated with various biological and pathological processes, such as aging and tumorigenesis. Although detection of DNA damage is attracting increasing attention, only a limited number of methods are available to quantify DNA lesions, and these techniques are tedious or only detect global DNA damage. In this study, we present a high-sensitivity long-run real-time PCR technique for DNA-damage quantification (LORD-Q) in both the mitochondrial and nuclear genome. While most conventional methods are of low-sensitivity or restricted to abundant mitochondrial DNA samples, we established a protocol that enables the accurate sequence-specific quantification of DNA damage in >3-kb probes for any mitochondrial or nuclear DNA sequence. In order to validate the sensitivity of this method, we compared LORD-Q with a previously published qPCR-based method and the standard single-cell gel electrophoresis assay, demonstrating a superior performance of LORD-Q. Exemplarily, we monitored induction of DNA damage and repair processes in human induced pluripotent stem cells and isogenic fibroblasts. Our results suggest that LORD-Q provides a sequence-specific and precise method to quantify DNA damage, thereby allowing the high-throughput assessment of DNA repair, genotoxicity screening and various other processes for a wide range of life science applications.

Effects of a Mangifera indica L. stem bark extract and mangiferin on radiation-induced DNA damage in human lymphocytes and lymphoblastoid cells

OBJECTIVES

Mangifera indica L. (mango) stem bark aqueous extract (MSBE) that has antioxidant, anti-inflammatory and immunomodulatory properties, can be obtained in Cuba. It is rich in polyphenols, where mangiferin is the main component. In this study, we have tested DNA damage and protection effects of MSBE and mangiferin on primary human lymphocytes and lymphoblastoid cells.

MATERIAL AND METHODS

Cell suspensions were incubated with the products (50-1000 μg/ml) for experiments on damage induction, and evaluation of any potential protective effects (5-100 μg/ml) for 60 min at 37 °C. Irradiation was performed using a γ-ray source, absorbed dose 5 Gy. At the end of exposure, DNA damage, protection and repair processes were evaluated using the comet assay.

RESULTS

MSBE (100-1000 μg/ml) induced DNA damage in a concentration dependent manner in both cell types tested, primary cells being more sensitive. Mangiferin (200 μg/ml) only induced light DNA damage at higher concentrations. DNA repair capacity was not affected after MSBE or mangiferin exposure. On the other hand, MSBE (25 and 50 μg/ml) and mangiferin (5-25 ug/ml) protected against gamma radiation-induced DNA damage.

CONCLUSIONS

These results show MSBE has protector or harmful effects on DNA in vitro depending on the experimental conditions, which suggest that the extract could be acting as an antioxidant or pro-oxidant product. Mangiferin was involved in protective effects of the extract.

Specialty supplement use and biologic measures of oxidative stress and DNA damage

BACKGROUND

Oxidative stress and resulting cellular damage have been suggested to play a role in the etiology of several chronic diseases, including cancer and cardiovascular disease. Identifying factors associated with reduced oxidative stress and resulting damage may guide future disease-prevention strategies.

METHODS

In the VITamins And Lifestyle (VITAL) biomarker study of 209 persons living in the Seattle area, we examined the association between current use of several specialty supplements and oxidative stress, DNA damage, and DNA repair capacity. Use of glucosamine, chondroitin, fish oil, methylsulfonylmethane (MSM), coenzyme Q10 (CoQ10), ginseng, ginkgo, and saw palmetto was ascertained by a supplement inventory/interview, whereas the use of fiber supplements was ascertained by questionnaire. Supplements used by more than 30 persons (glucosamine and chondroitin) were evaluated as the trend across number of pills/week (non-use, <14 pills/week, 14+ pills/week), whereas less commonly used supplements were evaluated as use/non-use. Oxidative stress was measured by urinary 8-isoprostane and PGF2α concentrations using enzyme immunoassays (EIA), whereas lymphocyte DNA damage and DNA repair capacity were measured using the Comet assay. Multivariate-adjusted linear regression was used to model the associations between supplement use and oxidative stress/DNA damage.

RESULTS

Use of glucosamine (Ptrend: 0.01), chondroitin (Ptrend: 0.003), and fiber supplements (P: 0.01) was associated with reduced PGF2α concentrations, whereas CoQ10 supplementation was associated with reduced baseline DNA damage (P: 0.003).

CONCLUSIONS

Use of certain specialty supplements may be associated with reduced oxidative stress and DNA damage.

IMPACT

Further research is needed to evaluate the association between specialty supplement use and markers of oxidative stress and DNA damage.

Base excision repair capacity in chronic renal failure patients undergoing hemodialysis treatment

The aim of this study was to determine if the differences observed in the levels of DNA damage in a group of patients suffering from chronic renal failure are due to differences in the repair capability. DNA damage was initially measured with the comet assay in 106 hemodialysis patients. A selected group of 21 patients representing high (ten patients) and low (11 patients) levels of DNA damage were obtained for determination of base excision repair capacity. This was measured in an in vitro assay where protein extracts from lymphocytes were incubated with a substrate of DNA containing 8-oxoguanine, and the rate of incision was measured with the comet assay. Patients with high levels of genomic damage showed, as an average, significantly lower repair capacity (12·73 ± 1·84) in comparison with patients with low levels of genomic damage (18·13 ± 1·13). Nevertheless, the correlation coefficient between repair ability and levels of genomic damage was found to be only close to the significance value (r:-0·423, p: 0·056). Although DNA damage was clearly related to time on hemodialysis, base excision repair capacity was not. This is one of the few studies providing information on the repair capacity of chronic renal failure patients undergoing hemodialysis. As a summary, our results would indicate that DNA damage levels are in part associated to the repair capacity of the patients, and this repair capacity is not associated with the duration of hemodialysis treatment.

Global and MGMT promoter hypomethylation independently associated with genomic instability of lymphocytes in subjects exposed to high-dose polycyclic aromatic hydrocarbon

Global hypomethylation, gene-specific methylation, and genome instability are common events in tumorigenesis. To date, few studies have examined the aberrant DNA methylation patterns in coke oven workers, who are highly at risk of lung cancer by occupational exposure to polycyclic aromatic hydrocarbons (PAHs). We recruited 82 PAH-exposed workers and 62 unexposed controls, assessed exposure levels by urinary 1-hydroxypyrene, and measured genetic damages by comet assay, bleomycin sensitivity, and micronucleus assay. The PAHs in coke oven emissions (COE) were estimated based on toxic equivalency factors. We used bisulfite-PCR pyrosequencing to quantitate DNA methylation in long interspersed nuclear element-1 (LINE-1) and O(6)-methylguanine-DNA methyltransferase (MGMT). Further, the methylation alteration was also investigated in COE-treated human bronchial epithelial (16HBE) cells. We found there are higher levels of PAHs in COE. Among PAH-exposed workers, LINE-1 and MGMT methylation levels (with CpG site specificity) were significantly lowered. LINE-1, MGMT, and its hot CpG site-specific methylation were negatively correlated with urinary 1-hydroxypyrene levels (r = -0.329, p < 0.001; r = -0.164, p = 0.049 and r = -0.176, p = 0.034, respectively). In addition, LINE-1 methylation was inversely associated with comet tail moment and micronucleus frequency, and a significant increase of micronucleus in low MGMT methylation group. In vitro study revealed that treatment of COE in 16HBE cells resulted in higher production of BPDE-DNA adducts, LINE-1 hypomethylation, hypomethylation, and suppression of MGMT expression. These findings suggest hypomethylation of LINE-1 and MGMT promoter could be used as markers for PAHs exposure and merit further investigation.

Evidence for exposure-induced DNA repair abnormality is indicative of health and genetic risk

A recent focus has been targeted toward the development of functional biomarkers that can be used to predict disease more reliably. One such biomarker is the challenge assay for DNA repair deficiency. Briefly, the assay involves challenging lymphocytes in culture to a DNA damaging agent in vitro and determining the repair outcome in chromosome aberrations and/or DNA strand breaks. The aim is to show that individuals who have chronic exposure to toxic substances will develop exposure-induced DNA repair deficiencies. Many studies around the world have shown that the assay detects DNA repair deficiency in environmentally/occupationally exposed populations and with significant exposure dose-response relationship. The prediction of health risk was also validated. In addition, exposure-induced repair deficiency which was apparently passed through the germ cells had caused genetic consequences in a 3-generation population. The assay is simple to conduct and is more sensitive than some traditional biomarker assays. Together with the functional significance of the assay, the challenge assay can be used with confidence in population studies for health risk assessment.

DNA repair capacity, DNA-strand break repair gene polymorphisms, and the incidence of hepatocellular carcinoma in southwestern Guangxi of China

The associations between DNA repair capacity (DRC), DNA repair gene polymorphisms, and the incidence of hepatocellular carcinoma (HCC) have not been determined in high-risk areas. The aims of this study were to investigate whether DRC is related to the incidence of HCC and to determine whether polymorphisms in the DNA repair genes that regulate DRC are associated with the risk of HCC. First, a small case-control study was conducted to examine the association between DRC and the incidence of HCC and the environmental and genetic factors regulating DRC. Then, a large case-control study was conducted to determine whether those DNA repair gene polymorphisms shown to regulate DRC were related to the risk of HCC. The median DRC was significantly lower among the cases (0.80) than the controls (0.93). A multivariate linear regression analysis showed that the HBsAg status (p<0.01), ethnicity (p=0.01), and polymorphisms in the XRCC3-241 (p=0.01) and APE1-148 (p=0.03) gene loci may be impact factors for DRC. In the large case-control study, a stratified analysis showed that individuals with the APE1-148-combined genotype GT+TT likely had a significantly higher HCC risk compared with those with only the GG genotype (crude odds ratio=1.93, 95% confidence interval=1.17-3.17) among the Zhuang ethnicity. However, nonsignificant differences were observed between XRCC3-241 polymorphisms and the HCC risk. DRC may be related to the incidence of HCC as determined by environmental and genetic factors found in southwestern part of the Guangxi Province. Gene-environment interactions play an important role in the incidence and progression of HCC.

DNA repair and mutagen sensitivity of epithelial cells and lymphocytes in oropharyngeal cancer

Tobacco-associated nitrosamines are known carcinogens causing DNA damage in epithelial cells of the head and neck. A matched case-control study was performed to evaluate the sensitivity of patients with squamous cell cancer (SCC) of the oropharynx, and controls to tobacco-associated nitrosamines. Quantitative DNA repair was evaluated following a period of 15 and 30 min. Fresh biopsies from 100 male donors of macroscopically healthy oropharyngeal cells and lymphocytes (50 SCC patients and 50 controls) were incubated with N-nitrosodiethylamine (NDEA), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) or N-nitrosonornicotine (NNN). DNA damage in epithelial cells and lymphocytes was assessed using the comet assay. Following incubation with NDEA, cells underwent a period of DNA repair. All of the nitrosamines caused equivalent genotoxic damage in mucosal cells and lymphocytes of the two groups. Lymphocyte DNA repair capacity in the control group (26.8 and 37.1% after 15 and 30 min) was comparable to the tumor group (23.6 and 40.6%). However, epithelial cell DNA repair capacity of carcinoma patients was significantly reduced to 17.1% (15 min) and 23% (30 min) compared to the DNA repair of the control group (36.2%, 15 min and 46.0%, 30 min). Mutagen sensitivity was comparable in patients and controls. Thus, reduced epithelial cell DNA repair capacity of tumor patients is a possible endogenous risk factor for the development of head and neck squamous cell cancer.

Impaired nucleotide excision repair pathway as a possible factor in pathogenesis of head and neck cancer

Tobacco smoking is one of the major risk factors in pathogenesis of head and neck squamous cell carcinomas (HNSCC). Many of the chemical compounds present in tobacco are well-known carcinogens which form adducts with DNA. Cells remove these adducts mainly by the nucleotide excision repair pathway (NER). NER also eliminates a broad spectrum of pyrimidine dimers (CPD) and photo-products (6-4PP) induced by UV-radiation or DNA cross-links after cisplatin anti-cancer treatment. In this study DNA damage and repair was examined in peripheral blood lymphocytes obtained from 20 HNSCC patients and 20 healthy controls as well as HTB-43 larynx and SSC-25 tongue cancer cell lines. DNA repair kinetics in the examined cells after cisplatin or UV-radiation treatment were investigated using alkaline comet assay during 240min of post-treatment incubation. MTT assay was used to analyse cell viability and the Annexin V-FITC kit specific for kinase-3 was employed to determine apoptosis after treating the cells with UV-radiation at dose range from 0.5 to 60J/m(2). NER capability was assessed in vitro with cell extracts by the use of a bacterial plasmid irradiated with UV-light as a substrate for the repair. The results show that lymphocytes from HNSCC patients and HTB-43 or SSC-25 cancer cells were more sensitive to genotoxic treatment with UV-radiation and displayed impaired DNA repair. Also evidenced was a higher rate of apoptosis induction after UV-radiation treatment of lymphocytes from the HNSCC patients and the HTB-43 cancer cells than after treatment of those from healthy donors. Finally, our results showed that there was a significant decrease in NER capacity in HTB-43 or SSC-25 cancer cells as well as in peripheral blood lymphocytes of HNSCC patients compared to controls. In conclusion, we suggest that the impaired NER pathway might be a critical factor in pathogenesis of head and neck cancer.

DNA repair: from genome maintenance to biomarker and therapeutic target

A critical link exists between an individual's ability to repair cellular DNA damage and cancer development, progression, and response to therapy. Knowledge gained about the proteins involved and types of damage repaired by the individual DNA repair pathways has led to the development of a variety of assays aimed at determining an individual's DNA repair capacity. These assays and their use in the analysis of clinical samples have yielded useful though somewhat conflicting data. In this review article, we discuss the major DNA repair pathways, the proteins and genes required for each, assays used to analyze activity, and the relevant clinical studies to date. With the recent results from clinical trials targeting specific DNA repair proteins for the treatment of cancer, accurate, reproducible, and relevant analysis of DNA repair takes on an even greater significance. We highlight the strengths and limitations of these DNA repair studies and assays, with respect to the clinical assessment of DNA repair capacity to determine cancer development and response to therapy.

DNA damage phenotype and prostate cancer risk

The capacity of an individual to process DNA damage is considered a crucial factor in carcinogenesis. The comet assay is a phenotypic measure of the combined effects of sensitivity to a mutagen exposure and repair capacity. In this paper, we evaluate the association of the DNA repair kinetics, as measured by the comet assay, with prostate cancer risk. In a pilot study of 55 men with prostate cancer, 53 men without the disease, and 71 men free of cancer at biopsy, we investigated the association of DNA damage with prostate cancer risk at early (0-15 min) and later (15-45 min) stages following gamma-radiation exposure. Although residual damage within 45 min was the same for all groups (65% of DNA in comet tail disappeared), prostate cancer cases had a slower first phase (38% vs. 41%) and faster second phase (27% vs. 22%) of the repair response compared to controls. When subjects were categorized into quartiles, according to efficiency of repairing DNA damage, high repair-efficiency within the first 15 min after exposure was not associated with prostate cancer risk while higher at the 15-45 min period was associated with increased risk (OR for highest-to-lowest quartiles=3.24, 95% CI=0.98-10.66, p-trend=0.04). Despite limited sample size, our data suggest that DNA repair kinetics marginally differ between prostate cancer cases and controls. This small difference could be associated with differential responses to DNA damage among susceptible individuals.

Influence of iron-overload on DNA damage and its repair in human leukocytes in vitro

Iron is an important element that modulates the production of reactive oxygen species, which are thought to play a causative role in biological processes such as mutagenesis and carcinogenesis. The potential genotoxicity of dietary iron has been seldom studied in human leukocyte and only few reports have investigated in human colon tumor cells. Therefore, DNA damage and repair capacity of human leukocytes were examined using comet assay for screening the potential toxicity of various iron-overloads such as ferric-nitrilotriacetate (Fe-NTA), FeSO(4), hemoglobin and myoglobin, and compared with 200μM of H(2)O(2) and HNE. The iron-overloads tested were not cytotoxic in the range of 10-1000 microM by trypan blue exclusion assay. The exposure of leukocytes to Fe-NTA (500 and 1000 microM), FeSO(4) (250-1000 microM), hemoglobin (10 microM) and myoglobin (250 microM) for 30 min induced significantly higher DNA damage than NC. Treatment with 500 and 1000 microM of Fe-NTA showed a similar genotoxic effect to H(2)O(2), and a significant higher genotoxic effect than HNE. The genotoxicity of FeSO(4) (250-1000 microM), hemoglobin (10 microM) and myoglobin (250 microM) was not significantly different from that of H(2)O(2) and HNE. Iron-overloads generated DNA strand break were rejoined from the first 1h. Their genotoxic effect was not observed at 24h. These data from this study provide additional information on the genotoxicity of iron-overloads and self-repair capacity in human leukocytes.

Prospective analysis of DNA damage and repair markers of lung cancer risk from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial

Mutagen challenge and DNA repair assays have been used in case-control studies for nearly three decades to assess human cancer risk. The findings still engender controversy because blood was drawn after cancer diagnosis so the results may be biased, a type called 'reverse causation'. We therefore used Epstein-Barr virus-transformed lymphoblastoid cell lines established from prospectively collected peripheral blood samples to evaluate lung cancer risk in relation to three DNA repair assays: alkaline Comet assay, host cell reactivation (HCR) assay with the mutagen benzo[a]pyrene diol epoxide and the bleomycin mutagen sensitivity assay. Cases (n = 117) were diagnosed with lung cancer between 0.3 and 6 years after blood collection and controls (n = 117) were frequency matched on calendar year and age at blood collection, gender and smoking history; all races were included. Case and control status was unknown to laboratory investigators. In unconditional logistic regression analyses, statistically significantly increased lung cancer odds ratios (OR(adjusted)) were observed for bleomycin mutagen sensitivity as quartiles of chromatid breaks/cell [relative to the lowest quartile, OR = 1.2, 95% confidence interval (CI): 0.5-2.5; OR = 1.4, 95% CI: 0.7-3.1; OR = 2.1, 95% CI: 1.0-4.4, respectively, P(trend) = 0.04]. The magnitude of the association between the bleomycin assay and lung cancer risk was modest compared with those reported in previous lung cancer studies but was strengthened when we included only incident cases diagnosed more than a year after blood collection (P(trend) = 0.02), supporting the notion the assay may be a measure of cancer susceptibility. The Comet and HCR assays were unrelated to lung cancer risk.

Biomarkers for early detection of malignant mesothelioma: diagnostic and therapeutic application

Malignant mesothelioma (MM) is a rare and aggressive tumour of the serosal cavities linked to asbestos exposure. Improved detection methods for diagnosing this type of neoplastic disease are essential for an early and reliable diagnosis and treatment. Thus, focus has been placed on finding tumour markers for the non-invasive detection of MM. Recently, some blood biomarkers have been described as potential indicators of early and advanced MM cancers. The identification of tumour biomarkers alone or in combination could greatly facilitate the surveillance procedure for cohorts of subjects exposed to asbestos, a common phenomenon in several areas of western countries.

Genotoxicity of anti-tumor necrosis factor therapy in patients with juvenile idiopathic arthritis

OBJECTIVE

To assess the possible effects of both inflammation and the anti-tumor necrosis factor agents (anti-TNF) on DNA damage with a specific assay, and their effects on the repair capacity of DNA.

METHODS

From a group of 20 children with juvenile idiopathic arthritis (JIA), 16 patients who completed the study and 16 control subjects were evaluated. DNA damage and repair capacity were analyzed by the comet assay at the level of peripheral lymphocytes before anti-TNF (etanercept) injections and on the 15th, 90th, and 180th days after the first injection.

RESULTS

The amount of damage as detected by the aforementioned assay was higher in patients with JIA compared with controls. On the 15th day after the initial anti-TNF injection, there was a decrease in the mean DNA tail length of JIA patients, however on the 90th day an increase was observed; thereafter, an upward trend was observed until the end of the study. JIA patients had a DNA repair capacity that was significantly less than that of controls.

CONCLUSION

The results of the comet technique suggests that JIA patients already have increased basal DNA damage before anti-TNF therapy; they are more sensitive to the DNA damage produced by H(2)O(2), and have a less efficient DNA repair system in comparison with control cells. After an initial improvement at 2 weeks, parameters of genotoxicity worsened, and DNA repair was further impaired 6 months after the addition of an anti-TNF agent to treatment.

Transient DNA damage induced by high-frequency electromagnetic fields (GSM 1.8 GHz) in the human trophoblast HTR-8/SVneo cell line evaluated with the alkaline comet assay

One of the most controversial issue regarding high-frequency electromagnetic fields (HF-EMF) is their putative capacity to affect DNA integrity. This is of particular concern due to the increasing use of HF-EMF in communication technologies, including mobile phones. Although epidemiological studies report no detrimental effects on human health, the possible disturbance generated by HF-EMF on cell physiology remains controversial. In addition, the question remains as to whether cells are able to compensate their potential effects. We have previously reported that a 1-h exposure to amplitude-modulated 1.8 GHz sinusoidal waves (GSM-217 Hz, SAR=2 W/kg) largely used in mobile telephony did not cause increased levels of primary DNA damage in human trophoblast HTR-8/SVneo cells. Nevertheless, further investigations on trophoblast cell responses after exposure to GSM signals of different types and durations were considered of interest. In the present work, HTR-8/SVneo cells were exposed for 4, 16 or 24h to 1.8 GHz continuous wave (CW) and different GSM signals, namely GSM-217 Hz and GSM-Talk (intermittent exposure: 5 min field on, 10 min field off). The alkaline comet assay was used to evaluate primary DNA damages and/or strand breaks due to uncompleted repair processes in HF-EMF exposed samples. The amplitude-modulated signals GSM-217 Hz and GSM-Talk induced a significant increase in comet parameters in trophoblast cells after 16 and 24h of exposure, while the un-modulated CW was ineffective. However, alterations were rapidly recovered and the DNA integrity of HF-EMF exposed cells was similar to that of sham-exposed cells within 2h of recovery in the absence irradiation. Our data suggest that HF-EMF with a carrier frequency and modulation scheme typical of the GSM signal may affect the DNA integrity.

Modulation of ethoxyquin genotoxicity by free radical scavengers and DNA damage repair in human lymphocytes

N-tert-butyl-alpha-phenylnitrone (PBN) and its new derivative N-(Pyridine-4-ylmethylidene)-2-carboxy-tert-butylamine N-oxide (PBNC) were synthesized and used to modulate ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline, EQ) genotoxicity. Ethoxyquin, an antioxidant used mainly as a preservative in animal feeds, was shown to cause DNA breaks in human lymphocytes. The aim of the study was to evaluate the involvement of free radicals in the genotoxicity of EQ and its modulation by cellular repair systems. Human lymphocytes treated with EQ (10-50 microM) and nitrone free radical scavengers (100 microM) were tested with the comet assay. It was shown that both PBN and PBNC reduced the level of EQ-induced DNA damage, but PBN was slightly more effective. The modulation of the level of DNA damage was also observed as a result of DNA repair by cellular repair systems. Moreover, induction of oxidized bases by ethoxyquin was showed; lymphocytes exposed to ethoxyquin and treated with endonuclease III (Endo III) and formamidopyrimidine-DNA glycosylase (FpG), enzymes recognizing oxidized bases, displayed greater extent of DNA damage than those not treated with the enzymes.

Gene expression profiles in human peripheral blood mononuclear cells as biomarkers for nutritional in vitro and in vivo investigations

Identification of chemopreventive substances may be achieved by measuring biological endpoints in human cells in vitro. Since generally only tumour cells are available for such investigations, our aim was to test the applicability of peripheral blood mononuclear cells (PBMC) as an in vitro primary cell model since they mimic the human in vivo situation and are relatively easily available. Cell culture conditions were refined, and the basal variation of gene expression related to drug metabolism and stress response was determined. Results were compared with profiles of an established human colon cell line (HT29) as standard. For biomarker development of nutritional effects, PBMC and HT29 cells were treated with potentially chemopreventive substances (chrysin and butyrate), and gene expression was determined. Key results were that relevant stress response genes, such as glutathione S-transferase T2 (GSTT2) and GSTM2, were modulated by butyrate in PBMC as in HT29 cells, but the blood cells were less sensitive and responded with high individual differences. We conclude that these cells may serve as a surrogate tissue in dietary investigations and the identified differentially expressed genes have the potential to become marker genes for population studies on biological effects.

The organic selenium compound selenomethionine modulates bleomycin-induced DNA damage and repair in human leukocytes

The objective of this work was to evaluate the effects of selenomethionine (SeMet) on the induction, repair, and persistence of DNA damage in human leukocytes challenged with bleomycin (BLM). Comet assay was used to determine DNA strand breaks and hOGG1 for the specific recognition of oxidative damage. Leukocytes were (A) stimulated with phytohemagglutinin, (B) damaged with BLM, and (C) incubated to allow DNA repair. Comet assay was performed after each phase. SeMet (50 microM) was supplemented either during phase A, B, or C, or AB, or ABC. Treatment with SeMet decreased BLM-induced stand breaks when added during phase AB. Results obtained after the repair period indicate that SeMet favors repair of DNA damage especially when applied during phase AB. The comparison between DNA damage before and after repair showed that BLM-induced damage was repaired better in the presence of SeMet. Our results showed antigenotoxic effect of SeMet on BLM-induced DNA and also on repair and persistence of this damage when applied before and simultaneously with BLM.

The evolving discipline of molecular epidemiology of cancer

Classical epidemiologic studies have made seminal contributions to identifying the etiology of most common cancers. Molecular epidemiology was conceived of as an extension of traditional epidemiology to incorporate biomarkers with questionnaire data to further our understanding of the mechanisms of carcinogenesis. Early molecular epidemiologic studies employed functional assays. These studies were hampered by the need for sequential and/or prediagnostic samples, viable lymphocytes and the uncertainty of how well these functional data (derived from surrogate lymphocytic tissue) reflected events in the target tissue. The completion of the Human Genome Project and Hapmap Project, together with the unparalleled advances in high-throughput genotyping revolutionized the practice of molecular epidemiology. Early studies had been constrained by existing technology to use the hypothesis-driven candidate gene approach, with disappointing results. Pathway analysis addressed some of the concerns, although the study of interacting and overlapping gene networks remained a challenge. Whole-genome scanning approaches were designed as agnostic studies using a dense set of markers to capture much of the common genome variation to study germ-line genetic variation as risk factors for common complex diseases. It should be possible to exploit the wealth of these data for pharmacogenetic studies to realize the promise of personalized therapy. Going forward, the temptation for epidemiologists to be lured by high-tech 'omics' will be immense. Systems Epidemiology, the observational prototype of systems biology, is an extension of classical epidemiology to include powerful new platforms such as the transcriptome, proteome and metabolome. However, there will always be the need for impeccably designed and well-powered epidemiologic studies with rigorous quality control of data, specimen acquisition and statistical analysis.

An aphidicolin-block nucleotide excision repair assay measuring DNA incision and repair capacity

The objective of the present study was to develop a cellular phenotype assay for nucleotide excision repair (NER), using benzo[a]pyrene diol epoxide (BPDE) as model mutagen. Since in vitro exposure to BPDE may lead to DNA strand breaks resulting from both direct interaction with DNA and incisions introduced by the repair enzymes, we aimed to discriminate between both types of breaks using the comet assay and quantified the DNA strand breaks after in vitro challenge of peripheral blood mononucleated cells (PBMCs) with BPDE in the presence or absence of the DNA polymerase inhibitor aphidicolin (APC). The assay was performed with a low (0.5 microM) and a high (2.5 microM) BPDE concentration. The individual NER capacity was defined as the amount of DNA damage induced by BPDE in presence of APC, diminished with the damage induced by BPDE and APC alone. First, the assay was applied to a NER-deficient human fibroblast cell line (XPA-/-) to validate the methodology. Lower repair capacity and a higher amount of BPDE-induced DNA adducts were observed for the XPA-/- fibroblasts as compared to the wild-type fibroblasts. Repeated experiments on PBMCs from four donors showed low intra-individual, intra-experimental and inter-assay variation for both concentrations, indicating the reliability of the method. To assess the inter-individual variation, the assay was applied to PBMCs from 22 donors, comparing the repair capacity after exposure to 0.5 microM (N = 10) and 2.5 microM (N = 12) BPDE. The repair capacity showed a higher inter-individual variation as compared to the intra-individual variation. Moreover, this difference was more pronounced using the low concentration. All these results indicate the adequacy of the method using this low concentration. Further improvement, however, should be recommended by applying the study with low BPDE concentration in a larger population and taking into account the relevant genotypes for NER.

Cytotoxic and genotoxic effects of matrices for cartilage tissue engineering

Customizing auricles with biodegradable polyurethane colonized with autologous chondrocytes as an approach for tissue engineering cartilage transplants has been suggested for the reconstruction of the external ear to repair auricular deformities. Dextrose, triethanolamine and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) are matrices of an open-pored polyurethane three-dimensional scaffold. After release from the polymer, these compounds can be absorbed into the human organism. Therefore, cytotoxic effects on human chondrocytes and lymphocytes and genotoxic effects on human lymphocytes were determined. Propidium iodide and fluoresceine diacetate staining as well as quantitative proliferations testing with EZ4U served to detect cytotoxic effects on chondrocytes. In lymphocytes cytotoxicity was checked by trypan blue staining and the alkaline single cell microgel electrophoresis (Comet) assay was used to study genotoxic effects. Dose-dependent cytotoxicity and genotoxicity of the matrices could be shown. Concentrations up to 4.25mg/ml for dextrose, 0.15 mg/ml for PEG-PPG-PEG and 0.9 mg/ml for triethanolamine did not show cytotoxic effects in chondrocytes or genotoxic effects in lymphocytes. These data suggest that dextrose, triethanolamine and PEG-PPG-PEG could be safely used if scaffolds made of open-pored polyurethane do not release these compounds at a rate giving higher concentrations at the site of implantation or in body fluids, respectively.

gamma-H2AX foci formation in peripheral blood lymphocytes of tumor patients after local radiotherapy to different sites of the body: Dependence on the dose-distribution, irradiated site and time from start of treatment

PURPOSE

To evaluate the relationship between an estimated integral total body radiation dose delivered and phosphorylated histone H2AX protein (gamma-H2AX) foci formation in peripheral blood lymphocytes of cancer patients.

MATERIAL AND METHODS

gamma-H2AX formation was quantified as the mean number of foci per lymphocyte (N(meanH2AX)) and the percentage of lymphocytes with > or =n foci. The integrated total body radiation dose was estimated from the dose volume histogram of patient's body corrected for the proportion of the body scanned by computed tomography for 3D treatment planning.

RESULTS

There was a strong linear correlation between the mean number of gamma-H2AX foci per lymphocyte in the peripheral blood sample and integrated total body radiation dose (r = 0.83, p < 0.0001). The slope of the relationship was dependent on the site of body irradiated. In comparison to chest irradiation with a slope of 8.7 +/- 0.8 foci Gy(-1), the slopes for brain, upper leg and pelvic sites were significantly shallower by -4.7, -4.3, and -3.8 Gy(-1), respectively (p < 0.0001), while the slope for upper abdomen irradiation was significantly larger by 9.1 +/- 2.6 Gy(-1) (p = 0.0007). There was a slight time effect since the start of radiotherapy on the slopes of the in vivo dose responses leading to shallower slopes (-1.5 +/- 0.7 Gy(-1), p = 0.03) later (> or =10 day) during radiotherapy. After in vitro irradiation, lymphocytes showed 10.41 +/- 0.12 foci per Gy with no evidence of inter-individual heterogeneity.

CONCLUSIONS

gamma-H2AX measurements in peripheral lymphocytes after local radiotherapy allow the estimation of the applied integral body dose. The site and time dependence have to be considered.

Mechanisms of primary cancer prevention by butyrate and other products formed during gut flora-mediated fermentation of dietary fibre

Dietary fibres are indigestible food ingredients that reach the colon and are then fermented by colonic bacteria, resulting mainly in the formation of short-chain fatty acids (SCFA) such as acetate, propionate, and butyrate. Those SCFA, especially butyrate, are recognised for their potential to act on secondary chemoprevention by slowing growth and activating apoptosis in colon cancer cells. Additionally, SCFA can also act on primary prevention by activation of different drug metabolising enzymes. This can reduce the burden of carcinogens and, therefore, decrease the number of mutations, reducing cancer risk. Activation of GSTs by butyrate has been studied on mRNA, protein, and enzyme activity level by real-time RT-PCR, cDNA microarrays, Western blotting, or photometrical approaches, respectively. Butyrate had differential effects in colon cells of different stages of cancer development. In HT29 tumour cells, e.g., mRNA GSTA4, GSTP1, GSTM2, and GSTT2 were induced. In LT97 adenoma cells, GSTM3, GSTT2, and MGST3 were induced, whereas GSTA2, GSTT2, and catalase (CAT) were elevated in primary colon cells. Colon cells of different stages of carcinogenesis differed in post-transcriptional regulatory mechanisms because butyrate increased protein levels of different GST isoforms and total GST enzyme activity in HT29 cells, whereas in LT97 cells, GST protein levels and activity were slightly reduced. Because butyrate increased histone acetylation and phosphorylation of ERK in HT29 cells, inhibition of histone deacetylases and the influence on MAPK signalling are possible mechanisms of GST activation by butyrate. Functional consequences of this activation include a reduction of DNA damage caused by carcinogens like hydrogen peroxide or 4-hydroxynonenal (HNE) in butyrate-treated colon cells. Treatment of colon cells with the supernatant from an in vitro fermentation of inulin increased GST activity and decreased HNE-induced DNA damage in HT29 cells. Additional animal and human studies are needed to define the exact role of dietary fibre and butyrate in inducing GST activity and reducing the risk of colon cancer.

Suboptimal DNA repair capacity predisposes coke-oven workers to accumulate more chromosomal damages in peripheral lymphocytes

DNA repair is an essential mechanism for cells to maintain their genomic integrity under endogenous or exogenous assault. Reduced DNA repair capacity (DRC) is associated with increased risk for several environmentally related cancers. The micronucleus in peripheral lymphocytes has been validated as a biomarker of chromosomal damage, increasing cancer risk in human populations. We hypothesized that suboptimal DRC is associated with the increase in chromosomal damage among 94 coke-oven workers and 64 noncoke-oven controls. DRC was evaluated in isolated lymphocytes by comet assay. Chromosomal damage in peripheral lymphocytes was detected by cytokinesis-block micronucleus assay. Four common coding single nucleotide polymorphisms in the XRCC1 gene were genotyped. Coke-oven workers have significantly increased urinary 1-hydroxypyrene (9.0; 6.8-11.7 microg/L versus 1.5, 1.3-1.7 microg/L; P<0.01) and micronucleus frequency (7.4 per thousand+/-4.3 per thousand versus 3.0 per thousand+/-3.0 per thousand; P<0.01), and decreased DRC (55.9%+/-16.4% versus 63.6%+/-18.5%; P<0.01) compared with controls. Significant correlations between DRC and micronucleus frequency were found in coke-oven workers (r=-0.32; P<0.01; n = 94) and all study subjects (r=-0.32; P<0.001; n=158) but not in controls (r=-0.21; P=0.11; n=64). Variants of the Arg399Gln polymorphism were associated with a decreased DRC in both coke-oven workers (51.6%+/-16.1% versus 60.6%+/-15.7%; P<0.01) and controls (59.1%+/-18.5% versus 68.4%+/-17.5%; P=0.04). The complicated interrelationship of these multiple biomarkers was also identified by path analysis. These findings should facilitate developing a biomarker-based risk assessment model for lung cancer in this occupational population.

Inhalative exposure to vanadium pentoxide causes DNA damage in workers: results of a multiple end point study

BACKGROUND

Inhalative exposure to vanadium pentoxide (V(2)O(5)) causes lung cancer in rodents.

OBJECTIVE

The aim of the study was to investigate the impact of V(2)O(5) on DNA stability in workers from a V(2)O(5) factory.

METHODS

We determined DNA strand breaks in leukocytes of 52 workers and controls using the alkaline comet assay. We also investigated different parameters of chromosomal instability in lymphocytes of 23 workers and 24 controls using the cytokinesis-block micronucleus (MN) cytome method.

RESULTS

Seven of eight biomarkers were increased in blood cells of the workers, and vanadium plasma concentrations in plasma were 7-fold higher than in the controls (0.31 microg/L). We observed no difference in DNA migration under standard conditions, but we found increased tail lengths due to formation of oxidized purines (7%) and pyrimidines (30%) with lesion-specific enzymes (formamidopyrimidine glycosylase and endonuclease III) in the workers. Bleomycin-induced DNA migration was higher in the exposed group (25%), whereas the repair of bleomycin-induced lesions was reduced. Workers had a 2.5-fold higher MN frequency, and nucleoplasmic bridges (NPBs) and nuclear buds (Nbuds) were increased 7-fold and 3-fold, respectively. Also, apoptosis and necrosis rates were higher, but only the latter parameter reached statistical significance.

CONCLUSIONS

V(2)O(5) causes oxidation of DNA bases, affects DNA repair, and induces formation of MNs, NPBs, and Nbuds in blood cells, suggesting that the workers are at increased risk for cancer and other diseases that are related to DNA instability.

Role of impaired DNA repair in genotoxic susceptibility of patients with head and neck cancer

DNA repair is critical for genotoxic susceptibility and cancer development. Forty-seven patients with head and neck squamous cell carcinoma (HNSCC) and 38 healthy controls were enrolled in this study. Among the patients, 16 subjects had metastasis of HNSCC. The extent of DNA damage, including oxidative lesions, and efficiency of repair after genotoxic treatment with hydrogen peroxide were examined using the alkaline comet assay. HNSCC cells were sensitive to genotoxic treatment and displayed impaired DNA repair. In particular, lesions caused by hydrogen peroxide were repaired less effectively in cancer cells from patients with metastasis than in cells from healthy controls. We suggest that impaired DNA repair might play a role in genotoxic susceptibility of patients with head and neck cancer. Finally, as a consequence of this finding we have shown that treatment with DNA-reactive drugs could be considered as an effective therapy strategy for head and neck cancer.

A modified alkaline comet assay for measuring DNA repair capacity in human populations

Trzeciak, A. R., Barnes, J. and Evans, M. K. A Modified Alkaline Comet Assay for Measuring DNA Repair Capacity in Human Populations. Radiat. Res. 169, 110-121 (2008). Use of the alkaline comet assay to assess DNA repair capacity in human populations has been limited by several factors, including lack of methodology for use of unstimulated cryopreserved peripheral blood mononuclear cells (PBMCs), insufficient control of interexperimental variability, and limited analysis of DNA repair kinetics. We show that unstimulated cryopreserved PBMCs can be used in DNA repair studies performed using the comet assay. We have applied data standardization for the analysis of DNA repair capacity using negative and positive internal standards as controls for interexperimental variability. Our standardization procedure also uses negative controls, which provides a way to minimize the interference of interindividual variation in baseline DNA damage levels on DNA repair capacity measurements in populations. DNA repair capacity was assessed in a small human cohort using the parameters described in the literature including initial DNA damage, half-time of DNA repair, and residual DNA damage after 30 and 60 min. We have also introduced new DNA repair capacity parameter, initial rate of DNA repair. There was no difference in DNA repair capacity between fresh and cryopreserved PBMCs when measured by the Olive tail moment and tail DNA. The use of DNA repair capacity parameters in assessment of fast and slow single-strand break repair components is discussed.

Quantification of DNA repair capacity in whole blood of patients with head and neck cancer and healthy donors by comet assay

Comet assay has been used to estimate cancer risk by quantification of DNA damage and repair in response to mutagen challenge. Our goal was to adopt best practices for the alkaline comet assay to measure DNA repair capacity of white blood cells in whole blood of patients with squamous cell carcinoma of the head and neck (HNSCC). The results show that initial damage by 10 Gy of gamma radiation expressed as percent DNA in comet tail was higher in stimulated lymphocytes (61.1+/-11.8) compared to whole blood (43.0+/-12.1) but subsequent repair was similar with comet tail of approximately 20% at 15 min and 13% at 45 min after exposure. Exposure of whole blood embedded in agarose from 5 to 10 Gy gamma radiation was followed by an approximately 70% repair of the DNA damage within 45 min with a faster repair phase in the first 15 min. Variability of the measurement was lower within repeated measurements of the same person compared to measurement of different healthy individuals. The repair during first 15 min was slower (p=0.01) in ex-/non-smokers (41.0+/-2.1%) compared to smokers (50.3+/-2.7%). This phase of repair was also slower (p=0.02) in HNSCC patients (36.8+/-2.1%) compared to controls matched on age and smoking (46.4+/-3.0%). The results of this pilot study suggest that quantification of repair in whole blood following a gamma radiation challenge is feasible. Additional method optimization would be helpful to improve the assay for a large population screening.

DNA base excision repair as a biomarker in molecular epidemiology studies

Base excision repair can be measured in human lymphocytes by a variety of techniques, the most convenient of which are probably in vitro assays of the activity of a cell extract on a DNA substrate containing specific lesions such as 8-oxoguanine. Inter-individual variation in base excision repair ranges from about 3-fold to 10-fold in different studies. Repair has been variously reported to decline or to increase with the age of the individual. Few studies of environmental or occupational exposure and repair have been carried out, but it seems that styrene exposure induces base excision repair activity. In several nutritional intervention trials, with kiwifruit, coenzyme Q(10) and carrots, a significant enhancement of repair has been noted. Activity of 8-oxoguanine DNA glycosylase is significantly affected by the Ser326Cys polymorphism in hOGG1. In cancer case-control studies, low repair activity is consistently associated with occurrence of the disease.

Improved alkaline comet assay protocol for adherent HaCaT keratinocytes to study UVA-induced DNA damage

The comet assay is one of the well-accepted tests to measure radiation-induced DNA damage. The most commonly used protocols require single-cell suspensions that are embedded in agarose in order to perform electrophoresis. For adherently growing cells such as human HaCaT skin keratinocytes this method bears several problems. We show that trypsinization required for maintaining single-cell suspensions is prolonged after UV radiation and thereby reduces cell viability and allows partial repair, with the consequence of reduced damage detection after irradiation. Therefore, we here introduce a modified version of the comet assay where HaCaT cells are seeded onto comet slides 24h before the assay and overlaid with agarose immediately after irradiation. Using this modification we are now able to reproducibly measure high DNA-damage levels (13-fold increase compared with controls) following irradiation with 60J/cm(2) UVA as well as a dose-dependent increase of DNA damage after 10, 20 and 60J/cm(2) UVA. Thus, by maintaining the cells in their natural configuration, i.e. adherently growing, we exclude several artefacts that are likely to influence the damage responses. These include: (i) trypsinization-dependent changes in cell morphology and polarity (clear lateral, i.e. adherent, and apical side of keratinocytes) which are likely of consequence for the gene-expression pattern, (ii) trypsin- and dislodgement-induced damage reducing cell viability, and (iii) the time delay between damage induction and damage evaluation to unpredictable results due to partial repair. Since these advantages pertain to all adherently growing cells, this improved protocol is not restricted to HaCaT cells but offers great potential also with all non-haematopoietic cells for obtaining accurate results and for studying repair processes in a highly reproducible manner.

Interindividual differences in initial DNA repair capacity when evaluating H2O2-induced DNA damage in extended-term cultures of human lymphocytes using the comet assay

It has been suggested that extended-term cultures of human lymphocytes could be used as a complement to cell lines based on transformed cells when testing the genotoxicity of chemicals. To investigate whether the pattern of induced DNA damage and its subsequent repair differs significantly between cultures based on different blood donors, hydrogen peroxide (H(2)O(2))-induced DNA damage was measured in cultures from four different subjects using the comet assay. The DNA damage was significantly increased in all cultures after 10 min exposure to 0.25 mmol/L H(2)O(2), and there was a significant decrease in the H(2)O(2)-induced DNA damage in all cultures after 30 min of DNA repair. The level of damage varied between the different donors, especially after the repair. Using PCR and DNA sequencing, exon 5 of the p53 gene was sequenced in the lymphocytes from the donors with the lowest and highest residual damage. No such mutation was found. Mouse lymphoma L5178Y cells carrying the p53 mutation in exon 5 were included as a reference. These cells were found to be less sensitive toward the H(2)O(2)-induced DNA damage, and they were also found to have a rather low DNA repair capacity. The demonstrated variation in H(2)O(2)-induced DNA damage and DNA repair capacity between the cultures from the different subjects may be important from a risk assessment perspective, but is obviously not of decisive importance when it comes to the development of a routine assay for genotoxicity.

Genetic risk profiles for cancer susceptibility and therapy response

Cells in the body are permanently attacked by DNA-reactive species, both from intracellular and environmental sources. Inherited and acquired deficiencies in host defense mechanisms against DNA damage (metabolic and DNA repair enzymes) can modify cancer susceptibility as well as therapy response. Genetic profiles should help to identify high-risk individuals who subsequently can be enrolled in preventive measures or treated by tailored therapy regimens. Some of our attempts to define such risk profiles are presented. Cancer susceptibility: Single nucleotide polymorphisms (SNPs) in metabolic and repair genes were investigated in a hospital-based lung cancer case-control study. When evaluating the risk associated with different genotypes for N-acetyltransferases (Wikman et al. 2001) and glutathione-S-transferases (Risch et al. 2001), it is mandatory to distinguish between the three major histological subtypes of lung tumors. A promoter polymorphism of the myeloperoxidase gene MPO was shown to decrease lung cancer susceptibility mainly in small cell lung cancer (SCLC) (Dally et al. 2002). The CYP3A4*1B allele was also linked to an increased SCLC risk and in smoking women increased the risk of lung cancer eightfold (Dally et al. 2003b). Polymorphisms in DNA repair genes were shown to modulate lung cancer risk in smokers, and reduced DNA repair capacity elevated the disease risk (Rajaee-Behbahani et al. 2001). Investigations of several DNA repair gene variants revealed that lung cancer risk was only moderately affected by a single variant but was enhanced up to approximately threefold by specific risk allele combinations (Popanda et al. 2004). Therapy response: Inter-individual differences in therapy response are consistently observed with cancer chemotherapeutic agents. Initial results from ongoing studies showed that certain polymorphisms in drug transporter genes (ABCB1) differentially affect response outcome in histological subgroups of lung cancer. Stronger beneficial effects were seen in non-small cell lung cancer (NSCLC) patients following gemcitabine and in SCLC patients following etoposide-based treatment. Several DNA repair parameters (polymorphisms, RNA expression, and DNA repair capacity) were measured in vitro in lymphocytes of patients before radiotherapy and correlated with the occurrence of acute side effects (radio-hypersensitivity). Our initial analysis of several repair gene variants in breast cancer patients (n = 446) who received radiotherapy revealed no association of single polymorphisms and the development of side effects (moist desquamation of the irradiated normal skin). The risk for this side effect was, however, strongly reduced in normal weight women carrying a combination of XRCC1 399Gln and APE1 148Glu alleles, indicating that these variants afford some protection against radio-hypersensitivity (Chang-Claude et al. 2005). Based on these data we conclude that specific metabolic and DNA repair gene variants can affect cancer risk and therapy outcome. Predisposition to hereditary cancer syndromes is dominated by the strong effects of some high-penetrance tumor susceptibility genes, while predisposition to sporadic cancer is influenced by the combination of multiple low-penetrance genes, of which as a major challenge, many disease-relevant combinations remain to be identified. Before translating these findings into clinical use and application for public health measures, large population-based studies and validation of the results will be required.

Bleomycin-induced DNA damage and repair inXenopus laevis andXenopus tropicalis

Microgel cell electrophoresis has been used with various species to measure breakage of DNA and DNA repair following exposure to the radiomimetic antibiotic, bleomycin. With humans, a high degree of DNA damage is considered to be predictive of cancer susceptibility. Non-isogeneic Xenopus laevis, the South African clawed toad, rarely develop spontaneous or induced cancers. Here, we investigate bleomycin-induced DNA damage and repair in splenic lymphocytes of this species to test consistency with cancer predictability. As X. laevis is pseudotetraploid in nature, while Xenopus tropicalis is diploid, we additionally explore the effect of polyploidy on DNA damage and repair in these vertebrates. The results show that higher doses of bleomycin are required to induce comparable levels of DNA damage in both Xenopus species, than in humans. X. tropicalis, the diploid, is more bleomycin-sensitive than is X. laevis. Additionally, repair rates of damaged DNA of X. laevis lymphocytes are more rapid than those of X. tropicalis, although both are hours slower than human leukocytes. While no data exist on cancer susceptibility in X. tropicalis, the results suggest greater susceptibility to cancer than X. laevis, but less than in humans. Thus, polyploidy serves as a protection against DNA damage and allows more rapid repair.

Effects of 1.8GHz radiofrequency field on DNA damage and expression of heat shock protein 70 in human lens epithelial cells

To investigate the DNA damage, expression of heat shock protein 70 (Hsp70) and cell proliferation of human lens epithelial cells (hLEC) after exposure to the 1.8 GHz radiofrequency field (RF) of a global system for mobile communications (GSM). An Xc-1800 RF exposure system was used to employ a GSM signal at 1.8 GHz (217 Hz amplitude-modulated) with the output power in the specific absorption rate (SAR) of 1, 2 and 3 W/kg. After 2 h exposure to RF, the DNA damage of hLEC was accessed by comet assay at five different incubation times: 0, 30, 60, 120 and 240 min, respectively. Western blot and RT-PCR were used to determine the expression of Hsp70 in hLECs after RF exposure. The proliferation rate of cells was evaluated by bromodeoxyuridine incorporation on days 0, 1 and 4 after exposure. The results show that the difference of DNA-breaks between the exposed and sham-exposed (control) groups induced by 1 and 2 W/kg irradiation were not significant at any incubation time point (P > 0.05). The DNA damage caused by 3 W/kg irradiation was significantly increased at the times of 0 and 30 min after exposure (P < 0.05), a phenomenon that could not be seen at the time points of 60, 120 or 240 min (P > 0.05). Detectable mRNA as well as protein expression of Hsp70 was found in all groups. Exposure at SARs of 2 and 3 W/kg for 2 h exhibited significantly increased Hsp70 protein expression (P < 0.05), while no change in Hsp70 mRNA expression could be found in any of the groups (P > 0.05). No difference of the cell proliferation rate between the sham-exposed and exposed cells was found at any exposure dose tested (P > 0.05). The results indicate that exposure to non-thermal dosages of RF for wireless communications can induce no or repairable DNA damage and the increased Hsp70 protein expression in hLECs occurred without change in the cell proliferation rate. The non-thermal stress response of Hsp70 protein increase to RF exposure might be involved in protecting hLEC from DNA damage and maintaining the cellular capacity for proliferation.