Resolving complex cartilage structures in developmental biology via deep learning-based automatic segmentation of X-ray computed microtomography images.

The complex shape of embryonic cartilage represents a true challenge for phenotyping and basic understanding of skeletal development. X-ray computed microtomography (µCT) enables inspecting relevant tissues in all three dimensions; however, most 3D models are still created by manual segmentation, which is a time-consuming and tedious task. In this work, we utilised a convolutional neural network (CNN) to automatically segment the most complex cartilaginous system represented by the developing nasal capsule. The main challenges of this task stem from the large size of the image data (over a thousand pixels in each dimension) and a relatively small training database, including genetically modified mouse embryos, where the phenotype of the analysed structures differs from the norm. We propose a CNN-based segmentation model optimised for the large image size that we trained using a unique manually annotated database. The segmentation model was able to segment the cartilaginous nasal capsule with a median accuracy of 84.44% (Dice coefficient). The time necessary for segmentation of new samples shortened from approximately 8 h needed for manual segmentation to mere 130 s per sample. This will greatly accelerate the throughput of µCT analysis of cartilaginous skeletal elements in animal models of developmental diseases.

Sustained induction of cytochrome P4501A1 in human hepatoma cells by co-exposure to benzo[a]pyrene and 7H-dibenzo[c,g]carbazole underlies the synergistic effects on DNA adduct formation.

To gain a deeper insight into the potential interactions between individual aromatic hydrocarbons in a mixture, several benzo[a]pyrene (B[a]P) and 7H-dibenzo[c,g]carbazole (DBC) binary mixtures were studied. The biological activity of the binary mixtures was investigated in the HepG2 and WB-F344 liver cell lines and the Chinese hamster V79 cell line that stably expresses the human cytochrome P4501A1 (hCYP1A1). In the V79 cells, binary mixtures, in contrast to individual carcinogens, caused a significant decrease in the levels of micronuclei, DNA adducts and gene mutations, but not in cell survival. Similarly, a lower frequency of micronuclei and levels of DNA adducts were found in rat liver WB-F344 cells treated with a binary mixture, regardless of the exposure time. The observed antagonism between B[a]P and DBC may be due to an inhibition of Cyp1a1 expression because cells exposed to B[a]P:DBC showed a decrease in Cyp1a1 mRNA levels. In human liver HepG2 cells exposed to binary mixtures for 2h, a reduction in micronuclei frequency was also found. However, after a 24h treatment, synergism between B[a]P and DBC was determined based on DNA adduct formation. Accordingly, the up-regulation of CYP1A1 expression was detected in HepG2 cells exposed to B[a]P:DBC. Our results show significant differences in the response of human and rat cells to B[a]P:DBC mixtures and stress the need to use multiple experimental systems when evaluating the potential risk of environmental pollutants. Our data also indicate that an increased expression of CYP1A1 results in a synergistic effect of B[a]P and DBC in human cells. As humans are exposed to a plethora of noxious chemicals, our results have important implications for human carcinogenesis.

Chromosomal damage among medical staff occupationally exposed to volatile anesthetics, antineoplastic drugs, and formaldehyde.

OBJECTIVES: Structural chromosomal aberrations in blood lymphocytes represent a biomarker for cellular damage caused by genotoxic carcinogens and are an indicator of increased cancer risk. We evaluated the association between frequencies of total chromosomal aberrations, chromatid- and chromosome-type aberrations, and occupational exposures to volatile anesthetics, antineoplastic agents, and formaldehyde among 601 medical professionals. METHODS: Chromosomal damage among exposed individuals and unexposed controls was determined by conventional cytogenetic analysis. We used binary logistic regression to evaluate the effects of workplace exposures and major confounders on chromosomal damage. RESULTS: Significantly higher frequencies of total chromosomal, chromatid-type and chromosome-type aberrations were observed among subjects occupationally exposed to volatile anesthetics, antineoplastic agents, and formaldehyde compared to age- and sex-matched controls (P<0.0001). The risk of an increased frequency of chromosomal aberrations was associated with exposure to anesthetics [odds ratio (OR) 3.9, 95% confidence interval (95% CI) 2.7-5.8], cytostatics (OR 2.7, 95% CI 1.9-3.9), and formaldehyde (OR 1.7, 95% CI 1.1-2.7). No other covariate contributed significantly to the model. Chromatid- and chromosome-type aberrations were associated with exposure to anesthetics and cytostatics without any contribution of other variables. Stratified data analysis showed the risk of increased chromosomal aberrations among non-smoking female nurses and physicians exposed to anesthetics, cytostatics and, partially, formaldehyde. Chromatid and chromosome exchanges were significantly higher in the exposed groups than among controls. CONCLUSION: Our findings indicate that the presence of genotoxic compounds in operating rooms, oncological units, and pathological departments results in a significant increase of chromosomal damage (impair of chromosomal integrity) among medical workers employed in these facilities.

Polymorphisms in miRNA-binding sites of nucleotide excision repair genes and colorectal cancer risk.

Reduced DNA repair capacity and DNA damage accumulation may lead to cancer development. Regulation of and coordination between genes involved in DNA repair pathways is fundamental for maintaining genome stability, and post-transcriptional gene regulation by microRNAs (miRNAs) may therefore be of particular relevance. In this context, the presence of single nucleotide polymorphisms (SNPs) within the 3'untranslated regions of target DNA repair genes could alter the binding with specific miRNAs, modulating gene expression and ultimately affecting cancer susceptibility. In this study, we investigated the role of genetic variations in miRNA-binding sites of nucleotide excision repair (NER) genes in association with colorectal cancer (CRC) risk. From 28 NER genes, we screened among SNPs residing in their 3'untranslated regions and simultaneously located in miRNA-binding sites, with an in silico approach. Through the calculation of different binding free energy according to both alleles of identified SNPs, and with global binding free energies median providing a threshold, we selected nine NER gene variants. We tested those SNPs in 1098 colorectal cancer cases and 1469 healthy controls from the Czech Republic. Rs7356 in RPA2 and rs4596 in GTF2H1 were associated with colorectal cancer risk. After stratification for tumor location, the association of both SNPs was significant only for rectal cancer (rs7356: OR 1.52, 95% CI 1.02-2.26, P = 0.04 and rs4596: OR 0.69, 95% CI 0.50-0.94, P = 0.02; results not adjusted for multiple testing). Variation in miRNA target binding sites in the 3'untranslated region of NER genes may be important for modulating colorectal cancer risk, with a different relevance according to tumor location.

Differences in nucleotide excision repair capacity between newly diagnosed colorectal cancer patients and healthy controls.

Alteration of DNA integrity is a potential cause of cancer and it is assumed that reduced DNA repair capacity and accumulation of DNA damage may represent intermediate markers in carcinogenesis. In this case-control study, DNA damage and nucleotide excision repair capacity (NER-DRC) were assessed in association with sporadic colorectal cancer (CRC). Both parameters were quantified by comet assay in blood cells of 70 untreated incident patients and 70 age-matched healthy controls. mRNA expression and polymorphisms in relevant NER genes were concurrently analyzed. The aim of this study was to characterize incident CRC patients for NER-DRC and to clarify possible relations between investigated variables. Comet assay and mRNA expression analysis showed that CRC patients differ in repair capacity as compared to controls. Patients had a lower NER-DRC and simultaneously they exhibited higher endogenous DNA damage (for both P < 0.001). Accumulation of DNA damage and decreasing NER-DRC behaved as independent modulating parameters strongly associated with CRC. Expression levels of 6 out of 9 studied genes differed between groups (P ≤ 0.001), but none of them was related to DRC or to any of the studied NER polymorphisms. However, in patients only, XPC Ala499Val modulated expression levels of XPC, XPB and XPD gene, whereas XPC Lys939Gln was associated with XPA expression level in controls (for all P < 0.05). This study provides evidence on altered DRC and DNA damage levels in sporadic CRC and proposes the relevance of the NER pathway in this malignancy. Further, alterations in a complex multigene process like DNA repair may be better characterized by functional quantification of repair capacity than by quantification of individual genes transcripts or gene variants alone.

Evaluating chromosomal damage in workers exposed to hexavalent chromium and the modulating role of polymorphisms of DNA repair genes.

PURPOSE: Welders have been chronically exposed to hexavalent chromium with potential consequences on chromosomal integrity. Our study is focused on the extent of any such chromosomal aberrations with respect to chromium levels in the blood of welders as well as on the tentative modulating role of polymorphisms in DNA repair genes XPD Lys751Gln, XPG Asn114His, XPC Lys939Gln, hOGG1 Ser326Cys and XRCC1 Arg399Gln on chromosomal damage. METHODS: The study was conducted on 144 individuals consisting of 73 welders exposed to chromium for 10.2 ± 1.67 years and 71 control individuals without known exposures. Chromosomal aberrations, their chromatid-type and chromosome-type aberrations were detected by conventional cytogenetic analysis. XPD, XPG, XPC, hOGG1 and XRCC1 gene polymorphisms were assayed for by Taqman SNP genotyping assay ("Assay-by-Demand") using Real-Time allelic discrimination on AB 7500 equipment. Chromium concentration in the blood was determined by atomic absorption spectrophotometry. RESULTS: The level of chromium in the blood of welders ranged between 0.032 and 0.182 µmol l(-1) and was significantly higher than that in controls (0.07 ± 0.04 µmol l(-1) vs. 0.03 ± 0.007 µmol l(-1)). Parameters of chromosomal damage were similar in both the exposed and the control individuals (1.89% vs. 1.70% for total chromosomal aberrations, 0.97% vs. 0.88% for chromosome-type and 0.92% vs. 0.80% for chromatid-type, respectively). Chromatid-type of aberrations positively correlated with the level of chromium in the blood (r = 0.28; P = 0.02). Significantly higher total chromosomal aberrations were detected in individuals with homozygous variant polymorphism in XRCC1 Arg399Gln gene as compared to those with heterozygous and homozygous wild-type genotypes (2.20, 1.89 and 1.48%, respectively; P = 0.01). A similar tendency was found for chromatid-type aberrations (1.30% for homozygous variant genotype bearers, 0.94% for those with heterozygous genotype and 0.75% for carriers of homozygous wild-type genotype, respectively; P = 0.04). CONCLUSIONS: Although no apparent increase in chromosomal damage was recorded in chromium-exposed welders in comparison with controls, genetic make-up in DNA repair genes may increase susceptibility toward adverse effect of chromium.

DNA damage and nucleotide excision repair capacity in healthy individuals.

Interindividual differences in DNA repair capacity (DRC) represent an important source of variability in genome integrity and thus influence health risk. In the last decade, DRC measurement has attracted attention as a potential biomarker in cancer prediction. Aim of the present exploratory study was to characterize the variability in DNA damage and DRC on 100 healthy individuals and to identify biological, lifestyle, or genetic factors modulating these parameters. The ultimate goal was to obtain reference data from cancer-free population, which may constitute background for further investigations on cancer patients. The endogenous DNA damage was measured as a level of DNA single-strand breaks and DRC, specific for nucleotide excision repair (NER), was evaluated using modified comet assay, following the challenge of peripheral blood mononuclear cells with benzo[a]pyrene diolepoxide. Additionally, genetic polymorphisms in NER genes (XPA, XPC, XPD, and XPG) were assessed. We have observed a substantial interindividual variability for both examined parameters. DNA damage was significantly affected by gender and alcohol consumption (P = 0.003 and P = 0.012, respectively), whereas DRC was associated with family history of cancer (P = 0.012). The stratification according to common variants in NER genes showed that DNA damage was significantly modulated by the presence of the variant T allele of XPC Ala499Val polymorphism (P = 0.01), while DRC was modulated by the presence of the A allele of XPA G23A polymorphism (P = 0.048). Our results indicate the range of endogenous DNA single-strand breaks and capacity of NER in healthy volunteers as well as the role of potentially relevant confounders. Environ. Mol. Mutagen. 2011. © 2011 Wiley-Liss, Inc.

MTHFR and MTRR genotype and haplotype analysis and colorectal cancer susceptibility in a case-control study from the Czech Republic.

Polymorphic variants in genes involved in one-carbon metabolism, in particular of dietary folate, may modulate the risk for colorectal cancer through aberrant DNA-methylation and altered nucleotide synthesis and repair. In the present study, we have assessed the association of six polymorphisms and relative haplotypes in the MTHFR gene (rs1801133 and rs1801131) and in the MTRR gene (rs1801394, rs1532268, rs162036, and rs10380) with the risk for colorectal cancer in 666 patients and 1377 controls from the Czech Republic. We found that the 677 C>T polymorphism in the MTHFR gene significantly decreased the risk for colorectal cancer in homozygous carriers of the variant allele (OR, 0.58; 95% CI, 0.39-0.87). Also, we noted a significantly different distribution of genotypes between cases and controls for the 66A>G polymorphism in the MTRR gene. In particular, homozygous carriers of the G-containing allele of this polymorphism were at an increased risk for colorectal cancer (OR, 1.39; 95% CI, 1.04-1.85). Haplotype analysis of the two MTHFR polymorphisms showed a moderate difference in the distribution of the TA haplotype between cases and controls. In comparison to the most common haplotype (CA), the TA haplotype was associated with a decreased risk for colorectal cancer (OR, 0.84; 95% CI, 0.71-0.99). No difference in the distribution between cases and controls was observed for the haplotypes based on the four polymorphisms in the MTRR gene. The present study suggests that the 677TT genotype and the TA haplotype in the MTHFR gene may also have a role in colorectal cancer risk in the Czech population, indicating the importance of genes involved in folate metabolism with respect to cancer risk. For MTRR, additional studies on larger populations are needed to clarify the possible role of variation in this gene in colorectal carcinogenesis.

DNA damage, DNA repair rates and mRNA expression levels of cell cycle genes (TP53, p21(CDKN1A), BCL2 and BAX) with respect to occupational exposure to styrene.

We studied the relationship between DNA damage, DNA repair rates and messenger RNA (mRNA) expression levels of cell cycle genes TP53, p21(CDKN1A), BCL2 and BAX in a group of 71 styrene-exposed workers and 51 control individuals. The exposure was assessed by measuring the concentration of styrene at workplace and in blood. Parameters of DNA damage [measured as single-strand breaks (SSBs) and endonuclease III-sensitive sites], γ-irradiation-specific DNA repair rates and mRNA levels of studied genes were analyzed in peripheral blood lymphocytes. The workers were divided into low (<50 mg/m³) and high (>50 mg/m³) styrene exposure groups. We found negative correlations between mRNA expression of TP53, BCL2, BAX and styrene exposure (P < 0.001 for all parameters). In contrast, p21(CDKN1A) mRNA expression significantly increased with increasing styrene exposure (P = 0.001). SSBs and endonuclease III-sensitive sites increased with increasing mRNA levels of TP53 (P < 0.001 for both) and BCL2 (P = 0.038, P = 0.002, respectively), whereas the same parameters decreased with increasing mRNA levels of p21(CDKN1A) (P < 0.001, P = 0.007, respectively). γ-Irradiation-specific DNA repair rates increased with p21(CDKN1A) mRNA levels up to the low exposure level (P = 0.044). Our study suggests a possible relationship between styrene exposure, DNA damage and transcript levels of key cell cycle genes.

Obesity accompanies narcolepsy with cataplexy but not narcolepsy without cataplexy.

BACKGROUND: Narcolepsy with cataplexy (NC) differs from narcolepsy without cataplexy (NwoC) in the cerebrospinal fluid levels of hypocretin. Since hypocretin is known to regulate not only wakefulness but also eating behaviour, we decided to compare the two entities for body mass index (BMI) and the presence of obesity. METHODS: Clinical data on patients with NC and NwoC was studied and examined, including nocturnal polysomnography and the Multiple Sleep Latency Test (MSLT). The results were rated against a group of age- and sex-matched healthy controls. RESULTS: The BMI in NC (29.1±SD=5.8) was significantly higher than in NwoC (25.4±4.4) or in the controls (25.8±3.9) (p<0.001, F=17.4, df= 323), while no difference in BMI was found between NwoC and the controls. The proportion of patients with BMI >30 was significantly greater in NC (39.0%) than in NwoC (13.8%) or than in the control group (13.0%). A negative correlation of BMI and sleep latency in MSLT (p=0.009) was found in the combined NC and NwoC groups. CONCLUSION: Unlike NC, NwoC has neither a higher BMI nor a higher incidence of obesity than the general population.

Modulation of DNA repair capacity and mRNA expression levels of XRCC1, hOGG1 and XPC genes in styrene-exposed workers.

Decreased levels of single-strand breaks in DNA (SSBs), reflecting DNA damage, have previously been observed with increased styrene exposure in contrast to a dose-dependent increase in the base-excision repair capacity. To clarify further the above aspects, we have investigated the associations between SSBs, micronuclei, DNA repair capacity and mRNA expression in XRCC1, hOGG1 and XPC genes on 71 styrene-exposed and 51 control individuals. Styrene concentrations at workplace and in blood characterized occupational exposure. The workers were divided into low (below 50 mg/m³) and high (above 50 mg/m³)) styrene exposure groups. DNA damage and DNA repair capacity were analyzed in peripheral blood lymphocytes by Comet assay. The mRNA expression levels were determined by qPCR. A significant negative correlation was observed between SSBs and styrene concentration at workplace (R=-0.38, p=0.001); SSBs were also significantly higher in men (p=0.001). The capacity to repair irradiation-induced DNA damage was the highest in the low exposure group (1.34±1.00 SSB/109 Da), followed by high exposure group (0.72±0.81 SSB/109 Da) and controls (0.65±0.82 SSB/109 Da). The mRNA expression levels of XRCC1, hOGG1 and XPC negatively correlated with styrene concentrations in blood and at workplace (p<0.001) and positively with SSBs (p<0.001). Micronuclei were not affected by styrene exposure, but were higher in older persons and in women (p<0.001). In this study, we did not confirm previous findings on an increased DNA repair response to styrene-induced genotoxicity. However, negative correlations of SSBs and mRNA expression levels of XRCC1, hOGG1 and XPC with styrene exposure warrant further highly-targeted study.

Chromosomal damage in peripheral blood lymphocytes of newly diagnosed cancer patients and healthy controls.

BACKGROUND: The majority of human cancers arise from cells unable to maintain genomic stability. Recent prospective studies indicated that enhanced chromosomal aberrations (CAs) frequencies are predictive of gastrointestinal and lung cancers. However, studies on incident cancer patients are lacking; thus, we investigated chromosomal damage in newly diagnosed cancer patients and healthy individuals. METHODS: We analyzed chromosomal damage in peripheral blood lymphocytes in a group of 300 incident cancer patients (with different malignancies) in comparison with 300 healthy controls. RESULTS AND CONCLUSIONS: The frequencies of aberrant cells (ACs) and CAs were significantly higher in patients (2.38 +/- 1.56 and 2.53 +/- 1.69, respectively) as compared with controls (1.81 +/- 1.31 and 1.94 +/- 1.47, respectively, P < 0.01). The percentual difference in chromatid-type aberrations (CTAs) between patients and controls was moderately significant (1.37 +/- 1.20 and 1.11 +/- 0.99, respectively, P

NBN 657del5 heterozygous mutations and colorectal cancer risk in the Czech Republic.

The most frequent Nijmegen breakage syndrome (NBS)-causing mutation is a 5-base pair deletion in gene coding for nibrin (NBN 657del5), which results in a non-fully functional protein product and is particularly frequent in Central and Eastern Europe. Recent studies have investigated whether NBN 657del5 carriage may predispose to an increased risk of different types of cancer. The Czech Republic has one of the highest incidences of colorectal cancer in the world as well as high incidence of NBS. To assess whether NBN 657del5 associates with an increased risk of sporadic colorectal cancer, we have screened 771 colorectal cancer patients, 614 controls with negative colonoscopy and 818 healthy blood donors from the Czech Republic. There were no significant differences between the frequencies of heterozygous carriers among the three groups. The present results do not provide any evidence that the exceeding risk of CRC in this population is attributable to the high frequency of heterozygous carriage of the NBN 657del5.

Effect of occupational exposure to cytostatics and nucleotide excision repair polymorphism on chromosomal aberrations frequency.

Authors evaluated the incidence of total chromosomal aberrations (CA) and their types - chromatid-type (CTA) and chromosome-type (CSA) in peripheral blood lymphocytes from 72 oncologic unit's workers occupationally exposed to cytostatics in relationship to polymorphisms of DNA repair genes XPD, XPG and XPC. The cytogenetic analysis was used for determination of chromosomal aberrations frequency and PCR-RFLP method for polymorphisms of genes. Statistically higher frequency of total CA was detected in exposed group as compared to control (1.90±1.34% vs. 1.26±0.93%; Mann-Whitney U-test, p=0.001). There was not detected any difference between CTA and CSA (0.92±1.04% vs. 0.98±1.17%). Similarly, in genes XPD exon 23 and XPC exon 15 wasn't detected any difference neither in total chromosomal aberrations nor in CTA and CSA types. Statistically significant decrease of total chromosomal aberrations and CTA-type with presence of variant allele C was detected in gene XPG exon 15. Authors pointed out the importance of individual susceptibility factors in evaluation of effects of genotoxic agents, in that event, when the concentration does not meet the occupational exposure limit.

Chromosomal damage and polymorphisms of DNA repair genes XRCC1 and XRCC3 in workers exposed to chromium.

OBJECTIVES: Welders, chronically exposed to hexavalent chromium, may exhibit disturbances in chromosomal integrity. Our study investigates chromosomal damage related to chromium exposure, considering the role of polymorphisms in relevant DNA repair genes. METHODS: 39 male welders exposed to chromium for 10.2+/-1.67 years and 31 male controls were assayed for structural chromosomal aberrations (conventional cytogenetic analysis). DNA repair gene polymorphisms were determined by Real-Time allelic discrimination assay. RESULTS: Total chromosomal aberrations were moderately, but statistically not significant, higher in exposed individuals (1.96%) than in controls (1.55%). Chromosomal type breaks were almost two-fold higher in exposed than in control individuals. The highest frequency of total chromosomal aberrations was recorded in individuals with homozygous variant Gln/Gln cariers (2.14%) in XRCC1* Arg-399Gln and the lowest in those with the wild-type Arg/Arg cariers (1.33%). Polymorphisms in XRCC3 gene did not modulate the frequencies of CAs, CTAs and CSAs. CONCLUSIONS: Understanding the effects of chromium on chromosomal integrity in relation to individual susceptibility may be a basis for preventive measures in working process.

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.

Association of DNA repair polymorphisms with DNA repair functional outcomes in healthy human subjects.

We investigated association between polymorphisms in DNA repair genes and the capacity to repair DNA damage induced by gamma-irradiation and by base oxidation in a healthy population. Irradiation-specific DNA repair rates were significantly decreased in individuals with XRCC1 Arg399Gln homozygous variant genotype (0.45 +/- 0.47 SSB/10(9) Da) than in those with wild-type genotype (1.10 +/- 0.70 SSB/10(9) Da, P=0.0006, Mann-Witney U-test). The capacity to repair oxidative DNA damage was significantly decreased among individuals with hOGG1 Ser326Cys homozygous variant genotype (0.37 +/- 0.28 SSB/10(9) Da) compared to those with wild-type genotype (0.83 +/- 0.79 SSB/10(9) Da, P=0.008, Mann-Witney U-test). Investigation of genotype combinations showed that the increasing number of variant alleles for both XRCC1 Arg399Gln and APE1 Asn148Glu polymorphisms resulted in a significant decrease of irradiation-specific repair rates (P=0.008, Kruskal-Wallis test). Irradiation-specific DNA repair rates also decreased with increasing number of variant alleles in XRCC1 Arg399Gln in combination with variant alleles for two other XRCC1 polymorphisms, Arg194Trp and Arg280His (P=0.002 and P=0.005, respectively; Kruskal-Wallis test). In a binary combination variant alleles of hOGG1 Ser326Cys and APE1 Asn148Glu polymorphisms were associated with a significant decrease in the capacity to repair DNA oxidative damage (P=0.018, Kruskal-Wallis test). In summary, XRCC1 Arg399Gln and hOGG1 Ser326Cys polymorphisms seem to exert the predominant modulating effect on irradiation-specific DNA repair capacity and the capacity to repair DNA oxidative damage, respectively.

Chromosomal damage and polymorphisms of DNA repair genes XRCC1 and XRCC3 in workers exposed to cytostatics.

OBJECTIVES: Medical workers in oncological units have chronically been exposed to low doses of cytostatics (C) with potential consequences on DNA and chromosomal integrity. Our study addresses relationships between chromosomal aberrations (CAs), chromosome (CSA), and chromatid (CTA) types and polymorphisms in DNA repair genes XRCC1 and XRCC3. METHODS: The study was conducted on 72 exposed individuals from hospitals in Martin (HMT; 28 individuals), Ruzomberok (HRK; 31 medical workers) and in Trstená (HTS; 13 individuals), and on 34 unexposed individuals. Conventional cytogenetic analysis was employed for the detection of CAs. XRCC1 and XRCC3 polymorphisms were assayed for by Taqman SNP genotyping assays ("Assay-by-Demand") using Real-Time allelic discrimination on AB 7 500 equipment (all from Applied Biosystems, Foster City, USA). RESULTS: Higher frequencies of CAs were detected in exposed individuals than in controls (1.78% versus 1.32%, respectively). The frequency of aberrant cells (Ab.c.) was highest among workers from HRK (1.97%), followed by those from HMT and HTS (1.54% and 1.85 %, respectively). In the exposed group a moderately higher frequency of CTA (0.93%) in comparison with CSA (0.85%) was detected. Higher CAs were detected in individuals with homozygous variant polymorphism in XRCC1 exon 10 gene than in those with wild-type genotype (1.87% versus 1.60%). Variant T allele in XRCC3 exon 7 was also associated with higher CAs (1.71% and 1.74%) as compared to the wild-type C allele (1.45%). CONCLUSIONS: The detection of individuals with increased susceptibility to genotoxic agents enables to take preventive measures during the working process.