Ludovit Musak

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.

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.

Structural chromosomal aberrations as potential risk markers in incident cancer patients

Epidemiological prospective studies have shown that increased chromosomal aberrations (CAs) in peripheral blood lymphocytes may predict cancer risk. Here, we report CAs in newly diagnosed 101 colorectal, 87 lung and 158 breast cancer patients and corresponding healthy controls. Strong differences in distributions of aberrant cells (ACs), CAs, chromatid-type aberrations (CTAs) and chromosome-type aberrations (CSAs) were observed in lung and breast cancer patients as compared to healthy controls. In colorectal cancer (CRC) patients, only CTAs were significantly elevated. Binary logistic regression, adjusted for main confounders, indicates that all the analysed cytogenetic parameters along with smoking were significantly associated with breast and lung cancer risks. Significant differences in terminal deletions between breast cancer patients and corresponding female controls were recorded (0.39 vs. 0.18; P ≤ 0.05). We did not find any association of CAs with TNM (tumor nodus metastasis) stages or histopathological grade in either cancer type. CAs were neither associated with additional tumor characteristics-invasivity, ductal and lobular character, estrogene/progesterone receptors in breast tumors nor with non-small/small cell and bronchogenic/pulmonary types of lung tumors. Our study demonstrates that CAs serve as a predictive marker for breast and lung cancer, whereas only CTAs were elevated in incident CRC patients.

Metabolic gene variants associated with chromosomal aberrations in healthy humans.

Nonspecific chromosomal aberrations (CAs) are found in about 1% of lymphocytes drawn from healthy individuals. They include chromosome‐type aberrations (CSAs), which are increased in exposure to ionizing radiation, and chromatid‐type aberrations (CTAs) which in experimental systems are formed by DNA binding carcinogens and mutagens. The frequency of CAs is associated with the risk of cancer, but the causes of CAs in general population are unknown. Here, we want to test whether variants in metabolic genes associate with CAs in healthy volunteers. Cases were considered those whose total CA (CAtot) frequency was >2% and for CSA and CTA the limit was >1%. Controls had lower frequencies of CAs. Functional polymorphisms in seven genes were selected for analysis: cytochrome P450 1B1 (CYP1B1), epoxide hydrolase 1 (EPHX1), NAD(P)H:quinone oxidoreductase 1 (NQO1), each coding for phase 1 enzymes, and glutathione S‐transferase P1 (GSTP1), glutathione S‐transferases M1 (GSTM1) and T1 (GSTT1), coding for enzymes which conjugate reactive metabolites, that is, phase 2 enzymes. The number of volunteers genotyped for each gene varied from 550 to 1,500. Only EPHX1 was individually associated with CAtot; high activity genotypes decreased CAtot. A total of six significant (P < 0.01) pair‐wise interactions were observed, most including a GST variant as one of the pair. In all genotype combinations with significant odds ratios for CAs a GST variant was involved. The present data provide evidence that variants in genes coding for metabolic enzymes, which individually have small effects, interact and are associated with CA frequencies in peripheral lymphocytes of healthy volunteers.

Interactions of DNA repair gene variants modulate chromosomal aberrations in healthy subjects

Human cancers are often associated with numerical and structural chromosomal instability. Structural chromosomal aberrations (CAs) in peripheral blood lymphocytes (PBL) arise as consequences of direct DNA damage or due to replication on a damaged DNA template. In both cases, DNA repair is critical and inter-individual differences in its capacity are probably due to corresponding genetic variations. We investigated functional variants in DNA repair genes (base and nucleotide excision repair, double-strand break repair) in relation to CAs, chromatid-type aberrations (CTAs) and chromosome-type aberrations (CSAs) in healthy individuals. Chromosomal damage was determined by conventional cytogenetic analysis. The genotyping was performed by both restriction fragment length polymorphism and TaqMan allelic discrimination assays. Multivariate logistic regression was applied for testing individual factors on CAs, CTAs and CSAs. Pair-wise genotype interactions of 11 genes were constructed for all possible pairs of single-nucleotide polymorphisms. Analysed individually, we observed significantly lower CTA frequencies in association with XPD Lys751Gln homozygous variant genotype [odds ratio (OR) 0.64, 95% confidence interval (CI) 0.48-0.85, P = 0.004; n = 1777]. A significant association of heterozygous variant genotype in RAD54L with increased CSA frequency (OR 1.96, 95% CI 1.01-4.02, P = 0.03) was determined in 282 subjects with available genotype. By addressing gene-gene interactions, we discovered 14 interactions significantly modulating CAs, 9 CTAs and 12 CSAs frequencies. Highly significant interactions included always pairs from two different pathways. Although individual variants in genes encoding DNA repair proteins modulate CAs only modestly, several gene-gene interactions in DNA repair genes evinced either enhanced or decreased CA frequencies suggesting that CAs accumulation requires complex interplay between different DNA repair pathways.

Cyclin D1 splice site variant triggers chromosomal aberrations in healthy humans.

Chromosomal aberrations (CAs) were suggested to be the cause of cancer by Boveri already a 100 years ago, but the detection of the Philadelphia chromosome about 50 years later provided the first direct evidence on the relationship (reviewed by Mitelman). CAs include recurrent aberrations, including specific translocations, deletions and amplifications of chromosomal regions or whole chromosomes. The detection of recurrent CAs was greatly facilitated when fluorescence in situ hybridization techniques were developed for interphase chromosomes. Non-specific CAs include missing, fragmented or fused chromosomal segments, divided into chromosome-type aberrations (CSAs) and chromatidtype aberrations (CTAs). These have been conventionally analyzed by microscopic scoring of metaphase nuclei from cultured lymphocytes. Modern sequencing techniques have revealed numerous gene fusions and rearrangements, in the extreme, chromothripsis, a catastrophic parsing of illegitimate chromosomal segments together. Non-specific CAs may arise as a result of direct DNA damage by, for example, ionizing radiation or replication on a damaged DNA template; the former lesions would be detected as CSAs, whereas the latter may be CSAs or CTAs. Non-specific CAs remain in lymphocytes for their lifetime. They have been used in monitoring of radiation exposure and exposure to genotoxic compounds and, together with sister chromatid exchanges and micronuclei, CAs have offered the only available method for human biomonitoring for genotoxic exposures. There are convincing data on the association of CA frequency with subsequent risk of many cancers. Furthermore, patients with many types of cancer show increased frequencies of CAs at diagnosis. CAs were assumed to be somatic events but our recent study on multiple myeloma showed that the recurrent t(11;14) (q13;q32) translocation was strongly associated with the cyclin D1 (CCND1) G870A genotype at a splice site. However, no effect was found for any other translocations or other CAs in myeloma. Here, we wanted to test the possible dependence of non-specific CAs on the CCND1 genotype by assaying for the G870A genotype in a large cohort of persons for whom CAs were measured. This polymorphism has been implicated as a risk factor for a number of cancers. The subjects (N1⁄4 731) were identified from occupational settings, including persons with defined exposures (553), and hospital staff without exposures (178) from Slovakia. Occupational exposures included small organic compounds (330), cytostatics (81), anesthetics (74) and metals (68). The median age was 40 years (range 19 to 71), whereas the mean was 40.6 years (s.d. 10.3); characteristics of the population are shown in Table 1. The sampling of peripheral blood was carried out according to the Helsinki Declaration and the study design was approved by the local Ethical Committee of the Jessenius Medical Faculty. The participants provided an informed consent. Cytogenetic analysis was performed on cultured lymphocytes, as previously described, by microscopically analyzing (two microscopists) in a double-blind fashion coded slides of 100 mitoses per person for the frequency of total CAs, CTAs and CSAs. Inter-arm and intra-arm interchanges of CTAs and CSAs (including dicentrics and centric rings) were also scored. In statistical analysis, non-parametric Mann–Whitney U-test was used for testing of differences between the groups. The CAs were categorized into a high-frequency group (42%) and low-frequency group (p2%); this arbitrary cutoff point was based on our previous experience. For CTA and CSA, the cutoff was 1%. Odds ratios (ORs) from multivariable linear regression analysis were employed to consider simultaneous effects of particular occupational exposures, age, gender and smoking habits on the frequencies of CAs, CTAs and CSAs. Genotyping of G870A (rs603965, also known as rs9344) was carried out by the PCR-restriction-fragment length polymorphism method (primer F 50-GTGAAGTTCATTTCCAATCCGC-30, primer R 50-GGGACATCACCCTCACTTAC-30). The amplified fragment was digested with the MspI restriction endonuclease and the digested PCR products were resolved on 3% agarose gels containing ethidium bromide for visualization under UV light. The quality control was performed by random re-genotyping of about 10% of sample. Occupational exposure information was lacking for six individuals. Genotyping of one idividual was not successful, thus 730 persons were successfully genotyped. The results for total CAs showed significant effects of occupational exposure (OR 1.68) and CCND1 AA genotype (OR 1.85, Table 1). In the separate analysis of CTAs and CSAs, the only significant effect of OR 1.99 (P1⁄4 0.003) was on CSAs (Table 2). Our recent study on multiple myeloma showed that the t(11;14) translocation was associated with the CCND1 GG genotype with an OR 1.95 (P1⁄4 2.07 10 ) (Weinhold et al.). The present results showed that AA genotype was associated with overall lymphocyte CAs and, specifically, CSAs in healthy individuals. The opposite genotype effects are likely to be explained by the cell type in question. In the earlier study, we found no genotype effect in mantle cell lymphoma, for which the t(11;14) translocation is a hallmark, most likely because in mantle cell lymphoma the translocations are formed during VDJ recombination when antigen receptor genes are rearranged, earlier than in multiple myeloma. Myeloma is thought to arise from post-germinal center memory B-cells in which immunoglobulin H (IgH) translocations take place during germinal center maturation when somatic hypermutation and class switch recombination take place. Both VDJ and class switch recombination involve complex doublestranded DNA repair events. VDJ recombination is initiated by recombination-activating genes, whereas the germinal center events are catalyzed by activation-induced cytidine deaminase, followed by classical non-homologous DNA end-joining and alternative end-joining repair activities. It is thus likely that the

Do GST polymorphisms modulate the frequency of chromosomal aberrations in healthy subjects

Rossi et al. (2009) described an association between chromosomal aberration (CA) frequency and cancer risk in a case–control study on 107 cancer cases and 291 controls, whereby they observed no modifying effect of polymorphisms in glutathione S-transferase M1 (GSTM1) and GSTT1. In our studies of 488 healthy individuals who shared the same environmental exposure in Slovakia and the Czech Republic, we observed a CA frequency of 2.35 ± 1.73 (mean ± SD) (Halasova et al. 2007; Musak et al. 2008; Naccarati et al. 2006; Slyskova et al. 2007; Vodicka et al. 2001, 2004a, 2004b). The frequencies (mean ± SD) for chromatid-type abberations (CTA) and chromosome-type aberrations (CSA) were 1.22 ± 1.21 and 1.15 ± 1.35, respectively. By analyzing modulating effects of genetic polymorphisms in GSTT1, GSTM1, and GSTP1 on CAs, CTAs, and CSAs (Table 1), we found no significant association between chromosomal damage and any of the studied polymorphisms. The results were further confirmed by logistic regression: for the GSTT1 null genotype, odds ratio (OR) = 1.35 [95% confidence interval (CI), 0.79–2.32; p = 0.27]; for the GSTM1 genotype, OR = 1.09 [95% CI, 0.74–1.62; p = 0.65]; and for a variant GSTP1 Val105Val genotype, OR = 0.83 [95% CI, 0.55–1.24; p = 0.36]. These data on a larger healthy population [previously published separately by Halasova et al. (2007), Musak et al. (2008), Naccarati et al. (2006), Slyskova et al. (2007), and Vodicka et al. (2001, 2004a, 2004b)] confirm the findings of Rossi et al. (2009) regarding GSTM1 and GSTT1 polymorphisms. Additionally, in our reanalysis, we did not observe any modulating effect of GSTP1 polymorphism on CA frequency. However, the modulating role of GST polymorphisms may not be excluded, particularly in interaction with heavy occupational exposure. In our study exploring chromosomal damage in tire-plant workers (Musak et al. 2008), CAs were significantly higher in subjects with GSTT1-null than in those with GSTT1-plus genotypes, particularly in association with smoking. Table 1 Distribution of analyzed genotypes and CA frequencies. In the past decade, CAs have been accepted as a predictive marker of cancer (Hagmar et al. 2004), particularly for colo-rectal and lung cancers (Boffetta et al. 2007; Norppa et al. 2006). Nevertheless, these studies, as well as the study of Rossi et al. (2009) may have limitations: For example, cohorts were recruited in various regions with different lifestyle and environmental backgrounds, and different laboratories were involved in processing and scoring the samples over many years. In earlier studies, virtually no data on individual susceptibility were available because of the lack of DNA for molecular analysis. The data on CAs presented here were obtained on healthy subjects from a homogeneous region with fairly similar socioeconomic background. The analysis of CAs reported in these studies (Halasova et al. 2007; Musak et al. 2008; Naccarati et al. 2006; Slyskova et al. 2007; Vodicka et al. 2001, 2004a, 2004b) were performed in two laboratories, using the same protocol and the same scoring criteria with regular slide exchanges to minimize interlaboratory and inter scorer differences. Also, native DNA from whole-blood samples for molecular genetic studies was collected simultaneously with the samples for cytogenetic investigations. Future prospective studies regarding CAs and cancer should be designed by taking into account the lifestyle and occupational/environmental exposures, along with factors of individual susceptibility. Some GST polymorphisms may modulate CA frequency through interaction with environmental factors. The next logical step for a confirmation of predictive values of CA frequencies in relation to cancer will be their determination in lymphocytes of cancer patients in association with clinical– pathological characteristics.

DNA and chromosomal damage in medical workers exposed to anaesthetic gases assessed by the lymphocyte cytokinesis-block micronucleus (CBMN) assay. A critical review

The lymphocyte cytokinesis-block micronucleus (CBMN) assay has been applied in hundreds of in vivo biomonitoring studies of humans exposed either environmentally or occupationally to genotoxic chemicals. However, there is an emerging need to re-evaluate the use of MN and other biomarkers within the lymphocyte CBMN cytome assay as quantitative indicators of exposure to main classes of chemical genotoxins. The main aim of the present report is to systematically review published studies investigating the use of the lymphocyte CBMN assay to determine DNA damage in subjects exposed to anaesthetic gases. We also compared performance of the CBMN assay with other DNA damage assays employed and identified strengths and weaknesses of the published studies. We have retrieved 11 studies, published between 1996 and 2013, reporting MN associated with occupational exposures (operating room personnel). The individual job categories were often described (anaesthesiologists, technicians, radiologists) among cases, as well as duration of exposure. All studies reported the compounds present at the workplace and, in some instances, the exposure levels were measured. Controls were usually recruited among personnel at the hospital not exposed to anaesthetics or they were healthy unexposed subjects from general population. The number of investigated subjects, due to the character of the occupation, was relatively smaller than those investigated in other occupational monitoring settings. Overall, the majority of the studies were age- and gender- matched (or investigated only males or females) while less attention was given to lifestyle confounders. Appropriate measurement of exposure, available in approximately half of the studies only, was compromised by the lack of the personal dosimetry-based determinations. In all studies, higher MN frequencies were observed in exposed individuals. The meta-analysis of mean MN frequency of combined studies confirmed this tendency (log mean ratio=0.56 [0.34-0.77]; P=3.51×10-7). Similar differences between the exposed and controls were also observed for other biomarkers.

Genetic variation in the major mitotic checkpoint genes associated with chromosomal aberrations in healthy humans

Non-specific chromosomal aberrations (CAs) are microscopically detected in about 1% of lymphocytes drawn from healthy persons. Causes of CAs in general population are not known but they may be related to risk of cancer. In view of the importance of the mitotic checkpoint machinery on maintaining chromosomal integrity we selected 9 variants in main checkpoint related genes (BUB1B, BUB3, MAD2L1, CENPF, ESPL1/separase, NEK2, PTTG1/securin, ZWILCH and ZWINT) for a genotyping study on samples from healthy individuals (N = 330 to 729) whose lymphocytes had an increased number of CAs compared to persons with a low number of CAs. Genetic variation in individual genes played a minor importance, consistent with the high conservation and selection pressure of the checkpoint system. However, gene pairs were significantly associated with CAs: PTTG1-ZWILCH and PTTG1-ZWINT. MAD2L1 and PTTG1 were the most common partners in any of the two-way interactions. The results suggest that interactions at the level of cohesin (PTTG1) and kinetochore function (ZWINT, ZWILCH and MAD2L1) contribute to the frequency of CAs, suggesting that gene variants at different checkpoint functions appeared to be required for the formation of CAs.

Genetic variation of acquired structural chromosomal aberrations

Human malignancies are often hallmarked with genomic instability, which itself is also considered a causative event in malignant transformation. Genomic instability may manifest itself as genetic changes in the nucleotide sequence of DNA, or as structural or numerical changes of chromosomes. Unrepaired or insufficiently repaired DNA double-strand breaks, as well as telomere shortening, are important contributors in the formation of structural chromosomal aberrations (CAs). In the present review, we discuss potential mechanisms behind the formation of CAs and their relation to cancer. Based on our own studies, we also illustrate how inherited genetic variation may modify the frequency and types of CAs occurring in humans. Recently, we published a series of studies on variations in genes relevant to maintaining genomic integrity, such as those encoding xenobiotic-metabolising enzymes, DNA repair, the tumour suppressor TP53, the spindle assembly checkpoint, and cyclin D1 (CCND1). While individually genetic variation in these genes exerted small modulating effects, in interactions they were associated with CA frequencies in peripheral blood lymphocytes of healthy volunteers. Moreover, we observed opposite associations between the CCND1 splice site polymorphism rs9344 G870A and the frequency of CAs compared to their association with translocation t(11,14). We discuss the functional consequences of the CCND1 gene in interplay with DNA damage response and DNA repair during malignant transformation. Our review summarizes existing evidence that gene variations in relevant cellular pathways modulate the frequency of CAs, predominantly in a complex interaction. More functional/mechanistic studies elucidating these observations are required. Several questions emerge, such as the role of CAs in malignancies with respect to a particular phenotype and heterogeneity, the formation of CAs during the process of malignant transformation, and the formation of CAs in individual types of lymphocytes in relation to the immune response.