Allelic polymorphisms of DNA repAiriNg geNes As mArkers of resistANce to Asbestos-coNtAiNiNg Aerosols

October 2019 We studied the frequency distribution of dNA repairing genes allelic polymorphisms in the occupational group of asbestos-cement plants workers (n = 95). The aim of the work was to determine the probable molecular genetic markers of resistance to the development of bronchopulmonary pathology under the action of chrysotile-asbestos-containing dust. In 46 workers with chronic forms of bronchopulmonary pathology and 49 workers of the same professions without chronic diseases of the respiratory system, allelic polymorphisms XPd (rs13181, rs799793), ercc1 (rs11615), Xrcc3 (rs861539), Xrcc1 (rs25487), ATM (rs664677), Xrcc7 (rs7003908) and MLh1 (rs1799977) were determined using the real-time polymerase chain reaction. It was established that XRCC1•G/A (rs25487) (OR = 0.45; 95% CI: 0.18–1.10; P = 0.050; χ 2 = 3.73); MLH1•A/A (rs1799977) (OR = 0.28; = 8.75) genotypes contribute to the resistance to bronchopulmonary pathology development, = 6.42) genotypes were found to be associated with the risk of respiratory disease development. The obtained results show interconnection between certain alleles of dNA repair genes and the risk of bronchopulmonary pathology development under the influence of industrial aerosols, including

We studied the frequency distribution of dNA repairing genes allelic polymorphisms in the occupational group of asbestos-cement plants workers (n = 95). The aim of the work was to determine the probable molecular genetic markers of resistance to the development of bronchopulmonary pathology under the action of chrysotile-asbestos-containing dust. In 46 workers with chronic forms of bronchopulmonary pathology and 49 workers of the same professions without chronic diseases of the respiratory system, allelic polymorphisms XPd (rs13181, rs799793), ercc1 (rs11615), Xrcc3 (rs861539), Xrcc1 (rs25487), ATM (rs664677), Xrcc7 (rs7003908) and MLh1 (rs1799977) were determined using the real-time polymerase chain reaction. It was established that XRCC1•G/A (rs25487) (OR = 0.45; 95% CI: 0. 18 T he type of the damage in the structure of a DNA molecule determines the way of repair and enzymes of repair provide restoration of the DNA molecule original structure. The main functions of the repair enzymes are the removal of short single-stranded DNA sequences with the false paired or damaged bases and their replacement with the complementary sequences. Single nucleotide poly morphism (SNP) of DNA repair genes can alter the structure and activity of enzymes that they encode [1,2].
Exquisite repair is based on the identification of the modified base with glycosylases, which cleave the N-glycoside bond between the base and the sugar-phosphate core of the DNA molecule. SNP of glycosylases genes which is associated with the replacement of one of the nucleotides in the gene coding sequence is shown to be related to increased carcinogenesis risk [3]. The nucleotide excision repair (NER) is realized with the help of insertase and deoxyribonuclease I, which recognize DNA damage and cleave phosphodiester bonds near lesions. NER enzymes include about 30 proteins, among them: XPB, XPC, XPD, etc. [4]. At the final repair stage, DNA-polymerase restores the cleaved section using the undamaged complementary DNA chain as a matrix and the polynucleotide ligase restores phosphodiester bonds [5]. The allelic polymorphism of genes encoding DNA polymerase or ligase III which are involved NER final stage significantly increases the cytotoxicity of adducts [4].
Double-strand DNA breaks appear during replication and under the action of damaging agents. Double-strand break repair (DSBR) errors cause mutations and chromosome rearrangements that induce genome instability and carcinogenesis [6,7]. There are two mechanisms of DSBR repair: nonhomologous end joining (NHEJ) and homologous recombination (HR) [6,8]. NHEJ provides the ligation of DNA ends with minimal enzymatic treatment on the site of their combination. HR provides a complete restoration of the initial DNA sequence and homologues or sister chromatids are involved in the process. The main components of HR enzyme system are: RAD51, XRCC2, XRCC3 [1,8,9]. NHEJ is followed by formation of a new combination of genes and often leads to malignant transformation [9]. The mismatch repair (MMR) occurs when the modified base has not been removed from the DNA or when a non-canonical pair of nucleotides appears during replication. MMR enzymes MLH1, MSH2, MSH3, MSH6 recognize the damage in the structure of the duplex and cut the affected area at specific sites. It has been established that the carcinogenic activity of mutagens depends on the activity of MMR enzymes due to their involvement in apoptosis regulation [10].
The main important factors of the carcinogenic risk are factors of high penetrance, which include carcinogen dose, imbalance of detoxifying enzymes system and impaired DNA repair [11]. A useful model for studying the influence of genes polymorphism of the factors of high penetrance on human carcinogenesis is tobacco smoking, since the multicomponent composition of tobacco smoke causes all possible damages of DNA and even infrequent variants of SNP and their protein products involved in DNA repair has been established [12]. In particular, smokers with a high level of CYP1A1 and CYP2D6 induction, which was detected in lymphocytes treated with polycyclic aromatic hydrocarbons, had significantly higher incidences of lung cancer [12,13]. And if smoking was combined with pneumoconiosis induced by asbestos dust, an 18-fold increase of the risk of lung cancer developing was observed [14].
Previously we studied the frequency of allelic variants of DNA repair genes polymorphisms in two independent groups of workers of hazardous and harmful industries in Ukraine [6]. To confirm the prognostic importance of the distribution of DNA repair genes allelic polymorphisms, it is necessary to standardize the results obtained and to prove that in workers of different harmful industries the frequencies of minor and dominant homozygotes and heterozygotes deviate significantly from the theoretically expected values.
The aim of the present study was to estimate the frequency and distribution of DNA repair genes allelic polymorphism in the occupational group of asbestic cement plants workers and to identify the possible genetic markers of resistance to bronchopulmonary pathology (BPP) development under the action of asbestos-containing aerosols.

characteristics of the research respondents.
The workers of the main occupations of the asbestoscement plants ( АCP) Kramatorsk Slate Ltd (n = 55) and "Balakliysky Slate" Ltd (n = 40) at the age from 20 to 62 years were included in the study. According to the results of the workplaces certification, the mean variation of chrysotile-asbestos maximum permissible concentration (MPC, which is 0.5 mg/m 3 ) in the air of the working area exceeded the average-shift of the MPC by 3.4-10.2 times.
For the comparative analysis, respondents were divided into two groups: "without obvious signs of BPP" (control), (n = 49) and a group of the workers "with signs of BPP" (study) (n = 46). BPP for nosology included: chronic bronchitis, chronic obstructive pulmonary disease, pneumoconiosis.
The verification of the BPP diagnosis was made in the clinic of occupational diseases at Kundiiev Institute of Occupational Health of the National Acade my of Medical Sciences of Ukraine by estimating the function of external respiration and the diffusing capacity of the lung for carbon monoxide (DLCo). The general characteristics of respondents are presented in Table 1.
Statistical analysis. The clinical data were analyzed for the normality of distribution using the Shapiro-Vilka test, as well as by the Levine Leuven test. Student's statistical criterion was used to determine the differences between the groups. A value of P < 0.05 was considered statistically significant. All calculations were made on the basis of SPSS ver.17.0, ver.23. The frequency of genotype distribution was analyzed using the Pearson Chi-square test. The SNP Analyzer program was used to verify the Hardy-Weinberg equilibrium.
The studies have been performed in accordance with the ethical standards, all patients participating in the study gave their consent and signed an informational agreement approved by the Bioethics Commission of the State Institution "Institute of Occupa-

results and Discussion
The frequency distribution of genotypes of different DNA repair systems genes in the control and BPP group of ACP workers was studied. It should be noted that the obtained values of the frequencies of genotypes of DNA repair genes in both studied groups were close to that in the population of the European race (Table 2).