**3. Gene polymorphisms as susceptibility biomarkers in the occupational setting**

It is widely known the exposure to dangerous substances and carcinogens is commonly associated to the individual capability of metabolizing such compounds which may vary between different individuals and among ethnicities, each characterized by its own specific genetic ancestry. In the occupational setting, the exposure risk is traditionally evaluated by the biological monitoring of workers manipulating hazardous agents. Common work-related substances are polycyclic aromatic hydrocarbons (PAH), a large class of organic compounds with carcinogenic properties (IARC group 1, 2B) used in the manufacture of chemicals, bitumen, and rubber and in shoe factories, while in fibreglass industries and in ship constructions, the most common dangerous substances are volatile organic compounds (VOCs) such as styrene (IARC group 2A), toluene (IARC group 3), xylene (IARC group 3), ethylbenzene (IARC group 2B) and benzene (IARC group I). The majority of these hazardous chemicals are highly toxic and carcinogenic to humans, and in each company, the officially approved occupational exposure limits (OELs) must be respected to ensure a safe environment for the workers' health. The procedure of workplace monitoring is generally standardized. It basically consists first of the environmental monitoring which measures the workers' airborne exposure to dangerous compounds and second of the biomonitoring which detects metabolites excreted in the biological specimens (urine, blood, saliva) and analyses the genotoxicity and gene polymorphisms in the subjects [12]. More specifically the biomonitoring allows to detect the following specific indicators: (i) the dose biomarkers, i.e. metabolites excreted in urine or in other bio-fluids; (ii) the early effect biomarkers, i.e. genotoxicity in peripheral blood lymphocytes and/or in buccal exfoliated cells; and (iii) the susceptibility biomarkers, i.e. the gene polymorphisms encoding for biotransformation enzymes during the exposure. This practice is carried out on exposed workers and nonexposed controls with the goal to assess the presence and quantify the potential health risks. While the dose biomarkers and the genotoxic damage may be immediately analyzed and quantified, the susceptibility biomarkers, being a qualitative parameter, are not quantifiable in terms of single polymorphism belonging to a subject. In such case the results obtained by the genetic analysis on groups of exposed workers have to be considered all together to quantify the relative susceptibility risk with respect to a control group. Based on our experience, the polymorphic genes of the worker population are identified following extraction of the genomic DNA of the subject to identify the genotype encoding the enzyme involved in the detoxification process. Once the worker genotype has been identified, it gives an important indication of the specific susceptibility to that substance by associating the genetic information with the dose and/or the early effect biomarker. In general the homozygous variant genotype (minor allele) is considered a risk allele with respect to the homozygous wild-type genotype (major allele) although there might be a few exceptions [13]. The workers exposed to potential hazardous substances are enrolled in the biomonitoring study only on a voluntary basis to allow the occupational health risk assessment. The results of the gene polymorphism assay together with the data gained by environmental and personal biomonitoring are analysed at the epidemiological level (1) to quantify the

**69**

*The Role of Genetic Polymorphisms in the Occupational Exposure*

identify specific or common susceptibilities in the exposed groups.

indoor exposure and the individual absorbed dose according to the company OELs for the specific hazardous agent, (2) to assess the potential genotoxic effect and (3) to evaluate the influence of the investigated polymorphic genes on the toxicant absorbed dose. Although workers make use of personal protection equipment (PPE), it is possible, in some cases, the high volatility of organic compounds might spread indoor, increasing the toxic substance threshold within the work environment. The finding of an association between the exposure to specific dangerous substances, the presence of cell genotoxicity and the variable functionality of gene polymorphisms are useful to

**3.1 Identification of gene polymorphisms relevant to the occupational exposure**

In our experience several biomonitoring studies have been promoted and carried out in industrial companies to assess the exposure risk of workers manipulating toxic and carcinogenic agents. Here we report the most recent results obtained during four different campaigns carried out in the last 6 years. In 2012, our research group analyzed the exposure of 315 workers to benzene in a petrochemical plant in Italy to evaluate the dose biomarkers S-phenylmercapturic acid (SPMA) and trans,transmuconic acid (t,t-MA) in the worker urine samples and the susceptibility biomarkers in the blood specimens [14]. Since the GST enzymes may influence the metabolite excretion, the research project analyzed the association between metabolite excretion and contribution of the glutathione S transferase T1 (GST-T1) and M1 (GST-M1) polymorphisms to the detoxification. The results confirmed the modulating effect on the excretion of SPMA metabolite in urine by the genetic polymorphism of GST-T1 after exposure to low benzene doses. The same modulating effect was caused by the GST-M1 polymorphism but only at higher benzene doses, like those produced by cigarette smoking. The genotype of the 315 workers has been characterized to identify groups with the highest susceptibility; the workers' gene frequency of GST-T1 positive/null genotype was 0.78 vs. 0.22, while the frequency of GST-M1 positive/null was 0.47 vs. 0.53. Taking into account the genotype frequency of both enzymes, it looks that the GST-M1 polymorphism positive/null is less efficient in the detoxification process than GST-T1. A second study on benzene exposure has been carried out on 301 employees in the oil refinery. The effect of polymorphic genes GST-T1, GST-M1, glutathione S transferase A1 (GST-A1), epoxide hydrolase 1 (EHPX1), NAD(P) H quinone dehydrogenase 1 (NQO1), cytochrome P450 2E1 (CYP2E1), cytochrome P450 1A1 (CYP1A1\*2A) and myeloperoxidase (MPO) involved in the detoxification of benzene has been analyzed. Here the dose biomarker was worked out as the ratio (R) between t,t-MA and S-PMA metabolites excreted in the urinary samples. The effect of smoking as confounding factor contributed to increase the relative production of S-PMA with respect to t,t-MA reducing the R value. This result was attributed to the higher levels of glutathione (GSH) in the red blood cells of smokers than in non-smokers. The analysis of susceptibility biomarkers showed a strong influence of GST-T1 positive polymorphism on the excretion of urinary S-PMA, reducing the conjugation rate of benzene epoxide with GSH in the GST-T1 null subjects. To a lesser extent, a similar effect was observed in individuals with GST-M1 null, GST-A1 and NQO1 mutant genotypes. It has been observed that in subjects with the double null GST-T1 and GST-M1 genotypes, an amplification of the t,t-MA biochemical pathway occurred with respect to the SPMA pathway [15]. However the activity of one GST is compensated by another in GST-M1 and GST-A1 defective subjects, but not in GST-T1 null genotypes, whose S-PMA average excretion is about 50% with respect to the positive genotypes for the same benzene exposure [16]. A further biomonitoring campaign has been conducted in two different manufacturing sites of central Italy on 30 styrene-exposed workers and 26 unexposed controls. In this work the authors

*DOI: http://dx.doi.org/10.5772/intechopen.86975*

## *The Role of Genetic Polymorphisms in the Occupational Exposure DOI: http://dx.doi.org/10.5772/intechopen.86975*

*The Recent Topics in Genetic Polymorphisms*

**occupational setting**

from the Ensembl project of genome databases.

previously elaborated to identify ethnic-specific differences in the susceptibility risk to the typical exposure found in the workplace. In such model a statistical analysis has been done using the publicly available genotype frequency of four ethnic groups (Africans, East Asians, South Asians and Europeans) downloaded

It is widely known the exposure to dangerous substances and carcinogens is commonly associated to the individual capability of metabolizing such compounds which may vary between different individuals and among ethnicities, each characterized by its own specific genetic ancestry. In the occupational setting, the exposure risk is traditionally evaluated by the biological monitoring of workers manipulating hazardous agents. Common work-related substances are polycyclic aromatic hydrocarbons (PAH), a large class of organic compounds with carcinogenic properties (IARC group 1, 2B) used in the manufacture of chemicals, bitumen, and rubber and in shoe factories, while in fibreglass industries and in ship constructions, the most common dangerous substances are volatile organic compounds (VOCs) such as styrene (IARC group 2A), toluene (IARC group 3), xylene (IARC group 3), ethylbenzene (IARC group 2B) and benzene (IARC group I). The majority of these hazardous chemicals are highly toxic and carcinogenic to humans, and in each company, the officially approved occupational exposure limits (OELs) must be respected to ensure a safe environment for the workers' health. The procedure of workplace monitoring is generally standardized. It basically consists first of the environmental monitoring which measures the workers' airborne exposure to dangerous compounds and second of the biomonitoring which detects metabolites excreted in the biological specimens (urine, blood, saliva) and analyses the genotoxicity and gene polymorphisms in the subjects [12]. More specifically the biomonitoring allows to detect the following specific indicators: (i) the dose biomarkers, i.e. metabolites excreted in urine or in other bio-fluids; (ii) the early effect biomarkers, i.e. genotoxicity in peripheral blood lymphocytes and/or in buccal exfoliated cells; and (iii) the susceptibility biomarkers, i.e. the gene polymorphisms encoding for biotransformation enzymes during the exposure. This practice is carried out on exposed workers and nonexposed controls with the goal to assess the presence and quantify the potential health risks. While the dose biomarkers and the genotoxic damage may be immediately analyzed and quantified, the susceptibility biomarkers, being a qualitative parameter, are not quantifiable in terms of single polymorphism belonging to a subject. In such case the results obtained by the genetic analysis on groups of exposed workers have to be considered all together to quantify the relative susceptibility risk with respect to a control group. Based on our experience, the polymorphic genes of the worker population are identified following extraction of the genomic DNA of the subject to identify the genotype encoding the enzyme involved in the detoxification process. Once the worker genotype has been identified, it gives an important indication of the specific susceptibility to that substance by associating the genetic information with the dose and/or the early effect biomarker. In general the homozygous variant genotype (minor allele) is considered a risk allele with respect to the homozygous wild-type genotype (major allele) although there might be a few exceptions [13]. The workers exposed to potential hazardous substances are enrolled in the biomonitoring study only on a voluntary basis to allow the occupational health risk assessment. The results of the gene polymorphism assay together with the data gained by environmental and personal biomonitoring are analysed at the epidemiological level (1) to quantify the

**3. Gene polymorphisms as susceptibility biomarkers in the** 

**68**

indoor exposure and the individual absorbed dose according to the company OELs for the specific hazardous agent, (2) to assess the potential genotoxic effect and (3) to evaluate the influence of the investigated polymorphic genes on the toxicant absorbed dose. Although workers make use of personal protection equipment (PPE), it is possible, in some cases, the high volatility of organic compounds might spread indoor, increasing the toxic substance threshold within the work environment. The finding of an association between the exposure to specific dangerous substances, the presence of cell genotoxicity and the variable functionality of gene polymorphisms are useful to identify specific or common susceptibilities in the exposed groups.
