High chromosomal instability in workers occupationally exposed to solvents and paint removers
The aim of the present study was to evaluate the genotoxic effect of occupational exposure to aromatic hydrocarbons used as solvents and paint removers, on the frequency of CAs and on the DNA-DI in PBLs of workers at ten car paint shops at the “7 de agosto” neighborhood in Bogota DC, Colombia.
Car paints shop workers are occupationally exposed to a wide range of aromatic hydrocarbons including BTX. Exposure to aromatic hydrocarbons, may take place via vapor inhalation or absorption through the intact skin. Many epidemiological studies have showed a clear relationship between the increase genotoxic damage and exposure to aromatic hydrocarbons, being neccesary to provide more relevant information regarding to the possible deleterious damage upon chromosomes. Although many studies have been conducted around of this topic, the specific type and frequency of such CAs have not been carefully characterized and these could be used as biomarkers of genotoxic damage and as predictors of future cancer risk. To the above is added that in Colombia the information available around the cytogenotoxic damage in car paint shop workers is limited.
The results obtained using high-resolution G-Banding analyses of a large number of metaphases, allowed us to detect previously unreported CAs in individuals exposed to BTX. The mean of CAs found in the exposed group was 3.6 times higher than in the unexposed group, thus indicating a potential cytogenetic hazard due to exposure to aromatic hydrocarbons used as solvents and paint removers in car paint shops.
Among the chromosomal alterations observed at high frequency in the exposed group, monosomies, fragilities, chbr and chrb showed statistically significant differences when were compared to those observed in the unexposed group. In several recent studies, this type of chromosomal alterations have been correlated with a heightened risk of cancer, especially hematological malignancies [33, 34]. For instance, monosomies, observed in gas station attendants and in individuals occupationally exposed to formaldehyde [35, 36], were associated with myeloid malignancies [37]. Further, monosomies of chromosomes 18 and 19, observed by us in the exposed group, were associated with risk of developing leukemia in individuals occupationally exposed to benzene [33]. Nevertheless, although the structural chromosomal alterations identify in the exposed group were not significant, some of them, including del(5)(q) and t(11)(q23), were detected in leukemia patients with likely prior exposure to benzene [12, 38].
In addition, a significant increase in the frequency of FRA, chrb and chtb in exposed compared to unexposed group was also observed. FRA, chrb and chtb are unstable CAs and regions of potential genome instability [39] that can lead to the formation of cancer-specific CAs such as translocations, deletions [39–43], duplications, amplifications [44, 45], sister chromatid exchanges [46], intrachromosomal gene amplification [47] and other chromosomal changes associated with human diseases [48, 49]. Further, many genes identified as tumor suppressors or oncogenes are located at or within fragile sites [50].
Among the FRA identified in this study, fra(9q12) was the most frequently observed in the exposed group. High frequency of this fragility was previously reported by us in a Colombian population with breast cancer [51]. On chromosome 9 are located the tumor suppressor genes CDKN2A, PIPSK1B, BTEB1, RECK and BAG1, the latter associated with antiapoptotic functions and overexpressed in invasive breast carcinomas.
Given the significantly high frequency of fra(9)(q12) in the exposed group, as well as its previous observation in patients with breast cancer, we considered that this fragility could be postulated as a cytogenetic biomarker of genotoxic damage associated to occupational exposure to BTX.
Our findings are consistent with previous reports in which increased chromosomal abnormalities in PBLs were associated with occupational exposure to benzene [3, 9, 35, 36]. However although most studies have mostly shown positive results, others have not found any association [52, 53].
Additionally, it is important to emphasize that increased genotoxic damage and, therefore a higher risk to develop cancer, have also been associated with other specific job occupations. For instance, a higher risk to develop hematologic diseases was observed in benzene exposed oil refinery workers [9], workers exposed to low levels of formaldehyde [35, 54], gas station attendants [36], painters [55] and petroleum refinery workers [56]. Further, an increased risk of laryngeal cancer was also reported in production-related workers, transport equipment operators, miners, tailors, blacksmith and toolmakers, painters, bricklayers and carpenters [57].
In our study, there was a significant increase in DNA-DI, evidenced by the comet assay, in exposed in comparison to the unexposed group. Comet assay has been used as a sensitive biomarker that reveals DNA damage caused either directly by reactive oxidant agents, or indirectly by substances that can generate free radicals [58, 59]. These findings are consistent with previous studies [55, 56, 60, 61] and allow us to confirm that occupational exposure to BTX induce genotoxic damage at both DNA and chromosomal level. However, we also note that smoking habit had no significant effect on DNA-DI among exposed and unexposed groups, which could be due to low cigarette consumption among the workers (1–3 cigarettes per day). Lack of association between DNA-DI and smoking habit in PBLs of individuals occupationally exposed to aromatic hydrocarbons, have been also indicated by several studies [55, 62–67].
In summary, our results demonstrated that occupational exposure to BTX is significantly associated with chromosomal and DNA damage in car paint shops workers and are indicative of high chromosomal instability (CIN). CIN, defined as a state of continuous formation of novel chromosome mutations at a rate higher than in normal cells, could predispose cells to further mutations and by that to an increased risk of malignant transformation [68, 69]. In fact, several prospective cancer studies have shown a linear trend between CAs in PBLs and subsequent cancer risk [35–37, 54, 70–73].