Biomonitoring studies focusing on the detection of genomic abnormalities have been carried out in pesticide exposed populations aiming to elucidate the risk associated to the exposure to specific compounds or classes of compounds (Bolognesi, 2003; Bolognesi & Holland, 2016; Paz-Y-Miño et al. 2012; Kori et al. 2018; Vinceti et al. 2017). Agricultural workers exposed to pesticides were found to present a greater risk to some malignancies such as leukemia, neuroblastoma, Wilm’s tumor, non-Hodgkin lymphoma, ovarian cancer, cancers of lung, and stomach cancer (Rapisarda et al. 2017; Kachuri et al. 2017; Andreotti et al. 2018; Bonner et al. 2017; Polanco Rodríguez et al. 2017). The overexpression of important genes linked to the cell cycle has been identified in several neoplasms. Aurora kinase gene family (AURKA and AURKB) is an example of these genes associated to malignancies. In this sense, this study sought to correlate the relationship between minimum levels of expression of aurora kinase genes in rural workers exposed to pesticides. From information obtained through interviews with rural workers associated with the results of gene expression, we demonstrated significant differences in the expression of the studied genes among the group of individuals categorized as "directly” or “indirectly” “exposed" and “not exposed” group, although, the levels of gene expression obtained here are not at the same degree as those found in biopsies of neoplastic tissues. However, our results suggest that possible damage to DNA may be ocurring, which on a temporal scale could promote genomic instability, and ultimately, tumor development.
DNA damage and subsequent genomic instability promotes gene mutations, that help to generate the hallmarks of cancer (Li et al. 2021; Guo et al. 2021; Macheret & Halazonetis, 2017). Additionally, extensive, or unrepaired DNA damage is toxic to cells. DNA damage may cause cell cycle arrest and/or, e led to apoptosis or necrotic cell death (Yedjou et al. 2015). Pesticides cause Reactive Oxygen Species (ROS)-mediated stress and DNA damage, leading to premature cellular senescence and programmed cell death (Peshin et al. 2014). Generation of ROS is associated with the risk of cancer. It can influence the expression of many genes involved in inflammation; cell transformation; and tumor cell death or survival, proliferation, invasion, angiogenesis, and metastasis (Peshin et al. 2014). In 1999, Infante-Rivera and colleagues (1999) demonstrated that mothers who got exposed to pesticides during pregnancies and if her child presents a CYP1A1m1 or a CYP1A1m2 mutation had increased risk to develop acute myeloid leukemia. or AML. Of note, CYP1A1, CYP2D6, GSTT1, and GSTM1 are genes that encode enzymes responsible for metabolizing carcinogenic substances. Cytochrome P-450 family are involved in the transformation of pro-carcinogenic compounds to reactive species which have genotoxic and cytotoxic effects (Infante-Rivard et al. 1999). These events may also render the repair machinery less efficient resulting in premature aging and apoptosis. ROS imbalances may also recruit aberrant proteins which may results in imbalance of the signaling pathway leading to tumorigenic processes (Wang & Yi, 2008). ROS generation may in turn result in polymorphisms that may change the expression of important genes, as for example, aurora kinase genes (Kumari et al. 2014; Zekri et al. 2017).
Some studies have reported different “degrees” of genomic instability in agricultural workers exposed, and not exposed to pesticide with significant difference between the groups (Garaj-Vrhovac & Zeljezic, 2000). Follow up of previously exposed agricultural workers who had not been exposed to pesticides for a period of six months showed that they continued presenting significant genotoxic damage, leading to the conclusion that pesticides can cause changes in the mechanisms that repair mutations (Collins et al. 2014). In this context, recent research also shows that exogenous or endogenous ROS caused by pesticides exposure promoted mitotic arrest. Delayed formation and abnormal function of the mitotic spindles directly impeded mitosis, promoted abnormal chromosome separation and was responsible for ROS-induced mitotic arrest (Wang et al. 2016). It is important to keep in mind that abnormal expression of aurora kinase genes play roles in centriole duplication, an important process during cell mitosis. An important study demonstrated that overexpression of AURKA and Plk4 was associated with emergence of amplified centrosomes (Donthamsetty et al. 2014), with production of aneuploid cells as result. Although, we have not performed a cytogenetic study on cells obtained from the exposed, and not exposed agricultural workers, we believe that structural chromosomal abnormalities, as for example chromosome gaps and breaks, could be found in the samples studied, based on AURKA/AURB expression profile, and in accordance with the results of the micronucleus test.
Benedetti and co-workers (2013) and, Kvitko and co-workers (2012) independently, observed significant differences for the quantification of DNA damage in agricultural workers subjected to the comet assay, corroborating with our results obtained from the micronucleus test. These studies were conducted among workers exposed to different formulations of pesticides in their work. In this context, the exposure to a mix of chemical formulations may be responsible to produce cross-link DNA-DNA and DNA-protein, rupture of the two chains of DNA, formation of DNA adducts, all affecting the gene expression profile of important genes, closed related to cell cycle (Garaj-Vrhovac & Zeljezic, 2000). This scenario may present itself worsened by the continual exposure to pesticides without proper protection with adequate equipment (PPE). According to our results, 53,4% of the agricultural workers reported have never used PPE. Thus, the persistent cytological damage can lead to a higher level of cytogenetic changes (Bull et al. 2006).
In addition, our results showed a clear correlation among individuals categorized as "directly” and “indirectly” “exposed" to pesticides and the damage rate, either by the micronucleus test or aurora kinase expression profile. This fact raises some concerns about possible risk for cancer development. Merhi and co-workers (2007) concluded a study that followed a group of agricultural workers through a long period of exposure to pesticides (more than 10 years). They observed an increased risk for the development of hematopoietic tumors and non-Hodgkin’s lymphoma. Ferraz and co-workers (2016), observed that among healthy subjects distributed in two groups (19–29 years old × over 60 years old), the frequency of micronuclei and nuclear degenerative changes was significantly higher among the older group. On the other hand, they showed that avoiding the use of pesticides or at least reducing their exposure, it could minimize the effects of aging, reducing the risk of developing degenerative diseases.
Epigenetic modifications have also been noted as consequence of pesticides exposure. Li and co-workers (2011) evaluated the epigenetic effects of pesticides, in a porcine kidney epithelial cell line (PK15) in order to achieve a better understanding of its non-neuronal cytotoxicity. Microarray analyses showed an altered miRNA and mRNA expression profile, showing that the epigenetic mechanisms involving miRNA expression modifications play a pivotal role in citotoxicity. In addition, Collotta and co-workers (2013) evaluated the effect of a mix of pesticides on miRNA expression in zebrafish. The expression profile of some miRNA was altered after treatment with these chemicals, suggesting their role in the toxicity mechanisms of these compounds and representing a possible novel toxicological biomarker. In general, the exposure to environmental factors can alter DNA methylation patterns, inducing destabilizing changes in gene expression patterns potentially leading to cell transformation and tumorigenesis (Collota et al. 2013). Thus, alteration on genome hypomethylation and/or hypermethylation of CpG islands of specific genes, including aurora kinase genes, and have been increasingly found in different types of tumors (Das & Singal, 2004; Krushkal et al. 2020).
the consequences of exposure to pesticides in humans have been reported in the literature. The use of pesticides around the world has reached unimaginable proportions, even though some countries have banned the use of pesticides and gradually are adopting strategies that offer fewer potential risks to human health, as for example the advent of transgenic foods. Our results showed, in an unprecedented way, alterations in the expression patterns of important genes of the aurora kinase family, often associated with neoplastic development. We note that even individuals not directly exposed to pesticides can present cell abnormalities and these abnormalities increase with exposure. The development of this work proposal progressed with several campaigns about the awareness of the risks caused by exposure to pesticides, as well as the importance of using PPE during pesticide management. As previously mentioned, changes in habits are the main attitudes aimed to avoiding health problems resulting from exposure to pesticides. From a genetic point of view, our results may be interpreted as "a warning sign" regarding the negative effect of pesticide exposure. We believe that biomonitoring strategies, based on the expression levels of the AURKA and AURKB genes may provide important indicator on the evolution of genomic instability in the cells of agricultural workers exposed to pesticides.