In the present study, no significant difference was observed in cytogenetic endpoints between exposed CKD and non-exposed CKD patients. A significant difference was noted between exposed CKD and exposed non-CKD patients in terms of MN frequency, NDI, chromatid breaks, and fragments. Several studies have shown that chronic kidney failure patients had higher levels of genetic damage [24–27]. In the present study, the cytogenetic alterations observed may not be solely assigned to toxic gas exposure because the effects of confounding variables too contribute to the genetic damage. Overproduction of reactive oxygen species in CKD patients may lead to DNA damage. The imbalance between antioxidant defense mechanisms and excess production of oxidants is augmented in CKD [28]. The conditions of hypertension and dyslipidemia are also being augmented by CKD that in turn encourages the progression of kidney failure [29]. It has been noticed that epigenetic alterations are linked with inflammation and cardiovascular ailment in CKD patients [30]. The increased angiotensin II levels found in CKD patients that enhance premature aging might directly impact the pathophysiology and therapeutics in CKD [27]. Several enhanced pro-oxidant actions also lead to CKD and these are age, hypertension, inflammation, and incompatibility of dialysis membranes [31]. It has been noted that a variety of factors prejudice the formation of MN in cells of CKD like age, sex, genetic makeup, physical and chemical agents as well as the habitual practice of chewing and/or smoking tobacco and drinking alcohol [32]. The conventional and molecular cytogenetic findings are too important in the management of CKD possibly for reducing genomic instability [33].
It was observed that the advanced CKD patients showed more DNA damage, and such damage was increased after hemodialysis in Type 2 Diabetes mellitus [34–35]. Exposure to metals in CKD patients can lead to reductions in kidney functions [36]. Thus, the confounders can be a lifestyle, living environment, nutritional factors, drinking water, and occupational exposure to other toxicants [37]. It was opined that alterations in NDI value are directly related to the proliferative ability of the cell [38]. The urinary cell-free mitochondrial DNA and nuclear DNA could be employed as prognostic biomarkers for kidney outcome in CKD [39]. Recently, observation was noted that CKD patients had increased levels of circulating cell-free DNA as well as different types of DNA damage [40].
The exposed non-CKD Group when compared to the non-exposed non-CKD Group, showed significant cytogenetic damage in terms of MN frequency and NDI. In Chromosomal assay, MI showed a significant decrease but no significant difference was observed for dicentrics, rings, chromatid breaks, and fragments. A few reports are available on the cytogenetic alterations of the individuals exposed to toxic gas [41–43]. The higher chromosomal damage was reported in toxic gas-exposed women [44]. The types of abnormalities recorded were chromosome breaks, gaps, dicentrics, rings, and triradial and quadriradial configurations. It was observed that the mean percentage of acrocentric associations in the toxic gas exposed population was significantly higher as compared to the control [45]. The persistence of genomic instability in terms of higher chromosomal aberrations and atypical lymphocytes was also noticed in the toxic gas-exposed population of Bhopal [46–47]. A pilot follow-up study after 30 years of the tragedy reported stable or clonal rearrangements even after 30 years in the increased SCE and decreased replicative index seen immediately after toxic gas exposure. It also demonstrated a correlation between age, exposure status, and cytogenetic alterations in toxic gas-exposed individuals [48].
The study has several limitations. Firstly the toxic gas exposure was subjectively done as there were not sufficient methods for exposure assessment 37 years back when the tragedy struck. It was crude based on the number of mortality that occurred at the time of the accident. Secondly, as the cases were recruited through the hospital, the information on many confounders of such cytogenetic changes was limited and thus limits the generalization of the findings of the study. Thirdly sequential measurement of cytogenetic parameters along with environmental measurement of various toxic pollutants would have given a better causal-effect relationship of toxic gas exposure with cytogenetic changes.
Thus, to conclude, though the cytogenetic changes are reported similar to earlier studies, it cannot be solely attributed to the exposure to toxic gas as many confounding factors may also contribute to genetic damage but such studies are significant for assessing the risk [49]. Further, because of the complex interactions between environment, disease susceptibility, and genetic susceptibility, the exploration of epigenetic mechanisms to meet the challenges of CKD through novel ideas of molecular mechanisms is warranted.