Arsenic exposure through drinking water leads to senescence and alteration of telomere length in humans: A case-control study in West Bengal, India.

Arsenic (As) induces pre-malignant and malignant dermatological lesions, non-dermatological health effects and cancers in humans. Senescence involves telomere length changes and acquisition of senescence-associated secretory phenotype (SASP), which promotes carcinogenesis. Though in vitro studies have shown that As induces senescence, population based studies are lacking. We investigated the arsenic-induced senescence, telomere length alteration and its contribution towards development of As-induced skin cancer. The study participants included 60 each of As-exposed individuals with skin lesion (WSL), without skin lesions (WOSL) and 60 unexposed controls. Exposure assessment of drinking water and urine was done. SA ß-gal activity, ELISA, and quantification of senescence proteins, alternative lengthening of telomere (ALT) associated proteins and telomerase activity were performed. Relative telomere length (RTL) was determined by qPCR. A significantly higher number of senescent cells, over-expression of p53 and p21 were observed in the As-exposed individuals when compared to unexposed. SASP markers, MMP-1/MMP-3 were significantly higher in the WSL but not IL-6/IL-8. A significant increase of RTL was observed in the WSL group, which was telomerase-independent but exhibited an over-expression of ALT associated proteins TRF-1 and TRF-2 with higher increase in TRF-2. An increased risk for developing As-induced skin lesions was found for individuals having RTL greater than 0.827 (odds ratio, 13.75; 95% CI: 5.66-33.41; P < 0.0001). Arsenic induces senescence in vivo, but the SASP markers are not strictly over-expressed in the As-induced skin lesion group, whereas telomerase-independent elongation of telomere length might be useful for predicting the risk of development of As-induced skin lesions.

Arsenic-induced promoter hypomethylation and over-expression of ERCC2 reduces DNA repair capacity in humans by non-disjunction of the ERCC2-Cdk7 complex.

Arsenic in drinking water is of critical concern in West Bengal, India, as it results in several physiological symptoms including dermatological lesions and cancers. Impairment of the DNA repair mechanism has been associated with arsenic-induced genetic damage as well as with several cancers. ERCC2 (Excision Repair Cross-Complementing rodent repair, complementation group 2), mediates DNA-repair by interacting with Cdk-activating kinase (CAK) complex, which helps in DNA proof-reading during transcription. Arsenic metabolism alters epigenetic regulation; we tried to elucidate the regulation of ERCC2 in arsenic-exposed humans. Water, urine, nails, hair and blood samples from one hundred and fifty seven exposed and eighty eight unexposed individuals were collected. Dose dependent validation was done in vitro using HepG2 and HEK-293. Arsenic content in the biological samples was higher in the exposed individuals compared with the content in unexposed individuals (p < 0.001). Bisulfite-modified methylation specific PCR showed a significant (p < 0.0001) hypomethylation of the ERCC2 promoter in the arsenic-exposed individuals. Densitometric analysis of immunoblots showed a nearly two-fold increase in expression of ERCC2 in exposed individuals, but there was an enhanced genotoxic insult as measured by micronuclei frequency. Immuno-precipitation and western blotting revealed an increased (p < 0.001) association of Cdk7 with ERCC2 in highly arsenic exposed individuals. The decrease in CAK activity was determined by observing the intensity of Ser(392) phosphorylation in p53, in vitro, which decreased with an increase in arsenic dose. Thus we infer that arsenic biotransformation leads to promoter hypomethylation of ERCC2, which in turn inhibits the normal functioning of the CAK-complex, thus affecting DNA-repair; this effect was highest among the arsenic exposed individuals with dermatological lesions.

Epigenetic modifications of DAPK and p16 genes contribute to arsenic-induced skin lesions and nondermatological health effects.

Over 26 million people in West Bengal, India, are exposed to very high levels of arsenic through drinking water, leading to several deleterious endpoints including cancers. To elucidate the role of promoter methylation in arsenic-induced dermatological and nondermatological health effects, methylation status of p16 and DAPK genes was determined. A case-control study was conducted involving 72 individuals with arsenic-induced skin lesions (cases) and 50 individuals without skin lesions (controls), having similar arsenic exposure through drinking water. Methylation status was determined by bisulfite conversion of genomic DNA and methylation-specific PCR. Expression of the genes was determined by real-time PCR and Western blot analysis. Associations between the promoter methylation status and nondermatological health effects were determined from epidemiological survey data. Significant hypermethylation was found in the promoters of both DAPK and p16 genes in the cases compared with the controls resulting in downregulation of both the genes in the cases. There was a 3.4-fold decrease in the expression of death-associated protein kinase and 2.2-fold decrease in gene expression of p16 in the cases compared to the controls, the lowest expression being in the cancer tissues. Promoter hypermethylation of the genes was also associated with higher risk of developing arsenic-induced skin lesions, peripheral neuropathy, ocular and respiratory diseases. This study for the first time makes an attempt to correlate epigenetic modifications of the tumor suppressor genes with dermatological and nondermatological health outcomes in a population chronically exposed to arsenic.

Arsenic-induced toxicity and carcinogenicity: a two-wave cross-sectional study in arsenicosis individuals in West Bengal, India.

In the state of West Bengal in India, over 26 million individuals are exposed to arsenic via drinking water. Dermatological, non-dermatological disorders and cancers are associated with arsenic toxicity. Of late, there has been a decrease in the arsenic concentration in drinking water owing to governmental efforts, raising the possibility of remediation. A cross-sectional study was conducted, where 189 arsenicosis and 171 unexposed individuals were recruited at two time points, (2005-06 and 2010-11) with concomitant decrease in the level of arsenic exposure via drinking water in the arsenicosis group in 2010-11. Parameters studied included dermatological, non-dermatological health status and cytogenetic damage. Decrease of arsenic exposure (190.1 µg/l to 37.94 µg/l) resulted in significant decline in the number of individuals having dermatological disorders (P<0.01) and in the severity of each dermatological outcome (P<0.0001). Micronucleus formation in urothelial cells and lymphocytes decreased significantly (P<0.001). However, there was a significant (P<0.001) rise in the incidence of each of the non-dermatological diseases, that is, peripheral neuropathy, conjunctivitis and respiratory distress over the period. Thirteen (6.87%) of the initially recruited arsenicosis individuals died of cancer, in this period. Remediation by arsenic-safe drinking water can reduce dermatological manifestations and cytogenetic insult; but is unable to counter the non-dermatological symptoms.

Arsenic exposure through drinking water increases the risk of liver and cardiovascular diseases in the population of West Bengal, India.

BACKGROUND: Arsenic is a natural drinking water contaminant affecting 26 million people in West Bengal, India. Chronic arsenic exposure causes cancer, cardiovascular disease, liver disease, neuropathies and ocular diseases. The aims of the present study were to assess bioindicators of hepatocellular injury as indicated by the levels of liver enzymes, to determine the auto immune status, as indicated by the amounts of anti-nuclear antibodies (ANA) and anti-dsDNA antibodies in their serum, and to predict cardiovascular risk in the arsenic exposed population. METHODS: Effect of chronic arsenic exposure on liver was determined by liver function tests. Autoimmune status was measured by measuring ANA and anti-dsDNA in serum. Inflammatory cytokines associated with increased cardiovascular disease risk, IL6, IL8 and MCP-1 were determined. RESULTS: Our results indicated that serum levels of bilirubin, alanine transaminase, aspartate transaminase, alkaline phosphatase and ANA were increased in the arsenic exposed population. Serum levels of IL6 and IL8 also increased in the arsenic exposed group. CONCLUSIONS: Chronic arsenic exposure causes liver injury, increases the serum levels of autoimmune markers and imparts increased cardiovascular risk.