Study of senescence and possible mechanisms involved in arsenic-induced carcinogenesis in humans

Arsenic (As) induces various patho-physiological outcomes in humans like cancers including skin cancers, peripheral neuropathy (PN) and respiratory diseases. Though reports have shown that arsenic induced senescence (AIS) in vitro; population based studies on AIS and epigenetic regulation of AIS contributing to As-induced diseases remains unexplored. We investigated AIS, senescence-associated secretory phenotype (SASP) markers, telomere length alteration, epigenetic regulation involving altered senescence associated miRNA (SAmiRs) expression in arsenic exposed individuals with characteristic skin lesions and peripheral neuropathy. We also made an attempt to check the genetic damage, overall health status and telomere length in arsenic exposed children. Exposure assessment was done from drinking water and urine collected from arsenic exposed (N=120) and unexposed (N=60) individuals recruited from West Bengal, India. Senescence and telomere length alteration was evaluated using SA β-gal activity, ELISA and quantification of senescence proteins, alternative lengthening of telomere (ALT) associated proteins and telomerase activity. Relative telomere length (RTL) and SA-miRs in AIS was determined by qPCR. The downstream molecule of the miRNA associated with As-induced PN was quantified by immuoblotting. In vitro studies were conducted with sodium arsenite exposed HEK 293 cells, to revalidate the observations. As-exposed individuals exhibited significantly increased senescent cells, upregulated senescence inducers, p53/p21 and SASP markers when compared to unexposed controls. Asexposed skin lesion group showed significantly increased RTL, which was telomeraseindependent but exhibited an over-expression of ALT associated proteins. All the SA-miRs assessed were upregulated in the As-exposed compared to controls, specifically miR-29a. Further analysis found that highest expression of miR29a and peripheral myelin protein 22 (PMP22), a direct target of miR 29a, was among As-exposed individuals with PN. Analyzing other intermediate players regulating PMP22 expression revealed up-regulation of β-catenin and down-regulation of GSK-3β. Our findings suggest that up-regulation of β-catenin, possibly by miR29a mediated negative regulation of β-catenin inhibitors, may play a predominant role in expression of PMP22 which leads to formation of aggresomes. Further work to validate this mechanism is in process in vitro. Arsenic exposed children showed considerable genetic damage as measured by micronucleus assay in the three cell types and also adverse health outcomes like decreased haemoglobin content and gastritis. Telomere length of arsenic exposed children was slightly elevated though it did not reach the significance level. Our findings suggest that arsenic exposure induces senescence in vivo and telomeraseindependent elongation of telomere length is strictly associated with As-induced skin lesions in adults. Epigenetically, arsenic alters the expression of SA-miRs and the mir29a/beta catenin/PMP22 axis might be responsible for arsenic induced PN. However, in children, the telomere length increase and genetic damage in the three cell types and adverse health outcomes suggested that children are equally at danger of arsenic poisoning

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 b-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 overexpression of ALT associated proteins TRF-1 and TRF-2 with higher increase in TRF-2. An increased risk for developing Asinduced 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 lesion

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

Abstract 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.</p

Arsenic Exposure Through Drinking Water Increases the rRsk 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. Keywords: Arsenic, Antinuclear antibody, Liver function tests, Cytokine