Methylation of arsenic compounds in the human body occurs following a series of biochemical reactions in the presence of methyl donor S-adenosylmethionine (SAM) and catalyzed by arsenite methyltransferase (AS3MT). However, the extent and pattern of methylation differs among the arsenic exposed individuals leading to differential susceptibility. The mechanism for such inter-individual difference is enigmatic. In the present case-control study we recruited exposed individuals with and without arsenic induced skin lesion (WSL and WOSL), and an unexposed cohort, each having 120 individuals. Using ELISA, we observed a reduction in SAM levels (p < 0.05) in WSL compared to WOSL. Linear regression analysis revealed a negative correlation between urinary arsenic concentration and SAM concentration between the study groups. qRT-PCR revealed a significant down-regulation (p < 0.01) of key regulatory genes like MTHFR, MTR, MAT2A and MAT2B of SAM biogenesis pathway in WSL cohort. Methylation-specific PCR revealed significant promoter hypermethylation of AS3MT (WSL vs. WOSL: p < 0.01) which resulted in its subsequent transcriptional repression (WSL vs. WOSL: p < 0.001). Linear regression analysis also showed a negative correlation between SAM concentration and percentage of promoter methylation. Taken together, these results indicate that reduction in SAM biogenesis along with a higher utilization of SAM results in a decreased availability of methyl donor. These along with epigenetic down-regulation of AS3MT may be responsible for higher susceptibility in arsenic exposed individuals.

Chronic arsenic toxicity has become a global concern due to its adverse pathophysiological outcome and carcinogenic potential. It is already established that arsenic induced reactive oxygen species alters mitochondrial functionality. Major regulatory genes for mitochondrial biogenesis, i.e., PGC1α, Tfam, NRF1and NRF2 are located in the nucleus. As a result, mitochondria-nucleus crosstalk is crucial for proper mitochondrial function. This previous hypothesis led us to investigateinvolvement of epigenetic alteration behindenhanced mitochondrial biogenesis in chronic arsenic exposure. An extensive case-control study was conducted with 390 study participants (unexposed, exposed without skin lesion, exposed with skin lesion and exposed skin tumour) from highly arsenic exposed areas ofWest Bengal, India. Methylation specific PCRrevealed significant promoter hypomethylation oftwo key biogenesis regulatory genes, PGC1αandTfam in arsenic exposed individuals and also in skin tumour tissues. Linear regression analysis indicated significant negative correlation between urinary arsenic concentration and promoter methylation status. Increased expression of biogenesis regulatory genes wasobtained by quantitative real-time PCR analysis. Moreover, altered mitochondrial fusion-fission regulatory gene expression was also observed in skin tumour tissues. miR663, having tumour suppressor gene like function was known to be epigenetically regulated through mitochondrial retrograde signal. Promoter hypermethylation with significantly decreased expression of miR663 was found in skin cancer tissues compared to non-cancerous control tissue. In conclusion, results indicated crucial role of epigenetic alteration in arsenic induced mitochondrial biogenesis and arsenical skin carcinogenesis for the first time. However, further mechanistic studies are necessary for detailed understanding of mitochondria-nucleus crosstalk in arsenic perturbation.

The painful invasive chelation therapy makes it challenging to continue the prolonged treatment against arsenic toxicity. Hence, the significance of the present preliminary investigation was to explore a noninvasive treatment strategy against sodium arsenite (As3+) by the use of a hydroethanolic extract of Moringa oleifera (MO) seed. Arsenic treatment (10 mg/kg body-weight) in animals showed significant level of oxidative stress as evidenced by increased serum levels of malondialdehyde (MDA), conjugated dienes (CD) and reduced level of non-protein thiol (NPSH). A significant diminution in the activities of enzymatic antioxidants was noted in As3+-treated rats. As3+ treatment showed a lengthy phase of metestrous in animals followed by significantly diminished ovarian steroidogenesis, increased ovarian follicular degeneration and distortion of uterine tissue histomorphology. In addition, there was a significant depletion of Vitamin-B9 (folate) and B12 following As3+ ingestion. The levels of circulating TNF-α, homocysteine (Hcy), uterine-IL-6, and liver metallothionein (MT-1) were significantly elevated in arsenic treated rats. MO at a dose of 100 mg/kg body-weight could successfully mitigate the uterine ROS generation by maintaining the uterine antioxidant status in As3+- treated rats. This seed extract prevented the deterioration of As3+-mediated ovarian-steroidogenesis and ovarian and uterine histoarchitecture significantly. B9 and B12 levels were also improved following the ingestion of the MO extract in arsenicated animals. Elevation of Hcy, TNF-α and IL-6 was also prevented by this MO seed extract in As3+-treated rats. A further increase of MT-1 level was achieved after MO ingestion in As3+-treated rats. Here, the alleviation of arsenic toxicity might involve via the regulation of the components of S-adenosine methionine (SAM) pool and MT-1.

BACKGROUND: Arsenic exposure is associated with decreased kidney function. The association between low to moderate arsenic exposure and kidney disease has not been fully clarified.
METHODS: The association between arsenic exposure from drinking water and chronic kidney disease (CKD) was examined in a long-term prospective observational study.
METHODS: 6,093 participants 40 years and older were recruited from arseniasis-endemic areas in northeastern Taiwan. Arsenic levels were 28.0, 92.8, and 295.7μg/L at the 50th, 75th, and 90th percentiles, respectively.
METHODS: Well-water arsenic and urinary total arsenic (inorganic plus methylated arsenic species) concentrations, adjusted for urinary creatinine concentration.
RESULTS: Kidney diseases (ICD-9 codes: 250.4, 274.1, 283.11, 403.*1, 404.*2, 404.*3, 440.1, 442.1, 447.3, or 580-589) and CKD (ICD-9 code: 585) ascertained using Taiwan\'s National Health Insurance database 1998 to 2011.
METHODS: HRs contrasting CKD risk across arsenic exposure levels were estimated using Cox regression. Prevalence ORs for proteinuria (protein excretion ≥ 200mg/g) comparing quartiles of total urinary arsenic concentrations were estimated using logistic regression.
RESULTS: We identified 1,104 incident kidney disease cases, including 447 CKD cases (incidence rates, 166.5 and 67.4 per 104 person-years, respectively). A dose-dependent association between well-water arsenic concentrations and kidney diseases was observed after adjusting for age, sex, education, body mass index, cigarette smoking, alcohol consumption, and analgesic use. Using arsenic concentration ≤ 10.0μg/L as reference, multivariable-adjusted HRs for incident CKD were 1.12 (95% CI, 0.88-1.42), 1.33 (95% CI, 1.03-1.72), and 1.33 (95% CI, 1.00-1.77) for arsenic concentrations of 10.1 to 49.9, 50.0 to 149.9, and ≥150.0μg/L, respectively (P for trend=0.02). The association between arsenic concentration and kidney diseases was stronger for women (P for interaction=0.06). Arsenic values in the range of 50th to 75th and 75th to 100th percentiles of total urinary arsenic concentrations were associated with 50% and 67% higher prevalences, respectively, of proteinuria.
CONCLUSIONS: Kidney diseases and CKD outcomes were based on diagnostic codes. Glomerular filtration rates were not available. Other heavy metals were not measured.
CONCLUSIONS: This study describes the temporal relationship between arsenic concentrations ≥ 10μg/L in drinking water and CKD. A dose-dependent association between well-water arsenic concentration and kidney diseases was observed. Higher creatinine-adjusted urinary total arsenic concentrations were associated with a higher prevalence of proteinuria.

OBJECTIVE: To study any possible correlation between arsenic toxicity and the development of oral carcinoma in West Bengal population.
METHODS: Ethical clearance for this study was obtained from the Vivekananda Institute of Medical Sciences. Out of 30 785 patients attending our hospital from November 2012 to July 2015, 107 cases and 50 control individuals were selected. The hair and buccal smear samples were obtained upon their consent for the purpose of the analysis of arsenic count and cytogenetic damage, respectively.
RESULTS: Ninety-six percent of cases came from the highly arsenic affected districts and 81.3% showed their arsenic count above the safe limit (0.8 μg/g) whereas 96% of the controls\' arsenic count was within the safe limit. The study showed a significant difference of the micronuclei and apoptosis frequency between the cases and controls.
CONCLUSIONS: The difference of micronuclei and apoptosis frequency between cases and controls was significant. The maximum number of cases came from highly arsenic affected areas and a higher percentage of cases showed elevated arsenic count, as compared to controls, which may indicate a possible link between arsenic toxicity and this disease. However, a larger sample size is required for a proper correlation. Int J Occup Med Environ Health 2017;30(2):271-279.