Cancer risks associated with arsenic in drinking water

Assessing the health risks of coal-burning arsenic-induced skin damage: A 22-year follow-up study in Guizhou, China

Risk assessment of arsenic-induced skin damage has always received significant global attention. Theories derived from arsenic exposure in drinking water may not be applicable to the coal-burning type to arsenic-exposed area. Furthermore, very few studies have successfully determined the reference value of cumulative arsenic (CA) exposure that leads to specific skin lesions. In this study, we conducted a 22-year follow-up investigation to assess the risk of skin lesions and cancer resulting from long-term, multi-channel arsenic exposure from hazard identification, dose-response assessment, exposure assessment, and risk characterization. The results show that the arsenic exposure can significantly increase the prevalence of skin lesions. For each interquartile range increase of hair arsenic (HA) and CA, the risk of skin damage increased by 1.91 and 3.90 times, respectively. The lower confidence limit of the benchmark dose of HA of arsenic-induced various skin lesions ranged from 0.07 to 0.12 μg·g-1, and 932.57 to 1368.92 mg for CA. The chronic daily intake, lifetime average daily dose in the arsenic-exposed area after the comprehensive prevention and control measures have decreased significantly, but remained higher than the daily baseline level of 3.0 μg·kg-1·d-1. Even as recently as 2020, the hazard quotients and hazard index still exceeded 1, measuring 155.33 and 55.20, and the lifetime excess risk of skin cancer (2.80 × 10-3) remains significantly higher than the acceptable level of 10-6. Our study underscores the effectiveness of comprehensive prevention and control measures in managing high arsenic exposure in coal-burning arsenic poisoning areas. However, it is crucial to acknowledge that the risk of both non-carcinogenic and carcinogenic effects on the skin remains substantially higher than the acceptable level. We recommend setting reference limits for monitoring skin damage among individuals exposed to arsenic, with a recommended upper limit of 0.07 μg·g-1 for HA and a maximum acceptable level of 935.57 mg for CA.

Epigenome: biosensor of cumulative exposure to chemical and nonchemical stressors related to environmental justice

Understanding differential disease susceptibility requires new tools to quantify the cumulative effects of environmental stress. Evidence suggests that social, physical, and chemical stressors can influence disease through the accumulation of epigenetic modifications. Geographically stable epigenetic alterations could identify plausible mechanisms for health disparities among the disadvantaged and poor. Relations between neighborhood-specific epigenetic markers and disease would identify the most appropriate targets for medical and environmental intervention. Complex interactions among genes, the environment, and disease require the examination of how epigenetic changes regulate susceptibility to environmental stressors. Progress in understanding disparities in disease susceptibility may depend on assessing the cumulative effect of environmental stressors on genetic substrates. We highlight key concepts regarding the interface between environmental stress, epigenetics, and chronic disease.

Specific Roles of MicroRNAs in Their Interactions with Environmental Factors

MicroRNAs (miRNAs) have emerged as critical regulators of gene expression by modulating numerous target mRNAs expression at posttranscriptional level. Extensive studies have shown that miRNAs are critical in various important biological processes, including cell growth, proliferation, differentiation, development, and apoptosis. In terms of their importance, miRNA dysfunction has been associated with a broad range of diseases. Increased number of studies have shown that miRNAs can functionally interact with a wide spectrum of environmental factors (EFs) including drugs, industrial materials, virus and bacterial pathogens, cigarette smoking, alcohol, nutrition, sleep, exercise, stress, and radiation. More importantly, the interactions between miRNAs and EFs have been shown to play critical roles in determining abnormal phenotypes and diseases. In this paper, we propose an outline of the current knowledge about specific roles of miRNAs in their interactions with various EFs and analyze the literatures detailing miRNAs-EFs interactions in the context of various of diseases.

Increased serum level of epidermal growth factor receptor in liver cancer patients and its association with exposure to arsenic

Arsenic is a human carcinogen and can activate epidermal growth factor receptor (EGFR) in human cell lines. As EGFR is associated with the occurrence of cancers, we conducted a study to evaluate whether serum EGFR may increase in liver cancer patients, particularly in those with exposure to arsenic. We recruited 100 patients of liver cancer and 100 age- and sex-matched controls in Taiwan and determined EGFR levels in sera by enzyme-linked immunosorbent assay. The patients had higher EGFR levels (668.1 vs. 243.1 fmol/mL, p<0.01), and after adjusting for hepatitis B and C, they still had an average EGFR level 406.1 fmol/mL higher than that of the controls (p<0.01). When we compared 22 patients residing in an endemic area of arsenic intoxication to 22 age- and sex-matched patients residing outside the area, we found that patients from the endemic area had higher EGFR levels (882.8 vs. 511.6 fmol/mL, p = 0.04). We concluded that EGFR is over-expressed in patients of liver cancer, particularly in those with exposure to arsenic, and therefore, serum EGFR level is not only a potential biomarker of liver cancer, but also a potential biomarker of cancers associated with arsenic exposure.

The effects of arsenic trioxide on DNA synthesis and genotoxicity in human colon cancer cells

Colon cancer is the third leading cause of cancer-related deaths worldwide. Recent studies in our laboratory have demonstrated that arsenic trioxide is cytotoxic in human colon cancer (HT-29), lung (A549) and breast (MCF-7) carcinoma cells. The purpose of the present study is to investigate the effects of arsenic trioxide on DNA synthesis and the possible genotoxic effects on human colon cancer cells. HT-29 cells were cultured according to standard protocol, followed by exposure to various doses (0, 2, 4, 6, 8, 10, and 12 μg/mL) of arsenic trioxide for 24 h. The proliferative response (DNA synthesis) to arsenic trioxide was assessed by [³H]thymidine incorporation. The genotoxic effects of arsenic-induced DNA damage in a human colon cancer cell line was evaluated by the alkaline single cell gel electrophoresis. Results indicated that arsenic trioxide affected DNA synthesis in HT-29 cells in a biphasic manner; showing a slight but not significant increase in cell proliferation at lower levels of exposure (2, 4 and 6 μg/mL) followed by a significant inhibition of cell proliferation at higher doses (i.e., 8 and 10 μg/mL). The study also confirmed that arsenic trioxide exposure caused genotoxicity as revealed by the significant increase in DNA damage, comet tail-lengths, and tail moment when compared to non-exposed cells. Results of the [³H]thymidine incorporation assay and comet assay revealed that exposure to arsenic trioxide affected DNA synthesis and exhibited genotoxic effects in human colon cancer cells.

Dual actions involved in arsenite-induced oxidative DNA damage

Arsenic is a recognized human carcinogen, but the mechanism of carcinogenesis is not well understood. Oxidative stress and inhibition of DNA damage repair have been postulated as potential carcinogenic actions of arsenic. The present study tests the hypothesis that arsenite not only induces oxidative stress but also inhibits the activity of the DNA base excision repair protein, poly(ADP-ribose) polymerase-1 (PARP-1), leading to exacerbation of the oxidative DNA damage induced by arsenic. HaCat cells were treated with arsenite for 24 h before measuring 8-hydroxyl-2'-deoxyguanosine (8-OHdG), PARP-1 activity, and reactive oxygen species (ROS). Zinc supplementation and PARP-1 siRNA were used to increase or decrease, respectively, the PARP-1 protein's physiological function. At high concentrations (10 microM or higher), arsenite greatly induced oxidative DNA damage, as indicated by 8-OHdG formation. At lower concentrations (1 microM), arsenite did not produce detectable 8-OHdG, but was still able to effectively inhibit PARP-1 activity. Zinc supplementation reduced the formation of 8-OHdG, restored the PARP-1 activity inhibited by arsenite, but did not decrease ROS production. SiRNA knockdown of PARP-1 did not affect the 8-OHdG level induced by arsenic, while it greatly increased the 8-OHdG level produced by hydrogen peroxide indicating that PARP-1 is a molecular target of arsenite. Our findings demonstrate that in addition to inducing oxidative stress at higher concentrations, arsenite can also inhibit the function of a key DNA repair protein, PARP-1, even at very low concentrations, thus exacerbating the overall oxidative DNA damage produced by arsenite, and potentially, by other oxidants as well.

Cytotoxic Effect of Arsenic Trioxide in Adenocarcinoma Colorectal Cancer (HT-29) Cells

Arsenic is a heavy metal that exhibits a high degree of toxicity to various organ systems. In humans, this compound is associated with an increase risk of skin cancer, and may cause cancers of the lung, liver, bladder, kidney, and colon. The mechanism of arsenic-related carcinogenicity remains to be elucidated. Hence, the aim of the present study was to investigate the cytotoxic effects of arsenic trioxide (As(2)O(3)) on adenocarcinoma colorectal cancer (HT-29) cells using the MTT [3-(4,5 dimethylthiazoyl-2-yl)-2,5- diphenyltetrazolium bromide] assay for cell viability. To achieve this objective, HT-29 cells were cultured and exposed to various doses (0, 2, 4, 6, 8, 10, 12, and 14 μg/ml) of arsenic trioxide for 24 h, 48 h, and 72 h respectively, and subsequently assessed for viability following a standard MTT test protocol. Experimental data indicated that arsenic trioxide is cytotoxic to colon cancer cells showing LD(50) values of 9.8, 9.4 and 9.0 μg/ml upon 24, 48 and 72 h of exposure, respectively. There was a dose-dependent response with regard to As(2)O(3) toxicity in HT-29 cells. Although there was a reduction in LD(50) value with increasing exposure time, this decrease was not statistically significant.