Dose-response for assessing the cancer risk of inorganic arsenic in drinking water: the scientific basis for use of a threshold approach

Bayesian benchmark dose analysis for inorganic arsenic in drinking water associated with bladder and lung cancer using epidemiological data

Abundant epidemiological evidence has shown that there is a strong causal relationship between long-term exposure to inorganic arsenic (iAs) through drinking water and a few types of cancer (e.g., lung and bladder cancer). Traditionally, a linear low-dose extrapolation assumption was applied in risk assessment for iAs which resulted in a relatively conservative cancer risk estimate. Growing biological evidence suggests that the mode of action of iAs-induced cancer follows a threshold process (e.g., sufficient concentration of trivalent arsenic is required to disrupt normal cellular function). In this study, we applied the benchmark dose (BMD) methodology to model the relationship between the relative risk of bladder and lung cancer and the iAs concentration in drinking water using the high-quality epidemiological data reported in recently published papers, with a special focus on the low exposure range (i.e., <150 μg/L). Because of its biological plausibility and statistical flexibility, the Hill model has been chosen to model the data under a Bayesian framework. A Bayesian hierarchal model together with a bootstrap method for exposure estimation were applied to quantify uncertainty from various sources, including the within-study, between-study, and exposure uncertainties. Dose-response assessment results obtained from a number of alternative model structures and methods consistently demonstrate a threshold type dose-response curve with a threshold in the range between 40-60 μg/L of iAs concentration in drinking water. The BMD for iAs in drinking water associated with 0.1 % increase in relative risk of bladder cancer is 42.2 μg/L (BMDL 39.2 μg/L); for 0.05 % increase, the BMD is 41.6 μg/L (BMDL 38.6 μg/L). For lung cancer, the two counterpart BMD estimates are 57.0 μg/L (BMDL 43.6 μg/L) and 55.7 μg/L (BMDL 42.5 μg/L) for 0.1 % and 0.05 % increase, respectively. These analyses provide additional statistical support for a non-linear dose response for cancer risk from inorganic arsenic which may have important policy implications.

Reactive oxygen species-evoked genotoxic stress mediates arsenic-induced suppression of male germ cell proliferation and decline in sperm quality

This study aimed to investigate whether genotoxic stress mediates arsenic (As)-induced decline in sperm quality. Mice drank ultrapure water containing NaAsO₂ (15 mg/L) for 70 days. The mature seminiferous tubules and epididymal sperm count were reduced in As-exposed mice. Cell proliferation, determined by immunostaining with Ki67, was suppressed in As-exposed seminiferous tubules and GC-1 cells. PCNA, a proliferation marker, was reduced in As-exposed mouse testes. Cell growth index was decreased in As-exposed GC-1 cells. Flow analysis showed that As-exposed GC-1 cells were retarded at G2/M phase. CDK1 and cyclin B1 were reduced in As-exposed GC-1 cells and mouse testes. Additional experiment revealed that p-ATR, a marker of genotoxic stress, was elevated in As-exposed mouse testes and GC-1 cells. Accordingly, p-p53 and p21, two downstream molecules of ATR, were increased in As-exposed GC-1 cells. Excess reactive oxygen species (ROS), measured by immunofluorescence, and DNA-strand break, determined by Comet assay, were observed in As-exposed GC-1 cells. γH2AX, a marker of DNA-strand break, was elevated in As-exposed seminiferous tubules and GC-1 cells. NAC alleviated As-evoked DNA damage, genotoxic stress, cell proliferation inhibition and sperm count reduction. In conclusion, ROS-evoked genotoxic stress mediates As-induced germ cell proliferation inhibition and decline in sperm quality.

Heavy metal associated health hazards: An interplay of oxidative stress and signal transduction

Heavy metal-induced cellular and organismal toxicity have become a major health concern in biomedical science. Indiscriminate use of heavy metals in different sectors, such as, industrial-, agricultural-, healthcare-, cosmetics-, and domestic-sectors has contaminated environment matrices and poses a severe health concern. Xenobiotics mediated effect is a ubiquitous cellular response. Oxidative stress is one such prime cellular response, which is the result of an imbalance in the redox system. Further, oxidative stress is associated with macromolecular damages and activation of several cell survival and cell death pathways. Epidemiological as well as laboratory data suggest that oxidative stress-induced cellular response following heavy metal exposure is linked with an increased risk of neoplasm, neurological disorders, diabetes, infertility, developmental disorders, renal failure, and cardiovascular disease. During the recent past, a relation among heavy metal exposure, oxidative stress, and signaling pathways have been explored to understand the heavy metal-induced toxicity. Heavy metal-induced oxidative stress and its connection with different signaling pathways are complicated; therefore, the systemic summary is essential. Herein, an effort has been made to decipher the interplay among heavy metals/metalloids (Arsenic, Chromium, Cadmium, and Lead) exposures, oxidative stress, and signal transduction, which are essential to mount the cellular and organismal response. The signaling pathways involved in this interplay include NF-κB, NRF2, JAK-STAT, JNK, FOXO, and HIF.

Relative roles of Arbuscular Mycorrhizae in establishing a correlation between soil properties, carbohydrate utilization and yield in Cicer arietinum L. under As stress

Accumulation of As (metalloid) degrades soil by negatively affecting the activities of soil enzymes, which in turn reduce growth and yield of the inhabiting plant. Arbuscular mycorrhizal (AM) symbiosis can impart metalloid tolerance in plants by secreting glomalin-related soil protein (GRSP) which binds with As or inertly adsorb in the extraradical mycelial surface. However, profitable use of AM requires selection of the most efficient combination of host plant and fungal species. The current study, therefore designed to study the efficacy of 3 a.m. fungal species: Rhizoglomus intraradices (Ri), Funneliformis mosseae (Fm) and Claroideoglomus claroideum (Cc) in imparting arsenate As(V) and arsenite As(III) stress tolerance in Cicer arietinum (chickpea) genotypes (G) - relatively metalloid tolerant- HC 3 and sensitive- C 235. Roots were found to be more severly affected as compared to shoots which resulted into a major decline in uptake of nutrients, chlorophyll concentrations and yield with As(III) inducing more toxic effects than As(V). HC 3 established more effective mycorrhizal symbiosis and was able to extract higher nutrients from the soil than C 235. Ri was most beneficial in improving plant biomass, carbohydrate utilization and productivity followed by Fm and Cc which could be due to its capability to initiate highest percent colonization and least metalloid uptake in roots through higher glomalin production in the soil. Moreover, Ri was highly efficient in improving soil enzymes activities-phosphatases (PHAs), β-glucosidase (BGA) and invertase (INV), thereby, imparting metalloid tolerance in chickpea genotypes. The results suggested use of Ri-chickpea symbiosis as a promising strategy for ameliorating As stress in chickpea.

Catalog of exogenous risk factors for bladder carcinogenesis

PURPOSE OF REVIEW

The aim of this article is to provide an overview of recent findings regarding the risk factors for bladder cancer.

RECENT FINDINGS

Most of the available data derive from retrospective analysis. Smoking represents the most common and important risk factor. Occupational, dietary, and environmental exogenic carcinogen exposure, as well as several lifestyle factors, can increase the risk of developing bladder cancer.

SUMMARY

Bladder cancer is a common malignancy worldwide. Cigarette smoking, exposure to aromatic amines and arsenic are known risk factors for bladder cancer. Evidence on other modifiable risk factors such as carcinogen exposure derived from the diet or environment as well as occupational hazards is still weak. Medical conditions leading to chronic inflammation, altering insulin resistance, negatively modulating the immune system and/or genetic alterations may have a role in bladder cancer carcinogenesis. Further studies are, however, necessary to identify possible exogenic risk factors, as well as their interactions, that partake in the carcinogenesis of bladder cancer.

Total Reflection X-Ray Fluorescence Spectroscopy (TXRF) Method Validation: Determination of Heavy Metals in Dietary Supplements

Dietary supplements may contain heavy metals with the property of bioaccumulation in humans. The aim of this research was to validate and apply two analytical methods to determine Pb, As, Cr, and Hg in dietary supplements by Total Reflection X-ray Fluorescence Spectroscopy (TXRF). Methods validation was conducted through a multivariate analysis using a central composite design (CCD) and a desirability function. Critical values for each study variable were established. The TXRF_DS_1 method was proposed for Pb, As, and Cr determinations, while the TXRF_DS_2 was established for Hg analysis. The digestion method with an acid mixture (HNO3 + HCl + H2O2) was used to break down the organic material of dietary supplements. A solution of 10 μg L−1 Ga was used as an internal standard. Excellent analytical performance was obtained as LODs of 0.59, 0.41, 0.57, and 0.75 μg L−1 and LOQs of 1.95, 1.35, 1.90, and 2.50 μgL −1 for Pb, As, Cr, and Hg, respectively. Calibration curves showed a good linearity for all elements (R2>0.999). Excellent accuracy and precision in measurements (% RSD) was achieved. The real and spiked samples analysis demonstrated the applicability of the TXRF technique (percentage recovery 91–108%). Besides, two samples were analyzed in a comparison study between the TXRF_DS_1 method and the ICP-OES method. The results obtained showed good agreement between both techniques. The TXRF technique allows the analysis of toxic heavy metals in dietary supplements, which are marketed in a wide variety of presentations.

Screening of hub genes and prediction of putative drugs in arsenic-related bladder carcinoma: An in silico study

BACKGROUND

Evidence showed that inorganic arsenic (iAs) can trigger malignant transformation in cells with complex mechanisms. Thus, we aimed to investigate the possible molecules, pathways and therapeutic drugs for iAs-induced bladder cancer (BC) by using bioinformatics approaches.

METHODS

Microarray-based data were analyzed to screen the differentially expressed genes (DEGs) between iAs-related BC cells and controls. Then, the roles of DEGs were annotated and the hub genes were screened out by protein-protein interaction network. The key genes were further selected from the hub genes through an assessment of the prognostic values. Afterward, potential drugs were predicted by using CMAP analysis.

RESULTS

Analysis of a dataset (GSE90023) generated 21 upregulated and 47 downregulated DEGs, which were enriched in various signaling pathways. Among the DEGs, four hub genes including WNT7B, SFRP1, DNAJB2, and ATF3, were identified as the key genes because they might predict poor prognosis in BC patients. Lastly, Cantharidin was predicted to be a potential drug reversing iAs-induced malignant transformation in urinary epithelium cells.

CONCLUSION

The present study found several hub genes involved in iAs-induced malignant transformation in urinary epithelium cells, and predicted several small agents for iAs toxicity prevention or therapy.

Dose-Response Analysis of Exposure to Arsenic in Drinking Water and Risk of Skin Lesions: A Systematic Review of the Literature

Background:

Exposure to high arsenic concentrations in drinking water has been associated with skin lesions. Our goal was to conduct a systematic review of studies on skin lesions and arsenic exposure, with emphasis on results at low level of exposure.

Methods:

We conducted a systematic review of studies reporting estimates of either prevalence or risk of skin lesions associated with exposure to more than 2 levels of arsenic in drinking water. We reviewed and abstracted the relevant results, with the aim of conducting a dose-response meta-analysis.

Results:

Nine studies of skin lesions were reviewed. Strong heterogeneity in the results did not meet the criteria for performing a meta-analysis. The relative risks for an increase of 10 μg/L arsenic in drinking water ranged from 1.002 to 1.140 (p-value of heterogeneity < 0.0001). Protection from bias and confounding was inadequate in most studies.

Conclusion:

Current studies are inadequate to conduct meta-analysis on dose-response relationship between exposure to arsenic in drinking water and skin lesions. Studies with complete exposure histories indicate skin lesions are associated with arsenic exposure in excess of 50 µg/L or higher.

Micro-RNAs: Crossroads between the Exposure to Environmental Particulate Pollution and the Obstructive Pulmonary Disease

Environmental pollution has reached a global echo and represents a serious problem for human health. Air pollution encompasses a set of hazardous substances, such as particulate matter and heavy metals (e.g., cadmium, lead, and arsenic), and has a strong impact on the environment by affecting groundwater, soil, and air. An adaptive response to environmental cues is essential for human survival, which is associated with the induction of adaptive phenotypes. The epigenetic mechanisms regulating the expression patterns of several genes are promising candidates to provide mechanistic and prognostic insights into this. Micro-RNAs (miRNAs) fulfil these features given their ability to respond to environmental factors and their critical role in determining phenotypes. These molecules are present in extracellular fluids, and their expression patterns are organ-, tissue-, or cell-specific. Moreover, the experimental settings for their quantitative and qualitative analysis are robust, standardized, and inexpensive. In this review, we provide an update on the role of miRNAs as suitable tools for understanding the mechanisms behind the physiopathological response to toxicants and the prognostic value of their expression pattern associable with specific exposures. We look at the mechanistic evidence associable to the role of miRNAs in the processes leading to environmental-induced pulmonary disease (i.e., chronic obstructive pulmonary disease).

Prostate Cancer Incidence in U.S. Counties and Low Levels of Arsenic in Drinking Water

Background: Although inorganic arsenic in drinking water at high levels (100s–1000s μg/L [ppb]) increases cancer risk (skin, bladder, lung, and possibly prostate), the evidence at lower levels is limited. Methods: We conducted an ecologic analysis of the dose-response relationship between prostate cancer incidence and low arsenic levels in drinking water in a large study of U.S. counties (N = 710). County arsenic levels were <200 ug/L with median <100 ug/L and dependency greater than 10%. Groundwater well usage, water arsenic levels, prostate cancer incidence rates (2009–2013), and co-variate data were obtained from various U.S. governmental agencies. Poisson and negative-binomial regression analyses and stratified analysis were performed. Results: The best fitting polynomial analysis yielded a J-shaped linear-quadratic model. Linear and quadratic terms were significant (p < 0.001) in the Poisson model, and the quadratic term was significant (p < 0.05) in the negative binomial model. This model indicated a decreasing risk of prostate cancer with increasing arsenic level in the low range and increasing risk above. Conclusions: This study of prostate cancer incidence in US counties with low levels of arsenic in their well-water arsenic levels finds a j-shaped model with decreasing risk at very low levels and increasing risk at higher levels.

Analysis of the dynamic aberrant landscape of DNA methylation and gene expression during arsenic-induced cell transformation

Inorganic arsenic is a well-known carcinogen associated with several types of cancer, but the mechanisms involved in arsenic-induced carcinogenesis are not fully understood. Recent evidence points to epigenetic dysregulation as an important mechanism in this process; however, the effects of epigenetic alterations in gene expression have not been explored in depth. Using microarray data and applying a multivariate clustering analysis in a Gaussian mixture model, we describe the alterations in DNA methylation around the promoter region and the impact on gene expression in HaCaT cells during the transformation process caused by chronic exposure to arsenic. Using this clustering approach, the genes were grouped according to their methylation and expression status in the epigenetic landscape, and the changes that occurred during the cellular transformation were identified adequately. Thus, we present a valuable method for identifying epigenomic dysregulation.

Arsenic-Induced Carcinogenesis and Immune Dysregulation

Arsenic, a metal ubiquitously distributed in the environment, remains an important global health threat. Drinking arsenic-contaminated water is the major route of human exposure. Exposure to arsenic contributes to several malignancies, in the integumentary, respiratory, hepatobiliary, and urinary systems. Cutaneous lesions are important manifestations after long-term arsenic exposure. Arsenical skin cancers usually herald the development of other internal cancers, making the arsenic-induced skin carcinogenesis a good model to investigate the progression of chemical carcinogenesis. In fact, only a portion of arsenic-exposed humans eventually develop malignancies, likely attributed to the arsenic-impaired immunity in susceptible individuals. Currently, the exact pathophysiology of arsenic-induced carcinogenesis remains elusive, although increased reactive oxidative species, aberrant immune regulations, and chromosome abnormalities with uncontrolled cell growth might be involved. This review discusses how arsenic induces carcinogenesis, and how the dysregulated innate and adaptive immunities in systemic circulation and in the target organs contribute to arsenic carcinogenesis. These findings offer evidence for illustrating the mechanism of arsenic-related immune dysregulation in the progression of carcinogenesis, and this may help explain the nature of multiple and recurrent clinical lesions in arsenic-induced skin cancers.

Arsenic Neurotoxicity in Humans

Arsenic (As) contamination affects hundreds of millions of people globally. Although the number of patients with chronic As exposure is large, the symptoms and long-term clinical courses of the patients remain unclear. In addition to reviewing the literature on As contamination and toxicity, we provide useful clinical information on medical care for As-exposed patients. Further, As metabolite pathways, toxicity, speculated toxicity mechanisms, and clinical neurological symptoms are documented. Several mechanisms that seem to play key roles in As-induced neurotoxicity, including oxidative stress, apoptosis, thiamine deficiency, and decreased acetyl cholinesterase activity, are described. The observed neurotoxicity predominantly affects peripheral nerves in sensory fibers, with a lesser effect on motor fibers. A sural nerve biopsy showed the axonal degeneration of peripheral nerves mainly in small myelinated and unmyelinated fibers. Exposure to high concentrations of As causes severe central nervous system impairment in infants, but no or minimal impairment in adults. The exposure dose-response relationship was observed in various organs including neurological systems. The symptoms caused by heavy metal pollution (including As) are often nonspecific. Therefore, in order to recognize patients experiencing health problems caused by As, a multifaceted approach is needed, including not only clinicians, but also specialists from multiple fields.

Low-Level Exposure to Arsenic in Drinking Water and Risk of Lung and Bladder Cancer: A Systematic Review and Dose-Response Meta-Analysis

BACKGROUND

Exposure to high levels of arsenic in drinking water has been associated with an increased risk of lung and bladder cancer, but the presence of an increased risk at low levels is questionable.

METHODS

A systematic review and a dose-response meta-analysis were conducted on risk estimates of lung and bladder cancer for exposure to arsenic in drinking water up to 150 µg/L, using a 2-stage approach based on a random-effects model.

RESULTS

Five studies of lung cancer were identified; the meta-relative risk (RR) for an increase of 10 µg/L arsenic level was 1.03 (95% confidence interval [CI]: 0.99-1.06; P heterogeneity = .05). The meta-analysis of bladder cancer included 8 studies; the meta-RR for an increase of 10 µg/L arsenic level was 1.02 (95% CI: 0.97-1.07, P heterogeneity = .01). Sensitivity analyses, including a 1-stage meta-regression, confirmed the main findings.

CONCLUSION

This systematic review and meta-analysis provided evidence of a lack of an increased risk of lung and bladder cancer for exposure to arsenic in drinking water up to 150 µg/L, the highest concentration studied.