Cancer in experimental animals exposed to arsenic and arsenic compounds

Arsenic inorganic exposure, metabolism, genetic biomarkers and its impact on human health: A mini-review

Inorganic arsenic species exist in the environment as a result of both natural sources, such as volcanic and geothermal activities, and geological formations, as well as anthropogenic activities, including smelting, exploration of fossil fuels, coal burning, mining, and the use of pesticides. These species deposit in water, rocks, soil, sediments, and the atmosphere. Arsenic-contaminated drinking water is a global public health issue because of its natural prevalence and toxicity. Therefore, chronic exposure to arsenic can have deleterious effect on humans, including cancer and other diseases. This work describes the mechanisms of environmental exposure to arsenic, molecular regulatory factors involved in its metabolism, genetic polymorphisms affecting individual susceptibility and the toxic effects of arsenic on human health (oxidative stress, DNA damage and cancer). We conclude that the role of single nucleotide variants affecting urinary excretion of arsenic metabolites are highly relevant and can be used as biomarkers of the intracellular retention rates of arsenic, showing new avenues of research in this field.

Analysis of Prospective Genetic Indicators for Prenatal Exposure to Arsenic in Newborn Cord Blood of Using Machine Learning

Using a machine learning methods, we aim to find biological effect biomarkers of prenatal arsenic exposure in newborn cord blood. From the Gene Expression Omnibus (GEO) database, two datasets (GSE48354 and GSE7967) pertaining to cord blood sequencing while exposed to arsenic were retrieved and merged for additional study. Using the "limma" package in the R, differentially expressed genes (DEGs) were eliminated. Machine learning techniques of the LASSO regression algorithm and SVM-RFE algorithm were used to find potential biological effect biomarkers for cord blood sequencing in pregnant women exposed to arsenic. To evaluate the efficacy of biomarkers, a receiver operating characteristic (ROC) curve was used. Furthermore, we investigated the proportion of invading immune cells in each sample using CIBERSORT, and we investigated the relationship between biomarkers and immune cells using the Spearman approach. Using LASSO regression and the SVM-RFE technique, 28 DEGs were discovered, and the main biomarkers of cord blood exposed to arsenic were discovered to be DENND2D, OLIG1, RGS18, CXCL16, DDIT4, FOS, G0S2, GPR183, JMJD6, and SOCS3. According to an immune infiltration analysis and correlation analysis, key biomarkers were substantially associated with the invading immune cells. Ten genes are important biomarkers of cord blood exposed to arsenic connected with infiltrating immune cells, and infiltrating immune cells may play important roles in cord blood exposed to arsenic, according to the study's findings.

Mechanism and thermodynamics of scorodite formation by oxidative precipitation from arsenic-bearing solution

Arsenic pollution is a challenging environmental issue caused by arsenic-bearing wastes from nonferrous metallurgy. Oxidative precipitation via introducing O2 into an ionic Fe(II)-As(V) solution is an advanced method for arsenic immobilization. However, the underlying mechanism is still not well understood. This study proposed a mechanism for scorodite formation by oxidative precipitation, and its thermodynamics were calculated using Gaussian software. Scorodite formation was divided into three stages: precursor formation (3-90 min), oxidative conversion (90-270 min) and crystallization (270-720 min) from the variation in precipitates and solution characterization and parameters such as initial pH, arsenic concentration, and ferrous dosage. In the scorodite formation mechanism, the precursors originate from the coordination polymerization of aqueous Fe(H2O)62+ and H2AsO4-, which contributes to the oxidative conversion of coordinated polymers ([Fe(H2O)4(H2O)]nn+) to basic Fe(H2O)2AsO4 until regular octahedral crystals are formed via nucleation and growth during crystallization. The ΔrGmθ for polymerization varied from -491.96 kJ mol-1 to -33.30 kJ mol-1, and the ΔrGmθ of oxidative conversion changed from -982.16 kJ mol-1 to -224.82 kJ mol-1, demonstrating the feasibility in scorodite formation. This research is significant for understanding scorodite formation in As(V) solutions. It can provide schemes for controlling and modifying the conditions of arsenic-bearing waste immobilization in the laboratories and industries.

Simultaneous stabilization of particulate and bioavailable arsenic in soils from the realgar mining area by polyacrylamide, nano-SiO2, and ferrihydrite composite materials

Arsenic (As) contamination in realgar mining areas poses a severe environmental and health risk, highlighting the critical need for effective strategies to manage As migration, particularly in its particulate and bioavailable states. Soil erosion and water leaching serve as significant pathways for spreading As, emphasizing the imperative to curtail its mobility. In the present study, we proposed an effective strategy that combines the utilization of polyacrylamide (PAM), nano-SiO2 (NS), and ferrihydrite (Fh) to elevate the stability of As in soils from a realgar mining area. The results show that this composite material demonstrates the capability to concurrently regulate soil erosion and mitigate the leaching of bioavailable As. The combination of the three materials in the proportion of 0.5 % PAM +0.1 % NS + 1.0 % Fh can reduce the soil particulate and bioavailable As content by 99.11 % and 93.98 %, respectively. The unconfined compressive strength of the soil can be increased by about 30 % under this condition. The SEM analyses show that the addition of PAM and NS can significantly enhance the aggregation of soil particles and then reduce the soil erosion rate. These findings highlight the significant potential of the proposed approach in mitigating As contamination in soil within mining environments. The approach offers a sustainable and comprehensive solution to address the transport of heavy metal contaminants in both particulate and bioavailable states in mining areas.

Effects of freeze-thaw action on in vivo and in vitro bioavailability of arsenic in soils from derelict industrial sites

Arsenic is a metalloid with carcinogenic properties and has been classified as a Category I carcinogen by the International Agency for Research on Cancer (IARC). Freeze-thaw processes affect the migration and transformation of soil heavy metals, as well as adsorption/desorption and redox reactions. However, there is limited research directly addressing the impact of freeze-thaw processes on the bioavailability of soil heavy metals. In this study, we focused on As and selected As-contaminated soil samples from three types of legacy sites in heavy industrial areas. Under controlled freeze-thaw experimental conditions, we utilized both in vivo and in vitro bioavailability measurement methods to investigate whether and how freeze-thaw processes affect the bioavailability of soil As. The results of this study showed that freeze-thaw processes reduced soil pH (P < 0.05), CEC, SOM, and particle size, with decreases of 0.33, 1.2 cmol/kg, 5.2 g/kg, and 54 µm, respectively. It also increased weight specific surface area (BET) (P < 0.05), with an increase of 300 m2/kg. Freeze-thaw processes increased the proportions of exchangeable (P < 0.05), carbonate-bound, and iron-manganese oxide-bound As (P < 0.05), but reduced the proportions of organic-bound and residual As (P < 0.05). Freeze-thaw processes significantly increased the relative bioavailability and bioaccessibility of As, with increases of 32 ± 9.6% and 13 ± 0.23%, respectively. Soil pH, SOM, BET and electronic conductivity (EC) were identified as factors which could contribute to the increased bioavailability of As due to freeze-thaw processes. These results provide new insights and evidence for refining the assessment of human health risks associated with heavy metal contamination in polluted soils.

Mechanisms of genotoxicity and proteotoxicity induced by the metalloids arsenic and antimony

Arsenic and antimony are metalloids with profound effects on biological systems and human health. Both elements are toxic to cells and organisms, and exposure is associated with several pathological conditions including cancer and neurodegenerative disorders. At the same time, arsenic- and antimony-containing compounds are used in the treatment of multiple diseases. Although these metalloids can both cause and cure disease, their modes of molecular action are incompletely understood. The past decades have seen major advances in our understanding of arsenic and antimony toxicity, emphasizing genotoxicity and proteotoxicity as key contributors to pathogenesis. In this review, we highlight mechanisms by which arsenic and antimony cause toxicity, focusing on their genotoxic and proteotoxic effects. The mechanisms used by cells to maintain proteostasis during metalloid exposure are also described. Furthermore, we address how metalloid-induced proteotoxicity may promote neurodegenerative disease and how genotoxicity and proteotoxicity may be interrelated and together contribute to proteinopathies. A deeper understanding of cellular toxicity and response mechanisms and their links to pathogenesis may promote the development of strategies for both disease prevention and treatment.

Potential of in vivo stress reporter models to reduce animal use and provide mechanistic insights in toxicity studies

Chemical risk assessment ensures protection from the toxic effects of drugs and manmade chemicals. To comply with regulatory guidance, studies in complex organisms are required, as well as mechanistic studies to establish the relevance of any toxicities observed to man. Although in vitro toxicity models are improving, in vivo studies remain central to this process. Such studies are invariably time-consuming and often involve large numbers of animals. New regulatory frameworks recommend the implementation of "smart" in vivo approaches to toxicity testing that can effectively assess safety for humans and comply with societal expectations for reduction in animal use. A major obstacle in reducing the animals required is the time-consuming and complexity of the pathological endpoints used as markers of toxicity. Such endpoints are prone to inter-animal variability, subjectivity and require harmonisation between testing sites. As a consequence, large numbers of animals per experimental group are required. To address this issue, we propose the implementation of sophisticated stress response reporter mice that we have developed. These reporter models provide early biomarkers of toxic potential in a highly reproducible manner at single-cell resolution, which can also be measured non-invasively and have been extensively validated in academic research as early biomarkers of stress responses for a wide range of chemicals at human-relevant exposures. In this report, we describe a new and previously generated models in our lab, provide the methodology required for their use and discuss how they have been used to inform on toxic risk (likelihood of chemical causing an adverse health effect). We propose our in vivo approach is more informative (refinement) and reduces the animal use (reduction) compared to traditional toxicity testing. These models could be incorporated into tiered toxicity testing and used in combination with in vitro assays to generate quantitative adverse outcome pathways and inform on toxic potential.

Potential of in vivo stress reporter models to reduce animal use and provide mechanistic insights in toxicity studies

Chemical risk assessment ensures protection from the toxic effects of drugs and manmade chemicals. To comply with regulatory guidance, studies in complex organisms are required, as well as mechanistic studies to establish the relevance of any toxicities observed to man. Although in vitro toxicity models are improving, in vivo studies remain central to this process. Such studies are invariably time-consuming and often involve large numbers of animals. New regulatory frameworks recommend the implementation of "smart" in vivo approaches to toxicity testing that can effectively assess safety for humans and comply with societal expectations for reduction in animal use. A major obstacle in reducing the animals required is the time-consuming and complexity of the pathological endpoints used as markers of toxicity. Such endpoints are prone to inter-animal variability, subjectivity and require harmonisation between testing sites. As a consequence, large numbers of animals per experimental group are required. To address this issue, we propose the implementation of sophisticated stress response reporter mice that we have developed. These reporter models provide early biomarkers of toxic potential in a highly reproducible manner at single-cell resolution, which can also be measured non-invasively and have been extensively validated in academic research as early biomarkers of stress responses for a wide range of chemicals at human-relevant exposures. In this report, we describe a new and previously generated models in our lab, provide the methodology required for their use and discuss how they have been used to inform on toxic risk (likelihood of chemical causing an adverse health effect). We propose our in vivo approach is more informative (refinement) and reduces the animal use (reduction) compared to traditional toxicity testing. These models could be incorporated into tiered toxicity testing and used in combination with in vitro assays to generate quantitative adverse outcome pathways and inform on toxic potential.

SLC1A5 regulates cell proliferation and self-renewal through β-catenin pathway mediated by redox signaling in arsenic-treated uroepithelial cells

Arsenic exposure increases the risk of bladder cancer in humans, but its underlying mechanisms remain elusive. The alanine, serine, cysteine-preferring transporter 2 (ASCT2, SLC1A5) is frequently overexpressed in cancer cells. The aim of this study was to evaluate the effects of arsenic on SLC1A5, and to determine the role of SLC1A5 in the proliferation and self-renewal of uroepithelial cells. F344 rats were exposed to 87 mg/L NaAsO₂ or 200 mg/L DMA^V for 12 weeks. The SV-40 immortalized human uroepithelial (SV-HUC-1) cells were cultured in medium containing 0.5 μM NaAsO₂ for 40 weeks. Arsenic increased the expression levels of SLC1A5 and β-catenin both in vivo and in vitro. SLC1A5 promoted cell proliferation and self-renewal by activating β-catenin, which in turn was dependent on maintaining GSH/ROS homeostasis. Our results suggest that SLC1A5 is a potential therapeutic target for arsenic-induced proliferation and self-renewal of uroepithelial cells.

Arsenic Contamination in Groundwater: Geochemical Basis of Treatment Technologies

Arsenic (As) is abundant in the environment and can be found in both organic (e.g., methylated) and inorganic (e.g., arsenate and arsenite) forms. The source of As in the environment is attributed to both natural reactions and anthropogenic activities. As can also be released naturally to groundwater through As-bearing minerals including arsenopyrites, realgar, and orpiment. Similarly, agricultural and industrial activities have elevated As levels in groundwater. High levels of As in groundwater pose serious health risks and have been regulated in many developed and developing countries. In particular, the presence of inorganic forms of As in drinking water sources gained widespread attention due to their cellular and enzyme disruption activities. The research community has primarily focused on reviewing the natural occurrence and mobilization of As. Yet, As originating from anthropogenic activities, its mobility, and potential treatment techniques have not been covered. This review summarizes the origin, geochemistry, occurrence, mobilization, microbial interaction of natural and anthropogenic-As, and common remediation technologies for As removal from groundwater. In addition, As remediation methods are critically evaluated in terms of practical applicability at drinking water treatment plants, knowledge gaps, and future research needs. Finally, perspectives on As removal technologies and associated implementation limitations in developing countries and small communities are discussed.

The interplay of arsenic, silymarin, and NF-ĸB pathway in male reproductive toxicity: A review

Arsenic toxicity is one of the most trending reasons for several malfunctions, particularly reproductive toxicity. The exact mechanism of arsenic poisoning is a big question mark. Exposure to arsenic reduces sperm count, impairs fertilization, and causes inflammation and genotoxicity through interfering with autophagy, epigenetics, ROS generation, downregulation of essential protein expression, metabolite changes, and hampering several signaling cascades, particularly by the alteration of NF-ĸB pathway. This work tries to give a clear idea about the different aspects of arsenic resulting in male reproductive complications, often leading to infertility. The first part of this article explains the implications of arsenic poisoning and the crosstalk of the NF-ĸB pathway in male reproductive toxicity. Silymarin is a bioactive compound that exerts anti-cancer and anti-inflammatory properties and has demonstrated hopeful outcomes in several cancers, including colon cancer, breast cancer, and skin cancer, by downregulating the hyperactive NF-ĸB pathway. The next half of this article thus sheds light on silymarin's therapeutic potential in inhibiting the NF-ĸB signaling cascade, thus offering protection against arsenic-induced male reproductive toxicity.

After a Century of Research into Environmental Mutagens and Carcinogens, Where Do We Stand?

Cancer is one of the longest-known human diseases, yet only in recent times have we begun to perceive that the percentage of neoplasms caused by environmental factors, lifestyle and chemicals, is likely underestimated. The first medical reports associating cancer with pollutants like tars appeared by the early 20th century, but despite initial evidence relating oncogenesis and chromosomal alterations, only after the structure of DNA had been elucidated in the 1950s have genetic disorders been fully perceived as cause. This led to a growing interest in genotoxic and mutagenic pollutants. Even though we are now familiar with a range of environmental carcinogens spanning between aromatic hydrocarbons and asbestos to radionuclides and forms of carbon nanomaterials, establishing causal networks between pollutants and cancer remains cumbersome. In most part, this is due to the complexity of toxicant matrices, unknown modes-of-action of chemicals or their mixtures, the widening array of novel pollutants plus difficulties in subtracting background effects from true aetiology of disease. Recent advances in analytical chemistry, high-throughput toxicology, next-generation sequencing, computational biology and databases that allocate whole normal and cancer genomes, all indicate that we are on the verge of a new age of research into mechanistic 'oncotoxicology', but how can it impact risk assessment and prevention?

Gene expression analysis of antioxidant and DNA methylation on the rat liver after 4-week wood preservative chromated copper arsenate exposure

Our previous 4-week repeated dose toxicity study showed that wood preservative chromated copper arsenate (CCA) induced hepatocellular hypertrophy accompanied by biochemical hepatic dysfunction and an increase in oxidative stress marker, 8-hydroxydeoxyguanosine, in female rats. To further explore the molecular mechanisms of CCA hepatotoxicity, we analyzed 10%-buffered formalin-fixed liver samples from female rats for cell proliferation, apoptosis, and protein glutathionylation and conducted microarray analysis on frozen liver samples from female rats treated with 0 or 80 mg/kg/day of CCA. Chemical analysis revealed that dimethylated arsenical was the major metabolite in liver tissues of male and female rats. CCA increase labeling indices of proliferating cell nuclear antigen and decrease terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling accompanied with increased expression of protein glutathionylation, indicating a decrease in glutathione (GSH) in hepatocytes of female rats. Microarray analysis revealed that CCA altered gene expression of antioxidants, glutathione-S-transferase (GST), heat shock proteins and ubiquitin-proteasome pathway, cell proliferation, apoptosis, DNA methylation, cytochrome P450, and glucose and lipid metabolism in female rats. Increased expression of GSTs, including Gsta2, Gsta3, Mgst1, and Cdkn1b (p27), and decreased expression of the antioxidant Mt1, and DNA methylation Dnmt1, Dnmt3a, and Ctcf were confirmed in the liver of female rats in a dose-dependent manner. Methylation status of the promoter region of the Mt1 was not evidently changed between control and treatment groups. The results suggested that CCA decreased GSH and altered the expression of several genes, including antioxidants, GST, and DNA methylation, followed by impaired cell proliferation in the liver of female rats.

Heavy metal and phthalate contamination and labeling integrity in a large sample of US commercially available cannabidiol (CBD) products

BACKGROUND

The demand and availability of commercially available cannabidiol (CBD) products has grown substantially, which is of particular interest among medically vulnerable people. Because the cannabis plant is recognized as a bioaccumulator, which is highly effective at absorbing and retaining contaminants (e.g., heavy metals) in soil, it is important to characterize the degree of contamination in CBD products and their label accuracy to better estimate potential health benefits and risks associated with consumption.

METHODS

Levels of lead, cadmium, arsenic, mercury, four phthalates, and CBD labeling accuracy were quantified in a selection of commercially available CBD products in the US. Heavy metal concentrations were quantified by inductively coupled plasma-mass spectrometry. Phthalates were quantified by liquid chromatography-tandem mass spectrometry. CBD labeling accuracy was determined by extracting samples into a suitable organic solvent and analyzing using liquid chromatography with diode array detection.

RESULTS

Lead was detected in 42 %, cadmium in 8 %, arsenic in 28 %, and mercury in 37 % of 121 edible CBD products. Four edible CBD products exceeded the California Proposition 65 threshold for daily lead consumption of 0.5μg in two servings. The percentage of edible products with detectable phthalate concentrations varied between 13 % and 80 % across the four phthalates, with DEHP being most prevalent. Among all products tested for CBD labeling accuracy (topicals, edibles, N = 516), 40 % contained <90 % of the CBD indicated on the product label, 18 % contained >110 %, and only 42 % of products fell within ±10 % of the CBD claimed on the manufacturer label. Concentrations of heavy metals and phthalates were not associated with CBD potency.

CONCLUSIONS

Low-level contamination of edible CBD products with heavy metals and phthalates is pervasive. There is substantial discrepancy between the product label claims for CBD potency and the amount measured in both edible and topical products, underscoring the need for tight regulations for CBD product label integrity to protect consumers.

Unravelling the emerging carcinogenic contaminants from industrial waste water for prospective remediation by electrocoagulation - A review

The need of the hour relies on finding new but sustainable ways to curb rising pollution levels. The accelerated levels of urbanization and increase in population deplete the finite resources essential for human sustenance. In this aspect, water is one of the non-renewable sources that is running out very fast and is polluted drastically day by day. One way of tackling the problem is to reduce the pollution levels by decreasing the usage of chemicals in the process, and the other is to find ways to reuse or reduce the contaminants in the effluent by treatment methods. Most of the available water recycling or treatment methods are not sustainable. Some of them even use toxic chemicals in the processing steps. Treatment of organic wastes from industries is a challenging task as they are hard to remove. Electrocoagulation is one of the emerging water treatment technologies that is highly sustainable and has a comparatively cheaper operating cost. Being a broad-spectrum treatment process, it is suitable for treating the most common water pollutants ranging from oils, bacteria, heavy metals, and others. The process is also straightforward, where electrical current is used to coagulate the contaminates. The presence of carcinogens in these waste water increases the need for its treatment towards further use. The present investigation is made as an extensive analysis of the emerging carcinogens and their various sources from process industries, especially in the form of organic waste and their removal by electrocoagulation and its coupled techniques. The paper also aims to ascertain why the electrocoagulation technique may be a better alternative compared with other methods for the removal of carcinogens in organic wastewater, an analysis which has not been explored before.

Exogenously-Sourced Salicylic Acid Imparts Resilience towards Arsenic Stress by Modulating Photosynthesis, Antioxidant Potential and Arsenic Sequestration in Brassica napus Plants

In the current study, salicylic acid (SA) assesses the physiological and biochemical responses in overcoming the potential deleterious impacts of arsenic (As) on Brassica napus cultivar Neelam. The toxicity caused by As significantly reduced the observed growth and photosynthetic attributes and accelerated the reactive oxygen species (ROS). Plants subjected to As stress revealed a significant (p ≤ 0.05) reduction in the plant growth and photosynthetic parameters, which accounts for decreased carbon (C) and sulfur (S) assimilation. Foliar spray of SA lowered the oxidative burden in terms of hydrogen peroxide (H2O2), superoxide anion (O2•-), and lipid peroxidation in As-affected plants. Application of SA in two levels (250 and 500 mM) protected the Brassica napus cultivar from As stress by enhancing the antioxidant capacity of the plant by lowering oxidative stress. Among the two doses, 500 mM SA was most effective in mitigating the adverse effects of As on the Brassica napus cultivar. It was found that SA application to the Brassica napus cultivar alleviated the stress by lowering the accumulation of As in roots and leaves due to the participation of metal chelators like phytochelatins, enhancing the S-assimilatory pathway, carbohydrate metabolism, higher cell viability in roots, activity of ribulose 1, 5-bisphosphate carboxylase (Rubisco), and proline metabolism through the active participation of γ-glutamyl kinase (GK) and proline oxidase (PROX) enzyme. The current study shows that SA has the capability to enhance the growth and productivity of B. napus plants cultivated in agricultural soil polluted with As and perhaps other heavy metals.

Arsenic as an immunotoxicant

Arsenic is world-wide contaminant to which millions of people are exposed. The health consequences of arsenic exposure are varied, including cancer, cardiometabolic disease, and respiratory disorders. Arsenic is also toxic to the immune system, which may link many of the pathologies associated with arsenic exposure. The immune system can be classified into two interconnected arms: the innate and the adaptive immune responses. Herein, we discuss the effects of arsenic on key cell types within each of these arms, highlighting both in vitro and in vivo responses. These cells include macrophages, neutrophils, dendritic cells, and both B and T lymphocytes. Furthermore, we will explore data from human populations where altered immune status is implicated in disease and identify several data gaps where research is needed to complete our understanding of the immunotoxic effects of arsenic.

Arsenic Exposure through Dietary Intake and Associated Health Hazards in the Middle East

Dietary arsenic (As) contamination is a major public health issue. In the Middle East, the food supply relies primarily on the import of food commodities. Among different age groups the main source of As exposure is grains and grain-based food products, particularly rice and rice-based dietary products. Rice and rice products are a rich source of core macronutrients and act as a chief energy source across the world. The rate of rice consumption ranges from 250 to 650 g per day per person in South East Asian countries. The source of carbohydrates through rice is one of the leading causes of human As exposure. The Gulf population consumes primarily rice and ready-to-eat cereals as a large proportion of their meals. Exposure to arsenic leads to an increased risk of non-communicable diseases such as dysbiosis, obesity, metabolic syndrome, diabetes, chronic kidney disease, chronic heart disease, cancer, and maternal and fetal complications. The impact of arsenic-containing food items and their exposure on health outcomes are different among different age groups. In the Middle East countries, neurological deficit disorder (NDD) and autism spectrum disorder (ASD) cases are alarming issues. Arsenic exposure might be a causative factor that should be assessed by screening the population and regulatory bodies rechecking the limits of As among all age groups. Our goals for this review are to outline the source and distribution of arsenic in various foods and water and summarize the health complications linked with arsenic toxicity along with identified modifiers that add heterogeneity in biological responses and suggest improvements for multi-disciplinary interventions to minimize the global influence of arsenic. The development and validation of diverse analytical techniques to evaluate the toxic levels of different As contaminants in our food products is the need of the hour. Furthermore, standard parameters and guidelines for As-containing foods should be developed and implemented.

A tau class glutathione-S-transferase (OsGSTU5) confers tolerance against arsenic toxicity in rice by accumulating more arsenic in root

Arsenic (As) considered as one of the hazardous metalloid that hampers various physiological activities in rice. To study the mechanism of As tolerance in rice, one differentially expressed tau class glutathione-S-transferase (OsGSTU5) has been selected and transgenic rice plants with knockdown (KD) and overexpressing (OE) OsGSTU5 were generated. Our results suggested that KD lines became less tolerant to As stress than WT plants, while OE lines showed enhanced tolerance to As. Under As toxicity, OE and KD lines showed enhanced and reduced antioxidant activities such as, SOD, PRX and catalase, respectively indicating its role in ROS homeostasis. In addition, higher malondialdehyde content, poor photosynthetic parameters and higher reactive oxygen species (ROS) in KD plant, suggests that knockdown of OsGSTU5 renders KD plants more susceptible to oxidative damage. Also, the relative expression profile of various transporters such as OsABCC1 (As sequestration), Lsi2 and Lsi6 (As translocaters) and GSH dependent activity of GSTU5 suggests that GSTU5 might help in chelation of As with GSH and sequester it into the root vacuole using OsABCC1 transporter and thus limits the upward translocation of As towards shoot. This study suggests the importance of GSTU5 as a good target to improve the As tolerance in rice.

Metabolomic dynamics of the arsenic-transformed bronchial epithelial cells and the derived cancer stem-like cells

Accumulating evidence indicates a carcinogenic role of environmental arsenic exposure, but mechanisms on how arsenic fosters malignant transformation of the normal cells are not fully established. By applying untargeted global metabolomics approach, we now show that arsenic is highly capable of perturbing the intracellular metabolic programs of the human bronchial epithelial cells, some of which are prominent hallmarks of cancer cell metabolism. To understand the spatiotemporal patterns of arsenic regulation on multiple metabolic pathways, we treated the cells with environmentally relevant concentration of arsenic, 0.25 μM, consecutively for 6 weeks to 24 weeks, and found that arsenic prompted heme metabolism, glycolysis, sphingolipid metabolism, phospholipid catabolism, protein degradation, and cholesterol breakdown constitutively, but inhibited metabolism of uracil-containing pyrimidine, carnitine, serotonin, polyamines, and fatty acid β-oxidation. A strong inhibition of all metabolites in mitochondrial tricarboxylic acid (TCA) cycle was noted in the cells treated with As³⁺ for 6 to 13 weeks. However, the metabolites in the earlier, but not the later steps of TCA cycle, including citrate, aconitate and isocitrate, were induced at 16 weeks through 24 weeks of arsenic treatment. This comprehensive metabolomics analysis provides new insights into metabolic perturbation by arsenic and may lead to more precise indications of arsenic in molecular carcinogenesis.

Delineating the Effects of Passaging and Exposure in a Longitudinal Study of Arsenic-Induced Squamous Cell Carcinoma in a HaCaT Cell Line Model

Cutaneous squamous cell carcinoma (cSCC) is a major deleterious health effect of chronic arsenic (iAs) exposure. The molecular mechanism of arsenic-induced cSCC remains poorly understood. We recently demonstrated that chronic iAs exposure leads to temporally regulated genome-wide changes in profiles of differentially expressed mRNAs and miRNAs at each stage of carcinogenesis (7, 19 and 28 weeks) employing a well-established passage-matched HaCaT cell line model of arsenic-induced cSCC. Here, we performed longitudinal differential expression analysis (miRNA and mRNA) between the different time points (7 vs. 19 weeks and 19 vs. 28 weeks) within unexposed and exposed groups, coupled to expression pairing and pathway analyses to differentiate the relative effects of long-term passaging and chronic iAs exposure. Data showed that 66-105 miRNA [p < 0.05; log2(Fold Change)>I1I] and 2826-4079 mRNA [p < 0.001; log2(Fold Change)>I1I] molecules were differentially expressed depending on the longitudinal comparison. Several mRNA molecules differentially expressed as a function of time, independent of iAs exposure were being targeted by miRNA molecules which were also differentially expressed in a time dependent manner. Distinct pathways were predicted to be modulated as a function of time or iAs exposure. Some pathways were also modulated both by time and exposure. Thus, the HaCaT model can distinguish between the effects of passaging and chronic iAs exposure individually and corroborate our previously published data on effects of iAs exposure compared to unexposed passage matched HaCaT cells. In addition, this work provides a template for cell line based longitudinal chronic exposure studies to follow for optimal efficacy.

Evaluation of toxic effects induced by arsenic trioxide or/and antimony on autophagy and apoptosis in testis of adult mice

Arsenic trioxide (ATO) and antimony (Sb) are well-known ubiquitous environmental contaminants and cause unpromising male reproductive effects in target and non-target exposed organisms. The main objective of this study was to investigate the effects of ATO or/and Sb on process of autophagy, apoptosis, and reproductive organ in adult mice. For this reason, a total of 32 adult mice were randomly divided into different groups like control group, ATO-treated group, Sb-treated group, and combined group. The duration of current experimental trial was 2 months. Various adverse effects of ATO or/and Sb on sperm parameters, oxidative stress, autophagy, and apoptosis were determined in testis of mice. Results indicated that parameters of sperm quality for organ coefficient, sperm count, ratio of sperm survival, testosterone level, and germ cells were significantly decreased, while malformation rate and vacuolization significantly increased in mice exposed to different treatments. Furthermore, the status of antioxidant index of T-AOC, SOD, and MsrB1 levels was reduced, while MDA increased significantly in ATO + Sb group. Results on TEM investigation determined that the autophagosomes, autolysosome, nuclear pyknosis, and chromatin condensation were prominent ailments, and the levels of autophagy and pro-apoptosis indictors including Beclin1, Atg-5, LC3B/LC3A, caspase-8, cytc, cleaved caspase-3, p53, and Bax were up-regulated in treated group, while the content of an anti-apoptosis maker (Bcl-2) was down-regulated. In conclusion, the results of our experiment suggested that abnormal process of autophagy and apoptosis was triggered by arsenic and antimony, and intensity of toxic effects increased in combined treatments of ATO and Sb.

Telomere Length and Arsenic: Improving Animal Models of Toxicity by Choosing Mice With Shorter Telomeres

Arsenic is both a chemotherapeutic drug and an environmental toxicant that affects hundreds of millions of people each year. Arsenic exposure in drinking water has been called the worst poisoning in human history. How arsenic is handled in the body is frequently studied using rodent models to investigate how arsenic both causes and treats disease. These models, used in a variety of arsenic-related testing, from tumor formation to drug toxicity monitoring, have virtually always been developed from animals with telomeres that are unnaturally long, likely because of accidental artificial selective pressures. Mice that have been bred in captivity in laboratory conditions, often for over 100 years, are the standard in creating animal models for this research. Using these mice introduces challenges to any work that can be affected by the length of telomeres and the related capacities for tissue repair and cancer resistance. However, arsenic research is particularly susceptible to the misuse of such animal models due to the multiple and various interactions between arsenic and telomeres. Researchers in the field commonly find mouse models and humans behaving very differently upon exposure to acute and chronic arsenic, including drug therapies which seem safe in mice but are toxic in humans. Here, some complexities and apparent contradictions of the arsenic carcinogenicity and toxicity research are reconciled by an explanatory model that involves telomere length explained by the evolutionary pressures in laboratory mice. A low-risk hypothesis is proposed which has the power to determine whether researchers can easily develop more powerful and accurate mouse models by simply avoiding mouse lineages that are very old and have strangely long telomeres. Swapping in newer mouse lineages for the older, long-telomere mice may vastly improve our ability to research arsenic toxicity with virtually no increase in cost or difficulty of research.

Arsenic-induced HER2 promotes proliferation, migration and angiogenesis of bladder epithelial cells via activation of multiple signaling pathways in vitro and in vivo

Arsenic (As) is a known human carcinogen with a hitherto unknown mechanism of action. Dimethylarsinic acid (DMA^V) is a methylated metabolite of arsenicals found in most mammals, and long-term exposure to DMA^V can lead to bladder cancer in rats. Human epidermal growth factor receptor 2 (HER2) is an oncogenic factor that is overexpressed in bladder cancer, but its role in the initiation and progression of As-induced bladder cancer has not been elucidated. We found that HER2 was up-regulated in human uroepithelial cells treated with arsenite as well as in the bladder tissues of DMA^V-exposed rats. HER2 overexpression correlated to increased cell proliferation, epithelial-to-mesenchymal transition (EMT), migration and angiogenesis in vitro. The anti-HER2 monoclonal antibody trastuzumab significantly decreased serum vascular endothelial-derived growth factor (VEGF) levels and that of proliferation-related proteins in the bladder tissues of DMA^V-exposed rats. Furthermore, inhibition of HER2, as well as that of the MAPK, AKT and STAT3 pathways, attenuated arsenite-induced proliferation, migration and angiogenesis of human uroepithelial cells, and increased apoptosis rates in vitro. These findings indicate that HER2 mediates the oncogenic effects of As on bladder epithelial cells by activating the MAPK, PI3K/AKT and Src/STAT3 signaling pathways, and is therefore a promising biomarker.

Protective effect of Mucuna pruriens against arsenic-induced liver and kidney dysfunction and neurobehavioral alterations in rats

BACKGROUND AND AIM

Intoxication of arsenic in rats is known to result in neurological effects as well as liver and kidney dysfunction. Mucuna pruriens has been identified for its medicinal properties. The aim of the study was to investigate the protective effect of aqueous seed extract of M. pruriens on sodium arsenite-induced memory impairment, liver, and kidney functions in rats.

MATERIALS AND METHODS

The experiment was divided into short-term treatment (45 days) and long-term treatment (90 days), with each group divided into nine sub-groups consisting of six animals each. Sub-groups 1 and 2 served as normal, and N-acetylcysteine (NAC) controls, respectively. Sub-groups 3-9 received sodium arsenite in drinking water (50 mg/L). In addition, sub-group 4 received NAC (210 mg/kg b.wt) orally once daily, sub-groups 5-7 received aqueous seed extract of M. pruriens (350 mg/kg b.wt, 530 mg/kg b.wt, and 700 mg/kg b.wt) orally once daily and sub-groups 8 and 9 received a combination of NAC and aqueous seed extract of M. pruriens (350 mg/kg b.wt and 530 mg/kg b.wt) orally once daily. Following the treatment, the blood was drawn retro-orbitally to assess the liver (serum alanine transaminase [ALT], serum aspartate transaminase, and serum alkaline phosphatase) and kidney (serum urea and serum creatinine) functions. Learning and memory were assessed by passive avoidance test. Animals were sacrificed by an overdose of ketamine, and their Nissl stained hippocampal sections were analyzed for alterations in neural cell numbers in CA1 and CA3 regions.

RESULTS

In the short-term treatment, groups administered with M. pruriens 530 mg/kg b.wt alone and combination of NAC + M. pruriens 350 mg/kg b.wt exhibited a significant improvement in memory retention, less severe neurodegeneration, and decrease in serum ALT levels. In long-term treatment, groups administered with M. pruriens 700 mg/kg b.wt alone and combination of NAC+M. pruriens 350 mg/kg b.wt, respectively, showed better memory retention, decreased neural deficits, and reduced levels of kidney and liver enzymes.

CONCLUSION

The seed extract of M. pruriens showed significant enhancement in memory and learning. The number of surviving neurons in the CA1 and CA3 regions also increased on treatment with M. pruriens. Serum ALT, serum urea, and serum creatinine levels showed significant improvement on long-term treatment with M. pruriens.

Effects of Inorganic Arsenic on Human Prostate Stem-Progenitor Cell Transformation, Autophagic Flux Blockade, and NRF2 Pathway Activation

BACKGROUND

Inorganic arsenic (iAs) is an environmental toxicant associated with an increased risk of prostate cancer in chronically exposed populations worldwide. However, the biological mechanisms underlying iAs-induced prostate carcinogenesis remain unclear.

OBJECTIVES

We studied how iAs affects normal human prostate stem-progenitor cells (PrSPCs) and drives transformation and interrogated the molecular mechanisms involved.

METHODS

PrSPCs were enriched by spheroid culture from normal human primary or immortalized prostate epithelial cells, and their differentiation capability was evaluated by organoid culture. Microarray analysis was conducted to identify iAs-dysregulated genes, and lentiviral infection was used for stable manipulation of identified genes. Soft agar colony growth assays were applied to examine iAs-induced transformation. For in vivo study, PrSPCs mixed with rat urogenital sinus mesenchyme were grafted under the renal capsule of nude mice to generate prostatelike tissues, and mice were exposed to 5 ppm (∼65μM) iAs in drinking water for 3 months.

RESULTS

Low-dose iAs (1μM) disturbed PrSPC homeostasis in vitro, leading to increased self-renewal and suppressed differentiation. Transcriptomic analysis indicated that iAs activated oncogenic pathways in PrSPCs, including the KEAP1-NRF2 pathway. Further, iAs-exposed proliferative progenitor cells exhibited NRF2 pathway activation that was sustained in their progeny cells. Knockdown of NRF2 inhibited spheroid formation by driving PrSPC differentiation, whereas its activation enhanced spheroid growth. Importantly, iAs-induced transformation was suppressed by NRF2 knockdown. Mechanistically, iAs suppressed Vacuolar ATPase subunit VMA5 expression, impairing lysosome acidification and inhibiting autophagic protein degradation including p62, which further activated NRF2. In vivo, chronic iAs exposure activated NRF2 in both epithelial and stroma cells of chimeric human prostate grafts and induced premalignant events.

CONCLUSIONS

Low-dose iAs increased self-renewal and decreased differentiation of human PrSPCs by activating the p62-NRF2 axis, resulting in epithelial cell transformation. NRF2 is activated by iAs through specific autophagic flux blockade in progenitor cells, which may have potential therapeutic implications. https://doi.org/10.1289/EHP6471.

MiADMSA ameliorate arsenic induced urinary bladder carcinogenesis in vivo and in vitro

BACKGROUND AND PURPOSE

Arsenicosis is a major threat to public health and is a major cause of the development of urinary bladder cancer. Oxidative/ nitrosative stress is one of the key factors for these effects but the involvement of other associated factors is less known. There is a lack of data for the efficacy of chelator against urinary bladder carcinogenesis. The present study demonstrates the early signs of arsenic exposed urinary bladder carcinogenesis and its attenuation by Monoisoamyl dimercaptosuccinic acid (MiADMSA).

METHODS

Male rats were exposed to 50 ppm of sodium arsenite and dimethylarsinic acid (DMA) via drinking water for 18 weeks and treated with MiADMSA (50 mg/kg, orally once daily for 5 days) for 3 weeks with a gap one week between the two courses of treatments. We compared in vivo data with in vitro by co-exposing 100 nM of sodium arsenite and DMA to rat (NBT-II) as well as human transitional epithelial carcinoma (T-24) cells with 100 nM of MiADMSA.

RESULTS

The data showed that sodium arsenite and DMA exposure significantly increased the tissue arsenic contents, ROS, TBARS levels, catalase, SOD activities and significantly decreased GSH level which might be responsible for an increased 8-OHdG level. These changes might have increased pro-oncogenic biomarkers like MMP-9 and survivin in serum, bladder tissues, NBT-II, and T-24 cells. High cell migration and clonogenic potential in NBT-II and T-24 cells exposed to arsenic suggest pronounced carcinogenic potential. Significant recovery in these biomarkers was noted on treatment with MiADMSA.

CONCLUSION

Early signs of urinary bladder carcinogenesis were observed in arsenic and DMA exposed rats which were linked to metal accumulation, oxidative/ nitrosative stress, 8-OHdG, MMP-9 and survivin which were reduced by MiADMSA possibly via its efficient chelation abilities in vivo and in vitro.

Overexpression of hsa-miR-186 induces chromosomal instability in arsenic-exposed human keratinocytes

The mechanism of arsenic-induced skin carcinogenesis is not yet fully understood. Chromosomal instability contributes to aneuploidy and is a driving force in carcinogenesis. Arsenic causes mitotic arrest and induces aneuploidy. hsa-miR-186 overexpression is associated with metastatic cancers as well as arsenic-induced squamous cell carcinoma and is reported to target several mitotic regulators. Decreased levels of these proteins can dysregulate chromatid segregation contributing to aneuploidy. This work investigates the potential aneuploidogenic role of hsa-miR-186 in arsenic carcinogenesis. Clones of immortalized human keratinocytes (HaCaT) stably transfected with a hsa-miR-186 expression or empty vector were isolated. Three clones with high and low hsa-miR-186 expression determined by RT-qPCR were selected for further analysis and cultured with 0 or 100 nM NaAsO2 for 8 weeks. Analysis of mitoses revealed that chromosome number and structural abnormalities increased in cells overexpressing hsa-miR-186 and were further increased by arsenite exposure. Double minutes were the dominant structural aberrations. The peak number of chromosomes also increased. Cells with >220 to >270 chromosomes appeared after 2 months in hsa-miR-186 overexpressing cells, indicating multiple rounds of endomitosis had occurred. The fraction of cells with increased chromosome number or structural abnormalities did not increase in passage matched control cells. Levels of selected target proteins were determined by western blot. Expression of BUB1, a predicted hsa-miR-186 target was suppressed in hsa-miR-186 overexpressing clones, but increased with arsenite exposure. CDC27 remained constant under all conditions. These results suggest that overexpression of miR-186 in arsenic exposed tissues likely induces aneuploidy contributing to arsenic-induced carcinogenesis.

Metal carcinogen exposure induces cancer stem cell-like property through epigenetic reprograming: A novel mechanism of metal carcinogenesis

Arsenic, cadmium, nickel and hexavalent chromium are among the most common environmental pollutants and potent carcinogens. Chronic exposure to these metals causes various types of cancer in humans, representing a significant environmental health issue. Although under active investigation, the mechanisms of metal carcinogenesis have not been clearly defined. One common feature of these metal carcinogens is that they are all able to cause various epigenetic dysregulations, which are believed to play important roles in their carcinogenicity. However, how metal carcinogen-caused epigenetic dysregulation contributes to metal carcinogenesis remains largely unknown. The evolution of cancer stem cell (CSC) theory has opened exciting new avenues for studying the mechanism of metal carcinogenesis. Increasing evidence indicates that chronic metal carcinogen exposure produces CSC-like cells through dysregulated epigenetic mechanisms. This review will first provide some brief introductions about CSC, epigenetics and epigenetic regulation of CSCs; then summarize progresses in recent studies on metal carcinogen-induced CSC-like property through epigenetic reprograming as a novel mechanism of metal carcinogenesis. Some perspectives for future studies in this field are also presented.

An improved rapid analytical method for the arsenic speciation analysis of marine environmental samples using high-performance liquid chromatography/inductively coupled plasma mass spectrometry

Arsenic contamination in marine environments is a serious issue because some arsenicals are very toxic, increasing the health risks associated with the consumption of marine products. This study describes the development of an improved rapid method for the quantification of arsenic species, including arsenite (As^III), arsenate (As^V), arsenocholine (AsC), arsenobetaine (AsB), dimethylarsinic acid (DMA), and monomethyl arsonic acid (MMA), in seaweed, sediment, and seawater samples using high-performance liquid chromatography/inductively coupled plasma-mass spectrometry (HPLC/ICP-MS). ICP-MS based on dynamic reaction cells was used to eliminate spectral interference. Ammonium nitrate- and phosphate-based eluents were used as the mobile phases for HPLC analysis, leading to shorter overall retention time (6 min) and improved peak separation. Arsenicals were extracted with a 1% HNO₃ solution that required no clean-up process and exhibited reasonable sensitivity and peak resolution. The optimized method was verified by applying it to hijiki seaweed certified reference material (CRM, NMIJ 7405-a) and to spiked blank samples of sediment and seawater. The proposed method measured the concentration of As^V in the CRM as 9.6 ± 0.6 μg/kg dry weight (dw), which is close to the certified concentration (10.1 ± 0.5 μg/kg dw). The recovery of the six arsenicals was 87-113% for the sediment and 99-101% for the seawater. In the analysis of real samples, As^V was the most abundant arsenical in hijiki and gulfweed, whereas AsB was dominant in other seaweed species. The two inorganic arsenicals (As^III and As^V) and As^V were the most dominant in the sediment and seawater samples, respectively.

Gene expression and DNA methylation regulation of arsenic in mouse bladder tissues and in human urothelial cells

According to a report of the International Agency for Research on Cancer, arsenic and inorganic arsenic compounds are classified into Group 1 carcinogens with regard to human health. Epidemiological studies indicate that arsenic is one of the main risk factors for the development of bladder cancer. In the present study, arsenic-altered gene expression in mouse bladder tissues and in human urothelial cells was compared. In the mouse model, sodium arsenite-induced mouse urothelial hyperplasia and intracellular inclusions were present. Following DNA array analysis, four genes with differential expression were selected for quantitative real-time PCR assay. The genes were the following: Cystathionine β-synthase (CBS), adenosine A1 receptor (ADORA1), metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and Wnt inhibitory factor 1 (Wif1). The results indicated a significant increase in the levels of Cbs and Adora1. The analysis of the DNA CpG methylation levels of the mouse Cbs and Adora1 genes revealed no significant change. In contrast to these observations, the four genes were further analyzed in the human normal urothelial cell line SV-HUC1. The data indicated that WIF1 gene expression was decreased by sodium arsenite, whereas this was not noted for CBS, MALAT1 and ADORA1. Sodium arsenite decreased mRNA and protein expression levels of the WIF1 gene. In addition, the methylation levels of the WIF1 gene were increased. Sodium arsenite inhibited cell proliferation and promoted cell migration as demonstrated in cell functional assays. The gene status was compared in 8 human urothelial cell lines, and WIF1 mRNA expression levels were determined to be higher, whereas DNA CpG methylation levels were lower in SV-HUC1 cells compared with those noted in the other 7 bladder cancer cell lines. In summary, the data indicated that sodium arsenite decreased WIF1 gene expression and promoted cell migration. The increased methylation levels of WIF1 DNA CpG could be a potential biomarker for bladder cancer.

Arsenic-Induced Neoplastic Transformation Involves Epithelial-Mesenchymal Transition and Activation of the β-Catenin/c-Myc Pathway in Human Kidney Epithelial Cells

Arsenic contamination is a serious environmental and public health issue worldwide including the United States. Accumulating evidence suggests that kidney is one of the target organs for arsenic-induced carcinogenesis. However, the mechanism of arsenic-induced renal carcinogenesis is not well understood. Therefore, the objective of this study was to evaluate the carcinogenicity of chronic exposure to an environmentally relevant concentration of arsenic on kidney epithelial cells and identify the molecular mechanism underlying this process. HK-2 kidney epithelial cells were treated with arsenic for acute, long-term, and chronic durations, and cellular responses to arsenic exposure at these time points were evaluated by the changes in growth, morphology, and expression of genes. The results revealed a significant growth increase after long-term and chronic exposure to arsenic in HK-2 cells. The morphological changes of EMT and stem cell sphere formation were also observed in long-term arsenic exposed cells. The anchorage-independent growth assay for colony formation and cell maintenance in cancer stem cell medium further confirmed neoplastic transformation and the induced cancer stem cell properties of arsenic-exposed cells. Additionally, the expression of marker genes confirmed the increased growth, EMT, and stemness during arsenic-induced carcinogenesis. Moreover, the increase expression of β-catenin and c-Myc further suggested the role of these signaling molecules during carcinogenesis in HK-2 cells. In summary, results of this study suggest that chronic exposure to arsenic even at a relatively lower concentration can induce neoplastic transformation through acquisitions of EMT, stemness, and MET phenotypes, which might be related to the β-catenin/c-Myc signaling pathway.

Cellular and Molecular Effects of Prolonged Low-Level Sodium Arsenite Exposure on Human Hepatic HepaRG Cells

Inorganic arsenic is a human carcinogen associated with several types of cancers, including liver cancer. Inorganic arsenic has been postulated to target stem cells, causing their oncogenic transformation. This is proposed to be one of the key events in arsenic-associated carcinogenesis; however, the underlying mechanisms for this process remain largely unknown. To address this question, human hepatic HepaRG cells, at progenitor and differentiated states, were continuously treated with a noncytotoxic concentration of 1 μM sodium arsenite (NaAsO2). The HepaRG cells demonstrated active intracellular arsenite metabolism that shared important characteristic with primary human hepatocytes. Treatment of proliferating progenitor-like HepaRG cells with NaAsO2 inhibited their differentiation into mature hepatocyte-like cells, up-regulated genes involved in cell growth, proliferation, and survival, and down-regulated genes involved in cell death. In contrast, treatment of differentiated hepatocyte-like HepaRG cells with NaAsO2 resulted in enhanced cell death of mature hepatocyte-like cells, overexpression of cell death-related genes, and down-regulation of genes in the cell proliferation pathway, while biliary-like cells remained largely unaffected. Mechanistically, the cytotoxic effect of arsenic on mature hepatocyte-like HepaRG cells may be attributed to arsenic-induced dysregulation of cellular iron metabolism. The inhibitory effect of NaAsO2 on the differentiation of progenitor cells, the resistance of biliary-like cells to cell death, and the enhanced cell death of functional hepatocyte-like cells resulted in stem-cell activation. These effects favored the proliferation of liver progenitor cells that can serve as a source of initiation and driving force of arsenic-mediated liver carcinogenesis.

Impact of prenatal arsenic exposure on chronic adult diseases

Exposure to environmental stressors during susceptible windows of development can result in negative health outcomes later in life, a concept known as the Developmental Origins of Health and Disease (DOHaD). There is a growing body of evidence that exposures to metals early in life (in utero and postnatal) increase the risk of developing adult diseases such as cancer, cardiovascular disease, non-alcoholic fatty liver disease, and diabetes. Of particular concern is exposure to the metalloid arsenic, a drinking water contaminant and worldwide health concern. Epidemiological studies of areas with high levels of arsenic in the drinking water, such as some regions in Chile and Bangladesh, indicate an association between in utero arsenic exposure and the development of adult diseases. Therefore, the need for experimental models to address the mechanism underlining early onset of adult diseases have emerged including the in utero and whole-life exposure models. This review will highlight the epidemiological events and subsequent novel experimental models implemented to study the impact of early life exposure to arsenic on the development of adult diseases. In addition, current research using these models will be discussed as well as possible underlying mechanism for the early onset of disease. Abbreviations: ALT: alanine aminotransferase; AMI: acute myocardial infarction; AST: aspartate aminotransferase; ATSDR: Agency for Toxic Substances and Disease Registry; CVD: cardiovascular disease; DMA: dimethylarsinate; DOHaD: Developmental Origins of Health and Disease; EPA: U.S. Environmental Protection Agency; ER-α: estrogen receptor alpha; HDL: high-density lipoprotein; HOMA-IR: homeostatic model assessment of insulin resistance; iAs: inorganic arsenic; LDL: low-density lipoprotein; MetS: metabolic syndrome; MMA: monomethylarsonate; NAFLD: non-alcoholic fatty liver disease; PND: postnatal day; ppb: parts per billion; ppm: parts per million; SAM: S-adenosylmethionine; USFDA: United States Food and Drug Administration.

Update in global trends and aetiology of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary cancer of the liver responsible for an increasing number of cancer-related deaths, especially in developing economies of Asia and Africa. A plethora of risk factors have been described in the literature. Some of the important ones include chronic viral hepatitis, liver cirrhosis, environmental toxins such as aflatoxin, non-alcoholic fatty liver disease, lifestyle factors like alcohol consumption, smoking, and dietary factors, metabolic diseases like diabetes mellitus and obesity, and genetic and hereditary disorders. The development of HCC is complex involving sustained inflammatory damage leading to hepatocyte necrosis, regeneration, and fibrotic deposition. It also poses multiple challenges in diagnosis and treatment despite advances in diagnostic, surgical, and other therapeutic advancements. This is a narrative review of findings of multiple studies that were retrieved from electronic databases like PubMed, MEDLINE, Embase, Google Scholar, Scopus, and Cochrane. We summarise the current knowledge regarding the epidemiology and various risk factors for the development of HCC with a brief note on various prevention strategies.

Arsenic promotes the COX2/PGE2-SOX2 axis to increase the malignant stemness properties of urothelial cells

Chronic arsenic exposure is associated with the development of urothelial carcinoma of the bladder (UCB). To elucidate the contribution of arsenic exposure to urothelial cancer stem cell (CSC) generation, we established an in vitro stepwise malignant model transformed by chronically exposing human urothelial cells to arsenic. Using this model, we found that chronic arsenic exposure endows urothelial cells with malignant stemness properties including increased expression of stemness-related factors such as SOX2, sphere formation, self-renewal, invasion and chemoresistance. SOX2 was gradually and irreversibly overexpressed in line with acquired sphere-forming and self-renewal abilities. Following gene set enrichment analyses of arsenic-exposed and arsenic-unexposed cells, we found COX2 as an enriched gene for oncogenic signature. Mechanistically, arsenic-induced COX2/PGE2 increases SOX2 expression that eventually promotes malignant stem cell generation and repopulation. In urine samples from 90 subjects exposed to arsenic and 91 control subjects, we found a significant linear correlation between SOX2 and COX2 expression and the potential of SOX2 and COX2 expression as urinary markers to detect subjects exposed to arsenic. Furthermore, the combination marker yielded a high sensitivity for UCB detection in a separate cohort. Finally, our in vitro model exhibits basal-type molecular features and dual inhibition of EGFR and COX2 attenuated stem cell enrichment more efficiently than an EGFR inhibitor alone. In conclusion, the COX2/PGE2-SOX2 axis promotes arsenic-induced malignant stem cell transformation. In addition, our findings indicate the possible use of SOX2 and COX2 expression as urinary markers for the risk stratification and detection of UCB.

Arjunolic Acid Improves the Serum Level of Vitamin B12 and Folate in the Process of the Attenuation of Arsenic Induced Uterine Oxidative Stress

Continuation of prolonged treatment against arsenicosis with conventional chelating therapy is a global challenge. The present study was intended to evaluate the defensive effect of arjunolic acid against arsenic-induced oxidative stress and female reproductive dysfunction. Wistar strain adult female rats were given sodium arsenite (10 mg/kg body weight) in combination with arjunolic acid (10 mg/kg body weight) orally for two estrous cycles. Electrozymographic analysis explored that arjunolic acid co-treatment counteracted As³⁺-induced ROS production in uterine tissue by stimulating the activities of endogenous enzymatic antioxidants. Arjunolic acid was able to enhance the protection against mutagenic uterine DNA breakage, necrosis, and ovarian-uterine tissue damages in arsenicated rats by improving the ovarian steroidogenesis. The mechanisms might be coupled with the augmentation of antioxidant defense system, partly through the elimination of arsenic with the involvement of S-adenosyl methionine pool where circulating levels of vitamin B₁₂, folic acid, and homocysteine play critical roles as evidenced from our present investigation.

The interaction of arsenic and N-butyl-N-(4-hydroxybutyl)nitrosamine on urothelial carcinogenesis in mice

The bladder is an important organ for the storage of excreted water and metabolites. If metabolites with carcinogenic characteristics are present in urine, the urothelial lining of the bladder could be damaged and genetically altered. In this study, we analyzed the interaction of arsenic and N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) on mouse bladder carcinogenesis. Our previous study found that arsenic affects BBN-altered urothelial enzymatic activity, protein expression, DNA oxidation and global DNA CpG methylation levels. In this study, two mouse models were used. First, after administering a co-treatment of BBN and arsenic for 20 weeks, BBN alone led to a urothelial carcinoma formation of 20%, and arsenic promoted a BBN-induced urothelial carcinoma formation of 10%. The protein expression of GSTM1, GSTO1, NQO1, and p21 did not change by arsenic along with the BBN co-treatment, but the Sp1 expression increased. In the second mouse model, BBN was a pretreatment promoter; arsenic dose-dependently deteriorated BBN-promoted dysplasia by 10% and 40% at 10 ppm and 100 ppm, respectively. Conversely, BBN pretreatment also accelerated arsenic-induced dysplasia by 30%. The urothelial carcinogenic effect reversed after ceasing BBN for a period of 20 weeks. In summary, three conclusions were drawn from this study. The first is the mutual promotion of arsenic and BBN in bladder carcinogenesis. Second, arsenic dosages without bladder carcinogenicity (10 ppm) or with slight carcinogenicity (100 ppm) promote BBN-induced mice bladder cancer progression. Finally, the dysplastic urothelium had reverted to near-normal morphology after ceasing BBN intake for 20 weeks, providing a good suggestion for people who want to quit smoking.

Non‑infective occupational risk factors for hepatocellular carcinoma: A review (Review)

Liver cancer is the second leading worldwide cause of cancer‑associated mortalities. Hepatocellular carcinoma, which accounts for the majority of liver tumors, ranks fifth among types of human cancer. Well‑established risk factors for liver cancer include the hepatitis B and C viruses, aflatoxins, alcohol consumption, and oral contraceptives. Tobacco smoking, androgenic steroids, and diabetes mellitus are suspected risk factors. Current knowledge regarding non‑infective occupational risk factors for liver cancer is inconclusive. The relevance of liver disorders to occupational medicine lies in the fact that the majority of chemicals are metabolized in the liver, and toxic metabolites generated via metabolism are the predominant cause of liver damage. However, their non‑specific clinical manifestations that are similar in a number of liver diseases make diagnosis difficult. Furthermore, concomitant conditions, such as viral hepatitis and alcohol or drug abuse, may mask liver disorders that result from occupational hepatotoxic agents and block the demonstration of an occupational cause. The identification of environmental agents that result in human cancer is a long and often difficult process. The purpose of the present review is to summarize current knowledge regarding the association of non‑infective occupational risk exposure and HCC, to encourage further research and draw attention to this global occupational public health problem.

The role of microRNAs in metal carcinogen-induced cell malignant transformation and tumorigenesis

MicroRNAs (miRNAs), an important component of epigenetic mechanisms of carcinogenesis, have been shown to play crucial roles in cancer initiation, metastasis, prognosis and responses to drug treatment and may serve as biomarkers for early diagnosis of cancer and tools for cancer therapy. Metal carcinogens, such as arsenic, cadmium, hexavalent chromium and nickel, are well-established human carcinogens causing various cancers upon long term exposure. However, the mechanism of metal carcinogenesis has not been well understood, which limits our capability to effectively diagnose and treat human cancers resulting from chronic metal carcinogen exposure. Over recent years, the role of miRNAs in metal carcinogenesis has been actively explored and a growing body of evidence indicates the critical involvement of miRNAs in metal carcinogenesis. This review aims to discuss recent studies showing that miRNAs play important roles in metal carcinogen-induced cell malignant transformation and tumorigenesis. Some thoughts for future further studies in this field are also presented.

Examination of in vivo mutagenicity of sodium arsenite and dimethylarsinic acid in gpt delta rats

Arsenic is a well-known human bladder and liver carcinogen, but its exact mechanism of carcinogenicity is not fully understood. Dimethylarsinic acid (DMA^V) is a major urinary metabolite of sodium arsenite (iAs^III) and induces urinary bladder cancers in rats. DMA^V and iAs^III are negative in in vitro mutagenicity tests. However, their in vivo mutagenicities have not been determined. The purpose of present study is to evaluate the in vivo mutagenicities of DMA^V and iAs^III in rat urinary bladder epithelium and liver using gpt delta F344 rats. Ten-week old male gpt delta F344 rats were randomized into 3 groups and administered 0, 92mg/L DMA^V, or 87mg/L iAs^III (each 50mg/L As) for 13weeks in the drinking water. In the mutation assay, point mutations are detected in the gpt gene by 6-thioguanine selection (gpt assay) and deletion mutations are identified in the red/gam genes by Spi^- selection (Spi^- assay). Results of the gpt and Spi^- assays showed that DMA^V and iAs^III had no effects on the mutant frequencies or mutation spectrum in urinary bladder epithelium or liver. These findings indicate that DMA^V and iAs^III are not mutagenic in urinary bladder epithelium or liver in rats.

Arsenic and ultraviolet radiation exposure: melanoma in a New Mexico non-Hispanic white population

Cases of cutaneous melanoma and controls were enrolled in a New Mexico population-based study; subjects were administered questionnaires concerning ultraviolet (UV) and inorganic arsenic (iAs) exposure. Historical iAs exposure was estimated. UV exposure estimates were also derived using geospatial methods. Drinking water samples were collected for iAs analysis. Blood samples were collected for DNA repair (Comet) and DNA repair gene polymorphism assays. Arsenic concentrations were determined in urine and toenail samples. UV exposures during the previous 90 days did not vary significantly between cases and controls. Mean (±SD) current home iAs drinking water was not significantly different for cases and controls [3.98 μg/L (±3.67) vs. 3.47 μg/L (±2.40)]. iAs exposure showed no effect on DNA repair or association with melanoma. Results did not corroborate a previously reported association between toenail As and melanoma risk. Arsenic biomarkers in urine and toenail were highly significantly correlated with iAs in drinking water. A UV-DNA repair interaction for UV exposure over the previous 7-90 days was shown; cases had higher DNA damage than controls at low UV values. This novel finding suggests that melanoma cases may be more sensitive to low-level UV exposure than are controls. A UV-APEX1 interaction was shown. Subjects with the homozygous rare APEX1 DNA repair gene allele had a higher risk of early melanoma diagnosis at low UV exposure compared with those with the homozygous wild type or the heterozygote. Notably, a UV-arsenic interaction on inhibition of DNA repair was not observed at iAs drinking water concentrations below 10 ppb (μg/L).

Hepatocellular carcinoma and the risk of occupational exposure

Hepatocellular carcinoma (HCC) is the most common type of liver cancer. The main risk factors for HCC are alcoholism, hepatitis B virus, hepatitis C virus, nonalcoholic steatohepatitis, obesity, type 2 diabetes, cirrhosis, aflatoxin, hemochromatosis, Wilson's disease and hemophilia. Occupational exposure to chemicals is another risk factor for HCC. Often the relationship between occupational risk and HCC is unclear and the reports are fragmented and inconsistent. This review aims to summarize the current knowledge regarding the association of infective and non-infective occupational risk exposure and HCC in order to encourage further research and draw attention to this global occupational public health problem.

Actions of Estrogenic Endocrine Disrupting Chemicals on Human Prostate Stem/Progenitor Cells and Prostate Carcinogenesis

Substantial evidences from epidemiological and animal-based studies indicate that early exposure to endocrine disrupting chemicals (EDCs) during the developmental stage results in a variety of disorders including cancer. Previous studies have demonstrated that early estrogen exposure results in life-long reprogramming of the prostate gland that leads to an increased incidence of prostatic lesions with aging. We have recently documented that bisphenol A (BPA), one of the most studied EDCs with estrogenic activity has similar effects in increasing prostate carcinogenic potential, supporting the connection between EDCs exposure and prostate cancer risk. It is well accepted that stem cells play a crucial role in development and cancer. Accumulating evidence suggest that stem cells are regulated by extrinsic factors and may be the potential target of hormonal carcinogenesis. Estrogenic EDCs which interfere with normal hormonal signaling may perturb prostate stem cell fate by directly reprogramming stem cells or breaking down the stem cell niche. Transformation of stem cells into cancer stem cells may underlie cancer initiation accounting for cancer recurrence, which becomes a critical therapeutic target of cancer management. We therefore propose that estrogenic EDCs may influence the development and progression of prostate cancer through reprogramming and transforming the prostate stem and early stage progenitor cells. In this review, we summarize our current studies and have updated recent advances highlighting estrogenic EDCs on prostate carcinogenesis by possible targeting prostate stem/progenitor cells. Using novel stem cell assays we have demonstrated that human prostate stem/progenitor cells express estrogen receptors (ER) and are directly modulated by estrogenic EDCs. Moreover, employing anin vivohumanized chimeric prostate model, we further demonstrated that estrogenic EDCs initiate and promote prostatic carcinogenesis in an androgen-supported environment. These findings support our hypothesis that prostate stem/progenitor cells may be the direct targets of estrogenic EDCs as a consequence of developmental exposure which carry permanent reprogrammed epigenetic and oncogenic events and subsequently deposit into cancer initiation and progression in adulthood.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.