Arsenic in the aetiology of cancer

Metabolism, toxicity and anticancer activities of arsenic compounds

A variety of studies indicated that inorganic arsenic and its methylated metabolites have paradoxical effects, namely, carcinogenic and anticancer effects. Epidemiological studies have shown that long term exposure to arsenic can increase the risk of cancers of lung, skin or bladder in man, which is probably associated with the arsenic metabolism. In fact, the enzymatic conversion of inorganic arsenic by Arsenic (+3 oxidation state) methyltransferase (AS3MT) to mono- and dimethylated arsenic species has long been considered as a major route for detoxification. However, several studies have also indicated that biomethylation of inorganic arsenic, particularly the production of trivalent methylated metabolites, is a process that activates arsenic as a toxin and a carcinogen. On the other hand, arsenic trioxide (As2O3) has recently been recognized as one of the most effective drugs for the treatment of APL. However, elaboration of the cytotoxic mechanisms of arsenic and its methylated metabolites in eradicating cancer is sorely lacking. To provide a deeper understanding of the toxicity and carcinogenicity along with them use of arsenic in chemotherapy, caution is required considering the poor understanding of its various mechanisms of exerting toxicity. Thereby, in this review, we have focused on arsenic metabolic pathway, the roles of the methylated arsenic metabolites in toxicity and in the therapeutic efficacy for the treatments of solid tumors, APL and/or non-APL malignancies.

Chronic exposure to arsenic, LINE-1 hypomethylation, and blood pressure: a cross-sectional study in Bangladesh

BACKGROUND

Chronic exposure to arsenic is associated with cancer and hypertension. Growing evidence suggests that altered methylation in long interspersed nuclear element-1 (LINE-1) is involved in many types of disorders, including cardiovascular disease. Here we evaluated the association between arsenic exposure and LINE-1 methylation levels, especially in relation to blood pressure (BP).

METHODS

A total of 236 subjects (175 from arsenic-endemic areas and 61 from a non-endemic area) in rural Bangladesh were recruited. The subjects' arsenic exposure levels (i.e., drinking water, hair and nail arsenic concentrations) were measured by inductively coupled plasma mass spectroscopy. The subjects' LINE-1 methylation levels were determined by pyrosequencing.

RESULTS

The average LINE-1 methylation levels of the subjects living in the arsenic-endemic areas were significantly (p < 0.01) lower than those of the subjects living in the non-endemic area. In a sex-stratified analysis, the arsenic exposure levels in female but not male subjects showed a significant inverse association with LINE-1 methylation levels before (water arsenic: p < 0.01, hair arsenic: p < 0.05, nail arsenic: p < 0.001) and after (water arsenic: p < 0.01, hair arsenic: p < 0.05, nail arsenic: p < 0.001) adjustment for age, body mass index and smoking. Analyses examining interactions among arsenic levels, BP and LINE-1 methylation showed that arsenic-related elevated levels of BP were associated with LINE-1 hypomethylation.

CONCLUSIONS

Our findings demonstrated that chronic exposure to arsenic was inversely associated with LINE-1 methylation levels in blood leukocyte DNA and this was more pronounced in females than males; in addition, the decreased levels of LINE-1 methylation might be involved in the arsenic-induced elevation of BP.

Tumor-augmenting effects of gestational arsenic exposure on F1 and F2 in mice

The consequences of early-life exposure to chemicals in the environment are emerging concerns. Chronic exposure to naturally occurring inorganic arsenic has been known to cause various adverse health effects, including cancers, in humans. On the other hand, animal studies by Dr. M. Waalkes’ group reported that arsenite exposure of pregnant F0 females, only from gestational day 8 to 18, increased hepatic tumors in the F1 (arsenite-F1) males of C3H mice, whose males tend to develop spontaneous hepatic tumors later in life. Since this mice model illuminated novel unidentified consequences of arsenic exposure, we wished to further investigate the background mechanisms. In the same experimental model, we identified a variety of factors that were affected by gestational arsenic exposure, including epigenetic and genetic changes, as possible constituents of multiple steps of late-onset hepatic tumor augmentation in arsenite-F1 males. Furthermore, our study discovered that the F2 males born to arsenite-F1 males developed hepatic tumors at a significantly higher rate than the control F2 males. The results imply that the tumor augmenting effect is inherited by arsenite-F2 males through the sperm of arsenite-F1. In this article, we summarized our studies on the consequences of gestational arsenite exposure in F1 and F2 mice to discuss novel aspects of biological effects of gestational arsenic exposure.

RKIP expression of liver and kidney after arsenic exposure

Arsenic is associated with cancers of kidney and liver. Raf kinase inhibitor protein (RKIP) has been identified as a member of a novel class of molecules that suppress the metastatic spread of tumors. In order to investigate the effect of arsenic to RKIP of liver and kidney, the expression of RKIP of liver and kidney with As (III) was explored in this study. Thirty male mice were chronically fed with 42.5 ppm, 85 ppm NaAsO₂ and water for 180 days. The kidney and liver accumulation levels of As (III) in mice were determined by electro-thermal atomic absorption spectrometry. The method of RT-PCR, Western blotting analysis and immunohistochemistry were used to determine gene expression and protein expression of RKIP. The results showed that arsenic level was significantly increased in kidney and liver of As (III)-exposed mice as compared with control group. The gene expression and protein expression of RKIP was significantly decreased in kidney and liver of As (III)-exposed mice in comparison with these of control mice. These data suggested that RKIP decrease of liver and kidney with As (III) may be dangerous index in formation of cancer. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1079-1082, 2017.

Nuclear lamins and progerin are dispensable for antioxidant Nrf2 response to arsenic and cadmium

Lamins are important constituents of the nuclear inner membrane and provide a platform for transcription factors and chromatin. Progerin, a C-terminal truncated lamin A mutant, causes premature aging termed Hutchinson-Gilford Progeria Syndrome (HGPS). Oxidative stress appears to be involved in the pathogenesis of HGPS, although the mechanistic role of progerin remains elusive. Here we examined whether nuclear lamins are important for a cellular antioxidant mechanism, and whether progerin compromises it. We investigated the activation of nuclear factor-E2-related factor 2 (Nrf2) which regulates various antioxidant genes including heme oxygenase-1 (HMOX1), following exposure to sodium arsenite or cadmium chloride in lamin knockdown human cell lines and primary HGPS human fibroblasts. Knocking down lamin A/C, or B, or all nuclear lamins simultaneously in three human cell lines (HaCaT, SW480, and K562) did not impair arsenite- or cadmium-induced activation of Nrf2. Progerin-expressing human primary HGPS fibroblasts showed lower basal levels of HMOX1 and NQO1 expression; however, in response to arsenic stress both normal and HGPS primary fibroblasts showed Nrf2 nuclear accumulation along with upregulation and phosphorylation of p62/SQSTM1 at Ser351, downregulation of Keap1, and comparable expression of an array of downstream Nrf2-regulated antioxidant genes. We also observed new forms of cleaved lamin A, B1 and B2 induced by cadmium stress although their roles in the Nrf2 antioxidant system need further investigation. These results suggest that the nuclear lamins and progerin have marginal roles in the activation of the antioxidant Nrf2 response to arsenic and cadmium.

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.

Arsenite Effects on Mitochondrial Bioenergetics in Human and Mouse Primary Hepatocytes Follow a Nonlinear Dose Response

Arsenite is a known carcinogen and its exposure has been implicated in a variety of noncarcinogenic health concerns. Increased oxidative stress is thought to be the primary cause of arsenite toxicity and the toxic effect is thought to be linear with detrimental effects reported at all concentrations of arsenite. But the paradigm of linear dose response in arsenite toxicity is shifting. In the present study we demonstrate that arsenite effects on mitochondrial respiration in primary hepatocytes follow a nonlinear dose response. In vitro exposure of primary hepatocytes to an environmentally relevant, moderate level of arsenite results in increased oxidant production that appears to arise from changes in the expression and activity of respiratory Complex I of the mitochondrial proton circuit. In primary hepatocytes the excess oxidant production appears to elicit adaptive responses that promote resistance to oxidative stress and a propensity to increased proliferation. Taken together, these results suggest a nonlinear dose-response characteristic of arsenite with low-dose arsenite promoting adaptive responses in a process known as mitohormesis, with transient increase in ROS levels acting as transducers of arsenite-induced mitohormesis.

Bacterial iron-oxide nanowires from biofilm waste as a new adsorbent for the removal of arsenic from water

Biofilm waste material generated by the bacteria in the groundwater pipelines was found is composed of amorphous twisted iron-oxide nanowires which are shown to have considerable adsorption properties for removal As(iii) and As(v) ions from waters.

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.

Interactive Influence of N6AMT1 and As3MT Genetic Variations on Arsenic Metabolism in the Population of Inner Mongolia, China

Chronic arsenic exposure via drinking water has become a worldwide public health concern. In humans, inorganic arsenic (iAs) is metabolized to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) mainly mediated by arsenic (+3 oxidation state) methyltransferase (As3MT). We reported recently that N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) was involved in arsenic metabolism, and examined its interactive effect with As3MT on arsenic metabolism in vitro To further evaluate the interactive effect of N6AMT1 and As3MT on arsenic biomethylation in humans, we conducted a human population-based study including 289 subjects living in rural villages in Inner Mongolia, China, and assessed their urinary arsenic metabolites profiles in relation to genetic polymorphisms and haplotypes of N6AMT1 and As3MT Five N6AMT1 single nucleotide polymorphisms (SNPs; rs1003671, rs7282257, rs2065266, rs2738966, rs2248501) and the N6AMT1 haplotype 2_GGCCAT were significantly associated with the percentage of iAs (% iAs) in urine (e.g., for rs7282257, mean was 9.62% for TT, 6.73% for AA). Rs1003671 was also in a significant relationship with urinary MMA and DMA (the mean of %MMA was 24.95% for GA, 31.69% for GG; the mean of % DMA was 69.21% for GA, 59.82% for GG). The combined effect of N6AMT1 haplotype 2_GGCCAT and As3MT haplotype 2_GCAC showed consistence with the additive significance of each haplotype on % iAs: the mean was 5.47% and 9.36% for carriers with both and null haplotypes, respectively. Overall, we showed that N6AMT1 genetic polymorphisms were associated with arsenic biomethylation in the Chinese population, and its interaction with As3MT was observed in specific haplotype combinations.

Chromated copper arsenate-treated wood: a potential source of arsenic exposure and toxicity in dermatology

Arsenic-contaminated drinking water presents a serious health hazard in certain geographic locations around the world. Chromated copper arsenate, a pesticide and preservative that was used to pressure treat residential lumber in the United States beginning in the 1940s and was banned by the Environmental Protection Agency in 2003, poses a potential source of arsenic exposure and toxicity. In this study, we review the clinical manifestations of arsenic intoxication with the focus on dermatologic manifestations. Dermatologists should be aware that although chromated copper arsenate-treated wood for residential use was banned in 2003, the exposure risk remains. Long-term follow up is necessary to detect arsenic induced cutaneous and visceral malignancy in patients with history of arsenic exposure.

Elevated concentrations of serum matrix metalloproteinase-2 and -9 and their associations with circulating markers of cardiovascular diseases in chronic arsenic-exposed individuals

BACKGROUND

Cardiovascular diseases (CVDs) and cancers are the major causes of chronic arsenic exposure-related morbidity and mortality. Matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9) are deeply involved in the pathogenesis of CVDs and cancers. This study has been designed to evaluate the interactions of arsenic exposure with serum MMP-2 and MMP-9 concentrations especially in relation to the circulating biomarkers of CVDs.

METHODS

A total of 373 human subjects, 265 from arsenic-endemic and 108 from non-endemic areas in Bangladesh were recruited for this study. Arsenic concentrations in the specimens were measured by inductively coupled plasma mass spectroscopy (ICP-MS) and serum MMPs were quantified by immunoassay kits.

RESULTS

Serum MMP-2 and MMP-9 concentrations in arsenic-endemic population were significantly (p < 0.001) higher than those in non-endemic population. Both MMPs showed significant positive interactions with drinking water (r s  = 0.208, p < 0.001 for MMP-2; r s  = 0.163, p < 0.01 for MMP-9), hair (r s  = 0.163, p < 0.01 for MMP-2; r s  = 0.173, p < 0.01 for MMP-9) and nail (r s  = 0.160, p < 0.01 for MMP-2; r s  = 0.182, p < 0.001 for MMP-9) arsenic of the study subjects. MMP-2 concentrations were 1.02, 1.03 and 1.05 times, and MMP-9 concentrations were 1.03, 1.06 and 1.07 times greater for 1 unit increase in log-transformed water, hair and nail arsenic concentrations, respectively, after adjusting for covariates (age, sex, BMI, smoking habit and hypertension). Furthermore, both MMPs were increased dose-dependently when the study subjects were split into three (≤10, 10.1-50 and > 50 μg/L) groups based on the regulatory upper limit of water arsenic concentration set by WHO and Bangladesh Government. MMPs were also found to be significantly (p < 0.05) associated with each other. Finally, the concentrations of both MMPs were correlated with several circulating markers related to CVDs.

CONCLUSIONS

This study showed the significant positive associations and dose-response relationships of arsenic exposure with serum MMP-2 and MMP-9 concentrations. This study also showed the interactions of MMP-2 and MMP-9 concentrations with the circulating markers of CVDs suggesting the MMP-2 and MMP-9 -mediated mechanism of arsenic-induced CVDs.

Occupational and environmental exposures and cancers in developing countries

BACKGROUND

Over the past few decades, there has been a decline in cancers attributable to environmental and occupational carcinogens of asbestos, arsenic, and indoor and outdoor air pollution in high-income countries. For low- to middle-income countries (LMICs), however, these exposures are likely to increase as industrialization expands and populations grow.

OBJECTIVE

The aim of this study was to review the evidence on the cancer risks and burdens of selected environmental and occupational exposures in less-developed economies.

FINDINGS

A causal association has been established between asbestos exposure and mesothelioma and lung cancer. For arsenic exposure, there is strong evidence of bladder, skin, lung, liver, and kidney cancer effects. Women are at the highest risk for lung cancer due to indoor air pollution exposure; however, the carcinogenic effect on the risk for cancer in children has not been studied in these countries. Cancer risks associated with ambient air pollution remain the least studied in LMICs, although reported exposures are higher than World Health Organization, European, and US standards. Although some associations between lung cancer and ambient air pollutants have been reported, studies in LMICs are weak or subject to exposure misclassification. For pulmonary cancers, tobacco smoking and respiratory diseases have a positive synergistic effect on cancer risks.

CONCLUSIONS

A precise quantification of the burden of human cancer attributable to environmental and occupational exposures in LMICs is uncertain. Although the prevalence of carcinogenic exposures has been reported to be high in many such countries, the effects of the exposures have not been studied due to varying country-specific limitations, some of which include lack of resources and government support.

Low-Concentration Arsenic Trioxide Inhibits Skeletal Myoblast Cell Proliferation via a Reactive Oxygen Species-Independent Pathway

Myoblast proliferation and differentiation are essential for skeletal muscle regeneration. Myoblast proliferation is a critical step in the growth and maintenance of skeletal muscle. The precise action of inorganic arsenic on myoblast growth has not been investigated. Here, we investigated the in vitro effect of inorganic arsenic trioxide (As₂O₃) on the growth of C2C12 myoblasts. As₂O₃ decreased myoblast growth at submicromolar concentrations (0.25–1 μM) after 72 h of treatment. Submicromolar concentrations of As₂O₃ did not induce the myoblast apoptosis. Low-concentration As₂O₃ (0.5 and 1 μM) significantly suppressed the myoblast cell proliferative activity, which was accompanied by a small proportion of bromodeoxyuridine (BrdU) incorporation and decreased proliferating cell nuclear antigen (PCNA) protein expression. As₂O₃ (0.5 and 1 μM) increased the intracellular arsenic content but did not affect the reactive oxygen species (ROS) levels in the myoblasts. Cell cycle analysis indicated that low-concentrations of As₂O₃ inhibited cell proliferation via cell cycle arrest in the G1 and G2/M phases. As₂O₃ also decreased the protein expressions of cyclin D1, cyclin E, cyclin B1, cyclin-dependent kinase (CDK) 2, and CDK4, but did not affect the protein expressions of p21 and p27. Furthermore, As₂O₃ inhibited the phosphorylation of Akt. Insulin-like growth factor-1 significantly reversed the inhibitory effect of As₂O₃ on Akt phosphorylation and cell proliferation in the myoblasts. These results suggest that submicromolar concentrations of As₂O₃ alter cell cycle progression and reduce myoblast proliferation, at least in part, through a ROS-independent Akt inhibition pathway.

Arsenic-induced S phase cell cycle lengthening is associated with ROS generation, p53 signaling and CDC25A expression

Cellular response to arsenic is strongly dependent on p53 functional status. Primarily arresting the cell cycle in G1 or G2/M phases, arsenic treatment also induces an increase in the S-phase time in wild-type p53 cells. In contrast, cells with a non-functional p53 display only a subtle increase in the S phase, indicating arsenic differentially affects the cell cycle depending on p53 status. Importantly, it has been reported that arsenic induces reactive oxygen species (ROS), a process counteracted by p53. To evaluate the participation of p53 in the lengthening of the S phase and the connection between the transient cell cycle arrest and oxidative stress, we evaluated the cell response to arsenic in MCF-7 and H1299 cells, and analyzed p53's role as a transcription factor in regulating genes involved in ROS reduction and S phase transition. Herein, we discovered that arsenic induced an increase in the population of S phase cells that was dependent on the presence and transcriptional activity of p53. Furthermore, for the first time, we demonstrate that arsenic activates p53-dependent transcription of ROS detoxification genes, such as SESN1, and by an indirect mechanism involving ATF3, genes that could be responsible for the S phase cell cycle arrest, such as CDC25A.

Tetraarsenictetrasulfide and Arsenic Trioxide Exert Synergistic Effects on Induction of Apoptosis and Differentiation in Acute Promyelocytic Leukemia Cells

Since arsenic trioxide (As³⁺) has been successfully used in the treatment of acute promyelocytic leukemia (APL), its adverse effects on patients have been problematic and required a solution. Considering the good therapeutic potency and low toxicity of tetraarsenictetrasulfide (As₄S₄) in the treatment of APL, we investigated the effects of combining As₄S₄ and As³⁺ on the apoptosis and differentiation of NB4 and primary APL cells. As₄S₄, acting similarly to As³⁺, arrested the G₁/S transition, induced the accumulation of cellular reactive oxygen species, and promoted apoptosis. Additionally, low concentrations of As₄S₄ (0.1–0.4 μM) induced differentiation of NB4 and primary APL cells. Compared with the As₄S₄- or As³⁺-treated groups, the combination of As₄S₄ and As³⁺ obviously promoted apoptosis and differentiation of NB4 and primary APL cells. Mechanistic studies suggested that As₄S₄ acted synergistically with As³⁺ to down-regulate Bcl-2 and nuclear factor-κB expression, up-regulate Bax and p53 expression, and induce activation of caspase-12 and caspase-3. Moreover, the combination of low concentrations of As₄S₄ and As³⁺ enhanced degradation of the promyelocytic leukemia-retinoic acid receptor α oncoprotein. In summary, As₄S₄ and As³⁺ synergistically induce the apoptosis and differentiation of NB4 and primary APL cells.

Interactive Effects of N6AMT1 and As3MT in Arsenic Biomethylation

In humans, arsenic is primarily metabolized by arsenic (+3 oxidation state) methyltransferase (As3MT) to yield both trivalent and pentavalent methylated metabolites. We recently reported that the putative N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) can biotransform monomethylarsonous acid (MMA(III)) to dimethylarsinic acid, conferring resistance of human cells to arsenic exposure. To further decipher the role of N6AMT1 and its interaction with As3MT in arsenic biomethylation, we examined the relative contribution of N6AMT1 and As3MT in metabolizing arsenic using several newly modified UROtsa human urothelial cells, ie, UROtsa cells with either a constant level of N6AMT1 or As3MT in combination with an inducible level of As3MT or N6AMT1, respectively. Our analysis confirmed the involvement of N6AMT1 in MMA(III) biomethylation but not for inorganic arsenic. In a comparable level of N6AMT1 and As3MT, the effect of N6AMT1 mediated MMA(III) biomethylation was obscured by the action of As3MT. Furthermore, we showed that the levels of N6AMT1 and As3MT proteins varied among and within human normal and cancerous tissues. Overall, the data showed that N6AMT1 has a role in MMA(III) biomethylation, but its effect is relatively minor and limited compared with As3MT. In addition, the varied levels and distributions of N6AMT1 and As3MT among human tissues may potentially contribute to the tissue specificity and susceptibility to arsenic toxicity and carcinogenicity.

Pharmacokinetic and Genomic Effects of Arsenite in Drinking Water on Mouse Lung in a 30-Day Exposure

The 2 objectives of this subchronic study were to determine the arsenite drinking water exposure dependent increases in female C3H mouse liver and lung tissue arsenicals and to characterize the dose response (to 0, 0.05, 0.25, 1, 10, and 85 ppm arsenite in drinking water for 30 days and a purified AIN-93M diet) for genomic mouse lung expression patterns. Mouse lungs were analyzed for inorganic arsenic, monomethylated, and dimethylated arsenicals by hydride generation atomic absorption spectroscopy. The total lung mean arsenical levels were 1.4, 22.5, 30.1, 50.9, 105.3, and 316.4 ng/g lung tissue after 0, 0.05, 0.25, 1, 10, and 85 ppm, respectively. At 85 ppm, the total mean lung arsenical levels increased 14-fold and 131-fold when compared to either the lowest noncontrol dose (0.05 ppm) or the control dose, respectively. We found that arsenic exposure elicited minimal numbers of differentially expressed genes (DEGs; 77, 38, 90, 87, and 87 DEGs) after 0.05, 0.25, 1, 10, and 85 ppm, respectively, which were associated with cardiovascular disease, development, differentiation, apoptosis, proliferation, and stress response. After 30 days of arsenite exposure, this study showed monotonic increases in mouse lung arsenical (total arsenic and dimethylarsinic acid) concentrations but no clear dose-related increases in DEG numbers.

Inorganic Arsenic-induced cellular transformation is coupled with genome wide changes in chromatin structure, transcriptome and splicing patterns

Background

Arsenic (As) exposure is a significant worldwide environmental health concern. Low dose, chronic arsenic exposure has been associated with a higher than normal risk of skin, lung, and bladder cancer, as well as cardiovascular disease and diabetes. While arsenic-induced biological changes play a role in disease pathology, little is known about the dynamic cellular changes resulting from arsenic exposure and withdrawal.

Results

In these studies, we sought to understand the molecular mechanisms behind the biological changes induced by arsenic exposure. A comprehensive global approach was employed to determine genome-wide changes to chromatin structure, transcriptome patterns and splicing patterns in response to chronic low dose arsenic and its subsequent withdrawal. Our results show that cells exposed to chronic low doses of sodium arsenite have distinct temporal and coordinated chromatin, gene expression, and miRNA changes consistent with differentiation and activation of multiple biochemical pathways. Most of these temporal patterns in gene expression are reversed when arsenic is withdrawn. However, some gene expression patterns remained altered, plausibly as a result of an adaptive response by cells. Additionally, the correlation of changes to gene expression and chromatin structure solidify the role of chromatin structure in gene regulatory changes due to arsenite exposure. Lastly, we show that arsenite exposure influences gene regulation both at the initiation of transcription as well as at the level of splicing.

Conclusions

Our results show that adaptation of cells to iAs-mediated EMT is coupled to changes in chromatin structure effecting differential transcriptional and splicing patterns of genes. These studies provide new insights into the mechanism of iAs-mediated pathology, which includes epigenetic chromatin changes coupled with changes to the transcriptome and splicing patterns of key genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1295-9) contains supplementary material, which is available to authorized users.

Associations of total arsenic in drinking water, hair and nails with serum vascular endothelial growth factor in arsenic-endemic individuals in Bangladesh

Arsenic exposure is associated with cancer and vascular diseases. Angiogenesis is an important step for the pathological development of cancer and vascular diseases. Vascular endothelial growth factor (VEGF) is a specific marker for angiogenesis. However, human study showing the association between arsenic exposure and serum VEGF levels has not yet been documented. This study was aimed to investigate the association between arsenic exposure and serum VEGF levels in the arsenic-endemic individuals in Bangladesh. A total of 260 individuals were recruited for this study. Arsenic exposure levels were measured by ICP-MS and VEGF levels were quantified using VEGF immunoassay kit. The study subjects were stratified into tertile (low, medium and high) groups based on the arsenic in water, hair and nails. Serum VEGF levels were correlated with water (rs = 0.363, p < 0.001), hair (rs = 0.205, p < 0.01) and nail (rs = 0.190, p < 0.01) arsenic. Further, VEGF levels showed dose-response relationships with water, hair and nail arsenic. Mean VEGF levels in ⩽ 10 μg L(-1), 10.1-50 μg L(-1) and > 50 μg L(-1) groups were 91.84, 129.54, and 169.86 pg mL(-1), respectively, however, significant (p < 0.01) difference in VEGF levels was only found in > 50 μg L(-1) versus ⩽ 10 μg L(-1) groups. Significant associations of arsenic exposure with VEGF levels were found even after adjusting with relevant covariates. Therefore, these results provide evidence that arsenic exposure has a pro-angiogenic effect on humans, which may be implicated in arsenic-induced tumorigenesis and vascular diseases.

Dose-dependent effects of selenite (Se(4+)) on arsenite (As(3+))-induced apoptosis and differentiation in acute promyelocytic leukemia cells

To enhance the therapeutic effects and decrease the adverse effects of arsenic on the treatment of acute promyelocytic leukemia, we investigated the co-effects of selenite (Se⁴⁺) and arsenite (As³⁺) on the apoptosis and differentiation of NB4 cells and primary APL cells. A 1.0-μM concentration of Se⁴⁺ prevented the cells from undergoing As³⁺-induced apoptosis by inhibiting As³⁺ uptake, eliminating As³⁺-generated reactive oxygen species, and repressing the mitochondria-mediated intrinsic apoptosis pathway. However, 4.0 μM Se⁴⁺ exerted synergistic effects with As³⁺ on cell apoptosis by promoting As³⁺ uptake, downregulating nuclear factor-кB, and activating caspase-3. In addition to apoptosis, 1.0 and 3.2 μM Se⁴⁺ showed contrasting effects on As³⁺-induced differentiation in NB4 cells and primary APL cells. The 3.2 μM Se⁴⁺ enhanced As³⁺-induced differentiation by promoting the degradation of promyelocytic leukemia protein–retinoic acid receptor-α (PML–RARα) oncoprotein, but 1.0 μM Se⁴⁺ did not have this effect. Based on mechanistic studies, Se⁴⁺, which is similar to As³⁺, might bind directly to Zn²⁺-binding sites of the PML RING domain, thus controlling the fate of PML–RARα oncoprotein.

Statistical analysis of causes of death (2005-2010) in villages of Simav Plain, Turkey, with high arsenic levels in drinking water supplies

The purpose of this research was to compare the causes of death in 5 villages situated in Simav Plain, Turkey, during 2005-2010 where different arsenic levels were detected in drinking water supplies. Since groundwater in Simav Plain had arsenic concentrations that ranged between 7.1 and 833.9 ppb, a two-phase research was formulated. In the first phase, public health surveys were conducted with 1,003 villagers to determine the distribution of diseases. In the second phase, verbal autopsy surveys and official death records were used to investigate the causes of death. In total, 402 death cases were found in the study area where cardiovascular system diseases (44%) and cancers (15.2%) were major causes. Cancers of lung (44.3%), prostate (9.8%), colon (9.8%), and stomach (8.2%) were comparably higher in villages with high arsenic levels in drinking water supplies. Furthermore, the majority of cases of liver, bladder, and stomach cancers were observed in villages with high arsenic levels.

MicroRNA-21, up-regulated by arsenite, directs the epithelial-mesenchymal transition and enhances the invasive potential of transformed human bronchial epithelial cells by targeting PDCD4

Arsenic is well established as a human carcinogen, but the molecular mechanisms leading to arsenic-induced carcinogenesis are complex and elusive. It is not been determined if the epithelial-mesenchymal transition (EMT) contributes to carcinogen-induced malignant transformation and subsequent tumor formation. We have found that, during the neoplastic transformation induced in human bronchial epithelial (HBE) cells by a low concentration (1.0μM) of arsenite, the cells undergo an EMT and show enhanced invasion and migration. With longer times for transformation of HBE cells, there was increased miR-21 expression. Further, during the transformation of HBE cells, inhibition of miR-21 with an miR-21 inhibitor increased levels of PDCD4, an inhibitor of neoplastic transformation; reduced Twist1, a transcription factor involved in cell differentiation; and inhibited cell invasion and migration. In addition, PDCD4 interacted with Twist1 and inhibited its expression function, which is involved in arsenite-induced EMT. Thus, miR-21, acting on PDCD4, which interacts with Twist1 and represses the expression of Twist1, contributes to the EMT induced by arsenite. These observations add to an understanding of the processes involved in arsenite-induced carcinogenesis.

The functions of crucial cysteine residues in the arsenite methylation catalyzed by recombinant human arsenic (III) methyltransferase

Arsenic (III) methyltransferase (AS3MT) is a cysteine (Cys)-rich enzyme that catalyzes the biomethylation of arsenic. To investigate how these crucial Cys residues promote catalysis, we used matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) to analyze Cys residues in recombinant human arsenic (III) methyltransferase (hAS3MT). We detected two disulfide bonds, Cys250-Cys32 and Cys368-Cys369, in hAS3MT. The Cys250-Cys32 disulfide bond was reduced by glutathione (GSH) or other disulfide bond reductants before the enzymatic methylation of arsenite (iAs3+). In addition to exposing residues around the active sites, cleavage of the Cys250-Cys32 pair modulated the conformation of hAS3MT. This adjustment may stabilize the binding of S-Adenosyl-L-methionine (AdoMet) and favor iAs3+ binding to hAS3MT. Additionally, we observed the intermediate of Cys250-S-adenosylhomocysteine (AdoHcy), suggesting that Cys250 is involved in the transmethylation. In recovery experiments, we confirmed that trivalent arsenicals were substrates for hAS3MT, methylation of arsenic occurred on the enzyme, and an intramolecular disulfide bond might be formed after iAs3+ was methylated to dimethylarsinous acid (DMA3+). In this work, we clarified both the functional roles of GSH and the crucial Cys residues in iAs3+ methylation catalyzed by hAS3MT.

Arsenic contamination of groundwater: a review of sources, prevalence, health risks, and strategies for mitigation

Arsenic contamination of groundwater in different parts of the world is an outcome of natural and/or anthropogenic sources, leading to adverse effects on human health and ecosystem. Millions of people from different countries are heavily dependent on groundwater containing elevated level of As for drinking purposes. As contamination of groundwater, poses a serious risk to human health. Excessive and prolonged exposure of inorganic As with drinking water is causing arsenicosis, a deteriorating and disabling disease characterized by skin lesions and pigmentation of the skin, patches on palm of the hands and soles of the feet. Arsenic poisoning culminates into potentially fatal diseases like skin and internal cancers. This paper reviews sources, speciation, and mobility of As and global overview of groundwater As contamination. The paper also critically reviews the As led human health risks, its uptake, metabolism, and toxicity mechanisms. The paper provides an overview of the state-of-the-art knowledge on the alternative As free drinking water and various technologies (oxidation, coagulation flocculation, adsorption, and microbial) for mitigation of the problem of As contamination of groundwater.

Elevated levels of plasma uric acid and its relation to hypertension in arsenic-endemic human individuals in Bangladesh

Blood uric acid has been recognized as a putative marker for cardiovascular diseases (CVDs). CVDs are the major causes of arsenic-related morbidity and mortality. However, the association of arsenic exposure with plasma uric acid (PUA) levels in relation to CVDs has not yet been explored. This study for the first time demonstrated the associations of arsenic exposure with PUA levels and its relationship with hypertension. A total of 483 subjects, 322 from arsenic-endemic and 161 from non-endemic areas in Bangladesh were recruited as study subjects. Arsenic concentrations in the drinking water, hair and nails of the study subjects were measured by inductively coupled plasma mass spectroscopy. PUA levels were measured using a colorimetric method. We found that PUA levels were significantly (p<0.001) higher in males and females living in arsenic-endemic areas than those in non-endemic area. Arsenic exposure (water, hair and nail arsenic) levels showed significant positive correlations with PUA levels. In multiple regression analyses, arsenic exposure levels were found to be the most significant contributors on PUA levels among the other variables that included age, body mass index, blood urea nitrogen, and smoking. There were dose-response relationships between arsenic exposure and PUA levels. Furthermore, diastolic and systolic blood pressure showed significant positive correlations with PUA levels. Finally, the average PUA levels were significantly higher in the hypertensive group than those in the normotensive group in both males and females living in arsenic-endemic areas. These results suggest that arsenic exposure-related elevation of PUA levels may be implicated in arsenic-induced CVDs.

Arsenite promotes intestinal tumor cell proliferation and invasion by stimulating epithelial-to-mesenchymal transition

Arsenite (AS) is a ubiquitous environmental element that is widely present in food, soil, and water. Environmental exposure to AS represents a major global health concern, because AS is a well-established human carcinogen. We hypothesize that low concentration of AS could enhance metastasis and proliferation of transformed cancer cells by promoting EMT. To test this hypothesis, we treated human colorectal cancer cells with low concentration of AS, and then measured the multiple readouts of cell viability, proliferation, migration, and adhesion in vitro and in vivo. Collectively, our data indeed strongly support our hypothesis and shed novel light into this important pathophysiological process. These novel insights are not only of high interests to basic cancer research, but may also have direct implications in cancer prevention and treatment.

Trichoderma spp. alleviate phytotoxicity in lettuce plants (Lactuca sativa L.) irrigated with arsenic-contaminated water

The influence of two strains of Trichoderma (T. harzianum strain T22 and T. atroviride strain P1) on the growth of lettuce plants (Lactuca sativa L.) irrigated with As-contaminated water, and their effect on the uptake and accumulation of the contaminant in the plant roots and leaves, were studied. Accumulation of this non-essential element occurred mainly into the root system and reduced both biomass development and net photosynthesis rate (while altering the plant P status). Plant growth-promoting fungi (PGPF) of both Trichoderma species alleviated, at least in part, the phytotoxicity of As, essentially by decreasing its accumulation in the tissues and enhancing plant growth, P status and net photosynthesis rate. Our results indicate that inoculation of lettuce with selected Trichoderma strains may be helpful, beside the classical biocontrol application, in alleviating abiotic stresses such as that caused by irrigation with As-contaminated water, and in reducing the concentration of this metalloid in the edible part of the plant.

Inhibitory mechanism of dimercaptopropanesulfonic acid (DMPS) in the cellular biomethylation of arsenic

Dimercaptopropanesulfonic acid (DMPS) has been approved for the treatment of arsenic poisoning through promoting arsenic excretion and modulating arsenic species. To clarify how DMPS regulates the excretion of arsenic species, we investigated the effects of DMPS on the biomethylation of arsenite (As(3+)) in HepG2 cells. In the experiments, we found that DMPS at low concentrations dramatically decreased the content of arsenic in HepG2 cells and inhibited the cellular methylation of As(3+). Three aspects, the expression of human arsenic (III) methyltransferase (hAS3MT), the accumulation of cellular reactive oxygen species (ROS) and the in vitro enzymatic methylation of arsenic, were considered to explain the reasons for the inhibition of DMPS in arsenic metabolism. The results suggested that DMPS competitively coordinated with As(3+) and monomethylarsonous acid (MMA(3+)) to inhibit the up-regulation of arsenic on the expression of hAS3MT and block arsenic involving in the enzymatic methylation. Moreover, DMPS eliminated arsenic-induced accumulation of ROS, which might contribute to the antidotal effects of DMPS on arsenic posing.

Arsenic and selenium toxicity and their interactive effects in humans

Arsenic (As) and selenium (Se) are unusual metalloids as they both induce and cure cancer. They both cause carcinogenesis, pathology, cytotoxicity, and genotoxicity in humans, with reactive oxygen species playing an important role. While As induces adverse effects by decreasing DNA methylation and affecting protein 53 expression, Se induces adverse effects by modifying thioredoxin reductase. However, they can react with glutathione and S-adenosylmethionine by forming an As-Se complex, which can be secreted extracellularly. We hypothesize that there are two types of interactions between As and Se. At low concentration, Se can decrease As toxicity via excretion of As-Se compound [(GS3)2AsSe](-), but at high concentration, excessive Se can enhance As toxicity by reacting with S-adenosylmethionine and glutathione, and modifying the structure and activity of arsenite methyltransferase. This review is to summarize their toxicity mechanisms and the interaction between As and Se toxicity, and to provide suggestions for future investigations.

MicroRNA-200b suppresses arsenic-transformed cell migration by targeting protein kinase Cα and Wnt5b-protein kinase Cα positive feedback loop and inhibiting Rac1 activation

MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase Cα (PKCα) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKCα 3'-untranslated region vector luciferase reporter assays, we showed that PKCα is a direct target of miR-200b. Inhibiting PKCα activity or knocking down PKCα expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKCα in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKCα in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKCα expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKCα increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKCα or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKCα and Wnt5b-PKCα positive feedback loop and subsequently inhibiting Rac1 activation.

Neuroglobin involvement in the course of arsenic toxicity in rat cerebellar granule neurons

Exposure to arsenic in drinking water results in a widespread environmental problem in the world, and the brain is a major target. Neuroglobin is a vertebrate heme protein regarded as playing neuroprotective role in hypoxia or oxidative stress. In this study, we investigated the toxic effects of sodium arsenite (NaAsO2) on primary cultured rat cerebellar granule neurons (CGNs) and detected neuroglobin (Ngb) expression in rat CGNs exposed to NaAsO2. Our results show that apoptosis was obviously induced by NaAsO2 treatment in rat CGNs by annexin V-fluorescein isothiocyanate assay. Intracellular reactive oxygen species generation increased significantly in the cells exposed to NaAsO2, and the apoptotic effects could be partially reversed by antioxidant N-acetyl-L-cysteine. Ngb protein and mRNA expression were significantly downregulated in rat CGNs shortly after NaAsO2 exposure and then upregulated after a longer time of exposure. Furthermore, mRNA expression changed more than protein expression and the toxic effect of NaAsO2 on Ngb expression is dose dependent. Higher Ngb expression was also detected in rat cerebellum, but not in other parts (cerebrum, hippocampus, and midbrain) of the brain exposed to NaAsO2 for 16 weeks. Taken together, cytotoxic effects of NaAsO2 on rat CGNs is induced at least partly by oxidative stress and Ngb may influence the course of arsenic toxicity in rat CGNs and rat cerebellum.

Multiple cysteine residues are necessary for sorting and transport activity of the arsenite permease Acr3p from Saccharomyces cerevisiae

The yeast transporter Acr3p is a low affinity As(III)/H(+) and Sb(III)/H(+) antiporter located in the plasma membrane. It has been shown for bacterial Acr3 proteins that just a single cysteine residue, which is located in the middle of the fourth transmembrane region and conserved in all members of the Acr3 family, is essential for As(III) transport activity. Here, we report a systematic mutational analysis of all nine cysteine residues present in the Saccharomyces cerevisiae Acr3p. We found that mutagenesis of highly conserved Cys151 resulted in a complete loss of metalloid transport function. In addition, lack of Cys90 and Cys169, which are conserved in eukaryotic members of Acr3 family, impaired Acr3p trafficking to the plasma membrane and greatly reduced As(III) efflux, respectively. Mutagenesis of five other cysteines in Acr3p resulted in moderate reduction of As(III) transport capacities and sorting perturbations. Our data suggest that interaction of As(III) with multiple thiol groups in the yeast Acr3p may facilitate As(III) translocation across the plasma membrane.

Chronic exposure to arsenic, estrogen, and their combination causes increased growth and transformation in human prostate epithelial cells potentially by hypermethylation-mediated silencing of MLH1

BACKGROUND

Chronic exposure to arsenic and estrogen is associated with risk of prostate cancer, but their mechanism is not fully understood. Additionally, the carcinogenic effects of their co-exposure are not known. Therefore, the objective of this study was to evaluate the effects of chronic exposure to arsenic, estrogen, and their combination, on cell growth and transformation, and identify the mechanism behind these effects.

METHODS

RWPE-1 human prostate epithelial cells were chronically exposed to arsenic and estrogen alone and in combination. Cell growth was measured by cell count and cell cycle, whereas cell transformation was evaluated by colony formation assay. Gene expression was measured by quantitative real-time PCR and confirmed at protein level by Western blot analysis. MLH1 promoter methylation was determined by pyrosequencing method.

RESULTS

Exposure to arsenic, estrogen, and their combinations increases cell growth and transformation in RWPE-1 cells. Increased expression of Cyclin D1 and Bcl2, whereas decreased expression of mismatch repair genes MSH4, MSH6, and MLH1 was also observed. Hypermethylation of MLH1 promoter further suggested the epigenetic inactivation of MLH1 expression in arsenic and estrogen treated cells. Arsenic and estrogen combination caused greater changes than their individual treatments.

CONCLUSIONS

Findings of this study for the first time suggest that arsenic and estrogen exposures cause increased cell growth and survival potentially through epigenetic inactivation of MLH1 resulting in decreased MLH1-mediated apoptotic response, and consequently increased cellular transformation.

Prevention of arsenic-mediated reproductive toxicity in adult female rats by high protein diet

CONTEXT

The detrimental effects of arsenic on female reproductive functions may involve overt oxidative stress. Casein and pea [Pisum sativum Linn. (Fabaceae)] proteins have antioxidant properties.

OBJECTIVE

To investigate the role of casein- and pea-supplemented high-protein diet (HPD) in utero-ovarian protection from arsenic toxicity.

MATERIALS AND METHODS

Adult female Wistar rats were orally gavaged with vehicle (Gr-I) or arsenic at 3 ppm/rat/d (Gr-II and Gr-III) for 30 consecutive days, when they were maintained on either regular diet containing 18% protein (Gr-I and Gr-II), or HPD containing 27% protein in the form of casein (20%) and pea (7%) (Gr-III). Reproductive functions were evaluated using a battery of biochemical and histological techniques.

RESULTS

As compared to Gr-I, the Gr-II rats suffered from loss of estrous cyclicity, reduction in weight (mg/100 g body weight) of ovary (Gr-I: 54.3 ± 4.2 versus Gr-II: 35.8 ± 1.6; p < 0.001) and uterus (Gr-I: 161.7 ± 24.6 versus Gr-II: 94.44 ± 13.2; p < 0.05), utero-ovarian degeneration, attenuated ovarian activities (unit/mg tissue/h) of Δ(5), 3β-hydroxysteroid dehydrogenase (Gr-I: 3.41 ± 0.12 versus Gr-II: 2.31 ± 0.09; p < 0.01) and 17β-hydroxysteroid dehydrogenase (Gr-I: 3.82 ± 0.57 versus Gr-II: 1.24 ± 0.19; p < 0.001), and decreased serum estradiol level (pg/ml) (Gr-I: 61.5 ± 2.06 versus 34.1 ± 2.34; p < 0.001). Ovarian DNA damage was preponderant with blatant generation of malondialdehyde (nM/mg tissue; Gr-I: 15.10 ± 2.45 versus Gr-II: 29.51 ± 3.44; p < 0.01) and attenuated superoxide dismutase activity (unit/mg tissue) (Gr-I: 2.18 ± 0.19 versus Gr-II: 1.33 ± 0.18; p < 0.05). The Gr-III rats were significantly protected from these ill effects of arsenic.

DISCUSSION AND CONCLUSION

HPD, by way of antioxidant properties, may find prospective role in the protection of reproductive damage caused by arsenic.

Oxidative stress and replication-independent DNA breakage induced by arsenic in Saccharomyces cerevisiae

Arsenic is a well-established human carcinogen of poorly understood mechanism of genotoxicity. It is generally accepted that arsenic acts indirectly by generating oxidative DNA damage that can be converted to replication-dependent DNA double-strand breaks (DSBs), as well as by interfering with DNA repair pathways and DNA methylation. Here we show that in budding yeast arsenic also causes replication and transcription-independent DSBs in all phases of the cell cycle, suggesting a direct genotoxic mode of arsenic action. This is accompanied by DNA damage checkpoint activation resulting in cell cycle delays in S and G2/M phases in wild type cells. In G1 phase, arsenic activates DNA damage response only in the absence of the Yku70-Yku80 complex which normally binds to DNA ends and inhibits resection of DSBs. This strongly indicates that DSBs are produced by arsenic in G1 but DNA ends are protected by Yku70-Yku80 and thus invisible for the checkpoint response. Arsenic-induced DSBs are processed by homologous recombination (HR), as shown by Rfa1 and Rad52 nuclear foci formation and requirement of HR proteins for cell survival during arsenic exposure. We show further that arsenic greatly sensitizes yeast to phleomycin as simultaneous treatment results in profound accumulation of DSBs. Importantly, we observed a similar response in fission yeast Schizosaccharomyces pombe, suggesting that the mechanisms of As(III) genotoxicity may be conserved in other organisms.

Genomic analysis of stress response against arsenic in Caenorhabditis elegans

Arsenic, a known human carcinogen, is widely distributed around the world and found in particularly high concentrations in certain regions including Southwestern US, Eastern Europe, India, China, Taiwan and Mexico. Chronic arsenic poisoning affects millions of people worldwide and is associated with increased risk of many diseases including arthrosclerosis, diabetes and cancer. In this study, we explored genome level global responses to high and low levels of arsenic exposure in Caenorhabditis elegans using Affymetrix expression microarrays. This experimental design allows us to do microarray analysis of dose-response relationships of global gene expression patterns. High dose (0.03%) exposure caused stronger global gene expression changes in comparison with low dose (0.003%) exposure, suggesting a positive dose-response correlation. Biological processes such as oxidative stress, and iron metabolism, which were previously reported to be involved in arsenic toxicity studies using cultured cells, experimental animals, and humans, were found to be affected in C. elegans. We performed genome-wide gene expression comparisons between our microarray data and publicly available C. elegans microarray datasets of cadmium, and sediment exposure samples of German rivers Rhine and Elbe. Bioinformatics analysis of arsenic-responsive regulatory networks were done using FastMEDUSA program. FastMEDUSA analysis identified cancer-related genes, particularly genes associated with leukemia, such as dnj-11, which encodes a protein orthologous to the mammalian ZRF1/MIDA1/MPP11/DNAJC2 family of ribosome-associated molecular chaperones. We analyzed the protective functions of several of the identified genes using RNAi. Our study indicates that C. elegans could be a substitute model to study the mechanism of metal toxicity using high-throughput expression data and bioinformatics tools such as FastMEDUSA.

Geography of non-melanoma skin cancer and ecological associations with environmental risk factors in England

BACKGROUND

This study investigates the geography of non-melanoma skin cancer (NMSC) in England, and ecological associations with three widespread environmental hazards: radon, arsenic and ultraviolet radiation from the sun.

METHODS

Age-/sex-standardised registration rates of NMSC were mapped for local authority (LA) areas (n=326), along with geographical data on bright sunshine, household radon and arsenic. Associations between NMSC and environmental variables, adjusted for socio-economic confounders, were investigated.

RESULTS

There was a substantial geographical variation in NMSC rates across English local authorities and between cancer registration regions. Forty percent of variance in rates was at registry region level and 60% at LA level. No association was observed between environmental arsenic and NMSC rates. Rates were associated with area-mean bright sunshine hours. An association with area-mean radon concentration was suggested, although the strength of statistical evidence was sensitive to model specification.

CONCLUSION

The significant geographical variation across England in NMSC registration rate is likely to be partly, but not wholly, explained by registry differences. Findings tentatively support suggestions that environmental radon may be a risk factor for NMSC. Although NMSC is rarely fatal, it has significant implications for individuals and health services, and further research into NMSC geographical and environmental risk factors is warranted.

Involvement of HIF-2α-mediated inflammation in arsenite-induced transformation of human bronchial epithelial cells

Arsenic is a well established human carcinogen that causes diseases of the lung. Some studies have suggested a link between inflammation and lung cancer; however, it is unknown if arsenite-induced inflammation causally contributes to arsenite-caused malignant transformation of cells. In this study, we investigated the molecular mechanisms underlying inflammation during neoplastic transformation induced in human bronchial epithelial (HBE) cells by chronic exposure to arsenite. The results showed that, on acute or chronic exposure to arsenite, HBE cells over-expressed the pro-inflammatory cytokines, interleukin-6 (IL-6), interleukin-8 (IL-8), and interleukin-1β (IL-1β). The data also indicated that HIF-2α was involved in arsenite-induced inflammation. Moreover, IL-6 and IL-8 were essential for the malignant progression of arsenite-transformed HBE cells. Thus, these experiments show that HIF-2α mediates arsenite-induced inflammation and that such inflammation is involved in arsenite-induced malignant transformation of HBE cells. The results provide a link between the inflammatory response and the acquisition of a malignant transformed phenotype by cells chronically exposed to arsenite and thus establish a previously unknown mechanism for arsenite-induced carcinogenesis.

Epithelial to mesenchymal transition in arsenic-transformed cells promotes angiogenesis through activating β-catenin-vascular endothelial growth factor pathway

Arsenic exposure represents a major health concern increasing cancer risks, yet the mechanism of arsenic carcinogenesis has not been elucidated. We and others recently reported that cell malignant transformation by arsenic is accompanied by epithelial to mesenchymal transition (EMT). However, the role of EMT in arsenic carcinogenesis is not well understood. Although previous studies showed that short term exposure of endothelial cells to arsenic stimulated angiogenesis, it remains to be determined whether cells that were malignantly transformed by long term arsenic exposure have a pro-angiogenic effect. The objective of this study was to investigate the effect of arsenic-transformed human bronchial epithelial cells that underwent EMT on angiogenesis and the underlying mechanism. It was found that the conditioned medium from arsenic-transformed cells strongly stimulated tube formation by human umbilical vein endothelial cells (HUVECs). Moreover, enhanced angiogenesis was detected in mouse xenograft tumor tissues resulting from inoculation of arsenic-transformed cells. Mechanistic studies revealed that β-catenin was activated in arsenic-transformed cells up-regulating its target gene expression including angiogenic-stimulating vascular endothelial growth factor (VEGF). Stably expressing microRNA-200b in arsenic-transformed cells that reversed EMT inhibited β-catenin activation, decreased VEGF expression and reduced tube formation by HUVECs. SiRNA knockdown β-catenin decreased VEGF expression. Adding a VEGF neutralizing antibody into the conditioned medium from arsenic-transformed cells impaired tube formation by HUVECs. Reverse transcriptase-PCR analysis revealed that the mRNA levels of canonical Wnt ligands were not increased in arsenic-transformed cells. These findings suggest that EMT in arsenic-transformed cells promotes angiogenesis through activating β-catenin-VEGF pathway.