Difference in uptake and toxicity of trivalent and pentavalent inorganic arsenic in rat heart microvessel endothelial cells

Simultaneous degradation of organoarsenic and immobilization of arsenate by an electroactive CuFe2O4-CNT/peroxymonosulfate platform: Insights into the distinct roles of the Cu and Fe sites

Phenylarsonic acid (PAA) compounds, widely used in animal husbandry, pose a considerable environmental threat owing to their potential transformation into toxic inorganic arsenic species. To efficiently decontaminate PAA and adsorb secondary As(V), a hybrid CuFe2O4-modified carbon nanotube (CuFe2O4-CNT) filter was developed in this study. The hybrid CuFe2O4-CNT filter functioned as an effective catalyst, convective filtration medium, electrode, and adsorbent. Moreover, it removed 97 % PAA within 80 min in circulation mode under optimal conditions (25 °C, pH0 = 7, peroxymonosulfate [PMS] = 1.5 mM, and voltage = 1.0 V), with a total As removal efficiency of 94 %. Experimental and theoretical studies showed that the (100) and (211) planes of CuFe2O4-CNT contributed to PMS activation and As(V) adsorption, respectively. Quantum chemical calculations and high-performance liquid chromatography-mass spectrometry analysis determined the energy barriers for reactions between the transient state and SO4•- and HO•, based on which potential PAA degradation pathways were proposed. Additionally, the negligible loss of efficiency in practical water samples and acceptable leached metal ion concentrations (Cu < 0.1 mg/L and Fe < 0.15 mg/L) confirmed the reusability and stability of the filter. This study provides a promising strategy for organoarsenic decontamination by combining electrocatalytic PMS oxidation and filtration techniques.

Novel findings from arsenic‑lead combined exposure in mouse testicular TM4 Sertoli cells based on transcriptomics

Arsenic (As) and lead (Pb) exist widespread in daily life, and they are common harmful substances in the environment. As and Pb pollute the environment more often in combination than in isolation. The TM4 Sertoli cell line is one of the most common normal mouse testicular Sertoli cell lines. In vitro, we found that the type of combined action of As and Pb on TM4 Sertoli cells was additive action by using the isobologram analysis. To further investigate the combined toxicity of As and Pb, we performed mRNA and miRNA sequencing on TM4 Sertoli cells exposed to As alone (4 μM NaAsO2) and AsPb combined (4 μM NaAsO2 and 150 μM PbAc), respectively. Compared with the control group, 1391 differentially expressed genes (DEGs) and 6 differentially expressed miRNAs (DEMs) were identified in the As group. Compared with the control group, 2384 DEGs and 44 DEMs were identified in the AsPb group. Compared with the As group, 387 DEGs and 4 DEMs were identified in the AsPb group. Through data analysis, we discovered for the first time that As caused the dysfunction of cholesterol synthesis and energy metabolism, and disrupted cyclic adenosine monophosphate signaling pathway and wingless/integrated (Wnt) signaling pathway in TM4 Sertoli cells. In addition to affecting cholesterol synthesis and energy metabolism, AsPb combined exposure also up-regulated the antioxidant reaction level of TM4 Sertoli cells. Meanwhile, the Wnt signaling pathway of TM4 Sertoli cells was relatively normal when exposed to AsPb. In conclusion, at the transcription level, the combined action of AsPb is not merely additive effect, but involves synergistic and antagonistic effects. The new discovery of the joint toxic mechanism of As and Pb breaks the stereotype of the combined action and provides a good theoretical basis and research clue for future study of the combined-exposure of harmful materials.

Metabolic Carcinogenesis

Several types of environmental, chemical and metabolic carcinogens exist both exogenously and endogenously. Humans are daily exposed to aforementioned carcinogens through various sources such as through water, air and food or through metabolic and inflammatory products. This chapter will summarize the links between exogenous and endogenous carcinogen exposure and their metabolism with the cancer pathogenesis and associated risks. This chapter will also cover the carcinogens acquired through lifestyle factors like tobacco use and occupational exposures to different chemicals like asbestos, arsenic, chloroform, vinyl chloride, etc. Moreover, environmental carcinogens such as radiation, sunlight, diet, smoke, etc. will also be discussed in this chapter. Furthermore, there are certain carcinogens that require bio-activation and various human enzymes that play a vital role in the metabolic carcinogenesis will also be recapitulated. Necessary preventive measures against carcinogenic exposure from the exogenous environment are significant to be taken into account to reduce the risks associated with the carcinogens.

Impact of Chronic Exposure to Arsenate through Drinking Water on the Intestinal Barrier

Chronic exposure to inorganic arsenic (As) [As(III) + As(V)], which affects millions of people, increases the incidence of some kinds of cancer and other noncarcinogenic pathologies. Although the oral pathway is the main source of exposure, in vivo studies conducted to verify the intestinal toxicity of this metalloid are scarce and are mainly focused on evaluating the toxicity of As(III). The aim of this study was to evaluate the effect of chronic exposure (6 months) of BALB/c mice to As(V) (15-60 mg/L) via drinking water on the different components of the intestinal barrier and to determine the possible mechanisms involved. The results show that chronic exposure to As(V) generates a situation of oxidative stress (increased lipid peroxidation and reactive species) and inflammation (increased contents of several proinflammatory cytokines and neutrophil infiltrations) in the intestinal tissues. There is also evidence of an altered expression of constituent proteins of the intercellular junctions (Cldn1, Cldn3, and Ocln) and the mucus layer (Muc2) and changes in the composition of the gut microbiota and the metabolism of short-chain fatty acids. All of these toxic effects eventually may lead to the disruption of the intestinal barrier, which shows an increased paracellular permeability. Moreover, signs of endotoxemia are observed in the serum of As(V)-treated animals (increases in lipopolysaccharide-binding protein LBP and the proinflammatory cytokine IL-1β). The data obtained suggest that chronic exposure to As(V) via drinking water affects the intestinal environment.

Arsenic Trioxide Triggers Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis via Nrf 2/Caspase 3 Signaling Pathway in Heart of Ducks

Arsenic is a common environmental pollutant and poses a serious threat to human and animal health. In this study, we used the ducks to mimic arsenic trioxide (ATO) exposure and investigated the mechanism of cardiac toxicity. The results indicated that ATO inhibited the body and organ growth of ducks, led to an increase in LDH content, and caused obvious deformity, ischemia infarction. It is found that ATO exacerbated the swell of mitochondrial and the contraction of cell nuclei in the heart of ducks through transmission electron microscopy (TEM). ATO also induced an increase in MDA content; inhibited the activation of the Nrf 2 pathway; downregulated the expression of mRNA and protein of Nrf 2, HO-1, and SOD-1; and upregulated the expression of mRNA and protein of Keap 1. At the same time, ATO induced apoptosis which not only upregulated the expression levels of mRNA and proteins (Caspase 3, Cyt-C, P53, Bax) but also decreased the mRNA and protein expression level of Bcl-2. These results indicated that ATO can lead to oxidative stress and apoptosis in the heart of ducks. In general, our research shows that ATO triggers mitochondrial dysfunction, oxidative stress, and apoptosis via Nrf 2/Caspase 3 signaling pathway in the heart of ducks.

Occurrence and behavior of arsenic in groundwater-aquifer system of irrigated areas

Groundwater arsenic pollution has received much attention worldwide for decades as a serious threat to public health, but the mechanisms responsible for arsenic mobilization are not fully understood. Groundwater and bore drilling sediment samples from Qiji county, a small geographical agricultural area with endemic arsenicosis, are collected for demonstrating the occurrence and speciation of arsenic in groundwater and sediments, and arsenic release between solid-liquid phase influenced by human activities. Results show that arsenic concentrations in groundwater vary from 5 μg/L to 19.6 μg/L, with 80% exceeding the maximum permissible limits required by WHO (10 μg/L) for drinking water and therefore constituting a health risk for humans. In a weak oxidizing environment (oxidation-reduction potential (ORP): 12.9 mV-151 mV), inorganic As(V) accounts for 85% of total dissolved As, which to some extent alleviates the harm of As pollution on humans. Total As content in the sediments is in the range of 6.98 mg/kg and 14.34 mg/kg (median of 10.71 mg/kg), three times higher than the average value of many countries. Sequential chemical leaching indicates that 11% of arsenic in sediments is labile bound and may be closely related to the arsenic in groundwater. Additionally, irrigation intensity contributes to arsenic release with diverse As³⁺/As⁵⁺ by dissolving weakly bound arsenic rapidly. Subsequently part of As(III) is oxidized to As(V). Competitive and/or alkaline desorption of As(V), which had been adsorbed by FeMn (hydrous)-oxides and carbonates in the unsaturated zone and the aquifer, exerts a significant role in releasing arsenic into the groundwater. Our study indicates that systematic management and regulation of irrigation intensity are required to prevent further deterioration of groundwater resources.

Melatonin: a pleiotropic hormone as a novel potent therapeutic candidate in arsenic toxicity

BACKGROUND

Arsenic is a natural element which exists in the environment in inorganic and organic forms. In humans, the main reason for the toxicity of arsenic is its uptake via water sources. As polluted water and the problems associated with it can be found in many countries. Therefore, considering all these positive effects of melatonin, this review is aimed at melatonin supplementation therapy on arsenic toxicity which seems to be a suitable therapeutic agent to eliminate the adverse effects of arsenic.

METHODS AND RESULTS

It is seen in previous studies that chronic exposure to arsenic could cause serious dys functions of organs and induce different degrees of toxicities that is one of the first hazardous materials in the classification of substances by the United States Environmental Protection Agency so leads to costly cleanup operations burdening the economy. Arsenic harmfulness degree depends on the bioavailability, chemical form, valence state, detoxification, and metabolism of human body. The oxidative stress has a major role in arsenic-induced toxicity; on the other hand, it was discovered that melatonin is a powerful scavenger for free radical and it's an extensive-spectrum antioxidant.

CONCLUSION

Due to its highly lipophilic and small size properties, melatonin accesses all intracellular organs by easily passing via the cell membrane and prevents protein, DNA damage, and lipid peroxidation. In particular, melatonin, by protecting and reducing oxidative stress in mitochondria, can normalize homeostasis and mitochondrial function and ultimately prevent apoptosis and cell death.

The gut microbiome and arsenic-induced disease-iAs metabolism in mice

PURPOSE OF REVIEW

This review summarizes inorganic arsenic (iAs) metabolism and toxicity in mice and the gut microbiome and how iAs and the gut microbiome interact to induce diseases.

RECENT FINDINGS

Recently, a variety of studies have started to reveal the interactions between iAs and the gut microbiome. Evidence shows that gut bacteria can influence iAs biotransformation and disease risks. The gut microbiome can directly metabolize iAs, and it can also indirectly be involved in iAs metabolism through the host, such as altering iAs absorption, cofactors, and genes related to iAs metabolism. Many factors, such as iAs metabolism influenced by the gut microbiome, and microbiome metabolites perturbed by iAs can lead to different disease risks. iAs is a widespread toxic metalloid in environment, and iAs toxicity has become a global health issue. iAs is subject to metabolic reactions after entering the host body, including methylation, demethylation, oxidation, reduction, and thiolation. Different arsenic species, including trivalent and pentavalent forms and inorganic and organic forms, determine their toxicity. iAs poisoning is predominately caused by contaminated drinking water and food, and chronic arsenic toxicity can cause various diseases. Therefore, studies of iAs metabolism are important for understanding iAs associated disease risks.

NETosis in the pathogenesis of acute lung injury following cutaneous chemical burns

Despite the high morbidity and mortality among patients with extensive cutaneous burns in the intensive care unit due to the development of acute respiratory distress syndrome, effective therapeutics remain to be determined. This is primarily because the mechanisms leading to acute lung injury (ALI) in these patients remain unknown. We test the hypothesis that cutaneous chemical burns promote lung injury due to systemic activation of neutrophils, in particular, toxicity mediated by the deployment of neutrophil extracellular traps (NETs). We also demonstrate the potential benefit of a peptidyl arginine deiminase 4 (PAD4) inhibitor to prevent NETosis and to preserve microvascular endothelial barrier function, thus reducing the severity of ALI in mice. Our data demonstrated that phenylarsine oxide (PAO) treatment of neutrophils caused increased intracellular Ca²⁺-associated PAD4 activity. A dermal chemical burn by lewisite or PAO resulted in PAD4 activation, NETosis, and ALI. NETs disrupted the barrier function of endothelial cells in human lung microvascular endothelial cell spheroids. Citrullinated histone 3 alone caused ALI in mice. Pharmacologic or genetic abrogation of PAD4 inhibited lung injury following cutaneous chemical burns. Cutaneous burns by lewisite and PAO caused ALI by PAD4-mediated NETosis. PAD4 inhibitors may have potential as countermeasures to suppress detrimental lung injury after chemical burns.

Underlying mechanisms of cytotoxicity in HepG2 hepatocarcinoma cells exposed to arsenic, cadmium and mercury individually and in combination

BACKGROUND

Toxicity data regarding combinational exposure of humans to arsenic, cadmium and mercury is scarce. Although hepatotoxicity has been reported, limited information is available on their mechanistic underpinnings. The cytotoxic mechanisms of these metals were determined in HepG2 hepatocarcinoma cell lines after individual and combinational exposure.

METHODS

HepG2 cells were exposed to heavy metals (sodium arsenite, cadmium chloride, and mercury chloride) individually or in combination for 24 h, after which cell density, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS), reduced glutathione (GSH), adenosine triphosphate (ATP) and caspase-3/7 activity was assessed.

RESULTS AND DISCUSSION

Cadmium (IC₅₀ = 0.43 mg/L) and the combination (0.45 mg/L, arsenic reference) were most cytotoxic, followed by arsenic (6.71 mg/L) and mercury (28.23 mg/L). Depolarisation of the ΔΨm and reductions in ROS, GSH and ATP levels occurred. Arsenic, cadmium and the combination increased caspase-3/7 activity, while mercury reduced it.

CONCLUSION

The combination produced a greater, albeit mechanistically similar, cytotoxicity compared to individual metals. Cytotoxicity was dependent on altered mitochondrial integrity, redox-status, and bioenergetics. Although the combination's cytotoxicity was associated with caspase-3/7 activity, this was not true for mercury. Heavy metal interactions should be assessed to elucidate molecular underpinnings of cytotoxicity.

Determination of arsenicals in mouse tissues after simulated exposure to arsenic from rice for sixteen weeks and the effects on histopathological features

The accumulation of arsenic in rice has become a worldwide concern. In this study, dose-dependency in tissues (intestine, liver and kidney) and blood distribution of inorganic arsenicals and their methylated metabolites were investigated in male C57BL/6 mice exposed to four arsenic species (arsenite [iAs]^III, arsenate [iAs]^V, monomethylarsonate [MMA]^V, and dimethylarsinate [DMA]^V) at four doses (control [C]: 0 μg/g, simulation [S]: 0.91 μg/g, medium [M]: 9.1 μg/g and high [H]: 30 μg/g) according to the arsenical composition in rice for 8 and 16 weeks. No adverse effects were observed, while body weight gain decreased in group H. Increases in total arsenic concentrations (C_tAs) and histopathological changes in the tissues occurred in all of the test groups. C_tAs presented a tendency of kidney > intestine > liver > blood and were time-/dose-dependent in the liver and kidney in groups M and H. In the intestine and blood, abundant iAs (23%-28% in blood and 36%-49% in intestine) was detected in groups M and H, and C_tAs decreased in group H from the 8th week to the 16th week. PMI decreased in the liver and SMI decreased in the kidney. These results indicate that the three tissues are injured through food arsenic. The intestine can also accumulate food arsenic, and the high arsenic dose will cause a deficiency in the absorbing function of the intestine. Thus, long-term exposure to arsenic-contaminated rice should be taken seriously attention.

Biotransformation of arsenic and toxicological implication of arsenic metabolites

Arsenic is a well-known environmental carcinogen and chronic exposure to arsenic through drinking water has been reported to cause skin, bladder and lung cancers, with arsenic metabolites being implicated in the pathogenesis. In contrast, arsenic trioxide (As₂O₃) is an effective therapeutic agent for the treatment of acute promyelocytic leukemia, in which the binding of arsenite (iAs^III) to promyelocytic leukemia (PML) protein is the proposed initial step. These findings on the two-edged sword characteristics of arsenic suggest that after entry into cells, arsenic reaches the nucleus and triggers various nuclear events. Arsenic is reduced, conjugated with glutathione, and methylated in the cytosol. These biotransformations, including the production of reactive metabolic intermediates, appear to determine the intracellular dynamics, target organs, and biological functions of arsenic.

Comparative Cytotoxicity of Inorganic Arsenite and Methylarsenite in Human Brain Cells

The overall goal of this study is to elucidate the potential effect(s) of arsenic on a variety of human brain cells. Arsenic is the most pervasive Group A human environmental carcinogen. Long-term exposure to arsenic is associated with human diseases including cancer, cardiovascular disease, and diabetes. More immediate are the health effects on neurological development and associated disorders in infants and children exposed to arsenic in utero. Arsenic is metabolized in various organs and tissues into more toxic methylated species, including methylarsenite (MAs(III)), so the question arises whether the methylate species are responsible for the neurological effects of arsenic. Arsenic enters the brain through the blood-brain barrier and produces toxicity in the brain microvascular endothelial cells, glia (astrocytes and microglia), and neurons. In this study, we first assessed the toxicity in different types of brain cells exposed to either inorganic trivalent As(III) or MAs(III) using both morphological and cytotoxicity cell-based analysis. Second, we determined the methylation of arsenicals and the expression levels of the methylation enzyme, As(III) S-adenosylmethionine (SAM) methyltransferase (AS3MT), in several types of brain cells. We showed that the toxicity to neurons of MAs(III) was significantly higher than that of As(III). Interestingly, the differences in cytotoxicity between cell types was not due to expression of AS3MT, as this was expressed in neurons and glia but not in endothelial cells. These results support our hypothesis that MAs(III) is the likely physiological neurotoxin rather than inorganic arsenic species.

Tissue-specific distributions of inorganic arsenic and its methylated metabolites, especially in cerebral cortex, cerebellum and hippocampus of mice after a single oral administration of arsenite

Groundwater contaminated with inorganic arsenic (iAs) is the main source of human exposure to arsenic and generates a global health issue. In this study, the urinary excretion, as well as the time-course distributions of various arsenic species in murine tissues, especially in different brain regions were determined after a single oral administration of 2.5, 5, 10 and 20mg/kg sodium arsenite (NaAsO₂). Our data showed that the peak times of urinary, hepatic and nephritic total arsenic (TAs) were happened at about 1h, then TAs levels decreased gradually and almost could not be observed after 72h. On contrast, the time course of TAs in lung, urinary bladder and different brain regions exhibited an obvious process of accumulation and elimination,and the peak times were nearly at 6h to 9h. TAs levels of 10 and 20mg/kg NaAsO₂ groups were significantly higher than 2.5 and 5mg/kg groups, and the amounts of TAs in 5mg/kg groups were in the order of liver>lung>kidney>urinary bladder>hippocampus>cerebral cortex>cerebellum. In addition, iAs was the most abundant species in liver and kidney, while lung and urinary bladder accumulated the highest concentrations of dimethylated arsenicals (DMA). What's more, the distributions of arsenic species were not homogeneous among different brain regions, as DMA was the sole species in cerebral cortex and cerebellum, while extremely high concentrations and percentages of monomethylated arsenicals (MMA) were found in hippocampus. These results demonstrated that distributions of iAs and its methylated metabolites were tissue-specific and even not homogeneous among different brain regions, which must be considered as to the tissue- and region-specific toxicity of iAs exposure. Our results thus provide useful information for clarifying and reducing the uncertainty in the risk assessment for this metalloid.

Low dose arsenite confers resistance to UV induced apoptosis via p53-MDM2 pathway in ketatinocytes

Chronic arsenite and ultraviolet (UV) exposure are associated with skin tumor. To investigate the details by low concentrations of arsenite and UV induced carcinogenesis in skin, hTERT-immortalized human keratinocytes were used as a cellular model with exposure to low concentrations of sodium arsenite and UV. The effect of NaAsO₂ on UV treatment-induced apoptosis was measured by flow cytometry and Hoechst staining. We found that the cell apoptosis induced by UV exposure was significantly attenuated after exposure to low-dose arsenite, and knockdown of p53 could block UV-induced apoptosis indicating that this phenomenon depended on p53. Interestingly, the expression of murine double minute 2 (MDM2), including its protein and transcriptional levels, was remarkably high after exposure to low-dose arsenite. Moreover, low-dose arsenite treatment dramatically decreased the MDM2 gene promoter activity, suggesting that this effect has been mediated through transcription. In addition, treatment of PD98059 reversed low-dose arsenite-induced MDM2 expression, and the inhibition of ERK2 expression could significantly block MDM2 expression as a consequence, and p53 expression automatically was increased. To validate the role of p53 in exposure to low-dose arsenite, the expression of p53 was examined by immunohistochemistry in the skin of Sprague−Dawley rats model by chronic arsenite exposure for 6 months and in patients with arsenic keratosis, and the results showed that the expression of p53 was decreased in those samples. Taken together, our results demonstrated that low-dose arsenite-induced resistance to apoptosis through p53 mediated by MDM2 in keratinocytes.

The relationships between arsenic methylation and both skin lesions and hypertension caused by chronic exposure to arsenic in drinking water

The associations between arsenic exposure, arsenic methylation, and the prevalence of skin lesions and hypertension are investigated. The results indicate that the HS (hypertension and skin lesions) group and the S (skin lesions) group have higher urinary concentrations of iAs (inorganic arsenic), MMA (monomethylarsonic acid), DMA (dimethylarsinous acid) and%MMA, and lower SMI (secondary arsenic methylation index) compared to the H (hypertension) and N (without both hypertension and skin lesions) groups. The arsenic content in water which caused H may be lower than that which caused HS and S. In addition, the odds ratios suggest that higher urinary concentrations of iAs and MMA, %iAs, %MMA and PMI elevate the prevalence of only hypertension and skin lesions, and both hypertension and skin lesions. However, higher%DMA and SMI, and lower%MMA increase the prevalence of both hypertension and skin lesions compared to that of only skin lesions. It can be concluded that skin lesions subjects have higher prevalence of hypertension. Hypertension subjects may have higher prevalence of skin lesions. Lower%DMA and SMI, higher%iAs, %MMA and PMI enhance the prevalence of only hypertension and skin lesions, and both hypertension and skin lesions. Moreover, iAs and MMA may have higher toxicity and lead to both hypertension and skin lesions than to only hypertension.

Deriving water quality criteria for trivalent and pentavalent arsenic

Arsenic (As) is a common trace element whose oxidation states mainly include four types (-3, 0, +3, and +5), and inorganic As(III) and As(V) are regarded as the most commonly existing forms in aqueous environments. Generally, As(III) has a higher toxicity than As(V) due to the different mechanisms in arsenic toxicity. However, there are few studies about the water quality criteria (WQC) of As(III) and As(V) respectively because of the deficiency of arsenic toxicity data coming from diverse taxonomic groups. In this research, eight native Chinese aquatic organisms were adopted to conduct toxicity tests for As(III) and As(V) to supplement the published toxicity data. The species sensitivity distribution (SSD) method on the basis of the Log-normal model which was the most optimal among eight models was applied to derive WQCs of As(III) and As(V). Results showed that crustaceans were the most sensitive to As(III) and As(V) among all tested species, thus they could be a biological indicator, and the influence of pH values on arsenic toxicity was complex and species-specific. Besides, the sensitivity differences between native and non-native species were observed. Finally, a criterion maximum concentration (CMC) of 167 and 384μg/L for As(III) and As(V), and a criterion continuous concentration (CCC) of 42 and 44μg/L for As(III) and As(V) were derived using native species, regardless of pH values. The WQCs were also verified by other two methods of ETX 2.0 and species sensitivity rank.

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.

Assessment of usefulness of synchrotron radiation techniques to determine arsenic species in hair and rice grain samples

The arseniasis in Southwest Guizhou, China has been identified as a unique case of endemic arseniasis caused by exposure to indoor combustion of high As-content coal. Present investigation targeted the microdistribution and speciation of the element arsenic in human hair and environmental samples collected in one of the hyper-endemic villages of arseniasis in the area. Analyses were performed by micro-beam X-ray fluorescence (μ-XRF) and X-ray absorption fine structure (XAFS). The total As level in hair samples of diagnosed patients was detected at almost the same level as in their asymptomatic neighbors. Concentrations in the lateral cut of hair samples were high-low-high (from surface to center). XAFS revealed the coexistence of both the As+3 and As+5 states in hair samples. However, the samples from patients displayed a tendency of higher As+3 / As+5 ratio than the asymptomatic fellow villagers. The μ-XRF mapping of rice grains shows that arsenic penetrates the endosperm, the major edible part of the grain, when rice grains were stored over the open fire of high As-content coal. Synchrotron radiation techniques are suitable to determine arsenic species concentrations in different parts of hair and rice grain samples. As arsenic penetrates the endosperm, rinsing the rice grains with water will remain largely ineffective.

Associations of arsenic metabolites, methylation capacity, and skin lesions caused by chronic exposure to high arsenic in tube well water

To investigate the interaction between skin lesion status and arsenic methylation profiles, the concentrations and proportions of arsenic metabolites in urine and arsenic methylation capacities of study subjects were determined. The results showed that the mean urinary concentrations of iAs (inorganic arsenic), MMA (monomethylarsonic acid), DMA (dimethylarsinic acid), and TAs (total arsenic) were 75.65, 68.78, 265.81, and 410.24 μg/L, respectively, in the skin lesions subjects. The highest values were observed in the multiple skin lesions subjects. Higher %iAs and %MMA, and lower %DMA, PMI (primary methylation index), and SMI (secondary methylation index) were found in skin lesions subjects. The multiple skin lesions subjects had highest %iAs and %MMA, and lowest %DMA, PMI, and SMI. The prevalence of skin lesions strongly, positively correlated with arsenic levels in drinking water. The elder persons also had higher frequency of skin lesions compared with younger persons. It can be concluded that arsenic levels in drinking water significantly affected the prevalence of skin lesions. Male subjects usually had higher proportions of skin lesions when compared with female subjects. Moreover, it may be concluded that MMA was significantly related to single skin lesion, whereas DMA and iAs were associated with multiple skin lesions. It seemed that MMA had greater toxicity to hyperkeratosis, whereas DMA and iAs had higher toxicity to depigmentation or pigmentation. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 28-36, 2017.

Comparative cytotoxicity of fourteen trivalent and pentavalent arsenic species determined using real-time cell sensing

The occurrence of a large number of diverse arsenic species in the environment and in biological systems makes it important to compare their relative toxicity. The toxicity of arsenic species has been examined in various cell lines using different assays, making comparison difficult. We report real-time cell sensing of two human cell lines to examine the cytotoxicity of fourteen arsenic species: arsenite (As^III), monomethylarsonous acid (MMA^III) originating from the oxide and iodide forms, dimethylarsinous acid (DMA^III), dimethylarsinic glutathione (DMAG^III), phenylarsine oxide (PAO^III), arsenate (As^V), monomethylarsonic acid (MMA^V), dimethylarsinic acid (DMA^V), monomethyltrithioarsonate (MMTTA^V), dimethylmonothioarsinate (DMMTA^V), dimethyldithioarsinate (DMDTA^V), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone, Rox), and 4-aminobenzenearsenic acid (p-arsanilic acid, p-ASA). Cellular responses were measured in real time for 72hr in human lung (A549) and bladder (T24) cells. IC₅₀ values for the arsenicals were determined continuously over the exposure time, giving rise to IC₅₀ histograms and unique cell response profiles. Arsenic accumulation and speciation were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). On the basis of the 24-hr IC₅₀ values, the relative cytotoxicity of the tested arsenicals was in the following decreasing order: PAO^III≫MMA^III≥DMA^III≥DMAG^III≈DMMTA^V≥As^III≫MMTTA^V>As^V>DMDTA^V>DMA^V>MMA^V≥Rox≥p-ASA. Stepwise shapes of cell response profiles for DMA^III, DMAG^III, and DMMTA^V coincided with the conversion of these arsenicals to the less toxic pentavalent DMA^V. Dynamic monitoring of real-time cellular responses to fourteen arsenicals provided useful information for comparison of their relative cytotoxicity.

MRP1 expression in bronchoalveolar lavage cells in subjects with lung cancer who were chronically exposed to arsenic

Alteration of multidrug resistance-associated protein-1 (MRP1) expression has been associated with certain lung diseases, and this protein may be pivotal in protecting the lungs against endogenous or exogenous toxic compounds. The aim of this study was to evaluate and compare the expression of MRP1 in bronchoalveolar cells from subjects with and without lung cancer who had been chronically exposed to arsenic through drinking water. MRP1 expression was assessed in bronchoalveolar cells in a total of 102 participants. MRP1 expression was significantly decreased in those with arsenic urinary levels >50 μg/L when compared with the controls. In conclusion, chronic arsenic exposure negatively correlates with the expression of MRP1 in BAL cells in patients with lung cancer.

Arsenic cardiotoxicity: An overview

Arsenic, a naturally ubiquitous element, is found in foods and environment. Cardiac dysfunction is one of the major causes of morbidity and mortality in the world. Arsenic exposure is associated with various cardiopathologic effects including ischemia, arrhythmia and heart failure. Possible mechanisms of arsenic cardiotoxicity include oxidative stress, DNA fragmentation, apoptosis and functional changes of ion channels. Several evidences have shown that mitochondrial disruption, caspase activation, MAPK signaling and p53 are the pathways for arsenic induced apoptosis. Arsenic trioxide is an effective and potent antitumor agent used in patients with acute promyelocytic leukemia and produces dramatic remissions. As2O3 administration has major limitations such as T wave changes, QT prolongation and sudden death in humans. In this review, we discuss the underlying pathobiology of arsenic cardiotoxicity and provide information about cardiac health effects associated with some medicinal plants in arsenic toxicity.

Association between lifetime exposure to inorganic arsenic in drinking water and coronary heart disease in Colorado residents

BACKGROUND

Chronic diseases, including coronary heart disease (CHD), have been associated with ingestion of drinking water with high levels of inorganic arsenic (> 1,000 μg/L). However, associations have been inconclusive in populations with lower levels (< 100 μg/L) of inorganic arsenic exposure.

OBJECTIVES

We conducted a case-cohort study based on individual estimates of lifetime arsenic exposure to examine the relationship between chronic low-level arsenic exposure and risk of CHD.

METHODS

This study included 555 participants with 96 CHD events diagnosed between 1984 and 1998 for which individual lifetime arsenic exposure estimates were determined using data from structured interviews and secondary data sources to determine lifetime residence, which was linked to a geospatial model of arsenic concentrations in drinking water. These lifetime arsenic exposure estimates were correlated with historically collected urinary arsenic concentrations. A Cox proportional-hazards model with time-dependent CHD risk factors was used to assess the association between time-weighted average (TWA) lifetime exposure to low-level inorganic arsenic in drinking water and incident CHD.

RESULTS

We estimated a positive association between low-level inorganic arsenic exposure and CHD risk [hazard ratio (HR): = 1.38, 95% CI: 1.09, 1.78] per 15 μg/L while adjusting for age, sex, first-degree family history of CHD, and serum low-density lipoprotein levels. The risk of CHD increased monotonically with increasing TWAs for inorganic arsenic exposure in water relative to < 20 μg/L (HR = 1.2, 95% CI: 0.6, 2.2 for 20-30 μg/L; HR = 2.2; 95% CI: 1.2, 4.0 for 30-45 μg/L; and HR = 3, 95% CI: 1.1, 9.1 for 45-88 μg/L).

CONCLUSIONS

Lifetime exposure to low-level inorganic arsenic in drinking water was associated with increased risk for CHD in this population.

N‑acetyl‑L‑cysteine reduces arsenite‑induced cytotoxicity through chelation in U937 monocytes and macrophages

In the present study, in order to clarify the preventive mechanism of N‑acetyl‑L‑cysteine (NAC) on arsenite‑induced apoptosis in U937 cells, which lack functional p53, the cytotoxicity among U937 cells [monocytes and 12‑O‑tetradecanoylphorbol‑13‑acetate (TPA)‑treated macrophages] receiving NAC treatment at different times post arsenite treatment was examined. TPA‑treated macrophages were more resistant to arsenite‑induced apoptosis than monocytes, which may be associated with the induction of Bcl‑2 expression. Pretreatment with 20 mM NAC prior to arsenite exposure suppressed apoptosis up to 75% in the monocytes and 100% in the macrophages. However, 6‑h NAC pretreatment and subsequent washing out of NAC from the culture medium prior to arsenite treatment did not inhibit the arsenite‑induced apoptosis. Post‑treatment by NAC up to 1 h following arsenite exposure almost completely inhibited the cytotoxic effects of arsenite in U937 monocytes and macrophages. The results of the current study indicate that the preventive mechanism of NAC on arsenite‑induced apoptosis in U937 monocytes and macrophages mainly involves chelation of arsenite in culture medium.

Arsenic trioxide and resveratrol show synergistic anti-leukemia activity and neutralized cardiotoxicity

Cardiotoxicity is an aggravating side effect of many clinical antineoplastic agents such as arsenic trioxide (As2O3), which is the first-line treatment for acute promyelocytic leukemia (APL). Clinically, drug combination strategies are widely applied for complex disease management. Here, an optimized, cardiac-friendly therapeutic strategy for APL was investigated using a combination of As2O3 and genistein or resveratrol. Potential combinations were explored with respect to their effects on mitochondrial membrane potential, reactive oxygen species, superoxide dismutase activity, autophagy, and apoptosis in both NB4 cells and neonatal rat left ventricular myocytes. All experiments consistently suggested that 5 µM resveratrol remarkably alleviates As2O3-induced cardiotoxicity. To achieve an equivalent effect, a 10-fold dosage of genistein was required, thus highlighting the dose advantage of resveratrol, as poor bioavailability is a common concern for its clinical application. Co-administration of resveratrol substantially amplified the anticancer effect of As2O3 in NB4 cells. Furthermore, resveratrol exacerbated oxidative stress, mitochondrial damage, and apoptosis, thereby reflecting its full range of synergism with As2O3. Addition of 5 µM resveratrol to the single drug formula of As2O3 also further increased the expression of LC3, a marker of cellular autophagy activity, indicating an involvement of autophagy-mediated tumor cell death in the synergistic action. Our results suggest a possible application of an As2O3 and resveratrol combination to treat APL in order to achieve superior therapeutics effects and prevent cardiotoxicity.

Trivalent methylated arsenic metabolites induce apoptosis in human myeloid leukemic HL-60 cells through generation of reactive oxygen species

Trivalent arsenic metabolites mediate HL-60 cell apoptosis via ROS.

Body composition and arsenic metabolism: a cross-sectional analysis in the Strong Heart Study

OBJECTIVE

The objective of this study was to evaluate the association between measures of body composition and patterns of urine arsenic metabolites in the 1989-1991 baseline visit of the Strong Heart Study, a cardiovascular disease cohort of adults recruited from rural communities in Arizona, Oklahoma, North Dakota and South Dakota.

METHODS

We evaluated 3,663 Strong Heart Study participants with urine arsenic species above the limit of detection and no missing data on body mass index, % body fat and fat free mass measured by bioelectrical impedance, waist circumference and other variables. We summarized urine arsenic species patterns as the relative contribution of inorganic (iAs), methylarsonate (MMA) and dimethylarsinate (DMA) species to their sum. We modeled the associations of % arsenic species biomarkers with body mass index, % body fat, fat free mass, and waist circumference categories in unadjusted regression models and in models including all measures of body composition. We also considered adjustment for arsenic exposure and demographics.

RESULTS

Increasing body mass index was associated with higher mean % DMA and lower mean % MMA before and after adjustment for sociodemographic variables, arsenic exposure, and for other measures of body composition. In unadjusted linear regression models, % DMA was 2.4 (2.1, 2.6) % higher per increase in body mass index category (< 25, ≥25 & <30, ≥30 & <35, ≥35 kg/m2), and % MMA was 1.6 (1.4, 1.7) % lower. Similar patterns were observed for % body fat, fat free mass, and waist circumference measures in unadjusted models and in models adjusted for potential confounders, but the associations were largely attenuated or disappeared when adjusted for body mass index.

CONCLUSION

Measures of body size, especially body mass index, are associated with arsenic metabolism biomarkers. The association may be related to adiposity, fat free mass or body size. Future epidemiologic studies of arsenic should consider body mass index as a potential modifier for arsenic-related health effects.

The Protective Role of Resveratrol against Arsenic Trioxide-Induced Cardiotoxicity

Arsenic trioxide (As₂O₃) shows substantial anticancer activity in patients with acute promyelocytic leukemia (APL). Unfortunately, limiting the application of this effective agent to APL patients is severe cardiotoxicity. Resveratrol, the natural food-derived polyphenolic compound, is well known for its antioxidant properties and protects the cardiovascular system. But the potential role of resveratrol against As₂O₃ in heart via nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) is unclear. The present study evaluated the effects of pretreatment with resveratrol and As₂O₃ on oxidative stress and cardiac dysfunction in rat. In the present study, resveratrol decreased As₂O₃-induced reactive oxygen species generation, oxidative DNA damage, and pathological alterations. In addition, cardiac dysfunction parameters, intracellular calcium and arsenic accumulation, glutathione redox ratio, and cAMP deficiency levels were observed in As₂O₃-treated rats; these changes were attenuated by resveratrol. Furthermore, resveratrol significantly prohibited the downregulation of both Nrf2 and HO-1 gene expressions that were downregulated by As₂O₃, whereas resveratrol did not alter As₂O₃-induced nitric oxide formation. Thus, the protective role of resveratrol against As₂O₃-induced cardiotoxicity is implemented by the maintenance of redox homeostasis (Nrf2-HO-1 pathway) and facilitating arsenic efflux. Our findings suggest coadministration with resveratrol, and As₂O₃ might provide a novel therapeutic strategy for APL.

Anticancer activity of small-molecule and nanoparticulate arsenic(III) complexes

Starting in ancient China and Greece, arsenic-containing compounds have been used in the treatment of disease for over 3000 years. They were used for a variety of diseases in the 20th century, including parasitic and sexually transmitted illnesses. A resurgence of interest in the therapeutic application of arsenicals has been driven by the discovery that low doses of a 1% aqueous solution of arsenic trioxide (i.e., arsenous acid) lead to complete remission of certain types of leukemia. Since Food and Drug Administration (FDA) approval of arsenic trioxide (As2O3) for treatment of acute promyelocytic leukemia in 2000, it has become a front-line therapy in this indication. There are currently over 100 active clinical trials involving inorganic arsenic or organoarsenic compounds registered with the FDA for the treatment of cancers. New generations of inorganic and organometallic arsenic compounds with enhanced activity or targeted cytotoxicity are being developed to overcome some of the shortcomings of arsenic therapeutics, namely, short plasma half-lives and a narrow therapeutic window.

Arsenic metabolism and thioarsenicals

Arsenic has received considerable attention in the world, since it can lead to a multitude of toxic effects and has been recognized as a human carcinogen causing cancers. Here, we focus on the current state of knowledge regarding the proposed mechanisms of arsenic biotransformation, with a little about cellular uptake, toxicity and clinical utilization of arsenicals. Since pentavalent methylated metabolites were found in animal urine after exposure to iAs(III), methylation was considered to be a detoxification process, but the discovery of methylated trivalent intermediates and thioarsenicals in urine has diverted the view and gained much interest regarding arsenic biotransformation. To further investigate the partially understood phenomena relating to arsenic toxicity and the uses of arsenic as a drug, it is important to elucidate the exact pathways involved in metabolism of this metalloid, as the toxicity and the clinical uses of arsenic can be best recognized in context of its biotransformation. Thereby, in this perspective, we have focused on arsenic metabolic pathways including three proposed mechanisms: a classic pathway by Challenger in 1945, followed by a new metabolic pathway proposed by Hayakawa in 2005 involving arsenic-glutathione complexes, while the third is a new reductive methylation pathway that is proposed by our group involving As-protein complexes. According to previous and present in vivo and in vitro experiments, we conclude that the methylation reaction takes place with simultaneous reductive rather than stepwise oxidative methylation. In addition, production of pentavalent methylated arsenic metabolites are suggested to be as the end product of metabolism, rather than intermediates.

Multidrug resistance protein 1 (ABCC1) confers resistance to arsenic compounds in human myeloid leukemic HL-60 cells

Arsenic trioxide (As(2)O(3)) is established as one of the most effective drugs for treatment of patients with acute promyelocytic leukemia, as well as other types of malignant tumors. However, HL-60 cells are resistant to As(2)O(3), and little is known about the underlying resistance mechanism for As(2)O(3) and its biomethylation products, namely, monomethylarsonous acid (MMA(III)) on the treatment of tumors. In the present study, we investigated the molecular mechanisms underlying iAs(III) and its intermediate metabolite MMA(III)-induced anticancer effects in the HL-60 cells. Here, we show that the HL-60 cells exhibit resistance to inorganic iAs(III) (IC(50) = 10 μM), but are relatively sensitive to its intermediate MMA(III) (IC(50) = 3.5 μM). Moreover, we found that the multidrug resistance protein 1 (MRP1), but not MRP2, is expressed in HL-60 cells, which reduced the intracellular arsenic accumulation, and conferred resistance to inorganic iAs(III) and MMA(III). Pretreatment of HL-60 with MK571, an inhibitor of MRP1, significantly increased iAs(III) and MMA(III)-induced cytotoxicity and arsenic accumulations, suggesting that the expression of MRP1/4 may lead to HL-60 cells resistance to trivalent arsenic compounds.

Metabolism of arsenic and its toxicological relevance

Arsenic is a worldwide environmental pollutant and a human carcinogen. It is well recognized that the toxicity of arsenicals largely depends on the oxidoreduction states (trivalent or pentavalent) and methylation levels (monomethyl, dimethyl, and trimethyl) that are present during the process of metabolism in mammals. However, presently, the specifics of the metabolic pathway of inorganic arsenicals have yet to be confirmed. In mammals, there are two possible mechanisms that have been proposed for the metabolic pathway of inorganic arsenicals, oxidative methylation, and glutathione conjugation. Oxidative methylation, which was originally proposed in fungi, is based on findings that arsenite (iAs(III)) is sequentially converted to monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) in both humans and in laboratory animals such as mice and rats. However, recent in vitro observations have demonstrated that arsenic is only methylated in the presence of glutathione (GSH) or other thiol compounds, which strongly suggests that arsenic is methylated in trivalent forms. The glutathione conjugation mechanism is supported by findings that have shown that most intracellular arsenicals are trivalent and excreted from cells as GSH conjugates. Since non-conjugated trivalent arsenicals are highly reactive with thiol compounds and are easily converted to less toxic corresponding pentavalent arsenicals, the arsenic-glutathione conjugate stability may be the most important factor for determining the toxicity of arsenicals. In addition, "being a non-anionic form" also appears to be a determinant of the toxicity of oxo-arsenicals or thioarsenicals. The present review discusses both the metabolism of arsenic and the toxicity of arsenic metabolites.

Speciation of arsenic metabolites in the free-living mouse Mus spretus from Doñana National Park used as a bio-indicator for environmental pollution monitoring

A speciation approach based on orthogonal chromatographic systems coupled to inductively coupled plasma mass spectrometry (ICP-MS) was used to characterise the biological response of free-living mice Mus spretus to environmental pollution caused by arsenic in different areas of the Doñana National Park (south-west Spain). The relative presence of inorganic and organic forms of arsenic was studied in cytosolic extracts from high metabolic activity organs of Mus spretus mice: kidneys, liver, and brain. An instrumental coupling of size-exclusion chromatography with UV and collision/reaction cell-ICP-MS detectors (SEC-UV-ICP-ORC-MS) both in analytical and preparative scale was used for this purpose. The results showed the presence of low molecular mass (LMM) molecules linked to arsenic in these tissues especially in the kidneys, where the presence of these arsenic metabolites was higher. On the other hand, the presence of these arsenicals varied from one area to the other, which can be related to a different occurrence of contaminants. These low molecular mass fractions were collected by preparative SEC chromatography for later study with ion exchange chromatography and detection by ICP-ORC-MS, using both anionic and cationic columns. The results showed the higher presence of MMA and DMA in kidneys of mice caught in contaminated areas and the existence of small amounts of unidentified arsenicals when cation-exchange chromatography was used, which could be related to the presence of dimethylarsinoylethanol (DMAE), thioarsenic species, or arsenocholine (AsC).