Time-dependent genomic response in primary human uroepithelial cells exposed to arsenite for up to 60 days.

Evidence from both in vivo and in vitro studies suggests that gene expression changes from long-term exposure to arsenite evolve markedly over time, including reversals in the direction of expression change in key regulatory genes. In this study, human uroepithelial cells from the ureter segments of 4 kidney-donors were continuously treated in culture with arsenite at concentrations of 0.1 or 1 µM for 60 days. Gene expression at 10, 20, 30, 40, and 60 days was determined using Affymetrix human genome microarrays and signal pathway analysis was performed using GeneGo Metacore. Arsenic treated cells continued to proliferate for the full 60-day period, whereas untreated cells ceased proliferating after approximately 30 days. A peak in the number of gene changes in the treated cells compared to untreated controls was observed between 30 and 40 days of exposure, with substantially fewer changes at 10 and 60 days, suggesting remodeling of the cells over time. Consistent with this possibility, the direction of expression change for a number of key genes was reversed between 20 and 30 days, including CFOS and MDM2. While the progression of gene changes was different for each subject, a common pattern was observed in arsenic treated cells over time, with early upregulation of oxidative stress responses (HMOX1, NQ01, TXN, TXNRD1) and down-regulation of immune/inflammatory responses (IKKα). At around 30 days, there was a transition to increased inflammatory and proliferative signaling (AKT, CFOS), evidence of epithelial-to-mesenchymal transition (EMT), and alterations in DNA damage responses (MDM2, ATM). A common element in the changing response of cells to arsenite over time appears to involve up-regulation of MDM2 by inflammatory signaling (through AP-1 and NF-κB), leading to inhibition of P53 function.

Knock-down of transcription factor skinhead-1 exacerbates arsenite-induced oxidative damage in Caenorhabditis elegans.

Transcription factor, skinhead-1 (skn-1) has been demonstrated to play central roles in regulation of oxidative damage. Arsenite is an oxidative damage inducer in the environment. However, the role of skn-1 in arsenite-induced oxidative damage remains unclear. Thus, in this study, by using RNAi feeding, different toxic responses of wild-type and skn-1 knockdown nematodes to arsenite were evaluated. Our results demonstrated that arsenite did not show any significant impacts on locomotory behaviors, but skn-1 knock-down worms were much more sensitive to arsenite treatment, manifested by an aggravated reduction of survival rate than that of wild-type nematodes. In arsenite-treated worms, down-regulation of skn-1 significantly exacerbated the arsenite-induced changed expressions of oxidative damage-related genes, xbp-1, apl-1 and trxr-2, but these regulated effects of skn-1 were not observed on spr-4 and sel-12 expressions under arsenite treatment. These findings together suggest that skn-1 may play a vital role in protection of C. elegans from arsenite-induced oxidative damage.

Phase I clinical trial of KML001 monotherapy in patients with advanced solid tumors.

BACKGROUND: We evaluated the tolerability, pharmacokinetics (PK) and preliminary efficacy of KML001, an oral trivalent arsenical, as a monotherapy in patients with advanced solid tumors. RESEARCH DESIGN AND METHODS: With a standard 3 + 3 design for dose-escalation stage, the planned dose levels of KML001 were 5, 7.5, 10, 12.5, and 15 mg/day for 28 days. Once the maximum tolerated dose was determined, 22 subjects were additionally enrolled for dose-expansion stage. PK analysis was performed in the 5, 10, and 15 mg/day cohort at the dose-escalation stage and also at the dose-expansion stage. Moreover, response was assessed using the standard RECIST 1.1. RESULTS: A total of 45 Korean subjects were enrolled. No DLT was reported at the dose-escalation stage. Three DLTs, two cases of prolonged QTc interval and one of neutropenia, were reported in the 12.5 mg/day cohort at the dose-expansion stage. Higher total daily doses up to 12.5 mg/day of KML001 resulted in higher trough plasma concentrations. Among the 18 subjects who completed 2 cycles of therapy, 15 had progressive disease and 3 had stable disease. CONCLUSIONS: Doses equal to or greater than 10 mg/day KML001 alone were tolerable and produced plasma concentrations higher than biologically relevant targets.

Protection against Mitochondrial Oxidative-Stress by Flesh-Extract of Edible Freshwater Snail Bellamya bengalensis Prevents Arsenic Induced DNA and Tissue Damage.

AIMS: Arsenic has carcinogenic properties because of the formation of Reactive Oxygen Species (ROS). ROS damages different macromolecules, tissues and organs, and severely exhausts cellular antioxidants. BACKGROUND: Cytosolic and mitochondrial contribution of ROS production by arsenic are not well reported. In regard to the issues of therapy against arsenic or any other toxicity, natural product has gained its popularity due to its less side-effects and non-invasive nature. OBJECTIVES: Here, as an ethnomedicine, the flesh-extract (BBE; 100mg/100g bw) of Bellamya bengalensis (an aquatic mollusk) was applied in arsenic intoxicated (0.6 ppm/100g bw/for 28 days alone or in combination with BBE) experimental rats. Our objective was to study the anti-oxidative and anti-apoptotic role of BBE in hepato-gastrointestinal tissue damage by arsenic. METHODS: DNA fragmentation assay, catalase activity (gel-zymogram assay) suggests that BBE has a strong protective role against arsenic toxicity, which is decisively demonstrated in hepatic histoarchitecture study by HE (hematoxylin and eosin) staining and by intestinal PAS (Periodic Acid Schiff) staining. RESULTS: Measurement of mitochondrial-membrane-potential by fluorescent microcopy clearly demonstrated less membrane damage and lower release of the redox-active inner-membrane product (cytochrome-C, ubiquinone, etc.) in BBE supplemented group compared to that of the only arsenic fed group. The present study clearly suggests that mitochondrial disintegrity is one of the major causes of ROS mediated tissue damage by arsenic. CONCLUSION: This study also offers an option for prevention/treatment against arsenic toxicity and its carcinogenicity by widely available low-cost, non-invasive Bellamya extract by protecting cytoskeleton, DNA and mitochondria in the cell.

Arsenic accumulation and speciation in strawberry plants exposed to inorganic arsenic enriched irrigation.

The accumulation and transformation of arsenic species have been studied in the context of hydroponic cultivation of strawberry plants. Cultivation experiments have been performed by adding inorganic arsenic at concentrations of 10, 100 and 1000 µg L-1 via root irrigation. The total arsenic content was determined by Hydride Generation-Atomic Fluorescence Spectrometry (HG-AFS). The accumulation was dependent on the concentration of arsenic added to the irrigation and the arsenic species. Arsenic (III) accumulated at higher rates than arsenic (V). A greater accumulation of arsenic was found in roots (0.44-4.10 mg kg-1) than in stems (0.43-1.27 mg kg-1) and fruits (0.22-0.30 mg kg-1). The speciation results obtained by HPLC-HG-AFS analysis indicated that the addition of As(III) resulted in a partial methylation producing monomethyl arsenic (MMA) and dimethyl arsenic (DMA). After As(V) addition, only MMA was observed and this was accompanied with a notable reduction in the ratio of As(V) to As(III).

Ferulic acid attenuates arsenic-induced cardiotoxicity in rats.

Arsenic (As), a potent environmental toxin, causes cardiac functional impairments. Ferulic acid (FA), a ubiquitous dietary hydroxycinnamate, exerts beneficial effects on human health. Hence, the present study investigated the effect of FA on myocardial oxidative stress parameters, ATP level, the status of cardiac cytoskeleton intermediate filaments-desmin and vimentin, and AMPK signaling proteins in As-intoxicated rats. Wistar rats were administered orally with FA-40 mg/kg and As-5 mg/kg alone and in combination for 30 days. Myocardial As content, serum cardiac marker enzyme activities including creatine kinase-isoenzyme, lactate dehydrogenase, and aspartate aminotransferase were increased in As-exposed rats. An accumulation of myocardial oxidants such as reactive oxygen species, lipid peroxidation, nitric oxide, protein carbonyl content, and histological aberrations was observed. A significant decrease of myocardial antioxidants comprises superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, and ascorbic acid and declined expression of desmin and vimentin was noted. Impaired energy signaling molecules AMPKα (Thr172), AMPKß1/2 (Ser108), ACC (Ser79), and intracellular myocardial ATP depletion were observed in As-intoxicated animals. FA attenuates As-induced cardiac dysfunction by restoring the expression of intermediate filaments and AMPK proteins. Based on the above findings, FA treatment could be used as a novel therapeutic against As-induced cardiac dysfunction.

Arsenite exposure suppresses adipogenesis, mitochondrial biogenesis and thermogenesis via autophagy inhibition in brown adipose tissue.

Arsenite, a trivalent form of arsenic, is an element that occurs naturally in the environment. Humans are exposed to high dose of arsenite through consuming arsenite-contaminated drinking water and food, and the arsenite can accumulate in the human tissues. Arsenite induces oxidative stress, which is linked to metabolic disorders such as obesity and diabetes. Brown adipocytes dissipating energy as heat have emerging roles for obesity treatment and prevention. Therefore, understanding the pathophysiological role of brown adipocytes can provide effective strategies delineating the link between arsenite exposure and metabolic disorders. Our study revealed that arsenite significantly reduced differentiation of murine brown adipocytes and mitochondrial biogenesis and respiration, leading to attenuated thermogenesis via decreasing UCP1 expression. Oral administration of arsenite in mice resulted in heavy accumulation in brown adipose tissue and suppression of lipogenesis, mitochondrial biogenesis and thermogenesis. Mechanistically, arsenite exposure significantly inhibited autophagy necessary for homeostasis of brown adipose tissue through suppression of Sestrin2 and ULK1. These results clearly confirm the emerging mechanisms underlying the implications of arsenite exposure in metabolic disorders.

Chronic exposure to submicromolar arsenite promotes the migration of human esophageal Het1A cells induced by heparin-binding EGF-like growth factor.

Chronic arsenic exposure causes cancers in multiple organs in humans. However, the mechanisms underlying arsenic-induced carcinogenesis remain obscure. Here, we examined whether chronic arsenite (As(III)) exposure promotes cell migration induced by heparin-binding EGF-like growth factor (HB-EGF) in human esophageal immortalized Het1A cells. When Het1A cells were exposed to 0.5 µM As(III) for 4 months, HB-EGF-induced migration was enhanced in As(III)-exposed Het1A cells compared to controls. To elucidate the mechanisms underlying the promotion of HB-EGF-induced migration by chronic exposure to As(III), we compared ERK phosphorylation between As(III)-exposed and control Het1A cells and found that HB-EGF-induced ERK phosphorylation was enhanced in the As(III)-exposed cells. We next measured mRNA levels of 88 genes related to cell cycle regulation. The results showed elevated cyclin D1 mRNA levels in As(III)-exposed Het1A cells. The inhibitors of ERK and cyclin D/Cdk4 markedly suppressed HB-EGF-induced upregulation of cyclin D1 and the migration of Het1A cells, respectively, suggesting that cyclin D1 is located downstream of ERK and is required for HB-EGF-induced migration of Het1A cells. Collectively, these findings indicate that the promotion of HB-EGF-induced migration of Het1A cells chronically exposed to submicromolar As(III) might be caused by increased expression of cyclin D1 mediated by enhanced activation of the ERK pathway.

Metabolism and disposition of arsenic species from controlled dosing with sodium arsenite in adult and neonatal rhesus monkeys. VI. Toxicokinetic studies following oral administration.

Arsenic is a common toxic contaminant in food and drinking water. Metabolic activation of arsenic species produces reactive trivalent intermediates that can disrupt cellular regulatory systems by covalent binding to thiol groups. Arsenic exposures have been associated with human diseases including cancer, diabetes, lung and cardiovascular disorders and there is accumulating evidence that early life exposures are important in the etiology. Previous toxicokinetic studies of arsenite ingestion in neonatal CD-1 mice showed consistent evidence for metabolic and physiologic immaturity that led to elevated internal exposures to trivalent arsenic species in the youngest mice, relative to adults. The current study in rhesus monkeys showed that metabolism and binding of trivalent intermediates after arsenite ingestion were similar between adult monkeys and CD-1 mice. Unlike neonatal mice, monkeys from the age of 5-70 days showed similar metabolism and binding profiles, which were also similar to those in adults. The absence of evidence for metabolic immaturity in monkeys suggests that toxicological effects observed in mice from early postnatal exposures to arsenic could over-predict those possible in primates, based on significantly higher internal exposures.

In vivo evaluation of the effect of arsenite on the intestinal epithelium and associated microbiota in mice.

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 non-carcinogenic pathologies. Although the oral pathway is the main form of exposure, in vivo studies have not been conducted to verify the intestinal toxicity of this metalloid. The aim of this study is to perform an in vivo evaluation of the intestinal toxicity of inorganic As, using female BALB/c mice exposed through drinking water to various concentrations of As(III) (20, 50, and 80 mg/L) for 2 months. An increase was observed in oxygen and/or nitrogen reactive species, and in gene and protein expression of pro-inflammatory cytokines (IL-1ß, IL-2, IL-6) at concentrations equal to or greater than 50 mg/L. These changes were accompanied by a profound remodeling of the intestinal microbial profile in terms of diversity and global composition, which could be at the basis or exacerbate As(III) toxic effects. The histological study showed that there was moderate inflammation of the mucosa and submucosa, accompanied by hyperplasia of crypts at the highest administered dose. In addition, all the treatments with As(III) resulted in a decreased expression of Muc2, which encodes one of the main components of the intestinal layer of mucus. The effects described are compatible with the increased intestinal permeability observed at concentrations equal to or greater than 50 mg/L, indicative of loss of barrier function.

Targeted arsenite-loaded magnetic multifunctional nanoparticles for treatment of hepatocellular carcinoma.

Arsenic trioxide (ATO), an FDA-approved drug for acute promyelocytic leukemia, also has great potential for treatment of solid tumors. Drug delivery powered by recent advances in nanotechnology has boosted the efficacy of many drugs, which is enlightening for applications of ATO in treating solid tumors. Herein, we reported arsenite-loaded multifunctional nanoparticles that are capable of pH-responsive ATO release for treating hepatocellular carcinoma (HCC) and real-time monitoring via magnetic resonance imaging. We fabricated these nanoparticles (designated as magnetic large-pore mesoporous silica nanoparticle (M-LPMSN)-NiAsO x ) by loading nanoparticulate ATO prodrugs (NiAsO x ) into the pores of large-pore mesoporous silica nanoparticles (LPMSNs) that contain magnetic iron oxide nanoparticles in the center. The surface of these nanodrugs was modified with a targeting ligand folic acid (FA) to further enhance the drug efficacy. Releasing profiles manifest the responsive discharging of arsenite in acidic environment. In vitro experiments with SMMC-7721 cells reveal that M-LPMSN-NiAsO x -FA nanodrugs have significantly higher cytotoxicity than traditional free ATO and induce more cell apoptosis. In vivo experiments with mice bearing H22 tumors further confirm the superior antitumor efficacy of M-LPMSN-NiAsO x -FA over traditional free ATO and demonstrate the outstanding imaging ability of M-LPMSN-NiAsO x -FA for real-time tumor monitoring. These targeted arsenite-loaded magnetic mesoporous silica nanoparticles integrating imaging and therapy hold great promise for treatment of HCC, indicating the auspicious potential of LPMSN-based nanoplatforms.

KML001, an arsenic compound, as salvage chemotherapy in refractory biliary tract cancers: A prospective study.

BACKGROUND: Sodium meta-arsenite (NaAsO2, KML001) is a potential oral anticancer agent acting on telomerase and telomere length. This prospective study evaluated its safety, tolerability, and effectiveness as salvage chemotherapy in patients with advanced biliary tract cancer (BTC) resistant to gemcitabine-based chemotherapy. METHODS: Forty-four patients (21 women and 23 men) with advanced BTC and failure history of gemcitabine-based chemotherapy, performance status (PS) 0-2, normal cardiac, hepatic, and renal function were enrolled. Daily dose of KML001 (7.5 mg. p.o.) was administered to eligible subjects for 24 weeks divided into six treatment cycles. Response was evaluated bimonthly using CT. RESULTS: After an average of 1.5 months of treatment (range: 0.5-10.0), 3 patients (6.8%) obtained progression-free status, 23 patients (52.3%) had disease progression, and 18 patients (40.9%) dropped out before evaluation. One patient (2.3%) completed six treatment cycles without progression. During the treatment, morphine dosage kept the same or decreased in 20 patients (47.6%). Nine patients (20.5%) experienced grade-3 adverse events (AEs), while no patient experienced grade-4 AEs. The most common AEs were liver enzyme elevation (11/44, 25%) and anemia (10/44, 22.7%). KML001 was discontinued in six patients (13.6%) due to AEs, including liver toxicity (n = 3), QTc prolongation (n = 2), and abdominal pain (n = 1). CONCLUSIONS: KML001 did not have enough anticancer effect on patients with advanced BTC resistant to gemcitabine. However, KML001 was safe and well-tolerable in terms of AEs and pain control when used as salvage therapy. Further studies are needed to establish arsenic agents as a reliable treatment option in patients with BTC.

Evaluation of metabolic reactivity in macrophages from mice with chronic sodium arsenite intake and experimental carcinogenesis.

 Arsenic is carcinogenic to human beings, and environmental exposure to arsenic is a public health issue that affects large populations around the world. Thus, studies are needed to determine the mode of action of arsenic and to prevent harmful effects that arise from arsenic intake. In particular, knowledge of the effects of arsenic exposure in individuals who are undergoing a carcinogenesis process is lacking. The present study was performed in mice to evaluate the effect of chronic As3+ administration on peritoneal and alveolar macrophages; the As3+ was administered in drinking water over 9 months and there was a two-stage carcinogenesis process. At the end of the experiment, the number of tumors stabilized to below the control values, but the tumors showed increased malignancy. Our objective was to evaluate the systemic effects of chronic As3+ingestion in a population of macrophages that was derived from the peritoneal cavity and the broncho-alveolar trunk of cancerized mice since they are the first line of defense in the immune system. The results showed that the macrophages under all conditions retained their ability to self-regulate their metabolic reactivity. This feature was more evident in peritoneal macrophages than in alveolar macrophages. Furthermore, an increase in the number of macrophages from animals receiving higher doses of As3+ compared to untreated animals was observed. These findings indicate that certain parameters associated with two-stage skin carcinogenesis are modified by the presence of As3+ in drinking water.

Low arsenic concentrations impair memory in rat offpring exposed during pregnancy and lactation: Role of α7 nicotinic receptor, glutamate and oxidative stress.

Inorganic arsenic (iAs) is an important natural pollutant. Millions of individuals worldwide drink water with high levels of iAs. Arsenic exposure has been associated to cognitive deficits. However, the underlying mechanisms remain unknown. In the present work we investigated in female adult offspring the effect of the exposure to low arsenite sodium levels through drinking water during pregnancy and lactation on short- and long-term memory. We also considered a possible underlying neurotoxic mechanism. Pregnant rats were exposed during pregnancy and lactation to environmentally relevant iAs concentrations (0.05 and 0.10 mg/L). In 90-day-old female offspring, short-term memory (STM) and long-term memory (LTM) were evaluated using a step-down inhibitory avoidance task. In addition, we evaluated the α7 nicotinic receptor (α7-nAChR) expression, the transaminases and the oxidative stress levels in hippocampus. The results showed that the exposure to 0.10 mg/L iAs in this critical period produced a significant impairment in the LTM retention. This behavioral alteration might be associated with several events that occur in the hippocampus: decrease in α7-nAChR expression, an increase of glutamate levels that may produce excitotoxicity, and a decrease in the antioxidant enzyme catalase (CAT) activity.

Protective Effect of Hydroxytyrosol Against Oxidative Stress Mediated by Arsenic-Induced Neurotoxicity in Rats.

The present study reports beneficial effect of hydroxytyrosol (HT) against arsenic (As)-induced oxidative stress in the rat brain. Rats were orally administered with sodium arsenite dissolved in distilled water (25 ppm, by oral gavage) for 8 weeks or HT (10 mg/kg b. wt.) in combination with As. Results showed increase in protein oxidation and lipid peroxidation, while catalase and superoxide dismutase (SOD) activities as well as GSH content were decreased after As exposure in rat brain. Fourier transform infrared analysis showed significant alteration in peak area values that also validated the oxidative damage to lipids and proteins. In addition, As exposure caused increase in protein expression of caspase-3 and Bax, while Bcl-2 expression was downregulated resulting in translocation of cytochrome c from mitochondria to cytosol. Treatment of HT with As reversed protein oxidation, lipid peroxidation, and increased GSH content as well as catalase and SOD activities. Administration of HT also prevented translocation of cytochrome c from mitochondria and increased mitochondria/cytosol ratio of cytochrome c. Hence, treatment of HT with As improved antioxidant system and efficiently lowered the generation of oxidative stress in rat brain.

iTRAQ-based quantitative proteomic analysis reveals important metabolic pathways for arsenic-induced liver fibrosis in rats.

Long-term consumption of sodium arsenite contaminated water can cause endemic arsenic disease. The proteome profile changes of liver fibrosis after exposure to arsenite containing water remain unclear. In this study, Sprague-Dawley (SD) male rats were treated with sodium arsenite (iAs3+), using a daily dose of 1.36 mg/kg body weight (medium dose group, M), 2.73 mg/kg body weight (high dose group, H) or deionized water (control group, C). Isobaric tags for relative and absolute quantitation (iTRAQ) were used to identify the different abundant proteins (DAPs) after arsenic-induced liver fibrosis. A total of 2987 high-quality proteins were detected (95% confident peptides ≥ 2), 608 of which were differentially expressed (fold change > 2 and p < 0.05) in M group and 475 in H group. Moreover, 431 DAPs were found in both M and H groups and used in subsequent bioinformatic analyses. Gene ontology (GO) analysis revealed 4,709 GO terms could be mapped, among which purine binding, actin filament binding and protein kinase binding were the most enriched terms for molecular function category. In addition, protein-protein interaction analysis showed six clusters of interaction networks. Our data provided new insights into the proteome changes after arsenic-induced liver fibrosis in model rats.

Protective Effect of Azadirachta indica and Vitamin E Against Arsenic Acid-Induced Genotoxicity and Apoptosis in Rats.

Sodium arsenite (NaAsO2) is one of the major environmental toxicants with severe toxicological consequences in some developing and developed countries. Rats in Group A received normal saline. Genotoxicity and apoptosis were induced by single intraperitoneal injection of 10 mg/kg sodium arsenite to rats in Groups B-F. Rats in Groups C and D had earlier been pretreated with Azadirachta indica (100 and 200 mg/kg) or E and F with vitamin E (50 and 100 mg/kg), respectively. Markers of oxidative stress, inflammation, hepatic damage, genotoxicity, and apoptosis were assessed. Pretreatment of rats with either Azadirachta indica or vitamin E led to a significant (p <.05) increase in the activities of glutathione-S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), and reduced glutathione (GSH) in the liver compared to the group that received NaAsO2 alone. Markers of oxidative stress and inflammation, malondialdehyde (MDA), hydrogen peroxide (H2O2) generation, nitric oxide (NO), and myeloperoxidase (MPO), were significantly (p <.05) lowered in rats pretreated with Azadirachta indica or vitamin E. The frequency of micronucleated polychromatic erythrocytes (MNPCEs) and expression of caspase-3 were significantly (p <.05) reduced in rats pretreated with either Azadirachta indica or vitamin E compared to rats intoxicated with arsenite. Histopathology of the liver showed areas of infiltration of inflammatory cells with deaths of numerous hepatocytes in NaAsO2-intoxicated rats, and these were reversed by Azadirachta indica. Together, we report for the first time the genoprotective and antiapoptotic effect of Azadirachta indica by a significant reduction in the frequency of micronuclei-induced apoptosis and oxidative stress by arsenic intoxication.

Arsenic Induces Thioredoxin 1 and Apoptosis in Human Liver HHL-5 Cells.

To further characterize the mechanisms underlying liver toxicity induced by arsenic, we examined in this study the effect of arsenic on thioredoxin (Trx) and the apoptotic signaling pathways in human liver HHL-5 cells. The cells were treated with 0, 2, 5, and 10 µM of sodium arsenite for 24 h, and the changes of Trx1 and thioredoxin reductase (TrxR1) as well as intracellular ROS and apoptosis were examined. A concentration-dependent increase in mRNA and protein levels of Trx1 and TrxR1 was observed in arsenic-treated cells. Intracellular ROS levels and apoptosis were also significantly increased in a concentration-dependent manner. In line with this, protein levels of Bax and cytochrome C were increased and Bcl-2 was decreased by arsenic treatments. Increases in caspase 3 activity were observed. These results indicate that Trx is involved in arsenic-induced liver cell injury, probably through the apoptotic signaling pathway. However, further studies are needed to elucidate on these findings.

Metabolism and disposition of arsenic species from controlled oral dosing with sodium arsenite in adult female CD-1 mice. I. Pilot study to determine dosing, analytical measurements, and sampling strategies.

Arsenic (As) is ubiquitous in the earth's crust, with typical dietary intake in developed countries <1 µg/kg bw/d, and atypical groundwater exposures in developing countries approaching 50 µg/kg bw/d. Arsenic exposures are linked with human diseases and doses of toxicological concern are similar to typical dietary intake estimates. The methylation of arsenite by arsenite-3-methyltransferase (As3MT) promotes the clearance of arsenic as pentavalent species, but also generates reactive trivalent intermediates. This study measured inorganic arsenic and its metabolites in pentavalent and trivalent states in blood, tissues, and excreta after oral administration of arsenite (50-200 µg/kg bw). While liver was a major site for clearance of arsenite and formation of methylated species, it also had extensive binding of trivalent intermediates; however, thiol exchange and oxidation reactions of trivalent arsenic were facile since dimethylarsinic acid (DMAV) was the predominant species in blood and urine. Consistent evidence was observed for a non-linear relationship between doses above 50 µg/kg bw and levels of bound trivalent As metabolites. The abundance of protein-bound trivalent arsenic within target tissues should correlate with disruption of critical cellular processes, which rely on defined interactions of thiol functional groups, and could provide dose-response relationships from animal models for human risk assessment.

Synergistic Effects of Arsenite on Radiosensitization of Glioblastoma Cells.

BACKGROUND/AIM: Glioblastoma is a frequent type of brain tumor and is radioresistant. Arsenite, which crosses the blood-brain barrier, shows synergistic effects with radiation in vitro and in vivo. The mechanism remains unclear. MATERIALS AND METHODS: As synergistic radiosensitization has been reported in p53-deficient cancer cells, radiosensitization was evaluated using the glioblastoma cell line, U87MG-E6, which harbors inactivated p53, in comparison with the cell line, HCT116 p53 (-/-). Radiosensitivity was evaluated using clonogenic assays and detection of abnormal amplification of centrosomes (AAC). RESULTS: Synergistic effects of arsenite on radiosensitivity were observed in both cell lines. The radiosensitization induced by arsenite was abolished by N-acetyl-l-cysteine, a reactive oxygen species (ROS) scavenger. Increased radiosensitivity by arsenite was also abolished following knock-down of BRCA2. In addition, the increased radiosensitization by arsenite was correlated with AAC, which was abolished by BRCA2 knock-down. CONCLUSION: We conclude that radiosensitization by arsenite is related to ROS and BRCA2 function.