Oral arsenite exposure induces inflammation and apoptosis in pulmonary tissue: acute and chronic evaluation in young and adult mice.

Inorganic arsenic is a well-known environmental toxicant, and exposure to this metalloid is strongly linked with severe and extensive toxic effects in various organs including the lungs. In the present study, we aimed to investigate the acute and chronic effects of arsenite exposure on pulmonary tissue in young and adult mice. In brief, young and adult female Balb/C mice were exposed to 3 and 30 ppm arsenite daily via drinking water for 30 and 90 days. Subsequently, the animals were sacrificed and various histological and immunohistochemistry (IHC) analyses were performed using lung tissues. Our findings showed arsenite was found to cause dose-dependent pathological changes such as thickening of the alveolar septum, inflammatory cell infiltrations and lung fibrosis in young and adult mice. In addition, arsenite exposure significantly increased the expression of inflammatory markers NF-κB and TNF-α, indicating that arsenite-exposed mice suffered from severe lung inflammation. Moreover, the IHC analysis of fibrotic proteins demonstrated an increased expression of TGF-ß1, α-SMA, vimentin and collagen-I in the arsenite-exposed mice compared to the control mice. This was accompanied by apoptosis, which was indicated by the upregulated expression of caspase-3 in arsenite-exposed mice compared to the control. Adult mice were generally found to be more prone to arsenite toxicity during chronic exposure relative to their younger counterparts. Overall, our findings suggest that arsenite in drinking water may induce dose-dependent and age-dependent structural and functional impairment in the lungs through elevating inflammation and fibrotic proteins.

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.

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.

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.

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.

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.

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.

Cell cycle pathway dysregulation in human keratinocytes during chronic exposure to low arsenite.

BACKGROUND: Arsenic is naturally prevalent in the earth's crust and widely distributed in air and water. Chronic low arsenic exposure is associated with several cancers in vivo, including skin cancer, and with transformation in vitro of cell lines including immortalized human keratinocytes (HaCaT). Arsenic also is associated with cell cycle dysregulation at different exposure levels in multiple cell lines. In this work, we analyzed gene expression in HaCaT cells to gain an understanding of gene expression changes contributing to transformation at an early time point. METHODS: HaCaT cells were exposed to 0 or 100nM NaAsO2 for 7weeks. Total RNA was purified and analyzed by microarray hybridization. Differential expression with fold change≥|1.5| and p-value≤0.05 was determined using Partek Genomic Suite™ and pathway and network analyses using MetaCore™ software (FDR≤0.05). Cell cycle analysis was performed using flow cytometry. RESULTS: 644 mRNAs were differentially expressed. Cell cycle/cell cycle regulation pathways predominated in the list of dysregulated pathways. Genes involved in replication origin licensing were enriched in the network. Cell cycle assay analysis showed an increase in G2/M compartment in arsenite-exposed cells. CONCLUSIONS: Arsenite exposure induced differential gene expression indicating dysregulation of cell cycle control, which was confirmed by cell cycle analysis. The results suggest that cell cycle dysregulation is an early event in transformation manifested in cells unable to transit G2/M efficiently. Further study at later time points will reveal additional changes in gene expression related to transformation processes.

Anti-tumoral effect of arsenic compound, sodium metaarsenite (KML001), in non-Hodgkin's lymphoma: an in vitro and in vivo study.

Arsenic compounds have been used in traditional medicine for several centuries. KML001 (sodium metaarsenite; NaAsO2) is an orally bio-available arsenic compound with potential anti-cancer activity. However, the effect of KML001 has not been studied in lymphoid neoplasms. The aim of this study is to evaluate the anti-proliferative effect of KML001 in non-Hodgkin's lymphoma and to compare its efficacy with As2O3. KML001 inhibited cellular proliferation in all tested lymphoma cell lines as well as JurkatR cells (adriamycin-resistant Jurkat cells) in a dose-dependent manner, while As2O3 was not effective. Cell cycle regulatory protein studies have suggested that KML001 induces G1 arrest via p27-induced inhibition of the kinase activities of CDK2, 4, and 6. Treatment of KML001 induced apoptosis in Jurkat and JurkatR cells. The apoptotic process was associated with down-regulation of Bcl-2 (antiapoptotic molecule), up-regulation of Bax (proapoptotic molecule), and inhibition of caspase-3, -8, and -9. In addition, cell signaling including the STAT, PI3K/Akt, MAPK, and NF-κB signal pathways were inhibited in KML001-treated Jurkat and JurkatR cells. Furthermore, targeting the telomere by KML001 was observed in the Jurkat and JurkatR cells. The In vivo anti-tumoral activity of KML001 was confirmed in a xenograft murine model. Interestingly, partial responses were seen in two lymphoma patients treated with 10 mg/day (follicular lymphoma for 16 weeks and mantle cell lymphoma for 24 weeks) without severe toxicities. These findings suggest that KML001 may be a candidate agent for the treatment of de novo, refractory, and relapsed non-Hodgkin's lymphoma patients.

Aortic smooth muscle cell alterations in mice systemically exposed to arsenic.

Previous epidemiological studies showed that chronic arsenic exposure is related to increased cardiovascular disease incidence. The detailed biochemical mechanisms by which arsenic exerts its effects remain unknown. Vascular disease progression is characterized by smooth muscle cell (SMC) phenotypic switching, vessel wall reorganization, and platelet-derived growth factor (PDGF) production. The objective of this study was to examine early biochemical and structural changes in the aortas of ICR mice systemically exposed to arsenic. Animals were fed sodium arsenite (20 mg/kg) via gavage 5 days/week or Milli-Q water only (control) for 8 weeks. Aortic proteins were subjected to two-dimensional (2-D) differential gel electrophoresis and proteomic studies. Two 2-D gel protein spots were identified as the same protein, smooth muscle (SM)22α, using proteomics. SM22α and Rho kinase 2 gene and protein expression were significantly decreased in the aortic tissue of arsenic-exposed mice compared with that of control mice. No atherosclerotic lesion formation or tissue injury was detected in the aortic wall of either the arsenic-fed or the control group. However, the percent (%) SMC area of the aortic wall was significantly decreased in arsenic-fed mice compared with that in control mice. Additionally, the expression levels of PDGF-BB and early growth response-1 (Egr-1) were significantly higher in the arsenic group than that in the control group. These findings reveal biochemical alterations of SM22α, PDGF, and Egr-1 in conjunction with decreased SMC area in the aortic wall of arsenic-fed mice. Arsenic may initiate aortic SMC alterations that subsequently lead to vascular dysfunction.

Knockout of arsenic (+3 oxidation state) methyltransferase results in sex-dependent changes in phosphatidylcholine metabolism in mice.

Arsenic (+3 oxidation state) methyltransferase is the key enzyme in the methylation pathway for inorganic arsenic. We have recently shown that As3mt knockout (KO) has a profound effect on metabolomic profiles in mice. Phosphatidylcholine species (PCs) were the largest group of metabolites altered in both plasma and urine. The present study used targeted analysis to investigate the KO-associated changes in PC profiles in the liver, the site of PC synthesis. Results show that As3mt KO has a systemic effect on PC metabolism and that this effect is sex dependent.

Bioavailability study of arsenic and mercury in traditional Chinese medicines (TCM) using an animal model after a single dose exposure.

Traditional Chinese medicines (TCM) are increasingly being used as alternative medicines in many countries, and this has caused concern because of adverse health effects from toxic metal bioavailability such as mercury (Hg) and arsenic (As). The aim of this study was to investigate the bioavailability of As and Hg from TCM after a single exposure dose using an animal model of female Sprague-Dawley rats. The rats were divided into 6 groups which included four groups treated with sodium arsenite (NaAsO2), arsenic sulfide (As2S3), mercuric chloride (HgCl2), mercuric sulfide (HgS), and two groups treated with TCM containing high Hg or As (Liu Shen Wan: As 7.7-9.1% and Hg 1.4-5.0%; Niuhang Jie du Pian: As 6.2-7.9% and Hg <0.001%). The samples of urine, faeces, kidney and liver were collected for analysis and histological assay. The results indicated that relatively low levels of As and Hg from these TCM were retained in liver and kidney tissues. The levels of As in these tissues after TCM treatment were consistent with the levels from the As sulphide treated group. With the exception of the mercuric chloride treated group, the levels of Hg in urine from other groups were very low, and high levels of As and Hg from TCM were excreted in faeces. The study showed poor bioavailability of As and Hg from TCM as indicated by low relative bioavailability of As (0.60-1.10%) and Hg (<0.001%). Histopathological examination of rat kidney and liver tissues did not show toxic effects from TCM.

[Study on congenital cardiac anomalies induced by arsenic exposure before and during maternal pregnancy in fetal rats].

OBJECTIVE: To investigate the effects of arsenic exposure before and during maternal pregnancy on heart development of fetal rats. METHODS: According to body weight, thirty-two female SD rats (30 to 40 days of age) were randomly divided into control group, low dose group, middle dose group and high dose group with 8 rats per group. They were allowed free access to drinking water with 0, 37.5, 75 and 150 mg/L of sodium arsenite (NaAsO2) for 6 weeks, respectively. Then all the female rats and adult male SD rats were caged together for mating. Once female rats were determined to be pregnant, they would continue to drink deionized distilled water containing different concentrations of sodium arsenite for another 2 weeks. On embryonic day 16, rats were sacrificed to harvest fetuses. Female rats' weight changes, abortions, absorbed fetus number, growth and development of fetal rats were observed. Hematoxylin-eosin staining of serial cardiac slices was performed in embryos to observe cardiac morphology and structure. Fur arsenic contents of female rats were determined with the method of atomic fluorescence spectrometry. RESULTS: Subchronic arsenic exposure caused slow weight growth in female rats. There were two cases of abortion in middle dose group and high dose group, respectively. Compared with these of control group, fetal and placental weight decreased (P < 0.05), and the incidence of fetal absorption increased (P < 0.05) in all arsenic-treated groups. Cardiac malformations in fetal rats including ventricular septal defect, atrial septal defect and tetralogy of Fallot were observed in low, middle and high dose group. The incidence of cardiac malformations increased with the increase of arsenic concentrations in drinking water. Compared with that of control group, the incidence of cardiac malformations remarkably increased in both middle and high dose groups (P < 0.05). Fur arsenic contents increased with the increase of arsenic concentrations in drinking water (P < 0.01). CONCLUSION: Arsenic exposure before and during maternal pregnancy could cause abnormal cardiac development in fetal rats, and increased the risk of congenital heart disease.

High accumulation of arsenic in the esophagus of mice after exposure to arsenite.

Arsenic-induced toxicity appears to be dependent on the tissue- or cell-specific accumulation of this metalloid. An early study showed that arsenic was retained in the esophagus as well as the liver, kidney cortex and skin of marmosets after intraperitoneal administration of (74)As-arsenite. However, there is little available information regarding the distribution of arsenic in the esophagus. Here, we compared the retention of arsenic in the esophagus, liver, lung, kidney and heart in mice intraperitoneally administered 1 or 5 mg/kg sodium arsenite (As(III)) daily for 3 or 7 days. The results showed that the arsenic concentration was highest in the esophagus. We compared the mRNA levels of aquaglyceroporin (AQP) 3, AQP7 and AQP9, which are responsible for arsenic influx, and those of multidrug-resistance protein (MRP) 1 and MRP2, which are responsible for arsenic efflux. The levels of AQP3 mRNA in the esophagus were much higher than those in liver, lung and heart, while the mRNA levels of MRP2 were very low in the esophagus. In addition, we found extremely low expression of Nrf2 in the esophagus at the basal and under the activated conditions, which might have resulted in low levels of glutamyl-cysteine ligase catalytic and modulatory subunits, and subsequently in the low levels of glutathione. Thus, the highest retention of arsenic was detected in the esophagus after intraperitoneal administration of As(III) to mice, and this appeared to result from multiple factors, including high expression of AQP3, low expression of MRP2, low capacity of glutathione synthesis and low activation of Nrf2.

Epigenetic mechanisms underlying arsenic-associated lung carcinogenesis.

Arsenic is an established human carcinogen, but the mechanisms through which it contributes to for instance lung cancer development are still unclear. As arsenic is methylated during its metabolism, it may interfere with the DNA methylation process, and is therefore considered to be an epigenetic carcinogen. In the present study, we hypothesize that arsenic is able to induce DNA methylation changes, which lead to changes in specific gene expression, in pathways associated with lung cancer promotion and progression. A549 human adenocarcinoma lung cells were exposed to a low (0.08 µM), intermediate (0.4 µM) and high (2 µM) concentration of sodium arsenite for 1, 2 and 8 weeks. DNA was isolated for whole-genome DNA methylation analyses using NimbleGen 2.1 M deluxe promoter arrays. In addition, RNA was isolated for whole-genome transcriptomic analysis using Affymetrix microarrays. Arsenic modulated DNA methylation and expression levels of hundreds of genes in a dose-dependent and time-dependent manner. By combining whole-genome DNA methylation and gene expression data with possibly involved transcription factors, a large molecular interaction network was created based on transcription factor-target gene pairs, consisting of 216 genes. A tumor protein p53 (TP53) subnetwork was identified, showing the interactions of TP53 with other genes affected by arsenic. Furthermore, multiple other new genes were discovered showing altered DNA methylation and gene expression. In particular, arsenic modulated genes which function as transcription factor, thereby affecting target genes which are known to play a role in lung cancer promotion and progression.

Time course of urothelial changes in rats and mice orally administered arsenite.

Inorganic arsenic (arsenite and arsenate) at high exposures is a known human carcinogen, inducing tumors of the urinary bladder, skin, and lungs. In two experiments, we examined the urothelial proliferative effects of treatment with 173 ppm sodium arsenite (100 ppm arsenic) in the drinking water for 6 and 24 hr, and 3, 7, and 14 days in female F344 rats and 43.3 ppm sodium arsenite (25 ppm arsenic) in female C57BL/6 wild-type and arsenic (+3 oxidation state) methyltransferase knockout (As3mt KO) mice that are unable to methylate arsenicals. In the rat and both mouse genotypes, scanning electron microscopy showed cytotoxic urothelial changes as early as 6 hr after the start of arsenic exposure. The severity of As(III)-induced cytotoxic urothelial changes increased over time in the rat and in the As3mt KO mouse. Light microscopy showed an increase in urothelial hyperplasia in the rat. No significant increases in bromodeoxyuridine-labeling index were observed. The data support the hypothesis that the sequence of events in the mode of action for urothelial effects of orally administered inorganic arsenic in the rat and mouse involves superficial cytotoxicity with consequent regenerative increased cell proliferation similar to the findings associated with the administration of dimethylarsinic acid (DMA(V)) in rats.

Acute and long-term effects of arsenite in HepG2 cells: modulation of insulin signaling.

Epidemiological studies have indicated a relationship between the prevalence of diabetes and exposure to arsenic. Mechanisms by which arsenic may cause this diabetogenic effect are largely unknown. The phosphoinositide 3'-kinase (PI3K)/Akt signaling pathway plays an important role in insulin signaling by controlling glucose metabolism, in part through regulating the activity of FoxO transcription factors. The present study aimed at investigating the effect of short and long-term exposure to arsenite on insulin signaling in HepG2 human hepatoma cells, the role of PI3K/Akt signaling therein and the modulation of target genes controlled by insulin. Exposure of cells to arsenite for 24 h rendered cells less responsive toward stimulation of Akt by insulin. At the same time, short-term exposure to arsenite induced a concentration-dependent increase in phosphorylation of Akt at Ser-473, followed by phosphorylation of FoxO proteins at sites known to be phosphorylated by Akt. Phosphorylation of FoxOs was prevented by wortmannin, pointing to the involvement of PI3K. Arsenite exposure resulted in attenuation of FoxO DNA binding and in nuclear exclusion of FoxO1a-EGFP. A 24-h exposure of HepG2 cells to submicromolar concentrations of arsenite resulted in downregulation of glucose 6-phosphatase (G6Pase) and selenoprotein P (SelP) mRNA levels. Curiously, arsenite had a dual effect on SelP protein levels, inducing a small increase in the nanomolar and a distinct decrease in the micromolar concentration range. Interestingly, arsenite-induced long-term effects on G6Pase and SelP mRNA or SelP protein levels were not blocked by the PI3K inhibitor, wortmannin. In conclusion, arsenite perturbs cellular signaling pathways involved in fuel metabolism: it impairs cellular responsiveness toward insulin, while at the same time stimulating insulin-like signaling to attenuate the expression of genes involved in glucose metabolism and the release of the hepatokine SelP, which is known to modulate peripheral insulin sensitivity.

The accumulations of HIF-1α and HIF-2α by JNK and ERK are involved in biphasic effects induced by different levels of arsenite in human bronchial epithelial cells.

The biphasic effects of arsenite, in which low levels of arsenite induce cell proliferation and high levels of arsenite induce DNA damage and apoptosis, apparently contribute to arsenite-induced carcinogenesis. However, the mechanisms underlying this phenomenon are not well understood. In this study, we investigated the effects of different levels of arsenite on cell proliferation, DNA damage and apoptosis as well as on signal transduction pathways in human bronchial epithelial (HBE) cells. Our results show that a low level of arsenite activates extracellular signal-regulated kinases (ERK), which probably mediate arsenite-inhibited degradation of ubiquitinated hypoxia-inducible factor-2α (HIF-2α) in HBE cells. ERK inhibition blocks cell proliferation induced by a low level of arsenite, in part via HIF-2α. In contrast, a high level of arsenite activates c-Jun N-terminal kinases (JNK), which provoke a response to suppress ubiquitinated HIF-1α degradation. Down-regulation of HIF-1α by inhibiting JNK, however, increases the DNA damage but decreases the apoptosis induced by a high level of arsenite. Thus, data in the present study suggest that the accumulations of HIF-1α and HIF-2α by JNK and ERK are involved in different levels of arsenite-induced biphasic effects, with low levels of arsenite inducing cell proliferation and high levels of arsenite inducing DNA damage and apoptosis in HBE cells.

Inorganic arsenic impairs differentiation and functions of human dendritic cells.

Experimental studies have demonstrated that the antileukemic trivalent inorganic arsenic prevents the development of severe pro-inflammatory diseases mediated by excessive Th1 and Th17 cell responses. Differentiation of Th1 and Th17 subsets is mainly regulated by interleukins (ILs) secreted from dendritic cells (DCs) and the ability of inorganic arsenic to impair interferon-γ and IL-17 secretion by interfering with the physiology of DCs is unknown. In the present study, we demonstrate that high concentrations of sodium arsenite (As(III), 1-2 µM) clinically achievable in plasma of arsenic-treated patients, block differentiation of human peripheral blood monocytes into immature DCs (iDCs) by inducing their necrosis. Differentiation of monocytes in the presence of non-cytotoxic concentrations of As(III) (0.1 to 0.5 µM) only slightly impacts endocytotic activity of iDCs or expression of co-stimulatory molecules in cells activated with lipopolysaccharide. However, this differentiation in the presence of As(III) strongly represses secretion of IL-12p70 and IL-23, two major regulators of Th1 and Th17 activities, from iDCs stimulated with different toll-like receptor (TLR) agonists in metalloid-free medium. Such As(III)-exposed DCs also exhibit reduced mRNA levels of IL12A and/or IL12B genes when activated with TLR agonists. Finally, differentiation of monocytes with non-cytotoxic concentrations of As(III) subsequently reduces the ability of activated DCs to stimulate the release of interferon-γ and IL-17 from Th cells. In conclusion, our results demonstrate that clinically relevant concentrations of inorganic arsenic markedly impair in vitro differentiation and functions of DCs, which may contribute to the putative beneficial effects of the metalloid towards inflammatory autoimmune diseases.