Differential influences of various arsenic compounds on glutathione redox status and antioxidative enzymes in porcine endothelial cells

Toxicity and speciation of inorganic arsenics and their adverse effects on in vivo endpoints and oxidative stress in the marine medaka Oryzias melastigma

Here, we investigate the effects of acute and chronic exposure to arsenate (AsV) and arsenite (AsIII) in the marine medaka Oryzias melastigma. In vivo effects, biotransformation, and oxidative stress were studied in marine medaka exposed to the two inorganic arsenics for 4 or 28 days. An investigation of embryonic development revealed no effect on in vivo parameters, but the hatching rate increased in the group exposed to AsIII. Exposure to AsIII also caused the greatest accumulation of arsenic in medaka. For acute exposure, the ratio of AsV to AsIII was higher than that of chronic exposure, indicating that bioaccumulation of inorganic arsenic can induce oxidative stress. The largest increase in oxidative stress was observed following acute exposure to AsIII, but no significant degree of oxidative stress was induced by chronic exposure. During acute exposure to AsV, the increase in the enzymatic activity of glutathione-S-transferase (GST) was twice as high compared with exposure to AsIII, suggesting that GST plays an important role in the initial detoxification process. In addition, an RNA-seq-based ingenuity pathway analysis revealed that acute exposure to AsIII may be related to cell-cycle progression. A network analysis using differentially expressed genes also revealed a potential link between the generation of inflammatory cytokines and oxidative stress due to arsenic exposure.

Metabolic Derangement by Arsenic: a Review of the Mechanisms

Studies have implicated arsenic exposure in various pathological conditions, including metabolic disorders, which have become a global phenomenon, affecting developed, developing, and under-developed nations. Despite the huge risks associated with arsenic exposure, humans remain constantly exposed to it, especially through the consumption of contaminated water and food. This present study provides an in-depth insight into the mechanistic pathways involved in the metabolic derangement by arsenic. Compelling pieces of evidence demonstrate that arsenic induces metabolic disorders via multiple pathways. Apart from the initiation of oxidative stress and inflammation, arsenic prevents the phosphorylation of Akt at Ser473 and Thr308, leading to the inhibition of PDK-1/Akt insulin signaling, thereby reducing GLUT4 translocation through the activation of Nrf2. Also, arsenic downregulates mitochondrial deacetylase Sirt3, decreasing the ability of its associated transcription factor, FOXO3a, to bind to the agents that support the genes for manganese superoxide dismutase and PPARg co-activator (PGC)-1a. In addition, arsenic activates MAPKs, modulates p53/ Bcl-2 signaling, suppresses Mdm-2 and PARP, activates NLRP3 inflammasome and caspase-mediated apoptosis, and induces ER stress, and ox-mtDNA-dependent mitophagy and autophagy. More so, arsenic alters lipid metabolism by decreasing the presence of 3-hydroxy-e-methylglutaryl-CoA synthase 1 and carnitine O-octanoyl transferase (Crot) and increasing the presence of fatty acid-binding protein-3 mRNA. Furthermore, arsenic promotes atherosclerosis by inducing endothelial damage. This cascade of pathophysiological events promotes metabolic derangement. Although the pieces of evidence provided by this study are convincing, future studies evaluating the involvement of other likely mechanisms are important. Also, epidemiological studies might be necessary for the translation of most of the findings in animal models to humans.

Systematic Myostatin Expression Screening Platform for Identification and Evaluation of Myogenesis-Related Phytogenic in Pigs

Skeletal muscle growth in livestock impacts meat quantity and quality. Concerns arise because certain feed additives, like beta-agonists, may affect food safety. Skeletal muscle is a specialized tissue consisting of nondividing and multinucleated muscle fibers. Myostatin (MSTN), a protein specific to skeletal muscle, is secreted and functions as a negative regulator of muscle mass by inhibiting the proliferation and differentiation of myoblasts. To enhance livestock muscle growth, phytogenic feed additives could be an alternative as they inhibit MSTN activity. The objective of this study was to establish a systematic screening platform using MSTN activity to evaluate phytogenics, providing scientific evidence of their assessment and potency. In this study, we established a screening platform to monitor myostatin promoter activity in rat L8 myoblasts. Extract of Glycyrrhiza uralensis (GUE), an oriental herbal medicine, was identified through this screening platform, and the active fractions of GUE were identified using a process-scale liquid column chromatography system. For in vivo study, GUE as a feed additive was investigated in growth-finishing pigs. The results showed that GUE significantly increased body weight, carcass weight, and lean content in pigs. Microbiota analysis indicated that GUE did not affect the composition of gut microbiota in pigs. In summary, this established rodent myoblast screening platform was used to identify a myogenesis-related phytogenic, GUE, and further demonstrated that the active fractions and compounds inhibited MSTN expression. These findings suggest a novel application for GUE in growth performance enhancement through modulation of MSTN expression. Moreover, this well-established screening platform holds significant potential for identifying and assessing a diverse range of phytogenics that contribute to the process of myogenesis.

Physiochemical characterization and toxicity assessment of colloidal mercuric formulation-'Sivanar amirtham'

The study aims to characterize and understand the toxicological effects of colloidal mercuric formulation. The physiochemical characterization was carried out using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray microanalysis system (EDS), Inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), Zeta potential, Brunauer-Emmett-Teller (BET) and electron microscopy. Based on the physiochemical characterizations, the pairwise relationship between the parameters such as size, surface area, surface charge, reactivity and band gap energy were described. The biological effects of the sample were studied by both in vitro and in vivo assays. The in vitro cytotoxicity assay confirmed that the colloidal mercuric formulation was effective against cancer cells (MCF-7) and less toxic to normal cells (Hek 293). The formulation was effective against MCF-7 with more than 85% of apoptotic and necrotic cells, positive for PI staining when treated with 100 μg/mL. The inflammatory response on the macrophage cell lines was studied. The colloidal mercuric formulation upregulated the expression of TGF-β, IL-6 and TNF-α, due to the presence of arsenic and other organic compounds such as piperine. The in vivo developmental toxicity was observed in Zebrafish hampered growth and survival in a dose and time dependent manner. The formulation was safe at lower concentration and exhibit a dose and time dependent toxicity. Based on the results obtained, it is confirmed that the selective toxicity towards MCF-7 cells is promising to develop an effective formulation for the treatment of cancer, provided more such proofs obtained from in vivo experiments.

Role of AIP56 disulphide bond and its reduction by cytosolic redox systems for efficient intoxication

Apoptosis-inducing protein of 56 kDa (AIP56) is a major virulence factor of Photobacterium damselae subsp. piscicida, a gram-negative pathogen that infects warm water fish species worldwide and causes serious economic losses in aquacultures. AIP56 is a single-chain AB toxin composed by two domains connected by an unstructured linker peptide flanked by two cysteine residues that form a disulphide bond. The A domain comprises a zinc-metalloprotease moiety that cleaves the NF-kB p65, and the B domain is involved in binding and internalisation of the toxin into susceptible cells. Previous experiments suggested that disruption of AIP56 disulphide bond partially compromised toxicity, but conclusive evidences supporting the importance of that bond in intoxication were lacking. Here, we show that although the disulphide bond of AIP56 is dispensable for receptor recognition, endocytosis, and membrane interaction, it needs to be intact for efficient translocation of the toxin into the cytosol. We also show that the host cell thioredoxin reductase-thioredoxin system is involved in AIP56 intoxication by reducing the disulphide bond of the toxin at the cytosol. The present study contributes to a better understanding of the molecular mechanisms operating during AIP56 intoxication and reveals common features shared with other AB toxins.

Arsenic trioxide, a cancer chemo drug hampers fibrotic liver regeneration by interrupting oxidative stress rekindling and stellate cell rejuvenation

After withdrawal of liver toxic insult, the spontaneous regenerative potential of the liver is well reported in the literature. On the other hand, various molecules have been reported to promote as well as delay such natural regeneration. This current study investigates the involvement of arsenic trioxide (ATO) medication at chemotherapeutic dose on the spontaneous regeneration of the CCl₄ induced fibrotic liver. Liver injury markers, such as albumin and SGOT, SGPT, and ALP activities, in serum indicated that ATO supplementation during liver regeneration hampers the rejuvenation process. The hepatic architecture as well as the degree of fibrosis by hematoxylin and eosin and Sirius red staining confirms the above findings. The reduced hepatic antioxidant system and elevated oxidative stress markers, such as lipid peroxidation and 8-hydroxy deoxy-guanosine-positive hepatocytes in ATO supplied rats, display the persistence of oxidative stress when compared with healthy controls and the normal regeneration model. Immuno-histochemical localization of Ki-67 indicates that mitotically active hepatocytes were fewer in the ATO given rats when compared with normal regeneration rats. Further delay in hepatic fibrinolysis was monitored by matrix metalloproteinase zymography assay in the ATO-given animals. Poly(ADP-ribose) polymerase 1 expression demonstrates elevated hepatocyte apoptosis with ATO. Furthermore, increased α-smooth muscle actin indicates that the stellate cells are in an activated state in ATO supplemented fibrotic animals. In conclusion, it's observed that ATO supplementation to the fibrotic liver delays oxidative stress revitalization and maintains stellate cells in the active form, thereby delaying liver regeneration, and the health status of the liver must be taken into account before administering drugs like ATO.

Arsenic trioxide ameliorates murine colon inflammation through inflammatory cell enzymatic modulation

Arsenic trioxide (As₂O₃) is a trending subject in recent therapy approaches despite its described toxicity. In this work, we have investigated the use of arsenic trioxide in a murine model of chemically induced inflammatory bowel disease "colitis." Male mice were randomly separated into four different groups. Controls received vehicle, arsenic group had a daily injection of As₂O₃ (2.5 mg/kg, i.p.) for 2 days. Colitis was induced through intra-rectal instillation of 4% (v/v) solution of acetic acid in the second day. The treatment group (As₂O₃ + acetic acid) received the same treatment as the two previous groups. Twenty-four hours after colitis challenge, animals were sacrificed and organs (colons, livers, and kidneys) were taken for analysis. Disease-related macroscopic and microscopic symptoms, as well as histologic observations, showed a high index in the colitis group, which was greatly reduced by the As₂O₃ pretreatment. Similarly, colon length was reduced during colon inflammation, which was prevented in the presence of As₂O₃. Inflammatory cells and oxidative stress markers significantly increased during inflammation accompanied by a considerable reduction of antioxidants. As₂O₃ treatment managed to reverse these observations to normal levels. Mitochondrial implication was observed through mPTP opening phenomena and semi-quantitative cell death estimation. Low-dose As₂O₃ use as a mean of preventing the acute phase of colitis can be seen as an interesting approach which counts as a great addition to IBD available treatments.

Arsenic trioxide exposure accelerates colon preneoplasic aberrant crypt foci induction regionally through mitochondrial dysfunction

Arsenic poisoning is a worldwide problem. Thus, we studied the effects of arsenic trioxide (ATO) administration on a 1,2-dimethylhydrazine (DMH)-induced preneoplasic colon carcinogenesis model. Mice were separated into four study groups; the control group received only vehicles. The ATO group received daily a 2.5 mg kg^-1 dose for 4 weeks. The DMH group received DMH (20 mg kg^-1) twice in two weeks. The third group (D-ATO) had the same as the DMH group with ATO administration starting at week 10. At the end of 14 weeks, colons from sacrificed mice were taken, segmented into distal and proximal and subjected to aberrant crypt foci (ACF), aberrant crypt (AC) counting, alcian blue, H&E and Hoechst histological study and lastly oxidative stress marker analysis as well as mitochondrial swelling assessment. Data showed a significant increase in ACF and AC after DMH treatment, which was further increased after ATO addition. A perturbed histological structure was observed and loss of mucin producing cells in the colon tissue was observed. An important impact on the distal colon compared to the proximal one was noticed. The oxidative stress balance showed a similar pattern with an increase in MPO, NO/l-ornithine balance and MDA, while a decrease was observed in the antioxidant enzymes (CAT, SOD and GSH). In all parameters analyzed, the distal colons showed higher values than proximal. Furthermore, histological cell death analysis in combination with mitochondrial permeability pore opening suggested ATO contribution in the pathological effect. Our study has shown that ATO administration accelerated colon cancer development suggesting the heaviness of such treatments and the need to explore combinations and cycle type formulas.

Citron Rho-interacting kinase mediates arsenite-induced decrease in endothelial nitric oxide synthase activity by increasing phosphorylation at threonine 497: Mechanism underlying arsenite-induced vascular dysfunction

We reported that arsenite causes an acute decrease in nitric oxide (NO) production by increasing phosphorylation of endothelial NO synthase at threonine 497 (eNOS-Thr(497)); however, the detailed mechanism has not yet been clarified. Here, we investigated the kinase involving in arsenite-stimulated eNOS-Thr(497) phosphorylation. Although treatment with H-89, a known protein kinase A (PKA) inhibitor, inhibited arsenite-stimulated eNOS-Thr(497) phosphorylation, no inhibition was found in cells treated with other PKA inhibitors, including Rp-8-Br-cAMPS or PKI. Based on previous reports, we also tested whether RhoA mediates arsenite-stimulated eNOS-Thr(497) phosphorylation and found that arsenite causes an acute increase in RhoA activity. Ectopic expression of dominant negative (DN)-RhoA significantly reversed arsenite-stimulated eNOS-Thr(497) phosphorylation. An in vitro phosphorylation assay also revealed that the well-known Rho effectors, Rho-associated protein kinase 1/2 (ROCK1/2), directly phosphorylate eNOS-Thr(497). Y27632, a selective ROCK inhibitor, reversed arsenite-stimulated eNOS-Thr(497) phosphorylation. However, overexpression of a small interfering RNA (siRNA) against ROCK1/2 or DN-ROCK did not reverse arsenite-stimulated eNOS-Thr(497) phosphorylation, thereby providing no conclusive evidence of a role for ROCK1/2. Knockdown of PKC-related protein kinase 1/2, another Rho effector, also did not reverse arsenite-stimulated eNOS-Thr(497) phosphorylation. In contrast, we found that transfection with an siRNA against citron Rho-interacting kinase (CRIK), the other downstream effector of Rho, significantly reversed the arsenite-induced eNOS-Thr(497) phosphorylation that was accompanied by restoration of eNOS enzymatic activity repressed by arsenite. Moreover, CRIK directly phosphorylated eNOS-Thr(497)in vitro. Finally, we also found that arsenite increased eNOS-Thr(497) phosphorylation and decreased acetylcholine-induced vessel relaxation in rat aortas. In conclusion, we demonstrate that arsenite acutely inhibits eNOS enzymatic activity and vessel relaxation in part by increasing the RhoA/CRIK/eNOS-Thr(497) phosphorylation signaling axis, which provides a molecular mechanism underlying arsenite-induced impaired vascular diseases.

Differential influences of various arsenic compounds on antioxidant defense system in liver and kidney of rats

In this study, oxidative stress-related parameters and As retention were examined in liver and kidneys of male Wistar rats exposed to arsenic trioxide, sodium arsenite (iAsIII), sodium arsenate (iAsV), and dimethylarsinic acid (DMAsV) at a single ip dose of 3.8 mgAs/kgbw, at 24h post-exposure. In liver, lipid peroxidation increased in iAsIII-exposed rats, glutathione peroxidase activity decreased in inorganic arsenic (iAs)-exposed rats, and catalase and thioredoxin reductase activities decreased significantly in all As-exposed groups. Both As(III) and As(V) exposure elevated GSH level with no effect on glutathione reductase activity. In kidneys, catalase activity decreased significantly in iAs-exposed, rats; GSH level, glutathione reductase and thioredoxin reductase activity decreased in DMAsV-treated, rats. The tissue As retention was higher in kidneys compared to liver and was also higher in As(III)-exposed compared to As(V)-exposed rats. The results demonstrate similar potency of inorganic As(III) and As(V) compounds to inhibit/induce antioxidant defense system, with liver being more vulnerable to acute As(III)- and As(V)-induced oxidative stress.

The glutathione reductase GSR-1 determines stress tolerance and longevity in Caenorhabditis elegans

Glutathione (GSH) and GSH-dependent enzymes play a key role in cellular detoxification processes that enable organism to cope with various internal and environmental stressors. However, it is often not clear, which components of the complex GSH-metabolism are required for tolerance towards a certain stressor. To address this question, a small scale RNAi-screen was carried out in Caenorhabditis elegans where GSH-related genes were systematically knocked down and worms were subsequently analysed for their survival rate under sub-lethal concentrations of arsenite and the redox cycler juglone. While the knockdown of γ-glutamylcysteine synthetase led to a diminished survival rate under arsenite stress conditions, GSR-1 (glutathione reductase) was shown to be essential for survival under juglone stress conditions. gsr-1 is the sole GSR encoding gene found in C. elegans. Knockdown of GSR-1 hardly affected total glutathione levels nor reduced glutathione/glutathione disulphide (GSH/GSSG) ratio under normal laboratory conditions. Nevertheless, when GSSG recycling was impaired by gsr-1(RNAi), GSH synthesis was induced, but not vice versa. Moreover, the impact of GSSG recycling was potentiated under oxidative stress conditions, explaining the enormous effect gsr-1(RNAi) knockdown had on juglone tolerance. Accordingly, overexpression of GSR-1 was capable of increasing stress tolerance. Furthermore, expression levels of SKN-1-regulated GSR-1 also affected life span of C. elegans, emphasising the crucial role the GSH redox state plays in both processes.

Growth inhibition and antioxidative status induced by selenium-enriched broccoli extract and selenocompounds in DNA mismatch repair-deficient human colon cancer cells

The effects of enzymatic-digested Se-enriched broccoli extracts (SeB) and selenocompounds on growth and antioxidative status in human colon cancer cells was investigated in this study. HCT116 and HCT116+Chr.3 cells were treated with selenocompounds (sodium selenite, sodium selenate, Se-Met, MeSeCys) or SeB [high-Se (H-SeB) or low-Se (L-SeB)]. The cytotoxicity induced by selenocompounds in HCT116 cells was not associated with cellular H2O2 level, while the differential cytotoxicity observed by sodium selenite between HCT116 and HCT116+Chr.3 cell lines was related to cellular H2O2 production with the change in antioxidative enzyme activity, and the restoration of chromosome 3. H-SeB was found to reduce the cellular H2O2 content in HCT116+Chr.3 cells. The results in this study indicate that regardless of Se content, the cytotoxicity in HCT116 cells of both SeB forms appeared to be H2O2-independent, whereas the cytotoxicity in HCT116+Chr.3 of either SeB form appeared to be H2O2-dependent with an increase in antioxidative ability for H-SeB.

Sodium arsenite-induced cardiotoxicity in rats: protective role of p-coumaric acid, a common dietary polyphenol

This study was performed to investigate the ameliorative role of p-coumaric acid against sodium arsenite-induced cardiotoxicity in rats. Sodium arsenite (5 mg/kg/b.wt) was orally administered once a day for 30 days to the animals to induce cardiotoxicity. After the experimental period, cardiotoxicity was assessed by estimating the levels of lipid peroxidation, anti-oxidant status (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, glutathione reductase, total reduced glutathione, protein sulfyhydryl and non-protein sulfhydryl groups) and DNA fragmentation in the cardiac tissue of control and experimental rats. In addition, cardiac tissue specific serum markers (triacylglycerides, total cholesterol, low-density lipoprotein cholesterol and high density lipoprotein cholesterol) in serum and histopathological changes in the cardiac tissue were also evaluated. From the results obtained in our study, sodium arsenite administration to the rats increased lipid peroxidation, DNA fragmentation, triacylglycerides, total cholesterol and low-density lipoprotein cholesterol, whereas antioxidant status and high-density lipoprotein cholesterol were found to be reduced. However, p-coumaric acid (75 and100 mg/kg/b.wt) treatment orally once per day for 30 days, immediately before a daily administration of sodium arsenite protected the abnormal biochemical abnormalities observed in the cardiac tissue of sodium arsenite treated rats as evidenced by the cardiac histopathology. For comparison purpose, a standard antioxidant vitamin C (100 mg/kg/b.wt) was used. In conclusion, this study concluded that p-coumaric acid could be a promising candidate for protecting the sodium arsenite-induced cardiotoxicity in rats through its antioxidant character.

Enhancement between environmental tobacco smoke and arsenic on emphysema-like lesions in mice

Chronic obstructive pulmonary diseases (COPD) have been the major cause of mortality worldwide. Early identification of populations at risk allows us to prevent the occurrence and to reduce the cost of health care. In human studies, exposure to environmental tobacco smoke (ETS) and arsenic respectively increased the risk of chronic lung diseases, including COPD. We suspected that ETS and arsenic might enhance the risk of COPD. In our present study, we evaluated this hypothesis in mice and tried to identify early biomarkers for chemicals-induced lung lesions. Mice inhaled ETS and/or administrated arsenite via gavage for 4 weeks. At the end of experiment, exposure to ETS or arsenite alone failed to cause lung lesions or inflammation. However, co-exposure to ETS and arsenite significantly induced emphysema-like lesions, characterized with enlarged alveolar spaces and destruction of alveolar structure, although inflammation was not observed. Furthermore, co-exposure to ETS and arsenite significantly increased plasma 8-oxodeoxyguanosine (8-OHdG) levels. Our results indicated that co-exposure to ETS and arsenite induced emphysematous lesions, and plasma 8-OHdG might serve as an early biomarker for co-exposure of ETS and arsenite. With information about ETS and arsenic exposure in human populations, plasma 8-OHdG will help us to identify individuals at risk.

Factors determining sensitivity and resistance of tumor cells to arsenic trioxide

Previously, arsenic trioxide showed impressive regression rates of acute promyelocytic leukemia. Here, we investigated molecular determinants of sensitivity and resistance of cell lines of different tumor types towards arsenic trioxide. Arsenic trioxide was the most cytotoxic compound among 8 arsenicals investigated in the NCI cell line panel. We correlated transcriptome-wide microarray-based mRNA expression to the IC(50) values for arsenic trioxide by bioinformatic approaches (COMPARE and hierarchical cluster analyses, Ingenuity signaling pathway analysis). Among the identified pathways were signaling routes for p53, integrin-linked kinase, and actin cytoskeleton. Genes from these pathways significantly predicted cellular response to arsenic trioxide. Then, we analyzed whether classical drug resistance factors may also play a role for arsenic trioxide. Cell lines transfected with cDNAs for catalase, thioredoxin, or the anti-apoptotic bcl-2 gene were more resistant to arsenic trioxide than mock vector transfected cells. Multidrug-resistant cells overexpressing the MDR1, MRP1 or BCRP genes were not cross-resistant to arsenic trioxide. Our approach revealed that response of tumor cells towards arsenic trioxide is multi-factorial.

Genetic polymorphisms in glutathione S-transferase (GST) superfamily and risk of arsenic-induced urothelial carcinoma in residents of southwestern Taiwan

Background

Arsenic exposure is an important public health issue worldwide. Dose-response relationship between arsenic exposure and risk of urothelial carcinoma (UC) is consistently observed. Inorganic arsenic is methylated to form the metabolites monomethylarsonic acid and dimethylarsinic acid while ingested. Variations in capacity of xenobiotic detoxification and arsenic methylation might explain individual variation in susceptibility to arsenic-induced cancers.

Methods

To estimate individual susceptibility to arsenic-induced UC, 764 DNA specimens from our long-term follow-up cohort in Southwestern Taiwan were used and the genetic polymorphisms in GSTM1, GSTT1, GSTP1 and arsenic methylation enzymes including GSTO1 and GSTO2 were genotyped.

Results

The GSTT1 null was marginally associated with increased urothelial carcinoma (UC) risk (HR, 1.91, 95% CI, 1.00-3.65), while the association was not observed for other GSTs. Among the subjects with cumulative arsenic exposure (CAE) ≥ 20 mg/L*year, the GSTT1 null genotype conferred a significantly increased cancer risk (RR, 3.25, 95% CI, 1.20-8.80). The gene-environment interaction between the GSTT1 and high arsenic exposure with respect to cancer risk was statistically significant (multiplicative model, p = 0.0151) and etiologic fraction was as high as 0.86 (95% CI, 0.51-1.22). The genetic effects of GSTO1/GSTO2 were largely confined to high arsenic level (CAE ≥ 20). Diplotype analysis showed that among subjects exposed to high levels of arsenic, the AGG/AGG variant of GSTO1 Ala140Asp, GSTO2 5'UTR (-183)A/G, and GSTO2 Asn142Asp was associated with an increased cancer risk (HRs, 4.91, 95% CI, 1.02-23.74) when compared to the all-wildtype reference, respectively.

Conclusions

The GSTs do not play a critical role in arsenic-induced urothelial carcinogenesis. The genetic effects of GSTT1 and GSTO1 on arsenic-induced urothelial carcinogenesis are largely confined to very high exposure level.

Cardiotoxic effects of arsenic trioxide/imatinib mesilate combination in rats

Cardiotoxicity is an important consideration in the evaluation of cancer chemotherapy, because chemotherapy-induced myocardial damage might be irreversible and lethal. This in-vivo study investigated the cardiotoxicity of either arsenic trioxide or imatinib mesilate, or a combination of both drugs, following repeated administration in male Wistar rats. Both arsenic trioxide and imatinib mesilate were administered daily at a dose of 5 mg kg−1 intraperitoneally and 30 mg kg−1 orally for 10 days, respectively. Cardiotoxicity was evaluated by biochemical and histopathological examination 48 h after the last dose. Treatment with either arsenic or imatinib, or both, resulted in significant increases in serum creatine kinase isoenzyme (CK-MB), glutathione peroxidase (GPx), lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) activity levels. Cardiac tissue of rats treated with arsenic showed significant increases in levels of reduced glutathione (GSH) content, GPx activity, malondialdehyde (MDA) and total nitrate/nitrite (NOx), whereas imatinib treatment significantly increased cardiac GSH content and MDA production level and decreased GPx activity level and NOx content. A combination of arsenic and imatinib produced significant increases in cardiac GSH content, GPx activity and MDA production levels, in addition to a reduction in NOx content. Combination arsenic/imatinib treatment extensively increased GPx activity and MDA production levels compared with imatinib treatment alone. Moreover, rats treated with arsenic or imatinib, or both, showed a significant increase in serum bilirubin, creatinine and urea levels. Histopathological examination of cardiac tissue of the combination-treated group revealed fibroblastic proliferation, myocardial disorganization and myocardial necrosis. Liver peroxidative alterations revealed that treatment with either arsenic or imatinib, or the two combined, increased levels of reduced-GSH and MDA production levels. However, imatinib treatment depleted liver GPx activity level contrary to treatment with the combination. Rats treated with arsenic alone or arsenic/imatinib combination showed significant elevation in liver NOx. In conclusion, both arsenic trioxide and imatinib mesilate might have significant cardiotoxicity and cardiac function should be monitored during treatment with them alone or in combination, as well as in the presence of pre-existing cardiac dysfunction.

Analysis of genomic dose-response information on arsenic to inform key events in a mode of action for carcinogenicity

A comprehensive literature search was conducted to identify information on gene expression changes following exposures to inorganic arsenic compounds. This information was organized by compound, exposure, dose/concentration, species, tissue, and cell type. A concentration-related hierarchy of responses was observed, beginning with changes in gene/protein expression associated with adaptive responses (e.g., preinflammatory responses, delay of apoptosis). Between 0.1 and 10 microM, additional gene/protein expression changes related to oxidative stress, proteotoxicity, inflammation, and proliferative signaling occur along with those related to DNA repair, cell cycle G2/M checkpoint control, and induction of apoptosis. At higher concentrations (10-100 microM), changes in apoptotic genes dominate. Comparisons of primary cell results with those obtained from immortalized or tumor-derived cell lines were also evaluated to determine the extent to which similar responses are observed across cell lines. Although immortalized cells appear to respond similarly to primary cells, caution must be exercised in using gene expression data from tumor-derived cell lines, where inactivation or overexpression of key genes (e.g., p53, Bcl-2) may lead to altered genomic responses. Data from acute in vivo exposures are of limited value for evaluating the dose-response for gene expression, because of the transient, variable, and uncertain nature of tissue exposure in these studies. The available in vitro gene expression data, together with information on the metabolism and protein binding of arsenic compounds, provide evidence of a mode of action for inorganic arsenic carcinogenicity involving interactions with critical proteins, such as those involved in DNA repair, overlaid against a background of chemical stress, including proteotoxicity and depletion of nonprotein sulfhydryls. The inhibition of DNA repair under conditions of toxicity and proliferative pressure may compromise the ability of cells to maintain the integrity of their DNA.

Thioredoxin system inhibitors as mediators of apoptosis for cancer therapy

The thioredoxin (Trx) system is a major antioxidant system integral to maintaining the intracellular redox state. It contains Trx, a redox active protein, which regulates the activity of various enzymes including those that function to counteract oxidative stress within the cell. Trx can also scavenge reactive oxygen species (ROS) and directly inhibits proapoptotic proteins such as apoptosis signal-regulating kinase 1 (ASK1). The oxidized form of Trx is reduced by thioredoxin reductase (TrxR). The cytoplasm and mitochondria contain equivalent Trx systems and inhibition of either system can lead to activation of apoptotic signaling pathways. There are a number of inhibitors with chemotherapy applications that target either Trx or TrxR to induce apoptosis in cancer cells. Suberoylanilide hydroxamic acid (SAHA) is effective against many cancer cells and functions by up-regulating an endogenous inhibitor of Trx. Other compounds target the selenocysteine-containing active site of TrxR. These include gold compounds, platinum compounds, arsenic trioxide, motexafin gadolinium, nitrous compounds, and various flavonoids. Inhibition of TrxR leads to an accumulation of oxidized Trx resulting in cellular conditions that promote apoptosis. In addition, some compounds also convert TrxR to a ROS generating enzyme. The role of Trx system inhibitors in cancer therapy is discussed in this review.

Antitumor effects of arsenic trioxide in transformed human thyroid cells

BACKGROUND

To improve radioiodine treatment of metastasized differentiated thyroid carcinomas, substances that increase iodide uptake are needed. Many tumors are not responsive to retinoic acid as a differentiating agent. Therefore, identification of other differentiating substances is needed. Arsenic trioxide (ATO) was investigated for its potential to increase iodide uptake.

METHODS

The action of ATO on proliferation, differentiation, and apoptosis was evaluated in follicular and papillary thyroid carcinoma cell lines. To get insight into the mode of action of ATO, coincubations with inhibitors of the phosphoinositide 3 (PI3) kinase pathway (V-Akt Murine Thymoma Viral Oncogene Homolog 1, Akt inhibitors) were performed; glutathione (GSH) levels were determined, as well as synergistic effects of ATO with inhibitors of GSH metabolism, inductors of oxidative stress. As a potential additional target of the pleiotropic action of ATO, its effect on glucose uptake was investigated. The expression of sodium iodide symporter, pendrin, phospho-Akt, and glucose transporter 1 was studied to reveal a potential effect of ATO on the transcription of specific genes.

RESULTS

ATO reduced proliferation, increased iodide uptake and apoptosis, and, as an additional new mechanism, decreased glucose uptake in transformed thyrocytes. The pharmacological reduction of the amount of reduced GSH was effective in enhancing the differentiating action of ATO, whereas the combination of ATO with Akt-1 inhibitors reduced cell number but did not increase differentiation.

CONCLUSIONS

Our study suggests a new therapeutic option for postoperative treatment of radioiodine nonresponsive differentiated thyroid carcinomas.

Arsenic-induced decreases in the vascular matrix

Chronic ingestion of arsenic is associated with increased incidence of respiratory and cardiovascular diseases. To investigate the role of arsenic in early events in vascular pathology, C57BL/6 mice ingested drinking water with or without 50 ppb sodium arsenite (AsIII) for four, five, or eight weeks. At five and eight weeks, RNA from the lungs of control and AsIII-exposed animals was processed for microarray. Sixty-five genes were significantly and differentially expressed. Differential expression of extracellular matrix (ECM) gene transcripts was particularly compelling, as 91% of genes in this category, including elastin and collagen, were significantly decreased. In additional experiments, real-time RT-PCR showed an AsIII-induced decrease in many of these ECM gene transcripts in the heart and NIH3T3 fibroblast cells. Histological stains for collagen and elastin show a distinct disruption in the ECM surrounding small arteries in the heart and lung of AsIII-exposed mice. Immunohistochemical detection of alpha-smooth muscle actin in blood vessel walls was decreased in the AsIII-exposed animals. These data reveal a functional link between AsIII exposure and disruption in the vascular ECM. These AsIII-induced early pathological events may predispose humans to respiratory and cardiovascular diseases linked to chronic low-dose AsIII exposure.

Targeting thioredoxin reductase is a basis for cancer therapy by arsenic trioxide

Arsenic trioxide (ATO) is an effective cancer therapeutic drug for acute promyelocytic leukemia and has potential anticancer activity against a wide range of solid tumors. ATO exerts its effect mainly through elevated oxidative stress, but the exact molecular mechanism remains elusive. The thioredoxin (Trx) system comprising NADPH, thioredoxin reductase (TrxR), and Trx and the glutathione (GSH) system composed of NADPH, glutathione reductase, and GSH supported by glutaredoxin are the two electron donor systems that control cellular proliferation, viability, and apoptosis. Recently, the selenocysteine-dependent TrxR enzyme has emerged as an important molecular target for anticancer drug development. Here, we have discovered that ATO irreversibly inhibits mammalian TrxR with an IC(50) of 0.25 microM. Both the N-terminal redox-active dithiol and the C-terminal selenothiol-active site of reduced TrxR may participate in the reaction with ATO. The inhibition of MCF-7 cell growth by ATO was correlated with irreversible inactivation of TrxR, which subsequently led to Trx oxidation. Furthermore, the inhibition of TrxR by ATO was attenuated by GSH, and GSH depletion by buthionine sulfoximine enhanced ATO-induced cell death. These results strongly suggest that the ATO anticancer activity is by means of a Trx system-mediated apoptosis. Blocking cancer cell DNA replication and repair and induction of oxidative stress by the inhibition of both Trx and GSH systems are suggested as cancer chemotherapeutic strategies.

Induction of oxidative stress by arsenic in Clarias batrachus: involvement of peroxisomes

Indian catfish, Clarias batrachus, were exposed to two nonlethal doses of arsenic for 10 days, which induced tissue lipid peroxidation, increased the ratio of oxidized to reduced glutathione and produced excess H(2)O(2) within 1-2 days of exposure. Furthermore, arsenic treatment increased the activity of antioxidant enzymes such as glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase but decreased glutathione reductase (GR) activity within a day of exposure, indicating the generation of oxidative stress in fish at an early stage. Reversibility of these arsenic-induced responses by pretreatment with N-acetylcysteine indicates that the oxidative stress was due to excess H(2)O(2) production, which was found to be partially contributed by altered H(2)O(2) metabolism in the peroxisomes. It is therefore concluded that peroxisomal H(2)O(2) metabolizing enzymes are potential targets of arsenic toxicity in C. batrachus.

Mechanism for proliferation inhibition by various selenium compounds and selenium-enriched broccoli extract in rat glial cells

The objective of this study was to investigate the differential effects of various selenium (Se) compounds and Se-enriched broccoli extracts on cell proliferation and the possible mechanism responsible for the Se-induced growth inhibition. C6 rat glial cells were incubated with graded concentrations up to 1000 nM of selenite, selenate, selenomethionine (SeM), Se-methyl-selenocysteine (SeMCys), high-Se broccoli (H-SeB) extract or low-Se broccoli (L-SeB) extract for 24 and 48 h. MTT results indicated that all Se sources and levels examined inhibited C6 cell proliferation at 48 h. The results from cell cycle progression and apoptosis analysis indicated that SeM, SeMCys, H-SeB or L-SeB treatments at the concentration of 1000 nM reduced the cell population in G(0)/G(1) phase, but induced G(2)/M phase arrest and increased apoptosis and secondary necrosis in C6 cells at 24 h. The populations of apoptotic cells and secondary necrotic cells were increased by all Se sources examined. The COMET assay indicated that there was no significant DNA single-strand break found for all Se treatments in C6 cells for 48 h. In addition, the Se-induced proliferation inhibition may involve a hydrogen peroxide (H(2)O(2))-dependent mechanism with elevated cellular glutathione peroxidase (cGPX) activity. Both H-SeB and L-SeB inhibited C6 cell proliferation but H-SeB was less inhibitory than L-SeB. The proliferation inhibition by H-SeB in C6 cells is apparently related to the increased H(2)O(2) with the elevated cGPX activity, but the inhibition by L-SeB was H(2)O(2)-independent without change in cGPX activity.

Comparative investigations of sodium arsenite, arsenic trioxide and cadmium sulphate in combination with gamma-radiation on apoptosis, micronuclei induction and DNA damage in a human lymphoblastoid cell line

In the field of radiation protection the combined exposure to radiation and other toxic agents is recognised as an important research area. To elucidate the basic mechanisms of simultaneous exposure, the interaction of the carcinogens and environmental toxicants cadmium and two arsenic compounds, arsenite and arsenic trioxide, in combination with gamma-radiation in human lymphoblastoid cells (TK6) were investigated. Gamma-radiation induced significant genotoxic effects such as micronuclei formation, DNA damage and apoptosis, whereas arsenic and cadmium had no significant effect on these indicators of cellular damage at non-toxic concentrations. However, in combination with gamma-radiation arsenic trioxide induced a more than additive apoptotic rate compared to the sum of the single effects. Here, the level of apoptotic cells was increased, in a dose-dependent way, up to two-fold compared to the irradiated control cells. Arsenite did not induce a significant additive effect at any of the concentrations or radiation doses tested. On the other hand, arsenic trioxide was less effective than arsenite in the induction of DNA protein cross-links. These data indicate that the two arsenic compounds interact through different pathways in the cell. Cadmium sulphate, like arsenite, had no significant effect on apoptosis in combination with gamma-radiation at low concentrations and, at high concentrations, even reduced the radiation-induced apoptosis. An additive effect on micronuclei induction was observed with 1muM cadmium sulphate with an increase of up to 80% compared to the irradiated control cells. Toxic concentrations of cadmium and arsenic trioxide seemed to reduce micronuclei induction. The results presented here indicate that relatively low concentrations of arsenic and cadmium, close to those occuring in nature, may interfere with radiation effects. Differences in action of the two arsenic compounds were identified.

Arsenic and cigarette smoke synergistically increase DNA oxidation in the lung

Epidemiological evidence has indicated that arsenic and cigarette smoking exposure act synergistically to increase the incidence of lung cancer. Since oxidative damage of DNA has been linked to cancer, our hypothesis is that aerosolized arsenic and cigarette smoke work synergistically to increase oxidative stress and increase DNA oxidation in the lung. To test this hypothesis male Syrian golden hamsters were exposed to room air (control), aerosolized arsenic compounds (3.2 mg/m3 for 30 minutes), cigarette smoke (5 mg/m3 for 30 minutes), or both smoke and arsenic. Exposures were for 5 days/week for 5 or 28-days. Animals were sacrificed one day after the last exposure. In the 28-day group, glutathione levels and DNA oxidation (8-oxo-2'-deoxyguanosine (8-oxo-dG)) were determined. Our results show that in the 28-day arsenic/smoke group there was a significant decrease in both the reduced and total glutathione levels compared with arsenic or smoke alone. This correlated with a 5-fold increase in DNA oxidation as shown by HPLC. Immunohistochemical localization of 8-oxo-dG showed increase staining in nuclei of airway epithelium and subadjacent interstitial cells. These results show that dual exposure of arsenic and cigarette smoke at environmentally relevant levels can act synergistically to cause DNA damage.

Arsenic trioxide: an anti cancer missile with multiple warheads

The proven efficacy of ATO in the treatment of APL and the emerging importance of ATO in other diseases prompted extensive studies of the mechanisms of action of ATO in APL and in other types of cancers. In this review we will focus on downstream events in ATO-induced intrinsic and extrinsic apoptotic pathways with an emphasis on the role of pro-apoptotic and anti-apoptotic proteins and the role of p53 in ATO-induced apoptosis including its effect on cell cycle, its anti-mitotic effect and the role of apoptosis inducing factors (AIF) in ATO-induced apoptosis, chromatin condensation and nuclear fragmentation in myeloma cells as a model.

Arsenic ingestion and increased microvascular disease risk: observations from the south-western arseniasis-endemic area in Taiwan

BACKGROUND

We established the association between arsenic ingestion and increased risk of vascular diseases associated with diabetes. However, the specific microvascular diseases in relation to arsenic exposure level have not been well reported.

METHODS

The study population was obtained through national health database linkage. A total of 28 499 subjects living in the study area were successfully linked with their medical records from the National Health Insurance database in 1999-2000. The arsenic concentrations of artesian well water in the villages of the study area were utilized as indices of previous ingestion level. Both stratified analysis and unconditional logistic regression were used to examine mainly neurological and renal disease in relation to the arsenic exposure taking into account diabetes status.

RESULTS

The age-adjusted and gender-adjusted prevalence of microvascular diseases was 7.51% [95% confidence interval (CI) 7.50-7.51] for arsenic level of <0.1 mg/litre, and then increased from 6.59% (6.59-6.60) for the arsenic concentrations of 0.1-0.29 mg/litre to 8.02% (8.02-8.03) and 11.82% (11.81-11.83) for those of 0.3-0.59 mg/litre and > or =0.6 mg/litre in non-diabetic subjects. For diabetic patients, the prevalence was 16.41% (95% CI 16.37-16.45), 15.85% (15.8-15.9), 21.69% (21.6-21.8), and 28.31% (28.2-28.4) for arsenic levels <0.1, 0.1-0.29, 0.3-0.59, and > or =0.6 mg/litre, respectively. The prevalence of microvascular diseases increased significantly with arsenic exposure, especially at higher levels, and the relationship is stronger in diabetics than in non-diabetic subjects. The results for neurological disease are very similar, and the patterns are the same for renal disease.

CONCLUSIONS

The increased prevalence of microvascular diseases, including neurological and renal disorders, is associated with arsenic ingestion. This excess risk was further elevated in diabetic subjects. Further studies are necessary to verify the hypotheses of threshold or dose-response relationships.

Vascular permeability alterations induced by arsenic

The impact of arsenic on the integrity of blood vessels in vivo via in situ exposure (local injection) of arsenic was investigated. Vascular permeability changes were evaluated by means of the Evans blue assay and the India ink tracer techniques. Rats were intravenously injected with Evans blue followed by intradermal injections of various doses of sodium arsenite on the back skins of the animals. Evans blue at different time points was extracted and assayed as indices of vascular leakage. Skin at various time point injection sites was sampled for arsenic measurement via graphite furnace atomic absorption spectroscopy. Our time course study with Evans blue technique demonstrated a biphasic pattern of vascular permeability change: an early phase of permeability reduction and a later phase of permeability promotion at all dose levels tested. The India ink tracer technique also demonstrated a time-correlated increase in vascular labelling in the tissues examined, signifying an increase in vascular leakage with time. Moreover, we found that despite an early increase in tissue arsenic content at time of injection, tissue arsenic declined rapidly and returned to near control levels after 30-60 min. Thus, an inverse correlation between tissue arsenic content and the extent of vascular permeability was apparent. This study provides the first demonstration that in situ exposure to arsenic will produce vascular dysfunction (vascular leakage) in vivo.

Arsenite and its biomethylated metabolites interfere with the formation and repair of stable BPDE-induced DNA adducts in human cells and impair XPAzf and Fpg

The underlying mechanisms of arsenic carcinogenicity are only poorly understood and especially the role of biomethylation is still a matter of debate. Besides the induction of oxidative DNA damage the interference with DNA repair processes have been proposed to contribute to arsenic-induced carcinogenicity. Within the present study the effects of arsenite and its mono- and dimethylated trivalent and pentavalent metabolites on BPDE-induced DNA adduct formation and repair has been investigated and compared in cultured human lung cells. Whereas only arsenite and MMA(III) increased BPDE-DNA adduct formation, arsenite (>/=5 microM), the trivalent (>/=2.5 microM) and the pentavalent (>/=250 microM) metabolites diminished their repair at non-cytotoxic concentrations. As potential molecular targets, interactions with the zinc finger domain of the human XPA protein (XPAzf) and the Escherichia coli zinc finger protein Fpg, involved in NER and BER, respectively, have been investigated. All trivalent arsenicals were able to release zinc from XPAzf; furthermore, MMA(III) and DMA(III) inhibited the activity of isolated Fpg. Altogether the results suggest that besides arsenite, especially the trivalent methylated metabolites may contribute to diminished NER at low concentrations.