The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform

Hua Naranmandura - One of the best experts on this subject based on the ideXlab platform.

  • Phenylarsine Oxide Can Induce the Arsenite-Resistance Mutant PML Protein Solubility Changes
    MDPI AG, 2017
    Co-Authors: Yu Han Jiang, Qian Qian Wang, Yong Fei Lan, Ye Jia Chen, Chao Wang, Chang Yang, Liaqat Hussain, Yasen Maimaitiying, Islam Khairul, Hua Naranmandura
    Abstract:

    Arsenic trioxide (As2O3) has recently become one of the most effective drugs for treatment of patient with acute promyelocytic leukemia (APL), and its molecular mechanism has also been largely investigated. However, it has been reported that As2O3 resistant patients are frequently found in relapsed APL after consolidation therapy, which is due to the point mutations in B-box type 2 motifs of promyelocytic leukemia (PML) gene. In the present study, we for the first time establish whether organic arsenic species phenylarsine oxide (PAO) could induce the mutant PML-IV (A216V) protein solubility changes and degradation. Here, three different PML protein variants (i.e., PML-IV, PML-V and mutant PML-A216V) were overexpressed in HEK293T cells and then exposed to PAO in time- and dose-dependent manners. Interestingly, PAO is found to have potential effect on induction of mutant PML-IV (A216V) protein solubility changes and degradation, but no appreciable effects were found following exposure to high concentrations of iAsIII, Dimethylarsinous Acid (DMAIII) and adriamycin (doxorubicin), even though they cause cell death. Our current data strongly indicate that PAO has good effects on the mutant PML protein solubility changes, and it may be helpful for improving the therapeutic strategies for arsenic-resistant APL treatments in the near future

  • Effect of Arsenic Compounds on the in Vitro Differentiation of Mouse Embryonic Stem Cells into Cardiomyocytes
    2015
    Co-Authors: Qian Qian Wang, Kanwal Rehman, Yong Fei Lan, Yu Han Jiang, Yasen Maimaitiyiming, Dan Yan Zhu, Hua Naranmandura
    Abstract:

    Arsenic is a known carcinogen; however, there is no information on the toxic effects of inorganic arsenic and its intermediate metabolites, monomethylarsonous Acid (MMAIII) and Dimethylarsinous Acid (DMAIII), during the differentiation of embryonic stem (ES) cells into cardiomyocytes. The objective of this study was to evaluate the effects of arsenic compounds on ES cell differentiation into cardiomyocytes in vitro and to predict the associated toxic effects. Although iAsIII is known to be toxic, here we found that iAsIII and DMAIII did not influence ES cellular differentiation, whereas MMAIII inhibited ES cell differentiation into cardiomyocytes, suggesting that MMAIII has adverse effects on embryonic stem cells

  • the combination of arsenic and cryptotanshinone induces apoptosis through induction of endoplasmic reticulum stress reactive oxygen species in breast cancer cells
    Metallomics, 2015
    Co-Authors: Yan Fang Zhang, Min Zhang, Lingling Bao, Qian Qian Wang, Yu Han Jiang, Yasen Maimaitiyiming, Xu Lei Huang, Guang Ji Zhang, Hua Naranmandura
    Abstract:

    Arsenic trioxide has been successfully used for the treatment of patients with acute promyelocytic leukemia (APL) worldwide. Recently, it has also been further developed to treat solid tumors in clinical trials. However, the therapeutic effects on malignant tumors appeared to be unsatisfactory, as these cells exhibited resistance towards arsenic. In this study, we explored new therapeutic strategies for treatment of human breast cancer MCF-7 cells based on arsenic metabolites. The MCF-7 cells were exposed to three arsenic species, namely, inorganic arsenite (iAsIII) and its intermediate metabolites monomethylarsonous Acid (MMAIII) and Dimethylarsinous Acid (DMAIII) either alone or in combination with cryptotanshinone (CPT) to establish their anticancer effects against MCF-7 cells. Surprisingly, MCF-7 cells were shown to be resistant to both iAsIII and CPT when used alone; however, they were shown to be relatively sensitive to treatment when exposed to MMAIII and DMAIII alone. Conversely, the combination of MMAIII with CPT showed significantly enhanced anticancer effects on MCF-7 cells at low doses, but no appreciable effect was observed upon exposure to the other two arsenic species with CPT. In addition, remarkable redistribution of pro-apoptosis related proteins Bax and Bak was observed in the mitochondria, together with activation of poly(ADP-ribose) polymerase (PARP) and caspase-9 after exposure to the combination of MMAIII with CPT. Furthermore, we clearly found that induction of apoptosis in MCF-7 cells was predominantly triggered by endoplasmic reticulum (ER) stress after exposure to the combination of MMAIII with CPT.

  • a novel pathway for arsenic elimination human multidrug resistance protein 4 mrp4 abcc4 mediates cellular export of dimethylarsinic Acid dmav and the diglutathione conjugate of monomethylarsonous Acid mmaiii
    Molecular Pharmacology, 2014
    Co-Authors: Mayukh Banerjee, Hua Naranmandura, Michael W Carew, Barbara A Roggenbeck, Brayden D Whitlock, Elaine M Leslie
    Abstract:

    Hundreds of millions of people worldwide are exposed to unacceptable levels of arsenic in drinking water. This is a public health crisis because arsenic is a Group I (proven) human carcinogen. Human cells methylate arsenic to monomethylarsonous Acid (MMA(III)), monomethylarsonic Acid (MMA(V)), Dimethylarsinous Acid (DMA(III)), and dimethylarsinic Acid (DMA(V)). Although the liver is the predominant site for arsenic methylation, elimination occurs mostly in urine. The protein(s) responsible for transport of arsenic from the liver (into blood), ultimately for urinary elimination, are unknown. Human multidrug resistance protein 1 (MRP1/ABCC1) and MRP2 (ABCC2) are established arsenic efflux pumps, but unlike the related MRP4 (ABCC4) are not present at the basolateral membrane of hepatocytes. MRP4 is also found at the apical membrane of renal proximal tubule cells, making it an ideal candidate for urinary arsenic elimination. In the current study, human MRP4 expressed in HEK293 cells reduced the cytotoxicity and cellular accumulation of arsenate, MMA(III), MMA(V), DMA(III), and DMA(V) while two other hepatic basolateral MRPs (MRP3 and MRP5) did not. Transport studies with MRP4-enriched membrane vesicles revealed that the diglutathione conjugate of MMA(III), monomethylarsenic diglutathione [MMA(GS)(2)], and DMA(V) were the transported species. MMA(GS)(2) and DMA(V) transport was osmotically sensitive, allosteric (Hill coefficients of 1.4 ± 0.2 and 2.9 ± 1.2, respectively), and high affinity (K0.5 of 0.70 ± 0.16 and 0.22 ± 0.15 μM, respectively). DMA(V) transport was pH-dependent, with highest affinity and capacity at pH 5.5. These results suggest that human MRP4 could be a major player in the elimination of arsenic.

  • the molecular mechanism of interaction of trivalent Dimethylarsinous Acid dma iii binding to rat hemoglobin
    Acta pharmaceutica Sinica, 2014
    Co-Authors: Min Zhang, Hua Naranmandura, Wenwen Wang, Huifang Jin, Lingling Bao, Yingjie Qin
    Abstract:

    In our previous work, we found that trivalent Dimethylarsinous Acid (DMA(III)) have high affinity binding to cysteine residue 13 of rat hemoglobin. However, it is still unknown why arsenic intermediate metabolite DMA(III) has high binding affinity for Cysl3 but not for other cysteine residues 93, 140, 111 and 125. In order to better understand the molecular mechanism of DMA(III) with rat hemoglobin, we have done current study. So, SD rats were divided into control and arsenic-treated groups randomly. Arsenic species in lysate of red blood cells were analyzed by HPLC-ICP-MS, and then determined by a hybrid quadrupole TOF MS. In addition, trivalent DMA(III) binds to different cysteine residues in rat hemoglobin alpha and beta chains were also simulated by Molecular Docking. Only Cys13 in alpha chain is able to bind to DMA(III) from the experiment results. Cys13 of alpha chain in rat hemoglobin is a specific binding site for DMA(III), and we found that amino Acids compose pockets structure and surround Cys13 (but not other cysteine residues), make DMA(III) much easy to bind cysteine 13. Taken together, the DMA(III) specific binding to Cys13 is related to spatial structure of Cys13.

Elaine M Leslie - One of the best experts on this subject based on the ideXlab platform.

  • multidrug resistance protein 1 mrp1 abcc1 mediated cellular protection and transport of methylated arsenic metabolites differs between human cell lines
    Drug Metabolism and Disposition, 2018
    Co-Authors: Mayukh Banerjee, Michael W Carew, Brayden D Whitlock, Gurnit Kaur, Elaine M Leslie
    Abstract:

    The ATP-binding cassette (ABC) transporter multidrug resistance protein 1 (MRP1/ABCC1) protects cells from arsenic (a proven human carcinogen) through the cellular efflux of arsenic triglutathione [As(GS)3] and the diglutathione conjugate of monomethylarsonous Acid [MMA(GS)2]. Previously, differences in MRP1 phosphorylation (at Y920/S921) and N-glycosylation (at N19/N23) were associated with marked differences in As(GS)3 transport kinetics between HEK293 and HeLa cell lines. In the current study, cell line differences in MRP1-mediated cellular protection and transport of other arsenic metabolites were explored. MRP1 expressed in HEK293 cells reduced the toxicity of the major urinary arsenic metabolite dimethylarsinic Acid (DMAV), and HEK-WT-MRP1-enriched vesicles transported DMAV with high apparent affinity and capacity (Km 0.19 µM, Vmax 342 pmol⋅mg-1protein⋅min-1). This is the first report that MRP1 is capable of exporting DMAV, critical for preventing highly toxic Dimethylarsinous Acid formation. In contrast, DMAV transport was not detected using HeLa-WT-MRP1 membrane vesicles. MMA(GS)2 transport by HeLa-WT-MRP1 vesicles had a greater than threefold higher Vmax compared with HEK-WT-MRP1 vesicles. Cell line differences in DMAV and MMA(GS)2 transport were not explained by differences in phosphorylation at Y920/S921. DMAV did not inhibit, whereas MMA(GS)2 was an uncompetitive inhibitor of As(GS)3 transport, suggesting that DMAV and MMA(GS)2 have nonidentical binding sites to As(GS)3 on MRP1. Efflux of different arsenic metabolites by MRP1 is likely influenced by multiple factors, including cell and tissue type. This could have implications for the impact of MRP1 on both tissue-specific susceptibility to arsenic-induced disease and tumor sensitivity to arsenic-based therapeutics.

  • a novel pathway for arsenic elimination human multidrug resistance protein 4 mrp4 abcc4 mediates cellular export of dimethylarsinic Acid dmav and the diglutathione conjugate of monomethylarsonous Acid mmaiii
    Molecular Pharmacology, 2014
    Co-Authors: Mayukh Banerjee, Hua Naranmandura, Michael W Carew, Barbara A Roggenbeck, Brayden D Whitlock, Elaine M Leslie
    Abstract:

    Hundreds of millions of people worldwide are exposed to unacceptable levels of arsenic in drinking water. This is a public health crisis because arsenic is a Group I (proven) human carcinogen. Human cells methylate arsenic to monomethylarsonous Acid (MMA(III)), monomethylarsonic Acid (MMA(V)), Dimethylarsinous Acid (DMA(III)), and dimethylarsinic Acid (DMA(V)). Although the liver is the predominant site for arsenic methylation, elimination occurs mostly in urine. The protein(s) responsible for transport of arsenic from the liver (into blood), ultimately for urinary elimination, are unknown. Human multidrug resistance protein 1 (MRP1/ABCC1) and MRP2 (ABCC2) are established arsenic efflux pumps, but unlike the related MRP4 (ABCC4) are not present at the basolateral membrane of hepatocytes. MRP4 is also found at the apical membrane of renal proximal tubule cells, making it an ideal candidate for urinary arsenic elimination. In the current study, human MRP4 expressed in HEK293 cells reduced the cytotoxicity and cellular accumulation of arsenate, MMA(III), MMA(V), DMA(III), and DMA(V) while two other hepatic basolateral MRPs (MRP3 and MRP5) did not. Transport studies with MRP4-enriched membrane vesicles revealed that the diglutathione conjugate of MMA(III), monomethylarsenic diglutathione [MMA(GS)(2)], and DMA(V) were the transported species. MMA(GS)(2) and DMA(V) transport was osmotically sensitive, allosteric (Hill coefficients of 1.4 ± 0.2 and 2.9 ± 1.2, respectively), and high affinity (K0.5 of 0.70 ± 0.16 and 0.22 ± 0.15 μM, respectively). DMA(V) transport was pH-dependent, with highest affinity and capacity at pH 5.5. These results suggest that human MRP4 could be a major player in the elimination of arsenic.

  • monomethylarsenic diglutathione transport by the human multidrug resistance protein 1 mrp1 abcc1
    Drug Metabolism and Disposition, 2011
    Co-Authors: Michael W Carew, Hua Naranmandura, Caley B Shukalek, Elaine M Leslie
    Abstract:

    The ATP-binding cassette (ABC) transporter protein multidrug resistance protein 1 (MRP1; ABCC1) plays an important role in the cellular efflux of the high-priority environmental carcinogen arsenic as a triglutathione conjugate [As(GS)(3)]. Most mammalian cells can methylate arsenic to monomethylarsonous Acid (MMA(III)), monomethylarsonic Acid (MMA(V)), Dimethylarsinous Acid (DMA(III)), and dimethylarsinic Acid (DMA(V)). The trivalent forms MMA(III) and DMA(III) are more reactive and toxic than their inorganic precursors, arsenite (As(III)) and arsenate (As(V)). The ability of MRP1 to transport methylated arsenicals is unknown and was the focus of the current study. HeLa cells expressing MRP1 (HeLa-MRP1) were found to confer a 2.6-fold higher level of resistance to MMA(III) than empty vector control (HeLa-vector) cells, and this resistance was dependent on GSH. In contrast, MRP1 did not confer resistance to DMA(III), MMA(V), or DMA(V). HeLa-MRP1 cells accumulated 4.5-fold less MMA(III) than HeLa-vector cells. Experiments using MRP1-enriched membrane vesicles showed that transport of MMA(III) was GSH-dependent but not supported by the nonreducing GSH analog, ophthalmic Acid, suggesting that MMA(III)(GS)(2) was the transported form. MMA(III)(GS)(2) was a high-affinity, high-capacity substrate for MRP1 with apparent K(m) and V(max) values of 11 μM and 11 nmol mg(-1)min(-1), respectively. MMA(III)(GS)(2) transport was osmotically sensitive and inhibited by several MRP1 substrates, including 17β-estradiol 17-(β-D-glucuronide) (E(2)17βG). MMA(III)(GS)(2) competitively inhibited the transport of E(2)17βG with a K(i) value of 16 μM, indicating that these two substrates have overlapping binding sites. These results suggest that MRP1 is an important cellular protective pathway for the highly toxic MMA(III) and have implications for environmental and clinical exposure to arsenic.

  • comparative toxicity of arsenic metabolites in human bladder cancer ej 1 cells
    Chemical Research in Toxicology, 2011
    Co-Authors: Hua Naranmandura, Michael W Carew, Elaine M Leslie, Jane Lee, Michael Weinfeld
    Abstract:

    The human bladder is one of the primary target organs for arsenic-induced carcinogenicity, and arsenic metabolites in urine have been suspected to be directly involved in carcinogenesis. Thioarsenicals are commonly found in human and animal urine and are also considered to be highly toxic arsenic metabolites. The present study was performed to gain insight into the toxicity and accumulation of arsenic species found in urine, including arsenate (iAs(V)), arsenite (iAs(III)), monomethylarsonic Acid (MMA(V)), monomethylmonothioarsonic Acid (MMMTA(V)), dimethylarsinic Acid (DMA(V)), Dimethylarsinous Acid (DMA(III)), dimethylmonothioarsinic Acid, (DMMTA(V)), and dimethyldithioarsinic Acid (DMDTA(V)) in human bladder cancer EJ-1 cells. The order of cytotoxicity of these arsenic compounds in EJ-1 human bladder cancer cells was DMA(III), DMMTA(V) > iAs(III) ≫ iAs(V) > MMMTA(V) > MMA(V), DMA(V), and DMDTA(V), indicating that the sulfur-containing DMMTA(V) was among the most toxic arsenic compounds similar to trivalent DMA(III). We further characterized the DNA damage, generation of highly reactive oxygen species (hROS), and expression of proteins p21 and p53 in cells after exposure to iAs(III), DMA(III), and DMMTA(V). Cellular exposure to DMMTA(V) resulted in reduced protein expression of p53 and p21, increased DNA damage, and increased intracellular hROS (hydroxyl radical). In contrast, iAs(III) significantly increased the protein expression of p21 and p53 and did not increase the hROS at the IC(50). Intracellular glutathione (GSH) was reduced by 60% after exposure to DMA(III) or DMMTA(V), suggesting that DMMTA(V) causes cell death through oxidative stress. In contrast, GSH levels increased in cells exposed to iAs(III), and hROS only increased after a long exposure to iAs(III). Our findings demonstrate that DMMTA(V) may be one of the most toxicologically potent arsenic species, relevant to arsenic-induced carcinogenicity in the urinary bladder.

Miroslav Styblo - One of the best experts on this subject based on the ideXlab platform.

  • comparative oxidation state specific analysis of arsenic species by high performance liquid chromatography inductively coupled plasma mass spectrometry and hydride generation cryotrapping atomic absorption spectrometry
    Journal of Analytical Atomic Spectrometry, 2013
    Co-Authors: Jenna M Currier, Tomáš Matoušek, Lan Ding, John T Creed, Jesse R Saunders, Wanda Bodnar, Peter Hans Cable, Miroslav Styblo
    Abstract:

    The formation of methylarsonous Acid (MAsIII) and Dimethylarsinous Acid (DMAsIII) in the course of inorganic arsenic (iAs) metabolism plays an important role in the adverse effects of chronic exposure to iAs. High-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) and hydride generation-cryotrapping-atomic absorption spectrometry (HG-CT-AAS) have been frequently used for the analysis of MAsIII and DMAsIII in biological samples. While HG-CT-AAS has consistently detected MAsIII and DMAsIII, HPLC-ICP-MS analyses have provided inconsistent and contradictory results. This study compares the capacities of both methods to detect and quantify MAsIII and DMAsIII in an in vitro methylation system consisting of recombinant human arsenic (+3 oxidation state) methyltransferase (AS3MT), S-adenosylmethionine as a methyl donor, a non-thiol reductant tris(2-carboxyethyl)phosphine, and arsenite (iAsIII) or MAsIII as substrate. The results show that reversed-phase HPLC-ICP-MS can identify and quantify MAsIII and DMAsIII in aqueous mixtures of biologically relevant arsenical standards. However, HPLC separation of the in vitro methylation mixture resulted in significant losses of MAsIII, and particularly DMAsIII with total arsenic recoveries ≤25%. Further analyses showed that MAsIII and DMAsIII bind to AS3MT or interact with other components of the methylation mixture, forming complexes that do not elute from the column. Oxidation of the mixture with H2O2 which converted trivalent arsenicals to their pentavalent analogs prior to HPLC separation increased total arsenic recoveries to ∼95%. In contrast, HG-CT-AAS analysis found large quantities of methylated trivalent arsenicals in mixtures incubated with either iAsIII or MAsIII and provided high (≥72%) arsenic recoveries. These data suggest that an HPLC-based analysis of biological samples can underestimate MAsIII and DMAsIII concentrations and that controlling for arsenic species recovery is essential to avoid artifacts.

  • Methylation of arsenic by recombinant human wild-type arsenic (+3 oxidation state) methyltransferase and its methionine 287 threonine (M287T) polymorph: Role of glutathione.
    Toxicology and applied pharmacology, 2012
    Co-Authors: Lan Ding, Zuzana Drobna, David J. Thomas, R. Jesse Saunders, Felecia S. Walton, Pencheng Xun, Miroslav Styblo
    Abstract:

    Arsenic (+3 oxidation state) methyltransferase (AS3MT) is the key enzyme in the pathway for methylation of arsenicals. A common polymorphism in the AS3MT gene that replaces a threonyl residue in position 287 with a methionyl residue (AS3MT/M287T) occurs at a frequency of about 10% among populations worldwide. Here, we compared catalytic properties of recombinant human wild-type (wt) AS3MT and AS3MT/M287T in reaction mixtures containing S-adenosylmethionine, arsenite (iAs(III)) or methylarsonous Acid (MAs(III)) as substrates and endogenous or synthetic reductants, including glutathione (GSH), a thioredoxin reductase (TR)/thioredoxin (Trx)/NADPH reducing system, or tris (2-carboxyethyl) phosphine hydrochloride (TCEP). With either TR/Trx/NADPH or TCEP, wtAS3MT or AS3MT/M287T catalyzed conversion of iAs(III) to MAs(III), methylarsonic Acid (MAs(V)), Dimethylarsinous Acid (DMAs(III)), and dimethylarsinic Acid (DMAs(V)); MAs(III) was converted to DMAs(III) and DMAs(V). Although neither enzyme required GSH to support methylation of iAs(III) or MAs(III), addition of 1mM GSH decreased K(m) and increased V(max) estimates for either substrate in reaction mixtures containing TR/Trx/NADPH. Without GSH, V(max) and K(m) values were significantly lower for AS3MT/M287T than for wtAS3MT. In the presence of 1mM GSH, significantly more DMAs(III) was produced from iAs(III) in reactions catalyzed by the M287T variant than in wtAS3MT-catalyzed reactions. Thus, 1mM GSH modulates AS3MT activity, increasing both methylation rates and yield of DMAs(III). AS3MT genotype exemplified by differences in regulation of wtAS3MT and AS3MT/M287T-catalyzed reactions by GSH may contribute to differences in the phenotype for arsenic methylation and, ultimately, to differences in the disease susceptibility in individuals chronically exposed to inorganic arsenic.

  • molecular mechanisms of the diabetogenic effects of arsenic inhibition of insulin signaling by arsenite and methylarsonous Acid
    Environmental Health Perspectives, 2007
    Co-Authors: David S Paul, Vicenta Devesa, David J. Thomas, Anne W Harmon, Miroslav Styblo
    Abstract:

    Arsenic (As) is a naturally occurring toxic metalloid and a potent human carcinogen [International Agency for Research on Cancer (IARC) 1987]. The cancer-promoting effects of environmental exposures to inorganic arsenic (iAs) have been examined by epidemiologic studies and in laboratory experiments. Much less attention has been paid to the adverse effects of iAs that do not involve malignancies. Epidemiologic evidence suggests that type 2 (noninsulin dependent) diabetes mellitus may be one of the most common noncancerous diseases associated with chronic exposures to iAs. Increased prevalences of type 2 diabetes or symptoms consistent with this disease have been associated with the consumption of drinking water containing high levels of iAs (Chen et al. 1995; Lai et al. 1994; Rahman et al. 1998, 1999; Tseng et al. 2000, 2002; Wang et al. 2003) or with chronic exposures to iAs in occupational settings (Jensen and Hansen 1998; Rahman and Axelson 1995; Rahman et al. 1996). Although not all epidemiologic studies support the association between iAs exposure and diabetes (Navas-Acien et al. 2006), the existing evidence provides sufficient basis for investigation of the diabetogenic effects of iAs. Type 2 diabetes is characterized by disruptions in whole-body glucose homeostasis due to insulin resistance and impaired glucose utilization by peripheral tissues, including skeletal muscle and adipose tissue. The insulin-dependent activation of glucose uptake in these tissues is one of the key mechanisms that regulates glucose homeostasis. The insulin-activated signal transduction mechanism that stimulates glucose uptake by adipocytes has been extensively studied. It includes the autophosphorylation of the β-subunit of the insulin receptor (IRβ) upon binding of insulin to the α-subunit of the receptor (IRα), the subsequent tyrosine phosphorylation of insulin receptor substrate 1 or 2 (IRS-1 or -2), and the binding of a phosphorylated IRS (p-IRS) to the regulatory (p85) subunit of the class IA phosphatidylinositol 3-kinase (PI-3K) that leads to the activation of its catalytic (p110) subunit. The activated PI-3K catalyzes the phosphorylation of phosphatidylinositol-4,5-bisphosphate (PIP2) at the plasma membrane to phosphatidylinositol-3,4,5-triphosphate (PIP3) (Farese 2001; Ruderman et al. 1990; White and Kahan 1994). PIP3 facilitates 3-phosphoinositide-dependent kinase-1/2 (PDK-1/2) dependent phosphorylation/activation of protein kinase B (PKB/Akt) and two atypical enzymes of the protein kinase C (PKC) family, PKCλ and ζ (Chou et al. 1998; Le Good et al. 1998; Standaert et al. 1997). The phosphorylation of PKB/Akt results in the translocation of intracellular vesicles containing glucose transporter-4 (GLUT4) from the perinuclear region to the plasma membrane and in the stimulation of glucose uptake (Kohn et al. 1996a; Tanti et al. 1997). In addition to phosphorylated PKB/Akt (p-PKB/Akt), phosphorylated PKCλ (p-PKCλ), and PKCζ (p-PKCζ) are thought to participate in the stimulation of GLUT4 translocation in response to insulin signaling (Elmendorf and Pessin 1999; Ruderman et al. 1990). The mechanism by which p-PKB/Akt, p-PKCλ and ζ induce the translocation and fusion of GLUT4-containing vesicles with the plasma membrane, as well as the degree to which each of these kinases participates in this event, are unclear. Recent studies have indicated that the PI-3K-dependent rearrangement of actin filaments (Patel et al. 2003) and activation of the microtubule-associated motor protein kinesin (Imamura et al. 2003) contribute to the translocation of GLUT4 to the plasma membrane. The disruption of cytoskeletal components may represent a potential mechanism by which As exposure inhibits insulin-stimulated glucose uptake (ISGU). Notably, As has been shown to bind to actin and tubulin in human lymphoblastoid cells (Menzel et al. 1999) and to inhibit the cytoskeletal protein synthesis in Swiss 3T3 mouse cells (Li and Chou 1992). The mechanisms by which exposure to iAs may induce impaired glucose tolerance have not been systematically studied. Data on the effects of As on glucose homeostasis have been generated almost exclusively in studies that examined the metabolism of nutrients under severe stress induced by chemical or physical stimuli. Results of in vitro studies have consistently shown significant increases in basal (insulin-independent) glucose uptake by various types of cells or dissected tissues exposed to cytotoxic concentrations of a trivalent iAs, arsenite (iAsIII), or an aromatic derivative of AsIII, phenylarsine oxide (PAO) (Bazuine et al. 2003, 2004; Brazy et al. 1980; McDowell et al. 1997; Pasternak et al. 1991; Short 1965; Sviderskaya et al. 1996; Widnell et al. 1990). Consistent with these findings, some in vivo studies have reported moderate or severe hypoglycemia in animals chronically exposed to toxic, often lethal, concentrations of iAsIII or arsenate (iAsV), in drinking water (Hughes and Thompson 1996; Pal and Chatterjee 2004a, 2004b, 2005). Only limited information is available on the effects of arsenicals on glucose metabolism at low concentrations that are compatible with environmental or occupational exposures. Micromolar concentrations of PAO have been shown to inhibit basal or ISGU by cultured cells (Liebl et al. 1992, 1995) and by intact skeletal muscle (Henriksen and Holloszy 1990; Sowell et al. 1988). PAO did not interfere with the insulin-dependent phosphorylation of IRβ and did not interact directly with glucose transporters (Frost and Lane 1985; Frost et al. 1987). The effects of physiologically relevant arsenicals on insulin-stimulated glucose metabolism have only recently been examined in this laboratory (Walton et al. 2004). We have shown that iAsIII and the products of iAs methylation in humans, methylarsonous Acid (MAsIII), and Dimethylarsinous Acid (DMAsIII) (Thomas et al. 2001), inhibit ISGU by 3T3-L1 adipocytes at concentrations that do not affect cell viability. Exposures to these arsenicals did not prevent IRβ and IRS phosphorylation or formation of the PI-3K–p-IRS complex. However, both iAsIII and MAsIII inhibited the insulin-dependent phosphorylation of PKB/Akt that mediates ISGU in adipocytes. In contrast, DMAsIII did not inhibit PKB/Akt phosphorylation, suggesting that this metabolite of iAs inhibits ISGU by a PKB/Akt-independent mechanism. In the present study we examined the molecular mechanisms of ISGU inhibition by iAsIII and MAsIII, focusing mainly on the components of the insulin-activated signal transduction pathway that regulate PKB/Akt phosphorylation in adipocytes. Results of this work show that iAsIII and MAsIII inhibit PDK-1 activity, thus suppressing PDK-1–catalyzed phosphorylation of PKB/Akt and p-PKB/Akt–mediated translocation of GLUT4 transporters to the plasma membrane. Notably, MAsIII was an order of magnitude more potent than iAsIII as an inhibitor of the PDK-1/PKB/Akt signal transduction step and of glucose uptake in insulin-stimulated adipocytes. Thus, the formation of MAsIII in the methylation pathway for iAs may play a critical role in determining the extent of the diabetogenic effects associated with chronic exposures to iAs.

  • comprehensive analysis of arsenic metabolites by ph specific hydride generation atomic absorption spectrometry
    Journal of Analytical Atomic Spectrometry, 2004
    Co-Authors: Vicenta Devesa, Miroslav Styblo, Zuzana Drobna, Stephen B. Waters, Blakely M Adair, Luz M Del Razo, Michael F Hughes, David J. Thomas
    Abstract:

    In a variety of biological systems, inorganic arsenic (iAs) is metabolized to yield methylated arsenicals that contain arsenic in +5 or +3 oxidation states. Atomic absorption spectrometry (AAS) coupled with a pH-specific generation of arsines has been used for selective analysis of trivalent and pentavalent inorganic, mono-, and dimethylated arsenicals in biological matrices. We have optimized this method to permit simultaneous detection and quantification of all relevant metabolites of iAs, including trimethylarsine oxide (TMAsVO). The optimization includes increasing the density of the chromatographic adsorbent used for cold-trapping of generated arsines and modification of the temperature gradient for release of arsines from the cold trap. These modifications improve the boiling-point separation of arsine, methylarsine, dimethylarsine, and trimethylarsine before the detection by AAS. Arsines from trivalent arsenicals and from TMAsVO are selectively generated at pH 6. At pH 1, arsines are generated from both tri- and pentavalent arsenicals. Thus, the optimized technique permits analysis of arsenite (iAsIII), arsenate (iAsV), monomethylarsonic Acid (MAsV), monomethylarsonous Acid (MAsIII), dimethylarsinic Acid (DMAsV), Dimethylarsinous Acid (DMAsIII), and TMAsVO. The detection limits range from 0.14 ng As (for TMAsVO) to 0.40 ng As (for iAsV). Calibration curves are linear over the concentration range of 0.5–100 ng As. Recoveries vary between 85 and 124%. The precision of the method in various biological matrices ranges from 1.0 to 14.5%. Using the optimized technique, both trivalent and pentavalent methylated and dimethylated arsenicals, but not TMAsVO, have been detected in cultured primary human hepatocytes exposed to iAsIII. In contrast, TMAsVO was detected as the final product of in vitro methylation of iAsIII by rat AsIII-methyltransferase, cyt19. TMAsVO was also detected in the urine of mice treated with MAsV or DMAsV. Thus, the optimized method improves the efficiency of arsenic speciation analysis in biological matrices, providing a more comprehensive picture of the role of metabolism in the disposition and action of iAs.

  • methylated metabolites of arsenic trioxide are more potent than arsenic trioxide as apoptotic but not differentiation inducers in leukemia and lymphoma cells
    Cancer Research, 2003
    Co-Authors: Guoqiang Chen, Miroslav Styblo, Felecia S. Walton, Li Zhou, Yongkui Jing, Rona Singer Weinberg, Zhu Chen, Samuel Waxman
    Abstract:

    Treatment with arsenic trioxide (As2O3) by inducing apoptosis and partial differentiation of acute promyelocytic leukemia (APL) cells results in clinical remission in APL patients resistant to chemotherapy and all-trans-retinoic Acid. As2O3 (iAs III ) is methylated in the liver to monoand dimethylated metabolites, including methylarsonic Acid, methylarsonous Acid, dimethylarsinic Acid, and Dimethylarsinous Acid. Methylated trivalent metabolites that are potent cytotoxins, genotoxins, and enzyme inhibitors may contribute to the in vivo therapeutic effect of iAs III . Therefore, we compared the potency of iAs III and trivalent metabolites using chemical precursors of methylarsonous Acid and Dimethylarsinous Acid to induce differentiation, growth inhibition, and apoptosis. Methylarsine oxide (MAs III O) and to a lesser extent iododimethylarsine were more potent growth inhibitors and apoptotic inducers than iAs III in NB4 cells, an APL cell line. This was also observed in K562 human leukemia, lymphoma cell lines, and in primary culture of chronic lymphocytic leukemia cells, but not human bone marrow progenitor cells. Apoptosis was associated with greater hydrogen peroxide accumulation and inhibition of glutathione peroxidase activity. MAs III O, in contrast to iAs III , did not induce PML-retinoic Acid receptor degradation, or restore PML nuclear bodies or differentiation in NB4 cells. In a cocultivation experiment, hepatoma-derived HepG2 cells, but not NB4 cells, methylate radiolabeled iAs III . Methylated metabolites released from HepG2 cells are preferentially accumulated by NB4 cells. This experimental model suggests that in vivo hepatic methylation of iAs III may contribute to As2O3induced apoptosis but not differentiation of APL cells. MAs III Oa s an apoptotic inducer should be considered in the treatment of other hematologic malignancies like lymphoma.

Michael W Carew - One of the best experts on this subject based on the ideXlab platform.

  • multidrug resistance protein 1 mrp1 abcc1 mediated cellular protection and transport of methylated arsenic metabolites differs between human cell lines
    Drug Metabolism and Disposition, 2018
    Co-Authors: Mayukh Banerjee, Michael W Carew, Brayden D Whitlock, Gurnit Kaur, Elaine M Leslie
    Abstract:

    The ATP-binding cassette (ABC) transporter multidrug resistance protein 1 (MRP1/ABCC1) protects cells from arsenic (a proven human carcinogen) through the cellular efflux of arsenic triglutathione [As(GS)3] and the diglutathione conjugate of monomethylarsonous Acid [MMA(GS)2]. Previously, differences in MRP1 phosphorylation (at Y920/S921) and N-glycosylation (at N19/N23) were associated with marked differences in As(GS)3 transport kinetics between HEK293 and HeLa cell lines. In the current study, cell line differences in MRP1-mediated cellular protection and transport of other arsenic metabolites were explored. MRP1 expressed in HEK293 cells reduced the toxicity of the major urinary arsenic metabolite dimethylarsinic Acid (DMAV), and HEK-WT-MRP1-enriched vesicles transported DMAV with high apparent affinity and capacity (Km 0.19 µM, Vmax 342 pmol⋅mg-1protein⋅min-1). This is the first report that MRP1 is capable of exporting DMAV, critical for preventing highly toxic Dimethylarsinous Acid formation. In contrast, DMAV transport was not detected using HeLa-WT-MRP1 membrane vesicles. MMA(GS)2 transport by HeLa-WT-MRP1 vesicles had a greater than threefold higher Vmax compared with HEK-WT-MRP1 vesicles. Cell line differences in DMAV and MMA(GS)2 transport were not explained by differences in phosphorylation at Y920/S921. DMAV did not inhibit, whereas MMA(GS)2 was an uncompetitive inhibitor of As(GS)3 transport, suggesting that DMAV and MMA(GS)2 have nonidentical binding sites to As(GS)3 on MRP1. Efflux of different arsenic metabolites by MRP1 is likely influenced by multiple factors, including cell and tissue type. This could have implications for the impact of MRP1 on both tissue-specific susceptibility to arsenic-induced disease and tumor sensitivity to arsenic-based therapeutics.

  • a novel pathway for arsenic elimination human multidrug resistance protein 4 mrp4 abcc4 mediates cellular export of dimethylarsinic Acid dmav and the diglutathione conjugate of monomethylarsonous Acid mmaiii
    Molecular Pharmacology, 2014
    Co-Authors: Mayukh Banerjee, Hua Naranmandura, Michael W Carew, Barbara A Roggenbeck, Brayden D Whitlock, Elaine M Leslie
    Abstract:

    Hundreds of millions of people worldwide are exposed to unacceptable levels of arsenic in drinking water. This is a public health crisis because arsenic is a Group I (proven) human carcinogen. Human cells methylate arsenic to monomethylarsonous Acid (MMA(III)), monomethylarsonic Acid (MMA(V)), Dimethylarsinous Acid (DMA(III)), and dimethylarsinic Acid (DMA(V)). Although the liver is the predominant site for arsenic methylation, elimination occurs mostly in urine. The protein(s) responsible for transport of arsenic from the liver (into blood), ultimately for urinary elimination, are unknown. Human multidrug resistance protein 1 (MRP1/ABCC1) and MRP2 (ABCC2) are established arsenic efflux pumps, but unlike the related MRP4 (ABCC4) are not present at the basolateral membrane of hepatocytes. MRP4 is also found at the apical membrane of renal proximal tubule cells, making it an ideal candidate for urinary arsenic elimination. In the current study, human MRP4 expressed in HEK293 cells reduced the cytotoxicity and cellular accumulation of arsenate, MMA(III), MMA(V), DMA(III), and DMA(V) while two other hepatic basolateral MRPs (MRP3 and MRP5) did not. Transport studies with MRP4-enriched membrane vesicles revealed that the diglutathione conjugate of MMA(III), monomethylarsenic diglutathione [MMA(GS)(2)], and DMA(V) were the transported species. MMA(GS)(2) and DMA(V) transport was osmotically sensitive, allosteric (Hill coefficients of 1.4 ± 0.2 and 2.9 ± 1.2, respectively), and high affinity (K0.5 of 0.70 ± 0.16 and 0.22 ± 0.15 μM, respectively). DMA(V) transport was pH-dependent, with highest affinity and capacity at pH 5.5. These results suggest that human MRP4 could be a major player in the elimination of arsenic.

  • monomethylarsenic diglutathione transport by the human multidrug resistance protein 1 mrp1 abcc1
    Drug Metabolism and Disposition, 2011
    Co-Authors: Michael W Carew, Hua Naranmandura, Caley B Shukalek, Elaine M Leslie
    Abstract:

    The ATP-binding cassette (ABC) transporter protein multidrug resistance protein 1 (MRP1; ABCC1) plays an important role in the cellular efflux of the high-priority environmental carcinogen arsenic as a triglutathione conjugate [As(GS)(3)]. Most mammalian cells can methylate arsenic to monomethylarsonous Acid (MMA(III)), monomethylarsonic Acid (MMA(V)), Dimethylarsinous Acid (DMA(III)), and dimethylarsinic Acid (DMA(V)). The trivalent forms MMA(III) and DMA(III) are more reactive and toxic than their inorganic precursors, arsenite (As(III)) and arsenate (As(V)). The ability of MRP1 to transport methylated arsenicals is unknown and was the focus of the current study. HeLa cells expressing MRP1 (HeLa-MRP1) were found to confer a 2.6-fold higher level of resistance to MMA(III) than empty vector control (HeLa-vector) cells, and this resistance was dependent on GSH. In contrast, MRP1 did not confer resistance to DMA(III), MMA(V), or DMA(V). HeLa-MRP1 cells accumulated 4.5-fold less MMA(III) than HeLa-vector cells. Experiments using MRP1-enriched membrane vesicles showed that transport of MMA(III) was GSH-dependent but not supported by the nonreducing GSH analog, ophthalmic Acid, suggesting that MMA(III)(GS)(2) was the transported form. MMA(III)(GS)(2) was a high-affinity, high-capacity substrate for MRP1 with apparent K(m) and V(max) values of 11 μM and 11 nmol mg(-1)min(-1), respectively. MMA(III)(GS)(2) transport was osmotically sensitive and inhibited by several MRP1 substrates, including 17β-estradiol 17-(β-D-glucuronide) (E(2)17βG). MMA(III)(GS)(2) competitively inhibited the transport of E(2)17βG with a K(i) value of 16 μM, indicating that these two substrates have overlapping binding sites. These results suggest that MRP1 is an important cellular protective pathway for the highly toxic MMA(III) and have implications for environmental and clinical exposure to arsenic.

  • comparative toxicity of arsenic metabolites in human bladder cancer ej 1 cells
    Chemical Research in Toxicology, 2011
    Co-Authors: Hua Naranmandura, Michael W Carew, Elaine M Leslie, Jane Lee, Michael Weinfeld
    Abstract:

    The human bladder is one of the primary target organs for arsenic-induced carcinogenicity, and arsenic metabolites in urine have been suspected to be directly involved in carcinogenesis. Thioarsenicals are commonly found in human and animal urine and are also considered to be highly toxic arsenic metabolites. The present study was performed to gain insight into the toxicity and accumulation of arsenic species found in urine, including arsenate (iAs(V)), arsenite (iAs(III)), monomethylarsonic Acid (MMA(V)), monomethylmonothioarsonic Acid (MMMTA(V)), dimethylarsinic Acid (DMA(V)), Dimethylarsinous Acid (DMA(III)), dimethylmonothioarsinic Acid, (DMMTA(V)), and dimethyldithioarsinic Acid (DMDTA(V)) in human bladder cancer EJ-1 cells. The order of cytotoxicity of these arsenic compounds in EJ-1 human bladder cancer cells was DMA(III), DMMTA(V) > iAs(III) ≫ iAs(V) > MMMTA(V) > MMA(V), DMA(V), and DMDTA(V), indicating that the sulfur-containing DMMTA(V) was among the most toxic arsenic compounds similar to trivalent DMA(III). We further characterized the DNA damage, generation of highly reactive oxygen species (hROS), and expression of proteins p21 and p53 in cells after exposure to iAs(III), DMA(III), and DMMTA(V). Cellular exposure to DMMTA(V) resulted in reduced protein expression of p53 and p21, increased DNA damage, and increased intracellular hROS (hydroxyl radical). In contrast, iAs(III) significantly increased the protein expression of p21 and p53 and did not increase the hROS at the IC(50). Intracellular glutathione (GSH) was reduced by 60% after exposure to DMA(III) or DMMTA(V), suggesting that DMMTA(V) causes cell death through oxidative stress. In contrast, GSH levels increased in cells exposed to iAs(III), and hROS only increased after a long exposure to iAs(III). Our findings demonstrate that DMMTA(V) may be one of the most toxicologically potent arsenic species, relevant to arsenic-induced carcinogenicity in the urinary bladder.

Lora L Arnold - One of the best experts on this subject based on the ideXlab platform.

  • Arsenic Speciation in the Blood of Arsenite-Treated F344 Rats
    2016
    Co-Authors: Baowei Chen, Lora L Arnold, Shengwen Shen, Samuel M. Cohen
    Abstract:

    Arsenic speciation in blood can improve understanding of the metabolism and toxicity of arsenic. In this study, arsenic species in the plasma and red blood cells (RBCs) of arsenite-treated female F344 rats were characterized using anion exchange and size exclusion chromatography separation with inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESI MS/MS) detection. Arsenite (iAsIII), arsenate (iAsV), monomethylarsonic Acid (MMAV), dimethylarsinic Acid (DMAV), trimethylarsine oxide (TMAOV), monomethylmonothioarsonic Acid (MMMTAV), and dimethylmonothioarsinic Acid (DMMTAV) were detected in the plasma, with DMAV being the predominant metabolite. Upon oxidative pretreatment with 5% hydrogen peroxide (H2O2), plasma proteins released bound arsenic in the form of DMAV as the major species and MMAV as the minor species. The ratio of protein-bound arsenic to total arsenic decreased with increasing dosage of iAsIII administered to the rats, suggesting a possible saturation of the binding capacity of the plasma proteins. The proportion of the protein-bound arsenic in the plasma varied among rats. In the H2O2-treated lysates of red blood cells of rats, DMAV was consistently found as the predominant arsenic species, probably reflecting the preferential binding of Dimethylarsinous Acid (DMAIII) to rat hemoglobin. iAsV, MMAV, and trimethylarsine oxide (TMAOV) were also detected in the hydrogen peroxide-treated lysates of red blood cells. Importantly, DMMTAV and MMMTAV have not been reported in rat blood, and the present finding of DMMTAV and MMMTAV in the rat plasma is toxicologically relevant because these pentavalent thioarsenicals are more toxic than their counterparts DMAV and MMAV. Identifying novel thiolated arsenicals and determining protein-bound arsenicals in the blood provide useful insights into the metabolism and toxicity of arsenic in animals

  • effect of dietary treatment with Dimethylarsinous Acid dmaiii on the urinary bladder epithelium of arsenic 3 oxidation state methyltransferase as3mt knockout and c57bl 6 wild type female mice
    Toxicology, 2013
    Co-Authors: Puttappa R Dodmane, Lora L Arnold, Karen L Pennington, David J. Thomas, Samuel Monroe Cohen
    Abstract:

    Abstract Chronic exposure to inorganic arsenic (iAs) is carcinogenic to the human urinary bladder. It produces urothelial cytotoxicity and proliferation in rats and mice. DMA V , a major methylated urinary metabolite of iAs, is a rat bladder carcinogen, but without effects on the mouse urothelium. DMA III was shown to be the likely urinary metabolite of DMA V inducing urothelial changes and is also postulated to be one of the active metabolites of iAs. To evaluate potential DMA III -induced urothelial effects, it was administered to As3mt knockout mice which cannot methylate arsenicals. Female C57BL/6 wild type and As3mt knockout mice (10/group) were administered DMA III , 77.3 ppm in water for four weeks. Urothelial effects were evaluated by light and scanning electron microscopy (EM) and immunohistochemical detection of bromodeoxyuridine (BrdU) incorporation. EM findings were rated 1–5, with higher rating indicating greater extent of cytotoxicity visualized. DMA III significantly increased the BrdU labeling index, a ratio of BrdU labeled cells to non-labeled cells, in the treated knockout group compared to control and wild type treated groups. DMA III induced simple hyperplasia in more knockout mice (4/10) compared to wild type mice (2/10). All treated knockout mice had more and larger intracytoplasmic granules compared to the treated wild type mice. Changes in EM classification were not significant. In conclusion, DMA III induces urothelial toxicity and regenerative hyperplasia in mice and most likely plays a role in inorganic arsenic-induced urothelial changes. However, DMA V does not induce hyperplasia in mice, suggesting that urinary concentrations of DMA III do not reach cytotoxic levels in DMA V -treated mice.

  • dietary administration of sodium arsenite to rats relations between dose and urinary concentrations of methylated and thio metabolites and effects on the rat urinary bladder epithelium
    Toxicology and Applied Pharmacology, 2010
    Co-Authors: Shugo Suzuki, Chris X Le, Lora L Arnold, Karen L Pennington, Baowei Chen, Hua Naranmandura, Samuel Monroe Cohen
    Abstract:

    Abstract Based on epidemiological data, chronic exposure to high levels of inorganic arsenic in drinking water is carcinogenic to humans, inducing skin, urinary bladder and lung tumors. In vivo , inorganic arsenic is metabolized to organic methylated arsenicals including the highly toxic Dimethylarsinous Acid (DMA III ) and monomethylarsonous Acid (MMA III ). Short-term treatment of rats with 100 μg/g trivalent arsenic (As III ) as sodium arsenite in the diet or in drinking water induced cytotoxicity and necrosis of the urothelial superficial layer, with increased cell proliferation and hyperplasia. The objectives of this study were to determine if these arsenic-induced urothelial effects are dose responsive, the dose of arsenic at which urothelial effects are not detected, and the urinary concentrations of the arsenical metabolites. We treated female F344 rats for 5 weeks with sodium arsenite at dietary doses of 0, 1, 10, 25, 50, and 100 ppm. Cytotoxicity, cell proliferation and hyperplasia of urothelial superficial cells were increased in a dose-responsive manner, with maximum effects found at 50 ppm As III . There were no effects at 1 ppm As III . The main urinary arsenical in As III -treated rats was the organic arsenical dimethylarsinic Acid (DMA V ). The thio-metabolites dimethylmonothioarsinic Acid (DMMTA V ) and monomethylmonothioarsinic Acid (MMMTA V ) were also found in the urine of As III -treated rats. The LC 50 concentrations of DMMTA V for rat and human urothelial cells in vitro were similar to trivalent oxygen-containing arsenicals. These data suggest that dietary As III -induced urothelial cytotoxicity and proliferation are dose responsive, and the urothelial effects have a threshold corresponding to the urinary excretion of measurable reactive metabolites.

  • effects of co administration of dietary sodium arsenite and an nadph oxidase inhibitor on the rat bladder epithelium
    Toxicology, 2009
    Co-Authors: Shugo Suzuki, Lora L Arnold, Karen L Pennington, Satoko Kakiuchikiyota, Samuel Monroe Cohen
    Abstract:

    Abstract Arsenite (As III ), an inorganic arsenical, is a known human carcinogen, inducing tumors of the skin, urinary bladder and lung. It is metabolized to organic methylated arsenicals. Oxidative stress has been suggested as a mechanism for arsenic-induced carcinogenesis. Reactive oxygen species (ROS) can be important factors for carcinogenesis and tumor progression. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is known to produce intracellular ROS, therefore, we investigated the ability of apocynin (acetovanillone), an NADPH oxidase inhibitor, to inhibit the cytotoxicity and regenerative cell proliferation of arsenic in vitro and in vivo . Apocynin had similar effects in reducing the cytotoxicity of As III and Dimethylarsinous Acid (DMA III ) in rat urothelial cells in vitro . When tested at the same concentrations as apocynin, other antioxidants, such as l -ascorbate and N-acetylcysteine, did not inhibit As III -induced cytotoxicity but they were more effective at inhibiting DMA III -induced cytotoxicity compared with apocynin. In vivo , female rats were treated for 3 weeks with 100 ppm As III . Immunohistochemical staining for 8-hydroxy-2′-deoxyguanosine (8-OHdG) showed that apocynin reduced oxidative stress partially induced by As III treatment on rat urothelium, and significantly reduced the cytotoxicity of superficial cells detected by scanning electron microscopy (SEM). However, based on the incidence of simple hyperplasia and the bromodeoxyuridine (BrdU) labeling index, apocynin did not inhibit As III -induced urothelial cell proliferation. These data suggest that the NADPH oxidase inhibitor, apocynin, may have the ability to partially inhibit arsenic-induced oxidative stress and cytotoxicity of the rat bladder epithelium in vitro and in vivo . However, apocynin did not inhibit the regenerative cell proliferation induced by arsenite in a short-term study.

  • effects of an epidermal growth factor receptor inhibitor on arsenic associated toxicity in the rat bladder epithelium
    Toxicology Letters, 2009
    Co-Authors: Shugo Suzuki, Chris X Le, Lora L Arnold, Karen L Pennington, Baowei Chen, Samuel Monroe Cohen
    Abstract:

    Abstract Arsenite (AsIII), an inorganic arsenical, is a known human carcinogen, inducing tumors of the skin, urinary bladder and lung. It is known to be metabolized to organic methylated arsenicals in vivo. AsIII has been reported to have the ability to up-regulate the epidermal growth factor receptor (EGFR)-associated pathway in epithelial cells, including human urothelial cells in vitro. EGFR is a cell-surface receptor belonging to the ErbB family of receptor tyrosine kinases, and the EGFR-associated signaling pathway has been reported to play an important role in carcinogenesis and cancer progression, including in bladder cancer. In this study, we investigated the growth effects of AsIII and an organic trivalent arsenical, Dimethylarsinous Acid (DMAIII), and the effects of co-exposure of gefitinib, an EGFR inhibitor, with AsIII to a rat urothelial cell line (MYP3). We also investigated the effects of co-administration of dietary AsIII and gefitinib in vivo. In vitro, concentrations of 1.0 μM AsIII or 0.5 μM DMAIII induced cytotoxicity. However, lower concentrations of AsIII treatment had a slight mitogenic growth effect whereas lower concentrations of DMAIII did not. Gefitinib blocked AsIII-induced cell growth in vitro. In vivo, a high dose of gefitinib alone induced slight urothelial cytotoxicity, and did not reduce cytotoxicity and regenerative cell proliferation when co-administered with AsIII. The majority of arsenic metabolites present in the urine of AsIII-treated rats were organic arsenicals, mainly dimethylarsinic Acid (DMAV). AsIII was also present, and its concentration was higher than the concentration required to produce cytotoxicity in vitro. These data suggest that an EGFR inhibitor has the ability to block AsIII-induced cell proliferation in vitro but not in vivo in a short-term study.