Michael P Waalkes

National Institute of Environmental Health Sciences, Durham, North Carolina, United States

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Publications (322)1295.67 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Macrophage-solubilized indium-containing particles (ICPs) were previously shown in vitro to be cytotoxic. In this study, we compared macrophage solubilization and cytotoxicity of indium phosphide (InP) and indium tin-oxide (ITO) with similar particle diameters (~1.5 μm) and then determined if relative differences in these in vitro parameters correlated with pulmonary toxicity in vivo. RAW 264.7 macrophages were treated with InP or ITO particles and cytotoxicity was assayed at 24 hr. Ionic indium was measured in 24 hr culture supernatants. Macrophage cytotoxicity and particle solubilization in vitro were much greater for InP compared to ITO. To correlate changes in vivo, B6C3F1 mice were treated with InP or ITO by oropharyngeal aspiration. On days 14 and 28, bronchoalveolar lavage (BAL) and pleural lavage (PL) fluids were collected and assayed for total leukocytes. Cell differentials, LDH activity and protein levels were also measured in BAL. All lavage parameters were greatly increased in mice treated with InP compared to ITO. These data suggest that macrophage solubilization and cytotoxicity of some ICPs in vitro are capable of predicting pulmonary toxicity in vivo. In addition, these differences in toxicity were observed despite the two particulate compounds containing similar amounts of indium suggesting that solubilization, not total indium content, better reflects the toxic potential of some ICPs. Soluble InCl3 was shown to be more cytotoxic than InP to macrophages and lung epithelial cells in vitro further suggesting that ionic indium is the primary cytotoxic component of InP. Published by Oxford University Press on behalf of the Society of Toxicology 2014. This work is written by US Government employees and is in the public domain in the US.
    Toxicological sciences : an official journal of the Society of Toxicology. 12/2014;
  • Wei Qu, Michael P Waalkes
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    ABSTRACT: We studied how the protein metallothionein (MT) impacts arsenic-induced oxidative DNA damage (ODD) using cells that poorly express MT (MT-I/II double knockout embryonic cells; called MT-null cells) and wild-type (WT) MT competent cells. Arsenic (as NaAsO2) was less cytolethal over 24h in WT cells (LC50=11.0±1.3μM; mean±SEM) than in MT-null cells (LC50=5.6±1.2μM). ODD was measured by the immuno-spin trapping method. Arsenic (1 or 5μM; 24h) induced much less ODD in WT cells (121% and 141% of control, respectively) than in MT-null cells (202% and 260%). In WT cells arsenic caused concentration-dependent increases in MT expression (transcript and protein), and in the metal-responsive transcription factor-1 (MTF-1), which is required to induce the MT gene. In contrast, basal MT levels were not detectable in MT-null cells and unaltered by arsenic exposure. Transfection of MT-I into the MT-null cells markedly reduced arsenic-induced ODD levels. The transport genes, Abcc1 and Abcc2 were increased by arsenic in WT cells but either showed no or very limited increases in MT-null cells. Arsenic caused increases in oxidant stress defense genes HO-1 and GSTa2 in both WT and MT-null cells, but to much higher levels in WT cells. WT cells appear more adept at activating metal transport systems and oxidant response genes, although the role of MT in these responses is unclear. Overall, MT protects against arsenic-induced ODD in MT competent cells by potentially sequestration of scavenging oxidant radicals and/or arsenic. Copyright © 2014. Published by Elsevier Inc.
    Toxicology and Applied Pharmacology 12/2014; · 3.98 Impact Factor
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    ABSTRACT: It is proposed that cadmium (Cd) is an environmental "metalloestrogen" and its action is mediated via the estrogen receptor (ER). Cd mimics the effects of estrogen in the rat uterus, and blood Cd concentrations positively correlate with ER levels in uteri of women with fibroids.
    Environmental Health Perspectives 10/2014; · 7.26 Impact Factor
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    ABSTRACT: Inorganic arsenic is a human carcinogen that likely targets the prostate. Chronic arsenic exposure malignantly transforms the RWPE-1 human prostate epithelial line to CAsE-PE cells, and a derivative normal prostate stem cell (SC) line, WPE-stem to arsenic-cancer SCs (As-CSCs). The KRAS oncogene is highly overexpressed in CAsE-PE cells and activation precedes transformation, inferring mechanistic significance. As-CSCs also highly overexpress KRAS. Thus, we hypothesize KRAS activation is key in causing and maintaining an arsenic-induced malignant phenotype, and hence, KRAS knockdown (KD) may reverse this malignant phenotype. RNA interference using shRNAmirs to obtain KRAS KD was used in CAsE-PE and As-CSC cells. Cells analyzed 2 weeks post transduction showed KRAS protein decreased to 5% of control after KD, confirming stable KD. KRAS KD decreased phosphorylated ERK, indicating inhibition of RAS/ERK signaling, a proliferation/survival pathway activated with arsenic transformation. Secreted metalloproteinase (MMP) activity was increased by arsenic-induced malignant transformation, but KRAS KD from 4 weeks on decreased secreted MMP-9 activity by 50% in As-CSCs. Colony formation, a characteristic of cancer cells, was decreased in both KRAS KD transformants. KRAS KD also decreased the invasive capacity of both cell types. KRAS KD decreased proliferation in As-CSCs, consistent with loss of rapid tumor growth. Genes predicted to impact cell proliferation (e.g. Cyclin D1, p16, and p21) changed accordingly in both KD cell types. Thus, KRAS silencing impacts aspects of arsenic-induced malignant phenotype, inducing loss of many typical cancer characteristics particularly in As-CSCs.
    Toxicological sciences : an official journal of the Society of Toxicology. 09/2014;
  • Archives of toxicology. 09/2014;
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    ABSTRACT: In mice, inorganic arsenic in the drinking water in the parts per million range via the dam during in utero life or with whole-life exposure is a multi-site carcinogen in the offspring. However, human arsenic exposure is typically in the parts per billion (ppb) range. Thus, we studied "whole-life" inorganic arsenic carcinogenesis in mice at levels more relevant to humans. Breeder male and female CD1 mice were exposed to 0, 50, 500 or 5,000 ppb arsenic (as sodium arsenite) in the drinking water for 3 weeks prior to breeding, during pregnancy and lactation, and after weaning (at week 3) groups of male and female offspring (initial n = 40) were exposed for up to 2 years. Tumors were assessed in these offspring. Arsenic exposure had no effect on pregnant dam weights or water consumption, litter size, offspring birthweight or weight at weaning compared to control. In male offspring mice, arsenic exposure increased (p < 0.05) bronchiolo-alveolar tumor (adenoma or carcinoma) incidence at 50-ppb group (51 %) and 500-ppb group (54 %), but not at 5,000-ppb group (28 %) compared to control (22 %). These arsenic-induced bronchiolo-alveolar tumors included increased (p < 0.05) carcinoma at 50-ppb group (27 %) compared to controls (8 %). An increase (p < 0.05) in lung adenoma (25 %) in the 50-ppb group compared to control (11 %) occurred in female offspring. Thus, in CD1 mice whole-life arsenic exposure induced lung tumors at human-relevant doses (i.e., 50 and 500 ppb).
    Archives of toxicology. 07/2014;
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    ABSTRACT: Inorganic arsenic (iAs), a human carcinogen, potentially targets the prostate. iAs malignantly transforms the RWPE-1 human prostate epithelial line to CAsE-PE cells, and a derivative normal stem cell (SC) line, WPE-stem to As-Cancer SC (As-CSC) line. MicroRNAs (miRNA) are non-coding but exert negative control on expression by degradation or translational repression of target mRNAs. Aberrant miRNA expression is important in carcinogenesis. A miRNA array of CAsE-PE and As-CSC revealed common altered expression in both for pathways concerning oncogenesis, miRNA biogenesis, cell signaling, proliferation, and tumor metastasis and invasion. The KRAS oncogene is overexpressed in CAsE-PE cells but not by mutation or promoter hypomethylation, and is intensely overexpressed in As-CSC cells. In both transformants, decreased miRNAs targeting KRAS and RAS superfamily members occurred. Reduced miR-134, miR-373, miR-155, miR-138, miR-205, miR-181d, miR-181c, and let-7 in CAsE-PE cells correlated with increased target RAS oncogenes, RAN, RAB27A, RAB22A mRNAs and KRAS protein. Reduced miR-143, miR-34c-5p, and miR-205 in As-CSC correlated with increased target RAN mRNA, and KRAS, NRAS, and RRAS proteins. The RAS/ERK and PI3K/PTEN/AKT pathways control cell survival, differentiation, and proliferation, and when dysregulated promote a cancer phenotype. iAs transformation increased expression of activated ERK kinase in both transformants, and altered components of the PI3K/PTEN/AKT pathway including decreased PTEN, and increases in BCL2, BCL-XL, and VEGF in the absence of AKT activation. Thus, dysregulated miRNA expression may be linked to RAS activation in both transformants.
    Toxicological Sciences 01/2014; · 4.33 Impact Factor
  • North Carolina Society of Toxicology annual meeting, RTP, NC, USA; 11/2013
  • Erik J Tokar, Chikara Kojima, Michael P Waalkes
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    ABSTRACT: Inorganic arsenic (iAs) and its toxic methylated metabolite, methylarsonous acid (MMA(III)), both have carcinogenic potential. Prior study shows iAs-induced malignant transformation in both arsenic methylation-proficient (liver) and methylation-deficient (prostate) cells, but only methylation-proficient cells show oxidative DNA damage (ODD) during this transformation. To further define whether arsenic methylation is necessary for transformation or ODD induction, here we chronically exposed these same liver or prostate cell lines to MMA(III) (0.25-1.0 μM) and tested for acquired malignant phenotype. Various metrics of oncogenic transformation were periodically assessed along with ODD during chronic MMA(III) exposure. Methylation-deficient and methylation-proficient cells both acquired a cancer phenotype with MMA(III) exposure at about 20 weeks, based on increased matrix metalloproteinase secretion, colony formation, and invasion. In contrast, prior work showed iAs-induced transformation took longer in biomethylation-deficient cells (~30 weeks) than in biomethylation-proficient cells (~18 weeks). In the present study, MMA(III) caused similar peak ODD levels at similar concentrations and at similar exposure times (18-22 weeks) in both cell types. At the approximate peak of ODD production, both cell types showed similar alterations in arsenic and oxidative stress adaptation factors (i.e., ABCC1, ABCC2, GST-π, SOD-1). Thus, MMA(III) causes oncogenic transformation associated with ODD in methylation-deficient cells, indicating that further methylation is not required to induce ODD. Together, these results show that MMA(III) and iAs cause an acquired malignant phenotype in methylation-deficient cells, yet iAs does not induce ODD. This indicates iAs likely has both genotoxic and non-genotoxic mechanisms dictated by the target cell's ability to methylate arsenic.
    Archives of Toxicology 10/2013; · 5.22 Impact Factor
  • Yuanyuan Xu, Erik J Tokar, Michael P Waalkes
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    ABSTRACT: Accumulating data suggest arsenic may be an endocrine disruptor and tentatively linked to breast cancer by some studies. Therefore, we tested the effects of chronic inorganic arsenic exposure on the normal estrogen receptor (ER)-negative breast epithelial cell line, MCF-10A. Cells were chronically exposed to a low-level arsenite (500 nM) for up to 24 weeks. Markers of cancer cell phenotype and the expression of critical genes relevant to breast cancer or stem cells (SCs) were examined. After 24 weeks, chronic arsenic-exposed breast epithelial (CABE) cells showed increases in secreted MMP activity, colony formation, invasion, and proliferation rate, indicating an acquired cancer cell phenotype. These CABE cells presented with basal-like breast cancer characteristics, including ER-α, HER-2, and progesterone receptor negativity, and overexpression of K5 and p63. Putative CD44(+)/CD24(-/low) breast SCs were increased to 80 % over control in CABE cells. CABE cells also formed multilayer cell mounds, indicative of loss of contact inhibition. These mounds showed high levels of K5 and p63, indicating the potential presence of cancer stem cells (CSCs). Epithelial-to-mesenchymal transition occurred during arsenic exposure. Overexpression of aromatase, a key rate-limiting enzyme in estrogen synthesis, occurred with arsenic starting early on in exposure. Levels of 17β-estradiol increased in CABE cells and their conditioned medium. The aromatase inhibitor letrozole abolished arsenic-induced increases in 17β-estradiol production and reversed cancer cell phenotype. Thus, chronic arsenic exposure drives human breast epithelia into a cancer cell phenotype with an apparent overabundance of putative CSCs. Arsenic appears to transform breast epithelia through overexpression of aromatase, thereby activating oncogenic processes independent of ER.
    Archives of Toxicology 09/2013; · 5.22 Impact Factor
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    ABSTRACT: Genome-wide disruption of the epigenetic code is a hallmark of malignancy that encompasses many distinct, highly interactive modifications. Delineating the aberrant epigenome produced during toxicant-mediated malignant transformation will help identify the underlying epigenetic drivers of environmental toxicant-induced carcinogenesis. Gene promoter DNA methylation and gene expression profiling of arsenite-transformed prostate epithelial cells showed a negative correlation between gene expression changes and DNA methylation changes; however, less than 10% of the genes with increased promoter methylation were downregulated. Studies described herein confirm that a majority of the DNA hypermethylation events occur at H3K27me3 marked genes that were already transcriptionally repressed. In contrast to aberrant DNA methylation targeting H3K27me3 pre-marked silent genes, we found that actively expressed C2H2 zinc finger genes (ZNFs) marked with H3K9me3 on their 3' ends, were the favored targets of DNA methylation linked gene silencing. DNA methylation coupled, H3K9me3 mediated gene silencing of ZNF genes was widespread, occurring at individual ZNF genes on multiple chromosomes and across ZNF gene family clusters. At ZNF gene promoters, H3K9me3 and DNA hypermethylation replaced H3K4me3, resulting in a widespread downregulation of ZNF gene expression, which accounted for 8% of all the downregulated genes in the arsenical-transformed cells. In summary, these studies associate toxicant exposure with widespread silencing of ZNF genes by DNA hypermethylation-linked H3K9me3 spreading, further implicating epigenetic dysfunction as a driver of toxicant associated carcinogenesis.
    Epigenetics: official journal of the DNA Methylation Society 08/2013; 8(10). · 4.58 Impact Factor
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    ABSTRACT: Indium-containing particles (ICPs) are used extensively in the microelectronics industry. Pulmonary toxicity is observed after inhalation exposure to ICPs; however, the mechanism(s) of pathogenesis is unclear. ICPs are insoluble at physiological pH and are initially engulfed by alveolar macrophages (and likely airway epithelial cells). We hypothesized that uptake of ICPs by macrophages followed by phagolysosomal acidification results in the solubilization of ICPs into cytotoxic indium ions. To address this, we characterized the in vitro cytotoxicity of indium phosphide (InP) or indium tin-oxide (ITO) particles with macrophages (RAW cells) and lung-derived epithelial (LA-4) cells at 24 hours using metabolic (MTT) and membrane integrity (LDH) assays. InP and ITO were readily phagocytosed by RAW and LA-4 cells; however, the particles were much more cytotoxic to RAW cells and cytotoxicity was dose-dependent. Treatment of RAW cells with cytochalasin D blocked particle phagocytosis and reduced cytotoxicity. Treatment of RAW cells with bafilomycin A1, a specific inhibitor of phagolysosomal acidification, also reduced cytotoxicity but did not block particle uptake. Based on direct indium measurements, the concentration of ionic indium was increased in culture medium from RAW but not LA-4 cells following 24 hour treatment with particles. Ionic indium derived from RAW cells was significantly reduced by treatment with cytochalasin D. These data implicate macrophage uptake and solubilization of InP and ITO via phagolysosomal acidification as requisite for particle-induced cytotoxicity and the release of indium ions. This may apply to other ICPs and strongly supports the notion that ICPs require solubilization in order to be toxic.
    Toxicological Sciences 07/2013; · 4.33 Impact Factor
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    ABSTRACT: Cadmium is a known human lung carcinogen. Here, we attempt to develop an in vitro model of cadmium-induced human lung carcinogenesis by chronically exposing the peripheral lung epithelia cell line, HPL-1D, to a low level of cadmium. Cells were chronically exposed to 5 μM cadmium, a noncytotoxic level, and monitored for acquired cancer characteristics. By 20 weeks of continuous cadmium exposure, these chronic cadmium treated lung (CCT-LC) cells showed marked increases in secreted MMP-2 activity (3.5-fold), invasion (3.4-fold), and colony formation in soft agar (2-fold). CCT-LC cells were hyperproliferative, grew well in serum-free media, and overexpressed cyclin D1. The CCT-LC cells also showed decreased expression of the tumor suppressor genes p16 and SLC38A3 at the protein levels. Also consistent with an acquired cancer cell phenotype, CCT-LC cells showed increased expression of the oncoproteins K-RAS and N-RAS as well as the epithelial-to-mesenchymal transition marker protein Vimentin. Metallothionein (MT) expression is increased by cadmium, and is typically overexpressed in human lung cancers. The major MT isoforms, MT-1A and MT-2A were elevated in CCT-LC cells. Oxidant adaptive response genes HO-1 and HIF-1A were also activated in CCT-LC cells. Expression of the metal transport genes ZNT-1, ZNT-5, and ZIP-8 increased in CCT-LC cells culminating in reduced cadmium accumulation, suggesting adaptation to the metal. Overall, these data suggest that exposure of human lung epithelial cells to cadmium causes acquisition of cancer cell characteristics. Furthermore, transformation occurs despite the cell's ability to adapt to chronic cadmium exposure.
    Toxicology and Applied Pharmacology 06/2013; · 3.98 Impact Factor
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    ABSTRACT: BACKGROUND: Cancer stem cells (CSCs) drive tumor initiation, progression and metastasis. Microenvironment is critical to the fate of CSCs. We have found that a normal stem cell (NSC) line from human prostate (WPE-stem) is recruited into CSC-like cells by nearby, but noncontiguous arsenic-transformed isogenic malignant epithelial cells (MECs). OBJECTIVE: It is unknown if this recruitment of NSCs into CSCs by non-contact co-culture is specific to arsenic-transformed MECs. Thus, here, we tested the effects of neighboring noncontiguous cadmium-transformed MECs (Cd-MECs) and N-methyl-N-nitrosourea-transformed MECs (MNU-MECs) co-culture on NSCs. RESULTS: After two weeks of non-contact Cd-MEC co-culture, NSCs showed elevated metalloproteinase-9 (MMP-9) and MMP-2 secretion, increased invasiveness, increased colony formation, decreased PTEN expression and formation of aggressive, highly branched ductal-like structures from single cells in Matrigel, all characteristics typical of cancer cells. These oncogenic characteristics did not occur if NSCs were co-cultured with MNU-MECs. The NSCs co-cultured with Cd-MECs retained self-renewal capacity as evidenced by multiple passages (>3) of structures formed in Matrigel. Cd-MEC co-cultured NSCs also showed molecular (increased VIMENTIN, SNAIL1 and TWIST1 expression; decreased E-CADHERIN expression) and morphologic evidence of epithelial-to-mesenchymal transition typical for conversion to CSCs. Dysregulated expression of SC-renewal genes, including ABCG2, OCT-4 and WNT-3, also occurred in NSCs during oncogenic transformation induced by non-contact co-culture with Cd-MECs. CONCLUSIONS: These data indicate that Cd-MECs can recruit nearby NSCs into a CSC-like phenotype, but MNU-MECs do not. Thus, the recruitment of NSCs into CSCs by nearby MECs is dependent on the carcinogen originally used to malignantly transform the MECs.
    Environmental Health Perspectives 05/2013; · 7.26 Impact Factor
  • Society of Toxicology annual meeting, San Antonio, Texas, USA; 03/2013
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    ABSTRACT: Today's developed world faces a major public health challenge in the rise in the obese population and the increased incidence in fatty liver disease. There is a strong association among diet induced obesity, fatty liver disease and development of nonalcoholic steatohepatitis but the environmental link to disease progression remains unclear. Here we demonstrate that in obesity, early steatohepatitic lesions induced by the water disinfection byproduct bromodichloromethane are mediated by increased oxidative stress and leptin which act in synchrony to potentiate disease progression. Low acute exposure to bromodichloromethane (BDCM), in diet-induced obesity produced oxidative stress as shown by increased lipid peroxidation, protein free radical and nitrotyrosine formation and elevated leptin levels. Exposed obese mice showed histopathological signs of early steatohepatitic injury and necrosis. Spontaneous knockout mice for leptin or systemic leptin receptor knockout mice had significantly decreased oxidative stress and TNF-α levels. Co-incubation of leptin and BDCM caused Kupffer cell activation as shown by increased MCP-1 release and NADPH oxidase membrane assembly, a phenomenon that was decreased in Kupffer cells isolated from leptin receptor knockout mice. In obese mice that were BDCM-exposed, livers showed a significant increase in Kupffer cell activation marker CD68 and, increased necrosis as assessed by levels of isocitrate dehydrogenase, events that were decreased in the absence of leptin or its receptor. In conclusion, our results show that exposure to the disinfection byproduct BDCM in diet-induced obesity augments steatohepatitic injury by potentiating the effects of leptin on oxidative stress, Kupffer cell activation and cell death in the liver.
    Toxicology and Applied Pharmacology 02/2013; · 3.98 Impact Factor
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    ABSTRACT: Abstract The carcinogen inorganic arsenic (iAs) undergoes biomethylation (BMT) in some cells. The methylated metabolite, monomethylarsonous (MMA(3+)), may cause oxidative DNA damage (ODD). With chronic iAs exposure, BMT-competent cells show ODD while BMT-deficient do not. To further define these events, we studied ODD produced by acute iAs or MMA(3+) in the BMT-deficient human prostate cell line, RWPE-1. ODD, measured by the immuno-spin trapping method, was assessed after exposure to iAs or MMA(3+) alone, with the arsenic BMT inhibitor selenite or after glutathione depletion. The expression of oxidative stress related genes (HO-1, SOD-1, SOD-2, Nrf2 and Keap-1) was also assessed. Exposure to iAs at 24 h (0-20 µM), stimulated ODD only at levels above the LC(50) of a 48 h exposure (17 µM). If iAs induced ODD it also activated oxidative stress-related genes. Selenium did not alter iAs-induced ODD. MMA(3+) at 24 h (0-0.5 µM) caused ODD at levels below the LC(50) of a 48 h exposure (1.5 µM), which were greatly increased by glutathione depletion but not selenite. MMA(3+) induced ODD at levels not activating oxidant stress response genes. Overall, iAs induced ODD in BMT deficient cells only at toxic levels. MMA(3+) caused ODD at non-toxic levels, independently of cellular BMT capacity and in a fashion not requiring further BMT.
    Toxicology mechanisms and methods 01/2013; · 1.37 Impact Factor
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    ABSTRACT: BACKGROUND AND AIMS: Progression from steatosis to steatohepatitic lesions is hypothesized to require a second hit. These lesions have been associated with increased oxidative stress, often ascribed to high levels of leptin and other proinflammatory mediators. Here we have examined the role of leptin in inducing oxidative stress and Kupffer cell activation in CCl(4)-mediated steatohepatitic lesions of obese mice. METHODS: Male C57BL/6 mice fed with a high fat diet (60%kcal) at 16 weeks were administered CCl(4) to induce steatohepatitic lesions. Approaches included use of immuno-spin trapping for measuring free radical stress, gene-deficient mice for leptin, p47 phox, iNOS and adoptive transfer of leptin primed macrophages in vivo. RESULTS: Diet-induced obese (DIO) mice, treated with CCl(4) increased serum leptin levels. Oxidative stress was significantly elevated in DIO mice liver but not in OB/OB mice, or in DIO mice treated with leptin antibody. In OB/OB mice, leptin supplementation restored markers of free radical generation. Markers of free radical formation were significantly decreased by the peroxynitrite decomposition catalyst FeTPPS, the iNOS inhibitor 1400W, the NADPH oxidase inhibitor apocynin, or in iNOS or p47 phox-deficient mice. These results correlated with the decreased expression of TNF-alpha and MCP-1. Kupffer cell depletion eliminated oxidative stress and inflammation, whereas in macrophage-depleted mice, the adoptive transfer of leptin-primed macrophages significantly restored inflammation. CONCLUSIONS: These results, for the first time, suggest that leptin action in macrophages of steatotic liver through induction of iNOS and NADPH oxidase caused peroxynitrite-mediated oxidative stress thus activating Kupffer cells.
    Journal of Hepatology 11/2012; · 9.86 Impact Factor
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    ABSTRACT: Inorganic arsenic in the drinking water is a multi-site human carcinogen that potentially targets the kidney. Recent evidence also indicates developmental arsenic exposure impacts renal carcinogenesis in humans and mice. Emerging theory indicates that cancer may be a disease of stem cells (SCs), and there are abundant active SCs during early life. Therefore, we hypothesized that inorganic arsenic targets SCs, or partially-differentiated progenitor cells (PCs), for oncogenic transformation. Thus, a rat kidney SC/PC cell line, RIMM-18, was chronically exposed to low-level arsenite (500 nM) for up to 28 weeks. Multiple markers of acquired cancer phenotype were assessed bi-weekly during arsenic exposure, including secreted matrix metalloproteinase (MMP) activity, proliferation rate, colony formation in soft agar, and cellular invasiveness. Arsenic exposure by 10 weeks and after also induced marked and sustained increases in colony formation, indicative of loss of contact inhibition, and increased invasiveness, both cancer cell characteristics. Compared to passage-matched control, chronic arsenic exposure caused exposure-duration dependent increases in secreted MMP-2 and MMP-9 activity, Cox-2 expression, and more rapid proliferation (all >2-fold), characteristics typical of cancer cells. Dysregulation of SC maintenance genes and signaling pathways are common during oncogenesis. During arsenite exposure, expression of several genes associated with normal kidney development and SC regulation and differentiation (i.e., Wt-1, Wnt-4, Bmp-7, etc.), were aberrantly altered. Arsenic-exposed renal SCs produced more non-adherent spheroid bodies that grew much more aggressively in Matrigel, typical of cancer SCs (CSCs). The transformed cells also showed gene over-expression typical of renal SCs/CSCs (CD24, Osr1, Ncam) and arsenic adaptation such as over-expression of Mt-1, Mt2, Sod-1, and Abcc2. These data suggest inorganic arsenic induced an acquired cancer phenotype in vitro in these rat kidney SCs potentially forming CSCs and, consistent with data in vivo, indicate these multipotent SCs may be targets of arsenic during renal carcinogenesis.
    Chemical Research in Toxicology 11/2012; · 3.67 Impact Factor
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    ABSTRACT: Epigenetic dysfunction is a known contributor in carcinogenesis, and is emerging as a mechanism involved in toxicant-induced malignant transformation for environmental carcinogens such as arsenicals or cadmium. In addition to aberrant DNA methylation of single genes, another manifestation of epigenetic dysfunction in cancer is agglomerative DNA methylation, which can participate in long-range epigenetic silencing that targets many neighboring genes and has been shown to occur in several types of clinical cancers. Using in vitro model systems of toxicant-induced malignant transformation, we found hundreds of aberrant DNA methylation events that emerge during malignant transformation, some of which occur in an agglomerative fashion. In an arsenite-transformed prostate epithelial cell line, the protocadherin (PCDH), HOXC and HOXD gene family clusters are targeted for agglomerative DNA methylation. The agglomerative DNA methylation changes induced by arsenicals appear to be common and clinically relevant events, since they occur in other human cancer cell lines and models of malignant transformation, as well as clinical cancer specimens. Aberrant DNA methylation in general occurred more often within histone H3 lysine-27 trimethylation stem cell domains. We found a striking association between enrichment of histone H3 lysine-9 trimethylation stem cell domains and toxicant-induced agglomerative DNA methylation, suggesting these epigenetic modifications may become aberrantly linked during malignant transformation. In summary, we found an association between toxicant-induced malignant transformation and agglomerative DNA methylation, which lends further support to the hypothesis that epigenetic dysfunction plays an important role in toxicant-induced malignant transformation.
    Epigenetics: official journal of the DNA Methylation Society 09/2012; 7(11). · 4.58 Impact Factor

Publication Stats

9k Citations
1,295.67 Total Impact Points

Institutions

  • 1998–2013
    • National Institute of Environmental Health Sciences
      • Laboratory of Toxicology and Pharmacology (LTP)
      Durham, North Carolina, United States
  • 2000–2012
    • Research Triangle Park Laboratories, Inc.
      Raleigh, North Carolina, United States
    • Kumamoto University
      • • Faculty of Education
      • • Department of Clinical Pharmaceutical Sciences
      Kumamoto, Kumamoto Prefecture, Japan
  • 1997–2012
    • National Institutes of Health
      • Laboratory of Human Carcinogenesis
      Bethesda, MD, United States
  • 1984–2011
    • National Cancer Institute (USA)
      • • Cancer Etiology Branch (CEB)
      • • Division of Cancer Biology
      Maryland, United States
  • 2007
    • Tokyo University of Marine Science and Technology
      • Department of Food Science and Technology
      Tokyo, Tokyo-to, Japan
  • 2002–2007
    • National Eye Institute
      Maryland, United States
    • Gunma University
      • School of Medicine
      Maebashi, Gunma Prefecture, Japan
  • 2006
    • Zunyi Medical University
      Tsun-i-ch’eng, Guizhou Sheng, China
    • China Animal Disease Control Center
      Peping, Beijing, China
  • 2005
    • Tokushima Bunri University
      • Faculty of Pharmaceutical Sciences
      Tokushima-shi, Tokushima-ken, Japan
  • 2004–2005
    • Tokyo University of Pharmacy and Life Science
      • School of Life Sciences
      Tokyo, Tokyo-to, Japan
    • St. Marianna University School of Medicine
      • Department of Preventive Medicine
      Kawasaki, Kanagawa-ken, Japan
    • Huazhong University of Science and Technology
      Wu-han-shih, Hubei, China
  • 2001–2003
    • Guiyang Medical University
      Kuei-yang, Guizhou Sheng, China
  • 1993–2002
    • The University of Western Ontario
      • Department of Pathology
      London, Ontario, Canada
  • 1999–2001
    • Meritorious Autonomous University of Puebla
      • Facultad de Ciencias Químicas
      Puebla, Estado de Baja California, Mexico
    • U.S. Food and Drug Administration
      Washington, Washington, D.C., United States
  • 1988–1998
    • Leidos Biomedical Research
      Maryland, United States
  • 1983–1987
    • Kansas City VA Medical Center
      Kansas City, Missouri, United States
  • 1981
    • West Virginia University
      Morgantown, West Virginia, United States