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Buck RA, Cordle CT, Thomas DJ, Winship TR, Schaller JP, Dugle JE. Longitudinal study of intracellular T cell cytokine production in infants compared to adults. Clin Exp Immunol 2009. [DOI: 10.1046/j.1365-2249.2002.t01-2-00001_129_3.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Drobna Z, Styblo M, Thomas DJ. An Overview of Arsenic Metabolism and Toxicity. CURRENT PROTOCOLS IN TOXICOLOGY 2009; 42:4.31.1-4.31.6. [PMID: 25419261 PMCID: PMC4240622 DOI: 10.1002/0471140856.tx0431s42] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
It is likely that at least some of the toxic and carcinogenic effects associated with exposure to inorganic arsenic are, in fact, due to actions of its methylated metabolites. Here, we provide an overview of current models for the biological methylation of arsenicals. This information provides a context for understanding the chemical, biochemical, and genetic approaches to elucidation of the formation and function of metahylated arsenicals which are presented in the following manuscripts.
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Hernández-Zavala A, Valenzuela OL, Matous̆ek T, Drobná Z, Dĕdina J, García-Vargas GG, Thomas DJ, Del Razo LM, Stýblo M. Speciation of arsenic in exfoliated urinary bladder epithelial cells from individuals exposed to arsenic in drinking water. ENVIRONMENTAL HEALTH PERSPECTIVES 2008; 116:1656-1660. [PMID: 19079716 PMCID: PMC2599759 DOI: 10.1289/ehp.11503] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2008] [Accepted: 07/18/2008] [Indexed: 05/25/2023]
Abstract
BACKGROUND The concentration of arsenic in urine has been used as a marker of exposure to inorganic As (iAs). Relative proportions of urinary metabolites of iAs have been identified as potential biomarkers of susceptibility to iAs toxicity. However, the adverse effects of iAs exposure are ultimately determined by the concentrations of iAs metabolites in target tissues. OBJECTIVE In this study we examined the feasibility of analyzing As species in cells that originate in the urinary bladder, a target organ for As-induced cancer in humans. METHODS Exfoliated bladder epithelial cells (BECs) were collected from urine of 21 residents of Zimapan, Mexico, who were exposed to iAs in drinking water. We determined concentrations of iAs, methyl-As (MAs), and dimethyl-As (DMAs) in urine using conventional hydride generation-cryotrapping-atomic absorption spectrometry (HG-CT-AAS). We used an optimized HG-CT-AAS technique with detection limits of 12-17 pg As for analysis of As species in BECs. RESULTS All urine samples and 20 of 21 BEC samples contained detectable concentrations of iAs, MAs, and DMAs. Sums of concentrations of these As species in BECs ranged from 0.18 to 11.4 ng As/mg protein and in urine from 4.8 to 1,947 ng As/mL. We found no correlations between the concentrations or ratios of As species in BECs and in urine. CONCLUSION These results suggest that urinary levels of iAs metabolites do not necessarily reflect levels of these metabolites in the bladder epithelium. Thus, analysis of As species in BECs may provide a more effective tool for risk assessment of bladder cancer and other urothelial diseases associated with exposures to iAs.
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Thomas DJ, Styblo M. In Memoriam: Kazuo T. Suzuki, Ph.D. Chem Res Toxicol 2008. [DOI: 10.1021/tx800314q] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Sparks DA, Dawood MY, Chase DM, Thomas DJ. Ischemic volvulus of the transverse colon: A case report and review of literature. CASES JOURNAL 2008; 1:174. [PMID: 18808679 PMCID: PMC2564907 DOI: 10.1186/1757-1626-1-174] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Accepted: 09/22/2008] [Indexed: 11/10/2022]
Abstract
A 75-year old male presented to the emergency room with worsening abdominal pain and distension. Plain radiographs were suggestive of a large bowel obstruction due to volvulus. An attempt to detorse the volvulus and decompress the colon endoscopically failed, after which the patient was taken for an exploratory laparotomy. A transverse colon volvulus was found, and an extended right hemicolectomy and ileostomy was performed. We discuss the diagnosis and management of transverse colon volvulus and review the pertinent literature.
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Chen Y, O'Brien T, Del Razo LM, Thomas DJ, Kitchin KT. Tissue levels of arsenicals and skin tumor response following administration of monomethylarsonous acid and arsenite to K6/ODC mice. J Environ Pathol Toxicol Oncol 2008; 27:43-52. [PMID: 18551895 DOI: 10.1615/jenvironpatholtoxicoloncol.v27.i1.50] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The effects of monomethylarsonous acid (MMA[III]) and arsenite, administered in drinking water on tissue levels of arsenicals, cytogenetics, and mouse skin tumorigenicity were determined. A low-methionine diet modified the pattern of arsenical tissue concentrations and decreased the tissue arsenical concentrations, particularly in kidney and urinary bladder, less so in liver, and had little effect in the lungs. In mice given 75 ppm arsenite and a low-methionine diet, the urinary bladder tissue levels were only 29%, 26%, and 38% of the inorganic arsenic (iAs), MMA, and dimethylarsinic acid (DMA) concentrations found in mice eating the control diet. In K6/ODC transgenic mice that consumed a normal diet (Purina 5002), a 26-week drinking water exposure to 10 ppm arsenite resulted in 5% of the treated animals having squamous skin tumors. Exposure to 10, 50, 75, or 150 ppm MMA(III) caused 5%, 6.7%, 5%, or 0% tumor-bearing animals. A low-methionine diet did not markedly change the incidence of skin tumors--10 ppm arsenite led to 10% tumors. With a low-methionine diet, 10 and 50 ppm, MMA(III) caused 5% and 6.7% tumor-bearing animals. In comparing the frequency of tumors in the concurrent control groups (1/70, 1.4%) with the frequency of tumors in the pooled arsenical-treated responsive groups (8/122, 6.6%), there is an excess of 6 mouse skin tumors observed in the pooled arsenical-responsive treatment groups compared to the expected number of tumors based on frequency of tumors observed in concurrent control mice. In summary, studies with MMA(III) and arsenite-treated K6/ODC transgenic mice showed (1) a low-methionine diet substantially altered mouse tissue arsenical levels and (2) numerically elevated incidence of mouse skin tumors following arsenical exposures.
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Matoušek T, Hernández-Zavala A, Svoboda M, Langrová L, Adair BM, Drobná Z, Thomas DJ, Stýblo M, Dědina J. Oxidation State Specific Generation of Arsines from Methylated Arsenicals Based on L- Cysteine Treatment in Buffered Media for Speciation Analysis by Hydride Generation - Automated Cryotrapping - Gas Chromatography-Atomic Absorption Spectrometry with the Multiatomizer. SPECTROCHIMICA ACTA. PART B, ATOMIC SPECTROSCOPY 2008; 63:396-406. [PMID: 18521190 PMCID: PMC2408738 DOI: 10.1016/j.sab.2007.11.037] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
An automated system for hydride generation - cryotrapping- gas chromatography - atomic absorption spectrometry with the multiatomizer is described. Arsines are preconcentrated and separated in a Chromosorb filled U-tube. An automated cryotrapping unit, employing nitrogen gas formed upon heating in the detection phase for the displacement of the cooling liquid nitrogen, has been developed. The conditions for separation of arsines in a Chromosorb filled U-tube have been optimized. A complete separation of signals from arsine, methylarsine, dimethylarsine, and trimethylarsine has been achieved within a 60 s reading window. The limits of detection for methylated arsenicals tested were 4 ng l(-1). Selective hydride generation is applied for the oxidation state specific speciation analysis of inorganic and methylated arsenicals. The arsines are generated either exclusively from trivalent or from both tri- and pentavalent inorganic and methylated arsenicals depending on the presence of L-cysteine as a prereductant and/or reaction modifier. A TRIS buffer reaction medium is proposed to overcome narrow optimum concentration range observed for the L-cysteine modified reaction in HCl medium. The system provides uniform peak area sensitivity for all As species. Consequently, the calibration with a single form of As is possible. This method permits a high-throughput speciation analysis of metabolites of inorganic arsenic in relatively complex biological matrices such as cell culture systems without sample pretreatment, thus preserving the distribution of tri- and pentavalent species.
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Nava GM, Lee DY, Cai S, Boyer JL, Hernández‐Zavala A, Thomas DJ, Gaskins HR. Arsenic (+3 oxidation state) methyltransferase and the methylation of arsenicals in the invertebrate chordate
Ciona intestinalis. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.796.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Hernández-Zavala A, Matoušek T, Drobná Z, Paul DS, Walton F, Adair BM, Jiří D, Thomas DJ, Stýblo M. Speciation analysis of arsenic in biological matrices by automated hydride generation-cryotrapping-atomic absorption spectrometry with multiple microflame quartz tube atomizer (multiatomizer). JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 2008; 23:342-351. [PMID: 18677417 PMCID: PMC2493051 DOI: 10.1039/b706144g] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Analyses of arsenic (As) species in tissues and body fluids of individuals chronically exposed to inorganic arsenic (iAs) provide essential information about the exposure level and pattern of iAs metabolism. We have previously described an oxidation state-specific analysis of As species in biological matrices by hydride-generation atomic absorption spectrometry (HG-AAS), using cryotrapping (CT) for preconcentration and separation of arsines. To improve performance and detection limits of the method, HG and CT steps are automated and a conventional flame-in-tube atomizer replaced with a recently developed multiple microflame quartz tube atomizer (multiatomizer). In this system, arsines from As(III)-species are generated in a mixture of Tris-HCl (pH 6) and sodium borohydride. For generation of arsines from both As(III)- and As(V)-species, samples are pretreated with L-cysteine. Under these conditions, dimethylthioarsinic acid, a newly described metabolite of iAs, does not interfere significantly with detection and quantification of methylated trivalent arsenicals. Analytical performance of the automated HG-CT-AAS was characterized by analyses of cultured cells and mouse tissues that contained mono- and dimethylated metabolites of iAs. The capacity to detect methylated As(III)- and As(V)-species was verified, using an in vitro methylation system containing recombinant rat arsenic (+3 oxidation state) methyltransferase and cultured rat hepatocytes treated with iAs. Compared with the previous HG-CT-AAS design, detection limits for iAs and its metabolites have improved significantly with the current system, ranging from 8 to 20 pg. Recoveries of As were between 78 and 117%. The precision of the method was better than 5% for all biological matrices examined. Thus, the automated HG-CT-AAS system provides an effective and sensitive tool for analysis of all major human metabolites of iAs in complex biological matrices.
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Paul DS, Devesa V, Hernandez-Zavala A, Adair BM, Walton FS, Drobnâ Z, Thomas DJ, Styblo M. Environmental arsenic as a disruptor of insulin signaling. METAL IONS IN BIOLOGY AND MEDICINE : PROCEEDINGS OF THE ... INTERNATIONAL SYMPOSIUM ON METAL IONS IN BIOLOGY AND MEDICINE HELD ... = LES IONS METALLIQUES EN BIOLOGIE ET EN MEDECINE : ... SYMPOSIUM INTERNATIONAL SUR LES IONS METALLIQUES ... 2008; 10:1-7. [PMID: 20467584 PMCID: PMC2868343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Previous laboratory studies have shown that exposures to inorganic As (iAs) disrupt insulin production or glucose metabolism in cellular and animal models. Epidemiological evidence has also linked chronic human exposures to iAs to an increased risk of diabetes mellitus, a metabolic disease characterized by impaired glucose tolerance and insulin resistance. We have recently shown that arsenite and its methylated metabolites inhibit insulin-stimulated glucose uptake in cultured adipocytes by disrupting insulin-activated signal transduction pathway and preventing insulin-dependent translocation of GLUT4 transporters to the plasma membrane. Here, we present results of follow-up studies using male C57BL/6 mice chronically exposed to arsenite (1 to 50 ppm As) or to its metabolite methylarsonite (0.1 to 5 ppm As) in drinking water for 8 weeks. Results of these studies show that only the exposure to arsenite at the highest level of 50 ppm As produces symptoms attributable to impaired glucose tolerance. Notably, tissue concentrations of iAs and its methylated metabolites in pancreas and in major glucose metabolizing tissues in mice in this exposure group were comparable to the concentrations of total As reported in livers of Bangladeshi residents exposed to much lower concentrations of iAs in drinking water. These results suggest that because mice clear iAs and its metabolites more rapidly than humans, much higher exposure levels may be needed in mouse studies to produce the diabetogenic effects of iAs commonly found in human populations exposed to iAs from environmental sources.
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Hughes MF, Devesa V, Adair BM, Conklin SD, Creed JT, Styblo M, Kenyon EM, Thomas DJ. Tissue dosimetry, metabolism and excretion of pentavalent and trivalent dimethylated arsenic in mice after oral administration. Toxicol Appl Pharmacol 2007; 227:26-35. [PMID: 18036629 DOI: 10.1016/j.taap.2007.10.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Revised: 10/05/2007] [Accepted: 10/15/2007] [Indexed: 12/01/2022]
Abstract
Dimethylarsinic acid (DMA(V)) is a rat bladder carcinogen and the major urinary metabolite of administered inorganic arsenic in most mammals. This study examined the disposition of pentavalent and trivalent dimethylated arsenic in mice after acute oral administration. Adult female mice were administered [(14)C]-DMA(V) (0.6 or 60 mg As/kg) and sacrificed serially over 24 h. Tissues and excreta were collected for analysis of radioactivity. Other mice were administered unlabeled DMA(V) (0.6 or 60 mg As/kg) or dimethylarsinous acid (DMA(III)) (0.6 mg As/kg) and sacrificed at 2 or 24 h. Tissues (2 h) and urine (24 h) were collected and analyzed for arsenicals. Absorption, distribution and excretion of [(14)C]-DMA(V) were rapid, as radioactivity was detected in tissues and urine at 0.25 h. For low dose DMA(V) mice, there was a greater fractional absorption of DMA(V) and significantly greater tissue concentrations of radioactivity at several time points. Radioactivity distributed greatest to the liver (1-2% of dose) and declined to less than 0.05% in all tissues examined at 24 h. Urinary excretion of radioactivity was significantly greater in the 0.6 mg As/kg DMA(V) group. Conversely, fecal excretion of radioactivity was significantly greater in the high dose group. Urinary metabolites of DMA(V) included DMA(III), trimethylarsine oxide (TMAO), dimethylthioarsinic acid and trimethylarsine sulfide. Urinary metabolites of DMA(III) included TMAO, dimethylthioarsinic acid and trimethylarsine sulfide. DMA(V) was also excreted by DMA(III)-treated mice, showing its sensitivity to oxidation. TMAO was detected in tissues of the high dose DMA(V) group. The low acute toxicity of DMA(V) in the mouse appears to be due in part to its minimal retention and rapid elimination.
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Thomas DJ, Hudgens EE, Calderon RL. The US EPA workshop on research and risk assessment for arsenic. Toxicol Appl Pharmacol 2007. [DOI: 10.1016/j.taap.2007.05.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Adair BM, Moore T, Conklin SD, Creed JT, Wolf DC, Thomas DJ. Tissue distribution and urinary excretion of dimethylated arsenic and its metabolites in dimethylarsinic acid- or arsenate-treated rats. Toxicol Appl Pharmacol 2007; 222:235-42. [PMID: 17559899 DOI: 10.1016/j.taap.2007.04.012] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Revised: 04/27/2007] [Accepted: 04/27/2007] [Indexed: 11/20/2022]
Abstract
Adult female Fisher 344 rats received drinking water containing 0, 4, 40, 100, or 200 parts per million of dimethylarsinic acid or 100 parts per million of arsenate for 14 days. Urine was collected during the last 24 h of exposure. Tissues were then taken for analysis of dimethylated and trimethylated arsenicals; urines were analyzed for these arsenicals and their thiolated derivatives. In dimethylarsinic acid-treated rats, highest concentrations of dimethylated arsenic were found in blood. In lung, liver, and kidney, concentrations of dimethylated arsenic exceeded those of trimethylated species; in urinary bladder and urine, trimethylated arsenic predominated. Dimethylthioarsinic acid and trimethylarsine sulfide were present in urine of dimethylarsinic acid-treated rats. Concentrations of dimethylated arsenicals were similar in most tissues of dimethylarsinic acid- and arsenate-treated rats, including urinary bladder which is the target for dimethylarsinic acid-induced carcinogenesis in the rat. Mean concentration of dimethylated arsenic was significantly higher (P<0.05) in urine of dimethylarsinic acid-treated rats than in arsenate-treated rats, suggesting a difference between treatment groups in the flux of dimethylated arsenic through urinary bladder. Concentrations of trimethylated arsenic concentrations were consistently higher in dimethylarsinic acid-treated rats than in arsenate-treated rats; these differences were significant (P<0.05) in liver, urinary bladder, and urine. Concentrations of dimethylthioarsinic acid and trimethylarsine sulfide were higher in urine from dimethylarsinic acid-treated rats than from arsenate-treated rats. Dimethylarsinic acid is extensively metabolized in the rat, yielding significant concentrations of trimethylated species and of thiolated derivatives. One or more of these metabolites could be the species causing alterations of cellular function that lead to tumors in the urinary bladder.
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Paul DS, Harmon AW, Devesa V, Thomas DJ, Stýblo M. Molecular mechanisms of the diabetogenic effects of arsenic: inhibition of insulin signaling by arsenite and methylarsonous acid. ENVIRONMENTAL HEALTH PERSPECTIVES 2007; 115:734-42. [PMID: 17520061 PMCID: PMC1867998 DOI: 10.1289/ehp.9867] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Accepted: 01/29/2007] [Indexed: 04/14/2023]
Abstract
BACKGROUND Increased prevalences of diabetes mellitus have been reported among individuals chronically exposed to inorganic arsenic (iAs). However, the mechanisms underlying the diabetogenic effects of iAs have not been characterized. We have previously shown that trivalent metabolites of iAs, arsenite (iAs(III)) and methylarsonous acid (MAs(III)) inhibit insulin-stimulated glucose uptake (ISGU) in 3T3-L1 adipocytes by suppressing the insulin-dependent phosphorylation of protein kinase B (PKB/Akt). OBJECTIVES Our goal was to identify the molecular mechanisms responsible for the suppression of PKB/Akt phosphorylation by iAs(III) and MAs(III). METHODS The effects of iAs(III) and MAs(III) on components of the insulin-activated signal transduction pathway that regulate PKB/Akt phosphorylation were examined in 3T3-L1 adipocytes. RESULTS Subtoxic concentrations of iAs(III) or MAs(III) had little or no effect on the activity of phosphatidylinositol 3-kinase (PI-3K), which synthesizes phosphatidylinositol-3,4,5-triphosphate (PIP(3)), or on phosphorylation of PTEN (phosphatase and tensin homolog deleted on chromosome ten), a PIP(3) phosphatase. Neither iAs(III) nor MAs(III) interfered with the phosphorylation of 3-phosphoinositide-dependent kinase-1 (PDK-1) located downstream from PI-3K. However, PDK-1 activity was inhibited by both iAs(III) and MAs(III). Consistent with these findings, PDK-1-catalyzed phosphorylation of PKB/Akt(Thr308) and PKB/Akt activity were suppressed in exposed cells. In addition, PKB/Akt(Ser473) phosphorylation, which is catalyzed by a putative PDK-2, was also suppressed. Notably, expression of constitutively active PKB/Akt restored the normal ISGU pattern in adipocytes treated with either iAs(III) or MAs(III). CONCLUSIONS These results suggest that inhibition of the PDK-1/PKB/Akt-mediated transduction step is the key mechanism for the inhibition of ISGU in adipocytes exposed to iAs(III) or MAs(III), and possibly for impaired glucose tolerance associated with human exposures to iAs.
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Fomenko DE, Xing W, Thomas DJ, Gladyshev VN. Identification of catalytic redox‐active cysteines by detecting sporadic cysteine/selenocysteine pairs in homologous sequences. FASEB J 2007. [DOI: 10.1096/fasebj.21.5.a114-a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Paez E, Reay E, Murthy LNS, Pickard RS, Thomas DJ. Percutaneous Treatment of Calculi in Reconstructed Bladder. J Endourol 2007; 21:334-6. [PMID: 17444782 DOI: 10.1089/end.2006.0251] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
PURPOSE To report our results with percutaneous removal of calculi from reconstructed bladders. PATIENTS AND METHODS Twelve patients with reconstructed bladders who underwent endoscopic cystolithotomy were identified from our departmental database, and retrospective review of case notes and imaging was performed. RESULTS Access was gained via an ultrasound-guided new tract in 9 patients (75%). An old suprapubic tract site was used in two patients, and the Mitrofanoff stoma was the route of access in one patient. The procedure was successful, with stone clearance achieved in all 12 cases. No major complications were observed. At a median follow up of 24 months, stone recurrence was observed in 5 patients (42%), 4 of whom underwent repeat procedures. Follow-up showed no change in continence in the patient with a Mitroffanoff stoma. CONCLUSION Percutaneous cystolithotomy is a safe and effective minimally invasive option for removal of stones in a reconstructed bladder. We recommend endoscopic removal as the treatment of choice in these patients.
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Thomas DJ. Molecular processes in cellular arsenic metabolism. Toxicol Appl Pharmacol 2007; 222:365-73. [PMID: 17397889 DOI: 10.1016/j.taap.2007.02.007] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2006] [Revised: 02/08/2007] [Accepted: 02/09/2007] [Indexed: 12/11/2022]
Abstract
Elucidating molecular processes that underlie accumulation, metabolism and binding of iAs and its methylated metabolites provides a basis for understanding the modes of action by which iAs acts as a toxin and a carcinogen. One approach to this problem is to construct a conceptual model that incorporates available information on molecular processes involved in the influx, metabolism, binding and efflux of arsenicals in cells. This conceptual model is initially conceived as a non-quantitative representation of critical molecular processes that can be used as a framework for experimental design and prediction. However, with refinement and incorporation of additional data, the conceptual model can be expressed in mathematical terms and should be useful for quantitative estimates of the kinetic and dynamic behavior of iAs and its methylated metabolites in cells. Development of a quantitative model will be facilitated by the availability of tools and techniques to manipulate molecular processes underlying transport of arsenicals across cell membranes or expression and activity of enzymes involved in methylation of arsenicals. This model of cellular metabolism might be integrated into more complex pharmacokinetic models for systemic metabolism of iAs and its methylated metabolites. It may also be useful in development of biologically based dose-response models describing the toxic and carcinogenic actions of arsenicals.
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Fomenko DE, Xing W, Adair BM, Thomas DJ, Gladyshev VN. High-throughput identification of catalytic redox-active cysteine residues. Science 2007; 315:387-9. [PMID: 17234949 DOI: 10.1126/science.1133114] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Cysteine (Cys) residues often play critical roles in proteins; however, identification of their specific functions has been limited to case-by-case experimental approaches. We developed a procedure for high-throughput identification of catalytic redox-active Cys in proteins by searching for sporadic selenocysteine-Cys pairs in sequence databases. This method is independent of protein family, structure, and taxon. We used it to selectively detect the majority of known proteins with redox-active Cys and to make additional predictions, one of which was verified. Rapid accumulation of sequence information from genomic and metagenomic projects should allow detection of many additional oxidoreductase families as well as identification of redox-active Cys in these proteins.
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Thomas DJ, Hawkes NP, Jones LN, Kolkowski P, Roberts NJ. Characterization and utilization of a Bonner sphere set based on gold activation foils. RADIATION PROTECTION DOSIMETRY 2007; 126:229-33. [PMID: 17496291 DOI: 10.1093/rpd/ncm047] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Bonner sphere (BS) sets which use activation foils as the central thermal neutron sensor have advantages over active BS systems in certain environments, for example, pulsed fields, or fields with high photon components. In such environments, they may be the only type of neutron spectrometer which can be used. This paper describes work, using both measurements and calculations, to validate the response functions for a BS set based on gold activation foils. As an illustration of the use of such a system, a measurement is described of the contaminant neutron spectrum in the treatment room of a 21 MV hospital linear accelerator providing photon beams for radiotherapy.
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Taylor GC, Thomas DJ, Bennett A. Results of field trials using the NPL simulated reactor neutron field facility. RADIATION PROTECTION DOSIMETRY 2007; 126:89-92. [PMID: 17848380 DOI: 10.1093/rpd/ncm018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The NPL simulated reactor neutron field facility provides neutron spectra similar to those found in the environs of UK gas-cooled reactors. Neutrons are generated by irradiating a thick lithium-alloy target with monoenergetic protons between 2.5 and 3.5 MeV (depending on the desired spectrum), and then moderated by a 40-cm diameter sphere of heavy water. This represents an extremely soft workplace field, with a mean neutron energy of 25 keV and, more significantly, a mean fluence to ambient dose equivalent conversion coefficient of the order of 20 pSv cm(2), approximately 20 times lower than those of the ISO standard calibration sources (252)Cf and (241)Am-Be. Results of field trials are presented, including readings from neutron spectrometers, personal dosimeters (active and passive) and neutron area survey meters, and issues with beam monitoring are discussed.
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Thomas DJ, Li J, Waters SB, Xing W, Adair BM, Drobna Z, Devesa V, Styblo M. Arsenic (+3 oxidation state) methyltransferase and the methylation of arsenicals. Exp Biol Med (Maywood) 2007; 232:3-13. [PMID: 17202581 PMCID: PMC2408740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023] Open
Abstract
Metabolic conversion of inorganic arsenic into methylated products is a multistep process that yields mono-, di-, and trimethylated arsenicals. In recent years, it has become apparent that formation of methylated metabolites of inorganic arsenic is not necessarily a detoxification process. Intermediates and products formed in this pathway may be more reactive and toxic than inorganic arsenic. Like all metabolic pathways, understanding the pathway for arsenic methylation involves identification of each individual step in the process and the characterization of the molecules which participate in each step. Among several arsenic methyltransferases that have been identified, arsenic (+3 oxidation state) methyltransferase is the one best characterized at the genetic and functional levels. This review focuses on phylogenetic relationships in the deuterostomal lineage for this enzyme and on the relation between genotype for arsenic (+3 oxidation state) methyltransferase and phenotype for conversion of inorganic arsenic to methylated metabolites. Two conceptual models for function of arsenic (+3 oxidation state) methyltransferase which posit different roles for cellular reductants in the conversion of inorganic arsenic to methylated metabolites are compared. Although each model accurately represents some aspects of enzyme's role in the pathway for arsenic methylation, neither model is a fully satisfactory representation of all the steps in this metabolic pathway. Additional information on the structure and function of the enzyme will be needed to develop a more comprehensive model for this pathway.
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Hawkes NP, Freedman R, Tagziria H, Thomas DJ. Measurement and calculation of the emission anisotropy of an X1 252Cf neutron source. RADIATION PROTECTION DOSIMETRY 2007; 126:78-82. [PMID: 17496296 DOI: 10.1093/rpd/ncm145] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
The authors have measured the emission anisotropy from a (252)Cf spontaneous fission neutron source in an X1 encapsulation. The measurements were made in a large low-scatter laboratory using a long counter, and data were taken at angles varying in 10 degrees steps from 0 degrees to 180 degrees relative to the cylindrical axis of the source. Corrections were made for room scatter, loss of neutrons due to air scatter and detector dead time. Calculations corresponding to these measurements were subsequently carried out using the two Monte Carlo codes MCNP and MCBEND, and the results are compared with the measurements and with each other.
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Thomas DJ, Li J, Waters SB, Xing W, Adair BM, Drobna Z, Devesa V, Styblo M. Arsenic (+3 oxidation state) methyltransferase and the methylation of arsenicals. Exp Biol Med (Maywood) 2007. [PMID: 17202581 DOI: 10.3181/00379727-207-2320003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2023] Open
Abstract
Metabolic conversion of inorganic arsenic into methylated products is a multistep process that yields mono-, di-, and trimethylated arsenicals. In recent years, it has become apparent that formation of methylated metabolites of inorganic arsenic is not necessarily a detoxification process. Intermediates and products formed in this pathway may be more reactive and toxic than inorganic arsenic. Like all metabolic pathways, understanding the pathway for arsenic methylation involves identification of each individual step in the process and the characterization of the molecules which participate in each step. Among several arsenic methyltransferases that have been identified, arsenic (+3 oxidation state) methyltransferase is the one best characterized at the genetic and functional levels. This review focuses on phylogenetic relationships in the deuterostomal lineage for this enzyme and on the relation between genotype for arsenic (+3 oxidation state) methyltransferase and phenotype for conversion of inorganic arsenic to methylated metabolites. Two conceptual models for function of arsenic (+3 oxidation state) methyltransferase which posit different roles for cellular reductants in the conversion of inorganic arsenic to methylated metabolites are compared. Although each model accurately represents some aspects of enzyme's role in the pathway for arsenic methylation, neither model is a fully satisfactory representation of all the steps in this metabolic pathway. Additional information on the structure and function of the enzyme will be needed to develop a more comprehensive model for this pathway.
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Bulone D, Masino L, Thomas DJ, San Biagio PL, Pastore A. The interplay between PolyQ and protein context delays aggregation by forming a reservoir of protofibrils. PLoS One 2006; 1:e111. [PMID: 17205115 PMCID: PMC1762411 DOI: 10.1371/journal.pone.0000111] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Accepted: 11/21/2006] [Indexed: 11/18/2022] Open
Abstract
Polyglutamine (polyQ) diseases are inherited neurodegenerative disorders caused by the expansion of CAG codon repeats, which code for polyQ in the corresponding gene products. These diseases are associated with the presence of amyloid-like protein aggregates, induced by polyQ expansion. It has been suggested that the soluble aggregates rather than the mature fibrillar aggregates are the toxic species, and that the aggregation properties of polyQ can be strongly modulated by the surrounding protein context. To assess the importance of the protein carrier in polyQ aggregation, we have studied the misfolding pathway and the kinetics of aggregation of polyQ of lengths above (Q41) and below (Q22) the pathological threshold fused to the well-characterized protein carrier glutathione S-transferase (GST). This protein, chosen as a model system, is per se able to misfold and aggregate irreversibly, thus mimicking the behaviour of domains of naturally occurring polyQ proteins. We prove that, while it is generally accepted that the aggregation kinetics of polyQ depend on its length and are faster for longer polyQ tracts, the presence of GST alters the polyQ aggregation pathway and reverses this trend. Aggregation occurs through formation of a reservoir of soluble intermediates whose populations and kinetic stabilities increase with polyQ length. Our results provide a new model that explains the toxicity of expanded polyQ proteins, in which the interplay between polyQ regions and other aggregation-prone domains plays a key role in determining the aggregation pathway.
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