Grantee Research Project Results
2000 Progress Report: Arsenicals, Glutathione Reductase and Cellular Redox Status
EPA Grant Number: R826136Title: Arsenicals, Glutathione Reductase and Cellular Redox Status
Investigators: Stýblo, Miroslav , Thomas, David J. , Del Razo, Luz M. , Cullen, William R. , Lin, Shan
Current Investigators: Stýblo, Miroslav , Beck, Melinda A. , Del Razo, Luz M. , Cullen, William R. , Walton, Felecia , Lin, Shan
Institution: University of North Carolina at Chapel Hill
Current Institution: University of North Carolina at Chapel Hill , University of British Columbia
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 1997 through August 31, 2000 (Extended to September 14, 2001)
Project Period Covered by this Report: September 1, 1999 through August 31, 2000
Project Amount: $322,936
RFA: Arsenic Health Effects Research (1997) RFA Text | Recipients Lists
Research Category: Drinking Water , Human Health , Water
Objective:
The major goal of this project is to study effects of inorganic arsenic on a major cellular redox enzyme, glutathione reductase (GR), and on the redox status of cells exposed to arsenic. To better understand the role of metabolism in the toxicity of arsenic, the correlation between effects induced by arsenic and the patterns of its metabolic conversions are systematically examined in live cells. Cells from tissues that metabolize arsenic (liver) and tissues that are targets for carcinogenic effects of arsenic (skin, lung, and bladder) are used in the study.Progress Summary:
The following is a summary of results obtained during the 3 years (1997-2000) of the study:
1. An inorganic form of trivalent arsenic, arsenite (iAsIII), is toxic for most cell types examined only at relatively high concentrations. It is a weak inhibitor of GR and of another major oxidoreductase, thioredoxin reductase (TR), in cultured cells. iAsIII is effectively metabolized to methylarsenic (MAs) and dimethylarsenic (DMAs) species in primary human hepatocytes. However, the capacity of human hepatocytes to methylate iAsIII varies significantly among individuals. Human epidermal keratinocytes and human bronchial epithelial cells are much less effective methylators of iAsIII than are hepatocytes. Epithelial cells derived from human bladder do not methylate iAsIII. There is no apparent correlation between the capacity of cells to methylate iAs and their susceptibility to acute toxicity of iAsIII. Trivalent methylated metabolites of iAsIII, methylarsonous acid (MAsIII) and dimethylarsinous acid (DMAsIII), are significantly more toxic for most cells types than is iAsIII. In addition, MAsIII is an order of magnitude more potent inhibitor of GR and TR than is iAsIII. An acute exposure of cells to MAsIII results in a significant reduction of intracellular levels of a major cellular antioxidant, glutathione (GSH). Pentavalent methylated metabolites of iAsIII, methylarsonic acid (MAsV) and dimethylarsinic acid (DMAsV), do not inhibit either GR or TR and are not cytotoxic. In cells exposed to iAsIII, inhibition of TR activity strongly correlates with intracellular MAs, suggesting that the trivalent form of MAsIII is a product of the metabolism of iAsIII in cells.
2. Treatments with antioxidants (catalase, N-acetylcysteine or glutathione-ethyl ester) partially protect cultured cells against toxicity of iAsIII, MAsIII, or DMAsIII, indicating that generation of reactive oxygen species may be in part responsible for cytotoxicity of trivalent arsenicals. On the other hand, concurrent exposure to selenite increases cytotoxicity of all three species.
3. Using an optimized hydride generation atomic absorption spectrometric technique, we found that trivalent methylated arsenicals, MAsIII and DMAsIII, are indeed products of the methylation of iAsIII in human hepatic (HepG2) cells (Figure 1). Both MAsIII and DMAsIII were also found in urine of individuals chronically exposed to iAs from drinking water (Table 1). The amounts of MAsIII and DMAsIII positively correlated with total urinary arsenic and thus, with the extent of the exposure to iAs.
In conclusion, trivalent methylated metabolites, MAsIII and DMAsIII, are more potent cytotoxins and enzyme inhibitors than is iAsIII. Trivalent methylated arsenicals are natural products of the metabolism of iAs in humans, suggesting that methylation of iAs is not necessarily a detoxification mechanism. In fact, these species may significantly contribute to the adverse effects associated with the exposure to iAs. Because of their pronounced biological effects, MAsIII and DMAsIII may become sensitive biomarkers of arsenic toxicity in humans.
Table 1. Arsenic metabolites in urine (ng/ml) collected from residents of Zimapan region, Mexico.
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Future Activities:
Continue to prepare publications for peer reviewed journals and prepare and submit the final report for the grant.Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 43 publications | 12 publications in selected types | All 12 journal articles |
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Type | Citation | ||
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Lin S, Del Razo LM, Styblo M, Wang C, Cullen WR, Thomas DJ. Arsenicals inhibit thioredoxin reductase in cultured rat hepatocytes. Chemical Research in Toxicology 2001;14(3):305-311. |
R826136 (2000) R826136 (Final) |
Exit |
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Styblo M, Thomas DJ. Selenium modifies the metabolism and toxicity of arsenic in primary rat hepatocytes. Toxicology and Applied Pharmacology 2001;172(1):52-61. |
R826136 (2000) R826136 (Final) |
Exit Exit |
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Vega L, Styblo M, Patterson R, Cullen W, Wang C, Germolec D. Differential effects of trivalent and pentavalent arsenicals on cell proliferation and cytokine secretion in normal human epidermal keratinocytes. Toxicology and Applied Pharmacology 2001;172(3):225-232. |
R826136 (2000) R826136 (Final) |
Exit Exit |
Supplemental Keywords:
drinking water, exposure, health effects, human health, metabolism, methylation, carcinogen, cellular, cell culture, cell viability, cytotoxicity, enzymes, inhibitor, inhibition, susceptibility, chemicals, metals, metalloids, arsenic, glutathione, antioxidants, oxidative stress, ROS, risk assessment, animal, mammalian, uptake, efflux, detoxification, arsenothiols, mechanism, protein binding, mouse., RFA, Health, Scientific Discipline, Toxics, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, National Recommended Water Quality, Arsenic, Fate & Transport, Risk Assessments, Disease & Cumulative Effects, Water Pollutants, Biology, Drinking Water, cancer risk, Pathology, fate and transport, health effects, carcinogenesis, human health effects, redox metabolism, cellular metabolism, arsenothiols, trivalent methylated arsenicals, detoxification, cellular biology, exposure and effects, cell biology, exposure, inorganic arsenic, cellular physiology, effects, human exposure, GSH, methylation, carcinogens, toxicity, metabolism, water quality, protein bindingProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.