Arsenicals, Glutathione Reductase and Cellular Redox StatusEPA Grant Number: R826136
Title: Arsenicals, Glutathione Reductase and Cellular Redox Status
Investigators: Stýblo, Miroslav , Beck, Melinda A. , Cullen, William R.
Current Investigators: Stýblo, Miroslav , Beck, Melinda A. , Cullen, William R. , Del Razo, Luz M. , Lin, Shan , Walton, Felecia
Institution: University of North Carolina at Chapel Hill , University of British Columbia
EPA Project Officer: Hiscock, Michael
Project Period: September 1, 1997 through August 31, 2000 (Extended to September 14, 2001)
Project Amount: $322,936
RFA: Arsenic Health Effects Research (1997) RFA Text | Recipients Lists
Research Category: Drinking Water , Health Effects , Human Health , Water
The proposed research will examine two related aspects on the mode of action of inorganic arsenic (iAs) as a carcinogen and toxin including (i) interactions of iAs and its metabolites with glutathione reductase (GR), a key enzyme in redox metabolism of glutathione (GSH), and (ii) effects of the arsenic-GR interactions on ratio of GSH to glutathione disulfide (GSSG) that is an indicator of cellular redox status.
Objectives/Hypothesis:The following hypothesis will be tested:
1. Exposure of cultured human cells or intact mice to arsenicals results in inhibition of GR activity.
2. Trivalent methylated arsenicals and/or arsenothiols are the most potent inhibitors of GR. Hence methylation of iAs yields potentially toxic compounds.
3. A consequence of the inhibition of GR by arsenicals is an alteration of the intracellular GSH/GSSG ratio and of the redox status of cells.
4. Other NAD(P)H-dependent oxidoreductases may be inhibited by the arsenicals and inhibition of these enzyme may also be a means by which arsenic alters the redox status of cells.
The proposed research will integrate studies at three levels of biological complexity: Purified enzyme, cultured cells and intact animals. The approaches and goals can be summarized as follows: (i) examination of the interactions of iAs and its metabolites (including pentavalent and trivalent methylated arsenicals and arsenothiols) with GR purified from human erythrocytes; (ii) examination of effects of arsenicals on GR activity, GSH/GSSH ratio and intracellular peroxides in cultured human cells as compared with patterns of arsenic metabolism (uptake and efflux, reduction, methylation and protein binding) in cells; and (iii) examination of the in vivo effects of arsenicals on GR activity and the GSH/GSSG ratio in tissue of mice.
Given the previously published data, the result of the proposed experiments are expected to show that trivalent methylated arsenicals and arsenothiols are potent inhibitors of GR from human erythrocytes, GR in cultured human cells and mouse tissues. These results will provide novel information about the relation between metabolic conversion of iAs and mechanism of its toxic effects. This finding would suggest that methylation of iAs is not necessarily a detoxification process as it yields potentially toxic trivalent methylated metabolites that may be responsible for some of the adverse effects in exposed organisms. Results of in vivo experiments on mice will provide data about critical levels of exposure to arsenicals that affect activity of GR and the GSH/GSSG ratio in tissues. These data may contribute to the evaluation of the risk of health effects associated with environmental and occupational exposure to arsenicals.