Reduction by, ligand exchange among, and covalent binding to glutathione and cellular thiols link metabolism and disposition of dietary arsenic species with toxicity

• Published in: Environment international Vol. 144; p. 106086
• Main Authors: Doerge, Daniel R., Twaddle, Nathan C., Churchwell, Mona I., Beland, Frederick A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.11.2020; Elsevier
• Subjects: Animals; Arsenic; Arsenic - toxicity; Arsenicals; Cacodylic Acid - toxicity; Glutathione; Humans; Kinetics; Ligands; Metabolism; Sulfhydryl Compounds; Kinetics; Arsenic; Metabolism; Glutathione
• ISSN: 0160-4120; 1873-6750
• DOI: 10.1016/j.envint.2020.106086

[Display omitted] •Reaction kinetics for glutathione (GSH) with inorganic and methylated arsenic species are reported.•GSH reactions include reduction of pentavalent and complexation with trivalent As species.•The GSH complex of arsenite is also the substrate for enzymatic methylation.•GSH is likely to participate in metabolic activation to and tissue transport of trivalent As species. Arsenic (As) is a common contaminant in the earth’s crust and widely distributed in food and drinking water. As exposures have been associated with human disease, including cancer, diabetes, lung and cardiovascular disorders, and there is accumulating evidence that early life exposures are important in the etiology. Mode-of-action analysis includes a critical role for metabolic activation of As species to reactive trivalent intermediates that disrupt cellular regulatory systems by covalent binding to thiol groups. The central role of glutathione (GSH) in the chemical reactions of metabolism and disposition of arsenic species was investigated here. The chemical kinetics were measured for reactions in which GSH is a ligand for trivalent As complex formation, a reductant for pentavalent As species, and a participant in ligand exchange reactions with other biological As-thiol complexes. The diverse reactions of GSH with As species demonstrate prominent roles in: (1) metabolic activation via reduction; (2) transport from tissues that are the primary sources of reactive trivalent As intermediates following ingestion (intestine and liver) to downstream target organs (e.g., lung, kidney, and bladder); and (3) oxidation to the terminal metabolite, dimethylarsinic acid (DMAV), which is excreted. Studies of As metabolism and disposition emphasize the link between metabolic activation vs. excretion of As (i.e., internal dosimetry of reactive species) and the disruption of critical cellular thiol-based regulatory processes that define the dose-response characteristics of disease in human epidemiological studies and animal models and underpin risk assessment.