title: Effects of selenite and chelating agents on mammalian thioredoxin reductase inhibited by mercury: implications for treatment of mercury poisoning.
abstract: Mercury toxicity is a highly interesting topic in biomedicine due to the severe endpoints and treatment limitations. Selenite serves as an antagonist of mercury toxicity, but the molecular mechanism of detoxification is not clear. Inhibition of the selenoenzyme thioredoxin reductase (TrxR) is a suggested mechanism of toxicity. Here, we demonstrated enhanced inhibition of activity by inorganic and organic mercury compounds in NADPH-reduced TrxR, consistent with binding of mercury also to the active site selenolthiol. On treatment with 5 μM selenite and NADPH, TrxR inactivated by HgCl(2) displayed almost full recovery of activity. Structural analysis indicated that mercury was complexed with TrxR, but enzyme-generated selenide removed mercury as mercury selenide, regenerating the active site selenocysteine and cysteine residues required for activity. The antagonistic effects on TrxR inhibition were extended to endogenous antioxidants, such as GSH, and clinically used exogenous chelating agents BAL, DMPS, DMSA, and α-lipoic acid. Consistent with the in vitro results, recovery of TrxR activity and cell viability by selenite was observed in HgCl(2)-treated HEK 293 cells. These results stress the role of TrxR as a target of mercurials and provide the mechanism of selenite as a detoxification agent for mercury poisoning.
authors.affiliation: Research Institute for Medicines and Pharmaceutical Sciences, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal. cristina.carvalho@ff.ul.pt
authors.forename: Cristina M L
authors.initials: CM
authors.lastname: Carvalho
authors.forename: Jun
authors.initials: J
authors.lastname: Lu
authors.forename: Xu
authors.initials: X
authors.lastname: Zhang
authors.forename: Elias S J
authors.initials: ES
authors.lastname: Arnér
authors.forename: Arne
authors.initials: A
authors.lastname: Holmgren
mesh_terms: D000818:Animals; D055162:Biocatalysis / Q000187:drug effects; D020134:Catalytic Domain; D002470:Cell Survival / Q000187:drug effects; D002614:Chelating Agents / Q000737:chemistry / Q000494:pharmacology*; D003545:Cysteine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005978:Glutathione / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D008627:Mercuric Chloride / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D008628:Mercury / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D017669:Mercury Compounds / Q000378:metabolism; D008630:Mercury Poisoning / Q000517:prevention & control; D008767:Methylmercury Compounds / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D015394:Molecular Structure; D009249:NADP / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D018036:Selenium Compounds / Q000378:metabolism; D017279:Selenocysteine / Q000378:metabolism; D018038:Sodium Selenite / Q000378:metabolism / Q000494:pharmacology*; D021241:Spectrometry, Mass, Electrospray Ionization; D013880:Thioredoxin-Disulfide Reductase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; D017669:Mercury Compounds; D008767:Methylmercury Compounds; D011994:Recombinant Proteins; D018036:Selenium Compounds; D017279:Selenocysteine; C032901:mercury-selenium complex; D009249:NADP; D008627:Mercuric Chloride; D013880:Thioredoxin-Disulfide Reductase; D008628:Mercury; D005978:Glutathione; D018038:Sodium Selenite; D003545:Cysteine; C004925:methylmercuric chloride