title: Mercury and selenium interaction in vivo: effects on thioredoxin reductase and glutathione peroxidase.
abstract: Mercury compounds exert toxic effects via interaction with many vital enzymes involved in antioxidant regulation, such as selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx). Selenium supplementation can reactivate the mercury-inhibited TrxR and recover the cell viability in vitro. To gain an insight on how selenium supplementation affects mercury toxicity in vertebrates, we investigated the effects of selenium on the mercury accumulation and TrxR and GPx activities in a fish model. Juvenile zebra-seabreams were exposed either to methylmercury (MeHg) or inorganic mercury (Hg(2+)) in the presence or absence of sodium selenite (Se) for 28 days followed by 14 days of depuration. Mercury accumulation was found to be 10-fold higher under MeHg exposure than under Hg(2+) exposure. Selenium supplementation caused a half decrease of the accumulation of MeHg but did not influence Hg(2+) accumulation. Exposure to both mercurials led to a decrease of the activity of TrxR (<50% of control) in all organs. Se supplementation coincident with Hg(2+) exposure protected the thioredoxin system in fish liver. However, supplementation of Se during the depuration phase had no effects. The activity of GPx was only affected in the brain of fishes upon the exposure to MeHg and coexposure to MeHg and Se. Selenium supplementation has a limited capacity to prevent mercury effects in brain and kidney. These results demonstrate that Se supplementation plays a protective role in a tissue-specific manner and also highlight the importance of TrxR as a main target for mercurials in vivo.
authors.affiliation: Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL), Faculty of Pharmacy, University of Lisbon, Av. Prof. Gama Pinto 1649-003 Lisbon, Portugal. vbranco@ipimar.pt
authors.forename: Vasco
authors.initials: V
authors.lastname: Branco
authors.forename: João
authors.initials: J
authors.lastname: Canário
authors.forename: Jun
authors.initials: J
authors.lastname: Lu
authors.forename: Arne
authors.initials: A
authors.lastname: Holmgren
authors.forename: Cristina
authors.initials: C
authors.lastname: Carvalho
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000493:pharmacokinetics / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D004347:Drug Interactions; D029941:Fish Proteins / Q000378:metabolism*; D005979:Glutathione Peroxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005980:Glutathione Reductase / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008628:Mercury / Q000493:pharmacokinetics / Q000633:toxicity*; D008767:Methylmercury Compounds / Q000493:pharmacokinetics / Q000633:toxicity*; D018482:Muscle, Skeletal / Q000187:drug effects; D021541:Sea Bream; D012643:Selenium / Q000493:pharmacokinetics / Q000494:pharmacology*; D013880:Thioredoxin-Disulfide Reductase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D000975:Antioxidants; D029941:Fish Proteins; D008767:Methylmercury Compounds; D013879:Thioredoxins; D005979:Glutathione Peroxidase; D005980:Glutathione Reductase; D013880:Thioredoxin-Disulfide Reductase; D008628:Mercury; D012643:Selenium; C004925:methylmercuric chloride