title: Low micromolar zinc exerts cytotoxic action under H2O2-induced oxidative stress: excessive increase in intracellular Zn2+ concentration.
abstract: The ability of zinc to retard oxidative processes has been recognized for many years. However, zinc is cytotoxic under certain oxidative stress. In this study, we investigated the effect of H2O2 on intracellular Zn2+ concentration of rat thymocytes and its relation to the cytotoxicity. Experiments were cytometrically performed by the use of fluorescent probes, propidium iodide, FluoZin-3-AM, and 5-chloromethylfluorescein diacetate. ZnCl2 potentiated cytotoxicity of H2O2 while TPEN, a chelator for intracellular Zn2+, attenuated it. Results suggested an involvement of intracellular Zn2+ in the cytotoxicity of H2O2. H2O2 at concentrations of 30microM or more (up to 1000microM) significantly increased intracellular Zn2+ concentration. There were two mechanisms. (1) H2O2 decreased cellular content of nonprotein thiols, possibly resulting in release of Zn2+ from thiols as cellular Zn2+ binding sites. (2) H2O2 increased membrane Zn2+ permeability because external ZnCl2 application further elevated intracellular Zn2+ concentration. Micromolar H2O2 may induce excessive elevation of intracellular Zn2+ concentration that is harmful to cellular functions. However, the incubation with micromolar ZnCl2 alone increased cellular content of nonprotein thiols, one of the factors protecting cells against oxidative stress. Though zinc is generally considered to be protective with its antioxidant property, this study reveals the toxic effect of zinc even in micromolar range under oxidative stress induced by H2O2.
authors.affiliation: Faculty of Dental Science, Kyushu University, Fukuoka 812-8582, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Matsui
authors.forename: Tomohiro M
authors.initials: TM
authors.lastname: Oyama
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Okano
authors.forename: Erika
authors.initials: E
authors.lastname: Hashimoto
authors.forename: Takuya
authors.initials: T
authors.lastname: Kawanai
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Oyama
mesh_terms: D000818:Animals; D001665:Binding Sites; D002712:Chlorides / Q000008:administration & dosage / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005452:Fluoresceins / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000633:toxicity*; D066298:In Vitro Techniques; D018384:Oxidative Stress / Q000187:drug effects*; D011083:Polycyclic Compounds / Q000737:chemistry; D011419:Propidium / Q000737:chemistry; D051381:Rats; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*; D017967:Zinc Compounds / Q000008:administration & dosage / Q000633:toxicity*
chemical_list: D002712:Chlorides; C451182:FluoZin-3; D005452:Fluoresceins; D005456:Fluorescent Dyes; D011083:Polycyclic Compounds; D017967:Zinc Compounds; C069306:5-chloromethylfluorescein; D011419:Propidium; C016837:zinc chloride; D006861:Hydrogen Peroxide; D015032:Zinc