title: Clioquinol-induced increase and decrease in the intracellular Zn2+ level in rat thymocytes.
abstract: OBJECTIVE
  Clioquinol is emerging as a potential therapy for some diseases, such as Alzheimer disease and cancer. This agent is a lipophilic chelator of Zn(2+). In this study, the effect of clioquinol on the intracellular Zn(2+) level was examined in order to gain insights into the toxicological profile of clioquinol.
  
  
  METHODS
  The effect of clioquinol was estimated using a flow cytometer and FluoZin-3, a fluorescent indicator for Zn(2+), in rat thymocytes.
  
  
  RESULTS
  Clioquinol, at concentrations ranging from 10 to 300 nM, augmented FluoZin-3 fluorescence in a concentration-dependent manner. However, the effect induced by 1 μM clioquinol was less than that by 300 nM clioquinol. Removal of extracellular Zn(2+), using the membrane impermeable Zn(2+)-chelator diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA), abolished the clioquinol-induced augmentation of FluoZin-3 fluorescence. Clioquinol did not augment Fluo-3 fluorescence, an indicator of intracellular Ca(2+), in the presence of DTPA. The results suggested that clioquinol caused an extracellular Zn(2+)-dependent increase in the intracellular Zn(2+) concentration. However, in the presence of DTPA, clioquinol at micromolar concentrations (1-10 μM) attenuated FluoZin-3 fluorescence in a concentration-dependent manner. Clioquinol even at 10 μM did not affect FluoZin-3 fluorescence under cell-free condition. The concentration-response relationship for the clioquinol induced change in Zn(2+) level appeared to be bell-shaped. These results indicate that micromolar concentrations of clioquinol, without chelated Zn(2+), decrease intracellular Zn(2+) concentration.
  
  
  CONCLUSIONS
  The effect of clioquinol on the intracellular Zn(2+) level varies, depending on the extracellular Zn(2+) concentration and the clioquinol concentration. Clioquinol may therefore exert various types of Zn(2+)-dependent cytotoxicity.
authors.affiliation: Laboratory of Cellular Signaling, Division of Environmental Symbiosis Studies, Graduate School of Integrated Arts and Sciences, The University of Tokushima, Tokushima 770-8502, Japan.
authors.forename: Tomohiro M
authors.initials: TM
authors.lastname: Oyama
authors.forename: Shiro
authors.initials: S
authors.lastname: Ishida
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Okano
authors.forename: Hakaru
authors.initials: H
authors.lastname: Seo
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Oyama
mesh_terms: D000818:Animals; D002614:Chelating Agents / Q000494:pharmacology*; D007464:Clioquinol / Q000494:pharmacology*; D005434:Flow Cytometry; D005453:Fluorescence; D004369:Pentetic Acid; D011083:Polycyclic Compounds; D051381:Rats; D060168:Thymocytes / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; C451182:FluoZin-3; D011083:Polycyclic Compounds; D004369:Pentetic Acid; D007464:Clioquinol; D015032:Zinc