title: Human renal organic anion transporter 1-dependent uptake and toxicity of mercuric-thiol conjugates in Madin-Darby canine kidney cells.
abstract: Mercuric ions are highly reactive and form a variety of organic complexes or conjugates in vivo. The renal proximal tubule is a primary target for mercury uptake and toxicity, and circumstantial evidence implicates organic anion transporters in these processes. To test this hypothesis directly, the transport and toxicity of mercuric-thiol conjugates were characterized in a Madin-Darby canine kidney cell line stably transfected with the human organic anion transporter 1 (hOAT1). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-terazolium bromide assays (for mitochondrial dehydrogenase) confirmed that mercuric conjugates of the thiols N-acetylcysteine (NAC), cysteine, or glutathione were more toxic in hOAT1-transfected cells than in the nontransfected cells. The NAC-Hg(2+) conjugate was most cytotoxic, inducing greater than 50% cellular death over 18 h at a concentration of 100 microM. The cytotoxic effects were fully reversed by probenecid (an OAT1 inhibitor) and partially reversed by p-aminohippurate (an OAT1 substrate). Toxicity of this conjugate was reduced by the OAT1-exchangeable dicarboxylates alpha-ketoglutarate, glutarate, and adipate, but not by succinate, a nonexchangeable dicarboxylate. (203)Hg-uptake studies showed probenecid-sensitive uptake of mercury-thiol conjugates in the hOAT1-transfected cells. The apparent K(m) for the NAC-Hg(2+) conjugate was 44 +/- 9 microM. Uptake of the NAC-Hg(2+) conjugate was cis-inhibited by glutarate, but not by methylsuccinate, paralleling their effects on toxicity. Probenecid-sensitive transport of the NAC-Hg(2+) conjugate was also shown to occur in Xenopus laevis oocytes expressing the hOAT1 or the rOAT3 transporters, suggesting that OAT3 may also transport thiol-Hg(2+) conjugates. Thus, renal accumulation and toxicity of thiol-Hg(2+) conjugates may depend in part on the activity of the organic transport system.
authors.affiliation: Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, USA.
authors.forename: Amy G
authors.initials: AG
authors.lastname: Aslamkhan
authors.forename: Yong-Hae
authors.initials: YH
authors.lastname: Han
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Yang
authors.forename: Rudolfs K
authors.initials: RK
authors.lastname: Zalups
authors.forename: John B
authors.initials: JB
authors.lastname: Pritchard
mesh_terms: D000818:Animals; D001692:Biological Transport; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004285:Dogs; D006801:Humans; D007668:Kidney / Q000166:cytology; D008628:Mercury / Q000633:toxicity*; D008629:Mercury Isotopes / Q000378:metabolism; D027362:Organic Anion Transport Protein 1 / Q000378:metabolism*
chemical_list: D008629:Mercury Isotopes; D027362:Organic Anion Transport Protein 1; D008628:Mercury