title: Chloride and other anions inhibit dichloroacetate-induced inactivation of human liver GSTZ1 in a haplotype-dependent manner.
abstract: The in vivo elimination rate of dichloroacetate (DCA), an investigational drug; is determined by the rate of its biotransformation to glyoxylate, catalyzed by glutathione transferase ζ1 (GSTZ1). DCA is a mechanism-based inactivator of GSTZ1, thus elimination of DCA is slowed with repeated dosing. We observed that chloride, a physiologically important anion, attenuated DCA-induced GSTZ1 inactivation in human liver cytosol in a concentration and GSTZ1 haplotype-dependent way. In the absence of chloride, incubation with 0.5mM DCA resulted in inactivation of GSTZ1 with a half-life of 0.4h (samples with the KRT haplotype) to 0.5h (EGT haplotype). At the hepatic physiological chloride concentration, 38mM, samples with the EGT haplotype retained more activity (80%) following a 2-h incubation with 0.5mM DCA than those possessing the KRT haplotype (55%). The chloride concentration that protected 50% of the GSTZ1 activity following 2-h incubation with 0.5mM DCA (EC50) was 15.0±3.1mM (mean±S.D., n=3) for EGT samples and 36.2±2.2mM for KRT samples. Bromide, iodide and sulfite also protected GSTZ1 from inactivation by DCA, however fluoride, sulfate, carbonate, acetate, cyanide did not. Protection by bromide varied by GSTZ1 haplotype: EC50 was 1.3±0.3mM for the EGT haplotype and 5.0±0.60mM for the KRT haplotype. The EC50 values for iodide and sulfite in liver cytosol samples with EGT haplotype were respectively 0.14±0.06mM and 9.6±1.1mM (mean±S.D., n=3). Because the in vivo half-life of DCA is determined by the fraction of active GSTZ1 in the liver, identifying factors that regulate GSTZ1 activity is important in determining appropriate DCA dosing in humans.
authors.affiliation: Department of Medicinal Chemistry, University of Florida, Gainesville, FL 32610-0485, United States.
authors.forename: Guo
authors.initials: G
authors.lastname: Zhong
authors.affiliation: Department of Medicinal Chemistry, University of Florida, Gainesville, FL 32610-0485, United States.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Li
authors.affiliation: Department of Medicinal Chemistry, University of Florida, Gainesville, FL 32610-0485, United States.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gu
authors.affiliation: Center for Pharmacogenomics, College of Pharmacy, University of Florida, Gainesville, FL 32610-0486, United States.
authors.forename: Taimour
authors.initials: T
authors.lastname: Langaee
authors.affiliation: Department of Medicine, University of Florida, Gainesville, FL 32610-0226, United States; Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610-0226, United States.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Stacpoole
authors.affiliation: Department of Medicinal Chemistry, University of Florida, Gainesville, FL 32610-0485, United States. Electronic address: mojames@ufl.edu.
authors.forename: Margaret O
authors.initials: MO
authors.lastname: James
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002712:Chlorides / Q000494:pharmacology*; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D003999:Dichloroacetic Acid / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D005260:Female; D005982:Glutathione Transferase / Q000378:metabolism*; D006239:Haplotypes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D002712:Chlorides; D003999:Dichloroacetic Acid; C407705:GSTZ1 protein, human; D005982:Glutathione Transferase
keywords: Anion protection; Chloride; DCA-induced inactivation; Dichloroacetate; Glutathione transferase zeta