title: Inhibition and recovery of rat hepatic glutathione S-transferase zeta and alteration of tyrosine metabolism following dichloroacetate exposure and withdrawal.
abstract: Dichloroacetate (DCA) is an investigational drug for certain metabolic disorders, a by-product of water chlorination and a metabolite of certain industrial solvents and drugs. DCA is biotransformed to glyoxylate by glutathione S-transferase zeta (GSTz1-1), which is identical to maleylacetoacetate isomerase, an enzyme of tyrosine catabolism. Clinically relevant doses of DCA (mg/kg/day) decrease the activity and expression of GSTz1-1, which alters tyrosine metabolism and may cause hepatic and neurological toxicity. The effect of environmental DCA doses (microg/kg/day) on tyrosine metabolism and GSTz1-1 is unknown, as is the time course of recovery from perturbation following subchronic DCA administration. Male Sprague-Dawley rats (200 g) were exposed to 0 microg, 2.5 microg, 250 microg, or 50 mg DCA/kg/day in drinking water for up to 12 weeks. Recovery was followed after the 8-week exposure. GSTz specific activity and protein expression (Western immunoblotting) were decreased in a dose-dependent manner by 12 weeks of exposure. Enzyme activity and expression decreased 95% after a 1-week administration of high-dose DCA. Eight weeks after cessation of high-dose DCA, GSTz activity had returned to control levels. At the 2.5 or 250 microg/kg/day doses, enzyme activity also decreased after 8 weeks' exposure and returned to control levels 1 week after DCA was withdrawn. Urinary excretion of the tyrosine catabolite maleylacetone increased from undetectable amounts in control rats to 60 to 75 microg/kg/24 h in animals exposed to 50 mg/kg/day DCA. The liver/body weight ratio increased in the high-dose group after 8 weeks of DCA. These studies demonstrate that short-term administration of DCA inhibits rat liver GSTz across the wide concentration range to which humans are exposed.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, University of Florida, FL 32610, USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Guo
authors.forename: Vaishali
authors.initials: V
authors.lastname: Dixit
authors.forename: Huiping
authors.initials: H
authors.lastname: Liu
authors.forename: Albert L
authors.initials: AL
authors.lastname: Shroads
authors.forename: George N
authors.initials: GN
authors.lastname: Henderson
authors.forename: Margaret O
authors.initials: MO
authors.lastname: James
authors.forename: Peter W
authors.initials: PW
authors.lastname: Stacpoole
mesh_terms: D000096:Acetone / Q000031:analogs & derivatives / Q000652:urine; D000284:Administration, Oral; D000375:Aging; D000818:Animals; D015153:Blotting, Western; D001835:Body Weight / Q000187:drug effects; D003999:Dichloroacetic Acid / Q000494:pharmacology / Q000652:urine; D004305:Dose-Response Relationship, Drug; D004326:Drinking / Q000187:drug effects; D004334:Drug Administration Schedule; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D008297:Male; D008298:Maleates / Q000652:urine; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D008298:Maleates; C460372:maleylacetone; D000096:Acetone; D014443:Tyrosine; D003999:Dichloroacetic Acid; C498692:Gstz1 protein, rat; D005982:Glutathione Transferase