title: Metabolic activation of tris(2,3-dibromopropyl)phosphate to reactive intermediates. II. Covalent binding, reactive metabolite formation, and differential metabolite-specific DNA damage in vivo.
abstract: Analogs of tris(2,3-dibromopropyl)phosphate (Tris-BP) either labeled at specific positions with carbon-14 and phosphorus-32 or dual-labeled with both deuterium and tritium were administered to male Wistar rats at a nephrotoxic dose of 360 mumol/kg. The covalent binding of Tris-BP metabolites to hepatic, renal, and testicular proteins was determined after 9 and 24 hr, and plasma concentrations of bis(2,3-dibromopropyl)-phosphate (Bis-BP) formed metabolically from Tris-BP were measured at intervals throughout the initial 9-hr postdosing period. The covalent binding of 14C-Tris-BP metabolites in the kidney (2495 +/- 404 pmol/mg protein) was greater than that in the liver (476 +/- 123 pmol/mg protein) or testes (94 +/- 11 pmol/mg protein); the extent of renal covalent protein binding of Tris-BP metabolites was decreased by 82 and 84% when deuterium was substituted at carbon-2 and carbon-3, respectively. Substitution of Tris-BP with deuterium at carbon-2 or carbon-3 also decreased the mean area under the curve for Bis-BP plasma concentration by 48 and 57%, respectively. The mechanism of Tris-BP-induced renal and hepatic DNA damage was evaluated in Wistar rats by an automated alkaline elution procedure after the administration of analogs of Tris-BP or Bis-BP labeled at specific positions with deuterium. Renal DNA damage was decreased when Tris-BP was substituted with deuterium at either carbon-2 or carbon-3; the magnitude of the change correlated with both a decrease in the area under the Bis-BP plasma curve and a decrease in renal covalent binding of Tris-BP metabolites for each of the deuterated analogs. In marked contrast, analogs of Bis-BP labeled with deuterium at carbon-2 or carbon-3 did not show a decrease in the severity of renal DNA damage compared to unlabeled Bis-BP. On the basis of these observations a metabolic scheme for hepatic P-450-mediated oxidation at either carbon-2 or carbon-3 of Tris-BP affording Bis-BP by two alternate pathways that are susceptible to primary deuterium kinetic isotope effects is proposed. The Tris-BP metabolite, Bis-BP, is subsequently metabolized to reactive intermediates that cause DNA damage and bind to kidney proteins in a mechanism independent of cytochrome P-450.
authors.affiliation: Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle 98195.
authors.forename: P G
authors.initials: PG
authors.lastname: Pearson
authors.forename: J G
authors.initials: JG
authors.lastname: Omichinski
authors.forename: J A
authors.initials: JA
authors.lastname: Holme
authors.forename: R H
authors.initials: RH
authors.lastname: McClanahan
authors.forename: G
authors.initials: G
authors.lastname: Brunborg
authors.forename: E J
authors.initials: EJ
authors.lastname: Søderlund
authors.forename: E
authors.initials: E
authors.lastname: Dybing
authors.forename: S D
authors.initials: SD
authors.lastname: Nelson
mesh_terms: D000818:Animals; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage; D003903:Deuterium; D005411:Flame Retardants / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D008297:Male; D010755:Organophosphates / Q000378:metabolism / Q000493:pharmacokinetics* / Q000633:toxicity; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar
chemical_list: D005411:Flame Retardants; D010755:Organophosphates; C012085:tris(2,3-dibromopropyl)phosphate; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D003903:Deuterium