title: The covalent binding to protein of valproic acid and its hepatotoxic metabolite, 2-n-propyl-4-pentenoic acid, in rats and in isolated rat hepatocytes.
abstract: The covalent binding of radioactivity to protein following administration of 14C-labeled analogs of valproic acid (VPA) and a hepatotoxic metabolite thereof, 2-n-propyl-4-pentenoic acid (delta 4-VPA), was investigated in male rats. Covalent binding occurred in a number of tissues, the level of binding being greatest to proteins in liver for each compound. Moreover, the binding of radioactivity from delta 4-VPA to hepatic macromolecules was higher than the corresponding value for VPA. When radiolabeled VPA and delta 4-VPA were incubated with rat hepatocytes, radiolabel again became bound to cellular proteins, the time-course of which suggested the existence of at least two underlying mechanisms. Thus, after initial rapid binding of both substrates, a secondary slow phase was evident, which favored binding of delta 4-VPA. Although phenobarbital pretreatment of rats had little effect on the covalent binding of either substrate to isolated hepatocytes, clofibrate pretreatment markedly enhanced the covalent binding of both VPA and delta 4-VPA to these cells. In contrast, the covalent binding of VPA and delta 4-VPA was suppressed strongly by 4-pentenoic acid, a potent inhibitor of beta-oxidation, but was not affected by metyrapone, an inhibitor of cytochrome P-450 activity. (-)-Borneol and 8-bromo-cAMP, two inhibitors of glucuronidation, acted to decrease the binding of both substrates, although this inhibition was evident only in the early stages of incubation. A similar effect was seen with valeric acid, the saturated analog of 4-pentenoic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle.
authors.forename: D J
authors.initials: DJ
authors.lastname: Porubek
authors.forename: M P
authors.initials: MP
authors.lastname: Grillo
authors.forename: T A
authors.initials: TA
authors.lastname: Baillie
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002849:Chromatography, Gas; D005229:Fatty Acids, Monounsaturated / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D005243:Feces / Q000032:analysis; D066298:In Vitro Techniques; D007274:Injections, Intraperitoneal; D008099:Liver / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014018:Tissue Distribution; D014635:Valproic Acid / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D005229:Fatty Acids, Monounsaturated; C045022:2-propyl-4-pentenoic acid; D014635:Valproic Acid