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

Drug Metab Dispos. 1989 Mar-Apr;17(2):123-30.


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)

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cells, Cultured
  • Chromatography, Gas
  • Fatty Acids, Monounsaturated / blood
  • Fatty Acids, Monounsaturated / pharmacokinetics*
  • Fatty Acids, Monounsaturated / urine
  • Feces / analysis
  • In Vitro Techniques
  • Injections, Intraperitoneal
  • Liver / metabolism*
  • Magnetic Resonance Spectroscopy
  • Male
  • Protein Binding
  • Rats
  • Rats, Inbred Strains
  • Time Factors
  • Tissue Distribution
  • Valproic Acid / analogs & derivatives
  • Valproic Acid / metabolism*


  • Fatty Acids, Monounsaturated
  • 2-propyl-4-pentenoic acid
  • Valproic Acid