Fluorinated analogues as mechanistic probes in valproic acid hepatotoxicity: Hepatic microvesicular steatosis and glutathione status

Article abstract of DOI:10.1021/tx00047a006

It is postulated that the hepatotoxicity of valproic acid (VPA) results from the mitochondrial β-oxidation of its cytochrome P450 metabolite, 2- propyl-4-pentenoic acid (4-ene VPA), to 2-propyl-(E)-2,4-pentadienoic acid ((E)-2,4-diene VPA) which, in the CoA thioester form, either depletes GSH or produces a putative inhibitor of β-oxidation enzymes. In order to test this hypothesis, 2-fluoro-2-propyl-4-pentenoic acid (α-fluoro-4-ene VPA) which was expected to be inert to β-oxidative metabolism was synthesized and its effect on rat liver studied in comparison with that of 4-ene VPA. Similarly, the known hepatotoxicant 4-pentenoic acid (4-PA) and 2,2-difluoro-4-pentenoic acid (F₂-4-PA) were compared. Male Sprague-Dawley rats (150-180 g, 4 rats per group) were dosed ip with 4-one VPA (0.7 mmol/kg per day), 4-PA (1.0 mmol/kg per day), or equivalent amounts of their α-fluorinated analogues for 5 days. Both 4-ene VPA and 4-PA induced severe hepatic microvesicular steatosis (> 85% affected hepatocytes), and 4-ene VPA produced mitochondrial alterations. By contrast, α-fluoro-4-ene VPA and F₂-4-PA were not observed to cause morphological changes in the liver. The major metabolite of 4-ene VPA in the rat urine and serum was the β-oxidation product (E)-2,4-diene VPA. The N-acetylcysteine (NAC) conjugate of (E)-2,4-diene VPA was also found in the urine. Neither (E)-2,4-diene VPA nor the NAC conjugate could be detected in the rats administered α-fluoro-4-ene VPA. In a second set of rats (3 rats per group), total liver GSH levels were determined to be depleted to 56% and 72% of control following doses of 4-ene VPA (1.4 mmol/kg) and equivalent α-fluoro-4-ene VPA, respectively. Mitochondrial GSH remained unchanged in the α-fluoro-4-ene VPA treated group but was reduced to 68% of control in the rats administered 4-ene VPA. These results strongly support the theory that hepatotoxicity of 4-ene VPA, and possibly VPA itself, is mediated largely through β-oxidation of 4-ene VPA to reactive intermediates that are capable of depleting mitochondrial GSH.