Vol. 29, Issue 9, 1210-1215, September 2001

Effect of -Fluorination of Valproic Acid on Valproyl-S-Acyl-CoA Formation in Vivo in Rats

Mark P. Grillo,¹ Grazia Chiellini, Marco Tonelli, and Leslie Z. Benet

Departments of Biopharmaceutical Sciences (M.P.G., L.Z.B.) and Pharmaceutical Chemistry (G.C., M.T.), University of California, San Francisco, California

Studies designed to compare valproic acid (VPA) with its -fluorinated derivative (F-VPA) for their abilities to form acyl-CoA thioester derivatives in vivo are described. Recent studies have shown that -fluorination of a hepatotoxic metabolite of VPA (⁴-VPA) resulted in a nonhepatotoxic derivative. We hypothesize that the decrease in hepatotoxicity may be related to a lack of formation of the intermediary acyl-CoA thioester. To determine the effect of -fluoro substitution on acyl-CoA formation, we synthesized F-VPA and compared it with VPA for its ability to form the acyl-CoA thioester derivative in vivo in rat liver. Thus, after dosing rats with VPA or F-VPA, animals were sacrificed (0.05-, 0.5-, 1-, 2-, and 5-h postadministration) for the analysis of liver tissue. High-performance liquid chromatography (HPLC) and electrospray ionization/tandem mass spectrometry analysis of liver extracts from VPA-dosed rats showed the presence of VPA-CoA that was maximal after 0.5 h (185 nmol/g of liver) and was still measurable 5-h postadministration (90 nmol/g of liver). In agreement with our hypothesis, F-VPA did not form the corresponding acyl-CoA derivative as determined by the absence of F-VPA-CoA upon HPLC analysis of liver extracts from F-VPA-dosed rats. Further examination of liver tissue for the presence of free acids revealed that the differences in acyl-CoA formation cannot be explained by differences in VPA and F-VPA free acid concentrations. From these observations and related studies showing the lack of toxicity due to -fluoro substitution, we propose that metabolism of VPA by acyl-CoA formation may mediate the hepatotoxicity of the drug.