Effects of sodium valproate and 4en-valproic acid on isolated hepatocytes of guinea pigs

Abstract

The effects of valproic acid (VPA) (100 to 2,000 micrograms/ml) and its metabolite 4en-valproic acid (4enVPA) (2 to 2,000 micrograms/ml) on plasma membrane permeability of isolated hepatocytes of guinea pigs were studied. The ability of hepatocytes to exclude trypan blue was decreased significantly (p less than 0.05) by VPA at concentrations higher than 100 micrograms/ml. The leakage of intracellular enzymes, lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) and gamma-glutamyl transpeptidase (GGT), were not significantly increased by VPA within therapeutic concentrations (100-200 micrograms/ml). However, GOT and GPT leakage were significantly increased (p less than 0.05) by VPA, 500 micrograms/ml, but tended to decrease with further increases in VPA concentration. The enzyme leakage or trypan blue exclusion was not significantly altered by 10 micrograms/ml 4enVPA unless phenytoin (PT) (20 micrograms/ml) or phenobarbital (PB) (20 micrograms/ml) was presented. Higher concentrations of 4enVPA significantly decreased the trypan blue exclusion as well as increased GOT and GPT leakage of hepatocytes. Under scanning electron microscopic examination some hepatocytes at therapeutic concentrations of VPA or 4enVPA showed blebs on the membrane. Higher drug concentrations caused serious membrane damage such as pits and pores. These results suggest that there may be at least two mechanisms for the hepatotoxic effect of VPA. One may occur at therapeutic concentrations of VPA, resulting in increases in membrane permeability and decreases in membrane tension of hepatocytes. The other mechanism may occur at high concentrations of VPA or 4enVPA, resulting in substantial damage to the hepatocyte membrane.