The toxicity of metabolites of sodium valproate in cultured hepatocytes

Inhibition of gluconeogenesis by sodium valproate and its metabolites in isolated rat hepatocytes

The effects of sodium valproate (VP) and the sodium salts of its metabolites (2-en-VP, 4-en-VP, 4-OH-VP, 5-OH-VP and 2-propylglutaric acid) on gluconeogenesis have been examined using isolated rat hepatocytes. VP and its metabolites have a concentration-dependent inhibitory effect on gluconeogenesis from lactate: with increasing drug concentration, the lag in the onset of gluconeogenesis increases and the rate of glucose synthesis decreases. The toxic effect on glucose synthesis from lactate is very dependent on the metabolite used: the inhibitory effect is highest for VP and 4-en-VP, followed by 5-OH-VP, 4-OH-VP, 2-en-VP and finally by 2-propylglutaric acid. Thus, delta-dehydrogenation and omega-oxidation products in particular have a toxic effect on gluconeogenesis in isolated rat hepatocytes. Induction of the omega-oxidation pathway by enzymes inducers such as phenobarbitone may play a role in the eventual hepatotoxicity of VP. With glycerol the gluconeogenic substrate, the inhibitory effect of VP is also present, although to a smaller extent than with lactate. Glucagon abolishes the inhibitory action of VP.

Effects of SKF525A, phenobarbital, fasting, and carnitine on the anticonvulsant activity and neurotoxicity of valproate in mice

The anticonvulsant potency of valproate (VPA), as measured by the maximal electroshock seizure model in mice, was improved by pretreatment with the microsomal inhibitor SKF525A and by fasting, but was reduced by chronic phenobarbital pretreatment. Carnitine did not significantly alter the anticonvulsant properties of VPA. These findings suggest that the efficacy of VPA can be improved by factors that alter its metabolic pattern.

Protection against sodium valproate injury in isolated hepatocytes by alpha-tocopherol and N,N'-diphenyl-p-phenylenediamine

The possibility that lipid peroxidation is involved in valproic acid (VPA) hepatotoxicity was explored by testing the ability of the free-radical scavengers alpha-tocopherol (vitamin E) and N,N'-diphenyl-p-phenylenediamine (DPPD) to protect against VPA toxicity. Rat hepatocyte cultures were treated with toxic doses of VPA, in conjunction with varying doses of vitamin E and DPPD. Lactate dehydrogenase (LDH) release into the culture media was used to calculate an LDH index as a measure of toxicity. Vitamin E afforded increasing protection against VPA toxicity at concentrations of 1.0 to 4.0 microM but then leveled off and did not give complete protection at concentrations up to 8.0 microM. No protection was seen at less than 1.0 microM. DPPD showed increasing protection from 0.05 to 0.50 microM, with complete protection at the highest concentration. These data indicate that VPA toxicity can be prevented by simultaneous administration of free-radical scavengers and support the concept that VPA hepatotoxicity is due to lipid peroxidation.