Transient decrease of hepatic NAD+ and amino acid alterations during treatment with valproate: new insights on drug-induced effects in vivo using targeted MS-based metabolomics

Abstract

Therapeutic administration of the drug valproate (VPA) results in metabolic changes at the hepatic level that have not been fully characterized. Interference of this branched-chain fatty acid with the oxidative metabolism of amino acids may have consequences for the downstream biosynthesis of essential cofactors. We aimed to evaluate the effect of VPA on amino acid and NAD+ metabolism using targeted MS-based metabolite profiling. Plasma samples from patients under chronic treatment with VPA were analyzed. VPA was administered to Wistar rats mimicking prolonged and acute treatment, the latter with two different doses. Plasma and liver samples were collected for targeted metabolomics studies using UPLC-MS/MS and GC-FID. Analysis of amino acids in rat plasma and liver and in human plasma demonstrated that drug intake is associated with a particularly significant drop in the levels of tryptophan, and increased levels of glycine and lysine. The lowered plasma tryptophan levels prompted us to study the intracellular content of tryptophan and various nicotinamide adenine dinucleotides. A significant decrease of NAD+ and NADP+ was observed in the liver of rats after the single administration of VPA at two different doses, but not after repeated administration. The observed accumulation of kynurenine intermediates in rat liver tissue suggests a drug-induced interference with the de novo pathway of NAD+ biosynthesis. These findings provide novel insights into the mechanisms of VPA associated hepatocellular dysfunction and/or toxicity, but with possible major relevance to the anticancer effects of the drug.