Inhibition of hepatic carnitine palmitoyl-transferase I (CPT IA) by valproyl-CoA as a possible mechanism of valproate-induced steatosis

Background/Aims: Carnitine Palmitoyl-transferase I (CPT I) catalyses the synthesis of long-chain (LC)-acylcarnitines from LC-acyl-CoA esters. It is the rate-limiting enzyme of mitochondrial fatty acid, beta-oxidation (FAO) pathway and its activity is regulated by malonyl-CoA. The antiepileptic drug valproic acid (VPA) is a branched chain fatty acid that is activated to the respective CoA ester in the intra- and extra-mitochondrial compartments. This drug has been associated with a clear inhibition of mitochondrial FAO, which motivated our study on its potential effect on hepatic CPT I. Methods: To investigate the effect of valproyl-CoA (VP-CoA) on CPT I, we performed in vitro studies using control human fibroblasts and rat CPT IA expressed in Saccharomyces cerevisiae. In addition to the wildtype enzyme, two mutant rCPT IAs were studied, one of which showing increased sensitivity towards malonyl-CoA (S24A/Q30A), whereas the other one is insensitive to malonyl-CoA (E3A). Results: We demonstrate that VP-CoA inhibits the CPT I activity in control fibroblasts. Similar results were obtained using rCPT IA WT and S24A/Q30A. Importantly, VP-CoA also inhibited the activity of the rCPT IA E3A. We show that VP-CoA inhibits CPT IA competitively with respect to palmitoyl-CoA, and noncompetitively to carnitine. Evidence is provided that VP-CoA interferes at the catalytic domain of CPT IA affecting the sensitivity for malonyl-CoA. Conclusions: The interference of VP-CoA with CPT IA, a pivotal enzyme in mitochondrial fatty acid oxidation, may be a crucial mechanism in the drug-induced hepatotoxicity and the weight gain frequently observed in patients under VPA therapy. (c) 2009 Elsevier Inc. All rights reserved.