Inhibition of hepatic carnitine palmitoyl-transferase I (CPT IA) by valproyl-CoA as a possible mechanism of valproate-induced steatosis.
OBJECTIVE
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 wild-type 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 non-competitively 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 beta-oxidation, may be a crucial mechanism in the drug-induced hepatotoxicity and the weight gain frequently observed in patients under VPA therapy.
Research Institute for Medicines and Pharmaceutical Sciences -iMED.UL, Metabolism and Genetics Group, Centro de Patogénese Molecular, Faculdade de Farmácia da Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
Cátia C P
CC
Aires
Lodewijk
L
Ijlst
Femke
F
Stet
Carina
C
Prip-Buus
Isabel Tavares
IT
de Almeida
Marinus
M
Duran
Ronald J A
RJ
Wanders
Margarida F B
MF
Silva
D000214:Acyl Coenzyme A / Q000494:pharmacology*; D000818:Animals; D000927:Anticonvulsants / Q000633:toxicity*; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism; D005234:Fatty Liver / Q000139:chemically induced* / Q000201:enzymology; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D010084:Oxidation-Reduction; D010957:Plasmids; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D014162:Transfection; D014635:Valproic Acid / Q000633:toxicity*
D000214:Acyl Coenzyme A; D000927:Anticonvulsants; D004791:Enzyme Inhibitors; D005227:Fatty Acids; C045335:valproyl-coenzyme A; D014635:Valproic Acid; D002334:Carnitine O-Palmitoyltransferase