Characterization of l-aminocarnitine, an inhibitor of fatty acid oxidation

The pathogenesis of hypoketotic hypoglycemia and cardiomyopathy in patients with fatty acid oxidation (FAO) disorders is still poorly understood. In vitro studies are hampered by the lack of natural mutants to asses the effect of FAO inhibition. In addition, only a few inhibitors of FAO are known. Furthermore, most inhibitors of FAO are activating ligands of peroxisome proliferator-activated receptors (PPARs). We show that l-aminocarnitine (l-AC), a carnitine analog, inhibits FAO efficiently, but does not activate PPAR. l-AC inhibits carnitine palmitoyltransferase (CPT) with different sensitivities towards CPT1 and CPT2, as well as carnitine acylcarnitine translocase (CACT). We further characterized l-AC using fibroblasts cell lines from controls and patients with different FAO defects. In these cell lines acylcarnitine profiles were determined in culture medium after loading with [U-¹³C]palmitic acid. In control fibroblasts, l-AC inhibits FAO leading to a reduction of C2-acylcarnitine and elevation of C16-acylcarnitine. In very long-chain acyl-CoA dehydrogenase (VLCAD)-deficient fibroblasts, l-AC decreased the elevated C14-acylcarnitine and increased C16-acylcarnitine. In CACT and CPT2-deficient cell lines, l-AC did not change the already elevated C16-acylcarnitine level, showing that CPT1 is not inhibited. Oxidation of pristanic acid was only partly inhibited at high l-AC concentrations, indicating minimal CACT inhibition. Therefore, we conclude that in intact cells l-AC inhibits CPT2. Combined with our observation that l-AC does not activate PPAR, we suggest that l-AC is useful to simulate a FAO defect in cells from different origin.