title: Fatty acid chain elongation in palmitate-perfused working rat heart: mitochondrial acetyl-CoA is the source of two-carbon units for chain elongation.
abstract: Rat hearts were perfused with [1,2,3,4-(13)C4]palmitic acid (M+4), and the isotopic patterns of myocardial acylcarnitines and acyl-CoAs were analyzed using ultra-HPLC-MS/MS. The 91.2% (13)C enrichment in palmitoylcarnitine shows that little endogenous (M+0) palmitate contributed to its formation. The presence of M+2 myristoylcarnitine (95.7%) and M+2 acetylcarnitine (19.4%) is evidence for β-oxidation of perfused M+4 palmitic acid. Identical enrichment data were obtained in the respective acyl-CoAs. The relative (13)C enrichment in M+4 (84.7%, 69.9%) and M+6 (16.2%, 17.8%) stearoyl- and arachidylcarnitine, respectively, clearly shows that the perfused palmitate is chain-elongated. The observed enrichment of (13)C in acetylcarnitine (19%), M+6 stearoylcarnitine (16.2%), and M+6 arachidylcarnitine (17.8%) suggests that the majority of two-carbon units for chain elongation are derived from β-oxidation of [1,2,3,4-(13)C4]palmitic acid. These data are explained by conversion of the M+2 acetyl-CoA to M+2 malonyl-CoA, which serves as the acceptor for M+4 palmitoyl-CoA in chain elongation. Indeed, the (13)C enrichment in mitochondrial acetyl-CoA (18.9%) and malonyl-CoA (19.9%) are identical. No (13)C enrichment was found in acylcarnitine species with carbon chain lengths between 4 and 12, arguing against the simple reversal of fatty acid β-oxidation. Furthermore, isolated, intact rat heart mitochondria 1) synthesize malonyl-CoA with simultaneous inhibition of carnitine palmitoyltransferase 1b and 2) catalyze the palmitoyl-CoA-dependent incorporation of (14)C from [2-(14)C]malonyl-CoA into lipid-soluble products. In conclusion, rat heart has the capability to chain-elongate fatty acids using mitochondria-derived two-carbon chain extenders. The data suggest that the chain elongation process is localized on the outer surface of the mitochondrial outer membrane.
authors.affiliation: From the Department of Pharmacology.
authors.forename: Janos
authors.initials: J
authors.lastname: Kerner
authors.forename: Paul E
authors.initials: PE
authors.lastname: Minkler
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Lesnefsky
authors.forename: Charles L
authors.initials: CL
authors.lastname: Hoppel
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism*; D000818:Animals; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D008316:Malonyl Coenzyme A / Q000378:metabolism; D008929:Mitochondria, Heart / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism* / Q000494:pharmacology*; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D010477:Perfusion; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D004791:Enzyme Inhibitors; D009124:Muscle Proteins; D010171:Palmitoyl Coenzyme A; D019308:Palmitic Acid; D008316:Malonyl Coenzyme A; D000105:Acetyl Coenzyme A; C558401:CPT1B protein, mouse; D002334:Carnitine O-Palmitoyltransferase
keywords: Carnitine; Coenzyme A; Fatty Acid Chain Elongation, Malonyl-CoA, Carnitine Palmitoyltransferase, Acylcarnitines, Acyl-CoAs; Fatty Acid Oxidation; Heart; Mitochondria