Fatty acid chain elongation in palmitate-perfused working rat heart: mitochondrial acetyl-CoA is the source of two-carbon units for chain elongation [Lipids]

February 20th, 2014 by Kerner, J., Minkler, P. E., Lesnefsky, E. J., Hoppel, C. L.

Rat hearts were perfused with [1,2,3,4-13C4]palmitic acid (M+4), and the isotopic patterns of myocardial acylcarnitines and acyl-CoAs analyzed using UHPLC-MS/MS. The 91.2% 13C-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 13C-enrichment in M+4 (84.7%, 69.9%) and M+6 (16.2%, 17.8%) in stearoyl- and arachidylcarnitine, respectively, clearly shows that the perfused palmitate is chain elongated. The observed enrichment of 13C 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 [1,2,3,4-13C4]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 13C-enrichment in mitochondrial acetyl-CoA (18.9%) and malonyl-CoA (19.9%) are identical. No 13C-enrichment was found in acylcarnitine species with carbon chain lengths between four and twelve, 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 14C from [2-14C]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.
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