Fatty Acid Chain Elongation in Palmitate-perfused Working Rat Heart MITOCHONDRIAL ACETYL-CoA IS THE SOURCE OF TWO-CARBON UNITS FOR CHAIN ELONGATION

Janos Kerner; Paul E. Minkler; Edward J. Lesnefsky; Charles L. Hoppel

doi:10.1074/jbc.M113.524314

Fatty Acid Chain Elongation in Palmitate-perfused Working Rat Heart

MITOCHONDRIAL ACETYL-CoA IS THE SOURCE OF TWO-CARBON UNITS FOR CHAIN ELONGATION*

From the ^‡Department of Pharmacology,
^§Center for Mitochondrial Disease, and
^¶Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106 and
the ^‖Louis Stokes Veterans Affairs Medical Center, Cleveland, Ohio 44106

↵1 To whom correspondence should be addressed: Case Western Reserve University, School of Medicine, Dept. of Pharmacology, Wood Bldg. Rm. W147C, 10900 Euclid Ave., Cleveland, OH 44106. Tel.: 216-368-5358; Fax: 216-368-5162; E-mail: janos.kerner{at}case.edu.

↵2 Present address: Dept. of Medicine, Division of Cardiology, Virginia Commonwealth University, Richmond, VA 23249.

Background: In [16,16,16-d₃]palmitic acid (M+3) perfused working hearts, M+3 stearoylcarnitine is formed.

Results: Rat hearts chain-elongate palmitate to stearate and arachidate. Furthermore, rat heart mitochondria catalyze the malonyl/acetyl-CoA-dependent chain elongation of palmitoyl-CoA.

Conclusion: The two-carbon units for fatty acid chain elongation are derived from mitochondrial fatty acid β-oxidation.

Significance: This pathway may represent the molecular basis for heart-specific fatty acid remodeling.

Abstract

Rat hearts were perfused with [1,2,3,4-¹³C₄]palmitic acid (M+4), and the isotopic patterns of myocardial acylcarnitines and acyl-CoAs were analyzed using ultra-HPLC-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%) 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 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 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.