Acetyl-L-carnitine flux to lipids in cells estimated using isotopomer spectral analysis.
Acetyl-L-carnitine is known as a reservoir of activated acetyl units and as a modulator of metabolic function. The objective of this study was to quantify the fate of the acetyl moiety of acetyl-L-carnitine in lipogenic pathways. Lipogenesis was studied in an adipocyte model, differentiated 3T3-L1 cells, and a hepatoma cell, HepG2 cells. Lipogenesis and ketogenesis were examined in rat hepatocytes. Both de novo synthesis and elongation of fatty acids were investigated using gas chromatography/mass spectrometry and [1,2-(13)C]acetyl-L-carnitine. Comparisons were performed with [13C]glucose and [13C]acetate. Isotopomer Spectral Analysis, a stable isotope method for differentiating between the enrichment of the precursor and the amount of synthesis was used to analyze the data. Acetyl-L-carnitine was generally less effective than acetate as a precursor for de novo lipogenesis. The effects of acetyl-L-carnitine were not identical to those of acetate plus carnitine as expected if acetyl-L-carnitine flux to acetyl CoA is controlled by carnitine acetyl transferase. Acetyl-L-carnitine (2 mM) contributed approximately 10% of the lipogenic acetyl-CoA used for synthesis and elongation as well as 6% of the ketogenic acetyl-CoA. No differences were found between the precursor enrichment for de novo lipogenesis and for elongation of saturated fatty acids. Flux of acetyl-L-carnitine to lipid was increased, not decreased, by the ATP citrate lyase inhibitor, -hydroxycitrate. In contrast, flux of glucose to lipid was dramatically decreased by this inhibitor. These results indicate that flux of acetyl-L-carnitine to lipid can bypass citrate and utilize cytosolic acetyl-CoA synthesis.
Lligona-Trulla
L
L
Department of Research, Sigma Tau S.p.A., Pomezia, Italy.
Arduini
A
A
Aldaghlas
T A
TA
Calvani
M
M
Kelleher
J K
JK
D016475:3T3 Cells; D000085:Acetates / Q000378:metabolism / Q000494:pharmacology; D000108:Acetylcarnitine / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002247:Carbon Isotopes; D006528:Carcinoma, Hepatocellular; D002784:Cholesterol / Q000096:biosynthesis; D003600:Cytosol / Q000378:metabolism; D005227:Fatty Acids / Q000096:biosynthesis / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D007657:Ketone Bodies / Q000096:biosynthesis; D050356:Lipid Metabolism; D008055:Lipids / Q000096:biosynthesis; D008113:Liver Neoplasms; D051379:Mice; D019308:Palmitic Acid / Q000378:metabolism; D051381:Rats; D014407:Tumor Cells, Cultured
D000085:Acetates; D002247:Carbon Isotopes; D005227:Fatty Acids; D007657:Ketone Bodies; D008055:Lipids; D019308:Palmitic Acid; D000108:Acetylcarnitine; D002784:Cholesterol