ABSTRACT
R-beta-Hydroxypentanoate and beta-ketopentanoate are homologues of physiological ketone bodies R-beta-hydroxybutyrate and acetoacetate. They derive from the oxidation in liver of the R-moiety of R,S-1,3-pentanediol, a potential nutrient. This report documents the metabolism of R-beta-hydroxypentanoate and beta-ketopentanoate in conscious dogs. Whether administered by bolus or constant infusion, the two substrates are interconverted and rapidly metabolized. When beta-ketopentanoate was infused at a rate corresponding to 75% of the dog's caloric requirement, the steady-state total plasma concentration of the two substrates was only 1.3 mM. Because the substrates are precursors of propionyl-CoA, we assayed the urinary concentrations of markers of propionic acidemia. Their accumulation was minor compared with what is observed in patients suffering from propionic acidemia. We conclude that, at least during short-term experiments, R-beta-hydroxypentanoate and beta-ketopentanoate are well metabolized in the dog without apparent intolerance to a large supply of propionyl-CoA.
Subject(s)
Glycols/metabolism , Pentanoic Acids/metabolism , Acyl Coenzyme A/metabolism , Animals , Blood Glucose/metabolism , Dogs , Fat Emulsions, Intravenous , Gas Chromatography-Mass Spectrometry , Liver/metabolism , Mass Spectrometry , Oxidation-Reduction , Parenteral Nutrition , Pentanoic Acids/administration & dosage , Pentanoic Acids/blood , Propionates/urineABSTRACT
We present two techniques for determining the concentration and 13C enrichment of acetate in biological fluids. After the sample has been spiked with an internal standard of [2,2,2,2H3,1-13C]acetate, acetate is first enzymatically converted to acetyl-coenzyme A, which is chemically converted to acetylglycine. The latter is analyzed by gas chromatography-mass spectrometry, either as a methyl ester by positive chemical ionization or as a pentafluorobenzyl ester by negative chemical ionization. The mole percentage enrichment of tissue acetyl-CoA can also be assayed after conversion to acetylglycine pentafluorobenzyl ester.
Subject(s)
Acetates/analysis , Acetyl Coenzyme A/analysis , Acetates/chemistry , Acetyl Coenzyme A/chemistry , Animals , Carbon Isotopes , Dogs , Female , Gas Chromatography-Mass Spectrometry , Linear Models , Male , Rats , Rats, Sprague-DawleyABSTRACT
The labeling of liver extra-mitochondrial acetyl-CoA was investigated in isolated rat livers perfused with [2-(13)C]acetate, [1-(13)C]octanoate, or [1,2,3,4-(13)C4]docosanoate and with drugs that undergo acetylation (phenylaminobutyrate, paraaminobenzoate, and sulfamethoxazole; singly or in combination). The 13C enrichment of mitochondrial acetyl-CoA was probed by the enrichment of R-beta-hydroxybutyrate. The latter was not enriched from [1,2,3,4-(13)C4]docosanoate, thus excluding mitochondrial beta-oxidation of docosanoate. The 13C enrichment of extra-mitochondrial acetyl-CoA was probed by the enrichments of acetylated drugs and of free acetate. In most cases, the four probes yielded different enrichments. Thus, extra-mitochondrial acetyl-CoA appears nonhomogeneous. Competition between drugs alters the labeling of individual acetyl-CoA sub-pools. The labeling pattern of acetylated drugs suggests the existence of more than the two N-acetyltransferases identified so far by others. Our data question the possibility of probing the pool of lipogenic acetyl-CoA via drug acetylation.
