Determination of human ketone body kinetics using stable-isotope labelled tracers

Abstract

In order to avoid the use of radioactive tracers for the determination of human ketone body turnover, we have developed a method using a primed-continuous infusion of 13C-labelled acetoacetate or D-β-hydroxybutyrate. Determination of the mole percent enrichment of blood acetoacetate and D-β-hydroxybutyrate was performed by gas chromatography/mass spectrometry. In the post-absorptive state, the mean total ketone body appearance rate, determined in four subjects, was 3.74 μmol · kg-1 · min-1 using [3,4-13 C2] acetoacetate and 2.76 μmol · kg-1 · min-1 using [3-13C]D-β-hydroxybutyrate, values in agreement with those reported in studies with 14C-labelled tracers. In order to evaluate the usefulness of the method for determination of ketone body kinetics in non steady-state conditions, we infused four subjects with natural sodium acetoacetate and calculated the isotopically determined total ketone body appearance rate using a single compartment model (volume of distribution 0.201/kg; functional pool fraction: 1). During the tests with [3,4-13C2]-acetoacetate, the actual infusion rates of natural acetoacetate were 7.3±0.3, 14.6±0.8, 21.9±1.2 and 10.9 ± 0.6 μ mol · kg-1 · min-1 whereas the corresponding isotopically determined total ketone body appearance rates were respectively 9.2±1.0, 16.3±0.7, 23.1±1.1 and 10.7±0.8 μmol· kg-1 · min-1. During the tests with [3-13C]D-β-hydroxybutyrate, the actual infusion rates were 8.4 ± 0.5, 16.8 ± 0.9, 25.2 ±1.4 and 12.6±0.8 μmol · kg-1 · min-1, and the isotopically determined appearance rates respectively 11.1±0.7, 16.7±0.7, 25.0±1.1 and 11.1 ± 0.7 μmol · kg-1 · min-1. Thus, using either tracer we found a good agreement between acetoacetate infusion rate and tracer-determined appearance rate of ketone bodies. In conclusion, the present method may be used to determine human ketone body kinetics under steady-state and non steady-state conditions. © 1986 Springer-Verlag.