AUTHORS: Bastiaansen JA, Tian C, Mishkovsky M, Duarte JM, Comment A, Gruetter R
Biochimica et Biophysica Acta (BBA), 1830(8): 4171-4178, August 2013
ABSTRACT
Methods
Hyperpolarized [1-13C]acetate prepared via dissolution dynamic nuclear polarization was injected intravenously at different concentrations into rats. The 13C magnetic resonance signals of [1-13C]acetate and [1-13C]acetylcarnitine were recorded in vivo for 1 min. The kinetic rate constants related to the transformation of acetate into acetylcarnitine were deduced from the 3 s time resolution measurements using two approaches, either mathematical modeling or relative metabolite ratios.
Results
Although separated by two biochemical transformations, a kinetic analysis of the 13C label flow from [1-13C]acetate to [1-13C]acetylcarnitine led to a unique determination of the activity of ACS. The in vivo Michaelis constants for ACS were KM = 0.35 ± 0.13 mM and Vmax = 0.199 ± 0.031 μmol/g/min.
Conclusions
The conversion rates from hyperpolarized acetate into acetylcarnitine were quantified in vivo and, although separated by two enzymatic reactions, these rates uniquely defined the activity of ACS. The conversion rates associated with ACS were obtained using two analytical approaches, both methods yielding similar results.
General significance
This study demonstrates the feasibility of directly measuring ACS activity in vivo and, since the activity of ACS can be affected by various pathological states such as cancer or diabetes, the proposed method could be used to non-invasively probe metabolic signatures of ACS in diseased tissue.
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Module: MRI