Hyperpolarized 13C allows a direct measure of flux through a single enzyme-catalyzed step by NMR.
(13)C NMR is a powerful tool for monitoring metabolic fluxes in vivo. The recent availability of automated dynamic nuclear polarization equipment for hyperpolarizing (13)C nuclei now offers the potential to measure metabolic fluxes through select enzyme-catalyzed steps with substantially improved sensitivity. Here, we investigated the metabolism of hyperpolarized [1-(13)C(1)]pyruvate in a widely used model for physiology and pharmacology, the perfused rat heart. Dissolved (13)CO(2), the immediate product of the first step of the reaction catalyzed by pyruvate dehydrogenase, was observed with a temporal resolution of approximately 1 s along with H(13)CO(3)(-), the hydrated form of (13)CO(2) generated catalytically by carbonic anhydrase. In hearts presented with the medium-chain fatty acid octanoate in addition to hyperpolarized [1-(13)C(1)]pyruvate, production of (13)CO(2) and H(13)CO(3)(-) was suppressed by approximately 90%, whereas the signal from [1-(13)C(1)]lactate was enhanced. In separate experiments, it was shown that O(2) consumption and tricarboxylic acid (TCA) cycle flux were unchanged in the presence of added octanoate. Thus, the rate of appearance of (13)CO(2) and H(13)CO(3)(-) from [1-(13)C(1)]pyruvate does not reflect production of CO(2) in the TCA cycle but rather reflects flux through pyruvate dehydrogenase exclusively.
Advanced Imaging Research Center, Department of Radiology, and Department of Internal Medicine, Division of Cardiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. matthew.merritt@utsouthwestern.edu
Matthew E
ME
Merritt
Crystal
C
Harrison
Charles
C
Storey
F Mark
FM
Jeffrey
A Dean
AD
Sherry
Craig R
CR
Malloy
D000818:Animals; D002247:Carbon Isotopes / Q000737:chemistry; D002384:Catalysis; D004798:Enzymes / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D009206:Myocardium / Q000201:enzymology; D051381:Rats
D002247:Carbon Isotopes; D004798:Enzymes