LAUSR

Hyperpolarized [1- 13 C]pyruvate enables direct in vivo assessment of real-time liver enzymatic activities by 13 C magnetic resonance. However, the technique usually requires the injection of a highly supraphysiological dose of pyruvate. We herein demonstrate that liver metabolism can be measured in vivo with hyperpolarized [1- 13 C]pyruvate administered at two- to three-fold the basal plasma concentration. The flux through pyruvate dehydrogenase, assessed by 13 C-labeling of bicarbonate in the fed condition, was found to be saturated or partially inhibited by supraphysiological doses of hyperpolarized [1- 13 C]pyruvate. The [ 13 C]bicarbonate signal detected in the liver of fasted rats nearly vanished after treatment with a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, indicating that the signal originates from the flux through PEPCK. In addition, the normalized [ 13 C]bicarbonate signal in fasted untreated animals is dose independent across a 10-fold range, highlighting that PEPCK and pyruvate carboxylase are not saturated and that hepatic gluconeogenesis can be directly probed in vivo with hyperpolarized [1- 13 C]pyruvate. Can et al. demonstrate the ability to use hyperpolarized [1-13C]pyruvate at nearphysiological concentrations to directly assess liver enzymatic activities by 13C magnetic resonance. While in the fed state, the normalized [13C]bicarbonate signal produced from hyperpolarized [1-13C]pyruvate derives from PDH activity, which is saturated at supraphysiological doses, it results from PEPCK in the fasted state and is dose-independent, allowing non-invasive in vivo detection of hepatic gluconeogenesis.”