Hyperpolarized [2-¹³C, 3-²H₃]Pyruvate Detects Hepatic Gluconeogenesis In Vivo

The feasibility of hyperpolarized [2-¹³C, 3-²H₃]pyruvate for probing gluconeogenesis in vivo was investigated in this study. Whereas hyperpolarized [1-¹³C]pyruvate has clear access to metabolic pathways that convert pyruvate to lactate, alanine, and bicarbonate, its utility for assessing pyruvate carboxylation and gluconeogenesis has been limited by technical challenges, including spectral overlap and an obscure enzymatic step that decarboxylates the labeled carbon. To achieve unambiguous detection of gluconeogenic products, the carbonyl carbon in pyruvate was labeled with ¹³C. To prolong the T₁ relaxation time, [2-¹³C, 3-²H₃]pyruvate was synthesized and dissolved with D₂O after dynamic nuclear polarization. The T₁ of [2-¹³C, 3-²H₃]pyruvate in D₂O could be improved by 76.9% (79.6 s at 1 T and 74.5 s at 3 T) as compared to [2-¹³C]pyruvate in water. Hyperpolarized [2-¹³C, 3-²H₃]pyruvate with D₂O dissolution was applied to rat livers in vivo under normal feeding and fasting conditions. A gluconeogenic product, [2-¹³C]phosphoenolpyruvate, was observed at 149.9 ppm from fasted rats only, highlighting the utility of [2-¹³C, 3-²H₃]pyruvate in detecting key gluconeogenic enzyme activities such as pyruvate carboxylase and phosphoenolpyruvate carboxykinase in vivo.