Probing hepatic metabolism of [2-C]dihydroxyacetone in vivo with H-decoupled hyperpolarized C-MR.

OBJECTIVES

To enhance detection of the products of hyperpolarized [2-C]dihydroxyacetone metabolism for assessment of three metabolic pathways in the liver in vivo. Hyperpolarized [2-C]DHAc emerged as a promising substrate to follow gluconeogenesis, glycolysis and the glycerol pathways. However, the use of [2-C]DHAc in vivo has not taken off because (i) the chemical shift range of [2-C]DHAc and its metabolic products span over 144 ppm, and (ii) H decoupling is required to increase spectral resolution and sensitivity. While these issues are trivial for high-field vertical-bore NMR spectrometers, horizontal-bore small-animal MR scanners are seldom equipped for such experiments.

METHODS

Real-time hepatic metabolism of three fed mice was probed by H-decoupled C-MR following injection of hyperpolarized [2-C]DHAc. The spectra of [2-C]DHAc and its metabolic products were acquired in a 7 T small-animal MR scanner using three purpose-designed spectral-spatial radiofrequency pulses that excited a spatial bandwidth of 8 mm with varying spectral bandwidths and central frequencies (chemical shifts).

RESULTS

The metabolic products detected in vivo include glycerol 3-phosphate, glycerol, phosphoenolpyruvate, lactate, alanine, glyceraldehyde 3-phosphate and glucose 6-phosphate. The metabolite-to-substrate ratios were comparable to those reported previously in perfused liver.

DISCUSSION

Three metabolic pathways can be probed simultaneously in the mouse liver in vivo, in real time,  using hyperpolarized DHAc.