Hyperpolarized ketone body metabolism in the rat heart

Abstract

The aim of this work was to investigate the use of 13C‐labelled acetoacetate and β‐hydroxybutyrate as novel hyperpolarized substrates in the study of cardiac metabolism. [1‐13C]Acetoacetate was synthesized by catalysed hydrolysis, and both it and [1‐13C]β‐hydroxybutyrate were hyperpolarized by dissolution dynamic nuclear polarization (DNP). Their metabolism was studied in isolated, perfused rat hearts. Hyperpolarized [1‐13C]acetoacetate metabolism was also studied in the in vivo rat heart in the fed and fasted states. Hyperpolarization of [1‐13C]acetoacetate and [1‐13C]β‐hydroxybutyrate provided liquid state polarizations of 8 ± 2% and 3 ± 1%, respectively. The hyperpolarized T 1 values for the two substrates were 28 ± 3 s (acetoacetate) and 20 ± 1 s (β‐hydroxybutyrate). Multiple downstream metabolites were observed within the perfused heart, including acetylcarnitine, citrate and glutamate. In the in vivo heart, an increase in acetylcarnitine production from acetoacetate was observed in the fed state, as well as a potential reduction in glutamate. In this work, methods for the generation of hyperpolarized [1‐13C]acetoacetate and [1‐13C]β‐hydroxybutyrate were investigated, and their metabolism was assessed in both isolated, perfused rat hearts and in the in vivo rat heart. These preliminary investigations show that DNP can be used as an effective in vivo probe of ketone body metabolism in the heart.

Metabolism of hyperpolarized 13C‐acetoacetate to β‐hydroxybutyrate detects real‐time mitochondrial redox state and dysfunction in heart tissue

“…HP 13 C-AcAc was first reported as an imaging probe by Jensen et al 43 In that study, ethyl [1,[3][4][5][6][7][8][9][10][11][12][13] 44 This study demonstrated that metabolism of HP 13 C-ketones can be detected in the heart, and several downstream metabolites of the HP 13 C-agents were observed. We first reported with preliminary results that it is possible to correlate altered mitochondrial redox in perfused rat hearts with the production of HP-β-HB from HP-AcAc.…”

“…HP 13 C‐AcAc was first reported as an imaging probe by Jensen et al In that study, ethyl [1,3‐ 13 C]AcAc was used as a marker for decreased esterase activity in liver tumors but HP‐β‐HB was not detected. Recently, Miller et al investigated the metabolism of HP‐[1‐ 13 C]AcAc and HP[1‐ 13 C]β‐HB in isolated, perfused rat hearts as well as in vivo . This study demonstrated that metabolism of HP 13 C‐ketones can be detected in the heart, and several downstream metabolites of the HP 13 C‐agents were observed.…”

Cardiac metabolic modulation upon low‐carbohydrate low‐protein ketogenic diet in diabetic rats studied in vivo using hyperpolarized 13C pyruvate, butyrate and acetoacetate probes

“…Using [3‐ 13 C]acetoacetate, we were also able to observe [3‐ 13 C]β‐OHB, in which the ratio of β‐OHB to acetoacetate can be used as a measure of redox state . The amplitude of [3‐ 13 C]β‐OHB, however, appeared to be an order smaller compared with the amplitude of [1‐ 13 C]β‐OHB in the study of Miller et al, which may be attributed to the lower T 1 of [3‐ 13 C]β‐OHB as well as the diabetic state of the GK rats compared with healthy rats. In the study of ketone body metabolism, hyperpolarized 13 C β‐OHB probe may be preferable as β‐OHB is the primary circulating ketone body.…”

“…Other hyperpolarized acetoacetate probes have also been reported (i.e. [1‐ 13 C]acetoacetate and [1,3‐ 13 C 2 ]acetoacetate) . Compared to [1‐ 13 C]acetoacetate, [3‐ 13 C]acetoacetate has the advantage of having the chemical shift downfield, away from the chemical shift of metabolic products, which allows more accurate quantification.…”

In vivo detection of γ-glutamyl-transferase up-regulation in glioma using hyperpolarized γ-glutamyl-[1-13C]glycine

“…γ-glutamyl-[1-13 C]glycine fits the essential technical requirements of a useful HP probe 24 . Thanks to localization of the GGT enzyme on the outer surface of the cell membrane, γ-glutamyl-[1-13 C]glycine metabolism occurs in the extracellular space and not in the cytosol or mitochondria as is the case for most HP probes including HP [1-13 C]pyruvate 24 and [1-13 C]dehydroascorbic acid (DHA) 34,35 , or [1,3-13 C]acetoacetate [36][37][38] , respectively. This is a significant advantage as additional transport though the cell membrane would increase the time between HP injection and enzymatic reaction and therefore decrease SNR.…”