Detecting de novo Hepatic Ketogenesis Using Hyperpolarized [2-13C] Pyruvate

Abstract

The role of ketones in metabolic health has progressed over the past two decades, moving from what was perceived as a simple byproduct of fatty acid oxidation to a central player in a multiplicity of disease states. Previous work with hyperpolarized (HP) 13C has shown that ketone production can be detected when using precursors that labeled acetyl-CoA at the C1 position, often in tissues that are not normally recognized as ketogenic. Here, we assay metabolism of HP [2-13C]pyruvate in the perfused mouse liver, a classic metabolic testbed where nutritional conditions can be precisely controlled. Livers perfused with long-chain fatty acids or the medium-chain fatty acid octanoate showed no evidence of ketogenesis in the 13C spectrum. In contrast, addition of dichloroacetate, a potent inhibitor of pyruvate dehydrogenase kinase, resulted in significant production of both acetoacetate and 3-hydroxybutyrate from the pyruvate precursor. This result indicates that ketones are readily produced from carbohydrates, but only in the case where pyruvate dehydrogenase activity is upregulated.

Observing exocrine pancreas metabolism using a novel pancreas perfusion technique in combination with hyperpolarized [1‐13C]pyruvate

“…The perfused rat heart was used to demonstrate an instantaneous loss of carbohydrate oxidation after ischemia, with profound upregulation of lactate production 5,7 . Additionally, methods have been developed to explore pyruvate carboxylase activity 8 as well as flux through the pentose phosphate pathway 9 and gluconeogenesis 3,10 . Determining substrate selection in disease states provides insights that can inform development of treatment approaches.…”

“…This research model retains the native cellular organization and microstructure of the specific organ while enabling precise control of the nutritional environment. Prior studies have applied the ex vivo perfusion extensively to the liver [1][2][3][4] and heart 5,6 to examine the metabolic state. Numerous diseases, such as cardiac ischemia, nonalcoholic fatty liver disease, and diabetes, can be characterized by alterations in metabolic substrate selection.…”

“…5,7 Additionally, methods have been developed to explore pyruvate carboxylase activity 8 as well as flux through the pentose phosphate pathway 9 and gluconeogenesis. 3,10 Determining substrate selection in disease states provides insights that can inform development of treatment approaches. For example, suppressing hepatic anaplerotic and cataplerotic flux in a mouse model of obesity was shown to restore regulation of gluconeogenesis and minimize insulin resistance by protecting against rises in oxidative stress.…”

Oxidation of hyperpolarized [1‐13C]pyruvate in isolated rat kidneys

“…The medium chain fatty acid has been previously used as a competing substrate and shown to alter the utilization of HP [1- 13 C]pyruvate in isolated perfused rat hearts 36,39 and mouse livers. 37,40,41 Kidneys were perfused with nonhyperpolarized [U- 13 C 3 ]pyruvate or a mixture of nonhyperpolarized [U- 13 C 3 ]pyruvate plus a medium chain fatty acid, [2,4,6,[8][9][10][11][12][13] C 4 ]octanoate, for metabolic flux analyses of tissue extracts.…”

Detection and alterations of acetylcarnitine (AC) in human liver by 1H MRS at 3T after supplementation with l‐carnitine

“…Non‐invasive techniques using magnetic resonance spectroscopy and hyperpolarized MRI have emerged, and these allow for direct investigation of hepatic acetylcarnitine in vivo. Acetylcarnitine has been imaged with [2‐ 13 C]pyruvate 8 and [(1,2‐ 13 C 2 )acetyl]‐ l ‐carnitine infusions 9 in rats using hyperpolarized MRI. This however requires specialized equipment, and no groups to date have measured in vivo hepatic acetylcarnitine using 1 H‐MRS.…”