Assessment of mouse liver [1-13C]pyruvate metabolism by dynamic hyperpolarized MRS

Abstract

Hyperpolarized [1-13C]pyruvate magnetic resonance (MR) spectroscopy has the unique ability to detect real-time metabolic changes in vivo owing to its high sensitivity compared with thermal MR and high specificity compared with other metabolic imaging methods. The aim of this study was to explore the potential of hyperpolarized MR spectroscopy for quantification of liver pyruvate metabolism during a hyperinsulinemic–isoglycemic clamp in mice. Hyperpolarized [1-13C]pyruvate was used for in vivo MR spectroscopy of liver pyruvate metabolism in mice. Mice were divided into two groups: (i) non-stimulated 5-h fasted mice and (ii) hyperinsulinemic-isoglycemic clamped mice. During clamp conditions, insulin and donor blood were administered at a constant rate, whereas glucose was infused to maintain isoglycemia. When steady state was reached, insulin-stimulated mice were rapidly infused with hyperpolarized [1-13C]pyruvate for real-time tracking of the dynamic distribution of metabolic derivatives from pyruvate, such as [1-13C]lactate, [1-13C]alanine and [13C]bicarbonate. Isotopomer analysis of plasma glucose confirmed 13C-incorporation from [1-13C]pyruvate into glucose was increased in fasted mice compared with insulin-stimulated mice, demonstrating an increased gluconeogenesis in fasted mice. The AUC ratios for [1-13C]alanine/[1-13C]pyruvate (38.2%), [1-13C]lactate/[1-13C]pyruvate (41.8%) and [13C]bicarbonate/[1-13C]pyruvate (169%) all increased significantly during insulin stimulation. Hyperpolarized [1-13C]pyruvate can be used for in vivo MR spectroscopy of liver pyruvate metabolism during hyperinsulinemic-isoglycemic clamp conditions. Under these conditions, insulin decreased gluconeogenesis and increased [1-13C]alanine, [1-13C]lactate and [13C]bicarbonate after a [1-13C]pyruvate bolus. This application of in vivo spectroscopy has the potential to identify impairments in specific metabolic pathways in the liver associated with obesity, insulin resistance and nonalcoholic fatty liver disease.

Non-Invasive Analysis of Human Liver Metabolism by Magnetic Resonance Spectroscopy

“…Thus, the transition from fasting to feeding, where hepatic carbohydrate metabolic fluxes must undergo acute rearrangements in order to maintain whole body glucose homeostasis-and is, therefore, the most critical and testing phase for glucoregulation-is little understood. The ability to observe fast real-time alterations in hepatic sugar phosphates and other metabolites following administration of tracers, such as [2-13 C]dihydroxyacetone [95][96][97], [1-13 C]pyruvate [98][99][100], and [1-13 C]gluconolactone [101], promises to be invaluable for unveiling the redirection of hepatic carbohydrate fluxes during the fasted to fed transition. Moreover, the direct observation of hepatic metabolites overcomes another important limitation of gluconeogenic tracer enrichment of blood glucose: the inability to resolve gluconeogenic activity of the liver from that of other tissues such as the kidney and intestine.…”

“…Among other things, it commits pyruvate to either a gluconeogenic or lipogenic fate. The metabolic path of hyperpolarized [1- 13 C]pyruvate can be followed in real time [98], thus providing the potential for a deeper understanding on the role of this critical metabolic control point in various nutritional and disease settings [99,100,108].…”

Non-invasive Analysis of Human Liver Metabolism by Magnetic Resonance Spectroscopy

“…In vivo assessment on the effects of insulin on hepatic pyruvate metabolism. 9.4 [81] Comparison of hyperpolarized [1- 13 C]alanine metabolism in rat models of Type 1 and Type 2 diabetes [1- 13 C]alanine had distinctive metabolic fates in the livers from the Type 1 versus the Type 2-diabetes model 3.0 [82] Administration of hyperpolarized 13 C-enriched ethyl acetyl carbonate for in situ generation and MR…”

“…Thus, the transition from fasting to feeding, where hepatic carbohydrate metabolic fluxes must undergo acute rearrangements in order to maintain whole body glucose homeostasis -and is therefore the most critical and testing phase for glucoregulation -is little understood. [79], [81], and [1-13 C]gluconolactone [80] promises to be invaluable for unveiling the redirection of hepatic carbohydrate fluxes during the fasted to fed transition. Moreover, the direct observation of hepatic metabolites overcomes another important limitation of gluconeogenic tracer enrichment of blood glucose: the inability to resolve gluconeogenic activity of the liver from that of other tissues such as the kidney and intestine.…”

“…Among other things, it commits pyruvate to either a gluconeogenic or lipogenic fate. The metabolic path of hyperpolarized [1- 13 C]pyruvate can be followed in real time [75] thus providing the potential for a deeper understanding on the role of this critical metabolic conrol point in various nutritional and disease settings [79,81,82].…”