In vivo investigation of hyperpolarized [1,3-13C2]acetoacetate as a metabolic probe in normal brain and in glioma

Chloé Najac,Marina Radoul,Pavithra Viswanath,Anne Marie Gillespie,Lydia M Le Page,Elavarasan Subramani,Georgios Batsios,Sabrina M Ronen

doi:10.1038/s41598-019-39677-2

Abstract

Dysregulation in NAD+/NADH levels is associated with increased cell division and elevated levels of reactive oxygen species in rapidly proliferating cancer cells. Conversion of the ketone body acetoacetate (AcAc) to β-hydroxybutyrate (β-HB) by the mitochondrial enzyme β-hydroxybutyrate dehydrogenase (BDH) depends upon NADH availability. The β-HB-to-AcAc ratio is therefore expected to reflect mitochondrial redox. Previous studies reported the potential of hyperpolarized 13C-AcAc to monitor mitochondrial redox in cells, perfused organs and in vivo. However, the ability of hyperpolarized 13C-AcAc to cross the blood brain barrier (BBB) and its potential to monitor brain metabolism remained unknown. Our goal was to assess the value of hyperpolarized [1,3-13C2]AcAc in healthy and tumor-bearing mice in vivo. Following hyperpolarized [1,3-13C2]AcAc injection, production of [1,3-13C2]β-HB was detected in normal and tumor-bearing mice. Significantly higher levels of [1-13C]AcAc and lower [1-13C]β-HB-to-[1-13C]AcAc ratios were observed in tumor-bearing mice. These results were consistent with decreased BDH activity in tumors and associated with increased total cellular NAD+/NADH. Our study confirmed that AcAc crosses the BBB and can be used for monitoring metabolism in the brain. It highlights the potential of AcAc for future clinical translation and its potential utility for monitoring metabolic changes associated with glioma, and other neurological disorders.

Highlights

It highlights the potential of AcAc for future clinical translation and its potential utility for monitoring metabolic changes associated with glioma, and other neurological disorders
Previous work demonstrated that 13C-AcAc fulfills the technical requirements for a useful hyperpolarized probe: its polarization enhancement, which represents the efficiency of the dissolution dynamic nuclear polarization (DNP) method, and the longitudinal T1 relaxation, that characterizes the lifetime of the hyperpolarized signal, are both sufficient to monitor metabolism[27,28,30]
Our goal was to assess the value of hyperpolarized acetoacetate as a probe to monitor redox in the brain and to develop a non-invasive MR-based method to image metabolic alterations associated with brain disorders

Summary

Introduction

It highlights the potential of AcAc for future clinical translation and its potential utility for monitoring metabolic changes associated with glioma, and other neurological disorders. The toxicity of DHA is likely to limit its clinical translation[25] Another redox probe recently reported is hyperpolarized 13C-acetoacetate (13C-AcAc), which was used to assess mitochondrial redox in lymphoma cells, perfused rat hearts under ischemia, rat hearts in vivo in fed and fasted conditions, and rat kidneys in vivo[26,27,28,29,30]. This approach is based on the fact that the reversible interconversion of AcAc and β-hydroxybutyrate (β-HB) depends on the availability of NADH and the β-hydroxybutyrate dehydrogenase enzyme (BDH), which is located on the inner mitochondrial membrane. To date, we have found no reports of the use of hyperpolarized 13C-AcAc in the brain

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