Investigation of pharmacological and physiological regulation of pyruvate dehydrogenase in diabetes using hyperpolarised magnetic resonance spectroscopy

Thesis

In type II diabetes, systemic metabolism is perturbed and on a cellular level the balance of fuel use is upset. More specifically, increased fatty acid use is seen alongside decreased glucose metabolism. This altered fuel use is mediated by changes in the activity and expression of multiple enzymes. One such enzyme within the glucose breakdown pathway is pyruvate dehydrogenase, whose activity is known to be reduced in the diabetic state.

The field of real-time metabolic investigation has rapidly expanded over the past few years due to the invention of technology that has enabled the production of ¹³C labelled hyperpolarised compounds, which can generate high signal levels in magnetic resonance spectroscopy. This has provided the opportunity to measure real-time metabolism of injected hyperpolarised tracers both ex vivo and in vivo.

This thesis aimed to develop the use of hyperpolarised compounds in vivo, to investigate the cardiac and hepatic metabolism of a diabetic rat model. We initially addressed the systemic nature of the disease by establishing a two-slice acquisition for obtaining cardiac and hepatic data during a single injection of hyperpolarised pyruvate. This was tested in the fed and fasted states before being used in the studies described in the subsequent chapters of this thesis.

The value of hyperpolarised compounds in following metabolic modulation by drug treatment was explored in the next chapter. The effect on metabolism of two drugs targeted at pyruvate dehydrogenase, which differed in their isoform specificity, was investigated first in the perfused heart and subsequently in vivo, both in control and diabetic animals. Hyperpolarised magnetic resonance spectroscopy was combined with other established techniques to help both our understanding of the systemic changes that had occurred following treatment, and provide links between cardiac metabolism and function.

The final chapter of this thesis explored the use of hyperpolarised ¹³C pyruvate to understand the effect of hypoxia on pyruvate dehydrogenase, firstly in healthy animals and subsequently in the diabetic, metabolically altered state. Understanding the combination of diabetes and hypoxia was interesting given the existence of several opposing metabolic effects seen in the two states.

Overall this thesis has demonstrated developments in the use of hyperpolarised pyruvate that, when appropriately combined with other techniques, can yield valuable metabolic information, in terms of following disease progression, drug development, and understanding basic metabolism.

Authors: Le Page, L

• Publication date: 2014
• DOI: 10.5287/ora-yxga4kego
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: cardiovascular disease; drug development; magnetic resonance imaging; magnetic resonance spectroscopy; diabetes; hyperpolarised; hypoxia; cardiac imaging
• Subjects: Metabolism; NMR spectroscopy; Diabetes; Physiology; Cardiovascular disease; Biology; Physiology and anatomy