Reverse-engineering the pancreatic Alpha Cell
Creators: name: Morris, Christina
Publisher: name: Imperial College London
Year: 2012

description: Type 1 diabetes is a chronic condition, in which the immune system attacks the insulin-secreting pancreatic beta cells compromising the reduction of blood glucose that prevents hyperglycaemia. Diabetic complications are correlated with hyperglycaemic events and glucose variability that results from inefficient treatment, and subsequently increases morbidity and mortality in type 1 diabetic individuals. It has been shown that insulin-intensive therapies, like an artificial pancreas system that uses a combination of real-time glucose sensing and continuous insulin delivery, can improve blood sugar control. Despite advances in available care, however, the incidence of hypoglycaemia (in which glucose drops too low) is a major limiting factor for treatment. As a result, the work in this thesis is dedicated to the study of pancreatic alpha cells, which produce glucagon hormone that acts to prevent hypoglycaemic episodes. To realise a more efficient diabetes management system, the aim was to improve our understanding of the secretion dynamics of pancreatic islet glucagon through the development of better measurement techniques and in so doing, to generate data for a glucagon model that can be implemented within Complementary Metal-Oxide Semiconductor technology (CMOS). Subsequently, this has the potential in future to form part of a biologically inspired bi-hormonal artificial pancreas system, to deliver more effective treatment for type 1 diabetic individuals. To obtain data for the glucagon model a novel perifusion device was fabricated and validated which provides high sensitivity in vitro analysis (compared to traditional measurement techniques) of glucagon secretion from pancreatic islets. Empirical glucagon secretion measurements taken under physiological glucose conditions from the perifusion system, in addition to previously published results, provided information for the basis of a model of pulsatile glucagon secretion. Additionally, a study investigating the intracellular alpha cell secretion mechanism via adenosine monophosphate-activated kinase (AMPK) is also presented. AMPK is ubiquitous to all cells where it acts as a glucose sensor for the regulation of glucose levels within the cell. Using quantitative techniques and a pharmaceutical activator, the link between glucose-stimulated glucagon release and the enzyme’s activity was analysed in alpha cells. Lastly, new mass spectrometric methods were examined as a potential alternative tool to the standard Radioimmunoassay/Enzyme-linked immunosorbent measurement techniques used for glucagon detection. Simultaneous multi-analyte monitoring of both mouse glucagon and the two mouse insulins was demonstrated in islet extracts, and glucagon from islet secretions was successfully recorded. This work also revealed specific glucagon peptide adsorption issues which should be addressed for future glucagon quantitative protocol development. In conclusion, the work presented in this thesis has led to the successful development and application of novel technologies, methods and strategies for the high time-resolution study of glucagon secretion. This has contributed towards an empirical model for glucose-stimulated glucagon release that has increased our knowledge base for the development of next generation artificial pancreas systems to tackle hypoglycaemia.