Endocrine Abstracts

Background: The beneficial effects of high protein diets on glucose homeostasis are thought to be in part mediated by the modulation of gastroenteropancreatic hormones by protein-derived metabolites such as amino acids. However, the precise mechanisms by which amino acids drive these beneficial effects are not well understood. Protein intake stimulates both insulin and glucagon release; glucagon is now recognized to have other metabolic roles besides increasing blood glucose levels during hyperglycaemia. Glucagon can promote weight loss and may play a role in stimulating insulin secretion via intra-islet signalling. Preliminary data from our group found that circulating levels of 15 amino acids were positively associated with circulating glucagon levels after a high protein meal in humans.

Aim: To identify the amino acids which mediate the effects of protein on glucagon release using isolated pancreatic islets from mice.

Method: The effects of amino acids on glucagon release were investigated using islets isolated from PPG-Cre; GCaMP6 mice, which express tamoxifen-inducible CreERT2 recombinase under the control of preproglucagon (PPG) promoter and have a floxed-STOP cassette upstream of the cytosolic calcium indicator GCaMP6f. Following tamoxifen induction, the islets specifically expressed GCaMP6f in α-cells. Islets were maintained in 6 mM glucose HKRB solution for an hour before being treated with amino acids; 30 mM KCl was used to confirm α-cells viability.

Results: Specific amino acids increased intracellular calcium signalling in α-cells, with the signal peaking 10-20 seconds after the addition of treatment at t60 and gradually returning to baseline at 260-300 seconds after t0. In particularly, compared to vehicle, 10 mM alanine increased the maximum calcium by signal sixfold, 10 mM asparagine and 10 mM ornithine resulted in a fourfold increase, and 10 mM phenylalanine a threefold increase. Understanding how amino acids, regulate glucose homeostasis may help identify new therapeutic targets for type 2 diabetes.