Involvement of Dipeptidyl Peptidase-4 and Sodium-glucose Co-transporter-2 in Extrapancreatic Glucagon Secretion

Glucagon is a 29-amino acid peptide hormone of essential importance for glucose homeostasis. Hitherto glucagon has been believed to be secreted only from the pancreas, but recent studies show that glucagon is also secreted from an extra pancreatic origin - most likely from enteroendocrine cells in the intestinal epithelium (Baekdal et al., unpublished data). This has fundamentally changed the understanding of glucagon physiology and provides new avenues for the investigation of several metabolic disorders in which hyperglucagonaemia represents a common and important pathophysiological characteristic (including type 2 diabetes). To delineate the physiological role of gut-derived glucagon and its potential pathophysiological implications, and thereby clear the way for new treatment modalities targeting gut glucagon, it is of importance to understand how glucagon secretion from the gut is regulated. In contrast to the regulation of pancreatic glucagon secretion, very little is known about the regulation of gut-derived glucagon. Inhibition of the enzyme dipeptidyl peptidase 4 (DPP-4) which under normal circumstances degrades, and thereby inactivates the two gut-derived incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), has been shown to decrease pancreatic glucagon secretion. This is most likely brought about by increased levels of intact, active GLP-1, which is known to suppress pancreatic glucagon secretion. Furthermore, the sodium-glucose transporter 2 (SGLT-2) seems to be implicated in pancreatic glucagon secretion as inhibitors of SGLT-2 have been shown to increase the secretion of pancreatic glucagon secretion. The present project will employ further investigations of totally pancreatectomised patients to delineate the regulation of gut-derived glucagon secretion with focus on the well-known modulators of pancreatic glucagon secretion, the enzyme DPP-4 and the sodium-glucose co-transporter SGLT-2, respectiv