Effect of portal glucose sensing on incretin hormone secretion in a canine model

Automated insulin delivery: benefits, challenges, and recommendations. A Consensus Report of the Joint Diabetes Technology Working Group of the European Association for the Study of Diabetes and the American Diabetes Association

A technological solution for the management of diabetes in people who require intensive insulin therapy has been sought for decades. The last 10 years have seen substantial growth in devices that can be integrated into clinical care. Driven by the availability of reliable systems for continuous glucose monitoring, we have entered an era in which insulin delivery through insulin pumps can be modulated based on sensor glucose data. Over the past few years, regulatory approval of the first automated insulin delivery (AID) systems has been granted, and these systems have been adopted into clinical care. Additionally, a community of people living with type 1 diabetes has created its own systems using a do-it-yourself approach by using products commercialised for independent use. With several AID systems in development, some of which are anticipated to be granted regulatory approval in the near future, the joint Diabetes Technology Working Group of the European Association for the Study of Diabetes and the American Diabetes Association has created this consensus report. We provide a review of the current landscape of AID systems, with a particular focus on their safety. We conclude with a series of recommended targeted actions. This is the fourth in a series of reports issued by this working group. The working group was jointly commissioned by the executives of both organisations to write the first statement on insulin pumps, which was published in 2015. The original authoring group was comprised by three nominated members of the American Diabetes Association and three nominated members of the European Association for the Study of Diabetes. Additional authors have been added to the group to increase diversity and range of expertise. Each organisation has provided a similar internal review process for each manuscript prior to submission for editorial review by the two journals. Harmonisation of editorial and substantial modifications has occurred at both levels. The members of the group have selected the subject of each statement and submitted the selection to both organisations for confirmation.

Automated Insulin Delivery: Benefits, Challenges, and Recommendations. A Consensus Report of the Joint Diabetes Technology Working Group of the European Association for the Study of Diabetes and the American Diabetes Association

A technological solution for the management of diabetes in people who require intensive insulin therapy has been sought for decades. The last 10 years have seen substantial growth in devices that can be integrated into clinical care. Driven by the availability of reliable systems for continuous glucose monitoring, we have entered an era in which insulin delivery through insulin pumps can be modulated based on sensor glucose data. Over the past few years, regulatory approval of the first automated insulin delivery (AID) systems has been granted, and these systems have been adopted into clinical care. Additionally, a community of people living with type 1 diabetes has created its own systems using a do-it-yourself approach by using products commercialized for independent use. With several AID systems in development, some of which are anticipated to be granted regulatory approval in the near future, the joint Diabetes Technology Working Group of the European Association for the Study of Diabetes and the American Diabetes Association has created this consensus report. We provide a review of the current landscape of AID systems, with a particular focus on their safety. We conclude with a series of recommended targeted actions. This is the fourth in a series of reports issued by this working group. The working group was jointly commissioned by the executives of both organizations to write the first statement on insulin pumps, which was published in 2015. The original authoring group was comprised by three nominated members of the American Diabetes Association and three nominated members of the European Association for the Study of Diabetes. Additional authors have been added to the group to increase diversity and range of expertise. Each organization has provided a similar internal review process for each manuscript prior to submission for editorial review by the two journals. Harmonization of editorial and substantial modifications has occurred at both levels. The members of the group have selected the subject of each statement and submitted the selection to both organizations for confirmation.

The effect of capromorelin on glycemic control in healthy dogs

Capromorelin is a ghrelin-receptor agonist widely used as an appetite stimulant in dogs. Capromorelin disrupts glucose homeostasis in cats but information regarding its effects on canine glucose homeostasis is lacking. The study objective was to evaluate the effect of capromorelin on glucose homeostatic mechanisms in healthy dogs. Eight clinically healthy client-owned adult dogs were enrolled in this prospective, cross-over, placebo-controlled study. Dogs were randomized to receive capromorelin (Entyce, 3 mg/kg) or placebo, q24h for 3 d. A wk later, treatments were crossed over. Interstitial glucose (IG) concentrations were measured using a flash glucose monitoring system throughout. On d 1 of each treatment, blood glucose (BG), insulin, glucagon, glucose-dependent insulinotropic peptide (GIP), and glucagon-like peptide-1 (GLP-1) concentrations were measured before drug administration, then before and 30-120 min after feeding a glucose-rich diet (Ensure Plus, 21 kcal/kg). Data were analyzed as a 2-period crossover design using generalized least squares estimation. Capromorelin administration increased mean 48 h IG by10% and mean BG by 20% at 90 and 120 min post-prandially (P < 0.0001). Post-prandially, there was a time-by-treatment effect for insulin (P = 0.03) and GIP (P = 0.0002) because capromorelin doubled geometric mean insulin concentrations at 120 min and increased geometric mean GIP concentrations more rapidly than after placebo. There were no differences in glucagon or GLP-1 concentrations between treatment groups. The increase in post-prandial blood glucose was not the result of overt suppression of incretin hormone secretion. There was also no suppressive effect of capromorelin on insulin.

The evolving story of incretins (GIP and GLP-1) in metabolic and cardiovascular disease: A pathophysiological update

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) have their main physiological role in augmenting insulin secretion after their nutrient-induced secretion from the gut. A functioning entero-insular (gut-endocrine pancreas) axis is essential for the maintenance of a normal glucose tolerance. This is exemplified by the incretin effect (greater insulin secretory response to oral as compared to "isoglycaemic" intravenous glucose administration due to the secretion and action of incretin hormones). GIP and GLP-1 have additive effects on insulin secretion. Local production of GIP and/or GLP-1 in islet α-cells (instead of enteroendocrine K and L cells) has been observed, and its significance is still unclear. GLP-1 suppresses, and GIP increases glucagon secretion, both in a glucose-dependent manner. GIP plays a greater physiological role as an incretin. In type 2-diabetic patients, the incretin effect is reduced despite more or less normal secretion of GIP and GLP-1. While insulinotropic effects of GLP-1 are only slightly impaired in type 2 diabetes, GIP has lost much of its acute insulinotropic activity in type 2 diabetes, for largely unknown reasons. Besides their role in glucose homoeostasis, the incretin hormones GIP and GLP-1 have additional biological functions: GLP-1 at pharmacological concentrations reduces appetite, food intake, and-in the long run-body weight, and a similar role is evolving for GIP, at least in animal studies. Human studies, however, do not confirm these findings. GIP, but not GLP-1 increases triglyceride storage in white adipose tissue not only through stimulating insulin secretion, but also by interacting with regional blood vessels and GIP receptors. GIP, and to a lesser degree GLP-1, play a role in bone remodelling. GLP-1, but not GIP slows gastric emptying, which reduces post-meal glycaemic increments. For both GIP and GLP-1, beneficial effects on cardiovascular complications and neurodegenerative central nervous system (CNS) disorders have been observed, pointing to therapeutic potential over and above improving diabetes complications. The recent finding that GIP/GLP-1 receptor co-agonists like tirzepatide have superior efficacy compared to selective GLP-1 receptor agonists with respect to glycaemic control as well as body weight has renewed interest in GIP, which previously was thought to be without any therapeutic potential. One focus of this research is into the long-term interaction of GIP and GLP-1 receptor signalling. A GLP-1 receptor antagonist (exendin [9-39]) and, more recently, a GIP receptor agonist (GIP [3-30] NH₂ ) and, hopefully, longer-acting GIP receptor agonists for human use will be helpful tools to shed light on the open questions. A detailed knowledge of incretin physiology and pathophysiology will be a prerequisite for designing more effective incretin-based diabetes drugs.

C-peptide enhances glucagon secretion in response to hyperinsulinemia under euglycemic and hypoglycemic conditions

Several studies have associated the presence of residual insulin secretion capability (also referred to as being C-peptide positive) with lower risk of insulin-induced hypoglycemia in patients with type 1 diabetes (T1D), although the reason is unclear. We tested the hypothesis that C-peptide infusion would enhance glucagon secretion in response to hyperinsulinemia during euglycemic and hypoglycemic conditions in dogs (5 male/4 female). After a 2-hour basal period, an intravenous (IV) infusion of insulin was started, and dextrose was infused to maintain euglycemia for 2 hours. At the same time, an IV infusion of either saline (SAL) or C-peptide (CPEP) was started. After this euglycemic period, the insulin and SAL/CPEP infusions were continued for another 2 hours, but the glucose was allowed to fall to approximately 50 mg/dL. In response to euglycemic-hyperinsulinemia, glucagon secretion decreased in SAL but remained unchanged from the basal period in CPEP condition. During hypoglycemia, glucagon secretion in CPEP was 2 times higher than SAL, and this increased net hepatic glucose output and reduced the amount of exogenous glucose required to maintain glycemia. These data suggest that the presence of C-peptide during IV insulin infusion can preserve glucagon secretion during euglycemia and enhance it during hypoglycemia, which could explain why T1D patients with residual insulin secretion are less susceptible to hypoglycemia.

Rapid hepatic metabolism blunts the endocrine action of portally infused GLP-1 in male rats

Glucagon-like peptide-1 (GLP-1) is an enteral peptide that contributes to the incretin effect. GLP-1 action is typically described as endocrine, but this mechanism has been questioned because rapid inactivation in the circulation by dipeptidylpeptidase 4 (DPP4) results in a short half-life, limiting the amount of the hormone that can reach the pancreatic islet. An alternative mechanism for GLP-1 to regulate insulin secretion through neuroendocrine signaling originating from sensors in the portal vein has been proposed. We hypothesized that portal infusion of GLP-1 would cause greater glucose-stimulated insulin secretion than equimolar administration into the jugular vein. To test this, hyperglycemic clamps with superimposed graded infusions of GLP-1 into the jugular or portal veins of male rats were performed. These experiments were repeated with pharmacologic DPP4 inhibition to determine the effect of GLP-1 metabolism in the jugular and portal venous beds. Contrary to our hypothesis, we found a higher insulinotropic effect with jugular compared with portal GLP-1, which was associated with higher plasma concentrations of intact GLP-1. The greater insulinotropic effect of jugular venous GLP-1 persisted even with pharmacological DPP4 inhibition. These findings do not support an important role of portal vein GLP-1 signaling for the incretin effect but highlight the hepatoportal bed as a major site of GLP-1 degradation that persists even with pharmacological inhibition. Together, these results support rapid inactivation of enterally released GLP-1 in the liver as limiting endocrine actions on the β-cell and raise questions about the conventional endocrine model of pharmacologic effects of DPP4 inhibitors.