Hormonal Responses to Cholinergic Input Are Different in Humans with and without Type 2 Diabetes Mellitus

The mechanism of esophagus dysmotility in diabetes and research progress of relating treatments

Introduction: Esophagus dysmotility is a crucial risk factor of gastroesophageal reflux disease (GERD), which is one of the most common diseases in digestive medicine globally. This review emphasizes the mechanisms of esophagus dysmotility in diabetes and summarizes more targeted treatments for these patients to avoid the overuse of proton pump inhibitors (PPIs).Areas covered: Diabetes mellitus (DM) is a clear factor that must not be neglected in the development of GERD. Previous studies have preliminarily researched the esophagus deterioration in diabetes. However, the multi-faceted mechanisms of esophagus dysmotility in diabetes need more studies. Besides, targeted treatments for these patients rather than conventional PPIs are urgently needed.Expert opinion: The treatments for GERD patients with diabetes should be further explored. Pharmacological approaches such as prokinetic agents, psychotherapy can be adopted. Meanwhile, it's feasible to explore non-drug treatments. For example, Electroacupuncture (EA) at Zusanli (ST-36) may be effective to protect the networks of intestinal cells of Cajal (ICCs) in diabetes. More effective approaches should be explored to achieve individualized treatment for these patients.

Sortilin in Glucose Homeostasis: From Accessory Protein to Key Player?

The pharmacological properties and physiological roles of the type I receptor sortilin, also called neurotensin receptor-3, are various and complex. Sortilin is involved in important biological functions from neurotensin and pro-Nerve Growth Factor signaling in the central nervous system to regulation of glucose and lipid homeostasis in the periphery. The peripheral functions of sortilin being less extensively addressed, the focus of the current review is to discuss recent works describing sortilin-induced molecular mechanisms regulating blood glucose homeostasis and insulin signaling. Thus, an overview of several roles ascribed to sortilin in diabetes and other metabolic diseases are presented. Investigations on crucial cellular pathways involved in the protective effect of sortilin receptor on beta cells, including recent discoveries about regulation of cell fate, are also detailed. In addition, we provide a special focus on insulin secretion regulation involving complexes between sortilin and neurotensin receptors. The last section comments on the future research areas which should be developed to address the function of new effectors of the sortilin system in the endocrine apparatus.

Cholinergic signaling mediates the effects of xenin-25 on secretion of pancreatic polypeptide but not insulin or glucagon in humans with impaired glucose tolerance

We previously demonstrated that infusion of an intestinal peptide called xenin-25 (Xen) amplifies the effects of glucose-dependent insulinotropic polypeptide (GIP) on insulin secretion rates (ISRs) and plasma glucagon levels in humans. However, these effects of Xen, but not GIP, were blunted in humans with type 2 diabetes. Thus, Xen rather than GIP signaling to islets fails early during development of type 2 diabetes. The current crossover study determines if cholinergic signaling relays the effects of Xen on insulin and glucagon release in humans as in mice. Fasted subjects with impaired glucose tolerance were studied. On eight separate occasions, each person underwent a single graded glucose infusion- two each with infusion of albumin, Xen, GIP, and GIP plus Xen. Each infusate was administered ± atropine. Heart rate and plasma glucose, insulin, C-peptide, glucagon, and pancreatic polypeptide (PP) levels were measured. ISRs were calculated from C-peptide levels. All peptides profoundly increased PP responses. From 0 to 40 min, peptide(s) infusions had little effect on plasma glucose concentrations. However, GIP, but not Xen, rapidly and transiently increased ISRs and glucagon levels. Both responses were further amplified when Xen was co-administered with GIP. From 40 to 240 min, glucose levels and ISRs continually increased while glucagon concentrations declined, regardless of infusate. Atropine increased resting heart rate and blocked all PP responses but did not affect ISRs or plasma glucagon levels during any of the peptide infusions. Thus, cholinergic signaling mediates the effects of Xen on insulin and glucagon release in mice but not humans.

Locally produced xenin and the neurotensinergic system in pancreatic islet function and β-cell survival

Modulation of neuropeptide receptors is important for pancreatic β-cell function. Here, islet distribution and effects of the neurotensin (NT) receptor modulators, xenin and NT, was examined. Xenin, but not NT, significantly improved glucose disposal and insulin secretion, in mice. However, both peptides stimulated insulin secretion from rodent β-cells at 5.6 mmglucose, with xenin having similar insulinotropic actions at 16.7 mmglucose. In contrast, NT inhibited glucose-induced insulin secretion. Similar observations were made in human 1.1B4 β-cells and isolated mouse islets. Interestingly, similar xenin levels were recorded in pancreatic and small intestinal tissue. Arginine and glucose stimulated xenin release from islets. Streptozotocin treatment decreased and hydrocortisone treatment increased β-cell mass in mice. Xenin co-localisation with glucagon was increased by streptozotocin, but unaltered in hydrocortisone mice. This corresponded to elevated plasma xenin levels in streptozotocin mice. In addition, co-localisation of xenin with insulin was increased by hydrocortisone, and decreased by streptozotocin. Furtherin vitroinvestigations revealed that xenin and NT protected β-cells against streptozotocin-induced cytotoxicity. Xenin augmented rodent and human β-cell proliferation, whereas NT displayed proliferative actions only in human β-cells. These data highlight the involvement of NT signalling pathways for the possible modulation of β-cell function.