Role of Glucagon and Its Receptor in the Pathogenesis of Diabetes

Research advances in understanding crosstalk between organs and pancreatic β-cell dysfunction

Obesity has increased dramatically worldwide. Being overweight or obese can lead to various conditions, including dyslipidaemia, hypertension, glucose intolerance and metabolic syndrome (MetS), which may further lead to type 2 diabetes mellitus (T2DM). Previous studies have identified a link between β-cell dysfunction and the severity of MetS, with multiple organs and tissues affected. Identifying the associations between pancreatic β-cell dysfunction and organs is critical. Research has focused on the interaction between the liver, gut and pancreatic β-cells. However, the mechanisms and related core targets are still not perfectly elucidated. The aims of this review were to summarize the mechanisms of β-cell dysfunction and to explore the potential pathogenic pathways and targets that connect the liver, gut, adipose tissue, muscle, and brain to pancreatic β-cell dysfunction.

Stilbenoids from fenugreek seeds alleviate insulin resistance by regulating the PI3K/AKT/mTOR signaling pathway in a type 2 diabetes zebrafish model

Insulin resistance (IR) is the main cause of type 2 diabetes mellitus (T2DM). The specific targets and underlying mechanisms responsible for the ameliorative effects of the stilbenoid compounds found in fenugreek seeds for ameliorating IR require further study. Here, we were predicted by using the network pharmacology prediction, molecular docking and molecular dynamics simulation approach the targets in common and the potential mechanismsof three stilbenoid compounds (rhaponticin, desoxyrhaponticin, and rhapontigenin) in relation to T2DM and IR. The results showed that the compounds may improve IR through the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway. Molecular docking studies revealed that they exhibit high binding affinity with the structural domains of peroxisome proliferator-activated receptor gamma (PPARG), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), PI3K, and AKT. These results suggest that PPARG and GAPDH may be the potential targets for these three compounds in the treatment of T2DM.Subsequently, experiments using the zebrafish T2DM model showed that the stilbenoid compounds had varying degrees of efficacy in improving IR through the PI3K/AKT/mTOR signaling pathway, and rhaponticin had the most promising effects. The findings implicate a potential mechanism of action for the three stilbenoid compounds in enhancing insulin resistance (IR) through modulation of the PI3K/AKT/mTOR pathway.

Tyrosine nitration of glucagon impairs its function: Extending the role of heme in T2D pathogenesis

New studies raise the possibility that the higher glucagon (GCG) level present in type 2 diabetes (T2D) is a compensatory mechanism to enhance β-cell function, rather than induce dysregulated glucose homeostasis, due to an important role for GCG that acts directly within the pancreas on insulin secretion by intra-islet GCG signaling. However, in states of poorly controlled T2D, pancreatic α cell mass increases (overproduced GCG) in response to insufficient insulin secretion, indicating decreased local GCG activity. The reason for this decrease is not clear. Recent evidence has uncovered a new role of heme in cellular signal transduction, and its mechanism involves reversible binding of heme to proteins. Considering that protein tyrosine nitration in diabetic islets increases and glucose-stimulated insulin secretion (GSIS) decreases, we speculated that heme modulates GSIS by transient interaction with GCG and catalyzing its tyrosine nitration, and the tyrosine nitration may impair GCG activity, leading to loss of intra-islet GCG signaling and markedly impaired insulin secretion. Data presented here elucidate a novel role for heme in disrupting local GCG signaling in diabetes. Heme bound to GCG and induced GCG tyrosine nitration. Two tyrosine residues in GCG were both sensitive to the nitrating species. Further, GCG was also demonstrated to be a preferred target peptide for tyrosine nitration by co-incubation with BSA. Tyrosine nitration impaired GCG stimulated cAMP-dependent signaling in islet β cells and decreased insulin release. Our results provided a new role of heme for impaired GSIS in the pathological process of diabetes.

From classical dualistic antagonism to hormone synergy: potential of overlapping action of glucagon, insulin and GLP-1 for the treatment of diabesity

The increasing prevalence of 'diabesity', a combination of type 2 diabetes and obesity, poses a significant global health challenge. Unhealthy lifestyle factors, including poor diet, sedentary behaviour, and high stress levels, combined with genetic and epigenetic factors, contribute to the diabesity epidemic. Diabesity leads to various significant complications such as cardiovascular diseases, stroke, and certain cancers. Incretin-based therapies, such as GLP-1 receptor agonists and dual hormone therapies, have shown promising results in improving glycaemic control and inducing weight loss. However, these therapies also come with certain disadvantages, including potential withdrawal effects. This review aims to provide insights into the cross-interactions of insulin, glucagon, and GLP-1, revealing the complex hormonal dynamics during fasting and postprandial states, impacting glucose homeostasis, energy expenditure, and other metabolic functions. Understanding these hormonal interactions may offer novel hypotheses in the development of 'anti-diabesity' treatment strategies. The article also explores the question of the antagonism of insulin and glucagon, providing insights into the potential synergy and hormonal overlaps between these hormones.

Insulin:Glucagon Bipolar Axis in Obesity With a Glimpse Into Its Association With Insulin Resistance in Different Glucose Tolerance States

BACKGROUND

Dysregulation of insulin and glucagon secretion alters the normal insulin:glucagon ratio (IGR) in type 2 diabetes mellitus, obesity, and metabolic syndrome. This study explores the scope of construing the role of these two diametrically opposing hormones on the glucose level not just in obesity but in different glucose tolerance states by looking at the hormone levels and at the insulin glucagon bipolar axis itself.

MATERIALS AND METHODS

This is an analytical cross-sectional study of 60 healthy adults consisting of an equal number of adults who are lean and adults who are obese. It was conducted at North Eastern Indira Gandhi Regional Institute of Health and Medical Sciences (NEIGRIHMS), located in Shillong City, Meghalaya, India. Fasting glucose, insulin, glucagon, and lipids were estimated. Postprandial estimation of glucose was done two hours after oral administration of 75 grams of glucose solution.

RESULT

The study demonstrated a state of hyperinsulinemia and hyperglucagonemia prevailing in obesity and all sub-categories of the group of persons who are obese. The study showed a higher fasting IGR in the group consisting of adults who were obese (with a mean of 4.11) when compared with the group of adults who are lean (with a mean of 2.24). Fasting IGR was seen to increase with increasing levels of insulin resistance and increasing impairment in glucose tolerance. IGR showed a positive correlation with the homeostatic model assessment for insulin resistance (HOMA-IR) in the impaired fasting glucose (IFG) category and strongly in the impaired glucose tolerance (IGT) category.

CONCLUSION

Hyperglucagonemia in the group of adult persons who are obese indicates a decreased sensitivity of alpha cells to insulin failing insulin to adequately suppress the secretion of glucagon. The study also demonstrated a positive correlation between IGR and HOMA-IR in obesity and all glucose tolerance states of the group of adults who are obese. It is telltale that the sturdier the insulin resistance, the higher the IGR.

Insulin therapy among diabetic patients in rural communities of Sub-Saharan Africa: a perspective review

In this perspective review, we describe a brief background on the status quo of diabetes mellitus-related therapies and glycemic control among patients in rural communities in sub-Saharan Africa. The article discusses insulin therapy as well as the difficulties in obtaining insulin and oral hypoglycemic medications for diabetic patients living in sub-Saharan Africa. We wrap up our discussion with suggestions on solutions and opportunities for future research to tackle this health challenge in these impoverished communities. We conducted a literature search from PubMed and Google Scholar up until August 2023. Key words were used to generate search terms used to retrieve the required information. All types of literature with pertinent information on the current topic were included in the study. Diabetes mellitus is on the rise in sub-Saharan Africa. Several studies have reported poor glycemic control, low screening rates for diabetes mellitus, cigarette smoking, high alcohol consumption, prescription of antidiabetic therapy, and associated costs as contributors to the uptake of antidiabetic treatment. Although there is paucity of data on the extent of insulin therapy uptake and its possible modifiable contributors among the diabetic patients in the region, the anticipated increase in the number of people with diabetes on the continent makes it critical for global leaders to address the research gaps in insulin therapy among rural communities of sub-Saharan Africa, thus reducing the burden of diabetes in these populations.

An orally available compound suppresses glucagon hypersecretion and normalizes hyperglycemia in type 1 diabetes

Suppression of glucagon hypersecretion can normalize hyperglycemia during type 1 diabetes (T1D). Activating erythropoietin-producing human hepatocellular receptor type-A4 (EphA4) on α cells reduced glucagon hypersecretion from dispersed α cells and T1D islets from both human donor and mouse models. We synthesized a high-affinity small molecule agonist for the EphA4 receptor, WCDD301, which showed robust plasma and liver microsome metabolic stability in both mouse and human preparations. In islets and dispersed islet cells from nondiabetic and T1D human donors, WCDD301 reduced glucagon secretion comparable to the natural EphA4 ligand, Ephrin-A5. In diabetic NOD and streptozotocin-treated mice, once-daily oral administration of WCDD301 formulated with a time-release excipient reduced plasma glucagon and normalized blood glucose for more than 3 months. These results suggest that targeting the α cell EphA4 receptor by sustained release of WCDD301 is a promising pharmacologic pathway for normalizing hyperglycemia in patients with T1D.

Pharmacological inhibitors of β-cell dysfunction and death as therapeutics for diabetes

More than 500 million adults suffer from diabetes worldwide, and this number is constantly increasing. Diabetes causes 5 million deaths per year and huge healthcare costs per year. β-cell death is the major cause of type 1 diabetes. β-cell secretory dysfunction plays a key role in the development of type 2 diabetes. A loss of β-cell mass due to apoptotic death has also been proposed as critical for the pathogenesis of type 2 diabetes. Death of β-cells is caused by multiple factors including pro-inflammatory cytokines, chronic hyperglycemia (glucotoxicity), certain fatty acids at high concentrations (lipotoxicity), reactive oxygen species, endoplasmic reticulum stress, and islet amyloid deposits. Unfortunately, none of the currently available antidiabetic drugs favor the maintenance of endogenous β-cell functional mass, indicating an unmet medical need. Here, we comprehensively review over the last ten years the investigation and identification of molecules of pharmacological interest for protecting β-cells against dysfunction and apoptotic death which could pave the way for the development of innovative therapies for diabetes.