Pancreatic alpha cells and glucagon secretion: Novel functions and targets in glucose homeostasis

Unlocking the multifaceted roles of GLP-1: Physiological functions and therapeutic potential

Glucagon (GCG) like peptide 1 (GLP-1) has emerged as a powerful player in regulating metabolism and a promising therapeutic target for various chronic diseases. This review delves into the physiological roles of GLP-1, exploring its impact on glucose homeostasis, insulin secretion, and satiety. We examine the compelling evidence supporting GLP-1 receptor agonists (GLP-1RAs) in managing type 2 diabetes (T2D), obesity, and other diseases. The intricate molecular mechanisms underlying GLP-1RAs are explored, including their interactions with pathways like extracellular signal-regulated kinase 1/2 (ERK1/2), activated protein kinase (AMPK), cyclic adenine monophosphate (cAMP), mitogen-activated protein kinase (MAPK), and protein kinase C (PKC). Expanding our understanding, the review investigates the potential role of GLP-1 in cancers. Also, microribonucleic acid (RNA) (miRNAs), critical regulators of gene expression, are introduced as potential modulators of GLP-1 signaling. We delve into the link between miRNAs and T2D obesity and explore specific miRNA examples influencing GLP-1R function. Finally, the review explores the rationale for seeking alternatives to GLP-1RAs and highlights natural products with promising GLP-1 modulatory effects.

Glucagon in glucose homeostasis and metabolic disease: from physiology to therapeutics

Glucagon, a key hormone in glucose homeostasis, plays a central role in maintaining blood glucose levels through hepatic glycogenolysis and gluconeogenesis. Historically, glucagon secretion was believed to be primarily regulated by insulin via the "insulin switch-off" hypothesis, where reduced insulin levels triggered glucagon release. However, this view has been revisited as emerging evidence highlights the complexity of glucagon regulation. New studies demonstrate that glucose itself, along with amino acids and fatty acid oxidation, directly influences glucagon secretion, challenging the insulin-centric perspective. These findings reveal the metabolic versatility of pancreatic α-cells and their capacity to adapt to nutrient availability. Recent therapeutic innovations, such as glucagon receptor antagonists, dual GLP-1/glucagon receptor agonists, and modulators of hepatic glucagon signalling, offer promising strategies to mitigate hyperglycemia, improve energy balance, and address metabolic dysregulation. This review provides an in-depth analysis of glucagon's role in health and disease, emphasizing its therapeutic potential in managing diabetes and related metabolic conditions.

A Bead-Based Quantum Dot Immunoassay Integrated with Multi-Module Microfluidics Enables Real-Time Multiplexed Detection of Blood Insulin and Glucagon

Analyzing diabetes-related hormones such as insulin and glucagon using conventional enzyme-linked immunosorbent assay (ELISA) has been the gold standard. However, ELISAs have a long sample processing time, including blood serum/plasma preparation which restricts the number of measurement time points, making it difficult to accurately track hormone dynamics in relation to each other and to blood glucose levels. Here, a multi-module microfluidic platform, named quantum dot integrated real-time (QIRT)-ELISA system, that uses a bead-based quantum dot-mediated immunoassay (BQI) to continuously monitor insulin and glucagon in whole blood samples and in a multiplexed setting is demonstrated. The use of BQI simplifies the technical aspect of the system, removes the need for bulky and expensive equipment, and most importantly enhances the sensitivity, specificity, and temporal resolution. Validation experiments measuring levels of insulin and glucagon in rats during glucose tolerance tests demonstrate the accuracy of QIRT-ELISA for simultaneously measuring endogenous hormones within the physiological range during an oral glucose load.

Therapeutic Prospects of Undaria pinnatifida Polysaccharides: Extraction, Purification, and Functional Activity

Undaria pinnatifida, an edible brown seaweed that is widely consumed in East Asia, has gained increasing recognition for its health benefits. Among its bioactive compounds, polysaccharides have attracted significant attention due to their diverse biological activity. This review provides a comprehensive overview of recent advancements in the extraction, purification, structural characterization, and bioactivity of U. pinnatifida polysaccharides. We discuss state-of-the-art extraction techniques, including ultrasound-assisted, microwave-assisted, and enzyme-assisted extraction, as well as purification strategies such as membrane separation and chromatographic methods. Furthermore, we highlight their potential biological activity, including antioxidant, immunomodulatory, anticancer, gut health-promoting, and anti-hyperglycemic effects, along with their underlying mechanisms of action. By summarizing the latest research, this review aims to provide valuable insights into the development and application of U. pinnatifida polysaccharides in functional foods and pharmaceuticals.

Use of continuous glucose monitoring when initiating glucagon-like peptide-1 receptor agonist therapy in insulin-treated diabetes

Glucagon-like peptide-1 receptor agonist (GLP-1RA) medications have been shown to be effective in achieving optimal glucose control and reducing all-cause death, cardiovascular death, nonfatal myocardial infarction, hospitalization for heart failure, and end-stage kidney disease in individuals with type 1 (T1D) and type 2 diabetes (T2D). However, use of these medications has been associated with increased hypoglycaemia risk in patients treated with concomitant antihyperglycaemic medications. The risk is particularly high in patients with T1D due to their loss of glucagon counter-regulatory response. This article reviews the effect of GLP-1RA formulations on the development of hypoglycaemia in individuals with T1D and T2D treated with insulin therapy, discusses the benefits of continuous glucose monitoring with GLP-1RA treatment, and presents strategies for safely initiating GLP-1RA therapy in these individuals.

Decoding the Significance of Alpha Cell Function in the Pathophysiology of Type 1 Diabetes

Alpha cells in the pancreas, traditionally known for their role in secreting glucagon to regulate blood glucose levels, are gaining recognition for their involvement in the pathophysiology of type 1 diabetes (T1D). In T1D, autoimmune destruction of beta cells results in insulin deficiency, which in turn may dysregulate alpha cell function, leading to elevated glucagon levels and impaired glucose homeostasis. This dysfunction is characterized by inappropriate glucagon secretion, augmenting the risk of life-threatening hypoglycemia. Moreover, insulin deficiency and autoimmunity alter alpha cell physiological responses, further exacerbating T1D pathophysiology. Recent studies suggest that alpha cells undergo transdifferentiation and interact with beta cells through mechanisms involving gamma-aminobutyric acid (GABA) signaling. Despite these advances, the exact pathways and interactions remain poorly understood and are often debated. Understanding the precise role of alpha cells in T1D is crucial, as it opens up avenues for developing new therapeutic strategies for T1D. Potential strategies include targeting alpha cells to normalize glucagon secretion, utilizing glucagon receptor antagonists, enhancing GABA signaling, and employing glucagon-like peptide-1 (GLP-1) receptor agonists. These approaches aim to improve glycemic control and reduce the risk of hypoglycemic events in individuals with T1D. This review provides an overview of alpha cell function in T1D, highlighting the emerging focus on alpha cell dysfunction in the context of historically well-developed beta cell research.

Intra-islet α-cell Gs signaling promotes glucagon release

Glucagon, a hormone released from pancreatic α-cells, is critical for maintaining euglycemia and plays a key role in the pathophysiology of diabetes. To stimulate the development of new classes of therapeutic agents targeting glucagon release, key α-cell signaling pathways that regulate glucagon secretion need to be identified. Here, we focused on the potential importance of α-cell Gs signaling on modulating α-cell function. Studies with α-cell-specific mouse models showed that activation of α-cell Gs signaling causes a marked increase in glucagon secretion. We also found that intra-islet adenosine plays an unexpected autocrine/paracrine role in promoting glucagon release via activation of α-cell Gs-coupled A2A adenosine receptors. Studies with α-cell-specific Gαs knockout mice showed that α-cell Gs also plays an essential role in stimulating the activity of the Gcg gene, thus ensuring proper islet glucagon content. Our data suggest that α-cell enriched Gs-coupled receptors represent potential targets for modulating α-cell function for therapeutic purposes.

Unveiling cell subpopulations in T1D mouse islets using single-cell RNA sequencing

Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of beta cells by immune cells. The interactions among cells within the islets may be closely linked to the pathogenesis of T1D. In this study, we used single-cell RNA sequencing (scRNA-Seq) to analyze the cellular heterogeneity within the islets of a T1D mouse model. We established a T1D mouse model induced by streptozotocin and identified cell subpopulations using scRNA-Seq technology. Our results revealed 11 major cell types in the pancreatic islets of T1D mice, with heterogeneity observed in the alpha and beta cell subgroups, which may play a crucial role in the progression of T1D. Flow cytometry further confirmed a mature alpha and beta cell reduction in T1D mice. Overall, our scRNA-Seq analysis provided insights into the cellular heterogeneity of T1D islet tissue and highlighted the potential importance of alpha and beta cells in developing T1D.NEW & NOTEWORTHY In this study, we created a comprehensive single-cell atlas of pancreatic islets in a T1D mouse model using scRNA-Seq and identified 11 major cell types in the islets, highlighting the role of alpha and beta cells in T1D. This study revealed a significant reduction in the maturity alpha and beta cells in T1D mice through flow cytometry. It also demonstrated the heterogeneity of alpha and beta cells, potentially crucial for T1D progression. Overall, our scRNA-Seq analysis provided new insights for understanding and treating T1D by studying cell subtype changes and functions.

Bone marrow stem cell-derived β-cells: New issue for diabetes cell therapy

This investigation aimed to establish the promising role of insulin-producing cells (IPCs) growing from bone marrow-mesenchymal stem cells (BM-MSCs) in relieving hyperglycemia induced in rats. BM-MSCs were differentiated into IPCs using three different protocols. The efficiency of BM-MSCs differentiation into IPCs in vitro was confirmed by detecting IPCs specific gene expression (Foxa-2, PDX-1 and Ngn-3) and insulin release assay. The in vivo study design included 3 groups of male Wistar rats; negative control group, diabetic group and IPCs-transfused group (5 ×106 cells of the most functional IPCs/rat). One month after IPCs infusion, serum glucose, insulin, c-peptide and visfatin levels as well as pancreatic glucagon level were quantified. Gene expression analysis of pancreatic Foxa-2 and Sox-17, IGF-1 and FGF-10 was done. Additionally, histological investigation of pancreatic tissue sections was performed. Our data clarified that, the most functional IPCs are those generated from BM-MSCs using differentiation protocol 3 as indicated by the significant up-regulation of Foxa-2, PDX-1 and Ngn-3 gene expression levels. These findings were further emphasized by releasing of a significant amount of insulin in response to glucose load. The transplantation of the IPCs in diabetic rats elicited significant decline in serum glucose, visfatin and pancreatic glucagon levels along with significant rise in serum insulin and c-peptide levels. Moreover, it triggered significant up-regulation in the expression levels of pancreatic Foxa-2, Sox-17, IGF-1 and FGF-10 genes versus the untreated diabetic counterpart. The histopathological examination of pancreatic tissue almost assisted the biochemical and molecular genetic analyses. These results disclose that the cell therapy holds potential to develop a new cure for DM based on the capability of BM-MSCs to generate β-cell phenotype using specific protocol.

Insights into the cellular, molecular, and epigenetic targets of gamma-aminobutyric acid against diabetes: a comprehensive review on its mechanisms

Diabetes is a metabolic disease due to impaired or defective insulin secretion and is considered one of the most serious chronic diseases worldwide. Gamma-aminobutyric acid (GABA) is a naturally occurring non-protein amino acid commonly present in a wide range of foods. A number of studies documented that GABA has good anti-diabetic potential. This review summarized the available dietary sources of GABA as well as animal and human studies on the anti-diabetic properties of GABA, while also discussing the underlying mechanisms. GABA may modulate diabetes through various pathways such as inhibiting the activities of α-amylase and α-glucosidase, promoting β-cell proliferation, stimulating insulin secretion from β-cells, inhibiting glucagon secretion from α-cells, improving insulin resistance and glucose tolerance, and increasing antioxidant and anti-inflammatory activities. However, further mechanistic studies on animals and human are needed to confirm the therapeutic effects of GABA against diabetes.

PEPCK and glucose metabolism homeostasis in arthropods

The fat body is responsible for a variety of functions related to energy metabolism in arthropods, by controlling the processes of de novo glucose production (gluconeogenesis) and glycogen metabolism. The rate-limiting factor of gluconeogenesis is the enzyme phosphoenolpyruvate carboxykinase (PEPCK), generally considered to be the first committed step in this pathway. Although the study of PEPCK and gluconeogenesis has been for decades restricted to mammalian models, especially focusing on muscle and liver tissue, current research has demonstrated particularities about the regulation of this enzyme in arthropods, and described new functions. This review will focus on arthropod PEPCK, discuss different aspects to PEPCK regulation and function, its general role in the regulation of gluconeogenesis and other pathways. The text also presents our views on potentially important new directions for research involving this enzyme in a variety of metabolic adaptations (e.g. diapause), discussing enzyme isoforms, roles during arthropod embryogenesis, as well as involvement in vector-pathogen interactions, contributing to a better understanding of insect vectors of diseases and their control.

Metabolic Messengers: glucagon

Plasma glucose is tightly regulated via the secretion of the two glucose-regulating hormones insulin and glucagon. Situated next to the insulin-secreting β-cells, the α-cells produce and secrete glucagon-one of the body's few blood glucose-increasing hormones. Diabetes is a bihormonal disorder, resulting from both inadequate insulin secretion and dysregulation of glucagon. The year 2023 marks the 100th anniversary of the discovery of glucagon, making it particularly timely to highlight the roles of this systemic metabolic messenger in health and disease.

The impact of macronutrient composition on metabolic regulation: An Islet-Centric view

AIM

The influence of dietary carbohydrates and fats on weight gain is inconclusively understood. We studied the acute impact of these nutrients on the overall metabolic state utilizing the insulin:glucagon ratio (IGR).

METHODS

Following in vitro glucose and palmitate treatment, insulin and glucagon secretion from islets isolated from C57Bl/6J mice was measured. Our human in vivo study included 21 normoglycaemia (mean age 51.9 ± 16.5 years, BMI 23.9 ± 3.5 kg/m² , and HbA1c 36.9 ± 3.3 mmol/mol) and 20 type 2 diabetes (T2D) diagnosed individuals (duration 12 ± 7 years, mean age 63.6 ± 4.5 years, BMI 29.1 ± 2.4 kg/m² , and HbA1c 52.3 ± 9.5 mmol/mol). Individuals consumed a carbohydrate-rich or fat-rich meal (600 kcal) in a cross-over design. Plasma insulin and glucagon levels were measured at -30, -5, and 0 min, and every 30 min until 240 min after meal ingestion.

RESULTS

The IGR measured from mouse islets was determined solely by glucose levels. The palmitate-stimulated hormone secretion was largely glucose independent in the analysed mouse islets. The acute meal tolerance test demonstrated that insulin and glucagon secretion is dependent on glycaemic status and meal composition, whereas the IGR was dependent upon meal composition. The relative reduction in IGR elicited by the fat-rich meal was more pronounced in obese individuals. This effect was blunted in T2D individuals with elevated HbA1c levels.

CONCLUSION

The metabolic state in normoglycaemic individuals and T2D-diagnosed individuals is regulated by glucose. We demonstrate that consumption of a low carbohydrate diet, eliciting a catabolic state, may be beneficial for weight loss, particularly in obese individuals.