The MODY-associated KCNK16 L114P mutation increases islet glucagon secretion and limits insulin secretion resulting in transient neonatal diabetes and glucose dyshomeostasis in adults.

The gain-of-function mutation in the TALK-1 K+ channel (p.L114P) is associated with maturity-onset diabetes of the young (MODY). TALK-1 is a key regulator of ß-cell electrical activity and glucose-stimulated insulin secretion. The KCNK16 gene encoding TALK-1 is the most abundant and ß-cell-restricted K+ channel transcript. To investigate the impact of KCNK16 L114P on glucose homeostasis and confirm its association with MODY, a mouse model containing the Kcnk16 L114P mutation was generated. Heterozygous and homozygous Kcnk16 L114P mice exhibit increased neonatal lethality in the C57BL/6J and the CD-1 (ICR) genetic background, respectively. Lethality is likely a result of severe hyperglycemia observed in the homozygous Kcnk16 L114P neonates due to lack of glucose-stimulated insulin secretion and can be reduced with insulin treatment. Kcnk16 L114P increased whole-cell ß-cell K+ currents resulting in blunted glucose-stimulated Ca2+ entry and loss of glucose-induced Ca2+ oscillations. Thus, adult Kcnk16 L114P mice have reduced glucose-stimulated insulin secretion and plasma insulin levels, which significantly impairs glucose homeostasis. Taken together, this study shows that the MODY-associated Kcnk16 L114P mutation disrupts glucose homeostasis in adult mice resembling a MODY phenotype and causes neonatal lethality by inhibiting islet insulin secretion during development. These data suggest that TALK-1 is an islet-restricted target for the treatment for diabetes.

Activation and inhibition of the sweet taste receptor TAS1R2-TAS1R3 differentially affect glucose tolerance in humans.

The sweet taste receptor, TAS1R2-TAS1R3, is expressed in taste bud cells, where it conveys sweetness, and also in intestinal enteroendocrine cells, where it may facilitate glucose absorption and assimilation. In the present study, our objective was to determine whether TAS1R2-TAS1R3 influences glucose metabolism bidirectionally via hyperactivation with 5 mM sucralose (n = 12) and inhibition with 2 mM sodium lactisole (n = 10) in mixture with 75 g glucose loads during oral glucose tolerance tests (OGTTs) in healthy humans. Plasma glucose, insulin, and glucagon were measured before, during, and after OGTTs up to 120 minutes post-prandially. We also assessed individual participants' sweet taste responses to sucralose and their sensitivities to lactisole sweetness inhibition. The addition of sucralose to glucose elevated plasma insulin responses to the OGTT (F(1, 11) = 4.55, p = 0.056). Sucralose sweetness ratings were correlated with early increases in plasma glucose (R2 = 0.41, p<0.05), as well as increases in plasma insulin (R2 = 0.38, p<0.05) when sucralose was added to the OGTT (15 minute AUC). Sensitivity to lactisole sweetness inhibition was correlated with decreased plasma glucose (R2 = 0.84, p<0.01) when lactisole was added to the OGTT over the whole test (120 minute AUC). In summary, stimulation and inhibition of the TAS1R2-TAS1R3 receptor demonstrates that TAS1R2-TAS1R3 helps regulate glucose metabolism in humans and may have translational implications for metabolic disease risk.

Rapid Correction of the Hypoglycemia State in Nonhuman Primates Using a Glucagon Long-Dissolving Microneedle Patch.

The timely administration of glucagon is a standard clinical practice for the treatment of severe hypoglycemia. However, the process involves cumbersome steps, including the reconstitution of labile glucagon and filling of the syringe, which cause considerable delays in emergency situations. Moreover, multiple dosages are often required to prevent the recurrence of the hypoglycemic episode because of the short half-life of glucagon in plasma. Herein, we develop a glucagon-loaded long-dissolving microneedle (GLMN) patch that exhibits the properties of fast onset and sustained activity for the effective treatment of severe hypoglycemia. Three types of MN patches were fabricated with different dimensions (long, medium, and short). The longer MN patch packaged a higher dosage of glucagon and exhibited supreme mechanical strength compared to the shorter one. Additionally, the longer MN patch could insert more deeply into the skin, resulting in higher permeability of glucagon across the skin tissue and more rapid systemic absorption as compared with the shorter MN patch. The GLMN patch was observed to reverse the effects of hypoglycemia within 15 min of application in animal models (specifically, rat and rhesus monkey models) and maintained long-term glycemic control, owing to highly efficient drug permeation and the drug reservoir effect of the MN base. The current study presents a promising strategy for the rapid reversal of severe hypoglycemia that exhibits the desirable properties of easy use, high efficiency, and sustained action.

Glucagon does not directly stimulate pituitary secretion of ACTH, GH or copeptin.

Glucagon is best known for its contribution to glucose regulation through activation of the glucagon receptor (GCGR), primarily located in the liver. However, glucagon's impact on other organs may also contribute to its potent effects in health and disease. Given that glucagon-based medicine is entering the arena of anti-obesity drugs, elucidating extrahepatic actions of glucagon are of increased importance. It has been reported that glucagon may stimulate secretion of arginine-vasopressin (AVP)/copeptin, growth hormone (GH) and adrenocorticotrophic hormone (ACTH) from the pituitary gland. Nevertheless, the mechanisms and whether GCGR is present in human pituitary are unknown. In this study we found that intravenous administration of 0.2 mg glucagon to 14 healthy subjects was not associated with increases in plasma concentrations of copeptin, GH, ACTH or cortisol over a 120-min period. GCGR immunoreactivity was present in the anterior pituitary but not in cells containing GH or ACTH. Collectively, glucagon may not directly stimulate secretion of GH, ACTH or AVP/copeptin in humans but may instead be involved in yet unidentified pituitary functions.

Maternal nutrient metabolism in the liver during pregnancy.

The liver plays pivotal roles in nutrient metabolism, and correct hepatic adaptations are required in maternal nutrient metabolism during pregnancy. In this review, hepatic nutrient metabolism, including glucose metabolism, lipid and cholesterol metabolism, and protein and amino acid metabolism, is first addressed. In addition, recent progress on maternal hepatic adaptations in nutrient metabolism during pregnancy is discussed. Finally, the factors that regulate hepatic nutrient metabolism during pregnancy are highlighted, and the factors include follicle-stimulating hormone, estrogen, progesterone, insulin-like growth factor 1, prostaglandins fibroblast growth factor 21, serotonin, growth hormone, adrenocorticotropic hormone, prolactin, thyroid stimulating hormone, melatonin, adrenal hormone, leptin, glucagon-like peptide-1, insulin glucagon and thyroid hormone. Our vision is that more attention should be paid to liver nutrient metabolism during pregnancy, which will be helpful for utilizing nutrient appropriately and efficiently, and avoiding liver diseases during pregnancy.

Glucagon kinetics assessed by mathematical modelling during oral glucose administration in people spanning from normal glucose tolerance to type 2 diabetes.

Background/Objectives: Glucagon is important in the maintenance of glucose homeostasis, with also effects on lipids. In this study, we aimed to apply a recently developed model of glucagon kinetics to determine the sensitivity of glucagon variations (especially, glucagon inhibition) to insulin levels ("alpha-cell insulin sensitivity"), during oral glucose administration. Subjects/Methods: We studied 50 participants (spanning from normal glucose tolerance to type 2 diabetes) undergoing frequently sampled 5-hr oral glucose tolerance test (OGTT). The alpha-cell insulin sensitivity and the glucagon kinetics were assessed by a mathematical model that we developed previously. Results: The alpha-cell insulin sensitivity parameter (named SGLUCA; "GLUCA": "glucagon") was remarkably variable among participants (CV=221%). SGLUCA was found inversely correlated with the mean glycemic values, as well as with 2-hr glycemia of the OGTT. When stratifying participants into two groups (normal glucose tolerance, NGT, N=28, and impaired glucose regulation/type 2 diabetes, IGR_T2D, N=22), we found that SGLUCA was lower in the latter (1.50 ± 0.50·10-2 vs. 0.26 ± 0.14·10-2 ng·L-1 GLUCA/pmol·L-1 INS, in NGT and IGR_T2D, respectively, p=0.009; "INS": "insulin"). Conclusions: The alpha-cell insulin sensitivity is highly variable among subjects, and it is different in groups at different glucose tolerance. This may be relevant for defining personalized treatment schemes, in terms of dietary prescriptions but also for treatments with glucagon-related agents.

Glucagon-based therapy for people with diabetes and obesity: What is the sweet spot?

People with obesity and type 2 diabetes have a high prevalence of metabolic-associated steatotic liver disease, hyperlipidemia and cardiovascular disease. Glucagon increases hepatic glucose production; it also decreases hepatic fat accumulation, improves lipidemia and increases energy expenditure. Pharmaceutical strategies to antagonize the glucagon receptor improve glycemic outcomes in people with diabetes and obesity, but they increase hepatic steatosis and worsen dyslipidemia. Co-agonism of the glucagon and glucagon-like peptide-1 (GLP-1) receptors has emerged as a promising strategy to improve glycemia in people with diabetes and obesity. Addition of glucagon receptor agonism enhances weight loss, reduces liver fat and ameliorates dyslipidemia. Prior to clinical use, however, further studies are needed to investigate the safety and efficacy of glucagon and GLP-1 receptor co-agonists in people with diabetes and obesity and related conditions, with specific concerns regarding a higher prevalence of gastrointestinal side effects, loss of muscle mass and increases in heart rate. Furthermore, co-agonists with differing ratios of glucagon:GLP-1 receptor activity vary in their clinical effect; the optimum balance is yet to be identified.

Analysis and dynamical structure of glucose insulin glucagon system with Mittage-Leffler kernel for type I diabetes mellitus.

In this paper, we propose a fractional-order mathematical model to explain the role of glucagon in maintaining the glucose level in the human body by using a generalised form of a fractal fractional operator. The existence, boundedness, and positivity of the results are constructed by fixed point theory and the Lipschitz condition for the biological feasibility of the system. Also, global stability analysis with Lyapunov's first derivative functions is treated. Numerical simulations for fractional-order systems are derived with the help of Lagrange interpolation under the Mittage-Leffler kernel. Results are derived for normal and type 1 diabetes at different initial conditions, which support the theoretical observations. These results play an important role in the glucose-insulin-glucagon system in the sense of a closed-loop design, which is helpful for the development of artificial pancreas to control diabetes in society.

Glucagon resistance and metabolic-associated steatotic liver disease: a review of the evidence.

Metabolic-associated steatotic liver disease (MASLD) is closely associated with obesity. MASLD affects over 1 billion adults globally but there are few treatment options available. Glucagon is a key metabolic regulator, and its actions include the reduction of liver fat through direct and indirect means. Chronic glucagon signalling deficiency is associated with hyperaminoacidaemia, hyperglucagonaemia and increased circulating levels of glucagon-like peptide 1 (GLP-1) and fibroblast growth factor 21 (FGF-21). Reduction in glucagon activity decreases hepatic amino acid and triglyceride catabolism; metabolic effects include improved glucose tolerance, increased plasma cholesterol and increased liver fat. Conversely, glucagon infusion in healthy volunteers leads to increased hepatic glucose output, decreased levels of plasma amino acids and increased urea production, decreased plasma cholesterol and increased energy expenditure. Patients with MASLD share many hormonal and metabolic characteristics with models of glucagon signalling deficiency, suggesting that they could be resistant to glucagon. Although there are few studies of the effects of glucagon infusion in patients with obesity and/or MASLD, there is some evidence that the expected effect of glucagon on amino acid catabolism may be attenuated. Taken together, this evidence supports the notion that glucagon resistance exists in patients with MASLD and may contribute to the pathogenesis of MASLD. Further studies are warranted to investigate the direct effects of glucagon on metabolism in patients with MASLD.

Urocortin 3 contributes to paracrine inhibition of islet alpha cells in mice.

Pancreatic alpha cell activity and glucagon secretion lower as glucose levels increase. While part of the decrease is regulated by glucose itself, paracrine signaling by their neighboring beta and delta cells also plays an important role. Somatostatin from delta cells is an important local inhibitor of alpha cells at high glucose. Additionally, urocortin 3 (UCN3) is a hormone that is co-released from beta cells with insulin and acts locally to potentiate somatostatin secretion from delta cells. UCN3 thus inhibits insulin secretion via a negative feedback loop with delta cells, but its role with respect to alpha cells and glucagon secretion is not understood. We hypothesize that the somatostatin-driven glucagon inhibition at high glucose is regulated in part by UCN3 from beta cells. Here, we use a combination of live functional Ca2+ and cAMP imaging as well as direct glucagon secretion measurement, all from alpha cells in intact mouse islets, to determine the contributions of UCN3 to alpha cell behavior. Exogenous UCN3 treatment decreased alpha cell Ca2+ and cAMP levels and inhibited glucagon release. Blocking endogenous UCN3 signaling increased alpha cell Ca2+ by 26.8 ± 7.6%, but this did not result in increased glucagon release at high glucose. Furthermore, constitutive deletion of Ucn3 did not increase Ca2+ activity or glucagon secretion relative to controls. UCN3 is thus capable of inhibiting mouse alpha cells, but, given the subtle effects of endogenous UCN3 signaling on alpha cells, we propose that UCN3-driven somatostatin may serve to regulate local paracrine glucagon levels in the islet instead of inhibiting gross systemic glucagon release.

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 ß-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 ß cells and decreased insulin release. Our results provided a new role of heme for impaired GSIS in the pathological process of diabetes.

Secretion of glucagon, GLP-1 and GIP may be affected by circadian rhythm in healthy males.

BACKGROUND: Glucagon is secreted from pancreatic alpha cells in response to low blood glucose and increases hepatic glucose production. Furthermore, glucagon enhances hepatic protein and lipid metabolism during a mixed meal. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted from gut endocrine cells during meals and control glucose homeostasis by potentiating insulin secretion and inhibiting food intake. Both glucose homeostasis and food intake have been reported to be affected by circadian rhythms and vice versa. In this study, we investigated whether the secretion of glucagon, GLP-1 and GIP was affected by circadian rhythms. METHODS: A total of 24 healthy men with regular sleep schedules were examined for 24 h at the hospital ward with 15 h of wakefulness and 9 h of sleep. Food intake was standardized, and blood samples were obtained every third hour. Plasma concentrations of glucagon, GLP-1 and GIP were measured, and data were analyzed by rhythmometric statistical methods. Available data on plasma glucose and plasma C-peptide were also included. RESULTS: Plasma concentrations of glucagon, GLP-1, GIP, C-peptide and glucose fluctuated with a diurnal 24-h rhythm, with the highest levels during the day and the lowest levels during the night: glucagon (p < 0.0001, peak time 18:26 h), GLP-1 (p < 0.0001, peak time 17:28 h), GIP (p < 0.0001, peak time 18:01 h), C-peptide (p < 0.0001, peak time 17.59 h), and glucose (p < 0.0001, peak time 23:26 h). As expected, we found significant correlations between plasma concentrations of C-peptide and GLP-1 and GIP but did not find correlations between glucose concentrations and concentrations of glucagon, GLP-1 and GIP. CONCLUSIONS: Our results demonstrate that under meal conditions that are similar to that of many free-living individuals, plasma concentrations of glucagon, GLP-1 and GIP were observed to be higher during daytime and evening than overnight. These findings underpin disturbed circadian rhythm as a potential risk factor for diabetes and obesity. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT06166368. Registered 12 December 2023.

Repressing miR-23a promotes the transdifferentiation of pancreatic α cells to ß cells via negatively regulating the expression of SDF-1α.

Pancreatic ß-cell failure is a pathological feature in type 1 diabetes. One promising approach involves inducing transdifferentiation of related pancreatic cell types, specifically α cells that produce glucagon. The chemokine stromal cell-derived factor-1 alpha (SDF-1α) is implicated in pancreatic α-to-ß like cell transition. Here, the serum level of SDF-1α was lower in T1D with C-peptide loss, the miR-23a was negatively correlated with SDF-1α. We discovered that exosomal miR-23a, secreted from ß cells, functionally downregulates the expression of SDF-1α, leading to increased Pax4 expression and decreased Arx expression in vivo. Adenovirus-vectored miR-23a sponge and mimic were constructed to further explored the miR-23a on pancreatic α-to-ß like cell transition in vitro, which yielded results consistent with our cell-based assays. Suppression of miR-23a upregulated insulin level and downregulated glucagon level in STZ-induced diabetes mice models, effectively promoting α-to-ß like cell transition. Our findings highlight miR-23a as a new therapeutic target for regenerating pancreatic ß cells from α cells.

Histology and immunofluorescent study of the pancreas in lovebird (Agapornis personatus).

BACKGROUND: Lovebird (Agapornis personatus) is a monotypic species of bird of the lovebird genus in the parrot family Psittaculidae and order Psittaciformes. OBJECTIVES: The present study was designed to investigate the histology and immunohistochemistry of the pancreas in the lovebird. METHODS: Totally, three adult birds were used. The pancreas was assessed using histological and immunofluorescent staining to detect insulin, glucagon, somatostatin, pancreatic polypeptide (PP) and neuropeptide Y (NY). RESULTS: The exocrine pancreas was composed of pyramidal acinar cells with zymogen granules at the apical cytoplasm. The endocrine pancreas was identified as large alpha, small beta and mixed islets of Langerhans. No intercalated duct was observed. Alpha cells with a density of 28.55% were the most numerous cell type, which were populated throughout the large islets, especially at the periphery. The beta cells with a density of 15.78% were accumulated mostly at the periphery of islets. The delta cells exhibited 17.81% intensity. Despite their lower density, the distribution of delta cells was like that of A cells throughout the islets. PP and NY cells were distinguished with densities of 14.69% and 20.63%, respectively. CONCLUSIONS: Although the arrangement of acinar cells, ductal systems and endocrine islets reflects patterns observed in various avian species, the absence of intercalated duct, the presence of three types of Langerhans islets as alpha, beta and mixed islets and the high expression of NY in the islets were some unique features observed in the current study. These findings contribute to the broader understanding of avian pancreas histology.

Fasting and post prandial pancreatic and enteroendocrine hormone levels in obese and non-obese participants.

Circulating insulin levels are known to be increased in people with higher body mass index (BMI) due to effects of adiposity on insulin resistance, whilst gut hormones have a more complex relationship, with fasting peptideYY (PYY) reported to be inversely related to BMI. This study aimed to further explore fasting and post prandial pancreatic and gut hormone concentrations in plasma samples from obese and non-obese participants. Participants with healthy BMI (n=15), overweight BMI (n=29) and obesity (n=161) had samples taken fasting and 30 min post mixed liquid meal for analysis of glucagon-like peptide-1 (GLP-1), PYY, glucose-dependent insulinotropic polypeptide (GIP), insulin and glucagon. Data visualiation used linear discriminant analysis for dimensionality reduction, to visualise the data and assess scaling of each hormone. Fasting levels of insulin, GIP and PYY were shown to be key classifiers between the 3 groups on ANCOVA analysis, with an observation of increased GIP levels in overweight, but not obese participants. In non-obese subjects, fasting GIP, PYY and insulin correlated with BMI, whereas in subjects with obesity only the pancreatic hormones glucagon and insulin correlated with BMI. Concentrations of total GLP-1 in the fasting state correlated strongly with glucagon levels, highlighting potential assay cross-reactivities. The study, which included a relatively large number of subjects with severe obesity, supported previous evidence of BMI correlating negatively with fasting PYY and positively with fasting insulin. The observation of increased fasting GIP levels in overweight but not obese participants deserves further validation and mechanistic investigation.

Exploring the modulatory effects of sotagliflozin on dyslipidemia in mice: The role of glucagon, fibroblast growth factor 21 and glucagon-like peptide 1.

Sotagliflozin is the first dual SGLT1/2 inhibitor antidiabetic drug approved by the US Food and Drug Administration for the management of heart failure. SGLT1/2 inhibition is observed to potentiate the secretion of the incretin hormone, glucagon-like peptide-1 (GLP-1). The current preclinical research sought to investigate the effect of sotagliflozin on the secretion of fat-regulating peptides such as GLP-1, glucagon and fibroblast growth factor 21 (FGF21) and their prospective association with sotagliflozin's potential beneficial effects on dyslipidaemia. During an oral fat tolerance test in mice, sotagliflozin substantially increased GLP-1 and insulin concentrations. Although sotagliflozin alone did not ameliorate postprandial lipemia, its combination with linagliptin (DPP-IV inhibitor) significantly improved lipid tolerance comparable to orlistat (lipase inhibitor). In a triton-induced hypertriglyceridemia model, sotagliflozin, along with other medications (fenofibrate, exenatide and linagliptin) reduced fat excursion; however, co-administration with linagliptin provided no extra advantage. Furthermore, sotagliflozin stimulated glucagon secretion in the alpha TC1.6 cells and healthy mice, which resulted in an increased circulating FGF21 and ß-hydroxybutyrate concentration. Finally, chronic treatment of sotagliflozin in high-fat diet (HFD)-fed obese mice resulted in reduced body weight gain, liver triglyceride, cholesterol, interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-α) levels compared with the placebo group. However, the addition of linagliptin did not provide any additional benefit. In conclusion, sotagliflozin was found to have an effect on GLP-1 and also stimulate the release of glucagon and FGF21, which are important for regulating fat metabolism. Therefore, sotagliflozin might represent a potential therapeutic approach for the treatment of diabetic dyslipidemia and steatohepatitis.

GLP-1/GLP-1RAs: New Options for the Drug Treatment of NAFLD.

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a global public health concern. Currently, the cornerstone of NAFLD treatment is lifestyle modification and, if necessary, weight loss. However, compliance is a challenge, and this approach alone may not be sufficient to halt and treat the more serious disease development, so medication is urgently needed. Nevertheless, no medicines are approved to treat NAFLD. Glucagon-like peptide-1 (GLP-1) is an enteropeptide hormone that inhibits glucagon synthesis, promotes insulin secretion, and delays gastric emptying. GLP-1 has been found in recent studies to be beneficial for the management of NAFLD, and the marketed GLP-1 agonist drugs have different degrees of effectiveness for NAFLD while lowering blood glucose. In this article, we review GLP-1 and its physiological roles, the pathogenesis of NAFLD, the correlation between NAFLD and GLP-1 signaling, and potential strategies for GLP-1 treatment of NAFLD.