Circulating Concentrations Of Glucagon Research Articles

Alpha-cells and therapy of diabetes: Inhibition, antagonism or death?

Absolute or relative hyperglucagonaemia is a characteristic of both Type 1 and Type 2 diabetes, resulting in fasting hyperglycaemia due in part to increased hepatic glucose production and lack of postprandial suppression of circulating glucagon concentrations. Consequently, therapeutics that target glucagon secretion or biological action may be effective antidiabetic agents. In this regard, specific glucagon receptor (GCGR) antagonists have been developed that exhibit impressive glucose-lowering actions, but unfortunately may cause off-target adverse effects in humans. Further to this, several currently approved antidiabetic agents, including GLP-1 mimetics, DPP-4 inhibitors, metformin, sulphonylureas and pramlintide likely exert part of their glucose homeostatic actions through direct or indirect inhibition of GCGR signalling. In addition to agents that inhibit the release of glucagon, compounds that enhance the transdifferentiation of glucagon secreting alpha-cells towards an insulin positive beta-cell phenotype could also help curb excess glucagon secretion in diabetes. Use of alpha-cell toxins represents another possible strategy to address hyperglucagonaemia in diabetes. In that respect, research from the 1920 s with diguanides such as synthalin A demonstrated effective glucose-lowering with alpha-cell ablation in both animal models and humans with diabetes. However, further clinical use of synthalin A was curtailed due its adverse effects and the increased availability of insulin. Overall, these observations with therapeutics that directly target alpha-cells, or GCGR signaling, highlight a largely untapped potential for diabetes therapy that merits further detailed consideration.

Sodium, Glucose and Dysregulated Glucagon Secretion: The Potential of Sodium Glucose Transporters.

Diabetes is defined by hyperglycaemia due to progressive insulin resistance and compromised insulin release. In parallel, alpha cells develop dysregulation of glucagon secretion. Diabetic patients have insufficient glucagon secretion during hypoglycaemia and a lack of inhibition of glucagon secretion at higher blood glucose levels resulting in postprandial hyperglucagonaemia, which contributes to the development of hyperglycaemia. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are an efficient pharmacologic approach for the treatment of hyperglycaemia in type 2 diabetes. While SGLT2 inhibitors aim at increasing glycosuria to decrease blood glucose levels, these inhibitors also increase circulating glucagon concentrations. Here, we review recent advances in our understanding of how SGLTs are involved in the regulation of glucagon secretion. Sodium plays an important role for alpha cell function, and a tight regulation of intracellular sodium levels is important for maintaining plasma membrane potential and intracellular pH. This involves the sodium-potassium pump, sodium-proton exchangers and SGLTs. While the expression of SGLT2 in alpha cells remains controversial, SGLT1 seems to play a central role for alpha cell function. Under hyperglycaemic conditions, SGLT1 mediated accumulation of sodium results in alpha cell dysregulation due to altered cellular acidification and ATP production. Taken together, this suggests that SGLT1 could be a promising, yet highly underappreciated drug target to restore alpha cell function and improve treatment of both type 1 and 2 diabetes.

Do sodium-glucose co-transporter-2 inhibitors increase plasma glucagon by direct actions on the alpha cell? And does the increase matter for the associated increase in endogenous glucose production?

Sodium-glucose co-transporter-2 inhibitors (SGLT2is) lower blood glucose and are used for treatment of type 2 diabetes. However, SGLT2is have been associated with increases in endogenous glucose production (EGP) by mechanisms that have been proposed to result from SGLT2i-mediated increases in circulating glucagon concentrations, but the relative importance of this effect is debated, and mechanisms possibly coupling SGLT2is to increased plasma glucagon are unclear. A direct effect on alpha-cell activity has been proposed, but data on alpha-cell SGLT2 expression are inconsistent, and studies investigating the direct effects of SGLT2 inhibition on glucagon secretion are conflicting. By contrast, alpha-cell sodium-glucose co-transporter-1 (SGLT1) expression has been found more consistently and appears to be more prominent, pointing to an underappreciated role for this transporter. Nevertheless, the selectivity of most SGLT2is does not support interference with SGLT1 during therapy. Paracrine effects mediated by secretion of glucagonotropic/static molecules from beta and/or delta cells have also been suggested to be involved in SGLT2i-induced increase in plasma glucagon, but studies are few and arrive at different conclusions. It is also possible that the effect on glucagon is secondary to drug-induced increases in urinary glucose excretion and lowering of blood glucose, as shown in experiments with glucose clamping where SGLT2i-associated increases in plasma glucagon are prevented. However, regardless of the mechanisms involved, the current balance of evidence does not support that SGLT2 plays a crucial role for alpha-cell physiology or that SGLT2i-induced glucagon secretion is important for the associated increased EGP, particularly because the increase in EGP occurs before any rise in plasma glucagon.

The Role of Glucagon in the Acute Therapeutic Effects of SGLT2 Inhibition.

Sodium–glucose cotransporter 2 inhibitors (SGLT2i) effectively lower plasma glucose (PG) concentration in patients with type 2 diabetes, but studies have suggested that circulating glucagon concentrations and endogenous glucose production (EGP) are increased by SGLT2i, possibly compromising their glucose-lowering ability. To tease out whether and how glucagon may influence the glucose-lowering effect of SGLT2 inhibition, we subjected 12 patients with type 2 diabetes to a randomized, placebo-controlled, double-blinded, crossover, double-dummy study comprising, on 4 separate days, a liquid mixed-meal test preceded by single-dose administration of either 1) placebo, 2) the SGLT2i empagliflozin (25 mg), 3) the glucagon receptor antagonist LY2409021 (300 mg), or 4) the combination empagliflozin + LY2409021. Empagliflozin and LY2409021 individually lowered fasting PG compared with placebo, and the combination further decreased fasting PG. Previous findings of increased glucagon concentrations and EGP during acute administration of SGLT2i were not replicated in this study. Empagliflozin reduced postprandial PG through increased urinary glucose excretion. LY2409021 reduced EGP significantly but gave rise to a paradoxical increase in postprandial PG excursion, which was annulled by empagliflozin during their combination (empagliflozin + LY2409021). In conclusion, our findings do not support that an SGLT2i-induced glucagonotropic effect is of importance for the glucose-lowering property of SGLT2 inhibition.

1910-P: Effects of Glucagon Concentrations on Splanchnic and Leg Glucagon Extraction in Healthy Humans

We have recently developed a novel isotope dilution method using nonradioactive, stable human Glucagon (Phe 6 13C9, 15N; Phe 22 13C9, 15N) tracer to measure glucagon turnover. In this study we combined this method with organ catheterization technique to estimate the effects of increasing circulating glucagon concentrations, spanning the physiological range, on splanchnic and leg glucagon extraction. We present data from the first 6 healthy subjects (age 25±3.6 yrs; BMI 26.7±4.5 kg/m2; fasting glucose 4.6±0.5 mM; HbA1c 5.1±0.3%) completed thus far. After IRB approval and informed consent, subjects were admitted in the morning after an overnight fast to Interventional Radiology, where catheters were placed in the right femoral artery and vein under local anesthesia with aseptic precautions. Under fluoroscopic guidance, a hepatic venous catheter was positioned through the femoral vein. Glucagon tracer was infused intravenously and Indocyanine Green infused via the femoral artery sheath to measure splanchnic and femoral plasma flows. After a 90 min period for basal sampling, exogenous glucagon was infused at 0.65 ng/kg/min for 60 minutes (low) followed by 1.5 ng/kg/min (high) for another 60 minutes. Plasma samples were collected periodically from femoral artery, femoral vein and hepatic vein for concentrations of Glucagon tracer (Tandem Mass Spectrometry), glucagon, glucose and Indocyanine Green (Spectrophotometry) concentrations. Arterial glucagon concentrations were 45.2±9.6 pg/ml (basal), 56.3±13.3 pg/ml (low) and 81.4±15.5 pg/ml (high). While fractional splanchnic glucagon extraction remained relatively unchanged (24.0±12.5% vs. 27.7±15.6% vs. 23.5±10.1%: basal vs. low vs. high), fractional leg glucagon extraction tended to increase (13.5±3.8% vs. 16.0±7.2% vs. 18.5±9.4%: basal vs. low vs. high) with increasing glucagon concentrations. These initial data suggest differing mechanisms of glucagon clearance across the splanchnic and leg tissues in humans. Disclosure F. Ruchi: None. Y.R. Yadav: None. D. Romeres: None. S. Sawleh: None. L.M. Benson: None. K.L. Johnson: None. C. Dalla Man: Research Support; Self; Sanofi-Aventis Deutschland GmbH. C. Cobelli: None. D.J. McCormick: None. L.R. Wilkins: None. R. Basu: Consultant; Self; GENFIT. Research Support; Self; AstraZeneca. A. Basu: Consultant; Spouse/Partner; GENFIT. Research Support; Spouse/Partner; AstraZeneca. Funding National Institutes of Health (R01DK029953 to R.B.), (R01DK085516 to A.B.), (DK059637, DK020593)

263-OR: Counterregulatory Responses to Hypoglycemia in Totally Pancreatectomized Patients

We have previously shown that totally pancreatectomized (PX) patients secrete substantial amounts of glucagon (most likely from enteroendocrine cells) during an oral glucose tolerance test (OGTT) whereas these patients suppress circulating glucagon concentrations during intravenous glucose infusions. Here, we investigated the effect of insulin-induced hypoglycemia on extrapancreatic glucagon secretion and other counterregulatory factors in PX patients and in healthy controls (CTRLs). On two separate days, 12 PX patients (age 65.5±5.5 [mean±SD] years; BMI: 23.8±3.6 kg/m2) and 12 matched, healthy CTRLs (age 64.8±6.5 years; BMI: 24.5±2.9 kg/m2) underwent 1) a 50-g OGTT with 1.5 g acetaminophen (for assessment of gastric emptying) and 2) an insulin-induced hypoglycemic clamp followed by a 30-minute recovery period and a subsequent 50-g OGTT with acetaminophen. Blood was intermittently sampled throughout both experimental days. Plasma glucagon responses to OGTT (as assessed by baseline-subtracted area under curve) were greater in PX patients compared to CTRLs (386±150 vs. -340±50 min×pmol/l [mean±SEM], P=0.0001). During the hypoglycemic clamp, PX patients did not increase plasma glucagon concentrations and, thus, glucagon responses to hypoglycemia were higher in CTRLs (903±104 vs. -21±16 min×pmol/l, P<0.001). Hypoglycemia-induced responses of catecholamines, growth hormone and cortisol were similar in the two groups. Gastric emptying was unaffected by hypoglycemia in CTRLs but was decelerated by hypoglycemia in PX patients. We conclude that 1) insulin-induced hypoglycemia, which powerfully stimulates glucagon secretion in CTRLs, does not stimulate extrapancreatic glucagon secretion in PX patients; 2) counterregulatory responses of catecholamines, growth hormone and cortisol were intact in PX patients, but hypoglycemia decelerated gastric emptying in these patients. This provides mechanistic insight into the high risk of hypoglycemia in PX patients. Disclosure M. Baekdal: None. A.B. Lund: Speaker’s Bureau; Self; AstraZeneca, Novo Nordisk A/S, Sanofi. M. Baldassarre: None. J.I. Egholk: None. K. Rose: None. C. Hansen: None. J.H. Storkholm: None. M.B. Christensen: None. B. Hartmann: None. J. Faber: None. J.J. Holst: Advisory Panel; Self; AstraZeneca, Merck Sharp & Dohme Corp., Novo Nordisk A/S, Zealand Pharma A/S. Other Relationship; Spouse/Partner; Antag Therapeutics. T. Vilsbøll: Advisory Panel; Self; AstraZeneca, Mundipharma International, Novo Nordisk A/S, Sun Pharmaceutical Industries Ltd. Consultant; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Lilly Diabetes, Medscape, Merck Sharp & Dohme Corp., Sanofi. F.K. Knop: Advisory Panel; Self; AstraZeneca, Merck Sharp & Dohme Corp., Mundipharma International, Novo Nordisk A/S, Sanofi. Consultant; Self; Carmot Therapeutics, Inc., Eli Lilly and Company, Novo Nordisk A/S. Research Support; Self; AstraZeneca, Gubra, Novo Nordisk A/S, Sanofi, Zealand Pharma A/S. Speaker’s Bureau; Self; AstraZeneca, Lupin Pharmaceuticals, Inc., Merck Sharp & Dohme Corp., Norgine B.V., Novo Nordisk A/S.

1916-P: Postprandial Glucagon Metabolism in Healthy Subjects: Use of 13C 15N Glucagon

Glucagon metabolism in humans is poorly understood and is currently under active investigation. We have recently developed a new isotope dilution method using nonradioactive, stable human glucagon (Phe 6 13C9, 15N; Phe 22 13C9, 15N) tracer to measure glucagon fluxes. To estimate postprandial glucagon turnover using this novel technique, we present data from the first 5 healthy subjects (3 males, age 26.2±7.9 years, BMI 25.4±2.6 kg/m2, fasting plasma glucose 4.7±0.2 mM, HbA1c 5.1±0.2 %) done thus far. After IRB approval and informed consent, subjects presented to the clinical research unit in the morning after an overnight fast. A catheter was inserted in a forearm vein for glucagon tracer infusion and another catheter placed in the contralateral hand and the hand kept in a heated box for periodic draws of arterialized venous samples for measurements of glucagon tracer (tandem mass spectrometry), glucagon and glucose concentrations during the study. A mixed meal (75 grams carb, 15% protein, 35% fat; 8 kcal/kg) was ingested at time 0 and the glucagon tracer infusion rate adjusted to mimic the anticipated changes in postprandial circulating glucagon concentrations for 6 hours. Systemic glucagon appearance rate (Ra glucagon) was calculated by the isotope dilution method. Fig 1 shows the Ra glucagon in all subjects. These initial data show that postprandial glucagon turnover can be calculated in humans applying this novel technique. Disclosure F. Ruchi: None. Y.R. Yadav: None. D. Romeres: None. S. Sawleh: None. L.M. Benson: None. K.L. Johnson: None. M. Schiavon: None. C. Dalla Man: Research Support; Self; Sanofi-Aventis Deutschland GmbH. C. Cobelli: None. D.J. McCormick: None. R. Basu: Consultant; Self; GENFIT. Research Support; Self; AstraZeneca. A. Basu: Consultant; Spouse/Partner; GENFIT. Research Support; Spouse/Partner; AstraZeneca. Funding National Institutes of Health (R01DK029953 to R.B.), (R01DK085516 to A.B.), (DK059637, DK020593)

A comparison of the nutritional physiology and gut microbiome of urban and rural house sparrows (Passer domesticus).

Urbanization influences food quality and availability for many wild species, but our knowledge of the consequences urbanization has on the nutritional physiology of these animals is currently limited. To fill this gap, we captured House Sparrows (Passer domesticus) from rural and urban environments and hypothesized that increased access to human refuse in urban areas may significantly alter the gut microbiome and nutritional physiology of Sparrows. While there were no significant differences in circulating triglycerides or free glycerol concentrations between populations, urban birds had significantly greater blood glucose concentrations, which suggests greater circulating glucagon concentrations, accessibility to carbohydrates, and/or higher rates of gluconeogenesis in an urban setting. Rural birds had significantly more plasma uric acid, suggesting that they may metabolize more proteins or experience lower inflammation than urban birds. Rural birds also had significantly higher liver free glycerol concentrations, indicating that they metabolize more fat than urban birds. There were no significant differences in the relative abundance of gut microbial taxa at the phyla level between the two populations, but linear discriminant analysis effect size (LEfSe) showed that urban House Sparrows were more enriched with class- and order-level microbes from the phylum Proteobacteria, which are implicated in several mammalian intestinal and extra-intestinal diseases. These findings demonstrate that urbanization significantly alters the nutritional physiology and the composition of the gut microbiome of House Sparrows.

SGLT2 inhibition and glucagon secretion in humans

With the increasing prevalence of type 2 diabetes (T2D), therapies aimed at delineating diabetes pathophysiology and understanding their mechanisms of action are of critical importance. As such, growing interest in the clinical pharmacology of sodium–glucose cotransporter 2 (SGLT2) and its inhibition by gliflozins in the treatment of T2D is becoming increasingly evident. SGLT2 inhibition results in urinary glucose excretion, thereby reducing blood glucose levels. The importance of this homoeostasis mechanism is evident from several clinical trials demonstrating that patients taking this class of compounds have reductions in glycaemia, body weight and blood pressure compared with other antidiabetic agents. Yet, while such outcomes are very encouraging, some studies have reported elevated plasma glucagon levels and endogenous glucose production (EGP), two traits that are already prevalent in T2D. However, these findings were later explained by the specific expression of SGLT2 by pancreatic alpha cells, where glucagon secretion is directly regulated. Although conflicting data are now emerging on SGLT2 regulation of glucagon secretion, as SGLT2 is not expressed in the intestines, circulating glucagon concentrations are most likely of pancreatic origin. Thus, the present review considers the mechanism of action of SGLT2 inhibitors in the regulation of glucagon secretion, and the discrepancies in data from mice compared with people. The pragmatic use of human islets to accurately decipher SGLT2 inhibition in the regulation of glucagon secretion is also discussed.

Peptides from frog skin with potential for development into agents for Type 2 diabetes therapy

Several frog skin peptides, first identified as result of their antimicrobial or immunomodulatory activities, have subsequently been shown to stimulate insulin release both in vitro and in vivo and so show potential for development into incretin-based drugs for treatment of patients with Type 2 diabetes mellitus. However, their therapeutic potential as anti-diabetic agents is not confined to this activity as certain frog skin-derived peptides, such as magainin-AM2 and CPF-SE1 and analogs of hymenochirin-1B, tigerinin-1R, and esculentin-2CHa, have been shown to increase insulin sensitivity, promote β-cell proliferation, suppress pancreatic and circulating glucagon concentrations, improve the lipid profile, and selectively alter expression of genes involved in insulin secretion and action in mice with diet-induced obesity, insulin resistance and impaired glucose tolerance. This review assesses the therapeutic possibilities of peptides from frogs belonging to the Pipidae, Dicroglossidae, and Ranidae families, focusing upon work that has been carried out since 2014.

Common variation in the sodium/glucose cotransporter 2 gene SLC5A2 does neither affect fasting nor glucose-suppressed plasma glucagon concentrations.

AimInhibition of sodium/glucose cotransporter 2 (SGLT2), the key transport protein in renal glucose reabsorption, promotes glucose excretion and represents a new concept in the therapy of type-2 diabetes. In addition, SGLT2 inhibition elevates circulating glucagon concentrations and enhances hepatic glucose production. Since SGLT2 is expressed in human pancreatic α-cells and regulates glucagon release, we tested whether common variants of the SGLT2 gene SLC5A2 associate with altered plasma glucagon concentrations in the fasting state and upon glucose challenge.MethodsA study population of 375 healthy subjects at increased risk for type-2 diabetes, phenotyped by a 5-point oral glucose tolerance test (OGTT) and genotyped for recently described SLC5A2 tagging single nucleotide polymorphisms (SNPs), was selected for plasma glucagon measurements.ResultsAfter adjustment for gender, age, body mass index, and insulin sensitivity, the four tagging SNPs (rs9924771, rs3116150, rs3813008, rs9934336), tested separately or as genetic score, were neither significantly nor nominally associated with plasma glucagon concentrations at any time during the OGTT, with the inverse AUC of glucagon or the glucagon fold-change during the OGTT (p ≥ 0.2, all). Testing for genotype-related differences in the time course of the glucagon response using MANOVA did also not reveal any significant or nominal associations (p ≥ 0.5, all).ConclusionWe could not obtain statistically significant evidence for a role of common SLC5A2 variants in the regulation of glucagon release in the fasting state or upon glucose challenge. Moreover, the reported nominal effects of individual SLC5A2 variants on fasting and post-challenge glucose levels may probably not be mediated by altered glucagon release.

Effects of gastric inhibitory polypeptide (GIP) and related analogues on glucagon release at normo- and hyperglycaemia in Wistar rats and isolated islets

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted by endocrine K-cells in response to nutrient absorption. This study has utilised numerous well-characterised dipeptidyl peptidase IV-resistant GIP analogues to evaluate the glucagonotropic actions of GIP in Wistar rats and isolated rat islets. Intraperitoneal administration of GIP analogues (25 nmol/kg body weight) in combination with glucose had no effect on circulating glucagon concentrations compared to controls in Wistar rats. However, plasma glucose concentrations were significantly (p<0.05 to p<0.001) lowered by the GIP-receptor agonists, N-AcGIP, GIP(Lys37)PAL and N-AcGIP(Lys37)PAL. The GIP antagonist, (Pro3)GIP, caused a significant (p<0.05) reduction in glucagon levels following concurrent administration with saline in Wistar rats. In isolated rat islets native GIP induced a significant (p<0.01) enhancement of glucagon release at basal glucose concentrations, which was completely annulled by (Pro3)GIP. Furthermore, glucagon release in the presence of GLP-1, GIP(Lys37)PAL, N-AcGIP(Lys37)PAL and (Pro3)GIP was significantly (p<0.05 to p<0.001) decreased compared to native GIP in isolated rat islets. These data indicate a modest effect of GIP on glucagon secretion from isolated rat islets, which was not observed in vivo. However, the GIP agonists N-AcGIP, GIP(Lys37)PAL and N-AcGIP(Lys37)PAL had no effect on glucagon release demonstrating an improved therapeutic potential for the treatment of type 2 diabetes.

Glycemic Control in Mice with Targeted Disruption of the Glucagon Receptor Gene

The action of glucagon in the liver is mediated by G-coupled receptors. To examine the role of glucagon in glucose homeostasis, we have generated mice in which the glucagon receptor was inactivated (GR−/− mice). Blood glucose levels were somewhat reduced in GR−/− mice relative to wild type, in both the fed and fasted state. Plasma insulin levels were not significantly affected. There was no significant effect on fasting plasma cholesterol or triglyceride levels associated with deletion of the glucagon receptor. Glucose tolerance, as assessed by an oral glucose tolerance test, improved. Plasma glucagon levels were strikingly elevated in both fed and fasted animals. Despite a total absence of glucagon receptors, these animals maintained near-normal glycemia and normal lipidemia, in the presence of circulating glucagon concentrations that were elevated by two orders of magnitude.

Effects of glucagon on renal and hepatic glutamine gluconeogenesis in normal postabsorptive humans.

Glutamine is an important gluconeogenic amino acid in postabsorptive humans. To assess the effect of glucagon on renal and hepatic glutamine gluconeogenesis, we infused six normal healthy postabsorptive subjects with glucagon at a rate chosen to produce circulating glucagon concentrations found during hypoglycemia and, using a combination of isotopic and net balance techniques, determined the systemic, renal, and hepatic glucose release and renal and hepatic production of glucose from glutamine. Infusion of glucagon increased systemic and hepatic glucose release (both P < .02), but had no effect on renal glucose release (P = .26). Systemic and hepatic glutamine gluconeogenesis increased from 0.45 +/- 0.3 and 0.11 +/- 0.02 micromol x kg(-1) x min(-1), respectively, to 0.61 +/- 0.04 (P = .002) and 0.31 +/- 0.03 micromol x kg(-1) x min(-1) (P = .001), respectively, whereas renal glutamine gluconeogenesis was unchanged (from 0.33 +/- 0.03 to 0.30 +/- 0.04 micromol x kg(-1) x min(-1), P = .20). The hepatic contribution to systemic glutamine gluconeogenesis increased from 25.2% +/- 6.2% to 51.6% +/- 5.5% (P = .002), while that of the kidney decreased from 74.8% +/- 6.2% to 48.4% +/- 5.5% (P = .003). Glucagon had no effect on the renal net balance, fractional extraction, or uptake and release of either glucose or glutamine. We thus conclude that glucagon stimulates glutamine gluconeogenesis in normal postabsorptive humans, predominantly due to an increase in hepatic glutamine conversion to glucose. Thus, under certain conditions such as counterregulation of hypoglycemia, the liver may be an important site of glutamine gluconeogenesis.

Clinical evaluation and preliminary studies on the use of an artificial pancreatic beta cell in juvenile diabetes mellitus

A newly developed artificial pancreatic beta cell is described and its use in five children with diabetes mellitus is evaluated. This device can be programmed to bring the blood glucose concentration rapidly to a preselected level and normalize glucose tolerance in juvenile diabetic patients with markedly different insulin requirements. It is portable, can be operated by one person, and has been used to regulate the blood glucose concentration before, during, and after surgery requiring general anesthesia. The potential value of the device as an investigational tool is shown by demonstrating that regulation of the blood glucose concentration with insulin for seven to 24 hours does not alter circulating glucagon concentrations in the juvenile diabetic patients studied.