Liraglutide is an acylated glucagon-like peptide-1 (GLP-1) analogue that binds to serum albumin in vivo and is approved for once-daily treatment of diabetes as well as obesity. The aim of the present ...studies was to design a once weekly GLP-1 analogue by increasing albumin affinity and secure full stability against metabolic degradation. The fatty acid moiety and the linking chemistry to GLP-1 were the key features to secure high albumin affinity and GLP-1 receptor (GLP-1R) potency and in obtaining a prolonged exposure and action of the GLP-1 analogue. Semaglutide was selected as the optimal once weekly candidate. Semaglutide has two amino acid substitutions compared to human GLP-1 (Aib8, Arg34) and is derivatized at lysine 26. The GLP-1R affinity of semaglutide (0.38 ± 0.06 nM) was three-fold decreased compared to liraglutide, whereas the albumin affinity was increased. The plasma half-life was 46.1 h in mini-pigs following i.v. administration, and semaglutide has an MRT of 63.6 h after s.c. dosing to mini-pigs. Semaglutide is currently in phase 3 clinical testing.
Although diabetic polyneuropathy (DPN) is the commonest diabetic complication, its pathology remains to be clarified. As previous papers have suggested the neuroprotective effects of glucagon-like ...peptide-1 in DPN, the current study investigated the physiological indispensability of glucagon gene-derived peptides (GCGDPs) including glucagon-like peptide-1 in the peripheral nervous system (PNS). Neurological functions and neuropathological changes of GCGDP deficient (gcg−/−) mice were examined. The gcg−/− mice showed tactile allodynia and thermal hyperalgesia at 12–18 weeks old, followed by tactile and thermal hypoalgesia at 36 weeks old. Nerve conduction studies revealed a decrease in sensory nerve conduction velocity at 36 weeks old. Pathological findings showed a decrease in intraepidermal nerve fiber densities. Electron microscopy revealed a decrease in circularity and an increase in g-ratio of myelinated fibers and a decrease of unmyelinated fibers in the sural nerves of the gcg−/− mice. Effects of glucagon on neurite outgrowth were examined using an ex vivo culture of dorsal root ganglia. A supraphysiological concentration of glucagon promoted neurite outgrowth. In conclusion, the mice with deficiency of GCGDPs developed peripheral neuropathy with age. Furthermore, glucagon might have neuroprotective effects on the PNS of mice. GCGDPs might be involved in the pathology of DPN.
•Deficiency of glucagon gene-derived peptides (GCGDPs) caused peripheral neuropathy with age in mice.•GCGDPs might have neuroprotective effects on the peripheral nervous system of mice.•Glucagon promoted neurite outgrowth of dorsal root ganglion neurons.
Glucagon supports glucose homeostasis by stimulating hepatic gluconeogenesis, in part by promoting the uptake and conversion of amino acids into gluconeogenic precursors. Genetic disruption or ...pharmacologic inhibition of glucagon signaling results in elevated plasma amino acids and compensatory glucagon hypersecretion involving expansion of pancreatic α cell mass. Recent findings indicate that hyperaminoacidemia triggers pancreatic α cell proliferation via an mTOR-dependent pathway. We confirm and extend these findings by demonstrating that glucagon pathway blockade selectively increases expression of the sodium-coupled neutral amino acid transporter Slc38a5 in a subset of highly proliferative α cells and that Slc38a5 controls the pancreatic response to glucagon pathway blockade; most notably, mice deficient in Slc38a5 exhibit markedly decreased α cell hyperplasia to glucagon pathway blockade-induced hyperaminoacidemia. These results show that Slc38a5 is a key component of the feedback circuit between glucagon receptor signaling in the liver and amino-acid-dependent regulation of pancreatic α cell mass in mice.
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•Glucagon receptor inhibition reduces hepatic uptake and catabolism of amino acids•Elevated circulating amino acids induce Slc38a5 expression in pancreatic α cells•Slc38a5 links plasma amino acids to α cell proliferation•mTOR controls Slc38a5 expression and α cell proliferation
Glucagon receptor inhibition reduces hepatic uptake and catabolism of amino acids. Kim et al. show that Slc38a5 is a key component of the amino acid sensing machinery linking circulating amino acids to control of pancreatic α cell function and mass.
Glucagon-like peptide 1 (GLP-1) is a hormone with essential roles in regulating insulin secretion, carbohydrate metabolism and appetite. GLP-1 effects are mediated through binding to the GLP-1 ...receptor (GLP-1R), a class B G-protein-coupled receptor (GPCR) that signals primarily through the stimulatory G protein G
. Class B GPCRs are important therapeutic targets; however, our understanding of their mechanism of action is limited by the lack of structural information on activated and full-length receptors. Here we report the cryo-electron microscopy structure of the peptide-activated GLP-1R-G
complex at near atomic resolution. The peptide is clasped between the N-terminal domain and the transmembrane core of the receptor, and further stabilized by extracellular loops. Conformational changes in the transmembrane domain result in a sharp kink in the middle of transmembrane helix 6, which pivots its intracellular half outward to accommodate the α5-helix of the Ras-like domain of G
. These results provide a structural framework for understanding class B GPCR activation through hormone binding.
Aims/hypothesis
The endocrine pancreas comprises the islets of Langerhans, primarily consisting of beta cells, alpha cells and delta cells responsible for secretion of insulin, glucagon and ...somatostatin, respectively. A certain level of intra-islet communication is thought to exist, where the individual hormones may reach the other islet cells and regulate their secretion. Glucagon has been demonstrated to importantly regulate insulin secretion, while somatostatin powerfully inhibits both insulin and glucagon secretion. In this study we investigated how secretion of somatostatin is regulated by paracrine signalling from glucagon and insulin.
Methods
Somatostatin secretion was measured from perfused mouse pancreases isolated from wild-type as well as diphtheria toxin-induced alpha cell knockdown, and global glucagon receptor knockout (
Gcgr
–/–
) mice. We studied the effects of varying glucose concentrations together with infusions of arginine, glucagon, insulin and somatostatin, as well as infusions of antagonists of insulin, somatostatin and glucagon-like peptide 1 (GLP-1) receptors.
Results
A tonic inhibitory role of somatostatin was demonstrated with infusion of somatostatin receptor antagonists, which significantly increased glucagon secretion at low and high glucose, whereas insulin secretion was only increased at high glucose levels. Infusion of glucagon dose-dependently increased somatostatin secretion approximately twofold in control mice. Exogenous glucagon had no effect on somatostatin secretion in
Gcgr
–/–
mice, and a reduced effect when combined with the GLP-1 receptor antagonist exendin 9-39. Diphtheria toxin-induced knockdown of glucagon producing cells led to reduced somatostatin secretion in response to 12 mmol/l glucose and arginine infusions. In
Gcgr
–/–
mice (where glucagon levels are dramatically increased) overall somatostatin secretion was increased. However, infusion of exendin 9-39 in
Gcgr
–/–
mice completely abolished somatostatin secretion in response to glucose and arginine. Neither insulin nor an insulin receptor antagonist (S961) had any effect on somatostatin secretion.
Conclusions/interpretation
Our findings demonstrate that somatostatin and glucagon secretion are linked in a reciprocal feedback cycle with somatostatin inhibiting glucagon secretion at low and high glucose levels, and glucagon stimulating somatostatin secretion via the glucagon and GLP-1 receptors.
Graphical abstract
Semaglutide, a glucagon-like peptide-1 receptor agonist, has been shown to reduce the risk of adverse cardiovascular events in patients with diabetes. Whether semaglutide can reduce cardiovascular ...risk associated with overweight and obesity in the absence of diabetes is unknown.
In a multicenter, double-blind, randomized, placebo-controlled, event-driven superiority trial, we enrolled patients 45 years of age or older who had preexisting cardiovascular disease and a body-mass index (the weight in kilograms divided by the square of the height in meters) of 27 or greater but no history of diabetes. Patients were randomly assigned in a 1:1 ratio to receive once-weekly subcutaneous semaglutide at a dose of 2.4 mg or placebo. The primary cardiovascular end point was a composite of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke in a time-to-first-event analysis. Safety was also assessed.
A total of 17,604 patients were enrolled; 8803 were assigned to receive semaglutide and 8801 to receive placebo. The mean (±SD) duration of exposure to semaglutide or placebo was 34.2±13.7 months, and the mean duration of follow-up was 39.8±9.4 months. A primary cardiovascular end-point event occurred in 569 of the 8803 patients (6.5%) in the semaglutide group and in 701 of the 8801 patients (8.0%) in the placebo group (hazard ratio, 0.80; 95% confidence interval, 0.72 to 0.90; P<0.001). Adverse events leading to permanent discontinuation of the trial product occurred in 1461 patients (16.6%) in the semaglutide group and 718 patients (8.2%) in the placebo group (P<0.001).
In patients with preexisting cardiovascular disease and overweight or obesity but without diabetes, weekly subcutaneous semaglutide at a dose of 2.4 mg was superior to placebo in reducing the incidence of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke at a mean follow-up of 39.8 months. (Funded by Novo Nordisk; SELECT ClinicalTrials.gov number, NCT03574597.).
2022 corresponds to the 100th anniversary of the discovery of glucagon. This TimeCapsule aims to recall the main steps leading to the discovery, characterisation, and clinical importance of the ...so-called second pancreatic hormone. We describe the early historical findings in basic research (ie, discovery, purification, structure, α-cell origin, radioimmunoassay, glucagon gene GCG, and glucagon receptor GLR), in which three future Nobel Prize laureates were actively involved. Considered as an anti-insulin hormone, glucagon was rapidly used to treat insulin-induced hypoglycaemic coma episodes in people with type 1 diabetes. A key step in the story of glucagon was the discovery of its role and the role of α cells in the physiology and pathophysiology (ie, paracrinopathy) of type 2 diabetes. This concept led to the design of different strategies targeting glucagon, among which GLP-1 receptor (GLP1R) agonists were a major breakthrough, and combination of inhibition of glucagon secretion with stimulation of insulin secretion (both in a glucose-dependent manner). Taking advantage of the glucagon-induced increase in energy metabolism, biased coagonists were developed. Besides the GLP-1 receptor, these coagonists also target the glucagon receptor to further promote weight loss. Thus, the 100-year story of glucagon has most probably not come to an end.
Obesity is a major public health issue, and new pharmaceuticals for weight management are needed. Therefore, we evaluated the efficacy and safety of the glucagon-like peptide-1 (GLP-1) analogue ...semaglutide in comparison with liraglutide and a placebo in promoting weight loss.
We did a randomised, double-blind, placebo and active controlled, multicentre, dose-ranging, phase 2 trial. The study was done in eight countries involving 71 clinical sites. Eligible participants were adults (≥18 years) without diabetes and with a body-mass index (BMI) of 30 kg/m2 or more. We randomly assigned participants (6:1) to each active treatment group (ie, semaglutide 0·05 mg, 0·1 mg, 0·2 mg, 0·3 mg, or 0·4 mg; initiated at 0·05 mg per day and incrementally escalated every 4 weeks or liraglutide 3·0 mg; initiated at 0·6 mg per day and escalated by 0·6 mg per week) or matching placebo group (equal injection volume and escalation schedule to active treatment group) using a block size of 56. All treatment doses were delivered once-daily via subcutaneous injections. Participants and investigators were masked to the assigned study treatment but not the target dose. The primary endpoint was percentage weight loss at week 52. The primary analysis was done using intention-to-treat ANCOVA estimation with missing data derived from the placebo pool. This study is registered with ClinicalTrials.gov, number NCT02453711.
Between Oct 1, 2015, and Feb 11, 2016, 957 individuals were randomly assigned (102–103 participants per active treatment group and 136 in the pooled placebo group). Mean baseline characteristics included age 47 years, bodyweight 111·5 kg, and BMI 39·3 kg/m2. Bodyweight data were available for 891 (93%) of 957 participants at week 52. Estimated mean weight loss was −2·3% for the placebo group versus −6·0% (0·05 mg), −8·6% (0·1 mg), −11·6% (0·2 mg), −11·2% (0·3 mg), and −13·8% (0·4 mg) for the semaglutide groups. All semaglutide groups versus placebo were significant (unadjusted p≤0·0010), and remained significant after adjustment for multiple testing (p≤0·0055). Mean bodyweight reductions for 0·2 mg or more of semaglutide versus liraglutide were all significant (−13·8% to −11·2% vs −7·8%). Estimated weight loss of 10% or more occurred in 10% of participants receiving placebo compared with 37–65% receiving 0·1 mg or more of semaglutide (p<0·0001 vs placebo). All semaglutide doses were generally well tolerated, with no new safety concerns. The most common adverse events were dose-related gastrointestinal symptoms, primarily nausea, as seen previously with GLP-1 receptor agonists.
In combination with dietary and physical activity counselling, semaglutide was well tolerated over 52 weeks and showed clinically relevant weight loss compared with placebo at all doses.
Novo Nordisk A/S.
The glucagon-like peptide 1 (GLP-1) system is a recently established target for type 2 diabetes treatment. In addition to regulating glucose homeostasis, GLP-1 also reduces food intake. Previous ...studies demonstrate that the anorexigenic effects of GLP-1 can be mediated through hypothalamic and brainstem circuits which regulate homeostatic feeding. Here, we demonstrate an entirely novel neurobiological mechanism for GLP-1-induced anorexia in rats, involving direct effects of a GLP-1 agonist, Exendin-4 (EX4) on food reward that are exerted at the level of the mesolimbic reward system. We assessed the impact of peripheral, central, and intramesolimbic EX4 on two models of food reward: conditioned place preference (CPP) and progressive ratio operant-conditioning. Food-reward behavior was reduced in the CPP test by EX4, as rats no longer preferred an environment previously paired to chocolate pellets. EX4 also decreased motivated behavior for sucrose in a progressive ratio operant-conditioning paradigm when administered peripherally. We show that this effect is mediated centrally, via GLP-1 receptors (GLP-1Rs). GLP-1Rs are expressed in several key nodes of the mesolimbic reward system; however, their function remains unexplored. Thus we sought to determine the neurobiological substrates underlying the food-reward effect. We found that the EX4-mediated inhibition of food reward could be driven from two key mesolimbic structures-ventral tegmental area and nucleus accumbens-without inducing concurrent malaise or locomotor impairment. The current findings, that activation of central GLP-1Rs strikingly suppresses food reward/motivation by interacting with the mesolimbic system, indicate an entirely novel mechanism by which the GLP-1R stimulation affects feeding-oriented behavior.
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