Impact of insulin glargine and lixisenatide on β‐cell function in patients with type 2 diabetes mellitus: A randomized open‐label study

It is known that β‐cell function can be enhanced by direct stimulation of insulin secretion or by induction of β‐cell rest, but whether both strategies can complement each other has not yet been examined. A total of 28 people with type 2 diabetes (glycated haemoglobin 7.8% ± 0.5%) were treated with either lixisenatide or titrated insulin glargine, followed by their combined administration, each over 4 weeks. First‐ and second‐phase insulin secretion during an intravenous glucose challenge were calculated. First‐ and second‐phase insulin secretion were not increased with glargine alone, but increased after addition of lixisenatide ( P < .001). Lixisenatide alone increased first‐ and second‐phase insulin secretion ( P < .01). Addition of insulin glargine tended to further increase first‐phase insulin secretion (P = .054), as well as insulin and C‐peptide concentrations ( P < .05). Second‐phase insulin secretion was not affected by the addition of glargine. The sequence of initiating lixisenatide or glargine had no effect on the final measures of glycaemia or insulin secretion. Thus, lixisenatide and, to a lesser extent, insulin glargine, increase glucose‐stimulated insulin secretion in an additive manner.     

Differential effects of once‐weekly glucagon‐like peptide‐1 receptor agonist dulaglutide and metformin on pancreatic β‐cell and insulin sensitivity during a standardized test meal in patients with type 2 diabetes

This substudy of the AWARD‐3 trial evaluated the effects of the once‐weekly glucagon‐like peptide‐1 receptor agonist, dulaglutide, versus metformin on glucose control, pancreatic function and insulin sensitivity, after standardized test meals in patients with type 2 diabetes. Meals were administered at baseline, 26 and 52 weeks to patients randomized to monotherapy with dulaglutide 1.5 mg/week (n = 133), dulaglutide 0.75 mg/week (n = 136), or metformin ≥1500 mg/day (n = 140). Fasting and postprandial serum glucose, insulin, C‐peptide and glucagon levels were measured up to 3 h post‐meal. β‐cell function and insulin sensitivity were assessed using empirical variables and mathematical modelling. At 26 weeks, similar decreases in area under the curve for glucose [AUC_glucose (0–3 h)] were observed among all groups. β‐cell function [AUC_insulin/AUC_glucose (0–3 h)] increased with dulaglutide and was unchanged with metformin (p ≤ 0.005, both doses). Dulaglutide improved insulin secretion rate at 9 mmol/l glucose (p ≤ 0.04, both doses) and β‐cell glucose sensitivity (p = 0.004, dulaglutide 1.5 mg). Insulin sensitivity increased more with metformin versus dulaglutide. In conclusion, dulaglutide improves postprandial glycaemic control after a standardized test meal by enhancing β‐cell function, while metformin exerts a greater effect on insulin sensitivity.     

The interleukin‐1 receptor antagonist anakinra improves first‐phase insulin secretion and insulinogenic index in subjects with impaired glucose tolerance

Inflammation at the level of the β cell appears to be involved in progressive β‐cell dysfunction in type 2 diabetes. We assessed the effect of blocking interleukin‐1 (IL‐1) by anakinra [recombinant human interleukin‐1 receptor antagonist (IL‐1Ra)] on β‐cell function. Sixteen participants with impaired glucose tolerance were treated with 150 mg anakinra daily for 4 weeks in a double blind, randomized, placebo‐controlled cross‐over study with a wash‐out period of 4 weeks. At the end of each treatment period, oral glucose tolerance tests (OGTTs) and hyperglycaemic clamps were performed. First‐phase insulin secretion improved after anakinra treatment compared with placebo, 148 ± 20 versus 123 ± 14 mU/l, respectively (p = 0.03), and the insulinogenic index was higher after anakinra treatment. These results support the concept of involvement of IL‐1β in the (progressive) decrease of insulin secretion capacity associated with type 2 diabetes.     

Review of methods for measuring β‐cell function: Design considerations from the Restoring Insulin Secretion (RISE) Consortium

The Restoring Insulin Secretion (RISE) study was initiated to evaluate interventions to slow or reverse the progression of β‐cell failure in type 2 diabetes (T2D). To design the RISE study, we undertook an evaluation of methods for measurement of β‐cell function and changes in β‐cell function in response to interventions. In the present paper, we review approaches for measurement of β‐cell function, focusing on methodologic and feasibility considerations. Methodologic considerations included: (1) the utility of each technique for evaluating key aspects of β‐cell function (first‐ and second‐phase insulin secretion, maximum insulin secretion, glucose sensitivity, incretin effects) and (2) tactics for incorporating a measurement of insulin sensitivity in order to adjust insulin secretion measures for insulin sensitivity appropriately. Of particular concern were the capacity to measure β‐cell function accurately in those with poor function, as is seen in established T2D, and the capacity of each method for demonstrating treatment‐induced changes in β‐cell function. Feasibility considerations included: staff burden, including time and required methodological expertise; participant burden, including time and number of study visits; and ease of standardizing methods across a multicentre consortium. After this evaluation, we selected a 2‐day measurement procedure, combining a 3‐hour 75‐g oral glucose tolerance test and a 2‐stage hyperglycaemic clamp procedure, augmented with arginine.     

Melatonin influences somatostatin secretion from human pancreatic δ‐cells via MT1 and MT2 receptors

Melatonin is an effector of the diurnal clock on pancreatic islets. The membrane receptor‐transmitted inhibitory influence of melatonin on insulin secretion is well established and contrasts with the reported stimulation of glucagon release from α‐cells. Virtually, nothing is known concerning the melatonin‐mediated effects on islet δ‐cells. Analysis of a human pancreatic δ‐cell model, the cell line QGP‐1, and the use of a somatostatin‐specific radioimmunoassay showed that melatonin primarily has an inhibitory effect on somatostatin secretion in the physiological concentration range. In the pharmacological range, melatonin elicited slightly increased somatostatin release from δ‐cells. Cyclic adenosine monophosphate (cAMP) is the major second messenger dose‐dependently stimulating somatostatin secretion, in experiments employing the membrane‐permeable 8‐Br‐cAMP. 8‐Br‐cyclic guanosine monophosphate proved to be of only minor relevance to somatostatin release. As the inhibitory effect of 1 nm melatonin was reversed after incubation of QGP‐1 cells with the nonselective melatonin receptor antagonist luzindole, but not with the MT2‐selective antagonist 4‐P‐PDOT (4‐phenyl‐2‐propionamidotetraline), an involvement of the MT1 receptor can be assumed. Somatostatin release from the δ‐cells at low glucose concentrations was significantly inhibited during co‐incubation with 1 nm melatonin, an effect which was less pronounced at higher glucose levels. Transient expression experiments, overexpressing MT1, MT2, or a deletion variant as a control, indicated that the MT1 and not the MT2 receptor was the major transmitter of the inhibitory melatonin effect. These data point to a significant influence of melatonin on pancreatic δ‐cells and on somatostatin release.     

Short‐acting glucagon‐like peptide‐1 receptor agonists as add‐on to insulin therapy in type 1 diabetes: A review

A large proportion of patients with type 1 diabetes do not reach their glycaemic target of glycated hemoglobin (HbA1c) <7.0% (53 mmol/mol) and, furthermore, an increasing number of patients with type 1 diabetes are overweight and obese. Treatment of type 1 diabetes is based on insulin therapy, which is associated with well‐described and unfortunate adverse effects such as hypoglycaemia and increased body weight. Glucagon‐like peptide‐1 (GLP‐1) receptor agonists (RAs) are the focus of increasing interest as a possible adjunctive treatment to insulin in type 1 diabetes because of their glucagonostatic and extrapancreatic effects. So far, the focus has mainly been on the long‐acting GLP‐1RAs, but the risk–benefit ratio emerging from studies evaluating the effect of long‐acting GLP‐1RAs as adjunctive therapy to insulin therapy in patients with type 1 diabetes has been disappointing. This might be attributable to a lack of glucagonostatic effect of these long‐acting GLP‐1RAs in type 1 diabetes, alongside development of tachyphylaxis to GLP‐1‐induced retardation of gastric emptying. In contrast, the short‐acting GLP‐1RAs seem to have a preserved and sustained effect on glucagon secretion and gastric emptying in patients with type 1 diabetes, which could translate into effective lowering of postprandial glucose excursions; however, these observations regarding short‐acting GLP‐1RAs are all derived from small open‐label trials and should thus be interpreted with caution. In the present paper we review the potential role of GLP‐1RAs, in particular short‐acting GLP‐1RAs, as add‐on to insulin in the treatment of type 1 diabetes.     

Glucagon‐like peptide 1‐potentiated insulin secretion and proliferation of pancreatic β‐cells GLP‐1促进胰岛素分泌和胰岛β细胞增殖的机制

Glucagon‐like peptide‐1 (GLP‐1) is the primary incretin hormone secreted from the intestine upon uptake of food to stimulate insulin secretion from pancreatic β‐cells. GLP‐1 exerts its effects by binding to its G‐protein coupled receptors and subsequently activating adenylate cyclase, leading to generation of cyclic adenosine monophosphate (cAMP). cAMP stimulates insulin secretion via activation of its effectors PKA and Epac2 in pancreatic β‐cells. In addition to its insulinotropic effects, GLP‐1 also preserves pancreatic β‐cell mass by stimulating β‐cell proliferation. Unlike the action of sulphonylureas in lowering blood glucose levels, action of GLP‐1 is affected by and interplays with glucose levels. Due to such advantages, GLP‐1‐based therapeutics have been rapidly developed and used clinically for treatment of type 2 diabetes. However, molecular mechanisms underlying how GLP‐1 potentiates diminished glucose‐stimulated insulin secretion and β‐cell proliferation under diabetic conditions are not well understood. Here, we review the actions of GLP‐1 in regulation of insulin secretion and pancreatic β‐cell proliferation.     

Evidence connecting old,new and neglected glucose‐lowering drugs to bile acid‐induced GLP‐1 secretion: A review

Bile acids are amphipathic water‐soluble steroid‐based molecules best known for their important lipid‐solubilizing role in the assimilation of fat. Recently, bile acids have emerged as metabolic integrators with glucose‐lowering potential. Among a variety of gluco‐metabolic effects, bile acids have been demonstrated to modulate the secretion of the gut‐derived incretin hormone glucagon‐like peptide‐1 (GLP‐1), possibly via the transmembrane receptor Takeda G‐protein‐coupled receptor 5 and the nuclear farnesoid X receptor, in intestinal L cells. The present article critically reviews current evidence connecting established glucose‐lowering drugs to bile acid‐induced GLP‐1 secretion, and discusses whether bile acid‐induced GLP‐1 secretion may constitute a new basis for understanding how metformin, inhibitors of the apical sodium‐dependent bile acids transporter, and bile acid sequestrants – old, new and neglected glucose‐lowering drugs – improve glucose metabolism.