Incretin therapy--present and future

Standardized Emblica officinalis fruit extract inhibited the activities of α-amylase, α-glucosidase, and dipeptidyl peptidase-4 and displayed antioxidant potential

BACKGROUND

Emblica officinalis, known as amla in Ayurveda, has been used as a folk medicine to treat numerous pathological conditions, including diabetes. However, the novel extract of E. officinalis fruit extract (amla fruit extract, AFE, Saberry®) containing 100 g kg^-1 β-glucogallin along with hydrolyzable tannins has not yet been extensively studied for its antidiabetic potential.

OBJECTIVE

The aim of this study was to investigate the antidiabetic and antioxidant activities of AFE and its stability during gastric stress as well as its thermostability.

METHODS

The effect of AFE on the inhibition of pancreatic α-amylase and salivary α-amylase enzymes was studied using starch and yeast α-glucosidase enzyme using 4-nitrophenyl α-d-glucopyranoside as substrate. Further, 2,2-diphenyl-1-picrylhydrazyl radical scavenging and reactive oxygen species inhibition assay was performed against AFE.

RESULTS

AFE potently inhibited the activities of α-amylase and α-glucosidase in a concentration-dependent manner with half maximal inhibitory concentration (IC₅₀ ) values of 135.70 μg mL^-1 and 106.70 μg mL^-1 respectively. Furthermore, it also showed inhibition of α-glucosidase (IC₅₀ 562.9 μg mL^-1 ) and dipeptidyl peptidase-4 (DPP-4; IC₅₀ 3770 μg mL^-1 ) enzyme activities. AFE is a potent antioxidant showing a free radical scavenging activity (IC₅₀ 2.37 μg mL^-1 ) and protecting against cellular reactive oxygen species (IC₅₀ 1.77 μg mL^-1 ), and the effects elicited could be attributed to its phytoconstituents.

CONCLUSION

AFE showed significant gastric acid resistance and was also found to be thermostable against wet heat. Excellent α-amylase, α-glucosidase, and DPP-4 inhibitory activities of AFE, as well as antioxidant activities, strongly recommend its use for the management of type 2 diabetes mellitus. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

GLP-1 RA Treatment and Dosing Patterns Among Type 2 Diabetes Patients in Six Countries: A Retrospective Analysis of Pharmacy Claims Data

INTRODUCTION

The glucagon-like peptide-1 receptor agonist (GLP-1 RA) class is evolving and expanding. This retrospective database study evaluated recent real-world treatment and dosing patterns of patients with type 2 diabetes (T2D) initiating GLP-1 RAs in Belgium (BE), France (FR), Germany (DE), Italy (IT), the Netherlands (NL), and Canada (CA).

METHODS

Adult T2D patients initiating GLP-1 RA therapy (dulaglutide [DULA], exenatide twice daily [exBID], exenatide once weekly [exQW], liraglutide [LIRA], or lixisenatide [LIXI]) from 2015 to 2016 were identified using the IQVIA (IQVIA, Durham, NC, and Danbury, CT, USA) Real-World Data Adjudicated Pharmacy Claims. The therapy initiation date was termed the 'index date.' Eligible patients had ≥ 180 days pre-index and ≥ 360 days post-index. Persistence (until discontinuation or switch) was evaluated over the variable follow-up using Kaplan-Meier (KM) survival analysis. Average daily dose (ADD) was calculated until discontinuation or switch.

RESULTS

A total of 34,649 DULA, 3616 exBID, 11,138 exQW, 48,317 LIRA, and 2,204 LIXI patients were included in the analysis (34.9-63.2% female; median age range 53-62 years; median follow-up 16-30 months). Proportion persistent at 1-year post-index was 36.8-67.2% for DULA, 5.9-44.4% for exBID, 24.7-44.2% for exQW, 22.2-57.5% for LIRA, and 15.5-40.0% for LIXI. Median time persistent (days) was 245-381 for DULA, 62-243 for exBID, 121-319 for exQW, 103-507 for LIRA, and 99-203 for LIXI. Mean ADD was 13.21-20.43 µg for exBID, 1.44-1.68 mg for LIRA, and 19.88-20.54 µg for LIXI. Mean average weekly dose (AWD) ranged from 2.03 to 2.14 mg for exQW. Mean AWD for DULA was 1.25 mg in Canada and ranged from 1.43 to 1.53 mg in the other countries.

CONCLUSION

Across six countries, persistence was highest among DULA patients and generally lowest among exBID patients. ADD/AWD for all GLP-1 RAs was in line with the recommended label. Longer-term data would be useful to obtain a better understanding of GLP-1 RA treatment patterns over time.

FUNDING

Eli Lilly and Company, Indianapolis, IN, USA.

Effects of Antidiabetic Drugs on Gut Microbiota Composition

Gut microbiota forms a catalog of about 1000 bacterial species; which mainly belong to the Firmicutes and Bacteroidetes phyla. Microbial genes are essential for key metabolic processes; such as the biosynthesis of short-chain fatty acids (SCFA); amino acids; bile acids or vitamins. It is becoming clear that gut microbiota is playing a prevalent role in pathologies such as metabolic syndrome; type 2 diabetes (T2D); inflammatory and bowel diseases. Obesity and related diseases; notably type 2 diabetes, induce gut dysbiosis. In this review; we aim to cover the current knowledge about the effects of antidiabetic drugs on gut microbiota diversity and composition as well as the potential beneficial effects mediated by specific taxa. Metformin is the first-line treatment against T2D. In addition to its glucose-lowering and insulin sensitizing effects, metformin promotes SCFA-producing and mucin-degrading bacteria. Other antidiabetic drugs discussed in this review show positive effects on dysbiosis; but without any consensus specifically regarding the Firmicutes to Bacteroidetes ratio. Thus, beneficial effects might be mediated by specific taxa.

Alogliptin for the treatment of type 2 diabetes: a drug safety evaluation

INTRODUCTION

Dipeptidyl peptidase-4 (DPP-4) inhibitors such as alogliptin are becoming more widely established as treatment options for patients with type 2 diabetes (T2DM) because of their ability to improve glycemic control without increasing the risk of hypoglycemia or weight gain. New therapies with improved safety profiles are needed, especially because of the chronic and progressive nature of T2DM.

AREAS COVERED

In this article, the overall safety and tolerability of alogliptin are evaluated based upon a review of the literature. In particular, adverse events (AEs) that have been of interest for the DPP-4 class of drugs, such as the risk of major cardiovascular (CV) events and acute pancreatitis, will be investigated in detail.

EXPERT OPINION

Alogliptin is generally well-tolerated in a broad range of patient populations including different ethnic groups and the elderly. In the pivotal EXAMINE clinical trial, alogliptin was found not to be associated with an increased risk of major CV events or acute pancreatitis/pancreatic cancer.

Reduced expression of ERp46 under diabetic conditions in β-cells and the effect of liraglutide

BACKGROUND

Diabetes mellitus is characterized by peripheral insulin resistance, hyperglycemia and defective insulin secretion. Insulin producing pancreatic β-cells are equipped with a highly developed endoplasmic reticulum (ER) and thus are affected by ER stress under hyperglycemic conditions. We have previously studied the influence of high glucose on cultured β-cells in vitro. Proteomic analysis revealed a number of proteins involved in glucose toxicity, while further biochemical analysis identified the endoplasmic reticulum protein ERp46 as a molecule with a possible role in insulin production at the post-translational level. In addition, the involvement of incretin hormone glucagon-like peptide 1 (GLP-1) in diabetes proposes that incretin-mimetic compounds may be among the optimal choices in future therapeutic interventions; therefore their effects on various aspects of the pathogenesis of diabetes mellitus should be explored in detail. Based on the above, we examined the possible involvement of ERp46 in insulin production and the effect of the GLP-1 analogue liraglutide on the expression of ERp46 in vitro, in β-cells cultured under high glucose conditions and in vivo, in the mouse db/db diabetic model, where pronounced hyperglycemia is a key characteristic.

RESULTS

Confocal microscopy revealed areas of co-localization of ERp46 and pro-insulin in pancreatic islets. In order to explore the possible interaction between ERp46 and insulin immunoprecipitation was used. In extracts from cultured β-cells, antibodies against pro-insulin co-precipitated ERp46 and antibodies against ERp46 co-precipitated pro-insulin, as shown by Western blotting. Furthermore, data from a proximity ligation assay positioned these two molecules closer than 30nm in distance. When pancreatic β-cells were cultured in high glucose conditions they exhibited a decrease in ERp46 expression, while treatment with the GLP-1 analogue liraglutide restored ERp46 levels, leading to a significant increase of ERp46 in comparison to hyperglycemic conditions. In the diabetic mouse model db(-)/db, ERp46 expression was reduced in pancreatic islets, as documented by morphological and biochemical techniques. This decrease was abolished after treatment with the GLP-1 analogue in a dose-dependent manner. In an attempt to understand the underlying mechanism, we examined the sequence of the promoter of ERp46 and found consensus motifs that can be recognized by transcription factors ATF6 and XBP1. Subsequently, we performed chromatin immunoprecipitation assay and demonstrated that treatment of β-TC-6 cells with 25mmol/L glucose decreases gradually the binding enrichment of ATF6 and XBP1 in ERp46 gene promoter.

CONCLUSIONS

We propose that since ERp46 is a member of the disulfide isomerases family, it is likely to play a key role in insulin biosynthesis and its reduction under high glucose conditions may be a novel contributor to the glucotoxicity of β-cells. In addition, the GLP-1 analogue liraglutide seems to interfere in this process and may exert its beneficial effects in diabetes by affecting insulin production via restoration of ERp46 expression.

[Potential of pharmacological modulation of level and activity incretins on diabetes mellitus type 2]

This review summarizes data on the main approaches used for the search of biologically active compounds modulating the level and physiological activity of incretins. Currently two groups of drugs are used in clinical practice: they either replenish the deficit of incretins (glucagon-like peptide-1 receptor agonists) or inhibit the degradation processes (dipeptidyl peptidase 4 inhibitors). In addition, new groups of substances are actively searched. These include non-peptide agonists of glucagon-like peptide-1 receptors, agonists/antagonists of glucose-dependent insulinotropic peptide, the hybrid polypeptides based on glucagon-like peptide-1 and glucagon.

Pharmacological characterization and antidiabetic activity of a long-acting glucagon-like peptide-1 analogue conjugated to an antithrombin III-binding pentasaccharide

AIMS

To examine the biological characteristics of a novel glucagon-like peptide-1 (GLP-1) conjugate, in which an antithrombin III (ATIII)-binding pentasaccharide is conjugated to d-Ala(8) GLP-1 using a tetraethylene glycol linker.

METHODS

We assessed GLP-1 receptor binding, cAMP generation and insulin secretory activity of the GLP-1 conjugate in vitro. Circulating half-life, glucose homeostatic and subchronic therapeutic effectiveness were then examined in vivo.

RESULTS

The half-life of the GLP-1 conjugate in mice was ∼11 h. In vitro insulin secretion from clonal β cells and islets was increased (p < 0.001) by the conjugate. The conjugate had half maximum effective concentration values of 1.3 × 10(-7) and 9.9 × 10(-8)  M for displacement of (125) I-GLP-1 in competitive GLP-1 receptor binding and cAMP generation, respectively. Glucose tolerance in normal mice, immediately and 4 h after conjugate injection, resulted in significant (p < 0.001) improvements in blood glucose. These effects persisted for >48 h after administration. Daily treatment (21 days) of high-fat-fed and ob/ob mice with 25 nmol/kg conjugate resulted in significant improvement in glucose tolerance (p < 0.001) and reductions in glycated haemoglobin (HbA1c; p < 0.01) equivalent to or better than with exenatide or liraglutide. Treatment of C57BL/KsJ db/db mice for 15 days with 100 nmol/kg conjugate significantly (p < 0.001) reduced glucose and raised plasma insulin. Oral glucose tolerance was significantly (p < 0.001) improved and both 24-h glucose profile (p < 0.001) and HbA1c levels (p < 0.001) were reduced. Islet size (p < 0.001) and pancreatic insulin content were increased without change of islet cell proliferation or apoptosis.

CONCLUSION

These data show that d-Ala(8) GLP-1(Lys(37) ) pentasaccharide exerts significant antidiabetic actions and has a projected pharmacokinetic/pharmacodynamic profile that merits further evaluation in humans for a possible once-weekly dosing regimen.

Degradation and Stabilization of Peptide Hormones in Human Blood Specimens

Plasma hormone peptides, including GLP-1, GIP, Glucagon, and OXM, possess multiple physiological roles and potential therapeutic and diagnostic utility as biomarkers in the research of metabolic disorders. These peptides are subject to proteolytic degradation causing preanalytical variations. Stabilization for accurate quantitation of these active peptides in ex vivo blood specimens is essential for drug and biomarker development. We investigated the protease-driven instability of these peptides in conventional serum, plasma, anticoagulated whole blood, as well as whole blood and plasma stabilized with protease inhibitors. The peptide was monitored by both time-course Matrix-Assisted Laser Desorption Ionization Time-to-Flight Mass Spectrometry (MALDI –TOF MS) and Ab-based assay (ELISA or RIA). MS enabled the identification of proteolytic fragments. In non-stabilized blood samples, the results clearly indicated that dipeptidyl peptidase-IV (DPP-IV) removed the N-terminal two amino acid residues from GLP-1, GIP and OXM(1-37) and not-yet identified peptidase(s) cleave(s) the full-length OXM(1-37) and its fragments. DPP-IV also continued to remove two additional N-terminal residues of processed OXM(3–37) to yield OXM(5–37). Importantly, both DPP-IV and other peptidase(s) activities were inhibited efficiently by the protease inhibitors included in the BD P800* tube. There was preservation of GLP-1, GIP, OXM and glucagon in the P800 plasma samples with half-lives > 96, 96, 72, and 45 hours at room temperature (RT), respectively. In the BD P700* plasma samples, the stabilization of GLP-1 was also achieved with half-life > 96 hours at RT. The stabilization of these variable peptides increased their utility in drug and/or biomarker development. While stability results of GLP-1 obtained with Ab-based assay were consistent with those obtained by MS analysis, the Ab-based results of GIP, Glucagon, and OXM did not reflect the time-dependent degradations revealed by MS analysis. Therefore, we recommended characterizing the degradation of the peptide using the MS-based method when investigating the stability of a specific peptide.

Synthesis and Evaluation of a Series of Long-Acting Glucagon-Like Peptide-1 (GLP-1) Pentasaccharide Conjugates for the Treatment of Type 2 Diabetes

The present study details the development of a family of novel D-Ala(8) glucagon-like peptide-1 (GLP-1) peptide conjugates by site specific conjugation to an antithrombin III (ATIII) binding carrier pentasaccharide through tetraethylene glycol linkers. All conjugates were found to possess potent insulin-releasing activity. Peptides with short linkers (<25 atoms) conjugated at Lys(34) and Lys(37) displayed strong GLP-1 receptor (GLP-1-R) binding affinity. All D-Ala(8) GLP-1 conjugates exhibited prominent glucose-lowering action. Biological activity of the Lys(37) short-linker peptide was evident up to 72 h post-injection. In agreement, the pharmacokinetic profile of this conjugate (t1/2 , 11 h) was superior to that of the GLP-1-R agonist, exenatide. Once-daily injection of the Lys(37) short-linker peptide in ob/ob mice for 21 days significantly decreased food intake and improved HbA1c and glucose tolerance. Islet size was decreased, with no discernible change in islet number. The beneficial effects of the Lys(37) short-linker peptide were similar to or better than either exenatide or liraglutide, another GLP-1-R agonist. In conclusion, GLP-1 peptides conjugated to an ATIII binding carrier pentasaccharide have a substantially prolonged bioactive profile compatible for possible once-weekly treatment of type 2 diabetes in humans.

Low-frequency and rare exome chip variants associate with fasting glucose and type 2 diabetes susceptibility

Fasting glucose and insulin are intermediate traits for type 2 diabetes. Here we explore the role of coding variation on these traits by analysis of variants on the HumanExome BeadChip in 60,564 non-diabetic individuals and in 16,491 T2D cases and 81,877 controls. We identify a novel association of a low-frequency nonsynonymous SNV in GLP1R (A316T; rs10305492; MAF=1.4%) with lower FG (β=-0.09±0.01 mmol l(-1), P=3.4 × 10(-12)), T2D risk (OR[95%CI]=0.86[0.76-0.96], P=0.010), early insulin secretion (β=-0.07±0.035 pmolinsulin mmolglucose(-1), P=0.048), but higher 2-h glucose (β=0.16±0.05 mmol l(-1), P=4.3 × 10(-4)). We identify a gene-based association with FG at G6PC2 (pSKAT=6.8 × 10(-6)) driven by four rare protein-coding SNVs (H177Y, Y207S, R283X and S324P). We identify rs651007 (MAF=20%) in the first intron of ABO at the putative promoter of an antisense lncRNA, associating with higher FG (β=0.02±0.004 mmol l(-1), P=1.3 × 10(-8)). Our approach identifies novel coding variant associations and extends the allelic spectrum of variation underlying diabetes-related quantitative traits and T2D susceptibility.

Benefits of healthy adipose tissue in the treatment of diabetes

The major malfunction in diabetes mellitus is severe perturbation of glucose homeostasis caused by deficiency of insulin. Insulin deficiency is either absolute due to destruction or failure of pancreatic β cells, or relative due to decreased sensitivity of peripheral tissues to insulin. The primary lesion being related to insulin, treatments for diabetes focus on insulin replacement and/or increasing sensitivity to insulin. These therapies have their own limitations and complications, some of which can be life-threatening. For example, exogenous insulin administration can lead to fatal hypoglycemic episodes; islet/pancreas transplantation requires life-long immunosuppressive therapy; and anti-diabetic drugs have dangerous side effects including edema, heart failure and lactic acidosis. Thus the need remains for better safer long term treatments for diabetes. The ultimate goal in treating diabetes is to re-establish glucose homeostasis, preferably through endogenously generated hormones. Recent studies increasingly show that extra-pancreatic hormones, particularly those arising from adipose tissue, can compensate for insulin, or entirely replace the function of insulin under appropriate circumstances. Adipose tissue is a versatile endocrine organ that secretes a variety of hormones with far-reaching effects on overall metabolism. While unhealthy adipose tissue can exacerbate diabetes through limiting circulation and secreting of pro-inflammatory cytokines, healthy uninflamed adipose tissue secretes beneficial adipokines with hypoglycemic and anti-inflammatory properties, which can complement and/or compensate for the function of insulin. Administration of specific adipokines is known to alleviate both type 1 and 2 diabetes, and leptin mono-therapy is reported to reverse type 1 diabetes independent of insulin. Although specific adipokines may correct diabetes, administration of individual adipokines still carries risks similar to those of insulin monotherapy. Thus a better approach is to achieve glucose homeostasis with endogenously-generated adipokines through transplantation or regeneration of healthy adipose tissue. Our recent studies on mouse models show that type 1 diabetes can be reversed without insulin through subcutaneous transplantation of embryonic brown adipose tissue, which leads to replenishment of recipients’ white adipose tissue; increase of a number of beneficial adipokines; and fast and long-lasting euglycemia. Insulin-independent glucose homeostasis is established through a combination of endogenously generated hormones arising from the transplant and/or newly-replenished white adipose tissue. Transplantation of healthy white adipose tissue is reported to alleviate type 2 diabetes in rodent models on several occasions, and increasing the content of endogenous brown adipose tissue is known to combat obesity and type 2 diabetes in both humans and animal models. While the underlying mechanisms are not fully documented, the beneficial effects of healthy adipose tissue in improving metabolism are increasingly reported, and are worthy of attention as a powerful tool in combating metabolic disease.

Call-to-action: timely and appropriate treatment for people with type 2 diabetes in Latin America

Latin America faces a unique set of challenges in the treatment of type 2 diabetes mellitus (T2DM). This report identifies these challenges and provides a framework for implementation of the strategies, policies and education programs which are needed to optimize the management of this condition. In order to improve future diabetes care, it will be necessary to address existing problems such as limitation of resources, inadequate management of hyperglycemia, and inappropriate education of healthcare team members and people with diabetes. Achieving these goals will require collaborative efforts by many individuals, groups and organizations. These include policymakers, international organizations, healthcare providers, those responsible for setting medical school curricula, patients and society as a whole. It is anticipated that improved/continuing education of healthcare professionals, diabetes self-management education and development of a team approach for T2DM care will lead to optimization of patient-centered care. Implementation of multicentric demonstration studies and rational use of antidiabetic treatments will be necessary to demonstrate the long-term favorable impact of these strategies upon quality of care, prevention of chronic complications, mortality, healthcare costs and patient quality of life.

Monotherapy with the once weekly GLP-1 receptor agonist dulaglutide for 12 weeks in Japanese patients with type 2 diabetes: dose-dependent effects on glycaemic control in a randomised, double-blind, placebo-controlled study

The aim of this study was to evaluate the dose-dependent effect of dulaglutide, a glucagon-like peptide-1 receptor agonist, on glycaemic control in Japanese patients with type 2 diabetes mellitus who were treated with diet/exercise or oral antidiabetic drug monotherapy. In this randomised, double-blind, placebo-controlled, parallel-group, 12-week study, patients received once weekly subcutaneous dulaglutide doses of 0.25, 0.5, or 0.75 mg (DU 0.25, DU 0.5, and DU 0.75, respectively) or placebo (n=36, 37, 35, and 37, respectively). The primary measure was change from baseline in glycated haemoglobin (HbA1c; %) at 12 weeks. Continuous variables were analysed using a mixed-effects model for repeated measures. Significant dose-dependent reductions in HbA1c were observed (least squares mean difference versus placebo [95% confidence interval]): DU 0.25=-0.72% (-0.95, -0.48), DU 0.5=-0.97% (-1.20, -0.73), and DU 0.75=-1.17% (-1.41, -0.93); p<0.001. Significant improvements in plasma glucose (PG), both fasting and average 7-point self-monitored blood glucose, were also observed with dulaglutide versus placebo (p<0.001). Dulaglutide was well-tolerated. Gastrointestinal adverse events (AEs) were more common in dulaglutide-treated patients, with nausea the most frequent (8 [5.5%]). Few dulaglutide-treated patients discontinued due to AEs (4 [3.7%]), and no serious AEs related to study medication occurred. Three patients (DU 0.5=1 and DU 0.75=2) reported asymptomatic hypoglycaemia (PG ≤70 mg/dL). The observed dose-dependent reduction in HbA1c and acceptable safety profile support further clinical development of dulaglutide for treatment of type 2 diabetes mellitus in Japan.

A tripeptide Diapin effectively lowers blood glucose levels in male type 2 diabetes mice by increasing blood levels of insulin and GLP-1

The prevalence of type 2 diabetes (T2D) is rapidly increasing worldwide. Effective therapies, such as insulin and Glucagon-like peptide-1 (GLP-1), require injections, which are costly and result in less patient compliance. Here, we report the identification of a tripeptide with significant potential to treat T2D. The peptide, referred to as Diapin, is comprised of three natural L-amino acids, GlyGlyLeu. Glucose tolerance tests showed that oral administration of Diapin effectively lowered blood glucose after oral glucose loading in both normal C57BL/6J mice and T2D mouse models, including KKay, db/db, ob/ob mice, and high fat diet-induced obesity/T2D mice. In addition, Diapin treatment significantly reduced casual blood glucose in KKay diabetic mice in a time-dependent manner without causing hypoglycemia. Furthermore, we found that plasma GLP-1 and insulin levels in diabetic models were significantly increased with Diapin treatment compared to that in the controls. In summary, our findings establish that a peptide with minimum of three amino acids can improve glucose homeostasis and Diapin shows promise as a novel pharmaceutical agent to treat patients with T2D through its dual effects on GLP-1 and insulin secretion.

Adipose tissue, hormones, and treatment of type 1 diabetes

Type 1 diabetes (T1D) is a serious disease with increasing incidence worldwide, with fatal consequences if untreated. Traditional therapies require direct or indirect insulin replacement, which involves numerous limitations and complications. While insulin is the major regulator of blood glucose, recent reports demonstrate the ability of several extra-pancreatic hormones to decrease blood glucose and improve metabolic homeostasis. Such hormones mainly include adipokines originating from adipose tissue (AT), while specific factors from the gut and liver also contribute to glucose homeostasis. Correction of T1D with adipokines is progressively becoming a realistic option, with the potential to overcome many problems associated with insulin replacement. Several recent studies demonstrate insulin-independent reversal or amelioration of T1D through administration of specific adipokines. Our recent work demonstrates the ability of healthy AT to compensate for the function of endocrine pancreas in long-term correction of T1D. This review discusses the potential of AT-related therapies for T1D as viable alternatives to insulin replacement.

The continuing need for drug development and clinical trials in type 2 diabetes and its complications: introduction to the RDS special issue

The increased burden of type 2 diabetes (T2D) necessitates the need for effective and safe novel drugs to treat this epidemic disease and its complications. By compiling this RDS Special Issue, our aim was to provide a comprehensive and critical overview on recent, ongoing, and future developments in this field. In collaboration with distinguished and renowned experts, we analyzed and discussed the most important advances in the field of incretin-based therapies, their extraglycemic effects, cardiovascular actions, and specific properties of the central nervous system. Another important drug class currently in development, the SGLT-2 inhibitors, and the role of the kidney in T2D are topics also covered by this issue. In addition to drug developments, new physiological insights into the understanding of the organ pathophysiology in T2D are presented that may eventually lead to additional therapeutic targets for obesity, T2D, and chronic inflammation acting on the brain, cardiovascular system, and pancreatic islets. The outcome of this Special Issue is a comprehensive reference work including bundled knowledge and expert opinions on the various aspects of the disease and its possible therapy strategies available now and in the near future. However, despite the advances delivered by modern incretin-based therapies today, there are still many limitations associated with efficacy data, application routes, and safety issues, which prevent the decline in diabetes complication rates. We conclude that further drug development and clinical trials are required to overcome these limitations, and to counteract the movement towards higher incidence rates of T2D and its complications.

The alpha-cell as target for type 2 diabetes therapy

Glucagon is the main secretory product of the pancreatic alpha-cells. The main function of this peptide hormone is to provide sustained glucose supply to the brain and other vital organs during fasting conditions. This is exerted by stimulation of hepatic glucose production via specific G protein-coupled receptors in the hepatocytes. Type 2 diabetic patients are characterized by elevated glucagon levels contributing decisively to hyperglycemia in these patients. Accumulating evidence demonstrates that targeting the pancreatic alpha-cell and its main secretory product glucagon is a possible treatment for type 2 diabetes. Several lines of preclinical evidence have paved the way for the development of drugs, which suppress glucagon secretion or antagonize the glucagon receptor. In this review, the physiological actions of glucagon and the role of glucagon in type 2 diabetic pathophysiology are outlined. Furthermore, potential advantages and limitations of antagonizing the glucagon receptor or suppressing glucagon secretion in the treatment of type 2 diabetes are discussed with a focus on already marketed drugs and drugs in clinical development. It is concluded that the development of novel glucagon receptor antagonists are confronted with several safety issues. At present, available pharmacological agents based on the glucose-dependent glucagonostatic effects of GLP-1 represent the most favorable way to apply constraints to the alpha-cell in type 2 diabetes.