Improving glycaemic control in type 2 diabetes: Stimulate insulin secretion or provide beta-cell rest?

The Anti-Diabetic Potential of Baicalin: Evidence from Rodent Studies

Baicalin is a biologically active flavonoid compound that benefits the organism in various pathological conditions. Rodent studies have shown that this compound effectively alleviates diabetes-related disturbances in models of type 1 and type 2 diabetes. Baicalin supplementation limited hyperglycemia and improved insulin sensitivity. The anti-diabetic effects of baicalin covered the main insulin-sensitive tissues, i.e., the skeletal muscle, the adipose tissue, and the liver. In the muscle tissue, baicalin limited lipid accumulation and improved glucose transport. Baicalin therapy was associated with diminished adipose tissue content and increased mitochondrial biogenesis. Hepatic lipid accumulation and glucose output were also decreased as a result of baicalin supplementation. The molecular mechanism of the anti-diabetic action of this compound is pleiotropic and is associated with changes in the expression/action of pivotal enzymes and signaling molecules. Baicalin positively affected, among others, the tissue insulin receptor, glucose transporter, AMP-activated protein kinase, protein kinase B, carnitine palmitoyltransferase, acetyl-CoA carboxylase, and fatty acid synthase. Moreover, this compound ameliorated diabetes-related oxidative and inflammatory stress and reduced epigenetic modifications. Importantly, baicalin supplementation at the effective doses did not induce any side effects. Results of rodent studies imply that baicalin may be tested as an anti-diabetic agent in humans.

Benefits and risks of drug combination therapy for diabetes mellitus and its complications: a comprehensive review

Diabetes is a chronic metabolic disease, and its therapeutic goals focus on the effective management of blood glucose and various complications. Drug combination therapy has emerged as a comprehensive treatment approach for diabetes. An increasing number of studies have shown that, compared with monotherapy, combination therapy can bring significant clinical benefits while controlling blood glucose, weight, and blood pressure, as well as mitigating damage from certain complications and delaying their progression in diabetes, including both type 1 diabetes (T1D), type 2 diabetes (T2D) and related complications. This evidence provides strong support for the recommendation of combination therapy for diabetes and highlights the importance of combined treatment. In this review, we first provided a brief overview of the phenotype and pathogenesis of diabetes and discussed several conventional anti-diabetic medications currently used for the treatment of diabetes. We then reviewed several clinical trials and pre-clinical animal experiments on T1D, T2D, and their common complications to evaluate the efficacy and safety of different classes of drug combinations. In general, combination therapy plays a pivotal role in the management of diabetes. Integrating the effectiveness of multiple drugs enables more comprehensive and effective control of blood glucose without increasing the risk of hypoglycemia or other serious adverse events. However, specific treatment regimens should be tailored to individual patients and implemented under the guidance of healthcare professionals.

A human antibody against pathologic IAPP aggregates protects beta cells in type 2 diabetes models

In patients with type 2 diabetes, pancreatic beta cells progressively degenerate and gradually lose their ability to produce insulin and regulate blood glucose. Beta cell dysfunction and loss is associated with an accumulation of aggregated forms of islet amyloid polypeptide (IAPP) consisting of soluble prefibrillar IAPP oligomers as well as insoluble IAPP fibrils in pancreatic islets. Here, we describe a human monoclonal antibody selectively targeting IAPP oligomers and neutralizing IAPP aggregate toxicity by preventing membrane disruption and apoptosis in vitro. Antibody treatment in male rats and mice transgenic for human IAPP, and human islet-engrafted mouse models of type 2 diabetes triggers clearance of IAPP oligomers resulting in beta cell protection and improved glucose control. These results provide new evidence for the pathological role of IAPP oligomers and suggest that antibody-mediated removal of IAPP oligomers could be a pharmaceutical strategy to support beta cell function in type 2 diabetes.

O304 ameliorates hyperglycemia in mice by dually promoting muscle glucose effectiveness and preserving β-cell function

Although insulin mediated glucose uptake in skeletal muscle is a major mechanism ensuring glucose disposal in humans, glucose effectiveness, i.e., the ability of glucose itself to stimulate its own uptake independent of insulin, accounts for roughly half of the glucose disposed during an oral glucose tolerance test. Both insulin dependent and insulin independent skeletal muscle glucose uptake are however reduced in individuals with diabetes. We here show that AMPK activator O304 stimulates insulin independent glucose uptake and utilization in skeletal muscle and heart in vivo, while preventing glycogen accumulation. Combined glucose uptake and utilization requires an increased metabolic demand and we show that O304 acts as a mitochondrial uncoupler, i.e., generates a metabolic demand. O304 averts gene expression changes associated with metabolic inflexibility in skeletal muscle and heart of diabetic mice and reverts diabetic cardiomyopathy. In Type 2 diabetes, insulin resistance elicits compensatory insulin hypersecretion, provoking β-cell stress and eventually compensatory failure. In db/db mice O304 preserves β-cell function by preventing decline in insulin secretion, β-cell mass, and pancreatic insulin content. Thus, as a dual AMPK activator and mitochondrial uncoupler O304 mitigates two central defects of T2D; impaired glucose uptake/utilization and β-cell failure, which today lack effective treatment.

Restoration of PITPNA in Type 2 diabetic human islets reverses pancreatic beta-cell dysfunction

Defects in insulin processing and granule maturation are linked to pancreatic beta-cell failure during type 2 diabetes (T2D). Phosphatidylinositol transfer protein alpha (PITPNA) stimulates activity of phosphatidylinositol (PtdIns) 4-OH kinase to produce sufficient PtdIns-4-phosphate (PtdIns-4-P) in the trans-Golgi network to promote insulin granule maturation. PITPNA in beta-cells of T2D human subjects is markedly reduced suggesting its depletion accompanies beta-cell dysfunction. Conditional deletion of Pitpna in the beta-cells of Ins-Cre, Pitpnaflox/flox mice leads to hyperglycemia resulting from decreasing glucose-stimulated insulin secretion (GSIS) and reducing pancreatic beta-cell mass. Furthermore, PITPNA silencing in human islets confirms its role in PtdIns-4-P synthesis and leads to impaired insulin granule maturation and docking, GSIS, and proinsulin processing with evidence of ER stress. Restoration of PITPNA in islets of T2D human subjects reverses these beta-cell defects and identify PITPNA as a critical target linked to beta-cell failure in T2D.

Silibinin alleviates ferroptosis of rat islet β cell INS-1 induced by the treatment with palmitic acid and high glucose through enhancing PINK1/parkin-mediated mitophagy

Type 2 diabetes (T2DM) is induced by the abundance of glucose and lipids, which causes glucolipotoxicity to the pancreatic β-cells. Silibinin is a natural flavonoid possessing the regulatory activity on insulin production and therapeutic activity in diabetic mice; however, its effect on glucolipotoxicity is not fully explained. This in vitro study investigates the effects of silibinin on palmitic acid (PA) and high glucose (HG)-induced cell loss and ferroptosis of rat insulinoma INS-1 cells. In the cells treated with PA and HG, expressions of glucose transporter 4 (Glut4) and carnitine acyltransferase I (CPT1) for β-oxidation of fatty acids are reduced. Mitochondria are the metabolic organelles for glucose and fatty acids. The mitochondrial membrane potential (MMP) and ATP production were decreased, while the ROS level was elevated in the cells treated with PA and HG, indicating an induction of mitochondrial disorder. Cell loss was partially rescued by ferroptosis inhibition, suggesting an involvement of ferroptosis in the cells treated with PA and HG. More importantly, the increases in total iron, lipid ROS, MDA and COX-2, and the decrease in ferroptosis inhibitory molecules GSH, GPX4 and FSP1 appeared in the cells treated with PA and HG, confirming the occurrence of ferroptosis. Moreover, PINK1/parkin-mediated mitophagy, a vital process for selective elimination of damaged mitochondria, was blocked. Interestingly, silibinin rescued the mitochondria, restricted the ferroptosis and restored the mitophagy. By using the pharmacological stimulator and inhibitor of mitophagy, and si-RNA transfection to silence PINK1 expression, silibinin's protective effect against ferroptosis caused by PA and HG treatment was found to depend on mitophagy. Collectively, our current study reveals the new mechanisms for the protection of silibinin against the injury of INS-1 cells treated with PA and HG, elucidates the participation of ferroptosis in glucolipotoxicity, highlighting the involvement of mitophagy in defense against ferroptotic cell death.

Steroidogenic factor 1 protects mice from obesity-induced glucose intolerance via improving glucose-stimulated insulin secretion by beta cells

As a potential druggable nuclear receptor, steroidogenic factor 1 (SF1) regulates obesity and insulin resistance in the ventromedial hypothalamic nucleus. Herein, we sought to demonstrate its expression and functions in islets in the development of obesity-induced diabetes. SF1 was barely detected in the beta cells of lean mice but highly expressed in those of non-diabetic obese mice, while decreased in diabetic ones. Conditional deletion of SF1 in beta cells predisposed diet-induced obese (DIO) mice to glucose intolerance by perturbing glucose-stimulated insulin secretion (GSIS). Consistently, forced expression of SF1 restored favorable glucose homeostasis in DIO and db/db mice by improving GSIS. In isolated islets and MIN6, overexpression of SF1 also potentiated GSIS, mediated by improvement of mitochondrial ATP production. The underlying mechanisms may involve oxidative phosphorylation and lipid metabolism. Collectively, SF1 in beta cell preserves GSIS to promote beta-cell adaptation to obesity and hence is a potential therapeutic target for obesity-induced diabetes.

Recent Developments in Islet Biology: A Review With Patient Perspectives

Navigating the coronavirus disease-2019 (COVID-19, now COVID) pandemic has required resilience and creativity worldwide. Despite early challenges to productivity, more than 2,000 peer-reviewed articles on islet biology were published in 2021. Herein, we highlight noteworthy advances in islet research between January 2021 and April 2022, focussing on 5 areas. First, we discuss new insights into the role of glucokinase, mitogen-activated protein kinase-kinase/extracellular signal-regulated kinase and mitochondrial function on insulin secretion from the pancreatic β cell, provided by new genetically modified mouse models and live imaging. We then discuss a new connection between lipid handling and improved insulin secretion in the context of glucotoxicity, focussing on fatty acid-binding protein 4 and fetuin-A. Advances in high-throughput "omic" analysis evolved to where one can generate more finely tuned genetic and molecular profiles within broad classifications of type 1 diabetes and type 2 diabetes. Next, we highlight breakthroughs in diabetes treatment using stem cell-derived β cells and innovative strategies to improve islet survival posttransplantation. Last, we update our understanding of the impact of severe acute respiratory syndrome-coronavirus-2 infection on pancreatic islet function and discuss current evidence regarding proposed links between COVID and new-onset diabetes. We address these breakthroughs in 2 settings: one for a scientific audience and the other for the public, particularly those living with or affected by diabetes. Bridging biomedical research in diabetes to the community living with or affected by diabetes, our partners living with type 1 diabetes or type 2 diabetes also provide their perspectives on these latest advances in islet biology.

The efficacy of GLP-1RAs for the management of postprandial hypoglycemia following bariatric surgery: a systematic review

OBJECTIVE

Postprandial hyperinsulinemic hypoglycemia with neuroglycopenia is an increasingly recognized complication of Roux-en-Y gastric bypass and gastric sleeve surgery that may detrimentally affect patient quality of life. One likely causal factor is glucagon-like peptide-1 (GLP-1), which has an exaggerated rise following ingestion of carbohydrates after bariatric surgery. This paper sought to assess the role of GLP-1 receptor agonists (GLP-1RAs) in managing postprandial hypoglycemia following bariatric surgery.

METHODS

MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, and Scopus were systematically and critically appraised for all peer-reviewed publications that suitably fulfilled the inclusion criteria established a priori. This systematic review was developed according to the Preferred Reporting Items for Systematic Review and Meta-Analyses Protocols (PRISMA-P). It followed methods outlined in the Cochrane Handbook for Systematic Reviews of Interventions and is registered with PROSPERO (International Prospective Register of Systematic Reviews; identifier CRD420212716429).

RESULTS AND CONCLUSIONS

Postprandial hyperinsulinemic hypoglycemia remains a notoriously difficult to manage metabolic complication of bariatric surgery. This first, to the authors' knowledge, systematic review presents evidence suggesting that use of GLP-1RAs does not lead to an increase of hypoglycemic episodes, and, although this approach may appear counterintuitive, the findings suggest that GLP-1RAs could reduce the number of postprandial hypoglycemic episodes and improve glycemic variability.

Beneficial metabolic effects of recurrent periods of beta-cell rest and stimulation using stable neuropeptide Y1 and glucagon-like peptide-1 receptor agonists

AIM

To examine whether sequential administration of (d-Arg³⁵ )-sea lamprey peptide tyrosine tyrosine (1-36) (SL-PYY) and the glucagon-like peptide-1 (GLP-1) mimetic, liraglutide, has beneficial effects in diabetes.

METHODS

SL-PYY is an enzymatically stable neuropeptide Y1 receptor (NPY1R) agonist known to induce pancreatic beta-cell rest and improve overall beta-cell health. We employed SL-PYY and liraglutide to induce appropriate recurrent periods of beta-cell rest and stimulation, to assess therapeutic benefits in high fat fed (HFF) mice with streptozotocin (STZ)-induced insulin deficiency, namely HFF-STZ mice.

RESULTS

Previous studies confirm that, at a dose of 0.25 nmol/kg, liraglutide exerts bioactivity over an 8-12 hour period in mice. Initial pharmacokinetic analysis revealed that 75 nmol/kg SL-PYY yielded a similar plasma drug time profile. When SL-PYY (75 nmol/kg) and liraglutide (0.25 nmol/kg) were administered sequentially at 08:00 AM and 08:00 PM, respectively, to HFF-STZ mice for 28 days, reductions in energy intake, body weight, circulating glucose, insulin and glucagon were noted. Similarly positive, but slightly less striking, effects were also apparent with twice-daily liraglutide-only therapy. The sequential SL-PYY and liraglutide treatment also improved insulin sensitivity and glucose-induced insulin secretory responses, which was not apparent with liraglutide treatment, although benefits on glucose tolerance were mild. Interestingly, combined therapy also elevated pancreatic insulin, decreased pancreatic glucagon and enhanced the plasma insulin/glucagon ratio compared with liraglutide alone. This was not associated with an enhancement of beneficial changes in islet cell areas, proliferation or apoptosis compared with liraglutide alone, but the numbers of centrally stained glucagon-positive islet cells were reduced by sequential combination therapy.

CONCLUSION

These data show that NPY1R-induced intervals of beta-cell rest, combined with GLP-1R-stimulated periods of beta-cell stimulation, should be further evaluated as an effective treatment option for obesity-driven forms of diabetes.

Gut-derived bacterial flagellin induces beta-cell inflammation and dysfunction

Hyperglycemia and type 2 diabetes (T2D) are caused by failure of pancreatic beta cells. The role of the gut microbiota in T2D has been studied, but causal links remain enigmatic. Obese individuals with or without T2D were included from two independent Dutch cohorts. Human data were translated in vitro and in vivo by using pancreatic islets from C57BL6/J mice and by injecting flagellin into obese mice. Flagellin is part of the bacterial locomotor appendage flagellum, present in gut bacteria including Enterobacteriaceae, which we show to be more abundant in the gut of individuals with T2D. Subsequently, flagellin induces a pro-inflammatory response in pancreatic islets mediated by the Toll-like receptor (TLR)-5 expressed on resident islet macrophages. This inflammatory response is associated with beta-cell dysfunction, characterized by reduced insulin gene expression, impaired proinsulin processing and stress-induced insulin hypersecretion in vitro and in vivo in mice. We postulate that increased systemically disseminated flagellin in T2D is a contributing factor to beta-cell failure in time and represents a novel therapeutic target.

Dual pancreatic adrenergic and dopaminergic signaling as a therapeutic target of bromocriptine

Bromocriptine is approved as a diabetes therapy, yet its therapeutic mechanisms remain unclear. Though bromocriptine's actions have been mainly attributed to the stimulation of brain dopamine D2 receptors (D2R), bromocriptine also targets the pancreas. Here, we employ bromocriptine as a tool to elucidate the roles of catecholamine signaling in regulating pancreatic hormone secretion. In β-cells, bromocriptine acts on D2R and α2A-adrenergic receptor (α2A-AR) to reduce glucose-stimulated insulin secretion (GSIS). Moreover, in α-cells, bromocriptine acts via D2R to reduce glucagon secretion. α2A-AR activation by bromocriptine recruits an ensemble of G proteins with no β-arrestin2 recruitment. In contrast, D2R recruits G proteins and β-arrestin2 upon bromocriptine stimulation, demonstrating receptor-specific signaling. Docking studies reveal distinct bromocriptine binding to α2A-AR versus D2R, providing a structural basis for bromocriptine's dual actions on β-cell α2A-AR and D2R. Together, joint dopaminergic and adrenergic receptor actions on α-cell and β-cell hormone release provide a new therapeutic mechanism to improve dysglycemia.

Opposing effects on regulated insulin secretion of acute vs chronic stimulation of AMP-activated protein kinase

AIMS/HYPOTHESIS

Although targeted in extrapancreatic tissues by several drugs used to treat type 2 diabetes, the role of AMP-activated protein kinase (AMPK) in the control of insulin secretion is still debatable. Previous studies have used pharmacological activators of limited selectivity and specificity, and none has examined in primary pancreatic beta cells the actions of the latest generation of highly potent and specific activators that act via the allosteric drug and metabolite (ADaM) site.

METHODS

AMPK was activated acutely in islets isolated from C57BL6/J mice, and in an EndoC-βH3 cell line, using three structurally distinct ADaM site activators (991, PF-06409577 and RA089), with varying selectivity for β1- vs β2-containing complexes. Mouse lines expressing a gain-of-function mutation in the γ1 AMPK subunit (D316a) were generated to examine the effects of chronic AMPK stimulation in the whole body, or selectively in the beta cell.

RESULTS

Acute (1.5 h) treatment of wild-type mouse islets with 991, PF-06409577 or RA089 robustly stimulated insulin secretion at high glucose concentrations (p<0.01, p<0.05 and p<0.001, respectively), despite a lowering of glucose-induced intracellular free Ca2+ dynamics in response to 991 (AUC, p<0.05) and to RA089 at the highest dose (25 μmol/l) at 5.59 min (p<0.05). Although abolished in the absence of AMPK, the effects of 991 were observed in the absence of the upstream kinase, liver kinase B1, further implicating 'amplifying' pathways. In marked contrast, chronic activation of AMPK, either globally or selectively in the beta cell, achieved using a gain-of-function mutant, impaired insulin release in vivo (p<0.05 at 15 min following i.p. injection of 3 mmol/l glucose) and in vitro (p<0.01 following incubation of islets with 17 mmol/l glucose), and lowered glucose tolerance (p<0.001).

CONCLUSIONS/INTERPRETATION

AMPK activation exerts complex, time-dependent effects on insulin secretion. These observations should inform the design and future clinical use of AMPK modulators.

Remission of type 2 diabetes after gastrectomy for gastric cancer: diabetes prediction score

BACKGROUND

Although type 2 diabetes (T2D) remission after gastric cancer surgery has been reported, little is known about the predictors of postoperative T2D remission.

METHODS

This study used data from a nationwide cohort provided by the National Health Insurance Service in Korea. We developed a diabetes prediction (DP) score, which predicted postoperative T2D remissions using a logistic regression model based on preoperative variables. We applied machine-learning algorithms [random forest, XGboost, and least absolute shrinkage and selection operator (LASSO) regression] and compared their predictive performances with those of the DP score.

RESULTS

The DP score comprised five parameters: baseline body mass index (< 25 or ≥ 25 kg/m²), surgical procedures (subtotal or total gastrectomy), age (< 65 or ≥ 65 years), fasting plasma glucose levels (≤ 130 or > 130 mg/dL), and antidiabetic medications (combination therapy including sulfonylureas, combination therapy not including sulfonylureas, single sulfonylurea, or single non-sulfonylurea]). The DP score showed a clinically useful predictive performance for T2D remission at 3 years after surgery [training cohort: area under the receiver operating characteristics (AUROC) 0.73, 95% confidence interval (CI), 0.71-0.75; validation cohort: AUROC 0.72, 95% CI 0.69-0.75], which was comparable to that of the machine-learning models (random forest: AUROC 0.71, 95% CI 0.68-0.74; XGboost: AUROC 0.70, 95% CI 0.67-0.73; LASSO regression: AUROC 0.75, 95% CI 0.73-0.78 in the validation cohort). It also predicted the T2D remission at 6 and 9 years after surgery.

CONCLUSIONS

The DP score is a useful scoring system for predicting T2D remission after gastric cancer surgery.

Changes in granule mobility and age contribute to changes in insulin secretion after desensitization or rest

INTRODUCTION

Functional impairment of the stimulus secretion coupling in pancreatic beta cells is an essential component of type 2 diabetes. It is known that prolonged stimulation desensitizes the secretion of insulin and thus contributes to beta cell dysfunction. Beta cell rest, in contrast, was shown to enhance the secretory response. Here, the underlying mechanisms were investigated.

RESEARCH DESIGN AND METHODS

To characterize the consequences of desensitization or rest for the number and mobility of submembrane granules, insulin-secreting MIN6 cells were desensitized by 18-hour culture with 500 µM tolbutamide or rested by 18-hour culture with 1 µM clonidine. The granules were labeled by hIns-EGFP or hIns-DsRed E5, imaged by TIRF microscopy of the cell footprint area and analyzed with an observer-independent program. Additionally, the insulin content and secretion were measured.

RESULTS

Concurrent with the insulin content, submembrane granules were only slightly reduced after desensitization but markedly increased after rest. Both types of pretreatment diminished arrivals and departures of granules in the submembrane space and increased the proportion of immobile long-term resident granules, but desensitization lowered and rest increased the number of exocytoses, in parallel with the effect on insulin secretion. Labeling with hIns-DsRed E5 ('timer') showed that desensitization did not affect the proportion of aged granules, whereas rest increased it. Aged granules showed a high mobility and made up only a minority of long-term residents. Long-term resident granules were more numerous after rest and had a lower lateral mobility, suggesting a firmer attachment to the membrane.

CONCLUSION

The number, mobility and age of submembrane granules reflect the preceding functional states of insulin-secreting cells. Representing the pool of releasable granules, their quantity and quality may thus form part of the beta cell memory on renewed stimulation.

Differential loss of β-cell function in youth vs. adults following treatment withdrawal in the Restoring Insulin Secretion (RISE) study

AIMS

To compare OGTT-derived estimates of β-cell function between youth and adults with impaired glucose tolerance (IGT) or recently diagnosed type 2 diabetes after treatment discontinuation in RISE.

METHODS

Youth (n = 89) and adults (n = 132) were randomized to 3 months glargine followed by 9 months metformin (G/M) or 12 months metformin (MET). Insulin sensitivity and β-cell responses were estimated from 3-hour OGTTs over 21 months. Linear mixed models tested for differences by time and age group within each treatment arm.

RESULTS

After treatment withdrawal, HbA1c increased in both youth and adults with a larger net increase in G/M youth vs. adults at 21 months. Among youth, β-cell function decreased starting at 12 months in G/M and 15 months in MET. Among adults, β-cell function remained relatively stable although insulin secretion rates decreased in G/M at 21 months. At 21 months vs. baseline β-cell function declined to a greater extent in youth vs. adults in both the G/M and MET treatment arms.

CONCLUSIONS

After treatment withdrawal youth demonstrated progressive decline in β-cell function after stopping treatment with either G/M or MET. In contrast, β-cell function in adults remained stable despite an increase in HbA1c over time. ClinicalTrials.gov Identifier: NCT01779375 and NCT01779362 at clinical trials.gov.

Altered islet prohormone processing: A cause or consequence of diabetes?

Peptide hormones are first produced as larger precursor prohormones that require endoproteolytic cleavage to liberate the mature hormones. A structurally conserved but functionally distinct family of nine prohormone convertase enzymes (PCs) are responsible for cleavage of protein precursors of which PC1/3 and PC2 are known to be exclusive to neuroendocrine cells and responsible for prohormone cleavage. Differential expression of PCs within tissues define prohormone processing; whereas glucagon is the major product liberated from proglucagon via PC2 in pancreatic α-cells, proglucagon is preferentially processed by PC1/3 in intestinal L cells to produce glucagon-like peptides 1 and 2 (GLP-1, GLP-2). Beyond our understanding of processing of islet prohormones in healthy islets, there is convincing evidence that proinsulin, proIAPP, and proglucagon processing is altered during prediabetes and diabetes. There is predictive value of elevated circulating proinsulin or proinsulin : C-peptide ratio for progression to type 2 diabetes and elevated proinsulin or proinsulin : C-peptide is predictive for development of type 1 diabetes in at risk groups. After onset of diabetes, patients have elevated circulating proinsulin and proIAPP and proinsulin may be an autoantigen in type 1 diabetes. Further, preclinical studies reveal that α-cells have altered proglucagon processing during diabetes leading to increased GLP-1 production. We conclude that despite strong associative data, current evidence is inconclusive on the potential causal role of impaired prohormone processing in diabetes, and suggest that future work should focus on resolving the question of whether altered prohormone processing is a causal driver or merely a consequence of diabetes pathology.

Glucokinase Inactivation Paradoxically Ameliorates Glucose Intolerance by Increasing β-Cell Mass in db/db Mice

Efficacy of glucokinase activation on glycemic control is limited to a short-term period. One reason might be related to excess glucose signaling by glucokinase activation toward β-cells. In this study, we investigated the effect of glucokinase haploinsufficiency on glucose tolerance as well as β-cell function and mass using a mouse model of type 2 diabetes. Our results showed that in db/db mice with glucokinase haploinsufficiency, glucose tolerance was ameliorated by augmented insulin secretion associated with the increase in β-cell mass when compared with db/db mice. Gene expression profiling and immunohistochemical and metabolomic analyses revealed that glucokinase haploinsufficiency in the islets of db/db mice was associated with lower expression of stress-related genes, greater expression of transcription factors involved in the maintenance and maturation of β-cell function, less mitochondrial damage, and a superior metabolic pattern. These effects of glucokinase haploinsufficiency could preserve β-cell mass under diabetic conditions. These findings verified our hypothesis that optimizing excess glucose signaling in β-cells by inhibiting glucokinase could prevent β-cell insufficiency, leading to improving glucose tolerance in diabetes status by preserving β-cell mass. Therefore, glucokinase inactivation in β-cells, paradoxically, could be a potential strategy for the treatment of type 2 diabetes.

Hundert Jahre – Insulin bleibt aktuell und notwendig

In der Behandlung des Typ-1-Diabetes ist die Therapie mit Insulin auch 100 Jahre nach seiner Entdeckung weiterhin eine lebensnotwendige Therapie. Der pharmakologische Fortschritt hat die Behandlung erheblich erleichtert und nähert sich der physiologischen Insulin-Sekretion zunehmend an. In der Behandlung des Typ-2-Diabetes hingegen ist die Insulin-Therapie bei den meisten Patienten zunächst nicht notwendig. Lebensstil-Interventionen und moderne Nicht-Insulin Antidiabetika können häufig zu einer lang andauernden Kontrolle der Erkrankung führen. Die Heterogenität des Typ-2-Diabetes führt jedoch dazu, dass einige Patienten früh von einer Insulin-Therapie profitieren. Auch beim Typ-2-Diabetes können moderne Insulin Präparate die Insulin-Behandlung deutlich erleichtern, auch in Kombination mit anderen Antidiabetika. Einleitung und Begleitung einer Insulin-Therapie gehören somit weiterhin zu den Kernaufgaben der Diabetologie.

Emerging Role of Caveolin-1 in GLP-1 Action

Glucagon-like peptide-1 (GLP-1) is a gut hormone mainly produced in the intestinal epithelial endocrine L cells, involved in maintaining glucose homeostasis. The use of GLP-1 analogous and dipeptidyl peptidase-IV (DPP-IV) inhibitors is well-established in Type 2 Diabetes. The efficacy of these therapies is related to the activation of GLP-1 receptor (GLP-1R), which is widely expressed in several tissues. Therefore, GLP-1 is of great clinical interest not only for its actions at the level of the beta cells, but also for the extra-pancreatic effects. Activation of GLP-1R results in intracellular signaling that is regulated by availability of downstream molecules and receptor internalization. It has been shown that GLP-1R co-localizes with caveolin-1, the main component of caveolae, small invagination of the plasma membrane, which are involved in controlling receptor activity by assembling signaling complexes and regulating receptor trafficking. The aim of this review is to outline the important role of caveolin-1 in mediating biological effects of GLP-1 and its analogous.

Beta-cell failure in type 2 diabetes: mechanisms, markers, and clinical implications

It is well known that type 2 diabetes mellitus (T2D) is a globally increasing health burden. Despite recent therapeutic advances and the availability of many different classes of antihyperglycemic therapy, a large proportion of people do not achieve glycemic control. A decline in pancreatic beta-cell function has been defined as a key contributing factor to progression of T2D. In fact, a significant proportion of beta-cell secretory capacity is thought to be lost well before the diagnosis of T2D is made. Several models have been proposed to explain the reduction in beta-cell function, including reduced beta-cell number, beta-cell exhaustion, and dedifferentiation or transdifferentiation into other cell types. However, there have been reports that suggest remission of T2D is possible, and it is believed that beta-cell dysfunction may be, in part, reversible. As such, the question of whether beta cells are committed to failure in people with T2D is complex. It is now widely accepted that early restoration of normoglycemia may protect beta-cell function. Key to the successful implementation of this approach in clinical practice is the appropriate assessment of individuals at risk of beta-cell failure, and the early implementation of appropriate treatment options. In this review, we discuss the progression of T2D in the context of beta-cell failure and describe how C-peptide testing can be used to assess beta-cell function in primary care practice. In conclusion, significant beta-cell dysfunction is likely in individuals with certain clinical characteristics of T2D, such as long duration of disease, high glycated hemoglobin (≥9%), and/or long-term use of therapies that continuously stimulate the beta cell. In these people, measurement of beta-cell status could assist with choice of appropriate therapy to delay or potentially reverse beta-cell dysfunction and the progression of T2D.

Why are South Asians prone to type 2 diabetes? A hypothesis based on underexplored pathways

South Asians have a high prevalence of type 2 diabetes, even at a lower BMI. This review sets out our perspective and hypothesis on the reasons for this. Emerging data from epidemiological studies indicate that South Asians may have a lower ability to secrete insulin, and thus may have less compensatory reserves when challenged with unhealthy lifestyles. Thus, insulin resistance may not be the primary driver of type 2 diabetes in this population. Furthermore, data also suggest that South Asians, on average, have lower muscle mass, and may have a specific propensity to ectopic hepatic fat accumulation and for intramyocellular fat deposition, which cause further disruption in insulin action. We hypothesise that the high diabetes susceptibility in South Asians is evolutionarily set through dual parallel and/or interacting mechanisms: reduced beta cell function and impaired insulin action owing to low lean mass, which is further accentuated by ectopic fat deposition in the liver and muscle. These areas warrant further research.

Effects of sequential treatment with lixisenatide, insulin glargine, or their combination on meal-related glycaemic excursions, insulin and glucagon secretion, and gastric emptying in patients with type 2 diabetes

AIM

To examine the glucose-lowering mechanisms of the glucagon-like peptide-1 receptor agonist lixisenatide after two subsequent meals and in combination with basal insulin.

MATERIALS AND METHODS

Twenty-eight metformin-treated patients with type 2 diabetes were randomly assigned to treatment sequences with either lixisenatide or insulin glargine alone for 4 weeks, and a combination of both treatments for 4 weeks. Metabolic examinations were performed before and after each treatment period following breakfast and a late lunch 8 hours later.

RESULTS

Lixisenatide mainly reduced postprandial glycaemia, while insulin glargine mainly reduced fasting glucose after breakfast (P < 0.05). This was partially preserved after a late lunch (P < 0.05). After breakfast, lixisenatide reduced insulin secretion and glucagon levels significantly. These effects were lost after a late lunch. Insulin glargine did not significantly reduce glucagon or insulin secretion. Gastric emptying was slowed by lixisenatide, but not by insulin glargine after breakfast. After the late lunch, lixisenatide slightly accelerated gastric emptying.

CONCLUSIONS

Lixisenatide decelerates gastric emptying after breakfast, thereby reducing glycaemic excursions, insulin secretion and glucagon levels. The glycaemic reduction persists until after a late lunch, despite accelerated gastric emptying. The combination with insulin glargine enhances the glucose-lowering effect because of complementary modes of action.

CCAP regulates feeding behavior via the NPF pathway in Drosophila adults

The intake of macronutrients is crucial for the fitness of any animal and is mainly regulated by peripheral signals to the brain. How the brain receives and translates these peripheral signals or how these interactions lead to changes in feeding behavior is not well-understood. We discovered that 2 crustacean cardioactive peptide (CCAP)-expressing neurons in Drosophila adults regulate feeding behavior and metabolism. Notably, loss of CCAP, or knocking down the CCAP receptor (CCAP-R) in 2 dorsal median neurons, inhibits the release of neuropeptide F (NPF), which regulates feeding behavior. Furthermore, under starvation conditions, flies normally have an increased sensitivity to sugar; however, loss of CCAP, or CCAP-R in 2 dorsal median NPF neurons, inhibited sugar sensitivity in satiated and starved flies. Separate from its regulation of NPF signaling, the CCAP peptide also regulates triglyceride levels. Additionally, genetic and optogenetic studies demonstrate that CCAP signaling is necessary and sufficient to stimulate a reflexive feeding behavior, the proboscis extension reflex (PER), elicited when external food cues are interpreted as palatable. Dopaminergic signaling was also sufficient to induce a PER. On the other hand, although necessary, NPF neurons were not able to induce a PER. These data illustrate that the CCAP peptide is a central regulator of feeding behavior and metabolism in adult flies, and that NPF neurons have an important regulatory role within this system.

The Underlying Mechanisms of Curcumin Inhibition of Hyperglycemia and Hyperlipidemia in Rats Fed a High-Fat Diet Combined With STZ Treatment

Curcumin is the main secondary metabolite of Curcuma longa and other Curcuma spp, and has been reported to have some potential in preventing and treating some physiological disorders. This study investigated the effect of curcumin in inhibiting high-fat diet and streptozotocin (STZ)-induced hyperglycemia and hyperlipidemia in rats. Twenty-six male Sprague-Dawley (SD) rats (170–190 g) were randomly divided into a standard food pellet diet group (Control group), a high-fat diet and streptozotocin group (HF + STZ group), and a high-fat diet combined with curcumin and STZ group (HF + Cur + STZ group). Compared with the HF + STZ group, the HF + Cur + STZ group exhibited significantly reduced fasting blood glucose (FBG), total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), alanine aminotransferase (AST), and aspartate transaminase (ALT) levels, as well as liver coefficients. In the livers of these rats, the expression of malondialdehyde (MDA) and Bax was downregulated, whereas that of superoxide dismutase (SOD) and Bcl-2 was upregulated. Moreover, the liver histology of these rats was improved and resembled that of the control rats. These results suggest that curcumin prevents high-fat diet and STZ-induced hyperglycemia and hyperlipidemia, mainly via anti-oxidant and anti-apoptotic mechanisms in the liver.

Reducing Glucokinase Activity to Enhance Insulin Secretion: A Counterintuitive Theory to Preserve Cellular Function and Glucose Homeostasis

Pancreatic beta-cells are the only cells in the body that can synthesize and secrete insulin. Through the process of glucose-stimulated insulin secretion, beta-cells release insulin into circulation, stimulating GLUT4-dependent glucose uptake into peripheral tissue. Insulin is normally secreted in pulses that promote signaling at the liver. Long before type 2 diabetes is diagnosed, beta-cells become oversensitive to glucose, causing impaired pulsatility and overstimulation in fasting levels of glucose. The resulting hypersecretion of insulin can cause poor insulin signaling and clearance at the liver, leading to hyperinsulinemia and insulin resistance. Continued overactivity can eventually lead to beta-cell exhaustion and failure at which point type 2 diabetes begins. To prevent or reverse the negative effects of overstimulation, beta-cell activity can be reduced. Clinical studies have revealed the potential of beta-cell rest to reverse new cases of diabetes, but treatments lack durable benefits. In this perspective, we propose an intervention that reduces overactive glucokinase activity in the beta-cell. Glucokinase is known as the glucose sensor of the beta-cell due to its high control over insulin secretion. Therefore, glycolytic overactivity may be responsible for hyperinsulinemia early in the disease and can be reduced to restore normal stimulus-secretion coupling. We have previously reported that reducing glucokinase activity in prediabetic mouse islets can restore pulsatility and enhance insulin secretion. Building on this counterintuitive finding, we review the importance of pulsatile insulin secretion and highlight how normalizing glucose sensing in the beta cell during prediabetic hyperinsulinemia may restore pulsatility and improve glucose homeostasis.

Subjects with high fasting insulin also have higher postprandial GLP-1 and glucagon levels than controls with lower insulin

Little is known about postprandial release of serum ghrelin, glucagon, and glucagon-like peptide-1 (GLP-1) in relation with differing fasting insulin levels. We hypothesized that these hormones are affected by insulin resistance, and hence, we compared different postprandial responses of GLP-1, glucagon, and ghrelin in subjects with relatively high (RHI) or relatively low (RLI) fasting insulin levels. The trial was a randomized crossover study with 4 different meal conditions. Fourteen nonobese or obese, healthy, men and 14 women were randomly assigned to the order of supervised intake of a 750 kcal drink with the same protein contents but with 20 energy-percent (E%) or 55 E% from carbohydrates, and the remaining energy from fat. Participants were also randomized to consume the drinks as 1 large beverage or as five 150-kcal portions every 30 minutes. The 28 subjects were divided into 2 equally sized groups based on fasting insulin levels. Statistics were done with general linear mixed model. Fasting insulin levels were 3-fold higher in the group with RHI compared with the RLI group (RHI: 1004 ± 510 pg/mL, RLI: 324 ± 123 pg/mL, P < .0005). Serum GLP-1 was highest in the RHI group after both single meals and after 5 drinks and following high- and low-carbohydrate meals (both P ≤ .002), and this was the case also for glucagon levels (both P ≤ .018), whereas ghrelin levels did not differ between groups. Thus, subjects with RHI displayed both higher postprandial serum GLP-1 and glucagon than the participants with RLI, suggesting that glucagon could play a role in the advent of dysglycemia by insulin resistance.

Improved skeletal muscle energy metabolism relates to the recovery of β cell function by intensive insulin therapy in drug naïve type 2 diabetes

AIMS

Diminished energy turnover of skeletal muscle is involved in the development of type 2 diabetes. Intensive insulin therapy has been reported to maintain glycaemic control in newly diagnosed type 2 diabetes, while the underlying mechanism remains unclear. Herein, we aimed to characterize the contribution of muscular mitochondrial oxidative phosphorylation (OxPhos) activity to insulin-induced glycaemic control.

MATERIALS AND METHODS

There were 21 drug naïve patients with type 2 diabetes receiving continuous subcutaneous insulin infusion for 7 days. Nine nondiabetics matched for age, body mass index, and physical activity were recruited as controls. We applied ³¹ P magnetic resonance spectroscopy to record in vivo muscular phosphocreatine (PCr) flux in controls and diabetics before and after insulin therapy. The mitochondrial OxPhos rate was calculated as ΔPCr / Δtime during the first 50 seconds after cessation of exercise.

RESULTS

In drug naïve type 2 diabetes, muscular mitochondrial OxPhos rate was restored after insulin therapy. Notably, this alteration was positively associated with the improvements of 1,5-anhydroglucitol, a serum marker for glucose control over the last 1 week, as well as homeostasis model assessment of β cell function and C-peptide/glucose ratio t₀ , two indices for basal insulin secretion. Furthermore, patients with diabetes family history and more severe glucotoxicity tend to achieve greater improvement in mitochondrial function by insulin.

CONCLUSIONS

This study provides evidence that intensive insulin therapy facilitates muscular energy metabolism in drug naïve type 2 diabetes. It correlates to the recovery of β cell function, contributing to insulin-induced glucose control.

Effects of dapagliflozin and/or insulin glargine on beta cell mass and hepatic steatosis in db/db mice

OBJECTIVE

To explore the beneficial effects of dapagliflozin and/or insulin glargine on the pancreatic beta cell mass and hepatic steatosis in db/db mice.

METHODS

Six-week-old db/db mice were assigned to one of four groups: untreated (Placebo), treated with dapagliflozin (Dapa), treated with insulin glargine (Gla), or treated with dapagliflozin and insulin glargine (Dapa+Gla). After 8 weeks of treatment, we determined glucose tolerance, beta cell mass, hepatic lipid content and gene expression.

RESULTS

Glucose tolerance was significantly ameliorated in the three treated groups to the same degree compared with the Placebo group. Immunohistochemical analysis revealed that the pancreatic beta cell mass was significantly maintained in the Dapa and Dapa+Gla groups, but not in the Gla group, compared with the Placebo group (Placebo 2.25 ± 1.44 mg, Dapa 5.01 ± 1.63 mg, Gla 3.79 ± 0.96 mg, Dapa+Gla 5.19 ± 1.78 mg). However, the triglyceride content of the liver was markedly elevated in the Gla group compared with that in the other three groups (Placebo 24.1 ± 11.5 mg, Dapa 30.6 ± 12.9 mg, Gla 128 ± 49.7 mg, Dapa+Gla 54.4 ± 14.1 mg per gram liver). The expression levels of genes related to fatty acid synthesis and lipid storage were significantly upregulated in the Gla group.

CONCLUSIONS

Our results showed that beta cell mass was sustained and hepatic steatosis was prevented, after 8 weeks of treatment with either dapagliflozin or dapagliflozin plus insulin glargine, but not with insulin glargine alone, in db/db mice.

Ion Channels of the Islets in Type 2 Diabetes

Ca²⁺ is an essential signal for pancreatic β-cell function. Ca²⁺ plays critical roles in numerous β-cell pathways such as insulin secretion, transcription, metabolism, endoplasmic reticulum function, and the stress response. Therefore, β-cell Ca²⁺ handling is tightly controlled. At the plasma membrane, Ca²⁺ entry primarily occurs through voltage-dependent Ca²⁺ channels. Voltage-dependent Ca²⁺ channel activity is dependent on orchestrated fluctuations in the plasma membrane potential or voltage, which are mediated via the activity of many ion channels. During the pathogenesis of type 2 diabetes the β-cell is exposed to stressful conditions, which result in alterations of Ca²⁺ handling. Some of the changes in β-cell Ca²⁺ handling that occur under stress result from perturbations in ion channel activity, expression or localization. Defective Ca²⁺ signaling in the diabetic β-cell alters function, limits insulin secretion and exacerbates hyperglycemia. In this review, we focus on the β-cell ion channels that control Ca²⁺ handling and how they impact β-cell dysfunction in type 2 diabetes.

Targeting TRP Channels - Valuable Alternatives to Combat Pain, Lower Urinary Tract Disorders, and Type 2 Diabetes?

Transient receptor potential (TRP) channels are a family of functionally diverse and widely expressed cation channels involved in a variety of cell signaling and sensory pathways. Research in the last two decades has not only shed light on the physiological roles of the 28 mammalian TRP channels, but also revealed the involvement of specific TRP channels in a plethora of inherited and acquired human diseases. Considering the historical successes of other types of ion channels as therapeutic drug targets, small molecules that target specific TRP channels hold promise as treatments for a variety of human conditions. In recent research, important new findings have highlighted the central role of TRP channels in chronic pain, lower urinary tract disorders, and type 2 diabetes, conditions with an unmet medical need. Here, we discuss how these advances support the development of TRP-channel-based pharmacotherapies as valuable alternatives to the current mainstays of treatment.

Sonodynamic therapy inhibits palmitate-induced beta cell dysfunction via PINK1/Parkin-dependent mitophagy

In type 2 diabetes mellitus (T2DM), the overload of glucose and lipids can promote oxidative stress and inflammatory responses and contribute to the failure of beta cells. However, therapies that can modulate the function of beta cells and thus prevent their failure have not been well explored. In this study, beta cell injury model was established with palmitic acid (PA) to simulate the lipotoxicity (high-fat diet) found in T2DM. Sonodynamic therapy (SDT), a novel physicochemical treatment, was applied to treat injured beta cells. We found that SDT had specific effects on mitochondria and induced transient large amount of mitochondrial reactive oxygen species (ROS) production in beta cells. SDT also improved the morphology and function of abnormal mitochondria, inhibited inflammatory response and reduced beta cell dysfunction. The improvement of mitochondria was mediated by PINK1/Parkin-dependent mitophagy. Additionally, SDT rescued the transcription of PINK1 mRNA which was blocked by PA treatment, thus providing abundant PINK1 for mitophagy. Moreover, SDT also increased insulin secretion from beta cells. The protective effects of SDT were abrogated when mitophagy was inhibited by cyclosporin A (CsA). In summary, SDT potently inhibits lipotoxicity-induced beta cell failure via PINK1/Parkin-dependent mitophagy, providing theoretical guidance for T2DM treatment in aspects of islet protection.

Sodium glucose cotransporter (SGLT)-2 inhibitors: Do we need them for glucose-lowering, for cardiorenal protection or both?

Sodium glucose cotransporter (SGLT)-2 inhibitors are the newest addition to our treatment armamentarium for the management of hyperglycemia in type 2 diabetes. Glucose-lowering per se reduces the risk of microvascular complications, but not the risk of cardiovascular disease, including heart failure and cardiovascular mortality. Also, even when embedded in optimal cardiovascular prevention, a large residual risk remains with respect to progression of diabetic kidney disease. SGLT-2 inhibitors lower blood glucose levels by inducing glucosuria. Through various proposed mechanisms, among which diuretic and natriuretic effects, SGLT-2 inhibitors decrease heart failure hospitalization, reduce cardiovascular mortality, and mitigate progression of diabetic kidney disease. In this perspective, we will discuss the glucose-lowering and other protective effects of SGLT-2 inhibitors on the cardiorenal axis, both in primary and secondary prevention. By comparing the glycemic and pleiotropic effects of these agents to other glucose-lowering drugs, we will address questions around whether SGLT-2 inhibitors should be considered primarily as glucose-lowering agents, cardiorenal drugs or both.

The effects of incretin-based therapies on β-cell function and insulin resistance in type 2 diabetes: A systematic review and network meta-analysis combining 360 trials

AIM

To evaluate the comparative effects of incretin-based therapies, including glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and dipeptidyl peptidase-4 inhibitors (DPP-4Is), on β-cell function and insulin resistance in patients with type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

Medline, Embase, the Cochrane Library and www.clinicaltrials.gov were searched for randomized controlled trials (RCTs) with a duration of at least 4 weeks. Network meta-analysis was performed, followed by subgroup analysis and meta-regression. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used to assess the quality of evidence. Outcomes of interest include homeostasis model assessment for β cell function (HOMA-β) and insulin resistance (HOMA-IR), fasting C-peptide and fasting plasma glucose (FPG). Weighted mean difference (WMD) with 95% confidence interval (CI) was calculated as the measure of effect size.

RESULTS

A total of 360 RCTs (74% at least double-blinded) with 157 696 patients were included. Incretin-based therapies were compared with six other classes of glucose-lowering drugs or with placebo. Compared with placebo, a significant increase in HOMA-β and fasting C-peptide was detected for GLP-1RAs (WMD = 20.31 [95% CI, 16.34-24.39] with low quality; WMD = 0.16 ng/mL [95% CI, 0.03-0.29] with low quality) and for DPP-4Is (WMD = 9.90 [95% CI, 8.27-11.61] with moderate quality; WMD = 0.09 ng/mL [95% CI, 0.04-0.14] with moderate quality) separately, while a significant reduction in HOMA-IR and FPG were found in favour of GLP-1RAs (WMD = -0.67 [95% CI, -1.08 to -0.27] with low quality; WMD = -1.04 mmol/L [95% CI, -1.26 to -0.83] with moderate quality) and DPP-4Is (WMD = -0.23 [95% CI, -0.38 to -0.08] with low quality; WMD = -0.77 mmol/L [95% CI, -0.98 to -0.57] with moderate quality), respectively.

CONCLUSIONS

Incretin-based therapies not only show an increase in HOMA-β and fasting C-peptide level, but also achieve a reduction in HOMA-IR and FPG in comparison with placebo. Although GRADE scores indicate low to moderate for most comparisons, incretin-based therapies seem to be an advisable option for long-term treatment to preserve β-cell function.

The Role of Glucagon-Like Peptide-1 Receptor Agonists in Type 2 Diabetes in Asia

The improvement of glycemic control in patients with type 2 diabetes (T2D) is an urgent need in Asia. East Asian T2D patients have distinct characteristics, including relatively low body weight, early impairment of islet beta cell function with reduced insulin secretion and a marked increase in postprandial blood glucose levels. Control of postprandial hyperglycemia and beta cell preservation are key elements of the therapeutic strategy for these patients. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) reduce HbA1c, fasting plasma glucose, and (in particular) postprandial glucose levels, and slow gastric emptying, while minimizing the risk of hypoglycemia and weight gain. Compared with long-acting GLP-1RAs, short-acting GLP-1RAs produce greater slowing of gastric emptying (which is a key factor driving the reduction of postprandial glycemia) and induce beta cell rest rather than promoting postprandial insulin secretion when used under physiological conditions. GLP-1RAs have greater efficacy in Asian than Caucasian patients. GLP-1RA add-on therapy provides clinically meaningful reductions in HbA1c and postprandial glucose in Asians with T2D inadequately controlled by oral antidiabetic drugs (OADs) or basal insulin ± OADs. Premixed insulin is often prescribed for T2D patients in China. A short-acting GLP-1RA plus basal insulin is an alternative to premixed insulin, resulting in better efficacy and a lower risk of hypoglycemia and weight gain. In conclusion, GLP-1RAs, especially short-acting GLP-1RAs, are a practical treatment option for East Asian patients with T2D inadequately controlled by OADs or basal insulin.Funding: Sanofi.

Comprehensive analysis of body composition and insulin traits associated with intra-pancreatic fat deposition in healthy individuals and people with new-onset prediabetes/diabetes after acute pancreatitis

Current knowledge of biomarkers of intra-pancreatic fat deposition (IFD) is limited. We aimed to analyse comprehensively body composition and insulin traits as biomarkers of IFD in healthy normoglycaemic individuals as well as in individuals with new-onset prediabetes or diabetes after acute pancreatitis (NODAP). A total of 29 healthy individuals and 34 individuals with NODAP took part in this cross-sectional study. The studied biomarkers belonged to the following domains: body composition (anthropometric and MRI-derived variables); indices of insulin secretion; indices of insulin sensitivity; incretins and related peptides; and pancreatitis-related factors. All MRI-derived variables (including IFD) were measured using ImageJ software. Univariate and step-wise regression analyses were conducted to determine variables that best explained variance in IFD. Visceral fat volume and oxyntomodulin were the best biomarkers of IFD in normoglycaemic healthy individuals, contributing to 64% variance. The Raynaud index was the best biomarker of IFD in individuals with NODAP, contributing to 20% variance. Longitudinal studies are warranted to investigate the cause and effect relationship between oxyntomodulin and IFD in healthy individuals, as well as insulin sensitivity and IFD in individuals with NODAP.

Endoplasmic reticulum stress alters ryanodine receptor function in the murine pancreatic β cell

Alterations in endoplasmic reticulum (ER) calcium (Ca2+) levels diminish insulin secretion and reduce β-cell survival in both major forms of diabetes. The mechanisms responsible for ER Ca2+ loss in β cells remain incompletely understood. Moreover, a specific role for either ryanodine receptor (RyR) or inositol 1,4,5-triphosphate receptor (IP3R) dysfunction in the pathophysiology of diabetes remains largely untested. To this end, here we applied intracellular and ER Ca2+ imaging techniques in INS-1 β cells and isolated islets to determine whether diabetogenic stressors alter RyR or IP3R function. Our results revealed that the RyR is sensitive mainly to ER stress-induced dysfunction, whereas cytokine stress specifically alters IP3R activity. Consistent with this observation, pharmacological inhibition of the RyR with ryanodine and inhibition of the IP3R with xestospongin C prevented ER Ca2+ loss under ER and cytokine stress conditions, respectively. However, RyR blockade distinctly prevented β-cell death, propagation of the unfolded protein response (UPR), and dysfunctional glucose-induced Ca2+ oscillations in tunicamycin-treated INS-1 β cells and mouse islets and Akita islets. Monitoring at the single-cell level revealed that ER stress acutely increases the frequency of intracellular Ca2+ transients that depend on both ER Ca2+ leakage from the RyR and plasma membrane depolarization. Collectively, these findings indicate that RyR dysfunction shapes ER Ca2+ dynamics in β cells and regulates both UPR activation and cell death, suggesting that RyR-mediated loss of ER Ca2+ may be an early pathogenic event in diabetes.

Pancreatic β-Cell Rest Replenishes Insulin Secretory Capacity and Attenuates Diabetes in an Extreme Model of Obese Type 2 Diabetes

The onset of common obesity-linked type 2 diabetes (T2D) is marked by exhaustive failure of pancreatic β-cell functional mass to compensate for insulin resistance and increased metabolic demand, leading to uncontrolled hyperglycemia. Here, the β-cell-deficient obese hyperglycemic/hyperinsulinemic KS db/db mouse model was used to assess consequential effects on β-cell functional recovery by lowering glucose homeostasis and/or improving insulin sensitivity after treatment with thiazolidinedione therapy or glucagon-like peptide 1 receptor agonism alone or in combination with sodium/glucose cotransporter 2 inhibition (SGLT-2i). SGLT-2i combination therapies improved glucose homeostasis, independent of changes in body weight, resulting in a synergistic increase in pancreatic insulin content marked by significant recovery of the β-cell mature insulin secretory population but with limited changes in β-cell mass and no indication of β-cell dedifferentiation. Restoration of β-cell insulin secretory capacity also restored biphasic insulin secretion. These data emphasize that by therapeutically alleviating the demand for insulin in vivo, irrespective of weight loss, endogenous β-cells recover significant function that can contribute to attenuating diabetes. Thus, this study provides evidence that alleviation of metabolic demand on the β-cell, rather than targeting the β-cell itself, could be effective in delaying the progression of T2D.

Effect of once weekly dulaglutide by baseline beta-cell function in people with type 2 diabetes in the AWARD programme

Glucagon-like peptide-1 receptor agonists lower blood glucose in type 2 diabetes (T2D) partially through glucose-dependent stimulation of insulin secretion. The aim of this study was to investigate whether beta-cell function (as measured by HOMA2-%B) at baseline affects the glycaemic response to dulaglutide. Dulaglutide-treated patients from AWARD-1, AWARD-3 and AWARD-6 clinical studies were categorised based on their homeostatic model assessment of beta-cell function (HOMA2-%B) tertiles. Changes in glycaemic measures in response to treatment with once-weekly dulaglutide were evaluated in each HOMA2-%B tertile. Patients with low HOMA2-%B had higher baseline glycated haemoglobin (HbA1c), fasting and postprandial blood glucose, and longer duration of diabetes (P < .001, all) (mean low, middle and high tertiles with dulaglutide 1.5 mg: HOMAB-2%B, 31%, 58%, 109%; HbA1c, 8.7%, 7.7%, 7.3%, respectively). At 26 weeks, the low tertile experienced larger reductions in HbA1c compared to the high tertile with dulaglutide 1.5 mg (mean; -1.55% vs. -0.98% [-16.94 vs. -10.71 mmol/mol]). Differences between low and high tertiles disappeared when adjusted for baseline HbA1c (LSM; -1.00 vs. -1.18% [-10.93 vs. -12.90 mmol/mol]). Greater decreases in fasting blood glucose and greater increases in fasting C-peptide were observed in the low tertile. Similar increases in HOMA2-%B were observed in all tertiles. Dulaglutide demonstrated clinically relevant HbA1c reduction irrespective of estimated baseline beta-cell function.

Diabetes Among Non-Overweight Individuals: an Emerging Public Health Challenge

PURPOSE OF REVIEW

Overweight and obesity are well-established risk factors for type 2 diabetes. However, a substantial number of individuals develop the disease at underweight or normal weight. In this review, we discuss the epidemiology of type 2 diabetes in non-overweight adults; pose questions about etiology, pathophysiology, diagnosis, and prognosis; and examine implications for prevention and treatment.

RECENT FINDINGS

In population-based studies, the prevalence of type 2 diabetes ranged from 1.4-10.9%. However, the prevalence of type 2 diabetes in individuals with BMI < 25 kg/m² ranged from 1.4-8.8%. In countries from Asia and Africa, the proportion of individuals with diabetes who were underweight or normal weight ranged from 24 to 66%, which is considerably higher than the US proportion of 10%. Impairments in insulin secretion, in utero undernutrition, and epigenetic alterations to the genome may play a role in diabetes development in this subgroup. A substantial number of individuals with type 2 diabetes, particularly those with recent ancestry from Asia or Africa, are underweight or normal weight. Future research should consist of comprehensive studies of the prevalence of type 2 diabetes in non-overweight individuals; studies aimed at understanding gaps in the mechanisms, etiology, and pathophysiology of diabetes development in underweight or normal weight individuals; and trials assessing the effectiveness of interventions in this population.

PAN-AMPK activator O304 improves glucose homeostasis and microvascular perfusion in mice and type 2 diabetes patients

AMPK activated protein kinase (AMPK), a master regulator of energy homeostasis, is activated in response to an energy shortage imposed by physical activity and caloric restriction. We here report on the identification of PAN-AMPK activator O304, which - in diet-induced obese mice - increased glucose uptake in skeletal muscle, reduced β cell stress, and promoted β cell rest. Accordingly, O304 reduced fasting plasma glucose levels and homeostasis model assessment of insulin resistance (HOMA-IR) in a proof-of-concept phase IIa clinical trial in type 2 diabetes (T2D) patients on Metformin. T2D is associated with devastating micro- and macrovascular complications, and O304 improved peripheral microvascular perfusion and reduced blood pressure both in animals and T2D patients. Moreover, like exercise, O304 activated AMPK in the heart, increased cardiac glucose uptake, reduced cardiac glycogen levels, and improved left ventricular stroke volume in mice, but it did not increase heart weight in mice or rats. Thus, O304 exhibits a great potential as a novel drug to treat T2D and associated cardiovascular complications.

Circulating triacylglycerols but not pancreatic fat associate with insulin secretion in healthy humans

BACKGROUND

Loss of adequate insulin secretion for the prevailing insulin resistance is critical for the development of type 2 diabetes and has been suggested to result from circulating lipids (triacylglycerols [TG] or free fatty acids) and/or adipocytokines or from ectopic lipid storage in the pancreas. This study aimed to address whether circulating lipids, adipocytokines or pancreatic fat primarily associates with lower insulin secretion.

SUBJECTS/METHODS

Nondiabetic persons (n=73), recruited from the general population, underwent clinical examinations, fasting blood drawing to measure TG and adipocytokines and oral glucose tolerance testing (OGTT) to assess basal and dynamic insulin secretion and sensitivity indices. Magnetic resonance imaging and ¹H-magnetic resonance spectroscopy were used to measure body fat distribution and ectopic fat content in liver and pancreas.

RESULTS

In age-, sex- and BMI-adjusted analyses, total and high-molecular-weight adiponectin were the strongest negative predictors of fasting beta-cell function (BCF; β=-0.403, p=0.0003 and β=-0.237, p=0.01, respectively) and adaptation index (AI; β=-0.210, p=0.006 and β=-0.133, p=0.02, respectively). Circulating TG, but not pancreatic fat content, related positively to BCF (β=0.375, p<0.0001) and AI (β=0.192, p=0.003). Similar results were obtained for the disposition index (DI).

CONCLUSIONS

The association of serum lipids and adiponectin with beta-cell function may represent a compensatory response to adapt for lower insulin sensitivity in nondiabetic humans.

Effect of chronic liraglutide therapy and its withdrawal on time to postchallenge peak glucose in type 2 diabetes

Delayed timing of peak serum glucose following an oral glucose challenge can predict declining β-cell function and worsening glucose tolerance over time. Accordingly, postchallenge peak glucose is typically delayed in patients with type 2 diabetes (T2DM). However, little is known about the capacity of antidiabetic medications to reverse this delay. Thus, we sought to evaluate the effect of the glucagon-like peptide-1 agonist liraglutide on time to peak glucose in early T2DM. In this secondary analysis of a double-blind placebo-controlled trial, 51 patients with T2DM of 2.6 ± 1.9 yr duration were randomized to daily subcutaneous liraglutide or placebo injection for 48 wk, with oral glucose tolerance test (OGTT) performed every 12 wk while on therapy and after a 2-wk washout. On each OGTT, time to peak glucose was determined from venous glucose measurements at 0, 10, 20, 30, 60, 90, and 120 min. At randomization, most patients in both arms exhibited peak glucose at 90 min postchallenge. By 12 wk, 65.4% of the liraglutide arm had shifted to an earlier peak (vs. 36% on placebo; P = 0.19), with little change thereafter at 24, 36, and 48 wk. After the 2-wk washout, however, 57.7% of those who had been on liraglutide reverted to a later peak (vs. 4.5% on placebo; P < 0.001). This shift was associated with declining β-cell function ( P = 0.001), resulting in higher 2-h blood glucose at washout in the liraglutide arm compared with placebo ( P = 0.001). Thus, although liraglutide possibly might improve the delay in peak glucose, its cessation yielded a worsening thereof and higher glycemia. The mechanisms underlying these observations and their clinical implications warrant further investigation.

AMPK and Friends: Central Regulators of β Cell Biology

If left unchecked, prediabetic hyperglycemia can progress to diabetes and often life-threatening attendant secondary complications. Central to the process of glucose homeostasis are pancreatic β cells, which sense elevations in plasma glucose and additional dietary components and respond by releasing the appropriate quantity of insulin, ensuring the arrest of hepatic glucose output and glucose uptake in peripheral tissues. Given that β cell failure is associated with the transition from prediabetes to diabetes, improved β cell function ('compensation') has a central role in preventing type 2 diabetes mellitus (T2DM). Recent data have shown that both insulin secretion and β cell mass dynamics are regulated by the liver kinase B1-AMP-activated kinase (LKB1-AMPK) pathway and related kinases of the AMPK family; thus, an improved understanding of the biological roles of AMPK in the β cell is now of considerable interest.

Misfolded proinsulin in the endoplasmic reticulum during development of beta cell failure in diabetes

The endoplasmic reticulum (ER) is broadly distributed throughout the cytoplasm of pancreatic beta cells, and this is where all proinsulin is initially made. Healthy beta cells can synthesize 6000 proinsulin molecules per second. Ordinarily, nascent proinsulin entering the ER rapidly folds via the formation of three evolutionarily conserved disulfide bonds (B7-A7, B19-A20, and A6-A11). A modest amount of proinsulin misfolding, including both intramolecular disulfide mispairing and intermolecular disulfide-linked protein complexes, is a natural by-product of proinsulin biosynthesis, as is the case for many proteins. The steady-state level of misfolded proinsulin-a potential ER stressor-is linked to (1) production rate, (2) ER environment, (3) presence or absence of naturally occurring (mutational) defects in proinsulin, and (4) clearance of misfolded proinsulin molecules. Accumulation of misfolded proinsulin beyond a certain threshold begins to interfere with the normal intracellular transport of bystander proinsulin, leading to diminished insulin production and hyperglycemia, as well as exacerbating ER stress. This is most obvious in mutant INS gene-induced Diabetes of Youth (MIDY; an autosomal dominant disease) but also likely to occur in type 2 diabetes owing to dysregulation in proinsulin synthesis, ER folding environment, or clearance.

Chemistry and biology of reactive species with special reference to the antioxidative defence status in pancreatic β-cells

BACKGROUND

Diabetes mellitus is a serious metabolic disease. Dysfunction and subsequent loss of the β-cells in the islets of Langerhans through apoptosis ultimately cause a life-threatening insulin deficiency. The underlying reason for the particular vulnerability of the β-cells is an extraordinary sensitivity to the toxicity of reactive oxygen and nitrogen species (ROS and RNS) due to its low antioxidative defense status.

SCOPE REVIEW

This review considers the different aspects of the chemistry and biology of the biologically most important reactive species and their chemico-biological interactions in the β-cell toxicity of proinflammatory cytokines in type 1 diabetes and of lipotoxicity in type 2 diabetes development.

MAJOR CONCLUSION

The weak antioxidative defense equipment in the different subcellular organelles makes the β-cells particularly vulnerable and prone to mitochondrial, peroxisomal and ER stress. Looking upon the enzyme deficiencies which are responsible for the low antioxidative defense status of the pancreatic β-cells it is the lack of enzymatic capacity for H₂O₂ inactivation at all major subcellular sites.

GENERAL SIGNIFICANCE

Diabetes is the most prevalent metabolic disorder with a steadily increasing incidence of both type 1 and type 2 diabetes worldwide. The weak protection of the pancreatic β-cells against oxidative stress is a major reason for their particular vulnerability. Thus, careful protection of the β-cells is required for prevention of the disease.