The incretin system in healthy humans: The role of GIP and GLP-1

Interkingdom signaling between gastrointestinal hormones and the gut microbiome

The interplay between the gut microbiota and gastrointestinal hormones plays a pivotal role in the health of the host and the development of diseases. As a vital component of the intestinal microecosystem, the gut microbiota influences the synthesis and release of many gastrointestinal hormones through mechanisms such as modulating the intestinal environment, producing metabolites, impacting mucosal barriers, generating immune and inflammatory responses, and releasing neurotransmitters. Conversely, gastrointestinal hormones exert feedback regulation on the gut microbiota by modulating the intestinal environment, nutrient absorption and utilization, and the bacterial biological behavior and composition. The distributions of the gut microbiota and gastrointestinal hormones are anatomically intertwined, and close interactions between the gut microbiota and gastrointestinal hormones are crucial for maintaining gastrointestinal homeostasis. Interventions leveraging the interplay between the gut microbiota and gastrointestinal hormones have been employed in the clinical management of metabolic diseases and inflammatory bowel diseases, such as bariatric surgery and fecal microbiota transplantation, offering promising targets for the treatment of dysbiosis-related diseases.

Unraveling the Mystery of Insulin Resistance: From Principle Mechanistic Insights and Consequences to Therapeutic Interventions

Insulin resistance (IR) is a significant factor in the development and progression of metabolic-related diseases like dyslipidemia, T2DM, hypertension, nonalcoholic fatty liver disease, cardiovascular and cerebrovascular disorders, and cancer. The pathogenesis of IR depends on multiple factors, including age, genetic predisposition, obesity, oxidative stress, among others. Abnormalities in the insulin-signaling cascade lead to IR in the host, including insulin receptor abnormalities, internal environment disturbances, and metabolic alterations in the muscle, liver, and cellular organelles. The complex and multifaceted characteristics of insulin signaling and insulin resistance envisage their thorough and comprehensive understanding at the cellular and molecular level. Therapeutic strategies for IR include exercise, dietary interventions, and pharmacotherapy. However, there are still gaps to be addressed, and more precise biomarkers for associated chronic diseases and lifestyle interventions are needed. Understanding these pathways is essential for developing effective treatments for IR, reducing healthcare costs, and improving quality of patient life.

The role of GIPR in food intake control

Glucose-dependent insulinotropic polypeptide (GIP) is one of two incretin hormones playing key roles in the control of food intake, nutrient assimilation, insulin secretion and whole-body metabolism. Recent pharmacological advances and clinical trials show that unimolecular co-agonists that target the receptors for the incretins - GIP and glucagon-like peptide 1 (GLP-1) - offer more effective treatment strategies for obesity and type 2 diabetes mellitus (T2D) compared with GLP-1 receptor (GLP1R) agonists alone, suggesting previously underappreciated roles of GIP in regulating food intake and body weight. The mechanisms by which GIP regulates energy balance remain controversial as both agonism and antagonism of the GIP receptor (GIPR) produce weight loss and improve metabolic outcomes in preclinical models. Recent studies have shown that GIPR signalling in the central nervous system (CNS), especially in regions of the brain that regulate energy balance, is essential for its action on appetite regulation. This finding has sparked interest in understanding the mechanisms by which GIP engages brain circuits to reduce food intake and body weight. In this review, we present key knowledge around the actions of GIP on food intake regulation and the potential mechanisms by which GIPR and GIPR/GLP1R agonists may regulate energy balance.

Theaflavin 3'-gallate activates G protein-coupled receptor 55 (GPR55) and enhances GLP-1 secretion via Ca2+/CaMKII/ERK signaling in enteroendocrine STC-1 cells, mitigating postprandial hyperglycemia in mice

The antihyperglycemic effect of black tea is well-known, and theaflavins (TFs) are considered active compounds. It is, however, unclear whether glucagon-like peptide-1 (GLP-1) is involved in the antihyperglycemic effects of TFs. We demonstrate that TFs suppress postprandial hyperglycemia by stimulating GLP-1 secretion in mice. In STC-1 cells, theaflavin 3'-gallate (TF2B), possessing a galloyl group at the 3'-position, showed the strongest effect on GLP-1 secretion among the four TFs. TF2B activated G protein-coupled receptor 55 (GPR55) and was confirmed to bind to the receptor, notably exhibiting the highest binding affinity. Moreover, GPR55 antagonist canceled TF2B-induced GLP-1 secretion. Downstream, TF2B increased intracellular Ca2+ levels and activated the Ca2+/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinases 1/2 (ERK1/2) pathways. Inhibitors of Ca2+ signaling, CaMKII, and ERK pathways abolished TF2B-stimulated GLP-1 secretion. These findings suggest that TF2B from black tea prevents hyperglycemia through GPR55-dependent stimulation of GLP-1 secretion via Ca2+-Ca2+/CaMKII and ERK1/2 pathways.

Ashitaba Chalcone 4-Hydroxydericcin Promotes Glucagon-Like Peptide-1 Secretion and Prevents Postprandial Hyperglycemia in Mice

Certain polyphenols improve glucose tolerance by stimulating glucagon-like peptide-1 (GLP-1) secretion from intestinal L-cells. Ashitaba chalcones, 4-hydroxyderricin (4-HD), and xanthoangelol (XAG) have antihyperglycemic effects, but their molecular mechanism, including whether they promote GLP-1 secretion is unknown. This study investigates the 4-HD-induced GLP-1 secretory mechanisms and its anti-hyperglycemic effects. The secretory mechanisms were examined in STC-1 cells and antihyperglycemic effects in male ICR mice. In STC-1 cells, 4-HD, but not XAG, stimulated GLP-1 secretion through membrane depolarization and intracellular Ca2+ increase [Ca2+]i, via the L-type Ca2+ channel (VGCC). Verapamil and nifedipine, blockers of VGCC, and treatment in Ca2+-free buffer abolished 4-HD effects on [Ca2+]i and GLP-1 secretion. Moreover, 4-HD activated CaMKII and ERK1/2. Consistently, oral 4-HD suppressed postprandial hyperglycemia in mice and increased plasma GLP-1 and insulin levels, GLUT4 translocation, and activation of LKB-1 and Akt pathways in skeletal muscle. Furthermore, exendin 9-39, a GLP-1R antagonist, and compound C, an AMPK inhibitor, completely canceled the 4-HD-caused anti-hyperglycemic activities. 4-HD stimulated GLP-1 secretion through membrane depolarization coupled with [Ca2+]i increase via VGCC in L-cells and activated AMPK- and insulin-induced GLUT4 translocation in skeletal muscle. Thus, 4-HD possesses dual mechanisms for the prevention of hyperglycemia.

Nutritional state-dependent modulation of insulin-producing cells in Drosophila

Insulin plays a key role in metabolic homeostasis. Drosophila insulin-producing cells (IPCs) are functional analogues of mammalian pancreatic beta cells and release insulin directly into circulation. To investigate the in vivo dynamics of IPC activity, we quantified the effects of nutritional and internal state changes on IPCs using electrophysiological recordings. We found that the nutritional state strongly modulates IPC activity. IPC activity decreased with increasing periods of starvation. Refeeding flies with glucose or fructose, two nutritive sugars, significantly increased IPC activity, whereas non-nutritive sugars had no effect. In contrast to feeding, glucose perfusion did not affect IPC activity. This was reminiscent of the mammalian incretin effect, where glucose ingestion drives higher insulin release than intravenous application. Contrary to IPCs, Diuretic hormone 44-expressing neurons in the pars intercerebralis (DH44PINs) responded to glucose perfusion. Functional connectivity experiments demonstrated that these DH44PINs do not affect IPC activity, while other DH44Ns inhibit them. Hence, populations of autonomously and systemically sugar-sensing neurons work in parallel to maintain metabolic homeostasis. Accordingly, activating IPCs had a small, satiety-like effect on food-searching behavior and reduced starvation-induced hyperactivity, whereas activating DH44Ns strongly increased hyperactivity. Taken together, we demonstrate that IPCs and DH44Ns are an integral part of a modulatory network that orchestrates glucose homeostasis and adaptive behavior in response to shifts in the metabolic state.

Long-Term clinical efficacy of liraglutide for type 2 diabetes: real-world evidence and outcomes from Pakistan

Background

Liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, has demonstrated efficacy in improving glycemic control and promoting weight loss in clinical trials. However, real-world data from diverse populations, particularly from South Asia, are limited. The study aims to evaluate the long-term efficacy and safety of liraglutide in a real-world setting among Pakistani patients with type 2 diabetes mellitus (T2DM).

Methodology

A retrospective cohort study of 624 patients initiated on liraglutide was conducted. Data were collected at baseline and 6, 12, 18, and 24 months. Primary outcomes were HbA1c and weight changes. Secondary outcomes included fasting plasma glucose, lipid profile, and blood pressure. Statistical analyses were performed using appropriate methods.

Results

In study population the mean HbA1c reduction of -1.45 ± 0.67% was observed at 24 months, with 30.6% achieving HbA1c ≤ 7.5%. A rapid and sustained weight loss of -7.51 kg was achieved, with 27.2% experiencing ≥5% weight loss. Additionally, liraglutide led to a significant reduction in LDL cholesterol, with 46.7% of patients achieving a ≥ 10% reduction at 24 months. Liraglutide was well-tolerated, with a low discontinuation rate of 4.6%.

Conclusion

Liraglutide demonstrated sustained efficacy and safety in a diverse Pakistani population with T2DM, regardless of baseline characteristics. These findings support the use of liraglutide as an effective treatment option for T2DM in real-world clinical practice.

Incretin-based therapy: a new horizon in diabetes management

Diabetes mellitus, a metabolic syndrome characterized by hyperglycemia and insulin dysfunction, often leads to serious complications such as neuropathy, nephropathy, retinopathy, and cardiovascular disease. Incretins, gut peptide hormones released post-nutrient intake, have shown promising therapeutic effects on these complications due to their wide-ranging biological impacts on various body systems. This review focuses on the role of incretin-based therapies, particularly Glucagon-like peptide-1 (GLP-1) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, in managing diabetes and its complications. We also discuss the potential of novel agents like semaglutide, a recently approved oral compound, and dual/triple agonists targeting GLP-1/GIP, GLP-1/glucagon, and GLP-1/GIP/glucagon receptors, which are currently under investigation. The review aims to provide a comprehensive understanding of the beneficial impacts of natural incretins and the therapeutic potential of incretin-based therapies in diabetes management.

Linking extent of return to fasting state after oral glucose tolerance test to future risk of prediabetes and type 2 diabetes: Insights from the TLGS

AIMS

To assess the risk of difference between 2 h post-load plasma glucose (2 h-PG) and fasting plasma glucose (FPG) on incident prediabetes/type 2 diabetes (T2DM) among normoglycemic individuals.

METHODS

Among 4,971 individuals aged ≥20 years, the associations of the difference between 2 h-PG and FPG with outcomes were examined using multivariable-adjusted Cox regression analysis. Participants were categorized into three groups: a low post-load group (2 h-PG ≤ FPG, as the reference group); a high post-load group (2 h-PG > FPG and ≥75th percentile of the difference); and a medium post-load group (2 h-PG > FPG and <75th percentile of the difference), which was further categorized into three groups by equal ranges.

RESULTS

Over a median of 11.5 years of follow-up, 2,331 new cases of prediabetes/type 2 diabetes and 360 cases of type 2 diabetes occurred. Greater risks of incident prediabetes/type 2 diabetes in second (9-16 mg/dL) and third (17-24 mg/dL) medium post-load, as well as high post-load (≥25 mg/dL) categories, were found, with hazard ratios (95% confidence intervals) of 1.26 (1.11-1.44), 1.32 (1.15-1.51), and 1.69 (1.51-1.90), respectively; the issue was more prominent among women (P for interaction = 0.005). The risk of incident type 2 diabetes was also higher for these categories. After further adjustment for the homeostasis model assessment of insulin resistance, result remained essentially unchanged. Even among individuals with low normal FPG (i.e., <90 mg/dL), ≥9 mg/dL difference between 2 h-PG and FPG increased the risk of composite prediabetes/ type 2 diabetes.

CONCLUSIONS

Greater levels of 2 h-PG as low as 9 mg/dL than FPG among normoglycemic individuals is a harbinger of prediabetes/type 2 diabetes development.

Therapeutic landscape of metabolic dysfunction-associated steatohepatitis (MASH)

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its severe subgroup metabolic dysfunction-associated steatohepatitis (MASH) have become a global epidemic and are driven by chronic overnutrition and multiple genetic susceptibility factors. The physiological outcomes include hepatocyte death, liver inflammation and cirrhosis. The first therapeutic for MASLD and MASH, resmetirom, has recently been approved for clinical use and has energized this therapeutic space. However, there is still much to learn in clinical studies of MASH, such as the scale of placebo responses, optimal trial end points, the time required for fibrosis reversal and side effect profiles. This Review introduces aspects of disease pathogenesis related to drug development and discusses two main therapeutic approaches. Thyroid hormone receptor-β agonists, such as resmetirom, as well as fatty acid synthase inhibitors, target the liver and enable it to function within a toxic metabolic environment. In parallel, incretin analogues such as semaglutide improve metabolism, allowing the liver to self-regulate and reversing many aspects of MASH. We also discuss how combinations of therapeutics could potentially be used to treat patients.

A double knockout for zinc transporter 8 and somatostatin in mice reveals their distinct roles in regulation of insulin secretion and obesity

BACKGROUND

Both zinc transporter 8 (ZnT8) and somatostatin (Sst) play crucial roles in the regulation of insulin and glucagon secretion. However, the interaction between them in controlling glucose metabolism was not well understood. The aim of this study was to explore the interactive effects of a double knockout of Znt8 and Sst on insulin and glucose metabolism in mice.

METHODS

Co-expression of ZnT8 with hormones secreted from gastrointestinal endocrine cells of mice was determined using immunofluorescence. Male Znt8 knockout (Znt8KO), Sst knockout (SstKO), double knockout for Sst and Znt8 (DKO), and the wild-type (WT) mice were fed a regular chow diet (CD) or a high-fat diet (HFD) at 3 weeks old for 15 weeks. Weights and fasting or fed glucose levels were determined. Glucose and insulin tolerance tests were performed; metabolic-relevant hormone levels including insulin, glucagon, glucagon-like peptide 1, Pyy, and leptin were determined.

RESULTS

ZnT8 is co-expressed with Sst in a subpopulation of endocrine D cells in the gastrointestinal tract. The absence of ZnT8 expression resulted in an increased density of the dense cores in the secretory granules of the D cell. DKO mice had reduced weight compared to WT when maintained on the CD. Compared to Znt8KO and SstKO, DKO mice did not show significant differences in fed or fasting blood glucose level regardless of dietary conditions. However, the CD-fed DKO mice had impaired insulin secretion without alterations in islet morphology or numbers. Moreover, DKO mice displayed diet-induced insulin resistance and disrupted secretion of metabolic-related hormones.

CONCLUSIONS

Somatostatin as well as a normal insulin sensitivity are required for normalizing glucose metabolism in Znt8KO mice. ZnT8 may play a role in regulating fat mass and leptin secretion. These findings shed light on the multifaceted nature of Znt8 and Sst interactions, opening new avenues to understand their roles in controlling glucose metabolism and fat mass.

Class B1 GPCRs: insights into multireceptor pharmacology for the treatment of metabolic disease

The secretin-like, class B1 subfamily of seven transmembrane-spanning G protein-coupled receptors (GPCRs) consists of 15 members that coordinate important physiological processes. These receptors bind peptide ligands and use a distinct mechanism of activation that is driven by evolutionarily conserved structural features. For the class B1 receptors, the C-terminus of the cognate ligand is initially recognized by the receptor via an N-terminal extracellular domain that forms a hydrophobic ligand-binding groove. This binding enables the N-terminus of the ligand to engage deep into a large volume, open transmembrane pocket of the receptor. Importantly, the phylogenetic basis of this ligand-receptor activation mechanism has provided opportunities to engineer analogs of several class B1 ligands for therapeutic use. Among the most accepted of these are drugs targeting the glucagon-like peptide-1 (GLP-1) receptor for the treatment of type 2 diabetes and obesity. Recently, multifunctional agonists possessing activity at the GLP-1 receptor and the glucose-dependent insulinotropic polypeptide (GIP) receptor, such as tirzepatide, and others that also contain glucagon receptor activity, have been developed. In this article, we review members of the class B1 GPCR family with focus on receptors for GLP-1, GIP, and glucagon, including their signal transduction and receptor trafficking characteristics. The metabolic importance of these receptors is also highlighted, along with the benefit of polypharmacologic ligands. Furthermore, key structural features and comparative analyses of high-resolution cryogenic electron microscopy structures for these receptors in active-state complexes with either native ligands or multifunctional agonists are provided, supporting the pharmacological basis of such therapeutic agents.

Probiotic therapy as a promising strategy for gestational diabetes mellitus management

INTRODUCTION

Gestational diabetes mellitus (GDM) has become the most common pregnancy medical complication, and its prevalence has increased in recent years. The GDM treatment primarily relies on adopting healthy eating habits, physical exercise, and insulin therapy. However, using probiotics to modulate the gut microbiota has been the subject of clinical trials as a promising therapeutic strategy for GDM management.

AREAS COVERED

Due to the adverse effects of gut dysbiosis in women with GDM, strategies targeting the gut microbiota to mitigate hyperglycemia, low-grade inflammation, and adverse pregnancy outcomes have been explored. Probiotic supplementation may improve glucose metabolism, lipid profile, oxidative stress, inflammation, and blood pressure in women with GDM. Furthermore, decreased fasting blood glucose, insulin resistance, and inflammatory markers, such as TNF-α and CRP, as well as increased total antioxidant capacity, lipid profile modulation, and improved blood pressure in women with GDM, are some of the important results reported in the available literature.

EXPERT OPINION

To fill the knowledge gap, further studies are needed focusing on modulating gut microbiota composition and metabolic activity and their systemic repercussions in GDM.

The influence of insulin and incretin-based therapies on renal tubular transport

The tubular function of the kidney is very complex and is finely regulated by many factors. These include a variety of hormonal signaling pathways which are involved in the expression, activation and regulation of renal transporters responsible for the handling of electrolytes. Glucose-lowering drugs such as insulin and incretin-based therapies, exert a well-known renal protective role in diabetic kidney disease, mainly acting at the glomerular level. In the literature, several studies have described the effect of insulin and the incretin hormones on tubular transport. Most of these studies focused on the variations in excretion and clearance of sodium but did not extensively and systematically investigate the possible variations that these hormones may induce in the tubular regulation of all the other electrolytes, urea metabolism, acid-base balance and urinary pH. While insulin action on the kidney is very well-described, the renal tubular impact of incretin-based therapies is less consistent and the results available are scarce. To our knowledge, this is the first review summarizing the effects induced on renal tubules by insulin, glucagon-like peptide-1 (GLP-1) receptor agonists and serine protease dipeptidyl peptidase-4 (DPP4) inhibitors in both healthy and diabetic human subjects. This is significant because it highlights the existence of a renal-gut and pancreas axis which also has a direct tubular effect and enables a deeper understanding of renal physiology.

Changes in 24-Hour Urine Chemistry in Patients with Nephrolithiasis during Weight Loss with Glucagon-Like Peptide 1-Based Therapies

Key Points

Background

Obesity is an independent risk factor of incident and recurrent nephrolithiasis. The effect of weight loss through glucagon-like peptide 1 (GLP-1) receptor agonists and dual GLP-1/gastric inhibitory polypeptide receptor agonists (GLP-based therapies) on nephrolithiasis is not well understood. This study examined the changes in 24-hour urine chemistry assessing for stone risk during weight loss through GLP-based therapies.

Methods

This retrospective analysis identified adult stone formers followed at our academic institution's weight wellness clinic between September 2015 and August 2023 and included patients with at least two 24-hour urine collections for stone risk assessment. 24-hour urine parameters before and during weight loss in patients on GLP-based therapies were compared.

Results

Forty-four obese patients with nephrolithiasis experienced significant weight reduction (−6.6±7.3 kg, P < 0.001) over a median 1.1 years of follow-up with GLP-based therapies. During this period, there was a significant decrease in 24-hour urine oxalate (40±16 to 32±11 mg/d, P = 0.002), sulfate (21±10 to 17±9 mmol/d, P = 0005), and ammonium (35±22 to 29±15 mEq/d, P = 0.01) excretion rates. There were nonsignificant changes in urine calcium, citrate, uric acid, pH, phosphorus, sodium, potassium, magnesium, chloride, creatinine, or total volume. In addition, there was no statistical difference in urine supersaturation indices with respect to calcium oxalate, calcium phosphate, and uric acid.

Conclusions

Our results indicate that weight loss through GLP-based therapies is not associated with prolithogenic changes in 24-hour urine chemistry in patients with nephrolithiasis, unlike what happens with other weight loss modalities.

Activation of Gs signaling in mouse enteroendocrine K cells greatly improves obesity- and diabetes-related metabolic deficits

Following a meal, glucagon-like peptide 1 (GLP1) and glucose-dependent insulinotropic polypeptide (GIP), the 2 major incretins promoting insulin release, are secreted from specialized enteroendocrine cells (L and K cells, respectively). Although GIP is the dominant incretin in humans, the detailed molecular mechanisms governing its release remain to be explored. GIP secretion is regulated by the activity of G protein-coupled receptors (GPCRs) expressed by K cells. GPCRs couple to 1 or more specific classes of heterotrimeric G proteins. In the present study, we focused on the potential metabolic roles of K cell Gs. First, we generated a mouse model that allowed us to selectively stimulate K cell Gs signaling. Second, we generated a mouse strain harboring an inactivating mutation of Gnas, the gene encoding the α-subunit of Gs, selectively in K cells. Metabolic phenotyping studies showed that acute or chronic stimulation of K cell Gs signaling greatly improved impaired glucose homeostasis in obese mice and in a mouse model of type 2 diabetes, due to enhanced GIP secretion. In contrast, K cell-specific Gnas-KO mice displayed markedly reduced plasma GIP levels. These data strongly suggest that strategies aimed at enhancing K cell Gs signaling may prove useful for the treatment of diabetes and related metabolic diseases.

The Therapeutic Potential of Glucagon-like Peptide 1 Receptor Agonists in Traumatic Brain Injury

Traumatic brain injury (TBI), which is a global public health concern, can take various forms, from mild concussions to blast injuries, and each damage type has a particular mechanism of progression. However, TBI is a condition with complex pathophysiology and heterogenous clinical presentation, which makes it difficult to model for in vitro and in vivo studies and obtain relevant results that can easily be translated to the clinical setting. Accordingly, the pharmacological options for TBI management are still scarce. Since a wide spectrum of processes, such as glucose homeostasis, food intake, body temperature regulation, stress response, neuroprotection, and memory, were demonstrated to be modulated after delivering glucagon-like peptide 1 (GLP-1) or GLP-1 receptor agonists into the brain, we aimed to speculate on their potential role in TBI management by comprehensively overviewing the preclinical and clinical body of evidence. Based on promising preclinical data, GLP-1 receptor agonists hold the potential to extend beyond metabolic disorders and address unmet needs in neuroprotection and recovery after TBI, but also other types of central nervous system injuries such as the spinal cord injury or cerebral ischemia. This overview can lay the basis for tailoring new research hypotheses for future in vitro and in vivo models in TBI settings. However, large-scale clinical trials are crucial to confirm their safety and efficacy in these new therapeutic applications.

Cow's Milk Bioactive Molecules in the Regulation of Glucose Homeostasis in Human and Animal Studies

Obesity disrupts glucose metabolism, leading to insulin resistance (IR) and cardiometabolic diseases. Consumption of cow's milk and other dairy products may influence glucose metabolism. Within the complex matrix of cow's milk, various carbohydrates, lipids, and peptides act as bioactive molecules to alter human metabolism. Here, we summarize data from human studies and rodent experiments illustrating how these bioactive molecules regulate insulin and glucose homeostasis, supplemented with in vitro studies of the mechanisms behind their effects. Bioactive carbohydrates, including lactose, galactose, and oligosaccharides, generally reduce hyperglycemia, possibly by preventing gut microbiota dysbiosis. Milk-derived lipids of the milk fat globular membrane improve activation of insulin signaling pathways in animal trials but seem to have little impact on glycemia in human studies. However, other lipids produced by ruminants, including polar lipids, odd-chain, trans-, and branched-chain fatty acids, produce neutral or contradictory effects on glucose metabolism. Bioactive peptides derived from whey and casein may exert their effects both directly through their insulinotropic effects or renin-angiotensin-aldosterone system inhibition and indirectly by the regulation of incretin hormones. Overall, the results bolster many observational studies in humans and suggest that cow's milk intake reduces the risk of, and can perhaps be used in treating, metabolic disorders. However, the mechanisms of action for most bioactive compounds in milk are still largely undiscovered.

Tirzepatide's innovative applications in the management of type 2 diabetes and its future prospects in cardiovascular health

Tirzepatide, a novel GLP-1/GIP dual receptor agonist, shows significant advantages in glycemic management and weight control. By summarizing the results of the SURMOUNT and SURPASS clinical trials, we evaluate the efficacy and safety of tirzepatide in reducing blood glucose and weight. These trials indicate that tirzepatide significantly lowers HbA1c levels (with a maximum reduction of 2.24%) and promotes weight loss (up to 11.2 kg) with good tolerability. However, there are still some challenges in its clinical application, including high treatment costs and gastrointestinal discomfort. Additionally, the safety and efficacy of tirzepatide in special populations, such as patients with renal impairment, require further investigation. Future large-scale clinical trials, such as SURPASS-CVOT and SUMMIT, are expected to further verify the long-term benefits of tirzepatide in cardiovascular health management, providing stronger evidence for its comprehensive treatment of diabetes and its complications.

Potassium voltage-gated channel subfamily H member 2 (KCNH2) is a promising target for incretin secretagogue therapies

Derived from enteroendocrine cells (EECs), glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) are pivotal incretin hormones crucial for blood glucose regulation. Medications of GLP-1 analogs and GLP-1 receptor activators are extensively used in the treatment of type 2 diabetes (T2D) and obesity. However, there are currently no agents to stimulate endogenous incretin secretion. Here, we find the pivotal role of KCNH2 potassium channels in the regulation of incretin secretion. Co-localization of KCNH2 with incretin-secreting EECs in the intestinal epithelium of rodents highlights its significance. Gut epithelial cell-specific KCNH2 knockout in mice improves glucose tolerance and increases oral glucose-triggered GLP-1 and GIP secretion, particularly GIP. Furthermore, KCNH2-deficient primary intestinal epithelial cells exhibit heightened incretin, especially GIP secretion upon nutrient stimulation. Mechanistically, KCNH2 knockdown in EECs leads to reduced K+ currents, prolonged action potential duration, and elevated intracellular calcium levels. Finally, we found that dofetilide, a KCNH2-specific inhibitor, could promote incretin secretion in enteroendocrine STC-1 cells in vitro and in hyperglycemic mice in vivo. These findings elucidate, for the first time, the mechanism and application of KCNH2 in regulating incretin secretion by EECs. Given the therapeutic promise of GLP-1 and GIP in diabetes and obesity management, this study advances our understanding of incretin regulation, paving the way for potential incretin secretagogue therapies in the treatment of diabetes and obesity.

Chronic exposure to incretin metabolites GLP-1(9-36) and GIP(3-42) affect islet morphology and beta cell health in high fat fed mice

The incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are rapidly degraded by dipeptidyl peptidase-4 (DPP-4) to their major circulating metabolites GLP-1(9-36) and GIP(3-42). This study investigates the possible effects of these metabolites, and the equivalent exendin molecule Ex(9-39), on pancreatic islet morphology and constituent alpha and beta cells in high-fat diet (HFD) fed mice. Male Swiss TO-mice (6-8 weeks-old) were maintained on a HFD or normal diet (ND) for 4 months and then received twice-daily subcutaneous injections of GLP-1(9-36), GIP(3-42), Ex(9-39) (25 nmol/kg bw) or saline vehicle (0.9% (w/v) NaCl) over a 60-day period. Metabolic parameters were monitored and excised pancreatic tissues were used for immunohistochemical analysis. Body weight and assessed metabolic indices were not changed by peptide administration. GLP-1(9-36) significantly (p<0.001) increased islet density per mm2 tissue, that was decreased (p<0.05) by HFD. Islet, beta and alpha cell areas were increased (p<0.01) following HFD and subsequently reduced (p<0.01-p<0.001) by GIP(3-42) and Ex(9-39) treatment. While GLP-1(9-36) did not affect islet and beta cell areas in HFD mice, it significantly (p<0.01) decreased alpha cell area. Compared to ND and HFD mice, GIP(3-42) treatment significantly (p<0.05) increased beta cell proliferation. Whilst HFD increased (p<0.001) beta cell apoptosis, this was reduced (p<0.01-p<0.001) by both GLP-1(9-36) and GIP(3-42). These data indicate that the major circulating forms of GLP-1 and GIP, namely GLP-1(9-36) and GIP(3-42) previously considered largely inactive, may directly impact pancreatic morphology, with an important protective effect on beta cell health under conditions of beta cell stress.

Clinical Outcomes of Tirzepatide or GLP-1 Receptor Agonists in Individuals With Type 2 Diabetes

Importance

Despite its demonstrated benefits in improving cardiovascular risk profiles, the association of tirzepatide with mortality and cardiovascular and kidney outcomes compared with glucagon-like peptide 1 receptor agonists (GLP-1 RAs) remains unknown.

Objective

To investigate the association of tirzepatide with mortality and adverse cardiovascular and kidney outcomes compared with GLP-1 RAs in patients with type 2 diabetes.

Design, Setting, and Participants

This retrospective cohort study used US Collaborative Network of TriNetX data collected on individuals with type 2 diabetes aged 18 years or older initiating tirzepatide or GLP-1 RA between June 1, 2022, and June 30, 2023; without stage 5 chronic kidney disease or kidney failure at baseline; and without myocardial infarction or ischemic or hemorrhagic stroke within 60 days of drug initiation.

Exposures

Treatment with tirzepatide compared with GLP-1 RA.

Main Outcomes and Measures

The primary outcome was all-cause mortality, and secondary outcomes included major adverse cardiovascular events (MACEs), the composite of MACEs and all-cause mortality, kidney events, acute kidney injury, and major adverse kidney events. All outcomes were analyzed using Cox proportional hazards regression models.

Results

There were 14 834 patients treated with tirzepatide (mean [SD] age, 55.4 [11.8] years; 8444 [56.9%] female) and 125 474 treated with GLP-1 RA (mean [SD] age, 58.1 [13.3] years; 67 474 [53.8%] female). After a median (IQR) follow-up of 10.5 (5.2-15.7) months, 95 patients (0.6%) in the tirzepatide group and 166 (1.1%) in the GLP-1 RA group died. Tirzepatide treatment was associated with lower hazards of all-cause mortality (adjusted hazard ratio [AHR], 0.58; 95% CI, 0.45-0.75), MACEs (AHR, 0.80; 95% CI, 0.71-0.91), the composite of MACEs and all-cause mortality (AHR, 0.76; 95% CI, 0.68-0.84), kidney events (AHR, 0.52; 95% CI, 0.37-0.73), acute kidney injury (AHR, 0.78; 95% CI, 0.70-0.88), and major adverse kidney events (AHR, 0.54; 95% CI, 0.44-0.67). Treatment with tirzepatide was associated with greater decreases in glycated hemoglobin (treatment difference, -0.34 percentage points; 95% CI, -0.44 to -0.24 percentage points) and body weight (treatment difference, -2.9 kg, 95% CI, -4.8 to -1.1 kg) compared with GLP-1 RA. An interaction test for subgroup analysis revealed consistent results stratified by estimated glomerular filtration rate, glycated hemoglobin level, body mass index, comedications, and comorbidities.

Conclusions and Relevance

In this study, treatment with tirzepatide was associated with lower hazards of all-cause mortality, adverse cardiovascular events, acute kidney injury, and adverse kidney events compared with GLP-1 RA in patients with type 2 diabetes. These findings support the integration of tirzepatide into therapeutic strategies for this population.

Can the postload-fasting glucose gap be used to determine risk of developing diabetes in chinese adults: A prospective cohort study

OBJECTIVE

To evaluate the relationship between fasting plasma glucose (FPG) and 2-hour postload plasma glucose (2hPG) measured during an oral glucose tolerance test, and the risk of developing diabetes in Chinese adults.

METHODS

We followed 3,094 participants without diabetes, categorizing them based on their oral glucose tolerance test (OGTT) results into low post load (2hPG ≤ FPG) and high post load (2hPG > FPG) at baseline. We monitored the incidence of diabetes, incidence of prediabetes, disease progression from prediabetes to diabetes and disease reversal from prediabetes to normal glucose tolerance (NGT) over an average of 3.2 years of follow-up. After the Schoenfeld residual test, Cox's time-varying covariate (Cox-TVC) models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) to compare the different clinical events between low and high post load groups.

RESULTS

In the cohort study, of the 3,094 participants, 702 (22.7 %) had low post load (2hPG ≤ FPG, mean postload-fasting gap: -0.8 ± 0.7 mmol/L) and 2,392 (77.3 %) had high post load (2hPG > FPG, mean postload-fasting gap: 1.8 ± 1.2 mmol/L). Over 3.2 ± 0.2 years of follow-up, 282 (9.1 %) developed diabetes. In the low post load group, the incidence rates per 1,000 person-years were: diabetes was 7.9, prediabetes was 70.0, disease progression from prediabetes to diabetes was 23.4 and disease reversal to NGT was 327.2. For the high post load group, incidence rates for diabetes was 13.9, prediabetes was 124.3, disease progression was 59.5 and disease reversal was 238.6 per 1,000 person-years. Participants with high post load showed higher incidence rates of diabetes, prediabetes, and progression from prediabetes to diabetes compared to those with low post load. HRs were significantly higher for incident diabetes and prediabetes, and disease progression from prediabetes to diabetes, whereas disease reversal was lower.

CONCLUSION

The risk of developing prediabetes/diabetes after 3.2 years of follow-up was higher in the participants with high post load. It suggested that postload-fasting gap may be a simple tool to predict the risk of developing prediabetes, diabetes or reversal to NGT.

An adipoincretin effect links adipostasis with insulin secretion

The current paradigm for the insulin system focuses on the phenomenon of glucose-stimulated insulin secretion and insulin action on blood glucose control. This historical glucose-centric perspective may have introduced a conceptual bias in our understanding of insulin regulation. A body of evidence demonstrating that in vivo variations in blood glucose and insulin secretion can be largely dissociated motivated us to reconsider the fundamental design of the insulin system as a control system for metabolic homeostasis. Here, we propose that a minimal glucose-centric model does not accurately describe the physiological behavior of the insulin system and propose a new paradigm focusing on the effects of incretins, arguing that under fasting conditions, insulin is regulated by an adipoincretin effect.

SUCNR1 regulates insulin secretion and glucose elevates the succinate response in people with prediabetes

Pancreatic β cell dysfunction is a key feature of type 2 diabetes, and novel regulators of insulin secretion are desirable. Here, we report that succinate receptor 1 (SUCNR1) is expressed in β cells and is upregulated in hyperglycemic states in mice and humans. We found that succinate acted as a hormone-like metabolite and stimulated insulin secretion via a SUCNR1-Gq-PKC-dependent mechanism in human β cells. Mice with β cell-specific Sucnr1 deficiency exhibited impaired glucose tolerance and insulin secretion on a high-fat diet, indicating that SUCNR1 is essential for preserving insulin secretion in diet-induced insulin resistance. Patients with impaired glucose tolerance showed an enhanced nutrition-related succinate response, which correlates with the potentiation of insulin secretion during intravenous glucose administration. These data demonstrate that the succinate/SUCNR1 axis is activated by high glucose and identify a GPCR-mediated amplifying pathway for insulin secretion relevant to the hyperinsulinemia of prediabetic states.

The Regulation Role of the Gut-Islets Axis in Diabetes

The gut-islets axis is an important endocrine signaling axis that regulates the function of islets by modulating the gut micro-environment and its endocrine metabolism. The discovery of intestinal hormones, such as GLP-1 and GIP, has established a preliminary link between the gut and the islet, paving the way for the development of GLP-1 receptor agonists based on the regulation theory of the gut-islets axis for diabetes treatment. This discovery has created a new paradigm for diabetes management and rapidly made the regulation theory of the gut-islets axis a focal point of research attention. Recent years, with in-depth study on gut microbiota and the discovery of intestinal-derived extracellular vesicles, the concept of gut endocrine and the regulation theory of the gut-islets axis have been further expanded and updated, offering tremendous research opportunities. The gut-islets axis refers to the complex interplay between the gut and the islet, which plays a crucial role in regulating glucose homeostasis and maintaining metabolic health. The axis involves various components, including gut microbiota, intestinal hormones, amino acids and ACE2, which contribute to the communication and coordination between the gut and the islet.

Preoperative Patient Evaluation: Newer Hypoglycemic Agents

New medications in the treatment of diabetes are an active area of research and drug development. Although many hypoglycemic therapies have been in use for decades, new evidence continues to emerge highlighting benefits of these medications for other indications. In this article, the authors review the classes of newer hypoglycemic agents and summarize medications currently in phase 2 and 3 clinical trials. The literature to support specific recommendations for perioperative management is scant, however, where it exists, we have included it. In other instances, the authors have noted a reasonable approach based on pharmacokinetics and principles of perioperative medication management.

Evaluating the effectiveness of a novel somatostatin receptor 2 antagonist, ZT-01, for hypoglycemia prevention in a rodent model of type 2 diabetes

Background: Elevated levels of somatostatin blunt glucagon counterregulation during hypoglycemia in type 1 diabetes (T1D) and this can be improved using somatostatin receptor 2 (SSTR2) antagonists. Hypoglycemia also occurs in late-stage type 2 diabetes (T2D), particularly when insulin therapy is initiated, but the utility of SSTR2 antagonists in ameliorating hypoglycemia in this disease state is unknown. We examined the efficacy of a single-dose of SSTR2 antagonists in a rodent model of T2D. Methods: High-fat fed (HFF), low dose streptozotocin (STZ, 35 mg/kg)-induced T2D and HFF only, nondiabetic (controls-no STZ) rats were treated with the SSTR2 antagonists ZT-01/PRL-2903 or vehicle (n = 9-11/group) 60 min before an insulin tolerance test (ITT; 2-12 U/kg insulin aspart) or an oral glucose tolerance test (OGTT; 2 g/kg glucose via oral gavage) on separate days. Results: This rodent model of T2D is characterized by higher baseline glucose and HbA1c levels relative to HFF controls. T2D rats also had lower c-peptide levels at baseline and a blunted glucagon counterregulatory response to hypoglycemia when subjected to the ITT. SSTR2 antagonists increased the glucagon response and reduced incidence of hypoglycemia, which was more pronounced with ZT-01 than PRL-2903. ZT-01 treatment in the T2D rats increased glucagon levels above the control response within 60 min of dosing, and values remained elevated during the ITT (glucagon Cmax: 156 ± 50 vs. 77 ± 46 pg/mL, p < 0.01). Hypoglycemia incidence was attenuated with ZT-01 vs. controls (63% vs. 100%) and average time to hypoglycemia onset was also delayed (103.1 ± 24.6 vs. 66.1 ± 23.6 min, p < 0.05). ZT-01 administration at the OGTT onset increased the glucagon response without exacerbating hyperglycemia (2877 ± 806 vs. 2982 ± 781), potentially due to the corresponding increase in c-peptide levels (6251 ± 5463 vs. 14008 ± 5495, p = 0.013). Conclusion: Treatment with SSTR2 antagonists increases glucagon responses in a rat model of T2D and results in less hypoglycemia exposure. Future studies are required to determine the best dosing periods for chronic SSTR2 antagonism treatment in T2D.

Exendin-4 affects calcium signalling predominantly during activation and activity of beta cell networks in acute mouse pancreas tissue slices

Tight control of beta cell stimulus-secretion coupling is crucial for maintaining homeostasis of energy-rich nutrients. While glucose serves as a primary regulator of this process, incretins augment beta cell function, partly by enhancing cytosolic [Ca2+] dynamics. However, the details of how precisely they affect beta cell recruitment during activation, their active time, and functional connectivity during plateau activity, and how they influence beta cell deactivation remain to be described. Performing functional multicellular Ca2+ imaging in acute mouse pancreas tissue slices enabled us to systematically assess the effects of the GLP-1 receptor agonist exendin-4 (Ex-4) simultaneously in many coupled beta cells with high resolution. In otherwise substimulatory glucose, Ex-4 was able to recruit approximately a quarter of beta cells into an active state. Costimulation with Ex-4 and stimulatory glucose shortened the activation delays and accelerated beta cell activation dynamics. More specifically, active time increased faster, and the time required to reach half-maximal activation was effectively halved in the presence of Ex-4. Moreover, the active time and regularity of [Ca2+]IC oscillations increased, especially during the first part of beta cell response. In contrast, subsequent addition of Ex-4 to already active cells did not significantly enhance beta cell activity. Network analyses further confirmed increased connectivity during activation and activity in the presence of Ex-4, with hub cell roles remaining rather stable in both control experiments and experiments with Ex-4. Interestingly, Ex-4 demonstrated a biphasic effect on deactivation, slightly prolonging beta cell activity at physiological concentrations and shortening deactivation delays at supraphysiological concentrations. In sum, costimulation by Ex-4 and glucose increases [Ca2+]IC during beta cell activation and activity, indicating that the effect of incretins may, to an important extent, be explained by enhanced [Ca2+]IC signals. During deactivation, previous incretin stimulation does not critically prolong cellular activity, which corroborates their low risk of hypoglycemia.

Rectal sensitivity correlated with gastrointestinal-mediated glucose disposal, but not the incretin effect

OBJECTIVE

The mechanisms behind the diminished incretin effect in type 2 diabetes are uncertain, but impaired vagal transmission has been suggested. We aimed to investigate the association between the incretin effect and autonomic neuropathy, and the degree of dysglycaemia and duration of diabetes.

DESIGN AND METHODS

For a cross-sectional study, we included participants with either longstanding type 2 diabetes, recent onset, untreated diabetes and controls without diabetes matched for age, sex and body mass index. Autonomic nerve function was assessed with cardiovascular reflex tests, heart rate variability and sudomotor function. Visceral afferent nerves in the gut were tested performing rapid rectal balloon distention. An oral glucose tolerance test and an intravenous isoglycaemic glucose infusion were performed to calculate the incretin effect and gastrointestinal-mediated glucose disposal (GIGD).

RESULTS

Sixty-five participants were recruited. Participants with diabetes had rectal hyposensitivity for earliest sensation (3.7 ± 1.1 kPa in longstanding, 4.0 ± 1.3 in early), compared to controls (3.0 ± 0.9 kPa), p = .005. Rectal hyposensitivity for earliest sensation was not associated with the incretin effect (rho = -0.204, p = .106), but an association was found with GIGD (rho -0.341, p = .005). Incretin effect and GIGD were correlated with all glucose values, HbA1c and duration of diabetes.

CONCLUSIONS

Rectal hyposensitivity was uncovered in both longstanding and early type 2 diabetes, and was not associated with the incretin effect, but with GIGD, implying a potential link between visceral neuropathy and gastrointestinal handling of glucose. Both the incretin effect and GIGD were associated with the degree of dysglycaemia and the duration of diabetes.

PREVIOUSLY PUBLISHED

Some of the data have previously been published and presented as a poster on the American Diabetes Association 83rd Scientific Sessions: Meling et al; 1658-P: Rectal Hyposensitivity, a Potential Marker of Enteric Autonomic Nerve Dysfunction, Is Significantly Associated with Gastrointestinally Mediated Glucose Disposal in Persons with Type 2 Diabetes. Diabetes 20 June 2023; 72 (Supplement_1): 1658-P. https://doi.org/10.2337/db23-1658-P.

GLP-1/GLP-1RAs: New Options for the Drug Treatment of NAFLD

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a global public health concern. Currently, the cornerstone of NAFLD treatment is lifestyle modification and, if necessary, weight loss. However, compliance is a challenge, and this approach alone may not be sufficient to halt and treat the more serious disease development, so medication is urgently needed. Nevertheless, no medicines are approved to treat NAFLD. Glucagon-like peptide-1 (GLP-1) is an enteropeptide hormone that inhibits glucagon synthesis, promotes insulin secretion, and delays gastric emptying. GLP-1 has been found in recent studies to be beneficial for the management of NAFLD, and the marketed GLP-1 agonist drugs have different degrees of effectiveness for NAFLD while lowering blood glucose. In this article, we review GLP-1 and its physiological roles, the pathogenesis of NAFLD, the correlation between NAFLD and GLP-1 signaling, and potential strategies for GLP-1 treatment of NAFLD.

Evolution of GCGR family ligand-receptor extensive cross-interaction systems suggests a therapeutic direction for hyperglycemia in mammals

Glucose is essential to the physiological processes of vertebrates. Mammalian physiological stability requires a relatively stable blood glucose level (~5 mM), whereas other vertebrates have greater flexibility in regulating blood glucose (0.5-25 mM). GCGR family receptors play an important role in vertebrate glucose regulation. Here, we examine the evolution of the GCGR family ligand-receptor systems in different species. Comparatively, we discover that the conserved sequences among GCG family ligands lead to the non-specific activation of ligands across species. In particular, we observe that glucagon-like peptide 1 receptor (GLP1R), glucagon-like peptide 2 receptor (GLP2R), and glucagon-like receptor (GCGLR, also called GCRPR) are arbitrarily activated by other members of the ligand family in birds. Moreover, we reveal that Gallus gallus GLP2 (gGLP2) effectively activates mammalian GLP1R and improves glucose tolerance in diabetic mice. Our study has important implications for understanding blood glucose stabilization in vertebrates and demonstrates that gGLP2 may be a potential drug for treating type 2 diabetes.

Pregnancy glucagon-like peptide 1 predicts insulin but not glucose concentrations

AIMS

Incretin hormones glucagon-like peptide 1 (GLP-1) and gastric inhibitory peptide (GIP) cause increased insulin secretion in non-pregnant adults, but their role in pregnancy, where there are additional metabolically-active hormones from the placenta, is less clear. The aim of the present study was to assess if fasting and post-load incretin concentrations were predictive of pregnancy insulin and glucose concentrations.

METHODS

Pregnant women (n = 394) with one or more risk factors for gestational diabetes were recruited at 28 weeks for a 75 g oral glucose tolerance test (OGTT). Glucose, insulin, GLP-1 and GIP were measured in the fasting state and 120 min after glucose ingestion.

RESULTS

Fasting plasma GLP-1 concentrations were associated with plasma insulin (standardised β' 0.393 (0.289-0.498), p = 1.3 × 10-12; n = 306), but not with glucose concentrations (p = 0.3). The association with insulin was still evident when adjusting for BMI (β' 0.271 (0.180-0.362), p = 1.1 × 10-8; n = 297). Likewise, at 120 min the OGTT GLP-1 concentrations were associated with plasma insulin concentrations (β' 0.216 (0.100-0.331), p  = 2.7 × 10-4; n = 306) even after adjusting for BMI (β' 0.178 (0.061-0.294), p = 2.9 × 10-3; n = 296), but not with glucose (p  = 0.9). GIP concentrations were not associated with insulin or glucose concentrations at either time point (all p  > 0.2). In pregnancy plasma GLP-1, but not GIP, concentrations appear to be predictive of circulating insulin concentrations, independently of associations with BMIs.

CONCLUSIONS

These results suggest that the relationship between insulin and incretins is preserved in pregnancy, but that other factors, such as placental hormones or counter-regulatory hormones, may be more important determinants of glycaemia and gestational diabetes aetiology.

The intestine as an endocrine organ and the role of gut hormones in metabolic regulation

Gut hormones orchestrate pivotal physiological processes in multiple metabolically active tissues, including the pancreas, liver, adipose tissue, gut and central nervous system, making them attractive therapeutic targets in the treatment of obesity and type 2 diabetes mellitus. Most gut hormones are derived from enteroendocrine cells, but bioactive peptides that are derived from other intestinal epithelial cell types have also been implicated in metabolic regulation and can be considered gut hormones. A deeper understanding of the complex inter-organ crosstalk mediated by the intestinal endocrine system is a prerequisite for designing more effective drugs that are based on or target gut hormones and their receptors, and extending their therapeutic potential beyond obesity and diabetes mellitus. In this Review, we present an overview of gut hormones that are involved in the regulation of metabolism and discuss their action in the gastrointestinal system and beyond.

GLP-1 and GIP receptors signal through distinct β-arrestin 2-dependent pathways to regulate pancreatic β cell function

Glucagon-like peptide 1 (GLP-1R) and glucose-dependent insulinotropic polypeptide (GIPR) receptors are G-protein-coupled receptors involved in glucose homeostasis. Diabetogenic conditions decrease β-arrestin 2 (ARRB2) levels in human islets. In mouse β cells, ARRB2 dampens insulin secretion by partially uncoupling cyclic AMP (cAMP)/protein kinase A (PKA) signaling at physiological doses of GLP-1, whereas at pharmacological doses, the activation of extracellular signal-related kinase (ERK)/cAMP-responsive element-binding protein (CREB) requires ARRB2. In contrast, GIP-potentiated insulin secretion needs ARRB2 in mouse and human islets. The GIPR-ARRB2 axis is not involved in cAMP/PKA or ERK signaling but does mediate GIP-induced F-actin depolymerization. Finally, the dual GLP-1/GIP agonist tirzepatide does not require ARRB2 for the potentiation of insulin secretion. Thus, ARRB2 plays distinct roles in regulating GLP-1R and GIPR signaling, and we highlight (1) its role in the physiological context and the possible functional consequences of its decreased expression in pathological situations such as diabetes and (2) the importance of assessing the signaling pathways engaged by the agonists (biased/dual) for therapeutic purposes.

Dual Activation of Calcium Channels Using Near-Infrared Responsive Conjugated Oligomer Nanoparticles for Precise Regulation of Blood Glucose Homeostasis

The rarity of efficient tools with spatiotemporal resolution and biocompatibility capabilities remains a major challenge for further progress and application of signaling manipulation. Herein, biomimetic conjugated oligomeric nanoparticles (CM-CONs) were developed to precisely modulate blood glucose homeostasis via the two-pronged activation of calcium channels. Under near-infrared (NIR) laser irradiation, CM-CONs efficiently generate local heat and reactive oxygen species (ROS), thereby simultaneously activating thermosensitive transient receptor potential V1 (TRPV1) and ROS-sensitive transient receptor potential A1 (TRPA1) calcium channels in small intestinal endocrine cells. The activation of the channels mediates inward calcium flow and then promotes glucagon-like peptide (GLP-1) secretion. Both in vitro and in vivo studies indicate that CM-CONs effectively regulate glucose homeostasis in diabetic model mice upon NIR light irradiation. This work develops a two-pronged attack strategy for accurately controlling blood glucose homeostasis, holding great prospects in the treatment for diabetes.

Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse

BACKGROUND

Identifying intake levels of nonstructural carbohydrates (NSCs) that limit the postprandial insulinaemic response in the insulin dysregulated (ID) horse may help reduce hyperinsulinaemia-associated laminitis (HAL) risk.

OBJECTIVE

To determine if ID horses have thresholds for pure sources of starch and sugar, above which there is an augmented insulin response.

STUDY DESIGN

Randomised crossover experiment.

METHODS

Fourteen adult horses (6 ID and 8 noninsulin dysregulated, NID; matched for bodyweight) were randomly fed eight dietary treatments. Dietary treatments were formulated using a base of low-nonstructural carbohydrate pellet (LNSC; 0.04 g of water-soluble carbohydrates (WSCs)/kg bwt and 0.01 g of starch/kg bwt), to which pure sugar (dextrose) or starch (50:50 mix of waxy-maize and oat starch powder) sources were titrated to create diets with increasing amounts of either WSC (0.06-0.17 g WSC/kg bwt), or starch (0.03-0.1 g starch/kg bwt). Horses were fed each dietary treatment at a rate of 1 g/kg bwt once over 12 weeks. Serial blood samples were collected pre- and up to 240 min postprandially. Insulin was determined via RIA and diet analytes were determined via wet chemistry. Statistical analysis was performed with a mixed effect model. Positive incremental area under the curve for insulin (IAUCi) was calculated for all horses and dietary treatments.

RESULTS

There was no significant effect of diet in NID horses but diets with NSC >0.1 g/kg bwt produced an augmented response in ID horses compared with the LNSC (p < 0.05). ID horses IAUCi were also significantly different to all NID IAUCi for diets with NSC >0.1 g/kg (p < 0.04). Apparent thresholds for sugar and starch addition varied.

CONCLUSIONS

Based on this study, using supplemental pure starch and sugar sources, ID horses seem to have an apparent threshold for NSC of around 0.1 g/kg bwt/meal, above which significantly increased insulin responses are seen compared with NID horses.

The importance of glucose-dependent insulinotropic polypeptide receptor activation for the effects of tirzepatide

Tirzepatide is a unimolecular co-agonist of the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors recently approved for the treatment of type 2 diabetes by the US Food and Drug Administration and the European Medicine Agency. Tirzepatide treatment results in an unprecedented improvement of glycaemic control and lowering of body weight, but the contribution of the GIP receptor-activating component of tirzepatide to these effects is uncertain. In this review, we present the current knowledge about the physiological roles of the incretin hormones GLP-1 and GIP, their receptors, and previous results of co-targeting the two incretin hormone receptors in humans. We also analyse the molecular pharmacological, preclinical and clinical effects of tirzepatide to discuss the role of GIP receptor activation for the clinical effects of tirzepatide. Based on the available literature on the combination of GLP-1 and GIP receptor activation, tirzepatide does not seem to have a classical co-activating mode of action in humans. Rather, in vitro studies of the human GLP-1 and GIP receptors reveal a biased GLP-1 receptor activation profile and GIP receptor downregulation. Therefore, we propose three hypotheses for the mode of action of tirzepatide, which can be addressed in future, elaborate clinical trials.

Safety issues of tirzepatide (pancreatitis and gallbladder or biliary disease) in type 2 diabetes and obesity: a systematic review and meta-analysis

Purpose

A systematic review and meta-analysis was conducted to synthesize the available data from clinical trials and assess the safety issues of tirzepatide (pancreatitis and gallbladder or biliary disease) in type 2 diabetes (T2D) and obesity.

Methods

A systematic search was conducted in three electronic databases, namely Embase, PubMed, and the Cochrane Library, up until March 1, 2023, to identify randomized controlled trials (RCTs) comparing tirzepatide to either placebo or active hypoglycemic drugs in individuals with T2D and obesity. Heterogeneity was assessed using the I2 value and Cochran's Q test, and a fixed effects model was employed to estimate the safety profile of tirzepatide. The safety outcomes of interest, including pancreatitis, the composite of gallbladder or biliary diseases, cholecystitis, and cholelithiasis and biliary diseases, were evaluated. (The composite of gallbladder or biliary diseases incorporated cholelithiasis, cholecystitis, other gallbladder disorders, and biliary diseases.).

Results

A total of nine trials with 9871 participants (6828 in the tirzepatide group and 3043 in the control group) that met the pre-specified criteria were included. When compared to all control groups consisting of basal insulin (glargine or degludec), selective GLP1-RA (dulaglutide or semaglutide once weekly), and placebo, an increased risk of pancreatitis was not found to be significantly associated with tirzepatide (RR 1.46, [95% CI] 0.59 to 3.61; I2 = 0.0%, p = 0.436). For gallbladder or biliary disease, the composite of gallbladder or biliary disease was significantly associated with tirzepatide compared with placebo or basal insulin (RR 1.97, [95% CI] 1.14 to 3.42; I2 = 0.0%, p = 0.558), but not with the risk of cholelithiasis, cholecystitis or biliary diseases.

Conclusion

Based on the currently available data, tirzepatide appears to be safe regarding the risk of pancreatitis. However, the increased risk of the composite outcome of gallbladder or biliary diseases observed in RCTs warrants further attention from physicians in clinical practice.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO, identifier CRD42023412400.

Treatment with the dual-incretin agonist DA-CH5 demonstrates potent therapeutic effect in a rat model of Wolfram Syndrome

Aim

Wolfram Syndrome (WS) is a rare condition caused by mutations in Wfs1, with a poor prognosis and no cure. Mono-agonists targeting the incretin glucagon-like-peptide 1 (GLP-1) have demonstrated disease-modifying potential in pre-clinical and clinical settings. Dual agonists that target GLP-1 and glucose-dependent insulinotropic polypeptide (GIP-1) are reportedly more efficacious; hence, we evaluated the therapeutic potential of dual incretin agonism in a loss-of-function rat model of WS.

Methods

Eight-month-old Wfs1 knock-out (KO) and wild-type control rats were continuously treated with either the dual agonist DA-CH5 or saline for four months. Glycemic profile, visual acuity and hearing sensitivity were longitudinally monitored pre-treatment, and then at 10.5 and 12 months. Pancreata and retina were harvested for immunohistological analysis.

Results

DA-CH5 therapy reversed glucose intolerance in KO rats and provided lasting anti-diabetogenic protection. Treatment also reversed intra-islet alterations, including reduced endocrine islet area and β-cell density, indicating its regenerative potential. Although no rescue effect was noted for hearing loss, visual acuity and retinal ganglion cell density were better preserved in DA-CH5-treated rats.

Conclusion

We present preclinical evidence for the pleiotropic therapeutic effects of long-term dual incretin agonist treatment; effects were seen despite treatment beginning after symptom-onset, indicating reversal of disease progression. Dual incretins represent a promising therapeutic avenue for WS patients.

Assessment of the incretin effect in healthy subjects: concordance between clamp and OGTT methods

The incretin effect describes the insulin response to nutrient ingestion that exceeds the response to glycemia per se. It is mediated by gastrointestinal factors and is necessary to maintain postprandial glucose homeostasis. The incretin effect results in a more than twofold increase of the insulin response to a meal in healthy people and two different techniques have been used in the past to measure its magnitude. Most studies employ an OGTT on 1 day, followed by a matching glucose infusion on a separate day. Another study design employs a hyperglycemic glucose clamp that is maintained after oral ingestion of glucose. Both protocols allow quantification of the incretin effect by comparing the insulin response to an identical glycemic stimulus. Here we performed a within-subject comparison of both techniques to quantify the incretin effect and suggest different calculation methods to interpret the results derived from the clamp experiment in a cohort of healthy young adults (n = 10, age 33 ± 4 yr). All subjects participated on four different study days: 1) OGTT, 2) isoglycemic glucose infusion (Iso-IV), 3) hyperglycemic clamp with oral glucose ingestion (clamp-OGTT), and 4) hyperglycemic clamp (clamp). With the classic OGTT/Iso-IV method, the insulin response to glucose ingestion increased more than twofold and was 60 ± 6% and 49 ± 5% for insulin and c-peptide. Different estimates of the incretin effect based on the clamp method ranged from 58% to 79% for insulin and 38% to 61% for c-peptide, both significantly higher than values derived from the OGTT/isoglycemic infusion method. However, when the effect of continuous hyperglycemia on insulin secretion was accounted for, using extrapolation from early time points of the clamp, good agreement was noted between the two methods. Based on these results, both techniques seem to be equally suited to measure the incretin effect and should be employed according to the scientific questions, experimental contingencies, and investigator experience.NEW & NOTEWORTHY This proof-of-concept study shows that the incretin effect can be reliably assessed by two different methods with similar quantitative results. A single-day hyperglycemic clamp with oral glucose ingestion allows the determination of the incretin effect with fewer study days and less day-to-day variability.

Why do some glucose-lowering agents improve non-alcoholic fatty liver disease whereas others do not? A narrative review in search of a unifying hypothesis

Non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2D) are metabolic disorders connected by common pathophysiological mechanisms. Since insulin resistance (IR) and metabolic alterations are common to both conditions, almost all glucose-lowering agents which improve IR have also been studied in patients with NAFLD. Some have shown great efficacy, others none. Thus, the mechanisms behind the efficacy of these drugs in improving hepatic steatosis, steatohepatitis, and eventually fibrosis remain controversial. Glycaemic control improves T2D, but probably has limited effects on NAFLD, as all glucose-lowering agents ameliorate glucose control but only a few improve NAFLD features. In contrast, drugs that either improve adipose tissue function, reduce lipid ingestion, or increase lipid oxidation are particularly effective in NAFLD. We therefore hypothesise that improved free fatty acid metabolism may be the unifying mechanism behind the efficacy of some glucose-lowering agents on NAFLD and may represent the key to NAFLD treatment.

The Cardiovascular Effect of Tirzepatide: A Glucagon-Like Peptide-1 and Glucose-Dependent Insulinotropic Polypeptide Dual Agonist

Glucagon-like peptide-1 (GLP-1) receptor agonists have been used extensively in the clinic and have an established safety profile in cardiovascular disease settings. For the treatment of peptide-secreting enteroendocrine cells, most research has focused on developing peptide multi-agonists as most of these cells are multihormonal. Among the various peptides secreted by enteroendocrine cells, the combination of GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) is an attractive strategy for treating type 2 diabetes mellitus (T2DM) because both of these hormones have glucose-lowering actions. Tirzepatide, a synthetic peptide composed of 39 amino acids, functions as a dual receptor agonist of both the GIP and GLP-1 receptors. This unique mechanism of action has earned tirzepatide the nickname "twincretin." Tirzepatide's dual agonist activity may be the mechanism by which tirzepatide significantly reduces glycated hemoglobin levels and body weight in patients with T2DM as observed in phase 3 clinical trials. Besides its glucose-lowering and anti-obesity effects, tirzepatide has been reported to have potential cardiovascular benefits. In this review, we discuss the cardiovascular effects of tirzepatide based on the available preclinical and clinical data.

Feeding enhances fibronectin adherence of quiescent lymphocytes through non-canonical insulin signalling

Nutritional availability during fasting and refeeding affects the temporal redistribution of lymphoid and myeloid immune cells among the circulating and tissue-resident pools. Conversely, nutritional imbalance and impaired glucose metabolism are associated with chronic inflammation, aberrant immunity and anomalous leukocyte trafficking. Despite being exposed to periodic alterations in blood insulin levels upon fasting and feeding, studies exploring the physiological effects of these hormonal changes on quiescent immune cell function and trafficking are scanty. Here, we report that oral glucose load in mice and healthy men enhances the adherence of circulating peripheral blood mononuclear cells (PBMCs) and lymphocytes to fibronectin. Adherence to fibronectin is also observed upon regular intake of breakfast following overnight fasting in healthy subjects. This glucose load-induced phenomenon is abrogated in streptozotocin-injected mice that lack insulin. Intra-vital microscopy in mice demonstrated that oral glucose feeding enhances the homing of PBMCs to injured blood vessels in vivo. Furthermore, employing flow cytometry, Western blotting and adhesion assays for PBMCs and Jurkat-T cells, we elucidate that insulin enhances fibronectin adherence of quiescent lymphocytes through non-canonical signalling involving insulin-like growth factor-1 receptor (IGF-1R) autophosphorylation, phospholipase C gamma-1 (PLCγ-1) Tyr783 phosphorylation and inside-out activation of β-integrins respectively. Our findings uncover the physiological relevance of post-prandial insulin spikes in regulating the adherence and trafficking of circulating quiescent T-cells through fibronectin-integrin interaction.

Incretins-Based Therapies and Their Cardiovascular Effects: New Game-Changers for the Management of Patients with Diabetes and Cardiovascular Disease

Atherosclerosis is the leading cause of death worldwide, especially in patients with type 2 diabetes mellitus (T2D). GLP-1 receptor agonists and DPP-4 inhibitors were demonstrated to play a markedly protective role for the cardiovascular system beyond their glycemic control. Several cardiovascular outcome trials (CVOT) reported the association between using these agents and a significant reduction in cardiovascular events in patients with T2D and a high cardiovascular risk profile. Moreover, recent evidence highlights a favorable benefit/risk profile in myocardial infarction and percutaneous coronary revascularization settings. These clinical effects result from their actions on multiple molecular mechanisms involving the immune system, platelets, and endothelial and vascular smooth muscle cells. This comprehensive review specifically concentrates on these cellular and molecular processes mediating the cardiovascular effects of incretins-like molecules, aiming to improve clinicians' knowledge and stimulate a more extensive use of these drugs in clinical practice as helpful cardiovascular preventive strategies.

Effect of onset of type 2 diabetes on risks of cardiovascular disease and heart failure among new Zealanders with impaired glucose tolerance over 25 years: tapered-matched landmark analysis

BACKGROUND

This study aimed to examine the association between the incident onset of T2DM and 5- and 10-year risks of CVD and HF in people with IGT identified in primary care in South and West Auckland, New Zealand (NZ) between 1994 and 2019.

METHODS

We compared CVD and HF risks in patients with IGT and with/without T2D newly diagnosed within the exposure window (1-5 years). Tapered matching and landmark analysis (to account for immortal bias) were used to control for potential effects of known confounders.

RESULTS

Among 26,794 patients enrolled with IGT, 845 had T2D newly diagnosed within 5 years from enrolment (landmark date) and 15,452 did not have T2D diagnosed. Patients progressing to T2D (vs. those not progressing) had a similar 5-year risk for CVD (hazard ratio 1.19; 95% CI 0.61-2.32) but significantly higher 10-year risk of CVD (2.45(1.40-4.29)), 5-year risk of HF (1.94(1.20-3.12)) and 10-year risk of HF (2.84(1.83-4.39). The association between the onset of T2D and risk of 10-year risk of CVD, 5-year and 10-year risk of HF was more likely among men, the socioeconomically deprived, those currently smoking, patients with higher metabolic measures and/or those with lower renal function. Patients of NZ European ethnicity had a lower 10-year risk of CVD.

CONCLUSIONS

The study suggests that the diagnosis of T2D mediates the risk of CVD and HF in people with IGT. The development of risk scores to identify and better manage individuals with IGT at high risk of T2D is warranted.

Pharmacogenetics of Glucagon-like-peptide-1 receptor in diabetes management

Type 2 diabetes mellitus (T2DM) is a complex metabolic disorder, primarily characterized by a decrease in insulin secretion and typically accompanied by insulin resistance. When untreated, T2DM is leading to an inevitable long-term complication. However, the novel treatment of T2DM like for example Glucagon-like Peptide-1 receptor agonists (GLP-1 RAs) give new perspectives for the patients to achieve a better glycemic control and additional metabolic improvements. Pharmacogenetics is a field in pharmacotherapy, which investigates the individual response to the medical treatment, according to polymorphic variations in the receptors of the drugs. This review aims to summarize current scientific evidence on the pharmacogenetics of the GLP-1 RA /liraglutide/ and the possible implementation in the treatment of T2D.

G Protein-Coupled Receptors and the Rise of Type 2 Diabetes in Children

The human genome counts hundreds of GPCRs specialized to sense thousands of different extracellular cues, including light, odorants and nutrients in addition to hormones. Primordial GPCRs were likely glucose transporters that became sensors to monitor the abundance of nutrients and direct the cell to switch from aerobic metabolism to fermentation. Human β cells express multiple GPCRs that contribute to regulate glucose homeostasis, cooperating with many others expressed by a variety of cell types and tissues. These GPCRs are intensely studied as pharmacological targets to treat type 2 diabetes in adults. The dramatic rise of type 2 diabetes incidence in pediatric age is likely correlated to the rapidly evolving lifestyle of children and adolescents of the new century. Current pharmacological treatments are based on therapies designed for adults, while youth and puberty are characterized by a different hormonal balance related to glucose metabolism. This review focuses on GPCRs functional traits that are relevant for β cells function, with an emphasis on aspects that could help to differentiate new treatments specifically addressed to young type 2 diabetes patients.

Rikkunshito increases appetite by enhancing gastrointestinal and incretin hormone levels in patients who underwent pylorus-preserving pancreaticoduodenectomy: A retrospective study

BACKGROUND

Rikkunshito (TJ-43) relieves gastrointestinal disturbance by increases in the levels of acylated ghrelin.

AIM

To investigate the effects of TJ-43 in patients undergoing pancreatic surgery.

METHODS

Forty-one patients undergoing pylorus-preserving pancreaticoduodenectomy (PpPD) were divided into two groups; patients took daily doses of TJ-43 after surgery or after postoperative day (POD) 21. The plasma levels of acylated and desacylated ghrelin, cholecystokinin (CCK), peptide YY (PYY), gastric inhibitory peptide (GIP), and active glucagon-like peptide (GLP)-1 were evaluated. Oral calorie intake was assessed at POD 21 in both groups. The primary endpoint of this study was the total food intake after PpPD.

RESULTS

The levels of acylated ghrelin were significantly greater in patients treated with TJ-43 than those in patients without TJ-43 administration at POD 21, and oral intake was significantly increased in patients treated with TJ-43. The CCK and PYY levels were significantly greater in patients treated with TJ-43 than those in patients without TJ-43 treatment. Furthermore, the GIP and active GLP-1 levels increased and values at POD 21 were significantly greater in patients treated with TJ-43 than those in patients without TJ-43 administration. Insulin secretion tended to increase in patients treated with TJ-43.

CONCLUSION

TJ-43 may have advantages for oral food intake in patients in the early phase after pancreatic surgery. Further investigation is needed to clarify the effects of TJ-43 on incretin hormones.