Glucagon-like peptide-1 (GLP-1) and glucose metabolism in human myocytes

Role of Incretin Mimetics in Cardiovascular Outcomes and Other Classical Cardiovascular Risk Factors beyond Obesity and Diabetes Mellitus in Nondiabetic Adults with Obesity: a Meta-analysis of Randomized Controlled Trials

BACKGROUND

Emerging data on cardiovascular outcomes, specifically major adverse cardiovascular events (MACE), are being reported from various trials involving incretin mimetics, such as glucagon-like peptide-1 receptor agonists (GLP-1 RA) and glucose-dependent insulinotropic polypeptide (GIP), especially among patients with obesity and diabetes. Our aim was to evaluate this matter, while also involving various traditional cardiovascular risk factors [e.g., several body weight (BW) parameters, blood pressure (BP), lipid profile].

METHODS

A search of PubMed, Europe PMC, ScienceDirect, Cochrane, and ClinicalTrials.gov up to September 2024 was performed to identify GLP-1 RA and GIP trials in MACE risk reduction as a primary endpoint. Our secondary endpoints included a reduction in BW, waist circumference (WC), body mass index (BMI), BP changes, and lipid modifying effects, while also yielding safety concerns surrounding the use of these pharmaceutical agents. Mean differences (MD) and risk ratios (RR) were summarized using random-effects model.

RESULTS

A total of 11 eligible randomized controlled trials (RCTs) comprising 8 GLP-1 RA trials and 3 dual GLP-1 RA/GIP (tirzepatide) trials were included. Compared with control groups, GLP-1 RA significantly reduced the MACE risk by 32% [RR 0.68 (95% CI 0.53-0.87); P = 0.002; I2 = 73%, P-heterogeneity < 0.001] and 59% for tirzepatide [RR 0.41 (95% CI 0.18-0.92); P = 0.03; I2 = 0%, P-heterogeneity = 0.96]. Incretin mimetics also substantially reduced BW, BP, and improved lipid panel measures. However, there was an increased risk of adverse events, specifically gastrointestinal disorders within the incretin mimetics subset.

CONCLUSIONS

Incretin mimetics have shown promise in reducing MACE risk while also enhancing cardiovascular risk factors, including blood pressure and lipid profile, in adults with obesity without diabetes.

The impact of GLP-1 signalling on the energy metabolism of pancreatic islet β-cells and extrapancreatic tissues

Glucagon-like peptide-1 signalling impacts glucose homeostasis and appetite thereby indirectly affecting substrate availability at the whole-body level. The incretin canonically produces an insulinotropic effect, thereby lowering blood glucose levels by promoting the uptake and inhibiting the production of the sugar by peripheral tissues. Likewise, GLP-1 signalling within the central nervous system reduces the appetite and food intake, whereas its gastric effect delays the absorption of nutrients, thus improving glycaemic control and reducing the risk of postprandial hyperglycaemia. We review the molecular aspects of the GLP-1 signalling, focusing on its impact on intracellular energy metabolism. Whilst the incretin exerts its effects predominantly via a Gs receptor, which decodes the incretin signal into the elevation of intracellular cAMP levels, the downstream signalling cascades within the cell, acting on fast and slow timescales, resulting in an enhancement or an attenuation of glucose catabolism, respectively.

Gut hormone analogues and skeletal health in diabetes and obesity: Evidence from preclinical models

Diabetes mellitus and obesity are rapidly growing worldwide. Aside from metabolic disturbances, these two disorders also affect bone with a higher prevalence of bone fractures. In the last decade, a growing body of evidence suggested that several gut hormones, including ghrelin, gastrin, glucose-dependent insulinotropic polypeptide (GIP), glucagon, and glucagon-like peptide-1 and 2 (GLP-1 and GLP-2, respectively) may affect bone physiology. Several gut hormone analogues have been developed for the treatment of type 2 diabetes and obesity, and could represent a new alternative in the therapeutic arsenal against bone fragility. In the present review, a summary of the physiological roles of these gut hormones and their analogues is presented at the cellular level but also in several preclinical models of bone fragility disorders including type 2 diabetes mellitus, especially on bone mineral density, microarchitecture and bone material properties. The present review also summarizes the impact of GLP-1 receptor agonists approved for the treatment of type 2 diabetes mellitus and the more recent dual or triple analogue on bone physiology and strength.

The Regulation of Metabolic Homeostasis by Incretins and the Metabolic Hormones Produced by Pancreatic Islets

In healthy humans, the complex biochemical interplay between organs maintains metabolic homeostasis and pathological alterations in this process result in impaired metabolic homeostasis, causing metabolic diseases such as diabetes and obesity, which are major global healthcare burdens. The great advancements made during the last century in understanding both metabolic disease phenotypes and the regulation of metabolic homeostasis in healthy individuals have yielded new therapeutic options for diseases like type 2 diabetes (T2D). However, it is unlikely that highly desirable more efficacious treatments will be developed for metabolic disorders until the complex systemic regulation of metabolic homeostasis becomes more intricately understood. Hormones produced by pancreatic islet beta-cells (insulin) and alpha-cells (glucagon) are pivotal for maintaining metabolic homeostasis; the activity of insulin and glucagon are reciprocally correlated to achieve strict control of glucose levels (normoglycaemia). Metabolic hormones produced by other pancreatic islet cells and incretins produced by the gut are also crucial for maintaining metabolic homeostasis. Recent studies highlighted the incomplete understanding of metabolic hormonal synergism and, therefore, further elucidation of this will likely lead to more efficacious treatments for diseases such as T2D. The objective of this review is to summarise the systemic actions of the incretins and the metabolic hormones produced by the pancreatic islets and their interactions with their respective receptors.

Effect of feeding sodium butyrate to beef female cows during pre- and post-partum period on concentrations of glucagon-like peptides in plasma and colostrum

The objective of this study was to evaluate the effect of feeding beef cows with sodium butyrate during the late pregnancy and early post-partum periods on concentrations of glucagon-like peptide (GLP)-1 and 2 in plasma, colostrum, and transition milk. Twelve Japanese Black female cows were fed concentrate feed without (CON; n = 6) or with (BUTY; n = 6) sodium butyrate supplementation at 1.1% of dietary dry matter from -60 d relative to the expected parturition date to 4 d after parturition. Plasma total cholesterol concentration was higher for the BUTY than for the CON (P = 0.04). In addition, plasma GLP-1 concentration was higher for the BUTY than for the CON at 3 d after calving (P < 0.05). This study showed for the first time that GLP-1 is present in the colostrum of Japanese Black cows at higher concentrations as compared to in plasma (P < 0.01). On the other hand, no treatment effect was observed for concentrations of metabolite and hormone in colostrum and transition milk. In summary, feeding beef cows with sodium butyrate during the late gestation and early post-partum period likely increases plasma GLP-1 concentrations post-partum without affecting the components of colostrum and transition milk.

GLP‑1 receptor agonist protects palmitate-induced insulin resistance in skeletal muscle cells by up-regulating sestrin2 to promote autophagy

In this study, we aimed to determine whether liraglutide could effectively reduce insulin resistance (IR) by regulating Sestrin2 (SESN2) expression in L6 rat skeletal muscle cells by examining its interactions with SESN2, autophagy, and IR. L6 cells were incubated with liraglutide (10-1000 nM) in the presence of palmitate (PA; 0.6 mM), and cell viability was detected using the cell counting kit-8 (CCK-8) assay. IR-related and autophagy-related proteins were detected using western blotting, and IR and autophagy-related genes were analyzed using quantitative real-time polymerase chain reaction. Silencing SESN2 was used to inhibit the activities of SESN2. A reduction in insulin-stimulated glucose uptake was observed in PA-treated L6 cells, confirming IR. Meanwhile, PA decreased the levels of GLUT4 and phosphorylation of Akt and affected SESN2 expression. Further investigation revealed that autophagic activity decreased following PA treatment, but that liraglutide reversed this PA-induced reduction in autophagic activity. Additionally, silencing SESN2 inhibited the ability of liraglutide to up-regulate the expression of IR-related proteins and activate autophagy signals. In summary, the data showed that liraglutide improved PA-induced IR in L6 myotubes by increasing autophagy mediated by SESN2.

Effects of GLP-1 Infusion Upon Whole-body Glucose Uptake and Skeletal Muscle Perfusion During Fed-state in Older Men

INTRODUCTION

Ageing skeletal muscles become both insulin resistant and atrophic. The hormone glucagon-like peptide 1 (GLP-1) facilitates postprandial glucose uptake as well as augmenting muscle perfusion, independent of insulin action. We thus hypothesized exogenous GLP-1 infusions would enhance muscle perfusion and positively affect glucose metabolism during fed-state clamps in older people.

METHODS

Eight men (71 ± 1 years) were studied in a randomized crossover trial. Basal blood samples were taken before postprandial (fed-state) insulin and glucose clamps, accompanied by amino acid infusions, for 3 hours. Reflecting this, following insertions of peripheral and femoral vessels cannulae and baseline measurements, peripheral IV infusions of octreotide, insulin (Actrapid), 20% glucose, and mixed amino acids; Vamin 14-EF with or without a femoral arterial GLP-1 infusion were started. GLP-1, insulin, and C-peptide were measured by ELISA. Muscle microvascular blood flow was assessed via contrast enhanced ultrasound. Whole-body glucose handling was assayed by assessing glucose infusion rate parameters.

RESULTS

Skeletal muscle microvascular blood flow significantly increased in response to GLP-1 vs feeding alone (5.0 ± 2.1 vs 1.9 ± 0.7 fold-change from basal, respectively; P = 0.008), while also increasing whole-body glucose uptake (area under the curve 16.9 ± 1.7 vs 11.4 ± 1.8 mg/kg-1/180 minutes-1, P = 0.02 ± GLP, respectively).

CONCLUSIONS

The beneficial effects of GLP-1 on whole-body glycemic control are evident with insulin clamped at fed-state levels. GLP-1 further enhances the effects of insulin on whole-body glucose uptake in older men, underlining its role as a therapeutic target. The effects of GLP-1 in enhancing microvascular flow likely also affects other glucose-regulatory organs, reflected by greater whole-body glucose uptake.

Liraglutide chronic treatment prevents development of tolerance to antiseizure effects of diazepam in genetically epilepsy prone rats

Glucagon-like peptide-1 (GLP-1) is a hormone that can regulate several neuronal functions. The modulation of GLP-1 receptors emerged as a potential target to treat several neurological diseases, such as epilepsy. Here, we studied the effects of acute and chronic treatment with liraglutide (LIRA), in genetically epilepsy prone rats (GEPR-9s). We have also investigated the possible development of tolerance to antiseizure effects of diazepam, and how LIRA could affect this phenomenon over the same period of treatment. The present data indicate that an acute treatment with LIRA did not diminish the severity score of audiogenic seizures (AGS) in GEPR-9s. By contrast, a chronic treatment with LIRA has shown only a modest antiseizure effect that was maintained until the end of treatment, in GEPR-9s. Not surprisingly, acute administration of diazepam reduced, in a dose dependent manner, the severity of the AGS in GEPR-9s. However, when diazepam was chronically administered, an evident development of tolerance to its antiseizure effects was detected. Interestingly, following an add-on treatment with LIRA, a reduced development of tolerance and an enhanced diazepam antiseizure effect was observed in GEPR-9s. Overall, an add-on therapy with LIRA demonstrate benefits superior to single antiseizure medications and could be utilized to treat epilepsy as well as associated issues. Therefore, the potential use of GLP1 analogs for the treatment of epilepsy in combination with existing antiseizure medications could thus add a new and long-awaited dimension to its management.

Effect of glucagon-like peptide-1 receptor agonists on body weight in adults with obesity without diabetes mellitus-a systematic review and meta-analysis of randomized control trials

Clinical trials have investigated the weight loss effect of glucagon-like peptide-1 receptor agonists (GLP-1 RA) in adults with obesity without diabetes mellitus, but results for weight loss efficacy were varied. We aimed to provide an up-to-date systematic review and meta-analysis for overall weight loss effect of GLP-1 RA in adults with obesity and overweight without diabetes mellitus. We retrieved eligible randomized control trials that assessed the weight loss effect of GLP-1 RA in adults (≥18 years old) without type 1/type 2 diabetes up to September 30, 2021, using Pubmed and Embase. Of 36 clinical trials assessed for eligibility, 12 trials were included, with a combined total of 11,459 participants. Compared with control groups, a more significant weight loss was seen in GLP-1 RA groups with an overall mean difference of -7.1 kg (95% CI -9.2 to -5.0) (I²  = 99%). The overall analysis results showed that GLP-1 RA improved glycemic control without increasing the risk of hypoglycemic events. Better control of blood pressure and plasma levels of LDL, HDL, and triglycerides was seen with GLP-1 RA treatment. Subgroup analysis showed greater treatment effect of semaglutide than liraglutide. Vomiting, nausea, dyspepsia, diarrhea, constipation, and abdominal pain were GLP-1 RA-associated common adverse effects.

Storage and Utilization of Glycogen by Mouse Liver during Adaptation to Nutritional Changes Are GLP-1 and PASK Dependent

Glucagon-like peptide 1 (GLP-1) and PAS kinase (PASK) control glucose and energy homeostasis according to nutritional status. Thus, both glucose availability and GLP-1 lead to hepatic glycogen synthesis or degradation. We used a murine model to discover whether PASK mediates the effect of exendin-4 (GLP-1 analogue) in the adaptation of hepatic glycogen metabolism to nutritional status. The results indicate that both exendin-4 and fasting block the Pask expression, and PASK deficiency disrupts the physiological levels of blood GLP1 and the expression of hepatic GLP1 receptors after fasting. Under a non-fasted state, exendin-4 treatment blocks AKT activation, whereby Glucokinase and Sterol Regulatory Element-Binding Protein-1c (Srebp1c) expressions were inhibited. Furthermore, the expression of certain lipogenic genes was impaired, while increasing Glucose Transporter 2 (GLUT2) and Glycogen Synthase (GYS). Moreover, exendin-4 treatment under fasted conditions avoided Glucose 6-Phosphatase (G6pase) expression, while maintaining high GYS and its activation state. These results lead to an abnormal glycogen accumulation in the liver under fasting, both in PASK-deficient mice and in exendin-4 treated wild-type mice. In short, exendin-4 and PASK both regulate glucose transport and glycogen storage, and some of the exendin-4 effects could therefore be due to the blocking of the Pask expression.

Atypical Antipsychotics and Metabolic Syndrome: From Molecular Mechanisms to Clinical Differences

Atypical antipsychotics (AAPs) are commonly prescribed medications to treat schizophrenia, bipolar disorders and other psychotic disorders. However, they might cause metabolic syndrome (MetS) in terms of weight gain, dyslipidemia, type 2 diabetes (T2D), and high blood pressure, which are responsible for reduced life expectancy and poor adherence. Importantly, there is clear evidence that early metabolic disturbances can precede weight gain, even if the latter still remains the hallmark of AAPs use. In fact, AAPs interfere profoundly with glucose and lipid homeostasis acting mostly on hypothalamus, liver, pancreatic β-cells, adipose tissue, and skeletal muscle. Their actions on hypothalamic centers via dopamine, serotonin, acetylcholine, and histamine receptors affect neuropeptides and 5'AMP-activated protein kinase (AMPK) activity, thus producing a supraphysiological sympathetic outflow augmenting levels of glucagon and hepatic glucose production. In addition, altered insulin secretion, dyslipidemia, fat deposition in the liver and adipose tissues, and insulin resistance become aggravating factors for MetS. In clinical practice, among AAPs, olanzapine and clozapine are associated with the highest risk of MetS, whereas quetiapine, risperidone, asenapine and amisulpride cause moderate alterations. The new AAPs such as ziprasidone, lurasidone and the partial agonist aripiprazole seem more tolerable on the metabolic profile. However, these aspects must be considered together with the differences among AAPs in terms of their efficacy, where clozapine still remains the most effective. Intriguingly, there seems to be a correlation between AAP's higher clinical efficacy and increase risk of metabolic alterations. Finally, a multidisciplinary approach combining psychoeducation and therapeutic drug monitoring (TDM) is proposed as a first-line strategy to avoid the MetS. In addition, pharmacological treatments are discussed as well.

Effects of feeding a moderate- or high-energy close-up diet to cows on response of newborn calves to milk replacer feeding and intravenous injection of glucagon-like peptide 1

In this study, we investigated the effects of feeding a moderate- or high-energy close-up diet to close-up cows on response of newborn calves to intravenously (i.v.) injected glucagon-like peptide 1 (GLP-1). Newborn Holstein heifer calves (n = 37) from cows fed with a moderate-energy [M, 1.54 Mcal/kg of dry matter (DM) NEl; 14% starch; n = 17] or high-energy (H, 1.63 Mcal/kg of DM NEl; 26% starch; n = 20) diet in the last 28 d prepartum were assigned to one of two treatment groups, which were i.v. injected with saline (MC and HC, n = 9 and 10, respectively) or GLP-1 solution at 1.0 μg/kg BW (MG and HG, n = 8 and 10, respectively) immediately after milk replacer (MR; 26% CP, 16% fat) feeding. Blood samples were obtained through a jugular vein catheter at -10, 0, 10, 20, 30, 40, 50, 60, 90, and 120 min relative to MR feeding at 2, 10, and 20 d after birth, and plasma glucose, insulin, and GLP-1 concentrations were measured. Plasma GLP-1 concentration tended to increase starting from 30 min after MR feeding in the MC relative to the HC group at 10 (0.77 ng/mL vs 0.69 ng/mL for MC and HC, respectively; P = 0.10) and 20 d after birth (0.47 ng/mL vs 0.35 ng/mL for MC and HC, respectively; P = 0.07). Plasma glucose and insulin concentrations after MR feeding did not differ between MC and HC groups at 2 and 20 d after birth but were higher (P < 0.05) in MC (158 mg/dL and 3.64 ng/mL for glucose and insulin, respectively) than in HC (143 mg/dL and 2.46 ng/mL for glucose and insulin, respectively) calves at 10 d after birth. The elevation in plasma glucose concentration after MR feeding was suppressed by direct glucose-lowering action of i.v. injected GLP-1 at 2, 10, and 20 d after birth in M and H calves; this direct glucose-lowering action by GLP-1 was greater (P < 0.05) for H than for M calves at 20 d after birth. These results indicate that feeding a high-energy close-up diet to cows affects glucose status in their female offspring via suppression of postprandial plasma concentrations of GLP-1 and insulin as well as the alteration in the glucose-lowering action of GLP-1 after feeding depending on the day after birth.

GLP-1 Analogues as a Complementary Therapy in Patients after Metabolic Surgery: a Systematic Review and Qualitative Synthesis

The evidence is strong that bariatric surgery is superior to medical treatment in terms of weight loss and comorbidities in patients with severe obesity. However, a considerable part of patients presents with unsatisfactory response in the long term. It remains unclear whether postoperative administration of glucagon-like peptide-1 analogues can promote additional benefits. Therefore, a systematic review of the current literature on the management of postoperative GLP-1 analogue usage after metabolic surgery was performed. From 4663 identified articles, 6 met the inclusion criteria, but only one was a randomized controlled trial. The papers reviewed revealed that GLP-1 analogues may have beneficial effects on additional weight loss and T2D remission postoperatively. Thus, the use of GLP-1 analogues in addition to surgery promises good results concerning weight loss and improvements of comorbidities and can be used in patients with unsatisfactory results after bariatric surgery.

Recent advances in understanding the role of glucagon-like peptide 1

The discovery that glucagon-like peptide 1 (GLP-1) mediates a significant proportion of the incretin effect during the postprandial period and the subsequent observation that GLP-1 bioactivity is retained in type 2 diabetes (T2D) led to new therapeutic strategies being developed for T2D treatment based on GLP-1 action. Although owing to its short half-life exogenous GLP-1 has no use therapeutically, GLP-1 mimetics, which have a much longer half-life than native GLP-1, have proven to be effective for T2D treatment since they prolong the incretin effect in patients. These GLP-1 mimetics are a desirable therapeutic option for T2D since they do not provoke hypoglycaemia or weight gain and have simple modes of administration and monitoring. Additionally, over more recent years, GLP-1 action has been found to mediate systemic physiological beneficial effects and this has high clinical relevance due to the post-diagnosis complications of T2D. Indeed, recent studies have found that certain GLP-1 analogue therapies improve the cardiovascular outcomes for people with diabetes. Furthermore, GLP-1-based therapies may enable new therapeutic strategies for diseases that can also arise independently of the clinical manifestation of T2D, such as dementia and Parkinson's disease. GLP-1 functions by binding to its receptor (GLP-1R), which expresses mainly in pancreatic islet beta cells. A better understanding of the mechanisms and signalling pathways by which acute and chronic GLP-1R activation alleviates disease phenotypes and induces desirable physiological responses during healthy conditions will likely lead to the development of new therapeutic GLP-1 mimetic-based therapies, which improve prognosis to a greater extent than current therapies for an array of diseases.

Phytochemicals in Garlic Extract Inhibit Therapeutic Enzyme DPP-4 and Induce Skeletal Muscle Cell Proliferation: A Possible Mechanism of Action to Benefit the Treatment of Diabetes Mellitus

Diabetes mellitus is a severe health problem in Mexico, and its prevalence is increasing exponentially every year. Recently, DPP-4 (dipeptidyl peptidase-4) inhibitors have become attractive oral anti-hyperglycemic agents to reduce the pathology of diabetes. Gliptin’s family, such as sitagliptin, vildagliptin, and alogliptin, are in clinical use to treat diabetes mellitus but possess side effects. Therefore, there is a specific need to look for new therapeutic scaffolds (biomolecules). Garlic bulb is widely used as a traditional remedy for the treatment of diabetes. The garlic extracts are scientifically proven to control glucose levels in patients with diabetes, despite the unknown mechanism of action. The aim of the study is to investigate the antidiabetic effects of ultrasonication assisted garlic bulb extract. To achieve this, in-vitro assays such as DPP-4 inhibitory and antioxidant activities were investigated. Further, functional group analysis using FTIR and identification of phytochemicals using mass spectrometry analysis was performed. The results showed that 70.9 µg/mL of garlic bulb extract inhibited 50% DPP-4 activity. On top of that, the garlic extract exhibited a 20% scavenging activity, equivalent to 10 µg/mL of ascorbic acid. Molecular docking simulations on identified phytochemicals using mass spectrometry revealed their potential binding at the DPP-4 druggable region, and therefore the possible DPP-4 inhibition mechanism. These results suggest that prepared garlic extract contains phytochemicals that inhibit DPP-4 and have antioxidant activity. Also, the prepared extract induces skeletal muscle cell proliferation that demonstrates the antidiabetic effect and its possible mechanism of action.

Perioperative Infusion of Glucagon-Like Peptide-1 Prevents Insulin Resistance After Surgical Trauma in Female Pigs

Insulin resistance is an independent negative predictor of outcome after elective surgery and increases mortality among surgical patients in intensive care. The incretin hormone glucagon-like peptide-1 (GLP-1) potentiates glucose-induced insulin release from the pancreas but may also increase insulin sensitivity in skeletal muscle and directly suppress hepatic glucose release. Here, we investigated whether a perioperative infusion of GLP-1 could counteract the development of insulin resistance after surgery. Pigs were randomly assigned to three groups; surgery/control, surgery/GLP-1, and sham/GLP-1. Both surgery groups underwent major abdominal surgery. Whole-body glucose disposal (WGD) and endogenous glucose release (EGR) were assessed preoperatively and postoperatively using D-[6,6-2H2]-glucose infusion in combination with hyperinsulinemic euglycemic step-clamping. In the surgery/control group, peripheral insulin sensitivity (i.e., WGD) was reduced by 44% relative to preoperative conditions, whereas the corresponding decline was only 9% for surgery/GLP-1 (P < 0.05). Hepatic insulin sensitivity (i.e., EGR) remained unchanged in the surgery/control group but was enhanced after GLP-1 infusion in both surgery and sham animals (40% and 104%, respectively, both P < 0.05). Intraoperative plasma glucose increased in surgery/control (∼20%) but remained unchanged in both groups receiving GLP-1 (P < 0.05). GLP-1 diminished an increase in postoperative glucagon levels but did not affect skeletal muscle glycogen or insulin signaling proteins after surgery. We show that GLP-1 improves intraoperative glycemic control, diminishes peripheral insulin resistance after surgery, and suppresses EGR. This study supports the use of GLP-1 to prevent development of postoperative insulin resistance.

Sitagliptin improves diastolic cardiac function but not cardiorespiratory fitness in adults with type 2 diabetes

BACKGROUND

People with type 2 diabetes mellitus (T2D) have preclinical cardiac and vascular dysfunction associated with low cardiorespiratory fitness (CRF). This is especially concerning because CRF is a powerful predictor of cardiovascular mortality, a primary issue in T2D management. Glucagon-like pepetide-1 (GLP-1) augments cardiovascular function and our previous data in rodents demonstrate that potentiating the GLP-1 signal with a dipeptidyl peptidase-4 (DPP4) inhibitor augments CRF. Lacking are pharmacological treatments which can target T2D-specific physiological barriers to exercise to potentially permit adaptations necessary to improve CRF and thereby health outcomes in people with T2D. We therefore hypothesized that administration of a DPP4-inhibitor (sitagliptin) would improve CRF in adults with T2D.

METHODS AND RESULTS

Thirty-eight participants (64 ± 1 years; mean ± SE) with T2D were randomized in a double-blinded study to receive 100 mg/day sitagliptin, 2 mg/day glimepiride, or placebo for 3 months after baseline measurements. Fasting glucose decreased with both glimepiride and sitagliptin compared with placebo (P = 0.002). CRF did not change in any group (Placebo: Pre: 15.4 ± 0.9 vs. Post: 16.1 ± 1.1 ml/kg/min vs. Glimepiride: 18.5 ± 1.0 vs. 17.7 ± 1.2 ml/kg/min vs. Sitagliptin: 19.1 ± 1.2 vs. 18.3 ± 1.1 ml/kg/min; P = 0.3). Sitagliptin improved measures of cardiac diastolic function, however, measures of vascular function did not change with any treatment.

CONCLUSIONS

Three months of sitagliptin improved diastolic cardiac function, however, CRF did not change. These data suggest that targeting the physiological contributors to CRF with sitagliptin alone is not an adequate strategy to improve CRF in people with T2D.

CLINICAL TRIALS REGISTRATION

www.clinicaltrials.gov NCT01951339.

Effect of extended colostrum feeding on plasma glucagon-like peptide-1 concentration in newborn calves

Glucagon-like peptide-1 (GLP-1) plays a role in the regulation of glucose homeostasis via the stimulation of insulin secretion. The objective of this study was to evaluate the effect of extended colostrum feeding on plasma concentration of GLP-1. Holstein bull calves (n = 27) were fed pooled colostrum at 7.5% of birth body weight at 2 h after birth and then fed mature milk (M), a 50:50 mixture of pooled colostrum and milk (CM), or pooled colostrum (C; n = 9 for each treatment) at 5% of birth body weight at 12 h after birth and every 12 h thereafter until 72 h after birth. Blood samples were obtained before (1 and 2 h after birth) and after (until 72 h after birth; 42 time points) the first colostrum feeding, and plasma concentrations of glucose, insulin, and GLP-1 were measured. Data were analyzed by ANOVA of JMP 13 (SAS Institute Inc., Cary, NC) with treatment, time, and treatment × time interaction as fixed effects. Treatment × time interaction was observed for plasma insulin and glucose concentrations, which were mainly the result of lower concentrations from 1 to 2 d after birth for C compared with M. Conversely, on d 3 after birth, the difference between treatments was not observed for insulin and glucose. For the entire experimental period, plasma GLP-1 concentration was higher for C (2.25 ng/mL) compared with M (1.41 ng/mL) and tended to be higher compared with CM (1.58 ng/mL). A treatment × time interaction was observed for GLP-1, but unlike glucose and insulin, this was mainly the result of higher concentrations from 54 to 72 h after birth (on d 3 after birth) for C compared with M or CM. Postprandial plasma concentration of glucose was not correlated with that of GLP-1 but was positively correlated with that of insulin for the 4-h period after feeding on d 1 (r = 0.30) and d 3 after birth (r = 0.33). Postprandial plasma concentration of GLP-1 was positively correlated with that of insulin for the 4-h period after feeding on d 3 after birth (r = 0.20). These results indicate that extended colostrum feeding may increase plasma GLP-1 concentrations, especially 3 d after birth, but further study is necessary to determine the effect on plasma insulin and glucose concentrations.

Exenatide once-weekly improves metabolic parameters, endothelial dysfunction and carotid intima-media thickness in patients with type-2 diabetes: An 8-month prospective study

AIM

To evaluate the effect of exenatide long acting release (LAR) on carotid intima-media thickness (IMT) and endothelial function in patients with type 2 diabetes mellitus.

METHODS

Sixty subjects with type 2 diabetes mellitus were treated with exenatide LAR as add-on to stable doses of metformin for 8 months in an open label study. Anthropometric variables, lipid profile and glycemic parameters were assessed by routine analysis. Carotid IMT by Doppler ultrasound and endothelial function by flow-mediated dilation of the brachial artery were also assessed.

RESULTS

Exenatide significantly improved fasting glycaemia (from 8.8 ± 2.8 to 7.3 ± 2.2 mmol/L, p < 0.0001), HbA1c (from 8.0 ± 0.4 to 6.9 ± 1.1%, p < 0.0001), body mass index (from 33 ± 9 to 31 ± 6 kg/m², p = 0.0348) and waist circumference (from 109 ± 13 to 106 ± 13 cm, p = 0.0105). There was a significant improvement of the lipid profile, except in triglyceride level where no changes were observed. Carotid IMT and flow-mediated dilation were also improved (from 0.98 ± 0.14 to 0.87 ± 0.15 mm and from 5.8 ± 1.3 to 6.8 ± 1.7%, respectively; p < 0.0001 for both).

CONCLUSIONS

Treatment with exenatide LAR led to improved cardio-metabolic parameters, including carotid IMT and flow-mediated dilation, independently of glucometabolic control. These results may help to explain, at least in part, the cardiovascular safety of exenatide LAR, as recently reported in cardiovascular outcome trials.

Diabetes pharmacotherapy and effects on the musculoskeletal system

Persons with type 1 or type 2 diabetes have a significantly higher fracture risk than age-matched persons without diabetes, attributed to disease-specific deficits in the microarchitecture and material properties of bone tissue. Therefore, independent effects of diabetes drugs on skeletal integrity are vitally important. Studies of incretin-based therapies have shown divergent effects of different agents on fracture risk, including detrimental, beneficial, and neutral effects. The sulfonylurea class of drugs, owing to its hypoglycemic potential, is thought to amplify the risk of fall-related fractures, particularly in the elderly. Other agents such as the biguanides may, in fact, be osteo-anabolic. In contrast, despite similarly expected anabolic properties of insulin, data suggests that insulin pharmacotherapy itself, particularly in type 2 diabetes, may be a risk factor for fracture, negatively associated with determinants of bone quality and bone strength. Finally, sodium-dependent glucose co-transporter 2 inhibitors have been associated with an increased risk of atypical fractures in select populations, and possibly with an increase in lower extremity amputation with specific SGLT2I drugs. The role of skeletal muscle, as a potential mediator and determinant of bone quality, is also a relevant area of exploration. Currently, data regarding the impact of glucose lowering medications on diabetes-related muscle atrophy is more limited, although preclinical studies suggest that various hypoglycemic agents may have either aggravating (sulfonylureas, glinides) or repairing (thiazolidinediones, biguanides, incretins) effects on skeletal muscle atrophy, thereby influencing bone quality. Hence, the therapeutic efficacy of each hypoglycemic agent must also be evaluated in light of its impact, alone or in combination, on musculoskeletal health, when determining an individualized treatment approach. Moreover, the effect of newer medications (potentially seeking expanded clinical indication into the pediatric age range) on the growing skeleton is largely unknown. Herein, we review the available literature regarding effects of diabetes pharmacotherapy, by drug class and/or by clinical indication, on the musculoskeletal health of persons with diabetes.

Pleiotropic Effects of GLP-1 and Analogs on Cell Signaling, Metabolism, and Function

The incretin hormone Glucagon-Like Peptide-1 (GLP-1) is best known for its "incretin effect" in restoring glucose homeostasis in diabetics, however, it is now apparent that it has a broader range of physiological effects in the body. Both in vitro and in vivo studies have demonstrated that GLP-1 mimetics alleviate endoplasmic reticulum stress, regulate autophagy, promote metabolic reprogramming, stimulate anti-inflammatory signaling, alter gene expression, and influence neuroprotective pathways. A substantial body of evidence has accumulated with respect to how GLP-1 and its analogs act to restore and maintain normal cellular functions. These findings have prompted several clinical trials which have reported GLP-1 analogs improve cardiac function, restore lung function and reduce mortality in patients with obstructive lung disease, influence blood pressure and lipid storage, and even prevent synaptic loss and neurodegeneration. Mechanistically, GLP-1 elicits its effects via acute elevation in cAMP levels, and subsequent protein kinase(s) activation, pathways well-defined in pancreatic β-cells which stimulate insulin secretion in conjunction with elevated Ca2+ and ATP. More recently, new studies have shed light on additional downstream pathways stimulated by chronic GLP-1 exposure, findings which have direct relevance to our understanding of the potential therapeutic effects of longer lasting analogs recently developed for clinical use. In this review, we provide a comprehensive description of the diverse roles for GLP-1 across multiple tissues, describe downstream pathways stimulated by acute and chronic exposure, and discuss novel pleiotropic applications of GLP-1 mimetics in the treatment of human disease.

The effect of glucagon-like peptide 1 and glucagon-like peptide 1 receptor agonists on energy expenditure: A systematic review and meta-analysis

AIM

We reviewed clinical trials addressing the effect of glucacon-like peptide 1 (GLP-1) or GLP-1 receptor agonists (GLP-1RA) on energy expenditure (EE) in adults.

MATERIALS AND METHODS

PubMed, Science Direct and Web of Science were searched for clinical trials investigating the effect of GLP-1 or GLP-1RA on EE in adults.

RESULTS

Ten trials (93 participants) assessed the effect of GLP-1 administration over 1 to 48 h and found no change in resting EE (REE). Two out of three trials (62 participants) reported a significant decrease in diet-induced thermogenesis (DIT) following GLP-1 administration. Ten trials with exenatide (10 μg bid, for 10-52 weeks) or liraglutide (0.6, 1.2, 1.8 or 3 mg, for 3 days-52 weeks), with a total of 282 participants, indicated a neutral effect of these GLP-1RA on REE, DIT or physical activity-induced EE. Importantly, the longest trial with GLP-1RA reported a significant increase in REE in response to treatment with both exenatide or liraglutide and most trials reported that GLP-1RA-induced weight loss was not accompanied by decreased REE.

CONCLUSIONS

This review indicates that GLP-1 has no short-term effect on REE but may decrease DIT. The GLP-1RA exenatide and liraglutide have a neutral effect on REE, although it is not possible to rule out an increase in REE following prolonged treatment.

Glucagon-like peptide-1 receptor antagonism impairs basal exercise capacity and vascular adaptation to aerobic exercise training in rats

Cardiorespiratory fitness (CRF) inversely predicts cardiovascular (CV) mortality and CRF is impaired in people with type 2 diabetes (T2D). Aerobic exercise training (ET) improves CRF and is associated with decreased risk of premature death in healthy and diseased populations. Understanding the mechanisms contributing to ET adaptation may identify targets for reducing CV mortality of relevance to people with T2D. The antihyperglycemic hormone glucagon-like peptide-1 (GLP-1) influences many of the same pathways as exercise and may contribute to CV adaptation to ET. We hypothesized that GLP-1 is necessary for adaptation to ET. Twelve-week-old male Wistar rats were randomized (n = 8-12/group) to receive PBS or GLP-1 receptor antagonist (exendin 9-39 (Ex(9-39)) via osmotic pump for 4 weeks ± ET. CRF was greater with ET (P < 0.01). Ex(9-39) treatment blunted CRF in both sedentary and ET rats (P < 0.001). Ex(9-39) attenuated acetylcholine-mediated vasodilation, while this response was maintained with Ex(9-39)+ET (P = 0.04). Aortic stiffness was greater with Ex(9-39) (P = 0.057) and was made worse when Ex(9-39) was combined with ET (P = 0.004). Ex vivo aortic vasoconstriction with potassium and phenylephrine was lower with Ex(9-39) (P < 0.0001). Carotid strain improved with PBS + ET but did not change in the Ex(9-39) rats with ET (P < 0.0001). Left ventricular mitochondrial respiration was elevated with Ex(9-39) (P < 0.02). GLP-1 receptor antagonism impairs CRF with and without ET, attenuates the vascular adaptation to ET, and elevates cardiac mitochondrial respiration. These data suggest that GLP-1 is integral to the adaptive vascular response to ET.

Short communication: The effect of delayed colostrum feeding on plasma concentrations of glucagon-like peptide 1 and 2 in newborn calves

Glucagon-like peptide (GLP)-1 is involved in glucose homeostasis via its role in stimulating insulin secretion, whereas GLP-2 increases mucosal growth of the small intestine. To our knowledge, the effect of delayed colostrum feeding on plasma GLP-1 and GLP-2 in neonatal calves has not been evaluated. To investigate the effect of delayed colostrum feeding on plasma concentrations of GLP-1 and GLP-2 in newborn calves, we randomly assigned 27 Holstein bull calves to 1 of 3 treatment groups: those fed colostrum within 1 h after birth (control), 6 h after birth (6H), and 12 h after birth (12H; n = 9 for each treatment). Blood samples were obtained before the colostrum feeding and every 3 h after each colostrum feeding for a 36-h period, and plasma concentrations of GLP-1, GLP-2, insulin, and glucose were measured. Plasma GLP-1 concentration at 12 h after colostrum feeding was lower in 12H than in control calves. In addition, plasma insulin concentration was lower in the 6H and 12H calves than in the controls. Plasma glucose and GLP-2 concentrations were, however, not affected by treatment. These results indicate that delayed colostrum feeding can decrease plasma GLP-1 and insulin concentrations without affecting glucose or GLP-2 concentration.

Secretion of GLP-1 but not GIP is potently stimulated by luminal d-Allulose (d-Psicose) in rats

Glucagon-like peptide 1 (GLP-1), an incretin gastrointestinal hormone, is secreted when stimulated by nutrients including metabolizable sugars such as glucose and fructose. d-Allulose (allulose), also known as d-psicose, is a C-3 isomer of d-fructose and a rare sugar with anti-diabetic or anti-obese effects in animal models. In the present study, we examined whether an oral administration of allulose could stimulate GLP-1 secretion in rats, and investigated the underlying mechanisms. Oral, but not intraperitoneal, administration of allulose (0.5-2.0 g/kg body weight) elevated plasma GLP-1 levels for more than 2 h in a dose-dependent manner. The effects of allulose on GLP-1 secretion were higher than that of dextrin, fructose, or glucose. In addition, oral allulose increased total and active GLP-1, but not glucose-dependent insulinotropic polypeptide (GIP), levels in the portal vein. In anesthetized rats equipped with a portal catheter, luminal (duodenum and ileum) administration of allulose increased portal GLP-1 levels, indicating the luminal effect of allulose. Allulose-induced GLP-1 secretion was abolished in the presence of xanthohumol (a glucose/fructose transport inhibitor), but not in the presence of inhibitors of the sodium-dependent glucose cotransporter 1 or the sweet taste receptor. These results demonstrate a potent and lasting effect of orally administered allulose on GLP-1 secretion in rats, without affecting GIP secretion. The potent and selective GLP-1-releasing effect of allulose holds promise for the prevention and treatment of glucose intolerance through promoting endogenous GLP-1 secretion.

Newer GLP-1 receptor agonists and obesity-diabetes

Obesity is a major risk factor for type 2 diabetes and may complicate type 1 diabetes. In parallel with the global epidemic of obesity, the incidence of type 2 diabetes is increasing exponentially. To reverse these alarming trends, weight loss becomes a major therapeutic priority in prevention and treatment of type 2 diabetes. Given that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve glycaemic control and cause weight loss, they are receiving increasing attention for the treatment of diabetes-obesity. This review discusses current and emerging therapeutic options with GLP-1 RAs and considers the next generation of novel peptide co-agonists with the potential for improved therapeutic outcomes in obesity and type 2 diabetes.

Incretin-based therapy for the treatment of bone fragility in diabetes mellitus

Bone fractures are common comorbidities of type 2 diabetes mellitus (T2DM). Bone fracture incidence seems to develop due to increased risk of falls, poor bone quality and/or anti-diabetic medications. Previously, a relation between gut hormones and bone has been suspected. Most recent evidences suggest indeed that two gut hormones, namely glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), may control bone remodeling and quality. The GIP receptor is expressed in bone cells and knockout of either GIP or its receptor induces severe bone quality alterations. Similar alterations are also encountered in GLP-1 receptor knock-out animals associated with abnormal osteoclast resorption. Some GLP-1 receptor agonist (GLP-1RA) have been approved for the treatment of type 2 diabetes mellitus and although clinical trials may not have been designed to investigate bone fracture, first results suggest that GLP-1RA may not exacerbate abnormal bone quality observed in T2DM. The recent design of double and triple gut hormone agonists may also represent a suitable alternative for restoring compromised bone quality observed in T2DM. However, although most of these new molecules demonstrated weight loss action, little is known on their bone safety. The present review summarizes the most recent findings on peptide-based incretin therapy and bone physiology.

Cardioprotection by exenatide: A novel mechanism via improving mitochondrial function involving the GLP-1 receptor/cAMP/PKA pathway

Accumulating evidence suggests that glucagon-like peptide-1 (GLP-1) and its analogues exert cardioprotective effects via modulating cardiomyocyte metabolism. Mitochondria play a pivotal role in the regulation of cell metabolism. It was hypothesized that treatment with exenatide, a GLP-1 analogue, may exert cardioprotective effects by improving mitochondrial function in an in vitro model of hypoxia/reoxygenation (H/R). H9c2 cells were employed to establish an in vitro model of H/R. Exenatide was added to the cells for 30 min prior to exposure to hypoxia. The GLP-1 receptor antagonist exendin‑(9‑39), the cyclic adenosine monophosphate (cAMP) inhibitor Rp-cAMPS and the protein kinase A (PKA) inhibitor H-89 were added to the cells for 10 min prior to treatment with exenatide. The release of lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) and cardiomyocyte apoptosis were evaluated. The characteristics of mitochondrial morphology and functions, including ATP synthesis, membrane potential (ΔΨm), mitochondrial permeability transition pore (mPTP), mitochondrial ATPase activity and oxidative stress, were determined. the mitochondrial uncoupling protein-3 (UCP-3) and nuclear respiratory factor-1 (Nrf-1) were also investigated by western blot analysis. Exenatide pretreatment significantly decreased LDH and CK-MB release and cardiomyocyte apoptosis in H9c2 cells subjected to H/R. More importantly, to the best of our knowledge, this is the first report of exenatide pretreatment decreasing mitochondrial abnormalities and reducing oxidative stress, while enhancing ATP synthesis, mitochondrial ATPase activity and ΔΨm in H9c2 cells subjected to H/R. Exenatide pretreatment also decreased mitochondrial calcium overload and inhibited the opening of mPTP in H9c2 cells subjected to H/R. Furthermore, exenatide pretreatment upregulated UCP-3 and Nrf-1 expression in H9c2 cells subjected to H/R. However, the abovementioned observed effects of exenatide were all abolished when exenatide was co-administered with exendin‑(9‑39), Rp-cAMPS and̸or H-89. Therefore, the GLP-1 analogue exenatide was found to exert cardioprotective effects in an in vitro model of H/R, and this cardioprotection may be attributed to the improvement of mitochondrial function. These effects are most likely associated with the activation of the GLP-1 receptor/cAMP/PKA signaling pathway.

Interplay between bone and incretin hormones: A review

Bone is a tissue with multiple functions that is built from the molecular to anatomical levels to resist and adapt to mechanical strains. Among all the factors that might control the bone organization, a role for several gut hormones called "incretins" has been suspected. The present review summarizes the current evidences on the effects of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) in bone physiology.

Glucagon-like Peptide-1 and the Central/Peripheral Nervous System: Crosstalk in Diabetes

Glucagon-like peptide-1 (GLP-1) is released in response to meals and exerts important roles in the maintenance of normal glucose homeostasis. GLP-1 is also important in the regulation of neurologic and cognitive functions. These actions are mediated via neurons in the nucleus of the solitary tract that project to multiple regions expressing GLP-1 receptors (GLP-1Rs). Treatment with GLP-1R agonists (GLP-1-RAs) reduces ischemia-induced hyperactivity, oxidative stress, neuronal damage and apoptosis, cerebral infarct volume, and neurologic damage, after cerebral ischemia, in experimental models. Ongoing human trials report a neuroprotective effect of GLP-1-RAs in Alzheimer's and Parkinson's disease. In this review, we discuss the role of GLP-1 and GLP-1-RAs in the nervous system with focus on GLP-1 actions on appetite regulation, glucose homeostasis, and neuroprotection.

Exenatide improves diastolic function and attenuates arterial stiffness but does not alter exercise capacity in individuals with type 2 diabetes

BACKGROUND

Exercise is recommended as a cornerstone of treatment for type 2 diabetes mellitus (T2DM), however, it is often poorly adopted by patients. Even in the absence of apparent cardiovascular disease, persons with T2DM have an impaired ability to carry out maximal and submaximal exercise and these impairments are correlated with cardiac and endothelial dysfunction. Glucagon-like pepetide-1 (GLP-1) augments endothelial and cardiac function in T2DM. We hypothesized that administration of a GLP-1 agonist (exenatide) would improve exercise capacity in T2DM.

METHODS AND RESULTS

Twenty-three participants (64±4years; mean±SE) with uncomplicated T2DM were randomized in a double-blinded manner to receive either 10μg BID of exenatide or matching placebo after baseline measurements. Treatment with exenatide did not improve VO_2peak (P=0.1464) or VO₂ kinetics (P=0.2775). Diastolic function, assessed via resting lateral E:E', was improved with administration of exenatide compared with placebo (Placebo Pre: 7.6±1.0 vs. Post: 8.4±1.2 vs. Exenatide Pre: 8.1±0.7 vs. Post: 6.7±0.6; P=0.0127). Additionally, arterial stiffness measured by pulse wave velocity, was reduced with exenatide treatment compared with placebo (Placebo Pre: 10.5±0.8 vs. Post: 11.5±1.1s vs. Exenatide Pre: 11.4±1.8 vs. Post: 10.2±1.4s; P=0.0373). Exenatide treatment did not improve endothelial function (P=0.1793).

CONCLUSIONS

Administration of exenatide improved cardiac function and reduced arterial stiffness, however, these changes were not accompanied by improved functional exercise capacity. In order to realize the benefits of this drug on exercise capacity, combining exenatide with aerobic exercise training in participants with T2DM may be warranted.

[Incretin as a Novel Treatment Strategy for NAFLD/NASH]

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) have been recognized as metabolic disorders characterized by fatty accumulation in the liver without alcohol consumption. The diseases can cause metabolic syndromes, consisting of obesity, diabetes mellitus (DM), dyslipidemia and hypertension. For the treatment of NAFLD/NASH, losing weight by exercise or diet remains the standard treatment, because no effective pharmacological therapy has yet been developed for NAFLD/NASH. Two incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), stimulate glucose-mediated insulin production in pancreatic β cells. Incretin has also been reported to have various extra-pancreatic effects, including the regulation of hepatic glucose production, appetite and satiety, as well as the stimulation of afferent sensory nerves. Therefore, incretin may have potential as a novel therapeutic agent for NAFLD/NASH.

Liraglutide prevents cognitive decline in a rat model of streptozotocin-induced diabetes independently from its peripheral metabolic effects

Diabetes has been identified as a risk factor for cognitive dysfunctions. Glucagone like peptide 1 (GLP-1) receptor agonists have neuroprotective effects in preclinical animal models. We evaluated the effects of GLP-1 receptor agonist, liraglutide (LIR), on cognitive decline associated with diabetes. Furthermore, we studied LIR effects against hippocampal neurodegeneration induced by streptozotocin (STZ), a well-validated animal model of diabetes and neurodegeneration associated with cognitive decline. Diabetes and/or cognitive decline were induced in Wistar rats by intraperitoneal or intracerebroventricular injection of STZ and then rats were treated with LIR (300μg/kg daily subcutaneously) for 6 weeks. Rats underwent behavioral tests: Morris water maze, passive avoidance, forced swimming (FST), open field, elevated plus maze, rotarod tests. Furthermore, LIR effects on hippocampal neurodegeneration and mTOR pathway (AKT, AMPK, ERK and p70S6K) were assessed. LIR improved learning and memory only in STZ-treated animals. Anxiolytic effects were observed in all LIR-treated groups but pro-depressant effects in CTRL rats were observed. At a cellular/molecular level, intracerebroventricular STZ induced hippocampal neurodegeneration accompanied by decreased phosphorylation of AMPK, AKT, ERK and p70S6K. LIR reduced hippocampal neuronal death and prevented the decreased phosphorylation of AKT and p70S6K; AMPK was hyper-phosphorylated in comparison to CTRL group, while LIR had no effects on ERK. LIR reduced animal endurance in the rotarod test and this effect might be also linked to a reduction in locomotor activity during only the last two minutes of the FST. LIR had protective effects on cognitive functions in addition to its effects on blood glucose levels. LIR effects in the brain also comprised anxiolytic and pro-depressant actions (although influenced by reduced endurance). Finally, LIR protected from diabetes-dependent hippocampal neurodegeneration likely through an effect on mTOR pathway.

Liraglutide and obesity in elderly: efficacy in fat loss and safety in order to prevent sarcopenia. A perspective case series study

BACKGROUND

For the growing numbers of obese elderly with diabetes, the glucagon-like peptide-1 (GLP-1) receptor analogue (liraglutide) appears a safe way to promote and maintain substantial weight loss. Given this background, the aim of this study was to assess the effect of the liraglutide treatment, at doses up to 3.0 mg per day, on the body composition, focusing on sarcopenia, in overweight and obese elderly with type 2 diabetes mellitus (T2DM).

METHODS

A perspective study was carried out in overweight and obese T2DM patients with HbA1c equal to 7.0 % (53 mmol/mol) ~10.0 % (86), under 3-month treatment (at least) of maximal dose of metformin at stable regime, and additional liraglutide at doses up to 3.0 mg per day. Body composition markers such as skeletal muscle index (SMI), android and gynoid fat mass, and arms and legs fat free mass, was measured by dual-energy X-ray densitometry (DXA) at baseline and after 24 weeks of liraglutide treatment. Glucose control was also carried out by glucose and HbA1c.

RESULTS

Nine subjects (male/female 6/3, mean age 68.22 ± 3.86 years, BMI 32.34 ± 4.89 kg/m²) were evaluated. We noted a median decrease in BMI (-0.78 kg/m²), weight (-2000 g), fat mass (-1498 g) and android fat (-0.9 %), and a increase in SMI (+0.03 kg/m²) from baseline. Glycemic control also improved, with a median change HbA1c of -0.80 %.

CONCLUSIONS

Twenty-four weeks of liraglutide treatment was associated with reductions in fat mass and android fat. In addition, in order to prevent sarcopenia, it preserved the muscular tropism.

Dipeptidyl peptidase-4 inhibitor improved exercise capacity and mitochondrial biogenesis in mice with heart failure via activation of glucagon-like peptide-1 receptor signalling

AIMS

Exercise capacity is reduced in heart failure (HF) patients, due mostly to skeletal muscle abnormalities including impaired energy metabolism, mitochondrial dysfunction, fibre type transition, and atrophy. Glucagon-like peptide-1 (GLP-1) has been shown to improve exercise capacity in HF patients. We investigated the effects of the administration of a dipeptidyl peptidase (DPP)-4 inhibitor on the exercise capacity and skeletal muscle abnormalities in an HF mouse model after myocardial infarction (MI).

METHODS AND RESULTS

MI was created in male C57BL/6J mice by ligating the left coronary artery, and a sham operation was performed in other mice. The mice were then divided into two groups according to the treatment with or without a DPP-4 inhibitor, MK-0626 [1 mg/kg body weight (BW)/day] provided in the diet. Four weeks later, the exercise capacity evaluated by treadmill test was revealed to be limited in the MI mice, and it was ameliorated in the MI + MK-0626 group without affecting the infarct size or cardiac function. The citrate synthase activity, mitochondrial oxidative phosphorylation capacity, supercomplex formation, and their quantity were reduced in the skeletal muscle from the MI mice, and these decreases were normalized in the MI + MK-0626 group, in association with the improvement of mitochondrial biogenesis. Immunohistochemical staining also revealed that a shift toward the fast-twitch fibre type in the MI mice was also reversed by MK-0626. Favourable effects of MK-0626 were significantly inhibited by treatment of GLP-1 antagonist, Exendin-(9-39) (150 pmol/kg BW/min, subcutaneous osmotic pumps) in MI + MK-0626 mice. Similarly, exercise capacity and mitochondrial function were significantly improved by treatment of GLP-1 agonist, Exendin-4 (1 nmol/kg/BW/h, subcutaneous osmotic pumps).

CONCLUSIONS

A DPP-4 inhibitor may be a novel therapeutic agent against the exercise intolerance seen in HF patients by improving the mitochondrial biogenesis in their skeletal muscle.

Alleviation of high-fat diet-induced atherosclerosis and glucose intolerance by a novel GLP-1 fusion protein in ApoE(-/-) mice

We have previously constructed an engineered anti-diabetic fusion protein using glucagon-like peptide-1 and the globular domain of adiponectin. Herein, we evaluated the therapeutic effects of this fusion protein (GAD) on high-fat diet (HFD)-fed ApoE(-/-) mice. The lipid-lowering effect of GAD was determined in C57BL/6 mice using a lipid tolerance test. The effects of GAD on HFD-induced glucose intolerance, atherosclerosis, and hepatic steatosis were evaluated in HFD-fed ApoE(-/-) mice using glucose tolerance test, histological examinations and real-time quantitative PCR. The anti-inflammation activity of GAD was assessed in vitro on macrophages. GAD improved lipid metabolism in C57BL/6 mice. GAD treatment alleviated glucose intolerance, reduced blood lipid level, and attenuated atherosclerotic lesion in HFD-fed ApoE(-/-) mice, which was associated with a repressed macrophage infiltration in the vessel wall. GAD treatment also blocked hepatic macrophage infiltration and prevented hepatic inflammation. GAD suppressed lipopolysaccharide-triggered inflammation responses on macrophages, which can be abolished by H89, an inhibitor of protein kinase A. These findings demonstrate that GAD is able to generate a variety of metabolic benefits in HFD-fed ApoE(-/-) mice and indicate that this engineered fusion protein is a promising lead structure for anti-atherosclerosis drug discovery.

Perspectives in GLP-1 Research: New Targets, New Receptors

The incretin hormone glucagon-like peptide-1 (GLP-1) binds to and activates its G-protein-coupled-receptor GLP-1R to reduce glycaemia through the stimulation of insulin and suppression of pancreatic glucagon secretion. Recently, GLP-1 effects unrelated to glucose homeostasis have been discovered in myocardium, bone, adipose tissue, and other target organs, which appear to be mainly mediated by GLP-1R-independent pathways. Here, we summarize knowledge on GLP-1R agonists (GLP-1RAs) as they relate to the improvement of glucose control, and focus on the most recently described effects, discussing the preclinical evidence of the involvement of alternative receptors and signalling mechanisms. It is now evident that the universe of GLP-1RAs is expanding further from the initial incretin effect, opening new unforeseen avenues for research and clinical applications.

The regulation of function, growth and survival of GLP-1-producing L-cells

Glucagon-like peptide-1 (GLP-1) is a peptide hormone, released from intestinal L-cells in response to hormonal, neural and nutrient stimuli. In addition to potentiation of meal-stimulated insulin secretion, GLP-1 signalling exerts numerous pleiotropic effects on various tissues, regulating energy absorption and disposal, as well as cell proliferation and survival. In Type 2 Diabetes (T2D) reduced plasma levels of GLP-1 have been observed, and plasma levels of GLP-1, as well as reduced numbers of GLP-1 producing cells, have been correlated to obesity and insulin resistance. Increasing endogenous secretion of GLP-1 by selective targeting of the molecular mechanisms regulating secretion from the L-cell has been the focus of much recent research. An additional and promising strategy for enhancing endogenous secretion may be to increase the L-cell mass in the intestinal epithelium, but the mechanisms that regulate the growth, survival and function of these cells are largely unknown. We recently showed that prolonged exposure to high concentrations of the fatty acid palmitate induced lipotoxic effects, similar to those operative in insulin-producing cells, in an in vitro model of GLP-1-producing cells. The mechanisms inducing this lipototoxicity involved increased production of reactive oxygen species (ROS). In this review, regulation of GLP-1-secreting cells is discussed, with a focus on the mechanisms underlying GLP-1 secretion, long-term regulation of growth, differentiation and survival under normal as well as diabetic conditions of hypernutrition.

Mechanisms for the cardiovascular effects of glucagon-like peptide-1

Over the past three decades, at least 10 hormones secreted by the enteroendocrine cells have been discovered, which directly affect the cardiovascular system through their innate receptors expressed in the heart and blood vessels or through a neural mechanism. Glucagon-like peptide-1 (GLP-1), an important incretin, is perhaps best studied of these gut-derived hormones with important cardiovascular effects. In this review, I have discussed the mechanism of GLP-1 release from the enteroendocrine L-cells and its physiological effects on the cardiovascular system. Current evidence suggests that GLP-1 has positive inotropic and chronotropic effects on the heart and may be important in preserving left ventricular structure and function by direct and indirect mechanisms. The direct effects of GLP-1 in the heart may be mediated through GLP-1R expressed in atria as well as arteries and arterioles in the left ventricle and mainly involve in the activation of multiple pro-survival kinases and enhanced energy utilization. There is also good evidence to support the involvement of a second, yet to be identified, GLP-1 receptor. Further, GLP-1(9-36)amide, which was previously thought to be the inactive metabolite of the active GLP-1(7-36)amide, may also have direct cardioprotective effects. GLP-1's action on GLP-1R expressed in the central nervous system, kidney, vasculature and the pancreas may indirectly contribute to its cardioprotective effects.

Intestinal Bile Acid Composition Modulates Prohormone Convertase 1/3 (PC1/3) Expression and Consequent GLP-1 Production in Male Mice

Besides an established medication for hypercholesterolemia, bile acid binding resins (BABRs) present antidiabetic effects. Although the mechanisms underlying these effects are still enigmatic, glucagon-like peptide-1 (GLP-1) appears to be involved. In addition to a few reported mechanisms, we propose prohormone convertase 1/3 (PC1/3), an essential enzyme of GLP-1 production, as a potent molecule in the GLP-1 release induced by BABRs. In our study, the BABR colestimide leads to a bile acid-specific G protein-coupled receptor TGR5-dependent induction of PC1/3 gene expression. Here, we focused on the alteration of intestinal bile acid composition and consequent increase of total TGR5 agonistic activity to explain the TGR5 activation. Furthermore, we demonstrate that nuclear factor of activated T cells mediates the TGR5-triggered PC1/3 gene expression. Altogether, our data indicate that the TGR5-dependent intestinal PC1/3 gene expression supports the BABR-stimulated GLP-1 release. We also propose a combination of BABR and dipeptidyl peptidase-4 inhibitor in the context of GLP-1-based antidiabetic therapy.

GLP-1 stimulates insulin secretion by PKC-dependent TRPM4 and TRPM5 activation

Strategies aimed at mimicking or enhancing the action of the incretin hormone glucagon-like peptide 1 (GLP-1) therapeutically improve glucose-stimulated insulin secretion (GSIS); however, it is not clear whether GLP-1 directly drives insulin secretion in pancreatic islets. Here, we examined the mechanisms by which GLP-1 stimulates insulin secretion in mouse and human islets. We found that GLP-1 enhances GSIS at a half-maximal effective concentration of 0.4 pM. Moreover, we determined that GLP-1 activates PLC, which increases submembrane diacylglycerol and thereby activates PKC, resulting in membrane depolarization and increased action potential firing and subsequent stimulation of insulin secretion. The depolarizing effect of GLP-1 on electrical activity was mimicked by the PKC activator PMA, occurred without activation of PKA, and persisted in the presence of PKA inhibitors, the KATP channel blocker tolbutamide, and the L-type Ca(2+) channel blocker isradipine; however, depolarization was abolished by lowering extracellular Na(+). The PKC-dependent effect of GLP-1 on membrane potential and electrical activity was mediated by activation of Na(+)-permeable TRPM4 and TRPM5 channels by mobilization of intracellular Ca(2+) from thapsigargin-sensitive Ca(2+) stores. Concordantly, GLP-1 effects were negligible in Trpm4 or Trpm5 KO islets. These data provide important insight into the therapeutic action of GLP-1 and suggest that circulating levels of this hormone directly stimulate insulin secretion by β cells.

Antidiabetic treatment with gliptins: focus on cardiovascular effects and outcomes

The traditional oral pharmacological therapy for type 2 diabetes mellitus (T2DM) has been based on the prescription of metformin, a biguanide, as first line antihyperglycemic agent world over. It has been demonstrated that after 3 years of treatment, approximately 50 % of diabetic patients could achieve acceptable glucose levels with monotherapy; but by 9 years this had declined to only 25 %. Therefore, the implementation of a combined pharmacological therapy acting via different pathways becomes necessary, and its combination with a compound of the sulfonylurea group was along decades the most frequently employed prescription in routine clinical practice. Meglitinides, glitazones and alpha-glucosidase inhibitors were subsequently developed, but the five mentioned groups of oral antihyperglycemic agents are associated with variable degrees of undesirable or even severe cardiovascular events. The gliptins—also called dipeptidyl peptidase 4 (DPP4) inhibitors—are an additional group of antidiabetic compounds with increasing clinical use. We review the status of the gliptins with emphasis on their capabilities to positively or negatively affect the cardiovascular system, and their potential involvement in major adverse cardiovascular events (MACE). Alogliptin, anagliptin, linagliptin, saxagliptin, sitagliptin, teneligliptin and vildagliptin are the compounds currently in clinical use. Regardless differences in chemical structure and metabolic pathways, gliptins as a group exert favorable changes in experimental models. These changes, as an almost general rule, include improved endothelial function, reduction of inflammatory markers, oxidative stress ischemia/reperfusion injury and atherogenesis. In addition, increased adiponectin levels and modest decreases in lipidemia and blood pressure were reported. In clinical settings, several trials—notably the longer one, employing sitagliptin, with a mean follow-up period of 3 years—did not show an increased risk for ischemic events. Anyway, it should be emphasized that the encouraging results from basic science were not yet translated into clinical evidence, probably due the multiple and pleiotropic enzymatic effects of DPP4 inhibition. Moreover, when employing saxagliptin, while the drug was not associated with an augmented risk for ischemic events, it should be pinpointed that the rate of hospitalization for heart failure was significantly increased. Gliptins as a group constitute a widely accepted therapy for the management of T2DM, usually as a second-line medication. Nonetheless, for the time being, a definite relationship between gliptins treatment and improved cardiovascular outcomes remains uncertain and needs yet to be proven.

Direct effect of incretin hormones on glucose and glycerol metabolism and hemodynamics

The objective of this study was to assess the insulin-independent effects of incretin hormones on glucose and glycerol metabolism and hemodynamics under euglycemic and hyperglycemic conditions. Young, healthy men (n=10) underwent three trials in a randomized, controlled, crossover study. Each trial consisted of a two-stage (euglycemia and hyperglycemia) pancreatic clamp (using somatostatin to prevent endogenous insulin secretion). Glucose and lipid metabolism was measured via infusion of stable glucose and glycerol isotopic tracers. Hemodynamic variables (femoral, brachial, and common carotid artery blood flow and flow-mediated dilation of the brachial artery) were also measured. The three trials differed as follows: 1) saline [control (CON)], 2) glucagon-like peptide (GLP-1, 0.5 pmol·kg(-1)·min(-1)), and 3) glucose-dependent insulinotropic polypeptide (GIP, 1.5 pmol·kg(-1)·min(-1)). No between-trial differences in glucose infusion rates (GIR) or glucose or glycerol kinetics were seen during euglycemia, whereas hyperglycemia resulted in increased GIR and glucose rate of disappearance during GLP-1 compared with CON and GIP (P<0.01 for all). However, when normalized to insulin levels, no differences between trials were seen for GIR or glucose rate of disappearance. Besides a higher femoral blood flow during hyperglycemia with GIP (vs. CON and GLP-1, P<0.001), no between-trial differences were seen for the hemodynamic variables. In conclusion, GLP-1 and GIP have no direct effect on whole body glucose metabolism or hemodynamics during euglycemia. On the contrary, during hyperglycemia, GIP increases femoral artery blood flow with no effect on glucose metabolism, whereas GLP-1 increases glucose disposal, potentially due to increased insulin levels.

Effect of liraglutide on proliferation and differentiation of human adipose stem cells

Glucagon-Like Peptide-1 (GLP-1) receptor agonists, used as glucose-lowering drugs, also induce weight loss by inhibiting food intake. The present study was aimed at the assessment of the in vitro effects of the GLP-1 receptor agonist liraglutide on proliferation and differentiation of human adipose stem cells (ASC) obtained from subcutaneous adipose tissue of morbidly obese subjects undergoing bariatric surgery. Liraglutide (10-100 nM) significantly inhibited ASC proliferation and viability, with a maximum effect at 6 days of culture (45% and 50%, for liraglutide 10 and 100 nM, respectively); the effect was reverted by exendin 9-39. Glucose uptake was significantly reduced by liraglutide in a dose dependent manner. Treatment with liraglutide reduced intracellular lipid accumulation in differentiating ASC, together with FABP-4 mRNA expression (-18%, -23%, -46%, for 1 nM, 10 nM and 100 nM, respectively), whereas it stimulated adiponectin (APN) expression (1.86-, 2.64-, 2.28-fold increase, for 1 nM, 10 nM and 100 nM, respectively). Liraglutide exerts effects on human adipose cell precursors, inhibiting proliferation and differentiation, while stimulating the expression of the insulin-sensitizing adipokine APN. These effects could contribute to the actions of GLP-1 receptor agonists on body weight and insulin sensitivity.

Resveratrol ameliorates mitochondrial dysfunction but increases the risk of hypoglycemia following hemorrhagic shock

BACKGROUND

Hemorrhagic shock (HS) may contribute to organ failure, by profoundly altering mitochondrial function. Resveratrol (RSV), a naturally occurring polyphenol, has been shown to promote mitochondrial function and regulate glucose homeostasis in diabetes. We hypothesized that RSV during resuscitation would ameliorate HS-induced mitochondrial dysfunction and improve hyperglycemia following acute blood loss.

METHODS

With the use a decompensated HS model, male Long-Evans rats (n = 6 per group) were resuscitated with lactated Ringer's solution with or without RSV (30 mg/kg) and were killed before hemorrhage (sham), at severe shock, following resuscitation, and 18 hours after resuscitation. At each time point, the liver and kidney mitochondria were isolated to assess individual respiratory complexes (CI, CII, and CIV) and the production of reactive oxygen species (ROS). Blood samples were assayed for glucose, insulin, corticosterone, total glucagon-like peptide (GLP-1), glucagon, and serum cytokine levels. The Homeostatic Model Assessment-Insulin Resistance index was used to quantify insulin resistance.

RESULTS

RSV supplementation following HS significantly improved mitochondrial function and decreased mitochondrial ROS production in both liver and kidney. RSV-treated animals had significantly lower blood glucose levels following resuscitation when compared with sham animals (116.0 ± 20.2 mg/dL vs. 227.7 ± 8.3 mg/dL, p < 0.05) or those resuscitated with lactated Ringer's solution (116.0 ± 20.2 mg/dL vs. 359.0 ± 79.5 mg/dL, p < 0.05). RSV supplementation was associated with significantly decreased plasma insulin levels (1.0 ± 0.4 ng/mL vs. 6.5 ± 3.7 ng/mL, p < 0.05), increased total GLP-1 levels (385.8 ± 56.6 ng/mL vs. 187.3 ± 11.1 ng/mL, p < 0.05), and a lower natural Log Homeostatic Model Assessment-Insulin Resistance index (1.30 ± 0.42 vs. 4.18 ± 0.68, p < 0.05) but had minimal effect on plasma corticosterone, glucagon, or cytokine levels.

CONCLUSION

Resuscitation with RSV restores mitochondrial function and decreases insulin resistance but may be associated with increased hypoglycemia. The observed antiglycemic effects of RSV may be mediated by decreased mitochondrial ROS and increased GLP-1 secretion.

Molecular mechanisms underlying physiological and receptor pleiotropic effects mediated by GLP-1R activation

The incidence of type 2 diabetes in developed countries is increasing yearly with a significant negative impact on patient quality of life and an enormous burden on the healthcare system. Current biguanide and thiazolidinedione treatments for type 2 diabetes have a number of clinical limitations, the most serious long-term limitation being the eventual need for insulin replacement therapy (Table 1). Since 2007, drugs targeting the glucagon-like peptide-1 (GLP-1) receptor have been marketed for the treatment of type 2 diabetes. These drugs have enjoyed a great deal of success even though our underlying understanding of the mechanisms for their pleiotropic effects remain poorly characterized even while major pharmaceutical companies actively pursue small molecule alternatives. Coupling of the GLP-1 receptor to more than one signalling pathway (pleiotropic signalling) can result in ligand-dependent signalling bias and for a peptide receptor such as the GLP-1 receptor this can be exaggerated with the use of small molecule agonists. Better consideration of receptor signalling pleiotropy will be necessary for future drug development. This is particularly important given the recent failure of taspoglutide, the report of increased risk of pancreatitis associated with GLP-1 mimetics and the observed clinical differences between liraglutide, exenatide and the newly developed long-acting exenatide long acting release, albiglutide and dulaglutide.