Exenatide (a GLP-1 agonist) improves the antioxidative potential of in vitro cultured human monocytes/macrophages

Acute hyperglycemia induces podocyte apoptosis by monocyte TNF-α release, a process attenuated by vitamin D and GLP-1 receptor agonists

Targeting optimal glycemic control based on hemoglobin A1c (A1c) values reduces but does not abolish the onset of diabetic kidney disease and its progression to chronic kidney disease (CKD). This suggests that factors other than the average glucose contribute to the residual risk. Vitamin D deficiency and frequent episodes of acute hyperglycemia (AH) are associated with the onset of albuminuria and CKD progression in diabetes. This study aimed to determine if moderate levels of AH harm podocytes directly or promote a pro-inflammatory monocyte/macrophage phenotype that leads to podocyte apoptosis, and whether vitamin D deficiency accelerates these processes. We found that AH (16.7 mM D- glucose) didn't induce podocyte apoptosis directly, but it did promote a pro-inflammatory response in human monocytes and macrophages, resulting in an increased TNF-α secretion causing podocyte apoptosis. The AH-induced monocyte TNF-α secretion was inversely correlated with healthy donors' serum 25(OH)D levels. AH induced monocyte TNF-α release by increasing oxidative and ER stress, which in turn increased ADAM17 (A Disintegrin And Metalloprotease 17) and iRhom2 (inactive Rhomboid protein 2) expression, both essential for TNF-α secretion. Additionally, monocyte activation of glucagon-like peptide-1 receptor (GLP-1R), using a GLP-1R agonist, downregulated ADAM17/iRhom2 expression, decreasing TNF-α release and reducing podocyte apoptosis. These results show that a normal vitamin D status may attenuate a mechanism by which AH contributes to podocyte apoptosis and CKD progression and might enhance a novel anti-inflammatory role of GLP-1 to prevent AH-driven CKD progression in diabetes.

Unraveling the role of gut microbiota and plasma metabolites in fibromyalgia: Insights from Mendelian randomization and dietary interventions

Fibromyalgia (FM) is a complex disorder characterized by chronic pain, fatigue, and functional impairments, with unclear pathological mechanisms. Gut microbiota and plasma metabolites have been implicated in FM, but their causal relationships remain unexplored. This study aims to assess the causal relationships between gut microbiota, plasma metabolites, and FM using Mendelian randomization (MR) analysis and to explore potential mediating mechanisms. Public genome-wide association study data were analyzed using bidirectional MR. Associations between gut microbiota, plasma metabolites, and FM were evaluated, and multivariable MR identified mediating metabolites. Results were validated with inverse variance weighted, MR-Egger, and weighted median methods, with metabolic pathway enrichment analysis for further insights. MR identified protective associations between FM and four taxa (family Enterobacteriaceae, genus Butyricicoccus, genus Coprococcus1, and order Enterobacteriales) and risk associations with genus Eggerthella and genus Ruminococcaceae UCG005. Additionally, 82 plasma metabolites linked to pathways such as caffeine metabolism, α-linolenic acid metabolism, GLP-1, and incretin regulation were associated with FM. Mediation analysis revealed Enterobacteriaceae and Enterobacteriales influenced FM risk through 2,3-dihydroxypyridine and palmitoylcholine. Personalized dietary interventions, such as limiting caffeine intake, increasing omega-3 fatty acid consumption, adopting a low glycemic index diet, and reducing the intake of high-oxalate foods, may effectively alleviate FM-related symptoms by modulating metabolic pathways, reducing inflammation, and mitigating oxidative stress. This study highlights the intricate interactions between the gut microbiota and metabolic pathways, providing critical scientific evidence and actionable targets for clinical interventions, dietary management, and precision medicine approaches in FM treatment.

Liraglutide Therapy in Obese Patients Alters Macrophage Phenotype and Decreases Their Tumor Necrosis Factor Alpha Release and Oxidative Stress Markers-A Pilot Study

Introduction: Obesity is one of the major healthcare challenges. It affects one in eight people around the world and leads to several comorbidities, including type 2 diabetes, hyperlipidemia, and arterial hypertension. GLP-1 analogs have become major players in the therapy of obesity, leading to significant weight loss in patients. However, benefits resulting from their usage seem to be greater than simple appetite reduction and glucose-lowering potential. Recent data show better cardiovascular outcomes, which are connected with the improvements in the course of atherosclerosis. Macrophages are crucial cells in the forming and progression of atherosclerotic lesions. Previously, it was shown that in vitro treatment with GLP-1 analogs can affect macrophage phenotype, but there is a paucity of in vivo data. Objective: To evaluate the influence of in vivo treatment with liraglutide on basic phenotypic and functional markers of macrophages. Methods: Basic phenotypic features were assessed (including inducible nitric oxide synthase, arginase 1 and mannose receptors), proinflammatory cytokine (IL-1β, TNFα) release, and oxidative stress markers (reactive oxygen species, malondialdehyde) in macrophages obtained prior and after 3-month therapy with liraglutide in patients with obesity. Results: Three-month treatment with subcutaneous liraglutide resulted in the alteration of macrophage phenotype toward alternative activation (M2) with accompanying reduction in the TNFα release and diminished oxidative stress markers. Conclusions: Our results show that macrophages in patients treated with GLP-1 can alter their phenotype and function. Those findings may at least partly explain the pleiotropic beneficial cardiovascular effects seen in subjects treated with GLP-1 analogs.

Chronotropic Responses to GLP-1 Receptor Agonists and Sitagliptin in Atria From Diabetic Rats

ABSTRACT

Type 2 diabetes mellitus increases the risk of cardiovascular diseases. Therefore, elucidation of the cardiovascular effects of antidiabetics is crucial. Incretin-based therapies are increasingly used for type 2 diabetes mellitus treatment as monotherapy and in combination. We aimed to study the effects of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and sitagliptin on beating rates in isolated atria from diabetic rats. The chronotropic responses to GLP-1 RAs and sitagliptin as monotherapy and in combinations with metformin, pioglitazone, and glimepiride in isolated atria from control and diabetic rats were determined. GLP-1 (7-36), GLP-1 (9-36), and exendin-4 (1-39) produced increases in beating rates in both control and diabetic rat atria. However, sitagliptin increased the beating frequency only in the diabetic group. Exendin (9-39), nitro- l -arginine methyl ester hydrochloride, and indomethacin blocked responses to GLP-1 RAs but not the response to sitagliptin. Glibenclamide, 4-aminopyridine, apamin, charybdotoxin, superoxide dismutase, and catalase incubations did not change responses to GLP-1 RAs and sitagliptin. GLP-1 RAs increase beating rates in isolated rat atrium through GLP-1 receptor, nitric oxide, and cyclooxygenase pathways but not potassium channels and reactive oxygen radicals.

Effects of Glucagon-Like Peptide-1 Receptor Agonists and Sodium-Glucose Cotransporter 2 Inhibitors on Intima-Media Thickness: Systematic Review and Meta-Analysis

Background

Beyond glycemic control, glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and sodium-glucose cotransporter 2 inhibitors (SGLT2is) have been proposed to reduce the risk of cardiovascular events. The aim of the present systematic review and meta-analysis is to demonstrate the effects of GLP-1 RA and SGLT2is on intima-media thickness (IMT).

Methods

PubMed, EMBASE, Web of Science, SCOPUS, and Google Scholar databases were searched from inception to September 9, 2023. All interventional and observational studies that provided data on the effects of GLP-1 RAs or SGLT2is on IMT were included. Critical appraisal was performed using the Joanna Briggs Institute checklists. IMT changes (preintervention and postintervention) were pooled and meta-analyzed using a random-effects model. Subgroup analyses were based on type of medication (GLP-1 RA: liraglutide and exenatide; SGLT2i: empagliflozin, ipragliflozin, tofogliflozin, and dapagliflozin), randomized clinical trials (RCTs), and diabetic patients.

Results

The literature search yielded 708 related articles after duplicates were removed. Eighteen studies examined the effects of GLP-1 RA, and eleven examined the effects of SGLT2i. GLP-1 RA and SGLT2i significantly decreased IMT (MD = -0.123, 95% CI (-0.170, -0.076), P < 0.0001, I2 = 98% and MD = -0.048, 95% CI (-0.092, -0.004), P = 0.031, I2 = 95%, respectively). Metaregression showed that IMT change correlated with baseline IMT, whereas it did not correlate with gender, duration of diabetes, and duration of treatment.

Conclusions

Treatment with GLP-1 RA and SGLT2i can lower IMT in diabetic patients, and GLP-1 RA may be more effective than SGLT2i.

The Role of Glucagon-Like Peptide-1 Receptor Agonists in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is one of the common diseases of the respiratory system. As the disease recurs, damage to the airways and lung tissue gradually worsens, leading to a progressive decline in lung function, affecting the patient's workforce and quality of life, and causing a huge social and economic burden. Diabetes is a common comorbidity of COPD and patients with COPD are at increased risk of developing diabetes, while hyperglycemia can also reduce lung function and contribute to the progression and poor prognosis of COPD. Glucagon-like peptide-1 receptor agonist (GLP-1RA) is a new type of hypoglycemic agent that has been shown to regulate blood glucose levels, reduce inflammatory responses and oxidative stress, and regulate lipid metabolism, among other effects. GLP-1RAs may benefit COPD patients by acting directly on the lung from mechanisms such as reducing the inflammatory response, improving oxidative stress, regulating protease/anti-protease imbalance, improving airway mucus homeostasis, and reducing airway remodeling. This study provides a review of the potential role of GLP-1RAs in COPD and offers new ideas for the prevention and treatment of COPD.

Reactive Oxygen Species Scavenging Nanomedicine for the Treatment of Ischemic Heart Disease

Ischemic heart disease (IHD) is the leading cause of disability and mortality worldwide. Reactive oxygen species (ROS) have been shown to play key roles in the progression of diabetes, hypertension, and hypercholesterolemia, which are independent risk factors that lead to atherosclerosis and the development of IHD. Engineered biomaterial-based nanomedicines are under extensive investigation and exploration, serving as smart and multifunctional nanocarriers for synergistic therapeutic effect. Capitalizing on cell/molecule-targeting drug delivery, nanomedicines present enhanced specificity and safety with favorable pharmacokinetics and pharmacodynamics. Herein, the roles of ROS in both IHD and its risk factors are discussed, highlighting cardiovascular medications that have antioxidant properties, and summarizing the advantages, properties, and recent achievements of nanomedicines that have ROS scavenging capacity for the treatment of diabetes, hypertension, hypercholesterolemia, atherosclerosis, ischemia/reperfusion, and myocardial infarction. Finally, the current challenges of nanomedicines for ROS-scavenging treatment of IHD and possible future directions are discussed from a clinical perspective.

Application of glucagon-like peptide-1 receptor antagonists in fibrotic diseases

Fibrosis can occur in various organs, leading to structural destruction, dysfunction, and even organ failure. Hence, organ fibrosis is being actively researched worldwide. Glucagon-like peptide-1 (GLP-1), a naturally occurring hormone, binds to a G-protein-coupled receptor widely distributed in the pancreas, kidney, lung, heart, gastrointestinal tract, and other organs. Synthetic GLP-1 analogs can be used as GLP-1 receptor agonists (GLP-1RAs) for treating diabetes mellitus. In recent years, GLP-1RAs have also been found to exert anti-inflammatory, antioxidant, and cardiovascular protective effects. GLP-1RAs have also been shown to inhibit fibrosis of solid organs, such as the lung, heart, liver, and kidney. In this review, we discuss the advancements in research on the role of GLP-1RAs in the fibrosis of the heart, lung, liver, kidney, and other organs to obtain new clues for treating organ fibrosis.

Nonalcoholic Steatohepatitis (NASH) and Atherosclerosis: Explaining Their Pathophysiology, Association and the Role of Incretin-Based Drugs

Nonalcoholic steatohepatitis (NASH) is the most severe manifestation of nonalcoholic fatty liver disease (NAFLD), a common complication of type 2 diabetes, and may lead to cirrhosis and hepatocellular carcinoma. Oxidative stress and liver cell damage are the major triggers of the severe hepatic inflammation that characterizes NASH, which is highly correlated with atherosclerosis and coronary artery disease. Regarding drug therapy, research on the role of GLP-1 analogues and DPP4 inhibitors, novel classes of antidiabetic drugs, is growing. In this review, we outline the association between NASH and atherosclerosis, the underlying molecular mechanisms, and the effects of incretin-based drugs, especially GLP-1 RAs, for the therapeutic management of these conditions.

Exenatide improves antioxidant capacity and reduces the expression of LDL receptors and PCSK9 in human insulin-secreting 1.1E7 cell line subjected to hyperglycemia and oxidative stress

Introduction

GLP-1 receptor agonists (e.g., exenatide) are novel drugs used in the treatment of diabetes. These drugs, working with other mechanisms of action, improve glycemic control by increasing secretion of insulin and improving survival of pancreatic islet beta cells. Alterations in the oxidative stress level or the expression of proteins associated with cholesterol uptake might be responsible for those findings. Currently, there are few in vitro studies on the impact of exenatide antioxidant capacity in human islet beta cell lines and none that assess the influence of exenatide on LDL receptors and PCSK9 under hyperglycemia and oxidative stress. Therefore, we evaluated the impact of exenatide on antioxidant capacity, insulin secretion, and proteins involved in cholesterol metabolism.

Materials and Method

An in vitro culture of insulin-secreting cells 1.1E7 was subjected to hyperglycemia and oxidative stress. Assessment was made of the expression of enzymes associated with oxidative stress (NADPH oxidase, catalase, glutathione peroxidase, superoxide dismutase, iNOS) and cholesterol uptake (LDL receptors, PCSK9). Additionally, insulin and nitrite levels in culture media were quantified.

Results

We showed that exenatide improves expression of catalase and reduces the amount of nitrite in cell cultures in a protein kinase A–dependent manner. Those results were accompanied by a drop in the expression of LDL receptors and PCSK9. Insulin secretion was modestly increased in the culture condition.

Conclusions

Our findings show potential protective mechanisms exerted by exenatide in human insulin-secreting pancreatic beta cell line (1.1E7), which may be exerted through increased antioxidant capacity and reduced accumulation of cholesterol.

Metabolic Hormones Modulate Macrophage Inflammatory Responses

Simple Summary

Macrophages are a type of immune cell which play an important role in the development of cancer. Obesity increases the risk of cancer and obesity also causes disruption to the normal levels of hormones that are produced to coordinate metabolism. Recent research now shows that these metabolic hormones also play important roles in macrophage immune responses and so through macrophages, disrupted metabolic hormone levels may promote cancer. This review article aims to highlight and summarise these recent findings so that the scientific community may better understand how important this new area of research is, and how these findings can be capitalised on for future scientific studies.

Abstract

Macrophages are phagocytotic leukocytes that play an important role in the innate immune response and have established roles in metabolic diseases and cancer progression. Increased adiposity in obese individuals leads to dysregulation of many hormones including those whose functions are to coordinate metabolism. Recent evidence suggests additional roles of these metabolic hormones in modulating macrophage inflammatory responses. In this review, we highlight key metabolic hormones and summarise their influence on the inflammatory response of macrophages and consider how, in turn, these hormones may influence the development of different cancer types through the modulation of macrophage functions.

What Is the Mechanism Driving the Reduction of Cardiovascular Events from Glucagon-like Peptide-1 Receptor Agonists?-A Mini Review

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are considered the standard of care for type 2 diabetes in many countries worldwide. These molecules have profound anti-hyperglycaemic actions with a favourable safety profile. They are now being considered for their robust cardiovascular (CV) protective qualities in diabetic patients. Most recent CV outcome trials have reported that GLP-1 RAs reduce major adverse cardiovascular events (MACE). Furthermore, the GLP-1 RAs seem to target the atherosclerotic CV disease processes preferentially. GLP-1 RAs also improve a wide range of routinely measured surrogate markers associated with CV risk. However, mediation analysis suggests these modest improvements may contribute indirectly to the overall anti-atherogenic profile of the molecules but fall short in accounting for the significant reduction in MACE. This review explores the body of literature to understand the possible mechanisms that contribute to the CV protective profile of GLP-1 RAs.

Antioxidative Potentials of Incretin-Based Medications: A Review of Molecular Mechanisms

Glucagon-like peptide 1 receptor agonists and dipeptidyl-peptidase 4 inhibitors are medications used for managing diabetes, mimicking the metabolic effects of incretin hormones. Recent evidence suggests that these medications have antioxidative potentials in the diabetic milieu. The pathophysiology of most diabetic complications involves oxidative stress. Therefore, if incretin-based antidiabetic medications can alleviate the free radicals involved in oxidative stress, they can potentially provide further therapeutic effects against diabetic complications. However, the molecular mechanisms by which these medications protect against oxidative stress are not fully understood. In the current review, we discuss the potential molecular mechanisms behind these pharmacologic agents' antioxidative properties.

Exenatide improves cardiovascular risk factors in obese patients with type 2 diabetes mellitus: a prospective study

Background/aim

The aim of this study was to evaluate the effects of a 6-month treatment regimen with exenatide on the lipid profile, high-sensitivity C-reactive protein (hsCRP), carotid intima media thickness (CIMT), visceral adiposity, and nonalcoholic fatty liver disease (NAFLD), all of which are important cardiovascular risk factors.

Materials and methods

This study included 45 obese patients with type 2 diabetes mellitus (T2DM). Baseline clinical findings, laboratory parameters, and ultrasonography findings were recorded. An exenatide recipe was given twice daily to the patients and, after 6 months of therapy, the same variables were compared. The compared parameters were lipid profiles, hsCRP, aspartat aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, liver craniocaudal diameter, visceral fat volume, subcutaneous fat thickness, and CIMT. Liver diameter, visceral fat volume, subcutaneous fat thickness, and CIMT were measured by ultrasonography.

Results

After therapy, statistically significant improvements were achieved in lipid profile, hsCRP, liver enzymes, body mass index, and waist and hip circumferences. Also, statistically significant decreases were obtained in liver craniocaudal diameter, subcutaneous fat thickness, visceral fat volume, and CIMT. The reduction of CIMT and liver diameter were not correlated with BMI and HbA_1c reduction.

Conclusion

This study showed improvement in lipid profile and hsCRP levels with exenatide treatment. We also showed decrease in both visceral fat volume and subcutaneous fat thickness. We demonstrated significant decrease in liver enzymes with significant decrease in liver diameter. These findings support the use of exenatide in patients with NAFLD and T2DM. Additionally, this study showed that exenatide treatment given twice daily reduces CIMT in obese T2DM patients.

Exenatide ameliorates experimental non-alcoholic fatty liver in rats via suppression of toll-like receptor 4/NFκB signaling: Comparison to metformin

AIMS

Non-alcoholic fatty liver disease (NAFLD) is a common liver disease. This study aimed to evaluate the role of exenatide compared with metformin in halting the progression of fatty liver stimulated by a high-fat diet (HiFD) in rats.

MAIN METHODS

Thirty male Wistar rats were allocated into 6 groups, 5 rats per each group. Group I: maintained on normal diet (normal group) for fourteen weeks. The other five groups were kept on HiFD throughout the experiment, HiFD was administered beside pharmacological treatments/or vehicle. Group II: (NAFLD control group), group III: received metformin (60 mg/kg/day, P.O.), group IV-VI: received exenatide (10, 20, and 40 μg/kg/day, S.C.) respectively for 7 weeks. At the end of the therapeutic period, fasting blood glucose was determined, and body weight was registered. Rats were sacrificed, and blood samples were taken to measure serum insulin, lipids, and liver enzymes. The liver index and homeostasis model of insulin resistance (HOMA-IR) index were calculated. Further, livers were dissected for histopathological examination and Western blot analysis.

KEY FINDINGS

NAFLD control group showed hyperglycemia, hyperinsulinemia, increased liver enzymes, hypertriglyceridemia, elevated hepatic lipid peroxides, and inflammatory mediators (interlukin 6, nuclear factor-κB, tumor necrosis factor-α and Toll-like receptor4) in addition to hepatic fatty degeneration. In a dose-dependent manner, exenatide significantly improved most of the above mentioned markers in comparsion with NAFLD at P≤0.05.

SIGNIFICANCE

The current results suggest that exenatide is equivalent to metformin in controlling insulin resistance, body weight gain, improving liver function, suppressing inflammation, and attenuating NAFLD progression in male rats.

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.

The impact of exenatide (a GLP-1 agonist) on markers of inflammation and oxidative stress in normal human astrocytes subjected to various glycemic conditions

GLP-1 agonists such as exenatide and liraglutide are novel drugs for the treatment of diabetes and obesity. While improvements in glycemic control can rely on an incretin effect, the mechanisms behind the loss of weight following therapy have yet to be completely elucidated, and seem to be associated with alterations in eating habits, resulting from changes in cytokines e.g. interleukin 1β (IL-1β) and oxidative signaling in the central nervous system (CNS). Increased levels of IL-1β and reactive oxygen species have been demonstrated to exert anorexigenic properties, and astrocytes appear to actively participate in maintaining the integrity of the CNS, which includes the paracrine secretion of inflammatory cytokines and involvement in the redox status. Therefore, the present study decided to explore the influence of exenatide [a glucagon-like peptide 1 (GLP-1 agonist)] on inflammatory and oxidative stress markers in cultured human astrocytes as a potential target for weight reduction therapies. In an experimental setting, normal human astrocytes were subjected to various glycemic conditions, including 40 mg/dl-hypoglycemic, 100 mg/dl-normoglycemic and 400 mg/dl-hyperglycemic, and exenatide, which is a GLP-1 agonist. The involvement of intracellular signaling by a protein kinase A (PKA) in the action of exenatide was estimated using a specific PKA inhibitor-PKI (14-22). The expression levels of IL-1β, nuclear factor kappa κB (NFκB), glial-fibrillary acidic protein (GFAP), p22 NADPH oxidase, glutathione peroxidase, catalase, superoxide dismutase 1, and reactive oxidative species were measured. The present study demonstrated that varying glucose concentrations in the culture media did not affect the protein expression or the level of reactive oxygen species. Conversely, exenatide led to an increase in IL-1β in normoglycemic culture conditions, which was accompanied by the increased expression of p22, glutathione peroxidase and the reduced expression of GFAP. Changes in the expression of IL-1β and p22 were dependent on the activation of PKA. The present study concluded that exenatide predominantly affected astrocytes in normoglycemic conditions, and hypothesize that this impact demonstrated one of novel mechanisms associated with astrocyte signaling that may contribute to weight loss.

Incretin-based therapy for diabetic ulcers: from bench to bedside

INTRODUCTION

Diabetic foot ulcers are a serious complication of diabetes and are associated with pain, disability, and poor quality of life. Incretin-based therapy is available for type-2 diabetes. Aside from glucose control, such treatment can impart numerous beneficial effects.

AREAS COVERED

This review summarizes the preclinical and clinical evidence supporting incretin-based treatment approaches for diabetic ulcers.

EXPERT OPINION

Incretin-based therapy may have a role in the treatment of diabetic foot ulcers; the benefits of such treatment arise from attenuation of inflammatory response, improvement of keratinocyte migration, induction of angiogenesis, and the enhancement of tissue remodeling. Large-scale clinical trials are required to determine the advantages of GLP-1 receptor agonists and DPP4 inhibitors. Future research on the topical application of incretin-based therapy is necessary. Such therapeutic approaches may provide new hope in improving the treatment of impaired diabetic foot ulcers.

Exenatide modulates expression of metalloproteinases and their tissue inhibitors in TNF-α stimulated human retinal pigment epithelial cells

BACKGROUND

Diabetic retinopathy (DR) is one of the most common complications of diabetes and the leading cause of acquired blindness in adults. In diabetic patients hyperglycemia induces complex metabolic abnormalities affecting retinal homeostasis, and promotes retinal inflammation and angiogenesis. Incretin mimetic drugs such exenatide, are a relatively new group of drugs used in the treatment of diabetes. We investigated the potential direct effects of exenatide on human retinal pigment epithelium (HRPE).

METHODS

cAMP production was measured after stimulation of HRPE cells with GLP-1 and exenatide. Intracellular signaling pathways were also examined. HRPE cells were stimulated with TNF-α and subsequently incubated with exenatide. The concentration of metalloproteinases, MMP-1, MMP-2 and MMP-9, and tissue inhibitors of metalloproteinases, TIMP-1, TIMP-2, and TIMP-3 were evaluated. Viability, cytotoxicity and caspase 3/7 activation were determined. Activity of dipeptidyl peptidase-4 (DPP-4), an enzyme involved in GLP-1 inactivation, was also determined.

RESULTS

Both GLP-1 and exenatide stimulation in HRPE cells caused no effect in cAMP levels suggesting alternative signaling pathways. Signaling pathway analysis showed that exenatide reduced phosphorylation of Akt-Ser473, PRAS40, SAPK/JNK, Bad, and S6 proteins but not Akt-Thr308. Exenatide also decreased MMP-1, MMP-9, and TIMP-2 protein levels whereas MMP-2 level in HRPE cells was increased. Finally, we show that exenatide decreased the activity of DPP-4 in TNF-α stimulated HRPE cells.

CONCLUSIONS

These findings indicate that exenatide modulates regulation of extracellular matrix components involved in retinal remodeling.

Cardiovascular Actions and Clinical Outcomes With Glucagon-Like Peptide-1 Receptor Agonists and Dipeptidyl Peptidase-4 Inhibitors

Potentiation of glucagon-like peptide-1 (GLP-1) action through selective GLP-1 receptor (GLP-1R) agonism or by prevention of enzymatic degradation by inhibition of dipeptidyl peptidase-4 (DPP-4) promotes glycemic reduction for the treatment of type 2 diabetes mellitus by glucose-dependent control of insulin and glucagon secretion. GLP-1R agonists also decelerate gastric emptying, reduce body weight by reduction of food intake and lower circulating lipoproteins, inflammation, and systolic blood pressure. Preclinical studies demonstrate that both GLP-1R agonists and DPP-4 inhibitors exhibit cardioprotective actions in animal models of myocardial ischemia and ventricular dysfunction through incompletely characterized mechanisms. The results of cardiovascular outcome trials in human subjects with type 2 diabetes mellitus and increased cardiovascular risk have demonstrated a cardiovascular benefit (significant reduction in time to first major adverse cardiovascular event) with the GLP-1R agonists liraglutide (LEADER trial [Liraglutide Effect and Action in Diabetes: Evaluation of Cardiovascular Ourcome Results], -13%) and semaglutide (SUSTAIN-6 trial [Trial to Evaluate Cardiovascular and Other Long-term Outcomes with Semaglutide], -24%). In contrast, cardiovascular outcome trials examining the safety of the shorter-acting GLP-1R agonist lixisenatide (ELIXA trial [Evaluation of Lixisenatide in Acute Coronary Syndrom]) and the DPP-4 inhibitors saxagliptin (SAVOR-TIMI 53 trial [Saxagliptin Assessment of Vascular Outcomes Recorded in Patients With Diabetes Mellitus-Thrombolysis in Myocardial Infarction 53]), alogliptin (EXAMINE trial [Examination of Cardiovascular Outcomes With Alogliptin Versus Standard of Care in Patients With Type 2 Diabetes Mellitus and Acute Coronary Syndrome]), and sitagliptin (TECOS [Trial Evaluating Cardiovascular Outcomes With Sitagliptin]) found that these agents neither increased nor decreased cardiovascular events. Here we review the cardiovascular actions of GLP-1R agonists and DPP-4 inhibitors, with a focus on the translation of mechanisms derived from preclinical studies to complementary findings in clinical studies. We highlight areas of uncertainty requiring more careful scrutiny in ongoing basic science and clinical studies. As newer more potent GLP-1R agonists and coagonists are being developed for the treatment of type 2 diabetes mellitus, obesity, and nonalcoholic steatohepatitis, the delineation of the potential mechanisms that underlie the cardiovascular benefit and safety of these agents have immediate relevance for the prevention and treatment of cardiovascular disease.

Extrapancreatic effects of incretin hormones: evidence for weight-independent changes in morphological aspects and oxidative status in insulin-sensitive organs of the obese nondiabetic Zucker rat (ZFR)

Incretin‐based therapies are widely used to treat type 2 diabetes. Although hypoglycemic actions of incretins are mostly due to their insulinotropic/glucagonostatic effects, they may also influence extrapancreatic metabolism. We administered exendin‐4 (Ex‐4), a long‐acting glucagon‐like peptide receptor agonist, at low dose (0.1 nmol/kg/day) for a short period (10 days), in obese nondiabetic fa/fa Zucker rats (ZFRs). Ex‐4‐treated ZFRs were compared to vehicle (saline)‐treated ZFRs and vehicle‐ and Ex‐4‐treated lean rats (LRs). Blood glucose levels were measured at days 0, 9, and 10. Ingested food and animal weight were recorded daily. On the day of sacrifice (d10), blood was sampled along with liver, epididymal, subcutaneous, brown adipose, and skeletal muscle tissues from animals fasted for 24 h. Plasma insulin and blood glucose levels, food intake, and body and epididymal fat weight were unchanged, but gross morphological changes were observed in insulin‐sensitive tissues. The average size of hepatocytes was significantly lower in Ex‐4‐treated ZFRs, associated with decreased number and size of lipid droplets and 4‐hydroxy‐2‐nonenal (HNE) staining, a marker of oxidative stress (OS). Myocytes, which were smaller in ZFRs than in LRs, were significantly enlarged and depleted of lipid droplets in Ex‐4‐treated ZFRs. Weak HNE staining was increased by Ex‐4. A similar observation was made in brown adipose tissue, whereas the elevated HNE staining observed in epididymal adipocytes of ZFRs, suggestive of strong OS, was decreased by Ex‐4. These results suggest that incretins by acting on OS in insulin‐sensitive tissues may contribute to weight‐independent improvement in insulin sensitivity.

Incretin hormones regulate microglia oxidative stress, survival and expression of trophic factors

The incretin hormones glucagon-like peptide (GLP)-1 and glucose-dependent insulinotropic polypeptide (GIP) are primarily known for their metabolic function in the periphery. GLP-1 and GIP are secreted by intestinal endocrine cells in response to ingested nutrients. Both GLP-1 and GIP stimulate the production and release of insulin from pancreatic β cells as well as exhibit several growth-regulating effects on peripheral tissues. GLP-1 and GIP are also present in the brain, where they provide modulatory and anti-apoptotic signals to neurons. However, very limited information is available regarding the effects of these hormones on glia, the immune and supporting cells of the brain. Therefore, we set out to resolve whether primary human microglia and astrocytes, two subtypes of glial cells, express the GLP-1 receptor (GLP-1R) and GIP receptor (GIPR), which are necessary to detect and respond to GLP-1 and GIP, respectively. We further tested whether these hormones, similar to their effects on neuronal cells, have growth-regulating, antioxidant and anti-apoptotic effects on microglia. We show for the first time expression of the GLP-1R and the GIPR by primary human microglia and astrocytes. We demonstrate that GLP-1 and GIP reduce apoptotic death of murine BV-2 microglia through the binding and activation of the GLP-1R and GIPR, respectively, with subsequent activation of the protein kinase A (PKA) pathway. Moreover, we reveal that incretins upregulate BV-2 microglia expression of brain derived neurotrophic factor (BDNF), glial cell-line derived neurotrophic factor (GDNF) and nerve growth factor (NGF) in a phosphoinositide 3-kinase (PI3K)- and PKA-dependent manner. We also show that incretins reduce oxidative stress in BV-2 microglia by inhibiting the accumulation of intracellular reactive oxygen species (ROS) and release of nitric oxide (NO), as well as by increasing the expression of the antioxidant glutathione peroxidase 1 (GPx1) and superoxide dismutase 1 (SOD1). We confirm these results by demonstrating that GLP-1 and GIP also inhibit apoptosis of primary murine microglia, and upregulate expression of BDNF by primary murine microglia. These results indicate that GLP-1 and GIP affect several critical homeostatic functions of microglia, and could therefore be tested as a novel therapeutic treatment option for brain disorders that are characterized by increased oxidative stress and microglial degeneration.

Exendin-4 in combination with adipose-derived stem cells promotes angiogenesis and improves diabetic wound healing

Background

Diminished wound healing is a major complication of diabetes mellitus and can lead to foot ulcers. However, there are limited therapeutic methods to treat this condition. Exendin-4 (Ex-4), a glucagon-like peptide-1 receptor agonist, is known to have many beneficial effects on diabetes. In addition, mesenchymal stem cells are known to have wound healing effects. We investigated the effects of Ex-4 in combination with human adipose tissue-derived stem cells (ADSCs) on diabetic wound healing in a diabetic animal model.

Methods

Diabetic db/db (blood glucose levels, >500 mg/dl) or C57BL/6 mice were subjected to wounding on the skin of the back. One day after wounding, each wound received ADSCs (2.5 × 10⁵ cells) injected intradermally around the wound and/or Ex-4 (50 μl of 100 nM Ex-4) topically applied on the wound with a fine brush daily. Wound size was monitored and wound histology was examined. Human endothelial cells and keratinocyte cells were used to assess angiogenesis and vascular endothelial growth factor expression in vitro.

Results

Topical administration of Ex-4 or injection of ADSCs resulted in a rapid reduction of wound size in both diabetic and normoglycemic animals compared with vehicle treatment. Histological analysis also showed rapid skin reconstruction in Ex-4-treated or ADSC-injected wounds. A combination of Ex-4 and ADSCs showed a significantly better therapeutic effect over either treatment alone. In vitro angiogenesis assays showed that both Ex-4 and ADSC-conditioned media (CM) treatment improved migration, invasion and proliferation of human endothelial cells. ADSC-CM also increased migration and proliferation of human keratinocytes. In addition, both Ex-4 and ADSC-CM increased the expression of vascular endothelial growth factor. Co-culture with ADSCs increased migration and proliferation of these cells similar to that found after ADSC-CM treatment.

Conclusions

We suggest that Ex-4 itself is effective for the treatment of diabetic skin wounds, and a combination of topical treatment of Ex-4 and injection of ADSCs has a better therapeutic effect. Thus, a combination of Ex-4 and ADSCs might be an effective therapeutic option for the treatment of diabetic wounds, such as foot ulcers.

Easy-to-use strategy for reference gene selection in quantitative real-time PCR experiments

Real-time PCR is an indispensable technique for mRNA expression analysis but conclusions depend on appropriate reference gene selection. However, while reference gene selection has been a topic of publications, this issue is often disregarded when measuring target mRNA expression. Therefore, we (1) evaluated the frequency of appropriate reference gene selection, (2) suggest an easy-to-use tool for least variability reference gene selection, (3) demonstrate application of this tool, and (4) show effects on target gene expression profiles. All 2015 published articles in Naunyn-Schmiedeberg's Archives of Pharmacology were screened for the use of quantitative real-time PCR analysis and selection of reference genes. Target gene expression (Vegfa, Grk2, Sirt4, and Timp3) in H9c2 cells was analyzed following various interventions (hypoxia, hyperglycemia, and/or isoflurane exposure with and without subsequent hypoxia) in relation to putative reference genes (Actb, Gapdh, B2m, Sdha, and Rplp1) using the least variability method vs. an arbitrarily selected but established reference gene. In the vast majority (18 of 21) of papers, no information was provided regarding selection of an appropriate reference gene. In only 1 of 21 papers, a method of appropriate reference gene selection was described and in 2 papers reference gene selection remains unclear. The method of reference gene selection had major impact on interpretation of target gene expression. With hypoxia, for instance, the least variability gene was Rplp1 and target gene expression (Vefga) heavily showed a 2-fold up-regulation (p = 0.022) but no change (p = 0.3) when arbitrarily using Gapdh. Frequency of appropriate reference gene selection in this journal is low, and we propose our strategy for reference gene selection as an easy tool for proper target gene expression.

Exenatide and metformin express their anti-inflammatory effects on human monocytes/macrophages by the attenuation of MAPKs and NFκB signaling

Metformin and exenatide are effective antidiabetic drugs, and they seem to have pleiotropic properties improving cardiovascular outcomes. Macrophages' phenotype is essential in the development of atherosclerosis, and it can be modified during antidiabetic therapy, resulting in attenuated atherogenesis. The mechanism orchestrating this phenomenon is not fully clear. We examined the impact of exenatide and metformin on the level of TNF alpha, MCP-1, reactive oxygen species (ROS), and the activation of mitogen-activated protein kinases (MAPK), nuclear factor kappa B (NFκB), and CCAAT/enhancer-binding protein beta (C/EBP beta) in human monocytes/macrophages. We found that both drugs reduced levels of TNF alpha, ROS, and NFκB binding activity to a similar extent. Compared to metformin, exenatide was more effective in reducing MCP-1 levels. We noted that Compound C (AMPK inhibitor) reduced the impact of exenatide on cytokines, ROS, and NFκB in cultures. Both drugs elevated the C/EBP beta phosphorylation level. Experiments on MAPKs showed effective inhibitory potential of exenatide toward p38, JNK, and ERK, whereas metformin inhibited JNK and ERK only. Exenatide was more effective in the inhibition of JNK than metformin. Interestingly, an in vitro setting additive effect of drugs was absent. In conclusion, here, we report that metformin and exenatide inhibit the proinflammatory phenotype of human monocytes/macrophages via influence on MAPK, C/EBP beta, and NFκB. Exenatide was more effective than metformin in reducing MCP-1 expression and JNK activity. We also showed that some effects of exenatide relied on AMPK activation. This shed light on the possible mechanisms responsible for pleiotropic effects of metformin and exenatide.

Chitinase 3 Like-1: An Emerging Molecule Involved in Diabetes and Diabetic Complications

Chitinase 3 like-1 (CHI3L1) is a chitinase-like protein member of family 18 chitinases, expressed in innate immune cells and involved in endothelial dysfunction and tissue remodelling. Since CHI3L1 is highly expressed in a variety of inflammatory diseases of infectious and non-infectious aetiology, it is recognised as a non-invasive prognostic biomarker for inflammation. A variety of studies revealing the increase in CHI3L1 levels in obesity, insulin resistance and in pathological conditions, such as atherosclerosis, coronary artery disease, acute ischaemic stroke, nephropathy, diabetic retinopathy and osteolytic processes, have suggested that CHI3L1 may also play a critical role in the evolution and complication of diabetes mellitus (DM). In this review we highlight the impact of CHI3L1 expression in DM and its contribution to the complication of this disease.

Metformin reduces the expression of NADPH oxidase and increases the expression of antioxidative enzymes in human monocytes/macrophages cultured in vitro

The treatment of diabetes and its complications is a key challenge for healthcare professionals. Accelerated atherosclerosis is associated with progressive diabetes, and it has been indicated that macrophages serve a crucial function in this process. Currently, the first-line treatment of diabetes is based on metformin, which is an inducer of AMP-activated protein kinase (AMPK) and belongs to the biguanide class of pharmaceuticals. It has been previously demonstrated that metformin exhibits more than just hypoglycemic effects. Therefore, the aim of the present study was to investigate the in vitro impact of metformin on cell viability and the expression levels of nicotinamide adenine dinucleotide phosphate (NAPDH) oxidase (p22phox), a major enzyme in reactive oxygen species generation, and the three antioxidative enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) in monocytes/macrophages derived from 10 healthy volunteers. The effects of metformin were observed in the presence or absence of lipopolysaccharide (LPS), which was administered to induce oxidative stress. Furthermore, certain cells were treated with compound C, an inhibitor of AMPK, in order to determine the mechanistic role played by AMPK in the oxidative changes in the macrophages. Cell viability was evaluated using trypan blue and MTT assays. The mRNA and protein expression levels of p22phox and the various antioxidative enzymes were determined using polymerase chain reaction and western blot analysis, respectively. The results indicated that metformin, predominantly in LPS-pretreated monocytes/macrophages, reduced the expression levels of p22phox and increased those of SOD and GPx, but had only a minor effect on CAT levels. Therefore, metformin appears to alter the oxidative status of macrophages toward increasingly antioxidative activity, which may account for the pleiotropic effects observed during metformin treatment.

Exenatide (a GLP-1 agonist) expresses anti-inflammatory properties in cultured human monocytes/macrophages in a protein kinase A and B/Akt manner

BACKGROUND

Incretin-based therapies in the treatment of type 2 diabetes mellitus are associated with significant improvements in glycemic control, which are accompanied by a beneficial impact on atherosclerosis. Macrophages are essential in the development of atherosclerotic plaques and may develop features that accelerate atherosclerosis (classically activated macrophages) or protect arterial walls against it (alternatively activated macrophages). Therefore, we explored whether beneficial actions of exenatide are connected with the influence on the macrophages' phenotype and synthesis of inflammatory and anti-inflammatory cytokines.

METHODS

Monocytes/macrophages were harvested from 10 healthy subjects. Cells were cultured in the presence of exenatide, exendin 9-39 (GLP-1 antagonist), LPS, IL-4, PKI (PKA inhibitor) and triciribine (PKB/Akt inhibitor). We measured the effects of the above-mentioned compounds on markers of macrophages' phenotype (inducible nitrous oxide (iNOS), arginase 1 (arg1) and mannose receptors) and concentration of nitrite, IL-1β, TNF-α and IL-10.

RESULTS

Exenatide significantly increased the level of IL-10 and decreased both TNF-α and IL-1β in LPS-treated monocytes/macrophages. Furthermore exenatide increased the expression of arg1-a marker of classical activation and reduced the LPS-induced expression of iNOS-a marker of classical activation. According to experiments with protein kinases inhibitors we found that proinflammatory markers were protein kinase A dependent, whereas the activation of alternative activation was similarly reliant on protein kinase A and B/Akt.

CONCLUSIONS

We showed that exenatide skewed the macrophages phenotype toward anti-inflammatory phenotype and this effect is predominantly attributable to protein kinase A and to a less extent to B/Akt activation.

Exploiting the Pleiotropic Antioxidant Effects of Established Drugs in Cardiovascular Disease

Cardiovascular disease is a leading cause of death and reduced quality of life worldwide. Arterial vessels are a primary target for endothelial dysfunction and atherosclerosis, which is accompanied or even driven by increased oxidative stress. Recent research in this field identified different sources of reactive oxygen and nitrogen species contributing to the pathogenesis of endothelial dysfunction. According to lessons from the past, improvement of endothelial function and prevention of cardiovascular disease by systemic, unspecific, oral antioxidant therapy are obviously too simplistic an approach. Source- and cell organelle-specific antioxidants as well as activators of intrinsic antioxidant defense systems might be more promising. Since basic research demonstrated the contribution of different inflammatory cells to vascular oxidative stress and clinical trials identified chronic inflammatory disorders as risk factors for cardiovascular events, atherosclerosis and cardiovascular disease are closely associated with inflammation. Therefore, modulation of the inflammatory response is a new and promising approach in the therapy of cardiovascular disease. Classical anti-inflammatory therapeutic compounds, but also established drugs with pleiotropic immunomodulatory abilities, demonstrated protective effects in various models of cardiovascular disease. However, results from ongoing clinical trials are needed to further evaluate the value of immunomodulation for the treatment of cardiovascular disease.