Improvement of islet graft function using liraglutide is correlated with its anti-inflammatory properties

Glucagon-like peptide 1 receptor activation: anti-inflammatory effects in the brain

The glucagon-like peptide 1 is a pleiotropic hormone that has potent insulinotropic effects and is key in treating metabolic diseases such as diabetes and obesity. Glucagon-like peptide 1 exerts its effects by activating a membrane receptor identified in many tissues, including different brain regions. Glucagon-like peptide 1 activates several signaling pathways related to neuroprotection, like the support of cell growth/survival, enhancement promotion of synapse formation, autophagy, and inhibition of the secretion of proinflammatory cytokines, microglial activation, and apoptosis during neural morphogenesis. The glial cells, including astrocytes and microglia, maintain metabolic homeostasis and defense against pathogens in the central nervous system. After brain insult, microglia are the first cells to respond, followed by reactive astrocytosis. These activated cells produce proinflammatory mediators like cytokines or chemokines to react to the insult. Furthermore, under these circumstances, microglia can become chronically inflammatory by losing their homeostatic molecular signature and, consequently, their functions during many diseases. Several processes promote the development of neurological disorders and influence their pathological evolution: like the formation of protein aggregates, the accumulation of abnormally modified cellular constituents, the formation and release by injured neurons or synapses of molecules that can dampen neural function, and, of critical importance, the dysregulation of inflammatory control mechanisms. The glucagon-like peptide 1 receptor agonist emerges as a critical tool in treating brain-related inflammatory pathologies, restoring brain cell homeostasis under inflammatory conditions, modulating microglia activity, and decreasing the inflammatory response. This review summarizes recent advances linked to the anti-inflammatory properties of glucagon-like peptide 1 receptor activation in the brain related to multiple sclerosis, Alzheimer's disease, Parkinson's disease, vascular dementia, or chronic migraine.

GLP-1 in the Hypothalamic Paraventricular Nucleus Promotes Sympathetic Activation and Hypertension

Glucagon-like peptide-1 (GLP-1) and its analogs are widely used for diabetes treatment. The paraventricular nucleus (PVN) is crucial for regulating cardiovascular activity. This study aims to determine the roles of GLP-1 and its receptors (GLP-1R) in the PVN in regulating sympathetic outflow and blood pressure. Experiments were carried out in male normotensive rats and spontaneously hypertensive rats (SHR). Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. GLP-1 and GLP-1R expressions were present in the PVN. PVN microinjection of GLP-1R agonist recombinant human GLP-1 (rhGLP-1) or EX-4 increased RSNA and MAP, which were prevented by GLP-1R antagonist exendin 9-39 (EX9-39) or GLP-1R antagonist 1, superoxide scavenger tempol, antioxidant N-acetylcysteine, NADPH oxidase (NOX) inhibitor apocynin, adenylyl cyclase (AC) inhibitor SQ22536 or protein kinase A (PKA) inhibitor H89. PVN microinjection of rhGLP-1 increased superoxide production, NADPH oxidase activity, cAMP level, AC, and PKA activity, which were prevented by SQ22536 or H89. GLP-1 and GLP-1R were upregulated in the PVN of SHR. PVN microinjection of GLP-1 agonist increased RSNA and MAP in both WKY and SHR, but GLP-1 antagonists caused greater effects in reducing RSNA and MAP in SHR than in WKY. The increased superoxide production and NADPH oxidase activity in the PVN of SHR were augmented by GLP-1R agonists but attenuated by GLP-1R antagonists. These results indicate that activation of GLP-1R in the PVN increased sympathetic outflow and blood pressure via cAMP-PKA-mediated NADPH oxidase activation and subsequent superoxide production. GLP-1 and GLP-1R upregulation in the PVN partially contributes to sympathetic overactivity and hypertension.

Liraglutide Protects Pancreatic Islet From Ischemic Injury by Reducing Oxidative Stress and Activating Akt Signaling During Cold Preservation to Improve Islet Transplantation Outcomes

BACKGROUND

Islet transplantation is a promising therapy for patients with type 1 diabetes. However, ischemic injury to the donor islets during cold preservation leads to reduced islet quality and compromises transplant outcome. Several studies imply that liraglutide, a glucagon-like peptide-1 receptor agonist, has a positive effect on promoting islet survival, but its impact on islet cold-ischemic injury remains unexplored. Therefore, the aim of this study was to investigate whether liraglutide can improve islet transplantation efficacy by inhibiting cold-ischemic injury and to explore the underlying mechanisms.

METHODS

Liraglutide was applied in a mouse pancreas preservation model and a human islets cold-preservation model, and islet viability, function, oxidative stress levels were evaluated. Furthermore, islet transplantation was performed in a syngeneic mouse model and a human-to-nude mouse islet xenotransplantation model.

RESULTS

The supplementation of liraglutide in preservation solution improved islet viability, function, and reduced cell apoptosis. Liraglutide inhibited the oxidative stress of cold-preserved pancreas or islets through upregulating the antioxidant enzyme glutathione levels, inhibiting reactive oxygen species accumulation, and maintaining the mitochondrial membrane integrity, which is associated with the activation of Akt signaling. Furthermore, the addition of liraglutide during cold preservation of donor pancreas or donor islets significantly improved the subsequent transplant outcomes in both syngeneic mouse islet transplantation model and human-to-nude mouse islet xenotransplantation model.

CONCLUSIONS

Liraglutide protects islets from cold ischemia-related oxidative stress during preservation and hence improved islet transplantation outcomes, and this protective effect of liraglutide in islets is associated with the activation of Akt signaling.

Advancements in innate immune regulation strategies in islet transplantation

As a newly emerging organ transplantation technique, islet transplantation has shown the advantages of minimal trauma and high safety since it was first carried out. The proposal of the Edmonton protocol, which has been widely applied, was a breakthrough in this method. However, direct contact between islets and portal vein blood will cause a robust innate immune response leading to massive apoptosis of the graft, and macrophages play an essential role in the innate immune response. Therefore, therapeutic strategies targeting macrophages in the innate immune response have become a popular research topic in recent years. This paper will summarize and analyze recent research on strategies for regulating innate immunity, primarily focusing on macrophages, in the field of islet transplantation, including drug therapy, optimization of islet preparation process, islet engineering and Mesenchymal stem cells cotransplantation. We also expounded the heterogeneity, plasticity and activation mechanism of macrophages in islet transplantation, providing a theoretical basis for further research.

Current practices in islet cell autotransplantation

INTRODUCTION

Chronic pancreatitis and recurrent acute pancreatitis comprise a spectrum of disease that results in complications related to exocrine and endocrine insufficiency and chronic pain with narcotic dependence and poor quality of life. The mainstay of therapy has been medical and endoscopic therapy; surgery, especially total pancreatectomy, was historically reserved for few select patients as the obligate exocrine insufficiency and pancreatogenic diabetes (type 3C) are challenging to manage. The addition of islet cell autotransplantation after total pancreatectomy helps to mitigate brittle type 3c diabetes and prevents mortality related to severe hypoglycemic episodes and hypoglycemic unawareness. There have been more recent data demonstrating the safety of surgery and the beneficial long-term outcomes.

AREAS COVERED

The purpose of this review is to describe the current practices in the field of islet cell autotransplantation including the selection and evaluation of patients for surgery, their preoperative work up and management, surgical approach, post-operative management and outcomes.

EXPERT OPINION

Total pancreatectomy and islet cell autotransplantation has the ability to drastically improve quality of life and prevent brittle diabetes for patients suffering with chronic pancreatitis.

GLP-1R agonist liraglutide attenuates pain hypersensitivity by stimulating IL-10 release in a nitroglycerin-induced chronic migraine mouse model

Glucagon-like peptide-1 receptor (GLP-1R) has been indicated to involve in chronic pain, however, the mechanism by which GLP-1R alleviates the central sensitization of chronic migraine (CM) remains unclear. Treatment with GLP-1R agonist liraglutide attenuated trigeminal allodynia and suppressed the protein levels of CM-associated molecules in the trigeminal nucleus caudalis (TNC). Further analysis showed that injection of liraglutide stimulated the release of IL-10 in the TNC. Treatment with IL-10 also alleviated pain hyperalgesia. Our findings illustrated that liraglutide might alleviate the central sensitization of CM by stimulating the release of IL-10, which reveals a novel mechanism of CM.

The anti-inflammatory and immunological properties of GLP-1 Receptor Agonists

In the last few years, a great interest has emerged in investigating the pleiotropic effects of Glucagon Like Peptide-1 Receptor Agonists (GLP-1RAs). While GLP-1RAs ability to lower plasma glucose and to induce weight loss has allowed them to be approved for the treatment of diabetes and obesity, consistent evidences from in vitro studies and preclinical models suggested that GLP-1RAs have anti-inflammatory properties and that may modulate the immune-system. Notably, such anti-inflammatory effects target different pathways in different tissues, underling the broad spectrum of GLP-1RAs actions. This review examines some of the currently proposed molecular mechanisms of GLP-1RAs actions and explores their potential benefits in reducing inflammatory responses, which may well suggest a future therapeutic use of GLP-1RAs in new indications.

New insight on the role of liraglutide in alleviating dexamethasone-induced pancreatic cytotoxicity via improving redox status, autophagy flux, and PI3K/Akt/Nrf2 signaling

Chronic glucocorticoids therapy is commonly complicated by steroid diabetes, although the underlying mechanisms are still elusive. Liraglutide, a glucagon-like peptide-1, was initially found to induce glycemic control and recently it was found to have many pleotropic effects; however, its role in pancreas remains unknown. The present study aims to estimate the protective role of liraglutide on dexamethasone-induced pancreatic cytotoxicity and hyperglycemia, highlighting the possible underlying biochemical, molecular, and cellular mechanisms. Twenty-eight male Wistar rats were involved in this study and were randomly divided into four groups. Group III and IV were treated with 1 mg/kg dexamethasone daily for 10 days. Group II and IV were treated with liraglutide in a dose of 0.8 mg/kg per day for 2 weeks. Pancreatic caspase-9, nuclear factor erythroid 2-related factor 2 (Nrf2), phospho-protein kinase-B (pAkt), and sequestrome 1 (p62) levels were assessed by immunoassay. Moreover, phosphoinositide 3-kinase (PI3K) expression by real-time PCR, microtubule-associated protein light chain 3 (LC3B) expression by immunohistochemistry, glycemic status, β-cell function by homoeostasis model assessment (HOMA) β index, and pancreatic redox status were assessed. Liraglutide improved blood glucose level, β-cell function, pancreatic caspase-9 level, redox status, and autophagy. Additionally, it increased pancreatic PI3K, pAkt, and Nrf2 levels. Moreover, preservation of pancreatic histological and the ultrastructural morphological features of β- and α-cells were observed. In conclusion, liraglutide protected against dexamethasone-induced pancreatic injury and hyperglycemia and decelerated the progression towards steroid diabetes via activating PI3K/Akt/Nrf2 signaling and autophagy flux pathways.

Comparison of the Effects of Liraglutide on Islet Graft Survival Between Local and Systemic Delivery

Islet transplantation has emerged as a promising treatment for type 1 diabetes mellitus. Liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, protects beta cells after islet transplantation by improving glycemic control through several mechanisms. In this study, we compared the effects of local pretreatment and systemic treatment with liraglutide on islet transplantation in a diabetic mouse model. Streptozotocin (STZ)-induced diabetic C57BL/6 mice were transplanted with syngeneic islets under the kidney capsule. Isolated islets were either locally treated with liraglutide before transplantation or mice were treated systemically by intraperitoneal injection after islet transplantation. Local pretreatment of islets with liraglutide was more effective in increasing body weight, decreasing hemoglobin A1c levels, and lowering blood glucose levels in STZ-diabetic mice transplanted with islets. Local pretreatment was also more effective in increasing insulin secretion and islet survival in STZ-diabetic mice. Histological analysis of the transplantation site revealed fewer apoptotic cells following local pretreatment compared with systemic injection of liraglutide. These findings indicate that liraglutide administered once locally before transplantation might have superior effects on islet preservation than systemic administration.

Towards Better Drug Repositioning: Targeted Immunoinflammatory Therapy for Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common and important microvascular complications of diabetes mellitus (DM). The main clinical features of DN are proteinuria and a progressive decline in renal function, which are associated with structural and functional changes in the kidney. The pathogenesis of DN is multifactorial, including genetic, metabolic, and haemodynamic factors, which can trigger a sequence of events. Controlling metabolic risks such as hyperglycaemia, hypertension, and dyslipidaemia is not enough to slow the progression of DN. Recent studies emphasized immunoinflammation as a critical pathogenic factor in the progression of DN. Therefore, targeting inflammation is considered a potential and novel treatment strategy for DN. In this review, we will briefly introduce the inflammatory process of DN and discuss the anti-inflammatory effects of antidiabetic drugs when treating DN.

GLP-1 receptor signaling increases PCSK1 and β cell features in human α cells

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that potentiates glucose-stimulated insulin secretion. GLP-1 is classically produced by gut L cells; however, under certain circumstances α cells can express the prohormone convertase required for proglucagon processing to GLP-1, prohormone convertase 1/3 (PC1/3), and can produce GLP-1. However, the mechanisms through which this occurs are poorly defined. Understanding the mechanisms by which α cell PC1/3 expression can be activated may reveal new targets for diabetes treatment. Here, we demonstrate that the GLP-1 receptor (GLP-1R) agonist, liraglutide, increased α cell GLP-1 expression in a β cell GLP-1R-dependent manner. We demonstrate that this effect of liraglutide was translationally relevant in human islets through application of a new scRNA-seq technology, DART-Seq. We found that the effect of liraglutide to increase α cell PC1/3 mRNA expression occurred in a subcluster of α cells and was associated with increased expression of other β cell-like genes, which we confirmed by IHC. Finally, we found that the effect of liraglutide to increase bihormonal insulin+ glucagon+ cells was mediated by the β cell GLP-1R in mice. Together, our data validate a high-sensitivity method for scRNA-seq in human islets and identify a potentially novel GLP-1-mediated pathway regulating human α cell function.

Implanted islet mass influences the effects of dipeptidyl peptidase-IV inhibitor LAF237 on transplantation outcomes in diabetic mice

Background

Previous studies showed inconsistent Results of the effects of dipeptidyl peptidase (DPP)-IV inhibitors on syngeneic mouse islet transplantation. We hypothesized that the implanted islet numbers are critical for the effects of DPP-IV inhibitors on the outcomes of transplantation.

Methods

One hundred and fifty or three hundred islets were syngeneically transplanted under the renal capsule of each streptozocin-diabetic C57BL/6 mouse and recipients were then treated without or with LAF237 (10 mg/kg/day, po) for 6 weeks. After transplantation, recipients’ blood glucose, body weight and intraperitoneal glucose tolerance test (IPGTT) were followed-up periodically. The graft was removed for the measurement of β-cell mass at 6 weeks.

Results

In recipients with 150 islets, it was not significantly different between the LAF237- treated group (n = 14) and control group (n = 14) in terms of the blood glucose, body weight, glucose tolerance at 2, 4 and 6 weeks or the graft β-cell mass at 6 weeks. In contrast, in recipients with 300 islets, the LAF237-treated group (n = 24) did have a lower area under the curve of the IPGTT at 4 weeks (p = 0.0237) and 6 weeks (p = 0.0113) as well as more graft β-cell mass at 6 weeks (0.655 ± 0.008 mg vs. 0.435 ± 0.006 mg, p = 0.0463) than controls (n = 24).

Conclusions

Our findings revealed 6-week treatment of LAF237 improves glucose tolerance and increases graft β-cell mass in diabetic mice transplanted with a sufficient number but not a marginal number of islets. These indicate that the effects of DPP-IV inhibitors are influenced by the implanted islet mass.

Liraglutide treatment improves the coronary microcirculation in insulin resistant Zucker obese rats on a high salt diet

BACKGROUND

Obesity, hypertension and prediabetes contribute greatly to coronary artery disease, heart failure and vascular events, and are the leading cause of mortality and morbidity in developed societies. Salt sensitivity exacerbates endothelial dysfunction. Herein, we investigated the effect of chronic glucagon like peptide-1 (GLP-1) receptor activation on the coronary microcirculation and cardiac remodeling in Zucker rats on a high-salt diet (6% NaCl).

METHODS

Eight-week old Zucker lean (+/+) and obese (fa/fa) rats were treated with vehicle or liraglutide (LIRA) (0.1 mg/kg/day, s.c.) for 8 weeks. Systolic blood pressure (SBP) was measured using tail-cuff method in conscious rats. Myocardial function was assessed by echocardiography. Synchrotron contrast microangiography was then used to investigate coronary arterial vessel function (vessels 50-350 µm internal diameter) in vivo in anesthetized rats. Myocardial gene and protein expression levels of vasoactive factors, inflammatory, oxidative stress and remodeling markers were determined by real-time PCR and Western blotting.

RESULTS

We found that in comparison to the vehicle-treated fa/fa rats, rats treated with LIRA showed significant improvement in acetylcholine-mediated vasodilation in the small arteries and arterioles (< 150 µm diameter). Neither soluble guanylyl cyclase or endothelial NO synthase (eNOS) mRNA levels or total eNOS protein expression in the myocardium were significantly altered by LIRA. However, LIRA downregulated Nox-1 mRNA (p = 0.030) and reduced ET-1 protein (p = 0.044) expression. LIRA significantly attenuated the expressions of proinflammatory and profibrotic associated biomarkers (NF-κB, CD68, IL-1β, TGF-β1, osteopontin) and nitrotyrosine in comparison to fa/fa-Veh rats, but did not attenuate perivascular fibrosis appreciably.

CONCLUSIONS

In a rat model of metabolic syndrome, chronic LIRA treatment improved the capacity for NO-mediated dilation throughout the coronary macro and microcirculations and partially normalized myocardial remodeling independent of changes in body mass or blood glucose.

Localized Controlled Release of Bilirubin from β-Cyclodextrin-Conjugated ε-Polylysine To Attenuate Oxidative Stress and Inflammation in Transplanted Islets

Islet transplantation has been considered the most promising therapeutic option with the potential to restore the physiological regulation of blood glucose concentrations in type 1 diabetes treatment. However, islets suffer from oxidative stress and nonspecific inflammation in the early stage of transplantation, which attributed to the leading cause of islet graft failure. Our previous study reported that bilirubin exerted antioxidative and anti-inflammatory effects on hypothermic preserved islets, which inspire us to utilize bilirubin to address the survival issue of grafted islets. However, the application of bilirubin for islet transplantation is limited by its poor solubility and fast clearance. In this study, we designed a supramolecular carrier (PLCD) that could improve the solubility of bilirubin and slowly release bilirubin to protect islets after cotransplantation. PLCD was synthesized by conjugating activated β-cyclodextrin (β-CD) to the side chain of ε-polylysine (PLL) and acted as a carrier to load bilirubin via host-guest interactions. The constructed bilirubin supramolecular system (PLCD-BR) significantly improved the solubility and prolonged the action time of bilirubin. In vitro results confirmed that PLCD-BR coculture substantially enhanced the resistance of islets to excessive oxidative stress and proinflammatory stimulation and maximumly maintained the islet function. In vivo, PLCD could prolong drug duration at the transplant site, and the localized released bilirubin could protect the islets from oxidative stress and suppress the production of inflammatory cytokines. Crucially, islet transplantation with PLCD-BR significantly extended the stable blood glucose time of diabetic mice and produced a faster glucose clearance compared to those cotransplanted with free bilirubin. Additionally, immunohistochemical analysis showed that PLCD-BR had superior antioxidative and anti-inflammatory abilities and beneficial effects on angiogenesis. These findings demonstrate that the PLCD-BR has great potentials to support successful islet transplantation.

Amniotic Membrane Extract Protects Islets From Serum-Deprivation Induced Impairments and Improves Islet Transplantation Outcome

Islet culture prior to transplantation is a standard practice in many transplantation centers. Nevertheless, the abundant islet mass loss and function impairment during this serum-deprivation culture period restrain the success of islet transplantation. In the present study, we used a natural biomaterial derived product, amniotic membrane extract (AME), as medium supplementation of islet pretransplant cultivation to investigate its protective effect on islet survival and function and its underlying mechanisms, as well as the engraftment outcome of islets following AME treatment. Results showed that AME supplementation improved islet viability and function, and decreased islet apoptosis and islet loss during serum-deprived culture. This was associated with the increased phosphorylation of PI3K/Akt and MAPK/ERK signaling pathway. Moreover, transplantation of serum-deprivation stressed islets that were pre-treated with AME into diabetic mice revealed better blood glucose control and improved islet graft survival. In conclusion, AME could improve islet survival and function in vivo and in vitro, and was at least partially through increasing phosphorylation of PI3K/Akt and MAPK/ERK signaling pathway.

Therapeutic Effects of Endogenous Incretin Hormones and Exogenous Incretin-Based Medications in Sepsis

BACKGROUND

Sepsis, a complex disorder characterized by a dysregulated immune response to an inciting infection, affects over one million Americans annually. Dysglycemia during sepsis hospitalization confers increased risk of organ dysfunction and death, and novel targets for the treatment of sepsis and maintenance of glucose homeostasis are needed. Incretin hormones are secreted by enteroendocrine cells in response to enteral nutrients and potentiate insulin release from pancreatic β cells in a glucose-dependent manner, thereby reducing the risk of insulin-induced hypoglycemia. Incretin hormones also reduce systemic inflammation in preclinical studies, but studies of incretins in the setting of sepsis are limited.

METHODS

In this bench-to-bedside mini-review, we detail the evidence to support incretin hormones as a therapeutic target in patients with sepsis. We performed a PubMed search using the medical subject headings "incretins," "glucagon-like peptide-1," "gastric inhibitory peptide," "inflammation," and "sepsis."

RESULTS

Incretin-based therapies decrease immune cell activation, inhibit proinflammatory cytokine release, and reduce organ dysfunction and mortality in preclinical models of sepsis. Several small clinical trials in critically ill patients have suggested potential benefit in glycemic control using exogenous incretin infusions, but these studies had limited power and were performed in mixed populations. Further clinical studies examining incretins specifically in septic populations are needed.

CONCLUSIONS

Targeting the incretin hormone axis in sepsis may provide a means of not only promoting euglycemia in sepsis but also attenuating the proinflammatory response and improving clinical outcomes.

Fighting Type-2 Diabetes: Present and Future Perspectives

BACKGROUND

Type-2 diabetes mellitus accounts for 80-90% of diabetic patients. So far, the treatment of diabetes mainly aims at elevating insulin level and lowering glucose level in the peripheral blood and mitigating insulin resistance. Physiologically, insulin secretion from pancreatic β cells is delicately regulated. Thus, how insulin-related therapies could titrate blood glucose appropriately and avoid the occurrence of hypoglycemia remains an important issue for decades. Similar question is addressed on how to attenuate vascular complication in diabetic subjects.

METHODS

We overviewed the evolution of each class of anti-diabetic drugs that have been used in clinical practice, focusing on their mechanisms, clinical results and cautions.

RESULTS

Glucagon-like peptide-1 receptor agonists stimulate β cells for insulin secretion in response to diet but not in fasting stage, which make them superior than conventional insulinsecretion stimulators. DPP-4 inhibitors suppress glucagon-like peptide-1 degradation. Sodium/ glucose co-transporter 2 inhibitors enhance glucose clearance through urine excretion. The appearance of these new drugs provides new information about glycemic control. We update the clinical findings of Glucagon-like peptide-1 receptor agonists, DPP-4 inhibitors and Sodium/glucose cotransporter 2 inhibitors in glycemic control and the risk or progression of cardiovascular disease in diabetic patients. Stem cell therapy might be an alternative tool for diabetic patients to improve β cell regeneration and peripheral ischemia. We summarize the clinical results of mesenchymal stem cells transplanted into patients with diabetic limb and foot.

CONCLUSION

A stepwise intensification of dual and triple therapy for individual diabetic patient is required to achieve therapeutic target.

Nonglycemic Effects of GLP-1 Agonists: From a Starling to Lizards to People

With the approval of exenatide in 2005, physicians had a new class of hypoglycemic agents available for the treatment of type 2 diabetes-the glucagon-like peptide-1 receptor agonists (or GLP-1 receptor agonists). As of this writing, there are seven drugs in this class available in the United States. In addition to demonstrating either cardiovascular risk neutrality or overt benefit, as now mandated by the United States Food and Drug Administration (FDA), many of these drugs have other, unexpected actions. It is our goal to outline these actions, some beneficial, some not. We have reviewed English-language articles in this area, not for an exhaustive study, but rather a broad search to define current understanding and perhaps generate further investigation.

Liraglutide Preserves Intracellular Calcium Handling in Isolated Murine Myocytes Exposed to Oxidative Stress

In ischemic/reperfusion (I/R) injured hearts, severe oxidative stress occurs and is associated with intracellular calcium (Ca2+) overload. Glucagon-Like Peptide-1 (GLP-1) analogues have been shown to exert cardioprotection in I/R heart. However, there is little information regarding the effects of GLP-1 analogue on the intracellular Ca2+ regulation in the presence of oxidative stress. Therefore, we investigated the effects of GLP-1 analogue, (liraglutide, 10 µM) applied before or after hydrogen peroxide (H2O2, 50 µM) treatment on intracellular Ca2+ regulation in isolated cardiomyocytes. We hypothesized that liraglutide can attenuate intracellular Ca2+ overload in cardiomyocytes under H2O2-induced cardiomyocyte injury. Cardiomyocytes were isolated from the hearts of male Wistar rats. Isolated cardiomyocytes were loaded with Fura-2/AM and fluorescence intensity was recorded. Intracellular Ca2+ transient decay rate, intracellular Ca2+ transient amplitude and intracellular diastolic Ca2+ levels were recorded before and after treatment with liraglutide. In H2O2 induced severe oxidative stressed cardiomyocytes (which mimic cardiac I/R) injury, liraglutide given prior to or after H2O2 administration effectively increased both intracellular Ca2+ transient amplitude and intracellular Ca2+ transient decay rate, without altering the intracellular diastolic Ca2+ level. Liraglutide attenuated intracellular Ca2+ overload in H2O2-induced cardiomyocyte injury and may be responsible for cardioprotection during cardiac I/R injury by preserving physiological levels of calcium handling during the systolic and diastolic phases of myocyte activation.

Liraglutide ameliorates cardiotoxicity induced by doxorubicin in rats through the Akt/GSK-3β signaling pathway

Doxorubicin (Dox)-induced cardiotoxicity constitutes the major adverse effect that limited its use. We investigated the possible protective effects of liraglutide on Dox-induced cardiotoxicity in rats. Rats were divided into the following groups: control group rats received normal saline [1 ml/kg, intraperitoneal (i.p.)]; doxorubicin group rats received doxorubicin (1.25 mg/kg, i.p.), four times per week for 4 weeks; and liraglutide group rats received doxorubicin (1.25 mg/kg, i.p.) four times per week for 4 weeks then received liraglutide (100 μg/kg, i.p) daily for 4 weeks. At the end of the study, animals were sacrificed and serum creatine kinase-MB (CK-MB) and troponin I levels were determined. Malondialdehyde (MDA), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and caspase-3 levels of the heart were determined. Cardiac AMPK, phosphorylated-Akt, tissue growth factor-β1 (TGF-β1), and GSK3-β levels of the heart were determined. Hematoxylin and eosin (H&E) stained sections form the heart were examined as well as immunohistochemical sections for detection of Bcl-2 expression. Dox treatment increased serum level of troponin I and CK-MB while decreased SOD activity, decreased AMPK, and p-Akt cardiac levels with increased in MDA, IL-6, TNF-α,GSK-3b, TGFB1, and caspase-3 levels in the heart with inflammation and necrosis in cardiac histopathology with decreased Bcl-2. Treatment with liraglutide decreased troponin I and CK-MB while increased SOD activity, AMPK, p-Akt with decrements in MDA, IL-6, TNF-α, GSK-3β, TGF-β1, and caspase-3 levels with attenuation of inflammation and necrosis while increased Bcl-2 expression. Liraglutide may thus represent a new clinical tool for the treatment of Dox-induced cardiotoxicity.

Improvement of islet graft function using liraglutide is correlated with its anti-inflammatory properties

Background and Purpose

Liraglutide improves the metabolic control of diabetic animals after islet transplantation. However, the mechanisms underlying this effect remain unknown. The objective of this study was to evaluate the anti‐inflammatory and anti‐oxidative properties of liraglutide on rat pancreatic islets in vitro and in vivo.

Experimental Approach

In vitro, rat islets were incubated with 10 μmol·L⁻¹ liraglutide for 12 and 24 h. Islet viability functionality was assessed. The anti‐inflammatory properties of liraglutide were evaluated by measuring CCL2, IL‐6 and IL‐10 secretion and macrophage chemotaxis. The anti‐oxidative effect of liraglutide was evaluated by measuring intracellular ROS and the total anti‐oxidative capacity. In vivo, 1000 islets were cultured for 24 h with or without liraglutide and then transplanted into the liver of streptozotocin‐induced diabetic Lewis rats with or without injections of liraglutide. Effects of liraglutide on metabolic control were evaluated for 1 month.

Key Results

Islet viability and function were preserved and enhanced with liraglutide treatment. Liraglutide decreased CCL2 and IL‐6 secretion and macrophage activation after 12 h of culture, while IL‐10 secretion was unchanged. However, intracellular levels of ROS were increased with liraglutide treatment at 12 h. This result was correlated with an increase of anti‐oxidative capacity. In vivo, liraglutide decreased macrophage infiltration and reduced fasting blood glucose in transplanted rats.

Conclusions and Implications

The beneficial effects of liraglutide on pancreatic islets appear to be linked to its anti‐inflammatory and anti‐oxidative properties. These findings indicated that analogues of glucagon‐like peptide‐1 could be used to improve graft survival.