Neuroprotective effect of the glucagon-like peptide-1 receptor agonist, synthetic exendin-4, in streptozotocin-induced diabetic rats

The Therapeutic Potential of Dipeptidyl Peptidase 4 Inhibitors and Glucagon-Like Peptide-1 Receptor Agonists in Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is one of the commonest complications of diabetes mellitus (DM). Current therapeutic approaches largely focus on pain management. However, less evidence is available on the clinical potential of two widely prescribed drug categories in DM management: dipeptidyl peptidase 4 inhibitors (DPP-4is) and glucagon-like peptide-1 receptor agonists (GLP-1RAs). In this review, we discuss evidence from both experimental and clinical studies on the potential utility of these drugs in the management of DPN. Immunohistochemical data indicate that agents in both categories promote neurite outgrowth, ion conduction, neuronal survival and Schwann cell function. Furthermore, intra-epidermal nerve fibre density has been reported to increase with DPP-4is or GLP-1RAs treatment. Moreover, electrophysiological studies have indicated a diverse, but mostly beneficial, effect on motor or sensory nerve conduction velocity. Clinical tests, such as the muscular grip or paw jumping control resembling neuropathic symptoms, have also confirmed the advantageous effect of DPP-4is and GLP-1RAs. Finally, limited but promising clinical data have shown improved somatosensory-evoked potentials and vibration perception threshold, as well as restored excitability and nerve size parameters. Nevertheless, further clinical studies are required to elucidate the exact role of DPP-4is and GLP-1RAs in DPN.

Advances in GLP-1 receptor agonists for pain treatment and their future potential

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) show substantial efficacy in regulating blood glucose levels and lipid metabolism, initially as an effective treatment for diabetes mellitus. In recent years, GLP-1RAs have become a focal point in the medical community due to their innovative treatment mechanisms, robust therapeutic efficacy, and expansive development prospects. Notably, GLP-1RAs benefit pain management through their neuroprotective and metabolic regulatory properties, such as inhibiting inflammation responses and oxidative stress, promoting β-endorphin release and modulating several other crucial biological pathways. Hence GLP-1RAs hold promise for repurposing as treatments for pain disorders. In this narrative review, we thoroughly trace the current preclinical and clinical evidence of seven pain modalities, including inflammatory pain, osteoarthritis, visceral pain, neuropathic pain, diabetic neuropathy, cancer pain and headache, to support the efficacy and underlying biological mechanisms of GLP-1RAs as therapeutic agents for pain suffering. Despite these promising findings, further research is necessary to establish their long-term efficacy, optimal dosing strategies, and potential synergistic interactions of GLP-1RAs with existing pain management therapies. Future clinical trials should aim to distinguish the direct analgesic effects of GLP-1RAs from their metabolic benefits and explore their broader applications in pain conditions. The ongoing exploration of new indications for GLP-1RAs further highlights their transformative potential in advancing medical treatments across diverse clinical fields.

Effect of the glucagon-like peptide-1 receptor agonists on diabetic peripheral neuropathy: A meta-analysis

Previous researches found that glucagon-like peptide 1 receptor agonists (GLP-1RA) offer benefits beyond their anti-diabetic properties, including weight loss and cardiovascular disease prevention. However, the effects of GLP-1RA on diabetic peripheral neuropathy (DPN) remain unclear. This meta-analysis aims to assess the potential benefits of GLP-1RA treatment in DPN patients by evaluating peripheral neural function. Following the Cochrane Collaboration and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we conducted a meta-analysis of the clinical trials investigating the impact of GLP-1RA treatment on peripheral neural function in patients with DPN. Outcomes were measured using electrophysiological tests, including nerve conduction velocity (NCV) and action potential amplitude. Our meta-analysis included six studies with 271 participants. Following GLP-1RA treatment, NCV significantly improved compared to the control group (MD 1.74; 95% CI 1.16 to 2.33; p < 0.001) and before treatment (MD 2.16; 95% CI 1.04 to 3.27; p < 0.001). Despite the improvement in NCV, blood glucose levels did not change significantly (MD -0.20 95% CI -0.87 to 0.46, p = 0.55) indicating that GLP-1RA enhances NCV through mechanisms other than glucose lowering. Nonetheless, as a result of the limited population studied, further research is needed to strengthen the reliability of these findings.

Impact of glucagon-like peptide-1 receptor agonists on axonal function in diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) affects approximately half of the 500 million people with type 2 diabetes worldwide. Previous studies have suggested that glucagon-like peptide-1 (GLP-1) receptors in the peripheral nervous system may be a suitable target for DPN treatment. Fourteen participants were consecutively recruited after being prescribed either semaglutide or dulaglutide as part of standard clinical care for type 2 diabetes. Participants underwent clinical assessment, nerve conduction studies, and axonal excitability assessment at baseline and at 3 mo following commencement of GLP-1 receptor agonist (GLP-1RA) therapy. These data were combined with 10 participants who had previously received exenatide therapy, and mathematical modeling of excitability data was undertaken. Clinical neuropathy scores improved at 3 mo following commencement of GLP-1 (baseline TNS 3.7 ± 4.5, posttreatment TNS 2.3 ± 3.4, P = 0.005). Nerve conduction studies demonstrated an improvement in sural amplitude at 3 mo (baseline 11.9 ± 8.5 μV, posttreatment 14.2 ± 9.2 μV; P = 0.013). Axonal excitability studies revealed changes consistent with improvements in Na+/K+-ATPase pump function and Na+ permeability, and this was supported by mathematical modeling. GLP-1RA therapy improves clinical and neurophysiological outcomes in DPN. Treatment with GLP-1RA may reverse axonal dysfunction by improving Na+/K+-ATPase pump function.NEW & NOTEWORTHY Diabetic peripheral neuropathy is known to be relentlessly progressive and irreversible. Prospective studies in 24 participants with diabetic peripheral neuropathy (DPN) treated with glucagon-like peptide-1 receptor agonists (GLP-1RA) demonstrated improvements in clinical neuropathy scores, nerve conduction studies, and axonal excitability recordings. Analysis of axonal excitability recordings revealed the mechanism for GLP-1RA improvement in DPN were changed consistent with improvements in Na+/K+-ATPase pump function, and this was supported by mathematical modeling.

Unlocking New Therapeutic Options for Vincristine-Induced Neuropathic Pain: The Impact of Preclinical Research

Vincristine, a vinca alkaloid, is used in chemotherapy protocols for cancers such as acute leukemia, Hodgkin's disease, neuroblastoma, cervical carcinoma, lymphomas, breast cancer, and melanoma. Among the common adverse effects of vincristine is peripheral neuropathy, with most patients receiving a cumulative dose over 4 mg/m2 who develop varying degrees of sensory neuropathy. The onset of vincristine-induced peripheral neuropathy can greatly affect patients' quality of life, often requiring dose adjustments or the discontinuation of treatment. Moreover, managing vincristine-induced peripheral neuropathy is challenging, with few effective therapeutic strategies available. In the past decade, preclinical studies have explored diverse substances aimed at preventing or alleviating VIPN. Our review consolidates these findings, focusing on the analgesic efficacy and potential mechanisms of various agents, including pharmaceutical drugs, natural compounds, and antioxidants, that show promise in reducing neuropathic pain and protecting neural integrity in preclinical models. Key novel therapeutic options, such as metabolic agents (liraglutide), enzyme inhibitors (ulinastatin), antipsychotics (aripiprazole), interleukin-1 receptor antagonists (anakinra), hormones (oxytocin), and antioxidants (thioctic acid), are highlighted for their neuroprotective, anti-inflammatory, and antioxidant effects. Through this synthesis, we aim to enhance the current understanding of VIPN management by identifying pharmacological strategies that target critical molecular pathways, laying the groundwork for future clinical studies. By clarifying these novel pharmacological approaches and elucidating their mechanisms of action, this review provides a foundation for developing more effective VIPN treatment strategies to ultimately improve patient outcomes.

GLP-1 and its derived peptides mediate pain relief through direct TRPV1 inhibition without affecting thermoregulation

Hormonal regulation during food ingestion and its association with pain prompted the investigation of the impact of glucagon-like peptide-1 (GLP-1) on transient receptor potential vanilloid 1 (TRPV1). Both endogenous and synthetic GLP-1, as well as a GLP-1R antagonist, exendin 9-39, reduced heat sensitivity in naïve mice. GLP-1-derived peptides (liraglutide, exendin-4, and exendin 9-39) effectively inhibited capsaicin (CAP)-induced currents and calcium responses in cultured sensory neurons and TRPV1-expressing cell lines. Notably, exendin 9-39 alleviated CAP-induced acute pain, as well as chronic pain induced by complete Freund's adjuvant (CFA) and spared nerve injury (SNI), in mice without causing hyperthermia associated with other TRPV1 inhibitors. Electrophysiological analyses revealed that exendin 9-39 binds to the extracellular side of TRPV1, functioning as a noncompetitive inhibitor of CAP. Exendin 9-39 did not affect proton-induced TRPV1 activation, suggesting its selective antagonism. Among the exendin 9-39 fragments, exendin 20-29 specifically binds to TRPV1, alleviating pain in both acute and chronic pain models without interfering with GLP-1R function. Our study revealed a novel role for GLP-1 and its derivatives in pain relief, suggesting exendin 20-29 as a promising therapeutic candidate.

GLP-1 and Its Derived Peptides Mediate Pain Relief Through Direct TRPV1 Inhibition Without Affecting Thermoregulation

Hormonal regulation during food ingestion and its association with pain prompted the investigation of the impact of glucagon-like peptide-1 (GLP-1) on the transient receptor potential vanilloid 1 (TRPV1). Both endogenous and synthetic GLP-1 and an antagonist of GLP-1, exendin 9-39, reduced heat sensitivity in naïve mice. GLP-1-derived peptides (liraglutide, exendin-4, and exendin 9-39) effectively inhibited capsaicin (CAP)-induced currents and calcium responses in cultured sensory neurons and TRPV1-expressing cell lines. Notably, the exendin 9-39 alleviated CAP-induced acute pain, as well as chronic pain induced by complete Freund's adjuvant (CFA) and spared nerve injury (SNI) in mice, without causing hyperthermia associated with other TRPV1 inhibitors. Electrophysiological analyses revealed that exendin 9-39 binds to the extracellular side of TRPV1, functioning as a noncompetitive inhibitor of CAP. Exendin 9-39 did not affect proton-induced TRPV1 activation, suggesting its selective antagonism. Among exendin 9-39 fragments, exendin 20-29 specifically binds to TRPV1, alleviating pain in both acute and chronic pain models without interfering with GLP-1R function. Our study revealed a novel role for GLP-1 and its derivatives in pain relief, proposing exendin 20-29 as a promising therapeutic candidate.

Glucagon-like peptide-1 receptor agonists reverse nerve morphological abnormalities in diabetic peripheral neuropathy

AIMS/HYPOTHESIS

Diabetic peripheral neuropathy (DPN) is a highly prevalent cause of physical disability. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are used to treat type 2 diabetes and animal studies have shown that glucagon-like peptide-1 (GLP-1) receptors are present in the central and peripheral nervous systems. This study investigated whether GLP-1 RAs can improve nerve structure.

METHODS

Nerve structure was assessed using peripheral nerve ultrasonography and measurement of tibial nerve cross-sectional area, in conjunction with validated neuropathy symptom scores and nerve conduction studies. A total of 22 consecutively recruited participants with type 2 diabetes were assessed before and 1 month after commencing GLP-1 RA therapy (semaglutide or dulaglutide).

RESULTS

There was a pathological increase in nerve size before treatment in 81.8% of the cohort (n=22). At 1 month of follow-up, there was an improvement in nerve size in 86% of participants (p<0.05), with 32% returning to normal nerve morphology. A 3 month follow-up study (n=14) demonstrated further improvement in nerve size in 93% of participants, accompanied by reduced severity of neuropathy (p<0.05) and improved sural sensory nerve conduction amplitude (p<0.05).

CONCLUSIONS/INTERPRETATION

This study demonstrates the efficacy of GLP-1 RAs in improving neuropathy outcomes, evidenced by improvements in mainly structural and morphological measures and supported by electrophysiological and clinical endpoints. Future studies, incorporating quantitative sensory testing and measurement of intraepidermal nerve fibre density, are needed to investigate the benefits for small fibre function and structure.

Glucagon-like peptide-1 receptor agonists for the management of diabetic peripheral neuropathy

Diabetes mellitus is a prevalent chronic disease characterized by hyperglycemia. Diabetic peripheral neuropathy (DPN) is one of the complications of diabetes mellitus and is caused by neuron injury induced by hyperglycemic circumstances. The incidence of DPN varies among different countries and regions, ranging from nearly 20% to over 70%. Patients with DPN may encounter symmetric pain or discomfort of the extremes, leading to reduced quality of life and even amputation. The pharmacological management for painful DPN mainly includes antidepressants due to their analgesic effects. Nevertheless, effective therapies to impact the pathogenesis and progression of DPN are lacking. Glucagon-like peptide-1 receptor (GLP-1R) agonists show efficacy in controlling blood glucose and serve as a treatment modality for diabetes mellitus. In recent years, evidence has been proposed that GLP-1R agonists exert neuroprotective effects through modulating inflammation, oxidative stress, and mitochondrial dysfunction. On the other hand, clinical evidence on the potential of GLP-1R agonists for treating DPN is still controversial and limited. This narrative review summarizes the preclinical and clinical studies investigating the capacity of GLP-1R agonists as therapeutic agents for DPN.

The Effect of Liraglutide on Axon Regeneration and Functional Recovery after Peripheral Nerve Lesion

Peripheral nerve injuries inflict severe consequences, necessitating innovative therapeutic strategies. This study investigates the potential of liraglutide, a glucagon-like peptide-1 receptor agonist, in mitigating the consequences of peripheral nerve injury. The existing treatment methods for such injuries underscore the importance of ongoing translational research efforts. Thirty adult Wistar rats underwent sciatic nerve dissection and repair surgery. The nerves were surgically transected using micro scissors at a precise location located 1.5 cm proximal to the trifurcation site. The study included a control group and two experimental groups, one treated with saline (placebo group) and the other with liraglutide (experimental group) for 12 weeks. Motor function, electromyography (EMG), and biochemical and histopathological analyses were performed after 12 weeks of treatment. Electrophysiological assessments revealed that liraglutide improved the compound muscle action potential (CMAP) amplitude and motor function compared to the saline-treated group. Histological and immunohistochemical analyses demonstrated increased NGF expression, total axon number, and diameter and reduced fibrosis in the liraglutide group. Biochemical analyses illustrated liraglutide's antioxidative properties, evidenced by reduced malondialdehyde (MDA) levels. Galectin-3 levels were suppressed and GDF-11 levels were modulated by liraglutide, indicating anti-inflammatory and anti-apoptotic effects. Liraglutide is a promising therapeutic intervention for peripheral nerve injuries, promoting functional recovery and histopathological improvement. Its multifaceted positive impact, beyond glycemic control, suggests constructive effects on the acute and chronic inflammatory processes associated with peripheral neuropathy. These findings warrant further research to elucidate molecular mechanisms and facilitate clinical translation. The study contributes valuable insights to the growing understanding of GLP-1 receptor agonists' neuroprotective properties in the context of peripheral nerve injuries.

Therapeutic potential of endoplasmic reticulum stress inhibitors in the treatment of diabetic peripheral neuropathy

Endoplasmic stress response, the unfolded protein response (UPR), is a homeostatic signaling pathway comprising transmembrane sensors that get activated upon alterations in ER luminal environment. Studies suggest a relation between activated UPR pathways and several disease states such as Parkinson, Alzheimer, inflammatory bowel disease, tumor growth, and metabolic syndrome. Diabetic peripheral neuropathy (DPN), a common microvascular complication of diabetes-related chronic hyperglycemia, causes chronic pain, loss of sensation, foot ulcers, amputations, allodynia, hyperalgesia, paresthesia, and spontaneous pain. Factors like disrupted calcium signaling, dyslipidemia, hyperglycemia, inflammation, insulin signaling, and oxidative stress disturb the UPR sensor levels manifesting as DPN. We discuss new effective therapeutic alternatives for DPN that can be developed by targeting UPR pathways like synthetic ER stress inhibitors like 4-PhenylButyric acid (4-PBA), Sephin 1, Salubrinal and natural ER stress inhibitors like Tauroursodeoxycholic acid (TUDCA), Cordycepin, Proanthocyanidins, Crocin, Purple Rice extract and cyanidin and Caffeic Acid Phenethyl Ester (CAPE).

A Review of Recent Pharmacological Advances in the Management of Diabetes-Associated Peripheral Neuropathy

Diabetic peripheral neuropathy is a common complication of longstanding diabetes mellitus. These neuropathies can present in various forms, and with the increasing prevalence of diabetes mellitus, a subsequent increase in peripheral neuropathy cases has been noted. Peripheral neuropathy has a significant societal and economic burden, with patients requiring concomitant medication and often experiencing a decline in their quality of life. There is currently a wide variety of pharmacological interventions, including serotonin norepinephrine reuptake inhibitors, gapentanoids, sodium channel blockers, and tricyclic antidepressants. These medications will be discussed, as well as their respective efficacies. Recent advances in the treatment of diabetes mellitus with incretin system-modulating drugs, specifically glucagon-like peptide-1 agonists, have been promising, and their potential implication in the treatment of peripheral diabetic neuropathy is discussed in this review.

Amelioration of inflammatory myopathies by glucagon-like peptide-1 receptor agonist via suppressing muscle fibre necroptosis

BACKGROUND

As glucocorticoids induce muscle atrophy during the treatment course of polymyositis (PM), novel therapeutic strategy is awaited that suppresses muscle inflammation but retains muscle strength. We recently found that injured muscle fibres in PM undergo FASLG-mediated necroptosis, a form of regulated cell death accompanied by release of pro-inflammatory mediators, contributes to accelerate muscle inflammation and muscle weakness. Glucagon-like peptide-1 receptor (GLP-1R) agonists have pleiotropic actions including anti-inflammatory effects, prevention of muscle atrophy, and inhibition of cell death, in addition to anti-diabetic effect. We aimed in this study to examine the role of GLP-1R in PM and the effect of a GLP-1R agonist on in vivo and in vitro models of PM.

METHODS

Muscle specimens of PM patients and a murine model of PM, C protein-induced myositis (CIM), were examined for the expression of GLP-1R. The effect of PF1801, a GLP-1R agonist, on CIM was evaluated in monotherapy or in combination with prednisolone (PSL). As an in vitro model of PM, C2C12-derived myotubes were treated with FASLG to induce necroptosis. The effect of PF1801 on this model was analysed.

RESULTS

GLP-1R was expressed on the inflamed muscle fibres of PM and CIM. The treatment of CIM with PF1801 in monotherapy (PF) or in combination with PSL (PF + PSL) suppressed CIM-induced muscle weakness (grip strength, mean ± SD (g); PF 227 ± 6.0 (P < 0.01), PF + PSL 224 ± 8.5 (P < 0.01), Vehicle 162 ± 6.0) and decrease in cross-sectional area of muscle fibres (mean ± SD (μm² ); PF 1896 ± 144 (P < 0.05), PF + PSL 2018 ± 445 (P < 0.01), Vehicle 1349 ± 199) as well as the severity of histological inflammation scores (median, interquartile range; PF 0.0, 0.0-0.5 (P < 0.05), PF + PSL 0.0, 0.0-0.0 (P < 0.01), Vehicle 1.9, 1.3-3.3). PF1801 decreased the levels of inflammatory mediators such as TNFα, IL-6, and HMGB1 in the serum of CIM. PF1801 inhibited necroptosis of the myotubes in an AMP-activated protein kinase (AMPK)-dependent manner. PF1801 activated AMPK and decreased the expression of PGAM5, a mitochondrial protein, which was crucial for necroptosis of the myotubes. PF1801 promoted the degradation of PGAM5 through ubiquitin-proteasome activity. Furthermore, PF1801 suppressed FASLG-induced reactive oxygen species (ROS) accumulation in myotubes, also crucial for the execution of necroptosis, thorough up-regulating the antioxidant molecules including Nfe2l2, Hmox1, Gclm, and Nqo1.

CONCLUSIONS

GLP-1R agonist could be a novel therapy for PM that recovers muscle weakness and suppresses muscle inflammation through inhi biting muscle fibre necroptosis.

Glucagon-Like Peptide-1 Receptor Agonists as Potential Myelination-Inducible and Anti-Demyelinating Remedies

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) were developed as insulinotropic and anti-hyperglycemic agents for the treatment of type 2 diabetes, but their neurotrophic and neuroprotective activities have been receiving increasing attention. Myelin plays a key role in the functional maintenance of the central and peripheral nervous systems, and recent in vivo and in vitro studies have shed light on the beneficial effects of GLP-1RAs on the formation and protection of myelin. In this article, we describe the potential efficacy of GLP-1RAs for the induction of axonal regeneration and remyelination following nerve lesions and the prevention and alleviation of demyelinating disorders, particularly multiple sclerosis.

Current and Emerging Pharmacotherapeutic Interventions for the Treatment of Peripheral Nerve Disorders

Peripheral nerve disorders are caused by a range of different aetiologies. The range of causes include metabolic conditions such as diabetes, obesity and chronic kidney disease. Diabetic neuropathy may be associated with severe weakness and the loss of sensation, leading to gangrene and amputation in advanced cases. Recent studies have indicated a high prevalence of neuropathy in patients with chronic kidney disease, also known as uraemic neuropathy. Immune-mediated neuropathies including Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy may cause significant physical disability. As survival rates continue to improve in cancer, the prevalence of treatment complications, such as chemotherapy-induced peripheral neuropathy, has also increased in treated patients and survivors. Notably, peripheral neuropathy associated with these conditions may be chronic and long-lasting, drastically affecting the quality of life of affected individuals, and leading to a large socioeconomic burden. This review article explores some of the major emerging clinical and experimental therapeutic agents that have been investigated for the treatment of peripheral neuropathy due to metabolic, toxic and immune aetiologies.

RETRACTED: Long-Lasting Exendin-4-Loaded PLGA Nanoparticles Ameliorate Cerebral Ischemia/Reperfusion Damage in Diabetic Rats

Exendin-4 (Ex-4) is an incretin mimetic agent approved for diabetes treatment and neuronal protection. However, the required frequent injections restrict its clinical application. We prepared Ex-4-loaded poly(d,l-lactide-co-glycolide) nanoparticles (PEx-4) and investigated their effect on cerebral ischemia/reperfusion (IR) injury associated with micturition center damage-induced cystopathy in diabetic rats. Using ten minutes of bilateral carotid artery occlusion combined with hemorrhage-induced hypotension of the IR model in streptozotocin-induced type 1 diabetic (T1DM) Wistar rats, we compared the effects of Ex-4 and PEx-4 on prefrontal cortex edema, voiding function and oxidative stress including cerebral spinal fluid (CSF) reference H2O2 (RH2O2) and HOCl (RHOCl) levels, endoplasmic reticulum (ER) stress, apoptosis, autophagy and pyroptosis signaling in brain and bladder by Western blot and immunohistochemistry. Single injection of PEx-4 displayed higher CSF antioxidant activity and a long-lasting hypoglycemic effect compared to Ex-4 in rats. T1DM and IR primarily enhanced CSF RH2O2, and pIRE-1/caspase-12/pJNK/CHOP-mediated ER stress, caspase-3/PARP-mediated apoptosis, Beclin-1/LC3B-mediated autophagy and caspase-1/IL-1β-mediated pyroptosis signaling in the damaged brains. Our data further evidenced that PEx-4 were more efficient than Ex-4 in attenuating IR-evoked prefrontal cortex edema, the impairment in micturition center and the enhanced level of CSF RH2O2 and HOCl, ER stress, apoptosis, autophagy and pyroptosis parameters in the damaged brains, but had less of an effect on IR-induced voiding dysfunction in bladders of T1DM rats. In summary, PEx-4 with stronger antioxidant activity and long-lasting bioavailability may efficiently confer therapeutic efficacy to ameliorate IR-evoked brain damage through the inhibitory action on oxidative stress, ER stress, apoptosis, autophagy and pyroptosis signaling in diabetic rats.

Spinal cord-wide structural disruption in type 2 diabetes rescued by exenatide "a glucagon-like peptide-1 analogue" via down-regulating inflammatory, oxidative stress and apoptotic signaling pathways

The mechanisms of spinal cord-wide structural and functional disruption in diabetic patients remain elusive. This study evaluated histopathological alterations of the spinal cord cytoarchitecture in T2DM model of rats and assessed the potential ameliorating effect of exenatide "a potent GLP-1 analogue". Thirty male rats were allocated into three groups; I (control), II (Diabetic): T2DM was induced by high fat diet for 8 weeks followed by a single I.P injection of STZ (25 mg/kg BW) and III (Diabetic/Exenatide): T2DM rats injected with exenatide (10 μg/Kg, S.C. twice daily for 2 weeks). Neurobehavioral sensory and motor tests were carried out and glycemic control biomarkers and indices of insulin resistance and sensitivity were measured. In addition, the spinal cord was processed for histological and immunohistochemical studies besides assessing its tissue homogenate levels of pro-inflammatory/anti-inflamatory cytokines and oxidant/antioxidant biomarkers. Moreover, RT-qPCR was performed to measure the expression of proapoptotic/antiapoptotic and neurotrophic genes. The diabetic rats exhibited thermal hyperalgesia, mechanical allodynia and decreased locomotor activity along with increased serum glucose, insulin, HbA1c, HOMA-IR while, quantitative insulin sensitivity check index (QUICKI) was decreased. Also, IL-1β NF-kB, MDA increased while IL-10, SOD activity and β-endorphin decreased in the spinal tissue. Up regulation of caspase-3 and down regulation of Bcl-2, nerve growth factor (NGF) and glial cell-derived neurotrophic (GDNF) in diabetic rats. Also, they exhibited histopathological changes and increased CD68 positive microglia and Bax immunoreactivity in the spinal cord. Subsequent to exenatide treatment, most biomolecular, structural and functional impairments of the spinal cord were restored in the diabetic rats. In conclusion, the neuro-modulating effect of exenatide against diabetic-induced spinal cord affection warrants the concern about its therapeutic relevance in confronting the devastating diabetic neuropathic complications.

Effect of exenatide on peripheral nerve excitability in type 2 diabetes

OBJECTIVE

To assess the effect of exenatide (a GLP-1 receptor agonist), dipeptidyl peptidase-IV (DPP-IV) inhibitors, and sodium-glucose co-transporter 2 (SGLT-2) inhibitors on measures of peripheral nerve excitability in patients with type 2 diabetes.

METHODS

Patients receiving either exenatide (n = 32), a DPP-IV inhibitor (n = 31), or a SGLT-2 inhibitor (n = 27) underwent motor nerve excitability assessments. Groups were similar in age, sex, HbA_1c, diabetes duration, lipids, and neuropathy severity. An additional 10 subjects were assessed prospectively over 3 months while oral anti-hyperglycaemic therapy was kept constant. A cohort of healthy controls (n = 32) were recruited for comparison.

RESULTS

Patients receiving a DPP-IV or SGLT-2 inhibitor demonstrated abnormalities in peak threshold reduction, S2 accommodation, superexcitability, and subexcitability. In contrast, patients treated with exenatide were observed to have normal nerve excitability. In the prospective arm, exenatide therapy was associated with an improvement in nerve function as patients demonstrated corrections in S2 accommodation, superexcitability, and subexcitability at follow-up. These changes were independent of the reductions in HbA_1c following exenatide treatment.

CONCLUSIONS

Exenatide was associated with an improvement in measures of nerve excitability in patients with type 2 diabetes.

SIGNIFICANCE

Exenatide may improve peripheral nerve function in type 2 diabetes.

Deciphering the Neuroprotective Role of Glucagon-like Peptide-1 Agonists in Diabetic Neuropathy: Current Perspective and Future Directions

Diabetic neuropathy is referred to as a subsequential and debilitating complication belonging to type 1 and type 2 diabetes mellitus. It is a heterogeneous group of disorders with a particularly complex pathophysiology and also includes multiple forms, ranging from normal discomfort to death. The evaluation of diabetic neuropathy is associated with hyperglycemic responses, resulting in an alteration in various metabolic pathways, including protein kinase C pathway, polyol pathway and hexosamine pathway in Schwann and glial cells of neurons. The essential source of neuronal destruction is analogous to these respective metabolic pathways, thus identified as potential therapeutic targets. These pathways regulating therapeutic medications may be used for diabetic neuropathy, however, only target specific drugs could have partial therapeutic activity. Various antidiabetic medications have been approved and marketed, which possess the therapeutic ability to control hyperglycemia and ameliorate the prevalence of diabetic neuropathy. Among all antidiabetic medications, incretin therapy, including Glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, are the most favorable medications for the management of diabetes mellitus and associated peripheral neuropathic complications. Besides enhancing glucose-evoked insulin release from pancreatic β-cells, these therapeutic agents also play a vital role to facilitate neurite outgrowth and nerve conduction velocity in dorsal root ganglion. Furthermore, incretin therapy also activates cAMP and ERK signalling pathways, resulting in nerve regeneration and repairing. These effects are evidently supported by a series of preclinical data and investigations associated with these medications. However, the literature lacks adequate clinical trial outcomes related to these novel antidiabetic medications. The manuscript emphasizes the pathogenesis, current pharmacological approaches and vivid description of preclinical and clinical data for the effective management of diabetic neuropathy.

Efficacy of exenatide, ozone, and methyl prednisolone for the recovery of infraorbital nerve paresthesia after injury in rats

BACKGROUND

Infraorbital nerve injury often occurs due to zygomatic complex fracture. There is no standard protocol to restore the sensory and motor function of the nerve after injury. Some medications are used to improve nerve function. This histopathological animal study aimed to assess the neurotrophic efficacy of exenatide, ozone, and methyl prednisolone for injured infraorbital nerve.

MATERIALS AND METHODS

In this animal study, 60 rats were randomly divided into five groups (n = 12) of control, saline, methyl prednisolone, exenatide, and ozone. Under general anesthesia, a unilateral infraorbital incision was made, and the nerve was compressed with a hemostat for 5 s. Depending on the study group, the rats received the designated medications. All rats were sacrificed after 14 days, and the nerve recovery was evaluated by observing the slides prepared from the area under a light microscope using histological and immunohistochemical parameters. Data were analyzed using Chi-square test and Tukey's least significant difference test (P < 0.05).

RESULTS

No inflammation in the peripheral tissue had a significantly higher frequency in the methyl prednisolone group (P < 0.05). Degeneration, intracellular inflammatory infiltrate, muscle injury, fibrosis around the nerve, granulation tissue, vascular proliferation, and infiltration of inflammatory cells around the nerve were more commonly absent in the exenatide group (P < 0.05).

CONCLUSION

Exenatide showed superior efficacy for the recovery of infraorbital nerve function after injury. Thus, it may be beneficial for postoperative care following infraorbital nerve injury.

Exendin-4 Promotes Schwann Cell Survival/Migration and Myelination In Vitro

Besides its insulinotropic actions on pancreatic β cells, neuroprotective activities of glucagon-like peptide-1 (GLP-1) have attracted attention. The efficacy of a GLP-1 receptor (GLP-1R) agonist exendin-4 (Ex-4) for functional repair after sciatic nerve injury and amelioration of diabetic peripheral neuropathy (DPN) has been reported; however, the underlying mechanisms remain unclear. In this study, the bioactivities of Ex-4 on immortalized adult rat Schwann cells IFRS1 and adult rat dorsal root ganglion (DRG) neuron–IFRS1 co-culture system were investigated. Localization of GLP-1R in both DRG neurons and IFRS1 cells were confirmed using knockout-validated monoclonal Mab7F38 antibody. Treatment with 100 nM Ex-4 significantly enhanced survival/proliferation and migration of IFRS1 cells, as well as stimulated the movement of IFRS1 cells toward neurites emerging from DRG neuron cell bodies in the co-culture with the upregulation of myelin protein 22 and myelin protein zero. Because Ex-4 induced phosphorylation of serine/threonine-specific protein kinase AKT in these cells and its effects on DRG neurons and IFRS1 cells were attenuated by phosphatidyl inositol-3′-phosphate-kinase (PI3K) inhibitor LY294002, Ex-4 might act on both cells to activate PI3K/AKT signaling pathway, thereby promoting myelination in the co-culture. These findings imply the potential efficacy of Ex-4 toward DPN and other peripheral nerve lesions.

Non-glucose risk factors in the pathogenesis of diabetic peripheral neuropathy

In this review, we consider the diverse risk factors in diabetes patients beyond hyperglycemia that are being recognized as contributors to diabetic peripheral neuropathy (DPN). Interest in such alternative mechanisms has been encouraged by the recognition that neuropathy occurs in subjects with metabolic syndrome and pre-diabetes and by the reporting of several large clinical studies that failed to show reduced prevalence of neuropathy after intensive glucose control in patients with type 2 diabetes. Animal models of obesity, dyslipidemia, hypertension, and other disorders common to both pre-diabetes and diabetes have been used to highlight a number of plausible pathogenic mechanisms that may either damage the nerve independent of hyperglycemia or augment the toxic potential of hyperglycemia. While pathogenic mechanisms stemming from hyperglycemia are likely to be significant contributors to DPN, future therapeutic strategies will require a more nuanced approach that considers a range of concurrent insults derived from the complex pathophysiology of diabetes beyond direct hyperglycemia.

Repurposing GLP1 agonists for neurodegenerative diseases

There is a large unmet medical need to find disease modifying therapies against neurodegenerative diseases. This review summarizes data indicating that insulin resistance occurs in neurodegeneration and strategies to normalize insulin sensitivity in neurons may provide neuroprotective actions. In particular, recent preclinical and clinical studies in Parkinson's disease and Alzheimer's disease have indicated that glucagon-like peptide 1 (GLP1) agonism and dipeptidyl peptidase-4 inhibition may exert neuroprotection. Mechanistic insights from these studies and future directions for drug development against neurodegeneration based on GLP1 agonism are discussed.

DPP-4 Inhibitor Linagliptin is Neuroprotective in Hyperglycemic Mice with Stroke via the AKT/mTOR Pathway and Anti-apoptotic Effects

Dipeptidyl peptidase 4 (DPP-4) inhibitors have been shown to have neuroprotective effects in diabetic patients suffering from stroke, but less research has focused on patients with mild hyperglycemia below the threshold for a diagnosis of diabetes. In this investigation, a hyperglycemic mouse model was generated by intraperitoneal injection of streptozotocin and then subjected to focal cerebral ischemia. We demonstrated that the DPP-4 inhibitor linagliptin significantly decreased the infarct volume, reduced neuronal cell death, decreased inflammation, and improved neurological deficit compared with control mice. Linagliptin up-regulated the expression of p-Akt and p-mTOR and regulated the apoptosis factors Bcl-2, Bax, and caspase 9. Taken together, these results suggest that linagliptin exerts a neuroprotective action likely through activation of the Akt/mTOR pathway along with anti-apoptotic and anti-inflammatory mechanisms. Therefore, linagliptin may be considered as a therapeutic treatment for stroke patients with mild hyperglycemia.

The investigation of therapeutic potential of oxytocin and liraglutide on vincristine-induced neuropathy in rats

The aim of this study was to assess the therapeutic potential of oxytocin and liraglutide (LIR), a GLP-1 analogue, in a rat model of vincristine-induced neuropathy. Rats were injected with vincristine (VCR) at a dose of 4 mg/kg twice a week for 5 weeks. The VCR-administered rats were divided into three groups and received saline, oxytocin, or liraglutide simultaneously with VCR. After the treatment period, electrophysiological, biochemical, histological, and immunohistochemical investigations were performed. Electromyography (EMG) recordings demonstrated significant alterations in the VCR + saline group (p < .001). Also, motor performance was decreased in the VCR + saline group (p < .05). Histologically, the axonal diameter was decreased in all groups. VCR + saline group showed significantly increased lipid peroxidation and decreased nerve growth factor (NGF) expression. However, the administration of oxytocin and liraglutide significantly prevented the EMG alterations, lipid peroxidation, and reduction in neuronal NGF expression. On the basis of these findings, oxytocin and liraglutide may be considered as potential agents for the prevention of VCR-induced neuropathy.

Diabetic neuropathy in children and adolescents with type 1 diabetes mellitus: Diagnosis, pathogenesis, and associated genetic markers

Diabetic neuropathy (DN) is a common long-term complication of type 1 (T1D) and type 2 (T2D) diabetes mellitus, with significant morbidity and mortality. DN is defined as impaired function of the autonomic and/or peripheral nervous system, often subclinical, particularly in children and adolescents with T1D. Nerve conduction studies (NCS) and skin biopsies are considered gold-standard methods in the assessment of DN. Multiple environmental and genetic factors are involved in the pathogenesis of DN. Specifically, the role of metabolic control and glycemic variability is of paramount importance. A number of recently identified genes, including the AKR1B1, VEGF, MTHFR, APOE, and ACE genes, contribute significantly in the pathogenesis of DN. These genes may serve as biomarkers to predict future DN development or treatment response. In addition, they may serve as the basis for the development of new medications or gene therapy. In this review, the diagnostic evaluation, pathogenesis, and associated genetic markers of DN in children and adolescents with T1D are presented and discussed.

GLP-1's role in neuroprotection: a systematic review

Glucagon-like peptide 1 (GLP-1) is a target for treatment of diabetes; however, its function in the brain is not well studied. In this systematic review, we aimed to analyze the neuroprotective role of GLP-1 and its defined mechanisms. Methods: We searched 'Web of Science' and 'Pubmed' to identify relevant studies using GLP-1 as the keyword. Two hundred and eighty-nine clinical and preclinical studies have been included. Data have been presented by grouping neurodegenerative, neurovascular and specific cell culture models. Results: Recent literature shows that GLP-1 and its agonists, DPP-4 inhibitors and combined GLP-1/GIP molecules are effective in partially or fully reversing the effects of neurotoxic compounds, neurovascular complications of diabetes, neuropathological changes related with Alzheimer's disease, Parkinson's disease or vascular occlusion. Possible mechanisms that provide neuroprotection are enhancing the viability of the neurons and restoring neurite outgrowth by increased neurotrophic factors, increasing subventricular zone progenitor cells, decreasing apoptosis, decreasing the level of pro-inflammatory factors, and strengthening blood-brain barrier. Conclusion: Based on the preclinical studies, GLP-1 modifying agents are promising targets for neuroprotection. On the other hand, the number of clinical studies that investigate GLP-1 as a treatment is low and further clinical trials are needed for a benchside to bedside translation of recent findings.

Anti-inflammatory and pro-healing impacts of exendin-4 treatment in Zucker diabetic rats: Effects on skin wound fibroblasts

Using male Zucker diabetic fatty (ZDF) rats implanted subcutaneously with polyethylene mesh pieces stimulating granulation tissue development, we investigated the effects of the in vivo and in vitro treatment with exendin-4, a glucagon-like peptide-1 agonist displaying a variety of antidiabetic actions, on the markers of metabolism, inflammation, and healing in addition to skin wound fibroblast/myofibroblast activities. Exendin-4 at increasing doses of 3-10 μg/kg or 0.9% saline was injected daily to ZDF rats pre-implanted with the mesh for 3 weeks. Then, fibroblasts/myofibroblasts isolated from the granulation tissue in both groups were further exposed in vitro to exendin-4 at concentrations of 0-100 nmol/l. After a 3-week administration period, cumulative food and water intake and body weight were reduced significantly. The serum and fibroblast culture medium C-reactive protein (CRP) concentrations and matrix metalloprotease-9/tissue matrix metalloproteinase inhibitor-1 (MMP-9/TIMP-1) ratio in the fibroblast culture medium were diminished significantly in the exendin-4 pretreated group, indicating the increased expression of anti-inflammatory and pro-healing biomarkers. In vivo exendin-4 treatment also increased the number of living fibroblasts/myofibroblasts in cell cultures. The subsequent in vitro exposure to exendin-4 significantly increased metabolic activity and total collagen content in fibroblast/myofibroblast colonies derived from exendin-4-pretreated rats but reduced the number of viable cells. A cytotoxic effect was noted at the highest exendin-4 concentrations used. To conclude, the treatment of diabetic rats with exendin-4 had beneficial effects on systemic and tissue metabolic, inflammatory, and healing markers and on fibroblast functions crucial for wound repair but showed some cytotoxicity on these cells.

GLP‑1R agonists ameliorate peripheral nerve dysfunction and inflammation via p38 MAPK/NF‑κB signaling pathways in streptozotocin‑induced diabetic rats

The present study aimed to investigate the mechanism of glucagon‑like peptide‑1 receptor (GLP‑1R) agonists in the progression of diabetic peripheral neuropathy (DPN) in streptozotocin (STZ)‑induced diabetic rats, through inflammatory signaling pathways. The DPN rat model was generated by intraperitoneal injection of STZ and then treated with the GLP‑1R agonist liraglutide or saline for 8 weeks. These animals were randomly divided into 4 groups (10 rats in each): The normal control + saline group, the normal control + liraglutide group, the diabetic + saline (DM) group and the diabetic + liraglutide (DML) group. The nerve conduction velocity (NCV) in the sciatic nerves of the rats was monitored over a period of 8 weeks. Peripheral serum was obtained for the measurement of blood glucose, tumor necrosis factor‑α (TNF‑α), interleukin‑6 (IL‑6) and IL‑1β level. The protein levels of phosphorylated (p‑) and total extracellular signal‑regulated kinase, c‑Jun NH2‑terminal kinases, p38 mitogen‑activated protein kinases (MAPK), and nuclear and cytoplasmic nuclear factor‑κB (NF‑κB) were measured through western blot analysis. Sciatic nerve mRNA expression levels of proinflammatory chemokines (TNF‑α, IL‑6 and IL‑1β), chemokines [monocyte chemoattractant protein‑1 (MCP‑1)], adhesion molecules [intercellular adhesion molecule 1 (ICAM‑1)], neurotrophic factors [neuritin, nerve growth factor (NGF) and neuron‑specific enolase (NSE)] and NADPH oxidase 4 (NOX4) were evaluated by reverse transcription-quantitative polymerase chain reaction. Subsequent to 8 weeks of treatment with liraglutide, the density of myelin nerve fibers was partially restored in the DML group. The delayed motor NCV and sensory NCV in the DML group were improved. The IOD value of NOX4 staining in the DML group (24.43±9.01) was reduced compared with that in the DM group (56.60±6.91). The levels of TNF‑α, IL‑1β and IL‑6 in the peripheral serum of the DML group were significantly suppressed compared with those of the DM group. It was also observed that the mRNA expression levels of TNF‑α, IL‑6, IL‑1β, MCP‑1, ICAM‑1 and NOX4 in the sciatic nerve were attenuated in the DML group. The mRNA expression of neuritin and NGF was significantly increased in the DML group compared with that of the DM group; NSE was reduced in the sciatic nerves of the DML group compared with that of the DM group. Additionally, the protein expression of p‑p38 MAPK and NF‑κB in the DML group was significantly suppressed. These data demonstrated that GLP‑1R agonists may prevent nerve dysfunction in the sciatic nerves of diabetic rats via p38 MAPK/NF‑κB signaling pathways independent of glycemic control. GLP‑1R agonists may be a useful therapeutic strategy for slowing the progression of DPN.

GLP1 and GIP are involved in the action of synbiotics in broiler chickens

Background

In order to discover new strategies to replace antibiotics in the post-antibiotic era in meat-type chicken production, two new synbiotics were tested: (Lactobacillus salivarius IBB3154 plus galactooligosaccharide (Syn1) and Lactobacillus plantarum IBB3036 plus raffinose family oligosaccharides (Syn2).

Methods

The synbiotics were administered via syringe, using a special automatic system, into the egg air chamber of Cobb 500 broiler chicks on the 12^th day of egg incubation (2 mg of prebiotics + 10⁵ cfu bacteria per egg). Hatched roosters (total 2,400) were reared on an experimental farm, kept in pens (75 animals per pen), with free access to feed and water. After 42 d animals were slaughtered. Blood serum, pancreas, duodenum and duodenum content were collected.

Results

Syn2 increased trypsin activity by 2.5-fold in the pancreas and 1.5-fold in the duodenal content. In the duodenum content, Syn2 resulted in ca 30% elevation in lipase activity and 70% reduction in amylase activity. Syn1 and Syn2 strongly decreased expression of mRNA for GLP-1 and GIP in the duodenum and for GLP-1 receptors in the pancreas. Simultaneously, concentrations of the incretins significantly diminished in the blood serum (P < 0.05). The decreased expression of incretins coincides with changed activity of digestive enzymes in the pancreas and in the duodenal content. The results indicate that incretins are involved in the action of Syn1 and Syn2 or that they may even be their target. No changes were observed in key hormones regulating metabolism (insulin, glucagon, corticosterone, thyroid hormones, and leptin) or in metabolic indices (glucose, NEFA, triglycerides, cholesterol). Additionally, synbiotics did not cause significant changes in the activities of alanine and aspartate aminotransferases in broiler chickens. Simultaneously, the activity of alkaline phosphatase and gamma glutamyl transferase diminished after Syn2 and Syn1, respectively.

Conclusion

The selected synbiotics may be used as in ovo additives for broiler chickens, and Syn2 seems to improve their potential digestive proteolytic and lipolytic ability. Our results suggest that synbiotics can be directly or indirectly involved in incretin secretion and reception.

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 promotes regeneration of injured rat sciatic nerve

Damage to peripheral nerves results in partial or complete dysfunction. After peripheral nerve injuries, a full functional recovery usually cannot be achieved despite the standard surgical repairs. Neurotrophic factors and growth factors stimulate axonal growth and support the viability of nerve cells. The objective of this study is to investigate the neurotrophic effect of exenatide (glucagon like peptide-1 analog) in a rat sciatic nerve neurotmesis model. We injected 10 μg/d exenatide for 12 weeks in the experimental group (n = 12) and 0.1 mL/d saline for 12 weeks in the control group (n = 12). We evaluated nerve regeneration by conducting electrophysiological and motor functional tests. Histological changes were evaluated at weeks 1, 3, 6, and 9. Nerve regeneration was monitored using stereomicroscopy. The electrophysiological and motor functions in rats treated with exenatide were improved at 12 weeks after surgery. Histological examination revealed a significant increase in the number of axons in injured sciatic nerve following exenatide treatment confirmed by stereomicroscopy. In an experimentally induced neurotmesis model in rats, exenatide had a positive effect on nerve regeneration evidenced by electromyography, functional motor tests, histological and stereomicroscopic findings.

DPP-4 inhibitors in diabetic complications: role of DPP-4 beyond glucose control

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are an emerging class of antidiabetic drugs that constitutes approximately fifty percent of the market share of the oral hypoglycemic drugs. Its mechanism of action for lowering blood glucose is essentially via inhibition of the rapid degradation of incretin hormones, such as glucagon-like peptide (GLP)-1 and gastric inhibitory polypeptide (GIP), thus the plasma concentration of GLP-1 increases, which promotes insulin secretion from the pancreatic β cells and suppresses glucagon secretion from the α cells. In addition to the direct actions on the pancreas, GLP-1 exhibits diverse actions on different tissues through its action on GLP-1 receptor, which is expressed ubiquitously. Moreover, DPP-4 has multiple substrates besides GLP-1 and GIP, including cytokines, chemokines, neuropeptides, and growth factors, which are involved in many pathophysiological conditions. Recently, it was suggested that DPP-4 is a new adipokine secreted from the adipose tissue, which plays an important role in the regulation of the endocrine function in obesity-associated type 2 diabetes. Consequently, DPP-4 inhibitors have been reported to exhibit cytoprotective functions against various diabetic complications affecting the liver, heart, kidneys, retina, and neurons. This review outlines the current understanding of the effect of DPP-4 inhibitors on the complications associated with type 2 diabetes, such as liver steatosis and inflammation, dysfunction of the adipose tissue and pancreas, cardiovascular diseases, nephropathy, and neuropathy in preclinical and clinical studies.

Endothelial Progenitor Cells in Diabetic Microvascular Complications: Friends or Foes?

Despite being featured as metabolic disorder, diabetic patients are largely affected by hyperglycemia-induced vascular abnormality. Accumulated evidence has confirmed the beneficial effect of endothelial progenitor cells (EPCs) in coronary heart disease. However, antivascular endothelial growth factor (anti-VEGF) treatment is the main therapy for diabetic retinopathy and nephropathy, indicating the uncertain role of EPCs in the pathogenesis of diabetic microvascular disease. In this review, we first illustrate how hyperglycemia induces metabolic and epigenetic changes in EPCs, which exerts deleterious impact on their number and function. We then discuss how abnormal angiogenesis develops in eyes and kidneys under diabetes condition, focusing on “VEGF uncoupling with nitric oxide” and “competitive angiopoietin 1/angiopoietin 2” mechanisms that are shared in both organs. Next, we dissect the nature of EPCs in diabetic microvascular complications. After we overview the current EPCs-related strategies, we point out new EPCs-associated options for future exploration. Ultimately, we hope that this review would uncover the mysterious nature of EPCs in diabetic microvascular disease for therapeutics.

The glucagon like peptide 1 analogue, exendin-4, attenuates oxidative stress-induced retinal cell death in early diabetic rats through promoting Sirt1 and Sirt3 expression

This study was aimed to further investigate the possible mechanisms by which the glucagon like peptide 1 analogue, exendin-4 (EX4), protects rat retinal cells at the early stage of diabetes. EX4 was injected intravitreally into normal and early-stage streptozotocin-diabetic rats. Cell death, reactive oxygen species (ROS), and electroretinogram (ERG) were measured. Sirtuin (Sirt) mRNA and protein were analyzed. In retinas of diabetic rats 1 month after diabetes onset, cell death and ROS level increased significantly, and the b-wave amplitudes and OPs were significantly reduced. Four days after intravitreal EX4 treatment, retinal cell death and ROS level in retinas reduced significantly, and visual function was recovered. In the retinas of early-stage diabetic rats, the expressions of Sirt1 and Sirt3 were also found to be significantly decreased, and both were back to normal levels after intravitreal injection of EX4. In R28 cells, hydrogen peroxide (H2O2) treatment increased ROS and cell death and decreased Sirt1 and Sirt3. With the addition of EX4 into the culture system, the expressions of Sirt1 and Sirt3 were increased, and the H2O2-induced ROS and cell death were significantly reduced. These results confirm a mechanism for EX4 to protect retinal cells from diabetic damage and oxidative injury. EX4 reduces retinal cell death and ROS generation by upregulating Sirt1 and Sirt3 expressions in the retina of early-stage diabetic rats as well as in H2O2-treated R28 cells.

Mechanisms of neuroprotective action of incretin mimetics

Recently, on the pharmacological market, new drugs from the class of incretin mimetics, or glucagon-like peptide-1 (GLP-1) receptor agonists, which have proven their high effectiveness in type 2 diabetes mellitus therapy, have appeared. At present, much attention has been paid to the pleotropic effects of incretin mimetics. In a number of both experimental and clinical studies, cardioprotective effects of this medication group have been demonstrated. The present review elucidates existing data about neuroprotective effects of GLP-1 receptor agonists in brain ischaemia and in nonischaemic nervous system diseases such as diabetic neuropathy and neurodegenerative disorders. The possible mechanisms for these effects, which appear to be primarily antioxidant effects, anti-inflammatory effects, antiapoptotic effects and an increase in neurons differentiation, are discussed.

Incretin-Based Therapy for Prevention of Diabetic Vascular Complications

Diabetic vascular complications are the most common cause of mortality and morbidity worldwide, with numbers of affected individuals steadily increasing. Diabetic vascular complications can be divided into two categories: macrovascular andmicrovascular complications. Macrovascular complications include coronary artery diseaseand cerebrovascular disease, while microvascular complications include retinopathy and chronic kidney disease. These complications result from metabolic abnormalities, including hyperglycemia, elevated levels of free fatty acids, and insulin resistance. Multiple mechanisms have been proposed to mediate the adverse effects of these metabolic disorders on vascular tissues, including stimulation of protein kinase C signaling and activation of the polyol pathway by oxidative stress and inflammation. Additionally, the loss of tissue-specific insulin signaling induced by hyperglycemia and toxic metabolites can induce cellular dysfunction and both macro- and microvascular complications characteristic of diabetes. Despite these insights, few therapeutic methods are available for the management of diabetic complications. Recently, incretin-based therapeutic agents, such as glucagon-like peptide-1 and dipeptidyl peptidase-4 inhibitors, have been reported to elicit vasotropic actions, suggesting a potential for effecting an actual reduction in diabetic vascular complications. The present review will summarize the relationship between multiple adverse biological mechanisms in diabetes and putative incretin-based therapeutic interventions intended to prevent diabetic vascular complications.

Pioglitazone and exenatide enhance cognition and downregulate hippocampal beta amyloid oligomer and microglia expression in insulin-resistant rats

Insulin resistance is known to be a risk factor for cognitive impairment, most likely linked to insulin signaling, microglia overactivation, and beta amyloid (Aβ) deposition in the brain. Exenatide, a long lasting glucagon-like peptide-1 (GLP-1) analogue, enhances insulin signaling and shows neuroprotective properties. Pioglitazone, a peroxisome proliferated-activated receptor-γ (PPAR-γ) agonist, was previously reported to enhance cognition through its effect on Aβ accumulation and clearance. In the present study, insulin resistance was induced in male rats by drinking fructose for 12 weeks. The effect of monotherapy with pioglitazone (10 mg·kg(-1)) and exenatide or their combination on memory dysfunction was determined and some of the probable underlying mechanisms were studied. The current results confirmed that (1) feeding male rats with fructose syrup for 12 weeks resulted in a decline of learning and memory registered in eight-arm radial maze test; (2) treatment with pioglitazone or exenatide enhanced cognition, reduced hippocampal neurodegeneration, and reduced hippocampal microglia expression and beta amyloid oligomer deposition in a manner that is equal to monotherapies. These results may give promise for the use of pioglitazone or exenatide for ameliorating the learning and memory deficits associated with insulin resistance in clinical setting.

Exenatide Facilitates Recovery from Oxaliplatin-Induced Peripheral Neuropathy in Rats

Background

Oxaliplatin has widely been used as a key drug in the treatment of colorectal cancer; however, it causes peripheral neuropathy. Exenatide, a glucagon-like peptide-1 (GLP-1) agonist, is an incretin mimetic secreted from ileal L cells, which is clinically used to treat type 2 diabetes mellitus. GLP-1 receptor agonists have been reported to exhibit neuroprotective effects on the central and peripheral nervous systems. In this study, we investigated the effects of exenatide on oxaliplatin-induced neuropathy in rats and cultured cells.

Methods

Oxaliplatin (4 mg/kg) was administered intravenously twice per week for 4 weeks, and mechanical allodynia was evaluated using the von Frey test in rats. Axonal degeneration was assessed by toluidine blue staining of sciatic nerves.

Results

Repeated administration of oxaliplatin caused mechanical allodynia from day 14 to 49. Although the co-administration of extended-release exenatide (100 μg/kg) could not inhibit the incidence of oxaliplatin-induced mechanical allodynia, it facilitated recovery from the oxaliplatin-induced neuropathy with reparation of axonal degeneration. Inhibition of neurite outgrowth was evaluated in cultured pheochromocytoma 12 (PC12) cells. Exenatide inhibited oxaliplatin-induced neurite degeneration, but did not affect oxaliplatin-induced cell injury in cultured PC12 cells. Additionally, extended-release exenatide had no effect on the anti-tumor activity of oxaliplatin in cultured murine colon adenocarcinoma 26 (C-26) cells or C-26 cell-implanted mice.

Conclusion

These results suggest that exenatide may be useful for treating peripheral neuropathy induced by oxaliplatin in colorectal cancer patients with type 2 diabetes.

Saxagliptin: a novel antiparkinsonian approach

The emergence of glucagon-like peptide-1 as a crucial contender in modifying neurodegenerative diseases in the preclinical studies has instigated interest in investigating the antiparkinsonian effect of dipeptidyl peptidase (DPP)-4 inhibition. Notably, saxagliptin (SAX), the DPP-4 inhibitor, recently showed efficacy in ameliorating streptozotocin-induced Alzheimer's disease; however, its effect on Parkinson's disease (PD) has not yet been elucidated. In a rat rotenone (ROT) model, SAX prominently improved motor performance as well as muscle coordination and corrected akinesia. Moreover, SAX preserved substantia nigra pars compacta tyrosine hydroxylase (TH) immunoreactivity while halting the reduction in the striatal TH, dopamine (DA) and complex I. Meanwhile, SAX prevented the ROT-induced increment of striatal DPP-4 and the decline in cAMP, ATP/ADP and brain-derived neurotropic factor levels. Improvement in striatal energy level was associated with partial hindrance of ROT-induced body weight reduction. In addition, through its anti-inflammatory potential, SAX decreased the ROT-induced nuclear factor-κΒ, inducible nitric oxide synthase, tumor necrosis factor-α, intracellular adhesion molecule-1 and myeloperoxidase. The antiapoptotic marker B-cell lymphoma-2 was enhanced by SAX, versus reduction in caspase-3 and its intrinsic apoptotic activator cytochrome C. Furthermore, SAX amended alterations induced by ROT in the thiobarbituric acid reactive substances and the transcriptional factor Nrf-2 level. In conclusion, SAX can be introduced as a novel approach for the management of PD based on the remarkable improvement in motor functions denoting antiparkinsonian efficacy via antioxidant, anti-inflammatory, antiapoptotic, neuroprotective and neurorestorative mechanisms. These effects were linked to DPP-4 inhibition, reduced neurodegeneration and enhanced DA synthesis.

Neurotrophic and neuroprotective properties of exendin-4 in adult rat dorsal root ganglion neurons: involvement of insulin and RhoA

Glucagon-like peptide-1 (GLP-1) is thought to preserve neurons and glia following axonal injury and neurodegenerative disorders. We investigated the neurotrophic and neuroprotective properties of exendin (Ex)-4, a synthetic GLP-1 receptor (GLP-1R) agonist, on adult rat dorsal root ganglion (DRG) neurons and PC12 cells. GLP-1R was predominantly localized on large and small peptidergic neurons in vivo and in vitro, suggesting the involvement of GLP-1 in both the large and small sensory fiber functions. Ex-4 dose-dependently (1 ≤ 10 ≤ 100 nM) promoted neurite outgrowth and neuronal survival at 2 and 7 days in culture, respectively. Treatment with 100 nM Ex-4 restored the reduced neurite outgrowth and viability of DRG neurons caused by the insulin removal from the medium and suppressed the activity of RhoA, an inhibitory regulator for peripheral nerve regeneration, in PC12 cells. Furthermore, these effects were attenuated by co-treatment with phosphatidylinositol-3'-phosphate kinase (PI3K) inhibitor, LY294002. These findings imply that Ex-4 enhances neurite outgrowth and neuronal survival through the activation of PI3K signaling pathway, which negatively regulates RhoA activity. Ex-4 and other GLP-1R agonists may compensate for the reduced insulin effects on neurons, thereby being beneficial for the treatment of diabetic neuropathy.

Effect of treatment with sitagliptin on somatosensory-evoked potentials and metabolic control in patients with type 2 diabetes mellitus

OBJECTIVE

To evaluate the effect of sitagliptin on somatosensory-evoked potentials (SEPs) and metabolic control in patients with type 2 diabetes mellitus without clinical diabetic neuropathy.

MATERIALS AND METHODS

Interventional, prospective, and open study. Patients with less than six months from the diagnosis were included. Examinations of SEPs and laboratory tests at fasting and after food stimulation were performed before and after three months of treatment with sitagliptin (100 mg/day).

RESULTS

There was a reduction in the mean levels of HbA1c (P < 0.0001), fasting glucose (P = 0.001), total cholesterol (P = 0.019), and ALT (P = 0.022). An increase in active GLP-1 was found at the end of the study (P = 0.0025). Several SEPs showed statistically significant differences when analyzed before and after treatment with sitagliptin.

CONCLUSION

The results give a glimpse of the possible use of sitagliptin in the treatment of some neurodegenerative conditions of the peripheral nervous system, in addition to its already established role in glycemic control.

The role of type 2 diabetes in neurodegeneration

A growing body of evidence links type-2 diabetes (T2D) with dementia and neurodegenerative diseases such as Alzheimer's disease (AD). AD is the most common form of dementia and is characterised neuropathologically by the accumulation of extracellular beta amyloid (Aβ) peptide aggregates and intracellular hyper-phosphorylated tau protein, which are thought to drive and/or accelerate inflammatory and oxidative stress processes leading to neurodegeneration. Although the precise mechanism remains unclear, T2D can exacerbate these neurodegenerative processes. Brain atrophy, reduced cerebral glucose metabolism and CNS insulin resistance are features of both AD and T2D. Cell culture and animal studies have indicated that the early accumulation of Aβ may play a role in CNS insulin resistance and impaired insulin signalling. From the viewpoint of insulin resistance and impaired insulin signalling in the brain, these are also believed to initiate other aspects of brain injury, including inflammatory and oxidative stress processes. Here we review the clinical and experimental pieces of evidence that link these two chronic diseases of ageing, and discuss underlying mechanisms. The evaluation of treatments for the management of diabetes in preclinical, and clinical studies and trials for AD will also be discussed.

GLP-1 receptor agonist liraglutide reverses long-term atypical antipsychotic treatment associated behavioral depression and metabolic abnormalities in rats

Mood disorder patients that are on long-term atypical antipsychotics treatment frequently experience metabolic dysfunctions. In addition to this, accumulating evidences points to increased risk of structural abnormalities, brain volume changes, altered neuroplasticity and behavioral depression with long-term antipsychotics use. However, there is paucity of preclinical evidences for long-term antipsychotic associated depression-like behavior. The objectives of the present study were: (1) to evaluate influence of long-term antipsychotic (olanzapine) treatment on rat behavior in forced swim test (FST) as a model for depression and; (2) to examine impact of glucagon-like peptide 1 (GLP-1) receptor agonist liraglutide - an antidiabetic medication for type II diabetes, on long-term olanzapine associated metabolic and behavioral changes in rats. Daily olanzapine treatment (0.5 mg/kg; p.o.) for 8-9 weeks significantly increased body weights, food and water intake, plasma cholesterol and triglycerides and immobility time in FST with parallel reduction in plasma HDL cholesterol levels. These results points to development of metabolic abnormalities and depression-like behavior with long-term olanzapine treatment. Acute liraglutide (50 μg/kg; i.p.) and imipramine (10 mg/kg, i. p.) treatment per se significantly decreased duration of immobility in FST compared to vehicle treated rats. Additionally, 3-week liraglutide treatment (50 μg/kg; i.p., daily) partially reversed metabolic abnormalities and depression-like behavior with long-term olanzapine-treatment in rats. None of these treatment regimens affected locomotor behavior of rats. In summary, add-on GLP-1 receptor agonists promise novel alternatives to counteract long-term antipsychotics associated behavioral and metabolic complications.

Extra-pancreatic effects of incretin-based therapies

Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and inhibits glucagon secretion in the pancreatic islets of Langerhans under hyperglycaemia. In type 2 diabetes (T2DM), GLP-1 improves glycaemic control without a hypoglycaemia risk. GLP-1 receptors have also been found in extra-pancreatic tissues, e.g., the cardiovascular system, the gastrointestinal system, and the central nervous system. Since cardiovascular comorbidities and degenerative neurological changes are associated with T2DM, the interest in the extrapancreatic effects of GLP-1 has increased. GLP-1-based therapies with either GLP-1 receptor agonists (GLP-1 RA) or DPP-4 inhibitors (that delay the degradation of endogenous GLP-1) have become widely used therapeutic options in T2DM. In clinical studies, GLP-1 RA have demonstrated a significant lowering of blood pressure that is independent of body weight changes. Preclinical data and small short-term studies with GLP-1 and GLP-1 RA have shown cardioprotective effects in ischaemia models. GLP-1 as well as a treatment with GLP-1 RA also induces a stable body weight loss by affecting GLP-1 signaling in the hypothalamus and by slowing gastric emptying. Regarding neuroprotective actions in degenerative neurological disease models for Parkinson's- or Alzheimer's disease or neurovascular complications like stroke, animal studies have shown positive results. In this article, a summary of the extrapancreatic effects of GLP-1 and GLP-1-based therapies is presented.

The extra-pancreatic effects of GLP-1 receptor agonists: a focus on the cardiovascular, gastrointestinal and central nervous systems

The glucagon-like peptide-1 receptor agonists (GLP-1RAs) exenatide, liraglutide and lixisenatide have been shown to improve glycaemic control and beta-cell function with a low risk of hypoglycaemia in people with type 2 diabetes. GLP-1 receptors are also expressed in extra-pancreatic tissues and trial data suggest that GLP-1RAs also have effects beyond their glycaemic actions. Preclinical studies using native GLP-1 or GLP-1RAs provide substantial evidence for cardioprotective effects, while clinical trial data have shown beneficial actions on hypertension and dyslipidaemia in people with type 2 diabetes. Significant weight loss has been reported with GLP-1RAs in both people with type 2 diabetes and obese people without diabetes. GLP-1RAs also slow down gastric emptying, but preclinical data suggest that the main mechanism behind GLP-1RA-induced weight loss is more likely to involve their effects on appetite signalling in the brain. GLP-1RAs have also been shown to exert a neuroprotective role in rodent models of stroke, Alzheimer's disease and Parkinson's disease. These extra-pancreatic effects of GLP-1RAs could provide multi-factorial benefits to people with type 2 diabetes. Potential adverse effects of GLP-1RA treatment are usually manageable but may include gastrointestinal effects, increased heart rate and renal injury. While extensive further research is still required, early data suggest that GLP-1RAs may also have the potential to favourably impact cardiovascular disease, obesity or neurological disorders in people without diabetes in the future.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1: Incretin actions beyond the pancreas

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine on ingestion of various nutrients to stimulate insulin secretion from pancreatic β-cells glucose-dependently. GIP and GLP-1 undergo degradation by dipeptidyl peptidase-4 (DPP-4), and rapidly lose their biological activities. The actions of GIP and GLP-1 are mediated by their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which are expressed in pancreatic β-cells, as well as in various tissues and organs. A series of investigations using mice lacking GIPR and/or GLP-1R, as well as mice lacking DPP-4, showed involvement of GIP and GLP-1 in divergent biological activities, some of which could have implications for preventing diabetes-related microvascular complications (e.g., retinopathy, nephropathy and neuropathy) and macrovascular complications (e.g., coronary artery disease, peripheral artery disease and cerebrovascular disease), as well as diabetes-related comorbidity (e.g., obesity, non-alcoholic fatty liver disease, bone fracture and cognitive dysfunction). Furthermore, recent studies using incretin-based drugs, such as GLP-1 receptor agonists, which stably activate GLP-1R signaling, and DPP-4 inhibitors, which enhance both GLP-1R and GIPR signaling, showed that GLP-1 and GIP exert effects possibly linked to prevention or treatment of diabetes-related complications and comorbidities independently of hyperglycemia. We review recent findings on the extrapancreatic effects of GIP and GLP-1 on the heart, brain, kidney, eye and nerves, as well as in the liver, fat and several organs from the perspective of diabetes-related complications and comorbidities.