Glucagon-like peptide-1 (GLP-1) protects against methylglyoxal-induced PC12 cell apoptosis through the PI3K/Akt/mTOR/GCLc/redox signaling pathway

Unlocking longevity with GLP-1: A key to turn back the clock?

Traditionally known for managing blood sugar, GLP-1, a gut hormone, is emerging as a potential key to both lengthening lifespan and combating age-related ailments. While widely recognized for its role in blood sugar control, GLP-1 is increasingly recognized for its diverse effects on various biological pathways beyond glucose metabolism. Research across organisms and humans suggests that activating GLP-1 receptors significantly impacts cellular processes linked to aging. Its ability to boost mitochondrial function, enhance cellular stress resistance, and quell inflammation hints at its wider influence on aging mechanisms. This intricate interplay between GLP-1 and longevity appears to act through multiple pathways. One key effect is its ability to modulate insulin sensitivity, potentially curbing age-related metabolic issues like type 2 diabetes. Its neuroprotective properties also make it a promising candidate for addressing age-related cognitive decline and neurodegenerative diseases. Furthermore, preclinical studies using GLP-1 analogs or agonists have shown promising results in extending lifespan and improving healthspan in various model organisms. These findings provide a compelling rationale for exploring GLP-1-based interventions in humans to extend healthy aging. However, despite the exciting therapeutic prospects of GLP-1 in promoting longevity, challenges remain. Determining optimal dosages, establishing long-term safety profiles, and investigating potential adverse effects require comprehensive clinical investigations before we can confidently translate these findings to humans. This article emphasises the wide applicability of GLP-1.

The Association of Circulating Glucagon-Like Peptide-1 with Cognitive Functions and Biomarkers in Alzheimer's Disease

Background

Alzheimer's disease (AD) is an age-related neurodegenerative disease that is clinically characterized by progressive cognitive decline. Glucagon-like peptide-1 (GLP-1) is a hormone that belongs to the incretin family and is released in response to nutrient intake. It plays a role in maintaining metabolic homeostasis and has been suggested to be involved in maintaining the brain microenvironment. However, the role of GLP-1 in AD pathogenesis has not been fully illustrated.

Objective

This study aims to investigate the clinical relevance of GLP-1 in AD and the effects of GLP-1 in amyloid-β (Aβ) metabolism in vitro.

Methods

In this study, 39 AD patients and 120 cognitively intact controls were included. Plasma levels of GLP-1 were measured using ELISA. SH-SY5Y cells overexpressing human amyloid precursor protein (APP) were treated with GLP-1. Western blot analysis was used to assess the effects of GLP-1 on the metabolism of Aβ.

Results

Plasma GLP-1 levels were decreased with aging. Plasma GLP-1 levels were lower in AD patients in comparison with healthy older adults. Plasma GLP-1 levels were positively associated with Mini-Mental State Examination scores but negatively associated with plasma pTau181 levels. GLP-1 dose-dependently increased the area fraction of mitochondrial staining in vitro. Furthermore, GLP-1 dose-dependently promoted the α-cleavage of APP, thus reducing the generation of Aβ.

Conclusions

GLP-1 has neuroprotective effects in AD, and therefore the decrease in GLP-1 levels during aging might contribute to the development of AD.

Management of Poststroke Hyperglycemia: Results of the TEXAIS Randomized Clinical Trial

BACKGROUND

Hyperglycemia in acute ischemic stroke reduces the efficacy of stroke thrombolysis and thrombectomy, with worse clinical outcomes. Insulin-based therapies are difficult to implement and may cause hypoglycemia. We investigated whether exenatide, a GLP-1 (glucagon-like peptide-1) receptor agonist, would improve stroke outcomes, and control poststroke hyperglycemia with minimal hypoglycemia.

METHODS

The TEXAIS trial (Treatment With Exenatide in Acute Ischemic Stroke) was an international, multicenter, phase 2 prospective randomized clinical trial (PROBE [Prospective Randomized Open Blinded End-Point] design) enrolling adult patients with acute ischemic stroke ≤9 hours of stroke onset to receive exenatide (5 µg BID subcutaneous injection) or standard care for 5 days, or until hospital discharge (whichever sooner). The primary outcome (intention to treat) was the proportion of patients with ≥8-point improvement in National Institutes of Health Stroke Scale score (or National Institutes of Health Stroke Scale scores 0-1) at 7 days poststroke. Safety outcomes included death, episodes of hyperglycemia, hypoglycemia, and adverse event.

RESULTS

From April 2016 to June 2021, 350 patients were randomized (exenatide, n=177, standard care, n=173). Median age, 71 years (interquartile range, 62-79), median National Institutes of Health Stroke Scale score, 4 (interquartile range, 2-8). Planned recruitment (n=528) was stopped early due to COVID-19 disruptions and funding constraints. The primary outcome was achieved in 97 of 171 (56.7%) in the standard care group versus 104 of 170 (61.2%) in the exenatide group (adjusted odds ratio, 1.22 [95% CI, 0.79-1.88]; P=0.38). No differences in secondary outcomes were observed. The per-patient mean daily frequency of hyperglycemia was significantly less in the exenatide group across all quartiles. No episodes of hypoglycemia were recorded over the treatment period. Adverse events of mild nausea and vomiting occurred in 6 (3.5%) exenatide patients versus 0 (0%) standard care with no withdrawal.

CONCLUSIONS

Treatment with exenatide did not reduce neurological impairment at 7 days in patients with acute ischemic stroke. Exenatide did significantly reduce the frequency of hyperglycemic events, without hypoglycemia, and was safe to use. Larger acute stroke trials using GLP-1 agonists such as exenatide should be considered.

REGISTRATION

URL: www.australianclinicaltrials.gov.au; Unique identifier: ACTRN12617000409370. URL: https://www.clinicaltrials.gov; Unique identifier: NCT03287076.

Dinotefuran exposure induces autophagy and apoptosis through oxidative stress in Bombyx mori

As a third-generation neonicotinoid insecticide, dinotefuran is extensively used in agriculture, and its residue in the environment has potential effects on nontarget organisms. However, the toxic effects of dinotefuran exposure on nontarget organism remain largely unknown. This study explored the toxic effects of sublethal dose of dinotefuran on Bombyx mori. Dinotefuran upregulated reactive oxygen species (ROS) and malondialdehyde (MDA) levels in the midgut and fat body of B. mori. Transcriptional analysis revealed that the expression levels of many autophagy and apoptosis-associated genes were significantly altered after dinotefuran exposure, consistent with ultrastructural changes. Moreover, the expression levels of autophagy-related proteins (ATG8-PE and ATG6) and apoptosis-related proteins (BmDredd and BmICE) were increased, whereas the expression level of an autophagic key protein (sequestosome 1) was decreased in the dinotefuran-exposed group. These results indicate that dinotefuran exposure leads to oxidative stress, autophagy, and apoptosis in B. mori. In addition, its effect on the fat body was apparently greater than that on the midgut. In contrast, pretreatment with an autophagy inhibitor effectively downregulated the expression levels of ATG6 and BmDredd, but induced the expression of sequestosome 1, suggesting that dinotefuran-induced autophagy may promote apoptosis. This study reveals that ROS generation regulates the impact of dinotefuran on the crosstalk between autophagy and apoptosis, laying the foundation for studying cell death processes such as autophagy and apoptosis induced by pesticides. Furthermore, this study provides a comprehensive insight into the toxicity of dinotefuran on silkworm and contributes to the ecological risk assessment of dinotefuran in nontarget organisms.

Everolimus attenuates glutamate-induced PC12 cells death

BACKGROUND

Glutamate-induced neuronal cell death plays a key role in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Some recent studies reported the potential immunomodulatory and neuroprotective properties of inhibitors of serine-threonine kinase, mTOR (mammalian target of rapamycin). However, no study was conducted about the neuroprotective potential of everolimus (EVR), a selective and potent mTOR inhibitor. Therefore, this study was planned to investigate whether EVR has protective effects against glutamate-induced toxicity in PC12 cells, which are used as model for neurons injury, and to elucidate the underlying mechanism.

METHODS

PC12 cells were concurrently treated with glutamate (8 mM) and EVR (0-40 nM) for 24 h. Then, the cells viability, apoptosis rate, and apoptosis-related proteins (caspase-3, bax and bcl-2) were measured using MTT, annexin V/PI and immunoblotting assays.

RESULTS

Analyzing the protective effect of different concentrations of EVR (0-40 nM) against glutamate-induced cytotoxicity revealed a significant increase in cell viability in co-treatment regimen (p < 0.01). Also, EVR (40 nM) significantly (p < 0.01) inhibited glutamate-induced apoptosis through depressing the elevation of bax/bcl-2 ratio and expression of cleaved caspase-3, concentration depend.

CONCLUSION

The results demonstrated, for the first time, that EVR could protect against glutamate-mediated PC12 cell death via inhibiting apoptosis.

Vildagliptin restores cognitive function and mitigates hippocampal neuronal apoptosis in cisplatin-induced chemo-brain: Imperative roles of AMPK/Akt/CREB/ BDNF signaling cascades

Cisplatin (CP) is a broad-spectrum antineoplastic agent used to treat many human cancers. Nonetheless, most patients receiving CP suffer from cognitive deficits, a phenomenon termed "chemo-brain". Recently, vildagliptin (Vilda), a DPP-4 inhibitor, has demonstrated promising neuroprotective properties against various neurological diseases. Therefore, the present study aims to investigate the potential neuroprotective properties of Vilda against CP-induced neurotoxicity and elucidate the underlying molecular mechanisms. Chemo-brain was induced in Sprague-Dawley rats by i.p injection of CP at a dose of 5 mg/kg once weekly for four weeks. Vilda was administered daily at a dose (10 mg/kg; P.O) for four weeks. The results revealed that Vilda restored the cognitive function impaired by CP, as assessed by the Morris water maze, Y-maze, and passive avoidance tests. Moreover, Vilda alleviated the CP-induced neurodegeneration, as shown by toluidine blue staining, besides markedly reduced amyloid plaque deposition, as evidenced by Congo red staining. Notably, Vilda boosted cholinergic neurotransmission through the downregulation of the acetylcholinesterase enzyme. In addition, the neuroprotective mechanisms of Vilda include diminishing oxidative stress by reducing MDA levels while raising GSH levels and SOD activity, repressing neuronal apoptosis as shown by elevated Bcl-2 levels together with diminished Bax and caspase-3 expressions, inhibiting neuroinflammation as shown by decreased GFAP expression, and finally boosting hippocampal neurogenesis and survival by upregulating expressions of BDNF and PCNA. These effects were mainly mediated by activating AMPK/Akt/CREB signaling cascades. In summary, Vilda can be considered a promising candidate for guarding against CP-induced chemo-brain and neurodegeneration, thus improving the quality of life of cancer patients.

The Interaction of Food Allergy and Diabetes: Food Allergy Effects on Diabetic Mice by Intestinal Barrier Destruction and Glucagon-like Peptide 1 Reduction in Jejunum

The increase in food allergies and diabetes leads to the assumption that they are related. This study aimed to (1) verify the interaction between food allergy and diabetes and (2) explore the potential mechanisms by which food allergy promotes diabetes. Female BALB/c mice were grouped into a control group (CK), an ovalbumin-sensitized group (OVA), a diabetes group (STZ), and a diabetic allergic group (STZ + OVA) (Mice were modeled diabetes with STZ first, then were given OVA to model food allergies), and an allergic diabetic group (OVA + STZ) (Mice were modeled food allergies with OVA first, then were given STZ to model diabetes). The results showed that OVA + STZ mice exhibited a more serious Th2 humoral response, and they were more susceptible to diabetes. Furthermore, when the OVA + STZ mice were in the sensitized state, the intestinal barrier function was severely impaired, and mast cell activation was promoted. Moreover, we found that the effect of food allergy on diabetes is related to the inhibition of GLP-1 secretion and the up-regulation of the PI3K/Akt/mTOR/NF-κB P65 signaling pathway in the jejunum. Overall, our results suggest that food allergies have interactions with diabetes, which sheds new light on the importance of food allergies in diabetes.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer’s and Parkinson’s disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer’s and Parkinson’s disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

A GLP1 receptor agonist diabetes drug ameliorates neurodegeneration in a mouse model of infantile neurometabolic disease

Infantile neuroaxonal dystrophy (INAD) is a rare paediatric neurodegenerative condition caused by mutations in the PLA2G6 gene, which is also the causative gene for PARK14-linked young adult-onset dystonia parkinsonism. INAD patients usually die within their first decade of life, and there are currently no effective treatments available. GLP1 receptor (GLP-1R) agonists are licensed for treating type 2 diabetes mellitus but have also demonstrated neuroprotective properties in a clinical trial for Parkinson's disease. Therefore, we evaluated the therapeutic efficacy of a new recently licensed GLP-1R agonist diabetes drug in a mouse model of INAD. Systemically administered high-dose semaglutide delivered weekly to juvenile INAD mice improved locomotor function and extended the lifespan. An investigation into the mechanisms underlying these therapeutic effects revealed that semaglutide significantly increased levels of key neuroprotective molecules while decreasing those involved in pro-neurodegenerative pathways. The expression of mediators in both the apoptotic and necroptotic pathways were also significantly reduced in semaglutide treated mice. A reduction of neuronal loss and neuroinflammation was observed. Finally, there was no obvious inflammatory response in wild-type mice associated with the repeated high doses of semaglutide used in this study.

Mechanistic Insights for Drug Repurposing and the Design of Hybrid Drugs for Alzheimer's Disease

The heterogeneity and complex nature of Alzheimer's disease (AD) is attributed to several genetic risk factors and molecular culprits. The slow pace and increasing failure rate of conventional drug discovery has led to the exploration of complementary strategies based on repurposing approved drugs to treat AD. Drug repurposing (DR) is a cost-effective, low-risk, and efficient approach for identifying novel therapeutic candidates for AD treatment. Similarly, hybrid drug design through the integration of distinct pharmacophores from known or failed drugs and natural products is an interesting strategy to target the multifactorial nature of AD. In this Perspective, we discuss the potential of DR and highlight promising drug candidates that can be advanced for clinical trials, backed by a detailed discussion on their plausible mechanisms of action. Our article fosters research on the hidden potential of DR and hybrid drug design with the goal of unravelling new drugs and targets to tackle AD.

The mechanism and efficacy of GLP-1 receptor agonists in the treatment of Alzheimer's disease

Since type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD) and both have the same pathogenesis (e.g., insulin resistance), drugs used to treat T2DM have been gradually found to reduce the progression of AD in AD models. Of these drugs, glucagon-like peptide 1 receptor (GLP-1R) agonists are more effective and have fewer side effects. GLP-1R agonists have reducing neuroinflammation and oxidative stress, neurotrophic effects, decreasing Aβ deposition and tau hyperphosphorylation in AD models, which may be a potential drug for the treatment of AD. However, this needs to be verified by further clinical trials. This study aims to summarize the current information on the mechanisms and effects of GLP-1R agonists in AD.

Potential new therapeutic target for Alzheimer's disease: Glucagon-like peptide-1

Increasing evidence shows a close relationship between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). Recently, glucagon-like peptide-1 (GLP-1), a gut incretin hormone, has become a well-established treatment for T2DM and is likely to be involved in treating cognitive impairment. In this mini review, the similarities between AD and T2DM are summarised with the main focus on GLP-1-based therapeutics in AD.

Improving Sperm Cryopreservation With Type III Antifreeze Protein: Proteomic Profiling of Cynomolgus Macaque (Macaca fascicularis) Sperm

Antifreeze protein III (AFP III) is used for the cryopreservation of germ cells in various animal species. However, the exact mechanism of its cryoprotection is largely unknown at the molecular level. In this study, we investigated the motility, acrosomal integrity, and mitochondrial membrane potential (MMP), as well as proteomic change, of cynomolgus macaque sperm after cryopreservation. Sperm motility, acrosomal integrity, and MMP were lower after cryopreservation (p < 0.001), but significant differences in sperm motility and MMP were observed between the AFP-treated sperm sample (Cryo+AFP) and the non-treated sample (Cryo-AFP) (p < 0.01). A total of 141 and 32 differentially expressed proteins were, respectively, identified in cynomolgus macaque sperm cryopreserved without and with 0.1 μg/ml AFP III compared with fresh sperm. These proteins were mainly involved in the mitochondrial production of reactive oxygen species (ROS), glutathione (GSH) synthesis, and cell apoptosis. The addition of AFP III in the sperm freezing medium resulted in significant stabilization of cellular molecular functions and/or biological processes in sperm, as illustrated by the extent of proteomic changes after freezing and thawing. According to the proteomic change of differentially expressed proteins, we hypothesized a novel molecular mechanism for cryoprotection that AFP III may reduce the release of cytochrome c and thereby reduce sperm apoptosis by modulating the production of ROS in mitochondria. The molecular mechanism that AFP III acts with sperm proteins for cellular protection against cryoinjuries needs further study.

Apoptotic Pathways and Alzheimer's Disease: Probing Therapeutic Potential

Apoptosis is an intrinsic biochemical, cellular process that regulates cell death and is crucial for cell survival, cellular homeostasis, and maintaining the optimum functional status. Apoptosis in a predetermined and programmed manner regulates several molecular events, including cell turnover, embryonic development, and immune system functions but may be the exclusive contributor to several disorders, including neurodegenerative manifestations, when it functions in an aberrant and disorganized manner. Alzheimer's disease (AD) is a fatal, chronic neurodegenerative disorder where apoptosis has a compelling and divergent role. The well-characterized pathological features of AD, including extracellular plaques of amyloid-beta, intracellular hyperphosphorylated tangles of tau protein (NFTs), inflammation, mitochondrial dysfunction, oxidative stress, and excitotoxic cell death, also instigate an abnormal apoptotic cascade in susceptible brain regions (cerebral cortex, hippocampus). The apoptotic players in these regions affect cellular organelles (mitochondria and endoplasmic reticulum), interact with trophic factors, and several pathways, including PI3K/AKT, JNK, MAPK, mTOR signalling. This dysregulated apoptotic cascade end with an abnormal neuronal loss which is a primary event that may precede the other events of AD progression and correlates well with the degree of dementia. The present review provides insight into the diverse and versatile apoptotic mechanisms that are indispensable for neuronal survival and constitute an integral part of the pathological progression of AD. Identification of potential targets (restoring apoptotic and antiapoptotic balance, caspases, TRADD, RIPK1, FADD, TNFα, etc.) may be valuable and advantageous to decide the fate of neurons and to develop potential therapeutics for treatment of AD.

Targeting impaired nutrient sensing with repurposed therapeutics to prevent or treat age-related cognitive decline and dementia: A systematic review

BACKGROUND

Dementia is a debilitating syndrome that significantly impacts individuals over the age of 65 years. There are currently no disease-modifying treatments for dementia. Impairment of nutrient sensing pathways has been implicated in the pathogenesis of dementia, and may offer a novel treatment approach for dementia.

AIMS

This systematic review collates all available evidence for Food and Drug Administration (FDA)-approved therapeutics that modify nutrient sensing in the context of preventing cognitive decline or improving cognition in ageing, mild cognitive impairment (MCI), and dementia populations.

METHODS

PubMed, Embase and Web of Science databases were searched using key search terms focusing on available therapeutics such as 'metformin', 'GLP1', 'insulin' and the dementias including 'Alzheimer's disease' and 'Parkinson's disease'. Articles were screened using Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia). The risk of bias was assessed using the Cochrane Risk of Bias tool v 2.0 for human studies and SYRCLE's risk of bias tool for animal studies.

RESULTS

Out of 2619 articles, 114 were included describing 31 different 'modulation of nutrient sensing pathway' therapeutics, 13 of which specifically were utilized in human interventional trials for normal ageing or dementia. Growth hormone secretagogues improved cognitive outcomes in human mild cognitive impairment, and potentially normal ageing populations. In animals, all investigated therapeutic classes exhibited some cognitive benefits in dementia models. While the risk of bias was relatively low in human studies, this risk in animal studies was largely unclear.

CONCLUSIONS

Modulation of nutrient sensing pathway therapeutics, particularly growth hormone secretagogues, have the potential to improve cognitive outcomes. Overall, there is a clear lack of translation from animal models to human populations.

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.

Liraglutide Protects Nucleus Pulposus Cells Against High-Glucose Induced Apoptosis by Activating PI3K/Akt/ mTOR/Caspase-3 and PI3K/Akt/GSK3β/Caspase-3 Signaling Pathways

Background and Objective: Diabetes mellitus (DM) is reportedly a significant risk factor for intervertebral disc degeneration (IDD). Incretin system and particularly glucagon-like peptide 1 (GLP-1) because of its glucose-lowering effects has become an important target in therapeutic strategies of type 2 diabetes (T2D). Liraglutide is a GLP-1 receptor (GLP-1R) agonist with glucoregulatory and insulinotropic functions as well as regulatory functions on cell proliferation, differentiation, and apoptosis. However, little is known on the roles and signaling pathways of apoptosis protecting effects of liraglutide in IDD. This study aimed to investigate the potential protective effects of liraglutide against high glucose-induced apoptosis of nucleus pulposus cells (NPCs) and the possible involved signaling pathways.

Methods: The human NPCs were incubated with 100 nM liraglutide alone or in combination with LY294002 (PI3K inhibitor), rapamycin (mTOR inhibitor), and SB216763 (GSK3β inhibitor) in a high glucose culture for 48 h. The four groups were assessed further for apoptosis and genes expressions. The apoptotic effect was evaluated by flow cytometry and further confirmed by cell death detection enzyme-linked immunoassay plus (ELISAPLUS). The gene and protein expression levels were assessed by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting techniques. The results were comparatively assessed between the four groups.

Results: The results confirmed the presence of GLP-1R in the NPCs indicating that liraglutide inhibited the high glucose-induced apoptosis, which was blocked by silencing GLP-1R with siRNA. Moreover, liraglutide stimulated the phosphorylation of Akt, mTOR and GSK3β. Treatment with LY294002 significantly increased the apoptosis of NPCs and reduced the levels of their downstream substrates (p-AKT, p-mTOR, and p-GSK3β). Further assessments revealed that activation of mTOR and GSK3β was almost completely inhibited by rapamycin and SB216763, respectively, which significantly increased the caspase-3 levels.

Conclusion: Liraglutide could protect NPCs against high glucose-induced apoptosis by activating the PI3K/AKT/mTOR/caspase-3 and PI3K/AKT/GSK3β/caspase-3 signaling pathways.

Association between exenatide use and incidence of Alzheimer's disease

INTRODUCTION

Recent developments suggest that insulin-sensitizing agents used to treat type II diabetes (T2DM) may also prove useful in reducing the risk of Alzheimer's disease (AD). The objective of this study is to analyze the association between exenatide use among Medicare beneficiaries with T2DM and the incidence of AD.

METHODS

We performed a retrospective cohort analysis on claims data from a 20% random sample of Medicare beneficiaries with T2DM from 2007 to 2013 (n = 342,608). We compared rates of incident AD between 2009 and 2013 according to exenatide use in 2007-2008, measured by the number of 30-day-equivalent fills. We adjusted for demographics, comorbidities, and use of other drugs. Unmeasured confounding was assessed with an instrumental variables approach.

RESULTS

The sample was mostly female (65%), White (76%), and 74 years old on average. Exenatide users were more likely to be male (38% vs. 35%), White (87% vs. 76%), and younger (by 4.2 years) than non-users. Each additional 30-day-equivalent claim was associated with a 2.4% relative reduction in incidence (odds ratio 0.976; 95% confidence interval 0.963-0.989; P < .001). There was no evidence of unmeasured confounding.

DISCUSSION

Exenatide use is associated with a reduced incidence of AD among Medicare beneficiaries aged 65 years or older with T2DM. The association shown in this study warrants consideration by clinicians prescribing insulin sensitizing agents to patients.

GLP-1 mimetics and cognition

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of antidiabetic drugs that improve the glycaemia via several molecular pathways. Recent evidence suggest that they also have additional effects modulating pathophysiologic pathways included in cognitive disorders. Since some forms of cognitive dysfunction such as Alzheimer's disease are more common among diabetic patients than in the normal population, antidiabetic drugs that have neuroprotective effects affording protection for cognitive disorders would be of benefit. Therefore, we reviewed the pharmacologic effects of GLP-1 analogues and found that they may have the additional benefit of improving cognitive performance via at least eight molecular mechanisms.

NGF receptors and PI3K/AKT pathway involved in glucose fluctuation-induced damage to neurons and α-lipoic acid treatment

BACKGROUND

Glucose fluctuation promotes neuronal apoptosis, which plays a central role in diabetic encephalopathy (DE). Nerve growth factor (NGF), and its interaction with high-affinity (TrkA) and low-affinity (p75NTR) receptors, are involved in neuronal survival. NGF/TrkA contributes to the activation of the PI3K/AKT pathway, which is beneficial for neuronal survival, and α-Lipoic acid (ALA) exerts clinically favorable neuroprotective effects in the periphery. Whether NGF receptors and the PI3K/AKT pathway are involved in glucose fluctuation-induced neuronal damage, as well as the potential molecular mechanism of ALA in protecting glucose fluctuation-induced neuronal damage, remain unclear.

RESULTS

The results indicated that constant high glucose (CHG) and intermittent high glucose (IHG) significantly increased the expression of Bax and caspase-3, and decreased the expression of TrkA/p75NTR and p-AKT/AKT, while ALA stimulation reversed the above proteins in PC12 cells. IHG stimulates apoptosis more effectively than CHG in PC12 cells, which is related to the PI3K/AKT pathway but not to the TrkA/p75NTR. Furthermore, neuronal apoptosis induced by IHG was aggravated by the TrkA inhibitor K252a or the PI3K/AKT inhibitor LY294002, but this effect was alleviated by the p75NTR inhibitor TAT-pep5.

CONCLUSION

Glucose fluctuation induced cell apoptosis by regulating the TrkA/p75NTR and PI3K/AKT pathway, meanwhile ALA exhibited neuroprotective effects in response to IHG and CHG. These observations indicated that the PI3K/AKT pathway and the balance of TrkA/p75NTR are likely to serve as potential therapeutic targets for DE. In addition, ALA could be a possible therapeutic drug for DE.

MicroRNA-182 exacerbates blood-brain barrier (BBB) disruption by downregulating the mTOR/FOXO1 pathway in cerebral ischemia

Cerebral ischemia causes damage to the structure and function of the blood-brain barrier (BBB) and alleviating BBB destruction will be of great significance for the treatment and prognosis of ischemic stroke. Recently, microRNAs have been shown to play a critical role in BBB integrity. However, the potential mechanism by which microRNA-182 (miR-182) affects the BBB in ischemic stroke remains unclear. We demonstrated for the first time that cerebral ischemia leads to a significant progressive increase in miR-182 after pMCAO, and bEnd.3 cells are the primary target cells of miR-182. In miR-182 KD transgenic mice, infarct volume, and BBB permeability were attenuated, and tight junction (TJ) proteins increased. Inhibition of miR-182 with an antagomir reduced OGD-induced apoptosis of bEnd.3 cells and the loss of ZO-1 and Occludin. To further explore the mechanism by which miR-182 regulates BBB integrity, we detected the apoptotic proteins Bcl-2/Bax and demonstrated that mTOR and FOXO1 were the targets of miR-182. Inhibition of mTOR/FOXO1 by rapamycin/AS1842856 decreased the ratio of Bcl-2/Bax and exacerbated TJ protein loss. Taken together, inhibition of miR-182 protects BBB integrity by reducing endothelial cell apoptosis through the mTOR/FOXO1 pathway. Thus, miR-182 may be a potential target for the treatment of BBB disruption during cerebral ischemia.

Neuroprotective Effects of Diabetes Drugs for the Treatment of Neonatal Hypoxia-Ischemia Encephalopathy

The perinatal period represents a time of great vulnerability for the developing brain. A variety of injuries can result in death or devastating injury causing profound neurocognitive deficits. Hypoxic-ischemic neonatal encephalopathy (HIE) remains the leading cause of brain injury in term infants during the perinatal period with limited options available to aid in recovery. It can result in long-term devastating consequences with neurologic complications varying from mild behavioral deficits to severe seizure, intellectual disability, and/or cerebral palsy in the newborn. Despite medical advances, the only viable option is therapeutic hypothermia which is classified as the gold standard but is not used, or may not be as effective in preterm cases, infection-associated cases or low resource settings. Therefore, alternatives or adjunct therapies are urgently needed. Ongoing research continues to advance our understanding of the mechanisms contributing to perinatal brain injury and identify new targets and treatments. Drugs used for the treatment of patients with type 2 diabetes mellitus (T2DM) have demonstrated neuroprotective properties and therapeutic efficacy from neurological sequelae following HIE insults in preclinical models, both alone, or in combination with induced hypothermia. In this short review, we have focused on recent findings on the use of diabetes drugs that provide a neuroprotective effect using in vitro and in vivo models of HIE that could be considered for clinical translation as a promising treatment.

The mTOR/GCLc/GSH Pathway Mediates the Dose-Dependent Bidirectional Regulation of ROS Induced by TiO2NPs in Neurogenic Cells

Objective. The effect of TiO2NP exposure on the nervous system and the underlying mechanism remain unclear. The antioxidant effect of TiO2NPs at a low dose was newly found in our study, which was different from the effect at high dose. This study is aimed at exploring the mechanism underlying the antioxidant effects of TiO2NPs at low dose and the induction of ROS accumulation by TiO2NPs at high dose in neurogenic cell lines.Methods. We measured the changes in key molecules in the ROS regulation pathway by western blotting, flow cytometry, and commercial assay kits, and these key molecules were further evaluated to verify their interactions and roles using SH-SY5Y, U251, and SK-N-SH cell lines treated with TiO2NPs.Results. Our results showed that the weak antioxidant effect at low dose was caused by mTOR/GCLc-induced GSH overproduction and GSH-Px activity impairment. ROS accumulation at high dose was caused by a mTOR/GCLc-mediated decrease in GSH production, GSH-Px activity impairment, and dramatic ROS production. Furthermore, we found that the ROS species were mainly O2-⋅, and that SOD played a crucial role in reducing O2-⋅levels before the mTOR protein was activated.Conclusion. We revealed the mechanism underlying the bidirectional regulation of ROS induced by TiO2NPs at different doses in neurogenic cell lines. Our study emphasized the potential neurotoxic effects of NPs at low dose, which should arouse concern about their safety.

GLP-1: Molecular mechanisms and outcomes of a complex signaling system

Meal ingestion provokes the release of hormones and transmitters, which in turn regulate energy homeostasis and feeding behavior. One such hormone, glucagon-like peptide-1 (GLP-1), has received significant attention in the treatment of obesity and diabetes due to its potent incretin effect. In addition to the peripheral actions of GLP-1, this hormone is able to alter behavior through the modulation of multiple neural circuits. Recent work that focused on elucidating the mechanisms and outcomes of GLP-1 neuromodulation led to the discovery of an impressive array of GLP-1 actions. Here, we summarize the many levels at which the GLP-1 signal adapts to different systems, with the goal being to provide a background against which to guide future research.

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.

Glucagon-Like Peptide-1 Receptor Agonist Protects Dorsal Root Ganglion Neurons against Oxidative Insult

OBJECTIVE

Diabetic polyneuropathy (DPN) is one of the most prevalent diabetic complications. We previously demonstrated that exendin-4 (Ex4), a glucagon-like peptide-1 receptor agonist (GLP-1RA), has beneficial effects in animal models of DPN. We hypothesized that GLP-1 signaling would protect neurons of the peripheral nervous system from oxidative insult in DPN. Here, the therapeutic potential of GLP-1RAs on DPN was investigated in depth using the cellular oxidative insult model applied to the dorsal root ganglion (DRG) neuronal cell line.

RESEARCH DESIGN AND METHODS

Immortalized DRG neuronal 50B11 cells were cultured with and without hydrogen peroxide in the presence or absence of Ex4 or GLP-1(7-37). Cytotoxicity and viability were determined using a lactate dehydrogenase assay and MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt), respectively. Antioxidant enzyme activity was evaluated using a superoxide dismutase assay. Alteration of neuronal characteristics of 50B11 cells induced by GLP-1RAs was evaluated with immunocytochemistry utilizing antibodies for transient receptor potential vanilloid subfamily member 1, substance P, and calcitonin gene-related peptide. Cell proliferation and apoptosis were also examined by ethynyl deoxyuridine incorporation assay and APOPercentage dye, respectively. The neurite projection ratio induced by treatment with GLP-1RAs was counted. Intracellular activation of adenylate cyclase/cyclic adenosine monophosphate (cAMP) signaling was also quantified after treatment with GLP-1RAs.

RESULTS

Neither Ex4 nor GLP-1(7-37) demonstrated cytotoxicity in the cells. An MTS assay revealed that GLP-1RAs amended impaired cell viability induced by oxidative insult in 50B11 cells. GLP-1RAs activated superoxide dismutase. GLP-1RAs induced no alteration of the distribution pattern in neuronal markers. Ex4 rescued the cells from oxidative insult-induced apoptosis. GLP-1RAs suppressed proliferation and promoted neurite projections. No GLP-1RAs induced an accumulation of cAMP.

CONCLUSIONS

Our findings indicate that GLP-1RAs have neuroprotective potential which is achieved by their direct actions on DRG neurons. Beneficial effects of GLP-1RAs on DPN could be related to these direct actions on DRG neurons.

Systemic L-buthionine-S-R-sulfoximine administration modulates glutathione homeostasis via NGF/TrkA and mTOR signaling in the cerebellum

Glutathione (GSH) is an essential component of intracellular antioxidant systems that plays a primordial role in the protection of cells against oxidative stress, maintaining redox homeostasis and xenobiotic detoxification. GSH synthesis in the brain is limited by the availability of cysteine and glutamate. Cystine, the disulfide form of cysteine is transported into endothelial cells of the blood-brain barrier (BBB) and astrocytes via the system x_c^-, which is composed of xCT and the heavy chain of 4F2 cell surface antigen (4F2hc). Cystine is reduced inside the cells and the L-type amino acid transporter 1 (LAT1) transports cysteine from the endothelial cells into the brain, cysteine is transported into the neurons through the excitatory amino acid transporter 3 (EAAT3), also known as excitatory amino acid carrier 1 (EAAC1). The mechanistic/mammalian target of rapamycin (mTOR) and neurotrophins can activate signaling pathways that modulate amino acid transporters for GSH synthesis. The present study found that systemic L-buthionine-S-R-sulfoximine (BSO) administration selectively altered GSH homeostasis and EAAT3 levels in the mice cerebellum. Intraperitoneal treatment of mice with 6 mmol/kg of BSO depleted GSH and GSSG in the liver at 2 h of treatment. The cerebellum, but not other brain regions, exhibited a redox response. The mTOR and the neuronal growth factor (NGF)/tropomyosin receptor kinase A (TrkA) signaling pathways were activated and lead to an increase in the protein levels of the EAAT3 transporter, which was linked to an increase in the GSH/GSSG ratio and GSH concentration in the cerebellum at 0.5 and 2 h, respectively. Therefore, the cerebellum responds to peripheral GSH depletion via activation of the mTOR and NGF/TrkA pathways, which increase the transport of cysteine for GSH synthesis.

GLP-1 treatment protects endothelial cells from oxidative stress-induced autophagy and endothelial dysfunction

Endothelial dysfunction and excessively stimulated autophagy, often caused by oxidant injury or inflammation, will lead to atherosclerosis development and progression in diabetes. The aim of this study is to investigate the protective effect of glucagon-like peptide-1 (GLP-1) treatment on preventing oxidative stress-induced endothelial dysfunction and excessively stimulated autophagy. Treatment of endothelial cells with GLP-1 significantly attenuated oxidative stress-induced endothelial dysfunction and autophagy, which was associated with the reduction of intracellular reactive oxygen species (ROS) levels. These protective effects of GLP-1 were likely mediated by reducing phosphorylation of ERK1/2. We further demonstrated that GLP-1 treatment could reverse downregulation of epigenetic factor histone deacetylase 6 (HDAC6), a downstream molecular of the EKR1/2, induced by oxidant injury. In conclusion, our results suggest that GLP-1 produces a protective effect on endothelial cells from oxidant injury by preventing endothelial dysfunction and autophagy, which may be dependent on restoring HDAC6 through a GLP-1R-ERK1/2-dependent manner.

Mitral cells and the glucagon-like peptide 1 receptor: The sweet smell of success?

The olfactory bulb (OB) is often affected at very early stages of neurodegenerative disorders, in the so-called "prodromal" phase. In Parkinson's disease (PD), olfactory disturbances appear years before motor symptoms arise. Additionally, pathological alpha-synuclein aggregates are found in olfactory regions before spreading to other areas of the brain. Being positioned at the frontier between the brain and a potentially hostile environment, could explain the particular vulnerability of the OB. Mitral cells (MCs), the principal projecting neurons of the olfactory system, are involved in the pathogenesis and in the prion-like progression of PD. They are affected by Lewy pathology and are thought to contribute to the axonal transport of misfolded alpha-synuclein to other regions of the brain. Here, we first describe the main markers reported to distinguish MCs from other olfactory neurons. We focus on the glucagon-like peptide 1 receptor (GLP-1R), a membrane protein specifically expressed in MCs. After summarizing OB pathology, we explore the idea of targeting specifically MCs with GLP-1 or its analogues. Exenatide has shown great promise as a neuroprotective and neurorestorative agent and has been used in a clinical trial for clinical PD. Since GLP-1R activation has the ability to mitigate many facets of prodromal PD pathology, we postulate that once a robust biomarker is in place that is capable of identifying individuals in the prodromal phase of PD, homing in on GLP-1R could assist in deferring, or eradicating to a significant degree, the clinical manifestation of this debilitating human disorder.

Treatment with exenatide in acute ischemic stroke trial protocol: A prospective, randomized, open label, blinded end-point study of exenatide vs. standard care in post stroke hyperglycemia

Rationale Post-stroke hyperglycemia occurs in up to 50% of patients presenting with acute ischemic stroke. It reduces the efficacy of thrombolysis, increases infarct size, and worsens clinical outcomes. Insulin-based therapies have generally not been beneficial in treating post-stroke hyperglycemia as they are difficult to implement, may cause hypoglycaemia, possibly increase mortality and worsen clinical outcomes. Exenatide may be a safer, simpler, and more effective alternative to insulin in acute ischemic stroke. Design TEXAIS is a three year, Phase 2, multi-center, prospective, randomized, open label, blinded end-point trial comparing exenatide to standard of care. It aims to recruit 528 patients with a primary end point of major neurological improvement at 7 days defined as a ≥8-point improvement in NIHSS score, or NIHSS 0-1. Secondary outcomes of hyper- and hypoglycaemia at 5 days and NIHSS and mRS at 90 days will be measured. The treatment arm will receive exenatide 5 µg subcutaneously twice daily. The control arm will receive standard stroke unit care. Continuous glucose monitors will track the dynamic variability of glucose. Conclusion TEXAIS aims to show that exenatide is safe and effective in the treatment of post-stroke hyperglycemia. It has been designed to be highly generalizable with an ability to enroll a large percentage of patients with acute ischemic stroke, regardless of admission blood glucose level, diabetes status, or stroke severity, with very low risk of hypoglycemia. Trial registration: ClinicalTrials.gov/ANZCTR NTA1127.

Neuroprotective effect of phosphocreatine on oxidative stress and mitochondrial dysfunction induced apoptosis in vitro and in vivo: Involvement of dual PI3K/Akt and Nrf2/HO-1 pathways

Methylglyoxal (MGO), an active metabolite of glucose, is observed in high levels in the tissues and blood of diabetic patients. Phosphocreatine (PCr), a high-energy phosphate compound, exhibits a range of pharmacological actions but little is well known of its neuroprotective action. The aim of the present study was to investigate the neuroprotective effects and the possible mechanisms of PCr. Diabetes is closely associated with neurodegenerative diseases, leading not only to the peripheral nervous system (PNS) and but also to central nervous system (CNS) damage. Therefore, we established two rat models of diabetes in vivo induced by MGO and streptozocin (STZ) respectively, while utilized differentiated PC-12 cells in vitro. Treatment of PC-12 cells with PCr markedly attenuated MGO-induced change of viability, apoptosis, accompanied by decreased levels of caspase-3, casapse-9 and Bcl-2/Bax protein ratio. Determination of cellular respiratory function was performed with intact PC-12 cells and homogenized hippocampal neuron tissue of rat. Reactive oxygen species (ROS) generation was assessed by membrane permeable fluorescent probe DCFH-DA. The expressions of Akt, Nrf2 and HO-1 were examined by Western blot. PCr pretreatment significantly reduced oxidative stress-induced high LDH, MDA level, and ROS production of PC-12 cells. PCr pretreatment also significantly decreased mitochondrial dysfunction in vitro and in vivo. In addition, PCr pretreatment increased the expression of p-Akt, Nrf2 and HO-1, and reduced the apoptosis. Moreover, the expression of Cleaved caspase3 was partially increased and the p-Akt, Nrf2 and HO-1 was partially reduced by a PI3K inhibitor (LY294002). While, compared with LY294002 groups, pre-treatment with PCr at the concentrations of 20 mM significantly reduced the expression of Cleaved caspase3 and increased the expression of p-Akt, Nrf2 and HO-1. Molecular docking assay showed that PCr possessed powerful affinity towards to Akt with lower binding energy. In conclusion, the neuroprotective effects of PCr in vitro and in vivo rely on normalizing mitochondrial function and reducing oxidative stress via Akt mediated Nrf2/HO-1 pathway, suggesting that PCr may be a novel therapeutic candidate for the treatment of diabetes-associated neurodegenerative diseases.

Liraglutide reduces hepatic glucolipotoxicity‑induced liver cell apoptosis through NRF2 signaling in Zucker diabetic fatty rats

The primary aim of the present study was to evaluate the effects of liraglutide on glucolipotoxicity-induced liver cell apoptosis and the underlying mechanisms in Zucker diabetic fatty (ZDF) rats. The results revealed that liraglutide significantly decreased the body weight, hyperglycemia and hyperlipidemia of ZDF rats relative to those of Zucker lean (ZL) rats (P<0.05). Furthermore, the reduced liver cell apoptosis was observed in the ZDF rats following 6 weeks of liraglutide therapy. These data validated the beneficial effects of liraglutide on diabetic and obese ZDF rats. In addition, novel data was obtained that demonstrated that liraglutide treatment increased the expression of the antioxidant transcription factor nuclear factor-erythroid 2-related factor 2 (NRF2), as well as the transcription of downstream target genes, including nicotinamide adenine dinucleotide phosphate quinone dehydrogenase 1 and heme oxygenase-1 (P<0.05). Additionally, serum and hepatic GSH and SOD levels increased following liraglutide therapy (P<0.05). Hence, it was proposed that liraglutide may enhance the antioxidant activity of liver cells by activating the NRF2 signaling pathway, thereby reducing liver cell apoptosis induced by glucolipotoxicity in ZDF rats, which may shed light on the application of liraglutide in the treatment of diabetes- and obesity-induced liver injury.

Liraglutide Inhibits the Apoptosis of MC3T3-E1 Cells Induced by Serum Deprivation through cAMP/PKA/β-Catenin and PI3K/AKT/GSK3β Signaling Pathways

In recent years, the interest towards the relationship between incretins and bone has been increasing. Previous studies have suggested that glucagon-like peptide-1 (GLP-1) and its receptor agonists exert beneficial anabolic influence on skeletal metabolism, such as promoting proliferation and differentiation of osteoblasts via entero-osseous-axis. However, little is known regarding the effects of GLP-1 on osteoblast apoptosis and the underlying mechanisms involved. Thus, in the present study, we investigated the effects of liraglutide, a glucagon-like peptide-1 receptor agonist, on apoptosis of murine MC3T3-E1 osteoblastic cells. We confirmed the presence of GLP-1 receptor (GLP-1R) in MC3T3-E1 cells. Our data demonstrated that liraglutide inhibited the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation, as detected by Annexin V/PI and Hoechst 33258 staining and ELISA assays. Moreover, liraglutide upregulated Bcl-2 expression and downregulated Bax expression and caspase-3 activity at intermediate concentration (100 nM) for maximum effect. Further study suggested that liraglutide stimulated the phosphorylation of AKT and enhanced cAMP level, along with decreased phosphorylation of GSK3β, increased β-catenin phosphorylation at Ser675 site and upregulated nuclear β-catenin content and transcriptional activity. Pretreatment of cells with the PI3K inhibitor LY294002, PKA inhibitor H89, and siRNAs GLP-1R, β-catenin abrogated the liraglutide-induced activation of cAMP, AKT, β-catenin, respectively. In conclusion, these findings illustrate that activation of GLP-1 receptor by liraglutide inhibits the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation through cAMP/PKA/β-catenin and PI3K/Akt/GSK3β signaling pathways.

GLP-1 receptor agonists show neuroprotective effects in animal models of diabetes

Enzyme-resistant receptor agonists of the incretin hormone glucagon-like peptide-1 (GLP-1) have shown positive therapeutic effects in people with type 2 diabetes mellitus (T2DM). T2DM has detrimental effects on brain function and impairment of cognition and memory formation has been described. One of the underlying mechanisms is most likely insulin de-sensitization in the brain, as insulin improves cognitive impairments and enhances learning. Treatment with GLP-1 receptor agonists improves memory formation and impairment of synaptic plasticity observed in animal models of diabetes-obesity. Furthermore, it has been shown that diabetes impairs growth factor signalling in the brain and reduces energy utilization in the cortex. Inflammation and apoptotic signalling was also increased. Treatment with GLP-1 receptor agonists improved neuronal growth and repair and reduced inflammation and apoptosis as well as oxidative stress. In comparison with the diabetes drug metformin, GLP-1 receptor agonists were able to improve glycemic control and reverse brain impairments, whereas metformin only normalized blood glucose levels. Clinical studies in non-diabetic patients with neurodegenerative disorders showed neuroprotective effects following administration with GLP-1 receptor agonists, demonstrating that neuroprotective effects are independent of blood glucose levels.

Incretin-based therapy for type 2 diabetes mellitus is promising for treating neurodegenerative diseases

Incretin hormones include glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Due to their promising action on insulinotropic secretion and improving insulin resistance (IR), incretin-based therapies have become a new class of antidiabetic agents for the treatment of type 2 diabetes mellitus (T2DM). Recently, the links between neurodegenerative diseases and T2DM have been identified in a number of studies, which suggested that shared mechanisms, such as insulin dysregulation or IR, may underlie these conditions. Therefore, the effects of incretins in neurodegenerative diseases have been extensively investigated. Protease-resistant long-lasting GLP-1 mimetics such as lixisenatide, liraglutide, and exenatide not only have demonstrated promising effects for treating neurodegenerative diseases in preclinical studies but also have shown first positive results in Alzheimer's disease (AD) and Parkinson's disease (PD) patients in clinical trials. Furthermore, the effects of other related incretin-based therapies such as GIP agonists, dipeptidyl peptidase-IV (DPP-IV) inhibitors, oxyntomodulin (OXM), dual GLP-1/GIP, and triple GLP-1/GIP/glucagon receptor agonists on neurodegenerative diseases have been tested in preclinical studies. Incretin-based therapies are a promising approach for treating neurodegenerative diseases.

Liraglutide and Metformin alone or combined therapy for type 2 diabetes patients complicated with coronary artery disease

BACKGROUND

This study is to compare the effects of Liraglutide and Metformin alone or combined treatment on the cardiac function in T2DM patients complicated with CAD.

METHODS

120 T2DM patients were included at Endocrinology Department of Tianjin First Center Hospital (Tianjin, China) from April 2012 to September 2013. The study contained two sections. Section 1: 30 patients in group 1 was treated with Liraglutide (Novo Nordisk) (1.2 mg/d), and 30 patients in group 2 with Metformin (Shiguibao) (1500 mg/d) for 24 weeks. Section 2: 30 patients in group1 was treated with Liraglutide (1.8 mg/d) and 30 in group 2 with Liraglutide (1.2 mg/d) plus Metformin (1500 mg/d) for 24 weeks. Fasting blood glucose (FBG), postprandial glucose (PPG), glycated hemoglobin (HbA1c), body mass index (BMI), blood pressure (BP), triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), C reactive protein (CRP), left ventricular end-diastolic diameter (LVEDD), ejection fraction (EF) and the ratio of early (E) to late (A) ventricular filling velocities (E/A ratio) were measured before and after the 24-week treatment.

RESULTS

After 24-week treatment, when blood glucose level was controlled in 4 groups, Liraglutide alone treatment showed better improvements than on all measuring except TG in Section 1, however, combined treatment of Liraglutide and Metformin showed better improvements on all measuring except BMI, TG and BP in Section 2.

CONCLUSIONS

With similar glycemic control, the Liraglutide (1.2 mg/d) monotherapy showed the better effects than either Metformin alone, or combination of Liraglutide and Metformin on lipid metabolism and cardiovascular function.

TRIAL REGISTRATION

This trial was registered at Chinese Clinical Trial Registry ( chictr.org.cn ) # ChiCTR-IPR-16008578 .

DPP-4 inhibition with linagliptin ameliorates the progression of premature aging in klotho-/- mice

BACKGROUND

The potential of anti-aging effect of DPP-4 inhibitors is unknown. This study was performed to determine whether linagliptin, a DPP-4 inhibitor, could protect against premature aging in klotho-/- mice.

METHODS

Klotho-/- mice exhibit multiple phenotypes resembling human premature aging, including extremely shortened life span, cognitive impairment, hippocampal neurodegeneration, hair loss, muscle atrophy, hypoglycemia, etc. To investigate the effect of linagliptin on these aging-related phenotypes, male klotho-/- mice were divided into two groups: (1) control group fed the standard diet, and (2) linagliptin group fed the standard diet containing linagliptin. Treatment with linagliptin was performed for 4 weeks. The effect of linagliptin on the above mentioned aging-related phenotypes was examined.

RESULTS

Body weight of klotho-/- mice was greater in linagliptin group than in control group (11.1 ± 0.3 vs 9.9 ± 0.3 g; P < 0.01), which was associated with greater gastrocnemius muscle weight (P < 0.01) and greater kidney weight (P < 0.05) in linagliptin group. Thus, linagliptin significantly prevented body weight loss in klotho-/- mice. Survival rate of klotho-/- mice was greater in linagliptin group (93%) compared to control group (67%), although the difference did not reach statistical significance (P = 0.08). None of linagliptin-treated klotho-/- mice had alopecia during the treatment (P < 0.05 vs control klotho-/- mice). Latency of klotho-/- mice in passive avoidance test was larger in linagliptin group than in control group (P < 0.05), indicating the amelioration of cognitive impairment by linagliptin. Cerebral blood flow of klotho-/- mice was larger in linagliptin group than in control group (P < 0.01), being associated with greater cerebral phospho-eNOS levels (P < 0.05) in linagliptin group. Neuronal cell number in hippocampal CA1 region was greater in linagliptin group than in control group (P < 0.05). Linagliptin group had greater cerebral phospho-Akt (P < 0.05) and phospho-CREB (P < 0.05) than control group. Thus, linagliptin ameliorated brain aging in klotho-/- mice. The degree of hypoglycemia in klotho-/- mice was less in linagliptin group than in control group, as estimated by the findings of OGTT.

CONCLUSIONS

Out work provided the evidence that DPP-4 inhibition with linagliptin slowed the progression of premature aging in klotho-/- mice, and provided a novel insight into the potential role of DPP-4 in the mechanism of premature aging.

Glucagon-like peptide-1 receptor agonist activation ameliorates venous thrombosis-induced arteriovenous fistula failure in chronic kidneyd isease

High shear stress that develops in the arteriovenous fistula of chronic kidney diseases (CKD) may increase H2O2 and thromboxane A2 (TXA2) release, thereby exacerbating endothelial dysfunction, thrombosis, and neointimal hyperplasia. We investigated whether glucagon-like peptide-1 receptor agonist/exendin-4, a potentially cardiovascular protective agent, could improve TXA2-induced arteriovenous fistula injury in CKD. TXA2 administration to H2O2-exposed human umbilical vein endothelial cells increased apoptosis, senescence, and detachment; these phenotypes were associated with the downregulation of phosphorylated endothelial nitric oxide synthase/heme oxygenase-1 (eNOS/HO-1) signalling. Exendin-4 reduced H2O2/TXA2-induced endothelial injury via inhibition of apoptosis-related mechanisms and restoration of phosphorylated eNOS/HO-1 signalling. Male Wistar rats subjected to right common carotid artery-external jugular vein anastomosis were treated with exendin-4 via cervical implant osmotic pumps for 16–42 days. High shear stress induced by the arteriovenous fistula significantly increased venous haemodynamics, blood and tissue H2O2 and TXB2 levels, macrophage/monocyte infiltration, fibrosis, proliferation, and adhesion molecule-1 expression. Apoptosis was also increased due to NADPH oxidase gp91 activation and mitochondrial Bax translocation in the proximal end of the jugular vein of CKD rats. Exendin-4-treatment of rats with CKD led to the restoration of normal endothelial morphology and correction of arteriovenous fistula function. Exendin-4 treatment or thromboxane synthase gene deletion in CKD mice markedly reduced ADP-stimulated platelet adhesion to venous endothelium, and prevented venous occlusion in FeCl3-injured vessels by upregulation of HO-1. Together, these data reveal that the use of glucagon-like peptide-1 receptor agonists is an effective strategy for treatment of CKD-induced arteriovenous fistula failure.

Progranulin gene delivery reduces plaque burden and synaptic atrophy in a mouse model of Alzheimer's disease

Progranulin (PGRN) is a multifunctional protein that is widely expressed throughout the brain, where it has been shown to act as a critical regulator of CNS inflammation and also functions as an autocrine neuronal growth factor, important for long-term neuronal survival. PGRN has been shown to activate cell signaling pathways regulating excitoxicity, oxidative stress, and synaptogenesis, as well as amyloidogenesis. Together, these critical roles in the CNS suggest that PGRN has the potential to be an important therapeutic target for the treatment of various neurodegenerative disorders, particularly Alzheimer’s disease (AD). AD is the leading cause of dementia and is marked by the appearance of extracellular plaques consisting of aggregates of amyloid-β (Aβ), as well as neuroinflammation, oxidative stress, neuronal loss and synaptic atrophy. The ability of PGRN to target multiple key features of AD pathophysiology suggests that enhancing its expression may benefit this disease. Here, we describe the application of PGRN gene transfer using in vivo delivery of lentiviral expression vectors in a transgenic mouse model of AD. Viral vector delivery of the PGRN gene effectively enhanced PGRN expression in the hippocampus of Tg2576 mice. This elevated PGRN expression significantly reduced amyloid plaque burden in these mice, accompanied by reductions in markers of inflammation and synaptic atrophy. The overexpression of PGRN was also found to increase activity of neprilysin, a key amyloid beta degrading enzyme. PGRN regulation of neprilysin activity could play a major role in the observed alterations in plaque burden. Thus, PGRN may be an effective therapeutic target for the treatment of AD.

RhGLP-1 (7-36) protects diabetic rats against cerebral ischemia-reperfusion injury via up-regulating expression of Nrf2/HO-1 and increasing the activities of SOD

The present study aimed to explore the neuroprotective effect and possible mechanisms of rhGLP-1 (7–36) against transient ischemia/reperfusion injuries induced by middle cerebral artery occlusion (MCAO) in type 2 diabetic rats. First, diabetic rats were established by a combination of a high-fat diet and low-dose streptozotocin (STZ) (30 mg/kg, intraperitoneally). Second, they were subjected to MCAO for 2 h, then treated with rhGLP-1 (7–36) (10, 20, 40 µg/kg i.p.) at the same time of reperfusion. In the following 3 days, they were injected with rhGLP-1 (7–36) at the same dose and route for three times each day. After 72 h, hypoglycemic effects were assessed by blood glucose changes, and neuroprotective effects were evaluated by neurological deficits, infarct volume and histomorphology. Mechanisms were investigated by detecting the distribution and expression of the nuclear factor erythroid-derived factor 2 related factor 2 (Nrf2) in ischemic brain tissue, the levels of phospho-PI3 kinase (PI3K)/PI3K ratio and heme-oxygenase-1 (HO-l), as well as the activities of superoxide dismutase (SOD) and the contents of malondialdehyde (MDA). Our results showed that rhGLP-1 (7–36) significantly reduced blood glucose and infarction volume, alleviated neurological deficits, enhanced the density of surviving neurons and vascular proliferation. The nuclear positive cells ratio and expression of Nrf2, the levels of P-PI3K/PI3K ratio and HO-l increased, the activities of SOD increased and the contents of MDA decreased. The current results indicated the protective effect of rhGLP-1 (7–36) in diabetic rats following MCAO/R that may be concerned with reducing blood glucose, up-regulating expression of Nrf2/HO-1 and increasing the activities of SOD.

Luteolin, a natural flavonoid, inhibits methylglyoxal induced apoptosis via the mTOR/4E-BP1 signaling pathway

Methylglyoxal (MG) accumulation has been observed in human cerebrospinal fluid and body tissues under hyperglycaemic conditions. Recent research has demonstrated that MG-induces neuronal cell apoptosis, which promotes the development of diabetic encephalopathy. Our previous animal study has shown that luteolin, a natural flavonoid, attenuates diabetes-associated cognitive dysfunction. To further explore the neuroprotective properties of luteolin, we investigated the inhibitive effect of luteolin on MG-induced apoptosis in PC12 neuronal cells. We found that MG inhibited cell viability in a dose-dependent manner and induced apoptosis in PC12 cells. Pretreatment with Luteolin significantly elevated cell viability, reduced MG-induced apoptosis, inhibited the activation of the mTOR/4E-BP1 signaling pathway, and decreased pro-apoptotic proteins, Bax, Cytochrome C as well as caspase-3. Furthermore, we found that pretreatment with the mTOR inhibitor, rapamycin, significantly reduced the expression of the pro-apoptotic protein Bax. Therefore, these observations unambiguously suggest that the inhibitive effect of Luteolin against MG-induced apoptosis in PC12 cells is associated with inhibition of the mTOR/4E-BP1 signaling pathway.

The Molecular Mechanism of Glucagon-Like Peptide-1 Therapy in Alzheimer's Disease, Based on a Mechanistic Target of Rapamycin Pathway

The mechanistic target of rapamycin (mTOR) is an important molecule that connects aging, lifespan, energy balance, glucose and lipid metabolism, and neurodegeneration. Rapamycin exerts effects in numerous biological activities via its target protein, playing a key role in energy balance, regulation of autophagy, extension of lifespan, immunosuppression, and protection against neurodegeneration. There are many similar pathophysiological processes and molecular pathways between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM), and pharmacologic agents used to treat T2DM, including glucagon-like peptide-1 (GLP-1) analogs, seem to be beneficial for AD. mTOR mediates the effects of GLP-1 analogs in the treatment of T2DM; hence, I hypothesize that mTOR is a key molecule for mediating the protective effects of GLP-1 for AD.

Polylysine-modified polyethylenimine (PEI-PLL) mediated VEGF gene delivery protects dopaminergic neurons in cell culture and in rat models of Parkinson's Disease (PD)

Parkinson's Disease (PD) is a chronic neurodegenerative disorder characterized by motor deficits which result from the progressive loss of dopaminergic neurons. Gene therapy using growth factors such as VEGF seems to be a viable approach for potential therapeutic treatment of PD. In this study, we utilized a novel non-viral gene carrier designated as PEI-PLL synthesized by our laboratory to deliver VEGF gene to study its effect by using both cell culture as well as animal models of PD. For cell culture experiments, we utilized 6-hydroxydopamine (6-OHDA) mediated cell death model of MN9D cells following transfection with either a control plasmid or VEGF expressing plasmid. As compared to control transfected cells, PEI-PLL mediated VEGF gene delivery to MN9D cells resulted in increased cell viability, increase in the number of Tyrosine hydroxylase (TH) positive cells and decreased apoptosis following 6-OHDA insult. Next, we studied the therapeutic potential of PEI-PLL mediated VEGF gene delivery in SNPc by using unilateral 6-OHDA Medial forebrain bundle (MFB) lesion model of PD in rats. VEGF administration prevented the loss of motor functions induced by 6-OHDA as determined by behavior analysis. Similarly, VEGF inhibited the 6-OHDA mediated loss of DA neurons in Substantia Nigra Pars Compacta (SNPc) as well as DA nerve fibers in striatum as determined by TH immunostaining. In addition, PEI-PLL mediated VEGF gene delivery also prevented apoptosis and microglial activation in PD rat models. Together, these results clearly demonstrated the beneficial effects of PEI-PLL mediated VEGF gene delivery on dopaminergic system in both cell culture and animal models of PD.

STATEMENT OF SIGNIFICANCE

In this report, we exploited the potential of PEI-PLL to deliver VEGF gene for the potential therapeutic treatment of PD by using both cell culture and animal models of PD. To the best of our knowledge, this is the first report describing the use of novel polymeric gene carriers for the delivery of VEGF gene to DA neurons with improved transfection efficiency. Finally, the study will lead to a significant advancement in the field of non-viral PD gene therapy treatment.

Hormetic effect of panaxatriol saponins confers neuroprotection in PC12 cells and zebrafish through PI3K/AKT/mTOR and AMPK/SIRT1/FOXO3 pathways

Hormesis is an adaptive response of living organisms to a moderate stress. However, its biomedical implication and molecular mechanisms remain to be intensively investigated. Panaxatriol saponins (PTS) is the major bioactive components extracted from Panax notoginseng, a widely used herbal medicine for cerebrovascular diseases. This study aims to examine the hormetic and neuroprotective effects of PTS in PC12 cells and zebrafish Parkinson's disease (PD) models. Our results demonstrated that PTS stimulated PC12 cell growth by about 30% at low doses, while PTS at high doses inhibited cell growth, which is a typical hormetic effect. Moreover, we found that low dose PTS pretreatment significantly attenuated 6-OHDA-induced cytotoxicity and up-regulated PI3K/AKT/mTOR cell proliferation pathway and AMPK/SIRT1/FOXO3 cell survival pathway in PC12 cells. These results strongly suggested that neuroprotective effects of PTS may be attributable to the hormetic effect induced by PTS through activating adaptive response-related signaling pathways. Notably, low dose PTS could significantly prevent the 6-OHDA-induced dopaminergic neuron loss and improve the behavior movement deficiency in zebrafish, whereas relative high dose PTS exhibited neural toxicity, further supporting the hormetic and neuroprotective effects of PTS. This study indicates that PTS may have the potential in the development of future therapeutic medicines for PD.