Lixisenatide rescues spatial memory and synaptic plasticity from amyloid β protein-induced impairments in rats

Role of Glucagon-Like Peptide-1 on Amyloid, Tau, and α-Synuclein: Target Engagement and Rationale for the Development in Neurodegenerative Disorders

INTRODUCTION

Glucagon-like Peptide-1 (GLP-1) and Glucagon-Like Peptide-1 receptor agonist (GLP-1 RA) administration has been associated with neuroprotective effects in neurodegenerative disorders. We conducted a comprehensive synthesis of known effects of GLP-1 and GLP-1 RAs on the cognitive, cellular, and molecular changes in neurodegenerative diseases.

METHODS

We examined preclinical and clinical paradigms that investigated changes in neurodegenerative disease pathology following administration of GLP-1 and GLP-1 RAs. Relevant articles were retrieved through OVID (MedLine, Embase, AMED, PsychINFO, JBI EBP Database), PubMed, and Web of Science from database inception to September 27th, 2024. Primary studies investigating the aforementioned changes following GLP-1 and GLP-1 RA administration were retrieved for analysis (n = 62).

RESULTS

GLP-1 and GLP-1 RAs (i.e. dulaglutide, exenatide, liraglutide, lixisenatide, semaglutide, and tirzepatide) improved cognitive and motor function in neurodegenerative diseases in preclinical and clinical paradigms. Additionally, GLP-1 and GLP-1 RAs were associated with modulating changes in neuroinflammation, oxidative stress, and proliferative pathways.

DISCUSSION

We observed that GLP-1 and GLP-1 RAs modulate molecular and cellular changes known to govern the phenomenology of neurodegenerative diseases. Future research should examine the interaction between signaling molecules, neuronal subpopulations, and cognitive effects affected by GLP-1 and GLP-1 RA administration.

The pharmacodynamics-based prophylactic benefits of GLP-1 receptor agonists and SGLT2 inhibitors on neurodegenerative diseases: evidence from a network meta-analysis

BACKGROUND

Glucagon-like peptide-1 (GLP-1) receptor agonists and sodium-glucose cotransporter 2 (SGLT2) inhibitors represent a new generation of antihyperglycemic agents that operate through mechanisms distinct from conventional diabetes treatments. Beyond their metabolic effects, these medications have demonstrated neuroprotective properties in preclinical studies. While clinical trials have explored their therapeutic potential in established neurodegenerative conditions, their role in disease prevention remains unclear. We conducted a network meta-analysis (NMA) to comprehensively evaluate the prophylactic benefits of these agents across multiple neurodegenerative diseases and identify the most promising preventive strategies.

METHODS

We systematically searched PubMed, Embase, ClinicalKey, Cochrane CENTRAL, ProQuest, ScienceDirect, Web of Science, and ClinicalTrials.gov through October 24th, 2024, for randomized controlled trials (RCTs) of GLP-1 receptor agonists or SGLT2 inhibitors. Our primary outcome was the incidence of seven major neurodegenerative diseases: Parkinson's disease, Alzheimer's disease, Lewy body dementia, multiple sclerosis, amyotrophic lateral sclerosis, frontotemporal dementia, and Huntington's disease. Secondary outcomes included safety profiles assessed through dropout rates. We performed a frequentist-based NMA and evaluated risk of bias with Risk of Bias tool. The main result of the primary outcome in the current study would be re-affirmed via sensitivity test with Bayesian-based NMA.

RESULTS

Our analysis encompassed 22 RCTs involving 138,282 participants (mean age 64.8 years, 36.4% female). Among all investigated medications, only dapagliflozin demonstrated significant prophylactic benefits, specifically in preventing Parkinson's disease (odds ratio = 0.28, 95% confidence intervals = 0.09 to 0.93) compared to controls. Neither GLP-1 receptor agonists nor other SGLT2 inhibitors showed significant preventive effects for any of the investigated neurodegenerative conditions. Drop-out rates were comparable across all treatments.

CONCLUSIONS

This comprehensive NMA reveals a novel and specific prophylactic effect of dapagliflozin against Parkinson's disease, representing a potential breakthrough in preventive neurology. The specificity of dapagliflozin's protective effect to Parkinson's disease might rely on its highly selective inhibition to SGLT2. These findings provide important direction for future research and could inform preventive strategies for populations at risk of Parkinson's disease.

TRIAL REGISTRATION

PROSPERO CRD42021252381.

Incretin-based therapeutics for the treatment of neurodegenerative diseases

Neurodegenerative diseases (NDDs) represent a heterogeneous group of disorders characterized by progressive neuronal loss, which results in significant deficits in memory, cognition, motor skills, and sensory functions. As the prevalence of NDDs rises, there is an urgent unmet need for effective therapies. Current drug development approaches primarily target single pathological features of the disease, which could explain the limited efficacy observed in late-stage clinical trials. Originally developed for the treatment of obesity and diabetes, incretin-based therapies, particularly long-acting GLP-1 receptor (GLP-1R) agonists and GLP-1R-gastric inhibitory polypeptide receptor (GIPR) dual agonists, are emerging as promising treatments for NDDs. Despite limited conclusive preclinical evidence, their pleiotropic ability to reduce neuroinflammation, enhance neuronal energy metabolism and promote synaptic plasticity positions them as potential disease-modifying NDD interventions. In anticipation of results from larger clinical trials, continued advances in next-generation incretin mimetics offer the potential for improved brain access and enhanced neuroprotection, paving the way for incretin-based therapies as a future cornerstone in the management of NDDs.

The immunomodulatory effects of GLP-1 receptor agonists in neurogenerative diseases and ischemic stroke treatment

Glucagon-like peptide-1 (GLP-1) receptor is widely distributed in the digestive system, cardiovascular system, adipose tissue and central nervous system. Numerous GLP-1 receptor-targeting drugs have been investigated in clinical studies for various indications, including type 2 diabetes and obesity (accounts for 70% of the total studies), non-alcoholic steatohepatitis, Alzheimer's disease, and Parkinson's disease. This review presented fundamental information regarding two categories of GLP-1 receptor agonists (GLP-1RAs): peptide-based and small molecule compounds, and elaborated their potential neuroprotective effects by inhibiting neuroinflammation, reducing neuronal apoptosis, and ultimately improving cognitive function in various neurodegenerative diseases. As a new hypoglycemic drug, GLP-1RA has a unique role in reducing the concurrent risk of stroke in T2D patients. Given the infiltration of various peripheral immune cells into brain tissue, particularly in the areas surrounding the infarct lesion, we further investigated the potential immune regulatory mechanisms. GLP-1RA could not only facilitate the M2 polarization of microglia through both direct and indirect pathways, but also modulate the quantity and function of T cell subtypes, including CD4, CD8, and regulatory T cells, resulting into the inhibition of inflammatory responses and the promotion of neuronal regeneration through interleukin-10 secretion. Therefore, we believe that the "Tregs-microglia-neuron/neural precursor cells" axis is instrumental in mediating immune suppression and neuroprotection in the context of ischemic stroke. Given the benefits of rapid diffusion, favorable blood-brain barrier permeability and versatile administration routes, these small molecule compounds will be one of the important candidates of GLP-1RA. We look forward to the further clinical evidence of small molecule GLP-1RA intervention in ischemic stroke or T2D complicated by ischemic stroke.

Interactions between antidiabetes medications and heart-brain axis

PURPOSE OF REVIEW

The heart - brain axis (HBA) is the physiological interactions between the cardiovascular and nervous systems through autonomic nerves, hormones, and cytokines. Patients diagnosed with diabetes mellitus have an increased risk of the cardiovascular and neurological diseases. However, recent evidence demonstrated that different antidiabetic drugs may delay cognitive impairment and improve cardiovascular outcomes. This review examines the impact of antidiabetic drugs on the HBA in patients with diabetes.

RECENT FINDINGS

Metformin improves the cardiovascular and cognitive outcomes through adenosine 5'-monophosphate-activated protein kinase activation. Sodium-glucose cotransporter-2 inhibitors reduce inflammation, oxidative stress by inhibiting the NLRP3 inflammasome thereby reducing the incidence of heart failure and formation of beta-amyloid and neurofibrillary tangles in the brain. Dipeptidyl peptidase-4 inhibitors exhibit neuroprotective effects in Alzheimer's disease by reducing amyloid-beta and tau pathology and inflammation but may exacerbate heart failure risk due to increased sympathetic activity and prolonged β-adrenergic stimulation. Glucagon-like peptide-1 receptor agonists exhibit neuroprotective effects in Alzheimer's and Parkinson's diseases by reducing neuroinflammation, but may increase sympathetic activity, potentially elevating heart rate and blood pressure, despite their cardioprotective benefits.

SUMMARY

Antidiabetes medications have the potential to improve cardiovascular and cognitive outcomes; however, additional studies are required to substantiate these effects.

Repurposing antidiabetic drugs for Alzheimer's disease: A review of preclinical and clinical evidence and overcoming challenges

Repurposing antidiabetic drugs for the treatment of Alzheimer's disease (AD) has emerged as a promising therapeutic strategy. This review examines the potential of repurposing antidiabetic drugs for AD treatment, focusing on preclinical evidence, clinical trials, and observational studies. In addition, the review aims to explore challenges and opportunities in repurposing antidiabetic drugs for AD, emphasizing the importance of well-designed clinical trials that consider patient selection criteria, refined outcome measures, adverse effects, and combination therapies to enhance therapeutic efficacy. Preclinical evidence suggests that glucagon-like peptide-1 (GLP-1) analogs, dipeptidyl peptidase-4 (DPP4) inhibitors, metformin, thiazolidinediones, and sodium-glucose co-transporter-2 (SGLT2) inhibitors exhibit neuroprotective effects in AD preclinical models. In preclinical studies, antidiabetic drugs have demonstrated neuroprotective effects by reducing amyloid beta (Aβ) plaques, tau hyperphosphorylation, neuroinflammation, and cognitive impairment. Antidiabetic drug classes, notably GLP-1 analogs and SGLT2 inhibitors, and a reduced risk of dementia in patients with diabetes mellitus. While the evidence for DPP4 inhibitors is mixed, some studies suggest a potential protective effect. On the other hand, alpha-glucosidase inhibitors (AGIs) and sulfonylureas may potentially increase the risk, especially in those experiencing recurrent hypoglycemic events. Repurposing antidiabetic drugs for AD is a promising therapeutic strategy, but challenges such as disease heterogeneity, limited biomarkers, and benefits versus risk evaluation need to be addressed. Ongoing clinical trials in mild cognitive impairment (MCI) and early AD patients without diabetes will be crucial in determining the clinical efficacy and safety of the antidiabetic drugs, paving the way for potential treatments for AD.

GSK3: A potential target and pending issues for treatment of Alzheimer's disease

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

Trial of Lixisenatide in Early Parkinson's Disease

BACKGROUND

Lixisenatide, a glucagon-like peptide-1 receptor agonist used for the treatment of diabetes, has shown neuroprotective properties in a mouse model of Parkinson's disease.

METHODS

In this phase 2, double-blind, randomized, placebo-controlled trial, we assessed the effect of lixisenatide on the progression of motor disability in persons with Parkinson's disease. Participants in whom Parkinson's disease was diagnosed less than 3 years earlier, who were receiving a stable dose of medications to treat symptoms, and who did not have motor complications were randomly assigned in a 1:1 ratio to daily subcutaneous lixisenatide or placebo for 12 months, followed by a 2-month washout period. The primary end point was the change from baseline in scores on the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III (range, 0 to 132, with higher scores indicating greater motor disability), which was assessed in patients in the on-medication state at 12 months. Secondary end points included other MDS-UPDRS subscores at 6, 12, and 14 months and doses of levodopa equivalent.

RESULTS

A total of 156 persons were enrolled, with 78 assigned to each group. MDS-UPDRS part III scores at baseline were approximately 15 in both groups. At 12 months, scores on the MDS-UPDRS part III had changed by -0.04 points (indicating improvement) in the lixisenatide group and 3.04 points (indicating worsening disability) in the placebo group (difference, 3.08; 95% confidence interval, 0.86 to 5.30; P = 0.007). At 14 months, after a 2-month washout period, the mean MDS-UPDRS motor scores in the off-medication state were 17.7 (95% CI, 15.7 to 19.7) with lixisenatide and 20.6 (95% CI, 18.5 to 22.8) with placebo. Other results relative to the secondary end points did not differ substantially between the groups. Nausea occurred in 46% of participants receiving lixisenatide, and vomiting occurred in 13%.

CONCLUSIONS

In participants with early Parkinson's disease, lixisenatide therapy resulted in less progression of motor disability than placebo at 12 months in a phase 2 trial but was associated with gastrointestinal side effects. Longer and larger trials are needed to determine the effects and safety of lixisenatide in persons with Parkinson's disease. (Funded by the French Ministry of Health and others; LIXIPARK ClinicalTrials.gov number, NCT03439943.).

Obesity and Depression: Common Link and Possible Targets

Depression is among the main causes of disability, and its protracted manifestations could make it even harder to treat metabolic diseases. Obesity is linked to episodes of depression, which is closely correlated to abdominal adiposity and impaired food quality. The present review is aimed at studying possible links between obesity and depression along with targets to disrupt it. Research output in Pubmed and Scopus were referred for writing this manuscript. Obesity and depression are related, with the greater propensity of depressed people to gain weight, resulting in poor dietary decisions and a sedentary lifestyle. Adipokines, which include adiponectin, resistin, and leptin are secretory products of the adipose tissue. These adipokines are now being studied to learn more about the connection underlying obesity and depression. Ghrelin, a gut hormone, controls both obesity and depression. Additionally, elevated ghrelin levels result in anxiolytic and antidepressant-like effects. The gut microbiota influences the metabolic functionalities of a person, like caloric processing from indigestible nutritional compounds and storage in fatty tissue, that exposes an individual to obesity, and gut microorganisms might connect to the CNS through interconnecting pathways, including neurological, endocrine, and immunological signalling systems. The alteration of brain activity caused by gut bacteria has been related to depressive episodes. Monoamines, including dopamine, serotonin, and norepinephrine, have been widely believed to have a function in emotions and appetite control. Emotional signals stimulate arcuate neurons in the hypothalamus that are directly implicated in mood regulation and eating. The peptide hormone GLP-1(glucagon-like peptide- 1) seems to have a beneficial role as a medical regulator of defective neuroinflammation, neurogenesis, synaptic dysfunction, and neurotransmitter secretion discrepancy in the depressive brain. The gut microbiota might have its action in mood and cognition regulation, in addition to its traditional involvement in GI function regulation. This review addressed the concept that obesity-related low-grade mild inflammation in the brain contributes to chronic depression and cognitive impairments.

Incretin Mimetics as Potential Disease Modifying Treatment for Alzheimer's Disease

Alzheimer's disease is a devastating neurodegenerative condition that exerts a significant global burden. Despite recent efforts, disease modifying therapies remain extremely limited, with a tremendous proportion of patients having to rely on symptomatic treatment only. Epidemiological and pathological overlaps exist between Alzheimer's disease and diabetes mellitus type 2, with people with diabetes mellitus type 2 at a significantly increased risk of developing Alzheimer's disease in the future. Incretin mimetics, also known as GLP-1/GIP receptor agonists, are useful tools licensed for the treatment of diabetes mellitus type 2 which have recently been the subject of news coverage for their off-label use as weight loss medications. Emerging evidence highlights the possible neuroprotective function of incretin mimetics in models of Alzheimer's disease as well as in clinical studies. This review details the pre-clinical and clinical studies that have explored the effectiveness of incretin mimetics to alleviate Alzheimer's disease associated pathology and cognitive impairment, while also highlighting the progress made to examine the effectiveness of these molecules in Parkinson's disease. Should clinical trials prove effective, incretin mimetics may be able to be repurposed and become useful novel tools as disease-modifying treatments for Alzheimer's disease and other neurodegenerative diseases.

GLP-1/GIP Agonist as an Intriguing and Ultimate Remedy for Combating Alzheimer's Disease through its Supporting DPP4 Inhibitors: A Review

BACKGROUND

Alzheimer's disease (AD) is a widespread neurological illness in the elderly, which impacted about 50 million people globally in 2020. Type 2 diabetes has been identified as a risk factor. Insulin and incretins are substances that have various impacts on neurodegenerative processes. Preclinical research has shown that GLP-1 receptor agonists decrease neuroinflammation, tau phosphorylation, amyloid deposition, synaptic function, and memory formation. Phase 2 and 3 studies are now occurring in Alzheimer's disease populations. In this article, we present a detailed assessment of the therapeutic potential of GLP-1 analogues and DPP4 inhibitors in Alzheimer's disease.

AIM

This study aimed to gain insight into how GLP-1 analogues and associated antagonists of DPP4 safeguard against AD.

METHODS

This study uses terms from search engines, such as Scopus, PubMed, and Google Scholar, to explore the role, function, and treatment options of the GLP-1 analogue for AD.

RESULTS

The review suggested that GLP-1 analogues may be useful for treating AD because they have been linked to anti-inflammatory, neurotrophic, and neuroprotective characteristics. Throughout this review, we discuss the underlying causes of AD and how GLP signaling functions.

CONCLUSION

With a focus on AD, the molecular and pharmacological effects of a few GLP-1/GIP analogs, both synthetic and natural, as well as DPP4 inhibitors, have been mentioned, which are in the preclinical and clinical studies. This has been demonstrated to improve cognitive function in Alzheimer's patients.

New insights toward molecular and nanotechnological approaches to antidiabetic agents for Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder affecting a major class of silver citizens. The disorder shares a mutual relationship on account of its cellular and molecular pathophysiology with type-II diabetes mellitus (DM). Chronic DM increases the risk for AD. Emerging evidence recommended that resistance in insulin production develops cognitive dysfunction, which generally leads to AD. Repurposing of antidiabetic drugs can be effective in preventing and treatment of the neurodegenerative disorder. Limitations of antidiabetic drugs restrict the repurposing of the drugs for other disorders. Therefore, nanotechnological intervention plays a significant role in the treatment of neurological disorders. In this review, we discuss the common cellular and molecular pathophysiologies between AD and type-II DM, the relevance of in vivo models of type II DM in the study of AD, and the repurposing of antidiabetic drugs and the nanodelivery systems of antidiabetic drugs against AD.

GLP-1 Analogs, SGLT-2, and DPP-4 Inhibitors: A Triad of Hope for Alzheimer's Disease Therapy

Alzheimer's is a prevalent, progressive neurodegenerative disease marked by cognitive decline and memory loss. The disease's development involves various pathomechanisms, including amyloid-beta accumulation, neurofibrillary tangles, oxidative stress, inflammation, and mitochondrial dysfunction. Recent research suggests that antidiabetic drugs may enhance neuronal survival and cognitive function in diabetes. Given the well-documented correlation between diabetes and Alzheimer's disease and the potential shared mechanisms, this review aimed to comprehensively assess the potential of new-generation anti-diabetic drugs, such as GLP-1 analogs, SGLT-2 inhibitors, and DPP-4 inhibitors, as promising therapeutic approaches for Alzheimer's disease. This review aims to comprehensively assess the potential therapeutic applications of novel-generation antidiabetic drugs, including GLP-1 analogs, SGLT-2 inhibitors, and DPP-4 inhibitors, in the context of Alzheimer's disease. In our considered opinion, antidiabetic drugs offer a promising avenue for groundbreaking developments and have the potential to revolutionize the landscape of Alzheimer's disease treatment.

Glucagon-like peptide 1 (GLP-1) receptor agonists in experimental Alzheimer's disease models: a systematic review and meta-analysis of preclinical studies

Alzheimer's disease (AD) is a degenerative disease of the nervous system. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs), a drug used to treat type 2 diabetes, have been shown to have neuroprotective effects. This systematic review and meta-analysis evaluated the effects and potential mechanisms of GLP-1 RAs in AD animal models. 26 studies were included by searching relevant studies from seven databases according to a predefined search strategy and inclusion criteria. Methodological quality was assessed using SYRCLE's risk of bias tool, and statistical analysis was performed using ReviewManger 5.3. The results showed that, in terms of behavioral tests, GLP-1 RAs could improve the learning and memory abilities of AD rodents; in terms of pathology, GLP-1 RAs could reduce Aβ deposition and phosphorylated tau levels in the brains of AD rodents. The therapeutic potential of GLP-1 RAs in AD involves a range of mechanisms that work synergistically to enhance the alleviation of various pathological manifestations associated with the condition. A total of five clinical trials were retrieved from ClinicalTrials.gov. More large-scale and high-quality preclinical trials should be conducted to more accurately assess the therapeutic effects of GLP-1 RAs on AD.

Crosstalk between Alzheimer's disease and diabetes: a focus on anti-diabetic drugs

Alzheimer's disease (AD) and Type 2 diabetes mellitus (T2DM) are two of the most common age-related diseases. There is accumulating evidence of an overlap in the pathophysiological mechanisms of these two diseases. Studies have demonstrated insulin pathway alternation may interact with amyloid-β protein deposition and tau protein phosphorylation, two essential factors in AD. So attention to the use of anti-diabetic drugs in AD treatment has increased in recent years. In vitro, in vivo, and clinical studies have evaluated possible neuroprotective effects of anti-diabetic different medicines in AD, with some promising results. Here we review the evidence on the therapeutic potential of insulin, metformin, Glucagon-like peptide-1 receptor agonist (GLP1R), thiazolidinediones (TZDs), Dipeptidyl Peptidase IV (DPP IV) Inhibitors, Sulfonylureas, Sodium-glucose Cotransporter-2 (SGLT2) Inhibitors, Alpha-glucosidase inhibitors, and Amylin analog against AD. Given that many questions remain unanswered, further studies are required to confirm the positive effects of anti-diabetic drugs in AD treatment. So to date, no particular anti-diabetic drugs can be recommended to treat AD.

Alternative role of glucagon-like Peptide-1 receptor agonists in neurodegenerative diseases

Aging is a crucial risk factor for common neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Limited options are available for the treatment of age-related, multiple pathogenic mechanism-contributed diseases that usually advance to irreversible conditions with severe neurological deficits and result in a heavy socioeconomic burden on patients, families, and society. A therapy that decelerates disease progression and reduces the socioeconomic burden stemming from these diseases is required. Glucagon-like peptide-1 receptor (GLP-1R) is an important class of medication for type 2 diabetes mellitus (T2DM). Through pancreatic effects, GLP-1R agonists can stimulate insulin secretion, increase β-cell proliferation, reduce β-cell apoptosis, and inhibit glucagon secretion in patients with T2DM. Currently, seven clinically approved GLP-1R agonists are used for T2DM: exenatide, liraglutide, lixisenatide, extended-release exenatide, albiglutide, dulaglutide, and semaglutide. Besides the pancreas, GLP-1Rs are also expressed in organs, such as the gastrointestinal tract, heart, lung, kidney, and brain, indicating their potential use in diseases other than T2DM. Emerging evidence reveals that GLP-1R agonists possess pleiotropic effects that enrich neurogenesis, diminish apoptosis, preclude neurons from oxidative stress, and reduce neuroinflammation in various neurological conditions. These favorable effects may also be employed in neurodegenerative diseases. Herein, we reviewed the recent progress, both in preclinical studies and clinical trials, regarding these clinically used GLP-1R agonists in aging-related neurodegenerative diseases, mainly AD and PD. We stress the pleiotropic characteristics of GLP-1R agonists as repurposing drugs to target multiple pathological mechanisms and for use in the future for these devastating neurodegenerative conditions.

Glucagon-like peptide-1 (GLP-1) receptor agonists and neuroinflammation: Implications for neurodegenerative disease treatment

Chronic, excessive neuroinflammation is a key feature of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). However, neuroinflammatory pathways have yet to be effectively targeted in clinical treatments for such diseases. Interestingly, increased inflammation and neurodegenerative disease risk have been associated with type 2 diabetes mellitus (T2DM) and insulin resistance (IR), suggesting that treatments that mitigate T2DM pathology may be successful in treating neuroinflammatory and neurodegenerative pathology as well. Glucagon-like peptide-1 (GLP-1) is an incretin hormone that promotes healthy insulin signaling, regulates blood sugar levels, and suppresses appetite. Consequently, numerous GLP-1 receptor (GLP-1R) stimulating drugs have been developed and approved by the US Food and Drug Administration (FDA) and related global regulatory authorities for the treatment of T2DM. Furthermore, GLP-1R stimulating drugs have been associated with anti-inflammatory, neurotrophic, and neuroprotective properties in neurodegenerative disorder preclinical models, and hence hold promise for repurposing as a treatment for neurodegenerative diseases. In this review, we discuss incretin signaling, neuroinflammatory pathways, and the intersections between neuroinflammation, brain IR, and neurodegenerative diseases, with a focus on AD and PD. We additionally overview current FDA-approved incretin receptor stimulating drugs and agents in development, including unimolecular single, dual, and triple receptor agonists, and highlight those in clinical trials for neurodegenerative disease treatment. We propose that repurposing already-approved GLP-1R agonists for the treatment of neurodegenerative diseases may be a safe, efficacious, and cost-effective strategy for ameliorating AD and PD pathology by quelling neuroinflammation.

Diabetes: Risk factor and translational therapeutic implications for Alzheimer's disease

Type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) commonly co-occur. T2DM increases the risk for AD by approximately twofold. Animal models provide one means of interrogating the relationship of T2DM to AD and investigating brain insulin resistance in the pathophysiology of AD. Animal models show that persistent hyperglycaemia results in chronic low-grade inflammation that may contribute to the development of neuroinflammation and accelerate the pathobiology of AD. Epidemiological studies suggest that patients with T2DM who received treatment with specific anti-diabetic agents have a decreased risk for the occurrence of AD and all-cause dementia. Agents such as metformin ameliorate T2DM and may have other important systemic effects that lower the risk of AD. Glucagon-like peptide 1 (GLP-1) agonists have been associated with a decreased risk for AD in patients with T2DM. Both insulin and non-insulin anti-diabetic treatments have been evaluated for the treatment of AD in clinical trials. In most cases, patients included in the trials have clinical features of AD but do not have T2DM. Many of the trials were conducted prior to the use of diagnostic biomarkers for AD. Trials have had a wide range of durations and population sizes. Many of the agents used to treat T2DM do not cross the blood brain barrier, and the effects are posited to occur via lowering of peripheral hyperglycaemia and reduction of peripheral and central inflammation. Clinical trials of anti-diabetic agents to treat AD are ongoing and will provide insight into the therapeutic utility of these agents.

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.

Glucagon-like peptide 1 and glucose-dependent insulinotropic peptide hormones and novel receptor agonists protect synapses in Alzheimer’s and Parkinson’s diseases

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) are peptide hormones and growth factors. A major pathological feature of both Alzheimer’s dis-ease (AD) and Parkinson’s disease (PD) is the loss of synaptic transmission in the cortex in AD and the loss of dopaminergic synapses in the nigra-striatal dopaminergic projection. Several studies demonstrate that GLP-1 and GIP receptor agonists protect synapses and synaptic transmission from the toxic events that underlie AD and PD. In a range of AD animal models, treatment with GLP-1, GIP, or dual-GLP-1/GIP receptor agonists effectively protected cognition, synaptic trans-mission, long-term potentiation (LTP), and prevented the loss of synapses and neurons. In PD models, dopaminergic production resumed and synapses became functional again. Importantly, the GLP-1 receptor agonists exendin-4 and liraglutide have shown good protective effects in clinical trials in AD and PD patients. Studies show that growth factors and peptide drugs that can cross the blood–brain barrier (BBB) better are more potent than those that do not cross the BBB. We therefore developed dual-GLP-1/GIP receptor agonists that can cross the BBB at an enhanced rate and showed superior protective properties on synapses in animal models of AD and PD.

GLP-1 Receptor Agonists in Neurodegeneration: Neurovascular Unit in the Spotlight

Defects in brain energy metabolism and proteopathic stress are implicated in age-related degenerative neuronopathies, exemplified by Alzheimer’s disease (AD) and Parkinson’s disease (PD). As the currently available drug regimens largely aim to mitigate cognitive decline and/or motor symptoms, there is a dire need for mechanism-based therapies that can be used to improve neuronal function and potentially slow down the underlying disease processes. In this context, a new class of pharmacological agents that achieve improved glycaemic control via the glucagon-like peptide 1 (GLP-1) receptor has attracted significant attention as putative neuroprotective agents. The experimental evidence supporting their potential therapeutic value, mainly derived from cellular and animal models of AD and PD, has been discussed in several research reports and review opinions recently. In this review article, we discuss the pathological relevance of derangements in the neurovascular unit and the significance of neuron–glia metabolic coupling in AD and PD. With this context, we also discuss some unresolved questions with regard to the potential benefits of GLP-1 agonists on the neurovascular unit (NVU), and provide examples of novel experimental paradigms that could be useful in improving our understanding regarding the neuroprotective mode of action associated with these agents.

Neuroprotective properties of Solanum leaves in Transgenic Drosophila melanogaster model of Alzheimer's disease

INTRODUCTION

We investigated the effect of African eggplant (AE) (Solanum macrocarpon L) and Black nightshade (BN) (Solanum nigrum L) leaves; two tropical vegetables consumed by humans on behavioral, biochemical and histological indices in Drosophila melanogaster model of Alzheimer's disease (AD).

MATERIALS AND METHOD

Transgenic flies expressing human Amyloid Precursor Protein (hAPP) and β-secretase (hBACE 1) were exposed to the pulverized leaf samples (0.1 and 1.0%) in their diets for fourteen days. Thereafter, the flies were assessed for their behavioral indices and routine histology of brain cells. Furthermore, fly head homogenates were assayed for β-amyloid level, activities of acetylcholinesterase (AChE) and β-secretase (BACE-1), as well as oxidative stress markers.

RESULTS

Result showed that the significantly lower (p < 0.05) behavioral parameters (survival, locomotor performance and memory index), higher AChE and BACE-1 activities, β-amyloid, ROS and lipid peroxidation levels, as well as reduced antioxidant indices observed in the AD flies, were significantly ameliorated (p < 0.05) in AD flies treated with the leaf samples.

DISCUSSION

This study has showed that leaves of AE and BN ameliorated behavioral and biochemical indices in AD flies via neural enzyme modulatory, and antioxidant mechanisms.

CONCLUSION

Hence, this study further justifies the neuroprotective properties of both AE and BN.

Linagliptin, a Selective Dipeptidyl Peptidase-4 Inhibitor, Reduces Physical and Behavioral Effects of Morphine Withdrawal

(1) Background: Recent data indicate that receptors for GLP-1 peptide are involved in the activity of the mesolimbic system. Thus, the purpose of the present study was to examine the effect of the selective dipeptidyl peptidase-4 (DPP-4) inhibitor, linagliptin, on morphine dependence in mice. (2) Methods: Morphine dependence in mice was obtained by administration of increasing doses of morphine for eight consecutive days, twice a day. On the 9th day of the experiment, the naloxone-induced (2 mg/kg, ip) morphine withdrawal signs (jumping) were assessed. Moreover, behavioral effects of short-term (60 h after morphine discontinuation) and long-term (14 days after morphine discontinuation) morphine withdrawal were observed. In terms of behavioral effects, the depressive effect in the forced swim test and anxiety in the elevated plus maze test were investigated. Locomotor activity of mice was also studied. (3) Results: The administration of linagliptin (10 and 20 mg/kg, ip) for 8 consecutive days before morphine injections significantly diminished the number of naloxone-induced morphine withdrawal signs (jumping) in mice. In addition, the cessation of morphine administration induced depressive behavior in mice which were observed during short- and long-term morphine withdrawal. Linagliptin administered during morphine withdrawal significantly reduced the depressive behavior in studied mice. Furthermore, the short-term morphine withdrawal evoked anxiety which also was reduced by linagliptin in mice. (4) Conclusions: The present study reveals that GLP-1 receptors are involved in morphine dependence. What is more, linagliptin might be a valuable drug in attenuating the physical symptoms of morphine dependence. It might be also a useful drug in reducing emotional disturbances which may develop during the morphine withdrawal period.

The Role of Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RA) in Diabetes-Related Neurodegenerative Diseases

Recent clinical guidelines have emphasized the importance of screening for cognitive impairment in older adults with diabetes, however, there is still a lack of understanding about the drug therapy. Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are widely used in the treatment of type 2 diabetes and potential applications may include the treatment of obesity as well as the adjunctive treatment of type 1 diabetes mellitus in combination with insulin. Growing evidence suggests that GLP-1 RA has the potential to treat neurodegenerative diseases, particularly in diabetes-related Alzheimer’s disease (AD) and Parkinson’s disease (PD). Here, we review the molecular mechanisms of the neuroprotective effects of GLP-1 RA in diabetes-related degenerative diseases, including AD and PD, and their potential effects.

Glucagon-like peptide-1 analogs mitigate neuroinflammation in Alzheimer's disease by suppressing NLRP2 activation in astrocytes

Neuroinflammation is closely linked to the pathogenesis of Alzheimer's disease (AD). Glucagon-like peptide-1 (GLP-1) analogs exhibit anti-inflammatory and neuroprotective effects; hence, we investigated whether they reduce cognitive impairment and protect astrocytes from oxidative stress. We found that 5 × FAD transgenic mice treated with the synthetic GLP-1 receptor agonist exenatide had improved cognitive function per the Morris water maze test. Immunohistochemistry, western blotting, and ELISAs used to detect inflammatory factors revealed reduced neuroinflammation in extracted piriform cortexes of exenatide-treated mice as well as lower amyloid β_1-42-induced oxidative stress and inflammation in astrocytes treated with exendin-4 (the natural analog of exenatide). Adenovirus-mediated overexpression of nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 2 (NLRP2) revealed that exenatide/exendin-4 function may be attributed to NLRP2 inflammasome inhibition. Collectively, our results indicate that GLP-1 analogs improve cognitive dysfunction in vivo and protect astrocytes in vitro, potentially via the downregulation of the NLRP2 inflammasome.

(D-Ser2) oxyntomodulin recovers hippocampal synaptic structure and theta rhythm in Alzheimer's disease transgenic mice

In our previous studies, we have shown that (D-Ser2) oxyntomodulin (Oxm), a glucagon-like peptide 1 (GLP-1) receptor (GLP1R)/glucagon receptor (GCGR) dual agonist peptide, protects hippocampal neurons against Aβ_1–42 -induced cytotoxicity, and stabilizes the calcium homeostasis and mitochondrial membrane potential of hippocampal neurons. Additionally, we have demonstrated that (D-Ser2) Oxm improves cognitive decline and reduces the deposition of amyloid-beta in Alzheimer's disease model mice. However, the protective mechanism remains unclear. In this study, we showed that 2 weeks of intraperitoneal administration of (D-Ser2) Oxm ameliorated the working memory and fear memory impairments of 9-month-old 3×Tg Alzheimer's disease model mice. In addition, electrophysiological data recorded by a wireless multichannel neural recording system implanted in the hippocampal CA1 region showed that (D-Ser2) Oxm increased the power of the theta rhythm. In addition, (D-Ser2) Oxm treatment greatly increased the expression level of synaptic-associated proteins SYP and PSD-95 and increased the number of dendritic spines in 3×Tg Alzheimer's disease model mice. These findings suggest that (D-Ser2) Oxm improves the cognitive function of Alzheimer's disease transgenic mice by recovering hippocampal synaptic function and theta rhythm.

Protective properties of GLP-1 and associated peptide hormones in neurodegenerative disorders

Type 2 diabetes mellitus and the associated desensitisation of insulin signalling has been identified as a risk factor for progressive neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and others. Glucagon-like peptide 1 (GLP-1) is a hormone that has growth factor-like and neuroprotective properties. Several clinical trials have been conducted, testing GLP-1 receptor agonists in patients with Alzheimer's disease, Parkinson's disease or diabetes-induced memory impairments. The trials showed clear improvements in Alzheimer's disease, Parkinson's disease and diabetic patients. Glucose-dependent insulinotropic polypeptide/gastric inhibitory peptide (GIP) is the 'sister' incretin hormone of GLP-1. GIP analogues have shown neuroprotective effects in animal models of disease and can improve on the effects of GLP-1. Novel dual GLP-1/GIP receptor agonists have been developed that can enter the brain at an enhanced rate. The improved neuroprotective effects of these drugs suggest that they are superior to single GLP-1 receptor agonists and could provide disease-modifying care for Alzheimer's disease and Parkinson's disease patients. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

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.

A GLP-1/GIP Dual Receptor Agonist DA4-JC Effectively Attenuates Cognitive Impairment and Pathology in the APP/PS1/Tau Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a degenerative disorder, accompanied by progressive cognitive decline, for which there is no cure. Recently, the close correlation between AD and type 2 diabetes mellitus (T2DM) has been noted, and a promising anti-AD strategy is the use of anti-T2DM drugs.

OBJECTIVE

To investigate if the novel glucagon-like peptide-1 (GLP-1)/glucose-dependent insulinotropic polypeptide (GIP) receptor agonist DA4-JC shows protective effects in the triple APP/PS1/tau mouse model of AD.

METHODS

A battery of behavioral tests were followed by in vivo recording of long-term potentiation (LTP) in the hippocampus, quantified synapses using the Golgi method, and biochemical analysis of biomarkers.

RESULTS

DA4-JC improved cognitive impairment in a range of tests and relieved pathological features of APP/PS1/tau mice, enhanced LTP in the hippocampus, increased numbers of synapses and dendritic spines, upregulating levels of post-synaptic density protein 95 (PSD95) and synaptophysin (SYP), normalized volume and numbers of mitochondria and improving the phosphatase and tensin homologue induced putative kinase 1 (PINK1) - Parkin mitophagy signaling pathway, while downregulating amyloid, p-tau, and autophagy marker P62 levels.

CONCLUSION

DA4-JC is a promising drug for the treatment of AD.

Treating cognitive impairment in schizophrenia with GLP-1RAs: an overview of their therapeutic potential

INTRODUCTION

Schizophrenia is a neuropsychiatric disorder that affects approximately 1% of individuals worldwide. There are no available medications to treat cognitive impairment in this patient population currently. Preclinical evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve cognitive function. There is a need to evaluate how GLP-1 RAs alter specific domains of cognition and whether they will be of therapeutic benefit in individuals with schizophrenia.

AREAS COVERED

This paper summarizes the effects of GLP-1 RAs on metabolic processes in the brain and how these mechanisms relate to improved cognitive function. We provide an overview of preclinical studies that demonstrate GLP-1 RAs improve cognition and comment on their potential therapeutic benefit in individuals with schizophrenia.

EXPERT OPINION

To understand the benefits of GLP-1 RAs in individuals with schizophrenia, further preclinical research with rodent models relevant to schizophrenia symptomology are needed. Moreover, preclinical studies must focus on using a wider range of behavioral assays to understand whether important aspects of cognition such as executive function, attention, and goal-directed behavior are improved using GLP-1 RAs. Further research into the specific mechanisms of how GLP-1 RAs affect cognitive function and their interactions with antipsychotic medication commonly prescribed is necessary.

Inflammation and Insulin Resistance as Risk Factors and Potential Therapeutic Targets for Alzheimer's Disease

Overnutrition and modern diets containing high proportions of saturated fat are among the major factors contributing to a low-grade state of inflammation, hyperglycemia and dyslipidemia. In the last decades, the global rise of type 2 diabetes and obesity prevalence has elicited a great interest in understanding how changes in metabolic function lead to an increased risk for premature brain aging and the development of neurodegenerative disorders such as Alzheimer's disease (AD). Cognitive impairment and decreased neurogenic capacity could be a consequence of metabolic disturbances. In these scenarios, the interplay between inflammation and insulin resistance could represent a potential therapeutic target to prevent or ameliorate neurodegeneration and cognitive impairment. The present review aims to provide an update on the impact of metabolic stress pathways on AD with a focus on inflammation and insulin resistance as risk factors and therapeutic targets.

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.

Glucagon-like peptide-1 analog improves neuronal and behavioral impairment and promotes neuroprotection in a rat model of aluminum-induced dementia

BACKGROUND

Alzheimer's disease (AD) is a worldwide severe medical and social burden. Liraglutide (LIR) has neuroprotective effects in preclinical animal models.

AIM

To explore the probable neuroprotective impact of Glucagon-like peptide-1 (GLP-1) on rats' behavior and to elucidate its underlying mechanisms.

METHODS

A total of 24 male albino rats were assigned to control, LIR (300 µg/kg subcutaneously (s.c.)), AD only (100 mg/kg aluminum chloride (AlCl3 ) orally) and LIR + AD treated groups. Eight radial arm maze was performed. Serum blood glucose, proinflammatory cytokines, oxidative stress markers were measured and hippocampal tissue homogenate neurotransmitters were evaluated. Histopathological and immunofluorescent examinations were performed.

RESULTS

LIR prevents the impairment of learning and improves both working memory and reference memory through significant reduction of serum tumor necrosis factor (TNF-α), interleukin 6 (IL-6) and interferon-γ (INF-γ) and malondialdehyde (MDA) and through the increase of superoxide dismutase (SOD), dopamine, adrenaline, and noradrenaline. LIR also improves hippocampal histological features of ALCL3 administrated rats and decreases the percentage of neuronal loss.

CONCLUSION

LIR normalizes ALCL3 -induced dementia. It improves cognitive dysfunction and ameliorates cerebral damage.

Liraglutide mends cognitive impairment by averting Notch signaling pathway overexpression in a rat model of polycystic ovary syndrome

AIMS

Polycystic ovary syndrome (PCOS), the rifest endocrine disorder in women, is involved in disrupting many metabolic processes. However, the impact of PCOS on cognitive deficits is still uncertain. Recently, Notch signaling pathway was identified as a key modifier in regulating the pathological process in the ovary and various neurodegenerative disorders. Liraglutide has favourable neuroprotective effects that may protect against the possible cognitive dysfunction in PCOS.

MAIN METHODS

PCOS was induced in rats by administrating Letrozole orally for 21 successive days. Then, Liraglutide (LIR) was administered intraperitoneally for 30 days. Memory was examined using Y-maze, novel object recognition (NOR), and Morris water maze (MWM) tests. Western blotting, enzyme immunoassay, and quantitative real-time PCR were used to examine Notch signaling downstream targets, as well as assessing the expression of the components of various pathways cross talked with Notch signaling in memory impairment. Furthermore, histopathological examination was performed to examine neuronal changes.

KEY FINDINGS

Notch signaling was overexpressed in PCOS rats, which increased Aβ aggregation, apoptosis, and neuroinflammation. Additionally, histopathological examination showed neuronal degeneration, which was marked by diminished acetylcholine levels in the PCOS rats' hippocampi. Finally, serum levels of insulin and testosterone were elevated while estradiol was reduced. Treatment with LIR repaired Notch signaling-attributed changes and improved the PCOS-induced memory impairment in rats.

SIGNIFICANCE

The obtained findings confirm that Notch signaling activation in the hippocampus of rats impairs cognitive functions in PCOS, which is mitigated by LIR. Therefore, LIR may offer a novel therapeutic intervention to impede PCOS-induced dementia.

Brain uptake pharmacokinetics of incretin receptor agonists showing promise as Alzheimer's and Parkinson's disease therapeutics

Among the more promising treatments proposed for Alzheimer's disease (AD) and Parkinson's disease (PD) are those reducing brain insulin resistance. The antidiabetics in the class of incretin receptor agonists (IRAs) reduce symptoms and brain pathology in animal models of AD and PD, as well as glucose utilization in AD cases and clinical symptoms in PD cases after their systemic administration. At least 9 different IRAs are showing promise as AD and PD therapeutics, but we still lack quantitative data on their relative ability to cross the blood-brain barrier (BBB) reaching the brain parenchyma. We consequently compared brain uptake pharmacokinetics of intravenous 125I-labeled IRAs in adult CD-1 mice over the course of 60 min. We tested single IRAs (exendin-4, liraglutide, lixisenatide, and semaglutide), which bind receptors for one incretin (glucagon-like peptide-1 [GLP-1]), and dual IRAs, which bind receptors for two incretins (GLP-1 and glucose-dependent insulinotropic polypeptide [GIP]), including unbranched, acylated, PEGylated, or C-terminally modified forms (Finan/Ma Peptides 17, 18, and 20 and Hölscher peptides DA3-CH and DA-JC4). The non-acylated and non-PEGylated IRAs (exendin-4, lixisenatide, Peptide 17, DA3-CH and DA-JC4) had significant rates of blood-to-brain influx (Ki), but the acylated IRAs (liraglutide, semaglutide, and Peptide 18) did not measurably cross the BBB. The brain influx of the non-acylated, non-PEGylated IRAs were not saturable up to 1 μg of these drugs and was most likely mediated by adsorptive transcytosis across brain endothelial cells, as observed for exendin-4. Of the non-acylated, non-PEGylated IRAs tested, exendin-4 and DA-JC4 were best able to cross the BBB based on their rate of brain influx, percentage reaching the brain that accumulated in brain parenchyma, and percentage of the systemic dose taken up per gram of brain tissue. Exendin-4 and DA-JC4 thus merit special attention as IRAs well-suited to enter the central nervous system (CNS), thus reaching areas pathologic in AD and PD.

Tau-Mediated Dysregulation of Neuroplasticity and Glial Plasticity

The inability of individual neurons to compensate for aging-related damage leads to a gradual loss of functional plasticity in the brain accompanied by progressive impairment in learning and memory. Whereas this loss in neuroplasticity is gradual during normal aging, in neurodegenerative diseases such as Alzheimer’s disease (AD), this loss is accelerated dramatically, leading to the incapacitation of patients within a decade of onset of cognitive symptoms. The mechanisms that underlie this accelerated loss of neuroplasticity in AD are still not completely understood. While the progressively increasing proteinopathy burden, such as amyloid β (Aβ) plaques and tau tangles, definitely contribute directly to a neuron’s functional demise, the role of non-neuronal cells in controlling neuroplasticity is slowly being recognized as another major factor. These non-neuronal cells include astrocytes, microglia, and oligodendrocytes, which through regulating brain homeostasis, structural stability, and trophic support, play a key role in maintaining normal functioning and resilience of the neuronal network. It is believed that chronic signaling from these cells affects the homeostatic network of neuronal and non-neuronal cells to an extent to destabilize this harmonious milieu in neurodegenerative diseases like AD. Here, we will examine the experimental evidence regarding the direct and indirect pathways through which astrocytes and microglia can alter brain plasticity in AD, specifically as they relate to the development and progression of tauopathy. In this review article, we describe the concepts of neuroplasticity and glial plasticity in healthy aging, delineate possible mechanisms underlying tau-induced plasticity dysfunction, and discuss current clinical trials as well as future disease-modifying approaches.

Alleviation of Depression by Glucagon-Like Peptide 1 Through the Regulation of Neuroinflammation, Neurotransmitters, Neurogenesis, and Synaptic Function

Depression has emerged as a major cause of mortality globally. Many studies have reported risk factors and mechanisms associated with depression, but it is as yet unclear how these findings can be applied to the treatment and prevention of this disorder. The onset and recurrence of depression have been linked to diverse metabolic factors, including hyperglycemia, dyslipidemia, and insulin resistance. Recent studies have suggested that depression is accompanied by memory loss as well as depressive mood. Thus, many researchers have highlighted the relationship between depressive behavior and metabolic alterations from various perspectives. Glucagon-like peptide-1 (GLP-1), which is secreted from gut cells and hindbrain areas, has been studied in metabolic diseases such as obesity and diabetes, and was shown to control glucose metabolism and insulin resistance. Recently, GLP-1 was highlighted as a regulator of diverse pathways, but its potential as the therapeutic target of depressive disorder was not described comprehensively. Therefore, in this review, we focused on the potential of GLP-1 modulation in depression.

Diabetes and dementia - the two faces of Janus

Patients with type 2 diabetes are at high risk for cognitive decline and dementia. Despite the limited data on the possible pathogenetic mechanisms, evidence suggests that cognitive decline, and thus dementia and Alzheimer's disease, might arise from a complex interplay between type 2 diabetes and the aging brain, including decreased insulin signalling and glucose metabolism, mitochondrial dysfunction, neuroinflammation, and vascular disease. Furthermore, there is increasing interest on the effects of antidiabetic agents on cognitive decline. There are many studies showing that antidiabetic agents might have beneficial effects on the brain, mainly through inhibition of oxidative stress, inflammation, and apoptosis. In addition, experimental studies on patients with diabetes and Alzheimer's disease have shown beneficial effects on synaptic plasticity, metabolism of amyloid-β, and microtubule-associated protein tau. Therefore, in the present review, we discuss the effects of antidiabetic agents in relation to cognitive decline, and in particular dementia and Alzheimer's disease, in patients with type 2 diabetes.

Type 2 Diabetes Mellitus Drugs for Alzheimer's Disease: Current Evidence and Therapeutic Opportunities

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) represent two major health burdens with steadily increasing prevalence and accumulating evidence indicates a close relationship between the two disorders. In view of their similar pathogenesis, the potential of T2DM drugs for the treatment of AD has attracted considerable attention in recent years, with inspiring outcomes. Here, we provide a comprehensive overview of the effects of a total of 14 individual drugs (among which are seven T2DM drug types) against AD. Further, we discuss the potential action mechanisms of these T2DM drugs against AD. We argue that these findings may open novel avenues for AD drug discovery, drug target identification, and cotreatment of the two disorders.

Insulin mediated novel therapies for the treatment of Alzheimer's disease

Alzheimer's disease, a progressive neurodegenerative disorder, is one of the leading causes of death in the USA, along with cancer and cardiac disorders. AD is characterized by various neurological factors like amyloid plaques, tau hyperphosphorylation, mitochondrial dysfunction, acetylcholine deficiency, etc. Together, impaired insulin signaling in the brain is also observed as essential factor to be considered in AD pathophysiology. Hence, currently researchers focused on studying the effect of brain insulin metabolism and relation of diabetes with AD. Based on the investigations, AD is also considered as type 3 or brain diabetes. Besides the traditional view of correlating AD with aging, a better understanding of various pathological factors and effects of other physical ailments is necessary to develop a promising therapeutic approach. There is a vast scope of studying the relation of systemic insulin level, insulin signaling, its neuroprotective potency and effect of diabetes on AD progression. The present work describes worldwide status of AD and its relation with diabetes mellitus and insulin metabolism; pathophysiology of AD; different metabolic pathways associating insulin metabolism with AD; insulin receptor and signaling in the brain; glucose metabolism; insulin resistance; and various preclinical and clinical studies reported insulin-based therapies to treat AD via systemic route and through direct intranasal delivery to the brain.

A dual GLP-1 and Gcg receptor agonist rescues spatial memory and synaptic plasticity in APP/PS1 transgenic mice

Alzheimer's disease (AD) is a neurodegenerative disease that severely affects the health and lifespan of the elderly worldwide. Recently, the correlation between AD and type 2 diabetes mellitus (T2DM) has received intensive attention, and a promising new anti-AD strategy is the use of anti-diabetic drugs. Oxyntomodulin (Oxm) is a peptide hormone and growth factor that acts on neurons in the hypothalamus. OXM activates glucagon-like peptide 1 (GLP-1) and glucagon (Gcg) receptors, facilitates insulin signaling and has neuroprotective effects against Aβ_1-42-induced cytotoxicity in primary hippocampal neurons. Here, we tested the effects of the protease-resistant analogue (D-Ser2)Oxm on spatial memory and synaptic plasticity and the underlying molecular mechanisms in the APP/PS1 transgenic mouse model of AD. The results showed that (D-Ser2)Oxm not only alleviated the impairments of working memory and long-term spatial memory, but also reduced the number of Aβ plaques in the hippocampus, and reversed the suppression of hippocampal synaptic long-term potentiation (LTP). Moreover, (D-Ser2)Oxm administration significantly increased p-PI3K/p-AKT1 expression and decreased p-GSK3β levels in the hippocampus. These results are the first to show an in vivo neuroprotective role of (D-Ser2)Oxm in APP/PS1 mice, and this role involves the improvement of synaptic plasticity, clearance of Aβ and normalization of PI3K/AKT/GSK3β cell signaling in the hippocampus. This study suggests that (D-Ser2)Oxm holds promise for the prevention and treatment of AD.

The Dual GLP-1/GIP Receptor Agonist DA4-JC Shows Superior Protective Properties Compared to the GLP-1 Analogue Liraglutide in the APP/PS1 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder for which there is no cure. Here, we test a dual GLP-1/GIP receptor agonist (DA4-JC) that has a cell penetrating sequence added to enhance blood-brain barrier penetration. We show in a receptor activity study that DA4-JC has balanced activity on both GLP-1 and GIP receptors but not on GLP-2 or Glucagon receptors. A dose-response study in the APP/PS1 mouse model of AD showed both a dose-dependent drug effect on the inflammation response and the reduction of amyloid plaques in the brain. When comparing DA4-JC with the GLP-1 analogue liraglutide at equal doses of 10nmol/kg bw ip. once-daily for 8 weeks, DA4-JC was more effective in reversing memory loss, enhancing synaptic plasticity (LTP) in the hippocampus, reducing amyloid plaques and lowering pro-inflammatory cytokine levels in the brain. The results suggest that DA4-JC may be a novel treatment for AD.

Transcriptomic and Network Analysis Highlight the Association of Diabetes at Different Stages of Alzheimer's Disease

Alzheimer's disease (AD) and type 2 diabetes (T2D) are among the most prevalent chronic diseases affecting the aging population. Extensive research evidence indicates that T2D is a well-established risk factor for AD; however, the molecular mechanisms underlying this association have not been fully elucidated. Furthermore, how T2D may contribute to the progression of AD is a subject of extensive investigation. In this study, we compared the blood transcriptome of patients with mild cognitive impairment (MCI), AD, and advanced AD to those afflicted with T2D to unveil shared and unique pathways and potential therapeutic targets. Blood transcriptomic analyses revealed a positive correlation between gene expression profiles of MCI, AD, and T2D in seven independent microarrays. Interestingly, gene expression profiles from women with advanced AD correlated negatively with T2D, suggesting sex-specific differences in T2D as a risk factor for AD. Network and pathway analysis revealed that shared molecular networks between MCI and T2D were predominantly enriched in inflammation and infectious diseases whereas those networks shared between overt AD and T2D were involved in the phosphatidylinositol 3-kinase and protein kinase B/Akt (PI3K-AKT) signaling pathway, a major mediator of insulin signaling in the body. The PI3K-AKT signaling pathway became more significantly dysregulated in the advanced AD and T2D shared network. Furthermore, endocrine resistance and atherosclerosis pathways emerged as dysregulated pathways in the advanced AD and T2D shared network. Interestingly, network analysis of shared differentially expressed genes between children with T2D and MCI subjects identified forkhead box O3 (FOXO3) as a central transcriptional regulator, suggesting that it may be a potential therapeutic target for early intervention in AD. Collectively, these results suggest that T2D may be implicated at different stages of AD through different molecular pathways disrupted during the preclinical phase of AD and more advanced stages of the disease.

Glucagon-Like Peptide-1: A Focus on Neurodegenerative Diseases

Diabetes mellitus is one of the major risk factors for cognitive dysfunction. The pathogenesis of brain impairment caused by chronic hyperglycemia is complex and includes mitochondrial dysfunction, neuroinflammation, neurotransmitters’ alteration, and vascular disease, which lead to cognitive impairment, neurodegeneration, loss of synaptic plasticity, brain aging, and dementia. Glucagon-like peptide-1 (GLP-1), a gut released hormone, is attracting attention as a possible link between metabolic and brain impairment. Several studies have shown the influence of GPL-1 on neuronal functions such as thermogenesis, blood pressure control, neurogenesis, neurodegeneration, retinal repair, and energy homeostasis. Moreover, modulation of GLP-1 activity can influence amyloid β peptide aggregation in Alzheimer’s disease (AD) and dopamine (DA) levels in Parkinson’s disease (PD). GLP-1 receptor agonists (GLP-1RAs) showed beneficial actions on brain ischemia in animal models, such as the reduction of cerebral infarct area and the improvement of neurological deficit, acting mainly through inhibition of oxidative stress, inflammation, and apoptosis. They might also exert a beneficial effect on the cognitive impairment induced by diabetes or obesity improving learning and memory by modulating synaptic plasticity. Moreover, GLP-1RAs reduced hippocampal neurodegeneration. Besides this, there are growing evidences on neuroprotective effects of these agonists in animal models of neurodegenerative diseases, regardless of diabetes. In PD animal models, GPL-1RAs were able to protect motor activity and dopaminergic neurons whereas in AD models, they seemed to improve nearly all neuropathological features and cognitive functions. Although further clinical studies of GPL-1RAs in humans are needed, they seem to be a promising therapy for diabetes-associated cognitive decline.

Of mice and men: incretin actions in the central nervous system

Incretins have risen to the forefront of therapies for obesity and related metabolic complications, primarily because of their efficacy and relatively few side effects. Importantly, their efficacy in altering energy balance and decreasing body weight is apparently through actions in the central nervous system (CNS); the latter may have implications beyond obesity per se, i.e. in other disease states associated with obesity including CNS-related disorders. Here, we first describe the role of the CNS in energy homeostasis and then the current state of knowledge in terms of incretin physiology, pathophysiology and efficacy in preclinical and clinical studies. In the future, more clinical studies are needed to fully map mechanistic pathways underlying incretin actions and outcomes in the human CNS. Additionally, future research will likely lead to the discovery of additional novel incretins and/or more efficacious medications with less side effects through the improvement of current compounds with properties that would allow them to have more favorable pharmacokinetic and pharmacodynamic profiles and/or by combining known and novel incretins into safe and more efficacious combination therapies leading ultimately to more tangible benefits for our patients.

Effects of glucagon-like peptide 1 receptor agonists on comorbidities in older patients with diabetes mellitus

Elderly patients with diabetes are at high risk of polypharmacy because of multiple coexisting diseases and syndromes. Polypharmacy increases the risk of drug–drug and drug–disease interactions in these patients, who may already have age-related sensory and cognitive deficits; such deficits may delay timely communication of early symptoms of adverse drug events. Several glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have been approved for diabetes: liraglutide, exenatide, lixisenatide, dulagluatide, semaglutide, and albiglutide. Some are also approved for treatment of obesity. The current review of literature along with clinical case discussion provides evidence supporting GLP-1 RAs as diabetes medications for polypharmacy reduction in older diabetes patients because of their multiple pleiotropic effects on comorbidities (e.g. hyperlipidemia, hypertension, and fatty liver) and syndromes (e.g. osteoporosis and sleep apnea) that commonly co-occur with diabetes. Using one medication (in this case, GLP-1 RAs) to address multiple conditions may help reduce costs, medication burden, adverse drug events, and medication nonadherence.