Neuroprotective effects of D-Ala(2)GIP on Alzheimer's disease biomarkers in an APP/PS1 mouse model

Glucose-dependent insulinotropic polypeptide (GIP)

BACKGROUND

Glucose-dependent insulinotropic polypeptide (GIP) was the first incretin identified and plays an essential role in the maintenance of glucose tolerance in healthy humans. Until recently GIP had not been developed as a therapeutic and thus has been overshadowed by the other incretin, glucagon-like peptide 1 (GLP-1), which is the basis for several successful drugs to treat diabetes and obesity. However, there has been a rekindling of interest in GIP biology in recent years, in great part due to pharmacology demonstrating that both GIPR agonism and antagonism may be beneficial in treating obesity and diabetes. This apparent paradox has reinvigorated the field, led to new lines of investigation, and deeper understanding of GIP.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GIP biology and discuss the therapeutic implications of GIPR signal modification on various diseases.

MAJOR CONCLUSIONS

Following its classification as an incretin hormone, GIP has emerged as a pleiotropic hormone with a variety of metabolic effects outside the endocrine pancreas. The numerous beneficial effects of GIPR signal modification render the peptide an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, drug-induced nausea and both bone and neurodegenerative disorders.

Microbial dipeptidyl peptidases of the S9B family as host-microbe isozymes

Human dipeptidyl peptidase 4 (hDPP-4) has been a pharmacological target for metabolic diseases, particularly diabetes, since the early 2000s. As a ubiquitous enzyme found in both prokaryotic and eukaryotic organisms, hDPP-4 plays crucial roles in host homeostasis and disease progression. While many studies have explored hDPP-4's properties, research on gut microbially derived DPP-4 (mDPP-4) remains limited. This review discusses the significance of mDPP-4 and its health implications, analyzing crystal structures of mDPP-4 in comparison to human counterparts. We examine how hDPP-4 inhibitors could influence gut microbiome composition and mDPP-4 activity. Additionally, this review connects ongoing discussions regarding DPP-4 substrate specificity and potential access routes for mDPP-4, emphasizing the urgent need for further research on mDPP-4's role in health and improve the precision of DPP-4 inhibitor therapies.

The role of GIPR in food intake control

Glucose-dependent insulinotropic polypeptide (GIP) is one of two incretin hormones playing key roles in the control of food intake, nutrient assimilation, insulin secretion and whole-body metabolism. Recent pharmacological advances and clinical trials show that unimolecular co-agonists that target the receptors for the incretins - GIP and glucagon-like peptide 1 (GLP-1) - offer more effective treatment strategies for obesity and type 2 diabetes mellitus (T2D) compared with GLP-1 receptor (GLP1R) agonists alone, suggesting previously underappreciated roles of GIP in regulating food intake and body weight. The mechanisms by which GIP regulates energy balance remain controversial as both agonism and antagonism of the GIP receptor (GIPR) produce weight loss and improve metabolic outcomes in preclinical models. Recent studies have shown that GIPR signalling in the central nervous system (CNS), especially in regions of the brain that regulate energy balance, is essential for its action on appetite regulation. This finding has sparked interest in understanding the mechanisms by which GIP engages brain circuits to reduce food intake and body weight. In this review, we present key knowledge around the actions of GIP on food intake regulation and the potential mechanisms by which GIPR and GIPR/GLP1R agonists may regulate energy balance.

The Dipeptidyl Peptidase-4 Inhibitor Saxagliptin as a Candidate Treatment for Disorders of Consciousness: A Deep Learning and Retrospective Clinical Analysis

BACKGROUND

Despite advancements in the neuroscience of consciousness, no new medications for disorders of consciousness (DOC) have been discovered in more than a decade. Repurposing existing US Food and Drug Administration (FDA)-approved drugs for DOC is crucial for improving clinical management and patient outcomes.

METHODS

To identify potential new treatments among existing FDA-approved drugs, we used a deep learning-based drug screening model to predict the efficacy of drugs as awakening agents based on their three-dimensional molecular structure. A retrospective cohort study from March 2012 to October 2024 tested the model's predictions, focusing on changes in Glasgow Coma Scale (GCS) scores in 4047 patients in a coma from traumatic, vascular, or anoxic brain injury.

RESULTS

Our deep learning drug screens identified saxagliptin, a dipeptidyl peptidase-4 inhibitor, as a promising awakening drug for both acute and prolonged DOC. The retrospective clinical analysis showed that saxagliptin was associated with the highest recovery rate from acute coma among diabetes medications. After matching patients by age, sex, initial GCS score, coma etiology, and glycemic status, brain-injured patients with diabetes on incretin-based therapies, including dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 analogues, recovered from coma at significantly higher rates compared to both brain-injured patients with diabetes on non-incretin-based diabetes medications (95% confidence interval of 1.8-14.1% higher recovery rate, P = 0.0331) and brain-injured patients without diabetes (95% confidence interval of 2-21% higher recovery rate, P = 0.0272). Post matching, brain-injured patients with diabetes on incretin-based therapies also recovered at a significantly higher rate than patients treated with amantadine (95% confidence interval for the difference 2.4-25.1.0%, P = 0.0364). A review of preclinical studies identified several pathways through which saxagliptin and other incretin-based medications may aid awakening from both acute and chronic DOC: restoring monoaminergic and GABAergic neurotransmission, reducing brain inflammation and oxidative damage, clearing hyperphosphorylated tau and amyloid-β, normalizing thalamocortical glucose metabolism, increasing neural plasticity, and mitigating excitotoxic brain damage.

CONCLUSIONS

Our findings suggest incretin-based medications in general, and saxagliptin in particular, as potential novel therapeutic agents for DOC. Further prospective clinical trials are needed to confirm their efficacy and safety in DOC.

Neuroprotective effects of GLP-1 class drugs in Parkinson's disease

Parkinson's disease (PD) is a chronic, progressive neurological disorder primarily affecting motor control, clinically characterized by resting tremor, bradykinesia, rigidity, and other symptoms that significantly diminish the quality of life. Currently, available treatments only alleviate symptoms without halting or delaying disease progression. There is a significant association between PD and type 2 diabetes mellitus (T2DM), possibly due to shared pathological mechanisms such as insulin resistance, chronic inflammation, and mitochondrial dysfunction. PD is caused by a deficiency of dopamine, a neurotransmitter in the brain that plays a critical role in the control of movement. Glucose metabolism and energy metabolism disorders also play an important role in the pathogenesis of PD. This review investigates the neuroprotective mechanisms of glucagon-like peptide-1 (GLP-1) and its receptor agonists, offering novel insights into potential therapeutic strategies for PD. GLP-1 class drugs, primarily used in diabetes management, show promise in addressing PD's underlying pathophysiological mechanisms, including energy metabolism and neuroprotection. These drugs can cross the blood-brain barrier, improve insulin resistance, stabilize mitochondrial function, and enhance neuronal survival and function. Additionally, they exhibit significant anti-inflammatory and antioxidative stress effects, which are crucial in neurodegenerative diseases like PD. Research indicates that GLP-1 receptor agonists could improve both motor and cognitive symptoms in PD patients, marking a potential breakthrough in PD treatment and prevention. Further exploration of GLP-1's molecular mechanisms in PD could provide new preventive and therapeutic approaches, especially for PD patients with concurrent T2DM. By targeting both metabolic and neurodegenerative pathways, GLP-1 receptor agonists represent a multifaceted approach to PD treatment, offering hope for better disease management and improved patient outcomes.

Exploring the Impact of Semaglutide on Cognitive Function and Anxiety-Related Behaviors in a Murine Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD), the most prevalent form of dementia, is characterized by progressive cognitive decline and behavioral disturbances, with an increasing incidence as the global population ages. This study investigates the effects of semaglutide (SEM), a glucagon-like peptide-1 analog, on cognitive function and anxiety-like behavior in a transgenic murine model of AD.

METHODS

20 mice were randomly distributed into the following groups (n = 5): (WT + VEH) group: C57BL/6J + saline, (WT + SEM) group: C57BL/6J + semaglutide, (AD + VEH) group: AD + saline, (AD + SEM) group: AD + semaglutide. The animals underwent a four-week treatment, during which we monitored blood glucose levels, body weight, and responses in an open field test, novel object recognition test, social chamber test, and 0-maze test.

RESULTS

Post-treatment, SEM significantly reduced blood glucose levels in AD mice, aligning them with those of wild-type controls. Cognitive assessments indicated an improvement in the investigation index for SEM-treated mice compared to those receiving a vehicle, suggesting cognitive benefits. Although SEM did not significantly enhance motor and exploratory activities, it displayed a potential anxiolytic effect, particularly evident in the combined anxiety index, with notable differences observed before and after treatment in the AD group.

CONCLUSIONS

The findings of this pilot study suggest that SEM may play a dual role in managing AD by improving glycemic control and potentially enhancing cognitive function. As the landscape of AD treatment evolves, the comprehensive approach of utilizing SEM could pave the way for innovative interventions targeting the complex interplay of metabolic and cognitive dysfunctions in this challenging neurodegenerative disorder.

Beyond insulin: The Intriguing role of GLP-1 in Parkinson's disease

GLP-1 (Glucagon-like peptide 1) serves as both a peptide hormone and a growth factor, is released upon nutrient intake and contributes to insulin secretion stimulated by glucose levels. Also, GLP-1 is synthesized within several brain areas and plays a vital function in providing neuroprotection and reducing inflammation through the activation of the GLP-1 receptor. Parkinson's Disease (PD) is a neurodegenerative illness that worsens with time and is defined by considerable morbidity. Presently, there are few pharmaceutical choices available, and none of the existing therapies are capable of modifying the course of the disease. There is a suggestion that type 2 diabetes mellitus (T2DM) could increase the risk of PD, and the presence of both conditions concurrently might exacerbate PD symptoms and hasten neurodegeneration. GLP-1 receptor (GLP-1R) agonists exhibit numerous implications like enhancement of glucose-dependent insulin release and biosynthesis, suppression of glucagon secretion and gastric emptying. Also, some GLP-1R agonists have received clinical approval for the management of T2DM. Moreover, the use of GLP-1R agonists has demonstrated counter-inflammatory, neurotrophic, and neuroprotective actions in various preclinical models of neurodegenerative disorders. Considering the significant amount of evidence backing the potential of GLP-1R agonists to protect the nervous system across different research settings, this article delves into examining the hopeful prospect of GLP-1R agonists as a treatment option for PD. This review sheds light on combined neuroprotective benefits of GLP-1R agonists and the possible mechanisms driving the protective effects on the PD brain, through the collection of data from various preclinical and clinical investigations.

Therapeutic potentials of glucose-dependent insulinotropic polypeptide (GIP) in T2DM: Past, present, and future

Type 2 diabetes mellitus (T2DM) is a worldwide health problem that has raised major concerns to the public health community. This chronic condition typically results from the cell's inability to respond to normal insulin levels. Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the primary incretin hormones secreted from the intestinal tract. While clinical research has extensively explored the therapeutic potential of GLP-1R in addressing various T2DM-related abnormalities, the possibility of GIPR playing an important role in T2DM treatment is still under investigation. Evidence suggests that GIP is involved in the pathophysiology of T2DM. This chapter focuses on examining the role of GIP as a therapeutic molecule in combating T2DM, comparing the past, present, and future scenarios. Our goal is to delve into how GIP may impact pancreatic β-cell function, adipose tissue uptake, and lipid metabolism. Furthermore, we will elucidate the mechanistic functions of GIP and its receptors in relation to other clinical conditions like cardiovascular diseases, non-alcoholic fatty liver diseases, neurodegenerative diseases, and renal disorders. Additionally, this chapter will shed light on the latest advancements in pharmacological management for T2DM, highlighting potential structural modifications of GIP and the repurposing of drugs, while also addressing the challenges involved in bringing GIP-based treatments into clinical practice.

Immunomodulation and inflammation: Role of GLP-1R and GIPR expressing cells within the gut

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are peptide hormones produced by enteroendocrine cells in the small intestine. Despite being produced in the gut, the leveraging of their role in potentiating glucose-stimulated insulin secretion, also known as the incretin effect, has distracted from discernment of direct intestinal signaling circuits. Both preclinical and clinical evidence have highlighted a role for the incretins in inflammation. In this review, we highlight the discoveries of GLP-1 receptor (GLP-1R)+ natural (TCRαβ and TCRγδ) and induced (TCRαβ+CD4+ cells and TCRαβ+CD8αβ+) intraepithelial lymphocytes. Both endogenous signaling and pharmacological activation of GLP-1R impact local and systemic inflammation, the gut microbiota, whole-body metabolism, as well as the control of GLP-1 bioavailability. While GIPR signaling has been documented to impact hematopoiesis, the impact of these bone marrow-derived cells in gut immunology is not well understood. We uncover gaps in the literature of the evaluation of the impact of sex in these GLP-1R and GIP receptor (GIPR) signaling circuits and provide speculations of the maintenance roles these hormones play within the gut in the fasting-refeeding cycles. GLP-1R agonists and GLP-1R/GIPR agonists are widely used as treatments for diabetes and weight loss, respectively; however, their impact on gut homeostasis has not been fully explored. Advancing our understanding of the roles of GLP-1R and GIPR signaling within the gut at homeostasis as well as metabolic and inflammatory diseases may provide targets to improve disease management.

Regulation of energy metabolism through central GIPR signaling

In recent years, significant progress has been made to pharmacologically combat the obesity pandemic, particularly with regard to biochemically tailored drugs that simultaneously target the receptors for glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP). But while the pharmacological benefits of GLP-1 receptor (GLP-1R) agonism are widely acknowledged, the role of the GIP system in regulating systems metabolism remains controversial. When given in adjunct to GLP-1R agonism, both agonism and antagonism of the GIP receptor (GIPR) improves metabolic outcome in preclinical and clinical studies, and despite persistent concerns about its potential obesogenic nature, there is accumulating evidence indicating that GIP has beneficial metabolic effects via central GIPR agonism. Nonetheless, despite growing recognition of the GIP system as a valuable pharmacological target, there remains great uncertainty as to where and how GIP acts in the brain to regulate metabolism, and how GIPR agonism may differ from GIPR antagonism in control of energy metabolism. In this review we highlight current knowledge on the central action of GIP, and discuss open questions related to its multifaceted biology in the brain and the periphery.

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.

Long-term normalization of calcineurin activity in model mice rescues Pin1 and attenuates Alzheimer's phenotypes without blocking peripheral T cell IL-2 response

BACKGROUND

Current treatments for Alzheimer's disease (AD) have largely failed to yield significant therapeutic benefits. Novel approaches are desperately needed to help address this immense public health issue. Data suggests that early intervention at the first stages of mild cognitive impairment may have a greater chance for success. The calcineurin (CN)-Pin1 signaling cascade can be selectively targeted with tacrolimus (FK506), a highly specific, FDA-approved CN inhibitor used safely for > 20 years in solid organ transplant recipients. AD prevalence was significantly reduced in solid organ recipients treated with FK506.

METHODS

Time release pellets were used to deliver constant FK506 dosage to APP/PS1 mice without deleterious manipulation or handling. Immunofluorescence, histology, molecular biology, and behavior were used to evaluate changes in AD pathology.

RESULTS

FK506 can be safely and consistently delivered into juvenile APP/PS1 mice via time-release pellets to levels roughly seen in transplant patients, leading to the normalization of CN activity and reduction or elimination of AD pathologies including synapse loss, neuroinflammation, and cognitive impairment. Pin1 activity and function were rescued despite the continuing presence of high levels of transgenic Aβ42. Indicators of neuroinflammation including Iba1 positivity and IL-6 production were also reduced to normal levels. Peripheral blood mononuclear cells (PBMC) obtained during treatment or splenocytes isolated at euthanasia activated normally after mitogens.

CONCLUSIONS

Low-dose, constant FK506 can normalize CNS CN and Pin1 activity, suppress neuroinflammation, and attenuate AD-associated pathology without blocking peripheral IL-2 responses making repurposed FK506 a viable option for early, therapeutic intervention in AD.

Alzheimer's Disease: Innovative Therapeutic Approaches Based on Peptides and Nanoparticles

Alzheimer's disease (AD) is the main cause of dementia in the world and its etiology is not yet fully understood. The pathology of AD is primarily characterized by intracellular neurofibrillary tangles and extracellular amyloid-β plaques. Unfortunately, few treatment options are available, and most treat symptoms, as is the case of acetylcholinesterase inhibitors (IAChE) and N-methyl-d-aspartate receptor antagonists. For more than 20 years pharmaceutical research has targeted the "amyloid cascade hypothesis," but this has not produced meaningful results, leading researchers to focus now on other characteristics of the disease and on multitarget approaches. This review aims to evaluate some new treatments that are being developed and studied. Among these are new treatments based on peptides, which have high selectivity and low toxicity; however, these compounds have a short half-life and encounter challenges when crossing the blood-brain barrier. The present review discusses up-and-coming peptides tested as treatments and explores some nanotechnological strategies to overcome the downsides. These compounds are promising, as they not only act on the symptoms but also aim to prevent progressive neuronal loss.

The Anti-Seizure Effect of Liraglutide on Ptz-Induced Convulsions Through its Anti-Oxidant and Anti-Inflammatory Properties

Epilepsy is a prevalent and frequently devastating neurological disorder defined by recurring spontaneous seizures caused by aberrant electrical activity in the brain. Over ten million people worldwide suffer from drug-resistant epilepsy. This severe condition requires novel treatment approaches. Both oxidative and nitrosative stress are thought to have a role in the etiology of epilepsy. Liraglutide is a glucagon-like peptide-1 (GLP-1) analogue that is used to treat type-2 diabetes mellitus. According to recent studies, Liraglutide also shows neuroprotective properties, improving memory retention and total hippocampus pyramidal neuronal population in mice. The purpose of this investigation was to determine the anti-seizure and anti-oxidative effects of liraglutide in a pentylenetetrazole (PTZ)-induced rat model of epilepsy. 48 rats were randomly assigned to two groups: those who had electroencephalography (EEG) recordings and those who underwent behavioral assessment. Rats received either intraperitoneal (IP) liraglutide at two different dosages (3-6 mg/kg) or a placebo, followed by pentylenetetrazole (IP). To determine if liraglutide has anti-seizure characteristics, we examined seizure activity in rats using EEG, the Racine convulsion scale (RCS), the time of first myoclonic jerk (FMJ), and MDA, SOD, TNF-α, IL-1β and GAD-67 levels. The mean EEG spike wave percentage score was reduced from 75.8% (placebo) to 59.4% (lower-dose) and 41.5% (higher-dose). FMJ had increased from a mean of 70.6 s (placebo) to 181.2 s (lower-dose) and 205.2 s (higher-dose). RCS was reduced from a mean of 5.5 (placebo) to 2.7 (lower-dose) and 2.4 (higher-dose). Liraglutide (3 and 6 mg/kg i.p.) successfully decreased the spike percentages and RCS associated with PTZ induced epilepsy, as well as considerably decreased MDA, TNF-α, IL-1β and elevated SOD, GAD-67 levels in rat brain. Liraglutide significantly decreased seizure activity at both dosages when compared to control, most likely due to its anti-oxidant and anti-inflammatory properties. The potential clinical role of liraglutide as an anti-seizure medication should be further explored.

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.

Neuroprotective Mechanisms of Glucagon-Like Peptide-1-Based Therapies in Ischemic Stroke: An Update Based on Preclinical Research

The public and social health burdens of ischemic stroke have been increasing worldwide. Hyperglycemia leads to a greater risk of stroke. This increased risk is commonly seen among patients with diabetes and is in connection with worsened clinical conditions and higher mortality in patients with acute ischemic stroke (AIS). Therapy for stroke focuses mainly on restoring cerebral blood flow (CBF) and ameliorating neurological impairment caused by stroke. Although choices of stroke treatment remain limited, much advance have been achieved in assisting patients in recovering from ischemic stroke, along with progress of recanalization therapy through pharmacological and mechanical thrombolysis. However, it is still necessary to develop neuroprotective therapies for AIS to protect the brain against injury before and during reperfusion, prolong the time window for intervention, and consequently improve neurological prognosis. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are broadly regarded as effective drugs in the treatment of type 2 diabetes mellitus (T2DM). Preclinical data on GLP-1 and GLP-1 RAs have displayed an impressive neuroprotective efficacy in stroke, Parkinson's disease (PD), Alzheimer's disease (AD), Amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases. Based on the preclinical studies in the past decade, we review recent progress in the biological roles of GLP-1 and GLP-1 RAs in ischemic stroke. Emphasis will be placed on their neuroprotective effects in experimental models of cerebral ischemia stroke at cellular and molecular levels.

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.

Alzheimer's disease: a step closer to understanding type 3 diabetes in African Americans

Alzheimer's disease (AD) is the fourth leading cause of death in the United States and the most common cause of adult-onset dementia. Recent results suggest an increased prevalence and severity in African Americans compared to Caucasians. Our understanding of the potential mechanism(s) underlying this ethnicity difference is limited. We previously described ethnicity-related differences in levels of neurodegenerative proteins and cytokines/chemokines in the BA21 region of African Americans and Caucasians with AD. Here, similar multiplex assays were used to examine those endpoints in patient postmortem cerebrospinal fluid (CSF). Additionally, we measured levels of C-peptide, ghrelin, gastric inhibitory polypeptide (GIP), glucagon-like peptide-1 (GLP-1), glucagon, insulin, leptin, PAI-1, resistin, and visfatin using a human diabetes 10-plex assay. The cytokine and chemokine assays revealed that levels of 26 chemokines or cytokines differed significantly with ethnicity, and three of those were significantly associated with gender. The neurodegenerative disease panel indicated that levels of soluble RAGE were significantly elevated in African Americans compared to Caucasians. All measures in the diabetes disease panel assay were significantly elevated in African Americans: ghrelin, GIP, GLP-1, glucagon, insulin, and visfatin. Through peripheral sample analysis, these results provide further evidence that ethnicity is critically involved in the manifestation of AD.

DAla2-GIP-GLU-PAL Protects Against Cognitive Deficits and Pathology in APP/PS1 Mice by Inhibiting Neuroinflammation and Upregulating cAMP/PKA/CREB Signaling Pathways

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive decline in cognitive function. Type 2 diabetes mellitus (T2DM) is an important risk factor for AD. Glucose-dependent insulinotropic polypeptide (GIP) has been identified to be effective in T2DM treatment and neuroprotection.

OBJECTIVE

The present study investigated the neuroprotective effects and possible mechanisms of DAla2GIP-Glu-PAL, a novel long-lasting GIP analogue, in APP/PS1 AD mice.

METHODS

Multiple behavioral tests were performed to examine the cognitive function of mice. In vivo hippocampus late-phase long-term potentiation (L-LTP) was recorded to reflect synaptic plasticity. Immunohistochemistry and immunofluorescence were used to examine the Aβ plaques and neuroinflammation in the brain. IL-1β, TNF-α, and cAMP/PKA/CREB signal molecules were also detected by ELISA or western blotting.

RESULTS

DAla2GIP-Glu-PAL increased recognition index (RI) of APP/PS1 mice in novel object recognition test, elevated spontaneous alternation percentage of APP/PS1 mice in Y maze test, and increased target quadrant swimming time of APP/PS1 mice in Morris water maze test. DAla2GIP-Glu-PAL treatment enhanced in vivo L-LTP of APP/PS1 mice. DAla2GIP-Glu-PAL significantly reduced Aβ deposition, inhibited astrocyte and microglia proliferation, and weakened IL-1β and TNF-α secretion. DAla2GIP-Glu-PAL also upregulated cAMP/PKA/CREB signal transduction and inhibited NF-κB activation in the hippocampus of APP/PS1 mice.

CONCLUSION

DAla2GIP-Glu-PAL can improve cognitive behavior, synaptic plasticity, and central pathological damage in APP/PS1 mice, which might be associated with the inhibition of neuroinflammation, as well as upregulation of cAMP-/PKA/CREB signaling pathway. This study suggests a potential benefit of DAla2GIP-Glu-PAL in the treatment of AD.

Structural insights into hormone recognition by the human glucose-dependent insulinotropic polypeptide receptor

Glucose-dependent insulinotropic polypeptide (GIP) is a peptide hormone that exerts crucial metabolic functions by binding and activating its cognate receptor, GIPR. As an important therapeutic target, GIPR has been subjected to intensive structural studies without success. Here, we report the cryo-EM structure of the human GIPR in complex with GIP and a Gs heterotrimer at a global resolution of 2.9 Å. GIP adopts a single straight helix with its N terminus dipped into the receptor transmembrane domain (TMD), while the C terminus is closely associated with the extracellular domain and extracellular loop 1. GIPR employs conserved residues in the lower half of the TMD pocket to recognize the common segments shared by GIP homologous peptides, while uses non-conserved residues in the upper half of the TMD pocket to interact with residues specific for GIP. These results provide a structural framework of hormone recognition and GIPR activation.

Alzheimer’s disease and type 2 diabetes mellitus: Pathophysiologic and pharmacotherapeutics links

At present, Alzheimer’s disease (AD) and type 2 diabetes mellitus (T2DM) are two highly prevalent disorders worldwide, especially among elderly individuals. T2DM appears to be associated with cognitive dysfunction, with a higher risk of developing neurocognitive disorders, including AD. These diseases have been observed to share various pathophysiological mechanisms, including alterations in insulin signaling, defects in glucose transporters (GLUTs), and mitochondrial dysfunctions in the brain. Therefore, the aim of this review is to summarize the current knowledge regarding the molecular mechanisms implicated in the association of these pathologies as well as recent therapeutic alternatives. In this context, the hyperphosphorylation of tau and the formation of neurofibrillary tangles have been associated with the dysfunction of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways in the nervous tissues as well as the decrease in the expression of GLUT-1 and GLUT-3 in the different areas of the brain, increase in reactive oxygen species, and production of mitochondrial alterations that occur in T2DM. These findings have contributed to the implementation of overlapping pharmacological interventions based on the use of insulin and antidiabetic drugs, or, more recently, azeliragon, amylin, among others, which have shown possible beneficial effects in diabetic patients diagnosed with AD.

GIPR Signaling in Immune Cells Maintains Metabolically Beneficial Type 2 Immune Responses in the White Fat From Obese Mice

Glucose-dependent insulinotropic polypeptide (GIP) communicates information on energy availability from the gut to peripheral tissues. Disruption of its signaling in myeloid immune cells during high-fat diet (HFD)-induced obesity impairs energy homeostasis due to the unrestrained metabolically deleterious actions of S100A8/A9 alarmin. White adipose tissue (WAT) type 2 immune cell networks are important for maintaining metabolic and energy homeostasis and limiting obesity-induced inflammation. Nevertheless, the consequences of losing immune cell GIP receptor (GIPR) signaling on type 2 immunity in WAT remains unknown. Bone marrow (BM) chimerism was used to generate mice with GIPR (Gipr^-/- BM) and GIPR/S100A8/A9 (Gipr^-/- /S100a9^-/- BM) deletion in immune cells. These mice were subjected to short (5 weeks) and progressive (14 weeks) HFD regimens. GIPR-deficiency was also targeted to myeloid cells by crossing Gipr^fl/fl mice and Lyz2^cre/+ mice (LysM^ΔGipr ). Under both short and progressive HFD regimens, Gipr^-/- BM mice exhibited altered expression of key type 2 immune cytokines in the epididymal visceral WAT (epiWAT), but not in subcutaneous inguinal WAT. This was further linked to declined representation of type 2 immune cells in epiWAT, such as group 2 innate lymphoid cells (ILC2), eosinophils, and FOXP3⁺ regulatory T cells (Tregs). Co-deletion of S100A8/A9 in Gipr^-/- immune cells reversed the impairment of type 2 cytokine expression in epiWAT, suggesting a mechanistic role for this alarmin in type 2 immune suppression. LysM^ΔGipr mice on HFD also displayed altered expression of type 2 immune mediators, highlighting that GIPR-deficiency in myeloid immune cells is responsible for the impairment of type 2 immune networks. Finally, abrogated GIPR signaling in immune cells also affected adipocyte fraction cells, inducing their increased production of the beiging interfering cytokine IL-10 and stress- related type 2 cytokine IL-13. Collectively, these findings attribute an important role for GIPR in myeloid immune cells in supporting WAT type 2 immunity.

Microbiota modulation as preventative and therapeutic approach in Alzheimer's disease

The gut microbiota coevolves with its host, and numerous factors like diet, lifestyle, drug intake and geographical location continuously modify its composition, deeply influencing host health. Recent studies demonstrated that gut dysbiosis can alter normal brain function through the so-called gut-brain axis, a bidirectional communication network between the central nervous system and the gastrointestinal tract, thus playing a key role in the pathogenesis of neurodegenerative disorders, such as Alzheimer's disease (AD). In this perspective, in the constant search for novel treatments in AD, the rational modulation of gut microbiota composition could represent a promising approach to prevent or delay AD onset or to counteract its progression. Preclinical and human studies on microbiota modulation through oral bacteriotherapy and faecal transplantation showed anti-inflammatory and antioxidant effects, upregulation of plasma concentration of neuroprotective hormones, restoration of impaired proteolytic pathways, amelioration of energy homeostasis with consequent decrease of AD molecular hallmarks and improvement of behavioural and cognitive performances. In this review, we dissect the role of gut microbiota in AD and highlight recent advances in the development of new multitarget strategies for microbiota modulation to be used as possible preventative and therapeutic approaches in AD.

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.

Incretin hormones, insulin, glucagon and advanced glycation end products in relation to cognitive function in older people with and without diabetes, a population-based study

AIM

The aim of this observational study was to investigate relationships between physiological levels of glucometabolic biomarkers and cognitive test results in a population-based setting.

METHODS

Cross-sectional data were obtained from the Swedish population-based Malmö Diet and Cancer Study Re-examination 2007-2012 comprising 3001 older people (mean age 72 years). Through oral glucose tolerance testing (OGTT), fasting and post-load levels of serum insulin, plasma glucagon, serum glucose-dependent insulinotropic peptide (GIP) and plasma glucagon-like peptide-1 (GLP-1) were measured. Insulin resistance and insulin sensitivity levels were calculated. In 454 participants, advanced glycation end products (AGEs) were estimated through skin autofluorescence. Associations between biomarkers and two cognitive tests, the Mini-Mental State Examination (MMSE) and A Quick Test of Cognitive Speed (AQT) respectively, were explored in multiple regression analyses.

RESULTS

Positive associations following adjustments for known prognostic factors were found between MMSE scores and insulin sensitivity (B = 0.822, P = 0.004), 2-h plasma glucagon (B = 0.596, P = 0.026), 2-h serum GIP (B = 0.581, P = 0.040) and 2-h plasma GLP-1 (B = 0.585, P = 0.038), whereas negative associations were found between MMSE scores and insulin resistance (B = -0.734, P = 0.006), fasting plasma GLP-1 (B = -0.544, P = 0.033) and AGEs (B = -1.459, P = 0.030) were found.

CONCLUSIONS

Higher levels of insulin sensitivity, GIP and GLP-1 were associated with better cognitive outcomes, but AGEs were associated with worse outcomes, supporting evidence from preclinical studies. Glucagon was linked to better outcomes, which could possibly reflect neuroprotective properties similar to the related biomarker GLP-1 which has similar intracellular properties. Longitudinal and interventional studies are needed to further evaluate neuromodulating effects of these biomarkers. Abstract presented at the European Association for the Study of Diabetes (EASD) 2019, Barcelona, Spain.

Can dipeptidyl peptidase-4 inhibitors treat cognitive disorders?

The linkage of neurodegenerative diseases with insulin resistance (IR) and type 2 diabetes mellitus (T2DM), including oxidative stress, mitochondrial dysfunction, excessive inflammatory responses and abnormal protein processing, and the correlation between cerebrovascular diseases and hyperglycemia has opened a new window for novel therapeutics for these cognitive disorders. Various antidiabetic agents have been studied for their potential treatment of cognitive disorders, among which the dipeptidyl peptidase-4 (DPP-4) inhibitors have been investigated more recently. So far, DPP-4 inhibitors have demonstrated neuroprotection and cognitive improvements in animal models, and cognitive benefits in diabetic patients with or without cognitive impairments. This review aims to summarize the potential mechanisms, advantages and limitations, and currently available evidence for developing DPP-4 inhibitors as a treatment of cognitive disorders.

Brain insulin resistance: role in neurodegenerative disease and potential for targeting

Introduction: This review evaluates the novel strategy of treating Alzheimer's and Parkinson's disease (AD and PD) withdrugs that initially have been developed to treat type 2 diabetes. As insulin signalling has been found to be de-sensitized in the brains of patients, drugs that can re-sensitize insulin signalling have been tested to evaluate if this strategy can alter disease progression.Areas covered: The review will give an overview of preclinical and clinical tests in AD and PD of drugs activating insulin receptors, glucagon-like peptide -1 (GLP-1) receptors, and glucose-dependent insulinotropic polypeptide (GIP) receptors.Expert opinion: Insulin, GLP-1 and GIP receptor agonists have shown good effects in preclinical studies. First clinical trials in MCI/AD patients have shown that insulin can improve on key pathological symptoms of AD such as memory impairment, brain activity, neuronal energy utilization, and inflammation markers. A GLP-1 receptor agonist has shown disease-modifying effects in PD patients, and first pilot studies have shown encouraging effects of a GLP-1 receptor agonist in AD patients. Novel dual GLP-1/GIP receptor agonists that cross the blood brain barrier show superior neuroprotective effects compared to single GLP-1 or GIP receptor agonists, and show great promise as novel treatments of AD and PD.

GIP has neuroprotective effects in Alzheimer and Parkinson's disease models

Glucose-dependent Insulinotropic polypeptide (GIP) is a peptide hormone of the incretin family. It has growth factor properties and can re-activate energy utilization. In progressive neurodegenerative disorders such as Alzheimer's and Parkinson's disease, energy utilization is much reduced, and GIP has the potential to reverse this. Furthermore, GIP can reduce the inflammation response in the brain and reduce levels of pro-inflammatory cytokines. Tests in animal models of Alzheimer's and Parkinson's disease show good neuroprotective effects. In Parkinson's disease models, motor activity is normalized, dopaminergic neurons are protected, synapse numbers and dopamine levels are maintained. Levels of growth factors that are essential for neuronal and synaptic function are increased and alpha-synuclein levels are reduced. The chronic inflammation response and mitochondrial damage is reduced. In Alzheimer's disease models, memory is rescued, synapse numbers and synaptic plasticity in the hippocampus is normalized, amyloid plaque load and the chronic inflammation is reduced. Similar protective effects have been previously reported with analogues of glucagon-like peptide 1 (GLP-1), the sister incretin hormone. First clinical trials show good protective effects in both diseases. Recently, novel dual GLP-1/GIP receptor agonists have been developed. The ability to cross the blood-brain barrier (BBB) is key to their neuroprotective effects. We have developed two dual GLP-1/GIP receptor agonist that have cell penetrating sequences added for better BBB penetration. In direct comparisons, these dual agonists show improved neuroprotection in a mouse model of Parkinson's disease. Therefore, such novel multiple receptor agonists hold great promise as potential treatments for Alzheimer's and Parkinson's disease.

Effects of gastric inhibitory polypeptide (GIP) immunoneutralization on mouse motor coordination and memory

Gastric inhibitory polypeptide (GIP) is a regulatory peptide expressed in the mammalian upper small intestine, and both GIP and its receptor (GIPR) are expressed in the cortex and hippocampus regions of the brain as well. While learning and memory deficits have been observed in GIPR^-/- mice, the effects of peripheral GIP immunoneutralization on motor-coordination, learning, and memory have not been examined. In the present study, adult GIPR^-/- mice (KO) and age-matched wild-type C57BL/6 J mice (WT) received weekly vehicle PBS injections for 12 weeks, while a third group of wild-type mice were injected weekly for 12 weeks with 30 mg/kg body weight humanized GIP-mAb (AB) to assess the possibility of long-term effects of peripheral GIP antagonism on rodent memory and behavior. All mice groups then underwent a battery of tests that evaluated motor behavior, body coordination, and memory. Performance deficits in several memory studies after 12 weeks of treatment were demonstrated in KO, but not in AB or WT mice. Body coordination performance showed no significant differences among the 3 groups. A similar short-term study (3 injections over 9 days) was also conducted and the results were similar to those from the long-term study. Thus, short-term and long-term peripheral GIP antagonism by GIP-mAb did not appear to affect learning and memory in mice, consistent with the notion that the GIP-mAb does not cross the blood brain barrier. Furthermore, our studies indicate that GIP signaling in the brain appears to involve local neurocrine pathways.

GIP as a Potential Therapeutic Target for Atherosclerotic Cardiovascular Disease-A Systematic Review

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are gut hormones that are secreted from enteroendocrine L cells and K cells in response to digested nutrients, respectively. They are also referred to incretin for their ability to stimulate insulin secretion from pancreatic beta cells in a glucose-dependent manner. Furthermore, GLP-1 exerts anorexic effects via its actions in the central nervous system. Since native incretin is rapidly inactivated by dipeptidyl peptidase-4 (DPP-4), DPP-resistant GLP-1 receptor agonists (GLP-1RAs), and DPP-4 inhibitors are currently used for the treatment of type 2 diabetes as incretin-based therapy. These new-class agents have superiority to classical oral hypoglycemic agents such as sulfonylureas because of their low risks for hypoglycemia and body weight gain. In addition, a number of preclinical studies have shown the cardioprotective properties of incretin-based therapy, whose findings are further supported by several randomized clinical trials. Indeed, GLP-1RA has been significantly shown to reduce the risk of cardiovascular and renal events in patients with type 2 diabetes. However, the role of GIP in cardiovascular disease remains to be elucidated. Recently, pharmacological doses of GIP receptor agonists (GIPRAs) have been found to exert anti-obesity effects in animal models. These observations suggest that combination therapy of GLP-1R and GIPR may induce superior metabolic and anti-diabetic effects compared with each agonist individually. Clinical trials with GLP-1R/GIPR dual agonists are ongoing in diabetic patients. Therefore, in this review, we summarize the cardiovascular effects of GIP and GIPRAs in cell culture systems, animal models, and humans.

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.

Neuroprotective Effects and Treatment Potential of Incretin Mimetics in a Murine Model of Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is a commonly occurring injury in sports, victims of motor vehicle accidents, and falls. TBI has become a pressing public health concern with no specific therapeutic treatment. Mild TBI (mTBI), which accounts for approximately 90% of all TBI cases, may frequently lead to long-lasting cognitive, behavioral, and emotional impairments. The incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are gastrointestinal hormones that induce glucose-dependent insulin secretion, promote β-cell proliferation, and enhance resistance to apoptosis. GLP-1 mimetics are marketed as treatments for type 2 diabetes mellitus (T2DM) and are well tolerated. Both GLP-1 and GIP mimetics have shown neuroprotective properties in animal models of Parkinson's and Alzheimer's disease. The aim of this study is to evaluate the potential neuroprotective effects of liraglutide, a GLP-1 analog, and twincretin, a dual GLP-1R/GIPR agonist, in a murine mTBI model. First, we subjected mice to mTBI using a weight-drop device and, thereafter, administered liraglutide or twincretin as a 7-day regimen of subcutaneous (s.c.) injections. We then investigated the effects of these drugs on mTBI-induced cognitive impairments, neurodegeneration, and neuroinflammation. Finally, we assessed their effects on neuroprotective proteins expression that are downstream to GLP-1R/GIPR activation; specifically, PI3K and PKA phosphorylation. Both drugs ameliorated mTBI-induced cognitive impairments evaluated by the novel object recognition (NOR) and the Y-maze paradigms in which neither anxiety nor locomotor activity were confounds, as the latter were unaffected by either mTBI or drugs. Additionally, both drugs significantly mitigated mTBI-induced neurodegeneration and neuroinflammation, as quantified by immunohistochemical staining with Fluoro-Jade/anti-NeuN and anti-Iba-1 antibodies, respectively. mTBI challenge significantly decreased PKA phosphorylation levels in ipsilateral cortex, which was mitigated by both drugs. However, PI3K phosphorylation was not affected by mTBI. These findings offer a new potential therapeutic approach to treat mTBI, and support further investigation of the neuroprotective effects and mechanism of action of incretin-based therapies for neurological disorders.

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.

Neuroprotective and restorative properties of the GLP-1/GIP dual agonist DA-JC1 compared with a GLP-1 single agonist in Alzheimer's disease

The sister incretins glucagon-like peptide-1 (GLP-1) and glucagon dependent insulinotropic polypeptide (GIP) are growth factors responsible for re-sensitizing insulin signalling. Interestingly, their analogues, originally developed to treat type 2 diabetes (T2D), have demonstrated a range of neuroprotective and neurorestorative properties. Novel peptide GLP-1/GIP dual agonist (DA) shows good effects in diabetic patients, superior to the effects demonstrated by single GIP or GLP-1 mimetics. Furthermore, novel DAs have shown considerable neuroprotection in neurodegenerative models. Here, we investigated the neuroprotective and restorative involvement of the DA DA-JC1 and liraglutide (Lg), a single GLP-1 receptor analogue, in vitro using human neuroblastoma (SH-SY5Y) against oxidative stress induced by oxygen peroxide (H₂O₂), and in vivo, in a mouse model of Alzheimer's disease (AD), APP/PS1. First, we determined the ideal concentration of the peptides and demonstrated that DA-JC1 protects cells against oxidative stress more than Lg, improving cell viability, normalizing reactive oxygen species (ROS) and attenuating DNA damage generated by H₂O₂. Moreover, in 10-to-12-months-old APP/PS1 animals treated for 4 weeks, both Lg and DA-JC1 were very efficient in stimulating neurogenesis and reducing some important hallmarks of AD, but DA-JC1 was better than Lg in attenuating crucial neuroinflammatory markers, especially reactive astrocyte, in both wild-type (WT) and APP/PS1 hippocampal regions. Altogether, this study suggests an interactive role of GLP-1 and GIP receptors, enhancing the efficiency of single GLP-1 analogues, especially in attenuating oxidative stress and neuroinflammation. We confirm that combining GLP-1 and GIP results in a variety of beneficial effects, providing key evidences for the development of a promising therapeutic strategy for AD.

Insulin Signaling Impairment in the Brain as a Risk Factor in Alzheimer's Disease

Type 2 diabetes is a risk factor for developing Alzheimer’s disease (AD). The underlying mechanism that links up the two conditions seems to be the de-sensitization of insulin signaling. In patients with AD, insulin signaling was found to be de-sensitized in the brain, even if they did not have diabetes. Insulin is an important growth factor that regulates cell growth, energy utilization, mitochondrial function and replacement, autophagy, oxidative stress management, synaptic plasticity, and cognitive function. Insulin desensitization, therefore, can enhance the risk of developing neurological disorders in later life. Other risk factors, such as high blood pressure or brain injury, also enhance the likelihood of developing AD. All these risk factors have one thing in common – they induce a chronic inflammation response in the brain. Pro-inflammatory cytokines block growth factor signaling and enhance oxidative stress. The underlying molecular processes for this are described in the review. Treatments to re-sensitize insulin signaling in the brain are also described, such as nasal insulin tests in AD patients, or treatments with re-sensitizing hormones, such as leptin, ghrelin, glucagon-like peptide 1 (GLP-1),and glucose-dependent insulinotropic polypeptide (GIP). The first clinical trials show promising results and are a proof of concept that utilizing such treatments is valid.

The impact of anorexigenic peptides in experimental models of Alzheimer's disease pathology

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder in the elderly population. Numerous epidemiological and experimental studies have demonstrated that patients who suffer from obesity or type 2 diabetes mellitus have a higher risk of cognitive dysfunction and AD. Several recent studies demonstrated that food intake-lowering (anorexigenic) peptides have the potential to improve metabolic disorders and that they may also potentially be useful in the treatment of neurodegenerative diseases. In this review, the neuroprotective effects of anorexigenic peptides of both peripheral and central origins are discussed. Moreover, the role of leptin as a key modulator of energy homeostasis is discussed in relation to its interaction with anorexigenic peptides and their analogs in AD-like pathology. Although there is no perfect experimental model of human AD pathology, animal studies have already proven that anorexigenic peptides exhibit neuroprotective properties. This phenomenon is extremely important for the potential development of new drugs in view of the aging of the human population and of the significantly increasing incidence of AD.

Targeting the Incretin/Glucagon System With Triagonists to Treat Diabetes

Glucagonlike peptide 1 (GLP-1) receptor agonists have been efficacious for the treatment of type 2 diabetes due to their ability to reduce weight and attenuate hyperglycemia. However, the activity of glucagonlike peptide 1 receptor-directed strategies is submaximal, and the only potent, sustainable treatment of metabolic dysfunction is bariatric surgery, necessitating the development of unique therapeutics. GLP-1 is structurally related to glucagon and glucose-dependent insulinotropic peptide (GIP), allowing for the development of intermixed, unimolecular peptides with activity at each of their respective receptors. In this review, we discuss the range of tissue targets and added benefits afforded by the inclusion of each of GIP and glucagon. We discuss considerations for the development of sequence-intermixed dual agonists and triagonists, highlighting the importance of evaluating balanced signaling at the targeted receptors. Several multireceptor agonist peptides have been developed and evaluated, and the key preclinical and clinical findings are reviewed in detail. The biological activity of these multireceptor agonists are founded in the success of GLP-1-directed strategies; by including GIP and glucagon components, these multireceptor agonists are thought to enhance GLP-1's activities by broadening the tissue targets and synergizing at tissues that express multiple receptors, such at the brain and pancreatic islet β cells. The development and utility of balanced, unimolecular multireceptor agonists provide both a useful tool for querying the actions of incretins and glucagon during metabolic disease and a unique drug class to treat type 2 diabetes with unprecedented efficacy.

Targeting glucose-dependent insulinotropic polypeptide receptor for neurodegenerative disorders

INTRODUCTION

Incretin hormones, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1) exert pleiotropic effects on endocrine pancreas and nervous system. Expression of GIP and GIP receptor (GIPR) in neurons, their roles in neurogenesis, synaptic plasticity, neurotransmission, and neuromodulation uniquely position GIPR for therapeutic applications in neurodegenerative disorders. GIP analogs acting as GIPR agonists attenuate neurobehavioral and neuropathological sequelae of neurodegenerative disorders in preclinical models, e.g. Alzheimer's disease (AD), Parkinson's disease (PD), and cerebrovascular disorders. Modulation of GIPR signaling offers an unprecedented approach for disease modification by arresting neuronal viability decline, enabling neuronal regeneration, and reducing neuroinflammation. Growth-promoting effects of GIP signaling and broad-based neuroprotection highlight the therapeutic potential of GIPR agonists. Areas covered: This review focuses on the role of GIPR-mediated signaling in the central nervous system in neurophysiological and neuropathological conditions. In context of neurodegeneration, the article summarizes potential of targeting GIPR signaling for neurodegenerative conditions such as AD, PD, traumatic brain injury, and cerebrovascular disorders. Expert opinion: GIPR represents a validated therapeutic target for neurodegenerative disorders. GIPR agonists impart symptomatic improvements, slowed neurodegeneration, and enhanced neuronal regenerative capacity in preclinical models. Modulation of GIPR signaling is potentially a viable therapeutic approach for disease modification in neurodegenerative disorders.

A novel GLP-1/GIP/Gcg triagonist reduces cognitive deficits and pathology in the 3xTg mouse model of Alzheimer's disease

Type 2 diabetes mellitus (T2DM) is an important risk factor for Alzheimer's disease (AD). Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) have been identified to be effective in T2DM treatment and neuroprotection. In this study, we further explored the effects of a novel unimolecular GLP-1/GIP/Gcg triagonist on the cognitive behavior and cerebral pathology in the 7-month-old triple transgenic mouse model of AD (3xTg-AD), and investigated its possible electrophysiological and molecular mechanisms. After chronic administration of the GLP-1/GIP/Gcg triagonist (10 nmol/kg bodyweight, once daily, i.p.) for 30 days, open field, Y maze and Morris water maze tests were performed, followed by in vivo electrophysiological recording, immunofluorescence and Western blotting experiments. We found that the chronic treatment with the triagonist could improve long-term spatial memory of 3xTg-AD mice in Morris water maze, as well as the working memory in Y maze task. The triagonist also alleviated the suppression of long-term potentiation (LTP) in the CA1 region of hippocampus. In addition, the triagonist significantly reduced hippocampal pathological damages, including amyloid-β (Aβ) and phosphorylated tau aggregates, and upregulated the expression levels of ^S133 p-CREB, ^T286 p-CAMKII and ^S9 p-GSK3β in the hippocampus of the 3xTg-AD mice. These results demonstrate for the first time that the novel GLP-1/GIP/Gcg triagonist is efficacious in ameliorating cognitive deficits and pathological damages of 3xTg-AD mice, suggesting that the triagonist might be potentially beneficial in the treatment of AD.

Novel dual GLP-1/GIP receptor agonists show neuroprotective effects in Alzheimer's and Parkinson's disease models

Type 2 diabetes is a risk factor for several chronic neurodegenerative disorders such as Alzheimer's or Parkinson's disease. The link appears to be insulin de-sensitisation in the brain. Insulin is an important neuroprotective growth factor. GLP-1 and GIP are growth factors that re-sensitise insulin and GLP-1 mimetics are used in the clinic to treat diabetes. GLP-1 and GIP mimetics initially designed to treat diabetes show good protective effects in animal models of Alzheimer's and Parkinson's disease. Based on these results, several clinical trials have shown first encouraging effects in patients with Alzheimer's or Parkinson' disease. Novel dual GLP-1/GIP receptor agonists have been developed to treat diabetes, and they also show good neuroprotective effects that are superior to single GLP-1 analogues. Several newer dual analogues have been tested that have been engineered to cross the blood -brain barrier. They show clear neuroprotective effects by reducing inflammation and oxidative stress and apoptotic signalling and protecting memory formation, synaptic numbers and synaptic activity, motor activity, dopaminergic neurons, cortical activity and energy utilisation in the brain. These results demonstrate the potential of developing disease-modifying treatments for Alzheimer's and Parkinson's disease that are superior to current single GLP-1 mimetics. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

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.

Microvascular ultrastructural changes precede cognitive impairment in the murine APPswe/PS1dE9 model of Alzheimer's disease

Cerebral and systemic organ microvascular pathologies coexist with human Alzheimer's disease (AD) neuropathology. In this study, we hypothesised that both cerebral and systemic microvascular pathologies exist in 4- to 5-month-old male APPswe/PS1dE9 (APP/PS1) transgenic mice prior to the onset of cognitive impairment. To assess this we examined recognition memory in both wild-type and APP/PS1 mice using the object recognition task (ORT; n = 11 per group) and counted thioflavin-S-positive plaques in brain (n = 6 per group). Vascular casts of brain, liver, spleen and kidneys were examined using scanning electron microscopy (n = 6 per group), and the urinary albumin-to-creatinine ratio (uACR; n = 5 per group) was measured as an index of glomerular permeability. Murine recognition memory was intact, as demonstrated by a significant preference for the novel object in the ORT paradigm. Brain sections of wild-type mice were devoid of thioflavin-S positivity, whereas age-matched APP/PS1 mice had an average of 0.88 ± 0.22 thioflavin-S-positive plaques in the cortex, 0.42 ± 0.17 plaques in the dentate gyrus and 0.30 ± 0.07 plaques in the cornus ammonis 1 region. The profiles of casted cerebral capillaries of wild-type mice were smooth and regular in contrast to those of APP/PS1 mice which demonstrate characteristic (0.5-4.6 μm) 'tags'. APP/PS1 mice also had a significantly reduced hepatic vessel number (p = 0.0002) and an increase in the number of splenic microvascular pillars (p = 0.0231), in the absence of changes in either splenic microvascular density (p = 0.3746) or glomerular ultrastructure. The highly significant reduction in uACR in APP/PS1 mice compared to wild-type (p = 0.0079) is consistent with glomerular microvascular dysfunction. These findings highlight early microvascular pathologies in 4- to 5-month-old APP/PS1 transgenic mice and may indicate an amenable target for pharmacological intervention in AD.

Microbiota modulation counteracts Alzheimer's disease progression influencing neuronal proteolysis and gut hormones plasma levels

Gut microbiota has a proven role in regulating multiple neuro-chemical pathways through the highly interconnected gut-brain axis. Oral bacteriotherapy thus has potential in the treatment of central nervous system-related pathologies, such as Alzheimer’s disease (AD). Current AD treatments aim to prevent onset, delay progression and ameliorate symptoms. In this work, 3xTg-AD mice in the early stage of AD were treated with SLAB51 probiotic formulation, thereby affecting the composition of gut microbiota and its metabolites. This influenced plasma concentration of inflammatory cytokines and key metabolic hormones considered therapeutic targets in neurodegeneration. Treated mice showed partial restoration of two impaired neuronal proteolytic pathways (the ubiquitin proteasome system and autophagy). Their cognitive decline was decreased compared with controls, due to a reduction in brain damage and reduced accumulation of amyloid beta aggregates. Collectively, our results clearly prove that modulation of the microbiota induces positive effects on neuronal pathways that are able to slow down the progression of Alzheimer’s disease.