A novel GLP-1/GIP dual agonist is more effective than liraglutide in reducing inflammation and enhancing GDNF release in the MPTP mouse model of Parkinson's disease

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

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

From diabetes to diverse domains: the multifaceted roles of GLP-1 receptor agonists

Glucagon-like Peptide-1 (GLP-1) receptor agonists (GLP-1RAs) emerged as a primary treatment for type-2 diabetes mellitus (T2DM), however, their multifaceted effects on various target organs beyond glycemic control opened a new era of treatment. We conducted a comprehensive literature search using databases including Scopus, Google Scholar, PubMed, and the Cochrane Library to identify clinical, in-vivo, and in-vitro studies focusing on the diverse effects of GLP-1 receptor agonists. Eligible studies were selected based on their relevance to the varied roles of GLP-1RAs in T2DM management and their impact on other physiological functions. Numerous studies have reported the efficacy of GLP-1RAs in improving outcomes in T2DM, with demonstrated benefits including glucose-dependent insulinotropic actions, modulation of insulin signaling pathways, and reductions in glycemic excursions. Additionally, GLP-1 receptors are expressed in various tissues and organs, suggesting their widespread physiological functions beyond glycemic control potentially include neuroprotective, anti-inflammatory, cardioprotective, and metabolic benefits. However, further scientific studies are still underway to maximize the benefits of GLP-1RAs and to discover additional roles in improving health benefits. This article sought to review not only the actions of GLP1RAs in the treatment of T2DM but also explore its effects on potential targets in other disorders.

Antidiabetic drugs in Parkinson's disease

This review explores the intricate connections between type 2 diabetes (T2D) and Parkinson's disease (PD), both prevalent chronic conditions that primarily affect the aging population. These diseases share common early biochemical pathways that contribute to tissue damage. This manuscript also systematically compiles potential shared cellular mechanisms between T2D and PD and discusses the literature on the utilization of antidiabetic drugs as potential therapeutic options for PD. This review encompasses studies investigating the experimental and clinical efficacy of antidiabetic drugs in the treatment of Parkinson's disease, along with the proposed mechanisms of action. The exploration of the benefits of antidiabetic drugs in PD presents a promising avenue for the treatment of this neurodegenerative disorder.

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.

Identification of the abnormalities in astrocytic functions as potential drug targets for neurodegenerative disease

INTRODUCTION

Historically, astrocytes were seen primarily as a supportive cell population within the brain; with neurodegenerative disease research focusing exclusively on malfunctioning neurons. However, astrocytes perform numerous tasks that are essential for maintenance of the central nervous system`s complex processes. Disruption of these functions can have negative consequences; hence, it is unsurprising to observe a growing amount of evidence for the essential role of astrocytes in the development and progression of neurodegenerative diseases. Targeting astrocytic functions may serve as a potential disease-modifying drug therapy in the future.

AREAS COVERED

The present review emphasizes the key astrocytic functions associated with neurodegenerative diseases and explores the possibility of pharmaceutical interventions to modify these processes. In addition, the authors provide an overview of current advancement in this field by including studies of possible drug candidates.

EXPERT OPINION

Glial research has experienced a significant renaissance in the last quarter-century. Understanding how disease pathologies modify or are caused by astrocyte functions is crucial when developing treatments for brain diseases. Future research will focus on building advanced models that can more precisely correlate to the state in the human brain, with the goal of routinely testing therapies in these models.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

GLP-1 Receptor Agonists: A New Treatment in Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Recent data highlight similarities between neurodegenerative diseases, including PD and type 2 diabetes mellitus (T2DM), suggesting a crucial interplay between the gut-brain axis. Glucagon-like peptide-1 receptor (GLP-1R) agonists, known for their use in T2DM treatment, are currently extensively studied as novel PD modifying agents. For this narrative review article, we searched PubMed and Scopus databases for peer-reviewed research, review articles and clinical trials regarding GLP-1R agonists and PD published in the English language with no time restrictions. We also screened the references of the selected articles for possible additional articles in order to include most of the key recent evidence. Many data on animal models and preclinical studies show that GLP1-R agonists can restore dopamine levels, inhibit dopaminergic loss, attenuate neuronal degeneration and alleviate motor and non-motor features of PD. Evidence from clinical studies is also very promising, enhancing the possibility of adding GLP1-R agonists to the current armamentarium of drugs available for PD treatment.

GLP-1/Sigma/RAGE receptors: An evolving picture of Alzheimer's disease pathology and treatment

According to the facts and figures 2023stated that 6.7 million Americans over the age of 65 have Alzheimer's disease (AD). The scenario of AD has reached up to the maximum, of 4.1 million individuals, 2/3rd are female patients, and approximately 1 in 9 adults over the age of 65 have dementia with AD dementia. The fact that there are now no viable treatments for AD indicates that the underlying disease mechanisms are not fully understood. The progressive neurodegenerative disease, AD is characterized by amyloid plaques and neurofibrillary tangles (NFTs) of abnormally hyperphosphorylated tau protein and senile plaques (SPs), which are brought on by the buildup of amyloid beta (Aβ). Numerous attempts have been made to produce compounds that interfere with these characteristics because of significant research efforts into the primary pathogenic hallmark of this disorder. Here, we summarize several research that highlights interesting therapy strategies and the neuroprotective effects of GLP-1, Sigma, and, AGE-RAGE receptors in pre-clinical and clinical AD models.

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.

Recent research progress on metabolic syndrome and risk of Parkinson's disease

Parkinson's disease (PD) is one of the most widespread neurodegenerative diseases. PD is associated with progressive loss of substantia nigra dopaminergic neurons, including various motor symptoms (e.g., bradykinesia, rigidity, and resting tremor), as well as non-motor symptoms (e.g., cognitive impairment, constipation, fatigue, sleep disturbance, and depression). PD involves multiple biological processes, including mitochondrial or lysosomal dysfunction, oxidative stress, insulin resistance, and neuroinflammation. Metabolic syndrome (MetS), a collection of numerous connected cerebral cardiovascular conditions, is a common and growing public health problem associated with many chronic diseases worldwide. MetS components include central/abdominal obesity, systemic hypertension, diabetes, and atherogenic dyslipidemia. MetS and PD share multiple pathophysiological processes, including insulin resistance, oxidative stress, and chronic inflammation. In recent years, MetS has been linked to an increased risk of PD, according to studies; however, the specific mechanism remains unclear. Researchers also found that some related metabolic therapies are potential therapeutic strategies to prevent and improve PD. This article reviews the epidemiological relationship between components of MetS and the risk of PD and discusses the potentially relevant mechanisms and recent progress of MetS as a risk factor for PD. Furthermore, we conclude that MetS-related therapies are beneficial for the prevention and treatment of PD.

The novel GLP-1/GIP dual agonist DA3-CH improves rat type 2 diabetes through activating AMPK/ACC signaling pathway

BACKGROUND

Type 2 diabetes mellitus (T2DM) accounts for more than 95% of all diabetes. DA3-CH is a novel dual receptor agonist of glucagon like peptide-1 (GLP-1) and glucose dependent insulin stimulating polypeptide (GIP). The regulatory role of DA3-CH in T2DM has not been reported.

METHODS

T2DM rat model was established successfully with high sugar and fat feed and streptomycin (STZ) induction. The mRNA and protein expression were measured with RT-PCR and western blotting. The apoptosis level in the pancreatic tissue was evaluated with Tunel staining. Blood glucose, fat, and oxidative stress indicators were measured.

RESULTS

DA3-CH greatly improved T2DM symptoms by reducing blood glucose, blood fat, pancreatic tissue injury, apoptosis, and oxidative stress condition. The inactivation of Adenylate activated protein kinase (AMPK)/acetyl CoA carboxylase (ACC) signaling pathway in T2DM rats was promoted by DA3-CH. The influence of DA3-CH was significantly reversed by Com-C, the inhibitor of AMPK/ACC signaling pathway.

CONCLUSIONS

DA3-CH might improve T2DM through targeting AMPK/ACC signaling pathway. This study might provide a novel therapeutic strategy for the prevention and treatment of T2DM through targeting DA3-CH and AMPK/ACC signaling pathway.

Antidiabetic agents as a novel treatment for Alzheimer's and Parkinson's disease

Therapeutic strategies for neurodegenerative disorders have commonly targeted individual aspects of the disease pathogenesis to little success. Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by several pathological features. In AD and PD, there is an abnormal accumulation of toxic proteins, increased inflammation, decreased synaptic function, neuronal loss, increased astrocyte activation, and perhaps a state of insulin resistance. Epidemiological evidence has revealed a link between AD/PD and type 2 diabetes mellitus, with these disorders sharing some pathological commonalities. Such a link has opened up a promising avenue for repurposing antidiabetic agents in the treatment of neurodegenerative disorders. A successful therapeutic strategy for AD/PD would likely require a single or several agents which target the separate pathological processes in the disease. Targeting cerebral insulin signalling produces numerous neuroprotective effects in preclinical AD/PD brain models. Clinical trials have shown the promise of approved diabetic compounds in improving motor symptoms of PD and preventing neurodegenerative decline, with numerous further phase II trials and phase III trials underway in AD and PD populations. Alongside insulin signalling, targeting incretin receptors in the brain represents one of the most promising strategies for repurposing currently available agents for the treatment of AD/PD. Most notably, glucagon-like-peptide-1 (GLP-1) receptor agonists have displayed impressive clinical potential in preclinical and early clinical studies. In AD the GLP-1 receptor agonist, liraglutide, has been demonstrated to improve cerebral glucose metabolism and functional connectivity in small-scale pilot trials. Whilst in PD, the GLP-1 receptor agonist exenatide is effective in restoring motor function and cognition. Targeting brain incretin receptors reduces inflammation, inhibits apoptosis, prevents toxic protein aggregation, enhances long-term potentiation and autophagy as well as restores dysfunctional insulin signalling. Support is also increasing for the use of additional approved diabetic treatments, including intranasal insulin, metformin hydrochloride, peroxisome proliferator-activated nuclear receptor γ agonists, amylin analogs, and protein tyrosine phosphatase 1B inhibitors which are in the investigation for deployment in PD and AD treatment. As such, we provide a comprehensive review of several promising anti-diabetic agents for the treatment of AD and PD.

Glucose Metabolism Impairment in Parkinson's Disease

Impairments in systematic and regional glucose metabolism exist in patients with Parkinson's disease (PD) at every stage of the disease course, and such impairments are associated with the incidence, progression, and special phenotypes of PD, which affect each physiological process of glucose metabolism including glucose uptake, glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, and pentose phosphate shunt pathway. These impairments may be attributed to various mechanisms, such as insulin resistance, oxidative stress, abnormal glycated modification, blood-brain-barrier dysfunction, and hyperglycemia-induced damages. These mechanisms could subsequently cause excessive methylglyoxal and reactive oxygen species production, neuroinflammation, abnormal aggregation of protein, mitochondrial dysfunction, and decreased dopamine, and finally result in energy supply insufficiency, neurotransmitter dysregulation, aggregation and phosphorylation of α-synuclein, and dopaminergic neuron loss. This review discusses the glucose metabolism impairment in PD and its pathophysiological mechanisms, and briefly summarized the currently-available therapies targeting glucose metabolism impairment in PD, including glucagon-likepeptide-1 (GLP-1) receptor agonists and dual GLP-1/gastric inhibitory peptide receptor agonists, metformin, and thiazoledinediones.

Type 2 Diabetes (T2DM) and Parkinson's Disease (PD): a Mechanistic Approach

Growing evidence suggest that there is a connection between Parkinson's disease (PD) and insulin dysregulation in the brain, whilst the connection between PD and type 2 diabetes mellitus (T2DM) is still up for debate. Insulin is widely recognised to play a crucial role in neuronal survival and brain function; any changes in insulin metabolism and signalling in the central nervous system (CNS) can lead to the development of various brain disorders. There is accumulating evidence linking T2DM to PD and other neurodegenerative diseases. In fact, they have a lot in common patho-physiologically, including insulin dysregulation, oxidative stress resulting in mitochondrial dysfunction, microglial activation, and inflammation. As a result, initial research should focus on the role of insulin and its molecular mechanism in order to develop therapeutic outcomes. In this current review, we will look into the link between T2DM and PD, the function of insulin in the brain, and studies related to impact of insulin in causing T2DM and PD. Further, we have also highlighted the role of various insulin signalling pathway in both T2DM and PD. We have also suggested that T2DM-targeting pharmacological strategies as potential therapeutic approach for individuals with cognitive impairment, and we have demonstrated the effectiveness of T2DM-prescribed drugs through current PD treatment trials. In conclusion, this investigation would fill a research gap in T2DM-associated Parkinson's disease (PD) with a potential therapy option.

Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP1) exhibit incretin activity, meaning that they potentiate glucose-dependent insulin secretion. The emergence of GIP receptor (GIPR)-GLP1 receptor (GLP1R) co-agonists has fostered growing interest in the actions of GIP and GLP1 in metabolically relevant tissues. Here, we update concepts of how these hormones act beyond the pancreas. The actions of GIP and GLP1 on liver, muscle and adipose tissue, in the control of glucose and lipid homeostasis, are discussed in the context of plausible mechanisms of action. Both the GIPR and GLP1R are expressed in the central nervous system, wherein receptor activation produces anorectic effects enabling weight loss. In preclinical studies, GIP and GLP1 reduce atherosclerosis. Furthermore, GIPR and GLP1R are expressed within the heart and immune system, and GLP1R within the kidney, revealing putative mechanisms linking GIP and GLP1R agonism to cardiorenal protection. We interpret the clinical and mechanistic data obtained for different agents that enable weight loss and glucose control for the treatment of obesity and type 2 diabetes mellitus, respectively, by activating or blocking GIPR signalling, including the GIPR-GLP1R co-agonist tirzepatide, as well as the GIPR antagonist-GLP1R agonist AMG-133. Collectively, we update translational concepts of GIP and GLP1 action, while highlighting gaps, areas of uncertainty and controversies meriting ongoing investigation.

The pleiotropic of GLP-1/GLP-1R axis in central nervous system diseases

Glucagon-like peptide-1(GLP-1) is a multifunctional polypeptide throughout the lifespan via activating Glucagon-like peptide-1 receptor (GLP-1R).GLP-1 can affect food ingestion, enhance the secretion of insulin from pancreatic islets induced by glucose and be utilized to treat type 2 diabetes mellitus(T2DM).But, accumulating evidences from the decades suggest that activation GLP-1R can not only regulate the blood glucose, but also sustain the homeostasis of intracellular environment and protect neuron from various damaged responses such as oxidative stress, inflammation, excitotoxicity, ischemia and so on. And more and more pre-clinical and clinical studies identified that GLP-1 and its analogues may play a significant role in improving multiple central nervous system (CNS) diseases including neurodegenerative diseases, epilepsy, mental disorders, ischemic stroke, hemorrhagic stroke, traumatic brain injury, spinal cord injury, chronic pain, addictive disorders, other diseases neurological complications and so on. In order to better reveal the relationship between GLP-1/GLP-1R axis and the growth, development and survival of neurons, herein, this review is aimed to summarize the multi-function of GLP-1/GLP-1R axis in CNS diseases.

Protective role of IGF-1 and GLP-1 signaling activation in neurological dysfunctions

Insulin-like growth factor-1 (IGF-1), a pleiotropic polypeptide, plays an essential role in CNS development and maturation. Glucagon-like peptide-1 (GLP-1) is an endogenous incretin hormone that regulates blood glucose levels and fatty acid oxidation in the brain. GLP-1 also exhibits similar functions and growth factor-like properties to IGF-1, which is likely how it exerts its neuroprotective effects. Recent preclinical and clinical evidence indicate that IGF-1 and GLP-1, apart from regulating growth and development, prevent neuronal death mediated by amyloidogenesis, cerebral glucose deprivation, neuroinflammation and apoptosis through modulation of PI3/Akt kinase, mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK/ERK). IGF-1 resistance and GLP-1 deficiency impair protective cellular signaling mechanisms, contributing to the progression of neurodegenerative diseases. Over the past decades, IGF-1 and GLP-1 have emerged as an essential component of the neuronal system and as potential therapeutic targets for several neurodegenerative and neuropsychiatric dysfunctions. There is substantial evidence that IGF-1 and GLP-1 analogues penetrate the blood-brain barrier (BBB) and exhibit neuroprotective functions, including synaptic formation, neuronal plasticity, protein synthesis, and autophagy. Conclusively, this review represents the therapeutic potential of IGF-1 and GLP-1 signaling target activators in ameliorating neurological disorders.

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.

Anti-Inflammatory Effects of GLP-1 Receptor Activation in the Brain in Neurodegenerative Diseases

The glucagon-like peptide-1 (GLP-1) is a pleiotropic hormone well known for its incretin effect in the glucose-dependent stimulation of insulin secretion. However, GLP-1 is also produced in the brain and displays a critical role in neuroprotection and inflammation by activating the GLP-1 receptor signaling pathways. Several studies in vivo and in vitro using preclinical models of neurodegenerative diseases show that GLP-1R activation has anti-inflammatory properties. This review explores the molecular mechanistic action of GLP-1 RAS in relation to inflammation in the brain. These findings update our knowledge of the potential benefits of GLP-1RAS actions in reducing the inflammatory response. These molecules emerge as a potential therapeutic tool in treating neurodegenerative diseases and neuroinflammatory pathologies.

Parkinson's Disease and Sugar Intake-Reasons for and Consequences of a Still Unclear Craving

Lately, studies have shown that patients with Parkinson’s disease (PD) report a strong craving for sweets and consume significantly more fast-acting carbohydrates than healthy controls. Consuming food with a high-sugar content is assumed to lead to an increase in insulin concentration, which could positively influence dopamine concentration in the brain and unconsciously be used by patients as kind of “self-medication” to compensate for a lack of dopamine in PD. On the other hand, high-sugar intake could also lead to insulin resistance and diabetes, which is discussed as a causative factor for progressive neurodegeneration in PD. In this critical appraisal, we discuss the role of sugar intake and insulin on dopamine metabolism in patients with PD and how this could influence the potential neurodegeneration mediated by insulin resistance.

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.

Semaglutide Protects against 6-OHDA Toxicity by Enhancing Autophagy and Inhibiting Oxidative Stress

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder for which no effective treatment is available. Studies have demonstrated that improving insulin resistance in type 2 diabetes mellitus (T2DM) can benefit patients with PD. In addition, a neuroprotective effect of glucagon-like peptide-1 (GLP-1) receptor agonists was demonstrated in experimental models of PD. In addition, there are some clinical trials to study the neuroprotective effect of GLP-1 analog on PD patients. Semaglutide is a long-acting, once-a-week injection treatment and the only available oral form of GLP-1 analog. In the present study, we treated the human neuroblastoma SH-SY5Y cell line with 6-hydroxydopamine (6-OHDA) as a PD in vitro model to explore the neuroprotective effects and potential mechanisms of semaglutide to protect against PD. Moreover, we compared the effect of semaglutide with liraglutide given at the same dose. We demonstrated that both semaglutide and liraglutide protect against 6-OHDA cytotoxicity by increasing autophagy flux and decreasing oxidative stress as well as mitochondrial dysfunction in SH-SY5Y cells. Moreover, by comparing the neuroprotective effects of semaglutide and liraglutide on PD cell models at the same dose, we found that semaglutide was superior to liraglutide for most parameters measured. Our results indicate that semaglutide, the new long-acting and only oral GLP-1 analog, may be represent a promising treatment for PD.

Therapeutic application of GLP-1 and GIP receptor agonists in Parkinson's disease

INTRODUCTION

Diabetes is a risk factor for Parkinson's disease (PD) and shares similar dysregulated insulin pathways. Glucagon-like peptide-1 (GLP-1) analogs originally designed to treat diabetes have shown potent neuroprotective activity in preclinical studies of PD. They are neuroprotective by inhibiting inflammation, improving neuronal survival, maintenance of synapses, and dopaminergic transmission in the brain. Building on this, three clinical studies have reported impressive effects in patients with PD, testing exendin-4 (Exenatide, Bydureon) or liraglutide (Victoza, Saxenda). Glucose-dependent insulinotropic peptide (GIP) is another peptide hormone that has shown good effects in animal models of PD. Novel dual GLP-1/GIP agonists have been developed that can penetrate the blood-brain barrier (BBB) and show superior effects in animal models compared to GLP-1 drugs.

AREAS COVERED

The review summarizes preclinical and clinical studies testing GLP-1R agonists and dual GLP-1/GIPR agonists in PD and discusses possible mechanisms of action.

EXPERT OPINION

Current strategies to treat PD by lowering the levels of alpha-synuclein have not shown effects in clinical trials. It is time to move on from the 'misfolding protein' hypothesis. Growth factors such as GLP-1 that can cross the BBB have already shown impressive effects in patients and are the future of drug discovery in PD.

Neuroprotective Effects of a Cholecystokinin Analogue in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Parkinson’s Disease Mouse Model

Parkinson’s disease (PD) is a chronic neurodegenerative disease. Type 2 diabetes mellitus (T2DM) has been identified as a risk factor for PD. Drugs originally developed for T2DM treatment such as liraglutide have shown neuroprotective effects in mouse models of PD. Cholecystokinin (CCK) is a peptide hormone with growth factor properties. Here, we demonstrate the neuroprotective effects of the (pGLu)-(Gln)-CCK8 analogue in an acute PD mouse model induced by 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Administration of CCK analogue (50 nmol/kg ip.) for 14 days treatment improved the locomotor and exploratory activity of mice, and improved bradykinesia and movement balance of mice. The CCK analogue administration also restored tyrosine hydroxylase (TH) positive dopaminergic neurons number and synapse number (synaptophysin levels) in the substantia nigra pars compacta (SNpc). The CCK analogue decreased glia activation and neuroinflammation in the SNpc, and regulated autophagy dysfunction induced by MPTP. CCK analogue protected against mitochondrial damage and ER stress, and also decreased the ratio of apoptosis signaling molecules Bax/Bcl-2. Importantly, the CCK analogue improved the decrease of p-CREBS¹³³ growth factor signaling in the SNpc. Therefore, the CCK analogue promotes cell survival of dopaminergic neuron in the SNpc by activating the cAMP/PKA/CREB pathway that also inhibits apoptosis and regulates autophagy impairment. The present results indicate that CCK analogue shows a promising potential for the treatment of PD.

The effect of GLP-1 receptor agonists in pre-clinical rodent models of Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

Parkinson's Disease (PD) is a progressive neurodegenerative condition associated with significant morbidity. Currently, there are limited pharmacological options and none of the therapies available are disease-modifying. This systematic review and meta-analysis considers a novel drug class through the research question - in pre-clinical rodent models of PD, is GLP-1 receptor agonist therapy neuroprotective when compared to vehicle controls?

METHODS

A literature search was conducted to locate relevant pre-clinical studies. Two separate outcomes were considered. The primary outcome was indicators of dopaminergic neurotransmission. The secondary outcome was indicators of motor symptoms. Untreated PD models were compared to PD-models treated with GLP-1 receptor agonists. The final meta-analysis was conducted using the Cochrane RevMan software and represented continuous data using the inverse variance statistical method and random effects analysis model. The final study statistic was represented as an SMD value with a p-value < 0.05 considered statistically significant. Study heterogeneity and publication bias was assessed using I2 values and funnel plots respectively.

RESULTS

Eleven studies fit the inclusion criteria and were included in the final analysis. For the primary outcome (n = 128), there was a statistically significant relative improvement of dopaminergic neurotransmission (SMD 1.71, 95% CI = 0.74-2.68, p = 0.0005, I2 = 76%). For the secondary outcome (n = 280), there was a statistically significant improvement in motor outcomes (SMD 2.11, 95% CI = 1.14-3.09, p < 0.0001, I2 = 89%).

CONCLUSIONS

GLP-1 receptor agonist therapy is neuroprotective in pre-clinical models of PD. This study provides the clinical foundation and research support for the design of rigorous clinical trials to further investigate these results in human PD populations.

Parkinson's disease and diabetes mellitus: common mechanisms and treatment repurposing

In the last decade, attention has become greater to the relationship between neurodegeneration and abnormal insulin signaling in the central nervous system, as insulin in the brain is implicated in neuronal survival, plasticity, oxidative stress and neuroinflammation. Diabetes mellitus and Parkinson’s disease are both aging-associated diseases that are turning into epidemics worldwide. Diabetes mellitus and insulin resistance not only increase the possibility of developing Parkinson’s disease but can also determine the prognosis and progression of Parkinsonian symptoms. Today, there are no available curative or disease modifying treatments for Parkinson’s disease, but the role of insulin and antidiabetic medications in neurodegeneration opens a door to treatment repurposing to fight against Parkinson’s disease, both in diabetic and nondiabetic Parkinsonian patients. Furthermore, it is essential to comprehend how a frequent and treatable disease such as diabetes can influence the progression of neurodegeneration in a challenging disease such as Parkinson’s disease. Here, we review the present evidence on the connection between Parkinson’s disease and diabetes and the consequential implications of the existing antidiabetic molecules in the severity and development of Parkinsonism, with a particular focus on glucagon-like peptide-1 receptor agonists.

Brain Imaging of the GLP-1 Receptor in Obesity Using 68Ga-NODAGA-Exendin-4 PET

Stimulation of glucagon-like peptide-1 (GLP-1) receptors increases the insulin release in the pancreas during high glucose levels, and also stimulates a feeling of satiety. Likewise, synthetic GLP-1 receptor agonists derived from exendin are used successfully in the treatment of type-2 diabetes mellitus and obesity. Interestingly, preclinical and clinical studies further suggest that GLP-1 receptor agonists may decrease motor, behavioral, and cognitive symptoms in (animal models) Parkinson’s disease and Alzheimer’s disease and may slow down neurodegeneration. These observations suggest stimulation of GLP-1 receptors in the brain. The GLP-1 positron emission tomography (PET) tracer ⁶⁸Ga-NODAGA-exendin-4 has been developed and successfully used for imaging in humans. In an ongoing study on the effects of bariatric surgery on GLP-1 receptor expression, we performed ⁶⁸Ga-NODAGA-exendin-4 PET in obese subjects. Here we evaluated whether GLP-1 receptor binding could be visualized in the central nervous system in 10 obese subjects (seven woman; body mass index: mean ± SD: 39 ± 4.4 kg/m²) before bariatric surgery. Although we observed clear uptake in the pituitary area (mean SUV_max 4.3 ± 2.3), we found no significant uptake in other parts of the brain. We conclude that ⁶⁸Ga-NODAGA-exendin-4 PET cannot be used to analyze GLP-1 receptors in the brain of obese subjects.

L-dopa-Dependent Effects of GLP-1R Agonists on the Survival of Dopaminergic Cells Transplanted into a Rat Model of Parkinson Disease

Cell therapy is a promising treatment for Parkinson's disease (PD), however clinical trials to date have shown relatively low survival and significant patient-to-patient variability. Glucagon Like Peptide-1 receptor (GLP-1R) agonists have potential neuroprotective effects on endogenous dopaminergic neurons. This study explores whether these agents could similarly support the growth and survival of newly transplanted neurons. 6-OHDA lesioned Sprague Dawley rats received intra-striatal grafts of dopaminergic ventral mesencephalic cells from embryonic day 14 Wistar rat embryos. Transplanted rats then received either saline or L-dopa (12 mg/kg) administered every 48 h prior to, and following cell transplantation. Peripheral GLP-1R agonist administration (exendin-4, 0.5 μg/kg twice daily or liraglutide, 100 μg/kg once daily) commenced immediately after cell transplantation and was maintained throughout the study. Graft survival increased under administration of exendin-4, with motor function improving significantly following treatment with both exendin-4 and liraglutide. However, this effect was not observed in rats administered with L-dopa. In contrast, L-dopa treatment with liraglutide increased graft volume, with parallel increases in motor function. However, this improvement was accompanied by an increase in leukocyte infiltration around the graft. The co-administration of L-dopa and exendin-4 also led to indicators of insulin resistance not seen with liraglutide, which may underpin the differential effects observed between the two GLP1-R agonists. Overall, there may be some benefit to the supplementation of grafted patients with GLP-1R agonists but the potential interaction with other pharmacological treatments needs to be considered in more depth.

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.

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.

The GLP-1/GIP dual-receptor agonist DA5-CH inhibits the NF-κB inflammatory pathway in the MPTP mouse model of Parkinson's disease more effectively than the GLP-1 single-receptor agonist NLY01

The GLP-1 receptor agonist exendin-4 has recently shown good effects in a phase II clinical trial in Parkinson's disease (PD) patients. Here, a comparison of the new GLP-1/GIP dual receptor agonist DA5-CH and NLY01, a 40 kDa pegylated form of exendin-4, on motor impairments and reducing inflammation in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) PD mouse model is provided. The drug groups received either DA5-CH or NLY01 (25 nmol/kg) i.p. after daily MPTP intraperitoneal injection. Both drugs showed improvements in motor activity, open field experiments, rotarod tests, and gait analysis, but DA5-CH was more potent. Tyrosine hydroxylase expression in dopaminergic neurons was much reduced by MPTP and improved by DA5-CH, while NLY01 showed weak effects. When analyzing levels of α-synuclein (α-Syn), DA5-CH reduced levels effectively while NLY01 had no effect. When measuring the levels of the inflammation markers Toll-like receptor 4 (TLR4), specific markers of microglia activation (Iba-1), the marker of astrocyte activation glial fibrillary acidic protein (GFAP), nuclear factor-κB (NF-κB), tumor necrosis factor (TNF-α), and transforming growth factor β1 (TGF-β1), DA5-CH was very effective in reducing the chronic inflammation response, while NLY01 did not show significant effects. Levels of key growth factors such as Glial cell-derived neurotrophic factor (GDNF) and Brain-derived neurotrophic factor (BDNF) were much reduced by MPTP, and DA5-CH was able to normalize levels in the brain, while NLY01 showed little effect. The levels of pro-inflammatory cytokines (IL-6 and IL-Iβ) were much reduced by DA5-CH, too, while NLY01 showed no effect. In a separate experiment, we tested the ability of the two drugs to cross the blood-brain barrier. After injecting fluorescin-labelled peptides peripherally, the fluorescence in brain tissue was measured. It was found that the pegylated NLY01 peptide did not cross the BBB in meaningful quantities while exendin-4 and the dual agonist DA5-CH did. The results show that DA5-CH shows promise as a therapeutic drug for PD.

The Novel Dual GLP-1/GIP Receptor Agonist DA-CH5 Is Superior to Single GLP-1 Receptor Agonists in the MPTP Model of Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disease for which there is no cure. In a clinical trial, the glucagon-like peptide-1 (GLP-1) receptor agonist exendin-4 has shown good protective effects in PD patients. The hormone glucose-dependent insulinotropic polypeptide (GIP) has also shown protective effects in animal models of PD.

OBJECTIVE

We tested DA-CH5, a novel dual GLP-1/GIP receptor agonist.

METHODS

DA-CH5 activity was tested on cells expressing GLP-1, GLP-2, GIP or glucagon receptors. The ability to cross the blood-brain barrier (BBB) of DA-CH5, exendin-4, liraglutide or other dual receptor agonists was tested with fluorescein-labelled peptides. DA-CH5, exendin-4 and liraglutide were tested in the MPTP mouse model of PD.

RESULTS

Analysing the receptor activating properties showed a balanced activation of GLP-1 and GIP receptors while not activating GLP-2 or glucagon receptors. DA-CH5 crossed the BBB better than other single or other dual receptor agonists. In a dose-response comparison, DA-CH5 was more effective than the GLP-1 receptor agonist exendin-4. When comparing the neuroprotective effect of DA-CH5 with Liraglutide, a GLP-1 analogue, both DA-CH5 and Liraglutide improved MPTP-induced motor impairments. In addition, the drugs reversed the decrease of the number of neurons expressing tyrosine hydroxylase (TH) in the SN, alleviated chronic inflammation, reduced lipid peroxidation, inhibited the apoptosis pathway (TUNEL assay) and increased autophagy -related proteins expression in the substantia nigra (SN) and striatum. Importantly, we found DA-CH5 was superior to Liraglutide in reducing microglia and astrocyte activation, improving mitochondrial activity by reducing the Bax/Bcl-2 ratio and normalising autophagy as found in abnormal expression of LC3 and p62.

CONCLUSION

The results demonstrate that the DA-CH5 is superior to liraglutide and could be a therapeutic treatment for PD.

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.

Diabetes, insulin and new therapeutic strategies for Parkinson's disease: Focus on glucagon-like peptide-1 receptor agonists

Parkinson's disease and diabetes mellitus are two chronic disorders associated with aging that are becoming increasingly prevalent worldwide. Parkinson is a multifactorial progressive condition with no available disease modifying treatments at the moment. Over the last few years there is growing interest in the relationship between diabetes (and impaired insulin signaling) and neurodegenerative diseases, as well as the possible benefit of antidiabetic treatments as neuroprotectors, even in non-diabetic patients. Insulin regulates essential functions in the brain such as neuronal survival, autophagy of toxic proteins, synaptic plasticity, neurogenesis, oxidative stress and neuroinflammation. We review the existing epidemiological, experimental and clinical evidence that supports the interplay between insulin and neurodegeneration in Parkinson's disease, as well as the role of antidiabetic treatments in this disease.

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.

Neuroprotection of Exendin-4 by Enhanced Autophagy in a Parkinsonian Rat Model of α-Synucleinopathy

Glucagon-like peptide-1 (GLP-1) receptor stimulation ameliorates parkinsonian motor and non-motor deficits in both experimental animals and patients; however, the disease-modifying mechanisms of GLP-1 receptor activation have remained unknown. The present study investigated whether exendin-4 (a GLP-1 analogue) can rescue motor deficits and exert disease-modifying effects in a parkinsonian rat model of α-synucleinopathy. This model was established by unilaterally injecting AAV-9-A53T-α-synuclein into the right substantia nigra pars compacta, followed by 4 or 8 weeks of twice-daily intraperitoneal injections of exendin-4 (5 μg/kg/day) starting at 2 weeks after AAV-9-A53T-α-synuclein injections. Positron emission tomography/computed tomography (PET/CT) scanning and immunostaining established that treatment with exendin-4 attenuated tyrosine-hydroxylase-positive neuronal loss and terminal denervation and mitigated the decrease in expression of vesicular monoamine transporter 2 within the nigrostriatal dopaminergic systems of rats injected with AAV-9-A53T-α-synuclein. It also mitigated the parkinsonian motor deficits assessed in behavioral tests. Furthermore, through both in vivo and in vitro models of Parkinson's disease, we showed that exendin-4 promoted autophagy and mediated degradation of pathological α-synuclein, the effects of which were counteracted by 3-methyladenine or chloroquine, the autophagic inhibitors. Additionally, exendin-4 attenuated dysregulation of the PI3K/Akt/mTOR pathway in rats injected with AAV-9-A53T-α-synuclein. Taken together, our results demonstrate that exendin-4 treatment relieved behavioral deficits, dopaminergic degeneration, and pathological α-synuclein aggregation in a parkinsonian rat model of α-synucleinopathy and that these effects were mediated by enhanced autophagy via inhibiting the PI3K/Akt/mTOR pathway. In light of the safety and tolerance of exendin-4 administration, our results suggest that exendin-4 may represent a promising disease-modifying treatment for Parkinson's disease.

The Future of Incretin-Based Approaches for Neurodegenerative Diseases in Older Adults: Which to Choose? A Review of their Potential Efficacy and Suitability

The current treatment options for neurodegenerative diseases in older adults rely mainly on providing symptomatic relief. Yet, it remains imperative to identify agents that slow or halt disease progression to avoid the most disabling features often associated with advanced disease stages. A potential overlap between the pathological processes involved in diabetes and neurodegeneration has been established, raising the question of whether incretin-based therapies for diabetes may also be useful in treating neurodegenerative diseases in older adults. Here, we review the different agents that belong to this class of drugs (GLP-1 receptor agonists, dual/triple receptor agonists, DPP-4 inhibitors) and describe the data supporting their potential role in treating neurodegenerative conditions including Parkinson's disease and Alzheimer's disease. We further discuss whether there are any distinctive properties among them, particularly in the context of safety or tolerability and CNS penetration, that might facilitate their successful repurposing as disease-modifying drugs. Proof-of-efficacy data will obviously be of the greatest importance, and this is most likely to be demonstrable in agents that reach the central nervous system and impact on neuronal GLP-1 receptors. Additionally, however, the long-term safety and tolerability (including gastrointestinal side effects and unwanted weight loss) as well as the route of administration of this class of agents may also ultimately determine success and these aspects should be considered in prioritising which approaches to subject to formal clinical trial evaluations.

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.

Neuroprotective Effects of a GLP-2 Analogue in the MPTP Parkinson's Disease Mouse Model

BACKGROUND

Glucagon-like peptide 2 (GLP-2) is a peptide hormone derived from the proglucagon gene expressed in the intestines, pancreas and brain. Some previous studies showed that GLP-2 improved aging and Alzheimer's disease related memory impairments. Parkinson's disease (PD) is a progressive neurodegenerative disorder, and to date, there is no particular medicine reversed PD symptoms effectively.

OBJECTIVE

The aim of this study was to evaluate neuroprotective effects of a GLP-2 analogue in the 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) PD mouse model.

METHODS

In the present study, the protease resistant Gly(2)-GLP-2 (50 nmol/kg ip.) analogue has been tested for 14 days by behavioral assessment, transmission electron microscope, immunofluorescence histochemistry, enzyme-linked immunosorbent assay and western blot in an acute PD mouse model induced by MPTP. For comparison, the incretin receptor dual agonist DA5-CH was tested in a separate group.

RESULTS

The GLP-2 analogue treatment improved the locomotor and exploratory activity of mice, and improved bradykinesia and movement imbalance of mice. Gly(2)-GLP-2 treatment also protected dopaminergic neurons and restored tyrosine hydroxylase expression levels in the substantia nigra. Gly(2)-GLP-2 furthermore reduced the inflammation response as seen in lower microglia activation, and decreased NLRP3 and interleukin-1β pro-inflammatory cytokine expression levels. In addition, the GLP-2 analogue improved MPTP-induced mitochondrial dysfunction in the substantia nigra. The protective effects were comparable to those of the dual agonist DA5-CH.

CONCLUSION

The present results demonstrate that Gly(2)-GLP-2 can attenuate NLRP3 inflammasome-mediated inflammation and mitochondrial damage in the substantia nigra induced by MPTP, and Gly(2)-GLP-2 shows neuroprotective effects in this PD animal model.

Crocetin Alleviates Inflammation in MPTP-Induced Parkinson's Disease Models through Improving Mitochondrial Functions

Parkinson's disease (PD) is the second most common neurodegenerative disease. Crocetin, derived from saffron, exerts multiple pharmacological properties, such as anti-inflammatory, antioxidant, antifatigue, and anticancer effects. However, the effect of crocetin on PD remains unclear. In this study, we designed experiments to investigate the effect of crocetin against MPTP-induced PD models and the underlying mechanisms. Our results showed that crocetin treatment attenuates MPTP-induced motor deficits and protects dopaminergic neurons. Both in vivo and in vitro experiments demonstrated that crocetin treatment decreased the expression of inflammatory associated genes and inflammatory cytokines. Furthermore, crocetin treatment protected mitochondrial functions against MPP+ induced damage by regulating the mPTP (mitochondrial permeability transition pore) viability in the interaction of ANT (adenine nucleotide translocase) and Cyp D (Cyclophilin D) dependent manner. Therefore, our results demonstrate that crocetin has therapeutic potential in Parkinson's disease.

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.

Glucagon-like peptide-1 (GLP-1)-based receptor agonists as a treatment for Parkinson's disease

INTRODUCTION

Accumulating evidence supports the evaluation of glucagon-like peptide-1 (GLP-1) receptor (R) agonists for the treatment of the underlying pathology causing Parkinson's Disease (PD). Not only are these effects evident in models of PD and other neurodegenerative disorders but recently in a randomized, double-blind, placebo-controlled clinical trial, a GLP-1R agonist has provided improved cognition motor functions in humans with moderate PD.

AREAS COVERED

In this mini-review, we describe the development of GLP-1R agonists and their potential therapeutic value in treating PD. Many GLP-1R agonists are FDA approved for the treatment of metabolic disorders, and hence can be rapidly repositioned for PD. Furthermore, we present preclinical data offering insights into the use of monomeric dual- and tri-agonist incretin-based mimetics for neurodegenerative disorders. These drugs combine active regions of GLP-1 with those of glucose-dependent insulinotropic peptide (GIP) and/or glucagon (Gcg).

EXPERT OPINION

GLP-1Ragonists offer a complementary and enhanced therapeutic value to other drugs used to treat PD. Moreover, the use of the dual- or tri-agonist GLP-1-based mimetics may provide combinatory effects that are even more powerful than GLP-1R agonism alone. We advocate for further investigations into the repurposing of GLP-1R agonists and the development of classes of multi-agonists for PD treatment.

Semaglutide is Neuroprotective and Reduces α-Synuclein Levels in the Chronic MPTP Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurological motor control disorder. A key feature is the loss of midbrain dopaminergic neurons and the accumulation of aggregated alpha-synuclein (α-syn). No current treatment is on the market that slows or halts disease progression. Previous studies have shown that glucagon-like peptide-1 (GLP-1) receptor agonists have neuroprotective effects in animal models of PD. In addition, in a phase II clinical trial, the GLP-1 receptor agonist exendin-4 has shown good protective effects in PD patients. In the present study, we have investigated the neuroprotective effects of the GLP-1 analogues semaglutide (25 nmol/kg ip. once every two days for 30 days) and liraglutide (25 nmol/kg ip. once daily for 30 days) in the chronic MPTP mouse model of PD. Both drugs are currently on the market as a treatment for Type II diabetes. Our results show that both semaglutide and liraglutide improved MPTP-induced motor impairments. In addition, both drugs rescued the decrease of tyrosine hydroxylase (TH) levels, reduced the accumulation of α-syn, alleviated the chronic inflammation response in the brain, reduced lipid peroxidation, and inhibited the mitochondrial mitophagy signaling pathway, and furthermore increased expression of the key growth factor GDNF that protects dopaminergic neurons in the substantia nigra (SN) and striatum. Moreover, the long- acting GLP-1 analogue semaglutide was more potent compared with once daily liraglutide in most parameters measured in this study. Our results demonstrate that semaglutide may be a promising treatment for PD. A clinical trial testing semaglutide in PD patients will start shortly.

Drug discovery approaches targeting the incretin pathway

Incretin pathway plays an important role in the development of diabetes medications. Interventions in DPP-4 and GLP-1 receptor have shown remarkable efficacy in experimental and clinical studies and imperatively become one of the most promising therapeutic approaches in the T2DM drug discovery pipeline. Herein, we analyzed the actionmechanismsof DPP-4 and GLP-1 receptor targeting the incretin pathway in T2DM treatment. We gave an insight into the structural requirements for the potent DPP-4 inhibitors and revealed a classification of DPP-4 inhibitors by stressing on the binding modes of these ligands to the enzyme. We then reviewed the drug discovery strategies for the development of peptide and non-peptide GLP-1 receptor agonists (GLP-1 RAs). Furthermore, the drug design strategies for DPP-4 inhibitors and GLP-1R agonists were detailed accurately. This review might provide an efficient evidence for the highly potent and selective DPP-4 inhibitors and the GLP-1 RAs, as novel medicines for patients suffering from T2DM.

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.

The glucose-dependent insulinotropic polypeptide signaling axis in the central nervous system

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone released from the epithelium of the upper small intestine. While GIP shares common actions on the pancreatic beta cell with glucagon-like peptide-1 (GLP-1), unlike GLP-1, GIP presents a complex target for the development of diabetes and obesity therapies due to its extra-pancreatic effects on fat mass. Recent pharmacological developments, however, have provided insight into a previously unrecognized role for GIP receptor (GIPR) signaling in regulating appetite. Additionally, GIP-based therapeutics have demonstrated promising neuroprotective properties. Together these observations identify an important central component of the GIP/GIPR signaling axis, and have triggered a resurgence of research interest into the central actions of GIP. In this review, we discuss what is currently known about where GIP may act in the central nervous system (CNS), the characteristics of its target cell populations, and the physiological effects of manipulating the activity Gipr-expressing cells in the brain.