incretins and Neurodegenerative-Diseases

Despite an ever-growing prevalence and increasing economic burden of Alzheimer's disease (AD) and Parkinson's disease (PD), recent advances in drug development have only resulted in minimally effective treatment. In AD, along with amyloid and tau phosphorylation, there is an associated increase in inflammation/glial activation, a decrease in synaptic function, an increase in astrocyte activation, and a state of insulin resistance. In PD, along with α-synuclein accumulation, there is associated inflammation, synaptic dysfunction, dopaminergic neuronal loss, and some data to suggest insulin resistance. Therapeutic strategies for neurodegenerative disorders have commonly targeted individual pathological processes. An effective treatment might require either utilization of multiple drugs which target the individual pathological processes which underlie the neurodegenerative disease or the use of a single agent which could influence multiple pathological processes. Insulin and incretins are compounds with multiple effects on neurodegenerative processes. Preclinical studies have demonstrated that GLP-1 receptor agonists reduce neuroinflammation, reduce tau phosphorylation, reduce amyloid deposition, increase synaptic function, and improve memory formation. Incretin mimetics may act through the restoration of insulin signaling pathways, inducing further neuroprotective effects. Currently, phase 2 and phase 3 trials are underway in AD and PD populations. Here, we provide a comprehensive review of the therapeutic potential of incretin mimetics and insulin in AD and PD.

Topics: Alzheimer Disease; Humans; Incretins; Inflammation; Insulin; Insulin Resistance; Neurodegenerative Diseases; Parkinson 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

Topics: Alzheimer Disease; Diabetes Mellitus, Type 2; Glucagon-Like Peptide-1 Receptor; Humans; Hypoglycemic Agents; Incretins; Inflammation; Insulin; Neurodegenerative Diseases; Neuroprotective Agents; Parkinson Disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most frequent neurodegenerative disorders. Despite their pathophysiological and clinical differences, they share several mechanistic similarities at cellular and sub-cellular levels. The current treatments of AD and PD are only symptomatic, since many clinically-tested drugs failed to prevent or halt their progression. There is now evidence that type 2 diabetes mellitus is among the main risk factors for AD and PD and that the insulin resistance in the brain plays a crucial role in their neuropathological processes. Therefore, insulin nasal administration was suggested for the treatment of AD and PD, both in diabetic and non-diabetic patients. However, the adverse effects of chronic insulin prompted the research of alternative strategies, such as the novel antidiabetic drugs based on the incretin hormones glucagon-like protein-1 (GLP-1) and glucose-dependent insulinotropic Peptide (GIP). The rapid inactivation of these incretins by dipeptidyl-peptidase IV (DPP-IV) suggested the development of DPP-IV-resistant GLP-1 receptor agonists (GLP-1Ras), the recent dual GLP-1/GIP receptor agonists and the DPP-IV inhibitors (DPP-IVis). This review will first describe the experimental, pathophysiological and clinical approach for AD and PD treatment with insulin. Afterwards, the main pharmacologic properties of GLP-1Ras and of DPP-IVis will be discussed, detailing their ability to cross the BBB and get access to the brain for GLP-1Ras, and the novel strategies for BBB crossing as regards DPP-IVis. Emphasis will be placed on the main findings obtained from AD and PD experimental models about the neuroprotective effects of these drugs. For AD, the improvement of learning and memory exerted by incretin-based drugs correlated with reduction of chronic inflammation, brain Aβ plaque, tau hyperphosphorylation, protection of mitochondria, enhancement of energy utilisation. For PD, both GLP-1Ras and of DPP-IVis reversed the nigrostriatal dopaminergic cell loss progression, restored dopamine synthesis, exerted anti-inflammatory activity and improved motor functions. Finally, the encouraging results of the first clinical trials on AD and PD patients and the adverse effects of GLP-1Ras and DPP-IVis will be discussed, highlighting how the above-mentioned neuroprotective effects have a great potential to be translated into clinical settings and that the incretin-based approach represents novel promising strategy for the

Topics: Diabetes Mellitus, Type 2; Dipeptidyl-Peptidase IV Inhibitors; Gastric Inhibitory Polypeptide; Glucagon-Like Peptide 1; Humans; Hypoglycemic Agents; Incretins; Insulin; Neurodegenerative Diseases; Neuroprotective Agents

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

Topics: Alzheimer Disease; Diabetes Mellitus, Type 2; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Humans; Incretins; Neurodegenerative Diseases; Neuroinflammatory Diseases; Parkinson Disease

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.

Topics: Aged; Dipeptidyl-Peptidase IV Inhibitors; Humans; Incretins; Neurodegenerative Diseases; Weight Loss

Incretin contains two peptides named glucagon-like peptide-1(GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Drug therapy using incretin has become a new strategy for diabetic treatments due to its significant effects on improving insulin receptors and promoting insulinotropic secretion. Considering the fact that diabetes millitus is a key risk factor for almost all age-related diseases, the extensive protective roles of incretin in chronic diseases have received great attention. Based on the evidence from animal experiments, where incretin can protect against the pathophysiological processes of neurodegenerative diseases, clinical trials for the treatments of Alzheimer's disease (AD) and Parkinson's disease (PD) patients are currently ongoing. Moreover, the protective effect of incretin on heart has been observed in cardiac myocytes, smooth muscle cells and endothelial cells of vessels. Meanwhile, incretin can also inhibit the proliferation of aortic vascular smooth muscle cells, which can induce atherosclerogenesis. Incretin is also beneficial for diabetic microvascular complications, including nephropathy, retinopathy and gastric ulcer, as well as the hepatic-related diseases such as NAFLD and NASH. Besides, the anti-tumor properties of incretin have been proven in diverse cancers including ovarian cancer, pancreas cancer, prostate cancer and breast cancer.

Topics: Aging; Animals; Cardiovascular Diseases; Diabetes Mellitus; Humans; Incretins; Liver Diseases; Neoplasms; Neurodegenerative Diseases; Stomach Ulcer

Incretin hormones, notably glucagon-like peptide-1 (GLP-1), are gluco-regulatory hormones with pleiotropic effects also in the central nervous system. Apart from a local production of GLP-1, systemic administration of the hormone has been shown to influence a number of cerebral pathologies, including neuroinflammation. Given the brains massive dependence on glucose as its major fuel, we here review the mechanistics of cerebral glucose transport and metabolism, focusing on the deleterious effects of both hypo- and hyperglycaemia. GLP-1, when administered as long-acting analogues or intravenously, appears to decrease transport of glucose in normoglycaemic conditions, without affecting the total cerebral glucose content. During hypoglycaemia this effect seems abated, whereas during hyperglycaemia GLP-1 regulates cerebral glucose metabolism towards stable levels resembling normoglycaemia. In Alzheimer's disease, a 6-month intervention with GLP-1 maintained cerebral glucose levels at baseline levels, contrasting the decline otherwise seen in Alzheimer's. Kinetic studies suggest blood-brain barrier (BBB) glucose transport as the key player in GLP-1 mediated effects on cerebral glucose metabolism. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Topics: Animals; Brain; Glucose; Humans; Incretins; Neurodegenerative Diseases

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

Topics: Animals; Blood Glucose; Brain; Cognition; Diabetes Mellitus, Type 2; Disease Models, Animal; Glucagon-Like Peptide-1 Receptor; Humans; Incretins; Metformin; Neurodegenerative Diseases; Neuroprotective Agents; Oxidative Stress

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.

Topics: Animals; Drug Development; Gastric Inhibitory Polypeptide; Glucagon-Like Peptide 1; Humans; Incretins; Neurodegenerative Diseases; Receptors, Gastrointestinal Hormone; Signal Transduction

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.

Topics: Animals; Diabetes Mellitus, Type 2; Exenatide; Gastric Inhibitory Polypeptide; Humans; Hypoglycemic Agents; Incretins; Neurodegenerative Diseases; Peptides; Venoms