Glucagon-like peptide-1 decreases endogenous amyloid-beta peptide (Abeta) levels and protects hippocampal neurons from death induced by Abeta and iron

Exploring the Potential of Therapeutic Agents Targeted towards Mitigating the Events Associated with Amyloid-β Cascade in Alzheimer's Disease

One of the most commonly occurring neurodegenerative disorders, Alzheimer's disease (AD), encompasses the loss of cognitive and memory potential, impaired learning, dementia and behavioral defects, and has been prevalent since the 1900s. The accelerating occurrence of AD is expected to reach 65.7 million by 2030. The disease results in neural atrophy and disrupted inter-neuronal connections. Amongst multiple AD pathogenesis hypotheses, the amyloid beta (Aβ) cascade is the most relevant and accepted form of the hypothesis, which suggests that Aβ monomers are formed as a result of the cleavage of amyloid precursor protein (APP), followed by the conversion of these monomers to toxic oligomers, which in turn develop β-sheets, fibrils and plaques. The review targets the events in the amyloid hypothesis and elaborates suitable therapeutic agents that function by hindering the steps of plaque formation and lowering Aβ levels in the brain. The authors discuss treatment possibilities, including the inhibition of β- and γ-secretase-mediated enzymatic cleavage of APP, the immune response generating active immunotherapy and passive immunotherapeutic approaches targeting monoclonal antibodies towards Aβ aggregates, the removal of amyloid aggregates by the activation of enzymatic pathways or the regulation of Aβ circulation, glucagon-like peptide-1 (GLP-1)-mediated curbed accumulation and the neurotoxic potential of Aβ aggregates, bapineuzumab-mediated vascular permeability alterations, statin-mediated Aβ peptide degradation, the potential role of ibuprofen and the significance of natural drugs and dyes in hindering the amyloid cascade events. Thus, the authors aim to highlight the treatment perspective, targeting the amyloid hypothesis, while simultaneously emphasizing the need to conduct further investigations, in order to provide an opportunity to neurologists to develop novel and reliable treatment therapies for the retardation of AD progression.

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

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

Repurposing GLP1 agonists for neurodegenerative diseases

There is a large unmet medical need to find disease modifying therapies against neurodegenerative diseases. This review summarizes data indicating that insulin resistance occurs in neurodegeneration and strategies to normalize insulin sensitivity in neurons may provide neuroprotective actions. In particular, recent preclinical and clinical studies in Parkinson's disease and Alzheimer's disease have indicated that glucagon-like peptide 1 (GLP1) agonism and dipeptidyl peptidase-4 inhibition may exert neuroprotection. Mechanistic insights from these studies and future directions for drug development against neurodegeneration based on GLP1 agonism are discussed.

Exenatide, a GLP-1 analog, has healing effects on LPS-induced autism model: Inflammation, oxidative stress, gliosis, cerebral GABA, and serotonin interactions

Previous studies have established anti-inflammatory, antioxidant, and neuroprotective effects of Exenatide in the central nervous system. Since these mechanisms are thought to have important roles in the pathophysiology of autism, we hypothesized that Exenatide may have healing effects in autism. We tested this hypothesis by examining the effects of Exenatide in an experimental autism model created by lipopolysaccharide (LPS) exposure in the womb, with behavioral tests, histopathological examinations, and biochemical measurements. The autism model was created by administration of LPS (i.p) to pregnant rats on the 10th day of their pregnancy at a dose of 100 µg/kg. On postnatal 21st day, a total of four groups were formed from offspring with regard to sex distribution and treatment. After a 45-day treatment, behavioral analysis tests were performed on rats. Subsequently, the rats were sacrificed and biochemical analysis [superoxide dismutase, tumor necrotizing factor alpha, nerve growth factor, 5-hydroxyindoleacetic acid, and glutamic acid decarboxylase-67] and histopathological analysis were performed. On the 10th day of the intrauterine period, LPS exposure was found to disrupt behavioral findings, increase inflammation and hippocampal gliosis, and decrease 5-HIAA, GAD-67, and NGF, especially in male rats. However, among the rats exposed to LPS in the intrauterine period, recipients of Exenatide demonstrated significant amelioration of findings. Exenatide therapy shows positive effects on behavioral disorders in an LPS-induced autism model. This agent probably exerts its effects by suppressing inflammation and oxidative stress and reducing hippocampal gliosis. In addition, Exenatide has also been shown to positively affect cerebral serotonergic and GABAergic effects.

Insulin deficiency, but not resistance, exaggerates cognitive deficits in transgenic mice expressing human amyloid and tau proteins. Reversal by Exendin-4 treatment

Epidemiological studies have pointed at diabetes as a risk factor for Alzheimer's disease (AD) and this has been supported by several studies in animal models of both type 1 and type 2 diabetes. However, side-by-side comparison of the two types of diabetes is limited. We investigated the role of insulin deficiency and insulin resistance in the development of memory impairments and the effect of Exendin-4 (Ex4) treatment in a mouse model of AD. Three-4-month-old female wild type (WT) mice and mice overexpressing human tau and amyloid precursor protein (TAPP) were injected with streptozotocin (STZ) or fed a high-fat diet (HFD). A second study was performed in TAPP-STZ mice treated with Ex4, a long-lasting analog of GLP-1. Plasma and brain were collected at study termination for ELISA, Western blot, and immunohistochemistry analysis. Learning and memory deficits were impaired in TAPP transgenic mice compared with WT mice at the end of the study. Deficits were exaggerated by insulin deficiency in TAPP mice but 12 weeks of insulin resistance did not affect memory performances in either WT or TAPP mice. Levels of phosphorylated tau were increased in the brain of WT-STZ and TAPP-STZ mice but not in the brain of WT or TAPP mice on HFD. In the TAPP-STZ mice, treatment with Ex4 initiated after established cognitive deficits ameliorated learning, but not memory, impairments. This was accompanied by the reduction of amyloid β and phosphorylated tau expression. Theses studies support the role of Ex4 in AD, independently from its actions on diabetes.

Can dipeptidyl peptidase-4 inhibitors treat cognitive disorders?

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

Recent advances in understanding the role of glucagon-like peptide 1

The discovery that glucagon-like peptide 1 (GLP-1) mediates a significant proportion of the incretin effect during the postprandial period and the subsequent observation that GLP-1 bioactivity is retained in type 2 diabetes (T2D) led to new therapeutic strategies being developed for T2D treatment based on GLP-1 action. Although owing to its short half-life exogenous GLP-1 has no use therapeutically, GLP-1 mimetics, which have a much longer half-life than native GLP-1, have proven to be effective for T2D treatment since they prolong the incretin effect in patients. These GLP-1 mimetics are a desirable therapeutic option for T2D since they do not provoke hypoglycaemia or weight gain and have simple modes of administration and monitoring. Additionally, over more recent years, GLP-1 action has been found to mediate systemic physiological beneficial effects and this has high clinical relevance due to the post-diagnosis complications of T2D. Indeed, recent studies have found that certain GLP-1 analogue therapies improve the cardiovascular outcomes for people with diabetes. Furthermore, GLP-1-based therapies may enable new therapeutic strategies for diseases that can also arise independently of the clinical manifestation of T2D, such as dementia and Parkinson's disease. GLP-1 functions by binding to its receptor (GLP-1R), which expresses mainly in pancreatic islet beta cells. A better understanding of the mechanisms and signalling pathways by which acute and chronic GLP-1R activation alleviates disease phenotypes and induces desirable physiological responses during healthy conditions will likely lead to the development of new therapeutic GLP-1 mimetic-based therapies, which improve prognosis to a greater extent than current therapies for an array of diseases.

Plasma N-Acetylaspartate Is Related to Age, Obesity, and Glucose Metabolism: Effects of Antidiabetic Treatment and Bariatric Surgery

Background: N-acetylaspartate (NAA) is synthesized only by neurons and is involved in neuronal metabolism and axonal myelination. NAA is the strongest signal on brain magnetic resonance spectroscopy, and its concentration have been associated with cognitive dysfunction in neurodegenerative diseases, obesity, and type 2 diabetes (T2D). Materials and Methods: We explored the impact of obesity and T2D on circulating NAA as well as the impact of bariatric surgery and antidiabetic treatments. We developed an LC-MS method for the accurate measurements of fasting plasma NAA levels in 505 subjects (156 subjects with normal glucose tolerance, 24 subjects with impaired glucose tolerance, and 325 patients with T2D) to examine the associations of NAA with obesity and dysglycemia. To validate cross-sectional findings, plasma NAA was measured 6 months after Roux-en-Y Gastric Bypass (RYGB) in 55 morbidly obese subjects, and after 1 year of antidiabetic treatment (with dapagliflozin, exenatide, or dapagliflozin plus exenatide) in 192 T2D patients. Results: In the whole population, NAA was associated with age (r = 0.31, p <0.0001) and BMI (r = -0.20, p <0.0001). Independently of age and BMI, NAA was reciprocally related to HbA1c and fasting plasma glucose (partial r = -0.13, both p = 0.01). Surgically-induced weight loss raised NAA (by 18 nmol/L on average, p <0.02). Glucose lowering treatment increased NAA in proportion to the drop in HbA1c (r = 0.31, p <0.0001) regardless of the agent used. Conclusions: Circulating NAA concentrations are modulated by age, obesity, and glycemic control. Whether they may mark for the corresponding metabolic effects on brain function remains to be established by joint measurements of spectroscopic signal and cognitive function.

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

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

Current and future clinical utilities of Parkinson's disease and dementia biomarkers: can they help us conquer the disease?

Introduction: Biomarkers for Parkinson's disease and Alzheimer's disease are essential, not only for disease detection, but also provide insight into potential disease relationships leading to better detection and therapy. As metabolic disease is known to increase neurodegeneration risk, such mechanisms may reveal such novel targets for PD and AD. Moreover, metabolic disease, including insulin resistance, offer novel biomarker and therapeutic targets for neurodegeneration, including glucagon-like-peptide-1, dipeptidyl peptidase-4 and adiponectin. Areas covered: The authors reviewed PubMed-listed research articles, including ours, on a number of putative PD, AD and neurodegenerative disease targets of interest, focusing on the relevance of metabolic syndrome and insulin resistance mechanisms, especially type II diabetes, to PD and AD. We highlighted various issues surrounding the current state of knowledge and propose avenues for future development. Expert opinion: Biomarkers for PD and AD are indispensable for disease diagnosis, prognostication and tracking disease severity, especially for clinical therapy trials. Although no validated PD biomarkers exist, their potential utility has generated tremendous interest. Combining insulin-resistance biomarkers with other core biomarkers or using them to predict non-motor symptoms of PD may be clinically useful. Collectively, although still unclear, potential biomarkers and therapies can aid in shedding new light on novel aspects of both PD and AD.

Exendin-4 attenuates brain mitochondrial toxicity through PI3K/Akt-dependent pathway in amyloid beta (1-42)-induced cognitive deficit rats

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory loss, disorientation and gradual deterioration of intellectual ability. In the pharmacotherapy of AD, the mitochondrial protective activity of Exendin-4 in experimental studies is yet to be established though its effectiveness is demonstrated in these patients. Therefore, the mitochondria protective activity of Exendin-4 (5 μg/kg, i.p.) was investigated in hippocampus and pre-frontal cortex (PFC) of AD-like animals. The amyloid beta (Aβ) was injected through bilateral intracerebroventricular route into lateral ventricles to induce AD-like manifestations in the male rats. Exendin-4 significantly attenuated Aβ-induced memory-deficits in the Morris water maze and Y-maze test protocols. Exendin-4 significantly decreased Aβ-induced increase in the level of Aβ in both brain regions. Exendin-4 significantly increased Aβ-induced decrease in acetylcholine level and activity of cholineacetyl transferase in all brain regions. Moreover, Exendin-4 significantly decreased Aβ-induced increase in the activity of acetylcholinestrase in both the brain regions. E4 significantly increased Aβ-induced decrease in mitochondrial function, integrity, respiratory control rate and ADP/O in all brain regions. Further, Exendin-4 significantly decreased Aβ-induced increase in the mitochondrial complex enzyme-I, IV and V activities in all brain regions. Furthermore, Exendin-4 significantly increased Aβ-induced decrease in the level of phosphorylated Akt and the ratio of phosphorylated Akt to Akt in both brain regions. However, LY294002 diminished the therapeutic effects of Exendin-4 on behavioral, biochemical and molecular observations in AD-like animals. Pearson's analysis showed that the attributes of mitochondrial dysfunction (MMP and RCR) exhibited significant correlation to the loss in memory formation, level of Aβ and cholinergic dysfunction in these animals. Thus, it can be speculated that Exendin-4 may mitigate AD-like manifestations including mitochondrial toxicity perhaps through PI3K/Akt-mediated pathway in the experimental animals. Hence, Exendin-4 could be a potential therapeutic alternative candidate in the management of AD.

Incretin Mimetics as Rational Candidates for the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is becoming an increasing public health issue. With an annually estimated 1.7 million TBIs in the United States (U.S) and nearly 70 million worldwide, the injury, isolated or compounded with others, is a major cause of short- and long-term disability and mortality. This, along with no specific treatment, has made exploration of TBI therapies a priority of the health system. Age and sex differences create a spectrum of vulnerability to TBI, with highest prevalence among younger and older populations. Increased public interest in the long-term effects and prevention of TBI have recently reached peaks, with media attention bringing heightened awareness to sport and war related head injuries. Along with short-term issues, TBI can increase the likelihood for development of long-term neurodegenerative disorders. A growing body of literature supports the use of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and glucagon (Gcg) receptor (R) agonists, along with unimolecular combinations of these therapies, for their potent neurotrophic/neuroprotective activities across a variety of cellular and animal models of chronic neurodegenerative diseases (Alzheimer's and Parkinson's diseases) and acute cerebrovascular disorders (stroke). Mild or moderate TBI shares many of the hallmarks of these conditions; recent work provides evidence that use of these compounds is an effective strategy for its treatment. Safety and efficacy of many incretin-based therapies (GLP-1 and GIP) have been demonstrated in humans for the treatment of type 2 diabetes mellitus (T2DM), making these compounds ideal for rapid evaluation in clinical trials of mild and moderate TBI.

Evaluating the effects of the novel GLP-1 analogue liraglutide in Alzheimer's disease: study protocol for a randomised controlled trial (ELAD study)

BACKGROUND

Liraglutide is a glucagon-like peptide-1 (GLP-1) analogue currently approved for type 2 diabetes and obesity. Preclinical evidence in transgenic models of Alzheimer's disease suggests that liraglutide exerts neuroprotective effects by reducing amyloid oligomers, normalising synaptic plasticity and cerebral glucose uptake, and increasing the proliferation of neuronal progenitor cells. The primary objective of the study is to evaluate the change in cerebral glucose metabolic rate after 12 months of treatment with liraglutide in participants with Alzheimer's disease compared to those who are receiving placebo.

METHODS/DESIGN

ELAD is a 12-month, multi-centre, randomised, double-blind, placebo-controlled, phase IIb trial of liraglutide in participants with mild Alzheimer's dementia. A total of 206 participants will be randomised to receive either liraglutide or placebo as a daily injection for a year. The primary outcome will be the change in cerebral glucose metabolic rate in the cortical regions (hippocampus, medial temporal lobe, and posterior cingulate) from baseline to follow-up in the treatment group compared with the placebo group. The key secondary outcomes are the change from baseline to 12 months in z scores for clinical and cognitive measures (Alzheimer's Disease Assessment Scale-Cognitive Subscale and Executive domain scores of the Neuropsychological Test Battery, Clinical Dementia Rating Sum of Boxes, and Alzheimer's Disease Cooperative Study-Activities of Daily Living) and the incidence and severity of treatment-emergent adverse events or clinically important changes in safety assessments. Other secondary outcomes are 12-month change in magnetic resonance imaging volume, diffusion tensor imaging parameters, reduction in microglial activation in a subgroup of participants, reduction in tau formation and change in amyloid levels in a subgroup of participants measured by tau and amyloid imaging, and changes in composite scores using support machine vector analysis in the treatment group compared with the placebo group.

DISCUSSION

Alzheimer's disease is a leading cause of morbidity worldwide. As available treatments are only symptomatic, the search for disease-modifying therapies is a priority. If the ELAD trial is successful, liraglutide and GLP-1 analogues will represent an important class of compounds to be further evaluated in clinical trials for Alzheimer's treatment.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01843075 . Registration 30 April 2013.

GLP-1's role in neuroprotection: a systematic review

Glucagon-like peptide 1 (GLP-1) is a target for treatment of diabetes; however, its function in the brain is not well studied. In this systematic review, we aimed to analyze the neuroprotective role of GLP-1 and its defined mechanisms. Methods: We searched 'Web of Science' and 'Pubmed' to identify relevant studies using GLP-1 as the keyword. Two hundred and eighty-nine clinical and preclinical studies have been included. Data have been presented by grouping neurodegenerative, neurovascular and specific cell culture models. Results: Recent literature shows that GLP-1 and its agonists, DPP-4 inhibitors and combined GLP-1/GIP molecules are effective in partially or fully reversing the effects of neurotoxic compounds, neurovascular complications of diabetes, neuropathological changes related with Alzheimer's disease, Parkinson's disease or vascular occlusion. Possible mechanisms that provide neuroprotection are enhancing the viability of the neurons and restoring neurite outgrowth by increased neurotrophic factors, increasing subventricular zone progenitor cells, decreasing apoptosis, decreasing the level of pro-inflammatory factors, and strengthening blood-brain barrier. Conclusion: Based on the preclinical studies, GLP-1 modifying agents are promising targets for neuroprotection. On the other hand, the number of clinical studies that investigate GLP-1 as a treatment is low and further clinical trials are needed for a benchside to bedside translation of recent findings.

Pharmacologic normalization of pathogenic dosage underlying genetic diseases: an overview of the literature and path forward

Most monogenic disorders are caused by a pathologic deficit or excess of a single transcript and/or protein. Given that small molecules, including drugs, can affect levels of mRNA and protein, the pharmacologic normalization of such pathogenic dosage represents a possible therapeutic approach for such conditions. Here, we review the literature exploring pharmacologic modulation of mRNA and/or protein levels for disorders with paralogous modifier genes, for haploinsufficient disorders (insufficient gene-product), as well as toxic gain-of-function disorders (surplus or pathologic gene-product). We also discuss challenges facing the development of rare disease therapy by pharmacologic modulation of mRNA and protein. Finally, we lay out guiding principles for selection of disorders which may be amenable to this approach.

Fructooligosaccharides Ameliorating Cognitive Deficits and Neurodegeneration in APP/PS1 Transgenic Mice through Modulating Gut Microbiota

Alzheimer's disease (AD) is closely related to gut microbial alteration. Prebiotic fructooligosaccharides (FOS) play major roles by regulating gut microbiota. The present study aimed to explore the effect and mechanism of FOS protection against AD via regulating gut microbiota. Male Apse/PSEN 1dE9 (APP/PS1) transgenic (Tg) mice were administrated with FOS for 6 weeks. Cognitive deficits and amyloid deposition were evaluated. The levels of synaptic plasticity markers including postsynaptic density protein 95 (PSD-95) and synapsin I, as well as phosphorylation of c-Jun N-terminal kinase (JNK), were determined. The intestinal microbial constituent was detected by 16S rRNA sequencing. Moreover, the levels of glucagon-like peptide-1 (GLP-1) in the gut and GLP-1 receptor (GLP-1R) in the brain were measured. The results indicated that FOS treatment ameliorated cognitive deficits and pathological changes in the Tg mice. FOS significantly upregulated the expression levels of synapsin I and PSD-95, as well as decreased phosphorylated level of JNK. The sequencing results showed that FOS reversed the altered microbial composition. Furthermore, FOS increased the level of GLP-1 and decreased the level of GLP-1R in the Tg mice. These findings indicated that FOS exerted beneficial effects against AD via regulating the gut microbiota-GLP-1/GLP-1R pathway.

Neuroprotective Actions of Glucagon-Like Peptide-1 (GLP-1) Analogues in Alzheimer's and Parkinson's Diseases

The current absence of effective treatments for Alzheimer's disease (AD) and Parkinson's disease (PD) reflects an incomplete knowledge of the underlying disease processes. Considerable efforts have been made to investigate the central pathological features of these diseases, giving rise to numerous attempts to develop compounds that interfere with such features. However, further characterization of the molecular targets within the interconnected AD and PD pathways is still required. Impaired brain insulin signaling has emerged as a feature that contributes to neuronal dysfunction in both AD and PD, leading to strategies aiming at restoring this pathway in the brain. Long-acting glucagon-like peptide-1 (GLP-1) analogues marketed for treatment of type 2 diabetes mellitus have been tested and have shown encouraging protective actions in experimental models of AD and PD as well as in initial clinical trials. We review studies revealing the neuroprotective actions of GLP-1 analogues in pre-clinical models of AD and PD and promising results from recent clinical trials.

Dulaglutide ameliorates STZ induced AD-like impairment of learning and memory ability by modulating hyperphosphorylation of tau and NFs through GSK3β

Dulaglutide, a novel long-acting glucagon-like peptide 1 (GLP-1) receptor agonist, is an incretin mimetic approved for type 2 diabetes mellitus (T2DM) treatment. Alzheimer's disease (AD) is called type 3 diabetes. The aim of this study is to explore the effects of dulaglutide on the learning and memory impairment in AD mice induced by injection of streptozocin (STZ) via intracerebroventricularly (i.c.v.). 32 male C57/BL6 mice were randomly divided into four groups: control group (CON); AD model group (STZ); dulaglutide treated (Dul); dulaglutide and exendin(9-39) (Ex). Western blotting was used to detect the levels of phosphorylated tau, neurofilament (NFs) proteins and phosphorylated PI3K/AKT/GSK3β signaling pathway. Morris water maze (MWM) test was used to assess the spatial learning and memory ability. The results displayed that the hyperphosphorylation of tau and NFs were increased in the STZ and Ex groups compared to the control and Dul groups. Dulaglutide also significantly shortened the escape latency and increased the number of hidden platform crossings in MWM test. The effects of dulaglutide on decreasing the hyperphosphorylation of tau and NFs proteins through improving the PI3K/AKT/GSK3β signaling pathway may be related to its protective effects on impairment of AD-like learning and memory.

Liraglutide Ameliorates β-Amyloid Deposits and Secondary Damage in the Ipsilateral Thalamus and Sensory Deficits After Focal Cerebral Infarction in Rats

Focal cerebral infarction causes β-amyloid (Aβ) deposition and secondary neuronal degeneration in the ipsilateral thalamus. Thalamus is the subcortical center of sensory, the damage of thalamus could cause sensory deficits. The present study aimed to investigate the protective effects of liraglutide, a long-acting glucagon-like peptide-1 (GLP)-1 receptor agonist, on Aβ deposits and secondary damage in the ipsilateral thalamus after focal cerebral infarction. In addition, this study was conducted to investigate whether liraglutide could improve sensory function after focal cerebral infarction. Forty-two male Sprague–Dawley rats were subjected to distal middle cerebral artery occlusion (MCAO) and then randomly divided into liraglutide and vehicle groups, and 14 sham-operated rats as control. At 1 h after MCAO, rats in the liraglutide and vehicle groups were subcutaneously injected with liraglutide (100 μg/kg/d) and isopyknic vehicle, respectively, once a day for 7 days. Sensory function and secondary thalamic damage were assessed using adhesive-removal test and Nissl staining and immunostaining, respectively, at 7 days after MCAO. Terminal deoxynucleotidyl transferase 2’-deoxyuridine 5’-triphosphate nick end labeling and Western blot were used to detect neuronal apoptosis. The results showed that liraglutide improved sensory deficit compared to the controls. Liraglutide treatment significantly reduced Aβ deposition compared with the vehicle treatment. Liraglutide treatment decreased the neuronal loss, astroglial and microglial activation, and apoptosis compared with the vehicle treatment. Liraglutide significantly down-regulated the expression of Bcl-2 and up-regulated that of Bax in the ipsilateral thalamus compared with the vehicle group. These results suggest that liraglutide ameliorates the deposition of Aβ and secondary damage in the ipsilateral thalamus, potentially contributing to improve sensory deficit after focal cerebral infarction.

Pleiotropic Effects of GLP-1 and Analogs on Cell Signaling, Metabolism, and Function

The incretin hormone Glucagon-Like Peptide-1 (GLP-1) is best known for its "incretin effect" in restoring glucose homeostasis in diabetics, however, it is now apparent that it has a broader range of physiological effects in the body. Both in vitro and in vivo studies have demonstrated that GLP-1 mimetics alleviate endoplasmic reticulum stress, regulate autophagy, promote metabolic reprogramming, stimulate anti-inflammatory signaling, alter gene expression, and influence neuroprotective pathways. A substantial body of evidence has accumulated with respect to how GLP-1 and its analogs act to restore and maintain normal cellular functions. These findings have prompted several clinical trials which have reported GLP-1 analogs improve cardiac function, restore lung function and reduce mortality in patients with obstructive lung disease, influence blood pressure and lipid storage, and even prevent synaptic loss and neurodegeneration. Mechanistically, GLP-1 elicits its effects via acute elevation in cAMP levels, and subsequent protein kinase(s) activation, pathways well-defined in pancreatic β-cells which stimulate insulin secretion in conjunction with elevated Ca2+ and ATP. More recently, new studies have shed light on additional downstream pathways stimulated by chronic GLP-1 exposure, findings which have direct relevance to our understanding of the potential therapeutic effects of longer lasting analogs recently developed for clinical use. In this review, we provide a comprehensive description of the diverse roles for GLP-1 across multiple tissues, describe downstream pathways stimulated by acute and chronic exposure, and discuss novel pleiotropic applications of GLP-1 mimetics in the treatment of human disease.

Exendin-4 promotes actin cytoskeleton rearrangement and protects cells from Nogo-A-Δ20 mediated spreading inhibition and growth cone collapse by down-regulating RhoA expression and activation via the PI3K pathway

Exendin-4 is a protein of the GLP-1 family currently used to treat diabetes. Recently, a greater number of biological properties have been associated with the GLP-1 family. Our data shows that exendin-4 treatment significantly increases the cytoskeleton rearrangement, which leads to an increasingly differentiated phenotype and reduced cell migration. We also found that exendin-4 could prevent SH-SY5Y and PC12 cells from Nogo-A-Δ20 mediated spreading inhibition and neurite collapse. Western blot analysis indicated that exendin-4 treatment both reduced the expression and activation of RhoA via the PI3K signaling pathway. These data suggest that exendin-4 may protect nerve regeneration by preventing the inhibition of Nogo-A via down-regulating RhoA expression and activation.

Aging and Alzheimer's disease: Comparison and associations from molecular to system level

Alzheimer's disease is the most prevalent cause of dementia, which is defined by the combined presence of amyloid and tau, but researchers are gradually moving away from the simple assumption of linear causality proposed by the original amyloid hypothesis. Aging is the main risk factor for Alzheimer's disease that cannot be explained by amyloid hypothesis. To evaluate how aging and Alzheimer's disease are intrinsically interwoven with each other, we review and summarize evidence from molecular, cellular, and system level. In particular, we focus on study designs, treatments, or interventions in Alzheimer's disease that could also be insightful in aging and vice versa.

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

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

Apelin, a promising target for Alzheimer disease prevention and treatment

Alzheimer's disease (AD) is a progressive neurodegenerative disease with high outbreak rates. It is estimated that about 35 million individuals around the world suffered from dementia in 2010. AD is expected to increase twofold every 20 years and, by 2030, approximately 65 million people could suffer from this illness. AD is determined clinically by a cognitive impairment and pathologically by the production of amyloid beta (Aβ), neurofibrillary tangles, toxic free radicals and inflammatory mediators in the brain. There is still no treatment to cure or even alter the progressive course of this disease; however, many new therapies are being investigated and are at various stages of clinical trials. Neuropeptides are signaling molecules used by neurons to communicate with each other. One of the important neuropeptides is apelin, which can be isolated from bovine stomach. Apelin and its receptor APJ have been shown to broadly disseminate in the neurons and oligodendrocytes of the central nervous system. Apelin-13 is known to be the predominant neuropeptide in neuroprotection. It is involved in the processes of memory and learning as well as the prevention of neuronal damage. Studies have shown that apelin can directly or indirectly prevent the production of Aβ and reduce its amounts by increasing its degradation. Phosphorylation and accumulation of tau protein may also be inhibited by apelin. Apelin is considered as an anti-inflammatory agent by preventing the production of inflammatory mediators such as interleukin-1β and tumor necrosis factor alpha. It has been shown that in vivo and in vitro anti-apoptotic effects of apelin have prevented the death of neurons. In this review, we describe the various functions of apelin associated with AD and present an integrated overview of recent findings that, in general, recommend apelin as a promising therapeutic agent in the treatment of this ailment.

DPP-4 inhibitors: a promising therapeutic approach against Alzheimer's disease

Alzheimer's disease (AD), the commonest cause of dementia in ageing adults, is characterized by gradual cognitive impairment and severe functional disability. Key pathophysiological hallmarks involve amyloid-β (Aβ) accumulation, tau hyper-phosphorylation and neuronal loss. Despite extensive basic and clinical investigations, the etiology of the disease remains elusive, although several risk factors have been associated with its development. Current pharmacotherapies including achetylocholinesterase inhibitors and memantine fail to halt disease progression. Interestingly, type 2 diabetes mellitus (T2DM) and AD share several common characteristics, including Aβ deposition, insulin resistance, degeneration, mitochondrial dysfunction, oxidative stress and excessive inflammation. Recent experimental and clinical evidence indicates that dipeptidyl peptidase-4 (DPP-4) inhibitors, being currently used for T2DM therapy, may also prove effective for AD treatment. They may specifically suppress Aβ accumulation, tau hyper-phosphorylation, neuroinflammation, mitochondrial dysfunction and reactive oxygen species (ROS) formation, resulting in the inhibition of cognitive impairment. In this review, we discuss the encouraging current data regarding the molecular and clinical effects of DPP-4 inhibitors in AD, highlighting the need of future studies elucidating their functional role in addressing this incurable disease.

Old Drugs as New Treatments for Neurodegenerative Diseases

Neurodegenerative diseases are increasing in number, given that the general global population is becoming older. They manifest themselves through mechanisms that are not fully understood, in many cases, and impair memory, cognition and movement. Currently, no neurodegenerative disease is curable, and the treatments available only manage the symptoms or halt the progression of the disease. Therefore, there is an urgent need for new treatments for this kind of disease, since the World Health Organization has predicted that neurodegenerative diseases affecting motor function will become the second-most prevalent cause of death in the next 20 years. New therapies can come from three main sources: synthesis, natural products, and existing drugs. This last source is known as drug repurposing, which is the most advantageous, since the drug’s pharmacokinetic and pharmacodynamic profiles are already established, and the investment put into this strategy is not as significant as for the classic development of new drugs. There have been several studies on the potential of old drugs for the most relevant neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Multiple Sclerosis and Amyotrophic Lateral Sclerosis.

Glucagon like peptide-1 (GLP-1) likes Alzheimer's disease

Glucagon-like peptide-1 (GLP-1) is a 30 amino acid long peptide hormone derived from the proglucagon gene and secreted in the distal small intestine when food enters the duodenum. GLP-1 is also produced in the central nervous system (CNS), predominantly in the brainstem, and subsequently transported to a large number of regions in the CNS. Neuronal cells in nucleus tractus solitarius (NTS) can synthesize GLP-1 and extends to hypothalamus, some thalamic and cortical areas. A G protein coupled receptor (GPCR) provides the majority of GLP-1 actions. GLP-1 receptor activation triggers some in vivo signaling pathways. GLP-1 receptor agonists (GLP-1 RA) are used in the treatment diabetes and obesity. GLP-1 stimulates insulin secretion, inhibits glucagon secretion, decreases food intake, reduces appetite, delays gastric emptying, provides weight reduction, and protects β cells from apoptosis. Alzheimer's disease (AD) is the most prevalent form of dementia. It is characterized by cognitive insufficiencies and behavioral changes that impact memory and learning abilities, daily functioning and quality of life. Hyperinsulinemia and insulin resistance, which are known as pathophysiological features of the T2DM, have also been demonstrated to have significant impact on cognitive impairment. It is thought that GLP-1 affects neurological and cognitive functions, as well as its regulatory effect on glucose metabolism. The pathophysiological relationship between GLP-1 and AD is discussed in this review.

Glucose-Dependent Insulinotropic Polypeptide Mitigates 6-OHDA-Induced Behavioral Impairments in Parkinsonian Rats

In the present study, the effectiveness of glucose-dependent insulinotropic polypeptide (GIP) was evaluated by behavioral tests in 6-hydroxydopamine (6-OHDA) hemi-parkinsonian (PD) rats. Pharmacokinetic measurements of GIP were carried out at the same dose studied behaviorally, as well as at a lower dose used previously. GIP was delivered by subcutaneous administration (s.c.) using implanted ALZET micro-osmotic pumps. After two days of pre-treatment, male Sprague Dawley rats received a single unilateral injection of 6-OHDA into the medial forebrain bundle (MFB). The neuroprotective effects of GIP were evaluated by apomorphine-induced contralateral rotations, as well as by locomotor and anxiety-like behaviors in open-field tests. Concentrations of human active and total GIP were measured in plasma during a five-day treatment period by ELISA and were found to be within a clinically translatable range. GIP pretreatment reduced behavioral abnormalities induced by the unilateral nigrostriatal dopamine (DA) lesion produced by 6-OHDA, and thus may be a novel target for PD therapeutic development.

The diabetes drug liraglutide reverses cognitive impairment in mice and attenuates insulin receptor and synaptic pathology in a non-human primate model of Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurological disorder that still lacks an effective treatment, and this has stimulated an intense pursuit of disease-modifying therapeutics. Given the increasingly recognized link between AD and defective brain insulin signaling, we investigated the actions of liraglutide, a glucagon-like peptide-1 (GLP-1) analog marketed for treatment of type 2 diabetes, in experimental models of AD. Insulin receptor pathology is an important feature of AD brains that impairs the neuroprotective actions of central insulin signaling. Here, we show that liraglutide prevented the loss of brain insulin receptors and synapses, and reversed memory impairment induced by AD-linked amyloid-β oligomers (AβOs) in mice. Using hippocampal neuronal cultures, we determined that the mechanism of neuroprotection by liraglutide involves activation of the PKA signaling pathway. Infusion of AβOs into the lateral cerebral ventricle of non-human primates (NHPs) led to marked loss of insulin receptors and synapses in brain regions related to memory. Systemic treatment of NHPs with liraglutide provided partial protection, decreasing AD-related insulin receptor, synaptic, and tau pathology in specific brain regions. Synapse damage and elimination are amongst the earliest known pathological changes and the best correlates of memory impairment in AD. The results illuminate mechanisms of neuroprotection by liraglutide, and indicate that GLP-1 receptor activation may be harnessed to protect brain insulin receptors and synapses in AD. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Cognitive dysfunction and metabolic comorbidities in mood disorders: A repurposing opportunity for glucagon-like peptide 1 receptor agonists?

Major depressive disorder and bipolar disorder are highly prevalent and disabling conditions. Cognition is considered a core domain of their psychopathology and a principle mediator of psychosocial impairment, disproportionately accounting for overall illness-associated costs. There are few interventions with replicated evidence of efficacy in treating cognitive deficits in mood disorders. Evidence also indicates that cognitive deficits are associated with obesity and involve significant impairment across multiple domains. Conversely, weight-loss interventions, such as physical exercise and bariatric surgery, have been shown to beneficially affect cognitive function. This convergent phenomenology suggests that currently available agents that target metabolic systems may also be capable of mitigating deficits in cognitive functions, and are, therefore, candidates for repurposing. The incretin glucagon-like peptide-1 (GLP-1) is a hormone secreted by intestinal epithelial cells. GLP-1 receptors (GLP-1R) are widely expressed in the central nervous system. Activation of GLP-1R leads to facilitation of glucose utilization and antiapoptotic effects in various organs. Pre-clinical trials have demonstrated significant neuroprotective effects of GLP-1, including protection from cell death, promotion of neuronal differentiation and proliferation; and facilitation of long-term potentiation. Liraglutide is a GLP-1R agonist that has been approved for the treatment of type 2 diabetes mellitus and obesity. Convergent preclinical and clinical evidence, including a proof-of-concept pilot study from group, has suggested that liraglutide may improve objective measures of cognitive function in adults with mood disorders. The safety and availability of GLP-1R agonists indicate that they are promising candidates for repurposing, and that they may be viable therapeutic options for mood disorders. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

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

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

Effects of Glucagon-Like Peptide-1 on Oxidative Stress and Nrf2 Signaling

Oxidative cellular damage caused by free radicals is known to contribute to the pathogenesis of various diseases such as cancer, diabetes, and neurodegenerative diseases, as well as to aging. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associated protein1 (Keap1) signaling pathways play an important role in preventing stresses including oxidative and inflammatory stresses. Nrf2 is a master regulator of cellular stress responses, induces the expression of antioxidant and detoxification enzymes, and protects against oxidative stress-induced cell damage. Glucagon-like peptide-1 (GLP-1) is an incretin hormone, which was originally found to increase insulin synthesis and secretion. It is now widely accepted that GLP-1 has multiple functions beyond glucose control in various tissues and organs including brain, kidney, and heart. GLP-1 and GLP-1 receptor agonists are known to be effective in many chronic diseases, including diabetes, via antioxidative mechanisms. In this review, we summarize the current knowledge regarding the role of GLP-1 in the protection against oxidative damage and the activation of the Nrf2 signaling pathway.

DPP4 Inhibitors Can Be a Drug of Choice for Type 3 Diabetes: A Mini Review

As well known to the scientific community, Alzheimer's disease (AD) is an irreversible neurodegenerative disease that ends up with impairment of memory and cognition due to neuronal and synapse loss. Patient's quality of life can be enhanced by targeting neurogenesis as a therapeutic paradigm. Moreover, several research evidences support the concept that AD is a type of metabolic disorder mediated by impairment in brain insulin responsiveness and energy metabolism. Growing evidence suggests that endogenous peptides such as glucagon-like peptide-1 (GLP-1) and stromal-derived factor-1α (SDF-1α) provide neuroprotection across a range of experimental models of AD. So, preserving functional activity of SDF-1α and GLP-1 by dipeptidyl peptidase-4 inhibition will enhance the homing/recruitment of brain resident and nonresident circulating stem cells/progenitor cells, a noninvasive approach for promoting neurogenesis. So, herewith we provide this in support of dipeptidyl peptidase-4 inhibitors as a new target of attention for treating AD.

Autocrine Interleukin-10 Mediates Glucagon-Like Peptide-1 Receptor-Induced Spinal Microglial β-Endorphin Expression

The glucagon-like peptide-1 (GLP-1) receptor agonist exenatide stimulates microglial β-endorphin expression and subsequently produces neuroprotection and antinociception. This study illustrated an unrecognized autocrine role of IL-10 in mediation of exenatide-induced β-endorphin expression. Treatment with exenatide in cultured primary spinal microglia concentration dependently stimulated the expression of the M2 microglial markers IL-10, IL-4, Arg 1, and CD206, but not the M1 microglial markers TNF-α, IL-1β, IL-6, or CD68. Intrathecal exenatide injection also significantly upregulated spinal microglial expression of IL-10, IL-4, Arg 1, and CD206, but not TNF-α, IL-1β, IL-6, or CD68. Intrathecal injection of exenatide stimulated spinal microglial expression of IL-10 and β-endorphin in neuropathic rats. Furthermore, treatment with IL-10 (but not IL-4) stimulated β-endorphin expression in cultured primary microglia, whereas treatment with β-endorphin failed to increase IL-10 expression. The IL-10-neutralizing antibody entirely blocked exenatide-induced spinal microglial expression of β-endorphin in vitro and in vivo and fully blocked exenatide mechanical antiallodynia in neuropathic rats. Moreover, specific cAMP/PKA/p38 signal inhibitors and siRNA/p38β, but not siRNA/p38α, completely blocked exenatide-induced IL-10 expression in cultured primary microglia. Knock-down of IL-10 receptor-α mRNA using siRNA fully inhibited exenatide-induced spinal microglial β-endorphin expression and mechanical antiallodynia in neuropathy. Exenatide also markedly stimulated phosphorylation of the transcription factor STAT3 in cultured primary microglia and β-endorphin stimulation was completely inhibited by the specific STAT3 activation inhibitor. These results revealed that IL-10 in microglia mediated β-endorphin expression after GLP-1 receptor activation through the autocrine cAMP/PKA/p38β/CREB and subsequent IL-10 receptor/STAT3 signal pathways.SIGNIFICANCE STATEMENT Activation of GLP-1 receptors specifically and simultaneously stimulates the expression of anti-inflammatory cytokines IL-10 and IL-4, as well as the neuroprotective factor β-endorphin from microglia. GLP-1 receptor agonism induces β-endorphin expression and antinociception through autocrine release of IL-10. Activation of GLP-1 receptors stimulates IL-10 and β-endorphin expression subsequently through the Gs-cAMP/PKA/p38β/CREB and IL-10/IL-10 receptor-α/STAT3 signal transduction pathways.

A New Treatment Strategy for Parkinson's Disease through the Gut-Brain Axis: The Glucagon-Like Peptide-1 Receptor Pathway

Molecular communications in the gut-brain axis, between the central nervous system and the gastrointestinal tract, are critical for maintaining healthy brain function, particularly in aging. Epidemiological analyses indicate type 2 diabetes mellitus (T2DM) is a risk factor for neurodegenerative disorders including Alzheimer's disease (AD) and Parkinson's diseases (PD) for which aging shows a major correlative association. Common pathophysiological features exist between T2DM, AD, and PD, including oxidative stress, inflammation, insulin resistance, abnormal protein processing, and cognitive decline, and suggest that effective drugs for T2DM that positively impact the gut-brain axis could provide an effective treatment option for neurodegenerative diseases. Glucagon-like peptide-1 (GLP-1)-based antidiabetic drugs have drawn particular attention as an effectual new strategy to not only regulate blood glucose but also decrease body weight by reducing appetite, which implies that GLP-1 could affect the gut-brain axis in normal and pathological conditions. The neurotrophic and neuroprotective effects of GLP-1 receptor (R) stimulation have been characterized in numerous in vitro and in vivo preclinical studies using GLP-1R agonists and dipeptidyl peptidase-4 inhibitors. Recently, the first open label clinical study of exenatide, a long-acting GLP-1 agonist, in the treatment of PD showed long-lasting improvements in motor and cognitive function. Several double-blind clinical trials of GLP-1R agonists including exenatide in PD and other neurodegenerative diseases are already underway or are about to be initiated. Herein, we review the physiological role of the GLP-1R pathway in the gut-brain axis and the therapeutic strategy of GLP-1R stimulation for the treatment of neurodegenerative diseases focused on PD, for which age is the major risk factor.

Exendin-4 does not modify growth or apoptosis of human colon cancer cells

AIM

Glucagon-like peptide-1 (GLP-1) receptor agonists are a kind of very popular antidiabetes drugs. They promote cell proliferation and survival through activation of signaling pathways in human islet cells involving phosphate idylinositol 3 kinase (PI3K) and extracellular regulated kinases 1 and 2 (ERK1/2), which are frequently activated in human colon cancer cells. Then, it is possible that taking GLP-1 receptor (GLP-1R) agonists persistently would induce proliferation of β cells as well as colon cancer cells. So, clarifying the effects and mechanisms of GLP-1R agonists on colon cancer cells has important clinical implications.

MATERIALS AND METHODS

We investigated GLP-1R expression in human colon cancer tissue samples with immunohistochemisty analysis and explored the effects of exendin-4, a GLP-1 receptor agonist, on colon cancer cells in vitro and in vivo.

RESULTS

The results showed lack of GLP-1R expression in both human colon cancer tissues and colon cancer cell lines. Exendin-4 did not enhance the proliferation and migration of colon cancer cell lines in vitro, and nor did it inhibit apoptosis induced by cytotoxic agents such as 5-fluorouracil (5-FU) or irinotecan. In addition, exendin-4 did not promote the propagation of colon cancer cells in vivo.

CONCLUSION

Our study suggests that GLP-1R agonists do not modify the growth or survival of human colon cancer cells and may be safe for diabetic patients with colon cancer.

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

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

Emerging treatments for Alzheimer's disease for non-amyloid and non-tau targets

INTRODUCTION

The number of people with dementia, including Alzheimer's disease, is growing as a result of an ageing global population. Treatments available for AD only alleviate the symptoms of the disease, and are effective in some people with AD for a limited time. There is no disease-modifying treatment available, and despite research efforts, the underlying mechanisms of AD and optimal treatment targets have not been fully elucidated. Amyloid and tau are key pathological markers of AD with ongoing trials targeting both. However, there are also many trials at various stages of development that primarily target other markers and processes implicated in the disease, which are now being investigated. Areas covered: This review summarizes current treatment approaches for AD and explores both repositioned and novel therapies that target non amyloid and non tau mechanisms that are in the clinical trials pipeline. This includes treatments for cognitive and neuropsychiatric symptoms and potentially disease modifying therapies. The studies included in this review have been obtained from searches of PubMed and clinical trials databases. Expert commentary: There is a renewed energy in identifying better treatments for behavioural symptoms of AD using both novel drugs and repositioning existing drugs. Lack of success in clinical trials of drugs targeting amyloid and tau have led to a surge in targeting alternative mechanisms. Progress in the development of biomarkers will provide further tools for clinical trials of potential therapeutics for both symptomatic treatment and disease modification in AD.

Islet amyloid polypeptide: Another key molecule in Alzheimer's pathogenesis?

Recent epidemiological evidence reveals that patients suffering from type 2 diabetes mellitus (T2DM) often experience a significant decline in cognitive function, and approximately 70% of those cases eventually develop Alzheimer's disease (AD). Although several pathological processes are shared by AD and T2DM, the exact molecular mechanisms connecting these two diseases are poorly understood. Aggregation of human islet amyloid polypeptide (hIAPP), the pathological hallmark of T2DM, has also been detected in brain tissue and is associated with cognitive decline and AD development. In addition, hIAPP and amyloid β protein (Aβ) share many biophysical and physiological properties as well as exert similar cytotoxic mechanisms. Therefore, it is important to examine the possible role of hIAPP in the pathogenesis of AD. In this article, we introduce the basics on this amyloidogenic protein. More importantly, we discuss the potential mechanisms of hIAPP-induced AD development, which will be beneficial for proposing novel and feasible strategies to optimize AD prevention and/or treatment in diabetics.

Novel GLP-1R/GIPR co-agonist "twincretin" is neuroprotective in cell and rodent models of mild traumatic brain injury

Several single incretin receptor agonists that are approved for the treatment of type 2 diabetes mellitus (T2DM) have been shown to be neuroprotective in cell and animal models of neurodegeneration. Recently, a synthetic dual incretin receptor agonist, nicknamed "twincretin," was shown to improve upon the metabolic benefits of single receptor agonists in mouse and monkey models of T2DM. In the current study, the neuroprotective effects of twincretin are probed in cell and mouse models of mild traumatic brain injury (mTBI), a prevalent cause of neurodegeneration in toddlers, teenagers and the elderly. Twincretin is herein shown to have activity at two different receptors, dose-dependently increase levels of intermediates in the neurotrophic CREB pathway and enhance viability of human neuroblastoma cells exposed to toxic concentrations of glutamate and hydrogen peroxide, insults mimicking the inflammatory conditions in the brain post-mTBI. Additionally, twincretin is shown to improve upon the neurotrophic effects of single incretin receptor agonists in these same cells. Finally, a clinically translatable dose of twincretin, when administered post-mTBI, is shown to fully restore the visual and spatial memory deficits induced by mTBI, as evaluated in a mouse model of weight drop close head injury. These results establish twincretin as a novel neuroprotective agent and suggest that it may improve upon the effects of the single incretin receptor agonists via dual agonism.

Intranasal administration of Exendin-4 antagonizes Aβ31-35-induced disruption of circadian rhythm and impairment of learning and memory

BACKGROUND

The deposition of β-amyloid protein (Aβ) is one of the pathological characteristics of Alzheimer's disease (AD) and can disrupt circadian rhythm and impair learning and memory. Exendin-4, a therapeutic drug for type II diabetes mellitus (T2DM), exerts neuroprotective effects from the toxicity of Aβ. However, it is not clear whether Exendin-4 protects against Aβ-induced disruption of circadian rhythm. The neuroprotective effects of Exendin-4 have been studied using injection of Exendin-4 into the lateral ventricle and abdomen. However, these procedures are not suitable for clinical application.

METHODS

First, male C57BL/6 mice received triple distilled water or Exendin-4 (0.1 nmol, 0.5 nmol) by intranasal administration. Exendin-4 levels were measured in the hippocampal samples using an ELISA Kit. Then, the study examined whether intranasal or hippocampal administration of Exendin-4 antagonized Aβ-induced disruption of circadian rhythm as well as impairment of learning and memory using the wheel-running activity assay and the Morris water maze test.

RESULTS

The study showed that intranasally administered Exendin-4 passed through the blood-brain barrier. Aβ31-35 given by intrahippocampal injection disrupted circadian rhythm and impaired learning and memory in C57BL/6 mice, and Exendin-4 given by nasal cavity or hippocampal administration ameliorated Aβ31-35-induced circadian rhythm disturbance of locomotor activity and impairment of learning and memory.

CONCLUSIONS

These findings provide pivotal experimental support for further study of the neuroprotective effects and clinical application of Exendin-4.