Glucagon-like peptide-1 receptor is involved in learning and neuroprotection

Regulation of Diabetes: a Therapeutic Strategy for Alzheimer's Disease?

Accumulated evidence suggests that sporadic cases of Alzheimer's disease (AD) make up more than 95% of total AD patients, and diabetes has been implicated as a strong risk factor for the development of AD. Diabetes shares pathological features of AD, such as impaired insulin signaling, increased oxidative stress, increased amyloid-beta (Aβ) production, tauopathy and cerebrovascular complication. Due to shared pathologies between the two diseases, anti-diabetic drugs may be a suitable therapeutic option for AD treatment. In this article, we will discuss the well-known pathologies of AD, including Aβ plaques and tau tangles, as well as other mechanisms shared in AD and diabetes including reactive glia and the breakdown of blood brain barrier in order to evaluate the presence of any potential, indirect or direct links of pre-diabetic conditions to AD pathology. In addition, clinical evidence of high incidence of diabetic patients to the development of AD are described together with application of anti-diabetic medications to AD patients.

Neuregulin1β improves both spatial and associative learning and memory in Alzheimer model of rats possibly through signaling pathways other than Erk1/2

BACKGROUND

Neuregulin-1β (NRG1 β) is associated with various neurological disorders such as schizophrenia, depression and Parkinson's disease. However, its role in Alzheimer's (AD) has not been understood yet. Here, we have studied the effect of NRG1 β and extracellular-signal-regulated kinase (ERK) signaling on special and associative memories and emotional stress in AD model of rats.

METHODS

Fifty six male Wistar rats were divided into eight groups of: Saline + Saline, Aβ + Saline, Aβ + NRG1β (5 μg/5 ul), Aβ + PBS, Aβ + NRG1β + PD98059 (PD, 5 μg/2 μl), Aβ + NRG1β + Saline and Saline + PD. AD model was induced by intracerebroventricular (ICV) injection of beta-amyloid protein (Aβ1-42, 4 μg/2 μl). The cognitive performances of rats were evaluated using Morris Water Maze (MWM) and Step through passive avoidance. Also locomotors activity and emotionality of animals were considered in an Open field test. Data were analyzed by one way Anova one way, repeated measure and T-test.

RESULTS

Significant improvement was found in spatial learning and memory assessed by total time spent in target quadrant [F (4, 32) = 12.4, p = 0.001], escape latency [F (4, 32) = 15.767, p = 0.001] and distance moved [F (4, 32) = 5.55, p = 0.002], in Aβ + NRG1β compared with Aβ + Saline in MWM. Also Aβ + NRG1β showed long latencies to enter into the dark compartment [F (4, 32) = 6.43, p = 0.001], but short time spent [F (4, 32) =6.93, p = 0.001] compared with control. Administration of an ERK inhibitor (PD98059, 5 μg, 15 min before NRG1β) didn't completely block learning memory restored by NRG1β in AD model (p = 0.7). No significant between groups differences was found in emotional stress characteristics in open field, except the grooming numbers which were higher in Saline + PD compared with Saline + Saline (p = 0.02).

CONCLUSION

Our findings indicate that NRG1β restores cognitive dysfunctions induced by amyloid β through signaling pathways possibly other than Erk1/2, with no significant change in anxiety, locomotion and vegetative activities.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent β-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases.

MAJOR CONCLUSIONS

Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Stereo- and Enantioselective Addition of Organolithiums to 2-Oxazolinylazetidines as a Synthetic Route to 2-Acylazetidines

A new synthetic route to N-alkyl-2-acylazetidines was developed through a highly stereoselective addition of organolithiums to N-alkyl-2-oxazolinylazetidines followed by acidic hydrolysis of the resulting oxazolidine intermediates. This study revealed an unusual reactivity of the C=N bond of the oxazoline group when reacted with organolithiums in a non-polar solvent such as toluene. The observed reactivity has been explained considering the role of the nitrogen lone pair of the azetidine ring as well as of the oxazolinyl group in promoting a complexation of the organolithium, thus ending up with the addition to the C=N double bond. The high level of stereoselectivity in this addition is supported by DFT calculations and NMR investigations, and a model is proposed for the formation of the oxazolidine intermediates, that have been isolated and fully characterized. Upon acidic conditions, the oxazolidine moieties were readily converted into 2-acylazetidines. This synthetic approach has been applied for the preparation of highly enantioenriched 2-acylazetidines starting from chiral not racemic N-alkyl-2-oxazolinylazetidines.

Inventing Liraglutide, a Glucagon-Like Peptide-1 Analogue, for the Treatment of Diabetes and Obesity

Glucagon-like peptide-1 (GLP-1) has been in focus since the early 1980s as a long looked for incretin hormone, released from the gastrointestinal tract and with an important effect on glucose-dependent insulin secretion, providing efficient glucose lowering, with little risk for hypoglycemia. The enzyme dipeptidyl peptidase-4 (DPP-4) degrades GLP-1 very fast, and the remaining metabolite is cleared rapidly by the kidneys. Liraglutide is a fatty acid acylated analogue of GLP-1 that provides efficacy for 24 h/day. The mechanism of action for liraglutide is reviewed in detail with focus on pancreatic efficacy and safety, thyroid safety, and weight loss mechanism. Evolving science hypothesizes that GLP-1 has important effects on atherosclerosis, relevant for the cardiovascular benefit seen in the treatment of diabetes and obesity. Also, GLP-1 may be relevant in neurodegenerative diseases.

The role of short-chain fatty acids in microbiota-gut-brain communication

Short-chain fatty acids (SCFAs), the main metabolites produced by bacterial fermentation of dietary fibre in the gastrointestinal tract, are speculated to have a key role in microbiota-gut-brain crosstalk. However, the pathways through which SCFAs might influence psychological functioning, including affective and cognitive processes and their neural basis, have not been fully elucidated. Furthermore, research directly exploring the role of SCFAs as potential mediators of the effects of microbiota-targeted interventions on affective and cognitive functioning is sparse, especially in humans. This Review summarizes existing knowledge on the potential of SCFAs to directly or indirectly mediate microbiota-gut-brain interactions. The effects of SCFAs on cellular systems and their interaction with gut-brain signalling pathways including immune, endocrine, neural and humoral routes are described. The effects of microbiota-targeted interventions such as prebiotics, probiotics and diet on psychological functioning and the putative mediating role of SCFA signalling will also be discussed, as well as the relationship between SCFAs and psychobiological processes. Finally, future directions to facilitate direct investigation of the effect of SCFAs on psychological functioning are outlined.

Short-term improvements in cognitive function following vertical sleeve gastrectomy and Roux-en Y gastric bypass: a direct comparison study

BACKGROUND

Cognitive deficits are observed in individuals with obesity. While bariatric surgery can reverse these deficits, it remains unclear whether surgery type differentially influences cognitive outcome. We compared the extent to which vertical sleeve gastrectomy (VSG) and Roux-en Y gastric bypass (RYGB) ameliorated cognitive impairments associated with obesity.

METHODS

Female participants approved for VSG (N = 18) or RYGB (N = 18) were administered cognitive measures spanning the domains of attention [Hopkins Verbal Learning Test (HVLT) Trial 1 and Letter Number Sequencing], processing speed [Stroop Color Trial, Symbol Digit Modalities Test, and Trail Making Part A], memory [HVLT Retained and HVLT Discrimination Index], and executive functioning (Stroop Color Word Trials and Trail Making Part B-A) prior to surgery and at 2 weeks and 3 months following surgery. Scores for each cognitive domain were calculated and compared between surgical cohorts using repeated measures analyses of variance.

RESULTS

Significant weight loss was observed 2 weeks and 3 months following RYGB and VSG and was accompanied by improvements in processing speed and executive functioning. Patients who received RYGB also experienced improved attention as early as 2 weeks, which persisted at 3 months. This was not observed in individuals who underwent VSG. No changes in memory were observed from baseline measures in either group.

CONCLUSIONS

This is the first report of cognitive improvements following VSG and the first direct comparison of cognitive improvements following RYGB and VSG. Short-term improvements in specific domains of cognitive function are observed at the beginning of the active weight loss phase following bariatric surgery that persisted to 3 months. The anatomical distinction between the two surgeries and resulting differential metabolic profiles may be responsible for the improvements in attention observed following RYGB but not following VSG.

Therapeutic Use of Intranasal Glucagon: Resolution of Hypoglycemia

Episodes of hypoglycemia are frequent in patients with diabetes treated with insulin or sulphonylureas. Hypoglycemia can lead to severe acute complications, and, as such, both prevention and treatment of hypoglycemia are important for the well-being of patients with diabetes. The experience of hypoglycemia also leads to fear of hypoglycemia, that in turn can limit optimal glycemic control in patients, especially with type 1 diabetes. Treatment of hypoglycemia is still based on administration of carbohydrates (oral or parenteral according to the level of consciousness) or of glucagon (intramuscular or subcutaneous injection). In 1983, it was shown for the first time that intranasal (IN) glucagon drops (with sodium glycocholate as a promoter) increase blood glucose levels in healthy volunteers. During the following decade, several authors showed the efficacy of IN glucagon (drops, powders, and sprays) to resolve hypoglycemia in normal volunteers and in patients with diabetes, both adults and children. Only in 2010, based on evaluation of patients' beliefs and patients' expectations, a canadian pharmaceutical company (Locemia Solutions, Montreal, Canada) reinitiated efforts to develop glucagon for IN administration. The project has been continued by Eli Lilly, that is seeking to obtain registration in order to make IN glucagon available to insulin users (children and adolescents) worldwide. IN glucagon is as effective as injectable glucagon, and devoid of most of the technical difficulties associated with administration of injectable glucagon. IN glucagon appears to represent a major breakthrough in the treatment of severe hypoglycemia in insulin-treated patients with diabetes, both children and adults.

Diabetes Therapies for Dementia

PURPOSE OF REVIEW

Type 2 diabetes (T2D) is a well-established risk factor for the development of dementia. Dementia and T2D share some underlying pathophysiology that has led to interest in the potential to repurpose drugs used in the management of T2D to benefit brain health. This review describes the scientific data available on the use of T2D medications for the risk reduction or management of dementia, in people with and without T2D.

RECENT FINDINGS

Results from basic laboratory research support the potential for commonly-used medications for T2D, including those with direct glucose-lowering properties, to have a beneficial effect on brain health. However, human studies have been mostly observational in nature and report conflicting results. Preliminary data suggest that intranasal insulin, metformin, and GLP-1 agonists show promise for dementia, but confirmatory evidence for their benefit in dementia is still lacking. Current evidence does not support the repurposing of T2D medications for dementia risk reduction or management. Research in the field of T2D and dementia is active, and further data are required before definitive conclusions can be drawn.

A New Perspective in Utilizing MMP-9 as a Therapeutic Target for Alzheimer's Disease and Type 2 Diabetes Mellitus

Matrix metalloprotease 9 (MMP-9) is a 92 kDa type IV collagenase and a member of the family of endopeptidases. MMP-9 is involved in the degradation of extracellular matrix components, tissue remodeling, cellular receptor stripping, and processing of various signaling molecules. In the CNS, the effects of MMP-9 are quite complex, since it exerts beneficial effects including neurogenesis, angiogenesis, myelogenesis, axonal growth, and inhibition of apoptosis, or destructive effects including apoptosis, blood-brain barrier disorder, and demyelination. Likewise, in the periphery, physiological events, as the involvement of MMP-9 in angiogenesis, for instance in wound healing, can be turned into pathological, such as in tumor metastasis, depending on the state of the organism. Alzheimer's disease is a neurodegenerative disorder, characterized by amyloid accumulation and deposition in the brain. Amyloidogenesis, however, also occurs in diseases of the periphery, such as type II diabetes mellitus, where an analogous type of amyloid, is deposited in the pancreas. Interestingly, both diseases exhibit similar pathology and disease progression, with insulin resistance being a major common denominator. Hence, combinatorial strategies searching new or existing molecules to apply for therapeutic use for both diseases are gaining momentum. MMP-9 is extensively studied due to its association with a variety of physiological and pathological processes. Consequently, meticulous design could render MMP-9 into a potential therapeutic target for Alzheimer's disease and type 2 diabetes mellitus; two seemingly unrelated diseases.

DPP-4 inhibitor improves learning and memory deficits and AD-like neurodegeneration by modulating the GLP-1 signaling

Glucagon-like peptide-1 (GLP-1) signaling in the brain plays an important role in the regulation of glucose metabolism, which is impaired in Alzheimer's disease (AD). Here, we detected the GLP-1 and GLP-1 receptor (GLP-1R) in AD human brain and APP/PS1/Tau transgenic (3xTg) mice brain, finding that they were both decreased in AD human and mice brain. Enhanced GLP-1 exerts its protective effects on AD, however, this is rapidly degraded into inactivated metabolites by dipeptidyl peptidase-4 (DPP-4), resulting in its extremely short half-time. DPP-4 inhibitors, thus, was applied to improve the level of GLP-1 and GLP-1R expression in the hippocampus and cortex of AD mice brains. It is also protected learning and memory and synaptic proteins, increased the O-Glycosylation and decreased abnormal phosphorylation of tau and neurofilaments (NFs), degraded intercellular β-amyloid (Aβ) accumulation and alleviated neurodegeneration related to GLP-1 signaling pathway.

Glucagon-Like Peptide-1 Receptor Agonists and Strategies To Improve Their Efficiency

Type 2 diabetes mellitus (T2DM) is increasing in global prevalence and is associated with serious health problems (e.g., cardiovascular disease). Various treatment options are available for T2DM, including the incretin hormone glucagon-like peptide-1 (GLP-1). GLP-1 is a therapeutic peptide secreted from the intestines following food intake, which stimulates the secretion of insulin from the pancreas. The native GLP-1 has a very short plasma half-life, owning to renal clearance and degradation by the enzyme dipeptidyl peptidase-4. To overcome this issue, various GLP-1 agonists with increased resistance to proteolytic degradation and reduced renal clearance have been developed, with several currently marketed. Strategies, such as controlled release delivery systems, methods to reduce renal clearance (e.g., PEGylation and conjugation to antibodies), and methods to improve proteolytic stability (e.g., stapling, cyclization, and glycosylation) provide means to further improve the ability of GLP-1 analogs. These will be discussed in this literature review.

Cracking the combination: Gut hormones for the treatment of obesity and diabetes

Obesity and type 2 diabetes are a veritable global pandemic. There is an imperative to develop new therapies for these conditions that can be delivered at scale to patients, which deliver effective and titratable weight loss, amelioration of diabetes, prevention of diabetic complications and improvements in cardiovascular health. Although agents based on glucagon-like peptide-1 (GLP-1) are now in routine use for diabetes and obesity, the limited efficacy of such drugs means that newer agents are required. By combining the effects of GLP-1 with other gut and metabolic hormones such as glucagon (GCG), oxyntomodulin, glucose-dependent insulinotropic peptide (GIP) and peptide YY (PYY), we may obtain improved weight loss, increased energy expenditure and improved metabolic profiles. Drugs based on dual agonism of GLP1R/GCGR and GLP1R/GIPR are being actively developed in clinical trials. Triple agonism, for example with GLPR1/GCGR/GIPR unimolecular agonists or using GLP-1/oxyntomodulin/PYY, is also being explored. Multi-agonist drugs seem set to deliver the next generation of therapies for diabetes and obesity soon.

Regulation of Memory Function by Feeding-Relevant Biological Systems: Following the Breadcrumbs to the Hippocampus

The hippocampus (HPC) controls fundamental learning and memory processes, including memory for visuospatial navigation (spatial memory) and flexible memory for facts and autobiographical events (declarative memory). Emerging evidence reveals that hippocampal-dependent memory function is regulated by various peripheral biological systems that are traditionally known for their roles in appetite and body weight regulation. Here, we argue that these effects are consistent with a framework that it is evolutionarily advantageous to encode and recall critical features surrounding feeding behavior, including the spatial location of a food source, social factors, post-absorptive processing, and other episodic elements of a meal. We review evidence that gut-to-brain communication from the vagus nerve and from feeding-relevant endocrine systems, including ghrelin, insulin, leptin, and glucagon-like peptide-1 (GLP-1), promote hippocampal-dependent spatial and declarative memory via neurotrophic and neurogenic mechanisms. The collective literature reviewed herein supports a model in which various stages of feeding behavior and hippocampal-dependent memory function are closely linked.

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.

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.

Liraglutide and its Neuroprotective Properties-Focus on Possible Biochemical Mechanisms in Alzheimer's Disease and Cerebral Ischemic Events

Liraglutide is a GLP-1 analog (glucagon like peptide-1) used primarily in the treatment of diabetes mellitus type 2 (DM2) and obesity. The literature starts to suggest that liraglutide may reduce the effects of ischemic stroke by activating anti-apoptotic pathways, as well as limiting the harmful effects of free radicals. The GLP-1R expression has been reported in the cerebral cortex, especially occipital and frontal lobes, the hypothalamus, and the thalamus. Liraglutide reduced the area of ischemia caused by MCAO (middle cerebral artery occlusion), limited neurological deficits, decreased hyperglycemia caused by stress, and presented anti-apoptotic effects by increasing the expression of Bcl-2 and Bcl-xl proteins and reduction of Bax and Bad protein expression. The pharmaceutical managed to decrease concentrations of proapoptotic factors, such as NF-κB (Nuclear Factor-kappa β), ICAM-1 (Intercellular Adhesion Molecule 1), caspase-3, and reduced the level of TUNEL-positive cells. Liraglutide was able to reduce the level of free radicals by decreasing the level of malondialdehyde (MDA), and increasing the superoxide dismutase level (SOD), glutathione (GSH), and catalase. Liraglutide may affect the neurovascular unit causing its remodeling, which seems to be crucial for recovery after stroke. Liraglutide may stabilize atherosclerotic plaque, as well as counteract its early formation and further development. Liraglutide, through its binding to GLP-1R (glucagon like peptide-1 receptor) and consequent activation of PI3K/MAPK (Phosphoinositide 3-kinase/mitogen associated protein kinase) dependent pathways, may have a positive impact on Aβ (amyloid beta) trafficking and clearance by increasing the presence of Aβ transporters in cerebrospinal fluid. Liraglutide seems to affect tau pathology. It is possible that liraglutide may have some stem cell stimulating properties. The effects may be connected with PKA (phosphorylase kinase A) activation. This paper presents potential mechanisms of liraglutide activity in conditions connected with neuronal damage, with special emphasis on Alzheimer's disease and cerebral ischemia.

Evidence of Repurposing Drugs and Identifying Contraindications from Real World Study in Parkinson's Disease

There is great unmet need in discovering novel treatment for Parkinson's disease (PD) and identifying the new agents potentially causing drug-induced parkinsonism. New indications and contraindications of drugs are typically approved following rigorous randomized controlled trial (RCT) evaluation. However, RCTs have their inherent limitations, since they are usually conducted in ideal conditions, with high cost and limited follow-up periods. In the past decade, large cohort studies with long follow-up outcome data was derived from a PD database in a real-world setting. Studies based on real world data (RWD) can help to augment and extrapolate data obtained in RCTs and provide information about the safety and effectiveness of a medication in heterogeneous, large populations. In the present review, we focus on the published real world studies designed to develop new treatment strategies for repurposing drugs and identifying contraindications for PD. We also outline the challenges and limitations in these studies. Subsequently we introduce PaWei app platform, which hopefully can facilitate PD management and address real-world problems associated with PD. Better understanding of RWD collection and analysis is needed if RWD is to achieve its full potential.

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 Hyperhomocysteinemia-Induced Alzheimer-Like Pathology and Memory Deficits in Rats via Multi-molecular Targeting

Hyperhomocysteinemia (Hhcy) is an independent risk factor for Alzheimer's disease (AD), and insulin-resistance is commonly seen in patients with Hhcy. Liraglutide (Lir), a glucagon-like peptide that increases the secretion and sensitivity of insulin, has a neurotrophic or neuroprotective effect. However, it is not known whether Lir ameliorates the AD-like pathology and memory deficit induced by Hhcy. By vena caudalis injection of homocysteine to produce the Hhcy model in rats, we found here that simultaneous administration of Lir for 2 weeks ameliorated the Hhcy-induced memory deficit, along with increased density of dendritic spines and up-regulation of synaptic proteins. Lir also attenuated the Hhcy-induced tau hyperphosphorylation and Aβ overproduction, and the molecular mechanisms involved the restoration of protein phosphatase-2A activity and inhibition of β- and γ-secretases. Phosphorylated insulin receptor substrate-1 also decreased after treatment with Lir. Our data reveal that Lir improves the Hhcy-induced AD-like spatial memory deficit and the mechanisms involve the modulation of insulin-resistance and the pathways generating abnormal tau and Aβ.

Exercise-linked FNDC5/irisin rescues synaptic plasticity and memory defects in Alzheimer's models

Defective brain hormonal signaling has been associated with Alzheimer’s disease (AD), a disorder characterized by synapse and memory failure. Irisin is an exercise-induced myokine released upon cleavage of membrane-bound precursor protein FNDC5, also expressed in the hippocampus. Here we show that FNDC5/irisin levels are reduced in AD hippocampi and cerebrospinal fluid, and in experimental AD models. Knockdown of brain FNDC5/irisin impaired long-term potentiation and novel object recognition memory in mice. Conversely, boosting brain levels of FNDC5/irisin rescued synaptic plasticity and memory in AD mouse models. Peripheral overexpression of FNDC5/irisin rescued memory impairment, whereas blockade of either peripheral or brain FNDC5/irisin attenuated the neuroprotective actions of physical exercise on synaptic plasticity and memory in AD mice. By showing that FNDC5/irisin is an important mediator of the beneficial effects of exercise in AD models, our findings place FNDC5/irisin as a novel agent capable of opposing synapse failure and memory impairment in AD.

The effect of body mass index on glucagon-like peptide receptor gene expression in the post mortem brain from individuals with mood and psychotic disorders

There is an increasing interest in the putative role of glucagon-like peptide 1 receptor (GLP-1R) agonists as novel therapeutic agents for mental disorders. Herein, we investigated the expressions of GLP-1R and GLP-2R genes, and its relationship with body mass index (BMI), in the post-mortem brain tissue of patients with mood (MD) and psychotic disorders. Brain samples were localized to the dorsolateral prefrontal cortex (dlPFC) (n = 459) and hippocampus (n = 378). After adjustment for age, sex, ethnicity, post-mortem interval (PMI) and BMI, we observed significant differences, between healthy controls and MD subjects, in GLP-1R and GLP-2R gene expression in the dlPFC (β = 1.504, p = 0.004; and β = 1.305, p = 0.011, respectively); whereas in the hippocampus, only GLP-1R expression was significantly associated with MD (β = -1.28, p = 0.029). No significant differences were found in relation to schizophrenia. In addition, we observed a moderating effect of MD diagnosis on the associations between BMI, GLP-1R and GLP-2R expression values in the dlPFC (β = -0.05, p = 0.003; and β = -0.04, p = 0.004, respectively). There was a similar moderating effect for GLP-1R in the hippocampus (β = 0.043, 95% CI 0.003; 0.08 p = 0.03), but in an opposite direction than observed in the dlPFC. This is the first evidence of abnormal gene expression of GLP-1R and GLP-2R in postmortem brain of individuals with MD, providing a rationale for further inquiry and proof of principle interventional studies.

Oral Semaglutide In The Management Of Type 2 Diabetes: A Report On The Evidence To Date

In recent years, newer drug classes for the treatment of type 2 diabetes mellitus have been released with significant effects on glucose lowering and weight reduction. One of the most promising classes in achieving these goals has been the glucagon-like peptide (GLP)-1 agonists. However, a difficulty with the use of these agents is the need for subcutaneous injections, which can be inconvenient to individuals living with type 2 diabetes. More recently, a GLP-1 agonist has been developed, semaglutide, that can be administered orally which has at least similar effects to the subcutaneous preparation from which this compound is derived. In this review article, we discuss the glycemic and cardiovascular effects of the GLP-1 agonists with special emphasis on oral semaglutide and the potential role of this therapy in individuals with type 2 diabetes.

The Discovery and Development of Liraglutide and Semaglutide

The discovery of glucagon-like peptide-1 (GLP-1), an incretin hormone with important effects on glycemic control and body weight regulation, led to efforts to extend its half-life and make it therapeutically effective in people with type 2 diabetes (T2D). The development of short- and then long-acting GLP-1 receptor agonists (GLP-1RAs) followed. Our article charts the discovery and development of the long-acting GLP-1 analogs liraglutide and, subsequently, semaglutide. We examine the chemistry employed in designing liraglutide and semaglutide, the human and non-human studies used to investigate their cellular targets and pharmacological effects, and ongoing investigations into new applications and formulations of these drugs. Reversible binding to albumin was used for the systemic protraction of liraglutide and semaglutide, with optimal fatty acid and linker combinations identified to maximize albumin binding while maintaining GLP-1 receptor (GLP-1R) potency. GLP-1RAs mediate their effects via this receptor, which is expressed in the pancreas, gastrointestinal tract, heart, lungs, kidneys, and brain. GLP-1Rs in the pancreas and brain have been shown to account for the respective improvements in glycemic control and body weight that are evident with liraglutide and semaglutide. Both liraglutide and semaglutide also positively affect cardiovascular (CV) outcomes in individuals with T2D, although the precise mechanism is still being explored. Significant weight loss, through an effect to reduce energy intake, led to the approval of liraglutide (3.0 mg) for the treatment of obesity, an indication currently under investigation with semaglutide. Other ongoing investigations with semaglutide include the treatment of non-alcoholic fatty liver disease (NASH) and its use in an oral formulation for the treatment of T2D. In summary, rational design has led to the development of two long-acting GLP-1 analogs, liraglutide and semaglutide, that have made a vast contribution to the management of T2D in terms of improvements in glycemic control, body weight, blood pressure, lipids, beta-cell function, and CV outcomes. Furthermore, the development of an oral formulation for semaglutide may provide individuals with additional benefits in relation to treatment adherence. In addition to T2D, liraglutide is used in the treatment of obesity, while semaglutide is currently under investigation for use in obesity and NASH.

Evaluation of intranasal delivery route of drug administration for brain targeting

The acute or chronic drug treatments for different neurodegenerative and psychiatric disorders are challenging from several aspects. The low bioavailability and limited brain exposure of oral drugs, the rapid metabolism, elimination, the unwanted side effects and also the high dose to be added mean both inconvenience for the patients and high costs for the patients, their family and the society. The reason of low brain penetration of the compounds is that they have to overcome the blood-brain barrier which protects the brain against xenobiotics. Intranasal drug administration is one of the promising options to bypass blood-brain barrier, to reduce the systemic adverse effects of the drugs and to lower the doses to be administered. Furthermore, the drugs administered using nasal route have usually higher bioavailability, less side effects and result in higher brain exposure at similar dosage than the oral drugs. In this review the focus is on giving an overview on the anatomical and cellular structure of nasal cavity and absorption surface. It presents some possibilities to enhance the drug penetration through the nasal barrier and summarizes some in vitro, ex vivo and in vivo technologies to test the drug delivery across the nasal epithelium into the brain. Finally, the authors give a critical evaluation of the nasal route of administration showing its main advantages and limitations of this delivery route for CNS drug targeting.

Liraglutide Activates mTORC1 Signaling and AMPA Receptors in Rat Hippocampal Neurons Under Toxic Conditions

The aim of the present study was to determine whether treatment with liraglutide, a glucagon-like peptide 1 (GLP-1) receptor agonist, would alter mammalian target of rapamycin complex 1 (mTORC1) signaling and/or α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor activity under dexamethasone-induced toxic conditions. Western blot analyses were performed to assess changes in mTORC1-mediated proteins, brain-derived neurotrophic factor (BDNF), and various synaptic proteins (PSD-95, synapsin I, and GluA1) in rat hippocampal cultures under toxic conditions induced by dexamethasone, which causes hippocampal cell death. Hippocampal dendritic outgrowth and spine formation were measured using immunostaining procedures. Dexamethasone significantly decreased the phosphorylation levels of mTORC1 as well as its downstream proteins. However, treatment with liraglutide prevented these reductions and significantly increased BDNF expression. The increase in BDNF expression was completely blocked by rapamycin and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX). Liraglutide also recovered dexamethasone-induced decreases in the total length of hippocampal dendrites and reductions in spine density in a concentration-dependent manner. However, the positive effects of liraglutide on neural plasticity were abolished by the blockade of mTORC1 signaling and AMPA receptors. Furthermore, liraglutide significantly increased the expression levels of PSD-95, synapsin I, and GluA1, whereas rapamycin and NBQX blocked these effects. The present study demonstrated that liraglutide activated mTORC1 signaling and AMPA receptor activity as well as increased dendritic outgrowth, spine density, and synaptic proteins under toxic conditions in rat primary hippocampal neurons. These findings suggest that GLP-1 receptor (GLP-1R) activation by liraglutide may affect neuroplasticity through mTORC1 and AMPA receptors.

Fasting enhances extinction retention and prevents the return of fear in humans

Fear is prone to return following extinction that is the basis of exposure therapy for fear-related disorders. Manipulations that enhance the extinction process can be beneficial for treatment. Animal studies have shown that fasting or caloric restriction can enhance extinction and inhibit the return of fear. The present study examined the effects of fasting on fear acquisition, extinction, and the return of fear in humans. One hundred and twenty-five male participants were randomized into a fasting group and food group and exposed to a Pavlovian fear conditioning paradigm. Changes in plasma cortisol and ghrelin levels were examined using enzyme-linked immunosorbent assays. One-night fasting had no effect on fear acquisition but enhanced fear extinction retention and prevented the return of fear, and this effect persisted for at least 6 months. This procedure was also effective for remote fear memory. Plasma ghrelin levels were elevated after fasting and had a negative relationship with the fear response in spontaneous recovery test. However, overnight fasting did not affect cortisol levels. These findings indicate that fasting enhances extinction retention and prevents the return of fear, without influencing fear memory formation. We propose that this novel procedure may open new avenues for promoting extinction-based therapies for fear-related disorders.

12-month effects of incretins versus SGLT2-Inhibitors on cognitive performance and metabolic profile. A randomized clinical trial in the elderly with Type-2 diabetes mellitus

AIM

The aim of the present study is to examine the effects on cognitive performance, anthropometric measures, and metabolic markers in 2 different treatments: Incretins vs sodium-glucose co-transporter-2 inhibitors (SGLT2-I).

MATERIALS AND METHODS

A randomized controlled clinical trial was carried out on 39 elderly subjects (23 men and 16 women) with type 2 diabetes mellitus, with a mean age of 77.21±8.07 years. Body mass index (BMI) of 29.92±4.31 kg/m2 and a cognitive status measured by a Mini Mental State Examination (scores >27 points). The subjects were on a 3-month treatment with a maximal dose of metformin as a stable regime, with the addition of incretins (liraglutide at doses of up to 1.8 mg/d; vildagliptin at 100 mg/d; sitagliptin 100 mg/d; and linagliptin 5 mg/d), or SGLT2-I (canagliflozin 300 mg/d; empagliflozin 25 mg/d; and dapagliflozin 10 mg/d). Glucose control was monitored by fasting glucose and glycosylated hemoglobin. Cognitive performance (by way of Verbal Fluency Test, Attentive Matrices Test, and Babcock Story Recall Test), anthropometric measures, and plasma lipids were also evaluated.

RESULTS

Cognitive status did not change significantly during the 12 months of treatment in either group: Verbal Fluency Test: (SGLT2-I: P=1.00, incretins: P=0.598); Babcock Story Recall Test (SGLT2-I: P=0.391; incretins: P=0.351); and Attentive Matrices Test (SGLT2-I: P=0.679, incretins: P=0.901). SGLT2-I also resulted in a reduction in weight (-1.95 kg; P<0.05), in BMI (-0.69 kg/m2; P<0.05) and an increase in high-density lipoprotein cholesterol (+5.73 mg/dl; P<0.01).

CONCLUSION

Preliminary data show that patients treated with incretins and SGLT2-I have not suffered a reduction in cognitive performance during the 1 year of treatment. Metabolic outcome seemed to benefit, in particular, in patients who were treated with SGLT2-I.

Inhibition of DPP4 enhances inhibitory synaptic transmission through activating the GLP-1/GLP-1R signaling pathway in a rat model of febrile seizures

Dipeptidyl peptidase-IV (DPP4) is a cell surface serine peptidase widely expressed in the brain. Recent studies suggest that DPP4 contributes to the development of febrile seizures (FS); however, the underlying mechanism is still unclear. Thus, we investigated the role of DPP4 in the progression of FS at the molecular and electrophysiological levels using FS models in vivo and in vitro. Herein, we found that both the mRNA and protein levels of DPP4 were upregulated in the FS model. Administration of the pharmacological DPP4 inhibitor sitagliptin suppressed the hyperthermia-induced neuronal excitability as determined via whole-cell patch-clamp recordings in vitro. Interestingly, sitagliptin administration activated the glucagon-like peptide-1 (GLP-1)/GLP-1 receptor (GLP-1R) pathway by increasing the expression of GLP-1 and GLP-1R in a rat model of FS. Moreover, administration of the GLP-1R inhibitor exendin9-39 increased seizure severity, and sitagliptin reversed the effect, as shown in the electroencephalogram (EEG) and patch-clamp results in a rat model of FS. Furthermore, the GLP-1R-mediated reduction in GABAergic transmission was enhanced by sitagliptin and DPP4 knockdown through increasing miniature inhibitory post-synaptic currents (mIPSCs) in vitro accompanied by increased synaptic release of GABA in vivo. Taken together, our results demonstrate a role of DPP4 in regulating GABAergic transmission via the GLP-1/GLP-1R pathway. These findings indicated that DPP4 may represent a novel therapeutic strategy and target for FS.

Intranasal glucagon for hypoglycaemia in diabetic patients. An old dream is becoming reality?

In 1983 it was shown that glucagon administered intranasally (IN) was absorbed through the nasal mucosa and increased blood glucose in healthy subjects. Shortly thereafter, it was shown that IN glucagon counteracts with hypoglycaemia in insulin-treated diabetic patients. In spite of this evidence, IN glucagon was not developed by any pharmaceutical company before 2010, when renewed interest led to intensive evaluation of a possible remedy for hypoglycaemia in insulin-treated diabetic adults and children. IN glucagon is now being developed as a needle-free device that delivers glucagon powder for treatment of severe hypoglycaemia; the ease of using this device stands in stark contrast to the difficulties encountered in use of the current intramuscular glucagon emergency kits. Studies have demonstrated the efficacy, safety and ease-of-use of this IN glucagon preparation, and suggest IN glucagon as a promising alternative to injectable glucagon for treating severe hypoglycaemia in children and adults who use insulin. This would meet the unmet medical need for an easily administered glucagon preparation.

Engineered commensal bacteria prevent systemic inflammation-induced memory impairment and amyloidogenesis via producing GLP-1

The anti-obesity drug GLP-1 has been proven to have an impact on central nervous system, while its extremely short half-life greatly limited its use. In this study, our group constructed two engineering strains MG1363-pMG36e-GLP-1 and VNP20009-pLIVE-GLP-1 to continuously express GLP-1, and supplementation of these strains, especially MG1363-pMG36e-GLP-1, had significantly restored the spatial learning and memory impairment of mice caused by LPS (p < 0.05), suppressed glia activation and Aβ accumulation, and downregulated inflammatory expressions of COX-2, TLR-4, TNF-a, and IL-1β. In addition, MG1363-pMG36e-GLP-1 had significantly blocked the translocation of NF-κB signal and inhibited the phosphorylation of redox-sensitive cytoplasmic signalings of MAPKs and PI3K/AKT. These data suggest that MG1363-pMG36e-GLP-1 could be used as a safe and effective nonabsorbed oral treatment for neuroinflammation-related diseases such as Alzheimer's disease (AD).

Intranasally Administered S100A9 Amyloids Induced Cellular Stress, Amyloid Seeding, and Behavioral Impairment in Aged Mice

Amyloid formation and neuroinflammation are major features of Alzheimer's disease pathology. Proinflammatory mediator S100A9 was shown to act as a link between the amyloid and neuroinflammatory cascades in Alzheimer's disease, leading together with Aβ to plaque formation, neuronal loss and memory impairment. In order to examine if S100A9 alone in its native and amyloid states can induce neuronal stress and memory impairment, we have administered S100A9 species intranasally to aged mice. Single and sequential immunohistochemistry and passive avoidance behavioral test were conducted to evaluate the consequences. Administered S100A9 species induced widespread cellular stress responses in cerebral structures, including frontal lobe, hippocampus and cerebellum. These were manifested by increased levels of S100A9, Bax, and to a lesser extent activated caspase-3 immunopositive cells. Upon administration of S100A9 fibrils, the amyloid oligomerization was observed in the brain tissues, which can further exacerbate cellular stress. The cellular stress responses correlated with significantly increased training and decreased retention latencies measured in the passive avoidance test for the S100A9 treated animal groups. Remarkably, the effect size in the behavioral tests was moderate already in the group treated with native S100A9, while the effect sizes were large in the groups administered S100A9 amyloid oligomers or fibrils. The findings demonstrate the brain susceptibility to neurotoxic damage of S100A9 species leading to behavioral and memory impairments. Intranasal administration of S100A9 species proved to be an effective method to study amyloid induced brain dysfunctions, and S100A9 itself may be postulated as a target to allay early stage neurodegenerative and neuroinflammatory processes.

Drug development for Alzheimer's disease: review

Alzheimer's disease (AD) is a chronic neurodegenerative disease, which is considered as one of the most intractable medical problems with heavy social and economic costs. The current drugs for AD, including acetylcholinesterase inhibitors (AChEIs) and memantine, a NMDA receptor antagonist, only temporarily ameliorate cognitive decline, but are unable to stop or reverse the progression of dementia. This paper reviewed the recent advance in AD drug development. The drug discovery programs under clinical trials targeting cholinergic system, α7 nicotinic acetylcholine receptors (nAChRs), N-methyl-d-aspartate receptor (NMDAR), β-secretase, γ-secretase modulators, tau, inflammatory mediators and glucagon-like peptide-1 (GLP-1) were discussed. Though several drug discovery programs are ongoing, the high failure rate is an outstanding issue. Novel techniques and strategies are desperately needed to significantly accelerate this process.

Impact of Early-Life Weight Status on Cognitive Abilities in Children

OBJECTIVE

Whether obesity is associated with childhood cognition is unknown. Given the sensitivity of the developing brain to environmental factors, this study examined whether early-life weight status was associated with children's cognition.

METHODS

Using data from mother-child pairs enrolled in the Health Outcomes and Measures of the Environment (HOME) Study (2003-2006), children's early-life weight status was assessed using weight-for-length/height standard deviation (SD) scores. A battery of neuropsychological tests was administered to assess cognition, executive function, and visual-spatial abilities at ages 5 and 8 years. Using linear mixed models, associations between early-life weight status and cognition were estimated.

RESULTS

Among 233 children, 167 were lean (≤1 SD) and 48 were nonlean (>1 SD). After covariate adjustment, the results suggest that full-scale intelligence quotient scores decreased with a 1-unit increase in weight-for-height SD score (β = -1.4, 95% CI: -3.0 to 0.1). For individual component scores, with a 1-unit increase in weight-for-height SD score, perceptual reasoning (β = -1.7, 95% CI: -3.3 to 0.0) and working memory (β: -2.4, CI: -4.4 to -0.4) scores decreased. Weight status was generally not associated with other cognition measures.

CONCLUSIONS

Within this cohort of typically developing children, early-life weight status was inversely associated with children's perceptual reasoning and working memory scores and possibly with full-scale intelligent quotient scores.

Glucagon-like peptide 1 receptor (GLP-1R) expression by nerve fibres in inflammatory bowel disease and functional effects in cultured neurons

INTRODUCTION

Glucagon like-peptide 1 receptor (GLP-1R) agonists diminish appetite and may contribute to the weight loss in inflammatory bowel disease (IBD).

OBJECTIVES

The aim of this study was to determine, for the first time, the expression of GLP-1R by colon nerve fibres in patients with IBD, and functional effects of its agonists in cultured rat and human sensory neurons.

METHODS

GLP-1R and other nerve markers were studied by immunohistochemistry in colon biopsies from patients with IBD (n = 16) and controls (n = 8), human dorsal root ganglia (DRG) tissue, and in GLP-1R transfected HEK293 cells. The morphological effects of incretin hormones oxyntomodulin, exendin-4 and glucagon were studied on neurite extension in cultured DRG neurons, and their functional effects on capsaicin and ATP signalling, using calcium imaging.

RESULTS

Significantly increased numbers of colonic mucosal nerve fibres were observed in IBD biopsies expressing GLP-1R (p = 0.0013), the pan-neuronal marker PGP9.5 (p = 0.0008), and sensory neuropeptide CGRP (p = 0.0014). An increase of GLP-1R positive nerve fibres in IBD colon was confirmed with a different antibody to GLP-1R (p = 0.016). GLP-1R immunostaining was intensely positive in small and medium-sized neurons in human DRG, and in human and rat DRG cultured neurons. Co-localization of GLP-1R expression with neuronal markers in colon and DRG confirmed the neural expression of GLP-1R, and antibody specificity was confirmed in HEK293 cells transfected with the GLP-1R. Treatment with oxyntomodulin, exendin-4 and GLP-1 increased neurite length in cultured neurons compared with controls, but did not stimulate calcium influx directly, or affect capsaicin responses. However, exendin-4 significantly enhanced ATP responses in human DRG neurons.

CONCLUSION

Our results show that increased GLP-1R innervation in IBD bowel could mediate enhanced visceral afferent signalling, and provide a peripheral target for therapeutic intervention. The differential effect of GLP-1R agonists on capsaicin and ATP responses in neurons suggest they may not affect pain mechanisms mediated by the capsaicin receptor TRPV1, but may enhance the effects of purinergic agonists.

Sustained high-fat diet modulates inflammation, insulin signalling and cognition in mice and a modified xenin peptide ameliorates neuropathology in a chronic high-fat model

AIMS

To demarcate pathological events in the brain as a result of short-term to chronic high-fat-diet (HFD) feeding, which leads to cognitive impairment and neuroinflammation, and to assess the efficacy of Xenin-25[Lys(13)PAL] in chronic HFD-fed mice.

METHODS

C57BL/6 mice were fed an HFD or a normal diet for 18 days, 34 days, 10 and 21 weeks. Cognition was assessed using novel object recognition and the Morris water maze. Markers of insulin signalling and inflammation were measured in brain and plasma using immunohistochemistry, quantitative PCR and multi-array technology. Xenin-25[Lys(13)PAL] was also administered for 5 weeks in chronic HFD-fed mice to assess therapeutic potential at a pathological stage.

RESULTS

Recognition memory was consistently impaired in HFD-fed mice and spatial learning was impaired in 18-day and 21-week HFD-fed mice. Gliosis, oxidative stress and IRS-1 pSer⁶¹⁶ were increased in the brain on day 18 in HFD-fed mice and were reduced by Xenin-25[Lys(13)PAL] in 21-week HFD-fed mice. In plasma, HFD feeding elevated interleukin (IL)-6 and chemokine (C-X-C motif) ligand 1 at day 34 and IL-5 at week 10. In the brain, HFD feeding reduced extracellular signal-regulated kinase 2 (ERK2), mechanistic target of rapamycin (mTOR), NF-κB1, protein kinase C (PKC)θ and Toll-like receptor 4 (TLR4) mRNA at week 10 and increased expression of glucacon-like peptide-1 receptor, inhibitor of NF-κB kinase β, ERK2, mTOR, NF-κB1, PKCθ and TLR4 at week 21, elevations that were abrogated by Xenin-25[Lys(13)PAL].

CONCLUSIONS

HFD feeding modulates cognitive function, synapse density, inflammation and insulin resistance in the brain. Xenin-25[Lys(13)PAL] ameliorated markers of inflammation and insulin signalling dysregulation and may have therapeutic potential in the treatment of diseases associated with neuroinflammation or perturbed insulin signalling in the brain.

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.