Glucagon-like peptide-1 suppresses neuroinflammation and improves neural structure

The therapeutic effects and mechanisms of glucagon-like peptide-1 receptor agonists in neurocognitive disorders

Chronic cerebral hypoperfusion (CCH) represents a key pathogenic contributor to neurocognitive disorders. It can lead to multifaceted pathological alterations including neuroinflammation, neuronal apoptosis, blood-brain barrier disruption, synaptic plasticity deficits, and mitochondrial dysfunction. The glucagon-like peptide-1 receptor (GLP-1R), ubiquitously expressed across multiple organ systems, exerts neuroprotective effects by maintaining intracellular homeostasis and mitigating neuronal damage triggered by oxidative stress, inflammatory cascades, apoptotic signaling, and ischemic insults. Furthermore, GLP-1R activity is modulated by gut microbiota composition and short-chain fatty acid abundance, implicating the gut-brain axis in its regulatory influence on neurological function. This review systematically examines the pathophysiological mechanisms underlying CCH and highlights the therapeutic potential of GLP-1R activation. Specifically, GLP-1R-targeted interventions attenuate hypoperfusion-induced damage through pleiotropic pathways and gut-brain crosstalk, thereby offering novel perspectives for advancing both fundamental research and clinical management of neurocognitive disorders.

GLP-1 as a regulator of sepsis outcomes: Insights into cellular metabolism, inflammation, and therapeutic potential

Glucagon-like peptide-1 (GLP-1) has been widely studied in the context of treating obesity and various forms of metabolic disease. Sepsis is a life-threatening medical emergency characterized by the widespread dysregulation of energy metabolism within cells. The potential for GLP-1 to improve sepsis patient outcomes through improvements in energy metabolism and inflammation has been a focus of growing research interest, with many studies of GLP-1 itself and related compounds, including GLP-1 receptor agonists (GLP-1RAs), and dipeptidyl peptidase-4 (DPP-4) inhibitors, having explored the impact on sepsis in cells and organs. Such studies require that attention be paid to both the physiological and potential pathological effects of GLP-1 in sepsis. In many reports, researchers have demonstrated that endogenous GLP-1, GLP-1RAs, or DPP-4 inhibitors (a GLP-1 depressant) can modulate glucose homeostasis, inflammatory activity, immune function, and organ dysfunction in studies of sepsis model systems in vitro and in vivo. To date, GLP-1-based treatments have yet to be specifically used to manage sepsis, but its pleiotropic effects suggest its significant potential in sepsis treatment. This review provides an overview of the relationship between GLP-1 and its related compounds with sepsis, aiming to offer novel perspectives for the diagnosis and treatment of this condition. It highlights that GLP-1 may serve as a new biomarker for assessing the severity and prognosis of sepsis, and potentially contribute to improving clinical outcomes in septic patients. Meanwhile, GLP-1 may function as a messenger of metabolic reprogramming, shifting cellular energy production from oxidative phosphorylation to glycolysis, thereby modulating immune responses and influencing inflammatory reactions to enhance the clearance of pathogens. However, GLP-1 may act as a double-edged sword, the enhanced inflammatory response can potentially induce cytotoxic and organ-damaging effects while exerting beneficial actions.

GLP-1RA and SGLT2i Medications for Type 2 Diabetes and Alzheimer Disease and Related Dementias

Importance

The association between glucagon-like peptide-1 receptor agonists (GLP-1RAs) and sodium-glucose cotransporter-2 inhibitors (SGLT2is) and risk of Alzheimer disease and related dementias (ADRD) remains to be confirmed.

Objective

To assess the risk of ADRD associated with GLP-1RAs and SGLT2is in people with type 2 diabetes (T2D).

Design, Setting, and Participants

This target trial emulation study used electronic health record data from OneFlorida+ Clinical Research Consortium from January 2014 to June 2023. Patients were 50 years or older with T2D and no prior diagnosis of ADRD or antidementia treatment. Among the 396 963 eligible patients with T2D, 33 858 were included in the GLP-1RA vs other glucose-lowering drug (GLD) cohort, 34 185 in the SGLT2i vs other GLD cohort, and 24 117 in the GLP-1RA vs SGLT2i cohort.

Exposures

Initiation of treatment with a GLP-1RA, SGLT2i, or other second-line GLD.

Main Outcomes and Measures

ADRD was identified using clinical diagnosis codes. Hazard ratios (HRs) with 95% CIs were estimated using Cox proportional hazard regression models with inverse probability of treatment weighting (IPTW) to adjust for potential confounders.

Results

This study included 33 858 patients in the GLP-1RA vs other GLD cohort (mean age, 65 years; 53.1% female), 34 185 patients in the SGLT2i vs other GLD cohort (mean age, 65.8 years; 49.3% female), and 24 117 patients in the GLP-1RA vs SGLT2i cohort (mean age, 63.8 years; 51.7% female). In IPTW-weighted cohorts, the incidence rate of ADRD was lower in GLP-1RA initiators compared with other GLD initiators (rate difference [RD], -2.26 per 1000 person-years [95% CI, -2.88 to -1.64]), yielding an HR of 0.67 (95% CI, 0.47-0.96). SGLT2i initiators had a lower incidence than other GLD initiators (RD, -3.05 per 1000 person-years [95% CI, -3.68 to -2.42]), yielding an HR of 0.57 (95% CI, 0.43-0.75). There was no difference between GLP-1RAs and SGLT2is, with an RD of -0.09 per 1000 person-years (95% CI, -0.80 to 0.63) and an HR of 0.97 (95% CI, 0.72-1.32).

Conclusion and Relevance

In people with T2D, both GLP-1RAs and SGLT2is were statistically significantly associated with decreased risk of ADRD compared with other GLDs, and no difference was observed between both drugs.

Glycated hemoglobin and body mass index as mediators of GLP-1RAs and Alzheimer's disease and related dementias in patients with type 2 diabetes

INTRODUCTION

Whether reductions in glycated hemoglobin (HbA1c) levels and body mass index (BMI) mediate the association between glucagon-like peptide-1 receptor agonists (GLP-1RAs) and Alzheimer's disease and related dementias (ADRD) risk is unknown.

METHODS

This cohort study included 22,908 patients aged ≥ 50 years with type 2 diabetes (T2D) newly prescribed GLP-1RA or other second-line glucose-lowering drugs (GLDs). Causal mediation analysis was used to estimate to what extent the effect of GLP-1RAs on ADRD risk was attributable to lowering HbA1c or BMI.

RESULTS

Compared to other GLD users, GLP-1RA users had significant reductions in HbA1c levels by 0.16% and BMI by 0.23 kg/m2, along with a 26% lower ADRD risk. The direct protective effect of GLP-1RAs on ADRD risk persisted even after accounting for HbA1c and BMI reductions, with minimal mediation effects observed through these factors.

DISCUSSION

GLP-1RAs reduce ADRD risk, largely independent of their effects on HbA1c and BMI.

HIGHLIGHTS

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) were associated with reductions in glycated hemoglobin (HbA1c) and body mass index (BMI) compared to other second-line glucose-lowering drugs(GLDs). GLP-1RA users were associated with a 26% lower risk of Alzheimer's disease and related dementias (ADRD) than other GLD users. The protective effect of GLP-1RAs against ADRD in adults with type 2 diabetes (T2D) is largely independent of their effects on HbA1c and BMI.

Effect and mechanism of GLP-1 on cognitive function in diabetes mellitus

Background

Diabetes mellitus (DM) is a metabolic disorder associated with cognitive impairment. Glucagon-like peptide-1 (GLP-1) and its receptor (GLP-1R) have shown neuroprotective effects.

Scope of review

This review explores the impact of DM on cognitive function. Diabetes-related cognitive impairment is divided into three stages: diabetes-associated cognitive decrements, mild cognitive impairment (MCI), and dementia. GLP-1R agonists (GLP-1RAs) have many functions, such as neuroprotection, inhibiting infection, and metabolic regulation, and show good application prospects in improving cognitive function. The mechanisms of GLP-1RAs neuroprotection may be interconnected, warranting further investigation. Understanding these mechanisms could lead to targeted treatments for diabetes-related cognitive dysfunction.

Major conclusions

Therefore, this paper reviewed the regulatory effects of GLP-1 on cognitive dysfunction and its possible mechanism. Further research is required to fully explore the potential of GLP-1 and its analogs in this context.

Dysregulation of Metabolic Peptides in the Gut-Brain Axis Promotes Hyperinsulinemia, Obesity, and Neurodegeneration

Metabolic peptides can influence metabolic processes and contribute to both inflammatory and/or anti-inflammatory responses. Studies have shown that there are thousands of metabolic peptides, made up of short chains of amino acids, that the human body produces. These peptides are crucial for regulating many different processes like metabolism and cell signaling, as they bind to receptors on various cells. This review will cover the role of three specific metabolic peptides and their roles in hyperinsulinemia, diabetes, inflammation, and neurodegeneration, as well as their roles in type 3 diabetes and dementia. The metabolic peptides glucagon-like peptide 1 (GLP-1), gastric inhibitor polypeptide (GIP), and pancreatic peptide (PP) will be discussed, as dysregulation within their processes can lead to the development of various inflammatory and neurodegenerative diseases. Research has been able to closely investigate the connections between these metabolic peptides and their links to the gut-brain axis, highlighting changes made in the gut that can lead to dysfunction in processes in the brain, as well as changes made in the brain that can lead to dysregulation in the gut. The role of metabolic peptides in the development and potentially reversal of diseases such as obesity, hyperinsulinemia, and type 2 diabetes will also be discussed. Furthermore, we review the potential links between these conditions and neuroinflammation and the development of neurodegenerative diseases like dementia, specifically Parkinson's disease and Alzheimer's disease.

Beyond metabolic messengers: Bile acids and TGR5 as pharmacotherapeutic intervention for psychiatric disorders

Psychiatric disorders pose a significant global health challenge, exacerbated by the COVID-19 pandemic and insufficiently addressed by the current treatments. This review explores the emerging role of bile acids and the TGR5 receptor in the pathophysiology of psychiatric conditions, emphasizing their signaling within the gut-brain axis. We detail the synthesis and systemic functions of bile acids, their transformation by gut microbiota, and their impact across various neuropsychiatric disorders, including major depressive disorder, general anxiety disorder, schizophrenia, autism spectrum disorder, and bipolar disorder. The review highlights how dysbiosis and altered bile acid metabolism contribute to the development and exacerbation of these neuropsychiatric disorders through mechanisms involving inflammation, oxidative stress, and neurotransmitter dysregulation. Importantly, we detail both pharmacological and non-pharmacological interventions that modulate TGR5 signaling, offering potential breakthroughs in treatment strategies. These include dietary adjustments to enhance beneficial bile acids production and the use of specific TGR5 agonists that have shown promise in preclinical and clinical settings for their regulatory effects on critical pathways such as cAMP-PKA, NRF2-mediated antioxidant responses, and neuroinflammation. By integrating findings from the dynamics of gut microbiota, bile acids metabolism, and TGR5 receptor related signaling events, this review underscores cutting-edge therapeutic approaches poised to revolutionize the management and treatment of psychiatric disorders.

GLP-1 programs the neurovascular landscape

Readily available nutrient-rich foods exploit our inherent drive to overconsume, creating an environment of overnutrition. This transformative setting has led to persistent health issues, such as obesity and metabolic syndrome. The development of glucagon-like peptide-1 receptor (GLP-1R) agonists reveals our ability to pharmacologically manage weight and address metabolic conditions. Obesity is directly linked to chronic low-grade inflammation, connecting our metabolic environment to neurodegenerative diseases. GLP-1R agonism in curbing obesity, achieved by impacting appetite and addressing associated metabolic defects, is revealing additional benefits extending beyond weight loss. Whether GLP-1R agonism directly impacts brain health or does so indirectly through improved metabolic health remains to be elucidated. In exploring the intricate connection between obesity and neurological conditions, recent literature suggests that GLP-1R agonism may have the capacity to shape the neurovascular landscape. Thus, GLP-1R agonism emerges as a promising strategy for addressing the complex interplay between metabolic health and cognitive well-being.

Neuromicrobiology Comes of Age: The Multifaceted Interactions between the Microbiome and the Nervous System

The past decade has seen an explosion in our knowledge about the interactions between gut microbiota, the central nervous system, and the immune system. The gut-brain axis has recently gained much attention due to its role in regulating host physiology. This review explores recent findings concerning potential pathways linking the gut-brain axis to the initiation, pathophysiology, and development of neurological disorders. Our objective of this work is to uncover causative factors and pinpoint particular pathways and therapeutic targets that may facilitate the translation of experimental animal research into practical applications for human patients. We highlight three distinct yet interrelated mechanisms: (1) disruptions of both the intestinal and blood-brain barriers, (2) persistent neuroinflammation, and (3) the role of the vagus nerve.

Diabetes and Osteoarthritis: Exploring the Interactions and Therapeutic Implications of Insulin, Metformin, and GLP-1-Based Interventions

Diabetes mellitus (DM) and osteoarthritis (OA) are prevalent chronic conditions with shared pathophysiological links, including inflammation and metabolic dysregulation. This study investigates the potential impact of insulin, metformin, and GLP-1-based therapies on OA progression. Methods involved a literature review of clinical trials and mechanistic studies exploring the effects of these medications on OA outcomes. Results indicate that insulin, beyond its role in glycemic control, may modulate inflammatory pathways relevant to OA, potentially influencing joint health. Metformin, recognized for its anti-inflammatory properties via AMPK activation, shows promise in mitigating OA progression by preserving cartilage integrity and reducing inflammatory markers. GLP-1-based therapies, known for enhancing insulin secretion and improving metabolic profiles in DM, also exhibit anti-inflammatory effects that may benefit OA by suppressing cytokine-mediated joint inflammation and supporting cartilage repair mechanisms. Conclusions suggest that these medications, while primarily indicated for diabetes management, hold therapeutic potential in OA by targeting common underlying mechanisms. Further clinical trials are warranted to validate these findings and explore optimal therapeutic strategies for managing both DM and OA comorbidities effectively.

Impact of alogliptin on lipopolysaccharide-induced experimental Parkinson's disease: Unrevealing neurochemical and histopathological alterations in rodents

BACKGROUND

Degeneration of the nigrostriatal dopaminergic pathway has been seen as a significant cause of movement disability in Parkinson's disease (PD) patients. However, the exact reason for these degenerative changes has remained obscure. In recent years, incretins have been neuroprotective in various pathologies. In the current study, we have investigated the neuroprotective potential of alogliptin (Alo), a dipeptidyl peptidase-IV (DPP-IV) inhibitor, in a lipopolysaccharide (LPS) induced experimental model of PD.

EXPERIMENTAL APPROACH

LPS (5μg/5 μl) was infused intranigrally to induce PD in experimental rats. Post-LPS infusion, these animals were treated with Alo for 21 days in three successive dosages of 10, 20, and 40 mg/kg/day/per oral. The study is well supported with the determinations of motor functions biochemical, neurochemical, and histological analysis.

KEY RESULTS

Intranigral infusion of LPS in rats produced motor deficit. It was accompanied by oxidative stress, elevation in neuroinflammatory cytokines, altered neurochemistry, and degenerative changes in the striatal brain region. While Alo abrogated LPS-induced biochemical/neurochemical alterations, improved motor functions, and preserved neuronal morphology in LPS-infused rats.

CONCLUSION

The observed neuroprotective potential of Alo may be due to its antioxidant and anti-inflammatory actions and its ability to modulate monoaminergic signals. Nonetheless, current findings suggest that improving the availability of incretins through DPP-IV inhibition is a promising strategy for treating Parkinson's disease.

Protocol for a double-blind placebo-controlled randomised controlled trial assessing the impact of oral semaglutide in amyloid positivity (ISAP) in community dwelling UK adults

INTRODUCTION

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs), currently marketed for type 2 diabetes and obesity, may offer novel mechanisms to delay or prevent neurotoxicity associated with Alzheimer's disease (AD). The impact of semaglutide in amyloid positivity (ISAP) trial is investigating whether the GLP-1 RA semaglutide reduces accumulation in the brain of cortical tau protein and neuroinflammation in individuals with preclinical/prodromal AD.

METHODS AND ANALYSIS

ISAP is an investigator-led, randomised, double-blind, superiority trial of oral semaglutide compared with placebo. Up to 88 individuals aged ≥55 years with brain amyloid positivity as assessed by positron emission tomography (PET) or cerebrospinal fluid, and no or mild cognitive impairment, will be randomised. People with the low-affinity binding variant of the rs6971 allele of the Translocator Protein 18 kDa (TSPO) gene, which can interfere with interpreting TSPO PET scans (a measure of neuroinflammation), will be excluded.At baseline, participants undergo tau, TSPO PET and MRI scanning, and provide data on physical activity and cognition. Eligible individuals are randomised in a 1:1 ratio to once-daily oral semaglutide or placebo, starting at 3 mg and up-titrating to 14 mg over 8 weeks. They will attend safety visits and provide blood samples to measure AD biomarkers at weeks 4, 8, 26 and 39. All cognitive assessments are repeated at week 26. The last study visit will be at week 52, when all baseline measurements will be repeated. The primary end point is the 1-year change in tau PET signal.

ETHICS AND DISSEMINATION

The study was approved by the West Midlands-Edgbaston Research Ethics Committee (22/WM/0013). The results of the study will be disseminated through scientific presentations and peer-reviewed publications.

TRIAL REGISTRATION NUMBER

ISRCTN71283871.

Glucagon-Like Peptide-1: New Regulator in Lipid Metabolism

Glucagon-like peptide-1 (GLP-1) is a 30-amino acid peptide hormone that is mainly expressed in the intestine and hypothalamus. In recent years, basic and clinical studies have shown that GLP-1 is closely related to lipid metabolism, and it can participate in lipid metabolism by inhibiting fat synthesis, promoting fat differentiation, enhancing cholesterol metabolism, and promoting adipose browning. GLP-1 plays a key role in the occurrence and development of metabolic diseases such as obesity, nonalcoholic fatty liver disease, and atherosclerosis by regulating lipid metabolism. It is expected to become a new target for the treatment of metabolic disorders. The effects of GLP-1 and dual agonists on lipid metabolism also provide a more complete treatment plan for metabolic diseases. This article reviews the recent research progress of GLP-1 in lipid metabolism.

Angiostrongylus cantonensis induces energy imbalance and dyskinesia in mice by reducing the expression of melanin-concentrating hormone

BACKGROUND

Infection with Angiostrongylus cantonensis (AC) in humans or mice can lead to severe eosinophilic meningitis or encephalitis, resulting in various neurological impairments. Developing effective neuroprotective drugs to improve the quality of life in affected individuals is critical.

METHODS

We conducted a Gene Ontology enrichment analysis on microarray gene expression (GSE159486) in the brains of AC-infected mice. The expression levels of melanin-concentrating hormone (MCH) were confirmed through real-time quantitative PCR (RT-qPCR) and immunofluorescence. Metabolic parameters were assessed using indirect calorimetry, and mice's energy metabolism was evaluated via pathological hematoxylin and eosin (H&E) staining, serum biochemical assays, and immunohistochemistry. Behavioral tests assessed cognitive and motor functions. Western blotting was used to measure the expression of synapse-related proteins. Mice were supplemented with MCH via nasal administration.

RESULTS

Postinfection, a marked decrease in Pmch expression and the encoded MCH was observed. Infected mice exhibited significant weight loss, extensive consumption of sugar and white fat tissue, reduced movement distance, and decreased speed, compared with the control group. Notably, nasal administration of MCH countered the energy imbalance and dyskinesia caused by AC infection, enhancing survival rates. MCH treatment also increased the expression level of postsynaptic density protein 95 (PSD95) and microtubule-associated protein-2 (MAP2), as well as upregulated transcription level of B cell leukemia/lymphoma 2 (Bcl2) in the cortex.

CONCLUSIONS

Our findings suggest that MCH improves dyskinesia by reducing loss of synaptic proteins, indicating its potential as a therapeutic agent for AC infection.

Positive Effects of Adiponectin, BDNF, and GLP-1 on Cortical Neurons Counteracting Palmitic Acid Induced Neurotoxicity

The prevalence of metabolic syndrome caused by diets containing excessive fatty acids is increasing worldwide. Patients with metabolic syndrome exhibit abnormal lipid profiles, chronic inflammation, increased levels of saturated fatty acids, impaired insulin sensitivity, excessive fat accumulation, and neuropathological issues such as memory deficits. In particular, palmitic acid (PA) in saturated fatty acids aggravates inflammation, insulin resistance, impaired glucose tolerance, and synaptic failure. Recently, adiponectin, brain-derived neurotrophic factor (BDNF), and glucose-like peptide-1 (GLP-1) have been investigated to find therapeutic solutions for metabolic syndrome, with findings suggesting that they are involved in insulin sensitivity, enhanced lipid profiles, increased neuronal survival, and improved synaptic plasticity. We investigated the effects of adiponectin, BDNF, and GLP-1 on neurite outgrowth, length, and complexity in PA-treated primary cortical neurons using Sholl analysis. Our findings demonstrate the therapeutic potential of adiponectin, BDNF, and GLP-1 in enhancing synaptic plasticity within brains affected by metabolic imbalance. We underscore the need for additional research into the mechanisms by which adiponectin, BDNF, and GLP-1 influence neural complexity in brains with metabolic imbalances.

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

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

Microglia in Central Control of Metabolism

Beyond their role as brain immune cells, microglia act as metabolic sensors in response to changes in nutrient availability, thus playing a role in energy homeostasis. This review highlights the evidence and challenges of studying the role of microglia in metabolism regulation.

Interaction of the Gut Microbiome and Immunity in Multiple Sclerosis: Impact of Diet and Immune Therapy

The bidirectional communication between the gut and central nervous system (CNS) through microbiota is known as the microbiota-gut-brain axis. The brain, through the enteric neural innervation and the vagus nerve, influences the gut physiological activities (motility, mucin, and peptide secretion), as well as the development of the mucosal immune system. Conversely, the gut can influence the CNS via intestinal microbiota, its metabolites, and gut-homing immune cells. Growing evidence suggests that gut immunity is critically involved in gut-brain communication during health and diseases, including multiple sclerosis (MS). The gut microbiota can influence the development and function of gut immunity, and conversely, the innate and adaptive mucosal immunity can influence microbiota composition. Gut and systemic immunity, along with gut microbiota, are perturbed in MS. Diet and disease-modifying therapies (DMTs) can affect the composition of the gut microbial community, leading to changes in gut and peripheral immunity, which ultimately affects MS. A high-fat diet is highly associated with gut dysbiosis-mediated inflammation and intestinal permeability, while a high-fiber diet/short-chain fatty acids (SCFAs) can promote the development of Foxp3 Tregs and improvement in intestinal barrier function, which subsequently suppress CNS autoimmunity in the animal model of MS (experimental autoimmune encephalomyelitis or EAE). This review will address the role of gut immunity and its modulation by diet and DMTs via gut microbiota during MS pathophysiology.

The role of the microbiota-gut-brain axis and intestinal microbiome dysregulation in Parkinson's disease

Parkinson's disease (PD) is a complex progressive neurodegenerative disease associated with aging. Its main pathological feature is the degeneration and loss of dopaminergic neurons related to the misfolding and aggregation of α-synuclein. The pathogenesis of PD has not yet been fully elucidated, and its occurrence and development process are closely related to the microbiota-gut-brain axis. Dysregulation of intestinal microbiota may promote the damage of the intestinal epithelial barrier, intestinal inflammation, and the upward diffusion of phosphorylated α-synuclein from the enteric nervous system (ENS) to the brain in susceptible individuals and further lead to gastrointestinal dysfunction, neuroinflammation, and neurodegeneration of the central nervous system (CNS) through the disordered microbiota-gut-brain axis. The present review aimed to summarize recent advancements in studies focusing on the role of the microbiota-gut-brain axis in the pathogenesis of PD, especially the mechanism of intestinal microbiome dysregulation, intestinal inflammation, and gastrointestinal dysfunction in PD. Maintaining or restoring homeostasis in the gut microenvironment by targeting the gut microbiome may provide future direction for the development of new biomarkers for early diagnosis of PD and therapeutic strategies to slow disease progression.

Circular RNA Tmcc1 improves astrocytic glutamate metabolism and spatial memory via NF-κB and CREB signaling in a bile duct ligation mouse model: transcriptional and cellular analyses

BACKGROUND

Hepatic encephalopathy-induced hyperammonemia alters astrocytic glutamate metabolism in the brain, which is involved in cognitive decline. To identify specific therapeutic strategies for the treatment of hepatic encephalopathy, various molecular signaling studies, such as non-coding RNA functional study, have been conducted. However, despite several reports of circular RNAs (circRNAs) in the brain, few studies of circRNAs in hepatic encephalopathy-induced neuropathophysiological diseases have been conducted.

METHODS

In this study, we performed RNA sequencing to identify whether the candidate circRNA cirTmcc1 is specifically expressed in the brain cortex in a bile duct ligation (BDL) mouse model of hepatic encephalopathy.

RESULTS

Based on transcriptional and cellular analysis, we investigated the circTmcc1-dysregulation-induced changes in the expression of several genes that are associated with intracellular metabolism and astrocyte function. We found that the circTmcc1 binds with the NF-κB p65-CREB transcriptional complex and regulates the expression of the astrocyte transporter EAAT2. Furthermore, circTmcc1 contributed to the secretion of proinflammatory mediators and glutamate metabolism in astrocytes and subsequently modulated an improvement in spatial memory by mediating neuronal synaptic plasticity.

CONCLUSIONS

Thus, circTmcc1 may be a promising circRNA candidate for targeted interventions to prevent and treat the neuropathophysiological complications that occur due to hepatic encephalopathy.

Glucagon-like peptide-1: a multi-faceted anti-inflammatory agent

Inflammation contributes to many chronic conditions. It is often associated with circulating pro-inflammatory cytokines and immune cells. GLP-1 levels correlate with disease severity. They are often elevated and can serve as markers of inflammation. Previous studies have shown that oxytocin, hCG, ghrelin, alpha-MSH and ACTH have receptor-mediated anti-inflammatory properties that can rescue cells from damage and death. These peptides have been studied well in the past century. In contrast, GLP-1 and its anti-inflammatory properties have been recognized only recently. GLP-1 has been proven to be a useful adjuvant therapy in type-2 diabetes mellitus, metabolic syndrome, and hyperglycemia. It also lowers HbA1C and protects cells of the cardiovascular and nervous systems by reducing inflammation and apoptosis. In this review we have explored the link between GLP-1, inflammation, and sepsis.

Effects of ultra-processed foods on the microbiota-gut-brain axis: The bread-and-butter issue

The topic of gut microbiota and the microbiota-gut-brain (MGB) axis has become the forefront of research and reports in the past few years. The gut microbiota is a dynamic interface between the environment, food, and the host, reflecting the health status as well as maintaining normal physiological metabolism. Modern ultra-processed foods (UPF) contain large quantities of saturated and trans fat, added sugar, salt, and food additives that seriously affect the gut and physical health. In addition, these unhealthy components directly cause changes in gut microbiota functions and microbial metabolism, subsequently having the potential to impact the neural network. This paper reviews an overview of the link between UPF ingredients and the MGB axis. Considerable studies have examined that high intake of trans fat, added sugar and salt have deleterious effects on gut and brain functions, but relatively less focus has been placed on the impact of food additives on the MGB axis. Data from several studies suggest that food additives might be linked to metabolic diseases and inflammation. They may also alter the gut microbiota composition and microbial metabolites, which potentially affect cognition and behavior. Therefore, we emphasize that food additives including emulsifiers, artificial sweeteners, colorants, and preservatives interact with the gut microbiota and their possible effects on altering the brain and behavior based on the latest research. Future studies should further investigate whether gut dysbiosis mediates the effect of UPF on brain diseases and behavior. This thesis here sheds new light on future research pointing to the potentially detrimental effects of processed food consumption on brain health.

Profiling and Cellular Analyses of Obesity-Related circRNAs in Neurons and Glia under Obesity-like In Vitro Conditions

Recent evidence indicates that the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease, is associated with metabolic disorders such as diabetes and obesity. Various circular RNAs (circRNAs) have been found in brain tissues and recent studies have suggested that circRNAs are related to neuropathological mechanisms in the brain. However, there is a lack of interest in the involvement of circRNAs in metabolic imbalance-related neuropathological problems until now. Herein we profiled and analyzed diverse circRNAs in mouse brain cell lines (Neuro-2A neurons, BV-2 microglia, and C8-D1a astrocytes) exposed to obesity-related in vitro conditions (high glucose, high insulin, and high levels of tumor necrosis factor-alpha, interleukin 6, palmitic acid, linoleic acid, and cholesterol). We observed that various circRNAs were differentially expressed according to cell types with many of these circRNAs conserved in humans. After suppressing the expression of these circRNAs using siRNAs, we observed that these circRNAs regulate genes related to inflammatory responses, formation of synaptic vesicles, synaptic density, and fatty acid oxidation in neurons; scavenger receptors in microglia; and fatty acid signaling, inflammatory signaling cyto that may play important roles in metabolic disorders associated with neurodegenerative diseases.

The GLP-1 receptor agonist exenatide ameliorates neuroinflammation, locomotor activity, and anxiety-like behavior in mice with diet-induced obesity through the modulation of microglial M2 polarization and downregulation of SR-A4

Obesity is associated with multiple comorbidities, such as metabolic abnormalities and cognitive dysfunction. Moreover, accumulating evidence indicates that neurodegenerative disorders are associated with chronic neuroinflammation. GLP-1 receptor agonists (RAs) have been extensively studied as a treatment for type 2 diabetes. Emerging evidence has demonstrated a protective effect of GLP-1 RAs on neurodegenerative disease, which is independent of its glucose-lowering effects. In this study, we aimed to examine the effects of a long-acting GLP-1 RA, exenatide, on high-fat diet (HFD)-induced neuroinflammation and related brain function impairment. First, mice treated with exenatide exhibited significantly reduced HFD-increased body weight and blood glucose. In an open field test, exenatide treatment ameliorated the reduction in local motor activity and anxiety in HFD-fed mice. Moreover, HFD induced astrogliosis, microgliosis, and upregulation of IL-1β, IL-6 and TNF-α in hippocampus and cortex. Exenatide treatment reduced HFD-induced astrogliosis and IL-1β and TNF-α expressions. Moreover, exenatide increased phosphor-ERK and M2-type microglia marker arginase-1 expression in the hippocampus and cortex. In addition, we found that scavenger receptor-A4 protein expression was induced by HFD and was subsequently inhibited by exenatide. SR-A4 knockout reversed the locomotor activity impairment but not the anxiety behavior caused by HFD consumption. SR-A4 knockout also reduced HFD-induced neuroinflammation, as shown by the reduced expression of GFAP and IBA-1 compared with that in wild-type control mice. These results demonstrate that exenatide decreases HFD-increased neuroinflammation and promotes anti-inflammatory M2 differentiation. The inhibition of SR-A4 by exenatide exerts anti-inflammatory activity.

Activation of IGF-1/GLP-1 Signalling via 4-Hydroxyisoleucine Prevents Motor Neuron Impairments in Experimental ALS-Rats Exposed to Methylmercury-Induced Neurotoxicity

Amyotrophic lateral sclerosis (ALS) is a severe adult motor neuron disease that causes progressive neuromuscular atrophy, muscle wasting, weakness, and depressive-like symptoms. Our previous research suggests that mercury levels are directly associated with ALS progression. MeHg+-induced ALS is characterised by oligodendrocyte destruction, myelin basic protein (MBP) depletion, and white matter degeneration, leading to demyelination and motor neuron death. The selection of MeHg+ as a potential neurotoxicant is based on our evidence that it has been connected to the development of ALS-like characteristics. It causes glutamate-mediated excitotoxicity, calcium-dependent neurotoxicity, and an ALS-like phenotype. Dysregulation of IGF-1/GLP-1 signalling has been associated with ALS progression. The bioactive amino acid 4-hydroxyisoleucine (HI) from Trigonella foenum graecum acts as an insulin mimic in rodents and increases insulin sensitivity. This study examined the neuroprotective effects of 4-HI on MeHg+-treated adult Wistar rats with ALS-like symptoms, emphasising brain IGF1/GLP-1 activation. Furthermore, we investigated the effect of 4-HI on MBP levels in rat brain homogenate, cerebrospinal fluid (CSF), blood plasma, and cell death indicators such as caspase-3, Bax, and Bcl-2. Rats were assessed for muscular strength, locomotor deficits, depressed behaviour, and spatial learning in the Morris water maze (MWM) to measure neurobehavioral abnormalities. Doses of 4-HI were given orally for 42 days in the MeHg+ rat model at 50 mg/kg or 100 mg/kg to ameliorate ALS-like neurological dysfunctions. Additionally, neurotransmitters and oxidative stress markers were examined in rat brain homogenates. Our findings suggest that 4-HI has neuroprotective benefits in reducing MeHg+-induced behavioural, neurochemical, and histopathological abnormalities in ALS-like rats exposed to methylmercury.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

New Advances on Pathophysiology of Diabetes Neuropathy and Pain Management: Potential Role of Melatonin and DPP-4 Inhibitors

Pre-diabetes and diabetes are growing threats to the modern world. Diabetes mellitus (DM) is associated with comorbidities such as hypertension (83.40%), obesity (90.49%), and dyslipidemia (93.43%), creating a substantial burden on patients and society. Reductive and oxidative (Redox) stress level imbalance and inflammation play an important role in DM progression. Various therapeutics have been investigated to treat these neuronal complications. Melatonin and dipeptidyl peptidase IV inhibitors (DPP-4i) are known to possess powerful antioxidant and anti-inflammatory properties and have garnered significant attention in the recent years. In this present review article, we have reviewed the recently published reports on the therapeutic efficiency of melatonin and DPP-4i in the treatment of DM. We summarized the efficacy of melatonin and DPP-4i in DM and associated complications of diabetic neuropathy (DNP) and neuropathic pain. Furthermore, we discussed the mechanisms of action and their efficacy in the alleviation of oxidative stress in DM.

The Role of Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RA) in Diabetes-Related Neurodegenerative Diseases

Recent clinical guidelines have emphasized the importance of screening for cognitive impairment in older adults with diabetes, however, there is still a lack of understanding about the drug therapy. Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are widely used in the treatment of type 2 diabetes and potential applications may include the treatment of obesity as well as the adjunctive treatment of type 1 diabetes mellitus in combination with insulin. Growing evidence suggests that GLP-1 RA has the potential to treat neurodegenerative diseases, particularly in diabetes-related Alzheimer’s disease (AD) and Parkinson’s disease (PD). Here, we review the molecular mechanisms of the neuroprotective effects of GLP-1 RA in diabetes-related degenerative diseases, including AD and PD, and their potential effects.

Metabolic factors in the regulation of hypothalamic innate immune responses in obesity

The hypothalamus is a central regulator of body weight and energy homeostasis. There is increasing evidence that innate immune activation in the mediobasal hypothalamus (MBH) is a key element in the pathogenesis of diet-induced obesity. Microglia, the resident immune cells in the brain parenchyma, have been shown to play roles in diverse aspects of brain function, including circuit refinement and synaptic pruning. As such, microglia have also been implicated in the development and progression of neurological diseases. Microglia express receptors for and are responsive to a wide variety of nutritional, hormonal, and immunological signals that modulate their distinct functions across different brain regions. We showed that microglia within the MBH sense and respond to a high-fat diet and regulate the function of hypothalamic neurons to promote food intake and obesity. Neurons, glia, and immune cells within the MBH are positioned to sense and respond to circulating signals that regulate their capacity to coordinate aspects of systemic energy metabolism. Here, we review the current knowledge of how these peripheral signals modulate the innate immune response in the MBH and enable microglia to regulate metabolic control.

Glucagon-like peptide-1 analogs mitigate neuroinflammation in Alzheimer's disease by suppressing NLRP2 activation in astrocytes

Neuroinflammation is closely linked to the pathogenesis of Alzheimer's disease (AD). Glucagon-like peptide-1 (GLP-1) analogs exhibit anti-inflammatory and neuroprotective effects; hence, we investigated whether they reduce cognitive impairment and protect astrocytes from oxidative stress. We found that 5 × FAD transgenic mice treated with the synthetic GLP-1 receptor agonist exenatide had improved cognitive function per the Morris water maze test. Immunohistochemistry, western blotting, and ELISAs used to detect inflammatory factors revealed reduced neuroinflammation in extracted piriform cortexes of exenatide-treated mice as well as lower amyloid β_1-42-induced oxidative stress and inflammation in astrocytes treated with exendin-4 (the natural analog of exenatide). Adenovirus-mediated overexpression of nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 2 (NLRP2) revealed that exenatide/exendin-4 function may be attributed to NLRP2 inflammasome inhibition. Collectively, our results indicate that GLP-1 analogs improve cognitive dysfunction in vivo and protect astrocytes in vitro, potentially via the downregulation of the NLRP2 inflammasome.

Neuroprotective effects of liraglutide against inflammation through the AMPK/NF-κB pathway in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease with increasing incidence in aged populations, second only to Alzheimer's disease. Increasing evidence has shown that inflammation plays an important role in the occurrence and development of Parkinson's disease. Growing evidence has shown that AMP-activated protein kinase (AMPK) and NF-κB are closely related to inflammation. Glucagon-like peptide 1 (GLP-1) is a hormone that is primarily secreted by intestinal endocrine L cells, and it has a variety of physiology through binding to GLP-1 receptor. GLP-1can be used for treatment of type 2 diabetes. In addition, GLP-1 also has anti-neuroinflammation activity. However, the exact mechanism behind how GLP-1 regulates neuroinflammation remains unclear. This study was designed to examine the effect of liraglutide on 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-induced injury in mice and its potential mechanism of action. Results showed that liraglutide dose-dependently ameliorated mouse behavior including swimming time and locomotor activity, increased the number of tyrosine hydroxylase (TH)-positive neurons and protein level, and reduced Iba1 and GFAP expression in the substantia nigra (SN). Liraglutide treatment also increased p-AMPK expression and reduced NF-κB protein level. Applying the AMPK inhibitor Dorsomorphin (Compound C) reversed the effect of liraglutide-reducing p-AMPK and increasing NF-κB expression. Finally, GFAP protein level increased, along with a decrease in TH expression. In conclusion, these results suggest that liraglutide can suppress neuroinflammation. Moreover, this effect is mediated through the AMPK/NF-κB signaling pathway.

Liraglutide attenuate central nervous inflammation and demyelination through AMPK and pyroptosis-related NLRP3 pathway

Aims

Multiple sclerosis (MS) still maintains increasing prevalence and poor prognosis, while glucagon‐like peptide‐1 receptor (GLP‐1R) agonists show excellent neuroprotective capacities recently. Thus, we aim to evaluate whether the GLP‐1R agonist liraglutide (Lira) could ameliorate central nervous system demyelination and inflammation.

Methods

The therapeutic effect of Lira was tested on experimental autoimmune encephalitis (EAE) in vivo and a microglia cell line BV2 in vitro.

Results

Lira administration could ameliorate the disease score of EAE mice, delay the disease onset, ameliorate pathological demyelination and inflammation score in lumbar spinal cord, reduce pathogenic T helper cell transcription in spleen, restore phosphorylated adenosine monophosphate‐activated protein kinase (pAMPK) level, autophagy level, and inhibit pyroptosis‐related NLR family, pyrin domain‐containing protein 3 (NLRP3) pathway in lumbar spinal cord. Additionally, cell viability test, lactate dehydrogenase release test, and dead/live cell staining test for BV2 cells showed Lira could not salvage BV2 from nigericin‐induced pyroptosis significantly.

Conclusion

Lira has anti‐inflammation and anti‐demyelination effect on EAE mice, and the protective effect of Lira in the EAE model may be related to regulation of pAMPK pathway, autophagy, and NLRP3 pathway. However, Lira treatment cannot significantly inhibit pyroptosis of BV2 cells in vitro. Our study provides Lira as a potential candidate for Multiple Sclerosis treatment.

The mechanism and efficacy of GLP-1 receptor agonists in the treatment of Alzheimer's disease

Since type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD) and both have the same pathogenesis (e.g., insulin resistance), drugs used to treat T2DM have been gradually found to reduce the progression of AD in AD models. Of these drugs, glucagon-like peptide 1 receptor (GLP-1R) agonists are more effective and have fewer side effects. GLP-1R agonists have reducing neuroinflammation and oxidative stress, neurotrophic effects, decreasing Aβ deposition and tau hyperphosphorylation in AD models, which may be a potential drug for the treatment of AD. However, this needs to be verified by further clinical trials. This study aims to summarize the current information on the mechanisms and effects of GLP-1R agonists in AD.

Impact of glucagon-like peptide 1 analogs on cognitive function among patients with type 2 diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Diabetes is an independent risk factor for cognitive impairment. However, little is known about the neuroprotective effects of glucagon-like peptide 1 (GLP-1) analogs on type 2 diabetes mellitus (T2DM). Herein, we assessed the impact of GLP-1 analogs on the general cognitive functioning among patients with T2DM.

METHODS

Relevant studies were retrieved from PubMed, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrials.gov databases from their inception till June 30, 2022, without any language restrictions. For continuous variables, the mean and standard deviation (SD) were extracted. Considering the heterogeneity in general cognitive functioning assessments among the pooled studies, the standardized mean differences (SMDs) with corresponding 95% confidence intervals (CIs), were calculated.

RESULTS

Five studies including 7,732 individuals with T2DM were selected for the meta-analysis. The use of GLP-1 analogs exerted no significant effects on the general cognitive functioning in self-controlled studies (SMD 0.33, 95% CI -0.03 to 0.69). Subgroup analyses among the self-controlled studies based on age and history of cardio-cerebrovascular disease showed that GLP-1 analogs significantly improved the general cognitive functioning in T2DM patients younger than 65 years (SMD 0.69, 95% CI 0.31 to 1.08) or those without cardio-cerebrovascular diseases (SMD 0.69, 95% CI 0.31 to 1.08). Similarly, differences in the general cognitive functioning for GLP-1 analogs between treated and non-treated patients with T2DM were significant in subgroups with patients younger than 65 years (SMD 1.04, 95% CI 0.61 to 1.47) or those with no history of cardio-cerebrovascular diseases (SMD 1.04, 95% CI 0.61 to 1.47).

CONCLUSION

Limited evidence suggests that the use of GLP-1 analogs exerts no significant effects on general cognitive functioning but may be beneficial for patients with T2DM younger than 65 years or those without a history of cardio-cerebrovascular diseases. Further prospective clinical studies with large sample sizes are needed to validate these findings.

SYSTEMATIC REVIEW REGISTRATION

www.inplasy.com, identifier 202260015.

Targeting the GLP-1/GLP-1R axis to treat osteoarthritis: A new opportunity?

Osteoarthritis (OA) is a degenerative joint disease affecting millions of people worldwide. In OA, chondrocytes, synovial cells and other joint cells become activated when exposed to an abnormal environment, including mechanical stress, inflammatory cytokines or disorganization of matrix proteins. Several analogues of the hormones called incretins have been developed and are used notably for treating type 2 diabetes mellitus. Data has accumulated to suggest that incretinomimetics, which bind to the glucagon-like peptide-1 receptor (GLP-1R), have beneficial pleiotropic effects such as immunomodulation, anti-inflammation and neuronal protection. Thus, because of their anti-inflammatory properties, GLP-1-based therapies could benefit OA patients. This review focuses on the GLP-1R pathway, molecular mechanisms and phenotypes related to OA pathogenesis.

The translational potential of this article

The search for new therapeutic targets to treat people suffering from OA remains urgent as there is currently no disease-modifyingtherapy available for this disease. This review discusses how GLP-1 analogues could be potential DMOADs for treating OA thanks to their anti-inflammatory, immunoregulatory and differentiation properties.

Myeloid cell modulation by a GLP-1 receptor agonist regulates retinal angiogenesis in ischemic retinopathy

Ischemic retinopathies including diabetic retinopathy are major causes of blindness. Although neurons and Müller glia are recognized as important regulators of reparative and pathologic angiogenesis, the role of mononuclear phagocytes (MPs) — particularly microglia, the resident retinal immune cells — is unclear. Here, we found MP activation in human diabetic retinopathy, especially in neovessels from human neovascular membranes in proliferative retinopathy, including TNF-α expression. There was similar activation in the mouse oxygen-induced retinopathy (OIR) model of ischemia-induced neovascularization. Glucagon-like peptide-1 receptor (GLP-1R) agonists are in clinical use for glycemic control in diabetes and are also known to modulate microglia. Herein, we investigated the effect of a long-acting GLP-1R agonist, NLY01. Following intravitreal administration, NLY01 selectively localized to MPs in retina with OIR. NLY01 modulated MPs but not retinal endothelial cell viability, apoptosis, and tube formation in vitro. In OIR, NLY01 treatment inhibited MP infiltration and activation, including MP expression of cytokines in vivo. NLY01 significantly suppressed global induction of retinal inflammatory cytokines, promoted reparative angiogenesis, and suppressed pathologic retinal neovascularization. Collectively, these findings indicate the important role of mononuclear phagocytes in regulation of retinal vascularization in ischemia and suggest modulation of MPs as a potentially new treatment strategy for ischemic retinopathies.

Microglia and BDNF at the crossroads of stressor related disorders: Towards a unique trophic phenotype

Stressors ranging from psychogenic/social to neurogenic/injury to systemic/microbial can impact microglial inflammatory processes, but less is known regarding their effects on trophic properties of microglia. Recent studies do suggest that microglia can modulate neuronal plasticity, possibly through brain derived neurotrophic factor (BDNF). This is particularly important given the link between BDNF and neuropsychiatric and neurodegenerative pathology. We posit that certain activated states of microglia play a role in maintaining the delicate balance of BDNF release onto neuronal synapses. This focused review will address how different "activators" influence the expression and release of microglial BDNF and address the question of tropomyosin receptor kinase B (TrkB) expression on microglia. We will then assess sex-based differences in microglial function and BDNF expression, and how microglia are involved in the stress response and related disorders such as depression. Drawing on research from a variety of other disorders, we will highlight challenges and opportunities for modulators that can shift microglia to a "trophic" phenotype with a view to potential therapeutics relevant for stressor-related disorders.

Teneligliptin Exerts Antinociceptive Effects in Rat Model of Partial Sciatic Nerve Transection Induced Neuropathic Pain

Neuropathic pain (NP), is a chronic pain resulting from nerve injury, with limited treatment options. Teneligliptin (TEN) is a dipeptidyl peptidase-4 inhibitor (DPP-4i) approved to treat type 2 diabetes. DPP-4is prevent the degradation of the incretin hormone glucagon-like peptide 1 (GLP-1) and prolong its circulation. Apart from glycemic control, GLP-1 is known to have antinociceptive and anti-inflammatory effects. Herein, we investigated the antinociceptive properties of TEN on acute pain, and partial sciatic nerve transection (PSNT)-induced NP in Wistar rats. Seven days post PSNT, allodynia and hyperalgesia were confirmed as NP, and intrathecal (i.t) catheters were implanted and connected to an osmotic pump for the vehicle (1 μL/h) or TEN (5 μg/1 μL/h) or TEN (5 μg) + GLP-1R antagonist Exendin-3 (9–39) amide (EXE) 0.1 μg/1 μL/h infusion. The tail-flick response, mechanical allodynia, and thermal hyperalgesia were measured for 7 more days. On day 14, the dorsal horn was harvested and used for Western blotting and immunofluorescence assays. The results showed that TEN had mild antinociceptive effects against acute pain but remarkable analgesic effects against NP. Furthermore, co-infusion of GLP-1R antagonist EXE with TEN partially reversed allodynia but not tail-flick latency. Immunofluorescence examination of the spinal cord revealed that TEN decreased the immunoreactivity of glial fibrillary acidic protein (GFAP). Taken together, our findings suggest that TEN is efficient in attenuation of PSNT-induced NP. Hence, the pleiotropic effects of TEN open a new avenue for NP management.

Treating cognitive impairment in schizophrenia with GLP-1RAs: an overview of their therapeutic potential

INTRODUCTION

Schizophrenia is a neuropsychiatric disorder that affects approximately 1% of individuals worldwide. There are no available medications to treat cognitive impairment in this patient population currently. Preclinical evidence suggests that glucagon-like peptide-1 receptor agonists (GLP-1 RAs) improve cognitive function. There is a need to evaluate how GLP-1 RAs alter specific domains of cognition and whether they will be of therapeutic benefit in individuals with schizophrenia.

AREAS COVERED

This paper summarizes the effects of GLP-1 RAs on metabolic processes in the brain and how these mechanisms relate to improved cognitive function. We provide an overview of preclinical studies that demonstrate GLP-1 RAs improve cognition and comment on their potential therapeutic benefit in individuals with schizophrenia.

EXPERT OPINION

To understand the benefits of GLP-1 RAs in individuals with schizophrenia, further preclinical research with rodent models relevant to schizophrenia symptomology are needed. Moreover, preclinical studies must focus on using a wider range of behavioral assays to understand whether important aspects of cognition such as executive function, attention, and goal-directed behavior are improved using GLP-1 RAs. Further research into the specific mechanisms of how GLP-1 RAs affect cognitive function and their interactions with antipsychotic medication commonly prescribed is necessary.

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

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

Reassessment of Pioglitazone for Alzheimer's Disease

Alzheimer's disease is a quintessential 'unmet medical need', accounting for ∼65% of progressive cognitive impairment among the elderly, and 700,000 deaths in the United States in 2020. In 2019, the cost of caring for Alzheimer's sufferers was $244B, not including the emotional and physical toll on caregivers. In spite of this dismal reality, no treatments are available that reduce the risk of developing AD or that offer prolonged mitiagation of its most devestating symptoms. This review summarizes key aspects of the biology and genetics of Alzheimer's disease, and we describe how pioglitazone improves many of the patholophysiological determinants of AD. We also summarize the results of pre-clinical experiments, longitudinal observational studies, and clinical trials. The results of animal testing suggest that pioglitazone can be corrective as well as protective, and that its efficacy is enhanced in a time- and dose-dependent manner, but the dose-effect relations are not monotonic or sigmoid. Longitudinal cohort studies suggests that it delays the onset of dementia in individuals with pre-existing type 2 diabetes mellitus, which small scale, unblinded pilot studies seem to confirm. However, the results of placebo-controlled, blinded clinical trials have not borne this out, and we discuss possible explanations for these discrepancies.

Dysregulation of IGF-1/GLP-1 signaling in the progression of ALS: potential target activators and influences on neurological dysfunctions

The prominent causes for motor neuron diseases like ALS are demyelination, immune dysregulation, and neuroinflammation. Numerous research studies indicate that the downregulation of IGF-1 and GLP-1 signaling pathways plays a significant role in the progression of ALS pathogenesis and other neurological disorders. In the current review, we discussed the dysregulation of IGF-1/GLP-1 signaling in neurodegenerative manifestations of ALS like a genetic anomaly, oligodendrocyte degradation, demyelination, glial overactivation, immune deregulation, and neuroexcitation. In addition, the current review reveals the IGF-1 and GLP-1 activators based on the premise that the restoration of abnormal IGF-1/GLP-1 signaling could result in neuroprotection and neurotrophic effects for the clinical-pathological presentation of ALS and other brain diseases. Thus, the potential benefits of IGF-1/GLP-1 signal upregulation in the development of disease-modifying therapeutic strategies may prevent ALS and associated neurocomplications.

Insights into a possible role of glucagon-like peptide-1 receptor agonists in the treatment of depression

Depression is a highly prevalent mood disorder and one of the major health concerns in modern society. Moreover, it is characterized by a high prevalence of coexistence with many other diseases including metabolic disorders such as type 2 diabetes mellitus (T2DM) and obesity. Currently used antidepressant drugs, which mostly target brain monoaminergic neurotransmission, have limited clinical efficacy. Although the etiology of depression has not been fully elucidated, current scientific data emphasize the role of neurotrophic factors deficiencies, disturbed homeostasis between the nervous system and the immune and endocrine systems, as well as disturbances in brain energy metabolism and dysfunctions in the gut-brain axis as important factors in the pathogenesis of this neuropsychiatric disorder. Therefore, therapeutic options that could work in a way other than classic antidepressants are being sought to increase the effectiveness of the treatment. Interestingly, glucagon-like peptide-1 receptor agonists (GLP-1RAs), used in the treatment of T2DM and obesity, are known to show pro-cognitive and neuroprotective properties, and exert modulatory effects on immune, endocrine and metabolic processes in the central nervous system. This review article discusses the potential antidepressant effects of GLP-1RAs, especially in the context of their action on the processes related to neuroprotection, inflammation, stress response, energy metabolism, gut-brain crosstalk and the stability of the gut microbiota.

The effect of dipeptidyl peptidase IV on disease-associated microglia phenotypic transformation in epilepsy

BACKGROUND

Accumulating evidence suggests that disease-associated microglia (DAM), a recently discovered subset of microglia, plays a protective role in neurological diseases. Targeting DAM phenotypic transformation may provide new therapeutic options. However, the relationship between DAM and epilepsy remains unknown.

METHODS

Analysis of public RNA-sequencing data revealed predisposing factors (such as dipeptidyl peptidase IV; DPP4) for epilepsy related to DAM conversion. Anti-epileptic effect was assessed by electroencephalogram recordings and immunohistochemistry in a kainic acid (KA)-induced mouse model of epilepsy. The phenotype, morphology and function of microglia were assessed by qPCR, western blotting and microscopic imaging.

RESULTS

Our results demonstrated that DPP4 participated in DAM conversion and epilepsy. The treatment of sitagliptin (a DPP4 inhibitor) attenuated KA-induced epilepsy and promoted the expression of DAM markers (Itgax and Axl) in both mouse epilepsy model in vivo and microglial inflammatory model in vitro. With sitagliptin treatment, microglial cells did not display an inflammatory activation state (enlarged cell bodies). Furthermore, these microglia exhibited complicated intersections, longer processes and wider coverage of parenchyma. In addition, sitagliptin reduced the activation of NF-κB signaling pathway and inhibited the expression of iNOS, IL-1β, IL-6 and the proinflammatory DAM subset gene CD44.

CONCLUSION

The present results highlight that the DPP4 inhibitor sitagliptin can attenuate epilepsy and promote DAM phenotypic transformation. These DAM exhibit unique morphological features, greater migration ability and better surveillance capability. The possible underlying mechanism is that sitagliptin can reduce the activation of NF-κB signaling pathway and suppress the inflammatory response mediated by microglia. Thus, we propose DPP4 may act as an attractive direction for DAM research and a potential therapeutic target for epilepsy.

GLP-1 improves the neuronal supportive ability of astrocytes in Alzheimer's disease by regulating mitochondrial dysfunction via the cAMP/PKA pathway

The glucagon-like peptide-1 (GLP-1) was shown to have neuroprotective effects in Alzheimer's disease (AD). However, the underlying mechanism remains elusive. Astrocytic mitochondrial abnormalities have been revealed to constitute important pathologies. In the present study, we investigated the role of astrocytic mitochondria in the neuroprotective effect of GLP-1 in AD. To this end, 6-month-old 5 × FAD mice were subcutaneously treated with liraglutide, a GLP-1 analogue (25 nmol/kg/qd) for 8 weeks. Liraglutide ameliorated mitochondrial dysfunction and prevented neuronal loss with activation of the cyclic adenosine 3',5'-monophosphate (cAMP)/phosphorylate protein kinase A (PKA) pathway in the brain of 5 × FAD mice. Next, we exposed astrocytes to β-amyloid (Aβ) in vitro and treated them with GLP-1. By activating the cAMP/PKA pathway, GLP-1 increased the phosphorylation of DRP-1 at the s637 site and mitigated mitochondrial fragmentation in Aβ-treated astrocytes. GLP-1 further improved the Aβ-induced energy failure, mitochondrial reactive oxygen species (ROS) overproduction, mitochondrial membrane potential (MMP) collapse, and cell toxicity in astrocytes. Moreover, GLP-1 also promoted the neuronal supportive ability of Aβ-treated astrocytes via the cAMP/PKA pathway. This study revealed a new mechanism behind the neuroprotective effect of GLP-1 in AD.

Exendin-4 improves long-term potentiation and neuronal dendritic growth in vivo and in vitro obesity condition

Metabolic syndrome, which increases the risk of obesity and type 2 diabetes has emerged as a significant issue worldwide. Recent studies have highlighted the relationship between metabolic imbalance and neurological pathologies such as memory loss. Glucagon-like peptide 1 (GLP-1) secreted from gut L-cells and specific brain nuclei plays multiple roles including regulation of insulin sensitivity, inflammation and synaptic plasticity. Although GLP-1 and GLP-1 receptor agonists appear to have neuroprotective function, the specific mechanism of their action in brain remains unclear. We investigated whether exendin-4, as a GLP-1RA, improves cognitive function and brain insulin resistance in metabolic-imbalanced mice fed a high-fat diet. Considering the result of electrophysiological experiments, exendin-4 inhibits the reduction of long term potentiation (LTP) in high fat diet mouse brain. Further, we identified the neuroprotective effect of exendin-4 in primary cultured hippocampal and cortical neurons in in vitro metabolic imbalanced condition. Our results showed the improvement of IRS-1 phosphorylation, neuronal complexity, and the mature of dendritic spine shape by exendin-4 treatment in metabolic imbalanced in vitro condition. Here, we provides significant evidences on the effect of exendin-4 on synaptic plasticity, long-term potentiation, and neural structure. We suggest that GLP-1 is important to treat neuropathology caused by metabolic syndrome.

Maternal fish oil consumption has a negative impact on mammary gland tumorigenesis in C3(1) Tag mice offspring

PURPOSE

Omega-3 fatty acids have been shown to reduce the incidence and slow the growth of mammary gland cancer in rodent models. Since exposure to dietary components during the critical developmental times of gestation and lactation may alter risk for mammary gland cancer in females, we tested whether exposure to increased levels of long-chain omega-3 fatty acids from fish oils would be preventive or promotional to mammary gland cancer in the offspring.

METHODS

Normal SV129 female mice were fed AIN 76 diets containing either 10% corn oil (control, 50% omega 6, n-6) or 5% of an omega-3 (n-3) fatty acid concentrate (fish oil 60% n-3) + 5% canola oil (10% n-3 + 20% n-6). Females were then mated with C(3)1 TAg transgenic mice. At weaning (3 weeks), pups were randomized to either the corn (C) or fish oil (F) diet, 15-17 mice per group. Four experimental groups were generated: FF, FC, CF and CC. Tumor incidence and multiplicity were assessed at the following time points 120, 130 and 140 days of age. A panel of genes encoding signal transduction proteins were analyzed in mammary glands at 130 days.

RESULTS

Mice never exposed to fish oil (CC group) had a significantly higher incidence and multiplicity of mammary gland tumors than mice exposed to fish oil throughout life (FF group). Mice exposed to fish oil during a portion of life (CF or FC) had intermediate tumor incidences and multiplicities. Results also indicate that maternal consumption of fish oil increased the expression of genes associated with immune system activation (Ccl20, Cd5, Il2, Lef1, Lta).

CONCLUSIONS

Adequate omega-3 fatty acids in the maternal diet may reduce the risk for mammary gland cancer in the offspring. If humans make dietary change by consuming more omega-3 fat instead of corn oil with 0% omega 3 fat, breast cancer may be reduced in the next generation.

GLP-1 improves the supportive ability of astrocytes to neurons by promoting aerobic glycolysis in Alzheimer's disease

Objective

Astrocytes actively participate in energy metabolism in the brain, and astrocytic aerobic glycolysis disorder is associated with the pathology of Alzheimer's disease (AD). GLP-1 has been shown to improve cognition in AD; however, the mechanism remains unclear. The objectives of this study were to assess GLP-1's glycolytic regulation effects in AD and reveal its neuroprotective mechanisms.

Methods

The Morris water maze test was used to evaluate the effects of liraglutide (an analog of GLP-1) on the cognition of 4-month-old 5×FAD mice, and a proteomic analysis and Western blotting were used to assess the proteomic profile changes. We constructed an astrocytic model of AD by treating primary astrocytes with Aβ_1-42. The levels of NAD+ and lactate were examined, and the oxidative levels were assessed by a Seahorse examination. Astrocyte-neuron co-culture was performed to evaluate the effects of GLP-1 on astrocytes’ neuronal support.

Results

GLP-1 improved cognition in 4-month-old 5×FAD mice by enhancing aerobic glycolysis and reducing oxidative phosphorylation (OXPHOS) levels and oxidative stress in the brain. GLP-1 also alleviated Aβ-induced glycolysis declines in astrocytes, which resulted in reduced OXPHOS levels and reactive oxygen species (ROS) production. The mechanism involved the activation of the PI3K/Akt pathway by GLP-1. Elevation in astrocytic glycolysis improved astrocyte cells’ support of neurons and promoted neuronal survival and axon growth.

Conclusions

Taken together, we revealed GLP-1's capacity to regulate astrocytic glycolysis, providing mechanistic insight into one of its neuroprotective roles in AD and support for the feasibility of energy regulation treatments for AD.

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GLP-1 mediates a metabolic shift from oxidative phosphorylation to aerobic glycolysis in Alzheimer's disease.

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GLP-1's mechanism of action involves activation of the PI3K/Akt pathway.

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GLP-1 enhances the supportive ability of astrocytes to neurons by promoting aerobic glycolysis.

Role of Exendin-4 in Brain Insulin Resistance, Mitochondrial Function, and Neurite Outgrowth in Neurons under Palmitic Acid-Induced Oxidative Stress

Glucagon like peptide 1 (GLP-1) is an incretin hormone produced by the gut and brain, and is currently being used as a therapeutic drug for type 2 diabetes and obesity, suggesting that it regulates abnormal appetite patterns, and ameliorates impaired glucose metabolism. Many researchers have demonstrated that GLP-1 agonists and GLP-1 receptor agonists exert neuroprotective effects against brain damage. Palmitic acid (PA) is a saturated fatty acid, and increases the risk of neuroinflammation, lipotoxicity, impaired glucose metabolism, and cognitive decline. In this study, we investigated whether or not Exentin-4 (Ex-4; GLP-1 agonist) inhibits higher production of reactive oxygen species (ROS) in an SH-SY5Y neuronal cell line under PA-induced apoptosis conditions. Moreover, pre-treatment with Ex-4 in SH-SY5Y neuronal cells prevents neural apoptosis and mitochondrial dysfunction through several cellular signal pathways. In addition, insulin sensitivity in neurons is improved by Ex-4 treatment under PA-induced insulin resistance. Additionally, our imaging data showed that neuronal morphology is improved by EX-4 treatment, in spite of PA-induced neuronal damage. Furthermore, we identified that Ex-4 inhibits neuronal damage and enhanced neural complexity, such as neurite length, secondary branches, and number of neurites from soma in PA-treated SH-SY5Y. We observed that Ex-4 significantly increases neural complexity, dendritic spine morphogenesis, and development in PA treated primary cortical neurons. Hence, we suggest that GLP-1 administration may be a crucial therapeutic solution for improving neuropathology in the obese brain.

GLP-1 mimetics and cognition

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of antidiabetic drugs that improve the glycaemia via several molecular pathways. Recent evidence suggest that they also have additional effects modulating pathophysiologic pathways included in cognitive disorders. Since some forms of cognitive dysfunction such as Alzheimer's disease are more common among diabetic patients than in the normal population, antidiabetic drugs that have neuroprotective effects affording protection for cognitive disorders would be of benefit. Therefore, we reviewed the pharmacologic effects of GLP-1 analogues and found that they may have the additional benefit of improving cognitive performance via at least eight molecular mechanisms.