Evidence of metabolic memory-induced neurodegeneration and the therapeutic effects of glucagon-like peptide-1 receptor agonists via Forkhead box class O

Polysaccharide extracted from Sarcandra glabra residue attenuate cognitive impairment by regulating gut microbiota in diabetic mice

Diabetic encephalopathy (DE), characterized by cognitive impairment, currently lacks targeted treatment. Previous studies have shown that Sarcandra glabra extracted residue polysaccharide (SERP) exhibited hypoglycemic effects either in vitro or in streptozotocin-induced diabetes mice. However, the therapeutic effect of SERP on DE was not elucidated. This study investigated the therapeutic effect of SERP on DE and its underlying mechanism. Our results revealed that SERP regulates glucose and lipid metabolism, improves cognitive function, and exhibits diminished activity post-antibiotic intervention. Importantly, we discovered a novel mechanism by which SERP modulates the gut microbiota, specifically enriching Bacteroidales S24-7, resulting in elevated levels of butyric acid in the intestine. This regulation modulates the intestinal endocrine cell lipid metabolism level, restores damaged intestinal barriers and neural epithelial circuits, thus exhibiting cure effects. Our findings suggest that SERP could become a candidate for treating DE, potentially involving the regulation mechanism of the "microbiota-gut-brain axis". This study underscores the unique therapeutic efficacy of SERP in managing DE, offering fresh drug candidates and innovative treatment strategies for this challenging condition.

Metabolic memory: mechanisms and diseases

Metabolic diseases and their complications impose health and economic burdens worldwide. Evidence from past experimental studies and clinical trials suggests our body may have the ability to remember the past metabolic environment, such as hyperglycemia or hyperlipidemia, thus leading to chronic inflammatory disorders and other diseases even after the elimination of these metabolic environments. The long-term effects of that aberrant metabolism on the body have been summarized as metabolic memory and are found to assume a crucial role in states of health and disease. Multiple molecular mechanisms collectively participate in metabolic memory management, resulting in different cellular alterations as well as tissue and organ dysfunctions, culminating in disease progression and even affecting offspring. The elucidation and expansion of the concept of metabolic memory provides more comprehensive insight into pathogenic mechanisms underlying metabolic diseases and complications and promises to be a new target in disease detection and management. Here, we retrace the history of relevant research on metabolic memory and summarize its salient characteristics. We provide a detailed discussion of the mechanisms by which metabolic memory may be involved in disease development at molecular, cellular, and organ levels, with emphasis on the impact of epigenetic modulations. Finally, we present some of the pivotal findings arguing in favor of targeting metabolic memory to develop therapeutic strategies for metabolic diseases and provide the latest reflections on the consequences of metabolic memory as well as their implications for human health and diseases.

New insights toward molecular and nanotechnological approaches to antidiabetic agents for Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder affecting a major class of silver citizens. The disorder shares a mutual relationship on account of its cellular and molecular pathophysiology with type-II diabetes mellitus (DM). Chronic DM increases the risk for AD. Emerging evidence recommended that resistance in insulin production develops cognitive dysfunction, which generally leads to AD. Repurposing of antidiabetic drugs can be effective in preventing and treatment of the neurodegenerative disorder. Limitations of antidiabetic drugs restrict the repurposing of the drugs for other disorders. Therefore, nanotechnological intervention plays a significant role in the treatment of neurological disorders. In this review, we discuss the common cellular and molecular pathophysiologies between AD and type-II DM, the relevance of in vivo models of type II DM in the study of AD, and the repurposing of antidiabetic drugs and the nanodelivery systems of antidiabetic drugs against AD.

Cognitive dysfunction in diabetes: abnormal glucose metabolic regulation in the brain

Cognitive dysfunction is increasingly recognized as a complication and comorbidity of diabetes, supported by evidence of abnormal brain structure and function. Although few mechanistic metabolic studies have shown clear pathophysiological links between diabetes and cognitive dysfunction, there are several plausible ways in which this connection may occur. Since, brain functions require a constant supply of glucose as an energy source, the brain may be more susceptible to abnormalities in glucose metabolism. Glucose metabolic abnormalities under diabetic conditions may play an important role in cognitive dysfunction by affecting glucose transport and reducing glucose metabolism. These changes, along with oxidative stress, inflammation, mitochondrial dysfunction, and other factors, can affect synaptic transmission, neural plasticity, and ultimately lead to impaired neuronal and cognitive function. Insulin signal triggers intracellular signal transduction that regulates glucose transport and metabolism. Insulin resistance, one hallmark of diabetes, has also been linked with impaired cerebral glucose metabolism in the brain. In this review, we conclude that glucose metabolic abnormalities play a critical role in the pathophysiological alterations underlying diabetic cognitive dysfunction (DCD), which is associated with multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, inflammation, and others. Brain insulin resistance is highly emphasized and characterized as an important pathogenic mechanism in the DCD.

Exenatide regulates Th17/Treg balance via PI3K/Akt/FoxO1 pathway in db/db mice

BACKGROUND

The T helper 17 (Th17)/T regulatory (Treg) cell imbalance is involved in the course of obesity and type 2 diabetes mellitus (T2DM). In the current study, the exact role of glucagon-like peptide-1 receptor agonist (GLP-1RA) exenatide on regulating the Th17/Treg balance and the underlying molecular mechanisms are investigated in obese diabetic mice model.

METHODS

Metabolic parameters were monitored in db/db mice treated with/without exenatide during 8-week study period. The frequencies of Th17 and Treg cells from peripheral blood and pancreas in db/db mice were assessed. The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/Forkhead box O1 (FoxO1) pathway in Th17 and Treg cells from the spleens of male C57BL/6J mice was detected by western blotting. In addition, the expression of glucagon-like peptide-1 receptor (GLP-1R) in peripheral blood mononuclear cells (PBMCs) of male C57BL/6J mice was analyzed.

RESULTS

Exenatide treatment improved β-cell function and insulitis in addition to glucose, insulin sensitivity and weight. Increased Th17 and decreased Treg cells in peripheral blood were present as diabetes progressed while exenatide corrected this imbalance. Progressive IL-17 + T cell infiltration of pancreatic islets was alleviated by exenatide intervention. In vitro study showed no significant difference in the level of GLP-1R expression in PBMCs between control and palmitate (PA) groups. In addition, PA could promote Th17 but suppress Treg differentiation along with down-regulating the phosphorylation of PI3K/Akt/FoxO1, which was reversed by exenatide intervention. FoxO1 inhibitor AS1842856 could abrogate all these effects of exenatide against lipid stress.

CONCLUSIONS

Exenatide could restore systemic Th17/Treg balance via regulating FoxO1 pathway with the progression of diabetes in db/db mice. The protection of pancreatic β-cell function may be partially mediated by inhibiting Th17 cell infiltration into pancreatic islets, and the resultant alleviation of islet inflammation.

FOXO and related transcription factors binding elements in the regulation of neurodegenerative disorders

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and others, are characterized by progressive loss of neuronal cells, which causes memory impairment and cognitive decline. Mounting evidence demonstrated the possible implications of diverse biological processes, namely oxidative stress, mitochondrial dysfunction, aberrant cell cycle re-entry, post-translational modifications, protein aggregation, impaired proteasome dysfunction, autophagy, and many others that cause neuronal cell death. The condition worsens as there is no effective treatment for such diseases due to their complex pathogenesis and mechanism. Mounting evidence demonstrated the role of regulatory transcription factors, such as NFκβ, FoxO, Myc, CREB, and others that regulate the biological processes and diminish the disease progression and pathogenesis. Studies demonstrated that forkhead box O (FoxO) transcription factors had been implicated in the regulation of aging and longevity. Further, the functions of FoxO proteins are regulated by different post-translational modifications (PTMs), namely acetylation, and ubiquitination. Various studies concluded that FoxO proteins exert both neuroprotective and neurotoxic properties depending on their regulation mechanism and activity in the brain. Thus, understanding the nature of FoxO expression and activity in the brain will help develop effective therapeutic strategies. Herein, firstly, we discuss the role of FoxO protein in cell cycle regulation and cell proliferation, followed by the regulation of FoxO proteins through acetylation and ubiquitination. We also briefly explain the activity and expression pattern of FoxO proteins in the neuronal cells and explain the mechanism through which FoxO proteins are rescued from oxidative stress-induced neurotoxicity. Later on, we present a detailed view of the implication of FoxO proteins in neurodegenerative disease and FoxO proteins as an effective therapeutic target.

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.

Repurposing of Anti-Diabetic Agents as a New Opportunity to Alleviate Cognitive Impairment in Neurodegenerative and Neuropsychiatric Disorders

Cognitive impairment is a shared abnormality between type 2 diabetes mellitus (T2DM) and many neurodegenerative and neuropsychiatric disorders, such as Alzheimer’s disease (AD) and schizophrenia. Emerging evidence suggests that brain insulin resistance plays a significant role in cognitive deficits, which provides the possibility of anti-diabetic agents repositioning to alleviate cognitive deficits. Both preclinical and clinical studies have evaluated the potential cognitive enhancement effects of anti-diabetic agents targeting the insulin pathway. Repurposing of anti-diabetic agents is considered to be promising for cognitive deficits prevention or control in these neurodegenerative and neuropsychiatric disorders. This article reviewed the possible relationship between brain insulin resistance and cognitive deficits. In addition, promising therapeutic interventions, especially current advances in anti-diabetic agents targeting the insulin pathway to alleviate cognitive impairment in AD and schizophrenia were also summarized.

Targeting impaired nutrient sensing with repurposed therapeutics to prevent or treat age-related cognitive decline and dementia: A systematic review

BACKGROUND

Dementia is a debilitating syndrome that significantly impacts individuals over the age of 65 years. There are currently no disease-modifying treatments for dementia. Impairment of nutrient sensing pathways has been implicated in the pathogenesis of dementia, and may offer a novel treatment approach for dementia.

AIMS

This systematic review collates all available evidence for Food and Drug Administration (FDA)-approved therapeutics that modify nutrient sensing in the context of preventing cognitive decline or improving cognition in ageing, mild cognitive impairment (MCI), and dementia populations.

METHODS

PubMed, Embase and Web of Science databases were searched using key search terms focusing on available therapeutics such as 'metformin', 'GLP1', 'insulin' and the dementias including 'Alzheimer's disease' and 'Parkinson's disease'. Articles were screened using Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia). The risk of bias was assessed using the Cochrane Risk of Bias tool v 2.0 for human studies and SYRCLE's risk of bias tool for animal studies.

RESULTS

Out of 2619 articles, 114 were included describing 31 different 'modulation of nutrient sensing pathway' therapeutics, 13 of which specifically were utilized in human interventional trials for normal ageing or dementia. Growth hormone secretagogues improved cognitive outcomes in human mild cognitive impairment, and potentially normal ageing populations. In animals, all investigated therapeutic classes exhibited some cognitive benefits in dementia models. While the risk of bias was relatively low in human studies, this risk in animal studies was largely unclear.

CONCLUSIONS

Modulation of nutrient sensing pathway therapeutics, particularly growth hormone secretagogues, have the potential to improve cognitive outcomes. Overall, there is a clear lack of translation from animal models to human populations.

Potential therapeutic role of fibroblast growth factor 21 in neurodegeneration: Evidence for ameliorating parkinsonism via silent information regulator 2 homolog 1 and implication for gene therapy

Parkinson's disease (PD) is one of the common complex neurodegenerative diseases and characterized by abnormal metabolic brain networks. Fibroblast growth factor 21 (FGF21), an endocrine hormone that belongs to the fibroblast growth factor superfamily, plays an extensive role in the regulation of metabolism. However, our understandings of the specific function and mechanisms of FGF21 on PD are still quite limited. Here we aimed to elucidate the actions and the underlying mechanisms of FGF21 on dopaminergic neurodegeneration using cellular and animal models of parkinsonism. To investigate the effects of FGF21 on dopaminergic neurodegeneration in vivo and in vitro, 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine models of PD were utilized, and animals were treated with recombinant FGF21 protein or FGF21 gene delivered via an adeno-associated virus. In the present study, systemic and continuous intracerebroventricular recombinant FGF21 protein administration to mice both prevented behavioral deficits, protected dopaminergic neurons against degeneration, and ameliorated α-synuclein pathology in PD models; and in vivo gene delivery of FGF21 improved PD-like symptoms and pathologies suggesting a potential implication of FGF21 in gene therapy for PD. In vitro evidence confirmed FGF21 mediated neuroprotective benefits against PD pathologies. Further, our data suggested that enhanced autophagy was involved in the FGF21 neuroprotection in PD models, and silent information regulator 2 homolog 1 may play a crucial role in molecular mechanisms underlying anti-PD activities of FGF21.

Diabetes and dementia - the two faces of Janus

Patients with type 2 diabetes are at high risk for cognitive decline and dementia. Despite the limited data on the possible pathogenetic mechanisms, evidence suggests that cognitive decline, and thus dementia and Alzheimer’s disease, might arise from a complex interplay between type 2 diabetes and the aging brain, including decreased insulin signalling and glucose metabolism, mitochondrial dysfunction, neuroinflammation, and vascular disease. Furthermore, there is increasing interest on the effects of antidiabetic agents on cognitive decline. There are many studies showing that antidiabetic agents might have beneficial effects on the brain, mainly through inhibition of oxidative stress, inflammation, and apoptosis. In addition, experimental studies on patients with diabetes and Alzheimer’s disease have shown beneficial effects on synaptic plasticity, metabolism of amyloid-β, and microtubule-associated protein tau. Therefore, in the present review, we discuss the effects of antidiabetic agents in relation to cognitive decline, and in particular dementia and Alzheimer’s disease, in patients with type 2 diabetes.

Modulation of the Astrocyte-Neuron Lactate Shuttle System contributes to Neuroprotective action of Fibroblast Growth Factor 21

A viewpoint considering Alzheimer's disease (AD) as “type 3 diabetes” emphasizes the pivotal role of dysfunctional brain energy metabolism in AD. The hormone fibroblast growth factor 21 (FGF21) is a crucial regulator in energy metabolism; however, our understanding of the therapeutic potential and mechanisms underlying the effect of FGF21 on neurodegeneration of AD is far from complete.

Methods: To further elucidate the effect of FGF21 on AD-related neurodegeneration, we used APP/PS1 transgenic mice to assess the effects of FGF21 on memory dysfunction, amyloid plaque pathology and pathological tau hyperphosphorylation. We also established an in vitro system to mimic astrocyte-neuron communication and an in vivo model of acute injury. Based on the in vivo and in vitro models, we analyzed the neuroprotective actions of FGF21 and pathways related to astrocyte-neuron communication and further focused on the astrocyte-neuron lactate shuttle system.

Results: Here, we report that FGF21 can ameliorate Alzheimer-like neurodegeneration in APP/PS1 transgenic mice. We detected defects in the astrocyte-neuron lactate shuttle system in the in vivo and in vitro models of AD and identified FGF21 as a neuroprotective molecule that can rescue these deficits. Administration of FGF21 can alleviate memory dysfunction, amyloid plaque pathology and pathological tau hyperphosphorylation, and the function of FGF21 in neurodegeneration is mediated in part by monocarboxylate transporters (MCTs). In vivo evidence also suggests that FGF21 acts centrally in mice to exert its effects on neurodegeneration and energy metabolism via its regulation of MCTs.

Conclusions: These results suggest that FGF21 alters metabolic parameters to mediate its neuroprotective functions. Modulation of the astrocyte-neuron lactate shuttle system can be one of the most efficient strategies for FGF21 in Alzheimer-like degeneration and contributes to improvements in brain metabolic defects and amyloid β-induced cytotoxicity. Our findings provide insights into the mechanisms underlying the effects of FGF21 on neurodegeneration and brain energy metabolism and suggest that FGF21 may have therapeutic value in the treatment of AD and other neurodegenerative diseases.