Sodium butyrate ameliorates the impairment of synaptic plasticity by inhibiting the neuroinflammation in 5XFAD mice

Altered cognitive function in obese patients: relationship to gut flora

Obesity is a risk factor for non-communicable diseases such as cardiovascular disease and diabetes, which are leading causes of death and disability. Today, China has the largest number of overweight and obese people, imposing a heavy burden on China's healthcare system. Obesity adversely affects the central nervous system (CNS), especially cognitive functions such as executive power, working memory, learning, and so on. The gradual increase in adult obesity rates has been accompanied by a increase in childhood obesity rates. In the past two decades, the obesity rate among children under 5 years of age has increased from 32 to 42 million. If childhood obesity is not intervened in the early years, it will continue into adulthood and remain there for life. Among the potential causative factors, early lifestyle may influence the composition of the gut flora in childhood obesity, such as the rate and intake of high-energy foods, low levels of physical activity, may persist into adulthood, thus, early lifestyle interventions may improve the composition of the gut flora in obese children. Adipose Axis plays an important role in the development of obesity. Adipose tissue is characterized by increased expression of nucleoside diphosphate-linked molecule X-type motif 2 (NUDT2), amphiphilic protein AMPH genes, which encode proteins that all play important roles in the CNS. NUDT2 is associated with intellectual disability. Furthermore, amphiphysin (AMPH) is involved in glutamatergic signaling, ganglionic synapse development, and maturation, which is associated with mild cognitive impairment (MCI) and Alzheimer's disease (AD). All of the above studies show that obesity is closely related to cognitive decline in patients. Animal experiments have confirmed that obesity causes changes in cognitive function. For example, high-fat diets rich in long- and medium-chain saturated fatty acids may adversely affect cognitive function in obese mice. This process may be attributed to the Short-Chain Fatty Acid (SCFA)-rich high-fat diet (HFD) activating enterocyte TLR signaling, especially TLR-2 and TLR-4, altering the downstream MyD88-4 signaling, thereby impacting the downstream MyD88-NF-κB signaling cascade and up-regulating the levels of pro-inflammatory factors and lipopolysaccharide (LPS). These changes result in the loss of integrity of the intestinal mucosa and cause an imbalance in the internal environment. Obesity may lead to the disruption of the intestinal flora and damage the intestinal barrier function, causing intestinal flora dysbiosis. In recent years, a growing number of studies have investigated the relationship between obesity and the intestinal flora. For example, high-fat and high-sugar diets have been found to lead to the thinning of the mucus layer of the colon, a decrease in the number of tight junction proteins, and an increase in intestinal permeability in mice. Such changes alter the composition of intestinal microorganisms, allow endotoxins into the blood circulation, and induce neuroinflammation and brain damage. Therefore, obesity affects cognitive function and is even hereditary. This paper reviews the obesity-induced cognitive dysfunction, the underlying mechanisms, the research progress of intestinal flora dysregulation in obese patients, the relationship between intestinal flora and cognitive function changes, and the research progress on intestinal flora dysregulation in obese patients. We want to regulate the internal environment of obese patients from the perspective of intestinal flora, improving the cognitive function of obese patients, and prevent obesity-induced changes in related neurological functions.

Elucidating the specific mechanisms of the gut-brain axis: the short-chain fatty acids-microglia pathway

In recent years, the gut microbiota has been increasingly recognized for its influence on various central nervous system diseases mediated by microglia, yet the underlying mechanisms remain unclear. As key metabolites of the gut microbiota, short-chain fatty acids (SCFAs) have emerged as a focal point in understanding microglia-related interactions. In this review, we further refine the connection between the gut microbiota and microglia by introducing the concept of the "SCFAs-microglia" pathway. We summarize current knowledge on this pathway, recent discoveries regarding its role in neurological diseases, and potential pharmacological strategies targeting it. Finally, we outlined the current challenges and limitations in this field of research. We hope this review provides new insights into the role of the gut microbiota in neuroimmune regulation.

From Obesity to Mitochondrial Dysfunction in Peripheral Tissues and in the Central Nervous System

Obesity is a condition of chronic low-grade inflammation affecting peripheral organs of the body, as well as the central nervous system. The adipose tissue dysfunction occurring under conditions of obesity is a key factor in the onset and progression of a variety of diseases, including neurodegenerative disorders. Mitochondria, key organelles in the production of cellular energy, play an important role in this tissue dysfunction. Numerous studies highlight the close link between obesity and adipocyte mitochondrial dysfunction, resulting in excessive ROS production and adipose tissue inflammation. This inflammation is transmitted systemically, leading to metabolic disorders that also impact the central nervous system, where pro-inflammatory cytokines impair mitochondrial and cellular functions in different areas of the brain, leading to neurodegenerative diseases. To date, several bioactive compounds are able to prevent and/or slow down neurogenerative processes by acting on mitochondrial functions. Among these, some molecules present in the Mediterranean diet, such as polyphenols, carotenoids, and omega-3 PUFAs, exert a protective action due to their antioxidant and anti-inflammatory ability. The aim of this review is to provide an overview of the involvement of adipose tissue dysfunction in the development of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and multiple sclerosis, emphasizing the central role played by mitochondria, the main actors in the cross-talk between adipose tissue and the central nervous system.

Butyrate: a key mediator of gut-brain communication in Alzheimer's disease

Alzheimer's disease (AD), a prevalent neurodegenerative disorder, represents a significant global health challenge, characterized by cognitive decline and neuroinflammation. Recent investigations have highlighted the critical role of the gut-brain axis in the pathogenesis of AD, particularly focusing on the influence of short-chain fatty acids (SCFAs), metabolites produced by the gut microbiota through the fermentation of dietary fiber. Among SCFAs, butyrate has emerged as a crucial mediator, positively impacting various pathological processes associated with AD, including epigenetic regulation, neuroinflammation modulation, maintenance of the blood-brain barrier (BBB), enhanced intestinal integrity, regulation of brain metabolism, and interference with amyloid protein formation as well as tau protein hyperphosphorylation. Furthermore, distinctions in butyrate profile and microbial communities have been observed between AD patients and healthy individuals, underscoring the importance of gut microbiota in AD progression. This review summarizes the current understanding of the many functions of butyrate in reducing the consequences of AD and emphasizes the possibility of addressing the gut microbiota as a therapeutic approach to managing AD.

A multi-omics approach reveals impaired lipid metabolism and oxidative stress in a zebrafish model of Alexander disease

Alexander disease (AxD) is a rare leukodystrophy caused by heterozygous mutations in the GFAP gene. To date, several in vitro and in vivo models have been generated in an attempt to unravel the main mechanisms underlying this complex disease. However, none of these models is suitable for investigating the global dysregulation caused by AxD. To address this shortcoming, we have generated a stable transgenic zebrafish line (zAxD) carrying the human GFAP p.R239C mutation, which is associated with severe phenotypes of AxD type I patients. We then performed transcriptomics and proteomics analyses on the whole larvae of our zAxD model, confirming the involvement of several pathways such as the immune system response and inflammation, oxidative stress, extracellular matrix, lipoxidation and lipid metabolism, which were previously reported in more limited omic studies. Interestingly, new pathways emerged as well, including tyrosine and butanoate metabolic processes. Biochemical assays confirmed alterations in cell respiration and lipid metabolism as well as elevated oxidative stress. These findings confirm the reliability of the zAxD model to apply a whole-organism approach to investigate the molecular basis of the disease.

Short-chain fatty acids in Huntington's disease: Mechanisms of action and their therapeutic implications

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor dysfunction, cognitive decline, and emotional instability, primarily resulting from the abnormal accumulation of mutant huntingtin protein. Growing research highlights the role of intestinal microbiota and their metabolites, particularly short-chain fatty acids (SCFAs), in modulating HD progression. SCFAs, including acetate, propionate, and butyrate, are produced by gut bacteria through dietary fiber fermentation and are recognized for their neuroprotective properties. Evidence suggests that SCFAs regulate neuroinflammation, neuronal communication, and metabolic functions within the central nervous system (CNS). In HD, these compounds may support neuronal health, reduce oxidative stress, and enhance blood-brain barrier (BBB) integrity. Their mechanisms of action involve binding to G-protein-coupled receptors (GPCRs) and modulating gene expression through epigenetic pathways, underscoring their therapeutic potential. This analysis examines the significance of SCFAs in HD, emphasizing the gut-brain axis and the benefits of dietary interventions aimed at modifying gut microbiota composition and promoting SCFA production. Further research into these pathways may pave the way for novel HD management strategies and improved therapeutic outcomes.

Bridging gap in the treatment of Alzheimer's disease via postbiotics: Current practices and future prospects

Aging is an extremely significant risk associated with neurodegeneration. The most prevalent neurodegenerative disorders (NDs), such as Alzheimer's disease (AD) are distinguished by the prevalence of proteinopathy, aberrant glial cell activation, oxidative stress, neuroinflammation, defective autophagy, cellular senescence, mitochondrial dysfunction, epigenetic changes, neurogenesis suppression, increased blood-brain barrier permeability, and intestinal dysbiosis that is excessive for the patient's age. Substantial body studies have documented a close relationship between gut microbiota and AD, and restoring a healthy gut microbiota may reduce or even ameliorate AD symptoms and progression. Thus, control of the microbiota in the gut has become an innovative model for clinical management of AD, and rising emphasis is focused on finding new techniques for preventing and/or managing the disease. The etiopathogenesis of gut microbiota in driving AD progression and supplementing postbiotics as a preventive and therapeutic treatment for AD is discussed. The review additionally discusses the use of postbiotics in AD prophylaxis and therapy, portraying them as substances that address senescence-triggered dysfunctions and are worthy of translating from bench to biopharmaceutical market in response to "silver consumers" needs. The current review examines and evaluates the impact of postbiotics as whole and specific metabolites, such as short-chain fatty acids (SCFAs), lactate, polyamines, polyphenols, tryptophan metabolites, exopolysaccharides, and bacterial extracellular vesicles, on the aging-associated processes that reinforce AD. Moreover, it provides an overview of the most recent data from both clinical and preclinical research involving the use of postbiotics in AD.

Metabolic preferences of astrocytes: Functional metabolic mapping reveals butyrate outcompetes acetate

Disruptions to the gut-brain-axis have been linked to neurodegenerative disorders. Of these disruptions, reductions in the levels of short-chain fatty acids (SCFAs), like butyrate, have been observed in mouse models of Alzheimer's disease (AD). Butyrate supplementation in mice has shown promise in reducing neuroinflammation, amyloid-β accumulation, and enhancing memory. However, the underlying mechanisms remain unclear. To address this, we investigated the impact of butyrate on energy metabolism in mouse brain slices, primary cultures of astrocytes and neurons and in-vivo by dynamic isotope labelling with [U-13C]butyrate and [1,2-13C]acetate to map metabolism via mass spectrometry. Metabolic competition assays in cerebral cortical slices revealed no competition between butyrate and the ketone body, β-hydroxybutyrate, but competition with acetate. Astrocytes favoured butyrate metabolism compared to neurons, suggesting that the astrocytic compartment is the primary site of butyrate metabolism. In-vivo metabolism investigated in the 5xFAD mouse, an AD pathology model, showed no difference in 13C-labelling of TCA cycle metabolites between wild-type and 5xFAD brains, but butyrate metabolism remained elevated compared to acetate in both groups, indicating sustained uptake and metabolism in 5xFAD mice. Overall, these findings highlight the role of astrocytes in butyrate metabolism and the potential use of butyrate as an alternative brain fuel source.

Dissecting the immune response of CD4+ T cells in Alzheimer's disease

The formation of amyloid-β (Aβ) plaques is a neuropathological hallmark of Alzheimer's disease (AD), however, these pathological aggregates can also be found in the brains of cognitively unimpaired elderly population. In that context, individual variations in the Aβ-specific immune response could be key factors that determine the level of Aβ-induced neuroinflammation and thus the propensity to develop AD. CD4+ T cells are the cornerstone of the immune response that coordinate the effector functions of both adaptive and innate immunity. However, despite intensive research efforts, the precise role of these cells during AD pathogenesis is still not fully elucidated. Both pathogenic and beneficial effects have been observed in various animal models of AD, as well as in humans with AD. Although this functional duality of CD4+ T cells in AD can be simply attributed to the vast phenotype heterogeneity of this cell lineage, disease stage-specific effect have also been proposed. Therefore, in this review, we summarized the current understanding of the role of CD4+ T cells in the pathophysiology of AD, from the aspect of their antigen specificity, activation, and phenotype characteristics. Such knowledge is of practical importance as it paves the way for immunomodulation as a therapeutic option for AD treatment, given that currently available therapies have not yielded satisfactory results.

The complex relationship between gut microbiota and Alzheimer's disease: A systematic review

Alzheimer's disease (AD) is a progressive, degenerative disorder of the central nervous system. Despite extensive research conducted on this disorder, its precise pathogenesis remains unclear. In recent years, the microbiota-gut-brain axis has attracted considerable attention within the field of AD. The gut microbiota communicates bidirectionally with the central nervous system through the gut-brain axis, and alterations in its structure and function can influence the progression of AD. Consequently, regulating the gut microbiota to mitigate the progression of AD has emerged as a novel therapeutic approach. Currently, numerous studies concentrate on the intrinsic relationship between the microbiota-gut-brain axis and AD. In this paper, we summarize the multifaceted role of the gut microbiota in AD and present detailed therapeutic strategies targeting the gut microbiota, including the treatment of AD with Traditional Chinese Medicine (TCM), which has garnered increasing attention in recent years. Finally, we discuss potential therapeutic strategies for modulating the gut microbiota to alleviate the progression of AD, the current challenges in this area of research, and provide an outlook on future research directions in this field.

Prebiotics Beyond the Gut: Omics Insights, Artificial Intelligence, and Clinical Trials in Organ-Specific Applications

Prebiotics, traditionally linked to gut health, are increasingly recognized for their systemic benefits, influencing multiple organ systems through interactions with the gut microbiota. Compounds like inulin, fructooligosaccharides (FOS), and galactooligosaccharides (GOS) enhance short-chain fatty acid (SCFA) production, benefiting neurocognitive health, cardiovascular function, immune modulation, and skin integrity. Advances in biotechnology, including deep eutectic solvents (DES) for extraction and machine learning (ML) for personalized formulations, have expanded prebiotic applications. Integrating these innovations with "omics" technologies enables precise microbial modulation, fostering personalized nutrition and precision therapies. This review examines organ-specific effects of prebiotics, highlights findings from clinical trials, and explores biotechnological innovations that enhance prebiotic efficacy, laying the groundwork for future personalized therapeutic strategies.

The Promise of Epigenetic Editing for Treating Brain Disorders

Brain disorders, especially neurodegenerative diseases, affect millions of people worldwide. There is no causal treatment available; therefore, there is an unmet clinical need for finding therapeutic options for these diseases. Epigenetic research has resulted in identification of various genomic loci with differential disease-specific epigenetic modifications, mainly DNA methylation. These biomarkers, although not yet translated into clinically approved options, offer therapeutic targets as epigenetic modifications are reversible. Indeed, clinical trials are designed to inhibit epigenetic writers, erasers, or readers using epigenetic drugs to interfere with epigenetic dysregulation in brain disorders. However, since such drugs elicit genome-wide effects and potentially cause toxicity, the recent developments in the field of epigenetic editing are gaining widespread attention. In this review, we provide examples of epigenetic biomarkers and epi-drugs, while describing efforts in the field of epigenetic editing, to eventually make a difference for the currently incurable brain disorders.

Natural products: Harnessing the power of gut microbiota for neurological health

BACKGROUND

Neurological diseases are the primary cause of disability and death and impose substantial financial burdens. However, existing treatments only relieve symptoms and may cause many adverse effects. Natural products are a promising source of neurological therapeutic agents due to their excellent neuroprotective effect and safety. The gut microbiota has an essential impact on maintaining brain homeostasis via the gut-brain axis. Multiple investigations show that natural products offer neuroprotective effects by regulating gut microbiota-driven signaling networks.

OBJECTIVES

This review aims to provide a systematic review of how natural products promote neurological health by harnessing the power of gut microbiota.

METHODS

The pre-January 1, 2024 literature was gathered from several databases, including Scopus, PubMed, Google Scholar, and Web of Science, utilizing appropriate keywords. The gathered publications underwent a review process and were classified based on their study content, specifically focusing on the impact of natural products on gut microbiota and neurological health.

RESULTS

Here, we review how natural products promote neurological health by regulating the gut microbiota-brain axis. Specifically, we focus on the following areas. (1) Altering microorganism community structure, including increasing α-diversity and altering β-diversity. (2) Regulating the population of certain bacteria, including enriching beneficial microorganisms Akkermansia and Bifidobacterium, and inhibiting potentially hazardous microorganisms Bilophila, Klebsiella, and Helicobacter. (3) Regulating microbial neuroactive metabolites levels, including short-chain fatty acids, tryptophan and its derivatives, trimethylamine N-oxide, dopa/dopamine, γ-aminobutyric acid, and lipopolysaccharide. Furthermore, we review how natural products promote neurological health by regulating intestinal barrier homeostasis.

CONCLUSION

Natural products promote neurological health by harnessing the power of gut microbiota. This review will contribute to understanding how natural products promote neurological health by orchestrating the gut microbiota-brain axis.

Effect of remimazolam toluene sulfonate on the cognitive function of juveniles and its mechanism of action

Remimazolam is a new benzodiazepine. Currently, it remains unclear how repeated exposure to remimazolam affects the cognitive function of the developing brain. In the present study, the equivalent doses of the two sedatives were derived from S-shaped dose-response curves, and the ED95 of remimazolam was 45 mg/kg (95% CI 37.579-79.280), and for midazolam, it was 77 mg/kg (95% CI 63.751-127.21) using probability analysis. Then, we evaluated the effects of remimazolam and midazolam on cognitive function in juvenile mice (C57BL/6) through Y-maze and MWM. TUNEL staining was used to observe the apoptosis of neurons in hippocampus, western blotting was used to detect the expression changes of related proteins, and the changes of LTP were observed by recording the activity of neurons through electrical stimulation. We found that there was no significant difference in the behavior of mice in MWM. However, the short-term memory of developing mice was impaired in Y-maze after repeated exposure to remimazolam and midazolam. Furthermore, our data demonstrated that the short-term memory damage caused by remimazolam is lighter than midazolam. Concurrently, the extent of caspase-3 upregulation, the number of neuronal apoptosis in CA1 and CA3 regions, a downward trend of PSD95 and BDNF in the hippocampus, and the inhibition of LTP were highly consistent with the behavior of short-term memory impairment. These results indicate that the degree of memory impairment caused by remimazolam is milder than that caused by midazolam, making it a potential replacement for midazolam in repeated medication and long-term sedation in children.

Microglia and gut microbiota: A double-edged sword in Alzheimer's disease

The strong association between gut microbiota (GM) and brain functions such as mood, behaviour, and cognition has been well documented. Gut-brain axis is a unique bidirectional communication system between the gut and brain, in which gut microbes play essential role in maintaining various molecular and cellular processes. GM interacts with the brain through various pathways and processes including, metabolites, vagus nerve, HPA axis, endocrine system, and immune system to maintain brain homeostasis. GM dysbiosis, or an imbalance in GM, is associated with several neurological disorders, including anxiety, depression, and Alzheimer's disease (AD). Conversely, AD is sustained by microglia-mediated neuroinflammation and neurodegeneration. Further, GM and their products also affect microglia-mediated neuroinflammation and neurodegeneration. Despite the evidence connecting GM dysbiosis and AD progression, the involvement of GM in modulating microglia-mediated neuroinflammation in AD remains elusive. Importantly, deciphering the mechanism/s by which GM regulates microglia-dependent neuroinflammation may be helpful in devising potential therapeutic strategies to mitigate AD. Herein, we review the current evidence regarding the involvement of GM dysbiosis in microglia activation and neuroinflammation in AD. We also discuss the possible mechanisms through which GM influences the functioning of microglia and its implications for therapeutic intervention. Further, we explore the potential of microbiota-targeted interventions, such as prebiotics, probiotics, faecal microbiota transplantation, etc., as a novel therapeutic strategy to mitigate neuroinflammation and AD progression. By understanding and exploring the gut-brain axis, we aspire to revolutionize the treatment of neurodegenerative disorders, many of which share a common theme of microglia-mediated neuroinflammation and neurodegeneration.

Tetradecyl 2,3-Dihydroxybenzoate Improves Cognitive Function in AD Mice by Modulating Autophagy and Inflammation Through IPA and Hsc70 Targeting

Drug development for Alzheimer's disease (AD) treatment is challenging due to its complex pathogenesis. Tetradecyl 2,3-dihydroxybenzoate (ABG-001), a leading compound identified in our prior research, has shown promising NGF-mimicking activity and anti-aging properties. In the present study, both high-fat diet (HFD)-induced AD mice and naturally aging AD mice were used to evaluate anti-AD effects. Meanwhile, RNA-sequences, Western blotting, immunofluorescence staining, enzyme-linked immunosorbent assay (ELISA), cellular thermal shift assay (CETSA), drug affinity-responsive target stability (DARTS) assay, construction of expression plasmid and protein purification, surface plasmon resonance (SPR) analysis, and 16S rRNA sequence analysis were used to identify the target protein of ABG-001 and clarify the mechanism of action for this molecule. ABG-001 effectively mitigates the memory dysfunction in both HFD-induced AD mice and naturally aging AD mice. The therapeutic effect of ABG-001 is attributed to its ability to promote neurogenesis, activate chaperone-mediated autophagy (CMA), and reduce neuronal inflammation. Additionally, ABG-001 positively influenced the gut microbiota, enhancing the production of indole-3-propionic acid (IPA), which is capable of crossing the blood-brain barrier (BBB) and contributes to neuronal regeneration. Furthermore, our research revealed that IPA, linked to the anti-AD properties of ABG-001, targets the heat shock cognate 70 kDa protein (Hsc70) and regulates the Hsc70/PKM2/HK2/LC3 and FOXO3a/SIRT1 signaling pathways. ABG-001 improves the memory dysfunction of AD mice by modulating autophagy and inflammation through IPA and Hsc70 targeting. These findings offer a novel approach for treating neurodegenerative diseases, focusing on the modification of the gut microbiota and metabolites coupled with anti-aging strategies.

Microbiota-derived short chain fatty acids in pediatric health and diseases: from gut development to neuroprotection

The infant gut microbiota undergoes significant changes during early life, which are essential for immune system maturation, nutrient absorption, and metabolic programming. Among the various microbial metabolites, short-chain fatty acids (SCFAs), primarily acetate, propionate, and butyrate, produced through the fermentation of dietary fibers by gut bacteria, have emerged as critical modulators of host-microbiota interactions. SCFAs serve as energy sources for colonic cells and play pivotal roles in regulating immune responses, maintaining gut barrier integrity, and influencing systemic metabolic pathways. Recent research highlights the potential neuroprotective effects of SCFAs in pediatric populations. Disruptions in gut microbiota composition and SCFA production are increasingly associated with a range of pediatric health issues, including obesity, allergic disorders, inflammatory bowel disease (IBD), and neurodevelopmental disorders. This review synthesizes current knowledge on the role of microbiota-derived SCFAs in pediatric health, emphasizing their contributions from gut development to neuroprotection. It also underscores the need for further research to unravel the precise mechanisms by which SCFAs influence pediatric health and to develop targeted interventions that leverage SCFAs for therapeutic benefits.

Gut microbial metabolism in Alzheimer's disease and related dementias

Multiple studies over the last decade have established that Alzheimer's disease and related dementias (ADRD) are associated with changes in the gut microbiome. These alterations in organismal composition result in changes in the abundances of functions encoded by the microbial community, including metabolic capabilities, which likely impact host disease mechanisms. Gut microbes access dietary components and other molecules made by the host and produce metabolites that can enter circulation and cross the blood-brain barrier (BBB). In recent years, several microbial metabolites have been associated with or have been shown to influence host pathways relevant to ADRD pathology. These include short chain fatty acids, secondary bile acids, tryptophan derivatives (such as kynurenine, serotonin, tryptamine, and indoles), and trimethylamine/trimethylamine N-oxide. Notably, some of these metabolites cross the BBB and can have various effects on the brain, including modulating the release of neurotransmitters and neuronal function, inducing oxidative stress and inflammation, and impacting synaptic function. Microbial metabolites can also impact the central nervous system through immune, enteroendocrine, and enteric nervous system pathways, these perturbations in turn impact the gut barrier function and peripheral immune responses, as well as the BBB integrity, neuronal homeostasis and neurogenesis, and glial cell maturation and activation. This review examines the evidence supporting the notion that ADRD is influenced by gut microbiota and its metabolites. The potential therapeutic advantages of microbial metabolites for preventing and treating ADRD are also discussed, highlighting their potential role in developing new treatments.

Gut microbiota metabolites: potential therapeutic targets for Alzheimer's disease?

Background

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive decline in cognitive function, which significantly increases pain and social burden. However, few therapeutic interventions are effective in preventing or mitigating the progression of AD. An increasing number of recent studies support the hypothesis that the gut microbiome and its metabolites may be associated with upstream regulators of AD pathology.

Methods

In this review, we comprehensively explore the potential mechanisms and currently available interventions targeting the microbiome for the improvement of AD. Our discussion is structured around modern research advancements in AD, the bidirectional communication between the gut and brain, the multi-target regulatory effects of microbial metabolites on AD, and therapeutic strategies aimed at modulating gut microbiota to manage AD.

Results

The gut microbiota plays a crucial role in the pathogenesis of AD through continuous bidirectional communication via the microbiota-gut-brain axis. Among these, microbial metabolites such as lipids, amino acids, bile acids and neurotransmitters, especially sphingolipids and phospholipids, may serve as central components of the gut-brain axis, regulating AD-related pathogenic mechanisms including β-amyloid metabolism, Tau protein phosphorylation, and neuroinflammation. Additionally, interventions such as probiotic administration, fecal microbiota transplantation, and antibiotic use have also provided evidence supporting the association between gut microbiota and AD. At the same time, we propose an innovative strategy for treating AD: a healthy lifestyle combined with targeted probiotics and other potential therapeutic interventions, aiming to restore intestinal ecology and microbiota balance.

Conclusion

Despite previous efforts, the molecular mechanisms by which gut microbes act on AD have yet to be fully described. However, intestinal microorganisms may become an essential target for connecting the gut-brain axis and improving the symptoms of AD. At the same time, it requires joint exploration by multiple centers and multiple disciplines.

Role of histone deacetylases and their inhibitors in neurological diseases

Histone deacetylases (HDACs) are zinc-dependent deacetylases that remove acetyl groups from lysine residues of histones or form protein complexes with other proteins for transcriptional repression, changing chromatin structure tightness, and inhibiting gene expression. Recent in vivo and in vitro studies have amply demonstrated the critical role of HDACs in the cell biology of the nervous system during both physiological and pathological processes and have provided new insights into the conduct of research on neurological disease targets. In addition, in vitro and in vivo studies on HDAC inhibitors show promise for the treatment of various diseases. This review summarizes the regulatory mechanisms of HDAC and the important role of its downstream targets in nervous system diseases, and summarizes the therapeutic mechanisms and efficacy of HDAC inhibitors in various nervous system diseases. Additionally, the current pharmacological situation, problems, and developmental prospects of HDAC inhibitors are described. A better understanding of the pathogenic mechanisms of HDACs in the nervous system may reveal new targets for therapeutic interventions in diseases and help to relieve healthcare pressure through preventive measures.

Brain-Gut and Microbiota-Gut-Brain Communication in Type-2 Diabetes Linked Alzheimer's Disease

The gastrointestinal (GI) tract, home to the largest microbial population in the human body, plays a crucial role in overall health through various mechanisms. Recent advancements in research have revealed the potential implications of gut-brain and vice-versa communication mediated by gut-microbiota and their microbial products in various diseases including type-2 diabetes and Alzheimer's disease (AD). AD is the most common type of dementia where most of cases are sporadic with no clearly identified cause. However, multiple factors are implicated in the progression of sporadic AD which can be classified as non-modifiable (e.g., genetic) and modifiable (e.g. Type-2 diabetes, diet etc.). Present review focusses on key players particularly the modifiable factors such as Type-2 diabetes (T2D) and diet and their implications in microbiota-gut-brain (MGB) and brain-gut (BG) communication and cognitive functions of healthy brain and their dysfunction in Alzheimer's Disease. Special emphasis has been given on elucidation of the mechanistic aspects of the impact of diet on gut-microbiota and the implications of some of the gut-microbial products in T2D and AD pathology. For example, mechanistically, HFD induces gut dysbiosis with driven metabolites that in turn cause loss of integrity of intestinal barrier with concomitant colonic and systemic chronic low-grade inflammation, associated with obesity and T2D. HFD-induced obesity and T2D parallel neuroinflammation, deposition of Amyloid β (Aβ), and ultimately cognitive impairment. The review also provides a new perspective of the impact of diet on brain-gut and microbiota-gut-brain communication in terms of transcription factors as a commonly spoken language that may facilitates the interaction between gut and brain of obese diabetic patients who are at a higher risk of developing cognitive impairment and AD. Other commonality such as tyrosine kinase expression and functions maintaining intestinal integrity on one hand and the phagocytic clarence by migratory microglial functions in brain are also discussed. Lastly, the characterization of the key players future research that might shed lights on novel potential pharmacological target to impede AD progression are also discussed.

New insights into sodium phenylbutyrate as a pharmacotherapeutic option for neurological disorders

Neurological disorders (NDs) are diseases of the central and peripheral nervous systems that affect more than one billion people worldwide. The risk of developing an ND increases with age due to the vulnerability of the different organs and systems to genetic, environmental, and social changes that consequently cause motor and cognitive deficits that disable the person from their daily activities and individual and social productivity. Intrinsic factors (genetic factors, age, gender) and extrinsic factors (addictions, infections, or lifestyle) favor the persistence of systemic inflammatory processes that contribute to the evolution of NDs. Neuroinflammation is recognized as a common etiopathogenic factor of ND. The study of new pharmacological options for the treatment of ND should focus on improving the characteristic symptoms and attacking specific molecular targets that allow the delay of damage processes such as neuroinflammation, oxidative stress, cellular metabolic dysfunction, and deregulation of transcriptional processes. In this review, we describe the possible role of sodium phenylbutyrate (NaPB) in the pathogenesis of Alzheimer's disease, hepatic encephalopathy, aging, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis; in addition, we describe the mechanism of action of NaPB and its beneficial effects that have been shown in various in vivo and in vitro studies to delay the evolution of any ND.

Frataxin deficiency shifts metabolism to promote reactive microglia via glucose catabolism

Immunometabolism investigates the intricate relationship between the immune system and cellular metabolism. This study delves into the consequences of mitochondrial frataxin (FXN) depletion, the primary cause of Friedreich's ataxia (FRDA), a debilitating neurodegenerative condition characterized by impaired coordination and muscle control. By using single-cell RNA sequencing, we have identified distinct cellular clusters within the cerebellum of an FRDA mouse model, emphasizing a significant loss in the homeostatic response of microglial cells lacking FXN. Remarkably, these microglia deficient in FXN display heightened reactive responses to inflammatory stimuli. Furthermore, our metabolomic analyses reveal a shift towards glycolysis and itaconate production in these cells. Remarkably, treatment with butyrate counteracts these immunometabolic changes, triggering an antioxidant response via the itaconate-Nrf2-GSH pathways and suppressing the expression of inflammatory genes. Furthermore, we identify Hcar2 (GPR109A) as a mediator involved in restoring the homeostasis of microglia without FXN. Motor function tests conducted on FRDA mice underscore the neuroprotective attributes of butyrate supplementation, enhancing neuromotor performance. In conclusion, our findings elucidate the role of disrupted homeostatic function in cerebellar microglia in the pathogenesis of FRDA. Moreover, they underscore the potential of butyrate to mitigate inflammatory gene expression, correct metabolic imbalances, and improve neuromotor capabilities in FRDA.

Psychobiotics for Mitigation of Neuro-Degenerative Diseases: Recent Advancements

Ageing is inevitable and poses a universal challenge for all living organisms, including humans. The human body experiences rapid cell division and metabolism until approximately 25 years of age, after which the accumulation of metabolic by-products and cellular damage leads to age-related diseases. Neurodegenerative diseases are of concern due to their irreversible nature, lack of effective treatment, and impact on society and the economy. Researchers are interested in finding drugs that can effectively alleviate ageing and age-related diseases without side-effects. Psychobiotics are a novel class of probiotic organisms and prebiotic interventions that confer mental health benefits to the host when taken appropriately. Psychobiotic strains affect functions related to the central nervous system (CNS) and behaviors mediated by the Gut-Brain-Axis (GBA) through various pathways. There is an increasing interest in researchers of these microbial-based psychopharmaceuticals. Psychobiotics have been reported to reduce neuronal ageing, inflammation, oxidative stress, and cortisol levels; increase synaptic plasticity and levels of neurotransmitters and antioxidants. The present review focuses on the manifestation of elderly neurodegenerative and mental disorders, particularly Alzheimer's disease (AD), Parkinson's disease (PD), and depression, and the current status of their potential alleviation through psychobiotic interventions, highlighting their possible mechanisms of action.

Amelioration of walnut, peony seed and camellia seed oils against D-galactose-induced cognitive impairment in mice by regulating gut microbiota

Diet adjustment will affect the health of gut microbiota, which in turn influences the development and function of the organism's brain through the gut-brain axis. Walnut oil (WO), peony seed oil (PSO) and camellia seed oil (CSO), as typical representatives of woody plant oils, have been shown to have the potential to improve cognitive impairment in mice, but the function mechanisms are not clear. In this study, we comparatively investigated the neuroprotective effects of these three oils on D-galactose (D-gal)-induced cognitive impairment in mice, and found that the ameliorative effect of WO was more prominent. During the behavioral experiments, supplementation with all three oils would improve spatial learning and memory functions in D-gal mice, with a significant reduction in the error times (p < 0.001) and a significant increase in step-down latency (p < 0.001); walnut oil supplementation also significantly increased the number of hidden platform traversals, the target quadrant spent times and percentage of distance (p < 0.05). The results of biomarker analysis showed that WO, in addition to significantly inhibiting D-gal-induced oxidative stress and neuroinflammation as did PSO, significantly increased the ACh content in the mouse brain (p < 0.05) and modulated neurotransmitter levels. The results of further microbiota diversity sequencing experiments also confirmed that dietary supplementation with all three oils affected the diversity and composition of the gut microbiota in mice. Among them, WO significantly restored the balance of the mouse gut microbiota by increasing the abundance of beneficial bacteria (Bacteroidetes, Actinobacteria, Firmicutes) and decreasing the abundance of harmful bacteria (Clostridium, Shigella, Serratia), which was consistent with the results of behavioral experiments and biomarker analyses. Based on the analysis of the fatty acid composition of the three oils and changes in the gut microbiota, it is hypothesized that there is a correlation between the fatty acid composition of the dietary supplement oils and neuroprotective effects. The superiority of WO over PSO and CSO in improving cognitive impairment is mainly attributed to its balanced composition of omega-6 and omega-3 fatty acids.

Butyrate as a potential therapeutic agent for neurodegenerative disorders

Maintaining an optimum microbial community within the gastrointestinal tract is intricately linked to human metabolic, immune and brain health. Disturbance to these microbial populations perturbs the production of vital bioactive compounds synthesised by the gut microbiome, such as short-chain fatty acids (SCFAs). Of the SCFAs, butyrate is known to be a major source of energy for colonocytes and has valuable effects on the maintenance of intestinal epithelium and blood brain barrier integrity, gut motility and transit, anti-inflammatory effects, and autophagy induction. Inducing endogenous butyrate production is likely to be beneficial for gut-brain homeostasis and for optimal neuronal function. For these reasons, butyrate has gained interest as a potential therapy for not only metabolic and immunological disorders, but also conditions related to the brain, including neurodegenerative diseases. While direct and indirect sources of butyrate, including prebiotics, probiotics, butyrate pro-drugs and glucosidase inhibitors, offer a promising therapeutic avenue, their efficacy and dosage in neurodegenerative conditions remain largely unknown. Here, we review current literature on effects of butyrate relevant to neuronal function, the impact of butyrate in a range of neurodegenerative diseases and related treatments that may have potential for the treatment of neurodegenerative diseases.

Short-chain fatty acids: Important components of the gut-brain axis against AD

Alzheimer's disease (AD) comprises a group of neurodegenerative disorders with some changes in the brain, which could lead to the deposition of certain proteins and result in the degeneration and death of brain cells. Patients with AD manifest primarily as cognitive decline, psychiatric symptoms, and behavioural disorders. Short-chain fatty acids (SCFAs) are a class of saturated fatty acids (SFAs) produced by gut microorganisms through the fermentation of dietary fibre ingested. SCFAs, as a significant mediator of signalling, can have diverse physiological and pathological roles in the brain through the gut-brain axis, and play a positive effect on AD via multiple pathways. Firstly, differences in SCFAs and microbial changes have been stated in AD cases of humans and mice in this paper. And then, mechanisms of three main SCFAs in treating with AD have been summarized, as well as differences of gut bacteria. Finally, functions of SCFAs played in regulating intestinal flora homeostasis, modulating the immune system, and the metabolic system, which were considered to be beneficial for the treatment of AD, have been elucidated, and the key roles of gut bacteria and SCFAs were pointed out. All in all, this paper provides an overview of SCFAs and gut bacteria in AD, and can help people to understand the importance of gut-brain axis in AD.

Microbiota-Gut-Brain Axis Dysregulation in Alzheimer's Disease: Multi-Pathway Effects and Therapeutic Potential

An essential regulator of neurodegenerative conditions like Alzheimer's disease (AD) is the gut microbiota. Alterations in intestinal permeability brought on by gut microbiota dysregulation encourage neuroinflammation, central immune dysregulation, and peripheral immunological dysregulation in AD, as well as hasten aberrant protein aggregation and neuronal death in the brain. However, it is unclear how the gut microbiota transmits information to the brain and how it influences brain cognition and function. In this review, we summarized the multiple pathways involved in the gut microbiome in AD and provided detailed treatment strategies based on the gut microbiome. Based on these observations, this review also discusses the problems, challenges, and strategies to address current therapeutic strategies.

Transcranial Magneto-Acoustic Stimulation Protects Synaptic Rehabilitation from Amyloid-Beta Plaques via Regulation of Microglial Functions

Transcranial magneto-acoustic stimulation (TMAS), which is characterized by high spatiotemporal resolution and high penetrability, is a non-invasive neuromodulation technology based on the magnetic-acoustic coupling effect. To reveal the effects of TMAS treatment on amyloid-beta (Aβ) plaque and synaptic plasticity in Alzheimer's disease, we conducted a comparative analysis of TMAS and transcranial ultrasound stimulation (TUS) based on acoustic effects in 5xFAD mice and BV2 microglia cells. We found that the TMAS-TUS treatment effectively reduced amyloid plaque loads and plaque-associated neurotoxicity. Additionally, TMAS-TUS treatment ameliorated impairments in long-term memory formation and long-term potentiation. Moreover, TMAS-TUS treatment stimulated microglial proliferation and migration while enhancing the phagocytosis and clearance of Aβ. In 5xFAD mice with induced microglial exhaustion, TMAS-TUS treatment-mediated Aβ plaque reduction, synaptic rehabilitation improvement, and the increase in phospho-AKT levels were diminished. Overall, our study highlights that stimulation of hippocampal microglia by TMAS treatment can induce anti-cognitive impairment effects via PI3K-AKT signaling, providing hope for the development of new strategies for an adjuvant therapy for Alzheimer's disease.

Therapeutics for neurodegenerative diseases by targeting the gut microbiome: from bench to bedside

The aetiologies and origins of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD), are complex and multifaceted. A growing body of evidence suggests that the gut microbiome plays crucial roles in the development and progression of neurodegenerative diseases. Clinicians have come to realize that therapeutics targeting the gut microbiome have the potential to halt the progression of neurodegenerative diseases. This narrative review examines the alterations in the gut microbiome in AD, PD, ALS and HD, highlighting the close relationship between the gut microbiome and the brain in neurodegenerative diseases. Processes that mediate the gut microbiome-brain communication in neurodegenerative diseases, including the immunological, vagus nerve and circulatory pathways, are evaluated. Furthermore, we summarize potential therapeutics for neurodegenerative diseases that modify the gut microbiome and its metabolites, including diets, probiotics and prebiotics, microbial metabolites, antibacterials and faecal microbiome transplantation. Finally, current challenges and future directions are discussed.

Sodium butyrate exerts a neuroprotective effect in rats with acute carbon monoxide poisoning by activating autophagy through the mTOR signaling pathway

Acute carbon monoxide (CO) poisoning is a prevalent type of poisoning that causes significant harm globally. Delayed encephalopathy after acute carbon monoxide poisoning (DEACMP) is a severe complication that occurs after acute CO poisoning; however, the exact underlying pathological cause of DEACMP remains unclear. Accumulating evidence indicates that abnormal inflammation and immune-mediated brain damage, cellular apoptosis and autophagy, and direct neuronal toxicity are involved in the development of delayed neurologic sequelae. Sodium butyrate, a histone deacetylase inhibitor, has gained increasing attention for its numerous beneficial effects on various diseases, such as obesity, diabetes, inflammatory diseases, and cerebral damage. In this study, an acute carbon monoxide poisoning (ACOP) model is established in rats to investigate the mechanism of CO poisoning and the therapeutic potential of sodium butyrate. The results suggested that the ACOP rats had impaired spatial memory, and cell apoptosis was observed in the hippocampi with activated autophagy. Sodium butyrate treatment further increased the activation of autophagy in the hippocampi of CO-exposed rats, inhibited apoptosis, and consolidated spatial memory. These findings indicated that sodium butyrate may improve memory and cognitive function in ACMP rats by promoting autophagy and inhibiting apoptosis.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Advances in Brain-Gut-Microbiome Interactions: A Comprehensive Update on Signaling Mechanisms, Disorders, and Therapeutic Implications

The complex, bidirectional interactions between the brain, the gut, and the gut microbes are best referred to as the brain gut microbiome system. Animal and clinical studies have identified specific signaling mechanisms within this system, with gut microbes communicating to the brain through neuronal, endocrine, and immune pathways. The brain, in turn, modulates the composition and function of the gut microbiota through the autonomic nervous system, regulating gut motility, secretion, permeability, and the release of hormones impacting microbial gene expression. Perturbations at any level of these interactions can disrupt the intricate balance, potentially contributing to the pathogenesis of intestinal, metabolic, neurologic, and psychiatric disorders. Understanding these interactions and their underlying mechanisms holds promise for identifying biomarkers, as well as novel therapeutic targets, and for developing more effective treatment strategies for these complex disorders. Continued research will advance our knowledge of this system, with the potential for improved understanding and management of a wide range of disorders. This review provides an update on the current state of knowledge regarding this system, with a focus on recent advancements and emerging research areas.

Current understanding of the Alzheimer's disease-associated microbiome and therapeutic strategies

Alzheimer's disease (AD) is a fatal progressive neurodegenerative disease. Despite tremendous research efforts to understand this complex disease, the exact pathophysiology of the disease is not completely clear. Recently, anti-Aβ antibodies have been shown to remove amyloid from the brain and slow the clinical progression of mild dementia by ~30%. However, exploring alternative strategies is crucial to understanding and developing more effective therapeutic interventions. In recent years, the microbiota-gut-brain axis has received significant attention in the AD field. Numerous studies have suggested that alterations in the gut microbiota composition are associated with the progression of AD, and several underlying mechanisms have been proposed. However, studies in this area are still in their infancy, and many aspects of this field are just beginning to be explored and understood. Gaining a deeper understanding of the intricate interactions and signaling pathways involved in the microbiota-AD interaction is crucial for optimizing therapeutic strategies targeting gut microbiota to positively impact AD. In this review, we aim to summarize the current understanding of the microbiota-gut-brain axis in AD. We will discuss the existing evidence regarding the role of gut microbiota in AD pathogenesis, suggested underlying mechanisms, biological factors influencing the microbiome-gut-brain axis in AD, and remaining questions in the field. Last, we will discuss potential therapeutic approaches to recondition the community of gut microbiota to alleviate disease progression. An ongoing exploration of the gut-brain axis and the development of microbiota-based therapies hold the potential for advancing AD management in the future.

Gut microbiota defined epigenomes of Alzheimer's and Parkinson's diseases reveal novel targets for therapy

The origins of Alzheimer's disease (AD) and Parkinson's disease (PD) involve genetic mutations, epigenetic changes, neurotoxin exposure and gut microbiota dysregulation. The gut microbiota's dynamic composition and its metabolites influence intestinal and blood-brain barrier integrity, contributing to AD and PD development. This review explores protein misfolding, aggregation and epigenetic links in AD and PD pathogenesis. It also highlights the role of a leaky gut and the microbiota-gut-brain axis in promoting these diseases through inflammation-induced epigenetic alterations. In addition, we investigate the potential of diet, probiotics and microbiota transplantation for preventing and treating AD and PD via epigenetic modifications, along with a discussion related to current challenges and future considerations. These approaches offer promise for translating research findings into practical clinical applications.

Gut microbiome-targeted therapies for Alzheimer's disease

The advent of high-throughput 'omics' technologies has improved our knowledge of gut microbiome in human health and disease, including Alzheimer's disease (AD), a neurodegenerative disorder. Frequent bidirectional communications and mutual regulation exist between the gastrointestinal tract and the central nervous system through the gut-brain axis. A large body of research has reported a close association between the gut microbiota and AD development, and restoring a healthy gut microbiota may curb or even improve AD symptoms and progression. Thus, modulation of the gut microbiota has become a novel paradigm for clinical management of AD, and emerging effort has focused on developing potential novel strategies for preventing and/or treating the disease. In this review, we provide an overview of the connection and causal relationship between gut dysbiosis and AD, the mechanisms of gut microbiota in driving AD progression, and the successes and challenges of implementing available gut microbiome-targeted therapies (including probiotics, prebiotics, synbiotics, postbiotics, and fecal microbiota transplantation) in preventive and/or therapeutic preclinical and clinical intervention studies of AD. Finally, we discuss the future directions in this field.

Stauntonia chinensis injection relieves neuropathic pain by increasing the expression of PSD-95 and reducing the proliferation of phagocytic microglia

Neuroinflammation induced by engulfment of synapses by phagocytic microglia plays a crucial role in neuropathic pain. Stauntonia chinensis is extracted from Stauntonia chinensis DC, which has been used as a traditional Chinese medicine to control trigeminal neuralgia or sciatica. However, the specific anti-neuralgia mechanism of Stauntonia chinensis is unknown. In this study, the analgesic effect of Stauntonia chinensis injection (SCI) in mice with neuropathic pain and the possible mechanisms are explored. We find that a local injection of 0.1 mL Stauntonia chinensis for 14 days can considerably relieve mechanical hyperalgesia and thermal hyperalgesia in mice with sciatic chronic constriction injury (CCI). Immunofluorescence staining shows that SCI reduces neuroinflammation in the spinal cord of CCI mice. RNA sequencing reveals that the expression of postsynaptic density protein 95 (PSD-95), a postsynaptic scaffold protein, is downregulated in the spinal cord of CCI mice, but upregulated after SCI administration. Immunofluorescence experiments also demonstrate that SCI administration reverses microglia proliferation and PSD-95 downregulation in CCI mice. These data suggest that SCI relieves neuropathic pain by increasing the expression of PSD-95 and reducing the proliferation of phagocytic microglia.

Activation of β2-adrenergic receptors prevents AD-type synaptotoxicity via epigenetic mechanisms

We previously reported that prolonged exposure to an enriched environment (EE) enhances hippocampal synaptic plasticity, with one of the significant mechanistic pathways being activation of β2-adrenergic receptor (β2-AR) signaling, thereby mitigating the synaptotoxic effects of soluble oligomers of amyloid β-protein (oAβ). However, the detailed mechanism remained elusive. In this work, we recorded field excitatory postsynaptic potentials (fEPSP) in the CA1 region of mouse hippocampal slices treated with or without toxic Aβ-species. We found that pharmacological activation of β2-AR, but not β1-AR, selectively mimicked the effects of EE in enhancing LTP and preventing oAβ-induced synaptic dysfunction. Mechanistic analyses showed that certain histone deacetylase (HDAC) inhibitors mimicked the benefits of EE, but this was not seen in β2-AR knockout mice, suggesting that activating β2-AR prevents oAβ-mediated synaptic dysfunction via changes in histone acetylation. EE or activation of β-ARs each decreased HDAC2, whereas Aβ oligomers increased HDAC2 levels in the hippocampus. Further, oAβ-induced inflammatory effects and neurite degeneration were prevented by either β2-AR agonists or certain specific HDAC inhibitors. These preclinical results suggest that activation of β2-AR is a novel potential therapeutic strategy to mitigate oAβ-mediated features of AD.

Sodium Butyrate Ameliorates Fluorosis-Induced Neurotoxicity by Regulating Hippocampal Glycolysis In Vivo

Fluorosis can induce neurotoxicity. Sodium butyrate (SB), a histone deacetylase inhibitor, has important research potential in correcting glucose metabolism disorders and is widely used in a variety of neurological diseases and metabolic diseases, but it is not yet known whether it plays a role in combating fluoride-induced neurotoxicity. This study aims to evaluate the effect of SB on fluoride neurotoxicity and the possible associated mechanisms. The results of HE staining and Morris water maze showed that, in mice exposed to 100 mg/L fluoride for 3 months, the hippocampal cells arranged in loosely with large cell gaps and diminished in number. One thousand milligram per kilogram per day SB treatment improved fluoride-induced neuronal cell damage and spatial learning memory impairment. Western blot results showed that the abundance of malate dehydrogenase 2 (MDH2) and pyruvate dehydrogenase (PDH) in the hippocampus of fluorosis mice was increased, the abundance of pyruvate kinase M (PKM), lactate dehydrogenase (LDH), hexokinase (HK), phosphatidylinositol 3-kinase (PI3K), phosphorylated Akt (P-AKT), and hypoxia-inducible factor 1α (HIF-1α) was inhibited, and the content of lactate and ATP was decreased. SB treatment reversed the decreased glycolysis in the hippocampus of fluorosis mice. These results suggested that SB could ameliorate fluorosis-induced neurotoxicity, which might be linked with its function in regulating glycolysis as well as inhibition of the PI3K/AKT/HIF-1α pathway. Sodium butyrate ameliorates fluorosis-induced neurotoxicity by regulating hippocampal glycolysis in vivo (created with MedPeer (www.medpeer.cn)).

Discovery of acylated isoquercitrin derivatives as potent anti-neuroinflammatory agents in vitro and in vivo

Neuroinflammation is considered as an important pathological mechanism in neurodegenerative diseases. The natural isoquercitrin (IQ) was reported to have potential anti-neuroinflammatory activity. The acylation of glycoside in IQ enhanced its hydrophobicity, which was expected to enhance the protective effect against inflammation. In this study, three carboxylic acids with anti-neuroinflammatory effects including cinnamic acid, ibuprofen (IBU) and acetylsalicylic acid were introduced into the 6''-OH of IQ through the corresponding vinyl esters intermediates (8a-8c). Ultimately, the acylated IQ derivatives (Compound 9a-9c) were obtained with 35-42% yields using immobilized lipase Novozym 435 as catalyst. Subsequently, their anti-neuroinflammatory activities were evaluated in lipopolysaccharide (LPS)-induced BV2 cells. Compound 9b improved cell viability in the range of ≤50 μM and significantly decreased NO, PGE2 production and TNF-α, IL-1β release and oxidative stress level with a concentration-dependent manner. Also, it could downregulate iNOS, COX-2, TNF-α and IL-1β expression levels, approximately 40% reduction were achieved when 15μM compound 9b was employed. In addition, compound 9b resisted phosphorylation and degradation of IkBαs, suppressing the activation of NF-κB signaling pathway, exhibiting excellent neuroinflammatory inhibition. Moreover, the administration of compound 9b (30, 60 mg/kg) alleviated behavioral disorders and neuronal damages in LPS-induced neuroinflammatory mice. Meanwhile, the decreased TNF-α, IL-1β release, expression and the inhibited glial cells activation were obtained in compound 9b-treated group, which was superior to that of IQ or IBU. Overall, these findings demonstrated that compound 9b, formed by the introduction of ibuprofen into IQ, can serve as a novel promising therapeutic agent for anti-neuroinflammation.

Dietary Fiber and Microbiota Metabolite Receptors Enhance Cognition and Alleviate Disease in the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder with poorly understood etiology. AD has several similarities with other "Western lifestyle" inflammatory diseases, where the gut microbiome and immune pathways have been associated. Previously, we and others have noted the involvement of metabolite-sensing GPCRs and their ligands, short-chain fatty acids (SCFAs), in protection of numerous Western diseases in mouse models, such as Type I diabetes and hypertension. Depletion of GPR43, GPR41, or GPR109A accelerates disease, whereas high SCFA yielding diets protect in mouse models. Here, we extended the concept that metabolite-sensing receptors and SCFAs may be a more common protective mechanism against Western diseases by studying their role in AD pathogenesis in the 5xFAD mouse model. Both male and female mice were included. Depletion of GPR41 and GPR43 accelerated cognitive decline and impaired adult hippocampal neurogenesis in 5xFAD and WT mice. Lack of fiber/SCFAs accelerated a memory deficit, whereas diets supplemented with high acetate and butyrate (HAMSAB) delayed cognitive decline in 5xFAD mice. Fiber intake impacted on microglial morphology in WT mice and microglial clustering phenotype in 5xFAD mice. Lack of fiber impaired adult hippocampal neurogenesis in both W and AD mice. Finally, maternal dietary fiber intake significantly affects offspring's cognitive functions in 5xFAD mice and microglial transcriptome in both WT and 5xFAD mice, suggesting that SCFAs may exert their effect during pregnancy and lactation. Together, metabolite-sensing GPCRs and SCFAs are essential for protection against AD, and reveal a new strategy for disease prevention.Significance Statement Alzheimer's disease (AD) is one of the most common neurodegenerative diseases; currently, there is no cure for AD. In our study, short-chain fatty acids and metabolite receptors play an important role in cognitive function and pathology in AD mouse model as well as in WT mice. SCFAs also impact on microglia transcriptome, and immune cell recruitment. Out study indicates the potential of specialized diets (supplemented with high acetate and butyrate) releasing high amounts of SCFAs to protect against disease.

Sodium butyrate facilitates CRHR2 expression to alleviate HPA axis hyperactivity in autism-like rats induced by prenatal lipopolysaccharides through histone deacetylase inhibition

Short-chain fatty acids (SCFAs, especially butyric acid) have been demonstrated to play a promising role in the development of autism spectrum disorders (ASD). Recently, the hypothalamic-pituitary-adrenal (HPA) axis is also suggested to increase the risk of ASD. However, the mechanism underlying SCFAs and HPA axis in ASD development remains unknown. Here, we show that children with ASD exhibited lower SCFA concentrations and higher cortisol levels, which were recaptured in prenatal lipopolysaccharide (LPS)-exposed rat model of ASD. These offspring also showed decreased SCFA-producing bacteria and histone acetylation activity as well as impaired corticotropin-releasing hormone receptor 2 (CRHR2) expression. Sodium butyrate (NaB), which can act as histone deacetylases inhibitors, significantly increased histone acetylation at the CRHR2 promoter in vitro and normalized the corticosterone as well as CRHR2 expression level in vivo. Behavioral assays indicated ameliorative effects of NaB on anxiety and social deficit in LPS-exposed offspring. Our results imply that NaB treatment can improve ASD-like symptoms via epigenetic regulation of the HPA axis in offspring; thus, it may provide new insight into the SCFA treatment of neurodevelopmental disorders like ASD. IMPORTANCE Growing evidence suggests that microbiota can affect brain function and behavior through the "microbiome-gut-brain'' axis, but its mechanism remains poorly understood. Here, we show that both children with autism and LPS-exposed rat model of autism exhibited lower SCFA concentrations and overactivation of HPA axis. SCFA-producing bacteria, Lactobacillus, might be the key differential microbiota between the control and LPS-exposed offspring. Interestingly, NaB treatment contributed to the regulation of HPA axis (such as corticosterone as well as CRHR2) and improvement of anxiety and social deficit behaviors in LPS-exposed offspring. The potential underlying mechanism of the ameliorative effect of NaB may be mediated via increasing histone acetylation to the CRHR2 promoter. These results enhance our understanding of the relationship between the SCFAs and the HPA axis in the development of ASD. And gut microbiota-derived SCFAs may serve as a potential therapeutic agent to neurodevelopmental disorders like ASD.

Metabolic Profile of Alzheimer's Disease: Is 10-Hydroxy-2-decenoic Acid a Pertinent Metabolic Adjuster?

Alzheimer's disease (AD) represents a significant public health concern in modern society. Metabolic syndrome (MetS), which includes diabetes mellitus (DM) and obesity, represents a modifiable risk factor for AD. MetS and AD are interconnected through various mechanisms, such as mitochondrial dysfunction, oxidative stress, insulin resistance (IR), vascular impairment, inflammation, and endoplasmic reticulum (ER) stress. Therefore, it is necessary to seek a multi-targeted and safer approach to intervention. Thus, 10-hydroxy-2-decenoic acid (10-HDA), a unique hydroxy fatty acid in royal jelly, has shown promising anti-neuroinflammatory, blood-brain barrier (BBB)-preserving, and neurogenesis-promoting properties. In this paper, we provide a summary of the relationship between MetS and AD, together with an introduction to 10-HDA as a potential intervention nutrient. In addition, molecular docking is performed to explore the metabolic tuning properties of 10-HDA with associated macromolecules such as GLP-1R, PPARs, GSK-3, and TREM2. In conclusion, there is a close relationship between AD and MetS, and 10-HDA shows potential as a beneficial nutritional intervention for both AD and MetS.

Investigating the Synergistic Potential of Low-Dose HDAC3 Inhibition and Radiotherapy in Alzheimer's Disease Models

We have previously shown that histone deacetylase (HDAC) inhibition and cranial radiotherapy (RT) independently improve molecular and behavioral Alzheimer's disease (AD)-like phenotypes. In the present study, we investigate the synergistic potential of using both RT and HDACi as a low-dose combination therapy (LDCT) to maximize disease modification (reduce neuroinflammation and amyloidogenic APP processing, increase neurotrophic gene expression) while minimizing the potential for treatment-associated side effects.LDCT consisted of daily administration of the HDAC3 inhibitor RGFP966 and/or bi-weekly cranial x-irradiation. Amyloid-beta precursor protein (APP) processing and innate immune response to LDCT were assessed in vitro and in vivo using human and murine cell models and 3xTg-AD mice. After 2 months of LDCT in mice, behavioral analyses as well as expression and modification of key AD-related targets (Aβ, tau, Csf1r, Bdnf, etc.) were assessed in the hippocampus (HIP) and prefrontal cortex (PFC).LDCT induced a tolerant, anti-inflammatory innate immune response in microglia and increased non-amyloidogenic APP processing in vitro. Both RT and LDCT improved the rate of learning and spatial memory in the Barnes maze test. LDCT induced a unique anti-AD HIP gene expression profile that included upregulation of neurotrophic genes and downregulation of inflammation-related genes. RT lowered HIP Aβ42/40 ratio and Bace1 protein, while LDCT lowered PFC p-tau181 and HIP Bace1 levels.Our study supports the rationale for combining complementary therapeutic approaches at low doses to target multifactorial AD pathology synergistically. Namely, LDCT with RGFP966 and cranial RT shows disease-modifying potential against a wide range of AD-related hallmarks.

Functional effects of gut microbiota-derived metabolites in Alzheimer's disease

The precise causation of Alzheimer's disease (AD) is unknown, and the factors that contribute to its etiology are highly complicated. Numerous research has been conducted to investigate the potential impact of various factors to the risk of AD development or prevention against it. A growing body of evidence suggests to the importance of the gut microbiota-brain axis in the modulation of AD, which is characterized by altered gut microbiota composition. These changes can alter the production of microbial-derived metabolites, which may play a detrimental role in disease progression by being involved in cognitive decline, neurodegeneration, neuroinflammation, and accumulation of Aβ and tau. The focus of this review is on the relationship between the key metabolic products of the gut microbiota and AD pathogenesis in the brain. Understanding the action of microbial metabolites can open up new avenues for the development of AD treatment targets.

Therapeutic Strategies Aimed at Improving Neuroplasticity in Alzheimer Disease

Alzheimer disease (AD) is the most prevalent form of dementia among elderly people. Owing to its varied and multicausal etiopathology, intervention strategies have been highly diverse. Despite ongoing advances in the field, efficient therapies to mitigate AD symptoms or delay their progression are still of limited scope. Neuroplasticity, in broad terms the ability of the brain to modify its structure in response to external stimulation or damage, has received growing attention as a possible therapeutic target, since the disruption of plastic mechanisms in the brain appear to correlate with various forms of cognitive impairment present in AD patients. Several pre-clinical and clinical studies have attempted to enhance neuroplasticity via different mechanisms, for example, regulating glucose or lipid metabolism, targeting the activity of neurotransmitter systems, or addressing neuroinflammation. In this review, we first describe several structural and functional aspects of neuroplasticity. We then focus on the current status of pharmacological approaches to AD stemming from clinical trials targeting neuroplastic mechanisms in AD patients. This is followed by an analysis of analogous pharmacological interventions in animal models, according to their mechanisms of action.

Clinical evidence of human pathogens implicated in Alzheimer's disease pathology and the therapeutic efficacy of antimicrobials: an overview

A wealth of pre-clinical reports and data derived from human subjects and brain autopsies suggest that microbial infections are relevant to Alzheimer's disease (AD). This has inspired the hypothesis that microbial infections increase the risk or even trigger the onset of AD. Multiple models have been developed to explain the increase in pathogenic microbes in AD patients. Although this hypothesis is well accepted in the field, it is not yet clear whether microbial neuroinvasion is a cause of AD or a consequence of the pathological changes experienced by the demented brain. Along the same line, the gut microbiome has also been proposed as a modulator of AD. In this review, we focus on human-based evidence demonstrating the elevated abundance of microbes and microbe-derived molecules in AD hosts as well as their interactions with AD hallmarks. Further, the direct-purpose and potential off-target effects underpinning the efficacy of anti-microbial treatments in AD are also addressed.

Novel Lipids to Regulate Obesity and Brain Function: Comparing Available Evidence and Insights from QSAR In Silico Models

Lipid molecules, such as policosanol, ergosterol, sphingomyelin, omega 3 rich phosphatidylcholine, α-tocopherol, and sodium butyrate, have emerged as novel additions to the portfolio of bioactive lipids. In this state-of-the-art review, we discuss these lipids, and their activity against obesity and mental or neurological disorders, with a focus on their proposed cellular targets and the ways in which they produce their beneficial effects. Furthermore, this available information is compared with that provided by in silico Absorption, Distribution, Metabolism, Excretion, and Toxicity (ADMET) models in order to understand the usefulness of these tools for the discovery of new bioactive compounds. Accordingly, it was possible to highlight how these lipids interact with various cellular targets related to the molecule transportation and absorption (e.g., α-tocopherol transfer protein for α-Tocopherol, ATP-binding cassette ABC transporters or Apolipoprotein E for sphingomyelins and phospholipids) or other processes, such as the regulation of gene expression (involving Sterol Regulatory Element-Binding Proteins for ergosterol or Peroxisome Proliferator-Activated Receptors in the case of policosanol) and inflammation (the regulation of interleukins by sodium butyrate). When comparing the literature with in silico Quantitative Structure-Activity Relationship (QSAR) models, it was observed that although they are useful for selecting bioactive molecules when compared in batch, the information they provide does not coincide when assessed individually. Our review highlights the importance of considering a broad range of lipids as potential bioactives and the need for accurate prediction of ADMET parameters in the discovery of new biomolecules. The information presented here provides a useful resource for researchers interested in developing new strategies for the treatment of obesity and mental or neurological disorders.

Short-chain fatty and carboxylic acid changes associated with fecal microbiota transplant communally influence microglial inflammation

The intestinal microbiota has been proposed to influence human mental health and cognition through the gut-brain axis. Individuals experiencing recurrent Clostridioides difficile infection (rCDI) frequently report depressive symptoms, which are improved after fecal microbiota transplantation (FMT); however, mechanisms underlying this association are poorly understood. Short-chain fatty acids and carboxylic acids (SCCA) produced by the intestinal microbiota cross the blood brain barrier and have been proposed to contribute to gut-brain communication. We hypothesized that changes in serum SCCA measured before and after successful FMT for rCDI influences the inflammatory response of microglia, the resident immune cells of the central nervous system. Serum SCCA were quantified using gas chromatography-mass spectroscopy from 38 patients who participated in a randomized trial comparing oral capsule-vs colonoscopy-delivered FMT for rCDI, and quality of life was assessed by SF-36 at baseline, 4, and 12 weeks after FMT treatment. Successful FMT was associated with improvements in mental and physical health, as well as significant changes in a number of circulating SCCA, including increased butyrate, 2-methylbutyrate, valerate, and isovalerate, and decreased 2-hydroxybutyrate. Primary cultured microglia were treated with SCCA and the response to a pro-inflammatory stimulus was measured. Treatment with a combination of SCCA based on the post-FMT serum profile, but not single SCCA species, resulted in significantly reduced inflammatory response including reduced cytokine release, reduced nitric oxide release, and accumulation of intracellular lipid droplets. This suggests that both levels and diversity of SCCA may be an important contributor to gut-brain communication.

Fecal microbiota transplantation and short-chain fatty acids protected against cognitive dysfunction in a rat model of chronic cerebral hypoperfusion

AIMS

Clear roles and mechanisms in explaining gut microbial dysbiosis and microbial metabolites short-chain fatty acids (SCFAs) alterations in chronic cerebral ischemic pathogenesis have yet to be explored. In this study, we investigated chronic cerebral hypoperfusion (CCH)-induced gut microbiota and metabolic profiles of SCFAs as well as the effects and mechanisms of fecal microbiota transplantation (FMT) and SCFAs treatment on CCH-induced hippocampal neuronal injury.

METHODS

Bilateral common carotid artery occlusion (BCCAo) was used to establish the CCH model. Gut microbiota and SCFAs profiles in feces and hippocampus were evaluated by 16S ribosomal RNA sequencing and gas chromatography-mass spectrometry. RNA sequencing analysis was performed in hippocampal tissues. The potential molecular pathways and differential genes were verified through western blot, immunoprecipitation, immunofluorescence, and ELISA. Cognitive function was assessed via the Morris water maze test. Ultrastructures of mitochondria and synapses were tested through a transmission electron microscope.

RESULTS

Chronic cerebral hypoperfusion induced decreased fecal acetic and propionic acid and reduced hippocampal acetic acid, which were reversed after FMT and SCFAs administration by changing fecal microbial community structure and compositions. Furthermore, in the hippocampus, FMT and SCFAs replenishment exerted anti-neuroinflammatory effects through inhibiting microglial and astrocytic activation as well as switching microglial phenotype from M1 toward M2. Moreover, FMT and SCFAs treatment alleviated neuronal loss and microglia-mediated synaptic loss and maintained the normal process of synaptic vesicle fusion and release, resulting in the improvement of synaptic plasticity. In addition, FMT and SCFAs supplement prevented oxidative phosphorylation dysfunction via mitochondrial metabolic reprogramming. The above effects of FMT and SCFAs treatment led to the inhibition of CCH-induced cognitive impairment.

CONCLUSION

Our findings highlight FMT and SCFAs replenishment would be the feasible gut microbiota-based strategy to mitigate chronic cerebral ischemia-induced neuronal injury.