Rapid improvement in Alzheimer's disease symptoms following fecal microbiota transplantation: a case report

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.

The same but different: impact of animal facility sanitary status on a transgenic mouse model of Alzheimer's disease

The gut-brain axis has emerged as a key player in the regulation of brain function and cognitive health. Gut microbiota dysbiosis has been observed in preclinical models of Alzheimer's disease and patients. Manipulating the composition of the gut microbiota enhances or delays neuropathology and cognitive deficits in mouse models. Accordingly, the health status of the animal facility may strongly influence these outcomes. In the present study, we longitudinally analyzed the fecal microbiota composition and amyloid pathology of 5XFAD mice housed in a specific opportunistic pathogen-free (SOPF) and a conventional facility. The composition of the microbiota of 5XFAD mice after aging in conventional facility showed marked differences compared to WT littermates that were not observed when the mice were bred in SOPF facility. The development of amyloid pathology was also enhanced by conventional housing. We then transplanted fecal microbiota (FMT) from both sources into wild-type (WT) mice and measured memory performance, assessed in the novel object recognition test, in transplanted animals. Mice transplanted with microbiota from conventionally bred 5XFAD mice showed impaired memory performance, whereas FMT from mice housed in SOPF facility did not induce memory deficits in transplanted mice. Finally, 18 weeks of housing SOPF-born animals in a conventional facility resulted in the reappearance of specific microbiota compositions in 5XFAD vs WT mice. In conclusion, these results show a strong impact of housing conditions on microbiota-associated phenotypes and question the relevance of breeding preclinical models in specific pathogen-free (SPF) facilities.

IMPORTANCE

Housing conditions affect the composition of the gut microbiota. Gut microbiota of 6-month-old conventionally bred Alzheimer's mice is dysbiotic. Gut dysbiosis is absent in Alzheimer's mice housed in highly sanitized facilities. Transfer of fecal microbiota from conventionally bred mice affects cognition. Microbiota of mice housed in highly sanitized facilities has no effect on cognition.

The microbiome: what a neurologist needs to know

The gastrointestinal tract is inhabited by trillions of micro-organisms that form the gut microbiome, which serves various functions that can influence neurological pathways. It can release metabolites that could affect the nervous system. The bidirectional communication between the intestine and the central nervous system is known as the gut-brain axis. This communication can be impacted by the microbiota in various direct and indirect ways. There has been a suggested connection between the microbiome and many neurological disorders, including epilepsy, Alzheimer's disease, Parkinson's disease and multiple sclerosis. This has been explored in human and animal studies. While no microbial biomarkers have been identified yet, alterations in several taxa have been suggested to be associated with disease states. The potential of the microbiome to modulate neurological function has sparked multiple clinical trials using gut-altering treatments, some with positive preliminary results.

Gut Microbiota Mediates Neuroinflammation in Alzheimer's Disease: Unraveling Key Factors and Mechanistic Insights

The gut microbiota, the complex community of microorganisms that inhabit the gastrointestinal tract, has emerged as a key player in the pathogenesis of neurodegenerative disorders, including Alzheimer's disease (AD). AD is characterized by progressive cognitive decline and neuronal loss, associated with the accumulation of amyloid-β plaques, neurofibrillary tangles, and neuroinflammation in the brain. Increasing evidence suggests that alterations in the composition and function of the gut microbiota, known as dysbiosis, may contribute to the development and progression of AD by modulating neuroinflammation, a chronic and maladaptive immune response in the central nervous system. This review aims to comprehensively analyze the current role of the gut microbiota in regulating neuroinflammation and glial cell function in AD. Its objective is to deepen our understanding of the pathogenesis of AD and to discuss the potential advantages and challenges of using gut microbiota modulation as a novel approach for the diagnosis, treatment, and prevention of AD.

Gut microbiota dysbiosis in Alzheimer's disease (AD): Insights from human clinical studies and the mouse AD models

Alzheimer's Disease (AD) is a debilitating neurocognitive disorder with an unclear underlying mechanism. Recent studies have implicated gut microbiota dysbiosis with the onset and progression of AD. The connection between gut microbiota and AD can significantly affect the prevention and treatment of AD patients. This systematic review summarizes primary outcomes of human and mouse AD models concerning gut microbiota alterations. A systematic literature search in February through March 2023 was conducted on PubMed, Embase, and Web of Science. We identified 711 as potential manuscripts of which 672 were excluded because of irrelevance to the identified search criteria. Primary outcomes include microbiota compositions of control and AD models in humans and mice. In total, 39 studies were included (19 mouse and 20 human studies), published between 2017 and 2023. We included studies involving well-established mice models of AD (5xFAD, 3xTg-AD, APP/PS1, Tg2576, and APPPS2) which harbor mutations and genes that drive the formation of Aß plaques. All human studies were included on those with AD or mild cognitive impairment. Among alterations in gut microbiota, most studies found a decreased abundance of the phyla Firmicutes and Bifidobacteria, a genus of the phylum Actinomycetota. An increased abundance of the phyla Bacteroidetes and Proteobacteria were identified in animal and human studies. Studies indicated that gut microbiota alter the pathogenesis of AD through its impact on neuroinflammation and permeability of the gastrointestinal tract. The ensuing increase in blood-brain barrier permeability may accelerate Aβ penetrance and formation of neuritic plaques that align with the amyloid hypothesis of AD pathogenesis. Further studies should assess the relationship between gut microbiota and AD progression and therapy preserving beneficial gut microbiota.

Gut microbiota in Alzheimer's disease: Understanding molecular pathways and potential therapeutic perspectives

Accumulating evidence suggests that gut microbiota (GM) plays a crucial role in Alzheimer's disease (AD) pathogenesis and progression. This narrative review explores the complex interplay between GM, the immune system, and the central nervous system in AD. We discuss mechanisms through which GM dysbiosis can compromise intestinal barrier integrity, enabling pro-inflammatory molecules and metabolites to enter systemic circulation and the brain, potentially contributing to AD hallmarks. Additionally, we examine other pathophysiological mechanisms by which GM may influence AD risk, including the production of short-chain fatty acids, secondary bile acids, and tryptophan metabolites. The role of the vagus nerve in gut-brain communication is also addressed. We highlight potential therapeutic implications of targeting GM in AD, focusing on antibiotics, probiotics, prebiotics, postbiotics, phytochemicals, and fecal microbiota transplantation. While preclinical studies showed promise, clinical evidence remains limited and inconsistent. We critically assess clinical trials, emphasizing challenges in translating GM-based therapies to AD patients. The reviewed evidence underscores the need for further research to elucidate precise molecular mechanisms linking GM to AD and determine whether GM dysbiosis is a contributing factor or consequence of AD pathology. Future studies should focus on large-scale clinical trials to validate GM-based interventions' efficacy and safety in AD.

Immune mechanisms and shared immune targets in neurodegenerative diseases

The immune system plays a major part in neurodegenerative diseases. In some, such as multiple sclerosis, it is the primary driver of the disease. In others, such as Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, it has an amplifying role. Immunotherapeutic approaches that target the adaptive and innate immune systems are being explored for the treatment of almost all neurological diseases, and the targets and approaches are often common across diseases. Microglia are the primary immune cells in the brain that contribute to disease pathogenesis, and are consequently a common immune target for therapy. Other therapeutic approaches target components of the peripheral immune system, such as regulatory T cells and monocytes, which in turn act within the CNS. This Review considers in detail how microglia, monocytes and T cells contribute to the pathogenesis of multiple sclerosis, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, and their potential as shared therapeutic targets across these diseases. The microbiome is also highlighted as an emerging therapeutic target that indirectly modulates the immune system. Therapeutic approaches being developed to target immune function in neurodegenerative diseases are discussed, highlighting how immune-based approaches developed to treat one disease could be applicable to multiple other neurological diseases.

Fecal Microbiota Transplantation (FMT) From a Human at Low Risk for Alzheimer's Disease Improves Short-Term Recognition Memory and Increases Neuroinflammation in a 3xTg AD Mouse Model

Human microbiota-associated murine models, using fecal microbiota transplantation (FMT) from human donors, help explore the microbiome's role in diseases like Alzheimer's disease (AD). This study examines how gut bacteria from donors with protective factors against AD influence behavior and brain pathology in an AD mouse model. Female 3xTgAD mice received weekly FMT for 2 months from (i) an 80-year-old AD patient (AD-FMT), (ii) a cognitively healthy 73-year-old with the protective APOEe2 allele (APOEe2-FMT), (iii) a 22-year-old healthy donor (Young-FMT), and (iv) untreated mice (Mice-FMT). Behavioral assessments included novel object recognition (NOR), Y-maze, open-field, and elevated plus maze tests; brain pathology (amyloid and tau), neuroinflammation (in situ autoradiography of the 18 kDa translocator protein in the hippocampus); and gut microbiota were analyzed. APOEe2-FMT improved short-term memory in the NOR test compared to AD-FMT, without significant changes in other behavioral tests. This was associated with increased neuroinflammation in the hippocampus, but no effect was detected on brain amyloidosis and tauopathy. Specific genera, such as Parabacteroides and Prevotellaceae_UGC001, were enriched in the APOEe2-FMT group and associated with neuroinflammation, while genera like Desulfovibrio were reduced and linked to decreased neuroinflammation. Gut microbiota from a donor with a protective factor against AD improved short-term memory and induced neuroinflammation in regions strategic to AD. The association of several genera with neuroinflammation in the APOEe2-FMT group suggests a collegial effect of the transplanted microbiome rather than a single-microbe driver effect. These data support an association between gut bacteria, glial cell activation, and cognitive function in AD.

The Role of Genetic, Environmental, and Dietary Factors in Alzheimer's Disease: A Narrative Review

Alzheimer's disease (AD) is one of the most common and severe forms of dementia and neurodegenerative disease. As life expectancy increases in line with developments in medicine, the elderly population is projected to increase in the next few decades; therefore, an increase in the prevalence of some diseases, such as AD, is also expected. As a result, until a radical treatment becomes available, AD is expected to be more frequently recorded as one of the top causes of death worldwide. Given the current lack of a cure for AD, and the only treatments available being ones that alleviate major symptoms, the identification of contributing factors that influence disease incidence is crucial. In this context, genetic and/or epigenetic factors, mainly environmental, disease-related, dietary, or combinations/interactions of these factors, are assessed. In this review, we conducted a literature search focusing on environmental factors such as air pollution, toxic elements, pesticides, and infectious agents, as well as dietary factors including various diets, vitamin D deficiency, social factors (e.g., tobacco and alcohol use), and variables that are affected by both environmental and genetic factors, such as dietary behavior and gut microbiota. We also evaluated studies on the beneficial effects of antibiotics and diets, such as the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) and Mediterranean diets.

Evolution of Alzheimer's Disease Therapeutics: From Conventional Drugs to Medicinal Plants, Immunotherapy, Microbiotherapy and Nanotherapy

Alzheimer's disease (AD) represents an escalating global health crisis, constituting the leading cause of dementia among the elderly and profoundly impairing their quality of life. Current FDA-approved drugs, such as rivastigmine, donepezil, galantamine, and memantine, offer only modest symptomatic relief and are frequently associated with significant adverse effects. Faced with this challenge and in line with advances in the understanding of the pathophysiology of this neurodegenerative condition, various innovative therapeutic strategies have been explored. Here, we review novel approaches inspired by advanced knowledge of the underlying pathophysiological mechanisms of the disease. Among the therapeutic alternatives, immunotherapy stands out, employing monoclonal antibodies to specifically target and eliminate toxic proteins implicated in AD. Additionally, the use of medicinal plants is examined, as their synergistic effects among components may confer neuroprotective properties. The modulation of the gut microbiota is also addressed as a peripheral strategy that could influence neuroinflammatory and degenerative processes in the brain. Furthermore, the therapeutic potential of emerging approaches, such as the use of microRNAs to regulate key cellular processes and nanotherapy, which enables precise drug delivery to the central nervous system, is analyzed. Despite promising advances in these strategies, the incidence of Alzheimer's disease continues to rise. Therefore, it is proposed that achieving effective treatment in the future may require the integration of combined approaches, maximizing the synergistic effects of different therapeutic interventions.

Viruses and neurodegeneration: a growing concern

Neurodegenerative diseases (NDDs) cause a progressive loss of neurons. Since NDDs are multifactorial, the precise etiology varies on the basis of the type of disease and patient history. Cohort studies and case studies have demonstrated a potential link between viral infections and the onset or progression of NDDs. Recent findings concerning the mechanisms by which neuropathic infections occur have provided more insights into the importance of such connections. In this review, we aim to elaborate on the occurrence of the neuropathic effects of viruses from epidemiological, clinical, and biological perspectives while highlighting potential treatments and challenges. One of the key players in viral neuropathogenesis is neuroinflammation caused by the immune response to the virus; this can occur due to both neurotropic and nonneurotropic viruses. The COVID-19 pandemic has raised concerns about whether vaccines are essential for preventing viruses or whether vaccines may play a part in exacerbating or accelerating NDDs. By classifying viruses and the common NDDs associated with them and further delving into their cellular pathways, this review provides insights to advance the development of potential treatments and diagnostic methods.

Shattering the Amyloid Illusion: The Microbial Enigma of Alzheimer's Disease Pathogenesis-From Gut Microbiota and Viruses to Brain Biofilms

For decades, Alzheimer's Disease (AD) research has focused on the amyloid cascade hypothesis, which identifies amyloid-beta (Aβ) as the primary driver of the disease. However, the consistent failure of Aβ-targeted therapies to demonstrate efficacy, coupled with significant safety concerns, underscores the need to rethink our approach to AD treatment. Emerging evidence points to microbial infections as environmental factors in AD pathoetiology. Although a definitive causal link remains unestablished, the collective evidence is compelling. This review explores unconventional perspectives and emerging paradigms regarding microbial involvement in AD pathogenesis, emphasizing the gut-brain axis, brain biofilms, the oral microbiome, and viral infections. Transgenic mouse models show that gut microbiota dysregulation precedes brain Aβ accumulation, emphasizing gut-brain signaling pathways. Viral infections like Herpes Simplex Virus Type 1 (HSV-1) and Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) may lead to AD by modulating host processes like the immune system. Aβ peptide's antimicrobial function as a response to microbial infection might inadvertently promote AD. We discuss potential microbiome-based therapies as promising strategies for managing and potentially preventing AD progression. Fecal microbiota transplantation (FMT) restores gut microbial balance, reduces Aβ accumulation, and improves cognition in preclinical models. Probiotics and prebiotics reduce neuroinflammation and Aβ plaques, while antiviral therapies targeting HSV-1 and vaccines like the shingles vaccine show potential to mitigate AD pathology. Developing effective treatments requires standardized methods to identify and measure microbial infections in AD patients, enabling personalized therapies that address individual microbial contributions to AD pathogenesis. Further research is needed to clarify the interactions between microbes and Aβ, explore bacterial and viral interplay, and understand their broader effects on host processes to translate these insights into clinical interventions.

A Review of the Consequences of Gut Microbiota in Neurodegenerative Disorders and Aging

Age-associated alterations in the brain lead to cognitive deterioration and neurodegenerative disorders (NDDs). This review with a particular focus on Alzheimer's disease (AD), emphasizes the burgeoning significance of the gut microbiota (GMB) in neuroinflammation and its impact on the gut-brain axis (GBA), a communication conduit between the gut and the central nervous system (CNS). Changes in the gut microbiome, including diminished microbial diversity and the prevalence of pro-inflammatory bacteria, are associated with AD pathogenesis. Promising therapies, such as fecal microbiota transplantation (FMT), probiotics, and prebiotics, may restore gut health and enhance cognitive performance. Clinical data remain insufficient, necessitating further research to elucidate causes, enhance therapy, and consider individual variances. This integrative approach may yield innovative therapies aimed at the GMB to improve cognitive function and brain health in older people.

Total Alkaloids of Rhizoma Corydalis regulates gut microbiota and restores gut immune barrier to ameliorate cognitive dysfunction in diabetic rats

Background and objectives

Given the widespread dysbiosis of gut microbiota in patients with T2DM, it has been found that the microbiota-gut-brain axis plays an influential regulatory role in diabetic cognitive dysfunction, and improving gut dysbiosis may be a potential strategy for treating diabetic cognitive dysfunction. Total Alkaloids of Rhizoma Corydalis (TAC) is the main active component extracted from Rhizoma Corydalis. Pharmacological studies have demonstrated its significant pharmacological effects on the cardiovascular and cerebrovascular systems, and berberine, the main component of TAC, has a certain regulatory effect on gut microbiota.

Materials and methods

Rats were randomly divided into Control group, Model group, TAC-low group, TAC-mid group and TAC-high group. Cognitive function of diabetic rats was evaluated through behavioral testing using the Morris water maze experiment. The relative abundance of gut bacteria in rat feces was determined via 16S rRNA analysis. IHC and Western blot techniques were employed to assess IL-22, IL-23, Reg3g, ZO-1, occludin 1 expression in the colon tissue; GPX4, xCT, NLRP3, Caspase-1 p20, GSDMD-N were detected in the hippocampus.

Results

The cognitive function of diabetic rats decreased significantly. TAC demonstrated a significant reduction in inflammatory factors in serum, hippocampus, and colon, thus alleviating inflammation. Additionally, it effectively decreased ferroptosis induced by NLRP3 and reduced pathological damage in the hippocampus of diabetic rats. After treatment, the differential microbiota such as Lachnoclotridium and Bacteroides. TAC improved gut barrier permeability and integrity in rats while remodeling gut mucosal homeostasis. Moreover, pyroptosis and ferroptosis caused by the inflammatory cascade in the rat hippocampus were also significantly inhibited.

Conclusion

The combination of high lipid and high glucose with STZ can result in gut microbiota disturbance, damage gut immune barrier, decreased gut mucosal permeability and integrity, aggravated gut inflammation, further spread inflammatory factors to brain tissue, cause inflammatory cascade reaction of encephalopathy, and ultimately resulting in neuronal ferroptosis and cognitive dysfunction in diabetes mellitus. Our study suggests that TAC may regulate gut microbiota, restore gut immune homeostasis, improve gut barrier permeability and integrity, inhibit brain tissue inflammatory cascade, reduce neuronal ferroptosis, and thus improve diabetes. This provides new targets for its treatment strategy.

Gut microbiome and Alzheimer's disease: What we know and what remains to be explored

With advancement in human microbiome research, an increasing number of scientific evidences have endorsed the key role of gut microbiota in the pathogenesis of Alzheimer disease. Microbiome dysbiosis, characterized by altered diversity and composition, as well as rise of pathobionts influence not only various gut disorder but also central nervous system disorders such as AD. On the basis of accumulated evidences of past few years now it is quite clear that the gut microbiota can control the functions of the central nervous system (CNS) through the gut-brain axis, which provides a new prospective into the interactions between the gut and brain. The main focus of this review is on the molecular mechanism of the crosstalk between the gut microbiota and the brain through the gut-brain axis, and on the onset and development of neurological disorders triggered by the dysbiosis of gut microbiota. Due to microbiota dysbiosis the permeability of the gut and blood brain barrier is increased which may mediate or affect AD. Along with this, bacterial population of the gut microbiota can secrete amyloid proteins and lipopolysaccharides in a large quantity which may create a disturbance in the signaling pathways and the formation of proinflammatory cytokines associated with the pathogenesis of AD. These topics are followed by a critical analysis of potential intervention strategies targeting gut microbiota dysbiosis, including the use of probiotics, prebiotics, metabolites, diets and fecal microbiota transplantation. The main purpose of this review includes the summarization and discussion on the recent finding that may explain the role of the gut microbiota in the development of AD. Understanding of these fundamental mechanisms may provide a new insight into the novel therapeutic strategies for AD.

Gut Microbiota and Immune System Dynamics in Parkinson's and Alzheimer's Diseases

The gut microbiota, a diverse collection of microorganisms in the gastrointestinal tract, plays a critical role in regulating metabolic, immune, and cognitive functions. Disruptions in the composition of these microbial communities, termed dysbiosis, have been linked to various neurodegenerative diseases (NDs), such as Parkinson's disease (PD) and Alzheimer's disease (AD). One of the key pathological features of NDs is neuroinflammation, which involves the activation of microglia and peripheral immune cells. The gut microbiota modulates immune responses through the production of metabolites and interactions with immune cells, influencing the inflammatory processes within the central nervous system. This review explores the impact of gut dysbiosis on neuroinflammation, focusing on the roles of microglia, immune cells, and potential therapeutic strategies targeting the gut microbiota to alleviate neuroinflammatory processes in NDs.

Microbes as medicine

Over the last two decades, advancements in sequencing technologies have significantly deepened our understanding of the human microbiome's complexity, leading to increased concerns about the detrimental effects of antibiotics on these intricate microbial ecosystems. Concurrently, the rise in antimicrobial resistance has intensified the focus on how beneficial microbes can be harnessed to treat diseases and improve health and offer potentially promising alternatives to traditional antibiotic treatments. Here, we provide a comprehensive overview of both established and emerging microbe-centric therapies, from probiotics to advanced microbial ecosystem therapeutics, examine the sophisticated ways in which microbes are used medicinally, and consider their impacts on microbiome homeostasis and health outcomes through a microbial ecology lens. In addition, we explore the concept of rewilding the human microbiome by reintroducing "missing microbes" from nonindustrialized societies and personalizing microbiome modulation to fit individual microbial profiles-highlighting several promising directions for future research. Ultimately, the advancements in sequencing technologies combined with innovative microbial therapies and personalized approaches herald a new era in medicine poised to address antibiotic resistance and improve health outcomes through targeted microbiome management.

Effects of Artemisia asiatica ex on Akkermansia muciniphila dominance for modulation of Alzheimer's disease in mice

The gut microbiome influences neurological disorders through bidirectional communication between the gut and the brain, i.e., the gut-brain axis. Artemisia asiatica ex, an extract of Artemisia asiatica Nakai (Stillen®, DA-9601) has been reported to improve depression by increasing brain-derived neurotropic factor. Therefore, we hypothesized that DA-9601 can be a potential therapeutic candidate for Alzheimer's disease (AD) acting through the gut-brain axis. Four groups of Tg2576 mice were used as the animal model for AD: wild type mice (n = 6), AD mice (n = 6), and DA-9601-administered AD mice given dosages of 30mg/kg/day (DA_30mg; n = 6) or 100mg/kg/day (DA_100mg; n = 6). Microglial activation, blood‒brain barrier integrity, amyloid beta accumulation, cognitive behavior, and changes in the gut microbiome were analyzed. DA-9601 improved the cognitive behavior of mice (DA_30mg **p<0.01; DA_100mg **p<0.01) and reduced amyloid beta accumulation (DA_30mg ***p<0.001; DA_100mg **p<0.01). Increased Iba-1 and upregulation of claudin-5 (DA_30mg *p<0.05) and occludin (DA_30mg **p<0.01; DA_100mg ***p<0.001) indicated altered microglial activation and improved blood‒brain barrier integrity. Akkermansia muciniphila was dramatically increased by DA-9601 administration (DA_30mg 47%; DA_100mg 61%). DA-9601 improved AD pathology with Akkermansia muciniphila dominance in the gut microbiome in a mouse model of AD, inferring that DA-9601 can affect AD through the gut-brain axis.

Intestinal endogenous metabolites affect neuroinflammation in 5×FAD mice by mediating "gut-brain" axis and the intervention with Chinese Medicine

BACKGROUND

Emerging evidence suggested the association between gut dysbiosis and Alzheimer's disease (AD) progression. However, it remained unclear how the gut microbiome and neuroinflammation in the brain mutually interact or how these interactions affect brain functioning and cognition. Here we hypothesized that "gut-brain" axis mediated by microbial derived metabolites was expected to novel breakthroughs in the fields of AD research and development.

METHODS

Multiple technologies, such as immunofluorescence, 16s rDNA sequencing, mass spectrometry-based metabolomics (LC-QQQ-MS and GC-MS), were used to reveal potential link between gut microbiota and the metabolism and cognition of the host.

RESULTS

Microbial depletion induced by the antibiotics mix (ABX) verified that "gut-brain" can transmit information bidirectionally. Short-chain fatty acid-producing (SCFAs-producing) bacteria and amino acid-producing bacteria fluctuated greatly in 5×FAD mice, especially the reduction sharply of the Bifidobacteriaceae and the increase of the Lachnospiraceae family. Concentrations of several Tryptophan-kynurenine intermediates, lactic acid, CD4+ cell, and CD8+ cells were higher in serum of 5×FAD mice, whilst TCA cycle intermediates and Th1/Th2 were lower. In addition, the levels of iso-butyric acid (IBA) in feces, serum, and brain of 5×FAD mice were increased compared with WT-M mice, especially in serum. And IBA in the brain was positively correlated with Aβ and proinflammatory factors.

CONCLUSION

Together, our finding highlighted that the alternation in gut microbiota affected the effective communication between the "gut-brain" axis in 5×FAD mice by regulating the immune system, carbohydrate, and energy metabolism.

Symposium: What Does the Microbiome Tell Us about Prevention and Treatment of AD/ADRD?

Alzheimer's disease (AD) and Alzheimer's disease-related dementias (ADRDs) are broad-impact multifactorial neurodegenerative diseases. Their complexity presents unique challenges for developing effective therapies. This review highlights research presented at the 2024 Society for Neuroscience meeting which emphasized the gut microbiome's role in AD pathogenesis by influencing brain function and neurodegeneration through the microbiota-gut-brain axis. This emerging evidence underscores the potential for targeting the gut microbiota to treat AD/ADRD.

A systematic review and meta-analysis of basal microbiota and cognitive function in Alzheimer's disease: A potential target for treatment or a contributor to disease progression?

A systematic review and meta-analysis examined the impact of gut microbiota in Alzheimer's disease (AD) pathogenesis. Dysbiosis may influence neurodegeneration by affecting gut permeability and neurotrophic factors, leading to cognitive decline. The study analyzed microbiome differences between patients with AD and healthy individuals, as well as the impact of various interventions in both preclinical and clinical studies. Of 60 studies reviewed, 12 were excluded from the meta-analysis due to unsuitable data or lack of control groups. Meta-analyses revealed significant cognitive impairment in AD patients and animal models, with specific tests identifying these deficits. Notably, Bacteroides levels were higher in patients with AD, whereas probiotics improved Prevotella levels. Natural treatments increased Bacteroidetes and reduced Firmicutes in animal models. The findings emphasize the need for standardized methods to develop therapies targeting the gut microbiota to restore cognition in AD. Understanding individual dysbiosis could further clarify the cognitive effects of the gut-brain axis.

Highlights

Dysbiosis in the gut microbiota is linked to cognitive decline in Alzheimer's disease (AD).Patients with AD show significant differences in Bacteroides levels compared to healthy individuals.Probiotic treatments increase Prevotella levels in AD animal models.Natural agents boost Bacteroidetes and reduce Firmicutes in AD animal models.Human studies show no consistent effects of gut microbiota interventions on cognitive function in AD.

The Gut Microbiota Modulates Neuroinflammation in Alzheimer's Disease: Elucidating Crucial Factors and Mechanistic Underpinnings

BACKGROUND AND PURPOSE

Alzheimer's disease (AD) is characterized by progressive cognitive decline and neuronal loss, commonly linked to amyloid-β plaques, neurofibrillary tangles, and neuroinflammation. Recent research highlights the gut microbiota as a key player in modulating neuroinflammation, a critical pathological feature of AD. Understanding the role of the gut microbiota in this process is essential for uncovering new therapeutic avenues and gaining deeper insights into AD pathogenesis.

METHODS

This review provides a comprehensive analysis of how gut microbiota influences neuroinflammation and glial cell function in AD. A systematic literature search was conducted, covering studies from 2014 to 2024, including reviews, clinical trials, and animal studies. Keywords such as "gut microbiota," "Alzheimer's disease," "neuroinflammation," and "blood-brain barrier" were used.

RESULTS

Dysbiosis, or the imbalance in gut microbiota composition, has been implicated in the modulation of key AD-related mechanisms, including neuroinflammation, blood-brain barrier integrity, and neurotransmitter regulation. These disruptions may accelerate the onset and progression of AD. Additionally, therapeutic strategies targeting gut microbiota, such as probiotics, prebiotics, and fecal microbiota transplantation, show promise in modulating AD pathology.

CONCLUSIONS

The gut microbiota is a pivotal factor in AD pathogenesis, influencing neuroinflammation and disease progression. Understanding the role of gut microbiota in AD opens avenues for innovative diagnostic, preventive, and therapeutic strategies.

The Role of Gastrointestinal Dysbiosis and Fecal Transplantation in Various Neurocognitive Disorders

This review explores the critical role of the human microbiome in neurological and neurodegenerative disorders, focusing on gut-brain axis dysfunction caused by dysbiosis, an imbalance in gut bacteria. Dysbiosis has been linked to diseases such as Alzheimer's disease, Parkinson's disease (PD), multiple sclerosis (MS), and stroke. The gut microbiome influences the central nervous system (CNS) through signaling molecules, including short-chain fatty acids, neurotransmitters, and metabolites, impacting brain health and disease progression. Emerging therapies, such as fecal microbiota transplantation (FMT), have shown promise in restoring microbial balance and alleviating neurological symptoms, especially in Alzheimer's and PD. Additionally, nutritional interventions such as probiotics, prebiotics, and specialized diets are being investigated for their ability to modify gut microbiota and improve patient outcomes. This review highlights the therapeutic potential of gut microbiota modulation but emphasizes the need for further clinical trials to establish the safety and efficacy of these interventions in neurological and mental health disorders.

The role of the gut microbiota in neurodegenerative diseases targeting metabolism

In recent years, the incidence of neurodegenerative diseases (NDs) has gradually increased over the past decades due to the rapid aging of the global population. Traditional research has had difficulty explaining the relationship between its etiology and unhealthy lifestyle and diets. Emerging evidence had proved that the pathogenesis of neurodegenerative diseases may be related to changes of the gut microbiota's composition. Metabolism of gut microbiota has insidious and far-reaching effects on neurodegenerative diseases and provides new directions for disease intervention. Here, we delineated the basic relationship between gut microbiota and neurodegenerative diseases, highlighting the metabolism of gut microbiota in neurodegenerative diseases and also focusing on treatments for NDs based on gut microbiota. Our review may provide novel insights for neurodegeneration and approach a broadly applicable basis for the clinical therapies for neurodegenerative diseases.

Deciphering the microbial map and its implications in the therapeutics of neurodegenerative disorder

Every facet of biological anthropology, including development, ageing, diseases, and even health maintenance, is influenced by gut microbiota's significant genetic and metabolic capabilities. With current advancements in sequencing technology and with new culture-independent approaches, researchers can surpass older correlative studies and develop mechanism-based studies on microbiome-host interactions. The microbiota-gut-brain axis (MGBA) regulates glial functioning, making it a possible target for the improvement of development and advancement of treatments for neurodegenerative diseases (NDDs). The gut-brain axis (GBA) is accountable for the reciprocal communication between the gastrointestinal and central nervous system, which plays an essential role in the regulation of physiological processes like controlling hunger, metabolism, and various gastrointestinal functions. Lately, studies have discovered the function of the gut microbiome for brain health-different microbiota through different pathways such as immunological, neurological and metabolic pathways. Additionally, we review the involvement of the neurotransmitters and the gut hormones related to gut microbiota. We also explore the MGBA in neurodegenerative disorders by focusing on metabolites. Further, targeting the blood-brain barrier (BBB), intestinal barrier, meninges, and peripheral immune system is investigated. Lastly, we discuss the therapeutics approach and evaluate the pre-clinical and clinical trial data regarding using prebiotics, probiotics, paraprobiotics, fecal microbiota transplantation, personalised medicine, and natural food bioactive in NDDs. A comprehensive study of the GBA will felicitate the creation of efficient therapeutic approaches for treating different NDDs.

Influence of human gut microbiome on the healthy and the neurodegenerative aging

The gut microbiome plays a crucial role in host health throughout the lifespan by influencing brain function during aging. The microbial diversity of the human gut microbiome decreases during the aging process and, as a consequence, several mechanisms increase, such as oxidative stress, mitochondrial dysfunction, inflammatory response, and microbial gut dysbiosis. Moreover, evidence indicates that aging and neurodegeneration are closely related; consequently, the gut microbiome may serve as a novel marker of lifespan in the elderly. In this narrative study, we investigated how the changes in the composition of the gut microbiome that occur in aging influence to various neuropathological disorders, such as mild cognitive impairment (MCI), dementia, Alzheimer's disease (AD), and Parkinson's disease (PD); and which are the possible mechanisms that govern the relationship between the gut microbiome and cognitive impairment. In addition, several studies suggest that the gut microbiome may be a potential novel target to improve hallmarks of brain aging and to promote healthy cognition; therefore, current and future therapeutic interventions have been also reviewed.

Interconnections between the Gut Microbiome and Alzheimer's Disease: Mechanisms and Therapeutic Potential

Alzheimer's disease (AD) is a neurodegenerative disease that is known to accumulate amyloid-β (Aβ) and tau protein. Clinical studies have not identified pathogenesis mechanisms or produced an effective cure for AD. The Aβ monoclonal antibody lecanemab reduces Aβ plaque formation for the treatment of AD, but more studies are required to increase the effectiveness of drugs to reduce cognitive decline. The lack of AD therapy targets and evidence of an association with an acute neuroinflammatory response caused by several bacteria and viruses in some individuals has led to the establishment of the infection hypothesis during the last 10 years. How pathogens cross the blood-brain barrier is highly topical and is seen to be pivotal in proving the hypothesis. This review summarizes the possible role of the gut microbiome in the pathogenesis of AD and feasible therapeutic approaches and current research limitations.

Personalized Paths: Unlocking Alzheimer's via the Gut-Brain Axis

Background

Alzheimer's disease (AD) is characterised by abnormal protein aggregates in the brain that lead to cognitive decline. While current therapies only treat symptoms, disease-modifying treatments are urgently needed. Studies suggest that the composition of the microbiota is altered in people with AD, suggesting a link between gut bacteria and AD-related brain changes.

Summary

In our narrative review, we explore various microbial interventions, such as faecal microbiota transplantation, probiotics, and diet, as powerful potential treatments. Studies suggest changes in microbiota composition following these interventions, with some beneficial effects on cognitive function. However, the mechanism of action of these microbial interventions is still unknown.

Key Message

Our aim was to highlight the importance of personalised approaches, taking into account individual metabolic and microbiome profiles. We try to address gaps in current research and emphasise the need for microbiota analysis at different stages of the disease and its integration with clinical parameters and lifestyle information for a comprehensive understanding of AD progression (summarised in online suppl. Fig. 1; for all online suppl. material, see https://doi.org/10.1159/000535869).

Dysregulation of Gut Microbiota-Derived Neuromodulatory Amino Acid Metabolism in Human Immunodeficiency Virus-Associated Neurocognitive Disorder: An Integrative Metagenomic and Metabolomic Analysis

OBJECTIVE

Although accumulating evidence implicating altered gut microbiota in human immunodeficiency virus (HIV) infection and neurodegenerative disorders; however, the association between dysbiosis of the gut microbiota and metabolites in the pathogenesis of HIV-associated neurocognitive disorder (HAND) remains unclear.

METHODS

Fecal and plasma samples were obtained from 3 cohorts (HAND, HIV-non-HAND, and healthy controls), metagenomic analysis and metabolomic profiling were performed to investigate alterations in the gut microbial composition and circulating metabolites in HAND.

RESULTS

The gut microbiota of people living with HIV (PLWH) had an increased relative abundance of Prevotella and a decreased relative abundance of Bacteroides. In contrast, Prevotella and Megamonas were substantially decreased, and Bacteroides and Phocaeicola were increased in HAND patients. Moreover, untargeted metabolomics identified several neurotransmitters and certain amino acids associated with neuromodulation, and the differential metabolic pathways of amino acids associated with neurocognition were depleted in HAND patients. Notably, most neuromodulatory metabolites are associated with an altered abundance of specific gut bacteria.

INTERPRETATION

Our findings provide new insights into the intricate interplay between the gut and microbiome-brain axis in the pathogenesis of HAND, highlighting the potential for developing novel therapeutic strategies that specifically target the gut microbiota. ANN NEUROL 2024;96:306-320.

The link between gut microbiome and Alzheimer's disease: From the perspective of new revised criteria for diagnosis and staging of Alzheimer's disease

Over the past decades, accumulating evidence suggests that the gut microbiome exerts a key role in Alzheimer's disease (AD). The Alzheimer's Association Workgroup is updating the diagnostic criteria for AD, which changed the profiles and categorization of biomarkers from "AT(N)" to "ATNIVS." Previously, most of studies focus on the correlation between the gut microbiome and amyloid beta deposition ("A"), the initial AD pathological feature triggering the "downstream" tauopathy and neurodegeneration. However, limited research investigated the interactions between the gut microbiome and other AD pathogenesis ("TNIVS"). In this review, we summarize current findings of the gut microbial characteristics in the whole spectrum of AD. Then, we describe the association of the gut microbiome with updated biomarker categories of AD pathogenesis. In addition, we outline the gut microbiome-related therapeutic strategies for AD. Finally, we discuss current key issues of the gut microbiome research in the AD field and future research directions. HIGHLIGHTS: The new revised criteria for Alzheimer's disease (AD) proposed by the Alzheimer's Association Workgroup have updated the profiles and categorization of biomarkers from "AT(N)" to "ATNIVS." The associations of the gut microbiome with updated biomarker categories of AD pathogenesis are described. Current findings of the gut microbial characteristics in the whole spectrum of AD are summarized. Therapeutic strategies for AD based on the gut microbiome are proposed.

Probiotics and the microbiota-gut-brain axis in neurodegeneration: Beneficial effects and mechanistic insights

Neurodegenerative diseases (NDs) are a group of heterogeneous disorders with a high socioeconomic burden. Although pharmacotherapy is currently the principal therapeutic approach for the management of NDs, mounting evidence supports the notion that the protracted application of available drugs would abate their dopaminergic outcomes in the long run. The therapeutic application of microbiome-based modalities has received escalating attention in biomedical works. In-depth investigations of the bidirectional communication between the microbiome in the gut and the brain offer a multitude of targets for the treatment of NDs or maximizing the patient's quality of life. Probiotic administration is a well-known microbial-oriented approach to modulate the gut microbiota and potentially influence the process of neurodegeneration. Of note, there is a strong need for further investigation to map out the mechanistic prospects for the gut-brain axis and the clinical efficacy of probiotics. In this review, we discuss the importance of microbiome modulation and hemostasis via probiotics, prebiotics, postbiotics and synbiotics in ameliorating pathological neurodegenerative events. Also, we meticulously describe the underlying mechanism of action of probiotics and their metabolites on the gut-brain axis in different NDs. We suppose that the present work will provide a functional direction for the use of probiotic-based modalities in promoting current practical treatments for the management of neurodegenerative-related diseases.

The influence of aging and the microbiome in multiple sclerosis and other neurologic diseases

The human gut microbiome is well-recognized as a key player in maintaining health. However, it is a dynamic entity that changes across the lifespan. How the microbial changes that occur in later decades of life shape host health or impact age-associated inflammatory neurological diseases such as multiple sclerosis (MS) is still unclear. Current understanding of the aging gut microbiome is largely limited to cross-sectional observational studies. Moreover, studies in humans are limited by confounding host-intrinsic and extrinsic factors that are not easily disentangled from aging. This review provides a comprehensive summary of existing literature on the aging gut microbiome and its known relationships with neurological diseases, with a specific focus on MS. We will also discuss preclinical animal models and human studies that shed light on the complex microbiota-host interactions that have the potential to influence disease pathology and progression in aging individuals. Lastly, we propose potential avenues of investigation to deconvolute features of an aging microbiota that contribute to disease, or alternatively promote health in advanced age.

Improvements in Gut Microbiome Composition and Clinical Symptoms Following Familial Fecal Microbiota Transplantation in a Nineteen-Year-Old Adolescent With Severe Autism

This case report describes a novel therapy for patients with severe autism spectrum disorder (ASD) that is worth further investigation. A 19-year-old male adolescent with ASD, who was not responding to standard treatment received fecal microbiota transplant (FMT) using donor material from his typically developing female sibling. The patient's ASD symptoms were assessed by assessors who were blind to the patient's past ASD symptomatology. Assessors used the Childhood Autism Rating Scale (CARS), an observation-based rating scale to assess developmental delay in children with autism (range of CARS scores is 15 - 60; a score > 28 is indicative of autism; higher score is positively correlated with degree of severity), at baseline and again at six timepoints post-FMT. The patient experienced marked improvements in microbiome diversity and composition over the year and a half period that followed the FMT procedure. Additionally, the patient who was previously nonverbal said his first two words and experienced a reduction in aggression 1-month post-FMT. To the authors' knowledge, this is the first report to demonstrate the use of familial FMT in an adolescent patient with ASD. Given that ASD symptom improvements post-FMT tend to occur in younger patients, the authors hypothesize that the use of a familial donor may be an important factor that contributed to the improved outcomes experienced by this older child.

Approach to the diagnosis and management of dysbiosis

All microorganisms like bacteria, viruses and fungi that reside within a host environment are considered a microbiome. The number of bacteria almost equal that of human cells, however, the genome of these bacteria may be almost 100 times larger than the human genome. Every aspect of the physiology and health can be influenced by the microbiome living in various parts of our body. Any imbalance in the microbiome composition or function is seen as dysbiosis. Different types of dysbiosis are seen and the corresponding symptoms depend on the site of microbial imbalance. The contribution of the intestinal and extra-intestinal microbiota to influence systemic activities is through interplay between different axes. Whole body dysbiosis is a complex process involving gut microbiome and non-gut related microbiome. It is still at the stage of infancy and has not yet been fully understood. Dysbiosis can be influenced by genetic factors, lifestyle habits, diet including ultra-processed foods and food additives, as well as medications. Dysbiosis has been associated with many systemic diseases and cannot be diagnosed through standard blood tests or investigations. Microbiota derived metabolites can be analyzed and can be useful in the management of dysbiosis. Whole body dysbiosis can be addressed by altering lifestyle factors, proper diet and microbial modulation. The effect of these interventions in humans depends on the beneficial microbiome alteration mostly based on animal studies with evolving evidence from human studies. There is tremendous potential for the human microbiome in the diagnosis, treatment, and prognosis of diseases, as well as, for the monitoring of health and disease in humans. Whole body system-based approach to the diagnosis of dysbiosis is better than a pure taxonomic approach. Whole body dysbiosis could be a new therapeutic target in the management of various health conditions.

Correlation between the gut microbiome and neurodegenerative diseases: a review of metagenomics evidence

A growing body of evidence suggests that the gut microbiota contributes to the development of neurodegenerative diseases via the microbiota-gut-brain axis. As a contributing factor, microbiota dysbiosis always occurs in pathological changes of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. High-throughput sequencing technology has helped to reveal that the bidirectional communication between the central nervous system and the enteric nervous system is facilitated by the microbiota's diverse microorganisms, and for both neuroimmune and neuroendocrine systems. Here, we summarize the bioinformatics analysis and wet-biology validation for the gut metagenomics in neurodegenerative diseases, with an emphasis on multi-omics studies and the gut virome. The pathogen-associated signaling biomarkers for identifying brain disorders and potential therapeutic targets are also elucidated. Finally, we discuss the role of diet, prebiotics, probiotics, postbiotics and exercise interventions in remodeling the microbiome and reducing the symptoms of neurodegenerative diseases.

Protective effects of fecal microbiota transplantation against ischemic stroke and other neurological disorders: an update

The bidirectional communication between the gut and brain or gut-brain axis is regulated by several gut microbes and microbial derived metabolites, such as short-chain fatty acids, trimethylamine N-oxide, and lipopolysaccharides. The Gut microbiota (GM) produce neuroactives, specifically neurotransmitters that modulates local and central neuronal brain functions. An imbalance between intestinal commensals and pathobionts leads to a disruption in the gut microbiota or dysbiosis, which affects intestinal barrier integrity and gut-immune and neuroimmune systems. Currently, fecal microbiota transplantation (FMT) is recommended for the treatment of recurrent Clostridioides difficile infection. FMT elicits its action by ameliorating inflammatory responses through the restoration of microbial composition and functionality. Thus, FMT may be a potential therapeutic option in suppressing neuroinflammation in post-stroke conditions and other neurological disorders involving the neuroimmune axis. Specifically, FMT protects against ischemic injury by decreasing IL-17, IFN-γ, Bax, and increasing Bcl-2 expression. Interestingly, FMT improves cognitive function by lowering amyloid-β accumulation and upregulating synaptic marker (PSD-95, synapsin-1) expression in Alzheimer's disease. In Parkinson's disease, FMT was shown to inhibit the expression of TLR4 and NF-κB. In this review article, we have summarized the potential sources and methods of administration of FMT and its impact on neuroimmune and cognitive functions. We also provide a comprehensive update on the beneficial effects of FMT in various neurological disorders by undertaking a detailed interrogation of the preclinical and clinical published literature.

A dynamic fuzzy rule-based inference system using fuzzy inference with semantic reasoning

The challenge of making flexible, standard, and early medical diagnoses is significant. However, some limitations are not fully overcome. First, the diagnosis rules established by medical experts or learned from a trained dataset prove static and too general. It leads to decisions that lack adaptive flexibility when finding new circumstances. Secondly, medical terminological interoperability is highly critical. It increases realism and medical progress and avoids isolated systems and the difficulty of data exchange, analysis, and interpretation. Third, criteria for diagnosis are often heterogeneous and changeable. It includes symptoms, patient history, demographic, treatment, genetics, biochemistry, and imaging. Symptoms represent a high-impact indicator for early detection. It is important that we deal with these symptoms differently, which have a great relationship with semantics, vary widely, and have linguistic information. This negatively affects early diagnosis decision-making. Depending on the circumstances, the diagnosis is made solo on imaging and some medical tests. In this case, although the accuracy of the diagnosis is very high, can these decisions be considered an early diagnosis or prove the condition is deteriorating? Our contribution in this paper is to present a real medical diagnostic system based on semantics, fuzzy, and dynamic decision rules. We attempt to integrate ontology semantics reasoning and fuzzy inference. It promotes fuzzy reasoning and handles knowledge representation problems. In complications and symptoms, ontological semantic reasoning improves the process of evaluating rules in terms of interpretability, dynamism, and intelligence. A real-world case study, ADNI, is presented involving the field of Alzheimer's disease (AD). The proposed system has indicated the possibility of the system to diagnose AD with an accuracy of 97.2%, 95.4%, 94.8%, 93.1%, and 96.3% for AD, LMCI, EMCI, SMC, and CN respectively.

A systematic review and meta-analysis of the effects of long-term antibiotic use on cognitive outcomes

Antibiotics are indispensable to infection management. However, use of antibiotics can cause gut microbiota dysbiosis, which has been linked to cognitive impairment by disrupting communication between the gut microbiota and the brain. We conducted a systematic review and meta-analysis on the effects of long-term antibiotic use on cognitive outcomes. We have searched PubMed, Web of Science, Embase, Cochrane Library and Scopus for English publications before March 2023 following the PRISMA guidelines. Screening, data extraction, and quality assessment were performed in duplicate. 960 articles were screened and 16 studies which evaluated the effect of any antibiotic compared to no antibiotics or placebo were included. Case-reports, in vitro and animal studies were excluded. We found that antibiotic use was associated with worse cognitive outcomes with a pooled effect estimate of - 0.11 (95% CI - 0.15, - 0.07, Z = 5.45; P < 0.00001). Subgroup analyses performed on adult vs pediatric patients showed a similar association of antibiotic on cognition in both subgroups. Antibiotic treatment was not associated with worse cognition on subjects with existing cognitive impairment. On the other hand, antibiotic treatment on subjects with no prior cognitive impairment was associated with worse cognitive performance later in life. This calls for future well-designed and well-powered studies to investigate the impact of antibiotics on cognitive performance.

Crosstalk between gut microbiome and neuroinflammation in pathogenesis of HIV-associated neurocognitive disorder

HIV-associated neurocognitive disorder (HAND) has become a chronic neurodegenerative disease affecting the quality of life in people living with HIV (PLWH). Despite an established association between HAND and neuroinflammation induced by HIV proteins (gp120, Tat, Rev., Nef, and Vpr), the pathogenesis of HAND remains to be fully elucidated. Accumulating evidence demonstrated that the gut microbiome is emerging as a critical regulator of various neurodegenerative diseases (e.g., Parkinson's disease, Alzheimer's disease), suggesting that the crosstalk between the gut microbiome and neuroinflammation may contribute to the development of these diseases, for example, gut dysbiosis and microbiota-derived metabolites can trigger inflammation in the brain. However, the potential role of the gut microbiome in the pathogenesis of HAND remains largely unexplored. In this review, we aim to discuss and elucidate the HAND pathogenesis correlated with gut microbiome and neuroinflammation, and intend to explore the probable intervention strategies for HAND.

Extra-Virgin Olive Oil in Alzheimer's Disease: A Comprehensive Review of Cellular, Animal, and Clinical Studies

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by several pathological hallmarks, including the deposition of amyloid-β (Aβ) plaques, neurofibrillary tangles, blood-brain barrier (BBB) dysfunction, increased oxidative stress, and neuroinflammation. Current treatment options include monoclonal antibody drugs, acetylcholinesterase, and n-methyl-d-aspartate (NMDA) antagonists. Although those treatments provide some improvements in patients' quality of life, they fail to prevent or cure AD. Current research aims to identify novel targets and tools for AD prevention and modification. In this context, several studies showed the beneficial effect of the Mediterranean diet in the prevention and treatment of AD. One integral component of the Mediterranean diet is olive oil and extra-virgin olive oil (EVOO), which is high in phenolic compounds. EVOO and other olive-related phenolic compounds have been shown to reduce the risk of developing mild cognitive impairment (MCI) and AD. In this review, we discuss the mechanisms by which EVOO and phenolic compounds exert neuroprotective effects, including modulation of AD pathologies and promotion of cognitive health. Findings indicate that EVOO and its phenolic constituents influence key pathological processes of AD, such as Aβ aggregation, tau phosphorylation, and neuroinflammation, while also enhancing BBB integrity and reducing oxidative stress. The human studies cited reveal a consistent trend where the consumption of olive oil is associated with cognitive benefits and a decreased risk of AD and related dementias. In conclusion, EVOO and its phenolic compounds hold promising potential for the prevention and treatment of AD, representing a significant shift towards more effective strategies against this complex neurodegenerative disorder.

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.

Effect of altered gene expression in lipid metabolism on cognitive improvement in patients with Alzheimer's dementia following fecal microbiota transplantation: a preliminary study

Background

The brain-gut axis has emerged as a potential target in neurodegenerative diseases, including dementia, as individuals with dementia exhibit distinct gut microbiota compositions. Fecal microbiota transplantation (FMT), the transfer of fecal solution from a healthy donor to a patient, has shown promise in restoring homeostasis and cognitive enhancement.

Objective

This study aimed to explore the effects of FMT on specific cognitive performance measures in Alzheimer's dementia (AD) patients and investigate the relationship between cognition and the gut microbiota by evaluating changes in gene expression following FMT.

Methods

Five AD patients underwent FMT, and their cognitive function [Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and Clinical Dementia Rating Scale Sum of Boxes (CDR-SOB)] was assessed before and after FMT. The patients' fecal samples were analyzed with 16S rRNA to compare the composition of their gut microbiota. We also assessed modifications in the serum mRNA expression of patients' genes related to lipid metabolism using serum RNA sequencing and quantitative real-time polymerase chain reaction.

Results

Significant improvements in cognitive function, as measured by the MMSE (pre- and post-FMT was 13.00 and 18.00) and MoCA were seen. The MoCA scores at 3 months post-FMT (21.0) were the highest (12.0). The CDR-SOB scores at pre- and post-FMT were 10.00 and 5.50, respectively. Analysis of the gut microbiome composition revealed changes via 16S rRNA sequencing with an increase in Bacteroidaceae and a decrease in Enterococcaceae. Gene expression analysis identified alterations in lipid metabolism-related genes after FMT.

Conclusion

These findings suggest a link between alterations in the gut microbiome, gene expression related to lipid metabolism, and cognitive function. The study highlights the importance of gut microbiota in cognitive function and provides insights into potential biomarkers for cognitive decline progression. FMT could complement existing therapies and show potential as a therapeutic intervention to mitigate cognitive decline in AD.

Gut Microbiome in Alzheimer's Disease: from Mice to Humans

Alzheimer's disease (AD) is the most prevalent type of dementia, but its etiopathogenesis is not yet fully understood. Recent preclinical studies and clinical evidence indicate that changes in the gut microbiome could potentially play a role in the accumulation of amyloid beta. However, the relationship between gut dysbiosis and AD is still elusive. In this review, the potential impact of the gut microbiome on AD development and progression is discussed. Pre-clinical and clinical literature exploring changes in gut microbiome composition is assessed, which can contribute to AD pathology including increased amyloid beta deposition and cognitive impairment. The gut-brain axis and the potential involvement of metabolites produced by the gut microbiome in AD are also highlighted. Furthermore, the potential of antibiotics, prebiotics, probiotics, fecal microbiota transplantation, and dietary interventions as complementary therapies for the management of AD is summarized. This review provides valuable insights into potential therapeutic strategies to modulate the gut microbiome in AD.

Implications of microbe-derived ɣ-aminobutyric acid (GABA) in gut and brain barrier integrity and GABAergic signaling in Alzheimer's disease

The gut microbial ecosystem communicates bidirectionally with the brain in what is known as the gut-microbiome-brain axis. Bidirectional signaling occurs through several pathways including signaling via the vagus nerve, circulation of microbial metabolites, and immune activation. Alterations in the gut microbiota are implicated in Alzheimer's disease (AD), a progressive neurodegenerative disease. Perturbations in gut microbial communities may affect pathways within the gut-microbiome-brain axis through altered production of microbial metabolites including ɣ-aminobutyric acid (GABA), the primary inhibitory mammalian neurotransmitter. GABA has been shown to act on gut integrity through modulation of gut mucins and tight junction proteins and may be involved in vagus nerve signal inhibition. The GABAergic signaling pathway has been shown to be dysregulated in AD, and may be responsive to interventions. Gut microbial production of GABA is of recent interest in neurological disorders, including AD. Bacteroides and Lactic Acid Bacteria (LAB), including Lactobacillus, are predominant producers of GABA. This review highlights how temporal alterations in gut microbial communities associated with AD may affect the GABAergic signaling pathway, intestinal barrier integrity, and AD-associated inflammation.

New Insights into the Relationship between Nutrition and Neuroinflammation in Alzheimer's Disease: Preventive and Therapeutic Perspectives

Neurodegenerative diseases are progressive brain disorders characterized by inexorable synaptic dysfunction and neuronal loss. Since the most consistent risk factor for developing neurodegenerative diseases is aging, the prevalence of these disorders is intended to increase with increasing life expectancy. Alzheimer's disease is the most common cause of neurodegenerative dementia, representing a significant medical, social, and economic burden worldwide. Despite growing research to reach an early diagnosis and optimal patient management, no disease-modifying therapies are currently available. Chronic neuroinflammation has been recognized as a crucial player in sustaining neurodegenerative processes, along with pathological deposition of misfolded proteins, including amyloid-β and tau protein. Modulating neuroinflammatory responses may be a promising therapeutic strategy in future clinical trials. Among factors that are able to regulate neuroinflammatory mechanisms, diet, and nutrients represent easily accessible and modifiable lifestyle components. Mediterranean diet and several nutrients, including polyphenols, vitamins, and omega-3 polyunsaturated fatty acids, can exert antioxidant and anti-inflammatory properties, impacting clinical manifestations, cognitive decline, and dementia. This review aims to provide an updated overview of the relationship between neuroinflammation, nutrition, gut microbiota, and neurodegeneration. We summarize the major studies exploring the effects of diet regimes on cognitive decline, primarily focusing on Alzheimer's disease dementia and the impact of these results on the design of ongoing clinical trials.

Parkinson's disease and gut microbiota: from clinical to mechanistic and therapeutic studies

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases. The typical symptomatology of PD includes motor symptoms; however, a range of nonmotor symptoms, such as intestinal issues, usually occur before the motor symptoms. Various microorganisms inhabiting the gastrointestinal tract can profoundly influence the physiopathology of the central nervous system through neurological, endocrine, and immune system pathways involved in the microbiota-gut-brain axis. In addition, extensive evidence suggests that the gut microbiota is strongly associated with PD. This review summarizes the latest findings on microbial changes in PD and their clinical relevance, describes the underlying mechanisms through which intestinal bacteria may mediate PD, and discusses the correlations between gut microbes and anti-PD drugs. In addition, this review outlines the status of research on microbial therapies for PD and the future directions of PD-gut microbiota research.

A reappraisal on amyloid cascade hypothesis: the role of chronic infection in Alzheimer's disease

Alzheimer disease (AD) is a progressive neurological disorder that accounted for the most common cause of dementia in the elderly population. Lately, 'infection hypothesis' has been proposed where the infection of microbes can lead to the pathogenesis of AD. Among different types of microbes, human immunodeficiency virus-1 (HIV-1), herpes simplex virus-1 (HSV-1), Chlamydia pneumonia, Spirochetes and Candida albicans are frequently detected in the brain of AD patients. Amyloid-beta protein has demonstrated to exhibit antimicrobial properties upon encountering these pathogens. It can bind to microglial cells and astrocytes to activate immune response and neuroinflammation. Nevertheless, HIV-1 and HSV-1 can develop into latency whereas Chlamydia pneumonia, Spirochetes and Candida albicans can cause chronic infections. At this stage, the DNA of microbes remains undetectable yet active. This can act as the prolonged pathogenic stimulus that over-triggers the expression of Aβ-related genes, which subsequently lead to overproduction and deposition of Aβ plaque. This review will highlight the pathogenesis of each of the stated microbial infection, their association in AD pathogenesis as well as the effect of chronic infection in AD progression. Potential therapies for AD by modulating the microbiome have also been suggested. This review will aid in understanding the infectious manifestations of AD.

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.

Brain modulation by the gut microbiota: From disease to therapy

BACKGROUND

The gut microbiota (GM) and brain are strongly associated, which significantly affects neuronal development and disorders. GM-derived metabolites modulate neuronal function and influence many cascades in age-related neurodegenerative disorders (NDDs). Because of the dual role of GM in neuroprotection and neurodegeneration, understanding the balance between beneficial and harmful bacteria is crucial for applying this approach to clinical therapies.

AIM OF THE REVIEW

This review briefly discusses the role of the gut-brain relationship in promoting brain and cognitive function. Although a healthy gut environment is helpful for brain function, gut dysbiosis can disrupt the brain's environment and create a vicious cycle of degenerative cascades. The ways in which the GM population can affect brain function and the development of neurodegeneration are also discussed. In the treatment and management of NDDs, the beneficial effects of methods targeting GM populations and their derivatives, including probiotics, prebiotics, and fecal microbial transplantation (FMT) are also highlighted.

KEY SCIENTIFIC CONCEPT OF THE REVIEW

In this review, we aimed to provide a deeper understanding of the mechanisms of the gut microbe-brain relationship and their twin roles in neurodegeneration progression and therapeutic applications. Here, we attempted to highlight the different pathways connecting the brain and gut, together with the role of GM in neuroprotection and neuronal development. Furthermore, potential roles of GM metabolites in the pathogenesis of brain disorders and in strategies for its treatment are also investigated. By analyzing existing in vitro, in vivo and clinical studies, this review attempts to identify new and promising therapeutic strategies for central nervous system (CNS) disorders. As the connection between the gut microbe-brain relationship and responses to NDD treatments is less studied, this review will provide new insights into the global mechanisms of GM modulation in disease progression, and identify potential future perspectives for developing new therapies to treat NDDs.