Gut Microbiota and Parkinson's Disease: Implications for Faecal Microbiota Transplantation Therapy

The microbiota-gut-brain-immune interface in the pathogenesis of neuroinflammatory diseases: a narrative review of the emerging literature

Importance

Research is beginning to elucidate the sophisticated mechanisms underlying the microbiota-gut-brain-immune interface, moving from primarily animal models to human studies. Findings support the dynamic relationships between the gut microbiota as an ecosystem (microbiome) within an ecosystem (host) and its intersection with the host immune and nervous systems. Adding this to the effects on epigenetic regulation of gene expression further complicates and strengthens the response. At the heart is inflammation, which manifests in a variety of pathologies including neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Multiple Sclerosis (MS).

Observations

Generally, the research to date is limited and has focused on bacteria, likely due to the simplicity and cost-effectiveness of 16s rRNA sequencing, despite its lower resolution and inability to determine functional ability/alterations. However, this omits all other microbiota including fungi, viruses, and phages, which are emerging as key members of the human microbiome. Much of the research has been done in pre-clinical models and/or in small human studies in more developed parts of the world. The relationships observed are promising but cannot be considered reliable or generalizable at this time. Specifically, causal relationships cannot be determined currently. More research has been done in Alzheimer's disease, followed by Parkinson's disease, and then little in MS. The data for MS is encouraging despite this.

Conclusions and relevance

While the research is still nascent, the microbiota-gut-brain-immune interface may be a missing link, which has hampered our progress on understanding, let alone preventing, managing, or putting into remission neurodegenerative diseases. Relationships must first be established in humans, as animal models have been shown to poorly translate to complex human physiology and environments, especially when investigating the human gut microbiome and its relationships where animal models are often overly simplistic. Only then can robust research be conducted in humans and using mechanistic model systems.

Advances in molecular mechanisms and therapeutic strategies for central nervous system diseases based on gut microbiota imbalance

BACKGROUD

Central nervous system (CNS) diseases pose a serious threat to human health, but the regulatory mechanisms and therapeutic strategies of CNS diseases need to be further explored. It has been demonstrated that the gut microbiota (GM) is closely related to CNS disease. GM structure disorders, abnormal microbial metabolites, intestinal barrier destruction and elevated inflammation exist in patients with CNS diseases and promote the development of CNS diseases. More importantly, GM remodeling alleviates CNS pathology to some extent.

AIM OF REVIEW

Here, we have summarized the regulatory mechanism of the GM in CNS diseases and the potential treatment strategies for CNS repair based on GM regulation, aiming to provide safer and more effective strategies for CNS repair from the perspective of GM regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The abundance and composition of GM is closely associated with the CNS diseases. On the basis of in-depth analysis of GM changes in mice with CNS disease, as well as the changes in its metabolites, therapeutic strategies, such as probiotics, prebiotics, and FMT, may be used to regulate GM balance and affect its microbial metabolites, thereby promoting the recovery of CNS diseases.

The Gut Microbiome and Acute Leukemia: Implications for Early Diagnostic and New Therapies

Acute leukemia (AL), one of the hematological malignancies, shows high heterogeneity. Tremendous progresses are achieved in treating AL with novel targeted drugs and allogeneic hematopoietic stem cell transplantation, there are numerous issues including pathogenesis, early diagnosis, and therapeutic efficacy of AL to be solved. In recent years, an increasing number of studies regarding microbiome have shed more lights on the role of gut microbiota in promoting AL progression. Mechanisms related to the role of gut microbiota in enhancing AL genesis are summarized in the present work, especially on critical pathways like leaky gut, bacterial dysbiosis, microorganism-related molecular patterns, and bacterial metabolites, resulting in AL development. Additionally, the potential of gut microbiota as the biomarker for early AL diagnosis is discussed. It also outlooks therapies targeting gut microbiota for preventing AL development.

Efficacy and mechanism study of Baichanting compound, a combination of Acanthopanax senticosus (Rupr. and Maxim.) Harms, Paeonia lactiflora Pall and Uncaria rhynchophylla (Miq.) Miq. ex Havil, on Parkinson's disease based on metagenomics and metabolomics

ETHNOPHARMACOLOGICAL RELEVANCE

Parkinson's disease (PD) is a rapidly progressing neurological disorder. Currently, Medication for PD has numerous limitations. Baichanting Compound (BCT) is a Chinese herbal prescription, a Combination of Acanthopanax senticosus (Rupr. and Maxim.) Harms, Paeonia lactiflora Pall and Uncaria rhynchophylla (Miq.) Miq. ex Havil, that was developed to treat PD and holds a national patent (ZL, 201110260536.3).

AIM OF THE STUDY

To clarify the therapeutic effect of BCT on PD and explore its possible mechanism based on metabolomics and metagenomics.

MATERIALS AND METHODS

C57BL/6 mice were used as a control group, and α-syn transgenic C57BL/6 mice were randomly assigned to the PD (without treatment) or BCT (with BCT treatment) group. UPLC-MS was performed to detect dopamine levels in brain tissue, while ELISA was used to determine inflammatory factors such as IL-1β, IL-6, TNF-α, IFN-γ and NO, and oxidative stress indicators such as malondialdehyde, superoxide dismutase and glutathione peroxidase enzyme activity. Fecal metabolomics was used to detect fecal metabolic profiles, screen differential metabolic markers, and predict metabolic pathways by KEGG enrichment analysis. Metagenomics was used to determine the intestinal microbial composition, and KO enrichment analysis was performed to predict the potential function of different gut microbiota. Finally, Spearman correlation analysis was used to find the possible relationships among intestinal flora, metabolic markers, inflammatory factors, oxidative stress and dopamine levels.

RESULTS

BCT increased the superoxide dismutase activity of α-Syn transgenic C57BL/6 mice (P < 0.01), decreased the levels of TNF-α, IFN-γ, IL-1β, IL-6, NO and malondialdehyde (P < 0.01, 0.05), and increased the release of dopamine (P < 0.01). Metabolomics results show that BCT could regulate Acetatifactor, Marvinbryantia, Faecalitalea, Anaeromassilibacillus, Anaerobium, Pseudobutyrivibrio and Lachnotalea and Acetatifactor_muris, Marvinbryantia_formatexigens, Lachnotalea_sp_AF33_28, Faecalitalea_sp_Marseille_P3755 and Anaerobium_acetethylicum, Gemmiger_sp_An120 abundance to restore intestinal flora function, and reverse fecal metabolism trend, restoring the content of α-D-glucose, cytidine, L-glutamate, L-glutamine, N-acetyl-L-glutamate, raffinose and uracil. In addition, it regulates arginine biosynthesis, D-glutamine and D-glutamate, pyrimidine, galactose and alanine, aspartate and glutamate metabolic pathways.

CONCLUSION

BCT may regulate the composition of the gut microbiota to reverse fecal metabolism in PD mice to protect the substantia nigra and striatum from oxidative stress and inflammatory factors and ultimately play an anti-PD role.

The Gut Microbiome and Autoimmune Hepatitis: Implications for Early Diagnostic Biomarkers and Novel Therapies

Autoimmune hepatitis (AIH) is a serious chronic liver disease that may last for decades and eventually develop into cirrhosis and liver failure. In recent years, people have paid more attention to the microbiome-gut-liver axis, which provides guidance for all to explore the role of microbiome in the occurrence and development of liver diseases. In this review, the possible mechanism of intestinal microbes promoting the occurrence of AIH, mainly expounding the key ways such as bacterial ecological imbalance, intestinal leakage, and molecular simulation between microbes and autoantigens is summarized. In addition, this paper also discusses that intestinal microbiome has great potential as a biomarker for early diagnosis of AIH, and intestinal microbiome is also a candidate target for prevention and treatment of AIH. Finally, the study summarizes and prospects the targeted therapy of intestinal microorganisms to prevent the occurrence and development of AIH.

The link between the gut microbiome, inflammation, and Parkinson's disease

As our society ages, the growing number of people with Parkinson's disease (PD) puts tremendous pressure on our society. Currently, there is no effective treatment for PD, so there is an urgent need to find new treatment options. In recent years, increasing studies have shown a strong link between gut microbes and PD. In this review, recent advances in research on gut microbes in PD patients were summarized. Increased potential pro-inflammatory microbes and decreased potential anti-inflammatory microbes are prominent features of gut microbiota in PD patients. These changes may lead to an increase in pro-inflammatory substances (such as lipopolysaccharide and H2S) and a decrease in anti-inflammatory substances (such as short-chain fatty acids) to promote inflammation in the gut. This gut microbiota-mediated inflammation will lead to pathological α-synuclein accumulation in the gut, and the inflammation and α-synuclein can spread to the brain via the microbiota-gut-brain axis, thereby promoting neuroinflammation, apoptosis of dopaminergic neurons, and ultimately the development of PD. This review also showed that therapies based on gut microbiota may have a bright future for PD. However, more research and new approaches are still needed to clarify the causal relationship between gut microbes and PD and to determine whether therapies based on gut microbiota are effective in PD patients. KEY POINTS: • There is a strong association between gut microbes and PD. • Inflammation mediated by gut microbes may promote the development of PD. • Therapies based on the gut microbiome provide a promising strategy for PD prevention.

The gut microbiome: an important role in neurodegenerative diseases and their therapeutic advances

There are complex interactions between the gut and the brain. With increasing research on the relationship between gut microbiota and brain function, accumulated clinical and preclinical evidence suggests that gut microbiota is intimately involved in the pathogenesis of neurodegenerative diseases (NDs). Increasingly studies are beginning to focus on the association between gut microbiota and central nervous system (CNS) degenerative pathologies to find potential therapies for these refractory diseases. In this review, we summarize the changes in the gut microbiota in Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis and contribute to our understanding of the function of the gut microbiota in NDs and its possible involvement in the pathogenesis. We subsequently discuss therapeutic approaches targeting gut microbial abnormalities in these diseases, including antibiotics, diet, probiotics, and fecal microbiota transplantation (FMT). Furthermore, we summarize some completed and ongoing clinical trials of interventions with gut microbes for NDs, which may provide new ideas for studying NDs.

Recent Advances in Microbiota-Associated Metabolites in Heart Failure

Heart failure is a risk factor for adverse events such as sudden cardiac arrest, liver and kidney failure and death. The gut microbiota and its metabolites are directly linked to the pathogenesis of heart failure. As emerging studies have increased in the literature on the role of specific gut microbiota metabolites in heart failure development, this review highlights and summarizes the current evidence and underlying mechanisms associated with the pathogenesis of heart failure. We found that gut microbiota-derived metabolites such as short chain fatty acids, bile acids, branched-chain amino acids, tryptophan and indole derivatives as well as trimethylamine-derived metabolite, trimethylamine N-oxide, play critical roles in promoting heart failure through various mechanisms. Mainly, they modulate complex signaling pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells, Bcl-2 interacting protein 3, NLR Family Pyrin Domain Containing inflammasome, and Protein kinase RNA-like endoplasmic reticulum kinase. We have also highlighted the beneficial role of other gut metabolites in heart failure and other cardiovascular and metabolic diseases.

Epigenetic effects of short-chain fatty acids from the large intestine on host cells

Adult humans harbor at least as many microbial cells as eukaryotic ones. The largest compartment of this diverse microbial population, the gut microbiota, encompasses the collection of bacteria, archaea, viruses, and eukaryotic organisms that populate the gastrointestinal tract, and represents a complex and dynamic ecosystem that has been increasingly implicated in health and disease. The gut microbiota carries ∼100-to-150-times more genes than the human genome and is intimately involved in development, homeostasis, and disease. Of the several microbial metabolites that have been studied, short-chain fatty acids emerge as a group of molecules that shape gene expression in several types of eukaryotic cells by multiple mechanisms, which include DNA methylation changes, histone post-translational modifications, and microRNA-mediated gene silencing. Butyric acid, one of the most extensively studied short-chain fatty acids, reaches higher concentrations in the colonic lumen, where it provides a source of energy for healthy colonocytes, and its concentrations decrease towards the bottom of the colonic crypts, where stem cells reside. The lower butyric acid concentration in the colonic crypts allows undifferentiated cells, such as stem cells, to progress through the cell cycle, pointing towards the importance of the crypts in providing them with a protective niche. In cancerous colonocytes, which metabolize relatively little butyric acid and mostly rely on glycolysis, butyric acid preferentially acts as a histone deacetylase inhibitor, leading to decreased cell proliferation and increased apoptosis. A better understanding of the interface between the gut microbiota metabolites and epigenetic changes in eukaryotic cells promises to unravel in more detail processes that occur physiologically and as part of disease, help develop novel biomarkers, and identify new therapeutic modalities.

NEMoE: a nutrition aware regularized mixture of experts model to identify heterogeneous diet-microbiome-host health interactions

BACKGROUND

Unrevealing the interplay between diet, the microbiome, and the health state could enable the design of personalized intervention strategies and improve the health and well-being of individuals. A common approach to this is to divide the study population into smaller cohorts based on dietary preferences in the hope of identifying specific microbial signatures. However, classification of patients based solely on diet is unlikely to reflect the microbiome-host health relationship or the taxonomic microbiome makeup.

RESULTS

We present a novel approach, the Nutrition-Ecotype Mixture of Experts (NEMoE) model, for establishing associations between gut microbiota and health state that accounts for diet-specific cohort variability using a regularized mixture of experts model framework with an integrated parameter sharing strategy to ensure data-driven diet-cohort identification consistency across taxonomic levels. The success of our approach was demonstrated through a series of simulation studies, in which NEMoE showed robustness with regard to parameter selection and varying degrees of data heterogeneity. Further application to real-world microbiome data from a Parkinson's disease cohort revealed that NEMoE is capable of not only improving predictive performance for Parkinson's Disease but also for identifying diet-specific microbial signatures of disease.

CONCLUSION

In summary, NEMoE can be used to uncover diet-specific relationships between nutritional-ecotype and patient health and to contextualize precision nutrition for different diseases. Video Abstract.

Role of Gut Microbiota in Neurological Disorders and Its Therapeutic Significance

In humans, the gut microbiota (GM) are known to play a significant role in the metabolism of nutrients and drugs, immunomodulation, and pathogen defense by inhabiting the gastrointestinal tract (GIT). The role of the GM in the gut-brain axis (GBA) has been documented for different regulatory mechanisms and associated pathways and it shows different behaviors with individualized bacteria. In addition, the GM are known as susceptibility factor for neurological disorders in the central nervous system (CNS), regulating disease progression and being amenable to intervention. Bidirectional transmission between the brain and the GM occurs in the GBA, implying that it performs a significant role in neurocrine, endocrine, and immune-mediated signaling pathways. The GM regulates multiple neurological disorders by supplementing them with prebiotics, probiotics, postbiotics, synbiotics, fecal transplantations, and/or antibiotics. A well-balanced diet is critically important for establishing healthy GM, which can alter the enteric nervous system (ENS) and regulate multiple neurological disorders. Here, we have discussed the function of the GM in the GBA from the gut to the brain and the brain to the gut, the pathways associated with neurology that interacts with the GM, and the various neurological disorders associated with the GM. Furthermore, we have highlighted the recent advances and future prospects of the GBA, which may require addressing research concerns about GM and associated neurological disorders.

The fecal arsenic excretion, tissue arsenic accumulation, and metabolomics analysis in sub-chronic arsenic-exposed mice after in situ arsenic-induced fecal microbiota transplantation

Arsenic can be specifically enriched by rice, and the health hazards caused by high arsenic rice are gradually attracting attention. This study aimed to explore the potential of microbial detoxification via gut microbiome in the treatment of sub-chronic arsenic poisoning. We first exposed mice to high-dose arsenic feed (30 mg/kg, rice arsenic composition) for 60 days to promote arsenic-induced microbes in situ in the gastrointestinal tract, then transplanted their fecal microbiota (FMT) into another batch of healthy recipient mice, and dynamically monitored the microbial colonization by 16S rRNA sequencing and ITS sequencing. The results showed that in situ arsenic-induced fecal microbiome can stably colonized and interact with indigenous microbes in the recipient mice in two weeks, and established a more stable network of gut microbiome. Then, the recipient mice continued to receive high-dose arsenic exposure for 52 days. After above sub-chronic arsenic exposure, compared with the non-FMT group, fecal arsenic excretion, liver and plasma arsenic accumulation were significantly lower (P < 0.05), and that in kidney, hair, and thighbone present no significant differences. Metabolomics of feces- plasma-brain axis were also disturbed, some up-regulated metabolites in feces, plasma, and cerebral cortex may play positive roles for the host. Therefore, microbial detoxification has potential in the treatment of sub-chronic arsenic poisoning. However, gut flora is an extremely complex community with different microorganisms have different arsenic metabolizing abilities, and various microbial metabolites. Coupled with the matrix effects, these factors will have various effects on the efflux and accumulation of arsenic. The definite effects (detoxification or non-detoxification) could be not assured based on the current study, and more systematic and rigorous studies are needed in the future.

Mapping trends and hotspot regarding gastrointestinal microbiome and neuroscience: A bibliometric analysis of global research (2002-2022)

BACKGROUND

Scholars have long understood that gastrointestinal microorganisms are intimately related to human disorders. The literature on research involving the gut microbiome and neuroscience is emerging. This study exposed the connections between gut microbiota and neuroscience methodically and intuitively using bibliometrics and visualization. This study's objectives were to summarize the knowledge structure and identify emerging trends and potential hotspots in this field.

MATERIALS AND METHODS

On October 18, 2022, a literature search was conducted utilizing the Web of Science Core Collection (WoSCC) database for studies on gut microbiota and neuroscience studies from 2002 to 2022 (August 20, 2022). VOSviewer and CiteSpace V software was used to conduct the bibliometrics and visualization analysis.

RESULTS

From 2002 to 2022 (August 20, 2022), 2,275 publications in the WoSCC database satisfied the criteria. The annual volume of publications has rapidly emerged in recent years (2016-2022). The most productive nation (n = 732, 32.18%) and the hub of inter-country cooperation (links: 38) were the United States. University College Cork had the most research papers published in this area, followed by McMaster University and Harvard Medical School. Cryan JF, Dinan TG, and Clarke G were key researchers with considerable academic influence. The journals with the most publications are "Neurogastroenterology and Motility" and "Brain Behavior and Immunity." The most cited article and co-cited reference was Cryan JF's 2012 article on the impact of gut microbiota on the brain and behavior. The current research hotspot includes gastrointestinal microbiome, inflammation, gut-brain axis, Parkinson's disease (PD), and Alzheimer's disease (AD). The research focus would be on the "gastrointestinal microbiome, inflammation: a link between obesity, insulin resistance, and cognition" and "the role of two important theories of the gut-brain axis and microbial-gut-brain axis in diseases." Burst detection analysis showed that schizophrenia, pathology, and psychiatric disorder may continue to be the research frontiers.

CONCLUSION

Research on "gastrointestinal microbiome, inflammation: a link between obesity, insulin resistance, and cognition" and "the role of two important theories of the gut-brain axis and microbial-gut-brain axis in diseases" will continue to be the hotspot. Schizophrenia and psychiatric disorder will be the key research diseases in the field of gut microbiota and neuroscience, and pathology is the key research content, which is worthy of scholars' attention.

The Gut Microbiome and Hepatocellular Carcinoma: Implications for Early Diagnostic Biomarkers and Novel Therapies

Hepatocellular carcinoma (HCC) ranks the third place among all causes inducing cancer-associated mortality, worldwide. HCC nearly exclusively occurs in cases suffering from chronic liver disease (CLD), which results from the vicious cycle of liver damage, inflammation, and regeneration possibly lasting for dozens of years. Recently, more and more investigation on microbiome-gut-liver axis enhances our understanding toward how gut microbiota promotes liver disease and even HCC development. In this review, we summarize the mechanisms underlying the effect of gut microbiota on promoting HCC occurrence, with the focus on key pathways such as bacterial dysbiosis, leaky gut, bacterial metabolites, and microorganism-related molecular patterns, which promote liver inflammation, genotoxicity, and fibrosis that finally lead to cancer occurrence. Furthermore, we discuss gut microbiota's important potential to be the early diagnostic biomarker for HCC. Gut microbiota may be the candidate targets to simultaneously prevent CLD and HCC occurrence among advanced liver disease cases. We outlook the gut microbiota-targeting treatments in detail to prevent CLD and HCC progression.

The gut microbiome as a target for adjuvant therapy in insomnia disorder

Insomnia is a type of sleep disorder which has negative impacts on the quality of life, mood, cognitive function and health of humans. The etiology of insomnia may be related to many factors such as genetics, biochemistry, neuroendocrine, immune, and psychosocial factors. However, the detailed pathological aspects of insomnia remain unclear. Recent investigation of the microbiome-gut-brain axis enhances our understanding of the role of the gut microbiota in brain-related diseases. Gut microbiome has been shown to be associated with insomnia. However, the available data in this field remain limited and the relevant scientific work has only recently begun. This review aims to summarize the recent literature as an aid to better understanding how the alteration of gut microbiota composition contributes to insomnia while evaluating and prospecting the therapeutic effect of modulating gut microbiota in the treatment of insomnia based on previous publications.

Differences in the Composition of Gut Microbiota between Patients with Parkinson's Disease and Healthy Controls: A Cohort Study

Gut microbiome and colonic inflammation can be associated with the predisposition and progression of Parkinson’s disease (PD). The presented study aimed to compare gastrointestinal microbiota composition between patients diagnosed with PD and treated only with Levodopa to healthy controls. In this prospective study, patients were recruited in 1 academic hospital from July 2019 to July 2020. The detailed demographic data and medical history were collected using a set of questionnaires. Fecal samples were obtained from all participants. Next-Generation Sequencing was used to assess the microbiota composition. The endpoint was the difference in composition of the gut microbiota. In this study, we enrolled 27 hospitalized PD patients with well-controlled symptoms. The control group included 44 healthy subjects matched for age. Among PD patients, our results presented a higher abundance of Bacteroides phylum, class Corynebacteria among phylum Actinobacteria, class Deltaproteobacteria among phylum Proteobacteria, and genera such as Butyricimonas, Robinsoniella, and Flavonifractor. The species Akkermansia muciniphila, Eubacterium biforme, and Parabacteroides merdae were identified as more common in the gut microbiota of PD patients. In conclusion, the patients diagnosed with PD have significantly different gut microbiota profiles in comparison with healthy controls.

Role of Gastrointestinal Dysbiosis and Fecal Transplantation in Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases with a high rate of morbidity. It is associated with dopaminergic neuron loss and is fairly common in the elderly population. Recently, there has been a growing interest in the role of the gut microbiome in the pathogenesis of PD and thus studies addressing the methods to modulate the microbiota are becoming increasingly popular. Fecal microbiota transplant (FMT) is one of these methods and is effective in certain intestinal and extraintestinal conditions. This review aims to talk about gastrointestinal dysbiosis and how the reconstruction of this microbiome via FMT could potentially be used as a treatment modality in the future. We went through various studies and collected data relevant to our topic from the previous five years. The studies selected include reviews, observational studies, animal studies, case reports, and some grey literature. We concluded that although it has great potential as a therapeutic modality in the future, it is limited by several factors such as variability among the results of most clinical studies and the lack of large sample sizes. Therefore, there is a need for high-quality clinical trials with larger sample sizes to gather enough clinical evidence so that FMT can qualify as a widely recommended therapeutic measure.