Alpha-synuclein alters the faecal viromes of rats in a gut-initiated model of Parkinson's disease

Distinct gut microbiome characteristics and dynamics in patients with Parkinson's disease based on the presence of premotor rapid-eye movement sleep behavior disorders

BACKGROUND

Alpha-synuclein aggregation, a hallmark of Parkinson's disease (PD), is hypothesized to often begin in the enteric or peripheral nervous system in "body-first" PD and progresses through the vagus nerve to the brain, therefore REM sleep behavior disorder (RBD) precedes the PD diagnosis. In contrast, "brain-first" PD begins in the central nervous system. Evidence that gut microbiome imbalances observed in PD and idiopathic RBD exhibit similar trends supports body-first and brain-first hypothesis and highlights the role of microbiota in PD pathogenesis. However, further investigation is needed to understand distinct microbiome changes in body-first versus brain-first PD over the disease progression.

RESULTS

Our investigation involved 104 patients with PD and 85 of their spouses as healthy controls (HC), with 57 patients (54.8%) categorized as PD-RBD(+) and 47 patients (45.2%) as PD-RBD(-) based on RBD presence before the PD diagnosis. We evaluated the microbiome differences between these groups over the disease progression through taxonomic and functional differential abundance analyses and carbohydrate-active enzyme (CAZyme) profiles based on metagenome-assembled genomes. The PD-RBD(+) gut microbiome showed a relatively stable microbiome composition irrespective of disease stage. In contrast, PD-RBD(-) microbiome exhibited a relatively dynamic microbiome change as the disease progressed. In early-stage PD-RBD(+), Escherichia and Akkermansia, associated with pathogenic biofilm formation and host mucin degradation, respectively, were enriched, which was supported by functional analysis. We discovered that genes of the UDP-GlcNAc synthesis/recycling pathway negatively correlated with biofilm formation; this finding was further validated in a separate cohort. Furthermore, fiber intake-associated taxa were decreased in early-stage PD-RBD(+) and the biased mucin-degrading capacity of CAZyme compared to fiber degradation.

CONCLUSION

We determined that the gut microbiome dynamics in patients with PD according to the disease progression depend on the presence of premotor RBD. Notably, early-stage PD-RBD(+) demonstrated distinct gut microbial characteristics, potentially contributing to exacerbation of PD pathophysiology. This outcome may contribute to the development of new therapeutic strategies targeting the gut microbiome in PD. Video Abstract.

Traumatic Brain Injury and Gut Microbiome: The Role of the Gut-Brain Axis in Neurodegenerative Processes

PURPOSE OF REVIEW

A deeper understanding of the communication network between the gut microbiome and the central nervous system, termed the gut-brain axis (GBA), has revealed new potential targets for intervention to prevent the development of neurodegenerative disease associated with tramatic brain injury (TBI). This review aims to comprehensively examine the role of GBA post-traumatic brain injury (TBI).

RECENT FINDINGS

The GBA functions through neural, metabolic, immune, and endocrine systems, creating bidirectional signaling pathways that modulate brain and gastrointestinal (GI) tract physiology. TBI perturbs these signaling pathways, producing pathophysiological feedback loops in the GBA leading to dysbiosis (i.e., a perturbed gut microbiome, impaired brain-blood barrier, impaired intestinal epithelial barrier (i.e., "leaky gut"), and a maladaptive, systemic inflammatory response. Damage to the CNS associated with TBI leads to GI dysmotility, which promotes small intestinal bacterial overgrowth (SIBO). SIBO has been associated with the early stages of neurodegenerative conditions such as Parkinson's and Alzheimer's disease. Many of the bacteria associated with this overgrowth promote inflammation and, in rodent models, have been shown to compromise the structural integrity of the intestinal mucosal barrier, causing malabsorption of essential nutrients and further exacerbating dysbiosis. TBI-induced pathophysiology is strongly associated with an increased risk of neurodegenerative diseases, including Parkinson's and Alzheimer's diseases, which represents a significant public health burden and challenge for patients and their families. A healthy gut microbiome has been shown to promote improved recovery from TBI and prevent the development of neurodegenerative disease, as well as other chronic complications. The role of the gut microbiome in brain health post-TBI demonstrates the potential for microbiome-targeted interventions to mitigate TBI-associated comorbidities. Promising new evidence on prebiotics, probiotics, diet, and fecal microbiota transplantation may lead to new therapeutic options for improving the quality of life for patients with TBI. Still, many of these preliminary findings must be explored further in clinical settings. This review covers the current understanding of the GBA in the setting of TBI and how the gut microbiome may provide a novel therapeutic target for treatment in this patient population.

Unraveling the dual role of bilirubin in neurological Diseases: A Comprehensive exploration of its neuroprotective and neurotoxic effects

Neurodegenerative disorders are characterized by a progressive loss of neurons, causing substantial deficits in motor and cognitive functioning. Bilirubin is a yellow by-product of heme, existing in two primary isoforms namely unconjugated and conjugated, while initially produced unconjugated isomer is lipophilic and cytotoxic in nature. At physiological levels, bilirubin has an important role in brain function by acting as a powerful antioxidant, preventing brain tissues from oxidative damage by eliminating reactive oxygen species (ROS). Additionally, it contributes to immune regulation through microglial activation, cytokine release, complement system interception, fragment crystallization (Fc) receptor modulation, and major histocompatibility complex (MHC II) expression modification, which lower the risk of inflammatory and autoimmune reactions in the central nervous system (CNS). As per the literature, serum bilirubin concentrations are associated with CNS diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), ischemic stroke, hemorrhagic stroke, traumatic brain injury (TBI), multiple sclerosis (MS), epilepsy, schizophrenia and kernicterus spectrum disorder (KSD), which causes neuronal damage, especially in regions like the basal ganglia and cerebellum, which causes movement abnormalities and cognitive deficits. The aim of this article is to explore the dual role of bilirubin as neuroprotective and neurotoxic, essential for establishing effective therapeutic outcomes for neurodegenerative diseases by looking at its cellular mechanisms and discussing how bilirubin's antioxidant properties can shield neurons and, in some situations, may induce oxidative stress and apoptosis.

Metagenomic symphony of the intestinal ecosystem: How the composition affects the mind

Mental health disorders and neurodegenerative diseases place a heavy burden on patients and societies, and, although great strides have been made to understand the pathophysiology of these conditions, advancement in drug development is lagging. The importance of gastrointestinal health in maintaining overall health and preventing disease is not a new concept. Hundreds of years ago, healers from various cultures and civilizations recognized the crucial role of the gut in sustaining health. More than a century ago, scientists began exploring the restorative effects of probiotics, marking the early recognition of the importance of gut microbes. The omics era brought more enlightenment and enabled researchers to identify the complexity of the microbial ecosystems we harbour, encompassing bacteria, eukaryotes (including fungi), archaea, viruses, and other microorganisms. The extensive genetic capacity of the microbiota is dynamic and influenced by the environment. The microbiota therefore serves as a significant entity within us, with evolutionarily preserved functions in host metabolism, immunity, development, and behavior. The significant role of the bacterial gut microbiome in mental health and neurodegenerative disorders has been realized and described within the framework of the microbiota-gut-brain axis. However, the bacterial members do not function unaccompanied, but rather in concert, and there is a substantial knowledge gap regarding the involvement of non-bacterial microbiome members in these disorders. In this review, we will explore the current literature that implicates a role for the entire metagenomic ensemble, and how their complex interkingdom relationships could influence CNS functioning in mental health disorders and neurodegenerative diseases.

More than just a number: the gut microbiota and brain function across the extremes of life

Understanding the interrelationship between the gut microbiota and host physiology, although still in its relative infancy, has taken important steps forward over the past decade. In the context of brain disorders including those characterized by neurodevelopmental and neurodegenerative changes there have been important advances. However, initially research involved correlational analyses, had limited translational scope, and lacked functional assessments. Thus, largescale longitudinal clinical investigations that assess causation and underlying mechanisms via in depth analysis methods are needed. In neurodegeneration research, strong causal evidence now links the gut microbiome to Alzheimer's (AD), and Parkinson's Disease (PD), as supported by human-to-animal transplantation studies. Longitudinal interventions are being conducted in AD, PD, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis. Neurodevelopmental research has also seen a boon in microbiome-related clinical research including in autism, Attention-deficit/hyperactivity disorder, and schizophrenia, which is confirming prior animal model work regarding the key time-windows in the gut microbiome important for infant cognition. While recent research advances represent important progress, fundamental knowledge gaps and obstacles remain. Knowing how and why the gut microbiome changes at the extremes of life will develop our mechanistic understanding and help build the evidence base as we strive toward counteracting microbial missteps with precision therapeutic interventions.

Interpersonal variability of the human gut virome confounds disease signal detection in IBD

Viruses are increasingly recognised as important components of the human microbiome, fulfilling numerous ecological roles including bacterial predation, immune stimulation, genetic diversification, horizontal gene transfer, microbial interactions, and augmentation of metabolic functions. However, our current view of the human gut virome is tainted by previous sequencing requirements that necessitated the amplification of starting nucleic acids. In this study, we performed an original longitudinal analysis of 40 healthy control, 19 Crohn's disease, and 20 ulcerative colitis viromes over three time points without an amplification bias, which revealed and highlighted the interpersonal individuality of the human gut virome. In contrast to a 16 S rRNA gene analysis of matched samples, we show that α- and β-diversity metrics of unamplified viromes are not as efficient at discerning controls from patients with inflammatory bowel disease. Additionally, we explored the intrinsic properties of unamplified gut viromes and show there is considerable interpersonal variability in viral taxa, infrequent longitudinal persistence of intrapersonal viruses, and vast fluctuations in the abundance of temporal viruses. Together, these properties of unamplified faecal viromes confound the ability to discern disease associations but significantly advance toward an unbiased and accurate representation of the human gut virome.

Gut Microbiome and Neurodevelopmental Disorders: A Link Yet to Be Disclosed

Τhe importance of the gut microbiome and its functions has only recently been recognized and researched in greater depth. The establishment of the human gut microbiome begins in utero, forming its adult-like phenotype in the first 2-3 years of life. Several factors affect and alter the gut microbiome composition and its metabolic functions, such as early onset of breastfeeding, mode of delivery, antibiotic administration, or exposure to chemical substances, among others. Existing data support the important connection between health status and gut microbiome homeostasis. In cases when this balance is disturbed, several disorders may arise, such as inflammatory reactions that lead to atopy, eczema, or allergic asthma. The so-called gut-brain axis refers to the complex biochemical pathways between the central nervous system and the gastrointestinal system. One of the most fascinating areas of ongoing research is the broad spectrum of neurodevelopmental disorders (NDDs) and how gut health may be associated with such disorders. The prevalence of NDDs, such as autism spectrum disorder or attention deficit hyperactivity disorder, has increased over recent years. Whether gut microbiota homeostasis plays a role in these disorders is not yet fully understood. The aim of this narrative review is to provide an account of current knowledge on how gut health is linked with these disorders. We performed a literature review in order to identify and synthesize available data that highlights the potential association between NDDs and a balanced gut microbiome in terms of composition and proper function. The connection between the gut microbiome and NDDs offers promising new opportunities for future research.

Congenital Infection Influence on Early Brain Development Through the Gut-Brain Axis

The mechanisms by which various pathogens cause congenital infections have been studied extensively, aiding in the understanding of the detrimental effects these infections can have on fetal/neonatal neurological development. Recent studies have focused on the gut-brain axis as pivotal in neurodevelopment, with congenital infections causing substantial disruptions. There remains controversy surrounding the purported sterility of the placenta as well as concerns regarding the effects of exposure to antibiotics used during pregnancy on neonatal microbiome development and how early exposure to microbes or antibiotics can shape the gut-brain axis. Long-term neurodevelopmental consequences, such as autism spectrum disorder, attention deficit hyperactivity disorder, and cerebral palsy, may be attributable, in part, to early life infection and changes in the immature gut microbiome. The goal of this review is thus to critically evaluate the current evidence related to early life infection affecting neurodevelopment through the gut-brain axis.

Gut Microbiota: A Novel Therapeutic Target for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease characterized by motor dysfunction. Growing evidence has demonstrated that gut dysbiosis is involved in the occurrence, development and progression of PD. Numerous clinical trials have identified the characteristics of the changed gut microbiota profiles, and preclinical studies in PD animal models have indicated that gut dysbiosis can influence the progression and onset of PD via increasing intestinal permeability, aggravating neuroinflammation, aggregating abnormal levels of α-synuclein fibrils, increasing oxidative stress, and decreasing neurotransmitter production. The gut microbiota can be considered promising diagnostic and therapeutic targets for PD, which can be regulated by probiotics, psychobiotics, prebiotics, synbiotics, postbiotics, fecal microbiota transplantation, diet modifications, and Chinese medicine. This review summarizes the recent studies in PD-associated gut microbiota profiles and functions, the potential roles, and mechanisms of gut microbiota in PD, and gut microbiota-targeted interventions for PD. Deciphering the underlying roles and mechanisms of the PD-associated gut microbiota will help interpret the pathogenesis of PD from new perspectives and elucidate novel therapeutic strategies for PD.