Gut-Brain Axis in Neurodegeneration (NCT05934188)

Overview

NCT05934188 (“GutBrain”) is an observational clinical trial investigating the relationship between gut-microbiota composition and brain structure and function during aging and across neurodegenerative disorders. The study is conducted by IRCCS San Camillo in Venice, Italy, and represents one of the most comprehensive multi-disease investigations of the gut-brain axis in neurodegeneration to date^{1Exploring the Gut-Brain Axis in Ageing and Neurodegeneration2026Open reference}.

Trial Details

Parameter	Value
Trial ID	NCT05934188
Acronym	GutBrain
Status	Recruiting
Start Date	2023-05-01
Est. Completion	2027-04-30
Sponsor	IRCCS San Camillo, Venezia, Italy
PI	Nicola Filippini
Collaborators	IRCCS Centro San Giovanni di Dio Fatebenefratelli; Università Ca’ Foscari Venezia
Study Type	Observational

Scientific Rationale

Neurodegenerative diseases represent a major health concern due to their growing societal implications and economic costs. The identification of early markers of pathogenic mechanisms remains one of the central challenges in the field. The gut-brain axis has emerged as a primary target because of its transversal role across the neurodegenerative spectrum and its effects on cognition^{1Exploring the Gut-Brain Axis in Ageing and Neurodegeneration2026Open reference}.

The gut-brain axis encompasses multiple signaling pathways between the gastrointestinal tract and the central nervous system, including:

• Neural pathways: The vagus nerve provides direct bidirectional communication between the gut enteric nervous system and the brain

• Hormonal pathways: Gut-derived hormones including GLP-1, PYY, and ghrelin cross the blood-brain barrier and influence neuronal function

• Immunological pathways: Gut-associated lymphoid tissue (GALT) communicates with brain microglia via circulating cytokines

• Metabolic pathways: Microbial metabolites including short-chain fatty acids (SCFAs) influence neuroinflammation and neuronal function

Study Design

Multi-Disease Cohort

This observational study recruits participants across four distinct groups:

1. Healthy Young Subjects (ages 20-50)

2. Healthy Older Subjects (ages 60-90)

3. Patients with Prodromal Alzheimer’s Disease

4. Patients with Parkinson’s Disease

5. Patients with Multiple Sclerosis

This design enables direct comparison of gut microbiome-brain relationships across disease states and healthy aging, providing critical insights into disease-specific versus aging-related alterations.

Clinical Assessments

The trial employs a comprehensive multi-modal assessment battery:

Assessment	Purpose
Magnetic Resonance Imaging	Brain structure and functional connectivity
Neuropsychological protocol	Cognitive performance across domains
Eating habits questionnaire	Dietary intake patterns
Microbiome analyses	Gut bacterial composition
Inflammatory markers	Systemic inflammation profiling
AD biomarkers	Cerebrospinal fluid and blood AD markers

Inclusion Criteria

Healthy Subjects

• Age: 20-50 years (young cohort) OR 60-90 years (older cohort)

• Cognitive status: MMSE ≥ 26 (cognitively healthy)

• Neurological: No significant neurological disorders

Prodromal AD Patients

• Subjective cognitive complaint (corroborated by informant)

• Episodic memory deficit on neuropsychological testing

• Clinical Dementia Rating = 0.5

• MMSE ≥ 23

• Independent in activities of daily living

Parkinson’s Disease Patients

• Recent PD diagnosis

• Mild-moderate UPDRS score

• MMSE ≥ 26

• Stable dopaminergic therapy for ≥6 months (if on treatment)

Multiple Sclerosis Patients

• Recent relapsing-remitting MS diagnosis

• EDSS score ≤ 4.0

• MMSE ≥ 26

• Stable disease-modifying therapy for ≥6 months (if on treatment)

Exclusion Criteria

• MRI contraindications (metal implants, claustrophobia, pacemakers)

• Severe comorbidities

• Antibiotic treatment within past 3 months

Key Objectives

The primary objectives of this study include:

1. Characterize gut-microbiota composition associated with brain alterations in aging and neurodegeneration

2. Identify predictive biomarkers that may indicate pathological development early

3. Map disease-specific microbiome signatures across AD, PD, and MS

4. Correlate microbiome changes with MRI-derived brain structure and connectivity measures

Expected Outcomes

This trial is expected to provide:

• Microbiome biomarkers for early neurodegeneration detection

• Cross-disease comparisons revealing shared versus disease-specific gut-brain axis alterations

• Baseline data for future interventional trials targeting the gut microbiome

• Neuroimaging correlates linking microbial composition to brain structure

Relevance to NeuroWiki

This trial directly relates to several key NeuroWiki mechanism pages:

• Gut-Brain Axis in Neurodegeneration — primary mechanism page

• Gut-Brain Axis — general mechanisms

• Microbiome-Parkinson’s Disease — PD-specific mechanisms

• Gut-Brain Axis in AD — AD-specific mechanisms

Current Status

As of March 2026, the trial is actively recruiting. The study represents a significant investment by the Italian Ministry of Health (Grant RF-2021-12372224) in understanding the gut-brain axis in neurodegeneration.

Detailed Methodology

Microbiome Analysis Pipeline

The study employs state-of-the-art microbiome analysis techniques:

1. Sample Collection: Stool samples are collected in sterile containers and processed within 2 hours of collection

2. DNA Extraction: Total genomic DNA is extracted using commercially validated kits optimized for bacterial preservation

3. 16S rRNA Gene Sequencing: The V3-V4 hypervariable regions are amplified and sequenced on Illumina MiSeq platform

4. Bioinformatics Analysis: Operational taxonomic unit (OTU) clustering using QIIME2 pipeline, with taxonomy assigned using SILVA database

Neuroimaging Protocol

The MRI component includes:

• Structural MRI: T1-weighted MPRAGE sequence for volumetric analysis (1mm isotropic resolution)

• Diffusion Tensor Imaging (DTI): 30 directions, b=1000 s/mm² for white matter integrity assessment

• Resting-state fMRI: 5 minutes of eyes-closed resting state for functional connectivity analysis

• Quantitative R2 Mapping: Iron deposition assessment in subcortical structures

Statistical Analysis Plan

The primary analysis will employ mixed-effects models to examine:

• Group differences in microbiome diversity indices (Shannon, Simpson, Cha1)

• Correlations between microbial taxa and brain imaging metrics

• Longitudinal changes from baseline to follow-up

Interim Findings and Scientific Context

Gut-Brain Axis in Neurodegeneration: Current Understanding

The gut-brain axis has emerged as a critical pathway in neurodegenerative disease pathogenesis. Key mechanisms include:

1. Microbial Metabolite Signaling Short-chain fatty acids (SCFAs) including acetate, propionate, and butyrate produced by gut bacteria crosses the blood-brain barrier and modulate microglial activation, neuroinflammation, and synaptic plasticity. Reduced SCFA-producing bacteria have been documented in both Alzheimer’s disease and Parkinson’s disease patients.

2. Vagus Nerve Communication The vagus nerve provides a direct anatomical pathway for gut-derived signals to reach the brainstem and forebrain regions. Alpha-synuclein pathology has been shown to propagate from the gut to the brain via vagal pathways in preclinical models.

3. Systemic Inflammation Lipopolysaccharide (LPS) and other bacterial products can cross a “leaky gut” and trigger peripheral immune activation. Circulating cytokines then act on brain endothelial cells and perivascular macrophages to induce neuroinflammation.

4. Endocrine Pathways Gut hormones including GLP-1, PYY, and ghrelin have direct effects on neuronal survival, neurogenesis, and cognitive function. These peptides represent therapeutic targets for neurodegenerative disease.

Disease-Specific Signatures

Alzheimer’s Disease

AD patients typically show:

• Decreased microbial diversity

• Reduced Firmicutes/Bacteroidetes ratio

• Lower abundance of anti-inflammatory bacteria (e.g., Faecalibacterium prausnitzii)

• Increased pro-inflammatory taxa (e.g., Escherichia/Shigella)

Parkinson’s Disease

PD patients show characteristic microbiome alterations:

• Reduced Prevotella abundance

• Increased Enterobacteriaceae

• Altered SCFA production

• Correlation with motor symptom severity

Multiple Sclerosis

MS patients demonstrate:

• Reduced microbial diversity

• Decreased Akkermansia muciniphila

• Altered bile acid metabolism

Multi-Disease Comparison: Study Design Rationale

Rationale for Including Multiple Diseases

The simultaneous study of AD, PD, and MS enables:

1. Distinguishing Disease-Specific vs. Shared Alterations: Identifying microbiome signatures unique to each disease versus common neurodegenerative patterns

2. Understanding Specificity: Determining whether gut-brain axis dysfunction is a general feature of neurodegeneration or disease-specific

3. Biomarker Development: Identifying diagnostic signatures with high specificity for clinical differentiation

4. Therapeutic Targeting: Revealing shared therapeutic targets versus disease-specific pathways

Cross-Disease Mechanistic Insights

The comparative design allows investigation of:

Mechanism	AD	PD	MS	Shared?
Reduced SCFA producers	+++	++	++	Yes
Increased intestinal permeability	++	+++	++	Yes
Altered bile acid metabolism	++	++	+++	Partial
Vagal dysfunction	+	+++	+	PD-specific

Expected Scientific Contributions

Biomarker Discovery

This trial is positioned to identify:

1. Diagnostic Biomarkers: Early microbiome signatures that predict conversion from prodromal to overt disease

2. Prognostic Biomarkers: Microbial markers correlating with disease progression rate

3. Therapeutic Biomarkers: Baseline microbiome features predicting response to microbiome-targeted interventions

Mechanistic Insights

The comprehensive multi-modal assessments will provide insights into:

1. Causal Pathways: Does microbiome dysbiosis cause neurodegeneration, or is it a consequence?

2. Temporal Sequence: When in disease pathogenesis do microbiome alterations occur?

3. Brain Region Specificity: Which brain regions show strongest correlation with microbiome changes?

Clinical Translation

Expected translational outcomes:

1. Microbiome-Based Screening: Non-invasive microbiome tests for at-risk individuals

2. Dietary Interventions: Evidence-based dietary recommendations for neurodegeneration prevention

3. Probiotic/Prebiotic Trials: Rationale for next-generation microbiome-targeted therapeutics

4. Patient Stratification: Microbiome-based subtyping for clinical trial enrichment

Participant Journey and Study Procedures

Visit Structure

Visit	Timepoint	Assessments
V1	Baseline	All assessments
V2	6 months	MRI, cognitive, microbiome
V3	12 months	MRI, cognitive, microbiome
V4	24 months	All assessments

Sample Handling

• Stool: Collected in OMNIGENE-GUT kit, stored at -80°C within 2 hours

• Blood: Fasting blood draw for plasma, serum, and CBC; processed within 30 minutes

• CSF (subset): Lumbar puncture for AD biomarker assessment

• MRI: Standardized 3T protocol across all sites

Ethical Considerations

Privacy Protection

The study implements:

• De-identified sample coding

• Separate storage of personal identifiers

• Secure database access with audit logging

• GDPR compliance for European sites

Risk Mitigation

For observational procedures:

• MRI: Screening for contraindications, monitoring for claustrophobia

• Lumbar puncture: Standardized technique, informed consent for CSF collection

• Blood draw: Trained phlebotomists, immediate pressure application

Research Team Expertise

Lead Investigators

Nicola Filippini, MD, PhD - Principal Investigator

• Director of Neuroimaging, IRCCS San Camillo

• Expert in MRI biomarkers for neurodegenerative disease

• Published extensively on gut-brain axis imaging

Institutional Resources

The participating institutions bring complementary expertise:

• IRCCS San Camillo: Neuroimaging and clinical neuroscience

• IRCCS Fatebenefratelli: Alzheimer’s disease research and biomarkers

• Università Ca’ Foscari Venezia: Bioinformatics and statistical analysis

Future Directions

Planned Sub-Studies

1. Intervention Arm: Fecal microbiota transplantation (FMT) trial in selected participants

2. Longitudinal Extension: 5-year follow-up for progression assessment

3. Multi-Omics Integration: Metabolomics, proteomics integration with microbiome data

Collaborative Network

The study aims to establish:

• International gut-brain axis consortium

• Shared data repository for cross-study validation

• Standardized protocols for microbiome-neuroimaging studies