Gut Microbiota and Tryptophan Metabolites in Parkinson's Disease

An Exploratory Case-Control Study of Fecal Microbiota and Targeted Tryptophan Metabolite Profiling in Patients With Parkinson's Disease

Parkinson's disease is a progressive neurological disorder that can also affect the digestive system. Changes in gut microorganisms and tryptophan metabolites may be associated with Parkinson's disease, but these relationships are not fully understood. This exploratory observational study will compare gut microbial communities and targeted tryptophan metabolite profiles between 15 participants with Parkinson's disease and 15 healthy controls matched by sex, age, and body mass index.

Each participant will provide clinical and lifestyle information and one stool sample. Stool samples will be analyzed using 16S ribosomal RNA gene sequencing and targeted liquid chromatography-tandem mass spectrometry. The study will evaluate differences in gut microbial composition and selected tryptophan metabolites and explore their associations with constipation, bowel habits, medication use, and clinical features of Parkinson's disease. No treatment will be assigned, and participants' usual medical care will not be changed. The findings are exploratory and are intended to guide larger future studies; they cannot establish causality or be used to diagnose Parkinson's disease.

Study Overview

• Status: Not yet recruiting
• Conditions: PARKINSON DISEASE (Disorder)
• Intervention / Treatment: Diagnostic test: Stool Microbiome and Targeted Tryptophan Metabolite Profiling

• Study Type: Observational
• Enrollment (Estimated): 30

Contacts and Locations

• Study Contact: Name: qinghan Guo; Phone Number: 86+17753626689; Email: ghqnxykd@163.com

Study Locations

• China
  • Shandong
    • Laizhou, Shandong, China, 261400
      • Laizhou People's Hospital
      • Contact: Xiumei Gong; Phone Number: +8618553631703; Email: 18553631703@163.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Thirty participants will be enrolled in this single-center observational study, including 15 participants with Parkinson disease and 15 individually matched healthy controls. Participants with Parkinson disease will be recruited from neurology outpatient or inpatient services. Healthy controls may be recruited from health-screening programs, the community, or non-cohabiting relatives. Each healthy control will be matched to a participant with Parkinson disease by sex, age within 5 years, and body mass index within 3 kg/m^2. All participants will provide clinical and lifestyle information and one stool sample.

Description

Inclusion Criteria:

• Participants aged 45 to 90 years, of any sex. Participants able to understand the study, provide written informed consent, and provide an acceptable stool sample according to the study procedures.

For the Parkinson disease group: clinically established or clinically probable Parkinson disease diagnosed by a neurologist according to the Movement Disorder Society Clinical Diagnostic Criteria.

For the Parkinson disease group: preferably a disease duration of 5 years or less and Hoehn-Yahr stage I to III.

For the Parkinson disease group: stable antiparkinsonian medication regimen for at least 4 weeks before enrollment.

For the healthy control group: no history of Parkinson disease, parkinsonism, or another neurodegenerative disorder and no evident parkinsonian symptoms at screening.

Healthy controls matched individually to participants with Parkinson disease by sex, age within 5 years, and body mass index within 3 kg/m^2

Exclusion Criteria:

• Use of systemic antibiotics within 3 months before stool collection. Use of probiotics, prebiotics, tryptophan, 5-hydroxytryptophan, live biotherapeutic products, or other microbiome-related supplements within 4 weeks before stool collection.

Acute infection, fever, acute diarrhea, gastroenteritis, colonoscopy preparation, or a major dietary change within 4 weeks before stool collection.

Active inflammatory bowel disease, celiac disease, short-bowel syndrome, gastrointestinal malignancy, or major gastrointestinal surgery within 6 months.

Active cancer, decompensated liver or kidney disease, severe cardiovascular or hematological disease, active autoimmune disease, or current systemic glucocorticoid or immunosuppressive treatment.

Pregnancy or breastfeeding. Long-term exclusive enteral or parenteral nutrition. Inability to provide an acceptable stool sample or essential clinical information.

Any other condition considered by the investigator to compromise participant safety, study adherence, or interpretation of the results.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Parkinson Disease Group; Participants aged 45 to 90 years with clinically established or clinically probable Parkinson disease. Participants will provide clinical and lifestyle information and one stool sample for 16S ribosomal RNA gene sequencing and targeted tryptophan metabolite analysis. No intervention will be assigned	Diagnostic test: Stool Microbiome and Targeted Tryptophan Metabolite Profiling; Each participant will provide one stool sample. Separate aliquots will be analyzed using 16S ribosomal RNA gene amplicon sequencing and targeted liquid chromatography-tandem mass spectrometry to characterize the gut microbiota and quantify prespecified tryptophan metabolites. These analyses are conducted for research purposes only and will not be used for clinical diagnosis or treatment decisions.
Healthy Control Group; Healthy participants aged 45 to 90 years who are matched to the Parkinson disease group by sex, age, and body mass index. Participants will provide clinical and lifestyle information and one stool sample for 16S ribosomal RNA gene sequencing and targeted tryptophan metabolite analysis. No intervention will be assigned	Diagnostic test: Stool Microbiome and Targeted Tryptophan Metabolite Profiling; Each participant will provide one stool sample. Separate aliquots will be analyzed using 16S ribosomal RNA gene amplicon sequencing and targeted liquid chromatography-tandem mass spectrometry to characterize the gut microbiota and quantify prespecified tryptophan metabolites. These analyses are conducted for research purposes only and will not be used for clinical diagnosis or treatment decisions.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Between-Group Differences in Fecal Tryptophan Metabolite Concentrations	Fecal concentrations of tryptophan, kynurenine, kynurenic acid, quinolinic acid, indole-3-acetic acid, indole-3-lactic acid, indole-3-propionic acid, and tryptamine will be quantified using targeted liquid chromatography-tandem mass spectrometry. Results will be reported as nanograms per gram or micromoles per kilogram of wet stool. Matched between-group differences will be summarized using effect estimates, 95 percent confidence intervals, and Benjamini-Hochberg false discovery rate-adjusted results	At enrollment, based on one stool sample collected from each participant
Between-Group Difference in Fecal Microbial Community Structure	Fecal microbial community structure will be characterized using Bray-Curtis and Aitchison beta-diversity metrics derived from 16S ribosomal RNA gene amplicon sequencing. Differences between the Parkinson disease group and the matched healthy control group will be evaluated using permutational multivariate analysis of variance, with pair identification used to restrict permutations	At enrollment, based on one stool sample collected from each participant

Collaborators and Investigators

• Sponsor: Ningxia Medical University

Study record dates

Study Major Dates

• Study Start (Estimated): August 20, 2026
• Primary Completion (Estimated): October 20, 2026
• Study Completion (Estimated): November 20, 2026

Study Registration Dates

• First Submitted: August 1, 2026
• First Submitted That Met QC Criteria: August 1, 2026
• First Posted (Actual): August 6, 2026

Study Record Updates

• Last Update Posted (Actual): August 6, 2026
• Last Update Submitted That Met QC Criteria: August 1, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Synucleinopathies; Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Neurodegenerative Diseases; Movement Disorders; Parkinsonian Disorders; Basal Ganglia Diseases; Parkinson Disease
• Other Study ID Numbers: 2026-0570

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: No public sharing of individual participant data is currently planned. Aggregate study results will be reported in scientific publications. Any future sharing of de-identified participant-level data would require confirmation of compatibility with participant consent, ethics approval, and an appropriate data-use agreement

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No