Gut Microbiome Analysis in de Novo Parkinson's Patients

Recent studies indicate a significant difference in gut microbiota composition
between PD patients and healthy controls. However, since the vast majority of
included patients in these studies were using dopaminergic medication, no
inferences could be made concerning the possible downstream effects of
dopaminergic medication on gut microbiota composition. Here, we will determine
the relative contributions of PD diagnosis and dopaminergic medication on
microbiome composition through investigation of gut microbiota composition of
initially treatment naive PD patients at baseline and after one- and
three-years follow-up.

The primary objective of this study is to determine the relative contributions
of PD diagnosis and dopaminergic medication use to the changes in microbiota
composition observed in PD patients. Secondary objectives are to determine the
relative contributions of other possible confounders, to microbiota composition
variability in PD patients.

We propose a case control study with a prospective outlook to compare changes
in microbiota composition between de novo PD patients without a history of
dopaminergic medication use and healthy age, sex and constipation matched
controls. Microbiota composition of said cohort of PD patients will again be
assessed after one year of dopaminergic medication use to establish the effect
of dopaminergic medication on microbiota composition. Both groups will be
assessed on in- and exclusion criteria, including motor and non-motor
symptomatology associated with (prodromal) PD and factors influencing gut
microbiota composition, using questionnaires.

The burden associated with participation consists of collecting a stool sample
using a stool sample collection kit and filling out the provided
questionnaires, which will take a total of about 1 hour. From participants
willing to participate in the genetic screening of genome-wide variants and/or
whole gene sequencing of the GBA1 gene, a saliva sample will be collected.
Participants willing to participate in the intestinal wall permeability
assessment will collect urine over a 24-hour period after ingestion of a
standardized sugar solution. The first five hours of urine collection, the
participant will fast, except for water consumption. Also, 30ml of blood will
be collected for markers of intestinal wall permeability and associated
intestinal inflammation. Additionally, one visit to the UMCG will take place to
assess the UPDRS and MoCA and collect blood (from participants of the
intestinal wall permeability assessment). This will be done during the same
visit as in which an F-DOPA PET scan will be performed, if warranted, as part
of the diagnostic workup (total dosage 6.7mSv). If no other visits to the UMCG
are planned and the participant does not take part in the intestinal wall
permeability assessment, all assessments can also be done from home. The
additional time needed for the purpose of this study will be a maximum of 2 to
3 hours at baseline spread out over multiple days. After one year, PD subjects
will be asked to hand in another fecal sample and fill out the stool diary and
food questionnaires. This will take approximately 40 minutes, whereas the
clinical assessments take about 20 minutes. After three years, the entire
baseline will be repeated. In addition, PD participants can opt-in for (1)
optional withdrawal of 60mL of blood for the assessment of intestinal wall
permeability similar to the baseline, as well as systemic inflammation,
single-cell RNA sequencing (sc-RNAseq) of peripheral blood mono-nuclear cells
(PBMCs) and glucocerebrocidase (GCase) activity; and (2) optional measurement
of colonic transit time using radio-opaque markers and an abdominal CT
(3.5mSv). The total workload of the study is therefore 5-7 hours spread out
over multiple days and visits. The associated risk is negligible and there are
no benefits associated with participation.
To make any inferences concerning a possible role of the microbiome in the
pathophysiology of PD or as an early marker of disease, it is essential to
establish the relation between PD diagnosis and gut microbiome composition
without the possible confounding effect of dopaminergic medication. For this
purpose, it is a necessity to compare the gut microbiota composition of
treatment naïve PD patients to healthy age-,sex- and constipation-matched
controls. Furthermore, determination of the gut microbiome composition after
one and three years will aid in quantifying the extent to which dopaminergic
medication use might alter gut microbiota composition and allows for PD subtype
comparisons in relation to disease progression.