Role of Nasal Dysbiosis in Parkinson Disease

Olfactory dysfunction is frequent in Parkinson Disease (PD) and may be present years before the motor symptoms appear. The early olfactory dysfunction could result from environmental factors acting through the nasal cavity such as microbial communities. Local inflammation induced by a nasal bacterial dysbiosis (microbiota imbalance) could lead to early neuronal dysfunctions in the olfactory system propagating in all the brain, thus inducing motor, cognitive and emotional manifestations in PD, in keeping with the Braak's stage hypothesis. We propose a translational project aiming at investigating the potential influence of nasal dysbiosis in PD pathogenesis. First, we will analyze both olfaction and nasal microbiota in a large series of PD patients and test the link between olfactory deficits and nasal dysbiosis. Then, we will take advantage of studying two populations of subjects with a very different environmental exposure (in mainland France and French West Indies) to isolate the abnormalities of the nasal microbiota that could be specific for PD. The study will be performed in 160 patients and 160 healthy volunteers. Patients will be enrolled in two investigators sites of which different environmental exposure: 1) Guadeloupe Hospital, French West Indies and 2) Pitie-Salpetriere Hospital, Paris, France. The patient selection will be conducted in consultation with the physician and it will be proposed to the spouse to participate as controls. The study subjects will be enrolled after collecting their informed consent.

As soon as the study subjects are included, the following measurements will be done at once at the inclusion:

• Neurological assessment: Idiopathic PD. Severity of the disease will be evaluated using the Hoehn and Yahr staging. Non-motor manifestations of the disease will be assessed using the Non-Motor Symptoms Scale (NMSS). Severity of REM behavior disorder will be evaluated using the Innsbruck REM sleep behaviour disorder inventory .
• Olfactory function: Olfactory performance will be measured using (a) the Sniffin' Stick test battery (Burghardt, Wedel, Germany) following a standardized procedure and (b) a discrimination test of odorant mixtures developed by the Research Unit.
• Global cognitive performance and executive functions: The Montreal Cognitive Assessment (MoCA) will be used to assess global cognitive performance. Frontal Assessment Battery (FAB) will be used to detect executive dysfunction.
• Memory: The delayed paragraph recall index from the Wechsler Memory Scale IV-Revised will be employed as a valid, sensitive measure of verbal declarative memory and a surrogate marker of hippocampal function.
• Mood disorders: Two self-questionnaires will be used: the Snaith-Hamilton pleasure scale to assess anhedonia severity, and the Quick inventory of depressive symptomatology-self-rated for depression intensity evaluation. Two clinician rating tests for depression severity will also be used: the Hamilton Depression Rating Scale 17 and the MINI.

Sampling of human microbiota will be performed at the end. Subjects will undergo nasal brushing from anterior nares after local epinephrine application with a sterile flocked swab inserted and gently rolled around the inside of both nostrils. Swabs (one per nostril) will be placed on ice immediately after collection and then frozen at -80°C before shipment to the Research Unit (Institut Pasteur) where analyses will be carried out:

• Immunohistochemistry analysis: The levels of Neuroinflammation and aSyn proteins will be analyzed in the nasal tissue samples.
• Microbiome analysis: Microbial composition will be determined by metagenomic (pan-bacterial 16S rRNA gene sequencing).