This is a study to determine the safety and tolerability of a new medicine (RQ10) for gastrointestinal symptoms in Parkinson's disease. The investigators will also begin to look at the effect of this medicine on gastrointestinal problems. The results will determine if future studies are appropriate. In this study, RQ10 will be compared to a placebo (a look-alike inactive substance). Participation will include multiple office visits. Approximately 48 people will participate.

This is a phase Ib study with the primary objectives of determining the safety and tolerability as well as pharmacokinetics after single ascending doses (SAD) and multiple ascending doses (MAD) of RQ10 in Parkinson's disease patients. A secondary objective will be to assess the impact of single doses of RQ10 on gastric emptying in Parkinson's Disease patients as well as the effects of RQ10 on gastroparesis symptoms. The expected results of this exploratory phase Ib study will allow deciding about whether to proceed with further development of RQ10 in Parkinson's Disease patients ("go-no go") and help design a formal phase IIa "proof of concept" study by informing repeat-dose selection and possible effect sizes in Parkinson's Disease patients.

Inclusion Criteria: For both the Single Ascending Dose and Multiple Ascending Dose studies: Idiopathic Parkinson's Disease (UK Brain Bank Criteria), Hoehn & Yahr stages 1-3, participants may be on oral levodopa, dopamine agonists, monoamine oxidase-B inhibitors, catechol-O-methyltransferase inhibitors, and amantadine, but doses must have remained stable for 28 days prior to enrollment and should be anticipated to remain stable throughout the study, participants may have deep brain stimulation (though stimulator settings must be expected to remain constant throughout the study) or ablative surgery for Parkinson's Disease.

Additional Inclusion criteria for the Multiple Ascending Dose study only: Must have symptoms suggestive of current gastroparesis or constipation as shown by any one or more of the following: 1. Need for regular use of prokinetics, laxatives, or stool softeners of any kind, 2. A total score of 2 or higher on the Gastroparesis Cardinal Symptoms Index (total score equals average of scores on the 3 subscales), 3. A score of 5 or higher on the gastroparesis subscale or 5 or higher on the constipation subscale of the Gastrointestinal Symptoms in Neurodegenerative Disease Scale.

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Exclusion Criteria: Dementia (Mini Mental Status Exam < 25), active psychosis, severe depression (score of 4 on question 1.3 of the Movement Disorder Society-United Parkinson Disease Rating Scale), active suicidality as measured by a most severe suicide ideation score of 4 or 5 on the Columbia-Suicide Severity Rating Scale (C-SSRS), or patients who answer "Yes" on any of the 5 C-SSRS Suicidal Behavior Items if the attempt or acts were performed within 1 year of screening, or patients who, in the opinion of the investigator, present a risk of suicide, any chronic gastrointestinal diseases except gastroesophageal reflux disease, history of any gastrointestinal surgery that might impact drug absorption (e.g. gastrectomy), use of apomorphine, anticholinergics, or carbidopa/levodopa intestinal gel for Parkinson's Disease, female participants who are pregnant or lactating, male or female participants of childbearing age who are not willing, or whose partners are not willing, to use contraception during the study, diabetes, symptomatic anemia, abnormal liver or kidney function, cardiac arrhythmia (past or present) or abnormal QT interval on entrance electrocardiogram, positive drug screen at screening visit, allergy to spirulina, egg, milk, or wheat, pulmonary dysfunction (e.g. Chronic Obstructive Pulmonary Disease), small bowel malabsorption, use of any medications affecting gastric emptying (macrolides, metoclopramide, domperidone, opiates, anticholinergics) within 3 days of visits 2 and 3, prisoners, and individuals with limited English proficiency.

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