Research Into the Safety of a New Agent (VT-5006) in People With and Without Parkinson's Disease

Parts A and B enroll healthy volunteers; only key entry criteria for Part C are described below. Inclusion Criteria: * Diagnosed with PD confirmed by a neurologist within a maximum of 10 years (based of year of diagnosis) prior to screening * Has current or history of GI motility dysfunction or persistent constipation * Score of \< 3 on the Modified Hoehn and Yahr Scale * Is able to swallow multiple and large capsules without assistance or difficulty, in the opinion of the investigator * Participants should be on a stable regimen of any prescribed (except levodopa/carbidopa, levodopa/benserazide or anticholinergic agents) or over-the-counter medications or supplements for at least 60 days prior to enrolment in the study. Participants should not change the dosage or frequency of these medications or supplements while in the study. If changes to medications or supplements are contemplated during the study, the Investigator should be contacted prior to any change. * Has suitable venous access for blood sampling Exclusion Criteria: * Has a known allergy or hypersensitivity to any component of the formulation of VT-5006 or matching placebo, or history of severe allergy or anaphylaxis to a drug, food, or other exposure * Participants taking levodopa/carbidopa or levodopa/benserazide must remain on a stable dose and regimen from at least 21 days prior to Day 1 visit to end of study (EOS) visit. Other treatments for PD symptoms may be allowed at the discretion of the medical monitor * Has any clinically significant arrhythmia(s) on ECG; specifically, the participant's corrected QT interval (QTcf) (Fridericia's correction) is \>450 ms for males or \>470 ms for females * Has clinically significant abnormalities, as judged by the investigator, in laboratory test results (including hepatic and renal panels, complete blood count, chemistry panel and urinalysis). In the case of uncertain or questionable results, tests performed during screening may be repeated before randomization to confirm eligibility or judged to be clinically irrelevant for healthy participants * Has any of the following test results: a serum total bilirubin value \>1.5 x upper limit of normal (ULN); a serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) value 2x ULN. As an exception, participants that present with elevated bilirubin in the absence of elevations in ALT or AST that fits the pattern of Gilbert's syndrome may be enrolled after discussion with the medical monitor if their conjugated bilirubin is not or slightly elevated and the level is considered to be not clinically significant. * Any history of lumbar surgery for any reason (e.g. herniated disc) that in the opinion of the Investigator would interfere with or pose risks to a lumbar puncture procedure * Other contraindications to having a lumbar puncture