A Two-Part Single and Multiple Ascending Dose Trial of the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of LBT-3627 in Healthy Participants and in Participants With Parkinson's Disease.

Both cohorts (Healthy Volunteers and Parkinson's Disease)

Key inclusion criteria

* Male or female, 30-89 years inclusive at screening
* BMI 18-32 kg/m²
* Vital signs, ECG (QTcF \<450 ms male / \<470 ms female), and safety labs without clinically significant abnormality; no orthostatic hypotension
* Women of non-childbearing potential, or using highly effective contraception per protocol

Key exclusion criteria

* Immunomodulators / steroids - HV: any (incl. OTC) within 90 days; PD: systemic within 60 days and topical/nasal-inhaled OTC within 7 days (both waivable only with Sponsor approval)
* Vaccine within 60 days (HV) / 45 days (PD) of first dose
* CoQ10 within 5 days
* Inadequate renal function (CrCl ≤ 60 mL/min; ≤ 79 if HV under 40), or LFTs / bilirubin \> 1.5× ULN
* Clinically significant cardiovascular, hepatic, renal, neurological, or psychiatric disease
* Active infection requiring systemic anti-infectives within 14 days; positive HBV/HCV/HIV serology

Parkinson's Disease participants - additional key inclusion criteria

* PD diagnosis by a neurologist/geriatrician, 6 months to \< 11 years before first dose, per MDS clinical diagnostic criteria
* Hoehn \& Yahr stage 1-3
* If on levodopa: stable ≥ 2 months and able to withhold ≥ 12 hours (overnight) around dosing/assessments; if not, remain treatment-naïve through end of study

Parkinson's Disease participants - additional key exclusion criteria

* Prior PD brain surgery, focused ultrasound, or neuromodulation; no anti-amyloid/anti-tau biologics
* Antibiotics within 30 days; OTC pre/probiotics; ≥ 3 unexplained falls in 12 months

Note: Additional protocol-defined criteria apply.