Phase IIb Study of Intranasal Glutathione in Parkinson's Disease

Reduced glutathione (GSH) is an endogenously synthesized tripeptide depleted early in the course of Parkinson's disease (PD) and GSH augmentation has been proposed as a therapeutic strategy in PD.

This Phase IIb study was designed to evaluate whether a Phase III study of intranasal GSH, (in)GSH, for symptomatic relief is warranted and to determine the most appropriate trial design for a disease-modification study.

This was a double-blind, placebo-controlled trial of 45 individuals with Hoehn & Yahr Stage 1-3 PD. Participants were randomized to receive intranasal placebo (saline), 100 mg GSH, or 200 mg GSH thrice daily for three months, and were observed over a one-month washout period.

All cohorts improved over the intervention period, including placebo. The high-dose group demonstrated improvement in total Unified PD Rating Scale (UPDRS) (-4.6 (4.7), P = 0.0025) and UPDRS motor subscore (-2.2 (3.8), P = 0.0485) over baseline, although neither treatment group was superior to placebo. One participant in the high-dose GSH cohort developed cardiomyopathy.

Although predicted improvements in PD total and motor scores were observed, these data do not suggest (in)GSH is superior to placebo after a three month intervention. The symptomatic effects are sufficient to warrant a delayed-start or wash-out design study for disease-modification trials. Whether long-term use of (in)GSH leads to clinical improvements that are sustained and significantly different than placebo will require appropriately-powered longer-duration studies in larger cohorts. The improvement in the placebo arm was more robust than has been observed in previous PD studies and warrants further investigation.