Objective: To evaluate the efficacy of the 5-Hydroxytryptophan (5-HTP) on levodopa-induced motor complications in patients with Parkinson’s disease (PD).

Background: Several studies have indicated that altered serotonergic neurotransmission may contribute to the motor features commonly associated with PD such as levodopa-induced dyskinesias (LIDs)[1]. 5-HTP is the immediate precursor of serotonin obtained through hydroxylation of L-tryptophan. We have recently demonstrated that 5-HTP produces significant antidyskinetic effect in the rat model of PD [2]. To date, there are no studies on the use of 5-HTP for treating levodopa-induced motor complications in PD patients.

Method: A single-center, randomized, double-blind placebo-controlled cross-over trial was performed; a total of 12 patients were diagnosed with LIDs and motor fluctuactions and subsequently were randomized to intervention. Eleven subjects completed the 16-week protocol. Patients received placebo and 50 mg of 5-HTP daily in a cross-over design over a period of 4 weeks. There were 4-weeks washouts between treatments. For the assessment of efficacy on the motor functions and levodopa-induced motor complications, the UPDRS (parts III and IV), Unified Dyskinesia Rating Scale (UDysRS), Wearing-Off Questionnaire (WOQ-19) and the self-reported 24-hour home dyskinesia diaries were respectively obtained at baseline, weeks 4, 8, 12 and 16 (T-end).

Results: Repeated measures analysis revealed a significant improvement of LIDs during the 50 mg 5-HTP treatment compared to placebo as assessed by the UDysRS and UPDRS-IV scores.

Conclusion: This study provides preliminary evidence of clinical benefit with 5-HTP for treating LIDs in PD. Larger studies with a longer treatment duration are needed to corroborate these early findings.

References: [1] Politis M, Wu K, Loane C, Brooks DJ, Kiferle L, Turkheimer FE, Bain P, Molloy S, Piccini P. Serotonergic mechanisms responsible for levodopa-induced dyskinesias in Parkinson’s disease patients. J Clin Invest. 2014 Mar;124(3):1340-9. [2] Tronci E, Lisci C, Stancampiano R, Fidalgo C, Collu M, Devoto P, Carta M. 5-Hydroxy-tryptophan for the treatment of L-DOPA-induced dyskinesia in the rat Parkinson’s disease model. Neurobiol Dis. 2013; 60: 108-114.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/efficacy-and-safety-of-the-5-hydroxytryptophan-on-levodopa-induced-motor-complications-in-parkinsons-disease/