Amino acid supplementation in l-dopa treated Parkinson's disease patients

The correlation between Parkinson disease and malnutrition is well established, however a protein-restricted diet is usually prescribed because of potentially negative interactions between dietary amino acids and l-dopa pharmacokinetics. This strategy could increase the risk of further nutritional deficits.

A monocentric, prospective, randomized, double-blind pilot study was performed on two groups of Parkinson-affected, protein-restricted, patients: Intervention (n = 7; amino acid supplementation twice daily) and Placebo (n = 7; placebo supplementation twice daily). At enrolment, after 3- and 6-month supplementation, neurological evaluations (UPDRS III, Hoenh-Yahr scale, l-dopa equivalent dose assessment) were performed and blood sample was collected to define insulin sensitivity (QUICKI index) and oxidative stress (oxidized and reduced glutathione). Repeated measure ANCOVA was applied to define time effect and time × treatment interaction.

Participants were comparable at baseline for all assessed parameters. Neurological outcomes and l-dopa requirement were comparable in both group after 6-month of supplementation, without time × treatment interaction. The decrease in insulin sensitivity, as assessed by QUICKI index, observed after 6 months in both groups, was greater in Placebo than in Intervention (time effect p < 0.001; time × treatment interaction p = 0.01). Moreover, despite no changes in total erythrocyte glutathione concentrations, oxidized glutathione levels decreased by 28 ± 17% in the Intervention while increased by 55 ± 38% in Placebo (time effect p = 0.05; time × treatment interaction p = 0.05), after 6-month supplementation.

Amino acid supplementation, assumed with shrewd temporal distribution, did not show detrimental effects on neurological and pharmacological control in protein-restricted Parkinson-affected patients, chronically treated with l-dopa. Furthermore, daily amino acid supplementation partially counteracted insulin resistance development and the loss in antioxidant availability.