Peripheral decarboxylase inhibitors paradoxically induce aromatic L-amino acid decarboxylase

Anouke van Rumund*, Lukas Pavelka, Rianne A.J. Esselink, Ben P.M. Geurtz, Ron A. Wevers, Brit Mollenhauer, Rejko Krüger, Bastiaan R. Bloem, Marcel M. Verbeek

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

16 Citations (Scopus)


Peripheral decarboxylase inhibitors (PDIs) prevent conversion of levodopa to dopamine in the blood by the enzyme aromatic L-amino acid decarboxylase (AADC). Alterations in enzyme activity may contribute to the required higher dosages of levodopa observed in many patients with Parkinson’s disease. We evaluated the effect of levodopa/PDI use on serum AADC enzyme activity. Serum AADC enzyme activity was evaluated in three independent cohorts of patients with Parkinson’s disease or parkinsonism (n = 301) and compared between patients on levodopa/PDI vs. patients not on this medication. AADC enzyme activity was elevated in 62% of patients on levodopa/PDI treatment, compared to 19% of patients not on levodopa/PDI (median 90 mU/L vs. 50 mU/L, p < 0.001). Patients with elevated AADC activity had longer disease duration and higher doses of levodopa/PDI. These findings may implicate that peripheral AADC induction could underlie a waning effect of levodopa, necessitating dose increases to maintain a sustained therapeutic effect.

Original languageEnglish
Article number29
Pages (from-to)29
Journalnpj Parkinson's Disease
Issue number1
Publication statusPublished - 19 Mar 2021


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