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.

外围脱羧酶抑制剂（PDI）可防止芳香族L-氨基酸脱羧酶（AADC）将左旋多巴转化为血液中的多巴胺。酶活性的改变可能有助于在许多帕金森氏病患者中观察到所需的左旋多巴更高剂量。我们评估了左旋多巴/ PDI对血清AADC酶活性的影响。在帕金森氏病或帕金森病患者（n  = 301）的三个独立队列中评估了血清AADC酶的活性，并比较了左旋多巴/ PDI患者与未服用该药物的患者之间的血清AADC酶活性。左旋多巴/ PDI治疗的患者中AADC酶活性升高了62％，而未左旋多巴/ PDI的患者中AADC酶活性升高了19％（中位数90 mU / L与50 mU / L，p <0.001）。AADC活性升高的患者病程更长，左旋多巴/ PDI剂量更高。这些发现可能暗示外周AADC诱导可能是左旋多巴的减弱作用的基础，需要增加剂量以维持持续的治疗作用。