Oxidative stress plays a central role in the pathogenesis of Parkinson's di
sease (PT). L-DOPA, the gold standard in PD therapy, may paradoxically cont
ribute to the progression of the disease because of its pra-oxidant propert
ies. The issue, however, is controversial. In this study, we evaluated peri
pheral markers of oxidative stress in normal subjects, unheated PD patients
and PD patients treated only with L-DOPA. We also measured platelet and pl
asma levels of L-DOPA, 3-O-methyldopa (the long-lasting metabolite of the d
rug), and dopamine. We found that isolated platelets of heated PD patients
form higher amounts of 2,3-dihydroxybenzoate, an index of hydroxyl radical
generation, than platelets of controls or untreated patients. In treated pa
tients, platelet levels of 2,3-dihydroxybenzoate were positively correlated
with platelet levels of L-DOPA, 3-O-methyldopa, and with the score of dise
ase severity. Disease severity was correlated with platelet and plasma leve
ls of L-DOPA, as well as with the daily intake of the drug. No significant
differences in platelet levels of cytosolic and mitochondrial isoforms of t
he antioxidant enzyme superoxide dismutase were found between PD patients,
either treated or unheated, and controls. Our findings lend further support
to the hypothesis that L-DOPA might promote free radical formation in PD p
atients. (C) 1999 Elsevier Science Inc.