Decrease of methionine and S-adenosylmethionine and increase of homocysteine in treated patients with Parkinson's disease

Levodopa is administered with dopa decarboxylase inhibitors (DDI) to preven t its peripheral degradation. This increases conversion of levodopa to 3-O- methyldopa (3-OMD) by catechol-O-methyltransferase (COMT). S-adenosyl methi onine (SAM), which is synthesized from adenosintriphosphate and methionine (MET), serves as methyl donor for this O-metabolisation of levodopa with re sulting conversion of SAM to total homocysteine (tHcy) via S-adenosylhomocy steine (SAH). Previous studies showed augmented plasma levels of tHcy in lo ng-term levodopa/DDI-treated patients with Parkinson's disease (PP). Object ive of this study was to compare MET, SAM, levodopa, 3-OMD, tHcy and SAH in plasma of 20 levodopa/DDI treated PP and corresponding controls. A signifi cant decrease of MET respectively SAM and an increase of tHcy appeared in P P. SAH with its short half-life did not differ. Levodopa/DDI long-term trea tment contributes to altered levels of substrates of the O-methylation cycl e in PP. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.