Cysteine elevation in levodopa-treated patients with Parkinson's disease

Homocysteine, cysteine, and cysteinyl-glycine are all metabolically interrelated. Levodopa/decarboxylase inhibitor (LD/DCI) administration increases total homocysteine (tHcy) plasma levels. Objectives were to investigate associations between LD/DCI intake, concentrations of tHcy, cysteine, and cysteinyl-glycine in PD patients and healthy controls. Cysteine levels were significant lower in controls and PD patients with tHcy below the treshold of 15 [micromol/L] when compared with PD patients with tHcy above 15. Cysteinyl-glycine did not significantly differ between the three cohorts. Significant associations appeared between tHcys and cysteine in PD patients. tHcy and cysteine concentrations correlated to LD/DCI intake and severity of PD. The cysteine increase may be due to the significant higher dosing of daily LD/DCI and the significant higher morning LD/DCI dose 1 hour before blood sampling in PD patients with tHcy above 15 when compared with the remaining PD patients and the controls. The correlation outcomes support the view that LD/DCI intake may also increase cysteine.