Effect of L-dopa on plasma homocysteine in PD patients: Relationship to B-vitamin status

Background: The antiparkinsonian drug L-dopa causes increased cellular synthesis of homocysteine and consequent hyperhomocysteinemia in rats. This effect of L-dopa on plasma homocysteine is accentuated under conditions of impaired homocysteine metabolism such as folate deficiency. Objective: To investigate the effect of L-dopa administration and B-vitamin status on plasma homocysteine concentrations in humans with PD. Methods: Plasma homocysteine, folate, vitamin B₁₂, and pyridoxal-5′-phosphate (PLP) concentrations were determined in 40 individuals diagnosed with idiopathic PD who were being treated as outpatients at the Boston University Medical Center Neurology Clinic. Twenty of the patients were on L-dopa therapy (treatment group) and 20 were L-dopa-naive (control group). Results: The mean plasma homocysteine concentration was higher in the treatment group than in the controls (p = 0.018). Plasma homocysteine was correlated with plasma folate, vitamin B₁₂, and PLP concentrations in the treatment group (p ≤ 0.007) but not in the controls. Conclusion: L-Dopa can cause hyperhomocysteinemia in PD patients, the extent of which is influenced by B-vitamin status. The B-vitamin requirements necessary to maintain normal plasma homocysteine concentrations are higher in L-dopa-treated patients than in those not on L-dopa therapy. B-Vitamin supplements may be warranted for PD patients on L-dopa therapy.