Levodopa (L-dopa) and catechol-O-methyltransferase (COMT) inhibition are widely used therapeutics in Parkinson's disease (PD). Despite their therapeutic effects, it was raised that nutrients involved in one-carbon metabolism can be deteriorated by PD therapies. The aim of this meta-analysis was to investigate the impact of L-dopa and COMT inhibitors on levels of homocysteine (Hcy), vitamin B12 and folate in patients with PD. A total of 35 case-control studies from 14 different countries were selected through PubMed, MEDLINE and Google Scholar and were meta-analyzed. In the L-dopa group, the Hcy level was higher compared to the PD without L-dopa group (SMD: 5.11 μmol/L, 95% CI: 3.56 to 6.66). Moreover, vitamin B12 and folate levels in the L-dopa group were lower compared to the healthy control (SMD: -62.67 pg/mL, 95% CI: -86.53 to -38.81; SMD: -0.89 ng/mL, 95% CI: -1.44 to -0.33, respectively). The COMT inhibitor group showed lower levels of Hcy (SMD: -3.78 μmol/L, 95% CI: -5.27 to -2.29) and vitamin B12 (SMD: -51.01 pg/mL, 95% CI: -91.45 to -10.57), but higher folate levels (SMD: 1.78 ng/mL, 95% CI: -0.59 to 4.15) compared to the L-dopa group. COMT inhibitors may ameliorate L-dopa-induced hyper-homocysteine and folate deficiency but exacerbate vitamin B12 deficiency.
Keywords: Parkinson’s disease; folate; homocysteine; levodopa; meta-analysis; one-carbon metabolism; vitamin B.