Elevation of Plasma Homocysteine and Minor Hallucinations in Parkinson’s Disease: A Cross-Sectional Study

Figure 1

The role of homocysteine in the methionine cycle. In the presence of folate and vitamin B12, homocysteine (Hcy) is converted to methionine. Methionine is converted back to Hcy through a series of reactions under the catalysis of catechol-O-methyltransferase, and this catalytic reaction can reduce levodopa. On the one hand, Hcy can cause synaptic dysfunction and cell death through DNA strand breakage, oxidative stress, and apoptosis. On the other hand, Hcy can be converted to cysteine, which is the raw material of glutathione. Glutathione can reduce the adverse effects of Hcy to a certain extent. 3-OMD: 3-O-methyldopa; 5-CH₃THF: 5-methyltetrahydrofolate; COMT: catechol-O-methyltransferase; Glu: glutamate; Gly: glycine; GSH: glutathione; Hcy: homocysteine; L-DOPA: levodopa; SAH: s-adenosyl-homocysteine; SAM: s-adenosyl-methionine; THF: tetrahydrofolate; VB12: vitamin B12; VB6: vitamin B6.