GDNF and Parkinson disease: The potential applications of MPs and NPs for PD therapy have been explored in the last few years for different drugs, such as levodopa [12,13], rasagiline [14,15], puerarin [16], schisantherin A [17], glial cell line-derived neurotrophic factor (GDNF) [18], ropinirole [19], and apomorphine [20].