Polygalae radix inhibits toxin-induced neuronal death in the Parkinson's disease models

Aim of the study: Polygalae radix, the root of Polygala tenuifolia Willd, has commonly been used for the treatment of amnesia and anxiety in traditional Korean medicine. The aim of this study was to investigate its neuroprotective effects and possible mechanisms of action in models of Parkinson's disease. Materials and methods: This study utilized a 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide assay, a reactive oxygen species (ROS) assay, a nitric oxide (NO) production assay, and a caspase-3 activity test as measures of cell viability in PC12 cells damaged by 6-hydroxydopamine (6-OHDA). The protective effects of PRE against 1-methyl-4-phenylpyridium (MPP ⁺)-induced neurotoxicity were assessed in rat primary dopaminergic neurons and in a mouse PD model in which PRE was administered (100 mg/kg/day, 3 days, p.o.) before acute 1-mehtyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity. Finally, TH immunohistochemistry tests were conducted in the substantia nigra pars compacta (SNpc) and striatum (ST). Results and conclusions: PRE significantly inhibited 6-OHDA-induced cell damage at doses of 0.05-1 μg/ml with a maximal effect at 0.1 μg/ml. Caspase-3 activity and the production of ROS and NO were alleviated at 0.1 μg/ml. Also at this dose, PRE protected mesencephalic dopaminergic neurons from MPP⁺-induced toxicity. In an in vivo mouse model of PD, PRE protected dopaminergic neurons and fibers from MPTP-induced toxicity in the SNpc and ST. These results demonstrate that PRE has protective effects on dopaminergic neurons via its anti-oxidant and anti-apoptotic activity.