Neuroprotective properties of the natural phenolic antioxidants curcumin and naringenin but not quercetin and fisetin in a 6-OHDA model of Parkinson's disease.

Although the cause of dopaminergic cell death in Parkinson's disease (PD) remains unknown, oxidative stress has been strongly implicated. Because of their ability to combat oxidative stress, diet derived phenolic compounds continue to be considered as potential agents for long-term use in PD. This study was aimed at investigating whether the natural phenolic compounds curcumin, naringenin, quercetin, fisetin can be neuroprotective in the 6-OHDA model of PD. Unilateral infusion of 6-OHDA into the medial forebrain bundle produced a significant loss of tyrosine hydroxylase (TH)-positive cells in the substantia nigra (SN) as well as a decreased of dopamine (DA) content in the striata in the vehicle-treated animals. Rats pretreated with curcumin or naringenin showed a clear protection of the number of TH-positive cells in the SN and DA levels in the striata. However, neither pretreatment with quercetin nor fisetin had any effects on TH-positive cells or DA levels. The ability of curcumin and naringenin to exhibit neuroprotection in the 6-OHDA model of PD may be related to their antioxidant capabilities and their capability to penetrate into the brain.