Protective mechanism of Syringic acid in an experimental model of Parkinson's disease

6-Hydroxydopamine (6-OHDA) is a widely used chemical to model Parkinson's disease (PD) in rats. Syringic acid (SA) is a polyphenolic compound which has antioxidant and anti-inflammatory properties. The present study aimed to evaluate the neuroprotective role of SA in a rat model of 6-OHDA-induced PD. Parkinson's disease was created by injection of 6-OHDA into the medial forebrain bundle via stereotaxic surgery. Syringic acid was administered daily by oral gavage, before or after surgery. All groups were tested for locomotor activity, rotarod performance and catatony. Dopamine levels in SN were determined by an optimized multiple reaction monitoring method using ultra-fast liquid chromatography coupled with tandem mass spectrometry (MS/MS). The immunoreactivities for tyrosine hydroxylase (TH) and inducible nitric oxide synthase (iNOS) were detected by immunohistochemistry in frozen substantia nigra (SN) sections. Nitrite/nitrate levels, iNOS protein, total oxidant (TOS) and total antioxidant (TAS) status were assayed in SN tissue by standard kits. Motor dysfunction, impaired nigral dopamine release, increased iNOS expression and elevated nitrite/nitrate levels induced by 6-OHDA were significantly restored by SA treatment. Syringic acid significantly improved the loss of nigral TH-positive cells, while increasing TAS capacity and reducing TOS capacity in SN of PD rats. These data conclude that SA is a potential therapeutic agent for the treatment of 6-OHDA-induced rat model of PD. Syringic acid reduced the progression of PD via its neuroprotective, antioxidant and anti-inflammatory effects.