Flavonoids from Stem and Leaf of Scutellaria Baicalonsis Georgi Inhibit the Phosphorylation on Multi-sites of Tau Protein Induced by Okadaic Acid and the Regulative Mechanism of Protein Kinases in Rats

Aim: The aim of the present study is to investigate the effect of flavonoids from stem and leaf of Scutellaria baicalonsis Georgi (SSF) on multi-sites phosphorylation of tau protein in cerebral cortex and hippocampus of rats induced by okadaic acid (OA) and the regulative mechanism of the protein kinases. Methods: The model of AD-like memory impairment and neuronal injuries was established in male SD rats who were microinjected with OA (200 ng/kg) to establish a memory impairment model and screened for successful model rats by Morris water maze on day 21 after surgery. The successful model rats were continuously administered with intragastric infusion (ig) SSF 25, 50, and 100 mg/kg or Ginkgo biloba leaves flavonoids (GLF) 200 mg/kg for 36 d. The relative protein expressed levels of phosphorylated tau protein at sites of Ser199, Ser202, Ser214, Ser404 and Thr231, protein kinases (CDK5, PKA, pTyr216-GSK3β and pSer9-GSK3β) were detected by Western blotting. Results: The relative protein expressed levels of p-tau(Ser199), p-tau(Ser202), p-tau(Ser214), p-tau(Ser404) p-tau(Thr231), and pTyr216-GSK3β were significantly increased in both cerebral cortex and hippocampus regions of the model rats subjected to intracerebroventricular injection of OA (P<0.01), while the protein expressed levels of CDK5, PKA and pSer9- GSK3β (P<0.01) were reduced. SSF can dramatically reverse these increments in phosphorylated tau protein levels (P<0.01) and differently regulate the protein expressed levels of CDK5, PKA, and GSK3β (P<0.01) in rats’ cerebral cortex and hippocampus induced by OA. GLF also exhibits a similar effect on SSF. Conclusion: The results demonstrated that SSF could inhibit the hyperphosphorylation of tau in rats’ cerebral cortex and hippocampus induced by microinjection of OA, which may be related to the activities of protein kinase CDK5, PKA, and GSK3β.