Baicalein inhibits MAPK cascade in C6 rat glioma cells

It is known that mitogen-activated protein kinase (MAPK) phosphorylates and activates cytosolic phospholipase A_2 , which liberates arachidonic acid (AA) from membrane phospholipid. We previously demonstrated that Scutellariae Radix potently inhibited prostaglandin E_2 (PGE_2 ) synthesis in C6 rat glioma cells. In the present study, we examined the effect of baicalein, a flavonoid derived from Scutellariae Radix, on PGE_2 synthesis and MAPK. C6 cells were grown in Dulbeccos modified Eagles medium with 10% FCS. PGE_2 was determined by radioimmunoassay. Immunoblotting was performed for analyzing phospho-tyrosine residue and phosphorylated MAPK. A23187, a Ca^2+ stimulated PGE_2 release from C6 glioma cells. Pretreatment of the cells with baicalein for 10 min resulted in the potent inhibition of A23187-induced PGE_2 release. A23187 also stimulated the phosphorylation of p42 and p44 MAPK, which was inhibited by baicalein in a concentration-dependent manner. On the other hand, histamine phosphorylated MAPK through H1histamine receptors. The phosphorylation was also concentration-dependently inhibited by baicalein. These results suggest that baicalein has an inhibitory ability of MAPK cascade, resulting in the inhibition of PGE_2 synthesis.