Protective effects of baicalein against excess L-DOPA-induced dopamine quinone neurotoxicity

Objectives: Baicalein, a flavonoid derived from the root of Scutelaria baicalensis Georgi, possesses antioxidative properties including reactive oxygen species scavenging and lipid peroxidation inhibiting activities. The present study was undertaken to investigate the neuroprotective effect of baicalein against dopamine (DA) neurotoxicity induced by exposure to a synthetic DA precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), in cultured dopaminergic CATH.a cells. Methods and results: Exposure to L-DOPA for 24 hours reduced the number of viable cells and enhanced protein-bound quinone (quinoprotein) formation in the cell. Both effects were prevented by simultaneous treatment with baicalein. In addition, baicalein prevented the formation of DA semiquinone radicals from DA in an in vitro cell-free system. Long-term baicalein treatment for 96 hours also protected against excess LDOPA-induced cell death, and also increased glutathione (GSH) levels in CATH.a cells. Discussion: Our results indicate that baicalein has neuroprotective properties against excess L-DOPAinduced DA neurotoxicity through the suppression of DA quinone formation. Furthermore, the long-term treatment of baicalein upregulates intracellular GSH contents, which may also exert neuroprotective effects against oxidative stress-induced neuronal damage.