Magnolol protects PC12 cells from hydrogen peroxide or 6-hydroxydopamine induced cytotoxicity

Magnoliae Cortex contains a range of bioactive components including terpenes (e.g. α-, β- and γ-eudesmol), phenylpropanoids (e.g. honokiol and magnolol) and alkaloids (e.g. magnocurarine). We recently reported that pretreatment of PC12 cells with Magnoliae Cortex extract significantly suppresses cytotoxicity induced by H₂O₂ or 6-hydroxydopamine (6-OHDA) through the induction of drug-metabolizing and antioxidant enzymes. In this study, we investigated whether honokiol and magnolol, which are known to be active components of Magnoliae Cortex, induce drug-metabolizing enzymes and antioxidant enzymes in PC12 cells. We also examined the cytoprotective effect of honokiol and magnolol against H₂O₂ or 6-OHDA induced cell death in PC12 cells. Our results revealed that honokiol and magnolol induced both NAD(P)H:quinone oxidoreductase 1 (NQO1) and catalase enzyme activities in a concentration-dependent manner. Pretreatment of PC12 cells with magnolol suppressed toxicity induced by H₂O₂ or 6-OHDA. However, pretreatment of PC12 cells with honokiol showed only a suppressive effect on toxicity induced by H₂O₂. Our results suggest that the cytoprotective effect of Magnoliae Cortex extract on PC12 cells is mainly attributable to magnolol and only partially to honokiol.