Objectives: Baicalin and its aglycone baicalein are the major flavonoid components of the root of Scutellaria baicalensis. Recent studies have shown that they can attenuate oxidative stress in various in vitro models as they possess potent antioxidant activities. This study investigated alternative protective mechanisms of baicalein in a cardiomyocyte model.

Methods: Neonatal rat cardiomyocytes pretreated with the test compound were subjected to hypoxia/reoxygenation. The extent of cellular damage was accessed by the amount of released lactate dehydrogenase

Results: Pretreatment with baicalein up to 10 μM reduced lactate dehydrogenase release significantly (P<0.001), while pretreatment with baicalin up to 100 μM was ineffective. The cardioprotective effect of baicalein is not due to its antioxidant effect, because an adverse effect rather than a protective effect was observed when baicalein was present during hypoxia. Cotreatment with N-acetylcysteine attenuated the protective effect of baicalein and concomitantly increased intracellular reactive oxygen species level and the cytotoxic effect of baicalein, but N-acetylcysteine alone did not have such effects. In addition, cotreatment with catalase, but not superoxide dismutase or mannitol, reversed the cardioprotective effect of baicalein, suggesting the involvement of hydrogen peroxide in the cardioprotective mechanism. The NAD(P)H:quinone oxidoreductase inhibitors dicoumarol and chrysin also abolished the cardioprotective effect of baicalein. While pretreatment with baicalein did not increase antioxidant enzyme activities, it alleviated calcium accumulation in cardiomyocytes undergoing simulated ischemia.

Conclusion: These results highlight the important role of hydrogen peroxide produced during the auto-oxidation of baicalein in the cardioprotective effect of baicalein.