Abstract P125: Baicalein Preconditioning Protects Murine Cardiomyocytes From Ischemia/reperfusion Injury via Mitochondrial Oxidant and Akt Signaling
Introduction: Most cardioprotection studies with flavonoid compounds focus on their antioxidant properties. However, others have reported that flavoinoids such as baicalein, derived from the root of Scutellaria baicalensis Georgi, can protect cardiomyocytes from hypoxia/reoxygenation injury via a prooxidant mechanism. Our prior work of preconditioning (PC) cardioprotection in chick cardiomyocytes suggests that both mitochondrial oxidant generation and related survival kinase signaling (e.g. PKC, Akt) are important components of adaptive PC. We hypothesized that baicalein triggers PC protection against murine cardiomyocyte ischemia/reperfusion (I/R) injury via non-lethal mitochondrial oxidant generation and Akt activation.
Methods: Cardiomyocytes, isolated from 1–2-day old C57Bl6/J mice, were exposed to 90 min simulated ischemia and 3 h reperfusion. Cells were preconditioned by 10 min baicalein (10 μM), then 10 min wash out followed by I/R. Cell viability was evaluated by propidium iodide. Oxidant production was measured using 6-carboxy-2′, 7′-dichloro-dihydrofluorescein diacetate (6-carboxy-H2DCFDA). Akt phosphorylation was analyzed by Western Blot.
Results: Baicalein pretreatment (10 μM) within 10 min prior to I/R significantly increased cell oxidant generation over 2-fold (p<0.05), which was partially attenuated by myxothiazol (2 μM), a mitochondrial electron transport chain complex III inhibitor (p<0.05). Baicalein-PC significantly reduced cell death compared to I/R control (48.3±3.3% vs. 30.4±4.4%, n=4; p<0.01) and decreased cardiac enzyme release. At early reperfusion (15 min), the phosphorylation of Akt at sites Ser473 and Thr308 was increased significantly in baicalein treated cells compared to I/R controls. This enhanced phosphorylation of Akt was blocked by the Akt inhibitor API-2 (10 μM).
Conclusion: Baicalein treatment of murine cardiomyocytes induced transient mitochondrial oxidant generation within 10 min at complex III that triggered PC protection against I/R injury. In addition to previously described antioxidant properties, bacailein has unique pro-oxidant effects on the mitochondria that enhance Akt signaling during reperfusion of ischemic heart cells.