The Protection And Mechanisms Of Orientin Against Ischemia/Reperfusion (I/R) Injury In Cardiomyocytes

Bamboo leaves, Phyllostachys nigra, have been a staple of Chinese medicine for many years, and have anti-free-radical activity. Bamboo leaves are comparable to the leaves of Ginkgo biloba, which is the important source of natural antioxidants and free radical scavengers. Previous studies revealed that bamboo leave extracts (BLEs) protect rat against myocardial ischemia. Four flavonoid C-glycosides, isoorientin, orientin, isovitexin and vitexin, were isolated from bamboo leaves at the beginning and have been found to be distributed in many other plants.Mitochondria are important targets of cardioprotective signaling. Their role during reperfusion is especially critical, reperfusion could cause apoptosis by mitochondrial apoptotic pathway via mitochondrial Ca2+ uniporter (MCU) and mitochondrial permeability transition pores (mPTP). After the process of myocardial ischemia, condition of mPTP is an important determinant of cardiomyocytes live or death. The relationship of orientin and mPTP in protecting heart against reperfusion-induced injury is still a new investigative area.In H9c2 cells, mitochondria are very important in calcium homoeostasis. In mitochondrial membrane, MCU controls the mitochondrial and cytosolic calcium levels, regulating cardiomyocytes apoptosis. Moreover, the relationship of orientin with MCU in H9c2 cells subjected to ischemia/reperfuison injury is still elusive.Recent studies have paied especial attention to the dynamics nature of mitochondria. Mitochondrial morphology and dynamics are both affectd by the interactions of mitochondria with cytoskeletal filaments. Furthermore, this influence could cause cellular changes during ischemia/reperfusion process.The results in this study indicated that the protective effect of orientin in H9c2 cardiomyocytes subjected to ischemia/reperfusion is associated with attenuation of mPTP opening, MCU opening, the following mitochondrial dysfunction. And further investigation revealed that all these benefical effects were associated with orientin-mediated inhibition of reactive oxygen species (ROS) generation, repolarization of mitochondrial membrane potential, increase of mitochondrial calcium level, improvement of Bcl-2 expression level, and inhibition of Bax and Smac/DIABLO expression levels. We found that orientin could reduce the release of cytochrome c. We also found that orientin could participate in the association of mitochondria with microtubules and sustain mitochondrial morphology and dynamics.In a word, we indicate that orientin protects H9c2 cells during reperfusion by inhibiting mPTP opening and MCU opening, the phosphatidylinositol 3-kinase (P13K) dependent pathway and ubiquitin-proteasome system (UPS) may be involved in these roles of orientin. As mitochondrial morphologies determine mitochondrial functions, research also reveals that a potentially important relationship between the orientin-mediated protection of microtubules and the regulation of mitochondria in H9c2 cells.