Quercetin, but not rutin, attenuated hydrogen peroxide-induced cell damage via heme oxygenase-1 induction in endothelial cells.

Oxidative stress plays an important role in the pathogenesis of cardiovascular disease. Quercetin, a naturally occurring flavonoid presents in plants and human diet, has been reported to exert antioxidant properties in vivo and in vitro. The upregulation of antioxidant enzyme heme oxygenase-1 (HMOX1) in endothelial cells is considered to be beneficial in cardiovascular disease. In this work, we tested whether quercetin might suppress hydrogen peroxide (H2O2)-induced cell damage in endothelial cells by augmenting this cellular antioxidant defense. It was found that quercetin upregulated HMOX1 expression to protect endothelial cells against oxidative stress, and the protective effects of quercetin on H2O2-induced endothelial cell damage (such as loss of cell viability and reduction of nitric oxide) could be abolished by the specific small-interfering RNA against HMOX1 expression or HMOX1 activity inhibitor. In addition, the activation of ERK/Nrf2 signaling pathway was critical to the upregulation of HMOX1 induced by quercetin. Consistent with its non-effective ability to induce HMOX1, rutin (the glycoside of quercetin) showed less protective effects on H2O2-induced cell damage than quercetin. Therefore, quercetin could attenuate oxidative stress-induced endothelial cell damage at least partly through ERK/Nrf2/HMOX1 pathway. Our results also suggested a novel mechanism for the anti-oxidant property of quercetin and might explain in part the protective cardiovascular effects of diets rich in these compounds.