Estrogen attenuates cardiac ischemia-reperfusion injury via inhibition of calpain-mediated Bid cleavage

Although several studies have shown that the administration of 17β-estradiol (estrogen) is cardioprotective to ischemia-reperfusion (l/R), the molecular mechanisms are largely unknown. Therefore, we investigated the effects of estrogen on myocardial l/R injury in rat that were sham operated (Sham), ovariectomized (OVX), or ovariectomized and then given estrogen supplementation (OE). Langendorff-perfused rat hearts were subjected to l/R stimuli and the effects of estrogen were examined on cardiac performance. Additionally, we examined the mechanism of estrogen-mediated inhibition of apoptosis. Depression in cardiac contractile function and an increment of calpain activity were observed during l/R in the OVX rats. Estrogen replacement recovered cardiac contractile function and attenuated calpain activity, Bid cleavage, and caspases activities. Through in vitro assay using cardiomyocytes, we demonstrated that addition of H₂O₂ (100 μM) significantly increased calpain activity, which was attenuated by estrogen. Moreover, calpain activity was inhibited by calpain inhibitors such as ALLN or leupeptin, but not by caspase-8 inhibitor peptide. These results suggest that estrogen protects the heart against l/R injury through the decrease of calpain activity, Bid cleavage and caspase-8 activity. These apoptotic mechanisms may play a critical role on l/R-associated cardiac damage.