Rapamycin treatment of healthy pigs subjected to acute myocardial ischemia-reperfusion injury attenuates cardiac functions and increases myocardial necrosis.

BACKGROUND: The mammalian target of rapamycin (mTOR) pathway is a major regulator of cell immunity and metabolism. mTOR is a well-known suppressor of tissue rejection in organ transplantation. However, it has other nonimmune functions: in the cardiovascular system, it is a regulator of heart hypertrophy and locally, in coated vascular stents, it inhibits vascular wall cell growth and hence neointimal formation/restenosis. Because the mTOR pathway plays major roles in normal cell growth, metabolism, and survival, we hypothesized that inhibiting it with rapamycin before an acute myocardial ischemia-reperfusion injury (IRI) would confer cardioprotection by virtue of slowing down cardiac function and metabolism. METHODS: Yorkshire pigs received either placebo or 4 mg/d rapamycin orally for 7 days before the IRI. All animals underwent median sternotomy, and the mid-left anterior descending coronary artery was occluded for 60 minutes followed by 120 minutes of reperfusion. Left ventricular pressure-volume data were collected throughout the operation. The ischemic and infarcted areas were determined by monastral blue and triphenyltetrazolium chloride staining, respectively, and plasma cardiac troponin I concentration. mTOR kinase activities were monitored in remote cardiac tissue by Western blotting with specific antibodies against mTOR substrates phosphorylating sites. RESULTS: Rapamycin before treatment impaired endothelial-dependent vasorelaxation, attenuated cardiac function during IRI, and increased myocardial necrosis. Western blotting confirmed effective inhibition of myocardial mTOR kinase activities. CONCLUSIONS: Acute myocardial IRI, in healthy pigs treated with rapamycin, is associated with decreased cardiac function and higher myocardial necrosis.

Oxidative stress improves coronary endothelial function through activation of the pro-survival kinase AMPK.

Age-associated decline in cardiovascular function is believed to occur from the deleterious effects of reactive oxygen species (ROS). However, failure of recent clinical trials using antioxidants in patients with cardiovascular disease, and the recent findings showing paradoxical role for NADPH oxidase-derived ROS in endothelial function challenge this long-held notion against ROS. Here, we examine the effects of endothelium-specific conditional increase in ROS on coronary endothelial function. We have generated a novel binary (Tet-ON/OFF) conditional transgenic mouse (Tet-Nox2:VE-Cad-tTA) that induces endothelial cell (EC)-specific overexpression of Nox2/gp91 (NADPH oxidase) and 1.8?0.42-fold increase in EC-ROS upon tetracycline withdrawal (Tet-OFF). We examined ROS effects on EC signaling and function. First, we demonstrate that endothelium-dependent coronary vasodilation was significantly improved in Tet-OFF Nox2 compared to Tet-ON (control) littermates. Using EC isolated from mouse heart, we show that endogenous ROS increased eNOS activation and nitric oxide (NO) synthesis through activation of the survival kinase AMPK. Coronary vasodilation in Tet-OFF Nox2 animals was CaMKK?-AMPK-dependent. Finally, we demonstrate that AMPK activation induced autophagy and thus, protected ECs from oxidant-induced cell death. Together, these findings suggest that increased ROS levels, often associated with cardiovascular conditions in advanced age, play a protective role in endothelial homeostasis by inducing AMPK-eNOS axis.