Ischemic and hypoxic preconditioning protect cardiac muscles via intracellular ROS signaling

Oxidative stress can cause extensive damage to cardiac tissue under reperfusion conditions. However, preconditioning the myocardium may diminish these negative effects and alleviate reperfusion injury. There are a variety of preconditioning therapies, such as ischemic preconditioning (IPC) and hypoxic preconditioning (HPC), each targeting specific channels, receptors, and/or intracellular molecules. Ischemic preconditioning involves brief periods of ischemia followed by brief periods of reperfusion, thus strengthening the cardiac resistance for a longer period of ischemia. IPC involves complex mechanisms, some of which are still not completely understood today. Nevertheless, many studies have already established models of IPC. In addition, similar to IPC, HPC has also been recognized as preventing reperfusion injury. Reactive oxygen species (ROS) are known mediators of IPC and HPC. Particularly, mitochondria-generated ROS initiate activity of several beneficial preconditioning pathways. The role of ROS is paradoxical; low levels of ROS are key factors in signaling IPC/HPC, but high levels of ROS can contribute to increased oxidative stress on cardiomyocytes. Therefore, it is important to determine the molecular mechanism of IPC and HPC to avoid excessive accumulation of ROS to prevent cardiac injury. In this review, we will outline IPC and HPC, explaining the putative role of ROS in both pathways. We will also discuss preconditioning efficacy in certain conditions such as exercise and how the aging myocardium responds to preconditioning therapies.