Reperfusion Injury

Cyclophilin D and myocardial ischemia-reperfusion injury: a fresh perspective

Reperfusion is characterized by a deregulation of ion homeostasis and generation of reactive oxygen species that enhance the ischemia-related tissue damage culminating in cell death. The mitochondrial permeability transition pore (mPTP) has been established as an important mediator of ischemia-reperfusion (IR)-induced necrotic cell death. Although a handful of proteins have been proposed to contribute in mPTP induction, cyclophilin D (CypD) remains its only bona fide regulatory component. In this review we summarize existing knowledge on the involvement of CypD in mPTP formation in general and its relevance to cardiac IR injury in specific. Moreover, we provide insights of recent advancements on additional functions of CypD depending on its interaction partners and post-translational modifications. Finally we emphasize the therapeutic strategies targeting CypD in myocardial IR injury. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".

Is further improvement of the treatment of acute coronary syndromes still possible?

Successful treatment of myocardial infarction related to early reperfusion therapy has caused growing interest in not only ischemic but also myocardial reperfusion injury. Most experimentally confirmed preservation myocardial reperfusion injury methods have failed in clinical practice. Probably one reason for their ineffectiveness was the very narrow "time window" necessitating application of protective methods before obtaining reperfusion. Reducing the myocardial necrosis and preservation of the left ventricular function are the main goals of the therapy. Experimental data suggest that up to 50% of the infarct size may be related to reperfusion injury. Function of the mitochondrial permeability transition pore (mPTP) in the inner mitochondrial membrane, being closed during myocardial ischemia and opening at the beginning of reperfusion, is the common element linking protective methods. Their opening gives rise to metabolic alterations and may lead to cardiomyocyte death (lethal reperfusion injury). That is why successful intervention, very difficult to achieve, has to take precedence over coronary blood flow restoration. Cyclosporin A, an mPTP blocker, was effective in the first small clinical trial in preservation of myocardial reperfusion injury in acute coronary syndrome intervention. Second mitochondrial injury action is related to generation of reactive oxygen species (ROS) including superoxide anions. Reactive oxygen species accumulation results in mitochondrial pH increase leading to mPTP opening. Discovery of a small molecule cationic peptide, readily penetrating cell membranes and concentrating in mitochondria, may give new therapy perspectives. Combining therapy may be possible as well.

Establishment of a reperfusion model in rabbits with acute myocardial infarction

Clinically effective cardioprotection under acute myocardial infarction (AMI) can only be achieved by establishing the mechanisms of reperfusion-induced cardiac cell death. In spite of the numerous earlier studies on the prevention of ischemia-reperfusion injury of myocardium, the problem of cardiac cell death upon reperfusion is not yet resolved. Even though animal models provide an immense opportunity in the understanding of the mechanisms of ischemia-reperfusion injury, clinically relevant animal models through which translation of this knowledge into clinic are lacking. In this work, we have established a reperfusion model in rabbits with induced AMI by obstructing and releasing the left anterior ventricular branch of left circumflex coronary artery, which is clinically more relevant. This was achieved by cutting the two left ribs of the rabbit followed by obstructing and releasing the artery unlike the traditional approach, which involves incision through sternum and blocking the anterior descending coronary artery. This animal model of ischemia-reperfusion more closely mimics the physiological condition and also the trauma the animal suffers is much smaller with higher survival rate and thus is a potentially better model for studying the pathology related to ischemia-reperfusion injury.