Participation of caspase-3-like protease in necrotic cell death of myocardium during ischemia-reperfusion injury in rat hearts

What can we do to optimize mitochondrial transplantation therapy for myocardial ischemia-reperfusion injury?

Mitochondrial transplantation is a promising solution for the heart following ischemia-reperfusion injury due to its capacity to replace damaged mitochondria and restore cardiac function. However, many barriers (such as inadequate mitochondrial internalization, poor survival of transplanted mitochondria, few mitochondria colocalized with cardiac cells) compromise the replacement of injured mitochondria with transplanted mitochondria. Therefore, it is necessary to optimize mitochondrial transplantation therapy to improve clinical effectiveness. By analogy, myocardial ischemia-reperfusion injury is like a withered flower, it needs to absorb enough nutrients to recover and bloom. In this review, we present a comprehensive overview of "nutrients" (source of exogenous mitochondria and different techniques for mitochondrial isolation), "absorption" (mitochondrial transplantation approaches, mitochondrial transplantation dose and internalization mechanism), and "flowering" (the mechanism of mitochondrial transplantation in cardioprotection) for myocardial ischemia-reperfusion injury.

Heart Preservation Using Continuous Ex Vivo Perfusion Improves Viability and Functional Recovery

BACKGROUND

Cold static storage (CS) is a proven preservation method for heart transplantion, yet early postoperative graft dysfunction remains prevalent, so continuous perfusion (CP) during ex vivo transport may improve viability and function of heart grafts.

METHODS AND RESULTS

Canine hearts underwent CP (n=9) or CS (n=9) for 6 h while intramyocardial pH was continuously monitored. Biopsies were assayed for ATP, caspase-3, malondialdehyde (MDA), and endothelin-1 (ET-1) levels at baseline, after preservation (t1), and after 1 h of blood reperfusion on a Langendorff model (t2). Functional recovery was determined at t2 by +dP/dt, -dP/dt, developed pressure, peak pressure and end-diastolic pressure. CP resulted in higher tissue pH and ATP stores and reduced caspase-3, MDA and ET-1 levels compared with CS at both t1 and t2. Post reperfusion recovery was significantly greater in CP vs CS for all myocardial functional parameters except end-diastolic pressure. Weight gain was significantly increased in CP vs CS at t1, but not at t2.

CONCLUSIONS

Low-grade tissue acidosis and energy depletion occur during CS and are associated with oxidative injury and apoptosis during reperfusion. CP attenuates these biochemical and pathologic manifestations of tissue injury, together with improved myocardial recovery, despite mild, transient edema.

CaMKII inhibition protects against necrosis and apoptosis in irreversible ischemia-reperfusion injury

OBJECTIVES

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the regulation of cardiac excitation-contraction coupling (ECC) as well as in apoptotic signaling and adverse remodeling. The goal of the present study is to investigate the role of CaMKII in irreversible ischemia and reperfusion (I/R) injury.

METHODS

Isovolumic Langendorff perfused rat hearts were subjected to global no-flow I/R (45 min/120 min), and isolated myocytes were subjected to a protocol of simulated I/R (45 min simulated ischemia/60 min reoxygenation) either in the absence or presence of CaMKII inhibition [KN-93 (KN) or the CaMKII inhibitory peptide (AIP)].

RESULTS

In I/R hearts, an increase in CaMKII activity at the beginning of reperfusion was confirmed by the significantly increased phosphorylation of the Thr(17) site of phospholamban. In the presence of KN, contractile recovery at the end of reperfusion was almost double that of I/R hearts. This recovery was associated with a significant decrease in the extent of infarction, lactate dehydrogenase release (necrosis), TUNEL-positive cells, caspase-3 activity, and an increase in the Bcl-2/Bax ratio (apoptosis). In isolated myocytes, both KN and AIP prevented simulated I/R-induced spontaneous contractile activity and cell mortality. Similar results were obtained when inhibiting the reverse mode Na(+)/Ca(2+) exchanger (NCX) with KB-R7943, sarcoplasmic reticulum (SR) function with ryanodine and thapsigargin, or SR Ca(2+) release with tetracaine. In contrast, overexpression of CaMKII decreased cell viability from 52+/-3% to 26+/-2%.

CONCLUSIONS

Taken together, the present findings are the first to establish CaMKII as a fundamental component of a cascade of events integrating the NCX, the SR, and mitochondria that promote cellular apoptosis and necrosis in irreversible I/R injury.

Minimally-Diluted Blood Cardioplegia Supplemented With Potassium and Magnesium for Combination of 'Initial, Continuous and Intermittent Bolus' Administration

BACKGROUND

The present study was designed to examine the hypothesis that minimally-diluted blood cardioplegia (BCP) supplemented with potassium and magnesium provides superior myocardial protection in comparison with the standard-diluted BCP for a combination of 'initial, continuous, and intermittent bolus' BCP administration.

METHODS AND RESULTS

Seventy patients undergoing elective coronary revascularization between 1997 and 2001 (M : F =55:15, mean age 67.6+/-7.5 years) were randomly divided into 2 groups: Group C (n=35) was given the standard 4:1-diluted blood-crystalloid BCP, and Group M (n=35) was given minimally-diluted BCP supplemented with potassium-chloride and magnesium-sulfate. The BCP temperature was maintained at 30 degrees C. Cardioplegic arrest was induced with 2 min of initial antegrade BCP infusion, followed by continuous retrograde BCP infusion. Intermittent antegrade BCP was infused every 30 min for 2 min. The time required for achieving cardioplegic arrest was significantly shorter in Group M (47.5+/-16.3 vs 62.5+/-17.6 s, p<0.0001). The number of patients showing spontaneous heart beat recovery after reperfusion was significantly larger in Group M (28 vs 15, p=0.0029), and the number of patients suffering from atrial fibrillation during the postoperative period was significantly smaller in Group M (n=3 vs 11, p=0.034). Both the postoperative maximum dopamine dose (3.57+/-2.46 vs 5.44+/-2.23 microg/kg per min, p=0.0014) and peak creatine kinase-MB (19.5+/-8.5 vs 25.8+/-11.9 IU/L, p=0.0128) were significantly less in Group M. The number of patients showing paradoxical movement of the ventricular septum in the early postoperative echocardiography was significantly smaller in Group M (9 vs 24, p=0.0007).

CONCLUSIONS

These results suggest that 'initial, continuous and intermittent bolus' administration of minimally-diluted BCP supplemented with potassium and magnesium is a reliable and effective technique for intraoperative myocardial protection.