In vivo hyperoxic preconditioning protects against rat-heart ischemia/reperfusion injury by inhibiting mitochondrial permeability transition pore opening and cytochrome c release.

In vivo hyperoxic preconditioning (PC) has been shown to protect against ischemia/reperfusion (I/R) myocardial damage. Mitochondrial permeability transition pore (MPTP) opening is an important event in cardiomyocyte cell death occurring during I/R and therefore a possible target for cardioprotection. We tested the hypothesis that in vivo hyperoxic PC, obtained by mechanical ventilation of animals, could protect heart against I/R injury by inhibiting MPTP opening and cytochrome c release from mitochondria. Mechanically ventilated rats were first exposed to a short period of hyperoxia and isolated hearts were subsequently subjected to I/R in a Langendorff apparatus. Hyperoxic PC significantly improved the functional recovery of hearts on reperfusion, reduced the infarct size, and decreased necrotic damage as shown by the reduced release of lactate dehydrogenase. Mitochondria from hyperoxic PC hearts were less sensitive than mitochondria from reperfused heart to MPTP opening. In addition, hyperoxic PC prevented mitochondrial NAD(+) depletion, an indicator of MPTP opening, and cytochrome c release as well as cardiolipin oxidation/depletion associated with I/R. Together, these results demonstrate that hyperoxic PC protects against heart I/R injury by inhibiting MPTP opening and cytochrome c release. Thus, in vivo hyperoxic PC may represent a useful strategy for the treatment of cardiac I/R injury and could have potential applications in clinical practice.

Protective effect of melatonin against mitochondrial dysfunction associated with cardiac ischemia- reperfusion: role of cardiolipin.

Reactive oxygen species (ROS) are considered an important factor in ischemia/reperfusion injury to cardiac myocytes. Mitochondrial respiration, mainly at the level of complex I and III, is an important source of ROS generation and hence a potential contributor of cardiac reperfusion injury. Appropriate antioxidant strategies could be particularly useful to limit this ROS generation and associated mitochondrial dysfunction. Melatonin has been shown to effectively protect against ischemic-reperfusion myocardial damage. The mechanism by which melatonin exerts this cardioprotective effect is not well established. In the present study we examined the effects of melatonin on various parameters of mitochondrial bioenergetics in a Langerdoff isolated perfused rat heart model. After isolation of mitochondria from control, ischemic-reperfused and melatonin-treated ischemic-reperfused rat heart, various bioenergetic parameters were evaluated such as rates of mitochondrial oxygen consumption, complex I and complex III activity, H2O2 production as well as the degree of lipid peroxidation, cardiolipin content, and cardiolipin oxidation. We found that reperfusion significantly altered all these mitochondrial parameters, while melatonin treatment had strong protective effect attenuating these alterations. This effect appears to be due, at least in part, to the preservation, by ROS attack, of the content and integrity of cardiolipin molecules which play a pivotal role in mitochondrial bioenergetics. Protection of mitochondrial dysfunction was associated with an improvement of post-ischemic hemodynamic function of the heart. Melatonin had also strong protective effect against oxidative alterations to complex I and III as well as to cardiolipin in isolated mitochondria.

Intraoperative antifibrinolysis and blood-saving techniques in cardiac surgery. Prospective trial of 3 antifibrinolytic drugs.

Sixty consecutive patients undergoing elective open-heart surgery were prospectively enrolled in a study to compare the efficacy of 3 different antifibrinolytic drugs to reduce postoperative bleeding and to reduce homologous blood requirements in combination with blood-saving techniques and restrictive indications for blood transfusion. The patients were randomized to 1 of 4 intraoperative treatment regimens: 1) control (no antifibrinolytic therapy); 2) epsilon-aminocaproic acid (10 g IV at induction of anesthesia, followed by infusion of 2 g/h for 5 hours); 3) tranexamic acid (10 mg/kg IV within 30 minutes after induction of anesthesia, followed by infusion of 1 mg/kg per hour for 10 hours); or 4) high-dose aprotinin (2 million KIU IV at induction of anesthesia and 2 million KIU added to the extracorporeal circuit, followed by infusion of 500 thousand KIU/h during surgery). Hemoconcentration and reinfusion of blood drained from the operative field and the extracorporeal circuit after operation were used in all patients. Indications for blood transfusion were hypotension, tachycardia, or both, with hemoglobin values < 8.5 g/dL; or severe anemia with hemoglobin values < 7 g/dL. Compared with the blood loss in the control group, patients receiving aprotinin and epsilon-aminocaproic acid showed significantly less postoperative blood loss at 1 hour (control, 128 +/- 94 mL; aprotinin, 54 +/- 47 mL, p = 0.01; and epsilon-aminocaproic acid, 69 +/- 35 mL, p = 0.03); this trend continued at 24 hours after operation (control, 724 +/- 280 mL; aprotinin, 344 +/- 106 mL, p < 0.0001; and epsilon-aminocaproic acid, 509 +/- 148 mL, p = 0.01). Aprotinin was significantly more efficient than epsilon-aminocaproic acid (p=0.002). Tranexamic acid did not have a statistically significant effect on blood loss. Homologous blood requirements were not significantly different among the groups; postoperative hematologic values and coagulation times were also comparable. Despite the efficacy of aprotinin and epsilon-aminocaproic acid shown in the present study, the blood requirements were not significantly different from those that are found when transfusions are restricted, autotransfusions are used, and blood from the operative field and extracorporeal circuit is concentrated and reinfused. Therefore, intraoperative antifibrinolysis may not be indicated in routine cardiac surgery when other blood-saving techniques are adopted.