[en] Reperfusion injury triggered by blood flow restoration following an ischemic event contributes significantly to cellular damage occurring during myocardial infarction. A burst of reactive oxygen species (ROS) production in the mitochondria at the onset of reperfusion has a prominent role in this process, by a mechanism known as reverse electron transfer (RET). During ischemia succinate, the endogenous substrate of succinate dehydrogenase (SDH), accumulates in the myocardium. At reperfusion, succinate is rapidly oxidized by SDH, a process coupled with ROS generation. Despite the extensive research done in this subject, many questions remain to be answered. RET inhibition during reperfusion by the SDH reversible inhibitor malonate has shown protection against ischemia-reperfusion injury. Since multitargeted approaches may be beneficial in the clinical setting, we assessed, in an in vivo porcine model of transient coronary occlusion, whether intracoronary malonate administration into the area at risk at reperfusion, had additive effects against infarction with remote ischemic conditioning (RIC), applied during ischemia. Our results confirm previous findings on the strong protective actions of both malonate and RIC and demonstrate that their combination does not result in additive effects. Part of the succinate that accumulates in the myocardium is released into circulation upon reperfusion. Accordingly, we also evaluated succinate and other citric acid cycle metabolites as potential biomarkers of myocardial injury. In our porcine model, plasma succinate levels markedly increased during reperfusion in the great cardiac vein, where they correlated with infarct size, but not in peripheral blood. No correlation was detected between peripheral plasma levels of succinate or other metabolites and cardiac magnetic resonance variables in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention. Therefore, the use of succinate as a biomarker would be restricted to blood obtained from the coronary sinus, and longer periods after reperfusion may be needed for increased succinate peripheral plasma concentrations. No data are available on endogenous RET modulators, and the gap junction protein connexin 43 (Cx43) is a good candidate, since it is found at the inner mitochondrial membrane of subsarcolemmal mitochondria. In a Cx43 transgenic knock-out mice, Cx43 deficiency decreased ROS production by RET in isolated subsarcolemmal mitochondria, as compared with control animals, but not in interfibrillar mitochondria. This effect was associated with a decrease in the amount of coenzyme Q and in its reduced state, but not with changes in mitochondrial membrane potential or succinate accumulation at the end of ischemia. This fact may explain, at least in part, the marked protection these Cx43-deficient animals have against myocardial ischemia-reperfusion injury, as assessed in isolated hearts submitted to global ischemia-reperfusion, and that transient, reversible inhibition of SDH with malonate does not exert additional protection. ROS production is crucial in the deleterious cardiovascular effects of air pollution. Thus, we assessed whether air pollution influences RET in rats intratracheally instilled with saline containing or not diesel exhaust particles. Particulate matter exposure reduced the number of viable mitochondria and enhanced mitochondrial ROS production when using substrates feeding complex I, but these effects were independent of RET. In addition, diesel exhaust particle exposure did not modify infarct size in isolated rat hearts submitted to global ischemia-reperfusion. In conclusion, despite combination of SDH inhibition and RIC do not show additive effects against infarct size, concentrations of its endogenous substrate succinate correlate with infarct size in blood from the great cardiac vein, but not in peripheral blood. In addition, RET is modulated by Cx43 in a coenzyme Q-dependent manner, but it is not altered by particulate matter exposure.

[es] El daño por reperfusion tras la restauración del flujo sanguíneo posterior a la isquemia contribuye significativamente al infarto de miocardio. La producción de especies reactivas del oxigeno (ROS) en la mitocondria al inicio de la reperfusión mediante la transferencia reversa de electrones (RET) es clave en este proceso. El succinato, substrato endogeno de la succinato deshidrogenasa (SDH), se acumula en el miocardio durante la isquemia, y su rápida oxidación por esta enzima durante la reperfusión está acoplada a la generación de ROS, aunque quedan preguntas por responder al respecto. La inhibicion de la RET durante la reperfusion mediante malonato, un inhibidor reversible de la SDH, protege contra el daño por isquemia-reperfusion. Hemos evaluado, en un modelo porcino de oclusion coronaria transitoria in vivo, si la administración intracoronaria de malonato en el área en riesgo en la reperfusion tiene efectos aditivos con el condicionamiento isquemico remoto (RIC) aplicado durante la isquemia. Nuestros resultados confirman los efectos protectores del malonato y del RIC observados en estudios anteriores, y demuestran que su combinacion no produce efectos aditivos. Parte del succinato acumulado en el miocardio durante la isquemia es liberado al torrente sanguineo al inicio de la reperfusion. Hemos determinado el potencial del succinato y otros metabolitos del ciclo de Krebs como biomarcadores de daño miocardico. En nuestro modelo porcino, el succinato aumentó durante la reperfusion en muestras plasmáticas de la gran vena cardiaca correlacionando con el tamaño del infarto, pero no en sangre periferica. En pacientes con infarto de miocardio con elevacion del segmento ST sometidos a angioplastia primaria no se encontró correlacion entre los niveles de succinato u otros metabolitos y las variables de resonancia magnetica cardiaca. Por lo tanto, el uso del succinato como biomarcador quedaria restringido a sangre del seno coronario. Ademas, periodos mas prolongados despues de la reperfusion podrían ser necesarios para observar un aumento en sangre periférica. No se conoce la existencia de moduladores endogenos de la RET, y un buen candidato sería la conexina 43 (Cx43), componente de las uniones gap y presente en la membrana mitocondrial interna de las mitocondrias subsarcolemales. La deficiencia de Cx43 en un modelo transgénico redujo la produccion de ROS por RET en mitocondrias subsarcolemales aisladas, pero no en interfibrilares. Este efecto se asoció con una disminución de la coenzima Q y de su estado reducido, pero sin cambios en el potencial de membrana mitocondrial o en la acumulacion de succinato al final de la isquemia. Estos hallazgos podrian explicar en parte la proteccion tan significativa que la deficiencia de Cx43 ejerce frente al daño por reperfusion, evaluada en corazones aislados tras isquemia global y reperfusion, y que la inhibicion reversible de la SDH con malonato no ejerza proteccion adicional. La produccion de ROS es crucial en los efectos cardiovasculares adversos de la exposicion a contaminacion ambiental. En ratas sometidas a instilacion intratraqueal de suero fisiologico con o sin particulas diesel, la exposición a materia particulada redujo el numero de mitocondrias viables y aumentó la produccion de ROS con substratos del complejo I de forma independiente de la RET. Ademas, la exposicion a particulas diesel no afectó al tamaño del infarto en corazones aislados de rata sometidos a isquemia-reperfusion global. En conclusion, aunque la combinacion de la inhibicion de la SDH y el RIC no muestra efectos aditivos contra el tamaño del infarto, las concentraciones de succinato en la gran vena cardíaca correlacionan con el tamaño del infarto, pero no en sangre periferica. Ademas, la RET esta modulada por la Cx43 de forma dependiente de la coenzima Q, pero no se ve alterada por la exposicion a particulas diesel.