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Myocardial infarction is a leading cause for morbidity and mortality worldwide. The only
viable treatment for the ischemic insult is timely reperfusion, which further exacerbates myocardial
injury. Maintaining mitochondrial function is crucial in preserving cardiomyocyte function in
ischemia reperfusion (IR) injury. Poloxamer (P) 188 has been shown to improve cardiac IR injury
by improving cellular and mitochondrial function. The aim of this study was to show if P188
postconditioning has direct protective effects on mitochondrial function in the heart. Langendorff
prepared rat hearts were subjected to IR injury ex-vivo and reperfused for 10 min with 1 mM P188
vs. vehicle. Cardiac mitochondria were isolated with 1 mM P188 vs. 1 mM polyethylene glycol
(PEG) vs. vehicle by differential centrifugation. Mitochondrial function was assessed by adenosine
triphosphate synthesis, oxygen consumption, and calcium retention capacity. Mitochondrial function
decreased significantly after ischemia and showed mild improvement with reperfusion. P188 did
not improve mitochondrial function in the ex-vivo heart, and neither further P188 nor PEG induced
direct mitochondrial protection after IR injury in this model.
With high prevalence and mortality, myocardial infarction constitutes a social and economic burden in Germany and worldwide. Current guidelines for MI treatment require prompt reperfusion to salvage heart tissue and minimize short- and long-term complications. However, there are currently no treatments available to attenuate reperfusion injury. Ischemic as well as pharmacological post-conditioning have been identified as important clinical strategies to improve outcome. Membrane stabilizers, like Poloxamer 188 (P188), have been shown to improve myocardial ischemia reperfusion (IR) injury and mitochondrial function but have not yet been proven to directly offer mitochondrial protection. Mitochondrial function is crucial for cardiomyocyte function, and mitochondrial dysfunction plays an important role in myocardial injury.
In this study, hearts from 79 Sprague Dawley rats were isolated and perfused ex-vivo with oxygenated Krebs Buffer for 20 min before 30 min of no-flow ischemia. Hearts were reperfused for 10 min with Krebs buffer or 1 mM P188. Cardiac mitochondria were isolated with 1 mM P188 vs 1 mM polyethylene glycol (PEG) vs vehicle by differential centrifugation. Mitochondrial function was assessed as adenosine triphosphate (ATP) synthesis, oxygen consumption and calcium retention for complex I and II substrates of the respiratory chain.
An improvement of myocardial function with 10 min P188 post-conditioning could not be shown. Direct mitochondrial protection of P188 or PEG could not be observed in this model either. Further research is needed to ascertain whether P188 has a direct protective effect on mitochondria and, if so, on what pathways of IR injury it acts.