Study on tolerance to ischemia-reperfusion injury and protection of ischemic preconditioning of type 1 diabetes rat heart

Ischemic preconditioning: Interruption of various disorders

Ischemic heart diseases are the leading cause of morbidity and mortality worldwide. Reperfusion of an ischemic heart is necessary to regain the normal functioning of the heart. However, abrupt reperfusion of an ischemic heart elicits a cascade of adverse events that leads to injury of the myocardium, i.e., ischemia-reperfusion injury. An endogenous powerful strategy to protect the ischemic heart is ischemic preconditioning, in which the myocardium is subjected to short periods of sublethal ischemia and reperfusion before the prolonged ischemic insult. However, it should be noted that the cardioprotective effect of preconditioning is attenuated in some pathological conditions. The aim of this article is to review present knowledge on how menopause and some metabolic disorders such as diabetes and hyperlipidemia affect myocardial ischemic preconditioning and the mechanisms involved.

What is Wrong With Cardiac Conditioning? We May be Shooting at Moving Targets

Early recanalization of the occluded culprit coronary artery clearly reduces infarct size in both animal models and patients and improves clinical outcomes. Unfortunately, reperfusion can seldom be accomplished before some myocardium infarcts. As a result there has been an intensive search for interventions that will make the heart resistant to infarction so that reperfusion could salvage more myocardium. A number of interventions have been identified in animal models, foremost being ischemic preconditioning. It protects by activating signaling pathways that prevent lethal permeability transition pores from forming in the heart’s mitochondria at reperfusion. Such conditioning can be accomplished in a clinically relevant manner either by staccato reperfusion (ischemic postconditioning) or by pharmacological activation of the conditioning signaling pathways prior to reperfusion. Unfortunately, clinical trials of ischemic postconditioning and pharmacologic conditioning have been largely disappointing. We suggest that this may be caused by inappropriate use as models intended to mimic the clinical scenario of young healthy animals that receive none of the many drugs currently given to our patients. Patients may be resistant to some forms of conditioning because of comorbidities, for example, diabetes, or they may already be conditioned by adjunct medications, for example, P2Y12 inhibitors or opioids. Incremental technological improvements in patient care may render some approaches to cardioprotection redundant, and thus the clinical target may be continually changing, while our animal models have not kept pace. In remote conditioning, a limb is subjected to ischemia/reperfusion prior to or during coronary reperfusion. Its mechanism is not as well understood as that of ischemic preconditioning, but the results have been very encouraging. In the present article, we will review ischemic, remote, and pharmacologic conditioning and possible confounders that could interfere with their efficacy in clinical trials in 2 settings of myocardial ischemia: (1) primary angioplasty in acute myocardial infarction and (2) elective angioplasty.

Adenosine transport blockade restores attenuated cardioprotective effects of adenosine preconditioning in the isolated diabetic rat heart: potential crosstalk with opioid receptors

Considering the reduced ability of cardiac fibroblasts to release adenosine and increased ability of interstitial adenosine uptake during diabetes mellitus, the present study investigated the effect of adenosine preconditioning and the existence of cross-talk with opioid receptor activation in the diabetic rat heart subjected to ischemia-reperfusion (I/R). Langendorff-perfused normal and streptozotocin (65 mg/kg, i.p., once)-administered diabetic (after 8-weeks) rat hearts were subjected to 30-min global ischemia and 120-min reperfusion. Myocardial infarct size using triphenyltetrazolium chloride staining, markers of cardiac injury such as lactate dehydrogenase (LDH) and creatine kinase (CK-MB) release, coronary flow rate (CFR) and myocardial oxidative stress were assessed. The diabetic rat heart showed high degree of I/R injury with increased LDH and CK-MB release, high oxidative stress and reduced CFR as compared to the normal rat heart. The adenosine preconditioning (10 μM) afforded cardioprotection against I/R injury in the normal rat heart that was prevented by naloxone (100 μM) pre-treatment. Conversely, adenosine preconditioning-induced cardioprotection was abolished in the diabetic rat heart. However, co-administration of dipyridamole (100 μM), adenosine reuptake inhibitor, markedly restored the cardioprotective effect of adenosine preconditioning in the diabetic rat heart, and this effect was also abolished by naloxone pre-treatment. The reduced myocardial availability of extracellular adenosine might explain the inability of adenosine preconditioning to protect the diabetic myocardium. The pharmacological elevation of extracellular adenosine restores adenosine preconditioning-mediated cardioprotection in the diabetic myocardium by possibly involving opioid receptor activation.