An update on cardioprotection: a review of the latest adjunctive therapies to limit myocardial infarction size in clinical trials

Endocrine protection of ischemic myocardium by FGF21 from the liver and adipose tissue

Myocardial ischemia, while causing cardiomyocyte injury, can activate innate protective processes, enhancing myocardial tolerance to ischemia. Such processes are present in not only the heart, but also remote organs. In this investigation, we demonstrated a cardioprotective process involving FGF21 from the liver and adipose tissue. In response to myocardial ischemia/reperfusion injury in the mouse, FGF21 was upregulated and released from the hepatic cells and adipocytes into the circulation and interacted with FGFR1 in cardiomyocytes under the mediation of the cell membrane protein β-Klotho, inducing FGFR1 phosphorylation. This action caused phosphorylation of the signaling molecules PI3K p85, Akt1, and BAD, thereby reducing caspase 3 activity, cell death, and myocardial infarction in association with improvement of myocardial function. These observations suggest that FGF21 is upregulated and released from the liver and adipose tissue in myocardial injury, contributing to myocardial protection by the mediation of the FGFR1/β-Klotho–PI3K–Akt1–BAD signaling network.

Impact of exercise training on redox signaling in cardiovascular diseases

Reactive oxygen and nitrogen species regulate a wide array of signaling pathways that governs cardiovascular physiology. However, oxidant stress resulting from disrupted redox signaling has an adverse impact on the pathogenesis and progression of cardiovascular diseases. In this review, we address how redox signaling and oxidant stress affect the pathophysiology of cardiovascular diseases such as ischemia-reperfusion injury, hypertension and heart failure. We also summarize the benefits of exercise training in tackling the hyperactivation of cellular oxidases and mitochondrial dysfunction seen in cardiovascular diseases.

Cardioprotection against myocardial reperfusion injury: successes, failures, and perspectives

The past few decades have witnessed an enormous number of research strategies aimed at protecting the heart against myocardial ischemia-reperfusion injury. Several randomized clinical trials are nowadays in progress testing whether promising therapeutic strategies aimed at preventing lethal reperfusion injury can be translated from bench to bedside. Many of these interventions, either pharmacological or mechanical, are targeting mitochondria as the final effectors of cardioprotection. Despite encouraging pre-clinical studies and small proof of concept clinical trials, there are still several limitations that may jeopardize the efficacy of cardioprotective strategies. These limitations include clinical setting, patient profile, drug administration, and methods for evaluating treatment efficacy. Identifying potential mechanistic and methodological pitfalls in the field may improve future translational research.

Is oxytocin a therapeutic factor for ischemic heart disease?

Ischemic heart disease (IHD) is among the most important and top ranked causes of death in the world, and its preventive and interventional mechanisms are actively being investigated. Preconditioning may still be beneficial in some situations such as IHD. Development of cardioprotective agents to improve myocardial function, to decrease the incidence of arrhythmias, to delay the onset of necrosis, and to limit the total extent of infarction during IHD is of great clinical importance. In order to reduce morbidity, a new treatment modality must be developed, and oxytocin may indeed be one of the candidates. There is increasing experimental evidence indicating that oxytocin may have cardioprotective effects either by decreasing the extent of reperfusion injury or by pharmacologic preconditioning activity. This review shows that in the presence of oxytocin, the cardioprotective effects may be increased to some extent. The presented board of evidence focuses on the valuable effects of oxytocin on myocardial function and candidates it for future clinical studies in the realm of ischemic heart diseases.

Selective kinin receptor agonists as cardioprotective agents in myocardial ischemia and diabetes

Cardiac ischemia is a leading cause of death, especially in diabetic patients. The diabetic ischemic heart is resistant experimentally to established cardioprotective treatments. New pharmacological approaches to cardiac protection are warranted. The kallikrein-kinin system is involved in myocardial protection in ischemia. Respective roles of B1 (B1R) and B2 (B2R) receptors remain controversial. We tested whether pharmacological activation of kinin receptors may have therapeutic effect in cardiac ischemia-reperfusion in nondiabetic (NDiab) and diabetic (Diab) mice. We assessed effect on infarct size (IS) and signaling pathways involved in myocardial protection of potent selective pharmacological agonists of B1R or B2R given at reperfusion. In NDiab mice, a B2R agonist reduced IS significantly by 47%, similarly to ramiprilat or ischemic postconditioning, via activation of phosphoinositide 3 kinase/Akt pathway leading to inhibition of glycogen synthase kinase-3β (GSK-3β). B1R agonist had no effect on IS. In contrast, in Diab mice, the B2R agonist, ramiprilat, or ischemic postconditioning failed to reduce IS but a B1R agonist significantly reduced IS by 44% via activation of phosphoinositide 3 kinase/Akt and extracellular signal-regulated kinase 1/2, both leading to GSK-3β inhibition. Differential effect of B2R or B1R agonists in NDiab and Diab mice can be linked to inactivation of B2R signaling and induction of B1R in heart of Diab mice. Thus, a pharmacological B2R agonist is cardioprotective in acute ischemia in nondiabetic animals. B1R agonist overcomes resistance of diabetic heart to cardioprotective treatments. Pharmacological activation of B1R and B2R may become a treatment for diabetic and nondiabetic patients, respectively, in acute coronary syndromes.

Imaging the myocardial microcirculation post-myocardial infarction

The myocardial microcirculation provides the vital pressure control and metabolic homeostasis for normal muscle function. Microvascular dysfunction is implicated in chronic cardiac disease and can signify higher risk, but its effect in acute myocardial infarction (AMI) can be profound. Modern management of AMI is focussed entirely on timely epicardial coronary patency, but as a result can leave microcirculatory devastation in its wake. The 'no-reflow' phenomenon occurs in up to 40 % of those successfully reperfused following an ST-elevation AMI (STEMI), and reflects significant microvessel injury that at its most severe involves both microvascular obstruction (MVO) and intramyocardial haemorrhage. Myocardial contrast echocardiography and cardiac magnetic resonance imaging have both led the field in establishing MVO as the prime determinant of adverse left ventricular (LV) remodeling, LV dysfunction, heart failure and increased mortality. These imaging techniques will be essential to support future research endeavours and shift focus to the maintenance of microvascular flow in AMI.

Magnesium orotate elicits acute cardioprotection at reperfusion in isolated and in vivo rat hearts

Orotic acid and its salts chronically administered have been shown to significantly improve cardiac function in pathological settings associated with ischemia–reperfusion (I/R) injury. The aim of our study was to investigate the effect of magnesium orotate (Mg-Or) administration at the onset of post-ischemic reperfusion on myocardial function and infarct size (IS). Ex-vivo experiments performed on isolated perfused rat hearts were used to compare Mg-Or administration with a control group (buffer treated), ischemic post-conditioning, orotic acid treatment, and MgCl2 treatment. Mg-Or administration was also investigated in an in-vivo model of regional I/R performed in rats undergoing reversible coronary ligation. The effect of Mg-Or on mitochondrial permeability transition pore (mPTP) opening after I/R was investigated in vitro to gain mechanistic insights. Both ex-vivo and in-vivo experiments showed a beneficial effect from Mg-Or administration at the onset of reperfusion on myocardial function and IS. In-vitro assays showed that Mg-Or significantly delayed mPTP opening after I/R. Our data suggest that Mg-Or administered at the very onset of reperfusion may preserve myocardial function and reduce IS. This beneficial effect may be related to a significant reduction of mPTP opening, a usual trigger of cardiac cell death following I/R.

Adaptive response, evidence of cross-resistance and its potential clinical use

Organisms and their cells are constantly exposed to environmental fluctuations. Among them are stressors, which can induce macromolecular damage that exceeds a set threshold, independent of the underlying cause. Stress responses are mechanisms used by organisms to adapt to and overcome stress stimuli. Different stressors or different intensities of stress trigger different cellular responses, namely induce cell repair mechanisms, induce cell responses that result in temporary adaptation to some stressors, induce autophagy or trigger cell death. Studies have reported life-prolonging effects of a wide variety of so-called stressors, such as oxidants, heat shock, some phytochemicals, ischemia, exercise and dietary energy restriction, hypergravity, etc. These stress responses, which result in enhanced defense and repair and even cross-resistance against multiple stressors, may have clinical use and will be discussed, while the emphasis will be on the effects/cross-effects of oxidants.

Effects of intracoronary delivery of allogenic bone marrow-derived stem cells expressing heme oxygenase-1 on myocardial reperfusion injury

Heme oxygenase-1 (HO-1) decreases apoptosis, inflammation and oxidative stress. The aim of the study was to investigate the effects of intracoronary infusion of allogenic bone marrow cells (BMC) overexpressing HO-1 in the porcine model of myocardial infarction (MI). MI was produced by balloon occlusion of a coronary artery. BMC were transduced with adenoviruses encoding for HO-1 (HO-1 BMC) or GFP (GFP-BMC) genes. Prior to reperfusion animals received HO-1 BMC, control BMC (unmodified or GFP-BMC) or placebo. Left ventricular (LV) ejection fraction (EF), shortening fraction (SF), end-systolic and end-diastolic diameters (EDD, ESD) were assessed by echocardiography before, 30 minutes (min) and 14 days after reperfusion. BMC significantly improved LVEF and SF early (30 min) after reperfusion as well as after 14 days. Early after reperfusion HO-1 BMC were significantly more effective than control BMC, but after 14 days, there were no differences. There were no effect of cells on LV remodelling and diastolic function. Both HO-1 BMC and control BMC significantly reduced the infarct size vs. placebo (17.2 ± 2.7 and 18.8 ± 2.5, respectively, vs. 27.5 ± 5.1, p= 0.02) in histomorphometry. HO-1-positive donor BMC were detected in the infarct border area in pigs receiving HO-1-cells. No significant differences in expression of inflammatory genes (SDF-1, TNF-α, IL-6, miR21, miR29a and miR133a) in the myocardium were found. In conclusion, intracoronary delivery of allogeneic BMC immediately prior to reperfusion improved the LVEF and reduced the infarct size. HO-1 BMC were not superior to control cells after 14 days, however, produced faster recovery of LVEF. Transplanted cells survived in the peri-infarct zone.