The ischemic heart--experimental models

The Coadministration of Levosimendan and Exenatide Offers a Significant Cardioprotective Effect to Isolated Rat Hearts against Ischemia/Reperfusion Injury

(1) Background: The present study aims to investigate the effect of administration of Levosimendan and Exenatide in various concentrations, as well as of the coadministration of those agents in an ischemia–reperfusion injury isolated heart model. (2) Methods: After 30 min of perfusion, the hearts underwent a 30 min period of regional ischemia followed by a 120 min period of reperfusion. All animals were randomly divided into 12 experimental groups of nine animals in each group: (1) Control, (2) Sham, (3) Digox (Negative control, Digoxin 1.67 μg/min), (4) Levo 1 (Levosimendan 0.01 μg/min), (5) Levo 2 (Levosimendan 0.03 μg/mL), (6) Levo 3 (Levosimendan 0.1 μg/min), (7) Levo 4 (Levosimendan 0.3 μg/min), (8) Levo 5 (Levosimendan 1 μg/min), (9) Exen 1 (Exenatide 0.001 μg/min), (10) Exen 2 (Exenatide 0.01 μg/min), (11) Exen 3 (Exenatide 0.1 μg/min) and (12) Combi (Levosimendan 0.1 µg/mL + Exenatide 0.001 μg/min). The hemodynamic parameters were recorded throughout the experiment. Arrhythmias and coronary flow were also evaluated. After every experiment the heart was suitably prepared and infarct size was measured. Markers of myocardial injury were also measured. Finally, oxidative stress was evaluated measuring reactive oxygen species. (3) Results: A dose-dependent improvement of the haemodynamic response was observed after the administration of both Levosimendan and Exenatide. The coadministration of both agents presented an even greater effect, improving the haemodynamic parameters further than the two agents separately. Levosimendan offered an increase of the coronary flow and both agents offered a reduction of arrhythmias. A dose-dependent reduction of the size of myocardial infarction and myocardial injury was observed after administration of Levosimendan and Exenatide. The coadministration of both agents offered a further improving the above parameters. Levosimendan also offered a significant reduction of oxidative stress. (4) Conclusions: The administration of Levosimendan and Exenatide offers a significant benefit by improving the haemodynamic response, increasing the coronary flow and reducing the occurrence of arrhythmias, the size of myocardial injury and myocardial oxidative stress in isolated rat hearts.

Protective effect of intermediate doses of hydrogen sulfide against myocardial ischemia-reperfusion injury in obese type 2 diabetic rats

OBJECTIVE

Subjects with type 2 diabetes (T2D) have lower circulating hydrogen sulfide (H₂S) levels following myocardial ischemia and a higher risk of mortality. The aim of this study was to determine the dose-dependent favorable effects of sodium hydrosulfide (NaSH) on myocardial ischemia-reperfusion (IR) injury in rats with T2D.

METHODS

T2D was induced using a high-fat diet (HFD) and low-dose of streptozotocin. Rats were divided into control, T2D, and T2D + NaSH groups. NaSH (0.28, 0.56, 1.6, 2.8, and 5.6 mg/kg) was administered intraperitoneally for 9 weeks. At the end of the study, heart from all rats were isolated and left ventricular developed pressure (LVDP) and the peak rates of positive and negative changes in LV pressure (±dp/dt) were recorded during baseline and following myocardial IR injury. In addition, infarct size as well as mRNA expression of H₂S- and nitric oxide (NO)-producing enzymes were measured.

RESULTS

In diabetic rats, NaSH only at doses of 0.56 and 1.6 mg/kg increased recovery of LVDP (16% and 42%), +dp/dt (25% and 35%) and -dp/dt (23% and 32%) as well as decreased infarct size (44% and 35%). At these doses, NaSH increased expressions of cystathionine γ-lyase (CSE) (440% and 271%) and endothelial NO synthase (eNOS) (232% and 148%) but it decreased the expressions of inducible NOS (iNOS) (55% and 71%). NaSH at 0.28, 2.8 and 5.6 mg/kg had no significant effects on these parameters.

CONCLUSION

NaSH had a bell-shaped cardioprotective effect against myocardial IR injury in rats with T2D. Higher tolerance to IR injury in heart isolated from type 2 diabetic rats treated with intermediate doses of NaSH is associated with higher CSE-derived H₂S and eNOS-derived NO as well as lower iNOS-derived NO.

Shenlian Extract Against Myocardial Injury Induced by Ischemia Through the Regulation of NF-κB/IκB Signaling Axis

Ischemic heart disease (IHD), caused predominantly by atherosclerosis, is a leading cause of global mortality. Our previous studies showed that Shenlian extract (SL) could prevent the formation of atherosclerosis and enhance the stability of atherosclerotic plaques. To further investigate the protective effects of SL on myocardial ischemic injury and its possible mechanisms, anesthetized dogs, ex vivo rat hearts, and H9c2 cardiomyocytes were used as models. The results showed that SL had a significant protective effect on the anesthetized dog ligating coronary artery model, reduced the degree of myocardial ischemia (Σ-ST), and reduced the scope of myocardial ischemia (N-ST). Meanwhile, SL alleviated ischemic reperfusion damage in ex vivo rat hearts with improved LVEDP and ± dp/dt_max values of the left ventricle. SL reduced the pathological changes of LDH, IL-1β, MDA, and NO contents, all of which are related to the expression of NF-κB. Further analysis by Bio-Plex array and signal pathway blocker revealed that the phosphorylation of IκB was a key factor for SL to inhibit myocardial ischemic injury, and the regulation of SL on IκB was primarily related to degradation of the IκB protein. These results provided dependable evidence that SL could protect against myocardial ischemic injury through the NF-κB signaling pathway.

Differential Effects of Anesthetics and Opioid Receptor Activation on Cardioprotection Elicited by Reactive Oxygen Species-Mediated Postconditioning in Sprague-Dawley Rat Hearts

BACKGROUND

Despite an array of cardioprotective interventions identified in preclinical models of ischemia-reperfusion (IR) injury, successful clinical translation has not been achieved. This study investigated whether drugs routinely used in clinical anesthesia influence cardioprotective effectiveness by reducing effects of reactive oxygen species (ROS), upstream triggers of cardioprotective signaling. Effects of propofol, sevoflurane, or remifentanil were compared on postischemic functional recovery induced by ROS-mediated postconditioning with Intralipid.

METHODS

Recovery of left ventricular (LV) work, an index of IR injury, was measured in isolated Sprague-Dawley rat hearts subjected to global ischemia (20 minutes) and reperfusion (30 minutes). Hearts were either untreated or were treated with postconditioning with Intralipid (1%, throughout reperfusion). Propofol (10 μM), sevoflurane (2 vol%), remifentanil (3 nM), or combinations thereof were administered peri-ischemically (before and during IR). The effects of anesthetics on ROS production were measured in LV cardiac fibers by Amplex Red assay under phosphorylating and nonphosphorylating conditions.

RESULTS

Recovery of LV work (expressed as percentage of the preischemic value ± standard deviation) in untreated hearts was poor (20% ± 7%) and was improved by Intralipid postconditioning (58% ± 8%, P = .001). In the absence of Intralipid postconditioning, recovery of LV work was enhanced by propofol (28% ± 9%, P = .049), sevoflurane (49% ± 5%, P < .001), and remifentanil (51% ± 6%, P < .001). The benefit of Intralipid postconditioning was abolished by propofol (33% ± 10%, P < .001), but enhanced by sevoflurane (80% ± 7%, P < .001) or remifentanil (80% ± 9%, P < .001). ROS signaling in LV fibers was abolished by propofol, but unaffected by sevoflurane or remifentanil. We conclude that propofol abolishes ROS-mediated Intralipid postconditioning by acting as a ROS scavenger. Sevoflurane and remifentanil are protective per se and provide additive cardioprotection to ROS-mediated cardioprotection.

CONCLUSIONS

These divergent effects of routinely used drugs in clinical anesthesia may influence the translatability of cardioprotective therapies such as Intralipid postconditioning.

Myocardial death and dysfunction after ischemia-reperfusion injury require CaMKIIδ oxidation

Reactive oxygen species (ROS) contribute to myocardial death during ischemia-reperfusion (I/R) injury, but detailed knowledge of molecular pathways connecting ROS to cardiac injury is lacking. Activation of the Ca²⁺/calmodulin-dependent protein kinase II (CaMKIIδ) is implicated in myocardial death, and CaMKII can be activated by ROS (ox-CaMKII) through oxidation of regulatory domain methionines (Met281/282). We examined I/R injury in mice where CaMKIIδ was made resistant to ROS activation by knock-in replacement of regulatory domain methionines with valines (MMVV). We found reduced myocardial death, and improved left ventricular function 24 hours after I/R injury in MMVV in vivo and in vitro compared to WT controls. Loss of ATP sensitive K⁺ channel (KATP) current contributes to I/R injury, and CaMKII promotes sequestration of KATP from myocardial cell membranes. KATP current density was significantly reduced by H₂O₂ in WT ventricular myocytes, but not in MMVV, showing ox-CaMKII decreases KATP availability. Taken together, these findings support a view that ox-CaMKII and KATP are components of a signaling axis promoting I/R injury by ROS.

Cardioprotective effect of 2,3-dehydrosilybin preconditioning in isolated rat heart

2,3-dehydrosilybin (DHS) is a minor component of silymarin, Silybum marianum seed extract, used in some dietary supplements. One of the most promising activities of this compound is its anticancer and cardioprotective activity that results, at least partially, from its cytoprotective, antioxidant, and chemopreventive properties. The present study investigated the cardioprotective effects of DHS in myocardial ischemia and reperfusion injury in rats. Isolated hearts were perfused by the Langendorff technique with low dose DHS (100 nM) prior to 30 min of ischemia induced by coronary artery occlusion. After 60 min of coronary reperfusion infarct size was determined by triphenyltetrazolium staining, while lactatedehydrogenase activity was evaluated in perfusate samples collected at several timepoints during the entire perfusion procedure. Signalosomes were isolated from a heart tissue after reperfusion and involved signalling proteins were detected. DHS reduced the extent of infarction compared with untreated control hearts at low concentration; infarct size as proportion of ischemic risk zone was 7.47 ± 3.1% for DHS versus 75.3 ± 4.8% for ischemia. This protective effect was comparable to infarct limitation induced by ischemic preconditioning (22.3 ± 4.5%). Selective inhibition of Src-family kinases with PP2 (4-Amino-3-(4-chlorophenyl)-1-(t-butyl)-1H-pyrazolo[3,4-d]pyrimidine) abrogated the protection afforded by DHS. This study provides experimental evidence that DHS can mediate Src-kinase-dependent cardioprotection against myocardial damage produced by ischemia/reperfusion injury.

Na/K-ATPase Signaling and Cardiac Pre/Postconditioning with Cardiotonic Steroids

The first reports of cardiac Na/K-ATPase signaling, published 20 years ago, have opened several major fields of investigations into the cardioprotective action of low/subinotropic concentrations of cardiotonic steroids (CTS). This review focuses on the protective cardiac Na/K-ATPase-mediated signaling triggered by low concentrations of ouabain and other CTS, in the context of the enduring debate over the use of CTS in the ischemic heart. Indeed, as basic and clinical research continues to support effectiveness and feasibility of conditioning interventions against ischemia/reperfusion injury in acute myocardial infarction (AMI), the mechanistic information available to date suggests that unique features of CTS-based conditioning could be highly suitable, alone /or as a combinatory approach.

Modified Langendorff technique for mouse heart cannulation: Improved heart quality and decreased risk of ischemia

Oscar Langendorff introduced the first method for isolating a heart with contractile activity in 1895. Since then, the Langendorff method has remained a powerful technique in cardiac research and has led to major advances in medicine. The primary goal of the Langendorff method is to provide an isolated heart with oxygen and metabolites via a cannula inserted into the aorta. The Langendorff heart is a complex in vitro technique used primarily in pharmacological and physiological research that allows the evaluation of multiple cardiac hemodynamic parameters including, but not limited to, contractility and heart rate. This article will first provide a brief background of the Langendorff method as well as details regarding organ isolation. Finally, the article will discuss the benefits of a new technique for hanging the isolated heart aorta and the benefits of this technique over traditional methods.

The Rapidly Evolving Concept of Whole Heart Engineering

Whole heart engineering represents an incredible journey with as final destination the challenging aim to solve end-stage cardiac failure with a biocompatible and living organ equivalent. Its evolution started in 2008 with rodent organs and is nowadays moving closer to clinical application thanks to scaling-up strategies to human hearts. This review will offer a comprehensive examination on the important stages to be reached for the bioengineering of the whole heart, by describing the approaches of organ decellularization, repopulation, and maturation so far applied and the novel technologies of potential interest. In addition, it will carefully address important demands that still need to be satisfied in order to move to a real clinical translation of the whole bioengineering heart concept.

The differential effects of FTY720 on functional recovery and infarct size following myocardial ischaemia/reperfusion

AIM

The aim of this study was to evaluate the effects of the sphingosine analogue, FTY720 (Fingolimod), on the outcomes of myocardial ischaemia/reperfusion (I/R) injury.

METHODS

Two concentrations of FTY720 (1 or 2.5 µM were administered either prior to (PreFTY), or following (PostFTY) 20 minutes' global (GI) or 35 minutes' regional ischaemia (RI) in the isolated, perfused, working rat heart. Functional recovery during reperfusion was assessed following both models of ischaemia, while infarct size (IFS) was determined following RI.

RESULTS

FTY720 at 1 µM exerted no effect on functional recovery, while 2.5 µM significantly impaired aortic output (AO) recovery when administered prior to GI (% recovery: control: 33.88 ± 6.12% vs PreFTY: 0%, n = 6-10; p < 0.001), as well as before and after RI ( % recovery: control: 27.86 ± 13.22% vs PreFTY: 0.62% ; p < 0.05; and PostFTY: 2.08%; p = 0.0585, n = 6). FTY720 at 1 µM administered during reperfusion reduced IFS (% of area at risk (AAR): control: 39.89 ± 3.93% vs PostFTY: 26.56 ± 4.32%, n = 6-8; p < 0.05), while 2.5 µM FTY720 reduced IFS irrespective of the time of administration ( % of AAR: control: 39.89 ± 3.93% vs PreFTY: 29.97 ± 1.03% ; and PostFTY: 30.45 ± 2.16%, n = 6; p < 0.05).

CONCLUSION

FTY720 exerted divergent outcomes on function and tissue survival depending on the concentration administered, as well as the timing of administration.

Effects of Curcumin on Parameters of Myocardial Oxidative Stress and of Mitochondrial Glutathione Turnover in Reoxygenation after 60 Minutes of Hypoxia in Isolated Perfused Working Guinea Pig Hearts

In cardiovascular surgery ischemia-reperfusion injury is a challenging problem, which needs medical intervention. We investigated the effects of curcumin on cardiac, myocardial, and mitochondrial parameters in perfused isolated working Guinea pig hearts. After preliminary experiments to establish the model, normoxia was set at 30 minutes, hypoxia was set at 60, and subsequent reoxygenation was set at 30 minutes. Curcumin was applied in the perfusion buffer at 0.25 and 0.5 μM concentrations. Cardiac parameters measured were afterload, coronary and aortic flows, and systolic and diastolic pressure. In the myocardium histopathology and AST in the perfusate indicated cell damage after hypoxia and malondialdehyde (MDA) levels increased to 232.5% of controls during reoxygenation. Curcumin protected partially against reoxygenation injury without statistically significant differences between the two dosages. Mitochondrial MDA was also increased in reoxygenation (165% of controls), whereas glutathione was diminished (35.2%) as well as glutathione reductase (29.3%), which was significantly increased again to 62.0% by 0.05 μM curcumin. Glutathione peroxidase (GPx) was strongly increased in hypoxia and even more in reoxygenation (255% of controls). Curcumin partly counteracted this increase and attenuated GPx activity independently in hypoxia and in reoxygenation, 0.25 μM concentration to 150% and 0.5 μM concentration to 200% of normoxic activity.

Acute Stress Decreases but Chronic Stress Increases Myocardial Sensitivity to Ischemic Injury in Rodents

Cardiovascular disease (CVD) is the largest cause of mortality worldwide, and stress is a significant contributor to the development of CVD. The relationship between acute and chronic stress and CVD is well evidenced. Acute stress can lead to arrhythmias and ischemic injury. However, recent evidence in rodent models suggests that acute stress can decrease sensitivity to myocardial ischemia-reperfusion injury (IRI). Conversely, chronic stress is arrhythmogenic and increases sensitivity to myocardial IRI. Few studies have examined the impact of validated animal models of stress-related psychological disorders on the ischemic heart. This review examines the work that has been completed using rat models to study the effects of stress on myocardial sensitivity to ischemic injury. Utilization of animal models of stress-related psychological disorders is critical in the prevention and treatment of cardiovascular disorders in patients experiencing stress-related psychiatric conditions.

Macrophages modulate engineered human tissues for enhanced vascularization and healing

Tissue engineering is increasingly based on recapitulating human physiology, through integration of biological principles into engineering designs. In spite of all progress in engineering functional human tissues, we are just beginning to develop effective methods for establishing blood perfusion and controlling the inflammatory factors following implantation into the host. Functional vasculature largely determines tissue survival and function in vivo. The inflammatory response is a major regulator of vascularization and overall functionality of engineered tissues, through the activity of different types of macrophages and the cytokines they secrete. We discuss here the cell-scaffold-bioreactor systems for harnessing the inflammatory response for enhanced tissue vascularization and healing. To this end, inert scaffolds that have been considered for many decades a "gold standard" in regenerative medicine are beginning to be replaced by a new generation of "smart" tissue engineering systems designed to actively mediate tissue survival and function.

Hydrogen sulfide reduces regional myocardial ischemia injury through protection of mitochondrial function

Hydrogen sulfide (H2S) is a signaling gasotransmitter, involved in various physiological and pathological processes. H2S-donating drugs have been tested to conjugate the beneficial effects of H2S with other pharmaceutical properties. It has been shown that the endogenous cystathionine-γ-lyase (CSE)/H2S pathway participates in myocardial ischemia injury in isolated hearts in rats. The present study aimed to investigate the cytoprotective action of H2S against acute myocardial ischemia injury in rats. Isolated rat hearts were perfused and subjected to ischemic conditions for 4 h. The hearts were assigned to five groups: Sham, model, infarct plus low-dose (5 µmol/l) NaHS, infarct plus middle-dose (10 µmol/l) NaHS and infarct plus high-dose (20 µmol/l) NaHS. The administration of NaHS enhanced the activity of CSE, increased the content of H2S and reduced infarct volumes following myocardial ischemia injury. Furthermore, the administration of NaHS attenuated the injury to organelles (including the mitochondria, nucleus and myofilaments) by reducing lactate dehydrogenase activity, decreasing the level of mitochondrial malondialdehyde and increasing the activities of superoxide dismutase and glutathione peroxidase in the ischemic myocardial mitochondria. These protective effects of H2S against myocardial ischemia injury appeared to be mediated by its antioxidant activities and the preservation of mitochondrial function.

An isolated working heart system for large animal models

Since its introduction in the late 19(th) century, the Langendorff isolated heart perfusion apparatus, and the subsequent development of the working heart model, have been invaluable tools for studying cardiovascular function and disease(1-15). Although the Langendorff heart preparation can be used for any mammalian heart, most studies involving this apparatus use small animal models (e.g., mouse, rat, and rabbit) due to the increased complexity of systems for larger mammals(1,3,11). One major difficulty is ensuring a constant coronary perfusion pressure over a range of different heart sizes - a key component of any experiment utilizing this device(1,11). By replacing the classic hydrostatic afterload column with a centrifugal pump, the Langendorff working heart apparatus described below allows for easy adjustment and tight regulation of perfusion pressures, meaning the same set-up can be used for various species or heart sizes. Furthermore, this configuration can also seamlessly switch between constant pressure or constant flow during reperfusion, depending on the user's preferences. The open nature of this setup, despite making temperature regulation more difficult than other designs, allows for easy collection of effluent and ventricular pressure-volume data.

Bioactive equivalence of combinatorial components identified in screening of an herbal medicine

Purpose

To identify bioactive equivalent combinatorial components (BECCs) in herbal medicines. The exact composition of effective components in herbal medicines is often elusive due to the lack of adequate screening methodology. Herein, we propose a hypothesis that BECCs accounting for the whole efficacy of original herbal medicines could be discovered from a complex mixture of constituents.

Methods

We developed a bioactive equivalence oriented feedback screening method and applied it to discover the BECCs from an herbal preparation Cardiotonic Pill (CP). The operations include chemical profiling of CP, followed by an iterative loop of determining, collecting and evaluating candidate BECCs.

Results

A combination of 18 compounds was identified as BECCs from CP, which accounts for 15.0% (w/w) of original CP. We have demonstrated that the BECCs were as effective as CP in cell models and in a rat model of myocardial infarction.

Conclusions

This work answers the key question of which are real bioactive components for CP that have been used in clinic for many years, and provides a promising approach for discovering BECCs from herbal medicines. More importantly, the BECCs could be extended to improve quality control of herbal products and inspire an herbal medicines based discovery of combinatorial therapeutics.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-013-1283-1) contains supplementary material, which is available to authorized users.

Establishment of a novel murine model of ischemic cardiomyopathy with multiple diffuse coronary lesions

Objectives

Atherosclerotic lesions of the coronary arteries are the pathological basis for myocardial infarction and ischemic cardiomyopathy. Progression of heart failure after myocardial infarction is associated with cardiac remodeling, which has been studied by means of coronary ligation in mice. However, this ligation model requires excellent techniques. Recently, a new murine model, HypoE mouse was reported to exhibit atherogenic Paigen diet-induced coronary atherosclerosis and myocardial infarction; however, the HypoE mice died too early to make possible investigation of cardiac remodeling. Therefore, we aimed to modify the HypoE mouse model to establish a novel model for ischemic cardiomyopathy caused by atherosclerotic lesions, which the ligation model does not exhibit.

Methods and Results

In our study, the sustained Paigen diet for the HypoE mice was shortened to 7 or 10 days, allowing the mice to survive longer. The 7-day Paigen diet intervention starting when the mice were 8 weeks old was adequate to permit the mice to survive myocardial infarction. Our murine model, called the “modified HypoE mouse”, was maintained until 8 weeks, with a median survival period of 36 days, after the dietary intervention (male, n = 222). Echocardiography demonstrated that the fractional shortening 2 weeks after the Paigen diet (n = 14) significantly decreased compared with that just before the Paigen diet (n = 6) (31.4±11.9% vs. 54.4±2.6%, respectively, P<0.01). Coronary angiography revealed multiple diffuse lesions. Cardiac remodeling and fibrosis were identified by serial analyses of cardiac morphological features and mRNA expression levels in tissue factors such as MMP-2, MMP-9, TIMP-1, collagen-1, and TGF-β.

Conclusion

Modified HypoE mice are a suitable model for ischemic cardiomyopathy with multiple diffuse lesions and may be considered as a novel and convenient model for investigations of cardiac remodeling on a highly atherogenic background.

Endothelin-B Receptors and Left Ventricular Dysfunction after Regional versus Global Ischaemia-Reperfusion in Rat Hearts

Background. Endothelin-1 (ET-1) is implicated in left ventricular dysfunction after ischaemia-reperfusion. ETA and ETB receptors mediate diverse actions, but it is unknown whether these actions depend on ischaemia type and duration. We investigated the role of ETB receptors after four ischaemia-reperfusion protocols in isolated rat hearts. Methods. Left ventricular haemodynamic variables were measured in the Langendorff-perfused model after 40- and 20-minute regional or global ischaemia, followed by 30-minute reperfusion. Wild-type (n = 39) and ETB-deficient (n = 41) rats were compared. Infarct size was measured using fluorescent microspheres after regional ischaemia-reperfusion. Results. Left ventricular dysfunction was more prominent in ETB-deficient rats, particularly after regional ischaemia. Infarct size was smaller (P = 0.006) in wild-type (31.5 ± 4.4%) than ETB-deficient (45.0 ± 7.3%) rats after 40 minutes of regional ischaemia-reperfusion. Although the recovery of left ventricular function was poorer after 40-minute ischaemia-reperfusion, end-diastolic pressure in ETB-deficient rats was higher after 20 than after 40 minutes of regional ischaemia-reperfusion. Conclusion. ETB receptors exert cytoprotective effects in the rat heart, mainly after regional ischaemia-reperfusion. Longer periods of ischaemia suppress the recovery of left ventricular function after reperfusion, but the role of ETB receptors may be more important during the early phases.

Longitudinal study of cardiac remodelling in rabbits following infarction

BACKGROUND

Cardiac remodelling following myocardial infarction (MI) is a complex, dynamic process. There have been few longitudinal studies of these changes.

METHODS

A 2-dimensional transthoracic echocardiography was performed on 20 rabbits, before and 1, 2, 4, 8, and 12 weeks after MI (n = 14) and twice for controls (n = 6). Chronic left ventricular (LV) infarct size was histologically characterized and correlated with mechanical function. A linear mixed model was used to analyze longitudinal and infarct size-related changes in LV end-systolic volume (ESV), end-diastolic volume (EDV), ejection fraction (EF), sphericity, circumferential strain, and wall motion score index.

RESULTS

Mean LV infarct size was 28.9% ± 9.3%. After MI, rapid remodelling occurred in LVESV, LVEF, and sphericity for 2 weeks and LVEDV for 4 weeks, with slower changes afterwards. LV infarct size correlated with LVESV (r = 0.76), LVEDV (r = 0.71), and LVEF (r = 0.69). Larger infarcts resulted in greater LVESV dilation (P = 0.04) and faster LVEDV (P < 0.01), LVEF (P < 0.01), and sphericity (P < 0.01) remodelling. Apical global circumferential strain and wall motion score index increased for 1 week, then stabilized, regardless of infarct size, and apical global circumferential strain was correlated with apical infarction (r = 0.58). Additionally, regional circumferential strain decreased in segments with severe (> 80%) infarction more quickly (P < 0.01) and by a greater degree (P = 0.04) compared with segments with minor (< 20%) infarction.

CONCLUSIONS

The most dynamic remodelling of cardiac function in this model occurred during the first 4 weeks, stabilizing thereafter, with changes maintained up to 12 weeks. Infarct size affected both the early rate and long-term extent of mechanical remodelling.

Optimizing dynamic interactions between a cardiac patch and inflammatory host cells

Damaged heart muscle has only a minimal ability for regeneration following myocardial infarction in which cardiomyocytes are lost to ischemia. The most clinically promising approach to regeneration of cardiac muscle currently under investigation is that of injecting cardiogenic repair cells or implanting a preformed tissue-engineered patch. While major advances are being made in the derivation of functional human cardiomyocytes and the development of tissue-engineering modalities for cardiac repair, the host environment into which the repair cells are placed is largely overlooked. Within seconds of myocardial ischemia, hypoxia sets in in the myocardium and the inflammatory response starts, characterized by rapid deployment of circulating cells and the release of paracrine and autocrine signals. Therefore, the inflammatory conditions under which these interactions take place, the design of the scaffold material used, and the maturity of the implanted cells will determine the outcomes of any stem cell-based therapy. We discuss here the interactions between implanted and inflammatory cells of the host, which are critical for the design of effective heart repair therapies.

Video Evaluation of the Kinematics and Dynamics of the Beating Cardiac Syncytium: An Alternative to the Langendorff Method

Many important observations and discoveries in heart physiology have been made possible using the isolated heart method of Langendorff. Nevertheless, the Langendorff method has some limitations and disadvantages such as the vulnerability of the excised heart to contusions and injuries, the probability of preconditioning during instrumentation, the possibility of inducing tissue edema, and high oxidative stress, leading to the deterioration of the contractile function. To avoid these drawbacks associated with the use of a whole heart, we alternatively used beating mouse cardiac syncytia cultured in vitro in order to assess possible ergotropic, chronotropic, and inotropic effects of drugs. To achieve this aim, we developed a method based on image processing analysis to evaluate the kinematics and the dynamics of the drug-stimulated beating syncytia starting from the video recording of their contraction movement. In this manner, in comparison with the physiological no-drug condition, we observed progressive positive ergotropic, positive chronotropic, and positive inotropic effects of 10 μM isoproterenol (β-adrenergic agonist) and early positive ergotropic, negative chronotropic, and positive inotropic effects of 10 μM phenylephrine (α-adrenergic agonist), followed by a late phase with negative ergotropic, positive chronotropic, and negative inotropic trends.

Our method permitted a systematic study of in vitro beating syncytia, producing results consistent with previous works. Consequently, it could be used in in vitro studies of beating cardiac patches, as an alternative to Langendorff's heart in biochemical and pharmacological studies, and especially when the Langendorff technique is inapplicable (e.g., in studies about human cardiac syncytium in physiological and pathological conditions, patient-tailored therapeutics, and syncytium models derived from induced pluripotent/embryonic stem cells with genetic mutations).

Furthermore, the method could be helpful in heart tissue engineering and bioartificial heart research to “engineer the heart piece by piece.” In particular, the proposed method could be useful in the identification of a suitable cell source, in the development and testing of “smart” biomaterials, and in the design and use of novel bioreactors and microperfusion systems.

Low-power light and isolated rat hearts after ischemia of myocardium

We studied the influence of low-intensity red light on restoration of isolated heart contractility, on lipid peroxidation processes and a state of the superoxide dismutase (SOD) activity in myocardial tissues of isolated hearts. It was found that after ischemia modeled and perfusion restored the light illumination results in acceleration of myocardial contractility recovery, rising of the SOD activity and reduction in the amount of molecular products of lipid peroxidation.

Preconditioning by subinotropic doses of ouabain in the Langendorff perfused rabbit heart

Short exposure to low concentrations of digitalis drugs like ouabain protects the rat heart against ischemia/reperfusion injury through the activation of the Na/K-adenosine triphosphatase (ATPase)/Src receptor complex and subsequent stimulation of key intracellular cardioprotective signals. Rat Na/K-ATPase, however, is relatively insensitive to digitalis, and it is not known if similar results could be obtained in species with higher sensitivity. Thus, to determine whether ouabain pretreatment protects against ischemic injury and activates the Na/K-ATPase signaling cascade in a species with cardiac glycoside sensitivity comparable to humans, the present study was conducted in the rabbit model. In Langendorff perfused rabbit hearts, 20-minute exposure to 500-nM ouabain resulted in positive inotropy as evidenced by a significant increase in +dP/dt, and this increase was accompanied by the activation of several well-characterized downstream mediators of the cardiac Na/K-ATPase receptor pathway, including Src, Akt, ERK1/2, and protein kinase Cepsilon. A short (4 minutes) administration of a subinotropic dose of ouabain (100 nM) followed by an 8-minute washout before 30 minutes of global ischemia and 120 minutes of reperfusion resulted in protection against cell death, as evidenced by a significant decrease in infarct size. These data indicate that ouabain administration activates the Na/K-ATPase signaling cascade and protects against ischemic injury in a species with high cardiac Na/K-ATPase sensitivity.

Epidermal growth factor protects the heart against low-flow ischemia-induced injury

The role of ErbB4 and ErbB2 in the heart of adult mammals is well established. The heart also expresses ErbB1 (the epidermal growth factor (EGF) receptor), but this receptor has received less attention. We studied the effect of EGF on the response of isolated mouse heart to low-flow ischemia and reperfusion. Reducing perfusate flow to 10% for 30 min resulted in an increase in anaerobic metabolism and the leakage of lactate dehydrogenase during reperfusion. In addition, left ventricle +dP/dt and developed pressure were depressed (20-25%) during reperfusion. The addition of EGF 5 min before and throughout the ischemic period prevented the increase in anaerobic metabolism and the leakage of intracellular lactate dehydrogenase during reperfusion. EGF improved both +dP/dt and developed pressure during ischemia and prevented the decrease in dP/dt during reperfusion. To determine whether the effect of EGF on cell integrity depends on its effect on contractility, we studied nonbeating isolated myocytes. In these cells, anoxia and reoxygenation reduced cell viability by nearly 25%. EGF prevented such a decrease. Our results indicate that, like ErbB4 and ErbB2, ErbB1 also has an important role in the heart of adult animals.

Animal models of myocardial and vascular injury

Over the past century, numerous animal models have been developed in an attempt to understand myocardial and vascular injury. However, the successful translation of results observed in animals to human therapy remains low. To understand this problem, we present several animal models of cardiac and vascular injury that are of particular relevance to the cardiac or vascular surgeon. We also explore the potential clinical implications and limitations of each model with respect to the human disease state. Our results underscore the concept that animal research requires an in-depth understanding of the model, animal physiology, and the potential confounding factors. Future outcome analyses with standardized animal models may improve translation of animal research from the bench to the bedside.

In vivochronic carvedilol treatment in rats attenuatesex vivoregional infarction of the heart

OBJECTIVE

Carvedilol is an alpha-and beta-blocking agent with antioxidant properties. We examined if treatment with carvedilol in vivo protected the heart against ischemic injury ex vivo.

METHODS

Isolated hearts from treated rats (80 mg/kg/day) were subjected to 30 min regional ischemia. Hearts from non-treated animals received either no drug, 10 min carvedilol (1 microM) acute or ischemic preconditioning (IP) by 5 min ischemia +5 min reperfusion prior to regional ischemia. In separate experiments isolated hearts were subjected to 15 min global ischemia and 30 min reperfusion.

RESULTS

Infarct size was significantly reduced by ischemic preconditioning or by chronic carvedilol treatment (9.0+/-0.9% and 7.2+/-1.9% of risk zone infarcted, respectively, vs. 33.8+/-6.4% in control hearts, mean+/-SEM, p < 0.05). Recovery of left ventricular developed pressure after global ischemia was not improved by carvedilol. Post-ischemic rise in left ventricular end diastolic pressure was, however, attenuated by chronic carvedilol treatment.

CONCLUSION

Chronic in vivo but not acute ex vivo pretreatment with carvedilol significantly limited infarct size in isolated rat hearts.

Effects of novel semiselective matrix metalloproteinase inhibitors on ex vivo cardiac structure-function

The purpose of this study was to evaluate the ability of novel semiselective matrix metalloproteinase inhibitors (MMPI) to protect myocardial structure-function in the setting of ischemia-reperfusion injury. For this purpose, an isolated rat model of myocardial stunning and infarction was used. Isolated hearts were subjected to 20-30 minutes of global no-flow ischemia and 30-minute reperfusion. Myocardial performance was assessed as the product of the heart rate and left ventricular developed pressure (rate-pressure product, RPP). Coronary flow rates, ventricular weights, indicators of muscle (troponin I), and fibrillar collagen damage (collagen opalation) were measured. Four MMPI were tested: 2 non-hydroxamate, semiselective inhibitors (PY-2 and 1,2-HOPO-2) and 2 broad-spectrum inhibitors (PD166793 and CGS27023A). The non-hydroxamate, semiselective inhibitors were shown to be nontoxic in cocultures of cardiac cells. Results indicate that semiselective inhibitors (in particular 1,2-HOPO-2) yield improved cardiac performance (approximately 23% higher RPP vs. controls) and coronary flow rates (approximately 22%), reducing muscle (approximately 25%) and fibrillar collagen damage (approximately 60%). Evidence suggests the involvement of matrix metalloproteinase-2 in these actions. Interestingly, broad-spectrum inhibitors only show modest improvement (approximately 8% higher RPP vs. controls) without affecting the other measured parameters. In conclusion, semiselective MMPI can act as cardioprotectors in isolated perfused rat hearts. Protection is observed in all structural components of the myocardium translating into improved contractile function. Based on these findings, non-hydroxamate, semiselective MMPI warrant further studies as to their ability to protect ischemic myocardium in the in vivo setting.

Zinc-binding groups modulate selective inhibition of MMPs

The need for selective matrix metalloproteinase (MMP) inhibition is of interest because of the range of pathologies mediated by different MMP isoforms. The development of more selective MMP inhibitors (MMPi) may help to overcome some of the undesired side effects that have hindered the clinical success of these compounds. In an effort to devise new approaches to selective inhibitors, herein we describe several novel MMPi and show that their selectivity is dependent on the nature of the zinc-binding group (ZBG). This is in contrast to most current MMPi, which obtain isoform selectivity solely from the peptidomimetic backbone portion of the compound. In the present study, six different hydroxypyrone and hydroxypyridinone ZBGs were appended to a common biphenyl backbone and the inhibition efficiency of each inhibitor was determined in vitro (IC(50) values) against MMP-1, -2, -3, -7, -8, -9, -12, and -13. The results show that the selectivity profile of each inhibitor is different as a result of the various ZBGs. Computational modeling studies were used to explain some trends in the observed selectivity profiles. To assess the importance of the ZBG in a biological model, two of the semiselective, potent MMPi (and one control) were evaluated using an isolated perfused rat heart system. Hearts were subjected to ischemia reperfusion injury, and recovery of contractile function was examined. In this model, only one of the two MMPi showed significant and sustained heart recovery, demonstrating that the choice of ZBG can have a significant effect in a relevant pathophysiological endpoint.

Milrinone administered before ischemia or just after reperfusion, attenuates myocardial stunning in anesthetized swine

PURPOSE

We assessed the dose or timing effect of milrinone administered against myocardial stunning in 37 anesthetized open-chest swine.

METHODS

All swine were subjected to 12-min ischemia followed by reperfusion to produce myocardial stunning. Group A (n = 12) received saline in place of milrinone both before and after ischemia. Group B (n = 9) and C (n = 9) received intravenous milrinone at a rate of 5 microg/kg/min for 10 min followed by 0.5 microg/kg/min for 10 min and 10 microg/kg/min for 10 min followed by 1 microg/kg/min for 10 min, respectively, until 30 min before coronary occlusion. Group D (n = 7) received the same dose of milrinone as group B starting 1 min after reperfusion. Myocardial contractility was assessed by percentage segment shortening (%SS).

RESULTS

Five swine in group A and two swine in groups B and C each had ventricular fibrillation or tachycardia after reperfusion, and were thus excluded from further analysis. The percentage changes of %SS from the baseline 90 min after reperfusion in groups B, C, and D were 78 +/- 9%, 82 +/- 13%, and 79 +/- 7%, respectively, which were significantly higher than those in group A (43 +/- 13%).

CONCLUSION

We conclude that milrinone administered before ischemia or just after reperfusion attenuates myocardial stunning.

Isolated heart perfusion according to Langendorff---still viable in the new millennium

The isolated perfused mammalian heart preparation was established in 1897 by Oscar Langendorff. The method was developed on the basis of the isolated perfused frog heart established by Elias Cyon at the Carl Ludwig Institute of Physiology in Leipzig, Germany in 1866. Observations made using both methods at the end of the 19th and at the beginning of the 20th century led to important discoveries, forming the basis for our understanding of heart physiology. This included the role of temperature, oxygen and calcium ions for heart contractile function, the origin of cardiac electrical activity in the atrium, the negative chronotropic effect of vagus stimulation and the chemical transmission of impulses in the vagus nerve by acetylcholine. Langendorff himself demonstrated that the heart receives its nutrients and oxygen from blood via the coronary arteries and that cardiac mechanical function is reflected by changes in the coronary circulation. The method underwent many modifications but its general principle remains the same today. Blood, or more commonly crystalloid perfusates, are delivered into the heart through a cannula inserted in the ascending aorta, either at constant pressure or constant flow. Retrograde flow in the aorta closes the leaflets of the aortic valve and as a consequence, the entire perfusate enters the coronary arteries via the ostia at the aortic root. After passing through the coronary circulation the perfusate drains into the right atrium via the coronary sinus. The simplicity of the isolated mammalian heart preparation, the broad spectrum of measurements which can be done using this method, its high reproducibility and relatively low cost make it a very useful tool in modern cardiovascular and pharmacological research, in spite of a few shortcomings. In the last decade the method has brought many important advances in many areas including ischemia-reperfusion injury, cell-based therapy and donor heart preservation for transplant.

Exercise and myocardial tolerance to ischaemia-reperfusion

It is well established that both short-term (1-5 days) and long-term (weeks to months) high intensity exercise (i.e. 70-75%VO2max) provides cardioprotection against ischaemia-reperfusion injury. However, it is unclear if moderate intensity exercise will also provide cardioprotection.

AIM

Therefore, these experiments compared the protective effects of moderate vs. high intensity exercise in providing defense against ischaemia-reperfusion injury.

METHODS

Male Sprague-Dawley rats were randomly assigned to one of three-experimental groups: (1) sedentary (control); (2) moderate intensity treadmill exercise (60 min day(-1) at approximately 55%VO2max); or (3) high intensity treadmill exercise (60 min day(-1) at approximately 75%VO2max). Hearts were exposed to 20 min of global ischaemia followed by 30 min reperfusion in an isolated working heart preparation.

RESULTS

Compared with sedentary rats, both moderate and high intensity exercised rats maintained a higher (P < 0.05) percentage of pre-ischaemia cardiac output and cardiac work (cardiac output x systolic blood pressure) during reperfusion. No differences in the percent recovery of cardiac output and heart work existed (P > 0.05) between the two exercise groups.

CONCLUSIONS

These data reveal that both moderate and high intensity exercise training provide equivalent protection against ischaemia-reperfusion injury.

Physiological and metabolic actions of mycophenolate mofetil on cultured newborn rat cardiomyocytes in normoxia and in simulated ischemia

Mycophenolate mofetil (MMF) is a new immunosuppressive drug used to reduce acute rejection after heart transplantation. As with other immunosuppressive drugs, MMF therapy is associated with several adverse effects. However, the direct effects of MMF on myocardial tissue has not been yet evaluated. The aim of the work was thus to evaluate the effects of MMF on isolated cardiomyocytes (CM) in normal conditions and in an in vitro model of simulated ischemia (SI; substrate-free hypoxia) and reperfusion (R; reoxygenation). Myocyte-enriched cultures were prepared from newborn rat heart ventricles. The transmembrane potentials were recorded using conventional microelectrodes and the cell contractions were monitored with a photoelectric device. In basal conditions, MMF (10(-6) and 10(-5) M) exerted no significant effects on the survival and on the electrical and contractile activities of CM in culture, even during long-term exposure (up to 48 h). SI per se led to a gradual decrease and then an abortion of the spontaneous automaticity and electromechanical activity of CM. Pretreating CM with either 10(-6) or 10(-5) M MMF was able to reduce the SI-induced cell dysfunctions. The presence of MMF at these concentrations did not hamper the post-SI functional recovery of CM during reoxygenation. At 10(-5) M, MMF applied during reoxygenation only permitted a better recovery of CM. However, the mitochondrial function after reoxygenation, as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl-tetrazolium bromide (MTT) test, was not significantly influenced by the addition of MMF before as well as after ischemia. Conversely, MMF was able to reduce in this model the postischemic rise in xanthine and hypoxanthine. These data from CM-enriched model show that MMF: (i) had no cytotoxic effect, (ii) displayed a cytoprotective effect during SI, and (iii) exerted its beneficial effect at least partly through the decrease in the xanthine oxidase-dependent free radical production.

Deep hypothermia during ischemia improves functional recovery and reduces free-radical generation in isolated reperfused rat heart

BACKGROUND

We investigated the influence of deep hypothermia (4 degrees C) during ischemia-reperfusion in the isolated rat heart model.

METHODS

Isolated, perfused rat hearts underwent either 30 minutes of normothermic ischemia (control group) or 30 minutes of hypothermic ischemia (hypothermia-treated group), followed by 30 minutes of reperfusion in both groups. We recorded functional parameters and used electron spin resonance (ESR) spectroscopy to detect ascorbyl radicals, as markers of free-radical production, in samples of coronary effluents.

RESULTS

Functional parameters were stable in the 2 groups during pre-ischemic and ischemic periods. During reperfusion, coronary flow, left diastolic ventricular pressure, left ventricular developed pressure, and heart rate more rapidly recovered to values close to those obtained during the pre-ischemic period in the hypothermia-treated group than in the control group. Moreover, the post-ischemic contracture observed in the control group did not appear in the hypothermia-treated group. Finally, ESR analysis showed that the post-ischemic release of ascorbyl radicals decreased in the hypothermia-treated group.

CONCLUSIONS

These results demonstrate that the protective effect of hypothermia against functional injury caused by ischemia-reperfusion may decrease the free-radical burst at reperfusion.

Effect of the Na+/H+ exchange inhibitor eniporide on cardiac performance and myocardial high energy phosphates in pigs subjected to cardioplegic arrest

BACKGROUND

Pharmacologic Na(+)/H(+) exchange inhibition has been suggested to ameliorate cardiac performance depression associated with myocardial ischemia/reperfusion. The purpose of our experimental study was to investigate the impact of the novel Na(+)/H(+) exchange inhibitor Eniporide (EMD 96785) on cardiac performance and high energy phosphate content in a clinically relevant pig model of cardioplegic arrest.

METHODS

We subjected 21 pigs (47 +/- 12 [SD] kg) to cardiopulmonary bypass (CPB) and 60 minutes cold (4 degrees C) crystalloid cardioplegic arrest (Bretschneider). The pigs were randomized to receive either systemic infusion of 3 mg/kg Eniporide before cardioplegia with added 2 micromol/L Eniporide (ENI-CP+iv; n = 7); 3 mg/kg Eniporide in cardioplegia only (ENI-CP; n = 7); or no Eniporide (control; n = 7). For cardiac performance determination we measured preload recruitable stroke work and Tau, the time constant of left ventricular (LV) isovolumic relaxation using sonomicrometry and micromanometry before CPB as well as 30, 60, and 120 minutes after weaning off CPB. LV and right ventricular myocardial adenine nucleotides (ATP, ADP, and AMP), glycogen, and water content were determined at the end of the experiments.

RESULTS

Neither for standard hemodynamics including vascular pressures and cardiac index nor for cardiac performance factors did we find statistically significant differences between the groups. Similarly, myocardial adenine nucleotides, glycogene, and water content did not differ significantly between the groups.

CONCLUSIONS

In this acute study we did not find significant effects of the Na(+)/H(+) exchange inhibitor Eniporide on cardiac performance and high energy phosphate content in healthy pig hearts subjected to ischemia/reperfusion induced by crystalloid cardioplegic arrest.

Antioxidants in myocardial ischemia-reperfusion injury: therapeutic potential and basic mechanisms

Oxidative stress is a constant threat to all living organisms and an immense repertoire of cellular defense systems is being employed by most pro- and eukaryotic systems to eliminate or to attenuate oxidative stress. Ischemia and reperfusion is characterized by both a significant oxidative stress and characteristic changes in the antioxidant defense. By focusing on this antioxidant response of the cardiovascular system in the setting of ischemia-reperfusion injury, the aim of this review was threefold. First, based on recent animal experiments and clinical studies we shall discuss how endogenous antioxidants respond to oxidative stress during ischemia-reperfusion injury and highlight the results of recent trials on the ability of antioxidants to modulate ischemia-reperfusion injury. In this aspect, we will particularly focus on the emerging concept that various lines of antioxidant defenses do not act individually but are linked to each other in a systematic relationship as part of an antioxidant network. It is well known that enzymatic mechanisms are important components of the endogenous antioxidant repertoire; however, the relative importance of the different enzyme systems and isoforms has been much debated. The second part will focus on recent suggestions attributing a potentially key role of mitochondrial MnSOD in cardiac ischemia-reperfusion injury. Finally, the third part of the review will critically examine how endogenous antioxidants might regulate the complex signal transduction pathways of cellular activation with particular attention to the NF-kappaB and MAPK systems that appears to determine outcome of injury, survival, and adaptation.

Loss of exercise-induced cardioprotection after cessation of exercise

Endurance exercise provides cardioprotection against ischemia-reperfusion (I/R) injury. Exercise-induced cardioprotection is associated with increases in cytoprotective proteins, including heat shock protein 72 (HSP72) and increases in antioxidant enzyme activity. On the basis of the reported half-life of these putative cardioprotective proteins, we hypothesized that exercise-induced cardioprotection against I/R injury would be lost within days after cessation of exercise. To test this, male rats (4 mo) were randomly assigned to one of five experimental groups: 1). sedentary control, 2). exercise followed by 1 day of rest, 3). exercise followed by 3 days of rest, 4). exercise followed by 9 days of rest, and 5). exercise followed by 18 days of rest. Exercise-induced increases (P < 0.05) in left ventricular catalase activity and HSP72 were evident at 1 and 3 days postexercise. However, at 9 days postexercise, myocardial HSP72 and catalase levels declined to sedentary control values. To evaluate cardioprotection during recovery from I/R, hearts were isolated, placed in working heart mode, and subjected to 20.5 min of global ischemia followed by 30 min of reperfusion. Compared with sedentary controls, exercised animals sustained less I/R injury as evidenced by maintenance of a higher (P < 0.05) percentage of preischemia cardiac work during reperfusion at 1, 3, and 9 days postexercise. The exercise-induced cardioprotection vanished by 18 days after exercise cessation. On the basis of the time course of the loss of cardioprotection and the return of HSP72 and catalase to preexercise levels, we conclude that HSP72 and catalase are not essential for exercise-induced protection during myocardial stunning. Therefore, other cytoprotective molecules are responsible for providing protection during I/R.

Cardiac-specific overexpression of fibroblast growth factor-2 protects against myocardial dysfunction and infarction in a murine model of low-flow ischemia

BACKGROUND

Preconditioning the heart before an ischemic insult has been shown to protect against contractile dysfunction, arrhythmias, and infarction. Pharmacological studies have suggested that fibroblast growth factor-2 (FGF2) is involved in cardioprotection. However, because of the number of FGFs expressed in the heart and the promiscuity of FGF ligand-receptor interactions, the specific role of FGF2 during ischemia-reperfusion injury remains unclear.

METHODS AND RESULTS

FGF2-deficient (Fgf2 knockout) mice and mice with a cardiac-specific overexpression of all 4 isoforms of human FGF2 (FGF2 transgenic [Tg]) were compared with wild-type mice to test whether endogenous FGF2 elicits cardioprotection. An ex vivo work-performing heart model of ischemia was developed in which murine hearts were subjected to 60 minutes of low-flow ischemia and 120 minutes of reperfusion. Preischemic contractile function was similar among the 3 groups. After ischemia-reperfusion, contractile function of Fgf2 knockout hearts recovered to 27% of its baseline value compared with a 63% recovery in wild-type hearts (P<0.05). In FGF2 Tg hearts, an 88% recovery of postischemic function occurred (P<0.05). Myocardial infarct size was also reduced in FGF2 Tg hearts compared with wild-type hearts (13% versus 30%, P<0.05). There was a 2-fold increase in FGF2 release from Tg hearts compared with wild-type hearts (P<0.05). No significant alterations in coronary flow or capillary density were detected in any of the groups, implying that the protective effect of FGF2 is not mediated by coronary perfusion changes.

CONCLUSIONS

These results provide evidence that endogenous FGF2 plays a significant role in the cardioprotective effect against ischemia-reperfusion injury.

[A new model of isolated perfused heart. Study of hypodermin A in hyperacute xenograft rejection]

AIMS OF THE STUDY

Isolated perfused heart (IPH) system and heart transplantation in the guinea-pig/rat combination represent a good model for the study of hyperacute xenograft rejection (HAR) in which the component plays a central role. Hypodermin A (HA), a protease cleaving the component, could be used to delay the HAR.

METHODS

Creation of an original IPH working with rat serum (30 mL) and ex vivo study of HAR and I'HA.

RESULTS

Study of HAR is possible with this IPH system. The mean guinea-pig heart survival after perfusion by normal rat serum was 38 +/- 7 min and was lower than survival observed after perfusion by guinea-pig serum (210 +/- 34 min) (p < 0.001), by decomplemented rat serum (177 +/- 45 min) (p < 0.001), and by rat serum with 20 micrograms/mL of HA (154 +/- 71 min) (p < 0.001).

CONCLUSION

We developed an original system of isolated perfused heart allowing ex vivo study of HAR. HA delayed the occurrence of the HAR and confirmed the central role of the component in the HAR.