Myocardial Protective Effect of Human Recombinant Hepatocyte Growth Factor for Prolonged Heart Graft Preservation in Rats

Perioperative ischaemic reperfusion injury and allograft function in the early post-transplantation period

OBJECTIVES

Ischaemic reperfusion injury (IRI) is an inevitable complication of heart transplantation (HTX) and is observed as a pathological finding in biopsies from transplanted allografts. The aim of this study was to evaluate the severity of IRI and determine the clinical outcomes of HTX in patients with severe IRI.

METHODS

We enrolled 74 consecutive patients who had undergone HTX since 2007. Endomyocardial biopsy samples were obtained from the right ventricle of the transplanted heart. IRI was graded as 'trivial', 'mild', 'moderate' or 'severe' according to the extent of IRI-specific findings in the samples. The cohort was divided into a moderate-to-severe IRI group with 21 patients [IRI(+)] and a low-grade group with 53 patients [IRI(-)].

RESULTS

The frequency of mechanical circulatory support and duration of catecholamine dependence in the early postoperative period were significantly higher in the IRI(+) group compared to the IRI(-) group. However, overall survival after HTX and mid-term cardiac allograft function were not significantly different between the groups. Among perioperative factors, cardiac ischaemic time was significantly different between the groups [IRI(-) vs IRI(+), 199 ± 38 min vs 239 ± 39 min; P < 0.001]. Incremental increases in cardiac ischaemic time were correlated with increases in IRI severity. Serum troponin T levels 3 h after donor heart reperfusion was significantly correlated with cardiac ischaemic time (r = 0.418, P = 0.0007).

CONCLUSIONS

IRI is associated with a complicated clinical course in the early post-HTX period due to temporary deterioration of allograft function. This may be attributable to myocardial stunning caused by long donor heart ischaemic time during HTX.

Preservation of the donor heart: from basic science to clinical studies

The methods of donor heart preservation are aimed at minimizing graft dysfunction caused by ischaemia-reperfusion injury (IRI) which inevitably occurs during the ex vivo transport interval. At present, the standard technique of heart preservation is cardiac arrest followed by static cold storage in a crystalloid heart preservation solution (HPS). This technique ensures an acceptable level of heart protection against IRI for <6 h. In clinical trials, comparable levels of myocardial protection against IRI were provided by various HPSs. The growing shortage of donor hearts is one of the major factors stimulating the development of new techniques of heart preservation. Here, we summarize new HPS formulations and provide a focus for optimization of the composition of existing HPSs. Such methods of donor heart preservation as machine perfusion, preservation at sub-zero temperature and oxygen persufflation are also discussed. Furthermore, we review experimental data showing that pre- and post-conditioning of the cardiac graft can improve its function when used in combination with cold storage. The evidence on the feasibility of cardiac donation after circulatory death, as well as the techniques of heart reconditioning after a period of warm ischaemia, is presented. The implementation of new techniques of donor heart preservation may contribute to the use of hearts from extended criteria donors, thereby expanding the total donor pool.

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.

Treatment of chronical myocardial ischemia by adenovirus-mediated hepatocyte growth factor gene transfer in minipigs

Growth factor gene transfer-induced therapeutic angiogenesis has become a novel approach for the treatment of myocardial ischemia. In order to provide a basis for the clinical application of an adenovirus with hepatocyte growth factor gene (Ad-HGF) in the treatment of myocardial ischemia, we established a minipig model of chronically ischemic myocardium in which an Ameroid constrictor was placed around the left circumflex branch of the coronary artery (LCX). A total of 18 minipigs were randomly divided into 3 groups: a surgery control group, a model group and an Ad-HGF treatment group implanted with Ameroid constrictor. Ad-HGF or the control agent was injected directly into the ischemic myocardium, and an improvement in heart function and blood supply were evaluated. The results showed that myocardial perfusion remarkably improved in the Ad-HGF group compared with that in both the control and model groups. Four weeks after the treatment, the density of newly formed blood vessels was higher and the number of collateral blood vessels was greater in the Ad-HGF group than in the model group. The area of myocardial ischemia reduced evidently and the left ventricular ejection fraction improved significantly in the Ad-HGF group. These results suggest that HGF gene therapy may become a novel approach in the treatment of chronically ischemic myocardium.

Improved myocardial function after cold storage with preservation solution supplemented with a carbon monoxide-releasing molecule (CORM-3)

BACKGROUND

Carbon monoxide-releasing molecules (CO-RMs) are pharmacologically active as they protect against cardiac graft rejection and cold ischemia-mediated renal dysfunction. We investigated the cardioprotective role of carbon monoxide (CO) released from CORM-3 against cold ischemia-mediated injury in the heart and evaluated its potential application in the clinical setting of cardiac transplantation.

METHODS

Isolated rat hearts underwent cold ischemic storage for 4 or 6 hours using St Thomas Hospital solution that was supplemented with either CORM-3 (50 mumol/liter) or its inactive counterpart (iCORM-3), which does not release CO. Hearts were then reperfused. Both functional parameters and release of cardiac enzymes were assessed.

RESULTS

Addition of CORM-3 to the preservation solution resulted in a significant improvement in systolic and diastolic function as well as coronary flow when compared with hearts treated with iCORM-3. In addition, lower levels of the cardiac enzymes creatine kinase and lactate dehydrogenase were measured in the perfusate of hearts stored with CORM-3.

CONCLUSIONS

The improved functional recovery and reduced enzyme release after cardiac cold storage with CORM-3, but not iCORM-3, indicate that CO is the main mediator of myocardial protection. Thus, CO-RMs can be used as adjuvants to improve the preservation of hearts for transplantation.

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.