Improvment in cardiac transplantation with NO

The major challenge in donor organ preservation is to minimize pathologic damage and impairment of function because during procurement7 storage, and implantation the heart is exposed to ischemia and reperfusion (I/R). Clinical practice used in heart preservation varies widely but is based on a single flush induction of cardioplegia and hypothermic storage m one of a number of storage solutions. The compositions of these solutions were designed to protect mainly the myocytes against hypothermic swelling, augment energy production on reperfusion, and ablate pathologic damage by reactive oxygen species formed during reperfusion. Changes to the vascular endothelium have been identified as a precursor to reperfusion damage leading to organ failure. One important aspect of this endothelial dysfunction is the inability of these cells to release nitric oxide on reperfusion. In models of myocardial I/R injury damage can be reduced by addition of exogenous nitric oxide either in the form of authentic nitric oxide gas, nitric oxide donating compounds, or L-arginine, the substrate for nitric oxide synthetase, immediately before reperfusion. Similarly, in the setting of organ transplantation, improved organ function has been observed when exogenous nitric oxide donating agents have been included in the hypothermic storage solution in a heart model. It therefore seems that additional to the protection of the myocyte a protection of the endothelium by NO is needed. Lt is the overall aim of this proposal to minimize YR damage in the setting of experimental heart transplantation (pig model). This goal shall be achieved with iv. infusion of S-Nitroso-Human Serum Albumin (S-NO-HSA) to donor and recipient. Two ischemic periods shall be tested, 4 and 14 hours. The substance has been developed by two co-investigators of this research proposal and shown to be protective in the peripheral muscle and in the heart in previous studies. This protocol should provide the experimental basis to expand the ischemic period and reduce acute early rejection. The results will have direct influence on the outcome of clinical heart transplantation.

Despite ambiguous experimental and clinical approaches and advances in medical therapy heart transplantation is still the golden standard in the treatment of end-stage heart disease. The demand of donor organs in heart transplantation is increasing, while the availability of donor hearts has decreased by 25% within the last 10 years. One way to increase the number and quality of donor hearts is improved organ preservation when the heart is harvested and transported to the transplantation clinic. Thereby (1) the time, tolerated by the heart outside the body, should be prolonged to allow procurement of hearts that are too remote for current explantation techniques and (2) borderline organs, which are those that are too old (>65 years) or have had temporary low function, should be made available to the donor pool. Currently preservation and storage during transport to the transplant clinic is done by cold solutions, so-called cardioplegic solutions (CP). However, the CP solutions that are used have been developed for protection of the heart muscle and not for the other important cell type in the heart, the cells that cover the vessels inside- the so-called endothelium. Members of our laboratory have recently developed a drug that is protecting the endothelium. The drug is a natural product of the endothelium, called nitric oxide (NO), and has been identified as one of the key players in regulating the function of the endothelium, leading to a reduction in vessel tension and consequently an increase in vessel diameter and vessel perfusion. It was the goal of this scientific proposal to test the hypothesis, if NO, given before and during the harvest of the heart as well as after transplantation, improves the function of the heart and if the time tolerated by the heart outside the body is expandable by this new treatment. As experimental model during the first two years a pig model was used, during the third year isolated rabbit hearts were investigated. The major results of this grant are: in both, the pig model and the rabbit model, the function of the transplanted heart was improved, when NO was given before, during and after transplantation. This functional improvement was based on hemodynamic (blood pressure, heart rhythm etc), and biochemical measurements (total content of energy), as well as on evaluation of endothelial function (NO concentration etc.). Additionally, the experiments in the rabbit showed that we were able to extend the time tolerated by the heart outside the body. The results of this experimental series were the last before clinical evaluation and therefore have direct impact on clinical transplantation.