Patients with end stage heart failure (HF) require mechanical circulatory support, and if eligible, heart transplantation (HT) to save their life. Up to 20% of patients die while listed for heart transplantation. The supply of donor hearts has reached a plateau since the only current source of donor hearts consists of patients with irreversible severe brain damage (donation after brain death, DBD). Thus, there is an urgent need to expand the heart donor pool. A potential source of such donor hearts is from DCD (donation after circulatory death) donors. DCD donors have increased the transplantation rates of solid organs including liver, lungs and kidney. Unfortunately, DCD protocol induces a sustained warm ischemic time that damages myocardium precluding its use for clinical transplantation. Thus, the ischemia (ISC) form DCD protocol, the potential myocardial injury from storage, and reperfusion (REP) associated injury combine to represent additional risks to exacerbate injury in the DCD heart precluding their use in clinical transplantation. Although the warm ischemia is inevitable in DCD hearts, REP injury can be decreased through proper interventions applied at the onset of REP. We propose that development of new strategies to prevent REP injury will reduce damage to the DCD heart. Mitochondria are critical targets and mediators of cardiac injury during REP. Our previous studies found that temporary and reversible inhibition of mitochondrial respiration at the time of REP in hearts following ISC decreases cardiac injury. Protection involved the reduction of the ROS generation and inhibition of the opening of the mitochondrial permeability transition pores. We propose that the use of rapid onset and reversible inhibitors of respiration immediately before and during early REP will decrease cardiac injury in DCD hearts. The ex vivo DCD human heart represents a unique opportunity to translate this robust cardiac protection derived from strong pre-clinical data to human disease. Myocytes injured during ISC-REP activate internal cell-based mechanisms of inflammation including the NOD like receptor protein 3 (NLRP3) inflammasome. ROS derived from damaged mitochondria activates the NLRP3 inflammasome and perpetuates tissue injury further. This project takes the unique approach to combine complimentary interventions to blunt acute mitochondrial-driven injury and attenuate longer-term REP damage from inhibition of inflammasome signaling. The potential mechanistic relationship of damaged mitochondria and the activation of inflammasome signaling are studied in the DCD heart model. We hypothesize that the initial protection of mitochondria followed by attenuation of mitochondria- activated inflammatory signaling will protect the DCD heart function, enabling it to be used for heart transplantation. Our novel strategy is to use amobarbital treatment to rapidly, reversibly and transiently modulate mitochondrial respiration to decrease acute ISC-REP injury followed by inhibition of inflammation mediated injury. The goal of this project is to protect the DCD heart during reanimation, sustain the preservation of functional mitochondria in order to reach the quality of a transplantable heart similar to DBD. Using a rat model of DCD heart, Aim 1 will evaluate the protection from reversible inhibition of electron transport at the onset of REP using the perfused heart ex vivo. This will be followed by Aim 2 where the syngeneic heterotopic HT of these mito-protected DCD hearts will be subjected to protection from inflammasome mediated delayed reperfusion injury. The heterotopic transplanted hearts will then be evaluated for graft survival, function and pathological assessment including the presence of inflammatory infiltrates and fibrosis on MRI, ECHO cardiogram and histological examination. Our planned experiments and the anticipated results will provide the initial insight into the protective strategies for DCD hearts. Using an integrated treatment approach as proposed we aim to move toward use of DCD hearts for clinical transplantation.
Veterans have a high incidence of progression of heart failure to end stage that requires heart transplantation. Unfortunately, the supply of hearts suitable for transplantation has plateaued, limiting availability of this life saving treatment. Many veteran patients with end-stage heart failure die while awaiting a transplant. An alternative source of organs, already used for liver and kidney transplants, are hearts from donors who have suffered circulatory death. Currently, these organs are not used due to the ischemic damage caused by the circulatory death process. This project will explore and harness novel mechanisms to rehabilitate experimental hearts using a circulatory death experimental model by manipulating mitochondria and subsequent cell-injury driven inflammation that injure the heart. This proposal builds upon our prior work to directly manipulate metabolism in mitochondria and heart cell inflammatory processes in order to salvage the donor circulatory death heart.
