Research Project
10150155
Novel therapy for myocardial ischemia-reperfusion injury Abstract Prompt restoration of the blood supply to the heart is considered the most effective treatment for acute myocardial infarction. However, reperfusion itself may aggravate the extent of myocardial injury, resulting in myocardial ischemia reperfusion injury (MIRI). MIRI may involve myocardial stunning, severe fatal ventricular arrhythmia, no reflow in coronary artery, or even enlargement of the myocardial infarct. While several methods, including ischemic preconditioning, ischemic post-conditioning, and remote ischemic pre-conditioning, have been demonstrated to alleviate MIRI, these procedures are of limited use in clinical practice for ethical reasons. Clinically viable and effective strategies to reduce MIRI are needed. We have identified an antibody to a novel cardiac target, which prolongs survival in an animal model and protects myocardium from ischemia-reperfusion injury. Cardiotonic steroids (CTS, e.g. digoxin, ouabain) are classically thought to have a positive inotropic effect by inhibiting the Na+/K+-ATPase (NKA), thus increasing intracellular Na+ which is exchanged with Ca2+ to augment contractility. Although this mechanism is undoubtedly more complex, our recent work, originally with an affinity- purified polyclonal antiserum and now with an anti-NKA human monoclonal antibody, demonstrates that NKA is more than an ion exchanger and is actually a critical nexus for cardiomyocyte cell signaling. We demonstrated that activation of the NKA by binding of antibodies to the L7/8 extracellular loop of the ?-subunit produces positive inotropy and activates the Src pro-survival signaling pathway and its downstream effectors Erk1/2 and PI3K/Akt. An affinity-purified antiserum specific for this extracellular site markedly augments NKA catalytic activity both in vitro and in vivo in rodents. The augmented NKA activity induces a positive cardiotonic effect and, perhaps most importantly, activates cardioprotective pathways in vivo. High-titer anti-NKA antibodies elicited in spontaneously hypertensive heart failure (SHHF) rats by active immunization completely prevented the lethal heart failure (HF) of these animals with no noticeable adverse effects over a period of 30 weeks. In preliminary work we have identified a high affinity anti-NKA human monoclonal antibody (huNKA). The overall goal of this Phase 1 project will be to 1) re-engineer the huNKA to remove effector functions; 2) demonstrate efficacy in a rat model of MIRI; and 3) confirm lack of toxicity in rats. The therapeutic antibody, or fragment thereof, developed from the proposed work will be used in conjunction with reperfusion technologies to reduce or eliminate damage from MIRI.
