Significant Reduction of Myocardial Injury Markers After Ischemia Minimization in the First Hour of an Ex Vivo Xeno Working Heart Model

Abstract

<h3>Purpose</h3> Previous studies showed ischemia minimization (IM), accomplished by perfusing the heart xenograft during storage, prevented ‘initial cardiac xenograft dysfunction' (ICXD) and prolonged survival following <i>in vivo</i> orthotopic cardiac xenotransplantation. We report initial observations in a model designed to evaluate effects associated with IM and genetic modifications on heart performance in a working <i>ex vivo</i> model. <h3>Methods</h3> Hearts from genetically modified (gm) and wildtype (WT) pigs were procured and stored for 3 hours either in cold saline (cold storage (CS)) or were perfused with oxygenated Steen's solution with RBCs (IM). The gm hearts either had combined knockouts of 3 xenogenic carbohydrate genes (GTKO, CMAHKO, β4GALNT2KO: TKO) with variable expression of human transgenes (n=13); or GTKO with expression of hCD55 (GTKO.hCD55; n=2). Heart function and troponin I as a marker for myocardial injury were assessed on a working heart rig while perfused with whole human blood. <h3>Results</h3> 19 hearts were perfused <i>ex vivo</i>, ten with CS (TKO n=6, GTKO.hCD55 n=1, WT n=3), 9 with IM (TKO n=7, GTKO.hCD55 n=1, WT n=1). Mean troponin I levels were significantly reduced after 1 hour of <i>ex vivo</i> perfusion in the IM group (70.2 ng/mL vs. 279.5 ng/mL; p = .038), but not at final time points (see fig. 1a-c). Cardiac function (cardiac output in response to increased filling pressures) decreased over time after CS, whereas the IM-stored heart function tended to improve over time (Fig. 2). <h3>Conclusion</h3> IM significantly decreased myocardial injury during the first hour of <i>ex vivo</i> working heart perfusion relative to CS hearts: heart injury (troponin release) was attenuated, and graft failure was delayed in some TKO hearts treated with IM. Evaluation of whether variation in expression of human transgenes may have influenced TKO graft protection from ICXD is in progress. We provisionally conclude that IM attenuates ICXD of genetically modified pig hearts during initial exposure to human blood.