Sagar Damle1, Ashok N. Babu1, Ernest E. Moore2, Michael Weyant1, Anirban Banerjee1, Lihau Ao1, Jeffrey L. Johnson2, Xianzhong Meng1, David Fullerton1; 1University of Colorado at Denver, Health Sciences Center, Denver, CO; 2Denver Health Medical Center, Denver, CO
Objective: Cardiac surgical operations are associated with the obligatory injuries of myocardial ischemia and reperfusion (I/R). Endogenous overexpression of heme-oxygenase-1 (HO-1) provides protection against I/R injury, which is abolished with selective inhibition of this enzyme. Heretofore, no clinically viable therapy has existed to safely induce HO-1 in myocardium. We have previously reported that administration of a hemoglobin-based oxygen carrier (HBOC) upregulated HO-1 in isolated endothelial cells. We therefore hypothesized that administration of a HBOC in vivo would induce expression of HO-1 in the heart. The purpose of this study was to determine whether HO-1 could be upregulated in myocardium by administration of an exogenous agent.Methods: Anesthetized rats (n=3-5 per group) received HBOC (PolyHeme®, human polymerized hemoglobin, pyridoxylated; Northfield Laboratories, Inc.) intravenously (femoral vein) in volumes of 5% or 10% of calculated blood volume. Control animals received either instrumentation alone or normal saline at 10% calculated blood volume. Recovering animals were subsequently maintained in a normothermic environment. For time course studies, animals were sacrificed at 0, 12 or 24 hours after injection. For dose response studies, animals were sacrificed at 12 hours. Hearts were isolated, washed and then flash frozen for tissue homogenization. Immunoblot of tissue samples were probed for HO-1 and heat shock protein 72 (HSP72, stress-inducible). Densitometry was performed using Kodak 1D software. Statistical analysis used ANOVA (*p<0.05).
Results: HBOC induced myocardial HO-1 expression in a dose-dependent fashion. Administration of HBOC at 10% of calculated blood volume produced 2.5- and 3.6-fold increases in myocardial HO-1 levels at 12 and 24 hours, respectively (* p<0.05) (see figure). In contrast, myocardial HSP72 levels did not change following HBOC administration.
Conclusion: HBOC selectively induced expression of the protective enzyme HO-1 in the heart. The absence of a rise in HSP72 suggests this is not a generalized response to an oxidant stress. These data demonstrate the potential of a novel therapeutic strategy in preventing cardiac injury from ischemia/reperfusion.
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