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.