Heme oxygenase-1 induction in macrophages by a hemoglobin-based oxygen carrier reduces endotoxin-stimulated cytokine secretion.

The inflammatory response after an insult may provoke further tissue damage, and the macrophage is central in this pathophysiology. Induction of heme oxygenase-1 (HO-1) attenuates postshock organ dysfunction, although the mechanism remains unclear. We hypothesized that HO-1 induction modifies the cytokine profile of LPS-stimulated macrophages. Heme oxygenase-1 was induced in murine and human macrophages with varying concentrations of a hemoglobin-based oxygen carrier (HBOC). Heme oxygenase-1 expression was analyzed by Western blotting of whole cell lysates. Macrophages were pretreated with HBOC for 4 h, then media with LPS were added for up to 24 h. The specific HO-1 inhibitor zinc protoporphyrin (ZnPP) was used to inhibit the effects of HO-1. Supernatants were analyzed for IL-6, IL-10, TNF-alpha, and monocyte chemotactic protein 1 (MCP-1) by enzyme-linked immunosorbent assay. Incubation of cells with HBOC produced a dose-dependent expression of HO-1. Heme oxygenase-1 expression decreased LPS-stimulated secretion of MCP-1, IL-6, IL-10, and TNF-alpha at both 4 and 24 h in murine and human macrophages. The addition of ZnPP to inhibit HO-1 partially restored MCP-1 and IL-6 secretion in murine macrophages. Furthermore, immunofluorescent microscopy revealed HBOC-induced HO-1 inhibited LPS-stimulated nuclear translocation of the p65 subunit of nuclear factor-kappaB. In summary, HBOC incubation of macrophages induced HO-1 expression, which reduced LPS-mediated cytokine release, and that MCP-1 and IL-6 secretion could be partially restored with ZnPP. These data encourage continued investigation into the role of HO-1 in protecting against posttraumatic organ dysfunction and the clinical potential of HBOC for HO-1 induction.