Induction of heme-oxygenase-1 prevents the systemic responses to hemorrhagic shock

Oxidant-mediated reperfusion injury of the gut is a major contributor of the systemic inflammatory response in hemorrhagic shock. Recent studies have suggested that heme-oxygenase-1 (HO-1) represents an endogenous protective mechanism against oxidant stress. We assessed whether HO-1 induction modulates the synthesis of tumor necrosis factor-alpha (TNF-alpha) in hemorrhagic shock. In rats submitted to hemorrhagic shock, pretreatment with hemoglobin (Hb) increased HO-1 mRNA expression in macrophages. This increased expression was associated with a decreased expression of TNF-alpha mRNA, as well as decreased plasma concentrations of TNF-alpha. These effects of Hb were reduced by the HO-1 inhibitor tin-protoporphyrin (Sn-PP 20 micromol/kg), while Sn-PP had no effect in the absence of Hb. In parallel, Hb pretreatment reduced pulmonary edema, vascular injury, and increased mesenteric blood flow, and these effects were reduced by Sn-PP. Thus, induction of HO-1 is protective in hemorrhagic shock, possibly through its antioxidant properties. Interventions that induce HO-1 may be beneficial in the treatment of shock states, leading to a reduced systemic inflammatory response.