Interactions of recombinant hemoglobin (rHb 1.1) and endotoxin in vivo: Effects on systemic tumor necrosis factor and interleukin-6 levels in lethal and sublethal murine models of endotoxemia

Abstract

The effects of acellular hemoglobin-based oxygen carriers in preclinical models of sepsis and endotoxemia have been inconclusive with regard to outcomes reported for survival. In the present study, mice were infused with 1 gm/kg of recombinant human hemoglobin, rHbl.1, and the effects on mortality and systemic tumor necrosis factor (TNF) and interleukin-6 (IL-6) levels were determined by using both lethal and sublethal bolus endotoxin challenge. Pretreatment of mice with rHb1.1 and challenge with 20 mg/kg of lipopolysaccharide (LPS) at an LD 100 resulted in a 100% mortality rate by 20 hours, whereas the same mortality rate with the vehicle or 5% albumin groups occurred at 50 hours. Mice challenged with lower LPS concentrations of 10 and 2.5 mg/kg, corresponding to LD 15 and LD 0, respectively, had 100% and 17% mortality rates in the rHb group and 17% and 0% mortality rates in the vehicle-treated animals. These doses of LPS resulted in maximal increases in systemic TNF, and there were only modest differences between the rHb and the vehicle groups at LPS challenge doses of 2.5 and 20 mg/kg, whereas no difference was observed at the 10 mg/kg concentration. At LPS concentrations below 10 μg/kg, the increases in circulating TNF were dose dependent and no differences were observed in serum TNF levels between the rHb1.1 and vehicle groups. In addition, there were generally no differences in IL-6 levels between the experimental groups, although at 10 mg/kg LPS, a twofold increase in plasma IL-6 levels over those in the controls was observed in the rHbl.1-treated animals. Infusion of rHbl.1 alone did not induce any increase in circulating IL-6 or TNF. These data demonstrate that endotoxin exacerbation, although apparent, was observed only at the highest doses of LPS and that at lower concentrations, there were no differences in the extent of cytokine elevation or in survival rate when rHbl.1-, albumin-, or vehicle-pretreated animals were compared.