INTERACTIONS OF RECOMBINANT HEMOGLOBIN (RHB1.1) AND ENDOTOXIN IN-VIVO- EFFECTS ON SYSTEMIC TUMOR-NECROSIS-FACTOR AND INTERLEUKIN-6 LEVELS IN LETHAL AND SUBLETHAL MURINE MODELS OF ENDOTOXEMIA

The effects of acellular hemoglobin-based oxygen carriers in preclinic al models of sepsis and endotoxemia have been inconclusive with regard to outcomes reported for survival. In the present study, mice were in fused with 1 gm/kg of recombinant human hemoglobin, rHb1.1, and the ef fects on mortality and systemic tumor necrosis factor (TNF) and interl eukin-6 (IL-6) levels were determined by using both lethal and subleth al bolus endotoxin challenge. Pretreatment of mice with rHb1.1 and cha llenge with 20 mg/kg of lipopolysaccharide (LPS) at an LD100 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 chall enged with lower LPS concentrations of 10 and 2.5 mg/kg, corresponding to LD15 and LD0, respectively, had 100% and 17% mortality rates in th e rHb group and 17% and 0% mortality rates in the vehicle-treated anim als. These doses of LPS resulted in maximal increases in systemic TNF, and there were only modest differences between the rHb and the vehicl e groups at LPS challenge doses of 2.5 and 20 mg/kg, whereas no differ ence was observed at the 10 mg/kg concentration. At LPS concentrations below 10 mu g/kg, the increases in circulating TNF were dose dependen t and no differences were observed in serum TNF levels between the rHb 1.1 and vehicle groups. In addition, there were generally no differenc es in IL-6 levels between the experimental groups, although at 10 mg/k g LPS, a twofold increase in plasma IL-6 levels over those in the cont rols was observed in the rHb1.1-treated animals. Infusion of rHb1.1 al one did not induce any increase in circulating IL-6 or TNF. These data demonstrate that endotoxin exacerbation, although apparent, was obser ved only at the highest doses of LPS and that at lower concentrations, there were no differences in the extent of cytokine elevation or in s urvival rate when rHb1.1-, albumin-, or vehicle-pretreated animals wer e compared.