Second-generation recombinant hemoglobin molecules do not stimulate sphincter of Oddi, gallbladder or duodenal motility in the Australian brush-tailed possum.

BACKGROUND: Several studies have investigated the effects of hemoglobin-based oxygen carriers on gastrointestinal motility. Diaspirin cross-linked hemoglobin reduces sphincter of Oddi trans-sphincteric flow and increases duodenal motility in the Australian brush-tailed possum, effects attributed to nitric oxide (NO) scavenging. Recently, second-generation recombinant hemoglobin molecules with reduced NO scavenging ability have been developed. AIM: To determine the effects of two second-generation recombinant hemoglobin solutions and the prototype recombinant hemoglobin with high NO binding, on duodenal and biliary motility in the Australian brush-tailed possum. METHOD: Blood pressure; duodenal, sphincter of Oddi and gallbladder motility; and trans-sphincteric flow were recorded. The effects of recombinant hemoglobin or human serum albumin (control) solutions on these parameters were investigated. Each solution was infused intravenously at 1 mL/kg/min to deliver 250 mg/kg or 500 mg/kg. RESULTS: Duodenal contraction frequency was stimulated by the high dose of prototype recombinant hemoglobin, but not by a comparable dose of second-generation recombinant hemoglobin. The induced duodenal activity occurred in the later phase of the experimental period. In contrast, biliary motility and trans-sphincteric flow were not altered by any hemoglobin solution. The high dose of all the hemoglobin solutions elevated blood pressure, whereas the low dose solutions did not alter any parameter measured. CONCLUSION: At the doses studied, the second-generation recombinant hemoglobin with reduced NO binding capacity did not significantly alter duodenal and biliary motility, supporting the need for further studies to evaluate their potential usefulness as blood substitutes.

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 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, rHb1.1, 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 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 challenged with lower LPS concentrations of 10 and 2.5 mg/kg, corresponding to LD15 and LD0, 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 microg/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 rHb1.1-treated animals. Infusion of rHb1.1 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 rHb1.1-, albumin-, or vehicle-pretreated animals were compared.

Regional vascular effects of rHb1.1, a hemoglobin-based oxygen carrier.

The goals of this study were to determine the effects of recombinant human hemoglobin (rHb1.1, 1 g/kg i.v.) on systemic hemodynamics, regional blood flows, and regional vascular resistances in rats. Cardiac output (CO) and regional blood flow in 13 tissues were determined by using the radiolabeled-microsphere method during halothane anesthesia. Microspheres were injected at three time points: before (control, t = 0), t = 30 [10 min after a 20-min infusion of vehicle (diluent) or rHb1.1], and at t = 120 min. Infusion of diluent did not alter CO, heart rate (HR), mean arterial pressure (MAP), or systemic vascular resistance (SVR) and had minimal effects on regional blood flows. Infusion of rHb1.1 did not alter CO or HR but did increase MAP and SVR compared with diluent. Infusion of rHb1.1 increased blood flow to the heart and decreased blood flow to the gastrointestinal tract (GIT) and liver. Compared with the corresponding values in the diluent-treated rats, resistance was increased after rHb1.1 in spleen, kidney, and hepatic artery. In conclusion, rHb1.1 administration increased MAP and SVR. The vasoconstriction was heterogeneous and was associated with increased coronary blood flow and with increased regional resistance in kidney, spleen, and hepatic artery, compared with diluent-infused controls.