Repeated injection of high doses of hemoglobin-encapsulated liposomes (hemoglobin vesicles) induces accelerated blood clearance in a hemorrhagic shock rat model.

The hemoglobin vesicle (HbV) is an artificial oxygen carrier in which a concentrated hemoglobin solution is encapsulated in a liposome. To apply liposome preparations in clinics, it is important to consider the accelerated blood clearance phenomenon (ABC phenomenon), which involves a loss in the long-circulation half-life after being administered repeatedly to the same animals. The objective of this study was to determine whether the ABC phenomenon is induced by repeated injection of HbV under conditions of hemorrhagic shock. We created a rat model of hemorrhagic shock and performed a pharmacokinetic study using (125)I-HbV, in which the Hb inside of HbV was labeled with (125)I. At 4 and 7 days after resuscitation from hemorrhagic shock by nonlabeled HbV (1400 mg Hb/kg), the second dose of (125)I-HbV (1400 mg Hb/kg) was rapidly cleared from the circulation compared with normal rats. Of interest, IgM against HbV was produced at 4 days after the first injection of HbV, but decreased at 7 days. In addition, phagocyte activity was increased at both 4 and 7 days after the first injection of HbV. These results suggest that repeated injections of HbV at a dose of 1400 mg Hb/kg induce the ABC phenomenon under conditions of hemorrhagic shock, which is strongly related to both the production of anti-HbV IgM and enhanced phagocyte activity. We thus conclude that it might be necessary to consider the ABC phenomenon in the dose regimen of HbV treatment in clinical settings.