Use of
liposome-encapsulated hemoglobin (LEH) for
oxygen delivery in the treatment of
cerebral ischemia has been studied previously and its expected benefits confirmed. However, the relationship between the timing of administration and the efficacy of LEH in
cerebral ischemia has not been studied in detail. We therefore investigated the therapeutic time window of LEH by using a rat model of
cerebral ischemia, as well as evaluating the contribution of
oxygen delivery to the efficacy of LEH. Dose-dependent effects and the therapeutic time window of LEH were studied using models of transient and permanent
middle cerebral artery occlusion (MCAO), respectively, in SD rats. LEH was intravenously administered at 0.5 h after the onset of
ischemia in the transient MCAO model and at 0.5, 2, 4, or 6 h in the permanent MCAO model. Efficacy of LEH treatment was evaluated using the
infarct volume, which was examined with
2,3,5-triphenyltetrazolium chloride staining and estimated by integrating the unstained areas in serial sections of cerebral tissue. Effects of
oxygen delivery by LEH were examined immunohistochemically with
pimonidazole to
stain for areas of low
oxygen tension in the tissue. LEH treatment dose-dependently reduced the
cerebral infarct volume, which was especially significant in the cortical region at doses of over 60 mg
hemoglobin (Hb)/kg. In rats with permanent MCAO, LEH administration at a dose of 300 mg Hb/kg at 0.5 h and 2 h after the onset of
cerebral ischemia significantly reduced
cerebral infarct volume. Furthermore, immunohistochemical staining with
pimonidazole showed that the areas of cerebral tissue that were hypoxic and had abnormal histological structure were reduced after LEH treatment. These results indicated that LEH is efficacious in the treatment of
cerebral infarction secondary to MCAO and that
oxygen delivery to ischemic cerebral tissues by LEH administered early after the onset of
cerebral ischemia contributes to this effect.