Neuroprotective effects of a hemoglobin-based oxygen carrier (stroma-free hemoglobin nanoparticle) on ischemia reperfusion injury

The application of hemoglobin (Hb)-based oxygen carriers (HBOCs) to the treatment of cerebral ischemia has been investigated. A cluster of 1 Hb and 3 human serum albumins (Hb-HSA3) was found to exert neuroprotective effects on ischemia/reperfusion injury. Stroma-free hemoglobin nanoparticles (SFHbNP), a subsequently developed HBOC consisting of a spherical polymerized stroma-free Hb core with a HSA shell, contains the natural antioxidant enzyme catalase and, thus, is expected to exert additive effects. We herein investigated whether SFHbNP exerted enhanced neuroprotective effects in a rat transient middle cerebral artery occlusion (tMCAO) model. Rats were subjected to 2-hour tMCAO and divided into the following 3 groups with the intravenous administration of the respective reagents: (1) phosphate-buffered saline (PBS), as a vehicle (2) Hb-HSA3, and (3) SFHbNP. After 24-hour reperfusion, infarct and edema volumes decreased in the order of the PBS, Hb-HSA3, and SFHbNP groups, with a significant difference (p < 0.05) between the PBS and SFHbNP groups. Similar reductions were observed in oxidative stress, leukocyte recruitment, and blood-brain barrier disruption in the order of the PBS, Hb-HSA3, and SFHbNP groups. In the early phase of reperfusion within 6 h, microvascular HBOC perfusion and cerebral blood flow were maintained at high levels during the reperfusion period in the Hb-HSA3 and SFHbNP groups. However, a difference was observed in tissue oxygen partial pressure levels, which significantly decreased after 6-hour reperfusion in the Hb-HSA3 group, but remained high in the SFHbNP group. A superior oxygen transport ability appears to be related to the enhanced neuroprotective effects of SFHbNP.