Hemoglobin-vesicles as oxygen carriers - Influence on phagocytic activity and histopathological changes in reticuloendothelial system

Hemoglobin-vesicles (HbV) have been developed for use as artificial oxygen carriers (particle diameter, 250 nm) in which a purified Rb solution is enc apsulated with a phospholipid bilayer membrane. The influence of HbV on the reticuloendothelial system was studied by carbon clearance measurements an d histopathological examination. The HbV suspension ([Hb] = 10 g/dl) was in travenously infused In male Wistar rats at dose rates of 10 and 20 ml/kg, a nd the phagocytic activity was measured by monitoring the rate of carbon cl earance at 8 hours and at 1, 3, 7, and 14 days after infusion. The phagocyt ic activity transiently decreased one day after infusion by about 40%, but it recovered and was enhanced at 3 days, showing a maximum of about twice t he quiescent level at 7 days, and then returned to the normal value at 14 d ays. The initial transient decreased activity indicates a partly, but not c ompletely, suppressed defensive function of the body. The succeeding increa sed phagocytic activity corresponds to the increased metabolism of HbV. The histopathological examination with anti-human Hb antibody, hematoxylin/eos in, and oil red O stainings; showed that HbV was metabolized within 7 days. Hemosiderin was very slightly confirmed with Berlin blue staining at 3 and 7 days in liver and spleen, though they completely disappeared at 14 days, indicating that the heme metabolism, excretion or recycling of iron procee ded smoothly and iron deposition was minimal. Electron microscopic examinat ion of the spleen and liver tissues clearly demonstrated the particles of H bV with a diameter of about 1/40 of red blood cells in capillaries, and in phagosomes; as entrapped in the spleen macrophages and Kupffer cells one da y after infusion. The vesicular structure could not be observed at 7 days. Even though the infusion of HbV modified the phagocytic activity for 2 week s, it does not seem to cause any irreversible damage to the phagocytic orga ns. These results offer important information for evaluating the safety iss ues of HbV for clinical use.