Effects of a hemoglobin-encapsulated liposomes, Neo Red Cell, in perfused rat coronary circulation

Effects of hemoglobin (Hb)-encapsulated liposome, Neo Red Cell (NRC), on the perfused circulatory vascular beds have been studied using Langendorf perfusion model in rats. In preliminary experiments, NRC in Krebs-Henseleit (KH) solution induced a remarkable increase in perfusion pressure (PP) and a disappearance of bradykinin (BK)-dependent vasodilation. Histological examinations revealed that these difficulties resulted from the embolism of NRC, which was probably induced by the crystal formation after the mixing of KH solution and NRC. We have searched ways to perform the perfusion with NRC, and finally found that the addition of 0.2% bovine serum and albumin into the KH solution could work even in the presence of NRC (Hb at 0.1%). We have next examined the vasoconstrictive properties of NRC and unmodified bovine Hb. Perfusion with unmodified Hb caused an increase in PP and a decrease in the duration of BK-dependent vasodilation. In contrast, NRC had no significant effects on PP and BK-responses. These results, provide the first information regarding the vasoconstrictive activity of liposome-encapsulated Hb in perfused circulatory model, and suggest that encapsulation of Hb into liposome is a suitable approach to develop oxygen carrier.