Whether hemoglobin (Hb) encapsulated liposomes have vasoconstrictive activity remains controversial. We therefore examined the vascular activity of a liposome Hb, Neo red cell (NRC), in a simple in vitro model of Langendorff perfusion of the rat heart using Krebs-Henseleit (KH) solution as the perfusate. In the KH solution, NRC (Hb at 1 mg/ml), however, induced an immediate and abnormal increase in perfusion pressure. Histological examinations revealed that embolisms were the likely cause of this disturbance. Inorganic crystals formed by the mixing of NRC with the perfusate were a possible source of the embolisms. We found that the addition of bovine serum albumin to the perfusate was effective in avoiding embolic events. This protocol was used to compare the vasoconstrictive properties of unmodified bovine Hb and NRC. Unmodified bovine Hb (1 mg/ml) caused an increase in perfusion pressure and a decrease in the duration of bradykinin-induced relaxation. In contrast, NRC (Hb at 1 mg/ml) had no such vasoconstrictive effects. These results provide the first information regarding perfusion of the circulatory vascular bed by NRC and further evidence that the encapsulation of Hb into liposomes is an effective approach to modulate Hb-related vasoconstrictive activity.
We examined the effects of liposome-encapsulated hemoglobin, neo red cells (NRCs), on hemorrhagic shock in a canine model. The dogs were divided into the three groups according to treatment. In group 1, composed of six dogs, NRCs were substituted for blood without shock being induced; in group 2, composed of six dogs, NRCs were administered immediately after mild shock had been induced by exsanguination through the vein; and in group 3, composed of seven dogs, NRCs were administered after they had been left untreated for 30 min inducing severe shock. In group 2, administration of NRCs at a dose equivalent to the volume of exsanguinated blood improved the symptoms of shock; however, in group 3, a dose of NRCs 1.6-times the volume of exsanguinated blood was required. Peripheral vascular resistance (PVR) decreased after NRC administration in groups 1 and 2, but increased in group 3. On the other hand, the cardiac index (CI) increased in groups 1 and 2, and decreased in group 3. Concerning oxygen kinetics, there were no increases in the oxygen requirements or arteriovenous differences of the oxygen content per hemoglobin (AV/Hb) for NRCs in groups 1 and 2. Conversely, in group 3, the oxygen requirements increased and the NRCs compensated for the decrease in CI with an increase in AV/Hb by enhancing the oxygen transport efficiency to cope with the increased oxygen requirements.
We developed a liposome encapsulated hemoglobin named Neo Red Cells (NRC), NRC (1) readily circulates, (2) shows a high oxygen transport efficiency, and (3) has a strong capsule membrane. In this study, we evaluated the effect of NRC as a priming solution for total cardiopulmonary bypass (TCPB) using a dog. The TCPB was started after removal of 57.1-73.3% of autologous blood and continued for 7 hours. During TCPB using NRC, the vascular resistance (VR) decreased to 1/4 of VR when red blood cells (RBC) were used. This change suggests that NRC, the viscosity of which is lower than that of RBC, reduced the load on the circulation system. The oxygen volume delivered by NRC was higher than that delivered by RBC, resulting in a greater oxygen consumption with NRC. During TCPB using NRC, the serum LDH level was lower than that using RBC. So we concluded that NRC compensated for the reduction in the oxygen transport ability, which is a disadvantage of dilution TCPB, and further increased the circulation improving effect and anti-hemolytic effect, which are advantages of the procedure. It, thus, enhanced both the safety and effectiveness of dilution TCPB.
The purpose of this study was to evaluate the effects of liposome encapsulated hemoglobin named "Neo Red Cells (NRC)" on canine hemorrhagic shock model and its safety for the vital organs in a whole blood exchange model. HEMORRHAGIC SHOCK: Nine adult mongrel dogs were used. Under mechanical ventilation inhaling room air, blood was withdrawn via an artery at a rate of 40 ml/min in order to induce hemorrhagic shock (systolic pressure below 60 mm Hg) and then NRC was transfused. For each animal, three to five cycles of bloodletting and NRC transfusion were performed. After blood exchange, total peripheral resistance index (TPRI) decreased and cardiac index (CI) increased. These changes were more marked in the high exchange group (exchange rate over 88%; five animals) than in the low exchange group (less than 88%; four animals), indicating that the low viscosity NRC reduced the load on the circulatory system. The A-V difference in oxygen content per lg hemoglobin was greater after blood exchange, indicating that oxygen binding capacity of NRC is higher than that of red blood cells. WHOLE BLOOD EXCHANGE: Five beagles were used for the blood exchange. The blood was withdrawn from an artery at a rate of 15 ml/min and NRC was infused at the same time. A dog whose blood was exchanged with hydroxyethylstarch instead of NRC died within 15 hours after blood exchange. Three dogs whose blood was exchanged with NRC (exchange rate was from 82 to 90%) have been living over a year without any side effects. A dog sacrificed on the 15th postoperative day for autopsy, microscopically showed no side effects in vital organs. We conclude that NRC is more suitable than natural blood for treatment of hemorrhagic shock and safe for vital organs.
The purpose of this study was to evaluate liposome-encapsulated hemoglobin, named Neo Red Cells (NRC), on hemodynamics and oxygen-transport capacity in a blood exchange experiment. The experiment was carried out in nine mongrel dogs. Depending on the percentage of blood exchange with NRC, the animals were divided into two groups; Group I (4 animals with an exchange rate less than 88%), and Group II (5 animals with an exchange rate over 88%). After blood exchange, total peripheral vascular resistance index (TPRI) decreased and cardiac index (CI) increased. These changes were more marked in Group II than in Group I, thus showing that NRC relieved the burden on the heart, probably due to the fact that the viscosity of NRC is 2 cp which is less than 1/3 that of whole blood. The oxygen binding capacity per 1g hemoglobin in NRC was 2-4 times as much as red blood cells. Thus, NRC was superior to natural red blood cells in terms of oxygen transport capacity and its effects on the circulatory system.
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