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Effects of hypothermic conditions on the oxygen carrying capacity of crosslinked hemoglobins
1Center for Biologics, Evaluation and Research, FDA, NIH, Bethesda, Maryland 20892.
In view of the potential application for hemoglobin-based oxygen carriers (HBOCs) in organ perfusion under hypothermic conditions, we examined the temperature dependence of oxygen equilibrium curves (OECs) at 15-37 degrees C of three HBOCs: HbA-FMDA and HbBv-FMDA, produced by the reaction of human or bovine oxyHb with fumaryl mono-dibromoaspirin, and HbA-DBBF, produced by the reaction of human deoxyHb with bis(3,5-dibromosalicyl) fumarate. OECs for HbA-DBBF, HbA-FMDA and HbBv-FMDA at 37 degrees C were right shifted (P50 = 24.5, 17 and 35 torr, respectively). van't Hoff's rule gave HbA-DBBF (-12.2 +/- 2.8), HbA-FMDA (-12.0 +/- 2.0), HbBv-FMDA (-10.5 +/- 1.8); these values do not significantly differ from that for native HbAo (-11.5 +/- 2.4). Among the hemoglobins included in this study, HbBv-FMDA had the most favorable oxygenation characteristics at low temperatures (a P50 of 6.0 torr at 15 degrees C as compared to only 2-3 torr for the other hemoglobins in the study). Recently, however, a human hemoglobin crosslinked with bis-pyridoxyl tetraphosphate was reported to have a P50 of 15 torr at 16 degrees C (Keipert et al, Transfusion 1989; 29: 768-773). Therefore, precise knowledge of the oxygen delivering capacity of any potential HBOC should be explored under hypothermic conditions as performance under these conditions may determine its usefulness as an organ perfusate.
In view of the potential application for hemoglobin-based oxygen carriers (HBOCs) in organ perfusion under hypothermic conditions, we examined the temperature dependence of oxygen equilibrium curves (OECs) at 15-37 degrees C of three HBOCs: HbA-FMDA and HbBv-FMDA, produced by the reaction of human or bovine oxyHb with fumaryl mono-dibromoaspirin, and HbA-DBBF, produced by the reaction of human deoxyHb with bis(3,5-dibromosalicyl) fumarate. OECs for HbA-DBBF, HbA-FMDA and HbBv-FMDA at 37 degrees C were right shifted (P50 = 24.5, 17 and 35 torr, respectively). van't Hoff's rule gave HbA-DBBF (-12.2 +/- 2.8), HbA-FMDA (-12.0 +/- 2.0), HbBv-FMDA (-10.5 +/- 1.8); these values do not significantly differ from that for native HbAo (-11.5 +/- 2.4). Among the hemoglobins included in this study, HbBv-FMDA had the most favorable oxygenation characteristics at low temperatures (a P50 of 6.0 torr at 15 degrees C as compared to only 2-3 torr for the other hemoglobins in the study). Recently, however, a human hemoglobin crosslinked with bis-pyridoxyl tetraphosphate was reported to have a P50 of 15 torr at 16 degrees C (Keipert et al, Transfusion 1989; 29: 768-773). Therefore, precise knowledge of the oxygen delivering capacity of any potential HBOC should be explored under hypothermic conditions as performance under these conditions may determine its usefulness as an organ perfusate.