Submitted on November 29, 2004
Accepted on January 24, 2005
Oxygen Release from Low and Normal P50 Hb-vesicles in Transiently Occluded Arterioles of the Hamster Window Model
Hiromi Sakai1, Pedro Cabrales2, Amy G Tsai2, Eishun Tsuchida1*, and Marcos Intaglietta2
1 Advanced Research Institute for Science and Engineering, Waseda University, Tokyo, Japan
2 Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA; La Jolla Bioengineering Institute, La Jolla, CA, USA
* To whom correspondence should be addressed. E-mail: eishun{at}waseda.jp.
A phospholipid vesicle encapsulating hemoglobin (Hb-vesicle, HbV) has been developed as a transfusion alternative. One characteristic of HbV is that the O2 affinity (P50) of Hb can be easily regulated by the amount of coencapsulated allosteric effector, pyridoxal 5'-phosphate. In this paper we prepared two HbVs with different P50s (8 and 29 mmHg, termed HbV8 and HbV29, respectively), and observed their O2 releasing behavior from an occluded arteriole in a hamster skinfold window model. Conscious hamsters received HbV8 or HbV29 at the dose rate of 7 mL/kg. In the microscopic view, an arteriole (diameter: 53.0 ± 6.6 µm) was occluded transcutaneously by a glass pipette on a manipulator and the reduction of the intra arteriolar O2 tension (pO2) 100 µm down from the occlusion was measured by the phosphorescence quenching of pre-infused Pd-porphyrin. The baseline arteriolar pO2 (50 - 52 mmHg) decreased to about 5 mmHg for all the groups. Occlusion after HbV8 infusion showed slightly slower rate of pO2 reduction in comparison with that after HbV29 infusion. The calculation of the arteriolar O2 content at each reducing pO2 in combination with the O2 equilibrium curves of HbVs indicated that HbV8 showed significantly slower rate of O2 release in comparison with HbV29 and was a primary source of O2 (maximum fraction, 0.55) overwhelming RBCs when the pO2 was reduced (e.g., < 10 mmHg) in spite of a small dosage of HbV. This result supports the possible utilization of Hb-based O2 carriers with lower P50 for oxygenation of ischemic tissues.
