Biophysical characteristics of hemoglobin intramolecularly cross-linked and polymerized

Hemoglobin modified by intramolecular cross-linking with 2-nor-2-formylpyridoxal 5'-phosphate (NFPLP) has potential application as an oxygen-carrying plasma expander with improved vascular retention time (threefold) and oxygen-transporting properties compared to native hemoglobin. Under some conditions a further prolongation is required. In this study polymerization of the purified modified hemoglobin (HbNFPLP) with glutaraldehyde was investigated. The influence of the degree of polymerization on the iso-oncotic concentration and the viscosity of the polymerized Hb-NFPLP (polyHbNFPLP) was investigated with three products polymerized to an increasing extent. Exchange transfusions in rats followed by gel filtration analyses of plasma samples provided information on the vascular retention time of four separate polymer fractions (i.e., monomers, dimers, trimers/tetramers, and polymers). The vascular retention time of these fractions correlated with their size. For lightly and highly polymerized HbNFPLP we found fivefold and sevenfold increases, respectively, compared to the retention time for native hemoglobin. This finding and the different shapes of the clearance curves suggested a different clearance mechanism from the vascular system for the monomer and polymer fractions. By polymerizing HbNFPLP the oxygen affinity was enhanced (oxygen half-saturation pressure shifted from 45 to 22 mm Hg), and it appeared to be independent of the degree of polymerization. Because hemoglobin was undetectable in the urine of the rats after the exchange transfusions, no accumulation of polyHbNFPLP will occur in the tubules of the kidney.(ABSTRACT TRUNCATED AT 250 WORDS)