In Vivo Evaluation of a Pyridoxalated-Hemoglobin-Polyoxyethylene Conjugate

Abstract

A pyridoxalated-hemoglobin-polyoxyethylene conjugate (PHP) was developed from outdated human red cell hemoglobin through chemical modifications. The PHP has a mean molecular weight of approximately 90,000 daltons, with an acceptable P₅₀ of 22 ± 0.7mmHg. This report describes exchange transfusion studies (ET) to a final hematocrit of 5 ± 2% (n = 5) with PHP in mongrel dogs. Hespan (a plasma expander) was used as a control (n = 6). All the animals with PHP tolerated the procedure well and have survived more than 8 months to date. Five out of the six dogs receiving Hespan died within a week (p = 0.004). Reduction of hematological and coagulation parameters occurred following the ET and returned to the normal range by 4 weeks post ET. Serum electrolytes and renal function parameters (urea, creatinine) remained in the normal range. A transient slight increase in the hepatic enzyme SGOT was observed. At 2 weeks post ET open biopsies of major organs showed vacuolized cells in the liver and kidneys. Normal histology was noted at 3 months. The oxygen transporting properties examined showed effective oxygen delivery to the tissues for 6 hours post ET. PHP continued to transport oxygen for up to 48 hours studied post ET. Half-life of PHP in the circulation was 36.3 ± 3.5 hours. Urinary loss of hemoglobin measured up to 48 hours after ET was 9.4 ± 1.6% of the injected net hemoglobin. The PHP effectively supported life at lethal levels of anemia and is a physiologically acceptable solution. It has a relatively long intravascular residence time and transports oxygen to the tissue effectively for at least 6 hours.