In vitro evaluation of a pyridoxalated hemoglobin polyoxyethylene conjugate in reversing cell sickling

In sickle cell disease (SCD) microcirculatory blockage by red blood cells (RBC) occurs because of their low oxygen concentration, which results in both sickling and painful crises. Pyridoxalated hemoglobin polyoxyethylene (PHP), developed from human RBC hemoglobin (Hb) by chemical modification as an oxygen carrier, was evaluated in vitro for its ability to reverse cell sickling. PHP solutions of 6 or 8 g % Hb and a P50 of 20 mmHg were evaluated. RBC were obtained from SCD patients treated by exchange transfusion. The in vitro positive pressure filtration method (47 mm 5 microns Nuclepore membrane) was used. Comparisons of PHP with low oxygen carrier solutions (Hespan, saline) were made at flows of 0.43 to 6.0 ml/min. PO2 increases in a 20% mixture of air saturated solutions with deoxygenated sickle cell suspensions (SCS), at a hematocrit of 1%, were significantly higher in PHP as compared with saline and Hespan. The filtration resistance of deoxygenated SCS mixed with PHP was significantly lower than that of deoxygenated SCS mixed with saline and Hespan, and was comparable to that of air oxygenated SCS. By the 20% (v/v) addition of air saturated PHP to deoxygenated SCS, 89 +/- 2% of the sickled cells were unsickled. A novel artificial capillary system (ACS) modeling the dynamics of the microcirculation of the body was used. With the ACS plugged with deoxygenated cells, perfusion with oxygenated cell-PHP solutions was significantly more efficient in reversing the blockage than oxygenated saline and Hespan solutions. PHP reverses cell sickling by its effective delivery of oxygen.