Rheological assessment of antisickling effects of pyridoxine and pyridoxal.

The antisickling effects of pyridoxine and pyridoxal on intact sickle erythrocytes (SRBCs) were assessed by microviscometry of cell suspensions at shear rates of 1.15 to 230.0/s, measurement of cellular deformability by cell filtration and scanning and transmission electron microscopy (EM). Incubation of fresh SRBCs in albuminated (0.1%) phosphate buffered saline, pH 7.4, with 5 to 30 mM, pyridoxine or pyridoxal at 37 degrees C for 90 min followed by deoxygenation to pO2 = 25 mmHg, decreased the percentage of sickled cells observed as a function of vitamin concentration. EM of fresh SRBCs incubated with 20 mM pyridoxine or pyridoxal at 25 mmHg pO2 showed mostly discocytes without intracellular fibers indicating absence of hemoglobin polymerization. Determination of fluidity (viscosity-1) versus shear stress showed that both pyridoxine and pyridoxal significantly (P less than 0.01) increased the fluidity of a deoxygenated suspension of SRBCs. The estimated apparent yield stress from Casson plots for the vitamin-treated deoxygenated cells and the deoxygenated control cells were 0.11 and 0.18 dynes/cm2 respectively. The relative resistance of 0.2% cell suspension to flow through 5 microns Nuclepore filters indicated a significant increase (greater than 75%) in the deformability of the vitamin-treated deoxygenated sickle cells. The ultrastructure of the SRBCs through the filter pores further suggested that the fluidity of the intracellular milieu of the vitamin-treated deoxygenated cells was higher than that of the deoxygenated controls. These data support the hypothesis that pyridoxylation of sickle hemoglobin inhibits sickling, increases the fluidity of sickle hemoglobin under low pO2, and thereby enhances the deformability of SRBCs in models of capillary blood flow.