DIMINISHED OSMOTIC FRAGILITY OF HUMAN-ERYTHROCYTES FOLLOWING THE MEMBRANE INSERTION OF OXYGENATED STEROL COMPOUNDS

Abstract

Oxygenated sterol compounds (OSC), when incubated for 1 h with human erythrocytes in lipoprotein-depleted medium at concentrations of 0.625-5 .times. 10-5 M, are inserted into the cell membrane and remain there despite subsequent washing of the cells. The insertion caused expansion of the surface area of the red cell ghost membrane, an increase in critical hemolytic volume and in diminished osmotic fragility of the erythrocytes. This effect is seen with echinocyte-forming and with non-echinocyte-forming OSC. Erythrocytes treated with OSC do not differ from control cells with respect to their mean cell volume (MCV) in isotonic solution, water content, ion fluxes and filterability through polycarbonate filters. The shift of the osmotic fragility curve toward lower NaCl concentrations is proportional to the amount of OSC inserted into the red cell membrane. 7.beta.-Hydroxycholesterol, 22-ketocholesterol and 20.alpha.-hydroxycholesterol are the most potent inhibitors of osmotic lysis. The effect of OSC on osmotic fragility is diminished if the erythrocytes are incubated in a lipoprotein-containing medium; free cholesterol does not change this effect. Various progesterones protect red cells from osmotic lysis, but only if the erythrocytes are directly exposed to the compounds present in the hypotonic NaCl solutions used for measurement of their osmotic fragility. Progesterones do not remain in the membrane after the cells were washed. The OSC are capable of correcting the osmotic fragility curve of red cells from patients with hereditary spherocytosis. These experiments may suggest an approach to the pharmacologic treatment of hereditary spherocytosis.