Modulation of Phospholipid Phase Structures and Transitions Induced by Oxysterols

Phase changes in membrane lipids in sickle red cell shed-vesicles and sickle red cells

Lipid phase transformations may occur in the membranes of sickle red cell shed-vesicles and sickle red cells. The presence of such phase changes could be important in sickle cell disease since membrane phase changes appear to contribute to the generation of antiphospholipid antibodies that are thrombophilic and occur in sickle cell disease. In the present study, we have evaluated sickle red cell shed-vesicles and sickle red cells for the presence of non-bilayer lipid phases using 31P-NMR spectroscopy. Results show that the spectra of both the shed-vesicles and the sickle red cells are compatible with the occurrence of non-bilayer phases in the membrane bilayers. The findings support the concept that these membranes could contribute to the generation of antiphospholipid antibodies in sickle cell disease.

Antiphospholipid antibodies in sickle cell disease

Antiphospholipid antibody formation can be induced in mice by phospholipid in a hexagonal II phase but not by phospholipid in a bilayer phase. Since sickle red cell membranes have increased hexagonal II phase content, we have measured serum antiphospholipid antibody levels in 25 patients with sickle cell disease to determine whether anti-phospholipid antibody may similarly be induced in these patients. Seventeen of the 25 patients (68%) had increased levels of antiphospholipid antibodies. Eleven patients (65%) had IgG and six each (35%) had IgM and IgA isotypes. Antiphosphatidylethanolamine, antiphosphatidylserine, antiphosphatidylinositol, and antiphosphatidic acid were the most frequently increased antibodies. The finding of increased antiphospholipid antibodies in these patients is compatible with the concept that antiphospholipid antibody formation is associated with structural changes in the red cell membrane and that such structural changes occur in the red cells of patients with sickle cell disease.