Abnormal Kinetics of Red Cell Membrane Cholesterol in Acanthocytes: Studies in Genetic and Experimental Abetalipoproteinaemia and in Spur Cell Anaemia

Summary. Abnormalities in the content and kinetics of red cell membrane cholesterol are described in several syndromes associated with spurring of red cells (‘acanthocytosis’). In all (hereditary abetalipoproteinaemia, ‘spur cell anaemia’ of severe hepatic failure, and in a lipid‐deprived infant with acquired hypobeta‐lipoproteinaemia) red cell membrane cholesterol was 15–50% increased. Free cholesterol normally flows bidirectionally between red cell membranes and plasma betalipoproteins, but plasmas from affected patients with acanthocytosis were uniformly inefficient in accepting cholesterol from red cells. Stagnation of the sterol on red cells resulted. Plasma from rats in which abetalipoproteinaemia was experimentally produced by prolonged feeding of orotic acid, demonstrated similar abnormalities. Thus, red cells from treated animals became acanthocytic within I mth; with the shape change an increase in membrane cholesterol of about 20% and a significant decrease in osmotic fragility occurred. ¹⁴C‐cholesterol flux from rat red cell membranes was 30–40% decreased into the experimentally‐abetalipoproteinaemic, relative to betalipoprotein‐replete, rat plasmas. We conclude that stagnation and, less importantly, accumulation of red cell cholesterol may be associated with conformational changes in the structural lipoproteins of the red cell membrane leading to spurring. Regardless of mechanism, this shape change causes acanthocytes to become abnormally rigid and resistant to flow, documented in the present studies by their increased viscosity in cone‐plate viscosimeters and by their diminished filterability through micropore filters. Both features are probably involved in the diminished survival of these cells in the circulation.