Differential electrophoretic behavior in aqueous polymer solutions of red blood cells from Alzheimer patients and from normal individuals

The recently reported phenomenon that red blood cells (RBC) from Alzheimer disease (AD) patients and normal individuals, which have identical electrophoretic mobilities (EPM) in phosphate-buffered saline (PBS), have different EPM in appropriately selected polymer solutions, has been further explored. Of a number of in vitro treatments to which AD and normal RBC were subjected prior to EPM measurements in bottom phase (from a dextran-poly(ethylene glycol) (PEG) aqueous phase system) only trypsin eliminated the difference. Thus, the differential polymer interaction between AD and normal RBC, thought to be the basis for their dissimilar EPM, can be abolished by appropriate proteolytic modification of the cell surfaces and suggests protein as a source of difference. Because young and old RBC from normal individuals, which have the same EPM in PBS, have different EPM in certain polymer solutions, and the RBC from AD patients have been reported to age abnormally, we also compared the young and old RBC subpopulations from these two sources. By the criterion of cell electrophoresis in polymer solutions the differences between AD and normal RBC and between young and old RBC are distinct. The EPM of AD and normal RBC differ in bottom phase or PEG but not in dextran solution; while the EPM of young and old RBC differ predominantly in dextran. We speculate that since the observed difference in EPM of RBC from AD patients and normals depends on protein(s) yet is anticoagulant-related (being obtained only when blood is collected in citrate or oxalate) it might be the result of an interaction (Ca(2+)-mediated?) between the surfaces of these cells and protein component(s) of their respective, compositionally differing sera.