Proliferation of internal membranes in platelets from patients with Alzheimer's disease.

Platelets from six moderately demented patients with probable Alzheimer's disease (NINCDS-ADRDA criteria) and six neurologically healthy controls were examined by electron microscopy. While platelet preparations from the control group contained infrequent examples (4.6%) of platelets with an unusually abundant internal system of smooth membranes, the frequency of these atypical cells (15.5%) was over three times higher in the samples prepared from the demented patients (p = 2.2 X 10(-2)). Consistent with our previous reports, platelet membranes from the Alzheimer's disease group exhibited a significant increase in membrane fluidity, as reflected by the rotation rate and fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) at 37 degrees C. Moreover, membrane fluidity was correlated with the frequency of atypical platelets visualized by electron microscopy. Since internal platelet membranes have been reported to be more fluid than external platelet membranes, these and other results presented suggest that the increase in platelet membrane fluidity associated with Alzheimer's disease may be the result of a dysregulation of platelet membrane biosynthesis.