Paired helical filaments associated with Alzheimer disease are readily soluble structures.

Considerable controversy exists concerning the origin and composition of Alzheimer neurofibrillary tangles (ANT) and of paired helical filaments (PHF), the abnormal cytoplasmic fibers which ultrastructurally are the major components of ANT. Thus far, the unusual solubility properties of PHF have hindered the analysis of ANT. A new procedure is presented for isolating purified PHF which are soluble in the presence of sodium dodecyl sulfate. The purification protocol involves differential and rate zonal centrifugation, treatment with the detergents sarcosyl and sulfobetain 3-14, and sonication. The isolated PHF from Alzheimer disease/senile dementia of the Alzheimer type (7 cases) and Down's syndrome (one case) have been characterized structurally by negative-stain electron microscopy, biochemically by PAGE, and immunologically by both the ELISA technique and Western blot analysis using a monoclonal antibody prepared against ANT. Distinct polypeptides were shown to be associated with this structure and not seen in preparations from young and age-matched normal brains.