Isolation and characterization of amyloid P component from Alzheimer's disease and other types of cerebral amyloidosis.

The presence of amyloid P-component (AP) within cerebral amyloid deposits was investigated by means of biochemical and immunocytochemical methods. Immunoperoxidase on formalin-fixed, paraffin-embedded tissue sections from Alzheimer's Disease, Down's Syndrome, asymptomatic age-related cerebral amyloidosis, sporadic cerebral amyloid angiopathy, hereditary cerebral hemorrhage with amyloidosis-Icelandic type, and hereditary cerebral hemorrhage with amyloidosis-Dutch type revealed the presence of AP in the affected vessel walls in all cases, and in parenchymal deposits resembling neuritic plaques of Alzheimer's disease, sporadic cerebral amyloid angiopathy, and hereditary cerebral hemorrhage with amyloidosis-Dutch type. A short digestion of tissue sections with pepsin was required for immunodetection of AP in these latter structures. After extraction of leptomeningeal amyloid fibrils, AP was characterized by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, Western blot, gel chromatography, and partial amino acid sequencing. Our results indicate that: (a) AP from cerebral amyloidosis has similar biochemical properties and homologous amino terminal sequence to AP from systemic amyloidosis; (b) AP is associated to a variety of brain amyloid deposits regardless of their chemical nature. The presence of AP, a serum protein, within the brain parenchyma points to an impairment of the blood-brain barrier in these diseases.