The neurotoxicity of amyloid beta protein in aged primates.

Amyloid beta protein deposition is a universal feature of Alzheimer's disease brain. To investigate the effects of amyloid beta protein in aged primates, intracerebral microinjections of solubilized amyloid beta (A beta (1-40)) and control peptides were made into the frontal cortex of 7 primates under stereotactic guidance. Control injections consisted of vehicle alone, a 37 amino acid non toxic peptide (A37), scrambled peptide (CA4), and reverse peptide (A beta (40-1)). Amyloid beta peptide produced dose-dependent cortical lesions that were significantly larger than those produced by vehicle or by isomolar control peptides (3.28 and 2.20 fold larger respectively) (p = < 0.005). In 5 aged primates, the cortex surrounding the amyloid beta lesions contained argyrophilic, thioflavine S fluorescent, Alz 50 and ubiquitin immunoreactive neurons and perikarya. The number of Alz 50 immunoreactive neurons surrounding the amyloid beta injections was significantly greater (mean 127 +/- 39) than the number found surrounding reverse peptide injections (mean 20 +/- 13) and other control peptides (mean 0.8 +/- 0.3) (p < 0.05). Neuronal and neuritic alterations were not found adjacent to the amyloid beta peptide lesions in young monkeys and control injections produced insignificant Alz 50 neuronal positivity. These findings suggest that amyloid beta peptide is neurotoxic in primate brain and that the cytoskeletal response to amyloid beta protein is specific and age-related.