Neurotoxicity of a fragment of the amyloid precursor associated with Alzheimer's disease

Amyloid and Alzheimer's disease--cause or effect?

The design of a rational therapeutic approach to Alzheimer's disease ultimately depends on an understanding of its pathogenesis. Amyloid deposition is a well-established, but poorly understood concomitant of Alzheimer's disease. Advances in our knowledge of the normal posttranslational processing of the amyloid precursor protein may help to elucidate the defect in Alzheimer's disease that leads to amyloid deposition. In addition, recent insights into the biological and pathological effects of amyloid on CNS neurons promise to help clarify the role of this protein in the disease mechanism.

The amyloid proteins of Alzheimer's disease as potential targets for drug therapy

Two amyloid proteins accumulate in Alzheimer's disease. These proteins, beta amyloid protein and paired helical filament protein, are present in the hallmark lesions of Alzheimer's disease, neuritic plaques and neurofibrillary tangles. Although the amino acid sequences of these two proteins are likely to be different, they nevertheless share certain physical characteristics which define each as belonging to a common class of proteins, amyloid proteins. Since these proteins are probably important in the pathology of Alzheimer's disease, drugs that prevent their accumulation should have therapeutic utility. Based on the amyloidoses associated with other diseases, three mechanisms for amyloid formation have emerged. These mechanisms form a framework for studying Alzheimer amyloids and designing interventions. One mechanism involves posttranslational events which render a normal protein amyloidogenic. Proteolysis, phosphorylation, glycosylation, and transglutamination may be relevant posttranslational events in Alzheimer's disease. If more conclusive evidence can be generated suggesting that these events are involved in the abnormal formation of amyloid in Alzheimer's disease, then these events will become viable targets for drug therapy. Another mechanism for amyloid formation results from expression of an abnormal gene which, in the case of familial Alzheimer's disease, may be an important etiological component. A third mechanism involves the accumulation of a normal protein to a threshold concentration that spontaneously forms amyloid. An effective therapeutic approach for these last two mechanisms could likely include pharmacological manipulation of gene expression.

NGF and Alzheimer's disease--considerations and caveats

The proposed use of NGF in the treatment of Alzheimer's disease is based on recent experimental evidence suggesting that NGF is a neurotrophic factor for basal forebrain cholinergic neurons. Although potentially efficacious, the effects of NGF in the setting of Alzheimer's disease have not been determined. A cause for concern is the recently demonstrated effect of NGF on amyloid synthesis raising the possibility that NGF could exacerbate the underlying pathology. Several issues relevant to the design of a clinical trial for NGF in Alzheimer's disease are addressed.