Physicochemical studies on those neurochemical factors that promote beta-amyloid deposition in APP trangenic mouse and human Alzheimer-diseased brain
Description
The present thesis focuses on deciphering the biochemical sequelae responsible for the precipitation of Alzheimer's disease (AD). The hallmark occurrence in AD is the assembly of Abeta (a normally soluble component of cerebrospinal fluid) into insoluble, extracellular plaques. The genetics of AD and recent observations of partial AD phenotype (i.e. Abeta plaque deposits) in transgenic mice overproducing Abeta indicate that Abeta amyloid deposition in the neocortex is intimately involved in the pathophysiology of the disorder. Hence, neurochemical candidates, which may impact the solubility of Abeta, were investigated. Recent studies conducted by our laboratory show that Abeta is a physiological metalloprotein, saturably binding zinc and copper. In fact, the interaction of Abeta with physiological concentrations of zinc, copper, and iron generate amyloid plaques in vitro, which can be resolubilized by the extraction of metal ions via chelation. Extending these findings, a vertically innovative approach was used to determine whether our in vitro findings are germane to AD pathology First, we investigated whether plaque deposited preferentially within cerebral regions enriched in zinc and copper. It was observed that brain regions targeted by AD (e.g. the hippocampal formation) experience drastic fluxes in metal ion concentrations, which may rise as much as 300muM in the case of zinc. In particular, it was noted that subdivisions of the inferior pulvinar that receive putative zinc-enriched projections from the primary visual cortex contain Abeta amyloid plaques. Interestingly, the region most affected in the thalamus is known to mediate visual attention which is compromised in AD Based on our above in vitro findings, the ability of metal chelators to resolubilize Abeta aggregates from the brains of transgenic mice overexpressing the human amyloid precursor protein (APP) and bearing cerebral amyloid was assessed. We noted that homogenization of APP transgenic mouse brains in the presence of metal chelators highly specific for zinc and copper significantly increased extractable Abeta (p < 0.01) as compared to homogenization in the presence of phosphate buffered saline alone. These findings suggest that the assembly of plaques in APP transgenic mouse brains appeared to parallel that in human, providing an exploitable model of AD amyloidosis Finally, United States Pharmacopeia (USP) drugs (i.e. clioquinol and triene), having zinc and copper chelating abilities, were administered daily to APP transgenic mice at 12 months of age. After 3 months of drug therapy, it was observed that animals receiving clioquinol, a chelator highly specific for zinc, were healthy and had more than a 50% reduction in Abeta load (p < 0.05) and a 60% decrease in sedimentable Abeta (p < 0.01). There was also a corresponding decrease (p < 0.05) in the progenitor pool of Abeta species, namely the APP beta-carboxyl terminal fragment concentration as measured by Western blot analysis. These findings suggest that chelation therapy may alter APP processing, thereby arresting Abeta production. Thus, metal chelators are one class of compounds that may be highly effective for the treatment of AD