Aqueous Dissolution of Alzheimer's Disease Aβ Amyloid Deposits by Biometal Depletion

Robert A Cherny,Jacinta T Legg,Catriona A Mclean,David P Fairlie,Xudong Huang,Craig S Atwood,Konrad Beyreuther,Rudolph E Tanzi,Colin L Masters,Ashley I Bush

doi:10.1074/jbc.274.33.23223

Abstract

Zn(II) and Cu(II) precipitate Abeta in vitro into insoluble aggregates that are dissolved by metal chelators. We now report evidence that these biometals also mediate the deposition of Abeta amyloid in Alzheimer's disease, since the solubilization of Abeta from post-mortem brain tissue was significantly increased by the presence of chelators, EGTA, N,N,N',N'-tetrakis(2-pyridyl-methyl) ethylene diamine, and bathocuproine. Efficient extraction of Abeta also required Mg(II) and Ca(II). The chelators were more effective in extracting Abeta from Alzheimer's disease brain tissue than age-matched controls, suggesting that metal ions differentiate the chemical architecture of amyloid in Alzheimer's disease. Agents that specifically chelate copper and zinc ions but preserve Mg(II) and Ca(II) may be of therapeutic value in Alzheimer's disease.

Highlights

Zn(II) and Cu(II) precipitate A␤ in vitro into insoluble aggregates that are dissolved by metal chelators
Extraction of Alzheimer’s disease (AD) brain into phosphate-buffered saline (PBS) alone liberated a small amount of A␤ into the soluble phase in every case, confirming previous reports [11,12,13]
These data indicate that there is a pool of A␤ within the affected neocortex in AD that is held in sedimentable aggregates by metal ions, likely to be Cu(I) and Zn(II), and that these aggregates are solubilized by treatment with chelators

Summary

EXPERIMENTAL PROCEDURES

Tissue Selection—Post-mortem tissues, stored at Ϫ80 °C, were obtained from the National Heath and Medical Research Council-supported Brain Bank at the University of Melbourne together with accompanying histopathological and clinical data. AD was assessed according to Consortium to Establish a Register for Alzheimer’s Disease criteria [7]. In order to examine the chemical architecture of the A␤ deposition that is observed in non-AD aged brain, A␤ immunohistochemistry was used to select age-matched control (AC) cases that did not reach Consortium to Establish a Register for Alzheimer’s Disease criteria and in which amyloid deposition, if present, was detectable only in the form of diffuse plaques but not neuritic plaques. To obtain the PBS-extractable fraction, the homogenate was centrifuged at 100,000 ϫ g for 30 min, and the supernatant was removed and divided into 1-ml aliquots. Protein within a 1-ml supernatant sample was precipitated using 1:5 ice-cold 10% trichloroacetic acid, and pelleted by centrifugation at 10,000 ϫ g for 20 min. Total A␤ in the cortical samples was obtained by homogenizing in 1 ml of PBS and boiling in sample buffer as above

Alzheimer Amyloid Is Dissolved by Chelators

RESULTS

PBS TPEN

AC subject

DISCUSSION