Alzheimer disease β-amyloid activity mimics cholesterol oxidase
Luigi Puglielli, … , Dora M. Kovacs, Ashley I. Bush
Luigi Puglielli, … , Dora M. Kovacs, Ashley I. Bush
Published September 1, 2005
Citation Information: J Clin Invest. 2005;115(9):2556-2563. https://doi.org/10.1172/JCI23610.
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Research Article Neuroscience

Alzheimer disease β-amyloid activity mimics cholesterol oxidase

Abstract

The abnormal accumulation of amyloid β-peptide (Aβ) in the form of senile (or amyloid) plaques is one of the main characteristics of Alzheimer disease (AD). Both cholesterol and Cu2+ have been implicated in AD pathogenesis and plaque formation. Aβ binds Cu2+ with very high affinity, forming a redox-active complex that catalyzes H2O2 production from O2 and cholesterol. Here we show that Aβ:Cu2+ complexes oxidize cholesterol selectively at the C-3 hydroxyl group, catalytically producing 4-cholesten-3-one and therefore mimicking the activity of cholesterol oxidase, which is implicated in cardiovascular disease. Aβ toxicity in neuronal cultures correlated with this activity, which was inhibited by Cu2+ chelators including clioquinol. Cell death induced by staurosporine or H2O2 did not elevate 4-cholesten-3-one levels. Brain tissue from AD subjects had 98% more 4-cholesten-3-one than tissue from age-matched control subjects. We observed a similar increase in the brains of Tg2576 transgenic mice compared with nontransgenic littermates; the increase was inhibited by in vivo treatment with clioquinol, which suggests that brain Aβ accumulation elevates 4-cholesten-3-one levels in AD. Cu2+-mediated oxidation of cholesterol may be a pathogenic mechanism common to atherosclerosis and AD.

Authors

Luigi Puglielli, Avi L. Friedlich, Kenneth D.R. Setchell, Seiichi Nagano, Carlos Opazo, Robert A. Cherny, Kevin J. Barnham, John D. Wade, Simon Melov, Dora M. Kovacs, Ashley I. Bush

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Figure 1

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Cholesterol oxidase activity of Aβ:Cu2+. (A) Chemical structure of chole...
Cholesterol oxidase activity of Aβ:Cu2+. (A) Chemical structure of cholesterol showing oxidation of the hydroxyl group at position C-3 by cholesterol oxidase activity. (B and C) The migrations of nonoxidized cholesterol and 4-cholesten-3-one standards are shown. (B) Oxidation of cholesterol (50 μM) after incubation with BSA/Cu2+ (1 μM:2 μM), Aβ42 (1 μM), Cu2+ (2 μM), Aβ42:Cu2+ complex (1 μM:2 μM), or bacterial cholesterol oxidase (BCO; 5 IU). (C) Effect of Cu2+ chelation (with 1 mM TETA) on 4-cholesten-3-one generation by the Aβ42:Cu2+ complex; conditions as in B. Data are representative of at least 3 experiments. (D) Generation of 4-cholesten-3-one on TLC of Aβ40 and Aβ42 complexed with Cu2+ (1 μM:2 μM), and inhibition by the Cu2+ chelator CQ (100 μM). Bars show mean ± SD. Significance was calculated by 2-tailed Student’s t test of CQ effect. *P < 0.05. RU, relative units. (E) Total ion current mass chromatograms obtained by repetitive scanning GC-MS analysis of the underivatized compound and methyloxime derivative of the sample eluted from the TLC spot were superimposed for comparison with pure standard of 4-cholesten-3-one. The retention indices of each compound are denoted in MU. (F) Electron ionization (70 electron volts) mass spectrum of a compound identified as 4-cholesten-3-one by TLC from extracts of AD brain tissue eluted from the TLC plate: underivatized compound (top), 4-cholesten-3-one standard (middle), methyloxime derivative of the TLC extract (bottom; syn-isomer only shown) confirming the expected shift in masses of the molecular and fragment ions.