Amyloid is essential but insufficient for Alzheimer causation: addition of subcellular cofactors is required for dementia.

Abstract

The aim of this study is to examine the hypotheses stating the importance of amyloid or of its oligomers in the pathogenesis of Alzheimer's disease (AD). Published studies were examined. The importance of amyloid in the pathogenesis of AD is well established, yet accepting it as the main cause for AD is problematic, because amyloid-centric treatments have provided no clinical benefit and about one-third of cognitively normal, older persons have cerebral amyloid plaques. Also problematic is the alternative hypothesis that, instead of amyloid plaques, it is oligomers of amyloid precursor protein that cause AD.Evidence is presented suggesting amyloid/oligomers as necessary but insufficient causes of the dementia and that, for dementia to develop, requires the addition of cofactors known to be associated with AD. Those cofactors include several subcellular processes: mitochondrial impairments; the Wnt signaling system; the unfolded protein response; the ubiquitin proteasome system; the Notch signaling system; and tau, calcium, and oxidative damage. A modified amyloid/oligomer hypothesis for the pathogenesis of AD is that activation of one or more of the aforementioned cofactors creates a burden of functional impairments that, in conjunction with amyloid/oligomers, now crosses a threshold of dysfunction that results in clinical dementia. Of considerable importance, several treatments that might reverse the activation of some of the subcellular processes are available, for example, lithium, pioglitazone, erythropoietin, and prazosin; they should be given in combination in a clinical trial to test their safety and efficacy. © 2017 John Wiley & Sons, Ltd.