Received for publication December 8, 2006.
Revised January 12, 2007.
Accepted for publication January 16, 2007.

Amyloid- in Alzheimer Disease: The Null Versus the Alternate Hypothesis

Abstract

For nearly twenty years, the primary focus for researchers studying Alzheimer disease has been centered on amyloid- such that the Amyloid Cascade Hypothesis has become the "Null Hypothesis". Indeed, amyloid- is, by the current definition of the disease, an obligate player in pathophysiology, is toxic to neurons in vitro, and, perhaps most compelling, is increased by all of the human genetic influences on the disease. Therefore, targeting amyloid- is the focus of considerable basic and therapeutic interest. However, an increasingly vocal group of investigators are arriving at an "Alternate Hypothesis" stating that amyloid-, while certainly involved in the disease, is not an initiating event but, rather, is secondary to other pathogenic events. Additionally, and perhaps most contrary to current thinking, the "Alternate Hypothesis" proposes that the role of amyloid- is not as a harbinger of death but rather a protective response to neuronal insult. To determine which hypothesis relates best to Alzheimer disease requires a broader view of disease pathogenesis and is discussed herein.

Key words: Alzheimer disease, amyloid-beta, antioxidants, cell death, oxidative stress, phosphorylated tau