Natural Medicines and Their Underlying Mechanisms of Prevention and Recovery from Amyloid Β-Induced Axonal Degeneration in Alzheimer's Disease

Abstract

In Alzheimer's disease (AD), amyloid β (Aβ) induces axonal degeneration, neuronal network disruption, and memory impairment. Although many candidate drugs to reduce Aβ have been clinically investigated, they failed to recover the memory function in AD patients. Reportedly, Aβ deposition occurred before the onset of AD. Once neuronal networks were disrupted by Aβ, they could hardly be recovered. Therefore, we speculated that only removal of Aβ was not enough for AD therapy, and prevention and recovery from neuronal network disruption were also needed. This review describes the challenges related to the condition of axons for AD therapy. We established novel in vitro models of Aβ-induced axonal degeneration. Using these models, we found that several traditional medicines and their constituents prevented or helped recover from Aβ-induced axonal degeneration. These drugs also prevented or helped recover from memory impairment in in vivo models of AD. One of these drugs ameliorated memory decline in AD patients in a clinical study. These results indicate that prevention and recovery from axonal degeneration are possible strategies for AD therapy.

Keywords: Polygalae Radix; amyloid β; axon; diosgenin; kihito; naringenin; traditional medicines.

Figure 1

Aβ-induced growth cone collapse via clathrin-mediated endocytosis [31].

Figure 2

Structures of Ashwagandha-related compounds.

Figure 3

Signaling mechanism of diosgenin-induced memory recovery in Alzheimer’s disease models [63,71,72].

Figure 4

Mechanisms of memory recovery induced by Drynariae Rhizoma extract in Alzheimer’s disease models [80,91].