1 We investigated whether withanolide A (WL-A), isolated from the Indian herbal drug Ashwagandha (root of Withania somnifera), could regenerate neurites and reconstruct synapses in severely damaged neurons. We also investigated the effect of WL-A on memory-deficient mice showing neuronal atrophy and synaptic loss in the brain. Axons, dendrites, presynapses, and postsynapses were visualized by immunostaining for phosphorylated neurofilament-H (NF-H), microtubule-associated protein 2 (MAP2), synaptophysin, and postsynaptic density-95 (PSD-95), respectively. 2 Treatment with Ab(25-35) (10 mM) induced axonal and dendritic atrophy, and pre-and postsynaptic loss in cultured rat cortical neurons. Subsequent treatment with WL-A (1 mM) induced significant regeneration of both axons and dendrites, in addition to the reconstruction of pre-and postsynapses in the neurons. 3 WL-A (10 mmol kg À1 day À1 , for 13 days, p.o.) recovered Ab(25-35)-induced memory deficit in mice. At that time, the decline of axons, dendrites, and synapses in the cerebral cortex and hippocampus was almost recovered. 4 WL-A is therefore an important candidate for the therapeutic treatment of neurodegenerative diseases, as it is able to reconstruct neuronal networks.

The aim of this study was to investigate the effects and the mechanism of diosgenin, a famous plant-derived steroidal sapogenin, on memory deficits in Alzheimer's disease (AD) model mice. Diosgenin-treated 5XFAD mice exhibited significantly improved performance of object recognition memory. Diosgenin treatment significantly reduced amyloid plaques and neurofibrillary tangles in the cerebral cortex and hippocampus. Degenerated axons and presynaptic terminals that were only observed in regions closely associated with amyloid plaques were significantly reduced by diosgenin treatment. The 1,25D3-membrane-associated, rapid response steroid-binding protein (1,25D3-MARRS) was shown to be a target of diosgenin. 1,25D3-MARRS knockdown completely inhibited diosgenin-induced axonal growth in cortical neurons. Treatment with a neutralizing antibody against 1,25D3-MARRS diminished the axonal regeneration effect of diosgenin in Aβ(1–42)-induced axonal atrophy. This is the first study to demonstrate that the exogenous stimulator diosgenin activates the 1,25D3-MARRS pathway, which may be a very critical signaling target for anti-AD therapy.

No abstract

The reconstruction of neuronal networks in the damaged brain is necessary for the therapeutic treatment of neurodegenerative diseases. We have screened the neurite outgrowth activity of herbal drugs, and identified several active constituents. In each compound, neurite outgrowth activity was investigated under amyloid-β-induced neuritic atrophy. Most of the compounds with neurite regenerative activity also demonstrated memory improvement activity in Alzheimer’s disease-model mice. Protopanaxadiol-type saponins in Ginseng drugs and their metabolite, M1 (20-O-β-D-glucopyranosyl-(20S)-protopanaxadiol), showed potent regeneration activity for axons and synapses, and amelioration of memory impairment. Withanolide derivatives (withanolide A, withanoside IV, and withanoside VI) isolated from the Indian herbal drug Ashwagandha, also showed neurite extension in normal and damaged cortical neurons. Trigonelline, a constituent of coffee beans, demonstrated the regeneration of dendrites and axons, in addition to memory improvement.

We previously screened neurite outgrowth activities of several Ginseng drugs in human neuroblastoma, and demonstrated that protopanaxadiol (ppd)-type saponins were active constituents. Since ppd-type saponins are known to be completely metabolized to 20-O-b-D-glucopyranosyl-20(S)-protopanaxadiol (M1) by intestinal bacteria when taken orally, M1 and ginsenoside Rb 1 , as a representative of ppd-type saponins, were examined for cognitive disorder. In a mouse model of Alzheimer's disease (AD) by Ab(25-35) i.c.v. injection, impaired spatial memory was recovered by p.o. administration of ginsenoside Rb 1 or M1. Although the expression levels of phosphorylated NF-H and synaptophysin were reduced in the cerebral cortex and the hippocampus of Ab(25-35)-injected mice, their levels in ginsenoside Rb 1 -and M1-treated mice were almost completely recovered up to control levels. Potencies of the effects were not different between ginsenoside Rb 1 and M1 when given orally, suggesting that most of the ginsenoside Rb 1 may be metabolized to M1, and M1 is an active principal of ppd-type saponins for the memory improvement. In cultured rat cortical neurons, M1 showed extension activity of axons, but not dendrites. The axon-specific outgrowth was seen even when neuritic atrophy had already progressed in response to administration of Ab(25-35) as well as in the normal condition. These results suggest that M1 has axonal extension activity in degenerated neurons, and improve memory disorder and synaptic loss induced by . M1 was shown to be effective in vitro and in vivo, indicating that Ginseng drugs containing ppd-type saponins may reactivate neuronal function in AD by p.o. administration.