Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by dementia. The most characteristic pathological changes in AD brain include extracellular amyloid-β (Aβ) accumulation and neuronal loss. Particularly, cholinergic neurons in the nucleus basalis of Meynert are some of the first neuronal groups to degenerate; accumulating evidence suggests that Aβ oligomers are the primary form of neurotoxicity. Bacopa monniera is a traditional Indian memory enhancer whose extract has shown neuroprotective and Aβ-reducing effects. In this study, we explored the low molecular weight compounds from B. monniera extracts with an affinity to Aβ aggregates, including its oligomers, using Aβ oligomer-conjugated beads and identified plantainoside B. Plantainoside B exhibited evident neuroprotective effects by preventing Aβ attachment on the cell surface of human induced pluripotent stem cell (hiPSC)-derived cholinergic neurons. Moreover, it attenuated memory impairment in mice that received intrahippocampal Aβ injections. Furthermore, radioisotope experiments revealed that plantainoside B has affinity to Aβ aggregates including its oligomers and brain tissue from a mouse model of Aβ pathology. In addition, plantainoside B could delay the Aβ aggregation rate. Accordingly, plantainoside B may exert neuroprotective effects by binding to Aβ oligomers, thus interrupting the binding of Aβ oligomers to the cell surface. This suggests its potential application as a theranostics in AD, simultaneously diagnostic and therapeutic drugs.
Keywords: Alzheimer’s disease; Bacopa monniera; amyloid-β oligomer; imaging; neuroprotection; plantainoside B.