Nobiletin Reduces Intracellular and Extracellular β-Amyloid in iPS Cell-Derived Alzheimer's Disease Model Neurons.

Alzheimer's disease (AD) is the most common cause of dementia, with progressive memory impairment. Recently, neprilysin, a β-amyloid (Aβ)-degrading enzyme has become featured as a drug target for AD. Previously, we identified nobiletin from citrus peels as a natural compound possessing anti-dementia activity. In addition, we demonstrated that nobiletin improved memory in memory-impaired animals and, further, that Aβ levels were markedly decreased in the brains of these animals. We demonstrated in vitro that nobiletin up-regulates neprilysin expression and activity in human neuroblastoma cells. However, the action of nobiletin with regard to Aβ degradation under in vitro AD pathological conditions remains unclear. In this study, we examined whether nobiletin could enhance the degradation of intra- and extracellular Aβ using human induced pluripotent stem cell-derived AD model neurons, which generate an excess of Aβ due to the familial AD presenilin-1 mutation. The neurons were treated in the presence or absence of nobiletin. The results of real-time quantitative RT-PCR indicated that neprilysin mRNA levels were significantly up-regulated by nobiletin. Furthermore, immunostaining with an anti-Aβ antibody revealed that nobiletin substantially reduced the intraneuronal content of Aβ. Interestingly, the results of Aβ immunoassays confirmed that nobiletin also significantly decreased the levels of Aβ released into the cellular medium. These results suggest that nobiletin enhanced the reduction of intra- and that extracellular Aβ levels under AD pathologic conditions, and this is associated with the up-regulation of neprilysin expression. Collectively, nobiletin appears to be a promising novel prophylactic seed drug or functional food for AD.