Xanthohumol (2',4',4-trihydroxy-6'-methoxy-3'-prenylchalcone, Xn), a polyphenol chalcone from hops (Humulus lupulus), has received increasing attention due to its multiple pharmacological activities. As an active component in beers, its presence has been suggested to be linked to the epidemiological observation of the beneficial effect of regular beer drinking. In this work, we synthesized Xn with a total yield of 5.0% in seven steps and studied its neuroprotective function against oxidative-stress-induced neuronal cell damage in the neuronlike rat pheochromocytoma cell line PC12. Xn displays moderate free-radical-scavenging capacity in vitro. More importantly, pretreatment of PC12 cells with Xn at submicromolar concentrations significantly upregulates a panel of phase II cytoprotective genes as well as the corresponding gene products, such as glutathione, heme oxygenase,
Nad(p)h: quinone oxidoreductase, thioredoxin, and thioredoxin reductase. A mechanistic study indicates that the α,β-unsaturated ketone structure in Xn and activation of the transcription factor Nrf2 are key determinants for the cytoprotection of Xn. Targeting the Nrf2 by Xn discloses a previously unrecognized mechanism underlying the biological action of Xn. Our results demonstrate that Xn is a novel small-molecule activator of Nrf2 in neuronal cells and suggest that Xn might be a potential candidate for the prevention of neurodegenerative disorders.
Keywords: Nrf2; antioxidant; neuroprotection; oxidative stress; xanthohumol.