Cognitive-enhancing effects of Rhus verniciflua bark extract and its active flavonoids with neuroprotective and anti-inflammatory activities.

The neuroprotective potential of flavonoids within the brain comprises anti-apoptosis of neuronal cells, anti-neuroinflammation and enhancement of cognitive function. We reported that Rhus vernciflua inhibits glutamate-induced neurotoxicity in primary cultured rat cortical cells. Here we narrowed it down to get neuroprotective fractions from the plant yielding flavonoid-rich ethyl acetate fraction (PREF). Among its active flavonoids, fisetin exhibited not only inhibitory effect against lipopolysaccharide (LPS)-induced neuroinflammation by suppressing inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 but also memory enhancing effects via reactivation of cAMP responsive element binding protein (CREB)-brain derived neurotrophic factor (BDNF) pathway in memory-impaired mice by scopolamine. Butein also showed a similar activity to fisetin even though to a lesser extent. The neuroprotection by PREF and selected flavonoids may involve maintenance of antioxidant defense mechanism including glutathione peroxidase (GSH-Px), glutathione reductase (GR) and superoxide dismutase (SOD). Conclusively, we demonstrate the R. vernciflua bark extract and its active flavonoids with potent neuroprotective and anti-inflammatory effects might be good therapeutic candidates as cognitive-enhancers.