Dehydroglyasperin C isolated from licorice caused Nrf2-mediated induction of detoxifying enzymes

Our preliminary experiment demonstrated that a n-hexane/EtOH (9:1, volume) extract of Glycyrrhiza uralensis (licorice) caused a significant induction of NAD(P)H:oxidoquinone reductase (NQO1), one of the well-known phase 2 detoxifying enzymes. We isolated dehydroglyasperin C (DGC) as a potent phase 2 enzyme inducer from licorice. DGC induced NQO1 both in wild-type murine hepatoma Hepa1c1c7 and ARNT-lacking BPRc1 cells, indicating that the compound is a monofunctional inducer. The compound induced not only NQO1 but also some other phase 2 detoxifying/antioxidant enzymes, such as glutathione S-transferase, gamma-glutamylcysteine synthase, glutathione reductase, and heme oxygenase 1. Similar to most monofunctional inducers, DGC caused the accumulation of Nrf2 in the nucleus in dose- and time-dependent manners and thereby activated expression of phase 2 detoxifying enzymes. It also resulted in a dose-dependent increase in the luciferase activity in the reporter assay, in which HepG2-C8 cells transfected with antioxidant response element (ARE)-luciferase construct were used, suggesting that the induction of phase 2 detoxifying and antioxidant enzymes could be achieved through the interaction of Nrf2 with the ARE sequence in the promoter region of their genes.