Chemopreventive activity of Angelica sinensis root extracts and its alkylphthalides

The roots of Angelica sinensis (Oliv.) Diels (Dang Gui; Apiaceae) have a long history in traditional Chinese medicine as an ailment for women's disorders and are often called „lady's ginseng“. Today, Dang Gui is popular worldwide with numerous dietary supplements used for women's health and as anti-aging products. In the current study, we examined the chemopreventive activity of a methanol extract of Dang Gui by measuring the relative ability to induce the detoxification enzyme, quinone reductase-1 (QR1) assay. The lipophilic fractions of this extract showed strong QR induction with concentrations to double activity (CD) of 5.5±0.7µg/mL (ether) and 3.9±0.5µg/mL (chloroform). Further fractionation led to the isolation of phenolic esters and alkylphthalides, especially a ligustilide rich fraction (CD=6.8±1.2µM), with strong QR inducing properties. One mechanism of QR induction could be through alkylation of Keap1 by electrophiles resulting in higher concentrations of Nrf2 in the nucleus. Enhanced levels of free Nrf2 will facilitate the transcription of chemopreventive enzymes through the antioxidative response element (ARE). Using MALDI mass spectrometry and LC-MS-MS, we demonstrated that the lipophilic extracts of A. sinensis and some alkylphthalides alkylated human Keap1 protein. The alkylphthalides were then incubated with glutathione and characterized using LC-UV-MS-MS to elucidate the structure of the ultimate electrophile reacting with Keap1 and thus inducing detoxification enzymes. These data suggest that lipophilic Dang Gui extracts might function as chemopreventive agents through induction of detoxification enzymes such as QR.