Nrf2-mediated Induction of Detoxifying Enzymes by Alantolactone Present in Inula helenium

It is widely recognized that induction of cellular defence genes, such as phase 2 detoxifying and antioxidant enzyme genes, play an important biological role in protection against carcinogenesis and in the attenuation of cancer development (Talalay et al., 2004; Jaiswal, 2000). A wide variety of chemical compounds including dithiolethiones, isothiocyanates, diphenols, quinones, Michael reaction acceptors and heavy metals can inhibit the carcinogenesis process by inducing phase 2 enzymes which detoxify toxic molecules by directly destroying their reactive centres and reactive oxygen species (ROS), or by conjugating them with endogenous ligands, facilitating their excretion from the cells (Begleiter and Fourier, 2004). The induction of phase 2 enzymes was reported to be mediated by Nrf2 (nuclear factor erythroidrelated factor 2), which is a leucine zipper-type transcription factor and known to regulate its various genes through a common DNA regulatory element, called antioxidant response element (ARE) (Sporn and Liby, 2005).

Our previous study showed that a methanol extract of Inula helenium contained a significantly high capacity to induce NAD(P)H:(quinone acceptor) oxidoreductase 1 (EC 1.6.99.2) (QR) activity (Im et al., 2007). The herb has been traditionally used for asthma, as an expectorant and insecticide (Chevallier, 2001). The methanol extract of the plant was further fractionated and it was found that the hexane fraction was most active in inducing detoxifying enzymes such as QR and glutathione S-transferase (GST). In this study the compounds responsible for induction of phase 2 detoxifying enzymes were isolated by using silica gel chromatography and vacuum liquid chromatography (VLC) and identified by spectrometry. Alantolactone identified as one of the QR inducers was subjected to further study to investigate its action mechanism in cultured cell system.