Pinostrobin from honey and Thai ginger (Boesenbergia pandurata): A potent flavonoid inducer of mammalian phase 2 chemoprotective and antioxidant enzymes

Over 60 different samples comprising 35 distinct honeys were evaluated for their ability to induce mammalian phase 2 detoxication enzymes using a microtiter plate assay of quinone reductase (QR) induction with murine hepatoma cells in microtiter plates. This assay has been used extensively to identify and isolate a variety of natural and synthetic inducers from plants. All 35 honeys examined induced elevations of mammalian QR activity ranging from 153 to 2155 units/g with a mean of 630 and a median of 417 units/g. The concentrations for doubling the QR activity (CD) of certain of the prominent flavonoids found in honey were also assessed (pinostrobin, 0.5 μM; pinocembrin, 110 μM; chrysin, 25 μM) and compared to those of related, more commonly described flavonoids such as quercetin (2.7 μM) and myricetin (58 μM). On the basis of the extremely high QR inducing potency of one of these compounds, pinostrobin (5-hydroxy-7-methoxyflavanone), a bioassay-guided search was conducted which revealed a dietary source of pinostrobin, Boesenbergia pandurata (fingerroot), with extraordinarily high ability to induce mammalian phase 2 detoxication enzymes. Although the QR inducing activity of buckwheat honeys was 2155 ± 951 units/g (n = 8 samples), which is less than 10% of the average values obtained from fresh broccoli, the potency of fingerroot rhizomes (ca. 110 000 units/g) is even higher than that of broccoli and the potencies of fingerroot oil and powdered rhizome (ca. 500 000 units/g) rival that of broccoli sprouts.