104C-15 |
Induction of Phase II enzyme activity in murine hepatoma (Hepa 1c1c7) cells by green onion (Allium fistulosum) isolates |
H. XIAO and K. L. Parkin. Dept. of Food Science, Univ. of Wisconsin, Madison, 1605 Linden Dr., A-109 Babcock Hall, Madison, WI 53706-1519 Justification: Several health-promoting effects have been ascribed to tissue preparations of Allium species, especially garlic and onion. By contrast, green onion has been less studied in terms of its bioactive effects, despite it being the most potent in vitro phase II enzyme inducer among >30 vegetables tested. Phase II enzymes are involved in detoxification of potential carcinogens in humans. Objectives: The objective of the study was to isolate and identify cancer preventive components from green onion in terms of isolates that could induce the activity of quinone reductase (QR, a representative phase II enzyme) in cultured Hepa 1c1c7 cells. Methods: Freeze-dried green onion was subjected to the bioassay-guided fractionation steps of solid-liquid and liquid-liquid extraction, low-pressure chromatography, flash chromatography and high pressure preparative liquid chromatography. Hepa cells were cultured in 96-well microtiter plates and treated with samples at concentrations ranging from 2 ¦Ìg/ml to 1 mg/ml. Induction of QR specific activity was measured by tetrazolium dye reduction, and cell viability was assayed by crystal violet (protein) staining. Active fractions were monitored by HPLC with diode array multi-wavelength detection. Results: More than 10 fractions containing components capable of inducing QR. QR activity was induced to levels as much as 8X that of the control, and the concentration for doubling QR activity was as low as 8¦Ìg/ml for some fractions. Spectral analysis of HPLC data revealed that major compounds present in the active fractions had maximal UV absorbance at 285nm, 322nm, 330nm and 365nm. The most active fractions (UVmax at 365nm) are being subjected to further isolation and identification steps. Significance: Endogenous constituents from green onion exhibit potent QR-inducing activities in vitro. Identification of the active compounds may facilitate in vivo trials and provide the basis for diets rich in green onion to deliver cancer chemopreventive benefits to humans.
Session 104C, Fruit & Vegetable Products: Vegetables (Processed)
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