Induction of quinone reductase activity in murine hepatoma cells by extracts of Thunbergia Laurifolia Lindl

Abstract

Thunbergia laurifolia Lindl or Rang Chuet (RC) is widely prescribed in traditional Thai medicine for protection against dietary and environmental toxicants with little substantiation. To better assess the potential of RC as a medicinal plant, extracts were prepared by infusion of dried leaves with water, ethanol and acetone. Extracts were subsequently assayed for major phytochemical constituents including phenolics, carotenoids and chlorophylls. Total phenolic content was 24.39, 4.14 and 1.42 mg gallic acid equivalents (GAE) per g dry leaf for water, ethanol and acetone extracts respectively. HPLC analysis tentatively identified caffeic acid and apenginin as primary constituents of water extracts. Acetone and ethanol extracts contained primarily chlorophyll a and b, pheophorbide a, pheophytin a and lutein. The detoxification potential of RC was determined by measuring the ability of standardized extracts to increase NAD(P)H:quinone oxidoreductase (QR) activity in Hepa 1c1c7 cells. Treatment of hepatoma cells with RC extracts resulted in a dose dependent increase in QR specific activity for all extracts. Acetone extracts (140 μg GAE/mL) increased QR activity 2.8 fold, compared to controls, while ethanol (120 μg GAE/mL) and water (1000 μg GAE/mL) extracts increased QR activity 1.56 and 1.35 fold, respectively. These results demonstrate that RC preparations have biological activities consistent with protection from toxicants and that both phenolic and natural pigment constituents likely contribute to these activities.