Components from the steamed leaves of Acanthopanax koreanum and their effects on PPAR activity in HepG2 cells

Three ent-kaurane diterpenes (1-3), four lupane-triterpene glycosides (4-7), and an oleanane-triterpene glycoside (8) were isolated from the ethyl acetate and water extracts of the steamed leaves of Acanthopanax koreanum using a combination of various column chromatographies. The structures of the isolates were determined by ¹H-, ¹³C-NMR spectroscopy and mass spectrometry. To investigate the biological effects of the eight compounds (1-8) on peroxisome proliferator-activated receptor gamma (PPARγ), luciferase reporter assays were used. Among the tested compounds, ent-kaur-16-en-19-oic acid (1), 16α-hydroxy-ent-kauran-19-oic acid (2), and 17-hydroxy-ent-kaur- 15-en-19-oic acid (3) showed considerable effects on PPARγ activity, compared with the positive control, troglitazone. To evaluate specificity and sensitivity of the active compounds (1-3) in the regulation of transactivation of PPARs, Gal4-PPARs-LBD luciferase reporter assays were examined. In this study, the three ent-kaurane diterpenes (1-3) were found to up-regulate PPARβ/δ ?and PPARγ activities, whereas they did not activate PPARα activity.