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Isolated ginsenosides aPPD and aPPT induced cytochrome P450 1 A 1 mRNA expression Zhao, Yang

Abstract

Introduction: Ginseng is commonly used in herbal preparations for traditional Chinese medicine. It contains over twenty ginsenosides amongst which aglycon protopanaxadiol (aPPD) and aglycon protopanaxatriol (aPPT) have been shown to be the primary circulating metabolites with potent medicinal properties. To evaluate the prospect of metabolic drug interactions the effects of aPPD and aPPT on expression and function of human cytochromes P450 CYP1A1 was assessed. Methods: Real Time RT-PCR and western blotting were used to measure CYP1A1 mRNA and protein expression in human HepG-2 and Caco-2 cells treated with aPPD or aPPT for 12 and 24 hours. A P450-CYP1A1 assay was used to measure CYP1A1 activity. Gudluc 1.1 was luciferase labeled and used as the CYP1A1 promoter constructs. It was co-transfected with Ary1 hydrocarbon receptor (AhR) and pRL-TK (control) plasmids to examine CYP1A1 mRNA induction via AhR. pGL3B-CYP1A1 plasmid was constructed containing longer CYP1A1 promoter sequence (-2425, +352) than Gudluc 1.1 (-1301, -819) and used to investigate the induction mechanism outside of AhR pathway. Results: There was a dose-dependent induction of CYP1A1 mRNA expression in both HepG-2 and Caco-2 cells dosed for 12h and 24h with either aPPD or aPPT. The result was statistically significant at concentrations of 5 [micro sign]M and above; however, this was not correlated with increased protein levels. P450-Glo[Trade Mark Sign] reporter assay produced a significant increase in CYP1A1 activity only after treatment with 80 and 160 [micro sign]M aPPD. No effects were found at lower concentrations of aPPD and all concentrations of aPPT. Induction of CYP1A1 mRNA by aPPD and aPPT was independent of AhR activation. Functional sequence was outside of the region from -2425 to +352. Conclusions: Overall, our results suggest that aPPD and aPPT exert a significant inductive effect on CYP1A1 mRNA level, while also activating CYP1A1 protein activity only with high concentrations of aPPD. This induction of mRNA level is not likely to be regulated by AhR.

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