Pharmacodynamics of dietary phytochemical indoles I3C and DIM: Induction of Nrf2-mediated Phase II drug metabolizing and antioxidant genes and synergism with isothiocyanates

摘要

The antioxidant response element (ARE) is a critical regulatory element for the expression of many phase II drug metabolizing enzymes (DME), phase III transporters, and anti-oxidant enzymes, mediated by the transcription factor Nrf2. The aim of this study was to examine the potential activation and synergism of Nrf2-ARE-mediated transcriptional activity between four common phytochemicals present in cruciferous vegetables, the indoles; indole-3-carbinol (I3C), 3,3’-diindolylmethane (DIM), and the isothiocyanates (ITCs); phenethyl isothiocyanate (PEITC) and sulforaphane (SFN). The cytotoxicity of the compounds was determined in human liver hepatoma cell line (HepG2-C8). The combination index was calculated to assess the synergistic effects on the induction of ARE-mediated gene expressions. qPCR was employed to measure the mRNA expressions of Nrf2 and Nrf2-mediated genes. I3C and DIM showed less cytotoxicity than SFN and PEITC. Compared to I3C, DIM was found to be a stronger inducer of ARE. Synergism was observed after combined treatments of I3C 6.25 µM + SFN 1 µM, I3C 6.25 µM + PEITC 1 µM and DIM 6.25 µM + PEITC 1 µM, while additive effect was observed for DIM 6.25 µM + SFN 1 µM. Induction of endogenous Nrf2, phase II genes (GSTm2, UGT1A1, and NQO1) and antioxidant genes (HO-1 and SOD1) was also observed. In summary, the indole I3C or DIM alone could induce or syngergistically induce in combination with the ITCs SFN or PEITC, Nrf2-ARE-mediated gene expression, which could potentially enhance cancer chemopreventive activity.