The activation of the Nrf2/ARE pathway in HepG2 hepatoma cells by phytochemicals and subsequent modulation of phase II a
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ORIGINAL PAPER
The activation of the Nrf2/ARE pathway in HepG2 hepatoma cells by phytochemicals and subsequent modulation of phase II and antioxidant enzyme expression Violetta Krajka-Kuźniak & Jarosław Paluszczak & Hanna Szaefer & Wanda Baer-Dubowska
Received: 26 November 2014 / Accepted: 10 March 2015 # University of Navarra 2015
Abstract Previous studies have shown that naturally occurring phytochemicals, indole-3-carbinol, phenethyl isothiocyanate, protocatechuic acid, and tannic acid increased the activity and protein level of hepatic phase II enzymes in animal models. In order to further explore the mechanism of this activity, we investigated the effect of these compounds on the activation of nuclear factor erythroid-2-related factor 2 (Nrf2)-regulated transcription in human hepatocellular carcinoma HepG2 cells. Treatment with all the tested compounds resulted in the translocation from the cytosol and nuclear accumulation of active phosphorylated Nrf2. Furthermore, phenethyl isothiocyanate and indole-3-carbinol increased the transcript and protein levels of GSTA, GSTP, GSTM, GSTT, and NQO1. On the other hand, protocatechuic and tannic acids enhanced only the expression of GSTA, GSTM, and GSTT. The expression of genes encoding antioxidant enzymes CAT, SOD, GR, and GPx was increased after the treatment with all the tested phytochemicals. These results indicate that isothiocyanates/indoles and protocatechuic and tannic acids induce phase II and antioxidant gene expression in HepG2 cells through the Nrf2-Keap1-ARE signaling pathway. Moreover, the results of this study confirmed that the degradation products of glucosinolates are more effective inducers of phase II and antioxidant enzymes than protocatechuic and tannic acids. V. Krajka-Kuźniak : J. Paluszczak : H. Szaefer : W. Baer-Dubowska (*) Department of Pharmaceutical Biochemistry, Poznań University of Medical Sciences, Poznań, Poland e-mail: [email protected]
Keywords Nrf2 . Antioxidant and phase II enzymes . HepG2 . Phenethyl isothiocyanate . Indole-3-carbinol . Protocatechuic and tannic acids Abbreviations ARE Antioxidant response element CAT Catalase DMEM Dulbecco’s modified Eagle’s medium DMSO Dimethyl sulfoxide FBS Fetal bovine serum GPx Glutathione peroxidase GR Glutathione reductase GST Glutathione S-transferase I3C Indole-3-carbinol Keap1 Kelch-like ECH-associated protein 1 NQO1 NADPH:quinone oxidoreductase 1 Nrf2 Nuclear factor erythroid-2-related factor 2 PCA Protocatechuic acid PEITC Phenethyl isothiocyanate ROS Reactive oxygen species SOD Superoxide dismutase TA Tannic acid
Introduction The induction of genes encoding phase II enzymes that protect against damage by electrophilic and reactive oxygen intermediates is considered as an important strategy in reducing the risk of cancer and other chronic degenerative diseases linked to oxidative stress [14, 32, 40]. The expression of phase II genes is controlled by
V. Krajka-Kuźniak et al.
antioxidant response element (ARE) sequences which are regulated by nuclear factor erythroid-2-related fact
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