The activation of the Nrf2/ARE pathway in HepG2 hepatoma cells by phytochemicals and subsequent modulation of phase II and antioxidant enzyme expression

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.

Ursodeoxycholic Acid Attenuates Acute Aortic Dissection Formation in Angiotensin II-Infused Apolipoprotein E-Deficient Mice Associated with Reduced ROS and Increased Nrf2 Levels

“…The target genes glutathione S-transferase (GST) [28]. Previous study has proved that a positive association was existed between Nrf2 and redox enzymes (Cu/Zn-SOD, Mn-SOD and CAT) [29]. Thus, to investigate the role of UDCA in the production of ROS, we examined the expression of NADPH oxidase, catalase and SOD in aortic tissue from Ang II-induced AAD mice and Ang II-induced AAD mice treated with UDCA.…”

The Role of Glucosinolate Hydrolysis Products from Brassica Vegetable Consumption in Inducing Antioxidant Activity and Reducing Cancer Incidence

“…Antioxidant (AO) enzymes generally act in the regulation of glutathione metabolism and quenching of free radicals via one- and two-electron reductions, thereby contributing to the reduction of oxidative stress. AO enzymes include catalases (CAT), superoxide dismutases (SOD), glutathione reductases (GSR), glutathione peroxidases (GPX), glutaredoxins (GLRX), thioredoxins (TXN), thioredoxin reductases (TXNRD), heme-oxygenase 1 (HO-1), and NAD(P)H:quinone oxidoreductase 1 (NQO1) [30,44]. Phase I/phase II detoxification enzymes are often called biotransformation enzymes because, as a team, they transform toxic xenobiotics into non-toxic forms that can be excreted from the body.…”

“…Most PII enzymes are transferases: UDP-glucuronosyltransferases (UGTs), sulfotransferases (SULTs), glutathione S-transferases (GSTs), N-acetyltransferases (NATs), and S- and O-methyltransferases (MTs) [30]. NQO1 is often included in the list of PII enzymes [44], although it is also often referred to it as an AO enzyme. The product of the PII reaction is a more polar compound that can be readily excreted by the body either through passive or active transport.…”

“…Both tested concentrations of PEITC increased expression and protein abundance of all four major classes of GSTs while NQO1 expression and abundance was only significantly increased by 5 µM PEITC treatment. Several AO enzymes (SOD, CAT, GPX, and GSR) also responded to both tested concentrations of PEITC with significant increases in both transcript and protein abundance [44]. In another study, PEITC was also shown to increase expression of HO-1 and an ARE-driven luciferase reporter gene in PC-3 cells.…”

Oxidative Stress: a Promising Target for Chemoprevention

“…After consumption of glucosinolate, the active organosulfur compounds indole-3-carbinol (I3C) and sulforaphane, which possess anti-cancer properties, are formed. Both the phytochemicals have potent antioxidant, anti-carcinogenic, and anti-atherogenic properties; however they increased the expression of genes encoding antioxidant enzymes (CAT, SOD, GR, and GPX) in hepatoma cells through Nrf2 and ARE signaling pathways (Krajka-Kuzniak et al 2015). Findings have also shown that the anti-tumorigenic effect of I3C is partly achieved by one of its major byproducts, diindolylmethane, which acts as an anti-angiogenic, inducing cell death.…”