Curcumin upregulates Nrf2 nuclear translocation and protects rat hepatic stellate cells against oxidative stress

Abstract

Abstract. The present study aimed to investigate the protective role of curcumin against oxidative stress in rat hepatic stellate cells (HSCs)-T6, and to determine the possible underlying mechanisms. HSC-T6 cells were divided into three groups: Negative control group, oxidant-treated group and curcumin-treated group. Flow cytometry and spectrophotometry were used to measure the production of reactive oxygen species (ROS), and the levels of malondialdehyde (MDA) and glutathione (GSH). Immunocytochemistry and a radioimmunoassay were used to determine the expression of smooth muscle α-actin (α-SMA) and the secretion of extracellular matrix (ECM) molecules. In addition, western blotting and immunocytochemistry were used to determine the expression levels of nuclear factor-erythroid 2-related factor (Nrf2). Treatment with glucose oxidase (GO) significantly stimulated the formation of ROS and increased the production of MDA, as compared with the control cells; however, the production of GSH was only slightly increased. In addition, treatment with GO significantly promoted the expression of α-SMA and the secretion of ECM molecules. Conversely, treatment with curcumin significantly decreased the levels of ROS and MDA, and significantly increased the levels of GSH. Curcumin significantly inhibited the expression of α-SMA and decreased the secretion of ECM molecules. Furthermore, treatment with curcumin significantly increased the nuclear expression levels of Nrf2. These results indicated that curcumin may protect rat HSCs against oxidative stress and inhibit the GO-induced activation and secretion of ECM molecules in vitro. These effects were mediated by the upregulation of Nrf2 nuclear translocation. IntroductionPrevious studies have demonstrated that oxidative stress has a significant role in the occurrence and progression of hepatitis and hepatic fibrosis (1-4). Oxidative stress results from the excessive production of reactive oxygen species (ROS), and the inability of an organism to eliminate them. Excessive ROS lead to lipid peroxidation, protein and DNA damage, and injury to cellular structure and function (5). Numerous studies have reported the important role of ROS in various types of hepatic injury (6-10). In addition to ROS-induced inflammation, ROS may lead to loss of normal regulatory functions, resulting in tissue injury and excessive repair, and the development of hepatitis and hepatic fibrosis (11,12). It has previously been demonstrated that activation of hepatic stellate cells (HSCs) has a key role in the progression of hepatic fibrosis; therefore, HSCs are considered important target cells in hepatic fibrosis research (13). Furthermore, HSCs can be activated by oxidative stress and transformed into myofibroblasts. Myofibroblasts synthesize abundant extracellular matrix (ECM) molecules, which may lead to hepatic fibrosis (14); therefore, how to inhibit the activation of HSCs exposed to oxidative stress requires further investigation. Nuclear factor-erythroid 2-related factor (Nrf2) is a transcription fa...

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