Activation of the Nrf2 signaling pathway in usnic acid-induced toxicity in HepG2 cells

• Published in: Archives of toxicology 2017-03, Vol.91 (3), p.1293-1307
• Main Authors: Chen, Si, Zhang, Zhuhong, Qing, Tao, Ren, Zhen, Yu, Dianke, Couch, Letha, Ning, Baitang, Mei, Nan, Shi, Leming, Tolleson, William H., Guo, Lei
• Format: Article
• Language: English
• Subjects: Antioxidant Response Elements - drug effects; Benzofurans - administration & dosage; Benzofurans - toxicity; Biomedical and Life Sciences; Biomedicine; Cytotoxicity; Dietary supplements; DNA damage; DNA Damage - drug effects; Dose-Response Relationship, Drug; Environmental Health; Gene Expression Regulation - drug effects; Glutathione - metabolism; Hep G2 Cells - drug effects; Hep G2 Cells - metabolism; Humans; Molecular Toxicology; NF-E2-Related Factor 2 - metabolism; Occupational Medicine/Industrial Medicine; Oxidative stress; Pharmacology/Toxicology; Product safety; Reactive Oxygen Species - metabolism; S Phase Cell Cycle Checkpoints - drug effects; Signal Transduction - drug effects; Weight loss products
• ISSN: 0340-5761; 1432-0738
• DOI: 10.1007/s00204-016-1775-y

Many usnic acid-containing dietary supplements have been marketed as weight loss agents, although severe hepatotoxicity and acute liver failure have been associated with their overuse. Our previous mechanistic studies revealed that autophagy, disturbance of calcium homeostasis, and ER stress are involved in usnic acid-induced toxicity. In this study, we investigated the role of oxidative stress and the Nrf2 signaling pathway in usnic acid-induced toxicity in HepG2 cells. We found that a 24-h treatment with usnic acid caused DNA damage and S-phase cell cycle arrest in a concentration-dependent manner. Usnic acid also triggered oxidative stress as demonstrated by increased reactive oxygen species generation and glutathione depletion. Short-term treatment (6 h) with usnic acid significantly increased the protein level for Nrf2 (nuclear factor erythroid 2-related factor 2), promoted Nrf2 translocation to the nucleus, up-regulated antioxidant response element (ARE)-luciferase reporter activity, and induced the expression of Nrf2-regulated targets, including glutathione reductase, glutathione S-transferase, and NAD(P)H quinone oxidoreductase-1 (NQO1). Furthermore, knockdown of Nrf2 with shRNA potentiated usnic acid-induced DNA damage and cytotoxicity. Taken together, our results show that usnic acid causes cell cycle dysregulation, DNA damage, and oxidative stress and that the Nrf2 signaling pathway is activated in usnic acid-induced cytotoxicity.