title: Activation of the Nrf2 signaling pathway in usnic acid-induced toxicity in HepG2 cells.
abstract: 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.
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research (NCTR)/U.S. Food and Drug Administration (FDA), HFT-110, 3900 NCTR Road, Jefferson, AR, 72079, USA.
authors.forename: Si
authors.initials: S
authors.lastname: Chen
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research/U.S. FDA, Jefferson, AR, 72079, USA.|Tianjin Medical University General Hospital, Tianjin, 300052, China.
authors.forename: Zhuhong
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: School of Pharmacy, School of Life Sciences, Fudan-Zhangjiang Center for Clinical Genomics and Zhanjiang Center for Translational Medicine, Fudan University, Shanghai, 200438, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Qing
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research (NCTR)/U.S. Food and Drug Administration (FDA), HFT-110, 3900 NCTR Road, Jefferson, AR, 72079, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Ren
authors.affiliation: Division of Systems Biology, National Center for Toxicological Research/U.S. FDA, Jefferson, AR, 72079, USA.
authors.forename: Dianke
authors.initials: D
authors.lastname: Yu
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research (NCTR)/U.S. Food and Drug Administration (FDA), HFT-110, 3900 NCTR Road, Jefferson, AR, 72079, USA.
authors.forename: Letha
authors.initials: L
authors.lastname: Couch
authors.affiliation: Division of Systems Biology, National Center for Toxicological Research/U.S. FDA, Jefferson, AR, 72079, USA.
authors.forename: Baitang
authors.initials: B
authors.lastname: Ning
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research/U.S. FDA, Jefferson, AR, 72079, USA.
authors.forename: Nan
authors.initials: N
authors.lastname: Mei
authors.affiliation: School of Pharmacy, School of Life Sciences, Fudan-Zhangjiang Center for Clinical Genomics and Zhanjiang Center for Translational Medicine, Fudan University, Shanghai, 200438, China.
authors.forename: Leming
authors.initials: L
authors.lastname: Shi
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research (NCTR)/U.S. Food and Drug Administration (FDA), HFT-110, 3900 NCTR Road, Jefferson, AR, 72079, USA.
authors.forename: William H
authors.initials: WH
authors.lastname: Tolleson
authors.affiliation: Division of Biochemical Toxicology, National Center for Toxicological Research (NCTR)/U.S. Food and Drug Administration (FDA), HFT-110, 3900 NCTR Road, Jefferson, AR, 72079, USA. lei.guo@fda.hhs.gov.
authors.forename: Lei
authors.initials: L
authors.lastname: Guo
mesh_terms: D061745:Antioxidant Response Elements / Q000187:drug effects; D001572:Benzofurans / Q000008:administration & dosage / Q000633:toxicity*; D004249:DNA Damage / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D005978:Glutathione / Q000378:metabolism; D056945:Hep G2 Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D059807:S Phase Cell Cycle Checkpoints / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D001572:Benzofurans; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D017382:Reactive Oxygen Species; C073339:usnic acid; D005978:Glutathione
keywords: Liver toxicity; Nrf2 pathway; Oxidative stress; Usnic acid