title: Protective roles of aldo-keto reductase 1B10 and autophagy against toxicity induced by p-quinone metabolites of tert-butylhydroquinone in lung cancer A549 cells.
abstract: tert-Butylhydroquinone (BHQ), an antioxidant used as a food additive, exhibits an anticancer effect at low doses, but is carcinogenic in rodents at high doses. BHQ is metabolized into cytotoxic tert-butylquinone (TBQ), which is further converted to 6-tert-butyl-2,3-epoxy-4-hydroxy-5-cyclohexen-1-one (TBEH) through 6-tert-butyl-2,3-epoxy-4-benzoquinone (TBE). Both TBQ and TBE are cytotoxic, but their toxic mechanisms have not been fully characterized. In this study, we have investigated the toxic mechanisms of TBQ and TBE, and the defense system against the two p-quinones using lung cancer A549 cells. TBQ and TBE, but not BHQ and TBEH, showed cytotoxicity to A549 cells. Neither caspase-3 activation nor an increase in the expression of endoplasmic reticulum stress-associating target genes was observed. TBQ and TBE reacted with reduced glutathione, and significantly decreased the glutathione level in A549 cells, suggesting that the cytotoxicity of the p-quinones is caused by their high electrophilicity reacting with biomolecules. The A549 cells treated with the p-quinones also showed increased levels of autophagic vacuoles and LC3-II protein, which are specific autophagy markers. An autophagy inhibitor, 3-methyladenine (3MA), decreased the LC3-II production by the p-quinones, but enhanced the cytotoxicity induced by TBQ and TBE, suggesting that autophagy contributes to alleviating the p-quinone-triggered cytotoxicity. In addition, the TBE-induced cytotoxicity and autophagy activation in the cells were significantly suppressed by overexpression of aldo-keto reductase (AKR)1B10 that efficiently reduces TBE into TBEH, and were augmented by pretreatment with a potent AKR1B10 inhibitor, C1. The effects of 3MA and C1 on the TBE-induced cytotoxicity were additive. The data provides evidence for the first time that autophagy and AKR1B10 contribute to the defense system against the cytotoxicity caused by the electrophilic p-quinone metabolites of BHQ.
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan. Electronic address: sendo@gifu-pu.ac.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Endo
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Nishiyama
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Suyama
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan.
authors.forename: Mayuko
authors.initials: M
authors.lastname: Takemura
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Soda
authors.affiliation: Department of Anatomy, Gifu University Graduate School of Medicine, Gifu 501-1193, Japan.
authors.forename: Huayue
authors.initials: H
authors.lastname: Chen
authors.affiliation: Faculty of Pharmaceutical Sciences, Hokuriku University, Kanazawa 920-1181, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tajima
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia.
authors.forename: Ossama
authors.initials: O
authors.lastname: El-Kabbani
authors.affiliation: Department of Legal Medicine, Graduate School of Medicine, Gifu University, Gifu 501-1193, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Bunai
authors.affiliation: Department of Legal Medicine, Graduate School of Medicine, Gifu University, Gifu 501-1193, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Hara
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsunaga
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Ikari
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000449:Aldehyde Reductase / Q000235:genetics*; D000074408:Aldo-Keto Reductases; D000975:Antioxidants / Q000494:pharmacology; D001343:Autophagy / Q000235:genetics*; D016227:Benzoquinones / Q000494:pharmacology*; D053148:Caspase 3 / Q000235:genetics; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000235:genetics; D005978:Glutathione / Q000235:genetics; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000235:genetics*; D008869:Microtubule-Associated Proteins / Q000235:genetics
chemical_list: D000975:Antioxidants; D016227:Benzoquinones; D006873:Hydroquinones; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; C091758:6-tert-butyl-2,3-epoxy-1,4-benzoquinone; C004532:quinone; C025946:3-methyladenine; C018855:2-tert-butylhydroquinone; C120471:AKR1B10 protein, human; D000074408:Aldo-Keto Reductases; D000449:Aldehyde Reductase; D053148:Caspase 3; C051290:2-tert-butyl-4-quinone; D005978:Glutathione; D000225:Adenine
keywords: 6-tert-Butyl-2,3-epoxy-4-benzoquinone; AKR1B10; Autophagy; tert-Butylhydroquinone; tert-Butylquinone