title: The effect of tert-butylhydroquinone-induced oxidative stress in MDBK cells using XTT assay: implication of tert-butylhydroquinone-induced NADPH generating enzymes.
abstract: Tetrazolium salts such as XTT and MTT are widely used to produce formazan for cell proliferation and cytotoxicity assays through bioreductase activity. However, the XTT assay showed significant increase in MDBK cell viability when cells were treated with both 50 and 100 muM of the pro-oxidant, tert-butylhydroquinone (t-BHQ), although the crystal violet assay showed no cytotoxic effect with these concentrations, and the induction of lipid peroxidation was not observed. We investigated the mechanism of enhancement of XTT substrate reduction after treatment of MDBK cells with t-BHQ, leading to apparent increase in cell viability. t-BHQ caused an increase in absorbance at 340 nm in culture medium, suggesting that t-BHQ increases cellular production and release of NADH and/or NADPH. Although t-BHQ did not change the NADH concentration in cell culture medium, the addition of NADP(+)-dependent glutathione reductase decreased the XTT reduction to the control level, indicating cellular release of NADPH. t-BHQ also increased intracellular glucose-6-phosphate dehydrogenase activity, producing NADPH. Taken together, our findings indicate that t-BHQ treatment activates NADPH generating enzymes such as glucose-6-phosphate dehydrogenase followed by release of NADPH in the cell culture medium, resulting in direct XTT reduction by NADPH.
authors.affiliation: Laboratory of Animal Nutritio, School of Veterinary Medicine, Kitasato University, Aomori 034-8628, Japan.
authors.forename: Tomoo
authors.initials: T
authors.lastname: Naoi
authors.forename: Naoko
authors.initials: N
authors.lastname: Shibuya
authors.forename: Haruka
authors.initials: H
authors.lastname: Inoue
authors.forename: Sakura
authors.initials: S
authors.lastname: Mita
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Watanabe
authors.forename: Koichi
authors.initials: K
authors.lastname: Orino
mesh_terms: D000818:Animals; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D005954:Glucosephosphate Dehydrogenase / Q000187:drug effects* / Q000378:metabolism; D006873:Hydroquinones / Q000494:pharmacology*; D015227:Lipid Peroxidation / Q000187:drug effects; D009243:NAD / Q000187:drug effects / Q000378:metabolism; D009249:NADP / Q000187:drug effects / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects*
chemical_list: D006873:Hydroquinones; D009243:NAD; D009249:NADP; C018855:2-tert-butylhydroquinone; D005954:Glucosephosphate Dehydrogenase