title: Methylated pentavalent arsenic metabolites are bifunctional inducers, as they induce cytochrome P450 1A1 and NAD(P)H:quinone oxidoreductase through AhR- and Nrf2-dependent mechanisms.
abstract: Activation of the aryl hydrocarbon receptor (AhR) ultimately leads to the induction of the carcinogen-activating enzyme cytochrome P450 1A1 (CYP1A1), and activation of the nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) in addition to the AhR pathway induces the expression of the NADP(H):quinone oxidoreductase (NQO1). Therefore, the aim of this study was to examine the effect of As(III) pentavalent metabolites, MMA(V), DMA(V), and TMA(V), on AhR and Nrf2 activation and on the expression of their prototypical downstream targets CYP1A1 and NQO1, respectively. Our results showed that treatment of HepG2 cells with MMA(V), DMA(V), or TMA(V) in the absence and presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin or sulforaphane significantly induced both CYP1A1 and NQO1 at the mRNA, protein, and catalytic activity levels. Furthermore, these metabolites increased the AhR-dependent XRE-driven and the Nrf2-dependent ARE-driven luciferase reporter activities, which coincided with increased nuclear accumulation of both transcription factors. However, none of these metabolites were shown to be AhR ligands. The induction of CYP1A1 by these metabolites seems to be ligand-independent, possibly through a decrease in HSP90 protein expression levels. The metabolites also increased ROS production, which was significantly higher than that produced by As(III). Upon knockdown of AhR and Nrf2 the MMA(V)-, DMA(V)-, and TMA(V)-mediated induction of both CYP1A1 and NQO1 proteins was significantly decreased. In conclusion, this study demonstrates for the first time that methylated pentavalent arsenic metabolites are bifunctional inducers, as they increase CYP1A1 by activating the AhR/XRE signaling pathway and they increase NQO1 by activating the Nrf2/ARE signaling pathway in addition to the AhR/XRE pathway.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E1.
authors.forename: Anwar
authors.initials: A
authors.lastname: Anwar-Mohamed
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E1.
authors.forename: Osama H
authors.initials: OH
authors.lastname: Elshenawy
authors.affiliation: Department of Environmental Toxicology, University of California at Davis, Davis, CA 95616, USA.
authors.forename: Anatoly A
authors.initials: AA
authors.lastname: Soshilov
authors.affiliation: Department of Environmental Toxicology, University of California at Davis, Davis, CA 95616, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Denison
authors.affiliation: Analytical and Environmental Toxicology, Department of Laboratory Medicine and Pathology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada T6G 2G3.
authors.forename: X
authors.initials: X
authors.lastname: Chris Le
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E1.
authors.forename: Lars-Oliver
authors.initials: LO
authors.lastname: Klotz
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E1; College of Pharmacy, Qatar University, Doha 02713, Qatar. Electronic address: aelkadi@ualberta.ca.
authors.forename: Ayman O S
authors.initials: AO
authors.lastname: El-Kadi
mesh_terms: D061745:Antioxidant Response Elements; D001152:Arsenicals / Q000494:pharmacology*; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D017879:Isothiocyanates / Q000494:pharmacology; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008745:Methylation; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000235:genetics* / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000235:genetics* / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013454:Sulfoxides
chemical_list: D001152:Arsenicals; D018841:HSP90 Heat-Shock Proteins; D017879:Isothiocyanates; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D013454:Sulfoxides; D008156:Luciferases; C569463:CYP1A1 protein, human; D019363:Cytochrome P-450 CYP1A1; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human; C016766:sulforaphane
keywords: ARE; AhR; Arsenic; CYP1A1; Free radicals; NQO1; Nrf2; XRE