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MODULATION OF ARYL HYDROCARBON RECEPTOR (AHR)-REGULATED CARCINOGEN ACTIVATING ENZYMES BY ORGANIC ARSENICALS: A POTENTIAL THERAPEUTIC TARGET

  • Author / Creator
    Elshenawy, Osama H. A.
  • Arsenic is a worldwide environmental pollutant that is associated with skin and several types of internal cancers, such as liver, lung, kidney, urinary bladder, and prostate cancers. Recent reports revealed that organic arsenic metabolites, such as trimethylarsine oxide (TMAO), dimethylarsinic acid (DMA(V)), and monomethylarsonous acid (MMA(III)) could activate the toxic and carcinogenic potential of arsenic. Therefore, the objectives of the current dissertation were to: 1) Investigate the effect of TMAO on the activation of hepatic aryl hydrocarbon receptor (AhR)-regulated genes, and to investigate the underlying mechanisms in vitro. 2) Examine the effect of TMAO on modulation of AhR-regulated genes in vivo in extrahepatic tissues. 3) Investigate the effect of DMA(V) on the alteration of AhR-regulated genes in the hepatic and extrahepatic tissues. 4) Examine the effects of MMA(III) as compared to its parent compound, As(III), on the expression of prototypical AhR-regulated gene, CYP1A1, in vitro. Our in vivo results demonstrated that TMAO increased carcinogen activating enzymes Cyp1a1, Cyp1a2, and Cyp1b1, in addition to Nqo1, Gsta1, and Ho-1 at the mRNA level. Upon co-exposure to TMAO and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), TMAO potentiated the TCDD-mediated induction of Cyp1a1, Cyp1b1, and Nqo1 mRNA levels. Western blotting revealed that TMAO increased Cyp1a1, Cyp1a2, Nqo1, Gsta, and Ho-1 protein levels, and potentiated the TCDD-mediated induction of Cyp1a1 and Cyp1b1 at the protein levels. In addition, TMAO significantly increased Cyp1a1, Cyp1a2, Nqo1, Gst, and Ho-1 activities, and significantly potentiated the TCDD-mediated induction of Cyp1a1 activity. At the in vitro level, TMAO induced Cyp1a1 and potentiated the TCDD-mediated induction of Cyp1a1 at mRNA, protein and activity levels. In addition, TMAO increased the nuclear localization of AhR and AhR-dependent XRE-driven luciferase activity. With regard to the effect of TMAO on the extrahepatic tissues, TMAO increased Cyp1a1 and Cyp1b1 mRNA, protein, and activity in the lung. TMAO potentiated the TCDD-mediated induction of Cyp1a1 and Cyp1a2 mRNA, protein and activity in the lung. In the kidney, TMAO increased Cyp1b1 mRNA and protein. TMAO potentiated the TCDD-mediated induction of Cyp1a1 and Cyp1b1 mRNA, protein and activity. In the heart, TMAO potentiated the TCDD-mediated induction of Cyp1a1 and Cyp1b1 mRNA. Moreover, TMAO induced Nqo1 mRNA in the lung, kidney and heart, with subsequent increase in Nqo1 protein and activity in the lung. TMAO increased Gsta1 mRNA in the heart, and increased Gsta protein and activity in the lung and kidney. TMAO increased Nqo1 mRNA compared to TCDD in the kidney and heart, and potentiated the TCDD-mediated induction of Gsta protein and activity in the kidney. As for the DMA(V), our results demonstrated that it has no significant effect on Cyp1a mRNA and protein expression levels or catalytic activity in the liver. On the other hand, DMA(V) significantly potentiated the TCDD-mediated induction of Cyp1a mRNA and protein expression levels, with a subsequent potentiation of catalytic activity in the lung. Moreover, DMA(V) significantly inhibited the TCDD-mediated induction of Cyp1a mRNA and protein expression levels with subsequent inhibition of catalytic activity in the kidney. Regarding phase II AhR-regulated genes, DMA(V) had no significant effect on Nqo1 mRNA and protein expression levels or activity in the liver, lung, or kidney. With regard to MMA(III) as compared to As(III), our in vitro results showed that MMA(III) and As(III) decreased CYP1A1 mRNA, protein, and catalytic activity levels, and inhibited the TCDD-mediated induction of CYP1A1 mRNA, protein, and catalytic activity levels. MMA(III) and As(III) significantly inhibited XRE-driven luciferase activity and inhibited the TCDD-mediated induction of XRE-driven luciferase activity, in addition both compounds showed inhibition of nuclear accumulation of the AhR transcription factor. MMA(III) and As(III) had no effect on CYP1A1 mRNA stability; however, MMA(III), but not As(III), decreased the protein stability of CYP1A1. As(III), but not MMA(III), induced HO-1 mRNA expression level. In addition, both MMA(III) and As(III) increased ROS production. In conclusion, the present work demonstrates for the first time that organic arsenic metabolites modulate phase I and phase II AhR-regulated genes in a tissue-, and enzyme-specific manner. This modulation could potentially participate in arsenic-induced toxicity and carcinogenicity. Our work opened new avenues for treatment of arsenic-induced carcinogenicity via using prodrugs that will be specifically activated inside tumor cells with CYP enzymes. The use of these rational therapies would decrease morbidity and mortality and hence diminish health care costs.

  • Subjects / Keywords
  • Graduation date
    2017-06
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R35H7C60G
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
    English
  • Institution
    University of Alberta
  • Degree level
    Doctoral
  • Department
    • Faculty of Pharmacy and Pharmaceutical Sciences
  • Specialization
    • Pharmaceutical Sciences
  • Supervisor / co-supervisor and their department(s)
    • El-Kadi, Ayman (Faculty of Pharmacy and Pharmaceutical Sciences)
  • Examining committee members and their departments
    • Brocks, Dion (Faculty of Pharmacy and Pharmaceutical Sciences)
    • Marsh, Sharon (Faculty of Pharmacy and Pharmaceutical Sciences)
    • Baker, Glen (Faculty of Medicine and Dentistry)
    • Sari, Youssef (Department of Pharmacology and Experimental Therapeutics, The University of Toledo)
    • Siraki, Arno (Faculty of Pharmacy and Pharmaceutical Sciences)