Modulation of Aryl Hydrocarbon Receptor Regulated-Genes by Mercury

• Modulation of Drug Metabolizing Enzymes by Mercury

• Author / Creator

  Amara, Issa

• Aryl hydrocarbon receptor (AhR) ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and metals, such as mercury (Hg), are environmental co-contaminants with multiple biological consequences. Therefore, the objectives of the current dissertation were to: 1) examine the potential effect of co-exposure to Hg and TCDD on the expression of the AhR-regulated phase I and phase II genes in HepG2 cells, isolated mouse hepatocytes, and in vivo in the liver, kidney, lung, and heart of C57Bl/6J mice, and 2) to explore the molecular mechanisms involved in this modulation. In vitro, Hg2+ significantly inhibited the TCDD-mediated induction of CYP1A1 at the mRNA, protein, and catalytic activity levels. Furthermore, co-exposure to Hg2+ and TCDD significantly decreased the TCDD-mediated induction of AhR-dependent luciferase reporter gene expression. At the post-translational level, Hg2+ significantly decreased the protein half-life, and increased the expression of heme oxygenase-1 (HO-1), which coincided with further decrease in the CYP1A1 catalytic activity levels. With regard to NQO1, Hg2+ increased its expression at the mRNA, protein, and activity levels in the absence and presence of both NQO1 inducers, TCDD and Sulforaphane (SUL), which coincided with increased nuclear accumulation of Nrf2 protein. Hg2+ was able to induce the antioxidant responsive element (ARE)-dependent luciferase reporter gene expression in an Nrf2 dependent mechanism. In vivo, Hg2+ differentially modulated phase I and phase II AhR-regulated genes at the constitutive and inducible levels. Interestingly, Hg2+ increased serum hemoglobin (Hb) levels in mice treated for 24 h with Hg2+. Upon treatment of isolated hepatocytes with Hb alone, there was an increase in the AhR-dependent luciferase activity with a subsequent increase in Cyp1a1 protein and catalytic activity levels. In conclusion, the present study demonstrates that exposure to Hg2+ and TCDD in vitro may decrease TCDD-mediated carcinogenicity by decreasing the induction of CYP1A1 and increasing the induction of NQO1. However; at the in vivo level, Hg2+ modulates the constitutive and inducible AhR-regulated genes in a time-, tissue- and, AhR-regulated enzyme specific manner. In addition, at the in vitro level HO-1 and Nrf2 are involved in the modulation of CYP1A1 and NQO1 respectively, while Hb was implicated as an in vivo specific modulator of Cyps.

• Subjects / Keywords

  • AhR
  • Mercury
  • TCDD CYP1A1
  • NQO1
  • in vitro and in vivo

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3ZS2KQ53

• 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.