Identification of 2,8-Dihydroxyquinoline as a Novel Agonist of the Human Aryl Hydrocarbon Receptor

Open Access
Author:
Cassel, Kaitlyn Marie
Area of Honors:
Veterinary and Biomedical Sciences
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Gary H Perdew, Thesis Supervisor
  • Robert John Vansaun, Honors Advisor
Keywords:
  • aryl hydrocarbon receptor
  • dihydroxyquinoline
  • gastrointestinal health
  • microbiome
  • xenobiotic metabolism
  • dietary ligands
Abstract:
The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor known for its ability to metabolize a vast array of xenobiotics, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Recent literature has implicated the role of AHR in intestinal homeostasis and immunity via activation by endogenous and dietary ligands, suggesting that certain ligands may impart a protective effect and increase barrier function of the intestinal epithelium. This study characterizes 2,8-dihydroxyquinoline (2,8-DHQ) as a novel AHR ligand, exhibiting specificity for the human AHR. 2,8-DHQ is a product of gastrointestinal microbial metabolism identified in body fluids. A number of dihydroxyquinoline compounds were investigated for potential AHR activity through a luciferase-based reporter assay, which identified 2,8-DHQ as having the highest affinity for the human receptor. Administration of 2,8-DHQ increased transcription of the AHR target gene CYP1A1 in a dose-dependent manner in cultured human cells. A photoaffinity ligand (PAL) competition assay identified 2,8-DHQ as a competitive ligand for the human AHR in cell culture, however it is interesting to note that this was not true when the assay was repeated in vitro in liver extracts. This may be due to the need for 2,8-DHQ to undergo metabolism, a process that also increases the affinity of indole to bind AHR when it becomes indoxyl sulfate. Finally, a nuclear retention assay was conducted that showed 2,8-DHQ treatment to cause a significant increase in nuclear translocation and retention of AHR. Further research is needed to investigate the ability of 2,8-DHQ to activate AHR in vivo and to characterize its potential to impact human health through attenuation of intestinal inflammation.