The Effects of Phthalate Metabolites on Hepatic Nuclear Receptor Activity
Open Access
- Author:
- Roman, Anthony Michael
- Area of Honors:
- Toxicology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Curtis John Omiecinski, Thesis Supervisor
Gary H. Perdew, Thesis Honors Advisor - Keywords:
- Toxicology
CAR
PXR
PPAR
Constitutive Androstane Receptor - Abstract:
- CAR2, PXR, PPARα, and PPARγ are nuclear receptors found in human hepatocytes and other cells that bind xenobiotics and within the nucleus regulate the transcription of a variety of genes, including those involved in biotransformation. Included among the xenobiotic receptor activators are the phthalates, chemicals used pervasively as plasticizers that are of toxicological concern. My thesis research used a series of transactivation, mammalian two hybrid and real-time PCR assays to compare the activation of these xenobiotic receptors by several phthalates. Phthalates are chemicals that have an aromatic ring base with two ortho alkyl or alkyl aryl groups. The phthalates addressed here include the most commonly used moieties, di-2-ethylhexyl phthalate (DEHP) and di-isononyl phthalate (DiNP), and phthalate metabolites, mono-2-ethylhexyl phthalate (MEHP), mono-isononyl phthalate (MiNP), and monobenzyl phthalate (MBzP). DEHP was shown to activate the human CAR2 splice variant selectively, and also PXR at higher doses, consistent with previously published findings. DiNP similarly activated CAR2 and PXR. The monophthalate derivatives of DEHP and DiNP are the primary metabolites generated in mammalian systems and have not been rigorously evaluated for their receptor activation potential. The main hypothesis of this research project was that these phthalate metabolites could also function as potent CAR2 activators. The results demonstrated that MEHP does in fact potently activate CAR2, PXR, and to a lesser extent PPARα. MiNP was also found to activate CAR2, and to slightly activate PPARα, while PXR exhibited as much as a 25-fold increase in receptor activity in the presence of MiNP. Therefore, the monophthalate metabolites examined in this study were indeed relatively potent activators of the human xenobiotic receptors, CAR2 and PXR. These results are novel and demonstrate that even the primary major metabolites of the di-phthalates retain biological activity.