RESEARCH ARTICLE


NRF2 Oxidative Stress Induced by Heavy Metals is Cell Type Dependent



Steven O Simmons *, 1, Chun-Yang Fan #, 1, 2, Kim Yeoman 3, John Wakefield 4, Ram Ramabhadran 1
1 Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory, US EPA, Research Triangle Park, North Carolina, USA
2 University of North Carolina- Chapel Hill, Chapel Hill, North Carolina, USA
3 U.S. Envirmental Agency, 109 TW Alexandar Drive MD B 105-03, Research Triangle Park, NC 27711, USA
4 Thermo Fisher Scientific, Huntsville, Alabama, USA


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© Simmons et al.; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory, US EPA, Research Triangle Park, North Carolina, USA; Tel: (919) 541-1475; Fax: (919) 541-3335; E-mail: simmons.steve@epamail.epa.gov
# Present Address: Syngenta Biotechnology, Inc., Research Triangle Park, North Carolina, USA.


Abstract

Exposure to metallic environmental toxicants has been demonstrated to induce a variety of oxidative stress responses in mammalian cells. The transcription factor Nrf2 is activated in response to oxidative stress and coordinates the expression of antioxidant gene products. In this study, we describe the development of an Nrf2-specific reporter gene assay that can be used to study the oxidative stress response in multiple cell types. Using five different cell lines, the Nrf2-activating potency of twenty metals was assessed across a range of concentrations. While ten of the metals tested (cadmium, cobalt, copper, gold, iron, lead, mercury, silver, sodium arsenite and zinc) stimulated Nrf2-dependent transcriptional activity in at least three of the engineered cell lines, only three (cadmium, copper and sodium arsenite) were active in all five cell lines. A comparison of metal-induced Nrf2 transcriptional activation revealed significant differences in the absolute magnitude of activation as well as the relative potencies between the cell lines tested. However, there was no direct correlation between activity and potency. Taken together, these results show that the capacity to stimulate Nrf2 activity and relative potencies of these test compounds are highly dependent on the cell type tested. Since oxidative stress is thought to be involved in the mode of action of many toxicological studies, this observation may inform the design of paradigms for toxicity testing for toxicant prioritization and characterization.

Keywords: Nrf2, metals, oxidative stress, reporter gene, cell lines, toxicity testing.