Research

Questions about possible adverse health effects from environmental and occupational exposures to uranium have arisen as a result of uranium mining, residual mine tailings, and the use of depleted uranium in the military.  It is generally accepted that uranium induces damage through a combination of chemical and radiological effects; however, the specific molecular mechanisms behind its action have not been clarified.  The overall goals of this research are to determine what types of DNA damage uranium can cause and what the consequences of that damage are within a cell.

We are finding that uranium may damage DNA as a heavy metal, independent of its radioactivity. 

Images: Uranium mines in northern Arizona and southern Utah

The first direction we explored in this project was to study the reaction of uranium as uranyl acetate with ascorbate, which is vitamin C. 

We learned that when supercoiled DNA is exposed to uranium(VI) there are strand breaks generated, and when vitamin C is added to this mixture there are more strand breaks.  Using spectroscopic methods and adding chemicals that scavenge free radicals we inferred that there was no significant electron transfer between the uranium and the ascorbate, rather the evidence suggested that a complex may have formed between the uranium and the ascorbate and the phosphate backbone of the DNA, which made the DNA easier to break.  

This work has been published:

Yazzie M; Gamble SL; Civitello ER; Stearns DM (2003)  Uranyl acetate causes DNA single strand breaks in vitro in the presence of ascorbate (vitamin C). Chemical Research in Toxicology 16(4):524-530. (view abstract)

Shania Gamble, then an M.S. student at NAU, uses the NMR spectrometer to study how uranium reacts with vitamin C.	Monica Yazzie, then an M.S. student at NAU, loads a gel to look at a reaction of uranium, ascorbate and DNA.

The second study looked at the ability of uranium as uranyl acetate to cause DNA damage in cells grown in the laboratory. 

We studied the toxicity of uranium(VI) in Chinese hamster ovary cells, which is a common cell line used to study metal toxicity.  We used the parental line, CHO AA8, and a line that is deficient in DNA repair, the CHO EM9 line.  We hypothesized that if uranium were causing DNA damage, then cells that can’t repair DNA damage should be more sensitive to uranium.  Our observations supported our hypothesis.  It took less uranium to kill the EM9 cells than the AA8 cells.  We also found more mutations in the repair-deficient EM9 cells than the normal AA8 cells.  Next we looked at the types of DNA lesions that occurred after uranium treatment.  We found DNA strand breaks, which were consistent with our previous work with isolated DNA, and we also found that uranium was bonded to the DNA, in other words it caused uranium-DNA adducts.  The observation suggests that uranium may be toxic and mutagenic in ways that go beyond its being a radioactive metal; therefore it implies that the health risks for uranium exposure could go beyond those for radiation exposure.  This is a relatively new and unexplored hypothesis. 

This work has been published:

Stearns DM; Yazzie M; Bradley AS; Coryell VH; Shelley JT; Ashby A; Asplund CS; Lantz RC. (2005) Uranyl acetate induces hprt mutations and uranium-DNA adducts in Chinese hamster ovary EM9 cells.  Mutagenesis 20(6):417-23. 

Link to the Mutagenesis web page: http://mutage.oxfordjournals.org/

These are images of CHO cells by the “comet assay” or single cell gel electrophoresis.  The cell on the left is an untreated cell with no DNA damage.  The cell on the right was exposed to uranyl acetate, and what looks like the comet tail is the broken DNA.
	Left: Cell survival in the presence of uranium depends on DNA repair.  Strand break deficient cells (red) are more susceptable to uranium than cells that can repair DNA strand breaks (green)
Right: Nizhoni Denaph performs cytotoxicity assays under the supervision of Drs. Clark Lantz and Louise Canfield.

The next study looked more closely at the way that uranium caused mutations in the CHO EM9 line. 

Based on how our previous data suggested that uranium was reacting with DNA, we hypothesized that if uranium was acting chemically as a heavy metal, and not just as a radioactive metal, then the types of mutations it caused should be unique, and different from those generated spontaneously and by the oxidant hydrogen peroxide.  Dr. Virginia Coryell isolated a total of 59 uranium-induced, 38 spontaneous, and 45 hydrogen peroxide-induced CHO EM9 mutants.  She characterized the changes in the hprt gene in these mutants. 

The amount of G " T or C " A base substitutions was not significantly different in spontaneous or hydrogen peroxide-induced mutants than in uranium-induced mutants, suggesting a possible role for oxidative damage in uranium mutagenesis. However, the observation that uranium produced significantly more major genomic rearrangements (multiexon insertions and deletions) than occurred spontaneously suggests the possibility that DNA strand breaks or crosslinks could also be involved in uranium mutagenesis. The unique mutation spectrum caused by uranium suggested that uranium generates mutations in ways that are different from spontaneous and free radical as well as radiological mechanisms, and supports our hypothesis that uranium can damage DNA as a heavy metal.

This work has been published:

Coryell VH; Stearns DM. Molecular analysis of hprt mutations generated in Chinese hamster ovary EM9 cells by uranyl acetate, by hydrogen peroxide, and spontaneously. (2006) Molecular Carcinogenesis 45(1):60-72.

Link to the Molecular Carcinogenesis web page:
http://www3.interscience.wiley.com/cgi-bin/jtoc/37603/

 

Current efforts

Current efforts in our labs are directed at investigating DNA damage and mutations caused by uranium in other types of cells, and at exploring the role of oxidative stress in these processes.  We will update this page with new information as it becomes available. 

Publications from this Project

Yazzie M; Gamble SL; Civitello ER; Stearns DM (2003)  Uranyl acetate causes DNA single strand breaks in vitro in the presence of ascorbate (vitamin C). Chemical Research in Toxicology 16(4):524-530. (view abstract)
http://pubs.acs.org/cgi-bin/abstract.cgi/crtoec/2003/16/i04/abs/tx025685q.html

Stearns DM; Yazzie M; Bradley AS; Coryell VH; Shelley JT; Ashby A; Asplund CS; Lantz RC. (2005) Uranyl acetate induces hprt mutations and uranium-DNA adducts in Chinese hamster ovary EM9 cells.  Mutagenesis 20(6):417-23. 
http://mutage.oxfordjournals.org/

Coryell VH; Stearns DM. Molecular analysis of hprt mutations generated in Chinese hamster ovary EM9 cells by uranyl acetate, by hydrogen peroxide, and spontaneously. (2006) Molecular Carcinogenesis 45(1):60-72.

Link to the Molecular Carcinogenesis web page:
http://www3.interscience.wiley.com/cgi-bin/jtoc/37603

Links to Uranium and Uranium Mining Web Sites

Agency for Toxic Substances and Disease Registry (ATSDR)  Fact Sheet on Uranium
http://www.atsdr.cdc.gov/tfacts150.html

World Health Organization’s description of depleted uranium
http://www.who.int/mediacentre/factsheets/fs257/en/

WISE uranium project
http://www.wise-uranium.org/

Uranium Medical Research Centre
http://www.umrc.net/default.aspx

Uranium and Radiation Education Outreach at NAU (2002)
http://www4.nau.edu/eeop/ureo/index.htm

Southwest Research and Information Center
http://www.sric.org/index.html

A Few Books on Uranium Mining

If You Poison Us: Uranium and Native Americans by Peter H. Eichstaedt
http://www.amazon.com/gp/product/1878610406/sr=8-1/qid=1156549156/ref=pd_bbs_1/102-6617951-6998556?
ie=UTF8

Cancer Factories: America's Tragic Quest for Uranium Self-Sufficiency (Contributions in Medical Studies) by Howard Ball
http://www.amazon.com/gp/product/0313275661/sr=1-1/qid=1156549351/ref=sr_1_1/102-6617951-6998556?
ie=UTF8&s=books

Yellowcake Towns: Uranium Mining Communities in the American West (Mining the American West by Michael A. Amundson (a History Professor at NAU)
http://www.amazon.com/gp/product/0870817655/sr=1-1/qid=1156549380/ref=pd_bbs_1/102-6617951-6998556?
ie=UTF8&s=books

The Navajo People and Uranium Mining by Steward L. Udall (Foreword), Doug Brugge (Editor), Timothy Benally (Editor), Esther Yazzie-Lewis (Editor)
http://www.amazon.com/gp/product/0826337783/sr=1-2/qid=1156549433/ref=sr_1_2/102-6617951-6998556?
ie=UTF8&s=books