South Maine: Research indicates Depleted Uranium exposure may lead to lung cancer Print E-mail

 Tuesday May 8 2007
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Wednesday May 9 2007

Study suggests cancer risk from depleted uranium

James Randerson

Depleted uranium, which is used in armour-piercing ammunition, causes widespread damage to DNA which could lead to lung cancer, according to a study of the metal's effects on human lung cells. The study adds to growing evidence that DU causes health problems on battlefields long after hostilities have ceased.

DU is a byproduct of uranium refinement for nuclear power. It is much less radioactive than other uranium isotopes, and its high density - twice that of lead - makes it useful for armour and armour piercing shells. It has been used in conflicts including Bosnia, Kosovo and Iraq and there have been increasing concerns about the health effects of DU dust left on the battlefield. In November, the Ministry of Defence was forced to counteract claims that apparent increases in cancers and birth defects among Iraqis in southern Iraq were due to DU in weapons.

Now researchers at the University of Southern Maine have shown that DU damages DNA in human lung cells. The team, led by John Pierce Wise, exposed cultures of the cells to uranium compounds at different concentrations. Scroll down to read the complete online report from

The compounds caused breaks in the chromosomes within cells and stopped them from growing and dividing healthily. "These data suggest that exposure to particulate DU may pose a significant [DNA damage] risk and could possibly result in lung cancer," the team wrote in the journal Chemical Research in Toxicology.

Previous studies have shown that uranium miners are at higher risk of lung cancer, but this has often been put down to the fact that miners are also exposed to radon, another cancer-causing chemical.

Prof Wise said it is too early to say whether DU causes lung cancer in people exposed on the battlefield because the disease takes several decades to develop.

"Our data suggest that it should be monitored as the potential risk is there," he said.

Prof Wise and his team believe that microscopic particles of dust created during the explosion of a DU weapon stay on the battlefield and can be breathed in by soldiers and people returning after the conflict.

Once they are lodged in the lung even low levels of radioactivity would damage DNA in cells close by. "The real question is whether the level of exposure is sufficient to cause health effects. The answer to that question is still unclear," he said, adding that there has as yet been little research on the effects of DU on civilians in combat zones. "Funding for DU studies is very sparse and so defining the disadvantages is hard," he added.

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 Web Release Date: April 14, 2007
Copyright © 2007 American Chemical Society

Particulate Depleted Uranium Is Cytotoxic and Clastogenic to Human Lung Cells

Sandra S. Wise,  W. Douglas Thompson,   AbouEl-Makarim Aboueissa,   Michael D. Mason,   and John Pierce Wise, Sr. *   

Wise Laboratory of Environmental and Genetic Toxicology, University of Southern Maine, 96 Falmouth Street, Portland, Maine 04104-9300, Maine Center for Toxicology and Environmental Health, University of Southern Maine, 96 Falmouth Street, Portland, Maine 04104-9300, Department of Applied Medical Science and Department of Mathematics and Statistics, University of Southern Maine, 96 Falmouth Street, Portland, Maine 04104-9300, and Institute for Molecular Biophysics, Department of Chemical and Biological Engineering, University of Maine, Orono, Maine 04469

Received January 18, 2007

Abstract:
Depleted uranium (DU) is commonly used in military armor and munitions, and thus, exposure of soldiers and non-combatants is potentially frequent and widespread. DU is considered a suspected human carcinogen, affecting the bronchial cells of the lung. However, few investigations have studied DU in human bronchial cells. Accordingly, we determined the cytotoxicity and clastogenicity of both particulate (water-insoluble) and soluble DU in human bronchial fibroblasts (WTHBF-6 cells). We used uranium trioxide (UO3) and uranyl acetate (UA) as prototypical particulate and soluble DU salts, respectively. After a 24 h exposure, both UO3 and UA induced concentration-dependent cytotoxicity in WTHBF-6 cells. Specifically, 0.1, 0.5, 1, and 5 g/cm2 UO3 induced 99, 57, 32, and 1% relative survival, respectively. Similarly, 100, 200, 400, and 800 M UA induced 98, 92, 70, and 56% relative survival, respectively. When treated with chronic exposure, up to 72 h, of either UO3 or UA, there was an increased degree of cytotoxicity. We assessed the clastogenicity of these compounds and found that at concentrations of 0, 0.5, 1, and 5 g/cm2 UO3, 5, 6, 10, and 15% of metaphase cells exhibit some form of chromosome damage. UA did not induce chromosome damage above background levels. There were slight increases in chromosome damage induced when we extended the UO3 treatment time to 48 or 72 h, but no meaningful increase in chromosome damage was observed with chronic exposure to UA.

Introduction

Uranium (U) is a naturally radioactive metal that consists of three isotopes: 235U, 234U, and 238U. The nuclear industry has used refined U for many years for energy production. The refinement of U results in the production of large quantities of depleted uranium (DU) consisting primarily of 238U (1). DU retains the same chemical properties of natural uranium; however, it is much less radioactive. These properties, high density and pyrophoricity in particular, have made DU ideal for military applications of armor-plating and armor-piercing munitions. Explosions and fires involving these DU products result in DU dust, which leads to significant inhalation of DU particles (2). These small DU particles, (<10 m) can be inhaled deeply into the lung, leading to longer retention and thus longer exposure.

DU is now becoming a major international concern as a possible health hazard and carcinogen (1-4). Little is currently known about DU mechanisms of effect, but reported data indicate that it may cause lung cancer (1-4), embryotoxicity and teratogenicity (5), reproductive and developmental damage (6), genomic instability (7), and single strand DNA breaks (8). Given the widespread use of uranium for military application and the present worldwide deployment of the United States military, it is imperative that we investigate the carcinogenicity and genotoxicity of DU.

It is difficult to address the issue of DU exposure in humans. Most of the epidemiologic data with regard to human exposure to U that show increases in cancer morbidity and mortality are associated with either radon or other chemical confounders (4). Chromosomal analysis performed on blood samples from war veterans exposed to DU 10 years prior shows aberrations typical of exposure to ionizing radiation (9). However, many experts suggest that because of DU's low specific activity, it does not pose a significant radiologic risk.

Only a few studies have considered the genotoxic and carcinogenic potential of DU. Animal studies using rodents embedded with DU fragments were found to induce mutations in several key oncogenes, to induce serum mutagenicity, and to cause soft tissue sarcomas in muscle tissue (10-12). DU particles inhaled by rats showed increased DNA damage and inflammatory effects (13). Studies in human osteosarcoma cells indicate that DU can induce transformation (14) and cause cytotoxicity, genomic instability, and micronuclei formation (7). Soluble DU caused micronuclei formation, sister chromatid exchanges, DNA adducts, hprt mutations, and chromosomal aberrations in Chinese hamster ovary (CHO) cells (15, 16). However, while these papers provide some evidence that DU is genotoxic and potentially carcinogenic, they do not focus on the target cells, and the genotoxic effect was not strong.

The major route of exposure to DU is through inhalation of particles (1, 4). Thus human bronchial cells (HBC) are a primary target of DU's effects; however, the effects of DU in the lung are poorly characterized (17). Only two studies have considered the interaction of uranium and HBC (18, 19). One study found that insoluble DU induced neoplastic transformation of HBC with chronic exposures (18). The other reported that uranium ore dust induced lipid peroxidation and micronuclei formation (19); however, the chemical analysis of that ore dust revealed no actual uranium content. No studies have considered the clastogenicity of DU in HBC. Accordingly, the purpose of this study was to improve our current understanding of DU by studying the clastogenicity of both particulate and soluble DU in human bronchial cells.

Materials and Methods

Chemicals and Reagents. Uranium trioxide was purchased from Strem Chemicals (Newburyport, MA). Uranyl acetate was purchased from Electron Microscopy Sciences (Fort Washington, PA). Colcemid and potassium chloride (KCl) were purchased from Sigma Chemical (St. Louis, MO). Giemsa stain was purchased from Biomedical Specialties Inc. (Santa Monica, CA). Crystal violet, methanol and acetone were purchased from J. T. Baker (Phillipsburg, NJ). D-MEM/F-12 was purchased from Mediatech Inc. (Herndon, VA). Cosmic calf serum (CCS) was purchased from Hyclone (Logan, UT). Gurr's buffer, trypsin-EDTA, sodium pyruvate, penicillin-streptomycin, and L-glutamine were purchased from Invitrogen Corporation (Grand Island, NY). Tissue culture dishes, flasks, and plasticware were purchased from Corning Inc. (Acton, MA).

Cells and Cell Culture. WTHBF-6 cells, a clonal cell line derived from normal human bronchial fibroblasts that ectopically express human telomerase, were used in all experiments. These cells have a similar doubling time (24 h) and clastogenic and cytotoxic responses to metals compared to those of their parent cells (20). Ectopically expressing telomerase can induce a variety of phenotypes in mass cultured cells from normal to genomically unstable cells (21); thus, this cell line was subcloned from a mass culture and chosen as a model system because it reflects the normal phenotype (20). After more than 1000 population doublings, these cells retain a normal diploid karyotype (data not shown). Cells were maintained as subconfluent monolayers in DMEM/F-12 supplemented with 15% CCS, 2 mM L-glutamine, 100 U/mL penicillin/100 g/mL streptomycin, and 0.1 mM sodium pyruvate and incubated in a 5% CO2 humidified environment at 37 C. CCS is a synthetic serum supplemented with iron and growth factors. The levels of iron in CCS reflect physiological concentrations and as such are higher than levels seen in bovine serum. Cells were fed three times a week and subcultured at least once a week using 0.25% trypsin/1 mM EDTA solution. All experiments were performed on logarithmically growing cells, and cell densities relative to surface area were kept the same across experimental assays.

Preparation of DU Compounds. Uranyl acetate (CAS# 541-09-3, ACS reagent minimum 99.6% purity) was used as a model soluble DU compound. Solutions of UA were prepared by weighing out the desired amount and dissolving it in double distilled water. Dilutions were made for appropriate treatment concentrations and then filter sterilized through a 10 mL syringe with a 0.2 m filter.

Uranium trioxide (CAS# 1344-58-7, ACS reagent minimum 99.8% purity) was used as a model particulate form of uranium. Suspensions of UO3 particles were prepared by rinsing twice in double distilled water to remove any water soluble contaminants and then twice in acetone to remove any organic contaminants. Air dried particles were weighed, placed in acetone (for sterilization) in a borosilicate scintillation vial, and homogenized for 3-5 min. The mean size distribution of the particles was 400 nm as measured with Zetasizer 3000 HS (Malvern Instruments, Worcestershire, UK). The particles were kept in suspension using a vortex mixer and diluted into appropriate suspensions for specific treatments. Dilutions were also maintained as a suspension using a vortex mixer, and treatments were directly dispensed into cultures from these suspensions. Control groups were treated with equivalent amounts of acetone to account for this vehicle.

Positive controls were treated with soluble (sodium chromate) or particulate (lead chromate) hexavalent chromium compounds. These solutions and suspensions were prepared as reported in previous studies (20, 22-24).

Cytotoxicity Assays. Cytotoxicity was determined using published methods (20) for a clonogenic assay, which measures a reduction in plating efficiency in treatment groups relative to the controls. Briefly, 90,000 cells were seeded in 2.3 mL of medium into each well of a 6 well tissue culture plate and allowed to grow for 48 h. The cultures were then treated for 24, 48, and 72 h with either UO3 or UA. After the respective exposure time, the treatment medium was collected (to include any loosely adherent mitotic cells); the cells were rinsed twice with phosphate buffered saline (PBS); and then removed from the dish with 0.25% trypsin/1 mM EDTA. The trypsinized cells were added to the collected medium to stop the trypsin and centrifuged at 1000 rpm for 5 min. The resulting pellet was resuspended in 10 mL of medium, counted with Coulter Multisizer III, and reseeded at colony forming density (1000 cells per 100 mm dish in 5 mL of media). The colonies were allowed to grow for 10 days, fixed with 100% methanol, stained with crystal violet, and the colonies counted. There were four dishes per treatment group, and each experiment was repeated at least three times.

Chromosome Preparation. Cells were prepared for chromosome analysis using published methods (20). Briefly, cells were seeded at 500,000 cells per 100-mm dish in 13 mL of media and allowed to grow for 48 h. The cultures were treated for 24, 48, and 72 h with UO3 or UA. One hour before the end of the treatment time, 0.1 g/mL colcemid was added to arrest the cells in metaphase. At the conclusion of treatment, medium was collected (to include any loosely adherent mitotic cells), the cells rinsed with phosphate buffered saline, and then removed from the dish with 0.25% trypsin/1 M EDTA. The trypsinized cells were added to the collected medium to stop the trypsin and centrifuged at 1000 rpm for 5 min. The supernatant was removed, and the pellet was resuspended in 10 mL of 0.075 M potassium chloride (KCl) hypotonic solution for 17 min to swell the cells and the nuclei. At the end of the hypotonic time, 1 mL of methanol/acetic acid fixative (3:1) was added and mixed with the hypotonic solution to condition the cells. The cells were centrifuged a second time for 5 min at 1000 rpm. Again, the supernatant was aspirated, the pellet was resuspended, and 10 mL of methanol/acetic acid fixative (3:1) was added. This cell suspension was kept at room temperature for 20 min, and then the fixative was changed twice. Finally, the cells were dropped on a clean, wet slide and uniformly stained using a 5% Giemsa stain in Gurr's buffer. Each experiment was repeated at least three times.

Chromosome Scoring Criteria. Clastogenesis was measured by the production of chromosomal aberrations, which were scored by standard criteria (22). Aberrations were pooled as described by Wise et al. (22). This is because deletions can only be unequivocally distinguished from achromatic lesions if the distal acentric fragment is displaced. Thus pooling aberrations avoids artificial discrepancies between scorers because of the different perceptions of the width of an achromatic lesion relative to the width of its chromatid. Accordingly, chromatid deletions and achromatic lesions were pooled as chromatid lesions, whereas isochromatid deletions and isochromatid achromatic lesions were pooled as isochromatid lesions. One hundred metaphases per data point were analyzed in each experiment.

Statistical Analysis. The Student's t-test was used to calculate p-values to determine the statistical significance of the difference in means. No adjustment was made for multiple comparisons. Interval estimates of differences are 95% confidence intervals, based also on Student's t distribution.

Results

Uranyl acetate induced a time- and concentration-dependent cytotoxicity in WTHBF-6 cells after treatment (Figure 1). Uranium trioxide also induced a time- and concentration-dependent cytotoxicity in WTHBF-6 cells (Figure 2). UO3 did not fully dissolve in our tissue culture conditions. If complete dissolution had occurred, the concentrations for UO3 would be 2.1, 4.2, 21, and 42 g/mL, and for UA, they would be 42, 85, 170, and 339 g/mL.

 


Figure 1 Cytotoxicity of uranyl acetate after 24, 48, and 72 h of treatment. This Figure shows that soluble uranyl acetate induced concentration-dependent cytotoxicity in human lung cells. Chronic exposures (48 and 72 h) to uranyl acetate induced significantly higher cytotoxicity than the 24 h treatment. The data represent the average of three experiments ± the standard error of the mean. * = statistically different from 50 M (p < 0.04); = statistically different from 24 h of the same treatment concentration (p < 0.04).
Figure 2 Cytotoxicity of uranium trioxide after 24, 48, and 72 h of treatment. This Figure shows that particulate uranium trioxide induced concentration-dependent cytotoxicity in human lung cells. Chronic exposure (48 and 72 h) to uranium trioxide induced dramatically higher cytotoxicity than the 24 h treatment. The data represent the average of three experiments ± the standard error of the mean. * = statistically different from 0.05 g/cm2 (p < 0.03).

UA was not clastogenic and did not induce increases in either the percent of metaphases with damage or the total aberrations (Figure 3). Sodium chromate, a soluble Cr(VI) compound, was a positive control for UA; at 24 h, 1 M induced damage in 34% of cells (data not shown). By contrast, UO3 was clastogenic in WTHBF-6 cells (Figure 4). Concentrations of 0.5, 1, 5, and 10 g/cm2 damaged 6, 10, 15, and 26% of metaphases, respectively. UO3 also increased the total number of chromosomal aberrations per metaphase as 0.5, 1, 5, and 10 g/cm2 induced 6, 11, 19, and 32 aberrations per 100 metaphases, respectively. The slight increase in total damage relative to the frequency of damage per cell indicates that few cells incurred damage to multiple chromosomes. Lead chromate was used as a positive control; at 24 h, 0.5 and 1 g/cm2 induced 27 and 37% of cells with damage, respectively.


Figure 3 Clastogenicity of uranyl acetate after 24 h of treatment. This Figure shows that uranyl acetate did not induce any damage in human bronchial cells. There was no increase in either the percent of cells with damage (panel A) or the total number of damaged chromosomes in 100 cells (panel B). The data represent the average of three experiments ± the standard error of the mean. One hundred metaphases per data point were analyzed in each experiment.
Figure 4 Clastogenicity of uranium trioxide after 24 h of treatment. This Figure shows that uranium trioxide induced a concentration-dependent increase in both the percent of cells with damage (panel A) as well as the total number of damaged chromosomes in 100 cells (panel B). The data represent the average of three experiments ± the standard error of the mean. * = statistically different from the control (p < 0.03). One hundred metaphases per data point were analyzed in each experiment.

We also considered the effects of more chronic exposures: treating WTHBF-6 cells for 48 or 72 h with UO3 or UA. These more chronic exposures produced even greater toxicity than the 24 h treatment for both compounds (Figures 1 and 2). However, there was only a slight increase in chromosome damage with 48 h treatment at the highest concentration of 800 M UA, and the 72 h treatment of the highest concentration induced cell cycle arrest. The spectrum of damage induced by UA included mainly chromatid and isochromatid lesions; other types of lesions were extremely rare. UO3 also showed an increase in the amount of chromosome damage over time with moderate concentrations but induced cell cycle arrest with the highest concentration of 5 g/cm2 (Figures 5 and 6). Table 1 shows the spectrum of damage seen in cells treated with UO3 for 24, 48, and 72 h. There is a time- and concentration- dependent increase in both chromatid lesions and isochromatid lesions. All other types of lesions were only seen in the higher concentration, and their occurrence was rare.


Figure 5 Clastogenicity of uranyl acetate after chronic treatment. This Figure shows that uranyl acetate induced only a small amount of damage in human bronchial cells. There was no increase in both the percent of cells with damage (panel A) and the total number of damaged chromosomes in 100 cells (panel B) for most of the time points and concentrations tested. The data represent the average of three experiments ± the standard error of the mean. * = statistically different from the respective control (p < 0.05); = statistically different from the 24 h treatment of the same concentration (p < 0.02). NM = no metaphases. One hundred metaphases per data point were analyzed in each experiment.
Figure 6 Clastogenicity of uranium trioxide after chronic treatment. This Figure shows that uranium trioxide induced a time- and concentration-dependent increase in the amount of damage in human bronchial cells. There was an increase in both the percent of cells with damage (panel A) and the total number of damaged chromosomes in 100 cells (panel B). The data represent the average of three experiments ± the standard error of the mean. * = statistically different from the respective control (p < 0.05); = statistically different from 24 h of the same treatment (p < 0.02). NM = no metaphases. One hundred metaphases per data point were analyzed in each experiment.

Discussion

This is the first article of the cytotoxicity and clastogenicity of particulate and soluble DU in human bronchial cells. Both compounds were cytotoxic in a time- and concentration-dependent manner. Particulate DU was clastogenic in a time- and concentration-dependent manner but soluble DU was not, even after chronic exposure. These data suggest that exposure to particulate DU may pose a significant genotoxic risk and could possibly result in lung cancer.

Our observations are consistent with two previous studies of uranium in HBC (18, 19). One study found that "uranium dust" caused lipid peroxidation and micronuclei formation; however, chemical analysis of the dust revealed that there was no uranium component in the dust, and thus, these results are likely due to the other chemical components of the dust or to the particles themselves (19). The other study found that insoluble DU induced neoplastic transformation of HBC consistent with the possibility that exposure to particulate DU may cause lung cancer, although that study did not consider specific genotoxic events that may have led to the transformation (18).

The particulate data are also consistent with studies in human osteosarcoma (HOS) cells that found sister chromatid exchanges (SCE), micronuclei formation (MN), dicentric formation, and DNA strand breaks after exposure to soluble DU (7). However, in our study, soluble DU was not clastogenic. This difference may be due to the cell models studied; the cells in our study reflect the behavior of normal primary cells (20), and the HOS cells are derived from a tumor and may have alterations in genes critical for genomic stability. This possibility is supported by the fact that they only reported dicentrics chromosomes after DU exposure and not more common lesions such as chromatid and isochromatid lesions. Dicentrics are rarely formed after chemical exposure in normal cells, and this likely reflects the fact that HOS cells are derived from a tumor. In our studies, we found no induction of dicentric chromosomes even when the cells were treated for up to 72 h with UA or UO3, which is consistent with our previous reports of another metal, particulate and soluble chromate (9). Interestingly, when we studied the effects of particulate chromate in a virally immortalized epithelial cell line, we then saw the formation of dicentrics (24).

Chinese hamster ovary (CHO) cells treated with soluble uranyl nitrate also were reported to exhibit significant increases in MN formation, SCE, and chromosomal aberrations (15). Treatment concentrations were comparable to those in our study; however, treatment time and harvest protocol were different. In the CHO cell study, cells were treated for 2 h, and only the highest treatment concentration of 100 M was reported to have significant chromosome damage above the control. However, these effects were very weak and reached only 8% (compared to 3% in the control). The micronuclei and SCE effects were also similarly weak. In this study of HBC, we did not see any increase in chromosome damage at 100 M uranium treatment for 24 and 48 h; 72 h of treatment produced a slight increase; however, it was not statistically significant. In addition, we did not see any increase in chromosome damage with the 24 h treatment of 800 M; there was an increase after 48 h of 800 M; however, compared to the large changes seen in the chronic exposures to UO3, this seems small. The explanation for these differences is uncertain, but again is likely due to the fact that CHO cells have been in culture for over 50 years and have acquired an aneuploid phenotype, whereas the HBC model used in our study is similar to normal HBC.

Our results are also consistent with studies of other genotoxic metals. We previously reported that hexavalent chromium, a known human lung carcinogen, causes a similar spectrum of chromosome aberrations including chromatid and isochromatid lesions (20, 23, 24). Nickel is also a carcinogenic metal that has been shown to damage chromosomes in a similar fashion (25). However, unlike nickel, which preferentially targets the X chromosome, there was no such effect seen after treatment with either DU compound.

Our data show that particulate DU is clastogenic, whereas soluble DU is not. The explanation for this is uncertain, but one possible explanation is that there is a difference in uptake mechanisms. That is, DU particles can enter the cell and intracellularly dissolve by phagocytosis, whereas soluble DU cannot. This mechanism has previously been elucidated for nickel to explain the differences between its soluble and particulate compounds (26). The WTHBF-6 cells used in our study are known to internalize metal particles by phagocytosis (27), and thus, this mechanism certainly is biologically possible in this model system. An alternative mechanism, observed for particulate chromate compounds, is that the DU particles provide chronic exposure to soluble DU with continuous occurrence of extracellular dissolution (27). We feel this is unlikely because chronic exposure to soluble DU was unable to cause an increase in clastogenicity.

For soluble DU, we found that cytotoxicity was concentration-dependent, whereas clastogenicity was not. These data indicate that cell death was not likely caused by chromosomal abnormalities. The cytotoxic mechanism is uncertain, but one non-genotoxic possibility is that DU may directly target the mitochondria, leading to apoptosis. This possibility is consistent with a previous in vitro study of rabbit proximal tubule cells which showed that concentrations of soluble uranyl nitrate of 1 mM or greater cause mitochondrial damage (28).

Epidemiological studies have had a difficult time ascertaining the lung cancer risk posed by DU. Our data suggest that in human lung cells, significant clastogenicity is only observed at highly cytotoxic concentrations. Thus, many of the damaged cells will be removed by cell death, and thus if DU is carcinogenic in human lung cells, it may require a high dose or involve a non-genotoxic mechanism. Other metals such as lead have been proposed to have significant non-genotoxic effects such as DNA repair inhibition or alterations in DNA conformation (29).

In summary, particulate DU compounds induced time and concentration-dependent cytotoxic and clastogenic effects in human lung cells. Soluble DU was cytotoxic but not clastogenic. The types of aberrations seen with treatment of particulate DU are consistent with those induced by other carcinogenic metals. Further research is aimed at looking at the effect in epithelial cells as well as looking at epigenetic changes to assess their role in the ability of DU to induce neoplastic transformation.

Acknowledgment

We thank Jon Moreland for technical assistance, Christy Gianios for IT support, and David Kirstein for administrative support. We would also like to thank Geron Corporation for the use of the hTERT materials. This work was supported by ARO Grant #W911NF-04-1-0240 (to J.P.W.) and the Maine Center for Toxicology and Environmental Health.

* To whom correspondence should be addressed. Phone: (207) 228-8050. Fax: (207) 228-8057. E-mail:

Wise Laboratory of Environmental and Genetic Toxicology, University of Southern Maine.

Maine Center for Toxicology and Environmental Health, University of Southern Maine.

Department of Applied Medical Science, University of Southern Maine.

Department of Mathematics and Statistics, University of Southern Maine.

University of Maine.

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Table 1. Spectrum of Chromosome Aberrations Induced by Uranium Trioxide in WHTBF-6 Cellsa

compd

concn (g/ cm2)

survival (% control)

chromatid lesions

iso- chromatid lesions

chromatid exchanges

double minutes

acentric fragments

24 h

VCb

 

 

4 (0.3)

0 (0)

0 (0.3)

0 (0.3)

0 (0.3)

UO3

0.1

99 (4.4)

ndc

nd

nd

nd

nd

UO3

0.5

57 (11.1)

5 (0.6)

1 (0.3)

0 (0)

0 (0.3)

0 (0.3)

UO3

1.0

32 (10.2)

8 (0.3)

2 (0.7)

0 (0)

1 (0.7)

0 (0.3)

UO3

5.0

1 (0.6)

17 (4.3)

1 (0)

0 (0)

1 (0.3)

0 (0.3)

UO3

10

0 (0)

27 (1.5)

3 (2)

1 (1)

1

0 (0)

48 h

VC

 

 

3 (1.3)

2 (0.6)

0 (0)

0 (0)

0 (0.3)

UO3

0.1

87 (4.6)

7 (0.7)

1 (0.3)

0 (0)

0 (0.3)

1 (0.3)

UO3

0.5

36 (3)

7 (0.3)

1 (0.3)

0 (0)

0 (0.3)

0 (0.3)

UO3

1.0

5 (1.2)

25 (6.2)

4 (1.8)

0 (0)

0 (0.3)

1 (0.6)

UO3

5.0

0 (0)

NMd

NM

NM

NM

NM

UO3

10

nd

nd

nd

nd

nd

nd

72 h

VC

 

 

3 (1.2)

0 (0.3)

0 (0)

0 (0.3)

0 (0.3)

UO3

0.1

80 (1.9)

7 (2.3)

3 (1.7)

0 (0)

0 (0.3)

1 (0.7)

UO3

0.5

28 (5.9)

11 (2.7)

4 (1.5)

0 (0)

1 (0.7)

0 (0)

UO3

1.0

4 (1.2)

16 (0.7)

5 (0.9)

0 (0)

1 (0.7)

2 (0.9)

UO3

5.0

1 (0.7)

NM

NM

NM

NM

NM

UO3

10

nd

nd

nd

nd

nd

nd

a The average of three experiments with standard error in parentheses is shown.b Vehicle control = acetone.c nd = not done.d NM = No metaphases