The Toxicologist - Society of Toxicology

in nose, larynx and lungs and showed a more usual exposure-related response in
both species. Published studies suggest vanadium pentoxide is mutagenic in vitro
and possibly in vivo in mice, but this does not explain the species or site specificity
of the neoplastic response. As a first step in an investigation of this problem, a noseonly
inhalation study was conducted in female B6C3F1 mice at vanadium pentoxide
concentrations of 0, 0.25, 1 and 4 mg/m3, 6h/day for 16 days. Observations included
atmospheric V, concentrations of V in lungs and blood, lung weight,
histopathology of the airways, cell proliferation in lungs, concentrations in lungs of
α-tocopherol, glutathione (reduced and total), F2-isoprostane and 9 specific DNAoxy-adducts
and DNA damage (comet assays) in lung and BAL fluid cells.
No effects were observed at 0.25 mg/m3. At 1 and 4 mg/m3, exposure-dependent
increases were observed in lung weight, alveolar histiocytosis, sub-acute alveolitis
and/or granulocytic infiltration and a generally time-dependent increased cell proliferation
rate. No DNA damage (comet) was detected and the only DNA oxyadducts
at or above the limit of detection were 8-oxodGuo and dCyd341, but only
8-oxodGuo showed a dose related increase.
This work was conducted in collaboration with Advanced Technology Institute,
Charleston, SC 29418, USA and sponsored by the US Army Research Laboratory
under Cooperative Agreement Number DAAD 19-03-2-0036.
290 TISSUE BURDEN AND HISTOPATHOLOGY IN
SPRAGUE-DAWLEY RATS AFTER INHALATION OF
TUNGSTEN ALLOY.
P. A. Ortiz 1 , C. U. Parkinson 2 , V. P. Mokashi 1 , M. G. Stockelman 1 and B. A.
Wong 1, 2 . 1 Naval Medical Research Unit - Dayton, Wright-Patterson AFB, OH and
2 The Hamner Institutes for Health Sciences, Research Triangle Park, NC.
Tungsten is a transition metal element with unique physicochemical properties that
have been used for a variety of military, medical, and industrial purposes. Tungsten
has largely replaced lead in high kinetic energy penetrators, small caliber ammunition,
and other U.S. military munitions. In addition, it has also replaced depleted
uranium in armor. These uses present an exposure risk to military personnel from
aerosolized metal following weapons firing or ballistic impact. Tungsten is typically
mixed with other metals such as nickel or cobalt to provide an alloy with strength
and ductility. The objective of this study was to determine the translocation and accumulation
of tungsten, nickel and cobalt in tissues of rats after inhalation of tungsten
metal alloy particles. To accomplish this, male Sprague Dawley rats underwent
a 2 week exposure to either air or tungsten alloy (approximately 5 mg/m 3 , 6 h/d, 5
d/wk, for 2 weeks). Animals were held for up to 21 days post-exposure to examine
the distribution of those metals. Animal body weights were not affected by the
tungsten alloy inhalation. Tissues were analyzed for tungsten alloy burden using
neutron activation analysis and histopathology. All three metals (tungsten, nickel
and cobalt) were detected in the lung. However, cobalt was the only metal detected
in other tissues, including kidney, liver and olfactory bulb. These results imply that
cobalt behaved like a soluble compound while tungsten results are consistent with
insoluble metal particles. Finally, there were no gross pathological observations detected
in the tissues. Our data indicate that the alloy plays no role in the distribution
of tungsten, including by olfactory translocation.
291 EFFECTS OF TUNGSTEN CHEMICAL SPECIES ON
PHOSPHATE-DEPENDENT PATHWAYS IN AN
OSTEOBLAST CELL LINE.
D. R. Johnson 1 and C. Ang 2 . 1 Environmental Laboratory, U.S. Army Engineer
Research & Development Center, Vicksburg, MS and 2 Badger Testing Services,
Vicksburg, MS.
Tungsten (W) is a metal that has numerous civil and military applications due to its
high strength and melting point. When W enters the environment, it is rapidly oxidized
and speciated based on the environmental matrix it is embedded in. Bone is
the long-term storage organ for W—and presumably W chemical species if present—when
taken up by organisms. It is unknown what long-term effects W has in
bone. Extensive polymerization of W to phosphate may deplete intracellular phosphate
stores, disrupting phosphorylation reactions in cells. Furthermore, disruption
of normal osteoblast function by W may impact bone formation and biomechanics.
Therefore, we evaluated the effects of W species on several phosphate-dependent
intracellular functions, including energy cycling (ATP production), regulation of
enzyme activity (protein tyrosine kinase [PTK]), and intracellular secondary messengers
(cyclic adenosine monophosphate [cAMP]). hFOB 1.19 osteoblastic cells
were exposed to vehicle control (water) or W chemical species (sodium tungstate,
phosphotungstate [PW], poly tungstate [polyW], and tungstosilicic acid [TSA]) at
0-10,000 μM for 24 h at 37 degrees C. Cells were then lysed and analyzed for cell
viability, ATP concentration, tyrosine kinase activity, and cAMP concentration. W
species did not affect ATP concentrations except at the highest concentration. PW,
62 SOT 2011 ANNUAL MEETING
polyW, and TSA, but not tungstate, significantly increased protein tyrosine kinase
activity at 10,000 μM after 4 h exposure. Tungstate and PT increased cellular
cAMP at ≥ 100 μM, while TSA decreased cellular cAMP at 10,000 μM. These data
demonstrate that W chemical species generally only affect phosphate-dependent
cell signaling and secondary messenger pathways in hFOB 1.19 cells. However, the
W chemical species concentrations needed to affect these phosphate-dependent
biochemical pathways greatly exceed the amount of W deposited in bone (100 μM
W = 18 mg/kg), thus providing evidence that W chemical species will not affect osteoblastic
cellular activity.
292 THE INFLUENCE OF GENETIC POLYMORPHISMS ON
MERCURY BIOMARKER DISTRIBUTION IN MEXICAN
MOTHER-CHILD PAIRS.
J. Goodrich 1 , D. Cantonwine 1 , B. N. Sánchez 2 , M. Hernández-Avila 3 , H. Hu 1 ,
M. M. Téllez-Rojo 4 and N. Basu 1 . 1 Environmental Health Sciences, University of
Michigan, Ann Arbor, MI, 2 Biostatistics, University of Michigan, Ann Arbor, MI,
3 Ministry of Health, México, Districto Federal, Mexico and 4 Statistics, Center for
Evaluation Research and Surveys, National Institute of Public Health, Cuermavaca,
Morelos, Mexico.
Mercury (Hg) risk assessment is complicated by variability in toxicokinetic parameters
and distribution to established biomarkers of exposure (blood, hair, urine).
This work hypothesizes that single nucleotide polymorphisms (SNPs) in key glutathione
S-transferase (GST), glutathione synthesizing, and selenoprotein genes
underlie inter-individual differences in Hg biomarker levels. The genotype of 17
SNPs and biomarker Hg levels were obtained from mother-child pairs of the Early
Life Exposures in Mexico to Environmental Toxicants (ELEMENT) cohort.
Mothers’ hair and children’s urine Hg levels (n=385; mean±SD=0.53±0.48 μg/g;
n=440; 0.96±2.97 μg/L) mirrored US population averages of similar groups.
Indicating higher methylmercury exposure, blood (n=415; 1.65±1.3 μg/L) and
hair (n=444; 0.5±0.46 μg/g) Hg biomarker levels in the children were 2-4 times
higher than that of US children. Mean biomarker Hg levels and biomarker ratios
(hair:blood, blood:urine) were compared across genotype groups using analysis of
variance. Initial analyses suggest that several SNPs (in GSTP1, GSTM3, GCLC,
SEPP1, GPX2) may influence accumulation of Hg and its distribution among the
biomarkers. Linear regression modeling will further explore these relationships. In
conclusion, genetic polymorphisms may modify the distribution of Hg to blood,
hair and urine. Such gene-environment studies may help to improve our understanding
of the mechanisms underscoring mercury distribution in the body and
minimize variation associated with common exposure biomarkers.
293 LEAD CAUSES BONE LOSS BY DEPRESSION OF
OSTEOBLASTIC FUNCTION THROUGH INHIBITION
OF WNT SIGNALING.
E. E. Beier 1, 2 , E. Puzas 1, 2 , M. Zuscik 2 , D. Cory-Slechta 1 and T. Sheu 2 .
1 Environmental Medicine, University of Rochester, Rochester, NY and 2 Orthopedics,
University of Rochester, Rochester, NY.
INTRODUCTION: We postulate that Pb exposure causes a weakening of the
skeletal structure that leads to an accelerated onset of osteoporotic-like reduction in
bone mineral density. We have found that Pb inhibits the ability of osteoblasts to
make bone while observing the novel induction of the SOST gene. SOST encodes
for the protein sclerostin, a potent repressor of the anabolic Wnt pathway in bone.
Thus, our central hypothesis is that Pb causes bone loss by suppressing osteoblast
function, and that this primarily occurs through induction of sclerostin and depression
of Wnt signaling. METHODS: Rat osteoblasts were isolated from neonatal rat
calvaria and were used to test the influence of Pb on bone nodule formation.
Female Long-Evans rats were given lifelong exposure to 50 ppm Pb and at 18
months were sacrificed and skeletal elements were harvested. Bone parameters were
measured by histomorphometry and μCT. Strength testing was performed on vertebral
specimens by compression to failure. Immunohistochemistry was assessed
using antibodies for β-catenin and sclerostin. RESULTS: Pb dose dependently decreased
bone nodule formation, which was paralleled by increased sclerostin levels.
Wnt3a offered a partial remediation of the Pb effect. We also observed that Wnt3a
induced β-catenin activation was blunted at 12 hours only with a 48 hour Pb pretreatment.
Rats exposed to Pb (9.16 μg/dL) had systemically lower bone density
compared to water controls. They also had weaker bones that were quicker to fracture
and displayed depressed β-catenin signaling. DISCUSSION: Our results indicate
that Pb inhibits osteoblastic activity. Pb exposure evokes significant changes
consistent with a low bone mass phenotype at continuous blood levels below 10
μg/dl. These studies are the first direct evidence identifying the inhibition of Pb on
a key signaling pathway providing insights into a molecular mechanism underlying
Pb toxicity in the skeleton.