The Toxicologist - Society of Toxicology

treated wood. Seventy-five of 132 wood samples (56.8%) were CCA treated wood.
A significant association (Fisher’s exact p-value = 0.348 x 10-6) was found between
CCA treated wood and soil As (n = 75). At one elementary school CCA treated
woodchips (range 813 – 1654 mg As/kg) covered the playgrounds. The situation in
New Orleans probably exists in play areas across the nation. These findings support
a precautionary program for testing soils and wood for hazardous substances at all
play areas intended for children.
969 A NOVEL NITRIC OXIDE DONOR, V-PROLI/NO,
PROTECTS AGAINST ARSENIC-INDUCED TOXICITY
IN LIVER CELLS.
W. Qu 1 , L. Cheng 1 , A. L. Dill 1 , J. E. Saavedra 2 , L. K. Keefer 2 and M. P.
Waalkes 1 . 1 Inorganic Carcinogenesis Section, NCI at NIEHS, Research Triangle Park,
NC and 2 Chemistry Section, LCC, NCI- Frederick, Frederick, MD.
Arsenic trioxide is used to treat certain leukemias and has potential for treatment of
solid tumors, but hepatotoxicity is a major limiting side effect. O 2 -vinyl 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate
(V-PROLI/NO) is a nitric oxide
(NO) donor prodrug that is metabolized by liver cytochromes P450 to release NO.
The effects of V-PROLI/NO pretreatment on the toxicity of arsenic (as NaAsO 2
)
were studied in vitro in a rat liver (TRL 1215) cell line. These cells acted upon the
prodrug to release NO, as assessed by nitrite levels, in a concentration- and timedependent
fashion to maximal levels of 40-fold above background. In cells pretreated
with V-PROLI/NO (200 μM, 24 h) then exposed to arsenic for additional
24 h, arsenic was much less toxic (LC50 = 65.8 μM) than in control cells (LC50 =
18.4 μM). The reduced cytolethality was related to the level of NO produced. V-
PROLI/NO increased Cyp1a1, Gst-π and HO-1 transcriptional expression. Indeed,
increased Cyp1a1 transcript was directly related to NO production. Similarly, the
increases in Cyp1a1 transcript stimulated by V-PROLI/NO were directly correlated
to increasing arsenic LC 50
. Increased GST-π is important in arsenic efflux while
HO-1 is important in adaptation to arsenic-induced oxidative stress. V-
PROLI/NO pretreatment markedly reduced arsenic-induced apoptosis, as measured
by DNA fragmentation, and suppressed phosphorylation of JNK1/2, a key
event in apoptosis. Arsenic alone increased metallothionein (MT), a metal-binding
protein important in arsenic tolerance, while V-PROLI/NO pre-treatment before
arsenic caused additional increases in MT levels. Thus, V-PROLI/NO protects
against arsenic toxicity in liver cells, reducing cytolethality, apoptosis and blocking
dysregulation of MAPKs. This appears to be through generation of NO formed
after metabolism by the liver cell enzymes, possibly including Cyp1a1.
970 FERRIHYDRITE AS AN ENTEROSORBENT FOR
ARSENIC.
J. F. Taylor, A. Robinson, A. Marroquin-Cardona, N. Johnson, N. Mitchell, B.
Brattin, R. Taylor and T. Phillips. Veterinary Integrative Biosciences, Texas A&M,
College Station, TX.
Arsenic in drinking water is a problem in many developing countries such as
Taiwan and Bangladesh. Currently, no oral binding agent has been clearly demonstrated
to be successful for the mitigation of arsenic toxicity. Ferrihydrite, an iron
oxy-hydroxide, was recently tested in vitro for its ability to serve as an enterosorbent
for arsenic found in drinking water. The goals of this research were to evaluate the
ability of an industrially produced ferrihydrite (IPF) to sorb arsenic in a series of in
vitro experiments and validate its safety when included in the diet of rats. IPF was
tested for its ability to bind arsenic as sodium arsenite, As(III) and sodium arsenate,
As(V) in binding isotherms and in a simulated gastro-intestinal (GI) model. IPF
was also tested for its ability to protect Hydra from toxicity. IPF was included in the
diet of 4-week old male Sprague-Dawley rats at 0.5% for 2 weeks, and subsequently,
serum was tested for iron levels and serum biochemistry. In the in vitro experiments,
IPF was found to strongly sorb both As(III) and As(V) with a Qmax of
0.452 mol/kg and 0.252 mol/kg, respectively. IPF also successfully removed As in a
simulated GI model exhibited by Qmax values of 0.246 mol/kg and 0.344 mol/kg
for As(III) in the simulated stomach and intestine, respectively, and 0.311 mol/kg
and 0.365 mol/kg for As(V) in the simulated stomach and intestine, respectively.
IPF protected Hydra at levels up to 200 and 2.5 times the minimal affective concentration
for As(III) and As(V), respectively. Rats eating 0.5% IPF in their diet
showed no significant differences in serum iron levels, serum biochemistry, serum
vitamin A and E, or feed conversion rates. These experiments demonstrate IPF’s
ability to sorb both As(III) and As(V) at a high capacity, and show that it protects a
simple aquatic organism from As toxicity. IPF at 0.5% was shown to be apparently
safe and was well tolerated by rats. Work is ongoing to verify IPF’s efficacy in a rodent
model.
971 EPIGENETIC ALTERATIONS IN FETAL MOUSE LIVERS
AFTER IN UTERO EXPOSURE TO ARSENIC.
Z. Drobna 1 , M. Niculescu 1, 3 , R. Fry 2 , I. Pogribny 4 , M. Waalkes 5 , S. Zeisel 1, 3
and M. Styblo 1 . 1 Nutrition, University of North Carolina at Chapel Hill, Chapel
Hill, NC, 2 Environmental Engineering and Sciences, University of North Carolina at
Chapel Hill, Chapel Hill, NC, 3 Nutrition Research Institute, Kannapolis, NC,
4
National Center for Toxicological Research, Jefferson, AR and 5 NCI at NIEHS,
Research Triangle Park, NC .
Inorganic arsenic (iAs), a common drinking water contaminant, is one of the environmental
carcinogens with a suspected epigenetic mode of action. Recent studies
using a mouse transplacental model for iAs carcinogenesis showed that exposures of
pregnant CD1 mice to iAs in drinking water result in an increased incidence of liver
tumors in adult male offsprings. S-adenosylmethionine (SAM) supplies methyl
groups for both the maintenance of normal DNA methylation pattern and the enzymatic
methylation of iAs. Thus, it is possible that the mechanisms underlying the
transplacental iAs carcinogenesis involve changes in the DNA methylation pattern
in the fetal liver due to competition between DNA methyltransferases and iAsmethyltransferase
for SAM. Results of our preliminary studies show that in utero
exposure to iAs significantly changes the genomic DNA methylation pattern in livers
of mouse fetuses and that the most affected genes and gene networks are associated
with one carbon metabolism, inflammation, and cancer. Expression of genes
involved in one-carbon metabolism and DNA methylation is increased in livers of
fetuses exposed to iAs as compared to untreated controls. In addition, in utero exposure
to iAs increases significantly SAM concentration in fetal livers in a manner
that is consistent with a compensatory response to an increased demand for methyl
groups. These results support the epigenetic mechanism for the transplacental iAs
carcinogenesis and provide basis for future studies that will examine the role of dietary
precursors of SAM in modulation of this mechanisms
972 INFLUENCE OF PHOSPHATE ON THE
BIOAVAILABILITY OF ARSENIC FROM SOIL IN
CYNOMOLGUS MONKEYS.
S. M. Roberts 1 , J. W. Munson 1 and Y. W. Lowney 2 . 1 Center for Environmental &
Human Toxicology, University of Florida, Gainesville, FL and 2 Exponent, Boulder, CO.
Relative oral bioavailability (RBA) of arsenic from soil is typically assessed in experiments
in which arsenic (in soil or in aqueous solution) is administered to animal
subjects on an empty stomach. The potential influence of dietary or other soil constituents
on arsenic RBA has not been well studied. Previous studies have suggested
that phosphate can diminish intestinal absorption of arsenic through competition
for intestinal transporters. Conversely, in vitro studies of arsenic bioaccessibility
have shown that phosphate can enhance liberation of arsenic from some soils,
which would be expected to increase RBA. In this study, sodium arsenate (0.3
mg/kg bw) in water, with or without phosphate (250 mg), was administered by
gavage to adult male cynomolgus monkeys. The extent of oral absorption was assessed
by measuring urinary arsenic excretion after the dose. Phosphate cotreatment
with the soluble arsenate dose decreased the percent of the arsenic dose excreted in
urine, suggesting an inhibition of arsenic absorption. The same subjects also received,
on separate occasions, single doses of arsenic-containing soil (1 g soil/kg
bw), with or without phosphate (250 mg). Consistent with bioaccessibility studies,
phosphate cotreatment increased the arsenic RBA in soil from a cattle-dip vat site.
Soil from a smelter site in which bioaccessibility was not increased by phosphate
was included in the study for comparison. These in vivo experiments confirm the
suggestion from bioaccessibility studies that the presence of phosphate can significantly
affect arsenic RBA from soil, but that the effect appears to depend on specific
soil characteristics and arsenic-soil interactions. It is likely that phosphate can influence
arsenic RBA through more than one mechanism.
973 METHYL-SELENIC ACID MODIFIES GENE
EXPRESSION AND RESPONSE TO ARSENIC
EXPOSURE IN HUMAN BLADDER CANCER CELLS.
A. S. Andrew 1 , R. A. Mason 1 , Z. Wei 2 , D. A. Jewell 1 and C. Gabel-Jenson 3 .
1
Dartmouth Medical School, Lebanon, NH, 2 Department of Biostatistics and
Epidemiology, University of Pennsylvania, Philadelphia, PA and 3 Danish University
of Pharmaceutical Sciences, Copenhagen, Denmark.
Human studies indicate that selenium may be an effective chemopreventive agent
for bladder and other cancers. Evidence suggests that methyl-selenic acid, a
metabolite of ingested selenium that can be detected in the urine, is the key intermediate.
The objective of this project was to clarify the biologic pathways that this
metabolite modifies in the bladder. Selenium has also been reported to counter-act
SOT 2010 ANNUAL MEETING 207