The Toxicologist - Society of Toxicology

XOMA 052. XOMA 052 or the vehicle was administered to pregnant Sprague
Dawley rats by subcutaneous injection once weekly on Gestation Day (GD) 6 and
13 at dose levels of 0, 3, 30, and 90 mg/kg. Dams were euthanized on GD 20.
Observations and evaluations included clinical signs, gestation body weight and
body weight change, food consumption, XOMA 052 serum concentration determination
(maternal and fetal), immunogenicity (maternal only), uterine and ovarian
examinations, fetal examinations (body weight, sex ratio, external, visceral and
skeletal examinations, and total malformations) and maternal macroscopic pathology.
All animals survived to scheduled necropsy on GD 20. Results showed no toxicologically
significant findings in caesarean section parameters or fetal morphological
observations. Serum collected for XOMA 052 concentration analysis on GD
20 from all treated dams and the five tested litters per dose group had similar
XOMA 052 concentration levels, demonstrating adequate levels of fetal exposure.
Based on these results, the no-observed-adverse-effect level (NOAEL) for maternal
and developmental toxicity, including teratogenicity, was considered to be 90
mg/kg, the highest dose level tested. In conclusion, XOMA 052 was well tolerated
and exposure did not result in fetal developmental or teratogenic effects when administered
to pregnant rats during the period of major organogenesis.
1618 DEVELOPMENTAL HYPOTHYROIDISM DISRUPTS
PERFORMANCE OF A SIGNAL DETECTION TASK IN
RATS.
M. Hasegawa 1, 2 and H. Wada 1 . 1 Psychology, Hokkaido University, Sapporo, Japan
and 2 Japan Society for the Promotion of Science, Tokyo, Japan. Sponsor: K. Crofton.
Transient hypothyroidism during development of the central nervous system
(CNS) impairs cognitive function in rats; however, specific effects on attention are
unknown. The effects of transient developmental hypothyroidism on the attention
of rats were assessed by utilizing a signal detection task. Pregnant Wistar rats were
treated with the anti-thyroid drug, methimazole [2-mercapto-1-methyl imidazole],
at concentrations of 0% or 0.02% (w/v) via the drinking water from gestational day
15 to postnatal day (PND) 21 to induce perinatal hypothyroidism. The male offspring
were tested on a signal detection task from PND 84. Operant chambers with
two response levers and a signal light were used. The signal detection task consisted
of signal and non-signal trials. In a signal trial, a brief signal light (500ms, 250ms or
50ms duration) was presented after the inter-trial interval (ITI) elapsed, and subsequently,
a limited hold (LH) period for a lever response was initiated. In a non-signal
trial, no signal light was presented before the LH period. Rats were required to
press the left lever in a non-signal trial and the right lever in a signal trial. Correct
responses for signal and non-signal trials were considered as hits and correct rejections
(CR), respectively. Hit (%) and CR (%) were calculated to analyze the performance.
The total number of lever pressing for left and right levers during the ITI
were also monitored. The hit (%) for developmentally hypothyroid rats was significantly
decreased from control rats when the durations of the signal light were
250ms and 50ms. The CR (%) and number of left-lever pressing during the ITI
were significantly increased for the hypothyroid rats. The decreased hit (%) of the
hypothyroid rats during shorter signal durations indicates that perinatal hypothyroidism
can impair attention. However, the higher CR (%) and number of leftlever
pressing in the hypothyroid rats also suggest the possibility that the decreased
hit (%) is due to differences in the response strategies between groups.
1619 PROBING THE TOXCAST CHEMICAL LIBRARY FOR
PREDICTIVE SIGNATURES OF DEVELOPMENTAL
TOXICITY.
N. S. Sipes 1 , N. C. Kleinstreuer 1 , R. S. Judson 1 , D. M. Reif 1 , A. V. Singh 3 , K.
J. Chandler 1, 2 , M. R. Rountree 1 , D. J. Dix 1 , R. J. Kavlock 1 and T. B. Knudsen 1 .
1 U.S. EPA/ORD/NCCT, Research Triangle Park, NC, 2 U.S. EPA/ORD/NHEERL,
Research Triangle Park, NC and 3 Lockheed Martin, Research Triangle Park, NC.
EPA’s ToxCast project is profiling the in vitro bioactivity of chemical compounds
to assess pathway-level and cell-based signatures that correlate with observed in vivo
toxicity. We hypothesize that cell signaling pathways are primary targets for diverse
environmental chemicals that disrupt embryogenesis via combinatorial effects on
cellular functions. To test this hypothesis, we built statistical associations based on
in vitro high-throughput screening (HTS) data from ToxCast and in vivo developmental
toxicity data from ToxRefDB. Univariate associations from 2x2 contingency
tables were used to filter HTS assays based on statistical correlation with distinct
in vivo endpoints. Machine learning algorithms then built predictive models
using linear discriminant analysis with multivariate feature selection trained by univariate
associations. Initial results gave 389 univariate associations with distinctly
348 SOT 2011 ANNUAL MEETING
different patterns for rat (308 associations) and rabbit (81 associations).
Aggregating the species endpoints into a generic model revealed strong correlations
between in vitro pathways and in vivo effects for urogenital defects and cleft palate.
As an example, a cleft palate signature emerged that included forkhead box (FOX)
transcription factor pathways and chromatin remodeling through histone deacetylase
(HDAC) signaling. Interestingly, a model built from developmental zebrafish
data implied the same target pathway signature for eye reduction defects.
Perturbations of these signaling pathways are known to be causally involved in zebrafish
craniofacial defects and mammalian (including human) cleft palate. This indicates
potential key signaling pathways involved in cleft palate induction may be
targets for chemical teratogens, and zebrafish as a model system may reveal similar
pathway disruption. This abstract does not necessarily reflect US EPA policy.
1620 IN OVO EXPOSURE TO PERFLUOROOCTANOIC ACID
DECREASES HATCHING MUSCLE GLYCOGEN IN
CHICKEN EMBRYOS.
J. DeWitt 1 , I. Bryan 2 and J. Loftis 3 . 1 Pharmacology and Toxicology, East Carolina
University, Greenville, NC, 2 Biology and Chemistry, East Carolina University,
Greenville, NC and 3 Summer Ventures in Science and Mathematics, East Carolina
University, Greenville, NC.
As a result of its use in the manufacture of myriad products, including firefighting
foams, stain and water resistant coatings, and fluids for electronics manufacturing,
perfluorooctanoic acid (PFOA) is part of the environmental milieu to which organisms
are exposed. Studies with laboratory models indicate that PFOA induces metabolic,
liver, brain, reproductive, developmental, and immunotoxicities. Of special
concern are effects on developing organisms. As PFOA has been reported to affect
hatchability in chickens, we evaluated its ability to affect glycogen stores in hatching
muscles of developmentally-exposed chicken embryos; glycogen in hatching
muscle is necessary for successful hatching. Fertile eggs were air cell injected prior to
incubation with 0, 0.5, 1, or 2 mg PFOA/kg egg weight in safflower oil vehicle.
After 19 days of incubation, hatching muscles and livers were removed from embryos
and immediately frozen. Glycogen was measured in prepared homogenates of
each tissue. Liver glycogen levels did not differ by dose. Hatching muscle glycogen
levels differed from controls by 43%, 36%, and 30% (0.5, 1, and 2 mg/kg doses,
respectively). β-oxidation of fatty acids, which PFOA increases, is most active in the
later part of incubation and glucose is derived from yolk fat. Glucose is generated
from protein rather than yolk near the end of incubation and is stored in liver and
muscles as glycogen (DeOliveira et al., 2008). It is our hypothesis that increased β -
oxidation by PFOA during development forces the embryo to utilize protein as energy
earlier in development and therefore decreases later glycogen stores, which can
affect hatchability and survival. Our data indicate that PFOA decreases hatching
muscle glycogen in 19-day-old embryos; additional studies to evaluate glycogen in
hatching muscle of hatchlings and at different time points during development are
planned.
1621 ARSENIC DELAYS THE MUSCLE DIFFERENTIATION
AND REPRESSES MYOGENIN EXPRESSION BY
RECRUITING EZH2 AND SUPPRESSING MEF2C IN
MOUSE MUSCLE CELLS.
G. Hong and L. Bain. Biological Sciences, Clemson University, Clemson, SC.
Arsenic is a toxicant commonly found in water systems around the world. Evidence
from epidemiological studies indicates that chronic arsenic exposure can result in
cancer, effects on development, and neuromuscular deficits. However, the molecular
mechanism of arsenic’s toxicity remains largely unclear. Our previous study indicated
that 20nM sodium arsenite exposure to C2C12 mouse myocyte cells results
in delayed differentiation, caused by a reduction myogenin expression. Repressed
myogenin expression was likely due to abnormal DNA methylation in myogenin
promoter, which includes two hypermethylated CpGs (-236 and -126) and one hypomethylated
CpG (-207). EZH2, which directly silences gene expression via recruiting
DNA methyltransferases, is induced by 2-fold in the arsenic treated cells.
Additionally, ChIP analysis demonstrated that arsenic exposed cells have a 4-fold
increase in the recruitment of EZH2 to the myogenin promoter (-40 to + 42),
where contains a MyoD response element and the transcription start site, suggesting
that EZH2 may play a regulatory role in myogenin expression.
To further understand the arsenic mediated regulatory mechanisms in muscle differentiation,
we are identifying other transcription factors differentially expressed
after arsenic exposure. For example, the RNA expression of Mef2c, a transcription
factor that is expressed during muscle differentiation, was reduced by 4-fold, while