The Toxicologist - Society of Toxicology

DNA assay corroborated the DASL data. This work showed that the use of degraded
RNA from FFPE blocks for microarray studies is possible. Therefore, retrospective
analysis without the need for new animal studies could be enabled by using
FFPE samples. Furthermore, in studies with unexpected organ toxicities were no
fresh frozen tissue is available, toxicogenomic evaluations are still possible and can
support mechanistic interpretations.
1591 TRANSCRIPTIONAL DOSE RESPONSE ANALYSIS IN
FEMALE MOUSE AND RAT LUNGS FOLLOWING
REPEATED INHALATION EXPOSURE TO 2-CHLORO-1,
3-BUTADIENE.
M. W. Himmelstein 1 and R. S. Thomas 2 . 1 DuPont Haskell Global Centers, Newark,
DE and 2 The Hamner Institutes for Health Sciences, Research Triangle Park, NC.
Beta-chloroprene (2-chloro-1,3-butadiene), a monomer used in the production of
neoprene elastomers, is of regulatory interest due to the production of mouse lung
tumors in a two-year rodent bioassay. A significant increase in female mouse lung
tumors was observed at 12.8 ppm while a small, but statistically insignificant increase
was observed in female rats at 80 ppm. Gene expression microarray and
histopathological analysis were performed in the lungs of female mice following exposure
at 0.3, 3, 13, and 90 ppm and in female rats following exposure at 5, 30, 90,
and 200 ppm. The exposures were selected to span the rodent bioassay concentrations
and provide approximately equal target tissue doses in the lung based on total
amount metabolized per gram tissue. Exposures were performed for a period of 5
and 15 days. For the mouse, minimal hyperplasia was observed in the terminal
bronchioles after 5- and 15 days of exposure at 90 ppm. No significant histopathological
changes were observed at any exposure concentration in the female rat lung.
Based on traditional analysis of variance, the number of genes with significantly altered
expression in the mouse lung at the 5- and 15-day time points was similar and
increased with dose. In the rat lung, the number of significantly altered genes was
higher at the 5-day time point. Benchmark dose (BMD) methods were used to
model the transcriptional dose-response data and calculate dose estimates at which
different signaling pathways were altered. The BMD values for the selected signaling
pathways were filtered to identify those with a transcriptional dose-response
consistent with the tumor response in the rodent bioassay. A small subset of signaling
pathways were identified and included changes in glutathione metabolism, oxidative
stress, mismatch DNA repair, and amino acid metabolism. The results serve
to identify potential modes-of-action for chloroprene for follow-up study.
1592 GENE EXPRESSION PROFILING OF LXR-MEDIATED
HEPATIC STEATOSIS IN RATS.
J. M. Maher, W. R. Buck, M. J. Liguori, J. Lai-Zhang, T. Sharapova, S. J.
Morgan, E. A. Blomme and Y. Yang. Investigative Toxicology and Pathology, Abbott
Laboratories, Abbott Park, IL.
The Liver-X Receptor (LXR) is a nuclear receptor that is activated by oxysterols,
and LXR mediates key steps in bile acid synthesis. T0901317 is a potent LXR agonist
known to markedly increase liver weights, induce fatty acid synthesis, and
cause significant hepatic steatosis. The purpose of the current study was to evaluate
gene expression changes caused by T0901317 to identify unique genes regulated by
LXR agonists that differentiate this profile from other steatotic compounds or from
changes observed in starvation-induced steatosis. In the current study, Sprague-
Dawley rats were dosed with T0901317 for five days at dosages of 5, 25, and 50
mg/kg/day in PEG400:Tween 80 (80:20 w/w). Livers were collected for both
pathology and toxicogenomics, and serum was collected for clinical chemistry.
Liver triglycerides (TGs) were markedly increased in a dose-dependent manner, yet
serum TGs were significantly decreased after 5 days in an inverse manner, a finding
which is seemingly species or timepoint specific when compared to mice.
T0901317 caused marked induction of pathways related to sterol regulatory element-binding
protein 1-C (SREBP-C) signaling, and these gene changes are generally
related to increases in fatty acid and cholesterol biosynthesis. LXR-induced
steatosis clustered away from other steatotic models due to marked induction of a
few key genes involved in beta-oxidation, including CD36, malic enzyme, SREBP-
C, and long chain fatty acyl-CoA synthetase. Furthermore, Angiopoietin-like 3, a
key gene in determining serum TG levels in rodents, was not upregulated in response
to T0901317 treatment, coinciding with the observed findings. Through
gene profiling, recognition of LXR agonism by microarray allows for an early signal
that may aid in the prediction of steatosis, which can then trigger the further characterization
of experimental compounds that may have LXR-mediated effects on
the liver.
342 SOT 2011 ANNUAL MEETING
1593 CHARACTERIZATION OF THE HEPATIC
TRANSCRIPTOME RESPONSE TO A MIXTURE OF LOW
MOLECULAR WEIGHT POLYBROMINATED
DIPHENYL ETHERS: DISEASE, SIGNATURE,
NETWORK, AND PATHWAY ANALYSIS.
S. S. Auerbach 1 , K. R. Shockley 1 , R. Thomas 2 , N.J.Machesky 4 , M. K.
Vallant 1 , C. D. Hebert 3 , H. C. Cunny 1 and J. K. Dunnick 1 . 1 National Toxicology
Program, National Institute of Environmental Health Sciences, Research Triangle
Park, NC, 2 Environmental Health Sciences, University of California, Berkeley, CA,
3 Southern Research Institute, Birmingham, AL and 4 Battelle Columbus Operations,
Columbus, OH.
Polybrominated diphenyl ethers (PBDEs) are widespread persistent organic pollutants
that produce toxicity in the liver, thyroid and brain. As a part of the ongoing
NTP studies of the PBDEs, liver transcriptome analysis was performed on liver
samples from 22-day old male rats exposed by gavage to a mixture of low molecular
weight PBDEs from gestation day 6 to postnatal day 21. Disease-centric enrichment
analysis showed differential expression of genes associated with hepatic
cholestasis, fibrosis, hepatitis, and hypercholesterolemia. Pertubations of genomic
pathways also predicted that the PBDE mixture will be hepatocarcinogenic by nongenotoxic
mechanisms. Genomic signature analysis indicated the PDBE transcriptome
response is strongly similar to that of phenobarbital, which has been shown to
cause liver and thyroid tumors in rats. Coexpression network analysis suggested that
the transcription factors CAR, PXR, FOXA3, NRF2, and SREBPF1, as well as the
bile salt transporter, NTCP, and the copper transporter, CTR1, play critical roles in
PBDE toxicity. Pathway analysis confirmed the role of these genes and their related
pathways in the global transcriptional response to PBDEs and further highlighted
the role of FXR and LXR signaling. Overall, these data indicate that PBDEs elicit
an integrated transcriptional response via perturbation of nuclear receptor, oxidative
stress and sterol/cholesterol signaling pathways. Disruption of these pathways
has the potential to induce carcinogenic responses in the liver and other organs.
1594 AGE AND SEX DIFFERENCES IN RENAL GENE
EXPRESSION DURING THE RAT LIFE CYCLE.
J. C. Kwekel, V. G. Desai, T. Han, W. S. Branham, C. L. Moland and J. C.
Fuscoe. Systems Toxicology/Center for Functional Genomics, U.S. FDA/National
Center for Toxicological Research, Jefferson, AR.
Age- and sex-related susceptibility to adverse drug reactions is a key concern in understanding
drug safety and disease progression. Age is a predisposing condition for
susceptibility to adverse effects of some drugs. There is also evidence from the study
of hepatic disease and cancer to suggest sexually dimorphic susceptibilities as well.
We hypothesize that the underlying suite of genes expressed at various developmental
and life-cycle stages will impact susceptibility to adverse drug reactions. Thus,
understanding the natural expression patterns of genes throughout the life span of
the rat surrogate model species in both sexes will inform our assessments of adverse
drug reactions. The kidney plays a central role in the pharmacokinetics and excretion
of drugs via key molecular transporters. Untreated, male and female F344 rats
were sacrificed at 2, 5, 6, 8, 15, 21, 78, and 104 weeks of age. Kidney tissues were
collected for histology and gene expression analysis. Whole-genome rat microarrays
(Agilent) were used to query global expression profiles. A 2-way ANOVA (p <
0.0001) along with 1.5 fold change in relative expression was used to identify 4,061
unique genes that were differentially expressed by sex or age. Principal component
analyses (PCA) revealed notable expression profile differences between different age
groups with greatest differences observed between 2 and 6 weeks of age. Adult and
aging animal expression profiles clustered in a large group with 104 week animals
showing slight divergence. PCA loadings analysis prioritized genes having the greatest
influence in sex and age related differences in expression and included metabolism
and transport genes Cyp1a1, Ugt2b3, Abcg5, Abcb11 and Abca8, among others.
K-means cluster analysis identified groups of genes exhibiting similar lifecycle
expression profiles. These results suggest specific groups of kidney genes that may
underlie specific periods of susceptibility to adverse drug reactions.