The Toxicologist - Society of Toxicology

egg yolk collected from turtles inhabiting a pond impacted by pollutants from the
Massachusetts Military Reservation (MMR) Superfund site (Cape Cod, MA).
Reproductive abnormalities have been seen in turtles from this site such as altered
responses to 17 β-estradiol and gonadotropin signaling, reduced testicular weight,
lower epididymal sperm counts, and increased germ cell apoptosis. Exposure to
these pesticides in laboratory raised turtles resulted in increased mortality and incidence
of deformations. We have also used the zebrafish embryo model to assess the
effects of each pesticide, alone and in mixture, and to predict effects in the turtle
model. Dieldrin has increased toxicity in the zebrafish model, relative to p,p’-DDE,
and microarray analysis of gene expression demonstrated that dieldrin has a much
greater effect than p,p’-DDE. A small proportion of genes were found to be induced
additively by the pesticides in the mixture, such as Cytochrome (Cyp) P450
24a1like and v-fos oncoprotein. Expression of (Cyp) P450 1a1, a marker of aryl hydrocarbon
signaling, was slightly induced following exposure. Cyp 1a1 expression
was not found to be altered additively by treatment with these pesticides. We conclude
that dieldrin and p,p’DDE may act additively in mixture and changes in gene
expression may be correlated with reproductive deficits seen in turtles collected
from the MMR Superfund site.
2093 JOINT TOXICITY OF PERMETHRIN AND ATRAZINE
TO ZEBRAFISH (DANIO RERIO).
P. Wages, A. Trimble and M. Posner. Biology/Toxicology, Ashland University,
Ashland, OH. Sponsor: P. Wages.
Determining the effects of individual pesticides to non-target organisms in the environment
remains an important aspect of toxicological research. However, the
characterization of a single pesticide is typically unrealistic in terms of environmental
exposure in aquatic systems. In both agricultural and urban landscapes farmers,
homeowners, and commercial pesticide applicators are often attempting to control
multiple pests through the joint application of herbicides and insecticides.
Frequently, atrazine (an herbicide) and permethrin (an insecticide) are applied
jointly since each is effective at controlling different pests. This study attempts to
elucidate the toxic effect of atrazine and permethrin as a mixture to non-target
aquatic species by first using binary mixtures and then examining possible physiological
effects using mixtures of specified concentrations. For the first objective, 96hour
static water-only binary mixture toxicity tests were conducted using zebrafish
embryos (Danio rerio) as the test organism. Analysis of the predicative models concentration
addition (CA) and independent action (IA) revealed that the EC50 to be
lower in the CA model, while the IA model provided better predictions of overall
mixture toxicity. The second objective’s conditions were identical to the previous
experiment, but instead of binary mixtures five known concentrations of permethrin
(6, 10, 14, 19, and 25 ppb) at three different atrazine conditions (0, 3, and 40
ppb) were conducted. Total body length was assessed after 96-hours revealing that
increased concentrations of permethrin resulted in reduced growth with a decrease
of 16% total body length by the mixture of 25 ppb permethrin and 3 ppb atrazine.
However, a trend of opposition to this growth inhibition occurred with the presence
of atrazine. Together, the data suggest that permethrin has the potential to
cause both acute and chronic toxic effects to non-target fish species while atrazine
could possibly resist permethrin’s toxic effect slightly, which could be valuable information
for urban and agricultural pesticide applicators.
2094 2, 4-DICHLOROPHENOXYACETIC ACID (2, 4-D):
EVALUATION OF ENDOCRINE MODULATING
POTENTIAL.
B. Neal 1 , M. S. Marty 2 , K. Coady 2 and J. C. Lamb 1 . 1 Center for Toxicology and
Mechanistic Biology, Exponent, Alexandria, VA and 2 Toxicology & Environmental
Research and Consulting, Dow Chemical Company, Midland, MI.
We have performed a comprehensive weight-of-the-evidence review of both published
and unpublished studies of 2,4-D. 2,4-D has a robust mammalian data base,
including developmental, sub-chronic and chronic toxicity studies, as well as an F1extended
one generation reproductive toxicity study assessing potential endocrine
toxicity, developmental neurotoxicity and immunotoxicity. These data show 2,4-D
has a low potential for endocrine modulation (androgenic, anti-androgenic, estrogenic,
anti-estrogenic or thyroid active) unless the threshold of renal clearance is exceeded,
at doses not relevant to human exposure. In vitro mechanistic and screening
assays also support a low likelihood of endocrine activity. The data base for
endocrine evaluation of 2,4-D in non-mammalian species is limited; this has recently
been supplemented by screening studies in Xenopus laevis tadpoles and fathead
minnows; no endocrine-specific effects were observed. In mammals, doses of
2,4-D well above saturation of renal clearance are associated with thyroid findings.
These effects are related to displacement of circulating thyroid hormone from
transthyretin binding protein, thus enhancing metabolism and excretion of thyroid
hormone. A detailed evaluation of thyroid function across life stages in rats, showed
only adaptive changes in dams exposed to 2,4-D at a dose exceeding the renal clearance
threshold; there were no adverse effects on offspring. Humans have higher levels
of a high-affinity thyroid binding protein, i.e., thyroxine binding globulin, compared
to the rat, which likely makes humans less sensitive to displacement of
thyroid hormone by 2,4-D. The progression and rate of frog metamorphosis, which
depends on thyroid function, was examined in 2,4-D-exposed tadpoles, and no
treatment-related effects were observed up to the limit concentration. Thus, based
on toxicity data in multiple species, there is low potential for 2,4-D to alter endocrine
function at environmentally relevant concentrations.
2095 LATE FETAL RESORPTIONS IN RATS INDUCED BY
EPOXICONAZOLE OCCUR IN THE PRESENCE OF
SIGNIFICANT MATERNAL TOXICITY AND CAN BE
ANTAGONIZED BY ESTRADIOL CO-TREATMENT.
S. Stinchcombe 1 , S. Schneider 2 , I. Fegert 1 , V. Strauss 2 , S. Gröters 2 , M. C. Rey
Moreno 2 and B. van Ravenzwaay 2 . 1 Regulatory Toxicology Pesticides, BASF SE,
Ludwigshafen, Germany and 2 Experimental Toxicology and Ecology, BASF SE,
Ludwigshafen, Germany. Sponsor: R. Parod.
In a recently published non-GLP study with different azoles, an increase in late fetal
resorptions was reported following treatment of rat dams with epoxiconazole (50
mg/kg bw/day) from gestation day (GD) 7-21 (Taxvig et al. 2008). Mechanistic investigations
in pregnant Wistar rats with epoxiconazole (CAS No. 133855-98-8)
treated by oral gavage from GD 7-18 or GD 7-21 have now revealed that late resorptions
at this dose level occurred in the presence of significant maternal toxicity
(e.g. reduced corrected body weight gain, signs of anemia). Beside changes in these
standard parameters, the increase in late fetal resorptions was associated with a drastically
reduced estradiol concentration in maternal serum. By co-administration of
dams with estradiol cyclopentylpropionate (0.5 or 1 μg/rat/day by s.c. injection),
the increase of late fetal resorptions could be reversed to background control levels.
2096 MICROARRAY ANALYSIS OF GENE EXPRESSION
CHANGES IN HUMAN HEPATOCYTES AFTER
CHLORPYRIFOS EXPOSURE.
A. D. Wallace 1 , R. Shah 2 , K. Choi 1 , H. Joo 1 and E. Hodgson 1 . 1 Environmental
and Molecular Toxicology, North Carolina State University, Raleigh, NC and 2 Sciome
LLC, Research Triangle Park, NC .
The organophophorothioate insecticide chlorpyrifos (CPS) is a registered pesticide
that is widely used in agriculture on crops such as corn, tree nuts, fruit trees, and
soybeans. CPS is bioactivated to the toxic metabolite chlorpyrifos-oxon (CPO) by
cytochromes P450 (CYPs), which acts as an insecticide by inhibiting acetylcholinesterase
(AChE) activity. Inhibition of AchE results in accumulation of the
neurotransmitter acetylcholine in neural junctions resulting in cholinergic toxicity.
Human epidemiological studies have led to concerns that human diseases are linked
to occupational CPS exposure and in vivo research suggests developmental delays
resulting from CPS exposure. Human metabolism of CPS by liver CYPs results in
the formation of CPO by a desulfuration reaction that can release a free sulfur that
can act to inhibit CYP enzymes, or alternatively, CPS can be metabolized to the
non-toxic metabolite 3,5,6-trichloro-2-pyridinol (TCP). Our recent studies have
found wide variation in human liver metabolism of CPS and the levels of production
of CPO and TCP. To further investigate individual differences in human responses
due to CPS exposure, human hepatocytes from multiple donors were
treated with CPS and samples were collected at time points of 12 and 24 hours.
RNA was prepared and microarray analysis was done using Affymetrix GeneChip
Human Genome Arrays to identify genes commonly regulated in multiple individuals,
but also to identify unique subsets of genes regulated by different individuals.
A number of genes were differentially expressed in response to CPS treatment in
multiple individuals, including detoxication enzymes such as CYP2B6, 3A4, and
1A1. Differential expression identified by microarray analysis was verified by quantitative
real time PCR. Our findings suggest that exposure to CPS leads to gene expression
changes that are largely common across individuals, but also indicate
unique attributes.
2097 HUMAN HEPATIC CYTOCHROME P450-SPECIFIC
METABOLISM OF CHLORPYRIFOS, PARATHION,
METHYL PARATHION, AND DIAZINON.
Y. Tian, C. A. Ellison, R. J. Foxenberg, B. P. McGarrigle, J. B. Knaak and J. R.
Olson. Pharmacology and Toxicology, University at Buffalo, Buffalo, NY.
Organophosphorous pesticides (OPs) remain a potential concern to human health
because of their continuing worldwide use. OPs are metabolized by cytochrome
P450s (CYPs) via a dearylation reaction which results in detoxification of the OP or
SOT 2011 ANNUAL MEETING 449