Monograph on the Potential Human Reproductive and ... - OEHHA

involved in cyclic AMP breakdown, was selected for
further study. Neonatal bisphenol A exposure resulted in
hypomethylation of the phosphodiesterase type 4 variant
gene and increased expression of that gene at 90 and 200
days of age, with or without 17b-estradiol/testosterone
exposure in adulthood. Similar responses in phosphodiesterase
type 4 variant gene methylation and expression
were observed with exposure to the low and high 17
estradiol benzoate doses. The study authors concluded
that developmental exposures of rats to bisphenol A
increased susceptibility to precancerous prostate lesions
resulting from prostate epigenomic alteration.
Strengths/Weaknesses: This is a carefully performed
study by a group with significant expertise in this area of
work. The study has many strengths, from the use of a
relatively low dose level of bisphenol A to the search to
identify molecular mechanisms, possibly including sitespecific
promoter methylation, underlying the observations
made. Weaknesses include the use of a single dose
level with subcutaneous dosing. It could be suggested
that carrying the study further in terms of animal age
might have produced more dramatic phenotypes and
clarified the relevance of PIN resulting from BPA
exposure to prostate cancer (potentially enhancing cancer
incidence) in this model. Failure to do this could be
considered a weakness of the work.
Utility (Adequacy) for CERHR Evaluation Process:
This study is adequate and of limited utility for the
evaluation process due to use of subcutaneous route of
administration.
3.2.4.2 Neurobehavioral endpoints: Ishido et al.
(2004), supported by the National Institute for Environmental
Studies and the Ministry of Economy, Trade, and
Industry, examined the effects of postnatal intracisternal
bisphenol A exposure on behavior of rats. Dams in this
study were fed standard laboratory chow (MF Diet;
Oriental Yeast Corp.). [No information was provided
about caging or bedding materials.] At 5 days of age, 5–
7 male Wistar rat pups/group were injected intracisternally
with a bisphenol A dose [purity not indicated] of 0
(ethanol/olive oil vehicle), 0.00002, 0.0002, 0.002, or
0.020 mg. Pups were weaned at 3 weeks of age.
Spontaneous motor activity was measured over a 12–
24-hr period at 4–5 weeks of age. Rats were killed at 4
and 8 weeks of age, and brains were removed. RNA was
isolated from midbrain and striatum for DNA microarray
analysis. Expression of the gene for dopamine
transporter in midbrain was studied by RT-PCR. Tyrosine
hydroxylase expression in brain was measured at 8
weeks of age using an immunostaining method. Statistical
analyses included ANOVA and Student t-test.
In 4–5-week-old rats from the 0.020 mg bisphenol A
group, motor activity was significantly increased and
was 1.6 times higher than in control rats during the
nocturnal period. In a dose response experiment, it was
noted that hyperactivity was increased significantly at
doses Z0.0002 mg. Microarray analysis revealed that
bisphenol A [at an unspecified dose] downregulated
expression of dopamine D4 receptor gene 2-fold at 4
weeks of age and dopamine transporter gene 2.8-fold at 8
weeks of age. Numerous other gene expression changes
were observed but not discussed in detail by study
authors. Analysis by RT-PCR confirmed that expression
of the dopamine transporter gene was downregulated 3fold
in the midbrain of 8-week-old rats treated with
Birth Defects Research (Part B) 83:157–395, 2008
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bisphenol A in the neonatal period. In rats from the
0.020 mg bisphenol A group, tyrosine hydroxylase
immunoreactivity was reduced in the substantia nigra
at 8 weeks of age. The study authors interpreted the
decrease in tyrosine hydroxylase immunoreactivity as
degeneration of dopaminergic neurons. They concluded
that bisphenol A affected the central dopaminergic
system, resulting in hyperactivity that most likely
occurred as a result of decreased tyrosine hydroxylase
activity in midbrain.
Strengths/Weaknesses: A significant weakness is the
inability to correlate the internal exposure to bisphenol A
provided by the intracisternal route with that seen by the
oral route. Strengths of this study include the use of a
range of concentrations of bisphenol A. The correlation of
changes in behavior patterns induced by bisphenol A
with expression of specific dopamine receptor sets is also
a strength. A significant weakness is the inability to
correlate the doses of bisphenol A provided by this
dosing mechanism with those seen by more common s.c.
or oral routes, as well as uncertainty about the disposition
of the bisphenol A that is injected into the
cerebrospinal fluid.
Utility (Adequacy) for CERHR Evaluation Process:
This study is inadequate for the evaluation process due
to uncertainties around the intracisternal route of
administration.
Masuo et al. (2004a), of the Japanese National Institute
of Advanced Industrial Science and Technology and
National Institute for Environmental Studies, investigated
the effects in rats of an acute neonatal exposure to
6-hydroxydopamine, bisphenol A, nonylphenol, p-octylphenol,
or diethylhexyl phthalate on spontaneous motor
activity, as well as catecholamine levels, dopaminergic
neuron integrity by immunohistochemistry, and gene
expression profiles. In the 6-hydroxydopamine group, 5day-old
male Wistar pups weighing about 10 g were first
pretreated with 25 mg/kg desipramine i.p. on PND 5 in
order to protect noradrenergic neurons from the effects
of 6-hydroxydopamine. These pups were then injected
intracisternally 30 min later with 6-hydroxydopamine
[not discussed here]. Other groups of pups were treated
intracisternally with 0 (olive oil vehicle) or 87 nmol
bisphenol A [purity not provided], nonylphenol, poctylphenol,
or diethylhexyl phthalate in olive oil (n 5 6
or 7/group). In additional experiments, intracisternal
bisphenol A treatments were used over a 0.087–87 nmol
[19.8 ng to 19.8 lg] dose range. Following treatment,
pups were randomly assigned to lactating dams and
weaned at 3 weeks of age. Animals were housed in
acrylic cages at 221C under 12-hr light/12-hr dark
conditions and given free access to water and chow from
Oriental Yeast Co.
Spontaneous motor activity was assessed at 4–5 weeks
of age using an automated activity-monitoring system
over a 12-hr light/12-hr dark cycle, apparently for a
single 24-hr period. [Total number of cycles not
indicated.] Brain sections from 8–10-week-old rats were
snap frozen in liquid nitrogen. The striatum and whole
mid-brains were used for cDNA microarray analyses.
The frontal cortex, striatum, limbic regions including
nucleus accumbens, septum, and olfactory tubercles
were used to measure catecholamine levels by HPLC.
Immunohistochemistry from whole brain sections was
used to evaluate dopamine neuron integrity using