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

210 CHAPIN ET AL.
related. No histopathological alterations were observed
for cecal wall morphology. Hemolyzed blood was
observed in the stomachs of three to seven of 10
males/group exposed to 50 and 150 mg/m 3 , but there
were no signs of histopathological alterations in the
gastrointestinal tract. Slight histopathological alterations,
consisting of hyperplasia in stratified squamous and
ciliated epithelium lining and inflammation of submucosal
tissues was observed in the anterior nasal cavities
of all (10/dose/sex) males and females exposed to
Z50 mg/m 3 . Slight-to-moderate hyperplasia of goblet
cells was also observed in the lateral nasal wall. No other
treatment-related histopathological alterations were observed,
including in reproductive organs.
During the 4-week recovery period, body weights
remained lower in males and females of the 50 and
150 mg/m 3 groups At 4 weeks following exposure,
terminal body weights of males and females in the
150 mg/m 3 group were B6% lower than control values.
A decrease in white blood cell count in females from the
10 and 150 mg/m 3 groups was the only hematological
effect observed. The clinical chemistry effects that were
somewhat consistent with effects observed immediately
following treatment were increased alkaline phosphatase
activity in females exposed to 10 and 150 mg/m 3 and
decreased serum glutamic pyruvic activity transaminase
activity in females exposed to 150 mg/m 3 ; the study
authors did not consider the clinical chemistry changes
to be treatment-related. The study authors concluded
that an increase in relative brain weight in males of the
150 mg/m 3 group was related to decreased body weights
in those animals. Enlarged cecal size was observed in 5 of
10 males of the 150 mg/m 3 group, a decreased incidence
compared to the period immediately following treatment.
Nasal histopathology was observed in the 150 mg/
m 3 but was reduced in magnitude and severity compared
to rats observed immediately following exposure.
In rats examined following 12 weeks of recovery, body
weights of males in the 150 mg/m 3 group remained
lower than controls, and terminal body weight was
decreased by B6%. An increase in white blood cell
counts but not differential counts was observed in male
rats of the 10 and 150 mg/m 3 group. The only clinical
chemistry finding consistent with earlier observations
was decreased total protein and globulin in females from
the 150 mg/m 3 group, but the study authors did not
consider the effect to be biologically significant. Organ
weight changes in the 150 mg/m 3 group included
decreased absolute kidney and lung weights in males
and decreased absolute and relative kidney weights in
females. No histopathological alterations were observed
in kidney or lung. No other gross or histopathological
alterations were observed, including cecal enlargement
and nasal histopathology, which were observed at earlier
time periods.
2.2.2 Estrogenicity. The first identification of bisphenol
A as an estrogen has been attributed to Dodds
and Lawson (1936), who reported that 100 mg injected by
an unspecified route twice daily for 3 days resulted in
maintenance of 5 of 5 rats in vaginal estrus for 40 days.
The estrogenicity of bisphenol A has since been
evaluated using several different kinds of assays. In
vitro studies are summarized in Table 52, and in vivo
studies are summarized in Table 53 using comparisons
with 17b-estradiol, ethinyl estradiol, diethylstilbestrol,
and, in one study, estrone. There is considerable
variability in the results of these studies with the
estrogenic potency of bisphenol A ranging over about 8
orders of magnitude, but similar means (Fig. 2).
The most common method of comparing potency is to
test responses over a range of concentrations and to
compare the concentrations producing the half-maximal
(or other fractional) response of the comparator estrogen.
An alternative is to compare the magnitude of the
response at an equimolar concentration of the 2 estrogens.
The difference in these two methods is illustrated
in Figure 3. An example of the difference in potency
estimations according to comparison method is the study
of Vivacqua et al. (2003), in which the fold-increase in
reporter activity for an estrogen-responsive gene was
compared over a range of concentrations for bisphenol A
and for 17b-estradiol. This study’s Figure 3 presents
curves analogous to Figure 3, but also presents a bar
graph comparing response of the reporter at a 10 -7 M
concentration of each estrogen. Based on the halfmaximal
response to 17b-estradiol, bisphenol-A
appeared 1000 times less potent than 17b-estradiol,
but based on the fold-difference in reporter activity
at 10 -7 M, bisphenol A was about half as potent.
Data for other estrogenicity comparisons in this study
and in many other studies are presented only using bar
graphs comparing responses at the same molar concentrations
of the 2 estrogens, thereby overestimating the
estrogenic potency of bisphenol A compared to studies in
which comparisons are based on the half-maximal
response.
Competitive binding assays, which evaluate the concentration
at which bisphenol A displaces labeled 17bestradiol
from ER, are summarized in the top part of
Table 52. The receptor binding of bisphenol A in these
assays varies over 3 orders of magnitude. Bisphenol A
competes for human ER binding at molar concentrations
20–10,000 times that of the native ligand. When bisphenol
A binding to ERa and ERb was compared in the same
study, 3 reports found little difference by receptor
subtype (Kuiper et al., 1998; Paris et al., 2002; Takayanagi
et al., 2006), and 3 studies found binding to ERb to be 4,
10, 47, and 254 times greater than binding to ERa
(Routledge et al., 2000; Matthews et al., 2001; Seidlová-
Wuttke et al., 2004, 2005; Takemura et al., 2005). Yeast
reporter systems, which reflect activation of post-receptor
pathways, show less variability; these studies show
bisphenol A activity to be 10,000–26,000 times less than
that of 17b-estradiol.
Some variability in estimating bisphenol A potency
appears to be due to differences between laboratories.
Andersen et al. (1999a) reported results from 3 laboratories
that evaluated the proliferative response of MCF-7
breast cancer cells to bisphenol A. The laboratories,
which were in the U.S., Spain, and Denmark, were sent
samples of the same stock of bisphenol A, 17b-estradiol,
and MCF-7 cells. Procedures were similar in the labs,
although two different counting methods were used. The
bisphenol A potencies relative to 17b-estradiol were
5 x 10 -7 , 3 x 10 -6 , and 1 x10 -5 . Laboratory variability
may underlie some of the large differences in cell-based
assays for ER activation; in those studies bisphenol A
molar potency compared to 17b-estradiol were reported
to vary by over 7 orders of magnitude (Table 52). Another
explanation for this wide range of reported values is the
Birth Defects Research (Part B) 83:157–395, 2008