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

Most in vivo estrogenicity studies examined effects on
uterine weights of intact weanling or ovariectomized
adult rats or mice. The potency of bisphenol A in
increasing uterine weight varied over B4 orders of
magnitude. Uterine weight findings can be affected by
the time period between dosing and measurement. Most,
but not all studies, showed a greater effect on uterine
weight with s.c. than with oral dosing. The greater
activity of s.c. than oral bisphenol A is presumably due to
glucuronidation of the orally administered compound
with consequent loss of estrogenicity (Matthews et al.,
2001). Inter-strain variability in rats has been evaluated
as a source of variability in estrogenicity assays. (see
Section 4.0 for additional discussion) Inter-laboratory
variability has been noted for uterotropic effects in intact
weanling mice exposed to bisphenol A (Tinwell and
Joiner, 2000); one factor that can result in variability is
body weight of the animal. Use of mice with lower body
weights results in lower and less variable control uterine
weights and greater likelihood of bisphenol A effect
(Tinwell and Joiner, 2000; Ashby et al., 2004). In in vivo
studies examining gene expression profiles, some but not
all gene expression changes were consistent between
bisphenol A and reference estrogens (Tinwell and Joiner,
2000; Naciff et al., 2002; Singleton et al., 2004; Terasaka
et al., 2006); ER-independent activity was suggested by
1investigator (Singleton et al., 2004). [Based on one
comprehensive study of the effects of bisphenol A
orally delivered from 60–1000 mg/kg for 3–7 days, the
Expert Panel concludes that the uterotrophic responses
were only found at higher does (Ashby, 2002; Kanno
et al., 2003a) whereas s.c. dosing produced consistent
uterine weight increases at lower doses.]
2.6.4 Androgenic activity. In the majority of in
vitro tests conducted, bisphenol A was not demonstrated
to have androgenic activity (Sohoni and Sumpter, 1998;
Gaido et al., 2000; Kitamura et al., 2005; Xu et al., 2005).
Anti-androgenic activity was demonstrated in systems
using cells transfected with three different androgen
receptor reporting systems (ARE-luc, MMTV-lacZ, and
C3-luc) (Table 56). No consistent effects were observed
on male accessory reproductive organ weights in 3 in
vivo studies in which rats were dosed with bisphenol A
at r600 mg/kg bw/day; the study authors concluded
that bisphenol A does not have anti-androgenic or
androgenic activity (Kim et al., 2002a; Yamasaki et al.,
2003; Nishino et al., 2006).
2.6.5 Genetic toxicity. In in vitro genetic toxicity
studies reviewed by the European Union (2003) and/or
Haighton et al. (2002), evidence of aneugenic potential,
chromosomal aberration, micronuclei formation, and
DNA adducts was observed (Table 57). Because of the
lack of chromosomal effects in in vivo studies (Table 58)
and unknown relevance of DNA adduct formation,
which only occurred at high-doses, both groups concluded
that bisphenol A is not likely to have genotoxic
activity in vivo.
2.6.6 Carcinogenicity. Carcinogenic potential of
bisphenol A was evaluated in rats and mice by the NTP
(1982) and Huff (2001). NTP concluded that under the
conditions of the study, there was no convincing
evidence that bisphenol A was carcinogenic in F344 rats
or B6C3F1 mice. However, NTP stated that there was
suggestive evidence of increased cancer in the hematopoietic
system based on marginally significant increases
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in leukemia in male rats, non-statistically significant
increases in leukemia in female rats, and a marginally
significant increase in combined incidence of lymphoma
and leukemia in male mice. A statistically significant
increase in testicular interstitial cell tumors in aging F344
rats was also considered suggestive evidence of carcinogenesis.
The effect was not considered conclusive
evidence because of the high incidence of the testicular
neoplasm in aging F344 rats (88% incidence in historical
controls). Both the European Union (2003) and Haighton
et al. (2002) stated that the evidence does not suggest
carcinogenic activity of bisphenol A in rats or mice.
Conclusions by the European Union (2003) and Haighton
et al. (2002) were based on factors such as lack of
statistical significance for leukemia, mammary gland
fibroadenoma, and Leydig cell tumors, lack of activity at
noncytotoxic concentrations in both in vitro genetic
toxicity tests and an in vivo mouse micronucleus test,
and unlikely formation of reactive intermediates at doses
that do not saturate detoxification pathways.
2.6.7 Potentially sensitive subpopulations. Studies
in humans and laboratory animals demonstrated
developmental changes in UDPGT gene expression or
enzyme activity that could potentially affect the concentration
of free bisphenol A reaching target organs because
of a differential capacity for bisphenol A glucuronidation.
In humans, activities for some UDPGT isozymes were
reported to be very low at birth but increased with age
(Coughtrie et al., 1988). No transcripts for UDPGT were
detected in samples from 20-week-old human fetuses and
activity for some UDPGT enzymes was lower in children
than adults (Strassburg et al., 2002). Compared to adults,
human fetal uridine 5 0 -diphosphoglucuronic acid concentrations
were 5-fold lower in liver and 1.5-fold lower in
kidney (Cappiello et al., 2000). It is not clear if any of the
isozymes examined are involved in bisphenol A glucuronidation
by humans. Human findings were consistent
with rodent studies that demonstrated no or limited
glucuronidation capacity by fetuses (Miyakoda et al.,
2000; Matsumoto et al., 2002; Domoradzki et al., 2003)
and lower glucuronidation capacity in immature than
adult rats (Matsumoto et al., 2002; European-Union, 2003;
Matsumoto et al., 2004).
Some studies suggested possible gender-related differences
in sulfation capacity in humans (Pritchett et al.,
2002; Kim et al., 2003b) and laboratory animals (Pritchett
et al., 2002). One study in humans demonstrated no
differences in urinary bisphenol A concentrations in
individuals carrying a sulfotransferase genotype associated
with greater activity (Yang et al., 2003).
3.0 DEVELOPMENTAL TOXICITY DATA
The Panel attended to multiple design and analysis
characteristics in judging the acceptability of individual
studies. It was our consensus that for a study to be
acceptable for this review process, several conditions had
to be met. First, effects related to litter of origin needed to
be accounted for in design and statistical procedures.
Second, animals needed to be dosed via the dam or
directly under individual housing conditions. Concern
that multiple exposures within a cage to different
animals could cause cross-animal contamination across
cage-mates led to the determination that this design was
not acceptable. Third, a minimum of 6 animals per