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

isphenol A glucuronide (41% of the dose). Bisphenol A
represented 0.3% of the dose in bile. The study authors
noted that as with oral or i.v. exposure to a smaller dose,
feces was the main route of elimination for bisphenol A
and bile was the main elimination route for bisphenol A
glucuronide.
A study by Yokota et al. (1999) examined the hepatic
isoform of uridine diphosphate glucuronosyltransferase
(UDPGT) involved in the metabolism of bisphenol A and
distribution of the enzyme in organs of Wistar rats. Using
yeast cells genetically engineered to express single rat
UDPGT enzymes, it was determined that UGT2B1 was
the only isoform capable of glucuronidating bisphenol A.
Microsomal UDPGT activity toward bisphenol A was
demonstrated in liver, kidney, and testis, but activity was
minimal in lung and brain. [Minimal activity was also
observed for intestine]. Northern blot analyses revealed
high expression of UGTB1 only in liver. It was demonstrated
that 65% of glucuronidation activity was absorbed
by binding with anti-UGTB1, indicating that
additional isoforms are likely involved in glucuronidation
of bisphenol A.
The intestine was determined to play a role in the
metabolism of bisphenol A in rats. Nine-week-old male
Sprague–Dawley rats were orally administered 0.1 mL of
a solution containing 50 g/L bisphenol A [5 mg total or
B17 mg/kg bw assuming a body weight of B0.3 kg
(USEPA, 1988)] (Sakamoto et al., 2002). Rats were killed
at multiple time intervals between 15 min and 12 hr
following exposure. The small intestine was removed
and separated into upper and lower portions. Intestinal
contents were removed from each section. Bisphenol A
and metabolite concentrations were measured by HPLC.
Activities and expression of b-glucuronidase were
determined. A large amount of bisphenol A glucuronide
was detected in the upper and lower portions of the
small intestine, and a large amount of free bisphenol A
was detected in the cecum. Less bisphenol A was
detected in colon and feces. The observations lead the
study authors to conclude that free bisphenol A
generated in the cecum as a result of deconjugation
was reabsorbed in the colon. The presence of large
amounts of bisphenol A glucuronide in the small
intestine at 12 hr following exposure suggested that
bisphenol A was reabsorbed in the colon and re-excreted
as the glucuronide. As determined in an assay using pnitrophenol-b-d-glucuronide
as a substrate, B70% of
total b-glucuronidase activity was present in the cecum
and 30% in the colon. Western blot analysis revealed a
large amount of bacterial b-glucuronidase protein in
cecum and colon contents.
Glucuronidation and absorption of bisphenol A in rat
intestine were studied by Inoue et al. (2003a). Intestines
were obtained from 8-week-old male Sprague–Dawley
rats, and the small intestine was divided into 4 sections.
Small intestine and colon were everted and exposed to 40
mL of a solution containing bisphenol A at 10, 50, or
100 mM [2.3, 11, or 23 mg/L, resulting in delivery of 91,
456, or 913 lg bisphenol A to the everted intestine].
Every 20 min during a 60-min time period, reaction
products were collected from serosal and mucosal sides
and analyzed by HPLC. Optimal glucuronidation was
observed at 50 mM [11 mg/L]. At 60 min following
exposure to 50 mM bisphenol A, B37% of bisphenol A
was absorbed by the small intestine and B83% was
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BISPHENOL A
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glucuronidated. Approximately 74.7% of the glucuronide
was excreted on the mucosal side and B25.3% transported
to the serosal side of small intestine. Slightly
greater absorption of bisphenol A in the colon (48.6%)
compared to the proximal jejunum (37.5%) was observed
at 60 min following exposure to the 50 mM solution.
Transport of both bisphenol A and bisphenol A glucuronide
to the serosal side of intestine increased distally
and was greatest in the colon. Minimal mucosal excretion
was observed in the colon.
Inoue et al. (2004) compared glucuronidation of
bisphenol A in pregnant, non-pregnant, and male rats.
Livers of 4 male and non-pregnant Sprague–Dawley
rats/group were perfused via the portal vein for 1 hr
with solutions containing bisphenol A at 10 or 50 mM [2.3
or 11 mg/L]. The total amount of bisphenol A infused into
livers was 1.5 or 7.5 mmol [0.34 or 1.7 mg]. On GD20or
21, livers of 4 pregnant Sprague–Dawley rats were
perfused for 1 hr with 10 mM [2.3 mg/L] bisphenol A. At
the start of perfusion, excreted bile and perfusate in the
vein were collected every 5 min for 1 hr. Samples were
analyzed by HPLC. Statistical analyses were conducted
by Student t-test and ANOVA. Bisphenol A glucuronidation
in the liver was 59% in male rats and 84% in nonpregnant
female rats perfused with the 10 mM solution.
The glucuronide was excreted primarily through bile in
both males and females, but a significantly higher
amount was excreted through bile in non-pregnant
females than in males. The total amount of glucuronide
excreted into bile and vein was B1.4-fold higher in
females than males following perfusion with the 10 mM
[2.3 mg/L] solution. At the 50 mM [11 mg/L] concentration,
bisphenol A glucuronidated within liver was 66% in
males and 91% in females. In males the glucuronide was
excreted mainly in bile, and in females, a higher amount
of glucuronide was excreted in the vein. In livers of
pregnant rats perfused with the 10 mM [2.3 mg/L] solution,
69% of bisphenol A was glucuronidated in the liver.
Percentages of glucuronide excretion were 54.5% through
bile and 45.5% through the vein in pregnant rats. In a
comparison of pregnant rats and non-pregnant rats
perfused with 10 mM [2.3 mg/L] bisphenol A, biliary
excretion in pregnant rats was half that observed in
non-pregnant rats, and venous excretion in pregnant rats
was 3-fold higher than in non-pregnant rats. To determine
the pathway of bisphenol A glucuronide excretion,
livers of 4 male Eisai hyperbilirubinemic rats, a strain
deficient in multidrug resistance-associated protein,
were perfused with 50 mM [11 mg/L] bisphenol A. During
and after perfusion, nearly all of the bisphenol A was
excreted into the vein, thus indicating that multidrug
resistance-associated protein mediates biliary excretion
of bisphenol A glucuronide. The study authors concluded
that bisphenol A is highly glucuronidated and
excreted into bile using a multidrug resistance-associated
protein-dependent mechanism, and that venous excretion
increases and biliary excretion decreases during
pregnancy.
Miyakoda et al. (2000) examined the production of
bisphenol A glucuronide in fetal and adult rats. Bisphenol
A was orally administered at 10 mg/kg bw to
pregnant Wistar rats on GD 19 and to 10-week-old adult
male Wistar rats. [The number of animals exposed was
not reported. In some legends for study figures, it was
stated that the data were from 4 experiments,