From the Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, D-69120 Heidelberg, Germany
Received for publication, June 8, 2000, and in revised form, December 12, 2000
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ABSTRACT |
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Bilirubin, the end product of heme catabolism, is
taken up from the blood circulation into the liver. This work
identifies a high-affinity transport protein mediating the uptake of
bilirubin and its conjugates into human hepatocytes. Human embryonic
kidney cells (HEK293) permanently expressing the recombinant organic anion-transporting polypeptide 2 (human OATP2, also known as LST-1 or
OATP-C; symbol SLC21A6) showed uptake of
[3H]monoglucuronosyl bilirubin,
[3H]bisglucuronosyl bilirubin, and
[3H]sulfobromophthalein with
Km values of 0.10, 0.28, and 0.14 µM,
respectively. High-affinity uptake of unconjugated
[3H]bilirubin by OATP2 occurred in the presence of
albumin and was not mediated by another basolateral hepatic uptake
transporter, human OATP8 (symbol SLC21A8). OATP2 and OATP8 differed by
their capacity to extract substrates from albumin before transport. In
comparison to the high-affinity transport by OATP2, OATP8 transported [3H]sulfobromophthalein and
[3H]monoglucuronosyl bilirubin with lower affinity, with
Km values of 3.3 and 0.5 µM,
respectively. The organic anion indocyanine green potently inhibited
transport mediated by OATP2, with a Ki value of 112 nM, but did not inhibit transport mediated by OATP8. Human
OATP2 may play a key role in the prevention of hyperbilirubinemia by
facilitating the selective entry of unconjugated bilirubin and its
glucuronate conjugates into human hepatocytes.
Bilirubin, the main bile pigment in most mammals, is the end
product of heme catabolism (1). In the blood circulation, bilirubin is
bound to serum albumin, which prevents its potential toxicity thought
to be caused by the free ligand (2). Despite high-affinity binding to
albumin, bilirubin is rapidly and selectively taken up into the liver
(3, 4), biotransformed upon conjugation with glucuronate (5), and
secreted into bile across the canalicular membrane of hepatocytes by an
ATP-dependent conjugate export pump termed multidrug
resistance protein 2 (transporter symbol ABCC2) (6, 7). In addition to
a reduction of UDP-glucuronosyl transferase activity (8), impaired
bilirubin uptake from the blood circulation into liver has been
suggested to contribute to a subgroup of patients with Gilbert's
syndrome (9), which is characterized by a mild unconjugated
hyperbilirubinemia. Uptake of bilirubin by hepatocytes was considered
to be a process mediated by specific membrane proteins, although
passive diffusion has also been proposed as a possible mechanism (1, 3,
10). Because of its instability and low solubility in aqueous
solution, hepatic uptake of bilirubin was studied predominantly by use
of structurally related anionic substances like sulfobromophthalein
(BSP)1 and indocyanine green
(ICG) (3, 9, 11, 12). A transport protein for BSP with a
Michaelis-Menten constant (Km) of 1.5 µM has been cloned from rat liver (13) and designated as
organic anion-transporting polypeptide 1 (rat OATP1). Rat OATP1 belongs
to a family of transport proteins (OATP family, symbol SLC21A)
mediating the transport of organic anions including bile salts, steroid
conjugates, thyroid hormones, prostaglandins, and BSP (14). For human
OATP1 (SLC21A3), which is expressed at high levels in brain and kidney
and at a low level in human liver, kinetic studies revealed only a
moderate affinity for BSP with a Km value of 20 µM (15). In a search for additional OATP isoforms in
human liver, we and other groups have recently cloned a new member of
this transporter family, human OATP2 (also known as LST1 or OATP-C,
gene symbol SLC21A6) (16-18). Most recently, we cloned an additional
human liver OATP isoform termed OATP8 (gene symbol SLC21A8), which
shares 80% identical amino acids with human OATP2 (19). Antibodies
raised against both transport proteins localized them to the
basolateral membrane of human hepatocytes (16, 19). Northern blot
analyses demonstrated an apparently exclusive hepatic expression of
both transporters (16, 19). The availability of cell lines stably
expressing human OATP2 and OATP8 enabled us to answer the question of
whether these two major human hepatic OATP family members are capable
of transporting bilirubin and its conjugates from blood across the
basolateral membrane into hepatocytes.
Cell Culture and Cell Lines--
HEK293 cells were cultured in
minimum essential medium (Sigma) supplemented with 10% fetal bovine
serum, 100 units/ml penicillin, and 100 µg/ml streptomycin at
37 °C, 95% humidity, and 5% CO2 as described recently
(16, 19). HEK-OATP2 cells (16) and HEK-OATP8 cells (19) permanently
expressed high levels of human recombinant OATP2 and OATP8,
respectively. The GenBankTM/European Molecular Biology
Laboratory accession numbers for the sequences of OATP2 and OATP8 are
AJ132573 and AJ251506, respectively.
Biosynthesis of
[3H]Bilirubin--
[3H]Bilirubin was
obtained biosynthetically in rats in a procedure similar to the one
described by Crawford et al. (20). Two Harlan Sprague-Dawley
rats were given an intravenous or intraportal injection of 500 µCi of [3,5-3H]delta-aminolevulinic acid (25.9 GBq/mmol; NEN Life Sciences, Boston, MA) at a dose of 83 and 42 MBq/kg
body weight, respectively. [3H]Bilirubin was isolated
from bile by hydrolysis of its glucuronides and extraction with
chloroform (20). The purity of the [3H]bilirubin was
confirmed by HPLC, and the specific radioactivity was 120,000-140,000
dpm/nmol (2.0-2.3 GBq/mmol) for the material obtained from both rats.
In all experiments, [3H]bilirubin was protected from
exposure to light.
Synthesis of [3H]Monoglucuronosyl Bilirubin and
[3H]Bisglucuronosyl Bilirubin--
Bilirubin
glucuronides were prepared using recombinant UDP-glucuronosyl
transferase 1A1 and UDP[1-3H]glucuronic acid (0.56 TBq/mmol; Biotrend, Köln, Germany) together with unlabeled
bilirubin as described previously (6, 7) and purified using
radio-HPLC.
Uptake Studies--
For uptake assays, cells were seeded in
6-well plates (coated with 0.1 mg/ml poly-D-lysine) at a
density of 1.5-2 × 106 cells/well and cultured with
10 mM sodium butyrate for 24 h. Before the uptake
experiments, cells were washed with uptake buffer (142 mM
NaCl, 5 mM KCl, 1 mM
KH2PO4, 1.2 mM MgSO4,
1.5 mM CaCl2, 5 mM glucose, and
12.5 mM HEPES, pH 7.3). The transport assay was started by
the addition of 1 ml of uptake buffer containing 3H-labeled
substrate (18.5-37 MBq/ml) to the cells. 3H-labeled
substrates were obtained from NEN Life Sciences.
[3H]BSP (0.5 TBq/mmol) was obtained by custom synthesis
(Hartmann Analytic, Köln, Germany); its purity (>98%) was
confirmed by reverse-phase HPLC analysis on a C18 Hypersil
column (5-µm particles; Shandon, Runcorn, United Kingdom) using two
different systems. The isocratic elution was performed with 45%
methanol/55% water containing 50 mM
NaH2PO4 and 5 mM
Na2SO4 at pH 2.8. The linear gradient elution
was performed from 100% buffer A (45% methanol/55% water containing
2 mM tetrabutylammonium hydroxide at pH 6.0) to 100%
buffer B (90% methanol/10% water containing 2 mM
tetrabutylammonium hydroxide at pH 6.0). The specific radioactivity of
[3H]BSP did not change during repeated HPLC analyses,
indicating that 3H exchange was below detectability.
[3H]BSP strictly co-chromatographed with unlabeled BSP
during HPLC. Moreover, the unlabeled BSP and the 3H-labeled
BSP were analyzed by nanoelectrospray mass spectrometry as described by
Lehmann and Kaspersen (21). The isotopic pattern of molecular ions of
unlabeled BSP and [3H]BSP was very similar, and
quantitative evaluation indicated the following relative amounts:
unlabeled BSP, 63.1%; singly labeled [3H]BSP 27.4%; and
doubly labeled [3H]BSP, 9.5%. These data correspond to a
specific radioactivity of 0.5 TBq/mmol.
For inhibition studies, inhibitors were included in the uptake buffer.
After incubation at 37 °C, transport was stopped at different time
points by the addition of 1 ml of cold uptake buffer. Cells were
subsequently washed three times with uptake buffer and lysed with 1 ml
of 0.2% SDS in water. Aliquots (250 µl) of the lysate were counted
for radioactivity. Protein content was determined by the Lowry method
using 100 µl of lysate.
Uptake Studies with [3H]Bilirubin--
Due to high
background binding of [3H]bilirubin to the
poly-D-lysine-coated plastic dishes, uptake of
[3H]bilirubin into transfected cells was measured in cell
suspension. Cells were cultured with 10 mM butyrate for
24 h as described previously (16). For uptake assays, cells were
detached from culture flasks by knocking, washed twice with uptake
buffer, and resuspended in uptake buffer at a density of 3 × 106 cells/ml. [3H]Bilirubin was diluted with
human serum albumin (HSA; Sigma; fatty acid-free) in uptake buffer
(75,000-100,000 dpm/ml). Unlabeled bilirubin was added to give the
desired final concentrations. Uptake was started by mixing 1 ml of cell
suspension with 1 ml of bilirubin/albumin solution to give a final
radioactivity of 37,500-50,000 dpm/ml and stopped at different time
points by centrifugation of the mixture at 13,000 rpm for 10 s.
Cell pellets were washed twice with 1 ml of uptake buffer containing
HSA and lysed in 2 ml of 0.2% SDS in water. Aliquots (300 µl) of the
lysate were counted for radioactivity. To determine the nonspecific
binding of [3H]bilirubin, cells were incubated with
[3H]bilirubin in the presence of HSA for 1 min at
4 °C. Cell-associated radioactivity measured under this condition
was used as a blank and subtracted from all other values. No
differences between this method and the method using adherent cells
were observed for other substrates like BSP.
Immunoblot Analysis--
Preparation of crude membrane fractions
from transfected cells and immunoblot analysis were performed as
described previously (16, 19). The polyclonal antibody ESL (16) was
used to detect recombinant human OATP2.
Sulfobromophthalein, Monoglucuronosyl Bilirubin, and
Bisglucuronosyl Bilirubin Are High-affinity Substrates for Human
OATP2--
BSP, a widely used anionic model compound for studies on
uptake into the liver, is a high-affinity substrate for OATP2 with a
Km value of 140 nM (Fig.
1). In comparison with OATP8, OATP2
showed a 24-fold higher affinity for BSP (Table
I). In addition, monoglucuronosyl
bilirubin and bisglucuronosyl bilirubin were identified as
high-affinity substrates for OATP2 with nanomolar Km
values. Monoglucuronosyl bilirubin was also a good substrate for human
OATP8 (Table I). Kinetic properties of additional substrates for OATP2
and OATP8 are summarized in Table I. Despite the remarkable difference
in their affinities for BSP, human OATP2 and OATP8 showed similar
affinities for 17 OATP2, but not OATP8, Transports Substrates in the Presence of
Albumin--
An important aspect with regard to BSP uptake mediated by
both transporters is the differential influence of HSA. As shown in
Fig. 2A, HSA, in a 20-fold
molar excess, did not significantly affect OATP2-mediated BSP uptake
but abolished OATP8-mediated BSP uptake. One-third of the respective
Km value (50 nM for OATP2 and 1 µM for OATP8) was chosen as the BSP concentration in
these experiments. A similar influence of HSA was observed when BSP
uptake was measured for both transporters at a constant BSP
concentration (1 µM) with varying HSA concentrations
(Fig. 2B). HSA caused only a minor decrease of
OATP2-mediated BSP uptake. Uptake assays using 1 µM
E217 Indocyanine Green Inhibits Transport Mediated by OATP2 but not
Transport Mediated by OATP8--
We tested a number of organic anions
for their ability to inhibit uptake by human OATP2 and OATP8. ICG did
not affect OATP8-mediated E217
Unlike ICG, the drugs pravastatin, rifamycin SV, and rifampicin
inhibited both OATP2- and OATP8-mediated uptake of
[3H]E217 Unconjugated Bilirubin Is Transported by OATP2 in the Presence of
Albumin--
The fact that BSP, monoglucuronosyl bilirubin, and
bisglucuronosyl bilirubin are high-affinity substrates for human OATP2 and the fact that ICG inhibits OATP2-mediated uptake competitively at
nanomolar concentrations suggested that OATP2 might be the long-sought
uptake transporter for unconjugated bilirubin in the basolateral
hepatocyte membrane. We therefore measured [3H]bilirubin
uptake by OATP2-transfected HEK293 cells (HEK-OATP2) at a
concentration of 1 µM in the presence of 2 µM HSA. The calculated free bilirubin concentration under
this condition, using the dissociation constant for HSA and bilirubin
(12), is about 25 nM. As shown in Fig.
4A,
[3H]bilirubin was taken up by HEK-OATP2 cells
time-dependently at 37 °C. The uptake rate into
HEK-OATP2 cells (8.5 pmol·min
Bilirubin, which was examined as a complex with HSA, inhibited the
uptake of E217 We conclude that uptake of bilirubin into human hepatocytes, the
first step of its detoxification, is mediated by OATP2, a major
transport protein localized to the basolateral membrane of hepatocytes,
but not by the isoform OATP8 localized to the same membrane domain. Our
conclusion is based on the following experimental data: (a)
the structurally and chemically related lipophilic anionic compounds
BSP, monoglucuronosyl bilirubin, and bisglucuronosyl bilirubin were
high-affinity substrates for OATP2, with nanomolar
Km values, whereas OATP8 transported BSP and
monoglucuronosyl bilirubin with markedly lower affinity (Fig. 1 and
Table I); (b) OATP2, but not OATP8, was able to extract substrates from albumin (Fig. 2) to which bilirubin binds with high
affinity; (c) ICG inhibited OATP2 at nanomolar
concentrations but exerted no inhibitory effect on OATP8 at
concentrations up to 10 µM (Fig. 3); and (d)
[3H]bilirubin uptake by OATP2 was directly demonstrated
by uptake studies with OATP2-expressing HEK transfectants (Fig. 4).
Together with previous data, we propose the following scheme for the
detoxification and elimination pathway of bilirubin in human liver
(Fig. 5): bilirubin (B) bound
to albumin is taken up across the basolateral membrane by OATP2 and
conjugated in the hepatocyte by the UDP-glucuronosyl transferase 1A
(UGT1A1), resulting in monoglucuronosyl bilirubin and
bisglucuronosyl bilirubin. Bilirubin glucuronides are finally excreted
into bile by the apical conjugate export pump multidrug resistance
protein 2 localized to the hepatocyte canalicular (apical) membrane (6,
7).
INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
EXPERIMENTAL PROCEDURES
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
RESULTS
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
-glucuronosyl estradiol (E217
G).
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Fig. 1.
BSP uptake mediated by human OATP2.
A, [3H]BSP transport into cells was measured
at a concentration of 1 µM using HEK293 cells transfected
with human OATP2 (HEK-OATP2) or with vector alone
(HEK-Co). B, concentration dependence of
[3H]BSP uptake. Uptake of [3H]BSP into
HEK-OATP2 cells ( ) and HEK-Co cells (
) was measured at
concentrations between 10 and 210 nM. The net uptake rates
(
) were calculated by subtracting values obtained with HEK-Co cells
from those obtained with HEK-OATP2 cells. Data are the means ± S.D. from two triplicate experiments.
Kinetic constants for substrate transport mediated by OATP2 and OATP8
G as substrate showed that 5 µM HSA
did not change the uptake rate with OATP2. The OATP2-mediated uptake
was not chloride-dependent in the presence or absence of HSA because replacement of chloride in uptake buffer by gluconate had
no effect on the rate of uptake. It is well known that many organic
anions bind to HSA in the blood circulation, and a particular role of
HSA in the hepatic uptake of organic anions has been proposed (22). It
is therefore conceivable that a hepatic transport protein like OATP2
has the ability to extract substrates from HSA. For OATP8, the
interaction with HSA is different (Fig. 2). We have identified four
lipophilic organic anions (monoglucuronosyl bilirubin, BSP,
E217
G, and dehydroepiandrosterone 3-sulfate) as
3H-labeled substrates for OATP8. These experiments,
however, were performed without HSA in the buffer (Table I). The fact
that OATP8 is not capable of extracting substrates from HSA raises the
question of the physiological function of OATP8 in the basolateral hepatocyte membrane. From the data obtained thus far, it is feasible that OATP8 functions predominantly under circumstances where the binding capacity of albumin for lipophilic organic anions is
exceeded.
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Fig. 2.
Effect of HSA on BSP uptake mediated by OATP2
and OATP8. A, uptake of [3H]BSP was
measured at 50 nM for OATP2 and 1 µM for
OATP8 in the presence of 1 µM (OATP2) or 20 µM (OATP8) HSA (BSP:HSA = 1: 20 in both cases). No
significant effect of albumin on [3H]BSP uptake was
observed for OATP2, whereas OATP8-mediated [3H]BSP uptake
was completely abolished by the addition of albumin. B,
uptake of 1 µM [3H]BSP measured with OATP2
and OATP8 in the presence of increasing concentrations of HSA ranging
from 0.2 to 5 µM. HSA had a much greater effect on
the OATP8-mediated [3H]BSP uptake than on the
OATP2-mediated uptake (p < 0.01). Data are the
means ± S.D. (n = 6).
G transport at
concentrations up to 10 µM (Fig.
3A) but inhibited OATP2-mediated uptake in a competitive manner with a
Ki value of 112 nM. Although BSP and ICG
were thought to be taken up into hepatocytes by the same mechanism (3),
patients with apparently normal hepatic BSP uptake but delayed ICG
clearance have been reported (11). Our studies raise the possibility
that such patients may have a deficiency in OATP2, leading to delayed ICG clearance, but normal OATP8, which may function in BSP uptake under
this condition.
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Fig. 3.
Inhibition of OATP2- and OATP8-mediated
transport. Uptake of 17 -glucuronosyl
[3H]estradiol
(E217
G; 2 µM)
by HEK293 cells transfected with OATP2 or OATP8
was measured in the presence of different inhibitors and in the absence
of HSA. A, uptake of [3H]E217
G
mediated by OATP2 was potently inhibited by ICG, whereas ICG exerted no
significant inhibition on OATP8-mediated uptake. B, both
OATP2 and OATP8 were inhibited by pravastatin (25 µM),
rifamycin SV (50 µM), and rifampicin (75 µM). Data are the means ± S.D. from two triplicate
experiments.
G (Fig. 3B). The
HMG-CoA reductase inhibitor pravastatin was a competitive inhibitor of
OATP2-mediated transport of E217
G with an inhibition
constant of 53 µM. This is in line with a recent study
showing that pravastatin is a substrate for human OATP2 with a
Km value of about 30 µM (17).
1·mg
protein
1) differed from that into
vector-transfected HEK293 cells (1.5 pmol·min
1·mg
protein
1) by a factor of 5.7 (p < 0.01). When the uptake was determined at 4 °C,
no significant difference in uptake rates was detected between
OATP2-expressing cells and control cells. Uptake of bilirubin mediated
by recombinant human OATP2 was concentration-dependent as
shown in Fig. 4B. In these experiments, the HSA
concentration was kept constant at 20 µM so that the
bilirubin:HSA ratio did not exceed 0.5. Because of the uncertainty of
calculated free bilirubin concentrations (12), the
Km value for free unconjugated bilirubin could only
be estimated and was about 160 nM. For comparison, we
investigated whether OATP8 would also transport unconjugated bilirubin.
At the same [3H]bilirubin and HSA concentrations and
under the same conditions used for OATP2 (Fig. 4), no significant
uptake of [3H]bilirubin was detected with HEK293 cells
expressing human OATP8 (data not shown).
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Fig. 4.
Bilirubin as a substrate for human
OATP2. A, uptake of [3H]bilirubin was
measured at 1 µM bilirubin in the presence of 2 µM HSA. Cell-associated radioactivity after incubation of
cells with [3H]bilirubin for 1 min at 4 °C was used as
a blank and subtracted from all other values. The uptake rate into
HEK-OATP2 cells was 8.5 pmol·min 1·mg
protein
1 (n = 10) and
differed significantly from the uptake rate into vector-transfected
HEK293 cells (1.5 pmol·min
1·mg
protein
1; n = 5).
B, concentration dependence of bilirubin uptake. Uptake of
[3H]bilirubin at different concentrations was measured at
a constant HSA concentration of 20 µM. The estimated free
bilirubin concentration ranged from 5 to 25 nM.
Measurements of [3H]bilirubin uptake at each
concentration were performed at 1 min (blank) and 10 min; the rate of
uptake was calculated from the difference between these two
measurements (n = 5). C, inhibition of
[3H]bilirubin uptake by BSP. Uptake of 10 µM [3H]bilirubin was measured in the
presence of 20 µM HSA (n = 5), and the
uptake was calculated as described in B; for inhibition
studies, 5 µM BSP was included into the uptake buffer.
All experiments were reproduced at least twice. Data are the means ± S.D. Asterisks indicate a significant difference compared
with controls (p < 0.01). Inset in
A, immunoblot with the polyclonal antibody ESL (16) of membranes (20 µg of protein) membranes (20 µg of protein)
from HEK-OATP2 cells (left lane) or HEK-Co cells
(right lane). The arrow points to the fully
glycosylated OATP2 at 90 kDa.
G and BSP by human OATP2, with 50%
inhibition at 5 µM with E217
G as substrate
and at 20 µM with BSP as substrate. Uptake of
[3H]bilirubin into HEK-OATP2 cells was strongly inhibited
by BSP (Fig. 4C), demonstrating mutual inhibition of BSP and
bilirubin uptake.
DISCUSSION
TOP
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
REFERENCES
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Fig. 5.
Bilirubin uptake and conjugate export by
human hepatocytes. Bilirubin (B) is taken up across the
basolateral membrane by human OATP2 (SLC21A6; Fig. 4A) and
conjugated with glucuronate (GA) by UDP-glucuronosyl
transferase 1A1 (UGT1A1), resulting in monoglucuronosyl
bilirubin (BGA) and bisglucuronosyl bilirubin
(B(GA)2) (5). The excretion of BGA and
B(GA)2 is mediated by the apical ATP-dependent
conjugate export pump, multidrug resistance protein 2 (symbol ABCC2)
(6, 7).
Our results here establish a carrier-mediated uptake of
bilirubin into hepatocytes. However, we do not exclude
additional bilirubin uptake through passive diffusion. The
differentiation between carrier-mediated and diffusional bilirubin
uptake into the liver will be supported by the identification of
mutations in the OATP2 (SLC21A6) gene leading to the loss or
functional impairment of OATP2 in the basolateral membrane of
hepatocytes. Moreover, in view of the fact that current knowledge of
the human OATP family is not complete, additional transport proteins
may further contribute to the selective uptake of bilirubin from the blood circulation into liver.
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ACKNOWLEDGEMENTS |
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We thank W. D. Lehmann (Deutsches Krebsforschungszentrum, Spectroscopy, Heidelberg, Germany) for analysis of the labeled and unlabeled BSP by nanoelectrospray mass spectrometry, J. M. Crawford (University of Florida, Department of Pathology, Gainesville, FL) and A. F. McDonagh (University of California, Division of Gastroenterology, San Francisco, CA) for advice on the preparation of [3H]bilirubin, K. Bode and M. Donner (Deutsches Krebsforschungszentrum, Division of Tumor Biochemistry, Heidelberg, Germany) for help during the biosynthesis of [3H]bilirubin, and G. Jedlitschky (Deutsches Krebsforschungszentrum, Division of Tumor Biochemistry, Heidelberg, Germany) for critical reading of the manuscript.
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FOOTNOTES |
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* The work was supported in part by Deutsche Forschungsgemeinschaft through SFB601 and the Fonds der Chemischen Industrie.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
To whom correspondence should be addressed: Division of Tumor
Biochemistry, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld
280, D-69120 Heidelberg, Germany. Tel.: 49-6221-422400; Fax: 49-6221-422402; E-mail: y.cui@dkfz-heidelberg.de.
Published, JBC Papers in Press, December 27, 2000, DOI 10.1074/jbc.M004968200
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ABBREVIATIONS |
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The abbreviations used are:
BSP, sulfobromophthalein;
E217G, 17
-glucuronosyl
estradiol;
HSA, human serum albumin;
ICG, indocyanine green;
OATP, organic anion-transporting polypeptide;
HPLC, high pressure liquid
chromatography.
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REFERENCES |
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1. | Chowdhury, J. R., Chowdhury, N. R., Wolkoff, A. W., and Arias, I. M. (1994) in The Liver: Biology and Pathobiology (Anas, I. M. , et al., eds), 3rd Ed. , pp. 471-504, Raven Press, New York |
2. | Brodersen, R., and Stern, L. (1990) Acta Paediatr. Scand. 79, 12-19[Medline] [Order article via Infotrieve] |
3. | Scharschmidt, B. F., Waggoner, J. G., and Berk, P. D. (1975) J. Clin. Invest. 56, 1280-1292[Medline] [Order article via Infotrieve] |
4. |
Arias, I. M.,
Johnson, L.,
and Wolfson, S.
(1961)
Am. J. Physiol.
200,
1091-1094 |
5. | Senafi, S. B., Clarke, D. J., and Burchell, B. (1994) Biochem. J. 303, 233-240[Medline] [Order article via Infotrieve] |
6. | Kamisako, T., Leier, I., Cui, Y., König, J., Buchholz, U., Hummel-Eisenbeiss, J., and Keppler, D. (1999) Hepatology 30, 485-490[CrossRef][Medline] [Order article via Infotrieve] |
7. | Jedlitschky, G., Leier, I., Buchholz, U., Hummel-Eisenbeiss, J., Burchell, B., and Keppler, D. (1997) Biochem. J. 327, 305-310[Medline] [Order article via Infotrieve] |
8. | Black, M., and Billing, B. H. (1969) N. Engl. J. Med. 280, 1266-1271[Medline] [Order article via Infotrieve] |
9. | Martin, J. F., Vierling, J. M., Wolkoff, A. W., Scharschmidt, B. F., Vergalla, J., Waggoner, J. G., and Berk, P. D. (1976) Gastroenterology 70, 385-391[Medline] [Order article via Infotrieve] |
10. | Mediavilla, M. G., Pascolo, L., Rodriguez, J. V., Guibert, E. E., Ostrow, J. D., and Tiribelli, C. (1999) FEBS Lett. 463, 143-145[CrossRef][Medline] [Order article via Infotrieve] |
11. | Okuda, K., Ohkubo, H., Musha, H., Kotoda, K., Abe, H., and Tanikawa, K. (1976) Gut 17, 588-594[Abstract] |
12. | Pascolo, L., Del Vecchio, S., Koehler, R. K., Bayon, J. E., Webster, C. C., Mukerjee, P., Ostrow, J. D., and Tiribelli, C. (1996) Biochem. J. 316, 999-1004[Medline] [Order article via Infotrieve] |
13. | Jacquemin, E., Hagenbuch, B., Stieger, B., Wolkoff, A. W., and Meier, P. J. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 133-137[Abstract] |
14. | Meier, P. J., Eckhardt, U., Schroeder, A., Hagenbuch, B., and Stieger, B. (1997) Hepatology 26, 1667-1677[Medline] [Order article via Infotrieve] |
15. | Kullak-Ublick, G. A., Hagenbuch, B., Stieger, B., Schteingart, C. D., Hofmann, A. F., Wolkoff, A. W., and Meier, P. J. (1995) Gastroenterology 109, 1274-1282[Medline] [Order article via Infotrieve] |
16. | König, J., Cui, Y., Nies, A. T., and Keppler, D. (2000) Am. J. Physiol. 278, G156-G164 |
17. |
Hsiang, B.,
Zhu, Y.,
Wang, Z.,
Wu, Y.,
Sasseville, V.,
Yang, W. P.,
and Kirchgessner, T. G.
(1999)
J. Biol. Chem.
274,
37161-37168 |
18. |
Abe, T.,
Kakyo, M.,
Tokui, T.,
Nakagomi, R.,
Nishio, T.,
Nakai, D.,
Nomura, H.,
Unno, M.,
Suzuki, M.,
Naitoh, T.,
Matsuno, S.,
and Yawo, H.
(1999)
J. Biol. Chem.
274,
17159-17163 |
19. |
König, J.,
Cui, Y.,
Nies, A. T.,
and Keppler, D.
(2000)
J. Biol. Chem.
275,
23161-23168 |
20. | Crawford, J. M., Ransil, B. J., Potter, C. S., Westmoreland, S. V., and Gollan, J. L. (1987) J. Clin. Invest. 79, 1172-1180[Medline] [Order article via Infotrieve] |
21. | Lehmann, W. D., and Kaspersen, F. M. (1984) J. Label. Comp. Radiopharm. 21, 455-469 |
22. | Weisiger, R. A. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 1563-1567[Abstract] |