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Introduction:
Transporters
are transmembrane carrier proteins that transport compounds across the
biological membranes. Additionally, they construct a defensive barrier to
toxicants by bringing their polarized excretion from the body.
Organic
Anion Transporting polypeptide 1B1 (OATP1B1) is a product of gene SLCO1B1 and
it is specifically expressed on the basolateral (sinusoidal) membrane of
human hepatocytes. Due to its liver-specific expression and its capacity for
transporting a large number of structurally different compounds, it has been
suggested that OATP1B1 plays an important role in hepatic drug uptake and
subsequently elimination. Thus,
inhibition of OATP1B1 can alter the pharmacokinetics of OATP1B1 substrate
drugs causing clinically relevant drug-drug interactions.
In
this study 12 co-medicants Pravastatin (PV), Paracetamol (PC), Metformin
(MT), Warfarin (WR), Enalapril (EN), Salbutamol (SB), Budesonide (BD),
Erythromycin (ER), Cimetiden (CM), Furosemide (FD), Ibuprofen (IB),
Probenecid (PB) and Methotrexate (MX) were examined as inhibitors of
OATP1B1 transporter in vitro. Among
the 12 co-medicants investigated, 7 drugs exhibited inhibition of OATP1B1
activity and then there inhibition potential determined and their clinical
interactions were predicted.
Methods:
HEK293-OATP1B1
and HEK293-MOCK cell cultures:
The
cells are grown on cell culture flasks at 37C and they sub-cultured
depending on their density. The cells were cultured in 12-well plates and
prepared to the uptake assays1.
OATP1B1-
mediated uptake assays:
OATP1B1‑mediated
transport was determined by measuring uptake of [3H] estradiol
17β-glucuronide as a substrate into plated HEK293-OATP1B1 cells
(approximately 0.45 million cells/well using a 12-well plate) versus HEK293-MOCK cells, at approximately
37C1.
Spot
inhibition experiment:
To
determine the inhibition of OATP1B1-mediated transport the uptake of the
probe substrate [3H] estradiol 17β-glucuronide (1 µM) by HEK293-OATP1B1 and
HEK293-MOCK cells was determined in the absence or presence the co-medicants
(100 µM) or rifamycin SV (500 µM) was studied.
Determination
of inhibition potential IC50 of co-medicants:
Uptake
of the probe substrate [3H] estradiol 17β-glucuronide by HEK293-OATP1B1 cells
was determined in the absence or the presence of a range of 6 concentrations
of co-medicants in order to determine apparent IC50 values for the inhibition
of OATP1B1-mediated transport. The IC50 were determined by curve-fitting
using XLfit 5.1
Result
and Discussion:
Screening
of co-medicants for OATP1B1 inhibition:
OATP1B1-mediated
uptake of [3H] estradiol 17β-glucuronide (1 µM) in HEK293-OATP1B1 cells and
HEK293-MOCK cells was studied in the presence and absence of co-medicants
(100 µM) and is shown in Figure 1. The passive transport of [3H] estradiol
17β-glucuronide in HEK293-MOCK cells was unchanged in the presence of
co-medicants but active transport due to OATP1B1 was inhibited by various
co-medicants to different levels.
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