Celulas

REVIEW
Drug Transporters in the Lung—Do They Play a Role in the
Biopharmaceutics of Inhaled Drugs?
CYNTHIA BOSQUILLON
Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD,
United Kingdom
Received 8 July 2009; accepted 25 September 2009
Published online 30 November 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.21995
ABSTRACT: The role of transporters in drug absorption, distribution and elimination processes
as well as in drug–drug interactions is increasingly being recognised. Although the lungs
express high levels of both efflux and uptake drug transporters, little is known of the implications for the biopharmaceutics of inhaled drugs. The current knowledge of the expression,
localisation and functionality of drug transporters in the pulmonary tissue and the few studies
that have looked at their impact on pulmonary drug absorption is extensively reviewed. The
emphasis is on transporters most likely to affect the disposition of inhaled drugs: (1) the ATPbinding cassette (ABC) superfamily which includes the efflux pumps P-glycoprotein (P-gp),
multidrug resistance associated proteins (MRPs), breast cancer resistance protein (BCRP) and
(2) the solute-linked carrier (SLC and SLCO) superfamily to which belong the organic cation
transporter (OCT) family, the peptide transporter (PEPT) family, the organic anion transporter
(OAT) family and the organic anion transporting polypeptide (OATP) family. Whenever available, expression and localisation in the intact human tissue are compared with those in animal
lungs and respiratory epithelial cell models in vitro. The influence of lung diseases or exogenous
agents on transporter expression is also mentioned. ß 2009 Wiley-Liss, Inc. and the American
Pharmacists Association J Pharm Sci 99:2240–2255, 2010

Keywords: drug inhalation; pulmonary delivery; multidrug resistance transporters; peptide
transporters; organic cation transporters; organic anion transporters; Calu-3 cells; isolated
perfused lungs; cell culture; permeability

INTRODUCTION
The implication of membrane transport proteins in
the pharmacokinetic, pharmacodynamic (PKPD) and
safety profiles of a large range of drugs is now well
established, although probably not yet fully appreciated.1,2 Due to their critical role in the successful
development of drug candidates,1 the study of drug
transporters is currently the topic of intense research.
The focus is essentially on transporters in the
intestine, liver, kidney, brain and their relevance to
drug disposition in those organs. Comparatively, the
influence of transporters on the disposition of inhaled
drugs has hardly been investigated, although access
Additional Supporting Information may be found in the online
version of this article.
Correspondence to: Cynthia Bosquillon (Telephone: 44-1158466078; Fax: 44-115-9515122;
E-mail: cynthia.bosquillon@nottingham.ac.uk)
Journal of Pharmaceutical Sciences, Vol. 99, 2240–2255 (2010)
ß 2009 Wiley-Liss, Inc. and the American Pharmacists Association

2240

to drug target sites in the lung tissue might partly
depend on their activity.
Although less than 40 drugs are currently administered by the pulmonary route, drug absorption,
distribution and elimination processes in the lung
remain overall poorly understood. Hence, the PKPD
profile of inhaled drugs is suboptimal in most cases.
Many transporters expressed in the intestine, liver,
kidney or brain are also present in the lung (Tab. 1;
Fig 1) and evidence indicates drugs commonly
administered as aerosols in the treatment of respiratory diseases, for example glucocorticoids, and
cationic b2-agonists, might interact with those
transporters (Tab. 2). An evaluation of the impact
of active transport systems on drug absorption from
the lungs would help in the interpretation and
optimisation of PKPD parameters after drug inhalation. This task is, nevertheless, complicated by the
complexity of the organ and the lack of validated
models to investigate drug transport mechanisms in
the lung.

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 99, NO. 5, MAY 2010

DRUG TRANSPORTERS IN THE LUNG

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Table 1. Summary of Drug Transporter Expression in Human Lungs
Protein
Name

Gene
Symbol

ABC transporters
P-gp
ABCB1

Expression in
Human Lungs
Moderate

MRP1

ABCC1

High

MRP2

ABCC2

No or low

MRP3
MRP4
MRP5
MRP6
MRP7
MRP8
MRP9
BCRP

ABCC3
ABCC4
ABCC5
ABCC6
ABCC10
ABCC11
ABCC12
ABCG2

Low or high
Moderate
High
Moderate
Moderate to high
Low or high
Low or high
Low or high

SLC transporters
OCT1
SLC22A1

Contradictory data

OCT2

SLC22A2

Contradictory data

OCT3

SLC22A3

Contradictory
data in airways

OCTN1

SLC22A4

Yes

OCTN2

SLC22A5

Yes

PEPT1
PEPT2

SLC15A1
SLC15A2

Low
High

OAT1
OAT2
OAT3
OAT4

SLC22A6
SLC22A7
SLC22A8
SLC22A11

No
Contradictory data
No
No

SLCO transporters
OATP1A2
SLCO1A2
OATP1B1
SLCO1B1
OATP1B3
SLCO1B3
OATP1C1
SLCO1C1
OATP2B1
SLCO2B1
OATP3A1
SLCO3A1
OATP4A1
SLCO4A1
OATP4C1
SLCO4C1
OATP5A1
SLCO5A1
OATP6A1
SLCO6A1

DOI 10.1002/jps

No
No
No
No
Yes
Yes
Yes
Yes
No
No

Cellular
Distribution
Bronchial/bronchiolar
epithelium
Alveolar epithelium
(contradictory data)
Alveolar macrophages
endothelium
epithelium
epithelium
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Airway epithelium
Seromucinous glands
Small capillaries
Tracheal/bronchial
ciliated cells
Tracheal/bronchial
ciliated cells
Basal cells
Basal cells
Airway smooth muscles
Endothelium
Tracheal epithelium
Airway epithelium
Alveolar epithelium
Bronchial epithelium
Airway epithelium
Type II pneumocytes
Endothelium
Unknown

Unknown
Unknown
Unknown
Unknown

Cellular
Localisation
Apical

Refs.
22–27

Apical

Basolateral

24,61,62

Apical

24,63

Apical

21,23,60
21,23,60
21,23,60
21,23,60
21,23,60
21,23,60
21,23,60
23,24,73,74

Apical/cytoplasmic

23,78,79

Apical

23,78,79

Entire membrane
Entire membrane

23,78,79

Apical
Cytoplasmic
Apical
Apical
Unknown
Apical
Cytoplasmic
Apical?
Unknown

Unknown
Unknown
Unknown
Unknown

23,79
23,79
23,101
23,102

23,109–111
23,109–111
23,109–111
23,109–111
23,120
23,120,121
23,120,121
23,122
23,120,125
23,120,126
23,120,127
23
23
23,123,124


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BOSQUILLON

Figure 1. Expression and localisation of drug transporters in human upper airway epithelial cells. Ã Indicates the
existence of conflicting data in the literature.

Human in vitro models of the epithelial barrier of
the lungs have been developed recently in response to
ethical concerns regarding the use of laboratory
animals.3,4 The two bronchial cell lines Calu-3 and
16HBE14o- as well as normal human epithelial
bronchial (NHBE) cells, when cultured as monolayers
on permeable supports at an air–liquid interface,
provide in vitro representations of the absorption
barrier of the upper airways morphologically close to
the native bronchial epithelium while exhibiting
similar permeability properties.5–7 In the absence of
an alveolar cell line suitable for permeability studies,
modelling the alveolar epithelium must exclusively
rely on primary cultured alveolar type-I like epithelial cells.3,4 To date, it is unclear whether those cell
culture models express the same range of transporters found in human lungs and hence, whether they
are of any utility for the identification of compounds
actively transported across the respiratory epithelium.

Besides in vitro models, isolated perfused lung
(IPL) techniques are gaining popularity as tools
to predict pulmonary drug absorption as, in contrast
to permeability studies in cell layers, pharmacokinetic data can be obtained following drug delivery to
an intact organ.8 Ex vivo systems offer the opportunity to quantify the actual contribution of active
transport mechanisms on pulmonary drug absorption
and consequently, rat IPL models have recently been
used to evaluate the influence of P-glycoprotein (P-gp)
on the transport of model substrates across
the respiratory barrier.9,10 Although models employing isolated and perfused human lung lobes have been
described,11,12 the majority of IPL systems are based
on rodent lungs.8 This entails inter-species variations
in drug permeability and renders any extrapolation
hypothetical with respect to the situation in humans.
The large majority of inhaled drugs are delivered
locally to treat respiratory conditions and are
administered to an inflamed or infected tissue. As
either origins or consequences of the pathology, the
expression and activity of drug transporters might be
altered in diseased lungs, which could potentially
affect drug PKPD profiles. Similarly, the progression
or remission of the disease state and chronic
pharmacotherapy might also modify the transporter
expression pattern in the lungs. However, with
the exception of ATP-binding cassette (ABC) transporters in chronic obstructive pulmonary disease
(COPD),13,14 how transporters are regulated in
common pulmonary affections has essentially not
been considered so far.

Table 2. Inhaled Compounds That Interfere With Drug Transporters
Drug Name

Drug Class

Transporter(s)

Refs.

Beclomethasone dipropionate

Corticosteroid

Budesonide

Corticosteroid

Ciclesonide
Flunisolide
Fluticasone propionate
Mometasone furoate
Triamcinolone acetonide
Albuterol/salbutamol

Corticosteroid
Corticosteroid
Corticosteroid
Corticosteroid
Corticosteroid
b2-agonist

Formoterol
Ipratropium

b2-agonist
Antimuscarinic

N-acetylcysteine
Tobramycin
Ciprofloxacin

Mucolytic
Antibiotic
Antibiotic

Pentamidine

Antiprotozoal

BCRP, P-gp
OCT1, OCT2
P-gp
MRP
OCT1, OCT2, OCT3
BCRP, P-gp
P-gp
OCT2, OCT3
BCRP, P-gp
P-gp
P-gp?
OCT, OCTN2
OCT3, OCTN2
MRP1
OCTN2
MRP1
P-gp?
BCRP
MRP4
OCTN2
OCT1, OCT2, OCT3

129
79
130
70
78,80
129
39
78,80
129
131
132
79,84
84
70
86
70,133
134
135
136
137
138

? Indicates inconclusive evidence.

DOI 10.1002/jps


This review aims to give an insight into the current
knowledge of the expression, localisation and activity
of drug transporters in the lungs from a drug delivery
perspective. Each family of transporters is reviewed
in terms of their expression in normal human lungs
and when data are available, expression in healthy
lungs is contrasted with that in diseased lungs,
excluding lung tumours which are not included in the
discussion. The few studies that have evaluated the
activity of transporters at the pulmonary absorption
barrier or their interaction with inhaled drugs are
summarised and the suitability of animal and cell
culture absorption models for the investigation of
active transport systems in the lungs is analysed.
Transporters considered herein are those known to
affect drug absorption, reabsorption or elimination in
the intestine, kidney, liver or at the blood–brain
barrier. Those encompass (1) the efflux pumps
belonging to the ABC superfamily of transporters:
P-gp, the multidrug resistance associated proteins
(MRPs) and breast cancer resistance protein (BCRP)
as well as (2) the uptake transporters members of the
solute-linked carrier (SLC or SLCO) superfamilies,
that is the organic cation transporters (OCTs), the
peptide transporters (PEPT1 and PEPT2), the
organic anion transporters (OATs) and the organic
anion transporting polypeptide (OATPs). Although
the lung resistance-related protein (LRP) is highly
expressed in the lung and its critical role in multidrug
resistance against chemotherapeutic agents is well
documented,15 little information is available on its
involvement in the transport of conventional molecules across the respiratory epithelium. Hence, that
transporter is not discussed in this review.

ATP-BINDING CASSETTE (ABC) TRANSPORTERS
ABC transporters are a large family of transmembrane proteins which function as ATP-dependent
efflux pumps capable of exporting a broad range
of chemically diverse substances from the cell
cytoplasm to the external environment. Approximately 50 members of the ABC family have been
identified in humans. Those transporters are classified into seven subfamilies designated from A to G.
Amongst those, P-gp, MRPs and BCRP are well
known for their role in multidrug resistance (MDR), a
phenomenon which results from the expulsion of
chemotherapeutic agents from cancerous cells that
overexpress efflux pumps.16 ABC transporters are
also present in normal tissues where they prevent the
accumulation of xenobiotics and therefore, they
actively contribute to the tissue defense mechanisms.17 In addition, their involvement in the poor oral
bioavailability and/or tissue distribution of a large
series of drugs as well as in their hepatobiliary and
DOI 10.1002/jps

2243

renal excretion has been demonstrated.18 Due to their
potential role in limiting the transport of inhaled
therapeutic molecules across the respiratory epithelium and in the pathophysiology of airway diseases,
the expression and functions of ABC transporters in
normal and diseased lungs have been granted great
attention. Those topics were first covered in an
excellent review published a few years ago.19 Several
subsequent publications have largely contributed to
the evaluation of the actual role of ABC transporters
in the pharmacokinetic profile of aerosolised drugs
and in the development of COPD. Those recent
studies together with older ones exploring the
expression of ABC transporters in respiratory cell
culture models in vitro are summarised below.

P-gp/MDR1
P-gp, also called MDR1 or ABCB1, is a 170 kDa
transporter mainly expressed in the apical membrane
of the enterocytes, hepatocytes, proximal renal
tubules and at the blood–brain barrier. The protein
is encoded by the MDR1 gene in humans and both the
mdr1a and mdr1b genes in rodents. Since it is well
established that P-gp limits the oral absorption of
drugs, prevents their entry into the central nervous
system and is responsible for many drug–drug
interactions,20 that transporter has been the most
extensively studied in the lungs.
P-gp in the Lung Tissue
P-gp mRNA was detected in normal human lung
tissue by RT-PCR21,22 and microarray analyses.23
The intensity of expression was lower than in other
major organs involved in drug absorption, distribution and elimination such as the small intestine, liver,
kidney and brain. Immunohistochemistry techniques
localised the transporter on the apical membrane of
the bronchial and bronchiolar epithelia,22,24–26 in the
endothelial cells of the bronchial capillaries18 and in
alveolar macrophages.24,25 Contradictory data has
been published regarding P-gp expression in the
alveolar region. No staining of the alveolar epithelium was observed in three studies24–26 while type I
pneumocytes stained positive at their apical side in
the study by Campbell et al.27
Both mdr1a and mdr1b mRNA are present in the
lungs of mice28 and rats,29 with highest levels of the
mdr1b messenger in both species. The cellular
distribution of P-gp in rodent lungs was nevertheless
shown to be similar to that in humans.24
P-gp expression in diseased lungs or in the lungs of
smokers compared to normal lungs has not or hardly
been quantified. mRNA levels in the lungs of smokers,
nonsmokers or ex-smokers were reported not to be
statistically different.22 However, the pulmonary

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BOSQUILLON

clearance rate of 99mTc-sestamibi, a P-gp substrate,
after aerosol delivery was reduced in healthy smokers
as compared to nonsmokers.30 This was assumed to
result from an upregulation of P-gp in the lungs of
smokers. As 99mTc-sestamibi is also a substrate for
MRP1,31 the delayed elimination of the tracer from
the lungs of smokers might also be due to
a downregulation of the basolaterally located MRP1
caused by cigarette smoke.14 While decreased P-gp
levels in the inflamed intestinal tissue of patients
suffering from gastrointestinal inflammatory disorders have been reported,32 no statistical difference
was found between the immunostaining intensity of
bronchial biopsies of COPD patients versus healthy
controls or of patients suffering from severe COPD
versus patients with a milder form of the disease.13 In
contrast, whether P-gp expression is altered in
the bronchial epithelium of asthmatic patients has
not been evaluated. Similarly, the effect of chronic
administration of inhaled glucocorticoids on P-gp
expression in the lungs has not been investigated
whereas related studies suggest they might upregulate the transporter in the pulmonary tissue. For
example, a stronger immunohistochemical staining
for P-gp was observed in nasal polyps of patients
treated with local doses of budesonide,33 a common
corticoid used in the prophylaxis of asthma. Also, P-gp
expression increased about twofold in the lungs of
rats following oral34 or intraperitoneal35 administration of dexamethasone.
Cystic fibrosis (CF) is a congenital disorder caused
by a mutation in the CF transmembrane conductance
regulator (CFTR) gene. CFTR is a member of the ABC
family of transporters which regulates the transport
of ions. Due to a structurally close similitude with Pgp, it has been hypothesised that some altered
functions of CFTR might be compensated by an
overexpression of P-gp in CF patients.36,37 On the
other hand, it has been reported that Cif, a toxin
produced by Pseudomonas aeruginosa whose infections are frequent in the lungs of CF patients,
inhibited P-gp as well as CFTR.38
P-gp in Respiratory Cell Culture Models In Vitro
P-gp has been detected in all in vitro human
respiratory cell models currently available for drug
permeability studies, that is the Calu-339–42 and
16HBE14o-14,41,43 bronchial cell lines, NHBE7,41,44
and alveolar type-I like cells41,45 with however,
contradictory data regarding its expression and
localisation on the cell membrane.9 For instance, no
vectorial transport of ciprofloxacin, digoxin and
vinblastine, all P-gp substrates, has been observed
in Calu-3 cell layers, suggesting those cells did not
express a functional transporter.46 Western blot
analysis however revealed that cell line expresses

P-gp.39,40,42,47 Functional studies in Calu-3 layers
using rhodamine 123,40 cyclosporine47 and digoxin9
as P-gp substrates showed a polarised transport in
the basolateral to apical (B-A) direction, indicating an
apical localisation of the efflux pump on the cell
membrane. By contrast, P-gp was localised in
immunofluorescence on the basolateral side of the
cell layer and flunisolide transport was enhanced in
the absorptive direction in the study by Florea et al.39
Those conflicting results can likely be explained by
differences in cell culture conditions and by the use
of nonspecific P-gp substrates and inhibitors. By
using GF120918a, a highly potent and more selective
P-gp inhibitor,48 Madlova et al.9 measured a P-gp
mediated polarised digoxin transport in the B-A
direction only in Calu-3 cell layers at passages over 50
grown for three weeks on cell culture inserts. It was
therefore suggested that layers of Calu-3 cells might
not express functional P-gp at low passages and when
cultured for a shorter period of time on permeable
filters. This hypothesis was however not confirmed by
Brillault et al.42 who detected P-gp by Western
blotting in Calu-3 layers at passages 22–30 grown
for 15 days on cell culture filters. In addition, they
measured a B-A polarised transport of the fluoroquinolone antibiotic moxifloxacin that was inhibited by
PSC-833, another P-gp potent inhibitor, while probenicid, an MRP inhibitor, had no effect.
A dependence of the time in culture on P-gp activity
was observed in NHBE cells with no vectorial
transport of digoxin after 14 days in culture and a
net absorptive transport reversed by GF120918A
after 21 days.9 This was in agreement with the
increased mRNA levels quantified by RT-PCR in
NHBE cells after 14 and 21 days on cell culture
inserts as compared to after 7 days on those inserts.7
Functional studies in NHBE using digoxin as the
substrate suggested a modest P-gp activity was
present at the basolateral side of the cells.9 However,
that assumption was not confirmed by localisation
studies.
The human bronchial CF epithelial cell line
CFBE41o- was shown to form tight monolayers
expressing P-gp when cultured under submerged
conditions on permeable supports and hence, was
deemed to be a suitable in vitro model for studying the
disease at the cellular level.49
Due to the unsuitability of the A549 alveolar cell
line to represent the absorption barrier of the deep
lung in vitro3 and the scarcity of human lung tissue,
animal primary cell culture models of the alveolar
epithelium have been developed as alternatives to
human systems. The expression and functionality of
P-gp was confirmed in monolayers of rat type-1 like
pneumocytes by Western blot and vinblastine bidirectional
transport
studies,
respectively.27
Although monolayers of porcine alveolar epithelial
DOI 10.1002/jps


cells stained positive for P-gp under a confocal
microscope, no asymmetric transport of several Pgp substrates was measured, indicating a lack of
functionality of the transporter in that model.50
Disposition Studies of P-gp Substrates in Ex Vivo
and In Vivo Animal Models
Uptake studies in isolated perfused animal lungs
demonstrated the contribution of efflux pumps
in drug accumulation from the perfusate into the
lungs and therefore a significant activity of ABC
transporters in that organ. Idarubicin concentrations
in rat perfused lungs were enhanced after its infusion
through the pulmonary circulation together with the
P-gp modulators cinchonine and rutin.51 Similarly, in
rabbit lungs, the disappearance of the P-gp substrate
rhodamine 6G from the perfusate was increased in
presence of the inhibitors verapamil and GF120918.52
In both studies, inhibitors were added in the
perfusion solution and could therefore modulate Pgp present on both the endothelial cells of the
pulmonary capillaries and the epithelial cells of the
airways. The enhanced pulmonary accumulation of
the substrates in presence of inhibitors suggests a
higher P-gp activity at the endothelium site than at
the airway epithelium since inhibition of the epithelial transporter would rather slow down the diffusion
of the substrates from the perfusate. This hypothesis
is in agreement with two absorption studies of inhaled
P-gp substrates that have failed to highlight any
significant influence of an efflux mechanism on their
disposition from the airspaces. The percentage of
losartan transferred from the airways to the perfusate in 120 min reached 94 Æ 2% after aerosolisation
to a rat IPL model, indicating a negligible P-gpmediated efflux at the apical membrane of the airway
epithelium.53 Nevertheless, relatively high drug
concentrations were used which might potentially
have saturated the transporter. In the second study,
the coinstillation of GF120918a with digoxin to a rat
IPL did not modify the pulmonary absorption profile
of that model P-gp substrate.9 In contrast, the
recovery of rhodamine123 in the perfusion solution
after intratracheal delivery to a rat IPL was enhanced
in presence of GF120918a both in the instillate and
perfusate,10 which indicates an efflux mechanism
restricted the pulmonary absorption of the dye.
However, GF120918a possesses some inhibitory
activity against BCRP48 and rhodamine123 is a
substrate for that transporter.54 The actual contribution of P-gp in the restricted absorption of rhodamine123 is therefore unclear.
The only in vivo study so far that aimed at
evaluating P-gp impact on drug disposition from
intact lungs showed that the pharmacokinetic profile
of digoxin after intratracheal instillation was similar
DOI 10.1002/jps

2245

in mdr1a (À/À) deficient and mdr1a (þ/þ) wild-type
mice.55 However, mdr1b P-gp is still expressed in the
lungs of mdr1a (À/À) mice and an upregulation of the
pulmonary mdr1b P-gp as a compensation mechanism in mdr1a knockout animals is conceivable.
Digoxin was used at concentrations below P-gp
saturation but, as in the study by Madlova et al.,9
the test solution was administered to the lungs of
animals by intratracheal instillation and an oversaturation of the transporter locally in the pulmonary
tissue cannot be excluded. Digoxin was shown to be
well and rapidly absorbed from the lungs.9,55 Hence,
an epithelial efflux mechanism might not impact
on its permeation profile to a significant extent
whereas it might hinder the absorption of a compound
with a prolonged retention in the airspaces. Digoxin is
also a substrate for members of the organic anion
transporting polypeptide (OATP) family of transporters;56,57 the presence of some of which has been
confirmed in the lungs (see below). The contribution
of an active uptake mechanism in digoxin pulmonary
absorption might therefore have counterbalanced a
potential P-gp-mediated efflux.

MRPs
The MRPs are nine organic anion efflux pumps
identified as MRP1–9. MRP1, 4, 5, 7, 8, 9 are present
in many tissues while MRP2, 3, 6 are mainly
expressed in the liver and kidneys.58 MRP1, 3, 4
are basolateral transporters while MRP2 and 5 are
located in the apical membrane of the cells.58 MRP2 is
known to play an important role in the biliary
excretion of drug conjugates, especially those with
glutathione.59
MRPs in the Lung Tissue
Using RT-PCR techniques,21,60 MRP1 and MRP5
were shown to be highly expressed in normal human
lung tissue while MRP6 and 7 were moderately
expressed and MRP2, MRP3, MRP4, MRP8 and
MRP9 levels were either low or undetectable.
Subsequent gene microarray analyses confirmed
the high expression of MRP1 and MRP5 and the
absence of MRP2 in the lungs.23 However, the
intensity of expression was found to be very high
for MRP7, high for MRP3, MRP8, MRP9 and
moderate for MRP4 and MRP6.23
The high expression of MRP1 in the lungs was
further corroborated by Western blotting61 and
immunohistochemistry.24,61,62 Bronchial/bronchiolar
epithelial cells were stained but while labelling was
localised in the cytoplasm of ciliated cells just below
the cilia in the study by Flens et al.,61 MRP1 was
found on the basolateral membrane of ciliated,
mucous-producing and basal cells in two other

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studies.24,62 Alveolar macrophages exhibited staining
in their cytoplasm whereas no staining was observed
in pneumocytes.24,61 In concordance with gene
expression data, weak63 or absent staining24 was
observed in bronchial/bronchiolar epithelial cells for
MRP2. MRP3 could not be detected in any area of the
lung.24
A similar expression pattern with high levels
of MRP1 mRNA and low levels of MRP2 was reported
in rats and mice23,64,65 although MRP1 expression
seemed to be lower in mice than in rats and
humans.23,65 Gene microarrays indicated the lungs
of rodents might express lower levels of MRP3 and
MRP6 but higher levels of MRP4 than human
lungs.23
MRP1 mRNA levels were not statistically different
in healthy smokers, ex-smokers and nonsmokers.62
However, MRP1 expression, as assessed by immunostaining, was lower in bronchial biopsies of COPD
patients as compared to that in healthy patients as
well as in patients affected by severe COPD versus
those with a mild to moderate form of the disease.13
Consequently, a role of that transporter in the
pathophysiology for COPD might be postulated.13
MRPs in Respiratory Cell Culture Models In Vitro
In accordance with gene microarray data in human
lungs, high levels of MRP1, MRP3, MRP5 and MRP7
mRNA were measured by RT-PCR in human epithelial respiratory cell culture models.41 MRP4 and
MRP8 transcripts were detected in normal human
bronchial and alveolar cells but were absent in the
Calu-3 and 16HBE14o- cell lines.41 MRP6 was
moderately expressed in bronchial models but highly
expressed in alveolar type-I like cells.41 The most
striking discrepancy with human lungs was the
presence of MRP2 transcripts in all in vitro models
while that transporter seems not to be expressed
in vivo.23
MRP1 was reported to be expressed both at
the mRNA and protein level in undifferentiated
NHBE and normal alveolar lung cells grown on cell
culture dishes, with nevertheless high intra-individual
variations.44,66
The
functionality
of
the transporter in normal lung cells was demonstrated by the decreased efflux of the MRP substrate
carboxydichlorofluorescein (CDF) in presence of the
MRP inhibitor MK-571.44 Immunodetection of
MRP1–5 in undifferentiated NHBE and alveolar cells
showed that MRP1 and MRP3 were localised in the
cell membrane while MRP2, MRP4 and MRP5 were
intracellular proteins.67 However, when cells were
cultured on inserts at an air–liquid interface, MRP1
and MRP2 were detected on the basolateral membrane of the cells or on both the apical and basolateral
membranes, respectively.67 This illustrates the

necessity of investigating transporter expression
and localisation in differentiated cells grown under
physiologically relevant conditions.
Torky et al.68 investigated the influence of proinflammatory mediators on MRP1 functions in
normal human respiratory epithelial cells. The
uptake of CDF by undifferentiated NHBE cells
exposed to arachidonic acid and prostaglandin E2
for 3 days was decreased as compared to that in
untreated cells while prostaglandin F2a had no effect
on MRP1 activity.68 In alveolar cells, only arachidonic
acid modified CDF efflux.68
In Calu-3 cells, MRP1 was localised on the
basolateral side of monolayers cultured on permeable
filters.69 Efflux and transport studies were carried out
using calcein as the substrate and indomethacin,
probenicid or MK-571 as inhibitors. However,
appraising the actual contribution of MRP1 in calcein
translocation across Calu-3 cells was rendered complex due to the dye interacting with P-gp.69
In 16HBE14o- cells, a strong immunohistochemical
staining was obtained for MRP1 while this was weak
for MRP4 and negative for MRP2, MRP3 and
MRP5.14 Because MRP1 was shown to be downregulated in the lungs of COPD patients,13 that cell
line was used to evaluate the effect of cigarette smoke
and drugs commonly used in the treatment of COPD
on MRP1 activity in the bronchial epithelium. The
efflux of the fluorescent dye CDF out of cells exposed
to cigarette smoke extracts was diminished when
compared to that in untreated cells.14 This inhibitory
effect was caused by a direct interaction of cigarette
smoke components with the transporter.14 In addition, in the cytotoxicity MTT assay, the reduction of
the metabolic activity of 16HBE14o- cells provoked by
cigarette smoke extracts was enhanced in presence of
the MRP inhibitor MK-571,14 confirming the protective role of MRP1 against cell damage induced by
cigarette smoke and hence, the probable role played
by the transporter in the development of COPD. The
intracellular accumulation of CDF by 16HBE14ocells was enhanced in presence of budesonide but this
inhibitory effect on MRP1 transport was reduced by
formoterol whereas formoterol on its own had little
effect on MRP1 activity.70 By contrast, ipratropium
and N-acetylcysteine decreased the accumulation of
the dye, suggesting they both stimulated MRP1mediated efflux.70 Whether those modulations of
MRP1 activity caused by drugs used in COPD are
beneficial or detrimental for the treatment of the
disease is currently unknown.
Both type I and type II rat pneumocytes in primary
culture stained positive for MRP1 at their basolateral
surface when grown on permeable filters and
indomethacin increased the basolateral to apical
transport
of
fluorescein
across
type
II
cell monolayers as well as the intracytoplasmic
DOI 10.1002/jps


accumulation of the dye by those cells.71 Similar
functionality studies could not be carried out using
type I cell monolayers as the monolayer integrity was
compromised in presence of indomethacin. Nevertheless, in absence of apical to basolateral permeability data and control experiments demonstrating
the involvement of an active mechanism in fluorescein translocation, transport data in type II
monolayers must be interpreted with caution. Fluorescein permeability data are indeed commonly used to
verify the integrity of epithelial cell monolayers as the
dye is assumed to be exclusively transported by a
passive paracellular route.3,4

2247

metabolites, xenobiotics and drugs.75 Their involvement in the intestinal absorption and renal excretion
of cationic drugs has been demonstrated and recent
studies indicate they play a crucial role in the
regulation of brain functions as well as those of
basophils.75
As the structure, tissue distribution, physiological
functions of OCTs and their roles in drug absorption
and elimination was reviewed recently,75–77 the focus
here is on their expression, localisation and functions
in the lung with an emphasis on their interaction with
inhaled drugs.
OCTs in the Lung Tissue

BCRP/ABCG2
BCRP is a 72 kDa transporter encoded by the ABCG2
gene which was first isolated from a breast cancer cell
line. Besides being overexpressed in many cancer
cells, it is also highly expressed in the placenta, the
gastrointestinal tract, the brain, the liver and the
breast tissue where it regulates the transfer and
accumulation of xenobiotics.72
Data regarding BCRP expression in the lung are
sparse and contradictory. In early studies, BCRP
mRNA was either not present73 or detected only at
a low level74 in normal human lung and a weak
but detectable immunostaining was observed in
the epithelium, in seromucinous glands and small
capillaries.24 Gene microarrays recently showed
BCRP was relatively highly expressed in human
lungs whereas its expression was comparatively low
in the lungs of rats and mice.23
Transcripts for BCRP were found in all human
lung epithelial cell culture models with however
underexpression in Calu-3 and overexpression in
16HBE14o-.41 A strong immunostaining for BCRP
was obtained in 16HBE14o- cells,14 which confirmed
the transporter is highly expressed in that cell line.

ORGANIC CATION TRANSPORTERS
OCTs are members of the SLC22A family of
transporters which belongs to the major facilitator
superfamily (MFS). They comprise five main subtypes of carriers; the electrogenic OCT1, OCT2, OCT3
and the electroneutral OCTN1, OCTN2. In addition,
OCT6 and octn3 have been cloned from humans or
rodents, respectively, where they are found mainly in
testis.75 They all have the capacity to translocate
various endogenous and exogenous molecules across
the plasma membrane in both directions. Although
neutral molecules can be transported, the majority of
their substrates are positively charged at physiological pH and include hormones, neurotransmitters,
DOI 10.1002/jps

The five main subtypes of OCTs have been detected in
healthy human lungs. However, conflicting observations have been made. Lips et al.78 found high levels of
OCT1, OCT2 and OCT3 mRNA in human lung tissue
but they did not quantify OCTN1 and OCTN2 levels.
Using immunohistochemistry techniques, OCT1
and OCT2 were localised on the apical membrane
of ciliated cells of the trachea and bronchi.
In addition, OCT1 was detected in the cytoplasm of
ciliated cells and OCT2 in the plasma membrane of
basal cells. Ciliated cells stained weakly for OCT3, by
contrast to the entire membrane of basal cells and the
basolateral membrane of intermediate cells which
was intensively labelled. In the gene microarray
analysis by Bleasby et al.,23 the intensity of expression in human lungs was weak for OCT2, moderate
for OCT1 and OCT3 and high for OCTN1 and OCTN2.
Horvath et al.79 measured high levels of OCTN1 and
OCTN2 mRNA and very low levels of OCT1-3 mRNA
in the airway tissue of both healthy and CF patients.
The same group also found high levels of OCT3 mRNA
in airway smooth muscle cells and using immunohistochemistry, they visualised the transporter in
bronchial and pulmonary blood vessels.80 The expression of the other OCT subtypes was low or undetectable in muscular and endothelial cells.80 OCTN1
positive staining was observed on the luminal side of
the trachea epithelium and less intensively in
alveolar macrophages while OCTN2 staining was
positive on the apical membrane of the airway and
alveolar epithelia.79
The intensity of OCT1, OCT2 and OCTN2 gene
expression was shown to be similar in human and
rodent lungs whereas that of OCT3 and OCTN1
appeared, respectively, higher or lower in rodents
compared to humans.23 OCT1, OCT2 and OCT3 were
identified in rat lungs at the protein level78,81 but
although the mRNA of all three transporters was
found in murine lungs, only OCT1 and OCT3 were
visualised by immunofluorescence in that species.82
In rats, the apical membrane of ciliated cells of the
trachea and bronchi stained positive for the three

2248

BOSQUILLON

transporters while that of alveolar epithelial cells
was stained for OCT1 and OCT3 only. OCT3 was, in
addition, detected in the plasma membrane of
bronchial basal cells. In mice, OCT1 was observed
on the apical side of ciliated cells and OCT3 mainly in
bronchial smooth muscles, although a weak staining
was obtained in the bronchial epithelium as well.82
The protein expression and localisation of OCTN1
and OCTN2 in the lungs of rodents have not been
investigated to date.
Pulmonary expression of OCTs in human lung
diseases has only been reported for CF, where the
expression pattern was unaltered compared to
normal lungs.79 The expression of OCT1-3 in rats
and mice lungs sensitised with ovalbumin and
exposed to the antigen by aerosol delivery was
compared with that in untreated animals in order
to evaluate the effects of acute allergic airway
inflammation on OCTs regulation.81 In allergic rats,
OCT1 was upregulated whereas OCT2 and OCT3
were downregulated 48 h after antigen challenge.
OCT2 expression was similarly reduced in challenged
mice but OCT1 and OCT3 levels were identical in
inflamed and healthy mice lungs, which suggests
inter-species variations in the regulation of OCTs.
Considering those data in animals, it is now paramount to determine whether OCT expression is
modified in chronic inflammatory respiratory diseases, especially since those transporters might have
implications in asthma/COPD pathophysiology and
pharmacotherapy. Indeed, based on uptake and
release studies in Xenopus laevis transfected with
OCT1-3 mRNA78 and the accumulation of acetylcholine in the bronchial epithelium of OCT1/2 doubleknockout mice,82 it has been proposed that OCT1 and
OCT2 mediate the release of the nonneuronal
acetylcholine produced by bronchial epithelial cells
into the airway lumen where it controls mucus
production, cilia beat frequency and epithelial cell
proliferation.83
OCTs in Respiratory Cell Culture Models In Vitro
In comparison to the extensive investigation on ABC
transporters in respiratory cell models in vitro, only a
limited number of studies have looked at OCTs in
cultured airway epithelial cells. A recent RT-PCR
analysis of drug transporters in human bronchial cell
culture models revealed OCT1 and OCTN2 were
moderately expressed while OCT2 was absent in both
normal cells and cell lines.41 Various OCT3 and
OCTN1 expression were observed amongst models.
While high levels of OCT3 mRNA were present in
normal bronchial cells and Calu-3 cells, the transporter was not detected in 16HBE14o-. Intense
signals were measured for OCTN1 transcripts in
Calu-3 and 16HBE14o- cells but not in normal cells.

In a previous study, normal human bronchial
epithelial cells were shown to highly express OCTN1
and OCTN2 on their apical membrane while expressing low amounts of OCT1-3 when grown on permeable filter at an air–liquid interface for 6–8 weeks.79
OCT expression profile in NHBE layers was similar to
that reported by the same research team in freshly
isolated human bronchial cells. In contrast to the
study by Endter et al.,41 mRNA for all the five OCTs
were detected in the bronchial cell lines Calu-3 and
16HBE14o- grown in cell culture flasks.84 Cells were,
however, screened for OCTs at passage numbers
higher than those commonly used for permeability
measurements in those cell lines.3 Unfortunately, the
passage number at which Endter et al.41 examined
bronchial cell lines was not specified. Therefore, it is
unknown whether discrepancies between the two
studies arose from an upregulation of transporter
expression in those in vitro models at high passage
numbers or from differences in culture conditions.
The uptake of the model organic cation
guanidine by layers of rabbit alveolar epithelial cells
grown on Transwell1 inserts was shown to be
saturable and was inhibited by a series of positively
charged molecules.85 This indicated a carriermediated transport process for organic cations is
present in the alveolar epithelium.
Interestingly, the b2-agonist salbutamol, which is
positively charged at physiological pH was actively
transported with a net absorptive flux in layers of the
two bronchial cell lines Calu-3 and 16HBE14o-.84
Although the transporter involved was not identified,
the organic cations TEA and guanidine significantly
decreased the A-B transport of salbutamol, suggesting the involvement of one or several member(s) of the
OCT family. This assumption was later supported by
evidence demonstrating salbutamol (albuterol) and
formoterol, another positively charged b2-mimetics,
modulate the activity of OCTs. Those two bronchodilators were shown to inhibit the uptake of the model
cationic fluorophore 4-[4-(demethylamino)-styryl]-Nmethylpyridinium (ASPþ) by undifferentiated normal human bronchial cells grown on coverslips.79 The
transporter involved was identified as OCTN2, based
on the reduction of ASPþ uptake in presence of the
OCTN2 inhibitor L-carnitine. However, an interaction of formoterol and salbutamol (albuterol) with
other members of the OCT family cannot be excluded
as cells used in that study did not express OCT1-3.
In a related work,80 formoterol was reported to
be internalised into human airway smooth muscle
cells by an OCT3-mediated process, which indicates it
is a substrate or inhibitor for more than one OCT
subtype.
The inhaled antimuscarinic bronchodilators ipratropium and tiotropium bear a permanent positive
charge due to their quaternary ammonium structure
DOI 10.1002/jps


and hence, it can intuitively be prophesied that they
are very likely to be substrates for OCTs. Ipratropium
inhibited the uptake of L-carnitine by the human
proximal tubule cell line Caki-1, which demonstrates
it is recognised by OCTN2.86 Besides cationic
bronchodilators, inhaled glucocorticoids were also
shown to interact with OCTs, although they are not
actually translocated by those transporters. Budesonide and fluticasone inhibited the uptake of acetylcholine by OCT2 transfected X. laevis78 as well
as the OCT3-mediated internalisation of formoterol
by human airway smooth muscle cells.80 Although
strong evidence has shown cationic bronchodilators
interact with OCTs, it is at present not known
whether those transporters actually contribute to
their absorption across the respiratory epithelium.
Similarly, the consequences on the treatment of
inflammatory respiratory diseases of inhaled bronchodilators and corticosteroids interacting with OCTs
are unclear.

PEPTIDE TRANSPORTERS
Peptide transporters are members of the SLC15
family which is part of the proton-coupled oligopeptide transporter (POT) superfamily. The structure
and physiological functions of the two main transporters of that family, PEPT1 and PEPT2 have been
extensively described elsewhere.87 Briefly, PEPT1
and PEPT2 are capable of transporting any di- or
tripeptide derived from the 20 L-a-amino acids in
association with proton translocation independently
of the substrate charge. PEPT1 is essentially
expressed in the apical membrane of epithelial cells
of the small intestine, renal tubules and bile ducts
while PEPT2 is present in many organs, such as the
kidneys, brain, lung, pituitary, mammary glands,
reproductive organs.88–90 Because of their very broad
substrate specificity, PEPT1 and PEPT2 have the
capacity to translocate peptidomimetic drugs such as
the angiotensin-converting enzyme inhibitors captopril, enalapril and fosinopril91 or the b-lactam
antibiotics,92 respectively, and it is now well established that PEPT1 and PEPT2 contribute to the high
bioavailability of peptide-like drug molecules.
Drug inhalation is an attractive route of delivery for
the treatment of pulmonary infections. Several antiinfectious agents active against respiratory pathogens are substrates for PEPT1/PEPT2, for example
penicillin and cephalosporin antibiotics and the
antiviral drugs valacyclovir and valganciclovir.93
The presence of peptide transporters in the respiratory tract can potentially affect the absorption and
distribution of those compounds, with consequences
on their anti-infectious efficiency.93
DOI 10.1002/jps

2249

PEPT1/PEPT2 in the Lung Tissue
High Pept2 mRNA levels have been measured in
the lungs of rabbits,94,95 rats90,96,97 and mice.90 By
contrast, weak or no signals have been observed for
Pept1 in rabbit,95,98 rat90,96,99 and murine90 lung
extracts. Based on expression data in animals, PEPT1
was assumed for years to be absent from the human
respiratory tract or at least, not to significantly
influence inhaled drug distribution in the lungs.93
However, Western blot analysis and uptake studies
using di- and tripeptides showed rat alveolar macrophages express functional Pept1 protein.100 Gene
microarrays revealed PEPT1 is expressed in the
lungs although to a lower extent than PEPT223 and
PEPT1 mRNA was detected very recently in the
human bronchi of healthy adults.101 The recent
discovery of PEPT1 in human lung implies the early
assumption that the transporter does not affect
pulmonary drug disposition might need reappraisal.
Due to the high expression of PEPT2 in human and
animal lungs,23 the regional distribution of that
transporter has been examined in rat,96 mice96 and
healthy or CF human102 lungs using immunohistochemistry techniques. In all species, a positive
staining was obtained on the apical membrane of
airway epithelial cells, in the cytoplasm of type II
pneumocytes and on the endothelium of small blood
vessels. The staining intensity was similar in healthy
and CF lung samples.102 The presence of Pept2 in rat
type II alveolar cells was later confirmed, although
the transporter appeared to be located on the apical
plasma membrane.103
The functionality of Pept2/PEPT2 in the lungs was
demonstrated by performing ex vivo uptake studies of
the fluorophore-conjugated dipeptide D-Ala-LysAMCA by isolated mice96 and human102 lung specimens. The model peptide accumulated in airway
epithelial cells and type II pneumocytes, two cell
types known to express the transporter. In addition,
the intracellular fluorescence was reduced after
incubation of the lung samples with high concentrations of the dipeptide glycyl-(L)-glutamine or the
synthetic cephalosporin and PEPT2 substrate cefadroxil, while addition of the PEPT1 substrate
captopril had no effect.
PEPT1/PEPT2 in Respiratory Cell Culture
Models In Vitro
Consistent with gene expression data in human
lungs, high PEPT2 mRNA levels were found in
human bronchial epithelial cells and bronchial cell
lines in vitro.41 In contradiction with expression
levels in vivo, PEPT1 was highly expressed in Calu-3
and 16HBE14o- but was absent in normal cells.41
Primary human airway epithelial cells grown on
permeable filters at an air–liquid interface were

2250

BOSQUILLON

shown to express PEPT2 on their apical cell
membrane.104 The two genetic variants previously
identified105 PEPT2Ã1 and PEPT2Ã2 were represented amongst the airway samples but the intensity
of the RT-PCR signal was similar in all donors. The
apical to basolateral transport of the dipeptide GlySar
across cell layers was saturable, unaffected by the
genotype and inhibited by b-lactam antibiotics
(PEPT2 inhibitors) while ACE inhibitors (PEPT1
inhibitors) had no effect. This indicated the transporter was functional in vitro and its activity was not
influenced by genetic variations, at least at the pH of
the lung fluid, which is about 6.5. Differences in
GlySar translocation were indeed observed previously between the two haplotypes at pH 6.105
Both PEPT1 and the PEPT2Ã1 variant were
detected in layers of Calu-3 cells grown at an air–
liquid interface.101 PEPT1 expression was confirmed
by Western blot and the transporter was localised on
the apical cell membrane. In contradiction with
previous studies which had concluded PEPT1 was
not involved in peptide transport across the airway
epithelium,102,104 the uptake and transport of GlySar
was shown to be mediated by PEPT1 and not PEPT2
in that cell line.
b-Ala-L-His uptake by rabbit tracheocytes cultured
as air–liquid interfaced monolayers increased when
the apical medium was buffered at pH 6.5 as
compared to 7.4 and was inhibited by Gly-L-Phe,
but neither by Gly-D-Phe or amino acids.106 Although
the transporter involved was not identified, the
marked effect of the pH gradient coupled to previous
evidence of its presence in the lungs suggested it to be
PEPT2. Surprisingly, the transport of Gly-L-Phe
across the cell layers was symmetrical at pH 7.4
and in the same order of magnitude as the paracellular marker mannitol. Decreasing the pH of the
apical medium to 6.5 reduced the A-B permeability
of the peptide, despite an enhanced uptake at that pH,
while the B-A transport was unchanged. As paracellular diffusion is hindered by the highest protonation of Gly-L-Phe at pH 6.5, a passive mechanism
was therefore assumed to be the unique permeation
pathway followed by the peptide across the tracheal
epithelium.

ORGANIC ANION TRANSPORTERS
Two families of structurally unrelated transporters
are known to mediate the absorption and elimination
of endogenous and exogenous organic anions: the
organic anion transporter (OAT) family and the
organic anion transporting polypeptide (OATP)
family (see below). OATs, like OCTs, belong to the
SLC22A family of transporters. The six members of
OATs identified so far (OAT1-4, URAT1 and oat5) are

all expressed in the kidneys.107,108 OAT2, OAT3,
OAT4 are additionally found in the liver, brain and
placenta, respectively.107,108 OATs are the main
mechanism by which organic anions are excreted
and reabsorbed in the kidneys.108 They also contribute to drug–drug interactions and to the nephrotoxicity of some drugs and toxins.107
None of the OAT members could be detected
by Northern blot in the lungs of humans,109–111
rats112–114 or mice.115,116 Gene microarrays confirmed
the absence of OAT1, OAT3 and OAT4 in the lungs of
all species. They nevertheless indicated OAT2 was
relatively highly expressed in human and murine
lungs.23
No OAT1, OAT2 and OAT3 transcripts were
detected in any of the human bronchial epithelial
cell culture models. As expected, OAT4 mRNA was
absent in normal cells, but that transporter was
highly expressed in the two bronchial cell lines Calu-3
and 16HBE14o-.41

ORGANIC ANION TRANSPORTING
POLYPEPTIDES
OATPs were originally designated by the SLC21 gene
symbol and each transporter was essentially named
by the researchers who had isolated them. This
resulted in huge confusion as a same transporter
isolated by independent groups was given different
names or a human transporter had a designation
similar to a rodent transporter whereas they were not
equivalent.117 OATPs are now classified under the
SLCO gene symbol according to a specific nomenclature whose details can be found elsewhere.57 The
11 human OATPs are divided into 6 families (OATP1–
6) further subdivided into subfamilies. Some of them
are organ specific while others are ubiquitious.57,117
To date, only four of them, OATP1A2 (widely
expressed), OATP1B1 (liver specific), OATP1B3 (liver
specific), OATP2B1 (widely expressed) have been well
characterised and shown to be responsible for drug–
drug interactions.118,119 Many OATP substrates are
also transported by the efflux pumps P-gp, MRP1,
MRP2 or BCRP57 and assessing the contribution of
each of those transporters in the pharmacokinetic
profile of organic anions is a major challenge in
absence of specific inhibitors and knockout mice for
OATPs. Overall, the actual tissue distribution,
physiological functions and substrate specificity of
OATPs remain largely unknown.57
RT-PCR, Northern blot or gene microarray analyses of human tissue samples indicated
OATP1A2,23,120 the two liver specific proteins
OATP1B1 and OATP1B3,23,120,121 OATP1C1,23,122
OATP5A123 and OATP6A123,123,124 were not
expressed in the lungs. By contrast, high levels of
DOI 10.1002/jps


OATP2B1,23,120,125
OATP3A123,120,126
and
23,120,127
OATP4A1
expression were detected in
human lungs while OATP4C1 was moderately present.23 Positive signals for oatp2b1 were also observed
in rat23,128 and mice23 lungs and for oatp3a1 in rat
lungs.126 Nevertheless, the actual expression of
OATPs at the protein levels and their cellular
localisation in the pulmonary tissue have not yet
been investigated.
Significant variations in the expression profiles of
OATPs were noticed amongst human bronchial
epithelial in vitro models.41 In accordance with gene
microarray
data,
normal
bronchial
cells
were reported to express high levels of OATP3A1
and OATP4A1 while not expressing OATP1B1,
OATP1B1 and OATP1C1. However, in contradiction
with expression profiles in human lungs, OATP1A2
was highly expressed and OATP2B1 was undetectable in those cells. The bronchial cell line Calu-3
appeared to express all OATP transporters except
OATP1A2 while none of OATP transcripts but those
for OATP3A1 and OATP4A1 were present in
16HBE14o- cells.

CONCLUSIONS
Based on the literature, it is manifest that the lungs
express elevated levels of several drug transporters.
Interestingly, transporter gene expression in the
lungs appeared to be the highest after that in the liver
and kidneys.23 Because techniques used to quantify
transporter levels in whole organs are incapable of
determining the cellular origin of the genes, the
extent of transporter expression at the epithelial drug
absorption site remains unknown. Not surprisingly,
as observed for the exploration of transporters in
other organs, the increasing number of studies
published in the last 5 years attests of a recent
interest in drug transporters in the lungs, both from
academic institutions and the pharmaceutical industry. Nevertheless, contribution in the area has been
limited and the physiological functions of drug
carriers in the lung tissue, their potential involvement in common respiratory diseases and their roles
in the disposition of inhaled drugs are essentially
unexplored.
This review discussed more specifically the role of
drug transporters in the biopharmaceutics
of aerosolised medications. To date, there is no strong
evidence to indicate active transport mechanisms
affect the distribution of drugs in the lungs.
Considering the large surface area offered by the
respiratory epithelium and rapidity of pulmonary
clearance observed for most inhaled drugs, drug
absorption from the lungs is less likely to be as
influenced by transporters as it is from
DOI 10.1002/jps

2251

the gastrointestinal tract. Delivery strategies currently under development nevertheless envisage
exploiting efflux pumps present in the lung tissue
to prolong drug retention in situ. However, it is
noteworthy that the impact of transporters on the
distribution of inhaled drugs might be influenced by
their regional deposition in the respiratory tract and
local metabolism.
Appraising the absorptive role played by drug
transporters in the lung tissue relies on simplified
models of the respiratory absorption barrier, none of
which has been validated yet for such an application.
The development of reliable systems to explore drug
transporters in the lungs is therefore a prerequisite to
the evaluation of their influence on the PKPD profile
of inhaled drugs. Understanding the regulation of
transporters in pulmonary pathologies is also paramount for a realistic appreciation of their contribution in inhaled drug disposition under therapeutic
conditions.

REFERENCES
1. Ayrton A, Morgan P. 2008. Role of transport proteins in drug
discovery and development: A pharmaceutical perspective.
Xenobiotica 38:676–708.
´
´
2. Szakacs G, Varadi A, Ozvegy-Laczka C, Sarkadi B. 2008. The
role of ABC transporters in drug absorption, distribution,
metabolism, excretion and toxicity (ADME-Tox). Drug Discov
Today 13:379–393.
3. Forbes B, Ehrhardt C. 2005. Human respiratory epithelial cell
culture for drug delivery applications. Eur J Pharm Biopharm
60:193–205.
´
´
4. Sporty JL, Horalkova L, Ehrhardt C. 2008. In vitro cell culture
models for the assessment of pulmonary drug disposition.
Expert Opin Drug Metab Toxicol 4:333–345.
5. Grainger CI, Greenwell LL, Lockley DJ, Martin GP, Forbes B.
2006. Culture of Calu-3 cells at the air interface provides a
representative model of the airway epithelial barrier. Pharm
Res 23: 1482–1490.
6. Forbes B, Shah A, Martin GP, Lansley AB. 2003. The human
bronchial epithelial cell line 16HBE14o- as a model system of
the airways for studying drug transport. Int J Pharm 12:161–
167.
7. Lin H, Li H, Cho HJ, Bian S, Roh HJ, Lee MK, Kim JS, Chung
SJ, Shim CK, Kim DD. 2007. Air-liquid interface (ALI) culture
of human bronchial epithelial cell monolayers as an in vitro
model for airway drug transport studies. J Pharm Sci 96:341–
350.
8. Tronde A, Bosquillon C, Forbes B. 2008. The isolated perfused
lung. In: Ehrhardt C, Kim KJ, editors. Preclinical biopharmaceutics—In situ, in vitro and in silico tools for drug absorption
studies. New York: Springer. pp 135–163.
9. Madlova M, Bosquillon C, Asker D, Dolezal P, Forbes B. 2009.
In-vitro respiratory drug absorption models possess nominal
functional P-glycoprotein activity. J Pharm Pharmacol
61:293–301.
10. Francombe D, Taylor G, Taylor S, Somers G, Edwards C,
Gumbleton M. 2008. Functional role of P-gp efflux in limiting
pulmonary drug absorption within an intact lung: Application
of an isolated perfused rat lung model. Proc Resp Drug Deliv
2:461–464.

2252

BOSQUILLON

¨
11. Linder A, Friedel G, Fritz P, Kivisto KT, McClellan M, Toomes
H. 1996. The ex-vivo isolated, perfused human lung model:
Description and potential applications. Thorac Cardiovasc
Surg 44:140–146.
12. Freiwald M, Valotis A, Kirschbaum A, McClellan M, Murdter
¨
¨
T, Fritz P, Friedel G, Thomas M, Hogger P. 2005. Monitoring
the initial pulmonary absorption of two different beclomethasone dipropionate aerosols employing a human lung reperfusion model. Respir Res 6:21–33.
13. van der Deen M, Marks H, Willemse BW, Postma DS, Muller
¨
M, Smit EF, Scheffer GL, Scheper RJ, de Vries EG, Timens W.
2006. Diminished expression of multidrug resistance-associated protein 1 (MRP1) in bronchial epithelium of COPD
patients. Virchows Arch 449:682–688.
14. van der Deen M, de Vries EG, Visserman H, Zandbergen W,
Postma DS, Timens W, Timmer-Bosscha H. 2007. Cigarette
smoke extract affects functional activity of MRP1 in bronchial
epithelial cells. J Biochem Mol Toxicol 21:243–251.
15. Steiner E, Holzmann K, Elbling L, Micksche M, Berger W.
2006. Cellular functions of vaults and their involvement in
multidrug resistance. Curr Drug Targets 7:923–934.
16. Sharom FJ. 2008. ABC multidrug transporters: Structure,
function and role in chemoresistance. Pharmacogenomics
9:105–127.
17. Leslie EM, Deeley RG, Cole SP. 2005. Multidrug resistance
proteins: Role of P-glycoprotein, MRP1, MRP2, and BCRP
(ABCG2) in tissue defense. Toxicol Appl Pharmacol
204:216–237.
18. Schinkel AH, Jonker JW. 2003. Mammalian drug efflux transporters of the ATP binding cassette (ABC) family: An overview. Adv Drug Deliv Rev 55:3–29.
19. van der Deen M, de Vries EG, Timens W, Scheper RJ, TimmerBosscha H, Postma DS. 2005. ATP-binding cassette (ABC)
transporters in normal and pathological lung. Respir Res 6:59.
20. Zhang L, Strong JM, Qiu W, Lesko LJ, Huang SM. 2006.
Scientific perspectives on drug transporters and their role in
drug interactions. Mol Pharm 3:62–69.
21. Langmann T, Mauerer R, Zahn A, Moehle C, Probst M,
Stremmel W, Schmitz G. 2003. Real-time reverse transcription-PCR expression profiling of the complete human ATPbinding cassette transporter superfamily in various tissues.
Clin Chem 49:230–238.
22. Lechapt-Zalcman E, Hurbain I, Lacave R, Commo F, Urban T,
Antoine M, Milleron B, Bernaudin JF. 1997. MDR1-Pgp 170
expression in human bronchus. Eur Respir J 10:1837–1843.
23. Bleasby K, Castle JC, Roberts CJ, Cheng C, Bailey WJ, Sina
JF, Kulkarni AV, Hafey MJ, Evers R, Johnson JM, Ulrich RG,
Slatter JG. 2006. Expression profiles of 50 xenobiotic transporter genes in humans and pre-clinical species: A resource for
investigations into drug disposition. Xenobiotica 36:963–988.
24. Scheffer GL, Pijnenborg AC, Smit EF, Muller M, Postma DS,
¨
Timens W, van der Valk P, de Vries EG, Scheper RJ. 2002.
Multidrug resistance related molecules in human and murine
lung. J Clin Pathol 55:332–339.
25. van der Valk P, van Kalken CK, Ketelaars H, Broxterman HJ,
Scheffer G, Kuiper CM, Tsuruo T, Lankelma J, Meijer CJ,
Pinedo HM, Scheper RG. 1990. Distribution of multi-drug
resistance-associated P-glycoprotein in normal and neoplastic
human tissues. Analysis with 3 monoclonal antibodies recognizing different epitopes of the P-glycoprotein molecule. Ann
Oncol 1:56–64.
26. Cordon-Cardo C, O’Brien JP, Boccia J, Casals D, Bertino JR,
Melamed MR. 1990. Expression of the multidrug resistance
gene product (P-glycoprotein) in human normal and tumor
tissues. J Histochem Cytochem 38:1277–1287.
27. Campbell L, Abulrob AN, Kandalaft LE, Plummer S, Hollins
AJ, Gibbs A, Gumbleton M. 2003. Constitutive expression of pglycoprotein in normal lung alveolar epithelium and functionJOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 99, NO. 5, MAY 2010

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

ality in primary alveolar epithelial cultures. J Pharmacol Exp
Ther 304:441–452.
Croop JM, Raymond M, Haber D, Devault A, Arceci RJ, Gros
P, Housman DE. 1989. The three mouse multidrug resistance
(mdr) genes are expressed in a tissue-specific manner in
normal mouse tissues. Mol Cell Biol 9:1346–1350.
Brady JM, Cherrington NJ, Hartley DP, Buist SC, Li N,
Klaassen CD. 2002. Tissue distribution and chemical induction of multiple drug resistance genes in rats. Drug Metab
Dispos 30:838–844.
Ruparelia P, Cheow HK, Evans JW, Banney L, Shankar S,
Szczepura KR, Swift AE, Ballinger JR, Hartman NG, Chilvers
ER, Peters AM. 2008. Pulmonary elimination rate of inhaled
99m
Tc-sestamibi radioaerosol is delayed in healthy cigarette
smokers. Br J Clin Pharmacol 65:611–614.
Hendrikse NH, Franssen EJ, van der Graaf WT, Meijer C,
Piers DA, Vaalburg W, de Vries EG. 1998. 99mTc-sestamibi is a
substrate for P-glycoprotein and the multidrug resistanceassociated protein. Br J Cancer 77:353–358.
Blokzijl H, Vander Borght S, Bok LI, Libbrecht L, Geuken M,
van den Heuvel FA, Dijkstra G, Roskams TA, Moshage H,
Jansen PL, Faber KN. 2007. Decreased P-glycoprotein (P-gp/
MDR1) expression in inflamed human intestinal epithelium is
independent of PXR protein levels. Inflamm Bowel Dis
13:710–720.
Henriksson G, Norlander T, Zheng X, Stierna P, Westrin KM.
1997. Expression of P-glycoprotein 170 in nasal mucosa may
be increased with topical steroids. Am J Rhinol 11:317–321.
´
Demeule M, Jodoin J, Beaulieu E, Brossard M, Beliveau R.
1999. Dexamethasone modulation of multidrug transporters
in normal tissues. FEBS Lett 442:208–214.
´
˜
Dinis-Oliveira RJ, Duarte JA, Remiao F, Sanchez-Navarro A,
Bastos ML, Carvalho F. 2006. Single high dose dexamethasone treatment decreases the pathological score and increases
the survival rate of paraquat-intoxicated rats. Toxicology
227:73–85.
Lallemand JY, Stoven V, Annereau JP, Boucher J, Blanquet
S, Barthe J, Lenoir G. 1997. Induction by antitumoral drugs of
proteins that functionally complement CFTR: A novel therapy
for cystic fibrosis? Lancet 350:711–712.
¨
Naumann N, Siratska O, Gahr M, Rosen-Wolff A. 2005. Pglycoprotein expression increases ATP release in respiratory
cystic fibrosis cells. J Cyst Fibros 4:157–168.
Ye S, MacEachran DP, Hamilton JW, O’Toole GA, Stanton
BA. 2008. Chemotoxicity of doxorubicin and surface expression of P-glycoprotein (MDR1) is regulated by the Pseudomonas aeruginosa toxin Cif. Am J Physiol Cell Physiol 295:C807–
C818.
Florea BI, van der Sandt IC, Schrier SM, Kooiman K, Deryckere K, de Boer AG, Junginger HE, Borchard G. 2001. Evidence
of P-glycoprotein mediated apical to basolateral transport of
flunisolide in human broncho-tracheal epithelial cells (Calu3). Br J Pharmacol 134:1555–1563.
Hamilton KO, Backstrom G, Yazdanian MA, Audus KL. 2001.
P-glycoprotein efflux pump expression and activity in Calu-3
cells. J Pharm Sci 90:647–658.
Endter S, Francombe D, Ehrhardt C, Gumbleton M. 2009. RTPCR analysis of ABC, SLC and SLCO drug transporters in
human lung epithelial cell models. J Pharm Pharmacol
61:583–591.
Brillault J, De Castro WV, Harnois T, Kitzis A, Olivier JC,
Couet W. 2009. P-glycoprotein-mediated transport of moxifloxacin in a Calu-3 lung epithelial cell model. Antimicrob
Agents Chemother 53:1457–1462.
Ehrhardt C, Kneuer C, Laue M, Schaefer UF, Kim KJ, Lehr
CM. 2003. 16HBE14o- human bronchial epithelial cell layers
express P-glycoprotein, lung resistance-related protein, and
caveolin-1. Pharm Res 20:545–551.
DOI 10.1002/jps


¨
44. Lehmann T, Kohler C, Weidauer E, Taege C, Foth H. 2001.
Expression of MRP1 and related transporters in human lung
cells in culture. Toxicology 167:59–72.
45. Endter S, Becker U, Daum N, Huwer H, Lehr CM, Gumbleton
M, Ehrhardt C. 2007. P-glycoprotein (MDR1) functional activity in human alveolar epithelial cell monolayers. Cell Tissue
Res 328: 77–84.
46. Cavet ME, West M, Simmons NL. 1997. Transepithelial transport of the fluoroquinolone ciprofloxacin by human airway
epithelial Calu-3 cells. Antimicrob Agents Chemother
41:2693–2698.
47. Patel J, Pal D, Vangal V, Gandhi M, Mitra AL. 2002. Transport of HIV-protease inhibitors across 1 alpha,25di-hydroxy
vitamin D3-treated Calu-3 cell monolayers: Modulation of Pglycoprotein activity. Pharm Res 19:1696–1703.
48. Hyafil F, Vergely C, Du Vignaud P, Grand-Perret T. 1993.
In vitro and in vivo reversal of multidrug resistance by
GF120918, an acridonecarboxamide derivative. Cancer Res
53:4595–4602.
49. Ehrhardt C, Collnot EM, Baldes C, Becker U, Laue M, Kim
KJ, Lehr CM. 2006. Towards an in vitro model of cystic fibrosis
small airway epithelium: Characterisation of the human bronchial epithelial cell line CFBE41o-. Cell Tissue Res 323:405–
415.
50. Steimer A, Franke H, Haltner-Ukomado E, Laue M, Ehrhardt
C, Lehr CM. 2007. Monolayers of porcine alveolar epithelial
cells in primary culture as an in vitro model for drug absorption studies. Eur J Pharm Biopharm 66:372–382.
51. Kuhlmann O, Hofmann HS, Muller SP, Weiss M. 2003.
¨
Pharmacokinetics of idarubicin in the isolated perfused rat
lung: Effect of cinchonine and rutin. Anticancer Drugs
14:411–416.
52. Roerig DL, Audi SH, Ahlf SB. 2004. Kinetic characterization of
P-glycoprotein-mediated efflux of rhodamine 6G in the intact
rabbit lung. Drug Metab Dispos 32:953–958.
´
53. Tronde A, Norden B, Jeppsson AB, Brunmark P, Nilsson E,
¨
Lennernas H, Bengtsson UH. 2003. Drug absorption from the
isolated perfused rat lung—Correlations with drug physicochemical properties and epithelial permeability. J Drug Target 11:61–74.
54. Litman T, Brangi M, Hudson E, Fetsch P, Abati A, Ross DD,
Miyake K, Resau JH, Bates SE. 2000. The multidrug-resistant
phenotype associated with overexpression of the new ABC
half-transporter, MXR (ABCG2). J Cell Sci 113:2011–2021.
55. Manford F, Riffo-Vasquez Y, Spina D, Page CP, Hutt AJ,
Moore V, Johansson F, Forbes B. 2008. Lack of difference
in pulmonary absorption of digoxin, a P-glycoprotein substrate, in mdr1a-deficient and mdr1a-competent mice.
J Pharm Pharmacol 60:1305–1310.
56. Funakoshi S, Murakami T, Yumoto R, Kiribayashi Y, Takano
M. 2005. Role of organic anion transporting polypeptide 2 in
pharmacokinetics of digoxin and beta-methyldigoxin in rats.
J Pharm Sci 94:1196–1203.
57. Hagenbuch B, Gui C. 2008. Xenobiotic transporters of the
human organic anion transporting polypeptides (OATP)
family. Xenobiotica 38:778–801.
58. Toyoda Y, Hagiya Y, Adachi T, Hoshijima K, Kuo MT, Ishikawa T. 2008. MRP class of human ATP binding cassette
(ABC) transporters: Historical background and new research
directions. Xenobiotica 38:833–862.
59. Jedlitschky G, Hoffmann U, Kroemer HK. 2006. Structure
and function of the MRP2 (ABCC2) protein and its role in drug
disposition. Expert Opin Drug Metab Toxicol 2:351–366.
60. Kool M, de Haas M, Scheffer GL, Scheper RJ, van Eijk MJ,
Juijn JA, Baas F, Borst P. 1997. Analysis of expression of
cMOAT (MRP2), MRP3, MRP4, and MRP5, homologues of the
multidrug resistance-associated protein gene (MRP1), in
human cancer cell lines. Cancer Res 57:3537–3547.
DOI 10.1002/jps

2253

61. Flens MJ, Zaman GJ, van der Valk P, Izquierdo MA, Schroeijers AB, Scheffer GL, van der Groep P, de Haas M, Meijer CJ,
Scheper RJ. 1996. Tissue distribution of the multidrug resistance protein. Am J Pathol 148:1237–1247.
´
62. Brechot JM, Hurbain I, Fajac A, Daty N, Bernaudin JF. 1998.
Different pattern of MRP localization in ciliated and basal
cells from human bronchial epithelium. J Histochem Cytochem 46: 513–517.
63. Sandusky GE, Mintze KS, Pratt SE, Dantzig AH. 2002.
Expression of multidrug resistance-associated protein 2
(MRP2) in normal human tissues and carcinomas using tissue
microarrays. Histopathology 41:65–74.
64. Cherrington NJ, Hartley DP, Li N, Johnson DR, Klaassen CD.
2002. Organ distribution of multidrug resistance proteins 1,2
and 3 (Mrp1, 2, and 3) mRNA and hepatic induction of Mrp3 by
constitutive androstane receptor activators in rats.
J Pharmacol Exp Ther 300:97–104.
65. Maher JM, Slitt AL, Cherrington NJ, Cheng X, Klaassen CD.
2005. Tissue distribution and hepatic and renal ontogeny of
the multidrug resistance-associated protein (Mrp) family in
mice. Drug Metab Dispos 33:947–955.
66. Lehmann T, Torky AR, Stehfest E, Hofmann S, Foth H. 2005.
Expression of lung resistance-related protein, LRP, and multidrug resistance-related protein, MRP1, in normal human lung
cells in long-term cultures. Arch Toxicol 79:600–609.
67. Torky AR, Stehfest E, Viehweger K, Taege C, Foth H. 2005.
Immuno-histochemical detection of MRPs in human lung cells
in culture. Toxicology 207: 437–450.
68. Torky A, Raemisch A, Glahn F, Foth H. 2008. Arachidonic acid
pathway activates multidrug resistance related protein in
cultured human lung cells. Arch Toxicol 82:323–332.
69. Hamilton KO, Topp E, Makagiansar I, Siahaan T, Yazdanian
M, Audus KL. 2001. Multidrug resistance-associated protein1 functional activity in Calu-3 cells. J Pharmacol Exp Ther
298:1199–1205.
70. van der Deen M, Homan S, Timmer-Bosscha H, Scheper RJ,
Timens W, Postma DS, de Vries EG. 2008. Effect of COPD
treatments on MRP1-mediated transport in bronchial epithelial cells. Int J Chron Obstruct Pulmon Dis 3:469–475.
71. Patel LN, Uchiyama T, Kim KJ, Borok Z, Crandall ED, Shen
WC, Lee VH. 2008. Molecular and functional expression of
multidrug resistance-associated protein-1 in primary cultured
rat alveolar epithelial cells. J Pharm Sci 97:2340–2349.
72. Robey RW, To KK, Polgar O, Dohse M, Fetsch P, Dean M,
Bates SE. 2009. ABCG2: A perspective. Adv Drug Deliv Rev
61:3–13.
73. Doyle LA, Yang W, Abruzzo LV, Krogmann T, Gao Y, Rishi
AK, Ross DD. 1998. A multidrug resistance transporter from
human MCF-7 breast cancer cells. Proc Natl Acad Sci
95:15665–15670.
74. Fetsch PA, Abati A, Litman T, Morisaki K, Honjo Y, Mittal K,
Bates SE. 2006. Localization of the ABCG2 mitoxantrone
resistance-associated protein in normal tissues. Cancer Lett
235:84–92.
75. Koepsell H, Lips K, Volk C. 2007. Polyspecific organic cation
transporters: Structure, function, physiological roles, and
biopharmaceutical implications. Pharm Res 24:1227–1251.
76. Ciarimboli G. 2008. Organic cation transporters. Xenobiotica
38:936–971.
77. Choi MK, Song IS. 2008. Organic cation transporters and their
pharmacokinetic and pharmacodynamic consequences. Drug
Metab Pharmacokinet 23:243–253.
78. Lips KS, Volk C, Schmitt BM, Pfeil U, Arndt P, Miska D,
Ermert L, Kummer W, Koepsell H. 2005. Polyspecific cation
transporters mediate luminal release of acetylcholine from
bronchial epithelium. Am J Respir Cell Mol Biol 33:79–88.
79. Horvath G, Schmid N, Fragoso MA, Schmid A, Conner GE,
Salathe M, Wanner A. 2007. Epithelial organic cation transJOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 99, NO. 5, MAY 2010

2254

80.

81.

82.

83.
84.

85.

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

96.

97.

BOSQUILLON

porters ensure pH-dependent drug absorption in the airway.
Am J Respir Cell Mol Biol 36:53–60.
Horvath G, Mendes ES, Schmid N, Schmid A, Conner GE,
Salathe M, Wanner A. 2007. The effect of corticosteroids on
the disposal of long-acting beta2-agonists by airway smooth
muscle cells. J Allergy Clin Immunol 120:1103–1109.
Lips KS, Luhrmann A, Tschernig T, Stoeger T, Alessandrini F,
¨
Grau V, Haberberger RV, Koepsell H, Pabst R, Kummer W.
2007. Down-regulation of the non-neuronal acetylcholine
synthesis and release machinery in acute allergic airway
inflammation of rat and mouse. Life Sci 80:2263–2269.
Kummer W, Wiegand S, Akinci S, Wessler I, Schinkel AH,
Wess J, Koepsell H, Haberberger RV, Lips KS. 2006. Role of
acetylcholine and polyspecific cation transporters in serotonin-induced bronchoconstriction in the mouse. Respir Res
7:65.
Kummer W, Lips KS, Pfeil U. 2008. The epithelial cholinergic
system of the airways. Histochem Cell Biol 130:219–234.
Ehrhardt C, Kneuer C, Bies C, Lehr CM, Kim KJ, Bakowsky
U. 2005. Salbutamol is actively absorbed across human bronchial epithelial cell layers. Pulm Pharmacol Ther 18:165–170.
Shen J, Elbert KJ, Yamashita F, Lehr CM, Kim KJ, Lee VHL.
1999. Organic cation transport in rabbit alveolar epithelial
cell monolayers. Pharm Res 16:1280–1287.
Glube N, Closs E, Langguth P. 2007. OCTN2-mediated carnitine uptake in a newly discovered human proximal tubule cell
line (Caki-1). Mol Pharm 4:160–168.
Daniel H, Kottra G. 2004. The proton oligopeptide cotransporter family SLC15 in physiology and pharmacology. Pflugers
Arch 447:610–618.
Berger UV, Hediger MA. 1999. Distribution of peptide transporter PEPT2 mRNA in the rat nervous system. Anat Embryol
(Berl) 199:439–449.
¨
Groneberg DA, Doring F, Theis S, Nickolaus M, Fischer A,
Daniel H. 2002. Peptide transport in the mammary gland:
Expression and distribution of PEPT2 mRNA and protein.
Am J Physiol Endocrinol Metab 282:E1172–E1179.
Lu H, Klaassen C. 2006. Tissue distribution and thyroid
hormone regulation of Pept1 and Pept2 mRNA in rodents.
Peptides 27:850–857.
Zhu T, Chen XZ, Steel A, Hediger MA, Smith DE. 2000.
Differential recognition of ACE inhibitors in Xenopus laevis
oocytes expressing rat PEPT1 and PEPT2. Pharm Res 17:526–
532.
Yang CY, Dantzig AH, Pidgeon C. 1999. Intestinal peptide
transport systems and oral drug availability. Pharm Res
16:1331–1343.
Groneberg DA, Fischer A, Chung KF, Daniel H. 2004. Molecular mechanisms of pulmonary peptidomimetic drug and
peptide transport. Am J Respir Cell Mol Biol 30:251–260.
Boll M, Herget M, Wagener M, Weber WM, Markovich D,
Biber J, Clauss W, Murer H, Daniel H. 1996. Expression
cloning and functional characterization of the kidney cortex
high-affinity proton-coupled peptide transporter. Proc Natl
Acad Sci 93:284–289.
¨
¨
Doring F, Walter J, Will J, Focking M, Boll M, Amasheh S,
Clauss W, Daniel H. 1998. Delta-aminolevulinic acid transport by intestinal and renal peptide transporters and its
physiological and clinical implications. J Clin Invest 101:
2761–2767.
Saito H, Terada T, Okuda M, Sasaki S, Inui K. 1996. Molecular cloning and tissue distribution of rat peptide transporter
PEPT2. Biochim Biophys Acta 1280:173–177.
¨
Groneberg DA, Nickolaus M, Springer J, Doring F, Daniel H,
Fischer A. 2001. Localization of the peptide transporter
PEPT2 in the lung: Implications for pulmonary oligopeptide
uptake. Am J Pathol 158:707–714.


98. Fei YJ, Kanai Y, Nussberger S, Ganapathy V, Leibach FH,
Romero MF, Singh SK, Boron WF, Hediger MA. 1994. Expression cloning of a mammalian proton-coupled oligopeptide
transporter. Nature 368:563–566.
99. Saito H, Okuda M, Terada T, Sasaki S, Inui K. 1995. Cloning
and characterization of a rat Hþ/peptide cotransporter mediating absorption of beta-lactam antibiotics in the intestine
and kidney. J Pharmacol Exp Ther 275:1631–1637.
100. Yang XD, Ma JY, Barger MW, Ma JK. 2002. Transport and
utilization of arginine and arginine-containing peptides by rat
alveolar macrophages. Pharm Res 19:825–831.
101. Søndergaard HB, Brodin B, Nielsen CU. 2008. hPEPT1 is
responsible for uptake and transport of Gly-Sar in the human
bronchial airway epithelial cell-line Calu-3. Pflugers Arch
456:611–622.
¨
102. Groneberg DA, Eynott PR, Doring F, Dinh QT, Oates T,
Barnes PJ, Chung KF, Daniel H, Fischer A. 2002. Distribution
and function of the peptide transporter PEPT2 in normal and
cystic fibrosis human lung. Thorax 57:55–60.
103. Granillo OM, Brahmajothi MV, Li S, Whorton AR, Mason SN,
McMahon TJ, Auten RL. 2008. Pulmonary alveolar epithelial
uptake of S-nitrosothiols is regulated by L-type amino acid
transporter. Am J Physiol Lung Cell Mol Physiol 295:L38–
L43.
´
104. Bahadduri PM, D’Souza VM, Pinsonneault JK, Sadee W, Bao
S, Knoell DL, Swaan PW. 2005. Functional characterization of
the peptide transporter PEPT2 in primary cultures of human
upper airway epithelium. Am J Respir Cell Mol Biol 32: 319–
325.
´
105. Pinsonneault J, Nielsen CU, Sadee W. 2004. Genetic variants
of the human Hþ/dipeptide transporter PET2: Analysis of
haplotype functions. J Pharmacol Exp Ther 311:1088–1096.
106. Yamashita F, Kim KJ, Lee VH. 1998. Dipeptide uptake and
transport characteristics in rabbit tracheal epithelial cell
layers cultured at an air interface. Pharm Res 15:979–983.
107. Miyazaki H, Sekine T, Endou H. 2004. The multispecific
organic anion transporter family: Properties and pharmacological significance. Trends Pharmacol Sci 25:654–662.
108. Anzai N, Kanai Y, Endou H. 2006. Organic anion transporter
family: Current knowledge. J Pharmacol Sci 100:411–426.
109. Hosoyamada M, Sekine T, Kanai Y, Endou H. 1999. Molecular
cloning and functional expression of a multispecific organic
anion transporter from human kidney. Am J Physiol
276:F122–F128.
110. Cha SH, Sekine T, Kusuhara H, Yu E, Kim JY, Kim DK,
Sugiyama Y, Kanai Y, Endou H. 2000. Molecular cloning and
characterization of multispecific organic anion transporter 4
expressed in the placenta. J Biol Chem 275:4507–4512.
111. Cha SH, Sekine T, Fukushima JI, Kanai Y, Kobayashi Y, Goya
T, Endou H. 2001. Identification and characterization of
human organic anion transporter 3 expressing predominantly
in the kidney. Mol Pharmacol 59:1277–1286.
112. Sekine T, Watanabe N, Hosoyamada M, Kanai Y, Endou H.
1997. Expression cloning and characterization of a novel
multispecific organic anion transporter. J Biol Chem
272:18526–18529.
113. Sekine T, Cha SH, Tsuda M, Apiwattanakul N, Nakajima N,
Kanai Y, Endou H. 1998. Identification of multispecific
organic anion transporter 2 expressed predominantly in the
liver. FEBS Lett 429:179–182.
114. Kusuhara H, Sekine T, Utsunomiya-Tate N, Tsuda M, Kojima
R, Cha SH, Sugiyama Y, Kanai Y, Endou H. 1999. Molecular
cloning and characterization of a new multispecific organic
anion transporter from rat brain. J Biol Chem 274: 13675–
13680.
115. Kobayashi Y, Ohshiro N, Shibusawa A, Sasaki T, Tokuyama
S, Sekine T, Endou H, Yamamoto T. 2002. Isolation, char-

DOI 10.1002/jps


116.

117.

118.

119.

120.

121.

122.

123.

124.

125.

126.

127.

acterization and differential gene expression of multispecific
organic anion transporter 2 in mice. Mol Pharmacol 62:7–14.
Youngblood GL, Sweet DH. 2004. Identification and functional assessment of the novel murine organic anion transporter Oat5 (Slc22a19) expressed in kidney. Am J Physiol
Renal Physiol 287:F236–F244.
Mikkaichi T, Suzuki T, Tanemoto M, Ito S, Abe T. 2004. The
organic anion transporter (OATP) family. Drug Metab Pharmacokinet 19:171–179.
Shitara Y, Sato H, Sugiyama Y. 2005. Evaluation of drug-drug
interaction in the hepatobiliary and renal transport of drugs.
Annu Rev Pharmacol Toxicol 45:689–723.
´
´
Poirier A, Funk C, Lave T, Noe J. 2007. New strategies to
address drug-drug interactions involving OATPs. Curr Opin
Drug Discov Dev 10:74–83.
Tamai I, Nezu J, Uchino H, Sai Y, Oku A, Shimane M, Tsuji A.
2000. Molecular identification and characterization of novel
members of the human organic anion transporter (OATP)
family. Biochem Biophys Res Commun 273:251–260.
¨
Konig J, Cui Y, Nies AT, Keppler D. 2000. A novel human
organic anion transporting polypeptide localized to the basolateral hepatocyte membrane. Am J Physiol Gastrointest
Liver Physiol 278: G156–G164.
Pizzagalli F, Hagenbuch B, Stieger B, Klenk U, Folkers G,
Meier PJ. 2002. Identification of a novel human organic anion
transporting polypeptide as a high affinity thyroxine transporter. Mol Endocrinol 16:2283–2296.
Suzuki T, Onogawa T, Asano N, Mizutamari H, Mikkaichi T,
Tanemoto M, Abe M, Satoh F, Unno M, Nunoki K, Suzuki M,
Hishinuma T, Goto J, Shimosegawa T, Matsuno S, Ito S, Abe
T. 2003. Identification and characterization of novel rat and
human gonad-specific organic anion transporters. Mol Endocrinol 17:1203–1215.
Lee SY, Williamson B, Caballero OL, Chen YT, Scanlan MJ,
Ritter G, Jongeneel CV, Simpson AJ, Old LJ. 2004. Identification of the gonad-specific anion transporter SLCO6A1 as a
cancer/testis (CT) antigen expressed in human lung cancer.
Cancer Immun 4:13.
Kullak-Ublick GA, Ismair MG, Stieger B, Landmann L, Huber
R, Pizzagalli F, Fattinger K, Meier PJ, Hagenbuch B. 2001.
Organic anion-transporting polypeptide B (OATP-B) and its
functional comparison with three other OATPs of human
liver. Gastroenterology 120:525–533.
Adachi H, Suzuki T, Abe M, Asano N, Mizutamari H, Tanemoto M, Nishio T, Onogawa T, Toyohara T, Kasai S, Satoh F,
Suzuki M, Tokui T, Unno M, Shimosegawa T, Matsuno S, Ito
S, Abe T. 2003. Molecular characterization of human and rat
organic anion transporter OATP-D. Am J Physiol Renal Physiol 285:F1188–F1197.
Fujiwara K, Adachi H, Nishio T, Unno M, Tokui T, Okabe M,
Onogawa T, Suzuki T, Asano N, Tanemoto M, Seki M, Shiiba
K, Suzuki M, Kondo Y, Nunoki K, Shimosegawa T, Iinuma K,

DOI 10.1002/jps

128.

129.

130.

131.

132.

133.

134.

135.

136.

137.

138.

2255

Ito S, Matsuno S, Abe T. 2001. Identification of thyroid
hormone transporters in humans: Different molecules are
involved in a tissue-specific manner. Endocrinology
142:2005–2012.
Nishio T, Adachi H, Nakagomi R, Tokui T, Sato E, Tanemoto
M, Fujiwara K, Okabe M, Onogawa T, Suzuki T, Nakai D,
Shiiba K, Suzuki M, Ohtani H, Kondo Y, Unno M, Ito S,
Iinuma K, Nunoki K, Matsuno S, Abe T. 2000. Molecular
identification of a rat novel organic anion transporter moat1,
which transports prostaglandin D(2), leukotriene C(4), and
taurocholate. Biochem Biophys Res Commun 275:831–838.
Cooray HC, Shahi S, Cahn AP, van Veen HW, Hladky SB,
Barrand MA. 2006. Modulation of p-glycoprotein and breast
cancer resistance protein by some prescribed corticosteroids.
Eur J Pharmacol 531:25–33.
Dilger K, Schwab M, Fromm MF. 2004. Identification of
budesonide and prednisone as substrates of the intestinal
drug efflux pump P-glycoprotein. Inflamm Bowel Dis
10:578–583.
Arya V, Issar M, Wang Y, Talton JD, Hochhaus G. 2005. Brain
permeability of inhaled corticosteroids. J Pharm Pharmacol
57:1159–1167.
´
´
Valenzuela B, Nacher A, Ruiz-Carretero P, Martın-Villodre A,
´
Lopez-Carballo G, Barettino D. 2004. Profile of P-glycoprotein
distribution in the rat and its possible influence on the salbutamol intestinal absorption process. J Pharm Sci 93: 1641–
1648.
Akan I, Akan S, Akca H, Savas B, Ozben T. 2004. N-acetylcysteine enhances multidrug resistance-associated protein 1
mediated doxorubicin resistance. Eur J Clin Invest 34:683–
689.
Banerjee SK, Jagannath C, Hunter RL, Dasgupta A. 2000.
Bioavailability of tobramycin after oral delivery in FVB mice
using CRL-1605 copolymer, an inhibitor of P-glycoprotein.
Life Sci 67:2011–2016.
Ando T, Kusuhara H, Merino G, Alvarez AI, Schinkel AH,
Sugiyama Y. 2007. Involvement of breast cancer resistance
protein (ABCG2) in the biliary excretion mechanism of fluoroquinolones. Drug Metab Dispos 35:1873–1879.
Marquez B, Caceres NE, Mingeot-Leclercq MP, Tulkens PM,
Van Bambeke F. 2009. Identification of the efflux transporter
of the fluoroquinolone antibiotic ciprofloxacin in murine
macrophages: Studies with ciprofloxacin-resistant cells. Antimicrob Agents Chemother 53:2410–2416.
Hirano T, Yasuda S, Osaka Y, Asari M, Kobayashi M, Itagaki
S, Iseki K. 2008. The inhibitory effects of fluoroquinolones on
L-carnitine transport in placental cell line BeWo. Int J Pharm
351:113–118.
Ming X, Ju W, Wu H, Tidwell RR, Hall JE, Thakker DR. 2009.
Transport of dicationic drugs pentamidine and furamidine by
human organic cation transporters. Drug Metab Dispos
37:424–430.


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