1. Introduction
The optimal function of placenta, the organ forming materno-fetal
interface, is necessary for the proper growth and development of fetus.
One of the important roles of this tissue is to ensure a sufficient
supply of nutrients and oxygen to the fetus, while enabling removal of
potentially toxic xenobiotics, waste compounds and fetal metabolites
back to the maternal blood.1 Although many endogenous
and exogenous molecules permeate placenta by simple diffusion, membrane
transporters localized in the trophoblast layer are critical for
ensuring their sufficient transplacental transfer.2,3
This study concerns the organic cation transporter novel type (OCTN)
subfamily, in particular its two members, OCTN1 and OCTN2 (encoded bySLC22A4 and SLC22A5 , respectively).4-6OCTN2 localized in the maternal blood facing microvillous membrane of
trophoblast is responsible for the sodium-dependent transport of
L-carnitine.7-9 This molecule plays essential role in
placental energy supply when ensuring transport of long chain fatty
acids for their mitochondrial β-oxidation.10 Defects
in the OCTN2 transporter were shown to be associated with maternal
complications in pregnancy and to have severe impact on reproductive
capacity in OCTN2 knock-out mice, thereby confirming placental uptake of
carnitine is pivotal for fetal organism.11 The
physiological role of OCTN1 is not yet completely
understood5, even though the transporter is believed
to be highly specific for ergothioneine, a natural compound acting as
intracellular antioxidant.12 In several non-placental
tissues, OCTN1 has been recently revealed as an important protective
component against oxidative stress5,13 and shown to
ensure anti-inflammatory effect.14,15 As shown
previously, human term placenta expresses one order of magnitude lower
number of OCTN1 mRNA transcripts thanOCTN2 .6,16 Analogically, lower levels ofOCTN1 than OCTN2 have been also found in BeWo cells, one
of the commonly used placental cellular models.16Besides uptake of ergothioneine, OCTN1 can also contribute to
L-carnitine transmembrane transfer, albeit as rather low-affinity
transporter.13,14 Moreover, OCTN1 was described as
potential transporter of wide range of nucleosides.17Both, OCTN1 as well as OCTN2 have been also shown to interact with
drugs, potentially affecting their transplacental pharmacokinetics and
fetal exposure.18,19
At the end of pregnancy, an inflammatory process is physiologically
triggered to stimulate labor, nonetheless, it can also appear in the
early stages or during pregnancy for pathophysiological reasons. The
origin of inflammation can be either bacterial or sterile and in both
cases can be linked to pathological pregnancies, such as preterm birth,
fetal growth restriction, stillbirth and
preeclampsia20-24 and can lead also to long-term
adverse outcomes in adulthood.25,26 Bacterial
inflammation occurs in the presence of an infectious agent and is mostly
mediated by so called pathogen‐associated molecular pattern molecules
(PAMPs), comprising among others bacterial lipopolysaccharide (LPS)
identified through the TLR-4 receptor.27 In contrary,
sterile inflammation is characterized by the absence of a clinical signs
of infection, but by the elevated levels of danger-associated molecular
patterns (DAMPs) or alarmins in the maternal blood.28Both, DAMPs and PAMPs activate nuclear factor kappa B (NF-κB) leading to
an increase in cytokine-mediated inflammatory
responses.29,30 It is known that both types of
inflammation, whether sterile, possibly modeled by alarmin release
stimulated e.g. by high mobility group box 1 (HMGB1) or bacterial
inflammation, which can be modeled by LPS, lead through NF-κB activation
to the release of a number of cytokines such as IL-6, IFN-γ,
TNF-α.31 It is, however, not clear whether the
placental OCTN1 and OCTN2-mediated transport can be affected as well or
the transporters might be even directly involved in the placental
pathophysiology.
In the present study, we hypothesized that inflammatory conditions could
change the expression of OCTN transporters. We therefore employedin vitro models of human placental cells, as well as ex
vivo cultured placental villous explants. Three placental models
including the immortalized first trimester trophoblast cell line
(HTR-8/SVneo), choriocarcinoma cell line (BeWo) and ex vivocultured placental villous explants were treated by several
pro-inflammatory cytokines (IL-6, IFN-γ, TNF-α) and inflammation
stimulants (LPS and HMGB1) and the mRNA expression of OCTN1 andOCTN2 was evaluated. This study is the first to investigate the
possible effects of pro-inflammatory environment in the gene expression
of OCTN1/2 transporters.