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.