The BeWo choriocarcinoma cell line as a model of iodide transport by placenta

Iodine and Thyroid Maternal and Fetal Metabolism during Pregnancy

Thyroid hormones and iodine are required to increase basal metabolic rate and to regulate protein synthesis, long bone growth and neuronal maturation. They are also essential for protein, fat and carbohydrate metabolism regulation. Imbalances in thyroid and iodine metabolism can negatively affect these vital functions. Pregnant women are at risk of hypo or hyperthyroidism, in relation to or regardless of their medical history, with potential dramatic outcomes. Fetal development highly relies on thyroid and iodine metabolism and can be compromised if they malfunction. As the interface between the fetus and the mother, the placenta plays a crucial role in thyroid and iodine metabolism during pregnancy. This narrative review aims to provide an update on current knowledge of thyroid and iodine metabolism in normal and pathological pregnancies. After a brief description of general thyroid and iodine metabolism, their main modifications during normal pregnancies and the placental molecular actors are described. We then discuss the most frequent pathologies to illustrate the upmost importance of iodine and thyroid for both the mother and the fetus.

Defending Effects of Iodide Transfer in Placental Barrier Against Maternal Iodine Deficiency

Objective: Placental iodide transport is necessary for maintaining an adequate iodide supply to the developing fetus. We hypothesized that compounds from the placental barrier can compensate for decreases in maternal iodine intake and normalize fetal iodine levels. Methods: Pregnant rats administered different amounts of iodine (1.24, 2.5, 5, or 10 μg/day) were evaluated on gestational day (gd) 16 and 20. The iodine levels in maternal blood, amniotic fluid (AF), and placental tissue were estimated using As-Ce catalytic spectrophotometry. The protein and/or messenger RNA (mRNA) levels of sodium iodide symporter (NIS), pendrin, alpha-smooth muscle actin (α-SMA), and CD31 in the placental labyrinth, trophoblast cells isolated using laser capture microdissection (LCM), and/or fetomaternal thyroid were detected using immunoblotting, real-time polymerase chain reaction, and/or immunohistochemistry. Results: When iodine intake was reduced, iodine levels in maternal blood gradually decreased; however, placental iodine levels were not significantly different between groups on gd16 and gd20. Minimal changes were observed in AF iodine levels on gd16, and a mild decreasing trend was observed (iodine dose, 10 to 1.24 μg/day) on gd20. NIS protein, which was linearly distributed along the basolateral membrane of maternal-fetal thyroid follicles, gradually increased with decreasing iodine levels. Regarding iodine deficiency in the placental labyrinth on gd16 and gd20, pendrin and glycosylated NIS proteins were significantly upregulated in a dose-dependent manner. However, the mRNA levels were unchanged. Furthermore, the conversion of NIS protein from the nonglycosylated to the glycosylated form increased. In trophoblast cells isolated using LCM, PDS mRNA levels increased in the 1.24-μg/day group on gd16 but not NIS mRNA levels. There was a smaller α-SMA+ area in the labyrinth zone on gd16 and gd20; however, the proportional CD31+ area increased on gd16 and reduced on gd20 with decreased iodine levels. Conclusions: All mechanisms upregulating the expression of iodine transporters and changes in villous stroma and microvessel area in the placental labyrinth can promote iodide transfer from mother to fetus in iodine deficiency, especially before the onset of fetal thyroid function. Compensatory NIS protein regulation in the placenta against decreased iodine intake mainly occurs during translation and glycosylation modification after translation. Pendrin may be more important than NIS in the mediation of placental iodide transport.

Divergence of Iodine and Thyroid Hormones in the Fetal and Maternal Parts of Human-Term Placenta

The human placenta is an important organ that forms a barrier where maternal and fetal exchange takes place. The placenta transport iodine to the fetal circulation by transfer of maternal iodine and deiodination of thyroid hormones (THs). The aim of the study was to examine the distribution of iodine and thyroid hormone transporters in the maternal and fetal sides of human-term placenta. A cross-sectional study was performed at the First Affiliated Hospital of China Medical University. Placental samples (maternal and fetal surfaces) were collected from 113 healthy-term pregnant women. The iodine content; the concentration of thyroxine (T4), triiodothyronine (T3), and reverse T3 (rT3); and the enzyme activity of placental type 2 iodothyronine deiodinase (D2) and D3 were examined. The mRNA and protein localization/expression of iodine and thyroid hormone transporters in the placenta were also studied. We also analyzed the association between expression level of Na+/I- symporter (NIS), thyroid hormone transporter protein, D3 activity in maternal and fetal surfaces of placenta with iodine content, and thyroid hormone levels. Iodine levels in placental samples from the maternal side were significantly higher than those in samples from the fetal side. T3 and T4 expression in fetal placenta was significantly lower than in maternal placenta. D3 activity in the fetal side of the placentas was significantly higher than that in the maternal side. The mRNA and protein expression of monocarboxylate transporters 8 (MCT8), L-amino acid transporters 1 (LAT1), organic anion transporting polypeptides 4A1 (OATP4A1), and TH binding protein transthyretin (TTR) were significantly increased in maternal side, while the NIS expression was higher in fetal side of human-term placenta. In conclusion, the enzymatic deiodination of thyroid hormones forms a barrier which reduces transplacental passage of the hormones and that the maternal part of the placenta is the primary factor in the mechanism regulating the hormonal transfer.

Thyroid hormones and female reproduction

Thyroid hormones are vital for the proper functioning of the female reproductive system, since they modulate the metabolism and development of ovarian, uterine, and placental tissues. Therefore, hypo- and hyperthyroidism may result in subfertility or infertility in both women and animals. Other well-documented sequelae of maternal thyroid dysfunctions include menstrual/estral irregularity, anovulation, abortion, preterm delivery, preeclampsia, intrauterine growth restriction, postpartum thyroiditis, and mental retardation in children. Several studies have been carried out involving prospective and retrospective studies of women with thyroid dysfunction, as well as in vivo and in vitro assays of hypo- and hyperthyroidism using experimental animal models and/or ovarian, uterine, and placental cell culture. These studies have sought to elucidate the mechanisms by which thyroid hormones influence reproduction to better understand the physiology of the reproductive system and to provide better therapeutic tools for reproductive dysfunctions that originate from thyroid dysfunctions. Therefore, this review aims to summarize and update the available information related to the role of thyroid hormones in the morphophysiology of the ovary, uterus, and placenta in women and animals and the effects of hypo- and hyperthyroidism on the female reproductive system.

Changes in trophoblasts gene expression in response to perchlorate exposition

Contaminated water with chlorates is a public health problem associated with iodine deficiency. Epidemiological evidence shows that iodine deficiency is a risk factor for preeclampsia (PE). In this study we use human BeWo trophoblast cells exposed to perchlorate (KClO₄) and changes in gene expression were analyzed by microarrays, quantitative RT-PCR (qRT-PCR) and immunoblot. The microarray analysis identified 48 transcripts up-regulated and 112 down-regulated in comparison with non-exposed trophoblast. The qRT-PCR analysis confirmed changes in GAS7, PKP2, Emilin, Dynatic 3, protocadherins 11, 15, gamma A12, EGFR, SAFB1, ACE2, ANXA2, Apoliprotein E, SREBF1, and C/EBP-β. KClO₄ exposition decreased the mRNA and protein of C/EBP-β and GPX4. Also, we observed a nuclear translocation of HIF1α protein, and increase in both Snail and ACE2 protein by immunoblot. These effects were accompanied by an increases in ROS and nitric oxide. In conclusion, our results show that exposure to KClO₄ alters genes involved in migration, adhesion, differentiation, and correlate with the increase of oxidative stress and nitric oxide production in trophoblast cells. It is possible that iodine deficiency is associated with these processes. However, further studies are required to corroborate the role of iodine in trophoblast cells.

The effect of smoking on placental pendrin expression

Pendrin is important for transport of iodine across the placenta. Thiocyanate coming from cigarette is a competitive inhibitor of iodine transport. We aimed to evaluate the pendrin immunostaining intensity in placentas of smoker and non-smoker women. Placental tissues from 61 women, of which 28 were in smoking, and 33 were in non-smoking group were evaluated by immunohistochemical staining. Positive immunostaining was evaluated using a semiquantitative score: 0, negative; +, mild; ++, moderate; and +++, intense. Birth weight was significantly lower in the smoker group (p = 0.024). There was a negative correlation between birth weight and intensity of placental pendrin immunostaining in the smoker group (r = -0.44, p = 0.02). Placentas of the smoking women showed significantly higher immunostaining with pendrin than the control group (p = 0.006). Thiocyonate coming from cigarettes may competitively inhibit pendrin mediated iodine transport in the placenta and adversely affect foetal development by this mechanism.

Glucocorticoid receptor-mediated insulin-like growth factor-I transcriptional regulation in BeWo trophoblast cells before and after syncytialisation

Prenatal exposure to excessive glucocorticoids (GCs) leads to intrauterine growth retardation and fetal programming of adult health and disease through deregulation of placental functions. Placental secretion of insulin-like growth factor-I (IGF-I) plays a critical role in the regulation of placental development and function. However, it remains elusive whether GCs affect placental functions through glucocorticoid receptor (GR)-mediated transcriptional regulation of IGF-I gene. In this study, human placental choriocarcinoma (BeWo) cells before and after syncytialization were used as cytotrophoblast and syncytiotrophoblast models, respectively, to explore the effects of dexamethasone (Dex) on transcriptional regulation of IGF-I gene at both stages. Dex significantly inhibited (P<0.05) cell proliferation in cytotrophoblasts and down-regulated amino acid transporter SLC7A5 in syncytiotrophoblasts. Concurrently, the abundance of IGF-I mRNA and its transcript variants, together with IGF-I level in culture media, were significantly reduced, in association with significantly enhanced (P<0.05) GR phosphorylation. GR antagonist RU486 was able to abolish all these effects. Two glucocorticoid response elements (GREs) were predicted in the promoter regions of IGF-I gene. GR binding to GRE1 was significantly enriched (P<0.05) in both cytotrophoblasts and syncytiotrophoblasts, but that to GRE2 was significantly diminished (P<0.05) in cytotrophoblasts but not in syncytiotrophoblasts, in response to Dex treatment. IGF-I supplementation completely rescued Dex-induced cell cycle arrest but not SLC7A5 down-regulation, indicating different regulatory mechanisms. Taken together, our results suggest that GR-mediated transcriptional regulation of IGF-I is involved in Dex-induced inhibition of placental cell proliferation and function.

Iodine Affects Differentiation and Migration Process in Trophoblastic Cells

Iodine deficiency is associated with oxidative stress increase and preeclampsia during gestation, suggesting that iodine concentration plays an important role in the normal placenta physiology. The question raised is to analyze the effect of iodine deficiency on oxidative stress, viability, differentiation, and migration process and changes in the expression of differentiation and migration markers. Iodine deprivation was done using potassium perchlorate (KCLO4) to block sodium iodide symporter (NIS) transporter and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid DIDS to inhibit pendrine (PEN) transport for 3-48 h. Then trophoblast cells were treated with low iodine doses of 5-500 μM and high iodine doses of 100-5000 μM. Oxidative stress, viability, and human chorionic gonadotropin (hGC) were measured by colorimetric methods. Migration throphoblast cells were evaluated by both wound healing and Boyden chamber assays. Changes in mRNA expression were analyzed by real-time RT-PCR. Iodine deprivation induces a significant increase of reactive oxygen species (ROS), viability, and migration process vs control cells. We found a significant overregulation in the mRNA's peroxisome proliferator-activated receptor (PPAR-gamma), Snail, and matrix metalloproteinase-9 (MMP-9) mRNA's in cells deprived of iodine, as well as a down glial cell missing-1 (GCM-1) regulation, hGC, pregnancy-associated plasma protein-A (PAPP-A), and E-cadherin mRNA expression. The expression of hypoxic induction factor alpha (HIFα) mRNA does not change with iodine deprivation. In cells deprived of iodine, supplementing low iodine doses (5-500 μM) does not induce any significant changes in viability. However, ROS and migration process were decreased, although we found an increased human chorionic gonadotropin (hCG) secretion as a differentiation marker. In addition, we found that PPAR-gamma, Snail, and MPP-9 mRNAs expression are downregulated with low iodine doses, in contrast with GCM-1, PAPP-A, hGC, and E-cadherin that increase their expression vs cells deprived of iodine. High iodine doses (1000-5000 μM) have shown cytotoxic effects. Based on our results, iodine is important for keeping the proliferation/differentiation balance in the placenta.

Molecular basis of thyrotropin and thyroid hormone action during implantation and early development

BACKGROUND

Implantation and early embryo development are finely regulated processes in which several molecules are involved. Evidence that thyroid hormones (TH: T4 and T3) might be part of this machinery is emerging. An increased demand for TH occurs during gestation, and any alteration in maternal thyroid physiology has significant implications for both maternal and fetal health. Not only overt but also subclinical hypothyroidism is associated with infertility as well as with obstetric complications, including disruptions and disorders of pregnancy, labor, delivery, and troubles in early neonatal life.

METHODS

We searched the PubMed and Google Scholar databases for articles related to TH action on ovary, endometrium, trophoblast maturation and embryo implantation. In addition, articles on the regulation of TH activity at cellular level have been reviewed. The findings are hereby summarized and critically discussed.

RESULTS

TH have been shown to influence endometrial, ovarian and placental physiology. TH receptors (TR) and thyrotropin (thyroid-stimulating hormone: TSH) receptors (TSHR) are widely expressed in the feto-maternal unit during implantation, and both the endometrium and the trophoblast might be influenced by TH either directly or through TH effects on the synthesis and activity of implantation-mediating molecules. Interestingly, due to the multiplicity of mechanisms involved in TH action (e.g. differential expression of TR isoforms, heterodimeric receptor partners, interacting cellular proteins, and regulating enzymes), the TH concentration in blood is not always predictive of their cellular availability and activity at both genomic and nongenomic level.

CONCLUSIONS

In addition to the known role of TH on the hormonal milieu of the ovarian follicle cycle, which is essential for a woman's fertility, evidence is emerging on the importance of TH signaling during implantation and early pregnancy. Based on recent observations, a local action of TH on female reproductive organs and the embryo during implantation appears to be crucial for a successful pregnancy. Furthermore, an imbalance in the spatio-temporal expression of factors involved in TH activity might induce early arrest of pregnancy in women considered as euthyroid, based on their hormonal blood concentration. In conclusion, alterations of the highly regulated local activity of TH may play a crucial, previously underestimated, role in early pregnancy and pregnancy loss. Further studies elucidating this topic should be encouraged.

Regulation of iodide uptake in placental primary cultures

BACKGROUND

Maintenance of adequate iodide supply to the developing fetus is dependent not only on maternal dietary iodine intake but also on placental iodide transport. The objective of this study was to examine the effects of different pregnancy-associated hormones on the uptake of radioiodide by the placenta and to determine if iodide transporter expression is affected by hormone incubation.

METHODS

Primary cultures of placental trophoblast cells were established from placentas obtained at term from pre-labor caesarean sections. They were pre-incubated with 17β-estradiol, prolactin, oxytocin, human chorionic gonadotropin (hCG) and progesterone either singly or in combination over 12 h with (125)I uptake being measured after 6 h. RNA was isolated from placental trophoblasts and real-time RT-PCR performed using sodium iodide symporter (NIS) and pendrin (PDS) probes.

RESULTS

Significant dose response increments in (125)I uptake by trophoblast cells (p < 0.01) were observed following incubation with hCG (60% increase), oxytocin (45% increase) and prolactin (32% increase). Although progesterone (50-200 ng/ml) and 17β-estradiol (1,000-15,000 pg/ml) alone produced no significant differences in uptake, they facilitated increased uptake when combined with prolactin or oxytocin, with a combination of all four hormones producing the greatest increase (82%). Increased (125)I uptake was accompanied by corresponding increments in NIS mRNA (ratio 1.52) compared to untreated control cells. No significantly increased expression levels of PDS were observed.

CONCLUSIONS

Pregnancy-associated hormones, particularly oxytocin and hCG, have a role in promoting placental iodide uptake which may protect the fetus against iodine deficiency.

Alterations in placental pendrin expression in pre-eclampsia

INTRODUCTION

Pendrin is an integral membrane protein and plays a key role in extracellular fluid volume and blood pressure control. We aimed to investigate the relationship between pendrin immunostaining intensity in normal and pre-eclamptic placental tissue.

METHODS

Fifty-six placental tissues, of which 26 were in pre-eclamptic, and 30 were in control group were evaluated by immunohistochemical staining. Positive immunostaining was evaluated using a semiquantitative score: 0, negative; +, mild; ++, moderate; and +++, intense.

RESULTS

There was more positive immunstaining in the pre-eclamptic placenta compared to the controls (p<0.001). A significant positive correlation was observed between immunostaining level and diastolic blood pressure (r=0.533, p=0.005) in the pre-eclamptic group. However, no significant correlation was observed between any condition and immunostaining level in the control group.

CONCLUSIONS

Placentas in the pre-eclamptic group were significantly more immunostained with pendrin than were those in the control group. In addition, a positive correlation between immunostaining intensity with pendrin and both systolic and diastolic blood pressure were observed. Pendrin may play a role in the mechanism of severe hypertension in women with pre-eclampsia.

Thyroglobulin in smoking mothers and their newborns at delivery suggests autoregulation of placental iodide transport overcoming thiocyanate inhibition

BACKGROUND

Placental transport of iodide is required for fetal thyroid hormone production. The sodium iodide symporter (NIS) mediates active iodide transport into the thyroid and the lactating mammary gland and is also present in placenta. NIS is competitively inhibited by thiocyanate from maternal smoking, but compensatory autoregulation of iodide transport differs between organs. The extent of autoregulation of placental iodide transport remains to be clarified.

OBJECTIVE

To compare the impact of maternal smoking on thyroglobulin (Tg) levels in maternal serum at delivery and in cord serum as markers of maternal and fetal iodine deficiency.

METHODS

One hundred and forty healthy, pregnant women admitted for delivery and their newborns were studied before the iodine fortification of salt in Denmark. Cotinine in urine and serum classified mothers as smokers (n=50) or nonsmokers (n=90). The pregnant women reported on intake of iodine-containing supplements during pregnancy and Tg in maternal serum at delivery and in cord serum were analyzed.

RESULTS

In a context of mild-to-moderate iodine deficiency, smoking mothers had significantly higher serum Tg than nonsmoking mothers (mean Tg smokers 40.2 vs nonsmokers 24.4 μg/l, P=0.004) and so had their respective newborns (cord Tg 80.2 vs 52.4 μg/l, P=0.006), but the ratio between Tg in cord serum and maternal serum was not significantly different in smokers compared with nonsmokers (smoking 2.06 vs nonsmoking 2.22, P=0.69).

CONCLUSION

Maternal smoking increased the degree of iodine deficiency in parallel in the mother and the fetus, as reflected by increased Tg levels. However, placental iodide transport seemed unaffected despite high thiocyanate levels, suggesting that thiocyanate-insensitive iodide transporters alternative to NIS are active or that NIS in the placenta is autoregulated to keep iodide transport unaltered.

Pendrin mediates uptake of perchlorate in a mammalian in vitro system

Perchlorate is a known endocrine disruptor present in groundwater, vegetables and dairy food products in many regions of the United States. It interferes with the uptake of iodide into the thyrocyte by the sodium-iodide symporter at the basolateral surface, thus potentially disrupting the synthesis of thyroid hormone. Because transport of iodide from the thyroid follicular cells to the follicular lumen is mediated by the protein pendrin at the apical surface, we hypothesized that perchlorate may also interact with this protein. Therefore, HeLa cells were transfected with the human SLC26A4 gene, which encodes pendrin, to generate an in vitro mammalian system expressing the recombinant pendrin protein (HeLa-PDS). The HeLa-PDS cells, along with untransfected cells, were then cultured in presence of iodide and/or perchlorate. Intracellular levels of these two chemicals were measured by ion chromatography tandem mass spectrometry. Results from this study show that iodide and perchlorate uptake increases significantly in HeLa-PDS cells as compared to untransfected cells. Thus, recombinant HeLa cells expressing pendrin protein accumulate iodide and perchlorate intracellularly, indicating that pendrin is involved in the uptake of perchlorate. Additional results from this study suggest that iodide and perchlorate competitively inhibit each other for uptake by pendrin. The ability of perchlorate to compete with iodide for uptake by both basal and apical transporters may increase the potential of perturbation of thyroid homeostasis and therefore the estimated risk posed to susceptible human populations.

Effect of oxygen concentrations on sodium iodide symporter expression and iodide uptake and hCG expression in human choriocarcinoma BeWo cells

Normal human fetal development requires an adequate supply of thyroid hormone from conception. Until about 16 wk gestation this is supplied entirely by placental transfer of maternal hormone. Subsequently, the fetal thyroid synthesizes thyroid hormones, requiring a supply of maternal iodide. Trophoblast iodide transfer is mediated by the apical sodium iodide symporter (NIS). Placental oxygen levels are low in early pregnancy (~1%), rising with placental vascularisation to a plateau of ~8% at about 16 wk. Although the impact of these changing oxygen levels on placental implantation is well recognized, effects on trophoblast materno-fetal exchange are less understood. We investigated expression of the NIS regulator hCG, NIS mRNA expression, and I(125) uptake in choriocarcinoma BeWo cells (a model of the trophoblast) cultured in 1 and 8% oxygen and in room air (21% oxygen). Expression of NIS and hCG mRNA and protein was low at 1% oxygen but rose significantly at 8 and at 21%. This was reflected in significant increases in I(125) uptake. Desferrioxamine, an iron chelator and hypoxia mimic, decreased NIS and hCG expression and I(125) uptake in BeWo cells. NIS expression and I(125) uptake in cells grown at 1% oxygen were not increased by addition of hCG (2,500 IU/l). We infer that placental NIS mRNA and protein expression are regulated by oxygen, rising with vascularization of the placenta in the late first trimester, a time when fetal iodide requirements are increasing.

The placenta as a compensatory iodine storage organ

BACKGROUND

The production of iodine-containing thyroid hormones necessary for brain development in the fetus depends not only on maternal dietary intake but also on placental iodine transport. The optimum level of iodine nutrition during pregnancy and the proportion of the pregnant population reaching this level have previously been evaluated. Little information exists on the ability of the placenta to either accumulate or store iodine. This study aims to investigate iodine uptake and tissue iodine content within placental tissue obtained from women delivering at term.

METHODS

Samples (∼1 cm(3)) obtained from placental cotyledons (n = 19), thyroid (n = 4), and uterine myometrial (n = 4) tissue were incubated for 6 hours with (125)I in the presence and absence of potassium perchlorate. To account for variation in tissue composition, results were expressed in cpm (125)I/μg DNA.

RESULTS

Placental uptake of (125)I (375 cpm/μg DNA) was significantly higher than that of control myometrial tissue (226 cpm/μg DNA) (p < 0.05) and was ∼25% that of thyroid tissue (1702 cpm/μg DNA). Uptake of (125)I could be partially blocked in the thyroid and placenta, respectively, by potassium perchlorate (100 μM), which had no effect on uptake by myometrial tissue. Iodine content of tissue samples measured using an alkaline ashing technique with Sandell-Kolthoff colorimetry gave a mean value for total iodine of 30.4 ng/g placental tissue (range 21-50 ng/g), 1.74 ng/g myometrial tissue, and 1037 ng/g thyroid tissue.

CONCLUSIONS

Placental iodine content was only ∼3% that of the thyroid, but on the basis that neonatal iodine stores are very low and highly sensitive to fluctuations in maternal iodine supply, we postulate that placental iodine bioavailability makes a significant contribution to protection against neonatal hypothyroidism. These findings suggest that the placenta has a role not only in uptake but also in storing iodine as a possible means of protecting the fetus from inadequacies in maternal dietary iodine intake.

Myostatin regulates glucose uptake in BeWo cells

Myostatin is a member of the transforming growth factor (TGF)-beta superfamily, known for its ability to inhibit muscle growth. It can also regulate metabolism and glucose uptake in a number of tissues. To determine the mechanism of myostatin's effect on glucose uptake, we evaluated its actions using choriocarcinoma cell lines that are widely used as models for placental cells. Protein and mRNA were determined using immunoblotting and RT-PCR/PCR, respectively. Glucose uptake was assessed by uptake of radiolabeled deoxyglucose in vitro. All choriocarcinoma cell lines tested i.e., BeWo, JEG, and Jar, are used as models of placental cells, and all expressed myostatin protein and mRNA. Treatment of BeWo cells with myostatin resulted in inhibition of glucose uptake in a concentration-dependent manner (P < 0.01). At all concentrations tested, follistatin, a functional inhibitor of myostatin, completely blocked the inhibitory effect of myostatin (40 nM) on glucose uptake by BeWo cells (0.4 nM, P < 0.05). Follistatin treatment alone also increased glucose uptake (0.4 and 4 nM, P < 0.001; 40 nM, P < 0.05). Because BeWo cells proliferated and greater cell densities were achieved, glucose uptake declined irrespective of treatment. Myostatin treatment of BeWo cells did not alter the levels of myostatin receptor, ActRII A/B proteins. The levels of glucose transport proteins also remained unaltered in BeWo cells with myostatin treatment. This study has shown that myostatin specifically inhibits glucose uptake into BeWo cells, suggesting that locally produced myostatin may control glucose metabolism within the placenta.

Effect of Iodide on Human Choriogonadotropin, Sodium-Iodide Symporter Expression, and Iodide Uptake in BeWo Choriocarcinoma Cells

CONTEXT

Active placental transport of maternal iodide by the thyroidal sodium iodide symporter (NIS) provides an essential substrate for fetal thyroid hormone synthesis. NIS is expressed in trophoblast and is regulated by human choriogonadotropin (hCG). In thyroid, iodide down-regulates expression of several genes including NIS. Placentas of iodine-deficient rats demonstrate up-regulation of NIS mRNA, suggesting a role for iodide in regulating placental NIS.

OBJECTIVES AND METHODS

The objectives were to examine effects of iodide on expression of NIS and hCG in BeWo choriocarcinoma cells. Gene expression was studied by quantitative real-time PCR. Effects on NIS protein expression were assessed by Western blotting. Functional activity of NIS was measured by (125)I uptake. Expression of hCG protein was assessed by immunoassay of secreted hormone.

RESULTS

Iodide inhibited NIS mRNA and membrane protein expression as well as (125)I uptake, which were paralleled by decreased betahCG mRNA expression and protein secretion. Iodide had no effects on pendrin expression. Addition of hCG increased NIS mRNA expression. This effect was partially inhibited by addition of iodide. The inhibitory effects of iodide on NIS mRNA expression were abolished by propylthiouracil and dithiothreitol.

CONCLUSIONS

We conclude that expression of placental NIS is modulated by maternal iodide. This may occur through modulation of hCG effects on NIS and hCG gene expression.

Kinetic analysis of the transport of salicylic acid, a nonsteroidal anti-inflammatory drug, across human placenta

The aim of this study was to develop a pharmacokinetic model to describe the transplacental transfer of drugs, based on the human placental perfusion study. The maternal and fetal sides of human placentas were perfused with salicylic acid together with antipyrine, a passive diffusion marker. The drug concentration in the placental tissue was determined at the end of perfusion. A compartment model consisting of maternal space, fetal intravascular space, and placental tissue was fitted to the observed concentration profiles of salicylic acid in the maternal and fetal effluents. The developed model could adequately explain the concentration profiles of salicylic acid in the effluents with influx clearances from maternal and fetal perfusates to placental tissue of 0.0407 and 0.0813 ml/min/g cotyledon and efflux rate constants from placental tissue to maternal and fetal perfusates (k2 and k3) of 0.0238 and 0.176 min(-1), respectively. The kinetics of antipyrine was adequately described by assuming rapid equilibrium between fetal perfusate and placental tissue compartments. The influx plasma clearance from the maternal side (K''1) in humans was estimated by taking into account the protein binding. The K''1/k2 value of salicylic acid was 1.07 ml/g cotyledon and was larger than that of antipyrine (0.642 ml/g cotyledon). We evaluated the transplacental transfer kinetics of salicylic acid by human placental perfusion study with various perfusion protocols. Based on the data obtained, we developed a pharmacokinetic model, which should enable us to estimate the influx profile of drugs into umbilical arterial blood from the maternal plasma concentration profile.

Functional characterization of a human organic anion transporter hOAT4 in placental BeWo cells

Human organic anion transporter 4 (hOAT4) belongs to a family of organic anion transporters which play critical roles in the body disposition of clinically important drugs, including anti-HIV therapeutics, anti-tumor drugs, antibiotics, anti-hypertensives, and anti-inflammatories. hOAT4 is expressed in the placenta and kidney. In the current study, we stably transfected hOAT4 into human placental BeWo cells and the functional properties of hOAT4 and its regulation were investigated in these cells. hOAT4-mediated uptake of estrone sulfate, a protypical organic anion for hOAT4, was dose- and time-dependent, and saturable (Km=4.2 microM). The substrate specificity of hOAT4 includes various steroid sulfates, such as beta-estradiol-3,17-disulfate, 17-beta-estradiol-3-sulfate, beta-estradiol-3-sulfate, and dehydroepiandrosterone-3-sulfate (DHEAS), but does not include p-aminohippuric acid (PAH) and tetraethylammonium (TEA). Pre-incubation of hOAT4-expressing BeWo cells with phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDBu), both of which are protein kinase C (PKC) activators, acutely inhibited the transport activity. The inhibition by PDBu resulted in a decreased Vmax without significant affecting the Km. Establishment of hOAT4-expressing BeWo cells provided useful tool for further pharmacological and molecular biological studies of placental transport of organic anions mediated by this carrier.