Placental Inositol Reduced in Gestational Diabetes as Glucose Alters Inositol Transporters and IMPA1 Enzyme Expression.

CONTEXT: Perturbed inositol physiology in insulin-resistant conditions has led to proposals of inositol supplementation for gestational diabetes (GDM) prevention, but placental inositol biology is poorly understood. OBJECTIVE: Investigate associations of maternal glycemia with placental inositol content, determine glucose effects on placental expression of inositol enzymes and transporters, and examine relations with birthweight. DESIGN AND PARTICIPANTS: Case-control study of placentae from term singleton pregnancies (GDM n = 24, non-GDM n = 26), and culture of another 9 placentae in different concentrations of glucose and myo-inositol for 48 hours. MAIN OUTCOME MEASURES: Placental inositol was quantified by the Megazyme assay. Relative expression of enzymes involved in myo-inositol metabolism and plasma membrane inositol transport was determined by quantitative RT-PCR and immunoblotting. Linear regression analyses were adjusted for maternal age, body mass index, ethnicity, gestational age, and sex. RESULTS: Placental inositol content was 17% lower in GDM compared with non-GDM. Higher maternal mid-gestation glycemia were associated with lower placental inositol. Increasing fasting glycemia was associated with lower protein levels of the myo-inositol synthesis enzyme, IMPA1, and the inositol transporters, SLC5A11 and SLC2A13, the expression of which also correlated with placental inositol content. In vitro, higher glucose concentrations reduced IMPA1 and SLC5A11 mRNA expression. Increasing fasting glycemia positively associated with customized birthweight percentile as expected in cases with low placental inositol, but this association was attenuated with high placental inositol. CONCLUSION: Glycemia-induced dysregulation of placental inositol synthesis and transport may be implicated in reduced placental inositol content in GDM, and this may in turn be permissive to accelerated fetal growth.

Levothyroxine in Women with Thyroid Peroxidase Antibodies before Conception.

BACKGROUND: Thyroid peroxidase antibodies are associated with an increased risk of miscarriage and preterm birth, even when thyroid function is normal. Small trials indicate that the use of levothyroxine could reduce the incidence of such adverse outcomes. METHODS: We conducted a double-blind, placebo-controlled trial to investigate whether levothyroxine treatment would increase live-birth rates among euthyroid women who had thyroid peroxidase antibodies and a history of miscarriage or infertility. A total of 19,585 women from 49 hospitals in the United Kingdom underwent testing for thyroid peroxidase antibodies and thyroid function. We randomly assigned 952 women to receive either 50 µg once daily of levothyroxine (476 women) or placebo (476 women) before conception through the end of pregnancy. The primary outcome was live birth after at least 34 weeks of gestation. RESULTS: The follow-up rate for the primary outcome was 98.7% (940 of 952 women). A total of 266 of 470 women in the levothyroxine group (56.6%) and 274 of 470 women in the placebo group (58.3%) became pregnant. The live-birth rate was 37.4% (176 of 470 women) in the levothyroxine group and 37.9% (178 of 470 women) in the placebo group (relative risk, 0.97; 95% confidence interval [CI], 0.83 to 1.14, P = 0.74; absolute difference, -0.4 percentage points; 95% CI, -6.6 to 5.8). There were no significant between-group differences in other pregnancy outcomes, including pregnancy loss or preterm birth, or in neonatal outcomes. Serious adverse events occurred in 5.9% of women in the levothyroxine group and 3.8% in the placebo group (P = 0.14). CONCLUSIONS: The use of levothyroxine in euthyroid women with thyroid peroxidase antibodies did not result in a higher rate of live births than placebo. (Funded by the United Kingdom National Institute for Health Research; TABLET Current Controlled Trials number, ISRCTN15948785.).

Vitamin D, the placenta and early pregnancy: effects on trophoblast function.

Pregnancy is associated with significant changes in vitamin D metabolism, notably increased maternal serum levels of active vitamin D, 1,25-dihydroxyvitamin (1,25(OH)2D). This appears to be due primarily to increased renal activity of the enzyme 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) that catalyzes synthesis of 1,25(OH)2D, but CYP27B1 expression is also prominent in both the maternal decidua and fetal trophoblast components of the placenta. The precise function of placental synthesis of 1,25(OH)2D remains unclear, but is likely to involve localized tissue-specific responses with both decidua and trophoblast also expressing the vitamin D receptor (VDR) for 1,25(OH)2D. We have previously described immunomodulatory responses to 1,25(OH)2D by diverse populations of VDR-expressing cells within the decidua. The aim of the current review is to detail the role of vitamin D in pregnancy from a trophoblast perspective, with particular emphasis on the potential role of 1,25(OH)2D as a regulator of trophoblast invasion in early pregnancy. Vitamin D deficiency is common in pregnant women, and a wide range of studies have linked low vitamin D status to adverse events in pregnancy. To date, most of these studies have focused on adverse events later in pregnancy, but the current review will explore the potential impact of vitamin D on early pregnancy, and how this may influence implantation and miscarriage.

Management of subclinical hypothyroidism in pregnancy: are we too simplistic?

Guideline advice of many societies on the management of subclinical hypothyroidism in pregnancy suggests treatment when TSH serum levels exceed 2.5 mU/l. Justification of this procedure is based on limited experience, mainly from studies carried out in patients with positive thyroid-specific antibodies and higher TSH levels that classically define the condition in the non-pregnant state. Taking into account a lack of clear understanding of the regulation of thyroid hormone transport through the utero-placental unit and in the absence of foetal markers to monitor the adequacy of thyroxine treatment, this review attempts to discuss currently available data and suggests a more cautious approach.

MCT8 expression in human fetal cerebral cortex is reduced in severe intrauterine growth restriction.

The importance of the thyroid hormone (TH) transporter, monocarboxylate transporter 8 (MCT8), to human neurodevelopment is highlighted by findings of severe global neurological impairment in subjects with MCT8 (SLC16A2) mutations. Intrauterine growth restriction (IUGR), usually due to uteroplacental failure, is associated with milder neurodevelopmental deficits, which have been partly attributed to dysregulated TH action in utero secondary to reduced circulating fetal TH concentrations and decreased cerebral thyroid hormone receptor expression. We postulate that altered MCT8 expression is implicated in this pathophysiology; therefore, in this study, we sought to quantify changes in cortical MCT8 expression with IUGR. First, MCT8 immunohistochemistry was performed on occipital and parietal cerebral cortex sections obtained from appropriately grown for gestational age (AGA) human fetuses between 19 weeks of gestation and term. Secondly, MCT8 immunostaining in the occipital cortex of stillborn IUGR human fetuses at 24-28 weeks of gestation was objectively compared with that in the occipital cortex of gestationally matched AGA fetuses. Fetuses demonstrated widespread MCT8 expression in neurons within the cortical plate and subplate, in the ventricular and subventricular zones, in the epithelium of the choroid plexus and ependyma, and in microvessel wall. When complicated by IUGR, fetuses showed a significant fivefold reduction in the percentage area of cortical plate immunostained for MCT8 compared with AGA fetuses (P<0.05), but there was no significant difference in the proportion of subplate microvessels immunostained. Cortical MCT8 expression was negatively correlated with the severity of IUGR indicated by the brain:liver weight ratios (r(2)=0.28; P<0.05) at post-mortem. Our results support the hypothesis that a reduction in MCT8 expression in the IUGR fetal brain could further compromise TH-dependent brain development.

Optimal treatment of hypothyroidism associated with live birth in cases of previous recurrent placental abruption and stillbirth.

OBJECTIVE: To examine the clinical management of and placentas from pregnant women with hypothyroidism and obstetric history of recurrent stillbirth in order to identify possible etiologic mechanisms. METHODS: Two cases involving 26-year-old women with hypothyroidism and history of recurrent stillbirth are reported. Placentas from all of the women's pregnancies were compared in order to identify histologic similarities. RESULTS: In both cases, multifocal hemorrhagic infarctions and abruptions were seen, indicating progressive uteroplacental ischemic damage leading to stillbirth. Thrombophilia, infection, and diabetes tests were all negative. With meticulous monitoring and normalization of thyroid function by end of first/early second trimester in subsequent pregnancies, there were live births and no evidence of infarction on placental histology. CONCLUSION: The 2 reported cases raise the possibility of uteroplacental ischemia and placental abruption being mechanisms by which hypothyroidism can lead to stillbirth; they also highlight the potential of minimizing this risk via adequate levothyroxine treatment from early pregnancy.

Monocarboxylate transporter 8 modulates the viability and invasive capacity of human placental cells and fetoplacental growth in mice.

Monocarboxylate transporter 8 (MCT8) is a well-established thyroid hormone (TH) transporter. In humans, MCT8 mutations result in changes in circulating TH concentrations and X-linked severe global neurodevelopmental delay. MCT8 is expressed in the human placenta throughout gestation, with increased expression in trophoblast cells from growth-restricted pregnancies. We postulate that MCT8 plays an important role in placental development and transplacental TH transport. We investigated the effect of altering MCT8 expression in human trophoblast in vitro and in a Mct8 knockout mouse model. Silencing of endogenous MCT8 reduced T3 uptake into human extravillous trophoblast-like cells (SGHPL-4; 40%, P<0.05) and primary cytotrophoblast (15%, P<0.05). MCT8 over-expression transiently increased T3 uptake (SGHPL-4∶30%, P<0.05; cytotrophoblast: 15%, P<0.05). Silencing MCT8 did not significantly affect SGHPL-4 invasion, but with MCT8 over-expression T3 treatment promoted invasion compared with no T3 (3.3-fold; P<0.05). Furthermore, MCT8 silencing increased cytotrophoblast viability (∼20%, P<0.05) and MCT8 over-expression reduced cytotrophoblast viability independently of T3 (∼20%, P<0.05). In vivo, Mct8 knockout reduced fetal:placental weight ratios compared with wild-type controls at gestational day 18 (25%, P<0.05) but absolute fetal and placental weights were not significantly different. The volume fraction of the labyrinthine zone of the placenta, which facilitates maternal-fetal exchange, was reduced in Mct8 knockout placentae (10%, P<0.05). However, there was no effect on mouse placental cell proliferation in vivo. We conclude that MCT8 makes a significant contribution to T3 uptake into human trophoblast cells and has a role in modulating human trophoblast cell invasion and viability. In mice, Mct8 knockout has subtle effects upon fetoplacental growth and does not significantly affect placental cell viability probably due to compensatory mechanisms in vivo.

Dietary vitamin D restriction in pregnant female mice is associated with maternal hypertension and altered placental and fetal development.

Epidemiology has linked vitamin D deficiency with preeclampsia in humans. We hypothesized that low vitamin D status in pregnant mice may lead to symptoms of preeclampsia. Female BL6 mice were raised on vitamin D-sufficient or -deficient diets from weeks 4 of age and then mated with vitamin D-sufficient BL6 males at week 8. The resulting pregnant mice were either allowed to deliver pups and monitored for blood pressure (BP) and weight of offspring or euthanized at day 14 or 18 of gestation (E14 or E18) for analysis of serum, placental/kidney tissues, and fetuses. At E14 serum concentrations of 25-hydroxyvitamin D (30.1 ± 5.0 vs 1.8 ± 0.6 ng/mL, P < .001) and 1,25-dihydroxyvitamin D (119.5 ± 18.7 vs 37.4 ± 5.1 pg/mL, P < .01) were higher in sufficient vs deficient pregnant mice. At E14 BP was significantly elevated in vitamin D-deficient pregnant mice relative to vitamin D-sufficient mice for both systolic BP (124.89 ± 2.28 vs 105.34 ± 3.61 mm Hg, P < .001) and mean arterial pressure (115.33 ± 1.93 vs 89.33 ± 5.02 mm Hg, P < .001). This elevation continued through pregnancy until 7 days postpartum (PP7) but returned to baseline by PP14. Analysis of maternal kidneys showed increased expression of mRNA for renin and the angiotensin II receptor (3- and 4-fold, respectively) in vitamin D-deficient vs -sufficient mice at E14. Histological analysis of E14 placentas from vitamin D-deficient mice showed decreased vascular diameter within the labyrinth region. E14 and E18 fetuses from vitamin D-deficient mice were larger than those from vitamin D-sufficient mothers. However, by PP14 pups from vitamin D-deficient mothers weighed significantly less than those from vitamin D-sufficient mothers. Resupplementation of vitamin D periconceptually partially reversed the effects of vitamin D deficiency. These data provide further evidence that low vitamin D status may predispose pregnant women to dysregulated placental development and elevated blood pressure.

Expression and function of thyroid hormone transporters in the microvillous plasma membrane of human term placental syncytiotrophoblast.

The transplacental passage of thyroid hormones (THs) from mother to fetus in humans has been deduced from observational clinical studies and is important for normal fetoplacental development. To investigate the transporters that regulate TH uptake by syncytiotrophoblast (the primary barrier to maternal-fetal exchange, which lies in direct contact with maternal blood), we isolated the microvillous plasma membrane (MVM) of human term syncytiotrophoblasts. We have demonstrated that MVM vesicles express plasma membrane TH transporter proteins, including system-L (L-type amino acid transporter 1 and CD98), monocarboxylate transporters (MCTs) 8 and 10, organic anion-transporting polypeptides 1A2 and 4A1. We provide the first definitive evidence that the human syncytiotrophoblast MVM is capable of rapid, saturable T(4) and T(3) uptake at similar rates and in a Na(+)-independent manner. These two major forms of THs could not significantly inhibit each others' uptake, suggesting that each is mediated by largely different transporters. No single transporter was noted to play a dominant role in either T(4) or T(3) uptake. Using combinations of transporter inhibitors that had an additive effect on TH uptake, we provide evidence that 67% of saturable T(4) uptake is facilitated by system-L and MCT10 with a minor role played by organic anion-transporting polypeptides, whereas 87% of saturable T(3) uptake is mediated by MCT8 and MCT10. Our data demonstrate that syncytiotrophoblast may control the quantity and forms of THs taken up by the human placenta. Thus, syncytiotrophoblast could be critical in regulating transplacental TH supply from the mother to the fetus.

The role of the placenta in thyroid hormone delivery to the fetus.

The transplacental passage of thyroid hormones from the maternal circulation to the fetal circulation within the human hemochorial placenta is important for normal fetal development, particularly the development of the central nervous system. The role of maternal thyroid hormones is particularly important in the first half of pregnancy, before the onset of endogenous thyroid hormone production in the fetus. The human placenta regulates the quantity and composition of different forms of transported thyroid hormones to ensure that the requisite levels are present in the fetus for each stage of development. Transplacental thyroid hormone supply to the fetus is modulated by several factors, including the following proteins: plasma membrane transporters, which regulate the passage of thyroid hormones in and out of cells; iodothyronine deiodinases, which metabolize thyroid hormones; and proteins within trophoblast cells, which bind thyroid hormones. In pathological situations of either maternal or fetal thyroid hormone deficiency during pregnancy, the placenta seems to lack the full compensatory mechanisms necessary to optimize maternal-fetal transfer of thyroid hormones. Inadequate passage of thyroid hormones can lead to suboptimal fetal thyroid hormone levels, which might contribute to the neurodevelopmental delay associated with such conditions. Thus, maintaining normal maternal thyroid hormone status is likely to be the primary factor in ensuring adequate transplacental thyroid hormone passage and appropriate iodide supply to the fetus.

Maternal nutrient deprivation induces sex-specific changes in thyroid hormone receptor and deiodinase expression in the fetal guinea pig brain.

Thyroid hormone deprivation during fetal life has been implicated in neurodevelopmental morbidity. In humans, poor growth in utero is also associated with fetal hypothyroxinaemia. In guinea pigs, a short period (48 h) of maternal nutrient deprivation at gestational day (gd) 50 results in fetuses with hypothyroxinaemia and increased brain/body weight ratios. Thyroid hormone action is mediated by nuclear thyroid hormone receptors (TRs) and is dependent upon the prereceptor regulation of supply of triiodothyronine (T3) by deiodinase enzymes. Examination of fetal guinea pig brains using in situ hybridization demonstrated widespread expression of mRNAs encoding TRalpha1, alpha2 and beta1, with regional colocalization of deiodinase type 2 (D2) mRNA in the developing forebrain, limbic structures, brainstem and cerebellum at gd52. With maternal nutrient deprivation, TRalpha1 and beta1 mRNA expression was significantly increased in the male, but decreased in the female fetal hippocampus and cerebellum and other areas showing high TR expression under euthyroid conditions. Maternal nutrient deprivation resulted in elevated D2 mRNA expression in males and females. Deiodinase type 3 (D3) mRNA expression was confined to the shell of the nucleus accumbens, the posterior amygdalohippocampal area, brainstem and cerebellum, and did not change with maternal nutrient deprivation. In conclusion, maternal nutrient deprivation resulted in sex-specific changes in TR mRNA expression and a generalized increase in D2 mRNAs within the fetal brain. These changes may represent a protective mechanism to maintain appropriate thyroid hormone action in the face of fetal hypothyroxinaemia in order to optimize brain development.