Glucose metabolism is elevated and vascular resistance and maternofetal transfer is normal in perfused placental cotyledons from severely growth-restricted fetuses

Molecular regulators of defective placental and cardiovascular development in fetal growth restriction

Placental insufficiency is one of the major causes of fetal growth restriction (FGR), a significant pregnancy disorder in which the fetus fails to achieve its full growth potential in utero. As well as the acute consequences of being born too small, affected offspring are at increased risk of cardiovascular disease, diabetes and other chronic diseases in later life. The placenta and heart develop concurrently, therefore placental maldevelopment and function in FGR may have profound effect on the growth and differentiation of many organ systems, including the heart. Hence, understanding the key molecular players that are synergistically linked in the development of the placenta and heart is critical. This review highlights the key growth factors, angiogenic molecules and transcription factors that are common causes of defective placental and cardiovascular development.

Cannabidiol Exposure During Rat Pregnancy Leads to Labyrinth-Specific Vascular Defects in the Placenta and Reduced Fetal Growth

Introduction: Cannabis use is increasing among pregnant people, and cannabidiol (CBD), a constituent of cannabis, is often perceived as "natural" and "safe" as it is non-intoxicating. In utero, cannabis exposure is associated with negative health outcomes, including fetal growth restriction (FGR). The placenta supplies oxygen and nutrients to the fetus, and alterations in placental development can lead to FGR. While there has been some investigation into the effects of Δ9-THC, there has been limited investigation into the impacts of in utero gestational CBD exposure on the placenta. Methods: This study used histological and transcriptomic analysis of embryonic day (E)19.5 rat placentas from vehicle and CBD (3 mg/kg intraperitoneal injection) exposed pregnancies (E6.5-18.5). Results: The study revealed that pups from CBD-exposed pregnancies were 10% smaller, with the placentae displaying a decreased fetal blood space perimeter-to-area ratio. The transcriptomic analysis supported compromised angiogenesis and blood vessel formation with downregulated biological processes, including tube morphogenesis, angiogenesis, blood vessel morphogenesis, blood vessel development and vasculature development. Further, the CBD-exposed placentas displayed changed expression of glucose transporters (decreased GLUT1 and GR expression and increased GLUT3 expression). Transcriptomic analysis further revealed upregulated biological processes associated with metabolism. Finally, histological and transcriptomic analysis revealed altered cell populations within the placenta, specifically to syncytiotrophoblast layer II and endothelial cells. Conclusion: Together these results suggest that the structural changes in CDB-exposed placentae, including the altered expression of nutrient transporters and the changes to the placental fetal vasculature, may underlie the reduced fetal growth.

Glycolysis: A fork in the path of normal and pathological pregnancy

Glucose metabolism is vital to the survival of living organisms. Since the discovery of the Warburg effect in the 1920s, glycolysis has become a major research area in the field of metabolism. Glycolysis has been extensively studied in the field of cancer and is considered as a promising therapeutic target. However, research on the role of glycolysis in pregnancy is limited. Recent evidence suggests that blastocysts, trophoblasts, decidua, and tumors all acquire metabolic energy at specific stages in a highly similar manner. Glycolysis, carefully controlled throughout pregnancy, maintains a dynamic and coordinated state, so as to maintain the homeostasis of the maternal-fetal interface and ensure normal gestation. In the present review, we investigate metabolic remodeling and the selective propensity of the embryo and placenta for glycolysis. We then address dysregulated glycolysis that occurs in the cellular interactive network at the maternal-fetal interface in miscarriage, preeclampsia, fetal growth restriction, and gestational diabetes mellitus. We provide new insights into the field of maternal-fetal medicine from a metabolic perspective, thus revealing the mystery of human pregnancy.

Differential Expression of Glucose Transporter Proteins GLUT-1, GLUT-3, GLUT-8 and GLUT-12 in the Placenta of Macrosomic, Small-for-Gestational-Age and Growth-Restricted Foetuses

Placental transfer of glucose constitutes one of the major determinants of the intrauterine foetal growth. The objective of the present study was to evaluate the expression of glucose transporter proteins GLUT-1, GLUT-3, GLUT-8 and GLUT-12 in the placenta of macrosomic, small-for-gestational-age (SGA) and growth-restricted foetuses (FGR). A total of 70 placental tissue samples were collected from women who delivered macrosomic ≥4000 g (n = 26), SGA (n = 11), growth-restricted (n = 13) and healthy control neonates (n = 20). Computer-assisted quantitative morphometry of stained placental sections was performed to determine the expression of selected GLUT proteins. Immunohistochemical staining identified the presence of all glucose transporters in the placental tissue. Quantitative morphometric analysis performed for the vascular density-matched placental samples revealed a significant decrease in GLUT-1 and increase in GLUT-3 protein expression in pregnancies complicated by FGR as compared to other groups (p < 0.05). In addition, expression of GLUT-8 was significantly decreased among SGA foetuses (p < 0.05). No significant differences in GLUTs expression were observed in women delivering macrosomic neonates. In the SGA group foetal birth weight (FBW) was negatively correlated with GLUT-3 (rho = −0.59, p < 0.05) and positively with GLUT-12 (rho = 0.616, p < 0.05) placental expression. In addition, a positive correlation between FBW and GLUT-12 expression in the control group (rho = 0.536, p < 0.05) was noted. In placentas derived from FGR-complicated pregnancies the expression of two major glucose transporters GLUT-1 and GLUT-3 is altered. On the contrary, idiopathic foetal macrosomia is not associated with changes in the placental expression of GLUT-1, GLUT-3, GLUT-8 and GLUT-12 proteins.

Growth impairment, increased placental glucose uptake and altered transplacental transport in VIP deficient pregnancies: Maternal vs. placental contributions

Glucose uptake by the placenta and its transfer to the fetus is a finely regulated process required for placental and fetal development. Deficient placentation is associated with pregnancy complications such as fetal growth restriction (FGR). The vasoactive intestinal peptide (VIP) has embryotrophic effects in mice and regulates human cytotrophoblast metabolism and function. Here we compared glucose uptake and transplacental transport in vivo by VIP-deficient placentas from normal or VIP-deficient maternal background. The role of endogenous VIP in placental glucose and amino acid uptake was also investigated. Wild type C57BL/6 (WT) or VIP^+/- (VIP HT) females were mated with WT, VIP knock-out (VIP KO) or VIP HT males. Glucose uptake and transplacental transport were evaluated by the injection of the fluorescent d-glucose analogue 2-NBDG in pregnant mice at gestational day (gd) 17.5. Glucose and amino acid uptake in vitro by placental explants were measured with 2-NBDG or ¹⁴C-MeAIB respectively. In normal VIP maternal background, fetal weight was reduced in association with placental VIP deficiency, whereas placental weight was unaltered. Paradoxically, VIP^+/- placentas presented higher glucose uptake and higher gene expression of GLUT1 and mTOR than VIP^+/+ placentas. However, in a maternal VIP-deficient environment placental uptake and transplacental transport of glucose increased while fetal weights were unaffected, regardless of feto-placental genotype. Results point to VIP-deficient pregnancy in a normal background as a suitable FGR model with increased placental glucose uptake and transplacental transport. The apparently compensatory actions are unable to sustain normal fetal growth and could result in complications later in life.

Deuterium Magnetic Resonance Imaging and the Discrimination of Fetoplacental Metabolism in Normal and L-NAME-Induced Preeclamptic Mice

Recent magnetic resonance studies in healthy and cancerous organs have concluded that deuterated metabolites possess highly desirable properties for mapping non-invasively and, as they happen, characterizing glycolysis and other biochemical processes in animals and humans. A promising avenue of this deuterium metabolic imaging (DMI) approach involves looking at the fate of externally administered ²H_6,6′-glucose, as it is taken up and metabolized into different products as a function of time. This study employs deuterium magnetic resonance to follow the metabolism of wildtype and preeclamptic pregnant mice models, focusing on maternal and fetoplacental organs over ≈2 h post-injection. ²H_6,6′-glucose uptake was observed in the placenta and in specific downstream organs such as the fetal heart and liver. Main metabolic products included ²H_3,3′-lactate and ²H-water, which were produced in individual fetoplacental organs with distinct time traces. Glucose uptake in the organs of most preeclamptic animals appeared more elevated than in the control mice (p = 0.02); also higher was the production of ²H-water arising from this glucose. However, the most notable differences arose in the ²H_3,3′-lactate concentration, which was ca. two-fold more abundant in the placenta (p = 0.005) and in the fetal (p = 0.01) organs of preeclamptic-like animals, than in control mice. This is consistent with literature reports about hypoxic conditions arising in preeclamptic and growth-restricted pregnancies, which could lead to an enhancement in anaerobic glycolysis. Overall, the present measurements suggest that DMI, a minimally invasive approach, may offer new ways of studying and characterizing health and disease in mammalian pregnancies, including humans.

Considering intrauterine location in a model of fetal growth restriction after maternal titanium dioxide nanoparticle inhalation

Fetal growth restriction (FGR) is a condition with several underlying etiologies including gestational disease (e.g., preeclampsia, gestational diabetes) and xenobiotic exposure (e.g., environmental contaminants, pharmaceuticals, recreational drugs). Rodent models allow study of FGR pathogenesis. However, given the multiparous rodent pregnancy, fetal growth variability within uterine horns may arise. To ascertain whether intrauterine position is a determinant of fetal growth, we redesigned fetal weight analysis to include litter size and maternal weight. Our FGR model is produced by exposing pregnant Sprague Dawley rats to aerosolized titanium dioxide nanoparticles at 9.44 ± 0.26 mg/m3 on gestational day (GD) 4, GD 12 or GD 17 or 9.53 ± 1.01 mg/m3 between GD 4-GD 19. In this study fetal weight data was reorganized by intrauterine location [i.e., right/left uterine horn and ovarian/middle/vaginal position] and normalized by maternal weight and number of feti per uterine horn. A significant difference in fetal weight in the middle location in controls (0.061g ± 0.001 vs. 0.055g ± 0.002), GD 4 (0.033g ± 0.003 vs. 0.049g ± 0.004), and GD 17 (0.047g ± 0.002 vs. 0.038g ± 0.002) exposed animals was identified. Additionally, GD 4 exposure produced significantly smaller feti in the right uterine horn at the ovarian end (0.052g ± 0.003 vs. 0.029g ± 0.003) and middle of the right uterine horn (0.060g ± 0.001 vs. 0.033g ± 0.003). GD 17 exposure produced significantly smaller feti in the left uterine horn middle location (0.055g ± 0.002 vs. 0.033 ± 0.002). Placental weights were unaffected, and placental efficiency was reduced in the right uterine horn middle location after GD 17 exposure (5.74g ± 0.16 vs. 5.09g ± 0.14). These findings identified: 1) differences in fetal weight of controls between the right and left horns in the middle position, and 2) differential effects of single whole-body pulmonary exposure to titanium dioxide nanoparticles on fetal weight by position and window of maternal exposure. In conclusion, these results indicate that consideration for intrauterine position, maternal weight, and number of feti per horn provides a more sensitive assessment of FGR from rodent reproductive and developmental studies.

Ex Vivo Human Placenta Perfusion, Metabolic and Functional Imaging for Obstetric Research-A Feasibility Study

Placenta metabolism is closely linked to pregnancy outcome, and few modalities are currently available for studying the human placenta. Here, we aimed to investigate a novel ex vivo human placenta perfusion system for metabolic imaging using hyperpolarized [1-¹³C]pyruvate. The metabolic effects of 3 different human placentas were investigated using functional and metabolic magnetic resonance imaging. The placenta glucose metabolism and hemodynamics were characterized with hyperpolarized [1-¹³C]pyruvate magnetic resonance imaging and by dynamic contrast-enhanced (DCE) imaging. Hyperpolarized [1-¹³C]pyruvate showed a decrease in the ¹³C-lactate/¹³C-pyruvate ratio from the highest to the lowest metabolic active placenta. The metabolic profile was complemented by a more homogenous distributed hemodynamic response, with a longer mean transit time and higher blood volume. This study shows different placenta metabolic and hemodynamic features associated with the placenta functional status using hyperpolarized magnetic resonance ex vivo. This study supports further studies using ex vivo metabolic imaging of the placenta alterations associated with pregnancy complications.

The placenta in fetal growth restriction: What is going wrong?

The placenta is essential for the efficient delivery of nutrients and oxygen from mother to fetus to maintain normal fetal growth. Dysfunctional placental development underpins many pregnancy complications, including fetal growth restriction (FGR) a condition in which the fetus does not reach its growth potential. The FGR placenta is smaller than normal placentae throughout gestation and displays maldevelopment of both the placental villi and the fetal vasculature within these villi. Specialized epithelial cells called trophoblasts exhibit abnormal function and development in FGR placentae. This includes an altered balance between proliferation and apoptotic death, premature cellular senescence, and reduced colonisation of the maternal decidual tissue. Thus, the placenta undergoes aberrant changes at the macroscopic to cellular level in FGR, which can limit exchange capacity and downstream fetal growth. This review aims to compile stereological, in vitro, and imaging data to create a holistic overview of the FGR placenta and its pathophysiology, with a focus on the contribution of trophoblasts.

Complex, coordinated and highly regulated changes in placental signaling and nutrient transport capacity in IUGR

The most common cause of intrauterine growth restriction (IUGR) in the developed world is placental insufficiency, a concept often used synonymously with reduced utero-placental and umbilical blood flows. However, placental insufficiency and IUGR are associated with complex, coordinated and highly regulated changes in placental signaling and nutrient transport including inhibition of insulin and mTOR signaling and down-regulation of specific amino acid transporters, Na+/K+-ATPase, the Na+/H+-exchanger, folate and lactate transporters. In contrast, placental glucose transport capacity is unaltered and Ca2+-ATPase activity and the expression of proteins involved in placental lipid transport are increased in IUGR. These findings are not entirely consistent with the traditional view that the placenta is dysfunctional in IUGR, but rather suggest that the placenta adapts to reduce fetal growth in response to an inability of the mother to allocate resources to the fetus. This new model has implications for the understanding of the mechanisms underpinning IUGR and for the development of intervention strategies.

Expression of placental glucose transporter proteins in pregnancies complicated by fetal growth disorders

During pregnancy fetal growth disorders, including fetal macrosomia and fetal growth restriction (FGR) are associated with numerous maternal-fetal complications, as well as due to the adverse effect of the intrauterine environment lead to an increased morbidity in adult life. Accumulating evidence suggests that occurrence of fetal macrosomia or FGR, may be associated with alterations in the transfer of nutrients across the placenta, in particular of glucose. The placental expression and activity of specific GLUT transporters are the main regulatory factors in the process of maternal-fetal glucose exchange. This review article summarizes the results of previous studies on the expression of GLUT transporters in the placenta, concentrating on human pregnancies complicated by intrauterine fetal growth disorders. Characteristics of each transporter protein found in the placenta is presented, alterations in the location and expression of GLUT isoforms observed in individual placental compartments are described, and the factors regulating the expression of selected GLUT proteins are examined. Based on the above data, the potential function of each GLUT isoform in the maternal-fetal glucose transfer is determined. Further on, a detailed analysis of changes in the expression of glucose transporters in pregnancies complicated by fetal growth disorders is given, and significance of these modifications for the pathogenesis of fetal macrosomia and FGR is discussed. In the final part novel interventional approaches that might reduce the risk associated with abnormalities of intrauterine fetal growth through modifications of placental GLUT-mediated glucose transfer are explored.

Early restriction of placental growth results in placental structural and gene expression changes in late gestation independent of fetal hypoxemia

Placental restriction and insufficiency are associated with altered patterns of placental growth, morphology, substrate transport capacity, growth factor expression, and glucocorticoid exposure. We have used a pregnant sheep model in which the intrauterine environment has been perturbed by uterine carunclectomy (Cx). This procedure results in early restriction of placental growth and either the development of chronic fetal hypoxemia (PaO_2≤17 mmHg) in late gestation or in compensatory placental growth and the maintenance of fetal normoxemia (PaO₂>17 mmHg). Based on fetal PaO₂, Cx, and Control ewes were assigned to either a normoxemic fetal group (Nx) or a hypoxemic fetal group (Hx) in late gestation, resulting in 4 groups. Cx resulted in a decrease in the volumes of fetal and maternal connective tissues in the placenta and increased placental mRNA expression of IGF2, vascular endothelial growth factor (VEGF), VEGFR‐2,ANGPT2, and TIE2. There were reduced volumes of trophoblast, maternal epithelium, and maternal connective tissues in the placenta and a decrease in placental GLUT1 and 11βHSD2 mRNA expression in the Hx compared to Nx groups. Our data show that early restriction of placental growth has effects on morphological and functional characteristics of the placenta in late gestation, independent of whether the fetus becomes hypoxemic. Similarly, there is a distinct set of placental changes that are only present in fetuses that were hypoxemic in late gestation, independent of whether Cx occurred. Thus, we provide further understanding of the different placental cellular and molecular mechanisms that are present in early placental restriction and in the emergence of later placental insufficiency.

Transplacental Nutrient Transport Mechanisms of Intrauterine Growth Restriction in Rodent Models and Humans

Although the causes of intrauterine growth restriction (IUGR) have been intensively investigated, important information is still lacking about the role of the placenta as a link from adverse maternal environment to adverse pregnancy outcomes of IUGR and preterm birth. IUGR is associated with an increased risk of cardiovascular, metabolic, and neurological diseases later in life. Determination of the most important pathways that regulate transplacental transport systems is necessary for identifying marker genes as diagnostic tools and for developing drugs that target the molecular pathways. Besides oxygen, the main nutrients required for appropriate fetal development and growth are glucose, amino acids, and fatty acids. Dysfunction in transplacental transport is caused by impairments in both placental morphology and blood flow, as well as by factors such as alterations in the expression of insulin-like growth factors and changes in the mTOR signaling pathway leading to a change in nutrient transport. Animal models are important tools for systematically studying such complex events. Debate centers on whether the rodent placenta is an appropriate tool for investigating the alterations in the human placenta that result in IUGR. This review provides an overview of the alterations in expression and activity of nutrient transporters and alterations in signaling associated with IUGR and compares these findings in rodents and humans. In general, the data obtained by studies of the various types of rodent and human nutrient transporters are similar. However, direct comparison is complicated by the fact that the results of such studies are controversial even within the same species, making the interpretation of the results challenging. This difficulty could be due to the absence of guidelines of the experimental design and, especially in humans, the use of trophoblast cell culture studies instead of clinical trials. Nonetheless, developing new therapy concepts for IUGR will require the use of animal models for gathering robust data about mechanisms leading to IUGR and for testing the effectiveness and safety of the intervention among pregnant women.

The chinchilla as a novel animal model of pregnancy

Several parameters are important when choosing the most appropriate animal to model human obstetrics, including gestation period, number of fetuses per gestation and placental structure. The domesticated long-tailed chinchilla (Chinchilla lanigera) is a well-suited and appropriate animal model of pregnancy that often will carry only one offspring and has a long gestation period of 105-115 days. Furthermore, the chinchilla placenta is of the haemomonochorial labyrinthine type and is therefore comparable to the human villous haemomonochorial placenta. This proof-of-concept study demonstrated the feasibility in laboratory settings, and demonstrated the potential of the pregnant chinchilla as an animal model for obstetric research and its potential usefulness for non-invasive measurements in the placenta. We demonstrate measurements of the placental and fetal metabolism (demonstrated in vivo by hyperpolarized MRI and in vitro by qPCR analyses), placental vessels (demonstrated ex vivo by contrast-enhanced CT angiography) and overall anatomy (demonstrated in vivo by whole-body CT).

Placental glucose transporter 3 (GLUT3) is up-regulated in human pregnancies complicated by late-onset intrauterine growth restriction

INTRODUCTION

Transport of glucose from maternal blood across the placental trophoblastic tissue barrier is critical to sustain fetal growth. The mechanism by which GLUTs are regulated in trophoblasts in response to ischemic hypoxia encountered with intrauterine growth restriction (IUGR) has not been suitably investigated.

OBJECTIVE

To investigate placental expression of GLUT1, GLUT3 and GLUT4 and possible mechanisms of GLUT regulation in idiopathic IUGR.

METHODS

We analyzed clinical, biochemical and histological data from placentas collected from women affected by idiopathic full-term IUGR (n = 10) and gestational age-matched healthy controls (n = 10).

RESULTS

We found increased GLUT3 protein expression in the trophoblast (cytotrophoblast greater than syncytiotrophoblast) on the maternal aspect of the placenta in IUGR compared to normal placenta, but no differences in GLUT1 or GLUT4 were found. No differential methylation of the GLUT3 promoter between normal and IUGR placentas was observed. Increased GLUT3 expression was associated with an increased nuclear concentration of HIF-1α, suggesting hypoxia may play a role in the up-regulation of GLUT3.

DISCUSSION

Further studies are needed to elucidate whether increased GLUT3 expression in IUGR is a marker for defective villous maturation or an adaptive response of the trophoblast in response to chronic hypoxia.

CONCLUSIONS

Patients with IUGR have increased trophoblast expression of GLUT3, as found under the low-oxygen conditions of the first trimester.

Diabetic and metabolic programming: mechanisms altering the intrauterine milieu

A wealth of epidemiological, clinical, and experimental studies have been linked to poor intrauterine conditions as well as metabolic and associated cardiovascular changes postnatal. These are novel perspectives connecting the altered intrauterine milieu to a rising number of metabolic diseases, such as diabetes, obesity, and hypercholesterolemia as well as the Metabolic Syndrome (Met S). Moreover, metabolic associated atherosclerotic diseases are connected to perigestational maternal health. The "Thrifty Phenotype Hypothesis" introduced cross-generational links between poor conditions during gestation and metabolic as well as cardiovascular alterations postnatal. Still, mechanisms altering the intrauterine milieu causing metabolic and associated atherosclerotic diseases are currently poorly understood. This paper will give novel insights in fundamental concepts connected to specific molecular mechanisms "programming" diabetes and associated metabolic as well as cardiovascular diseases.

Reactivity of blood vessels in response to prostaglandin E2 in placentas from pregnancies complicated by fetal growth restriction

OBJECTIVE

The authors aimed to study the contractility responses of normal and fetal growth restriction (FGR) placentas to prostaglandin E(2) (PGE(2) ) and to correlate the results to subsequent placental histological analysis.

METHOD

A dual-perfused single cotyledon model was used. Placentas from pregnancies complicated by FGR and from normal pregnancies were obtained. Selected cotyledons were cannulated and dually perfused. Following stabilization, three concentrations of PGE(2) (0.05, 0.1, and 0.15 mg/mL) were administered to the fetal arterial side causing contraction/relaxation response. Fetal perfusion pressure was measured continuously during these contraction and relaxation phases. Following the perfusion experiments, the placentas were analyzed for fetal or maternal origin vascular lesions.

RESULTS

A total of 21 complete experiments were performed (16 normal, 5 FGR). In response to PGE(2) , FGR placentas exhibited lower change in the perfusion pressure and lower relaxation time constant. Basal perfusion pressure did not differ significantly between the two groups. Placental histopathology lesions, fetal or maternal origin, were more common in the FGR compared with the controls placentas, 80% versus 25%, respectively, P=  0.047.

CONCLUSIONS

The lower vascular reactivity in response to PGE(2) and the presence of fetal and maternal vascular placental lesions suggest a mechanism explaining the altered vascular supply in FGR.

Placental transport in pregnancy pathologies

The placenta is positioned between the maternal and fetal circulation and hence plays a key role in transporting maternal nutrients to the developing fetus. Fetal growth changes in the 2 most frequent pregnancy pathologies, gestational diabetes mellitus and fetal growth restriction, are predominantly characterized by an exaggerated and restricted fat accretion, respectively. Glucose, by its regulating effect on fetal insulin concentrations, and lipids have been strongly implicated in fetal fat deposition. Transplacental glucose flux is highly efficient and limited only by nutrient availability (flow-limited)--ie, driven by the maternal-fetal glucose concentration gradient and blood flow, with little, if any, effect of placental morphology, glucose consumption, and transporter expression. This explains why, despite changes in these determinants in both pathologies, transplacental glucose flux is unaltered.

Glucose transporter 3 (GLUT3) protein expression in human placenta across gestation

Conflicting information regarding expression of GLUT3 protein in the human placenta has been reported and the localization and pattern of expression of GLUT3 protein across gestation has not been clearly defined. The objective of this study was characterization of syncytial GLUT3 protein expression across gestation. We hypothesized that GLUT3 protein is present in the syncytial microvillous membrane and that its expression decreases over gestation. GLUT3 protein was measured in samples from a range of gestational ages (first to third trimester), with human brain and human bowel used as a positive and negative control respectively. As an additional measure of specificity, we transfected BeWo choriocarcinoma cells, a trophoblast cell line expressing GLUT3, with siRNA directed against GLUT3 and analyzed expression by Western blotting. GLUT3 was detected in the syncytiotrophoblast at all gestational ages by immunohistochemistry. Using Western blotting GLUT3 was detected as an integral membrane protein at a molecular weight of ∼50 kDa in microvillous membranes from all trimesters but not in syncytial basal membranes. The identity of the primary antibody target was confirmed by demonstrating that expression of the immunoblotting signal in GLUT3 siRNA-treated BeWo was decreased to 18 ± 6% (mean ± SEM) of that seen in cells transfected with a non-targeting siRNA. GLUT3 expression in microvillous membranes detected by Western blot decreased through the trimesters such that expression in the second trimester (wks 14-26) was 48 ± 7% of that in the first trimester and by the third trimester (wks 31-40) only 34 ± 10% of first trimester expression. In addition, glucose uptake into BeWo cells treated with GLUT3 siRNA was reduced to 60% of that measured in cells treated with the non-targeting siRNA. This suggests that GLUT3-mediated uptake comprises approximately 50% of glucose uptake into BeWo cells. These results confirm the hypothesis that GLUT3 is present in the syncytial microvillous membrane early in gestation and decreases thereafter, supporting the idea that GLUT3 is of greater importance for glucose uptake early in gestation.

Obesity and the placenta: A consideration of nutrient exchange mechanisms in relation to aberrant fetal growth

The obesity epidemic, including childhood obesity, is rapidly gaining strength as one of the most significant challenges to the health of the global community in the 21st Century. The proportion of women who are obese at the beginning of pregnancy is also increasing. These women and their babies are at high risk of pregnancy complications, and of programming for metabolic disease in adult life. In particular, maternal obesity is associated with aberrant fetal growth, encompassing both growth restricted and large for gestational age, or macrosomic fetuses. This article considers the potential effect of obesity and adipose tissue on placental nutrient exchange mechanisms in relation to aberrant fetal growth. The review emphasizes the dearth of work on this topic to date despite its importance to current and future healthcare of the population.

Chronic hypoxia increases fetoplacental vascular resistance and vasoconstrictor reactivity in the rat

An increase in fetoplacental vascular resistance caused by hypoxia is considered one of the key factors of placental hypoperfusion and fetal undernutrition leading to intrauterine growth restriction (IUGR), one of the serious problems in current neonatology. However, although acute hypoxia has been shown to cause fetoplacental vasoconstriction, the effects of more sustained hypoxic exposure are unknown. This study was designed to test the hypothesis that chronic hypoxia elicits elevations in fetoplacental resistance, that this effect is not completely reversible by acute reoxygenation, and that it is accompanied by increased acute vasoconstrictor reactivity of the fetoplacental vasculature. We measured fetoplacental vascular resistance as well as acute vasoconstrictor reactivity in isolated perfused placentae from rats exposed to hypoxia (10% O2) during the last week of a 3-wk pregnancy. We found that chronic hypoxia shifted the relationship between perfusion pressure and flow rate toward higher pressure values (by ∼20%). This increased vascular resistance was refractory to a high dose of sodium nitroprusside, implying the involvement of other factors than increased vascular tone. Chronic hypoxia also increased vasoconstrictor responses to angiotensin II (by ∼75%) and to acute hypoxic challenges (by >150%). We conclude that chronic prenatal hypoxia causes a sustained elevation of fetoplacental vascular resistance and vasoconstrictor reactivity that are likely to produce placental hypoperfusion and fetal undernutrition in vivo.

The herbal medicine Tokishakuyakusan increases fetal blood glucose concentrations and growth hormone levels and improves intrauterine growth retardation induced by N(omega)-nitro-L-arginine methyl ester

N(omega)-Nitro-L-arginine methyl ester (L-NAME) induces a pre-eclampsia-like syndrome in pregnant rats. We have previously reported the anti-hypertensive effects of several Japanese traditional (Kampo) medicines in this model, and one of these, Tokishakuyakusan (TS), also improved intrauterine growth retardation (IUGR). In the present study, we characterized the effect of TS on IUGR. TS administration reversed the decrease in fetal body weight and fetal blood glucose concentration induced by the infusion of L-NAME. Growth hormone (GH) levels in the fetal blood, which were decreased by L-NAME infusion, were also significantly elevated by TS; however, levels of GH releasing hormone (GHRH) and insulin-like growth factor I (IGF-I) were unchanged and only slightly changed, respectively. Treatment with L-NAME with or without TS had no apparent effect on GH, GHRH, and IGF-I levels of dams. In an immunocytochemical study, the number of GH-positive cells in the fetal pituitary gland was significantly increased in TS-treated rats. These data suggest that enhanced proliferation of somatotrope cells of the pituitary gland and the resultant increase in GH secretion in the fetus may be involved in the improvement of IUGR by TS.

Relaxation of human placental arteries and veins by ATP-sensitive potassium channel openers

BACKGROUND

Adenosine triphosphate (ATP)-sensitive potassium channels (K(ATP)) are important modulators of vascular tone. Preliminary data from our laboratory suggests that K(ATP) channels are expressed in the fetoplacental vasculature where addition of pinacidil, a specific K(ATP) opener, promotes relaxation. We aimed to assess the effects of KRN2391 and KRN4884 on the fetoplacental vasculature, which are putative K(ATP) channel openers.

MATERIALS AND METHODS

Functional activity of K(ATP) channels was assessed in chorionic plate arteries and veins using wire myography. Cromakalim-, KRN2391- and KRN4884-induced relaxations were assessed in the presence and absence of agonist-induced pretone. Cromakalim, an established K(ATP) channel opener, acted as control.

RESULTS

KRN2391 evoked significantly greater relaxation of chorionic plate arteries and veins than either KRN4884 or cromakalim. KRN2391-induced relaxation of precontracted arteries and veins was reduced in the presence of inhibitors of the nitric oxide pathway (L-NNA or LY83583). With KRN4884, there was no contribution of nitric oxide to the induced relaxation.

CONCLUSIONS

We conclude that K(ATP) channels play an important role in controlling placental vascular tone. KRN2391 induces relaxation of human placental blood vessels by activation of K(ATP) channels and via activation of nitric oxide-dependent pathways.

Reactivity of Human Placental Chorionic Plate Vessels from Pregnancies Complicated by Intrauterine Growth Restriction (IUGR)1

A successful pregnancy is dependent on liberal placental perfusion via the maternal and fetal circulations. Doppler waveform analyses of umbilical arteries suggest increased resistance to flow in the fetoplacental circulation of pregnancies complicated by intrauterine growth restriction (IUGR). Neither the site nor the mediators responsible for this altered vascular reactivity are known, to date. In placentas in normal pregnancy, reduced oxygenation promotes contraction of the in vitro-perfused placental cotyledon and modulates agonist-induced contraction of chorionic plate arteries and veins. Placental oxygenation has also been suggested to be reduced in IUGR. We tested the hypothesis that oxygen tension could directly modify placental chorionic plate vessel vasoreactivity in IUGR. Small arteries and veins from the chorionic plate were dissected from biopsies from placentas of pregnancies complicated by IUGR and were studied using parallel wire myography. Vasoconstriction at 20%, 7%, and 2% oxygen was assessed utilizing the thromboxane mimetic U46619. Experiments were also performed in the presence of 4-aminopyridine (4AP), a blocker of voltage-gated potassium channels. Increased oxygenation reduced venous vasoconstriction but did not modify arterial vasoconstriction. 4AP increased basal tone in arteries and veins. We suggest that venoconstriction in response to hypoxia may provide a mechanism for increased fetoplacental vascular resistance associated with IUGR.

Glibenclamide Inhibits Agonist-induced Vasoconstriction of Placental Chorionic Plate Arteries

BACKGROUND

Preliminary data suggest that K(ATP) channels may be expressed in placental arteries and veins [Wareing M, Turner C, Greenwood SL, Baker PN, Fyfe GK. Expression of mRNA encoding K+ channels in chorionic plate arteries and veins. J Soc Gynecol Investig 2004;11:353A]. However, no data exist on glibenclamide's effects in placental chorionic plate arteries.

AIM

To assess the effect of glibenclamide on placental chorionic plate arterial vasoconstriction.

METHODS

Arteries were dissected from placental chorionic plate biopsies obtained at term from uncomplicated pregnancies (N=63). Arteries were mounted onto a wire myograph in HCO3- -buffered physiological salt solution (PSS) at 37 degrees C (5% O2/5% CO2 bubbling) and normalised at 0.9 of L5.1 kPa. Constriction viability was assessed with 120 mmol l(-1) potassium solution (KPSS). Dose-response curves were produced with the thromboxane-mimetics U46619 and U44069 (10(-10)-2 x 10(-6)M), arginine vasopressin (10(-10)-5 x 10(-8)M) and endothelin-1 (10(-11)-3 x 10(-7)M) in the presence or absence of 50 micromol l(-1) glibenclamide. The effect of glibenclamide on arginine vasopressin- and U46619-induced constriction was also assessed in the presence of the cyclo-oxygenase inhibitor indomethacin (10 micromol l(-1)).

RESULTS

Pre-incubation with 50 micromol l(-1) glibenclamide significantly right-shifted dose-response curves to all vasoconstrictive agonists tested (repeated measures ANOVA). Indomethacin did not modify the inhibitory effect of glibenclamide.

CONCLUSION

Glibenclamide's effects on agonist-induced constrictions are unlikely to be via an inhibition of ATP-sensitive K+ channels, and with U46619- and U44069-induced constrictions, glibenclamide may be acting as a competitive antagonist of thromboxane receptors.

Endocrine regulation of human fetal growth: the role of the mother, placenta, and fetus

The environment in which the fetus develops is critical for its survival and long-term health. The regulation of normal human fetal growth involves many multidirectional interactions between the mother, placenta, and fetus. The mother supplies nutrients and oxygen to the fetus via the placenta. The fetus influences the provision of maternal nutrients via the placental production of hormones that regulate maternal metabolism. The placenta is the site of exchange between mother and fetus and regulates fetal growth via the production and metabolism of growth-regulating hormones such as IGFs and glucocorticoids. Adequate trophoblast invasion in early pregnancy and increased uteroplacental blood flow ensure sufficient growth of the uterus, placenta, and fetus. The placenta may respond to fetal endocrine signals to increase transport of maternal nutrients by growth of the placenta, by activation of transport systems, and by production of placental hormones to influence maternal physiology and even behavior. There are consequences of poor fetal growth both in the short term and long term, in the form of increased mortality and morbidity. Endocrine regulation of fetal growth involves interactions between the mother, placenta, and fetus, and these effects may program long-term physiology.

Chorionic plate artery function and Doppler indices in normal pregnancy and intrauterine growth restriction

BACKGROUND

In fetal growth restriction (FGR) abnormal umbilical artery (UA) Doppler waveform indices suggest increased vascular resistance and impaired placental blood flow. This study aimed to determine whether UA Doppler waveform indices were related to the vasoreactivity of placental chorionic plate small arteries in normal and FGR pregnancies.

MATERIALS AND METHODS

UA Doppler waveform analysis was performed 24 h before delivery in 23 normal term and 15 FGR pregnancies. Post-delivery responses of chorionic plate arteries to vasoactive agents were examined using the technique of wire myography.

RESULTS

Altered vascular reactivity to agonists was demonstrated in chorionic plate arteries in FGR pregnancy. Constriction to U46619 (thromboxane mimetic) and relaxation to sodium nitroprusside (nitric oxide donor) were significantly increased in the arteries of FGR pregnancies compared with normal pregnancies. No relationship existed between Doppler indices and chorionic plate responses in normal or FGR pregnancies.

CONCLUSIONS

Fetoplacental vascular reactivity is altered in FGR pregnancy independently of UA Doppler waveform indices. Altered function may be additive to the pathophysiology underlying abnormal Doppler waveforms and could contribute to the inappropriate control of vascular tone in FGR.

Developmental biology of the placenta and the origins of placental insufficiency

Defects in all the trophoblast-differentiating pathways--endovascular, interstitial and chorionic villous--play a role in the pathogenesis of early-onset intra-uterine growth restriction (IUGR). There are two types of extravillous trophoblast: endovascular trophoblast, that forms the definitive placenta by occlusion of the spiral arteriole at the implantation site, and interstitial extravillous trophoblast, responsible for the anatomical erosion of the distal spiral arteriole and the secretion of angiogenic and vasodilator signals to improve uterine blood flow. Defective endovascular erosion may render the basal plate inadequate to meet the demands of the fetus. Failed interstitial invasion of spiral arterioles could lead to failure of local angiogenic and systemic cardiovascular adaptation signals that could be the underlying basis for early-onset IUGR and pre-eclampsia. As debate persists regarding the relative importance of cord, stem and terminal villous pathology, the study of factors controlling trophoblast turnover from immature intermediate villi to conductance stem villi and gas-exchanging terminal villi, translation of our knowledge from mouse placental genetics into human placental development, and defining causes of thrombo-occlusive damage to the placenta would help our understanding of the pathophysiology of early-onset IUGR.

Glucose Metabolism in the Human Preterm and Term Placenta of IUGR Fetuses

Many fetuses suffering from intrauterine growth restriction (IUGR) are hypoglycaemic. However, the underlying mechanisms are not well established. An increased placental glucose consumption in IUGR could impair glucose transfer across the placenta. In this study we used two different approaches to investigate glucose metabolism in preterm and term placentae of IUGR fetuses. We determined activity and protein expression of the three rate-limiting glycolytic enzymes phosphofructo kinase (PFK), pyruvate kinase (PK) and hexokinase (HXK) in a cytoplasmic fraction of homogenates of placentae obtained from IUGR and appropriate for gestational age (AGA) pregnancies. Protein expression was assessed using Western blot and enzyme activities were determined in a spectrophotometer by measuring the rate of NADH oxidation (PFK and PK) or NADP reduction (HXK) in enzyme reactions coupled to the respective enzyme. To determine the distribution of the glycolytic enzymes immunocytochemistry was performed. We also measured glucose consumption and lactate production in fresh placental villous tissue using a perifusion system. The expression of PFK, PK and HXK as well as the activity of PK and HXK was unaltered in IUGR placentae. The activity of PFK on the other hand was 32 per cent lower in IUGR placentae (n=24, P<0.05). Immunocytochemistry confirmed the distribution of the enzymes to the cytoplasm of the syncytiotrophoblast. Placental glucose consumption in IUGR [0.06+/-0.01 micromol/(min*g), n=5] was not different from AGA [0.06+/-0.005 micromol/(min*g), n=12], whereas lactate production was decreased by 28 per cent in IUGR. These results do not support the hypothesis of increased placental glucose consumption but suggest an altered glycolytic pathway in the IUGR placenta.

The effect of oscillating low intensity magnetic field on the Na+, K+, Ca++, and Mg++ concentrations in the maternal and fetal circulation of the dually perfused human placental cotyledon

Dual-sided perfusions of the human placental cotyledon in vitro were used to study effects of low intensity magnetic fields (MFs) of 2 mT, 50 Hz (E1, 10 perfusions) and 5 mT, 50 Hz (E2, 10 perfusions). In the control group C (10 experiments) no field was used. Perfusions lasted 180 min each. Increased release of calcium ions from the placental cotyledon was found in the fetal circulation during perfusion when the 2 mT, 50 Hz MF was used. No changes in the release of sodium and magnesium ions were observed compared to the control group. The 5 mT, 50 Hz oscillating MF intensified the release of sodium ions from the perfused cotyledon both to the fetal and maternal circulation up to the 150th min of the experiment. Increased release of magnesium ions was observed only to the fetal circulation between 120 and 180 min and of calcium ions to the fetal circulation between 60 and 180 min. No significant differences in K concentrations were found between the control and MF exposed cotyledons under conditions of these experiments.

Decreased vascularization and cell proliferation in placentas of intrauterine growth-restricted fetuses with abnormal umbilical artery flow velocity waveforms

OBJECTIVE

The purpose of this study was to compare the morphologic features of placentas in severe intrauterine fetal growth restriction with abnormal umbilical artery blood flow velocity waveforms and normal gestation.

STUDY DESIGN

Immunohistochemical methods were used to evaluate cell proliferation, vascular density, and alpha-smooth muscle actin expression by stromal cells in a group of 9 age-matched intrauterine growth-restricted and control placentas at 25 to 41 weeks of gestation.

RESULTS

Fewer MIB1-positive nuclei were observed in both trophoblast and stromal cell populations in intrauterine growth restriction, which indicates fewer cells in cycle. Furthermore, a greatly reduced vascular density was observed, along with higher levels of alpha-smooth muscle actin expression in stromal cells.

CONCLUSION

Intrauterine growth-restricted placentas show reduced cell proliferation in both trophoblast and stromal cell compartments. Peripheral villous vascularization is highly reduced.

Activated protein C in normal human pregnancy and pregnancies complicated by severe preeclampsia: a therapeutic opportunity?

OBJECTIVES

Given the efficacy and safety of recombinant human activated protein C (rhAPC) in the systemic inflammatory response syndrome, this study was designed to review the evidence for a role for APC in the pathogenesis of preeclampsia. Preeclampsia is a proinflammatory and procoagulant state, and it is a pregnancy-specific condition that mimics the systemic inflammatory response syndrome. rhAPC reduces mortality in patients with systemic inflammatory response syndrome and could potentially have a role as disease-modifying therapy in preeclampsia. To determine which patients would be offered rhAPC, the literature pertaining to fetal/neonatal outcomes for preeclampsia remote from term, transplacental transport of protein C, and pregnancy experience with the compound were reviewed.

DATA SOURCES

MEDLINE, review papers, hand searches of relevant nonindexed journals, and the bibliographies of relevant textbooks and articles reviewed.

STUDY SELECTION

Randomized controlled trials were considered to provide the best quality of clinical data. Case-control series were considered over uncontrolled data. Some data were not available in the published literature (e.g., neonatal outcomes at various gestational ages and birthweights after a hypertensive pregnancy; and transplacental transfer of protein C), and these data were determined by us.

DATA EXTRACTION

Data were extracted by systematic review onto data collection sheets. Because of the quality of the data, this review is primarily qualitative.

DATA SYNTHESIS

APC levels fall during normal gestation, returning to normal values by 6 wks postpartum. Limited data suggest that early onset preeclampsia is a state of further, and inappropriate, reduction in APC. Preeclampsia resembles systemic inflammatory response syndrome in this regard. After hypertensive pregnancies, neonates have a 50% chance of intact survival if delivered after 27 + 0 wks of gestation with a birthweight of >600 g. It would seem ethical to offer women with preeclampsia with <50% chance of intact perinatal survival novel and potentially disease-modifying therapy such as rhAPC, especially as there is no transplacental transfer of protein C. Limited evidence would support the use of rhAPC in women with severe postpartum preeclampsia.

CONCLUSIONS

Sufficient data exist to support the use of rhAPC in phase II clinical studies for women with either early onset preeclampsia or severe or deteriorating postpartum disease.

Glucose transport and system A activity in syncytiotrophoblast microvillous and basal plasma membranes in intrauterine growth restriction

The mechanisms underlying the reduced fetal plasma concentrations of amino acids and glucose associated with intrauterine growth restriction (IUGR) remain to be fully established. The activity of the amino acid transporter system A has been shown to be reduced in the syncytiotrophoblast microvillous membrane (MVM) in IUGR, however the impact of these changes on transplacental transport is difficult to assess without information on system A activity in the basal plasma membrane (BM). In this study we measured system A activity and mediated D-glucose uptake using radiolabelled substrates and rapid filtration techniques, and glucose transporter isoform 1 (GLUT 1) protein expression using Western blots in MVM and BM isolated from human placentas. In term IUGR (n=11) MVM system A activity was unaltered compared to controls (n=9). In contrast, system A activity in MVM was reduced by 50 per cent (P< 0.05) in preterm IUGR (n=8, gestational age 28-36 weeks) as compared to controls (n=8, gestational age 28-35 weeks). BM system A activity was unaltered in both IUGR groups. Similarly, MVM and BM GLUT 1 expression and mediated D-glucose uptake was not affected by IUGR. In all preterm IUGR pregnancies signs of severe fetal compromise were present whereas term IUGR fetuses were less affected. These data support the view that MVM system A activity is related to the severity of compromise in IUGR. The markedly reduced system A activity in MVM in preterm IUGR together with the unaltered activity in BM is consistent with a decreased transplacental transport of neutral amino acids in this pregnancy complication. The hypoglycemia present in utero in some IUGR fetuses is not caused by a decreased glucose transport capacity across the syncytiotrophoblast plasma membranes.

Mild maternal undernutrition in the first half of ovine pregnancy influences placental morphology but not fetal Doppler flow velocity waveforms and fetal heart size

AIMS

We wanted to investigate whether experimental dietary manipulations during early pregnancy influence placental growth and subsequently the cardiovascular system as assessed non-invasively by ultrasonography in the sheep fetus.

METHODS

21 ewes bearing singletons of uniform age were randomly assigned for the first half of pregnancy to one of the following study groups: fed 100% of their nutritional requirements (i.e. controls), global reduction in total intake by 30% (i.e. 70% global) and reduction in protein intake by 30% (i.e. 70% protein).

RESULTS

Placentas from the 70% protein group had significantly more small placentomes, but significantly fewer large placentomes compared to the 70% global group. However, there were no significant differences between the three dietary groups for either the aortic or the umbilical Doppler velocimetry parameters and the fetal heart rate or heart size.

CONCLUSIONS

The present study shows that early mild maternal undernutrition produces subtle changes in cotelydonary weight. However, Doppler and echocardiographic parameters were not affected by these changes.