Placental glucose transfer and fetal growth

Effects of L-carnitine supplementation in pregnant sows on plasma concentrations of insulin-like growth factors, various hormones and metabolites and chorion characteristics

Previous studies have shown that supplementation of sow diets with L-carnitine increases the body weight of piglets at birth. This study was conducted to elucidate the reasons for this phenomenon. Three experiments with 24 (experiment 1), 40 (experiment 2) and 12 (experiment 3) sows were conducted. In all three experiments, sows were allotted to two groups which had free access to a nutritionally adequate diet. Sows of one group were supplemented with 125 mg L-carnitine/day during pregnancy; sows of the other group (control group) did not receive L-carnitine. In experiment 1, plasma samples were collected at day 95 of pregnancy, in experiment 2 plasma samples were collected at days 80 and 100 of pregnancy. In experiment 3, chorions of the sows were collected at parturition. L-carnitine-treated sows had higher plasma concentrations of total L-carnitine than control sows (p < 0.05). The number of piglets born and weights of litter and individual piglets at birth were not different between both groups in all three experiments. L-carnitine-treated sows had higher plasma concentrations of insulin-like growth factor-I (IGF-I) on day 80 of pregnancy (experiment 2, p < 0.05) and on day 95 (experiment 1, p < 0.10), and a higher plasma concentration of IGF-II on day 80 (experiment 2, p < 0.05) than control sows. Moreover, sows supplemented with L-carnitine had heavier chorions (+22%, p =0.10) with greater amounts of protein (+45%, p < 0.05) and DNA (+38%, p < 0.10) and a higher protein concentration of glucose transporter-1 (+62%, p < 0.05). Plasma concentrations of 17beta-oestradiol, progesterone and thyroid hormones as well as concentrations of urea and total free amino acids were not different between both groups of sows. Plasma concentrations of non-esterified fatty acids, ketone bodies, triacylglycerols and cholesterol were also largely indifferent between both groups of sows. In conclusion, this study shows that L-carnitine has less influence on lipid metabolism and utilization of nitrogen in pregnant sows but increases their plasma concentrations of IGFs. This in turn may enhance development of the placentae and the intrauterine nutrition of the fetuses. This may be the reason for increased birth weights observed in recent studies in sows supplemented with L-carnitine.

Structure-based modelling in reproductive toxicology: (Q)SARs for the placental barrier

The replacement of animal testing for endpoints such as reproductive toxicity is a long-term goal. This study describes the possibilities of using simple (quantitative) structure-activity relationships ((Q)SARs) to predict whether a molecule may cross the placental membrane. The concept is straightforward, if a molecule is not able to cross the placental barrier, then it will not be a reproductive toxicant. Such a model could be placed at the start of any integrated testing strategy. To develop these models the literature was reviewed to obtain data relating to the transfer of molecules across the placenta. A reasonable number of data were obtained and are suitable for the modelling of the ability of a molecule to cross the placenta. Clearance or transfer indices data were sought due to their ability to eliminate inter-placental variation by standardising drug clearance to the reference compound antipyrine. Modelling of the permeability data indicates that (Q)SARs with reasonable statistical fit can be developed for the ability of molecules to cross the placental barrier membrane. Analysis of the models indicates that molecular size, hydrophobicity and hydrogen-bonding ability are molecular properties that may govern the ability of a molecule to cross the placental barrier.

Localized expression of histamine H1 receptors in syncytiotrophoblast cells of human placenta

The previous Northern blot analysis and in situ hybridization studies showed that histamine H1-receptor (H1R) mRNA is expressed in human placenta and suggested that H(1)R plays some roles in the function of placenta in pregnancy. To investigate further, it is essential to show the precise location of H1R in the placenta. In the present study, we investigated H1R expression in human placenta by radioligand binding assay and immunohistochemical study using an antibody against human H1R. Placentas were obtained from normal uncomplicated deliveries. Membranes prepared from the tissue exhibited saturable [3H]mepyramine binding (K(d) = 4.0 +/- 0.6 nM and B(max) = 91.4 +/- 4.9 fmol/mg of protein). Stereoisomers of chlorpheniramine inhibited [(3)H]mepyramine binding; d-chlorpheniramine inhibited more potently than l-chlorpheniramine, K(i) values being 1.1 +/- 0.4 and 270 +/- 170 nM, respectively. The placenta tissues were positively immunostained with anti-H1R antibody only in the region of the syncytiotrophoblast of chorionic villus. The tissues were double stained with anti-H1R antibody and an antibody against human chorionic gonadotoropin (hCG) that is solely expressed in placental syncytiotrophoblast cells. The results showed that H1R and hCG were expressed on the same cells, that is, syncytiotrophoblast cells. These results indicate that H1Rs are specifically expressed in syncytiotrophoblast cells of human placenta organ.

Transforming growth factor-beta induces differentiation of the labyrinthine trophoblast stem cell line SM10

The mammalian placenta consists of different trophoblast cell types that assist in the variety of functions required for the maintenance of pregnancy. In rodents, labyrinthine trophoblasts of the placenta are especially important, because they are capable of differentiating into fused labyrinthine cells, which form the feto-maternal exchange surface. Even though the molecular signals triggering labyrinthine trophoblast differentiation are poorly understood, transforming growth factor-beta (TGF-beta) has been shown to be present in the placental environment and alter trophoblast development. In this study, we investigated the effects of TGF-beta on the differentiation of the labyrinthine trophoblast stem cell lines SM10 and HRP-1. RT-PCR analyses demonstrated that while the molecular expression of labyrinthine-specific lineage markers (Esx1, Tfeb, and Tec) was maintained in TGF-beta-treated SM10 and HRP-1 cells, TGF-beta induced the down-regulation of trophoblast stem cell markers Id2 and Cdx2. In contrast, TGF-beta induced the expression of a marker of differentiated labyrinthine trophoblasts, Gcm1, only in the SM10 cell line. Furthermore, we demonstrated an increased glucose uptake in the TGF-beta-treated SM10 cells, indicative of functional differentiation. Finally, cell fusion in TGF-beta-treated SM10 and HRP-1 cells was investigated by western blotting analysis of placental alkaline phosphatase and cadherin-11 and by microscopic analyses of cell morphology using green fluorescent protein (GFP) and rhodamine phalloidin staining. The western blotting and morphological analyses indicate TGF-beta-induced cell fusion and morphological differentiation in the SM10 cell line. The SM10 cell line will provide a new and unique model for detailed analysis of TGF-beta-induced molecular events associated with labyrinthine trophoblast differentiation and function.

Influence of Endurance Exercise and Diet on Human Placental Development and Fetal Growth

The delivery of oxygen and substrate to the maternal-fetal interphase is the major maternal environmental stimulus which either up- or down-regulates feto-placental growth. During pregnancy, sustained exercise sessions cause an intermittent reduction in oxygen and substrate delivery to the interphase that may exceed 50% during the exercise but, it is probable that regular bouts of sustained exercise or exercise training may improve oxygen and substrate delivery at rest. The type of maternal carbohydrate intake (low- versus high-glycemic sources) and food intake frequency also influence substrate availability through their effects on maternal blood glucose levels and insulin sensitivity. As a result, different exercise regimens and/or different types of carbohydrate intake modify feto-placental growth. The magnitude and direction of the effect is determined by their average 24-h effect on oxygen and substrate availability at different time-points in pregnancy. In general, exercise in early and mid pregnancy stimulates placental growth while the relative amount of exercise in late pregnancy determines its effect on late fetal growth. Low-glycemic food sources in the diet decrease growth rate and size at birth while high-glycemic food sources increase it. Thus, it may be possible to improve pregnancy outcomes in both healthy, low-risk women and a variety of high-risk populaces by simply modifying maternal physical activity and dietary carbohydrate intake during pregnancy.

Proteomic analysis of apical microvillous membranes of syncytiotrophoblast cells reveals a high degree of similarity with lipid rafts

Brush borders (microvilli) are cell membrane specialized structures that function mainly as high-throughput absortive/secretory areas. It has been well-established that brush borders are particularly rich in membrane lipids characteristic to lipid rafts. Here, we report 57 proteins identified from microvillous membranes (MVM) isolated from human syncytiotrophoblast cells using an experimental method that avoids the use of nonionic detergents. About 60% of the proteins reported here have been described previously as lipid-raft specific. Well-known lipid raft-markers such as Annexin A2 and alkaline phosphatase were identified. Cytoskeleton structural constituents and proteins related with the control and modulation of the cytoskeletal architecture as well as the regulation of the interaction of cytoskeletal constituents with the cell membrane and particularly with lipid raft domains were found (Ezrin, IQGAP1 and 2, EBP50). Other proteins identified include signal transduction molecules, such as Ras-related protein Rab-1B and Rab-7, and ADP-ribosylation factor 1. Several proteins harbor putative post-translational modifications that favor its localization in the lipid-raft environment, such as GPI (alkaline phosphatase and 5'-nucleotidase) and myristoylation (BASP1 and MARCKS). On the whole, this extensive description demonstrates from the protein composition point of view that brush border membranes are indeed highly enriched in lipid raft microdomains.

Effects of chronic hypoxia in vivo on the expression of human placental glucose transporters

Birth weight is reduced and the risk of preeclampsia is increased in human high altitude pregnancies. There has been little work to determine whether hypoxia acts directly to reduce fetal growth (e.g. reduced blood flow and oxygen delivery), or via changes in functional capacities such as nutrient transport. We therefore investigated the expression of a primary nutrient transporter, the GLUT1 glucose transporter and two in vitro markers of hypoxia (erythropoietin receptor, EPO-R, and transferrin receptor, TfR) in the syncytial microvillous (MVM) and basal membrane fractions (BMF) of 13 high (3100 m) and 12 low (1600 m) altitude placentas from normal term pregnancies. Birth weight was lower at 3100 m than at 1600 m despite similar gestational age, but none of the infants were clinically designated as fetal growth restriction. EPO-R, TfR and GLUT1 were examined by immunoblotting and maternal circulating erythropoietin and transferrin by ELISA. EPO-R was greater on the MVM (+75%) and BMF (+25%) at 3100 m. TfR was 32% lower on the MVM at 3100 m. GLUT1 was 40% lower in the BMF at 3100 m. Circulating EPO was greater at high altitude, while transferrin was similar, and neither correlated with their membrane receptors. BMF GLUT1 was positively correlated with birth weight at high, but not low altitude. In this in vivo model of chronic placental hypoxia, syncytial EPO-R increased as expected, while nutrient transporters decreased, opposite to what has been observed in vitro. Therefore, hypoxia acts to reduce fetal growth not simply by reducing oxygen delivery, but also by decreasing the density of nutrient transporters.

High-fat feeding during gestation and nursing period have differential effects on the insulin secretory capacity in offspring from normal Wistar rats

Restriction of protein or energy intake during gestation or early life is linked to developmental defects in the endocrine pancreas and insulin resistance.

AIMS

To study whether a saturated fatty acid-rich diet during gestation and/or after the weaning period may be detrimental to the insulin secretory capacity later in life.

STUDY DESIGN

Female Wistar rats were fed diets rich in carbohydrate (CHO) or saturated fat (SAFA) during pregnancy. The male offspring were split into five subgroups: after birth group 1 (control) continued on CHO and group 3 on SAFA. Group 2 continued on the CHO diet during the nursing period but changed to SAFA post weaning. Group 4 continued on SAFA, but changed to CHO post weaning. For group 5 the offspring of mothers given a SAFA diet were changed to nursing mothers on a CHO diet immediately after birth, and continued on the same diet post weaning. After 14 wk, the islets of Langerhans were isolated for determination of insulin secretory capacity in static incubation and dynamic perifusion experiments.

RESULTS

We found a negative correlation (Coef: -3.1, 95% CI: -6.1 to -0.0, p < 0.05) between a diet rich in saturated fat fed to mothers during gestation and a positive correlation (Coef: 4.4, 95% CI: 0.9 to 7.8, p = 0.01) between nursing mothers' diet and the capability to secrete insulin in the offspring.

CONCLUSION

Our results indicate the importance of applying a nutrient-balanced diet during pregnancy and the nursing period on the later insulin secretory capacity in the offspring.

Expression of GLUT12 in the fetal membranes of the human placenta

The aim of this study was to characterize the expression of the novel glucose transporter GLUT12 in the fetal membranes of the human placenta. RT-PCR and Western blotting of extracts of amnion and choriodecidua from four normal term placentas identified GLUT12 mRNA and protein expression. In all four samples the signals for GLUT12 were markedly stronger in the choriodecidua than in the amnion, whereas the signals for GLUT1, a glucose transporter know to be expressed in fetal membranes, were similar for the two tissues. In further studies, paraffin sections of fetal membranes were analyzed by immunohistochemistry with GLUT12 and GLUT1-specific polyclonal antibodies. GLUT12 immunoreactivity was localized predominantly to the trophoblast cells in the chorion and to a lesser extent to decidual cells and to epithelial and fibroblast cells of the amnion. GLUT1 was localized to chorionic trophoblast cells and amniotic epithelial and fibroblast cells. GLUT12 expression was predominantly cytoplasmic, whereas GLUT1 was associated with the membrane of the cells. These results show that GLUT12 is expressed in cells of human fetal membranes and suggest that GLUT12 may play a role in the facilitation of glucose transport into these cells.

Growth and function of the normal human placenta

The placenta is the highly specialised organ of pregnancy that supports the normal growth and development of the fetus. Growth and function of the placenta are precisely regulated and coordinated to ensure the exchange of nutrients and waste products between the maternal and fetal circulatory systems operates at maximal efficiency. The main functional units of the placenta are the chorionic villi within which fetal blood is separated by only three or four cell layers (placental membrane) from maternal blood in the surrounding intervillous space. After implantation, trophoblast cells proliferate and differentiate along two pathways described as villous and extravillous. Non-migratory, villous cytotrophoblast cells fuse to form the multinucleated syncytiotrophoblast, which forms the outer epithelial layer of the chorionic villi. It is at the terminal branches of the chorionic villi that the majority of fetal/maternal exchange occurs. Extravillous trophoblast cells migrate into the decidua and remodel uterine arteries. This facilitates blood flow to the placenta via dilated, compliant vessels, unresponsive to maternal vasomotor control. The placenta acts to provide oxygen and nutrients to the fetus, whilst removing carbon dioxide and other waste products. It metabolises a number of substances and can release metabolic products into maternal and/or fetal circulations. The placenta can help to protect the fetus against certain xenobiotic molecules, infections and maternal diseases. In addition, it releases hormones into both the maternal and fetal circulations to affect pregnancy, metabolism, fetal growth, parturition and other functions. Many placental functional changes occur that accommodate the increasing metabolic demands of the developing fetus throughout gestation.

Insulin and nitric oxide stimulates glucose transport in human placenta

The present work examines whether insulin and NO can act as regulators of glucose transport in placenta. Glucose uptake (2-deoxy D-[(3)H]glucose) was measured in the absence (control or basal values) and in the presence of insulin (1200 microU/ml) or SNP (20 microM) in isolated perfused cotyledons and tissue slices preparations of human placenta. Both insulin and NO significantly increased glucose uptake by 20 and 27 per cent, respectively. Insulin decreased the Km of glucose transport from 42.5 +/- 2.69 to 35.1 +/- 2.58 mM. The stimulatory effect of SNP was mimicked by 8-CPT-cGMP and was completely blocked by the guanylate cyclase inhibitor, ODQ (10 microM). ODQ and the NOS inhibitor, L-NAME (100 microM), decreased basal glucose uptake but did not affect insulin-stimulated glucose transport. Taken together, these findings indicate that insulin and NO stimulate glucose uptake in human placenta and suggest that both potential regulators of glucose transport use different signaling pathways.

Maternal Hyperglycemia Improves Fetal Cardiac Function During Tachycardia-Induced Heart Failure in Pigs

Background— Fetal tachycardia often leads to cardiac failure, which in experimental settings can be prevented by direct fetal glucose-insulin administration. In this study, we hypothesize that similar effects can be obtained indirectly by inducing maternal hyperglycemia.

Methods and Results— Systolic and diastolic indices (dP/dt max and τ) of left ventricular function were measured by use of high-fidelity catheters during 180 minutes of aggressive atrial pacing (≈300 bpm) in 12 preterm porcine fetuses. In 6 fetuses, maternal hyperglycemia (15 mmol/L) was induced for the last 120 minutes of pacing. The remaining fetuses served as controls. Glucose, insulin, and free fatty acid levels were determined, as was fetal myocardial glycogen content. Maternal glucose infusion led to significant fetal hyperglycemia and hyperinsulinemia but did not change the inherently low fetal levels of free fatty acids. There were no differences between groups with regard to dP/dt max (1025±226 and 1037±207 mm Hg, P =NS) and τ (20.6±2.0 and 21.4±1.6 ms, P =NS) at baseline (100%). During the 180 minutes of pacing, systolic function (dP/dt max ) and diastolic function (τ) deteriorated more in the control group than in the hyperglycemic group ( P <0.001 for both). At 180 minutes, dP/dt max was 62±18% of baseline in controls and 85±11% in hyperglycemic fetuses ( P =0.03), and τ was 117±12% and 98±4%, respectively ( P =0.004).

Conclusions— Induced maternal hyperglycemia improves fetal cardiac function during fetal tachycardia and suggests a possible additional therapeutic option to improve the function of the failing fetal heart before or during antiarrhythmic therapy. The findings may be relevant in fetal heart failure in general.

Endocytic and Transcytotic Processes in Villous Syncytiotrophoblast: Role in Nutrient Transport to the Human Fetus

The supply of nutrients to the developing fetus is a major function of the human hemochorial placenta, a placenta type in which the fetal chorion is in direct contact with the maternal blood. At term, nutrients have to be transported across two cell layers in chorionic villi, the syncytiotrophoblast (STB) and fetal endothelial cells. The STB is a continuous syncytium covering the entire surface of chorionic villi. This polarized epithelium is specialized in exchange processes and membrane trafficking between the apical membrane facing the maternal blood and the basal membrane facing the fetal endothelium. To meet placental and fetal requirements, the STB selectively takes up and transports a variety of nutrients, hormones, growth factors and cytokines and also transfers passive immunity to the fetus by receptor-mediated transcytosis. In this review in vivo and in vitro systems currently used to study STB functions are discussed and the potential mechanisms of transplacental IgG, iron, lipoprotein and glucose transport are presented. As revealed in this article, the placenta is a tissue where intensive cell biological research is required to unravel endocytic trafficking pathways in a highly specialized cell such as the STB.

Exposure to maternal diabetes is associated with altered fetal growth patterns: A hypothesis regarding metabolic allocation to growth under hyperglycemic-hypoxemic conditions

The prevalence of diabetes is rising worldwide, including women who grew poorly in early life, presenting intergenerational health problems for their offspring. It is well documented that fetuses exposed to maternal diabetes during pregnancy experience both macrosomia and poor growth outcomes in birth size. Less is known about the in utero growth patterns that precede these risk factor expressions. Fetal growth patterns and the effects of clinical class and glycemic control were investigated in 37 diabetic pregnant women and their fetuses and compared to 29 nondiabetic, nonsmoking maternal/fetal pairs who were participants in a biweekly longitudinal ultrasound study with measurements of the head, limb, and trunk dimensions. White clinical class of the diabetic women was recorded (A2-FR) and glycosylated hemoglobin levels taken at the time of measurement assessed glycemic control (median 6.9%, interquartile range 5.6-9.2%). No significant difference in fetal weight was found by exposure. The exposed sample had greater abdominal circumferences from 21 weeks (P < or = 0.05) and shorter legs, but greater upper arm and thigh circumferences accompanied increasing glycemia in the second trimester. In the third trimester, exposed fetuses had a smaller slope for the occipital frontal diameter (P = 0.00) and were brachycephalic. They experienced a proximal/distal growth gradient in limb proportionality with higher humerus / femur ratios (P = 0.04) and arms relatively long by comparison with legs (P = 0.02). HbA1c levels above 7.5% accompanied shorter femur length for thigh circumference after 30 gestational weeks of age. Significant effects of diabetic clinical class and glycemic control were identified in growth rate timing. These growth patterns suggest that hypoxemic and hyperglycemic signals cross-talk with their target receptors in a developmentally regulated, hierarchical sequence. The increase in fetal fat often documented with diabetic pregnancy may reflect altered growth at the level of cell differentiation and proximate mechanisms controlling body composition. These data suggest that the maternal-fetal interchange circuit, designed to share and capture resources on the fetal side, may not have had a long evolutionary history of overabundance as a selective force, and modern health problems drive postnatal sequelae that become exacerbated by increasing longevity.

Determinants of fetal growth

Fetal growth is the end product of a variety of genetic, maternal, fetal, and placental factors. Maternal size is a dominant determinant of birth weight. Specific nutrients and their availability modify the expression of genetically determined metabolic and transfer systems. Hormones and growth factors of maternal, fetal, and placental origin regulate nutrient transfer and fetal organ development. Fetal development is ultimately determined by dynamic interactions between all of these factors beginning prior to conception and proceeding to delivery.