Transplacental supply of mannose and inositol in uncomplicated pregnancies using stable isotopes

Maternal hypothyroidism in rats impairs placental nutrient transporter expression, increases labyrinth zone size, and impairs fetal growth

INTRODUCTION

Hypothyroidism during pregnancy is associated with fetal growth restriction (FGR). FGR is commonly caused by placental insufficiency and yet the role of hypothyroidism in placental regulation of fetal growth is unknown. This study aimed to investigate the effects of maternal hypothyroidism on placental nutrient transporter expression, placental morphology, and placental metabolism.

METHODS

Hypothyroidism was induced in female Sprague-Dawley rats by adding methimazole (MMI) to drinking water at moderate (MOD, MMI at 0.005% w/v) and severe (SEV, MMI at 0.02% w/v) doses from one week prior to pregnancy and throughout gestation. Maternal and fetal tissues were collected on embryonic day 20 (E20).

RESULTS

Hypothyroidism reduced fetal weight (PTrt<0.001) despite causing fetal hyperglycaemia (PTrt = 0.016). Placental weight was not affected by hypothyroidism however placental efficiency was reduced (PTrt<0.001), as was the junctional zone (JZ):labyrinth zone (LZ) weight ratio (PTrt = 0.005). LZ glycogen content was increased (PTrt = 0.029) and while mRNA expression of glucose transporters was reduced by hypothyroidism, only GLUT1 protein expression was reduced in male LZs. Maternal hypothyroidism reduced mitochondrial content (PTrt = 0.031), particularly in SEV males relative to CON males (P = 0.004). Protein expression of Complex V (P < 0.001) and Complex III (P = 0.002) of the electron transport chain were also reduced in males. Maternal hypothyroidism reduced LZ (PTrt<0.001) and fetal plasma triglycerides (P = 0.019) while fetal free fatty acids and the expression of LZ lipid transporters was not affected.

DISCUSSION

Overall, maternal hypothyroidism may lead to FGR through reduced maternal T4 availability, changes to placental morphology, altered nutrient transporter expression and sex-specific effects on placental metabolism. Changes to LZ glycogen and triglyceride stores as well as mitochondrial content suggest a metabolic shift from oxidative phosphorylation to anaerobic glycolysis in males. These changes also likely impact fetal substrate availability and therefore fetal growth.

The Human Milk Metabolome: A Scoping Literature Review

BACKGROUND

Human milk is a complex source of nutrition and other bioactives that protects infants from disease, holding a lifetime of beneficial effects. The field of metabolomics provides a robust platform through which we can better understand human milk at a level rarely examined.

RESEARCH AIM

To Identify, describe, synthesize, and critically analyze the literature within the past 5 years related to the human milk metabolome.

METHODS

We conducted a scoping literature review and quality analysis of the recent science reflecting untargeted metabolomic approaches to examining human milk. We searched six databases using the terms "breast milk," "metabolome," "metabolite," and "human milk," Out of more than 1,069 abstracts, we screened and identified 22 articles that met our inclusion criteria.

RESULTS

We extracted data related to the study author, geographic location, research design, analyses, platform used, and results. We also extracted data related to human milk research activities, including collection protocol, infant/maternal considerations, and time. Selected studies focused on a variety of phenotypes, including maternal and infant disease. Investigators used varying approaches to evaluate the metabolome, and differing milk collection protocols were observed.

CONCLUSION

The human milk metabolome is informed by many factors-which may contribute to infant health outcomes-that have resulted in disparate milk metabolomic profiles. Standardized milk collection and storage procedures should be implemented to minimize degradation. Investigators may use our findings to develop research questions that test a targeted metabolomic approach.

Regulations of myo-inositol homeostasis: Mechanisms, implications, and perspectives

Phosphorylation is the most common module of cellular signalling pathways. The dynamic nature of phosphorylation, which is conferred by the balancing acts of kinases and phosphatases, allows this modification to finely control crucial cellular events such as growth, differentiation, and cell cycle progression. Although most research to date has focussed on protein phosphorylation, non-protein phosphorylation substrates also play vital roles in signal transduction. The most well-established substrate of non-protein phosphorylation is inositol, whose phosphorylation generates many important signalling molecules such as the second messenger IP₃, a key factor in calcium signalling. A fundamental question to our understanding of inositol phosphorylation is how the levels of cellular inositol are controlled. While the availability of protein phosphorylation substrates is known to be readily controlled at the levels of transcription, translation, and/or protein degradation, the regulatory mechanisms that control the uptake, synthesis, and removal of inositol are underexplored. Potentially, such mechanisms serve as an important layer of regulation of cellular signal transduction pathways. There are two ways in which mammalian cells acquire inositol. The historic use of radioactive ³H-myo-inositol revealed that inositol is promptly imported from the extracellular environment by three specific symporters SMIT1/2, and HMIT, coupling sodium or proton entry, respectively. Inositol can also be synthesized de novo from glucose-6P, thanks to the enzymatic activity of ISYNA1. Intriguingly, emerging evidence suggests that in mammalian cells, de novo myo-inositol synthesis occurs irrespective of inositol availability in the environment, prompting the question of whether the two sources of inositol go through independent metabolic pathways, thus serving distinct functions. Furthermore, the metabolic stability of myo-inositol, coupled with the uptake and endogenous synthesis, determines that there must be exit pathways to remove this extraordinary sugar from the cells to maintain its homeostasis. This essay aims to review our current knowledge of myo-inositol homeostatic metabolism, since they are critical to the signalling events played by its phosphorylated forms.

Genetic Effects of ITPK1 Polymorphisms on the Risk of Neural Tube Defects: a Population-Based Study

Inositol is closely related to the occurrence of neural tube defects (NTDs). Inositol 1, 3, 4-trisphosphate 5/6-kinase (ITPK1) gene encoded an essential regulatory enzyme ITPK1, which is involved in inositol metabolism and has a critical role in the development of neural tube and axial mesoderm. It had been reported that some polymorphisms of critical genes in inositol pathways, including ITPK1, were associated with NTDs in Chinese pregnant women; however, the association between fetus ITPK1 polymorphisms and NTDs had not been reported. In a high incidence of NTDs region of China, a case-control study was performed to evaluate the association between fetal ITPK1 polymorphisms and NTDs. The ITPK1 polymorphisms were genotyped by iPLEX® Gold assay. Inositol levels in fetus brain tissues were analyzed. Three genetic polymorphisms of fetus ITPK1's, including rs3818175, rs2295394, and rs4586354, were statistically associated with spina bifida (NTD subtypes). A higher risk of spina bifida was associated with genotype GG of rs3818175, genotype CC of rs4586354, and genotype TT of rs2295394 (OR = 2.66, 95% CI [1.17-6.05], P = 0.017; OR = 2.22, 95% CI [1.02-4.80], P = 0.041; and OR = 2.33, 95% CI [1.00-5.48], P = 0.047), when compared with the other wild-type genotypes CC, TT, and CC, respectively. Decreased brain inositol level was found in NTDs fetuses, compared to normal controls. Inositol levels were found to significantly decrease with rs2295394 (CC genotype), rs4586354 (TT genotype), and rs3818175 (GC genotype) (P < 0.05). The polymorphisms of fetus ITPK1 were associated with the incidence of NTDs and might be a genetic risk factor for spina bifida.

Second-trimester and third-trimester maternal lipid profiles significantly correlated to LGA and macrosomia

BACKGROUND

According to the theory of fetal-derived adult diseases, abnormal fetal development might affect the occurrence of diseases in adulthood, and appropriate fetal growth status intrauterine might have a beneficial effect on it. To adapt properly for fetal development, there are numerous changes in the maternal physiology during pregnancy, including blood lipid metabolism. The aim of this study is to evaluate the association between lipid profiles in the second and third trimesters of normal pregnancy and fetal birth weight.

MATERIALS AND METHODS

The study population was derived from 5695 pregnant women, who maintained routine prenatal care at the women's hospital of Zhejiang University, School of medicine January 1, 2014, and December 31, 2014. The pregnant women in this study all carried uncomplicated singleton pregnancies to at least 37 weeks.

RESULTS

The mean (standard deviation) birth weight was 3361.00 (385.94) g; 413 (7.3%) of the infants were large for gestational age, and 330 (5.8%) were macrosomia. On multiple linear regression analysis, positive determinants of birth weight were gravidity, parity, gestational age at delivery, male infant, maternal height, and weight before pregnancy, weight gain during pregnancy, fasting blood glucose (FBG) level, second-trimester cholesterol (TC) and third-trimester triglyceride (TG), gestational albumin (ALB), and third-trimester high-density lipoprotein (HDL-C) levels were each negatively associated with birth weight. On logistic regression analysis, the significant metabolic lipid predictors of delivering a large-for-gestational-age infant were second- and third-trimester TG (aOR = 1.178, 95% CI 1.032-1.344, p = 0.015; aOR = 1.106, 95% CI 1.043-1.173, p = 0.001, respectively) and second- and third-trimester HDL-C level (aOR = 0.655, 95% CI 0.491-0.874, p = 0.004; aOR = 0.505, 95% CI 0.391-0.651, p < 0.001, respectively). Third-trimester TG and HDL-C were stable predictors of large-for-gestational-age infants in stratification analysis. High TG and low HDL-C level during third trimester could be considered as indicators of a high risk of large for gestational age (LGA) and macrosomia, regardless of infant gender.

CONCLUSION

These results suggest that future lifestyle programs in women of reproductive age with a focus on lowering TG levels (i.e., diet, weight reduction, and physical activity) may help to reduce the incidence of LGA and macrosomia.

Blood myo-inositol concentrations in preterm and term infants

OBJECTIVE

To describe relationship between cord blood (representing fetal) myo-inositol concentrations and gestational age (GA) and to determine trends of blood concentrations in enterally and parenterally fed infants from birth to 70 days of age.

DESIGN/METHODS

Samples were collected in 281 fed or unfed infants born in 2005 and 2006. Myo-inositol concentrations were displayed in scatter plots and analyzed with linear regression models of natural log-transformed values.

RESULTS

In 441 samples obtained from 281 infants, myo-inositol concentrations varied from nondetectable to 1494 μmol/L. Cord myo-inositol concentrations decreased an estimated 11.9% per week increase in GA. Postnatal myo-inositol concentrations decreased an estimated 14.3% per week increase in postmenstrual age (PMA) and were higher for enterally fed infants compared to unfed infants (51% increase for fed vs. unfed infants).

CONCLUSIONS

Fetal myo-inositol concentrations decreased with increasing GA. Postnatal concentrations decreased with increasing PMA and were higher among enterally fed than unfed infants.

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.

A review of the role of inositols in conditions of insulin dysregulation and in uncomplicated and pathological pregnancy

Inositols, a group of 6-carbon polyols, are highly bioactive molecules derived from diet and endogenous synthesis. Inositols and their derivatives are involved in glucose and lipid metabolism and participate in insulin-signaling, with perturbations in inositol processing being associated with conditions involving insulin resistance, dysglycemia and dyslipidemia such as polycystic ovary syndrome and diabetes. Pregnancy is similarly characterized by substantial and complex changes in glycemic and lipidomic regulation as part of maternal adaptation and is also associated with physiological alterations in inositol processing. Disruptions in maternal adaptation are postulated to have a critical pathophysiological role in pregnancy complications such as gestational diabetes and pre-eclampsia. Inositol supplementation has shown promise as an intervention for the alleviation of symptoms in conditions of insulin resistance and for gestational diabetes prevention. However, the mechanisms behind these affects are not fully understood. In this review, we explore the role of inositols in conditions of insulin dysregulation and in pregnancy, and identify priority areas for research. We particularly examine the role and function of inositols within the maternal-placental-fetal axis in both uncomplicated and pathological pregnancies. We also discuss how inositols may mediate maternal-placental-fetal cross-talk, and regulate fetal growth and development, and suggest that inositols play a vital role in promoting healthy pregnancy.

Maternal Inositol Status and Neural Tube Defects: A Role for the Human Yolk Sac in Embryonic Inositol Delivery?

Supplementation with myo-inositol during the periconceptional period of pregnancy may ameliorate the recurrence risk of having a fetus affected by a neural tube defect (NTD; e.g., spina bifida). This could be of particular importance in providing a means for preventing NTDs that are unresponsive to folic acid. This review highlights the characteristics of inositol and describes the role of myo-inositol in the prevention of NTDs in rodent studies and the evidence for its efficacy in reducing NTD risk in human pregnancy. The possible reduction in NTD risk by maternal myo-inositol implies functional and developmentally important maternal-embryonic inositol interrelationships and also suggests that embryonic uptake of myo-inositol is crucial for embryonic development. The establishment of active myo-inositol cellular uptake mechanisms in the embryonic stages of human pregnancy, when the neural tube is closing, is likely to be an important determinant of normal development. We draw attention to the generation of materno-fetal inositol concentration gradients and relationships, and outline a transport pathway by which myo-inositol may be delivered to the early developing human embryo. These considerations provide novel insights into the mechanisms that may underpin inositol's ability to confer embryonic developmental benefit.

Diabetes Leads to Alterations in Normal Metabolic Transitions of Pregnancy as Revealed by Time-Course Metabolomics

Women with diabetes during pregnancy are at increased risk of poor maternal and neonatal outcomes. Despite this, the effects of pre-gestational (PGDM) or gestational diabetes (GDM) on metabolism during pregnancy are not well understood. In this study, we utilized metabolomics to identify serum metabolic changes in women with and without diabetes during pregnancy and the cord blood at birth. We observed elevations in tricarboxylic acid (TCA) cycle intermediates, carbohydrates, ketones, and lipids, and a decrease in amino acids across gestation in all individuals. In early gestation, PGDM had elevations in branched-chain amino acids and sugars compared to controls, whereas GDM had increased lipids and decreased amino acids during pregnancy. In both GDM and PGDM, carbohydrate and amino acid pathways were altered, but in PGDM, hemoglobin A1c and isoleucine were significantly increased compared to GDM. Cord blood from GDM and PGDM newborns had similar increases in carbohydrates and choline metabolism compared to controls, and these alterations were not maternal in origin. Our results revealed that PGDM and GDM have distinct metabolic changes during pregnancy. A better understanding of diabetic metabolism during pregnancy can assist in improved management and development of therapeutics and help mitigate poor outcomes in both the mother and newborn.

High placental inositol content associated with suppressed pro-adipogenic effects of maternal glycaemia in offspring: the GUSTO cohort

Background/Objectives

Maternal glycaemia promotes fetal adiposity. Inositol, an insulin sensitizer, has been trialled for gestational diabetes prevention. The placenta has been implicated in how maternal hyperglycaemia generates fetal pathophysiology, but no studies have examined whether placental inositol biology is altered with maternal hyperglycaemia, nor whether such alterations impact fetal physiology. We aimed to investigate whether the effects of maternal glycaemia on offspring birthweight and adiposity at birth differed across placental inositol levels.

Methods

Using longitudinal data from the Growing Up in Singapore Towards healthy Outcomes cohort, maternal fasting glucose (FPG) and 2-hour plasma glucose (2hPG) were obtained in pregnant women by a 75-g oral glucose tolerance test around 26 weeks’ gestation. Relative placental inositol was quantified by liquid chromatography-mass spectrometry. Primary outcomes were birthweight (n = 884) and abdominal adipose tissue (AAT) volumes measured by neonatal MRI scanning in a subset (n = 262) of term singleton pregnancies. Multiple linear regression analyses were performed.

Results

Placental inositol was lower in those with higher 2hPG, no exposure to tobacco smoke antenatally, with vaginal delivery and shorter gestation. Positive associations of FPG with birthweight (adjusted β [95% CI] 164.8 g [109.1, 220.5]) and AAT (17.3 ml [11.9, 22.6] per mmol glucose) were observed, with significant interactions between inositol tertiles and FPG in relation to these outcomes (p < 0.05). Stratification by inositol tertiles showed that each mmol/L increase in FPG was associated with increased birthweight and AAT volume among cases within the lowest (birthweight = 174.2 g [81.2, 267.2], AAT = 21.0 ml [13.1, 28.8]) and middle inositol tertiles (birthweight = 202.0 g [103.8, 300.1], AAT = 19.7 ml [9.7, 29.7]). However, no significant association was found among cases within the highest tertile (birthweight = 81.0 g [−21.2, 183.2], AAT = 0.8 ml [−8.4, 10.0]).

Conclusions

High placental inositol may protect the fetus from the pro-adipogenic effects of maternal glycaemia. Studies are warranted to investigate whether prenatal inositol supplementation can increase placental inositol and reduce fetal adiposity.

Inositol and antioxidant supplementation: Safety and efficacy in pregnancy

Pregnancies complicated by diabetes have largely increased in number over the last 50 years. Pregnancy is characterized by a physiologic increase in insulin resistance, which, associated with increased oxidative stress and inflammations, could induce alterations of glucose metabolism and diabetes. If not optimally controlled, these conditions have a negative impact on maternal and foetal outcomes. To date, one can resort only to diet and lifestyle to treat obesity and insulin resistance during pregnancy, and insulin remains the only therapeutic option to manage diabetes during pregnancy. However, in the last years, in a variety of experimental models, inositol and antioxidants supplementation have shown insulin-sensitizing, anti-inflammatory, and antioxidant properties, which could be mediated by some possible complementary mechanism of action. Different isomers and multiple combinations of these compounds are presently available: Aim of the present review article is to examine the existing evidence in order to clarify and/or define the effects of different inositol- and antioxidant-based supplements during pregnancy complicated by insulin resistance and/or by diabetes. This could help the clinician's evaluation and choice of the appropriate supplementation regimen.

Placental DNA Methylation Adaptation to Maternal Glycemic Response in Pregnancy

Maternal hyperglycemia during pregnancy is associated with excess fetal growth and adverse perinatal and developmental outcomes. Placental epigenetic maladaptation may underlie these associations. We performed an epigenome-wide association study (>850,000 CpG sites) of term placentas and prenatal maternal glycemic response 2-h post oral glucose challenge at 24-30 weeks of gestation among 448 mother-infant pairs. Maternal 2-h glycemia postload was strongly associated with lower DNA methylation of four CpG sites (false discovery rate [FDR] q <0.05) within the phosphodiesterase 4B gene (PDE4B). Additionally, three other individual CpG sites were differentially methylated relative to maternal glucose response within the TNFRSF1B, LDLR, and BLM genes (FDR q <0.05). DNA methylation correlated with expression of its respective genes in placental tissue at three out of four independent identified loci: PDE4B (r = 0.31, P < 0.01), TNFRSF1B (r = -0.24, P = 0.013), and LDLR (r = 0.32, P < 0.001). In an independent replication cohort (N = 65-108 samples), results were consistent in direction but not significantly replicated among tested CpG sites in PDE4B and TNFRSF1B Our study provides evidence that maternal glycemic response during pregnancy is associated with placental DNA methylation of key inflammatory genes whose expression levels are partially under epigenetic control.

Effects of inositol on glucose homeostasis: Systematic review and meta-analysis of randomized controlled trials

BACKGROUND & AIMS

The effect of inositol on glucose homeostasis is not well characterized. The aim of the present meta-analysis is to synthesize the effects of inositol on glucose homeostasis in different clinical conditions.

METHODS

We performed a systematic review (CRD42017057927) following PRISMA guidelines. Web of Science and Medline were searched for randomized controlled trials (RCTs) that addressed supplementation with compounds of the inositol family in humans and assessed their effects on glucose homeostasis.

RESULTS

We screened 476 abstracts and included 20 RCTs with a total of 1239 subjects. Meta-analysis showed in the treatment arm a reduction in fasting plasma glucose (Mean difference (MD) -0.44 mmol/l, 95% CI -0.65, -0.23), 2 h PG after 75 g OGTT (MD -0.69 mmol/l, 95% CI -1.14, -0.23), abnormal glucose tolerance (Relative risk (RR) 0.28, 95% CI 0.12, 0.66), fasting insulin (MD -38.49 pmol/l, 95% CI -52.63, -24.36), and HOMA-IR (MD -1.96 mmol × mUI/l, 95% CI -2.62, -1.30). No differences were observed in BMI, HbA1c and % of patients requiring insulin treatment. Sensitivity analysis did not change treatment estimates. Mention to adverse events was only present in 13 articles with no sign of seriousness.

CONCLUSIONS

Inositol supplementation decreases blood glucose through an improvement in insulin sensitivity that is independent of weight. Assessment of adverse effects is scarce among published trials and should be fully addressed before considering inositol as a therapeutic agent for glucose-related outcomes. The characterization of the subjects achieving benefit from the intervention and the formulations to be used should also be known.

Maternal fuels and metabolic measures during pregnancy and neonatal body composition: the healthy start study

CONTEXT

The impact of specific maternal fuels and metabolic measures during early and late gestation on neonatal body composition is not well defined.

OBJECTIVE

To determine how circulating maternal glucose, lipids, and insulin resistance in the first and second halves of pregnancy influence neonatal body composition.

DESIGN

A prospective pre-birth cohort enrolling pregnant women, the Healthy Start Study, was conducted, in which fasting maternal serum samples were collected twice during pregnancy to measure glucose, insulin, hemoglobin A1c, triglyceride, total cholesterol, high-density lipoprotein, and free fatty acids. Neonatal body composition was measured with air displacement plethysmography.

SETTING

An observational epidemiology study of pregnant women attending obstetric clinics at the University of Colorado, Anschutz Medical Center.

PARTICIPANTS

This analysis includes 804 maternal-neonate pairs.

RESULTS

A strong positive linear relationship between maternal estimated insulin resistance (homeostasis model of assessment for insulin resistance) in the first half of pregnancy and neonatal fat mass (FM) and FM percentage (FM%) was detected, independent of prepregnancy body mass index (BMI). In the second half of pregnancy, positive linear relationships between maternal glucose levels and offspring FM and FM% were observed, independent of prepregnancy BMI. An inverse relationship was detected between high-density lipoprotein in the first half of pregnancy and FM, independent of prepregnancy BMI. Free fatty acid levels in the second half of pregnancy were positively associated with higher birth weight, independent of prepregnancy BMI.

CONCLUSION

Maternal insulin resistance in the first half of pregnancy is highly predictive of neonatal FM%, whereas maternal glycemia, even within the normal range, is an important driver of neonatal adiposity in later pregnancy, independent of prepregnancy BMI. Our data provide additional insights on potential maternal factors responsible for fetal fat accretion and early development of adiposity.

Changes in fetal mannose and other carbohydrates induced by a maternal insulin infusion in pregnant sheep

BACKGROUND

The importance of non-glucose carbohydrates, especially mannose and inositol, for normal development is increasingly recognized. Whether pregnancies complicated by abnormal glucose transfer to the fetus also affect the regulation of non-glucose carbohydrates is unknown. In pregnant sheep, maternal insulin infusions were used to reduce glucose supply to the fetus for both short (2-wk) and long (8-wk) durations to test the hypothesis that a maternal insulin infusion would suppress fetal mannose and inositol concentrations. We also used direct fetal insulin infusions (1-wk hyperinsulinemic-isoglycemic clamp) to determine the relative importance of fetal glucose and insulin for regulating non-glucose carbohydrates.

RESULTS

A maternal insulin infusion resulted in lower maternal (50%, P < 0.01) and fetal (35-45%, P < 0.01) mannose concentrations, which were highly correlated (r(2) = 0.69, P < 0.01). A fetal insulin infusion resulted in a 50% reduction of fetal mannose (P < 0.05). Neither maternal nor fetal plasma inositol changed with exogenous insulin infusions. Additionally, maternal insulin infusion resulted in lower fetal sorbitol and fructose (P < 0.01).

CONCLUSIONS

Chronically decreased glucose supply to the fetus as well as fetal hyperinsulinemia both reduce fetal non-glucose carbohydrates. Given the role of these carbohydrates in protein glycosylation and lipid production, more research on their metabolism in pregnancies complicated by abnormal glucose metabolism is clearly warranted.

Materno-fetal transfer of docosahexaenoic acid is impaired by gestational diabetes mellitus

Better knowledge on the disturbed mechanisms implicated in materno-fetal long-chain polyunsaturated fatty acid (LC-PUFA) transfer in pregnancies with gestational diabetes mellitus (GDM) may have potentially high implications for later on in effective LC-PUFA supplementation. We studied in vivo placental transfer of fatty acids (FA) using stable isotope tracers administrated to 11 control and 9 GDM pregnant women (6 treated with insulin). Subjects received orally [(13)C]palmitic, [(13)C]oleic and [(13)C]linoleic acids, and [(13)C]docosahexaenoic acid ((13)C-DHA) 12 h before elective caesarean section. Maternal blood samples were collected at -12, -3, -2, and -1 h, delivery, and +1 h. Placental tissue and venous cord blood were also collected. FA were quantified by gas chromatography (GC) and (13)C enrichments by GC-isotope ratio mass spectrometry. [(13)C]FA concentration was higher in total lipids of maternal plasma in GDM vs. controls, except for [(13)C]DHA. Moreover, [(13)C]DHA showed lower placenta/maternal plasma ratio in GDM vs. controls and significantly lower cord/maternal plasma ratio. For the other studied FA, ratios were not different between GDM and controls. Disturbed [(13)C]DHA placental uptake occurs in both GDM treated with diet or insulin, whereas the last ones also have lower [(13)C]DHA in venous cord. The tracer study pointed toward impaired placental DHA uptake as critical step, whereas the transfer of the rest of [(13)C]FA was less affected. GDM under insulin treatment could also have higher fetal fat storage, contributing to reduce [(13)C]DHA in venous cord. DHA transfer to the fetus was reduced in GDM pregnancies compared with controls, which might affect the programming of neurodevelopment in their neonates.

Placental regulation of fetal nutrient supply

PURPOSE OF REVIEW

Placental nutrient uptake and transfer may have a unique role, as changes in trophoblast nutrient-sensing signaling pathways regulate cell metabolism and may affect the fetal growth and health programming in the offspring.

RECENT FINDINGS

The functionality of the placenta could affect the neonatal adiposity and the fetal levels of key nutrients such as long-chain polyunsaturated fatty acids. Insulin, oxygen and amino acid concentrations may regulate the mammalian target of rapamycin (mTOR) nutrient sensor in the human placenta affecting trophoblast metabolism and nutrient delivery.

SUMMARY

The mechanisms involved in both placental uptake and transfer of macronutrients are reviewed. Fatty acid, cholesterol and amino acid transport across the placenta involves a complex system to ensure nutrient delivery to the growing fetus. The placental glucose transfer is important for fetal macrosomia, but lipid disturbances in both maternal and placental compartments may contribute to neonatal fat accretion. Maternal insulin has little effect on the avidity of glucose transport by the placenta, but may interfere in placental metabolism via mTOR nutrient sensor. mTOR is a positive regulator of the amino acid carriers and constitutes a critical link between maternal nutrient availability and fetal growth, thereby influencing the long-term health of the fetus.