Location of insulin receptors in the placenta and its progenitor tissues

Placenta: an old organ with new functions

The transition from oviparity to viviparity and the establishment of feto-maternal communications introduced the placenta as the major anatomical site to provide nutrients, gases, and hormones to the developing fetus. The placenta has endocrine functions, orchestrates maternal adaptations to pregnancy at different periods of pregnancy, and acts as a selective barrier to minimize exposure of developing fetus to xenobiotics, pathogens, and parasites. Despite the fact that this ancient organ is central for establishment of a normal pregnancy in eutherians, the placenta remains one of the least studied organs. The first step of pregnancy, embryo implantation, is finely regulated by the trophoectoderm, the precursor of all trophoblast cells. There is a bidirectional communication between placenta and endometrium leading to decidualization, a critical step for maintenance of pregnancy. There are three-direction interactions between the placenta, maternal immune cells, and the endometrium for adaptation of endometrial immune system to the allogeneic fetus. While 65% of all systemically expressed human proteins have been found in the placenta tissues, it expresses numerous placenta-specific proteins, whose expression are dramatically changed in gestational diseases and could serve as biomarkers for early detection of gestational diseases. Surprisingly, placentation and carcinogenesis exhibit numerous shared features in metabolism and cell behavior, proteins and molecular signatures, signaling pathways, and tissue microenvironment, which proposes the concept of "cancer as ectopic trophoblastic cells". By extensive researches in this novel field, a handful of cancer biomarkers has been discovered. This review paper, which has been inspired in part by our extensive experiences during the past couple of years, highlights new aspects of placental functions with emphasis on its immunomodulatory role in establishment of a successful pregnancy and on a potential link between placentation and carcinogenesis.

Maternal body mass index and placental weight: a role for fetal insulin, maternal insulin and leptin

PURPOSE

Placental weight (PW) has been found to mediate the main effect of maternal BMI on fetal size. Still, the BMI-PW association is poorly understood. Therefore, we aimed to explore potential explanatory variables, including gestational weight gain (GWG), early- and late-pregnancy circulating levels of maternal glucose, insulin, leptin, adiponectin, triglycerides, LDL-C, and HDL-C, and fetal insulin.

METHODS

We included two studies of pregnant women from Oslo University Hospital, Norway: the prospective STORK (n = 263) and the cross-sectional 4-vessel method study (4-vessel; n = 165). We used multiple linear regression for data analyses. A non-linear BMI-PW association was observed, which leveled off from BMI25. Therefore, BMI <25 and ≥25 were analyzed separately (n = 170/122 and 93/43 for STORK/4-vessel). Confounding variables included maternal age, parity, and gestational age.

RESULTS

PW increased significantly per kg m-2 only among BMI <25 (univariate model's std.β[p] = 0.233 [0.002] vs. 0.074[0.48]/0.296[0.001] vs. -0.030[0.85] for BMI <25 vs. ≥25 in STORK/4-vessel). Maternal early- but not late-pregnancy insulin and term fetal insulin were associated with PW. The estimated effect of early pregnancy insulin was similar between the BMI groups but statistically significant only among BMI <25 (std.β[p] = 0.182[0.016] vs. 0.203[0.07] for BMI <25 vs. ≥25). Late pregnancy leptin was inversely associated with PW with a 1.3/1.7-fold greater effect among BMI ≥25 than BMI <25 in the STORK/4-vessel.

CONCLUSIONS

The BMI-PW association was non-linear: an association was observed for BMI <25 but not for BMI ≥25. Leptin may be involved in the non-linear association through a placental-adipose tissue interplay. Maternal early pregnancy insulin and fetal insulin at term were associated with PW.

Insulin increases placental triglyceride as a potential mechanism for fetal adiposity in maternal obesity

OBJECTIVE

Maternal obesity increases the incidence of excess adiposity in newborns, resulting in lifelong diabetes risk. Elevated intrauterine fetal adiposity has been attributed to maternal hyperglycemia; however, this hypothesis does not account for the increased adiposity seen in newborns of mothers with obesity who have euglycemia. We aimed to explore the placental response to maternal hyperinsulinemia and the effect of insulin-like growth factor 2 (IGF-2) in promoting fetal adiposity by increasing storage and availability of nutrients to the fetus.

METHODS

We used placental villous explants and isolated trophoblasts from normal weight and obese women to assess the effect of insulin and IGF-2 on triglyceride content and insulin receptor signaling. Stable isotope tracer methods were used ex vivo to determine effect of hormone treatment on de novo lipogenesis (DNL), fatty acid uptake, fatty acid oxidation, and esterification in the placenta.

RESULTS

Here we show that placentae from euglycemic women with normal weight and obesity both have abundant insulin receptor. Placental depth and triglyceride were greater in women with obesity compared with normal weight women. In syncytialized placental trophoblasts and villous explants, insulin and IGF-2 activate insulin receptor, induce expression of lipogenic transcription factor SREBP-1 (sterol regulatory element-binding protein 1), and stimulate triglyceride accumulation. We demonstrate elevated triglyceride is attributable to increased esterification of fatty acids, without contribution from DNL and without an acceleration of fatty acid uptake.

CONCLUSIONS

Our work reveals that obesity-driven aberrations in maternal metabolism, such as hyperinsulinemia, alter placental metabolism in euglycemic conditions, and may explain the higher prevalence of excess adiposity in the newborns of obese women.

Hyperinsulinaemia in pregnancy and gestational outcomes: A case series

Background: Pathological insulin resistance in pregnancy is associated with an increased risk for complications such as gestational diabetes mellitus and pre-eclampsia. Individuals with pathological insulin resistance also exhibit hyperinsulinaemia. Currently, there are no diagnostic criteria for pathological hyperinsulinaemia in pregnancy that may be used to indicate risk of adverse outcomes.Aim: This case series aimed to explore the relationship between first trimester insulin response patterns and gestational outcomes.Setting: Auckland, New Zealand.Methods: Participants included four pregnant women with prepregnancy body mass index ≥ 25 kg/m2 and aged 25–35 years. Glucose and insulin response patterns were examined following a 120 min oral glucose tolerance test (OGTT) at 12–15 weeks of gestation using a modified Kraft methodology. Outcomes assessed at 25 and 35 weeks of gestation included gestational weight gain (GWG), blood pressure, fasting capillary blood glucose and foetal growth. Lifestyle and medical information were collected at each trimester. After delivery, total GWG, infant size, delivery method and clinical outcomes were recorded.Results: Kraft pattern IIB hyperinsulinaemia was identified in two cases. Amongst them, Case #1 experienced excessive GWG, induction of labour and surgically assisted delivery. Case #4 delivered by emergency caesarean, and the neonate required intensive care admission for 17 h. No cases developed hyperglycaemia or hypertension. Infant weights were between 3.75 kg and 3.86 kg.Conclusion: Dynamic insulin assay provides a promising template to assess metabolic risk in the first trimester of pregnancy. Diagnosing hyperinsulinaemia early in pregnancy means that lifestyle-based initiatives could be introduced earlier to mitigate excess GWG and potential adverse outcomes.

Placental expression of glucose transporters GLUT-1, GLUT-3, GLUT-8 and GLUT-12 in pregnancies complicated by gestational and type 1 diabetes mellitus

AIMS/INTRODUCTION

The aim of the present study was to evaluate the placental expression of glucose transporters GLUT-1, GLUT-3, GLUT-8 and GLUT-12 in term pregnancies complicated by well-controlled gestational (GDM) and type 1 pregestational diabetes mellitus (PGDM).

MATERIALS AND METHODS

A total of 103 placental samples were obtained from patients diagnosed with GDM (n = 60), PGDM (n = 20) and a non-diabetic control group (n = 23). Computer-assisted quantitative morphometry of stained placental sections was performed to determine the expression of selected GLUT proteins.

RESULTS

Immunohistochemical techniques used for the identification of GLUT-1, GLUT-3, GLUT-8 and GLUT-12 revealed the presence of all glucose transporters in the placental tissue. Morphometric evaluation performed for the vascular density-matched placental samples demonstrated a significant increase in the expression of GLUT-1 protein in patients with PGDM as compared to GDM and control groups (P < 0.05). With regard to the expression of the other GLUT isoforms, no statistically significant differences were observed between patients from the diabetic and control populations. Positive correlations between fetal birthweight and the expression of GLUT-1 protein in the PGDM group (rho = 0.463, P < 0.05) and GLUT-12 in the control group (rho = 0.481, P < 0.05) were noted.

CONCLUSIONS

In term pregnancies complicated by well-controlled GDM/PGDM, expression of transporters GLUT-3, GLUT-8 and GLUT-12 in the placenta remains unaffected. Increased expression of GLUT-1 among women with type 1 PGDM might contribute to a higher rate of macrosomic fetuses in this population.

Insulin-mediated immune dysfunction in the development of preeclampsia

Epidemiological observations implicate insulin resistance as a predisposing factor in the development of preeclampsia (PE). It is also well established that PE manifests in the context of a dysregulated immune response at the maternal-foetal interface, though all the underlying drivers of such immune dysregulation remains to be accounted for. Although it has long been known that various immune cells express insulin receptors following immune activation, it is only recently that insulin signalling has been shown to play a key role in immune cell differentiation, survival and effector function through its canonical activation of the PI3K/Akt/mTOR pathway. Here we argue that hyperinsulinemia, manifesting either from insulin resistance or from intensive insulin therapy, likely plays a direct role in driving immune cell dysfunction which plays a central role in the development of PE. This line of reasoning also explains the superior results of insulin-sparing interventions compared to intensive insulin therapy as monotherapy.

Hormonal fine-tuning of clock in decidual region of mouse placenta by dopamine, melatonin, insulin, leptin and ghrelin

INTRODUCTION

The maternal part of the rodent placenta harbors a circadian clock which robustly responds to glucocorticoids, however, its sensitivity to other hormones has not been elucidated. In this study, we tested five selected hormones (dopamine, melatonin, insulin, leptin and ghrelin) for their effectiveness to affect the clock in decidual region of mouse placenta in vitro.

METHODS

We administered the hormones or corresponding vehicles at various time points over 24 h to organotypic placental explants of mPer2^Luc mice containing the decidua basalis (DB) region and monitored their effects on amplitude, period, median expression level (mesor) and phase of PER2-driven bioluminescence rhythms.

RESULTS

Dopamine significantly increased the amplitude, robustly dampened the mesor, and during a narrow time interval (corresponding to daytime) induced phase delays of the rhythms. In contrast, melatonin had no effect on amplitude, but induced phase advances of the rhythms at the opposite time window than dopamine (corresponding to nighttime). Leptin and ghrelin, but not insulin, slightly increased amplitudes and moderately modulated phase delays of the clock, suggesting that the DB clock, in contrast to other peripheral clocks, is rather resilient to abrupt changes in levels of feeding- and metabolism-related hormones.

DISCUSSION

The results demonstrate for the first time that dopamine and melatonin exhibit delicate yet specific effects on parameters of the DB clock and may thus potentially contribute to fine-tuning of its phase under in vivo conditions. It also implies that dysregulation of their levels, which accompany various pathologies, may account for malfunction of the clock in DB.

Nutritional and developmental programming effects of insulin

The discovery of insulin in 1921 was a major breakthrough in medicine and for therapy in patients with diabetes. The dramatic rise in the prevalence of overweight and obesity has been tightly linked to an increased prevalence of gestational diabetes mellitus (GDM), which poses major health concerns. Babies born to GDM mothers are more likely to develop obesity, type 2 diabetes and cardiovascular disease later in life. Evidence accumulated during the past two decades has revealed that high levels insulin, such as those observed during GDM, can have a widespread effect on the development and function of a variety of organs. This review summarises our current knowledge on the role of insulin in the placenta, cardiovascular system and brain during critical periods of development, as well as how it can contribute to lifelong metabolic regulation. We also discuss possible intervention strategies to ameliorate and hopefully reverse the developmental defects associated with obesity and GDM.

Defective insulin receptor signaling in patients with gestational diabetes is related to dysregulated miR-140 which can be improved by naringenin

Gestational diabetes (GDM) affects about 20 % of pregnancies globally. Defective insulin receptor (IR) signaling has been found in the placenta from patients with GDM, but the underly mechanism is still unclear. In the present study, the mRNA and protein levels of IR-α, insulin receptor substrate 1(IRS-1) and inulin like growth factor 1 receptor (IGF1R) were detected in the placenta tissue samples from 33 GDM patients and 20 healthy controls. Reduced IR-α protein level was observed in both obese and non-obese GDM patients, and decreased IGF1R protein level was found in obese GDM patients. However, the IR-α and IGF1R mRNAs level was not significantly altered in GDM patients. Subsequently, the expression of 10 miRNAs that have the potential targeting IR-α and IGF1R was examined by qRT-PCR in the placenta, and miR-140-3p was found overexpressed. Through dual-luciferase assay and immunoblotting, miR-140-3p was confirmed to suppress IR-α and IGF1R expression via targeting the 3'UTRs. As a treatment candidate, naringenin downregulated miR-140-3p level in trophoblasts and endothelial cells. Meanwhile, IR-α and IGF1R expression was upregulated by naringenin, and the glucose uptake was increased in naringenin treated trophoblasts and endothelial cells. Finally, naringenin upregulated cell viability, migration capacity of HTR-8/SVneo and HUVEC cells, and increased HUVEC cells angiogenesis in high glucose condition. In conclusion, miR-140-3p overexpression contributes to the defective placental IR signaling in patients with GDM. Naringenin treatment protects trophoblasts and endothelial cells from the harmful high glucose environment which have the potential for GDM treatment.

Increased placental mitochondrial fusion in gestational diabetes mellitus: an adaptive mechanism to optimize feto-placental metabolic homeostasis?

INTRODUCTION

Gestational diabetes mellitus (GDM), a common pregnancy disorder, increases the risk of fetal overgrowth and later metabolic morbidity in the offspring. The placenta likely mediates these sequelae, but the exact mechanisms remain elusive. Mitochondrial dynamics refers to the joining and division of these organelles, in attempts to maintain cellular homeostasis in stress conditions or alterations in oxygen and fuel availability. These remodeling processes are critical to optimize mitochondrial function, and their disturbances characterize diabetes and obesity.

METHODS AND RESULTS

Herein we show that placental mitochondrial dynamics are tilted toward fusion in GDM, as evidenced by transmission electron microscopy and changes in the expression of key mechanochemical enzymes such as OPA1 and active phosphorylated DRP1. In vitro experiments using choriocarcinoma JEG-3 cells demonstrated that increased exposure to insulin, which typifies GDM, promotes mitochondrial fusion. As placental ceramide induces mitochondrial fission in pre-eclampsia, we also examined ceramide content in GDM and control placentae and observed a reduction in placental ceramide enrichment in GDM, likely due to an insulin-dependent increase in ceramide-degrading ASAH1 expression.

CONCLUSIONS

Placental mitochondrial fusion is enhanced in GDM, possibly as a compensatory response to maternal and fetal metabolic derangements. Alterations in placental insulin exposure and sphingolipid metabolism are among potential contributing factors. Overall, our results suggest that GDM has profound impacts on placental mitochondrial dynamics and metabolism, with plausible implications for the short-term and long-term health of the offspring.

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.

Insulin stimulates GLUT4 trafficking to the syncytiotrophoblast basal plasma membrane in the human placenta

CONTEXT

Placental transport capacity influences fetal glucose supply. The syncytiotrophoblast is the transporting epithelium in the human placenta, expressing glucose transporters (GLUT) and insulin receptors (IR) in its maternal-facing microvillous (MVM) and fetal-facing basal plasma membrane (BM).

OBJECTIVE

The objectives of this study were to (1) determine the expression of the insulin-sensitive GLUT4 glucose transporter and IR in the syncytiotrophoblast plasma membranes across gestation in normal pregnancy and in pregnancies complicated by maternal obesity and (2) assess the effect of insulin on GLUT4 plasma membrane trafficking in human placental explants.

DESIGN, SETTING, PARTICIPANTS

Placental tissue was collected across gestation from women with normal body mass index (BMI) and obese mothers with appropriate for gestational age (AGA) and macrosomic infants. MVM and BM were isolated.

MAIN OUTCOME MEASURES

Protein expression of GLUT4, GLUT1 and IR were determined by western blot.

RESULTS

GLUT4 was exclusively expressed in the BM and IR was predominantly expressed in the MVM, with increasing expression across gestation. BM GLUT1 expression was increased and BM GLUT4 expression was decreased in obese women delivering macrosomic babies. In placental villous explants incubation with insulin stimulated Akt (S473) phosphorylation (+76%, p=0.0003, n=13) independent of maternal BMI and increased BM GLUT4 protein expression (+77%, p=0.0013, n=7) in placentas from lean but not obese women.

CONCLUSION

We propose that maternal insulin stimulates placental glucose transport by promoting GLUT4 trafficking to the BM, which may enhance glucose transfer to the fetus in response to postprandial hyperinsulinemia in women with normal BMI.

Relationship between elevated serum level of placental growth factor and status of gestational diabetes mellitus

Objective: As only limited and confusing evidence about serum placental growth factor (PlGF) level in gestational diabetes mellitus (GDM) exist in the known literature, the aim of this study was to evaluate the association of maternal serum PlGF level with GDM status.Methods: The pregnant women attending the Obstetrics Outpatient Unit of Hitit University Hospital were screened at 24 and 28 weeks of gestation for GDM according to the suggestions of the American College of Obstetricians and Gynecologists (ACOG). Concisely, all of the low-risk pregnant women were evaluated with a 50 g glucose challenge test (GCT). Women with serum glucose ≥140 mg/dL at 1 h after GCT were subjected to a 100 g oral glucose tolerance test (OGTT). According to the criteria of Carpenter and Coustan, the GDM diagnosis was confirmed. Consequently, a total of 158 pregnant women eligible for inclusion criteria were categorized into two main groups; 76 of the GDM group, 82 of the control group. The demographic characteristic and biochemical parameters of the study population including age, body mass index (BMI), gestational age were recorded at the second trimester. The assays for glucose, insulin, and PlGF were carried out.Results: The mean maternal age of control and GDM groups were 27.9 and 30.5 years, respectively. The parameters such as age, BMI, and gestational age were statistically similar in both groups (p>.05, for all). As expected, serum insulin level and homeostasis model assessment-insulin resistance (HOMA-IR) value were significantly elevated in women with GDM (p<.001, for both). Moreover, maternal PlGF concentration was found to be higher in the GDM group compared to the control group (p=.029). Pearson's correlation analysis of PlGF with other study parameters revealed that there was a negative moderate and significant correlation in only control group (r= -0.416, p<.05). However, this correlation was not detected in the GDM group (r = 0.099, p>.05). None of the variables including maternal age, BMI, insulin, and HOMA-IR showed significant correlations in GDM and control groups.Conclusion: Our findings revealed that maternal serum PlGF level is increased in pregnant women complicated with GDM. Early identification of pregnant women who subsequently will pose GDM risk could improve the pregnancy outcomes.

Human placental glucose transport in fetoplacental growth and metabolism

While efficient glucose transport is essential for all cells, in the case of the human placenta, glucose transport requirements are two-fold; provision of glucose for the growing fetus in addition to the supply of glucose required the changing metabolic needs of the placenta itself. The rapidly evolving environment of placental cells over gestation has significant consequences for the development of glucose transport systems. The two-fold transport requirement of the placenta means also that changes in expression will have effects not only for the placenta but also for fetal growth and metabolism. This review will examine the localization, function and evolution of placental glucose transport systems as they are altered with fetal development and the transport and metabolic changes observed in pregnancy pathologies.

Maternal Gestational Diabetes Mellitus increases placental and foetal lipoprotein-associated Phospholipase A2 which might exert protective functions against oxidative stress

Increased Lipoprotein associated phospholipase A2 (LpPLA2) has been associated with inflammatory pathologies, including Type 2 Diabetes. Studies on LpPLA2 and Gestational Diabetes Mellitus (GDM) are rare, and have focused mostly on maternal outcome. In the present study, we investigated whether LpPLA2 activity on foetal lipoproteins is altered by maternal GDM and/or obesity (a major risk factor for GDM), thereby contributing to changes in lipoprotein functionality. We identified HDL as the major carrier of LpPLA2 activity in the foetus, which is in contrast to adults. We observed marked expression of LpPLA2 in placental macrophages (Hofbauer cells; HBCs) and found that LpPLA2 activity in these cells was increased by insulin, leptin, and pro-inflammatory cytokines. These regulators were also increased in plasma of children born from GDM pregnancies. Our results suggest that insulin, leptin, and pro-inflammatory cytokines are positive regulators of LpPLA2 activity in the foeto-placental unit. Of particular interest, functional assays using a specific LpPLA2 inhibitor suggest that high-density lipoprotein (HDL)-associated LpPLA2 exerts anti-oxidative, athero-protective functions on placental endothelium and foetus. Our results therefore raise the possibility that foetal HDL-associated LpPLA2 might act as an anti-inflammatory enzyme improving vascular barrier function.

Placental Origins of Chronic Disease

Epidemiological evidence links an individual's susceptibility to chronic disease in adult life to events during their intrauterine phase of development. Biologically this should not be unexpected, for organ systems are at their most plastic when progenitor cells are proliferating and differentiating. Influences operating at this time can permanently affect their structure and functional capacity, and the activity of enzyme systems and endocrine axes. It is now appreciated that such effects lay the foundations for a diverse array of diseases that become manifest many years later, often in response to secondary environmental stressors. Fetal development is underpinned by the placenta, the organ that forms the interface between the fetus and its mother. All nutrients and oxygen reaching the fetus must pass through this organ. The placenta also has major endocrine functions, orchestrating maternal adaptations to pregnancy and mobilizing resources for fetal use. In addition, it acts as a selective barrier, creating a protective milieu by minimizing exposure of the fetus to maternal hormones, such as glucocorticoids, xenobiotics, pathogens, and parasites. The placenta shows a remarkable capacity to adapt to adverse environmental cues and lessen their impact on the fetus. However, if placental function is impaired, or its capacity to adapt is exceeded, then fetal development may be compromised. Here, we explore the complex relationships between the placental phenotype and developmental programming of chronic disease in the offspring. Ensuring optimal placentation offers a new approach to the prevention of disorders such as cardiovascular disease, diabetes, and obesity, which are reaching epidemic proportions.

Impact of pre-gestational and gestational diabetes mellitus on the expression of glucose transporters GLUT-1, GLUT-4 and GLUT-9 in human term placenta

PURPOSE

Various studies in placental tissue suggest that diabetes mellitus alters the expression of glucose transporter (GLUT) proteins, with insulin therapy being a possible modulatory factor. The aim of the present study was quantitative evaluation of the expression of glucose transporters (GLUT-1, GLUT-4, GLUT-9) in the placenta of women in both, uncomplicated and diabetic pregnancy. Additionally, the effect of insulin therapy on the expression of selected glucose transporter isoforms was analyzed.

METHODS

Term placental samples were obtained from healthy control (n = 25) and diabetic pregnancies, including diet-controlled gestational diabetes mellitus (GDMG1) (n = 16), insulin-controlled gestational diabetes mellitus (GDMG2) (n = 6), and pre-gestational diabetes mellitus (PGDM) (n = 6). Computer-assisted quantitative morphometry of stained placental sections was performed to determine the expression of selected glucose transporter proteins.

RESULTS

Morphometric analysis revealed a significant increase in the expression of GLUT-4 and GLUT-9 in insulin-dependent diabetic women (GDMG2 + PGDM) as compared to both, control and GDMG1 groups (p < .05). Significantly increased GLUT-1 expression was observed only in placental specimens from patients with PGDM (p < .05). No statistically significant differences in GLUT expression were found between GDMG1 patients and healthy controls.

CONCLUSIONS

The results of the study confirmed the presence of GLUT-1, GLUT-4 and GLUT-9 proteins in the trophoblast from both, uncomplicated and diabetic pregnancies. In addition, insulin therapy may increase placental expression of GLUT-4 and GLUT-9, and partially GLUT-1, in women with GDMG2/PGDM.

Role of Insulin in Placental Transport of Nutrients in Gestational Diabetes Mellitus

BACKGROUND

Gestational diabetes mellitus (GDM) is associated with increased fetal adiposity, which may increase the risk of obesity in adulthood. The placenta has insulin receptors and maternal insulin can activate its signaling pathways, affecting the transport of nutrients to the fetus. However, the effects of diet or insulin treatment on the placental pathophysiology of GDM are unknown.

SUMMARY

There are very few studies on possible defects in the insulin signaling pathway in the GDM placenta. Such defects could influence the placental transport of nutrients to the fetus. In this review we discuss the state of insulin signaling pathways in placentas of women with GDM, as well as the role of exogenous insulin in placental nutrient transport to the fetus, and fetal adiposity. Key Messages: Maternal insulin in the third trimester is correlated with fetal abdominal circumference at that time, suggesting the important role of insulin in this process. Since treatment with insulin at the end of pregnancy may activate placental nutrient transport to the fetus and promote placental fatty acid transfer, it would be interesting to improve maternal hyperlipidemia control in GDM subjects treated with this hormone. More research in this area with high number of subjects is necessary.

Insulin receptor isoforms: an integrated view focused on gestational diabetes mellitus

The human insulin receptor (IR) exists in two isoforms that differ by the absence (IR-A) or the presence (IR-B) of a 12-amino acid segment encoded by exon 11. Both isoforms are functionally distinct regarding their binding affinities and intracellular signalling. However, the underlying mechanisms related to their cellular functions in several tissues are only partially understood. In this review, we summarize the current knowledge in this field regarding the alternative splicing of IR isoform, tissue-specific distribution and signalling both in physiology and disease, with an emphasis on the human placenta in gestational diabetes mellitus (GDM). Furthermore, we discuss the clinical relevance of IR isoforms highlighted by findings that show altered insulin signalling due to differential IR-A and IR-B expression in human placental endothelium in GDM pregnancies. Future research and clinical studies focused on the role of IR isoform signalling might provide novel therapeutic targets for treating GDM to improve the adverse maternal and neonatal outcomes.

Insulin Is a Key Modulator of Fetoplacental Endothelium Metabolic Disturbances in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is a disease of the mother that associates with altered fetoplacental vascular function. GDM-associated maternal hyperglycaemia result in fetal hyperglycaemia, a condition that leads to fetal hyperinsulinemia and altered L-arginine transport and synthesis of nitric oxide, i.e., endothelial dysfunction. These alterations in the fetoplacental endothelial function are present in women with GDM that were under diet or insulin therapy. Since these women and their newborn show normal glycaemia at term, other factors or conditions could be altered and/or not resolved by restoring normal level of circulating D-glucose. GDM associates with metabolic disturbances, such as abnormal handling of the locally released vasodilator adenosine, and biosynthesis and metabolism of cholesterol lipoproteins, or metabolic diseases resulting in endoplasmic reticulum stress and altered angiogenesis. Insulin acts as a potent modulator of all these phenomena under normal conditions as reported in primary cultures of cells obtained from the human placenta; however, GDM and the role of insulin regarding these alterations in this disease are poorly understood. This review focuses on the potential link between insulin and endoplasmic reticulum stress, hypercholesterolemia, and angiogenesis in GDM in the human fetoplacental vasculature. Based in reports in primary culture placental endothelium we propose that insulin is a factor restoring endothelial function in GDM by reversing ERS, hypercholesterolaemia and angiogenesis to a physiological state involving insulin activation of insulin receptor isoforms and adenosine receptors and metabolism in the human placenta from GDM pregnancies.

Placental growth response to maternal insulin in early pregnancy

CONTEXT

The sensitivity of the placenta to maternal insulin remains controversial. Early pregnancy may be a time of increased placental sensitivity to maternal insulin because insulin receptors are abundant on the syncytiotrophoblast in the first trimester but are far fewer at term.

HYPOTHESIS

Maternal insulin secretory response in early, but not late, pregnancy is positively associated with placental growth.

DESIGN

This is a secondary analysis of a cohort of women (n = 40) recruited before pregnancy.

OUTCOME MEASURES

An iv glucose tolerance test was administered before pregnancy and in early (12-14 weeks) and late (34-36 weeks) pregnancy. Placental volume throughout gestation (in a subset of women via 3-dimensional ultrasound) and weight at birth were recorded.

RESULTS

Total insulin secretory response in early pregnancy was positively associated with placental volume in early pregnancy (R = 0.79, P = 0.04) and placental weight at term (R = 0.42, P = 0.007). Insulin secretory response before and in late pregnancy was not significantly associated with placental growth. Although neonatal fat mass was strongly correlated with placental weight at term (R = 0.449, P = 0.0003), maternal insulin secretory response was related to neonatal fat mass only at birth in male offspring (R = 0.59, P = 0.008).

CONCLUSIONS

Maternal insulin secretory response in early pregnancy was strongly related to placental weight at birth. Thus, in early pregnancy, increased maternal insulin response as seen in obesity and gestational diabetes mellitus may be a key influence on placental growth, possibly due to the enhanced presence of placental insulin receptors on the maternal villous membrane early in gestation.

Glucose, insulin, and oxygen interplay in placental hypervascularisation in diabetes mellitus

The placental vasculature rapidly expands during the course of pregnancy in order to sustain the growing needs of the fetus. Angiogenesis and vascular growth are stimulated and regulated by a variety of growth factors expressed in the placenta or present in the fetal circulation. Like in tumors, hypoxia is a major regulator of angiogenesis because of its ability to stimulate expression of various proangiogenic factors. Chronic fetal hypoxia is often found in pregnancies complicated by maternal diabetes as a result of fetal hyperglycaemia and hyperinsulinemia. Both are associated with altered levels of hormones, growth factors, and proinflammatory cytokines, which may act in a proangiogenic manner and, hence, affect placental angiogenesis and vascular development. Indeed, the placenta in diabetes is characterized by hypervascularisation, demonstrating high placental plasticity in response to diabetic metabolic derangements. This review describes the major regulators of placental angiogenesis and how the diabetic environment in utero alters their expression. In the light of hypervascularized diabetic placenta, the focus was placed on proangiogenic factors.

Gestational diabetes mellitus alters apoptotic and inflammatory gene expression of trophobasts from human term placenta

AIM

Increased placental growth secondary to reduced apoptosis may contribute to the development of macrosomia in GDM pregnancies. We hypothesize that reduced apoptosis in GDM placentas is caused by dysregulation of apoptosis related genes from death receptors or mitochondrial pathway or both to enhance placental growth in GDM pregnancies.

METHODS

Newborn and placental weights from women with no pregnancy complications (controls; N=5), or with GDM (N=5) were recorded. Placental villi from both groups were either fixed for TUNEL assay, or snap frozen for gene expression analysis by apoptosis PCR microarrays and qPCR.

RESULTS

Maternal, placental and newborn weights were significantly higher in the GDM group vs. Controls. Apoptotic index of placentas from the GDM group was markedly lower than the Controls. At a significant threshold of 1.5, seven genes (BCL10, BIRC6, BIRC7, CASP5, CASP8P2, CFLAR, and FAS) were down regulated, and 13 genes (BCL2, BCL2L1, BCL2L11, CASP4, DAPK1, IκBκE, MCL1, NFκBIZ, NOD1, PEA15, TNF, TNFRSF25, and XIAP) were unregulated in the GDM placentas. qPCR confirmed the consistency of the PCR microarray. Using Western blotting we found significantly decreased placental pro-apoptotic FAS receptor and FAS ligand (FASL), and increased mitochondrial anti-apoptotic BCL2 post GDM insult. Notably, caspase-3, which plays a central role in the execution-phase of apoptosis, and its substrate poly (ADP-ribose) polymerase (PARP) were significantly down regulated in GDM placentas, as compared to non-diabetic Control placentas.

CONCLUSION

Maternal GDM results in heavier placentas with aberrant placental apoptotic and inflammatory gene expression that may account, at least partially, for macrosomia in newborns.

Trying to understand gestational diabetes

Women with normal glucose tolerance pre-gravid and developing gestational diabetes in late gestation have subclinical metabolic dysfunction prior to conception compared with women with normal glucose tolerance. Because of the 60% decrease in insulin sensitivity with normal pregnancy, these women develop clinical hyperglycaemia/gestational diabetes in late gestation. The metabolic dysfunction includes impaired insulin response, decreased hepatic suppression of glucose production during insulin infusion and decreased insulin-stimulated glucose uptake in skeletal muscle, i.e. peripheral insulin resistance. The insulin resistance in normal glucose tolerance pregnancy is related to a decrease in the post-receptor insulin signalling cascade, specifically decreased insulin receptor substrate 1 tyrosine phosphorylation. In women with normal glucose tolerance this is reversed post-partum. In contrast, in gestational diabetes, in addition to the decrease in insulin receptor substrate 1 tyrosine phosphorylation, there is an additional decrease in tyrosine phosphorylation of the intracellular portion of the insulin receptor that is not related to the insulin receptor protein content. Post-partum women with gestational diabetes, who had retention of gestational weight gain, had no significant improvement in insulin sensitivity and increased inflammation expressed as increased plasma and skeletal muscle tumour necrosis factor alpha. The increased inflammation or meta-inflammation is a hallmark of obesity and during pregnancy develops in both white adipose tissue and placenta. Last gene array studies of placenta were associated with alterations in gene expression relating primarily to lipid in contrast to glucose metabolic pathways in gestational diabetes compared with Type 1 diabetes. Future studies are directed at decreasing inflammation prior to and during pregnancy using various lifestyle and nutritional interventions.

Regulation of nutrient transport across the placenta

Abnormal fetal growth, both growth restriction and overgrowth, is associated with perinatal complications and an increased risk of metabolic and cardiovascular disease later in life. Fetal growth is dependent on nutrient availability, which in turn is related to the capacity of the placenta to transport these nutrients. The activity of a range of nutrient transporters has been reported to be decreased in placentas of growth restricted fetuses, whereas at least some studies indicate that placental nutrient transport is upregulated in fetal overgrowth. These findings suggest that changes in placental nutrient transport may directly contribute to the development of abnormal fetal growth. Detailed information on the mechanisms by which placental nutrient transporters are regulated will therefore help us to better understand how important pregnancy complications develop and may provide a foundation for designing novel intervention strategies. In this paper we will focus on recent studies of regulatory mechanisms that modulate placental transport of amino acids, fatty acids, and glucose.

Placental-specific Igf2 deficiency alters developmental adaptations to undernutrition in mice

The pattern of fetal growth is a major determinant of the subsequent health of the infant. We recently showed in undernourished (UN) mice that fetal growth is maintained until late pregnancy, despite reduced placental weight, through adaptive up-regulation of placental nutrient transfer. Here, we determine the role of the placental-specific transcript of IGF-II (Igf2P0), a major regulator of placental transport capacity in mice, in adapting placental phenotype to UN. We compared the morphological and functional responses of the wild-type (WT) and Igf2P0-deficient placenta in WT mice fed ad libitium or 80% of the ad libitium intake. We observed that deletion of Igf2P0 prevented up-regulation of amino acid transfer normally seen in UN WT placenta. This was associated with a reduction in the proportion of the placenta dedicated to nutrient transport, the labyrinthine zone, and its constituent volume of trophoblast in Igf2P0-deficient placentas exposed to UN on d 16 of pregnancy. Additionally, Igf2P0-deficient placentas failed to up-regulate their expression of the amino acid transporter gene, Slc38a2, and down-regulate phosphoinositide 3-kinase-protein kinase B signaling in response to nutrient restriction on d 19. Furthermore, deleting Igf2P0 altered maternal concentrations of hormones (insulin and corticosterone) and metabolites (glucose) in both nutritional states. Therefore, Igf2P0 plays important roles in adapting placental nutrient transfer capacity during UN, via actions directly on the placenta and/or indirectly through the mother.

Insulin and the IGF system in the human placenta of normal and diabetic pregnancies

The insulin/insulin-like growth factor (IGF) system regulates fetal and placental growth and development. In maternal diabetes, components of this system including insulin, IGF1, IGF2 and various IGF-binding proteins are deregulated in the maternal or fetal circulation, or in the placenta. The placenta expresses considerable amounts of insulin and IGF1 receptors at distinct locations on both placental surfaces. This makes the insulin and the IGF1 receptor accessible to fetal and/or maternal insulin, IGF1 and IGF2. Unlike the receptor for IGF1, the insulin receptor undergoes a gestational change in expression site from the trophoblast at the beginning of pregnancy to the endothelium at term. Insulin and IGFs are implicated in the receptor-mediated regulation of placental growth and transport, trophoblast invasion and placental angiogenesis. The dysregulation of the growth factors and their receptors may be involved in placental and fetal changes observed in diabetes, i.e. enhanced placental and fetal growth, placental hypervascularization and higher levels of fetal plasma amino acids.

Kinetics of gold nanoparticles in the human placenta

We studied the transfer of PEGylated gold nanoparticles through perfused human placenta. In 'once-through' perfusions using 15 and 30nm nanoparticles both maternal and fetal outflows were collected. Recirculating perfusions using 10 or 15nm nanoparticles lasted 6h. The gold concentration in samples was analysed on ICP-MS. The reference compound antipyrine crossed the placenta rapidly, as expected. In open perfusions nanoparticles were detected in maternal but not in fetal outflow, suggesting the lack of placental transfer. During 6h re-circulating perfusions, no particles were detected in fetal circulation. Using transmission electron microscopy (TEM) and silver enhancement, nanoparticles could be visualized in the placental tissue mainly in the trophoblastic cell layer. In in vitro experiments, nanoparticles were taken up by BeWo choriocarcinoma cells and retained inside the cells for an extended period of 48h. In conclusion, PEGylated gold nanoparticles of the size 10-30nm did not cross the perfused human placenta in detectable amounts into the fetal circulation within 6h. Whether PEGylated gold nanoparticles eventually are able to cross placenta and whether nanoparticles affect placental functions needs to be further studied.

Mutations in the glucokinase gene of the fetus result in reduced placental weight

OBJECTIVE

In human pregnancy, placental weight is strongly associated with birth weight. It is uncertain whether there is regulation of the placenta by the fetus or vice versa. We aimed to test the hypothesis that placental growth is mediated, either directly or indirectly, by fetal insulin.

RESEARCH DESIGN AND METHODS

Birth weight and placental weight were measured in 43 offspring of 21 parents with mutations in the glucokinase (GCK) gene (25 had inherited the mutation and 18 had not), which results in reduced fetal insulin secretion. Birth weight, placental weight, umbilical cord insulin, and maternal glucose and insulin concentrations were measured in 573 nondiabetic, healthy, term pregnancies.

RESULTS

GCK mutation carriers were lighter and also had smaller placentas (610 vs. 720 g, P = 0.042). This difference was also seen in 17 discordant sibling pairs (600 vs. 720 g, P = 0.003). GCK mRNA was not detected in the placenta by RT-PCR. In the normal pregnancies, placental weight was strongly correlated with birth weight (r = 0.61, P < 0.001). Cord insulin concentrations were directly related to placental weight (r = 0.28) and birth weight (r = 0.36) (P < 0.001 for both).

CONCLUSIONS

These results suggest that insulin, directly or indirectly, plays a role in placental growth, especially as a mutation in the GCK gene, which is known to only alter fetal insulin secretion, results in altered placental weight. This finding is consistent with the preferential localization of the insulin receptors in the fetal endothelium of the placenta in the last trimester of pregnancy.

Regulation of Placental Nutrient Transport – A Review

Fetal growth is primarily determined by nutrient availability, which is intimately related to placental nutrient transport. Detailed information on the regulation of placental nutrient transporters is therefore critical in order to understand the mechanisms underlying altered fetal growth and fetal programming. After briefly summarizing the cellular mechanisms for placental transport of glucose, amino acids and free fatty acids, we will discuss factors shown to regulate placental nutrient transporters and review the data describing how these factors are altered in pregnancy complications associated with abnormal fetal growth. We propose an integrated model of regulation of placental nutrient transport by maternal and placental factors in IUGR.

Effect of maternal triglycerides and free fatty acids on placental LPL in cultured primary trophoblast cells and in a case of maternal LPL deficiency

Maternal hypertriglyceridemia is a normal condition in late gestation and is an adaptation to ensure an adequate nutrient supply to the fetus. Placental lipoprotein lipase (LPL) is involved in the initial step in transplacental fatty acid transport as it hydrolyzes maternal triglycerides (TG) to release free fatty acids (FFA). We investigated LPL activity and protein (Western blot) and mRNA expression (real-time RT-PCR) in the placenta of an LPL-deficient mother with marked hypertriglyceridemia. The LPL activity was fourfold lower, LPL protein expression 50% lower, and mRNA expression threefold higher than that of normal, healthy placentas at term (n = 4-7). To further investigate the role of maternal lipids in placental LPL regulation, we isolated placental cytotrophoblasts from term placentas and studied LPL activity and protein and mRNA expression after incubation in Intralipid (as a source of TG) and oleic, linoleic, and a combination of oleic, linoleic, and arachidonic acids as well as insulin. Intralipid (40 and 400 mg/dl) decreased LPL activity by approximately 30% (n = 10-14, P < 0.05) and 400 microM linoleic and linoleic-oleic-arachidonic acid (n = 10) decreased LPL activity by 37 and 34%, respectively. No major changes were observed in LPL protein or mRNA expression. We found no effect of insulin on LPL activity or protein expression in the cultured trophoblasts. To conclude, the activity of placental LPL is reduced by high levels of maternal TG and/or FFA. This regulatory mechanism may serve to counteract an excessive delivery of FFA to the fetus in conditions where maternal TG levels are markedly increased.

Effects of gestational diabetes mellitus on proteins implicated in insulin signaling in human placenta

OBJECTIVE

Placenta plays a central role in fetal nutrition. During gestational diabetes mellitus (GDM), it suffers structural and functional alterations which affect the health of both mother and fetus. In the present study we aimed to clarify if GDM modifies the amounts of leptin receptor (Ob-R) and of the main proteins implicated in insulin signal transmission (insulin receptor, insulin receptor substrate-1 and phosphatidylinositol-3-kinase subunit p85alpha) in human placenta; we also attempted to confirm the presence of estrogen receptor-alpha to determine the effect of GDM on its amount.

METHODS

Placentas were recovered from 30 women with uncomplicated pregnancies and 20 women who developed GDM. Western blotting and immunocytochemistry experiments were performed to investigate the above-mentioned proteins.

RESULTS

We observed that all proteins studied were increased in GDM. However, it is unknown if this is a consequence of GDM or the result of medical treatments used to mitigate the injurious effects of GDM.

CONCLUSIONS

Probably, the changes we found are indicative of the protective role of the placenta prior to the injurious effects of GDM and/or an important indicator of placental aging. Some aspects related to the link between non-genomic estrogen action, the mitogenic action of insulin and the role of Ob-R in placenta from normal and GDM women need to be investigated in greater depth.

Placental insulin and insulin-like growth factor I receptors in normal and preeclamptic pregnancies

OBJECTIVES

To assess the ligand binding characteristics of insulin and insulin-like growth factor I receptors in normal and preeclamptic placentas.

DESIGN AND METHODS

This study was done cross sectionally in trophoblast membranes obtained from 10 normotensive and 9 preeclamptic pregnant women. The affinity and number of binding sites of insulin and insulin-like growth factor I receptors were assessed by binding assays and Scatchard plot analysis.

RESULTS

Placental and newborn birth weights were significantly (P < 0.001) lower in the preeclamptic group. The K(d) values of placental insulin receptors (IR) were significantly higher in the preeclamptic group than in the normotensive group (1.08 +/- 0.24 x 10(-9) vs. 0.81 +/- 0.13 x 10(-9) M, P < 0.01), without differences in the number of receptors. In contrast, no differences were observed in the affinity and the number of insulin-like growth factor I receptors (IGF-1R) between groups. Placental weight was associated negatively with the K(d) values of IR (P < 0.05) and positively with the number of placental IGF-1R (P < 0.05); while newborn birth weight was associated positively with the number of IGF-1R (P < 0.05). In addition, both systolic and diastolic blood pressure correlated significantly with K(d) values of placental IR (P < 0.01).

CONCLUSIONS

These data demonstrate that preeclampsia is associated with low placental IR affinity. In addition, this study suggests an association between the affinity of IR and number of IGF-1R with placental and/or fetal growth. Furthermore, high blood pressure may affect the affinity of placental IR, but not the affinity or number of placental IGF-1 receptors.

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.

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.

Pregnancy impairs the counterregulatory response to insulin-induced hypoglycemia in the dog

The impact of pregnancy on the counterregulatory response to insulin-induced hypoglycemia was examined in six nonpregnant (NP) and six pregnant (P; 3rd trimester) conscious dogs by tracer and arteriovenous difference techniques. After basal sampling, insulin was infused intraportally at 30 pmol.kg(-1).min(-1) for 180 min. Insulin rose from 70 +/- 15 to 1,586 +/- 221 pmol/l and 27 +/- 4 to 1,247 +/- 61 pmol/l in the 3rd h in NP and P, respectively. Arterial glucose fell from 5.9 +/- 0.2 to 2.3 +/- 0.2 mmol/l in P. Glucose was infused in NP to equate the rate of fall of glucose and the steady-state concentrations in the groups (5.9 +/- 0.2 to 2.3 +/- 0.1 mmol/l in NP). Glucagon was 32 +/- 6, 69 +/- 11, and 48 +/- 10 ng/l (basal and 1st and 3rd h) in NP, but the response was attenuated in P (34 +/- 5, 46 +/- 6, 41 +/- 9 ng/l). Cortisol and epinephrine rose similarly in both groups, but norepinephrine rose more in NP (Delta3.01 +/- 0.46 and Delta1.31 +/- 0.13 nmol/l, P < 0.05). Net hepatic glucose output (NHGO; micromol.kg(-1).min(-1)) increased from 10.6 +/- 1.8 to 21.2 +/- 3.3 in NP (3rd h) but did not increase in P (15.1 +/- 1.5 to 15.3 +/- 2.8 micromol.kg(-1).min(-1), P < 0.05 between groups). The glycogenolytic contribution to NHGO in NP increased from 5.8 +/- 0.7 to 10.4 +/- 2.5 micromol.kg(-1).min(-1) by 90 min but steadily declined in P. The increase in glycerol levels and the gluconeogenic contribution to NHGO were 50% less in P than in NP, but ketogenesis did not differ. The glucagon and norepinephrine responses to insulin-induced hypoglycemia are blunted in late pregnancy in the dog, impacting on the magnitude of the metabolic responses to the fall in glucose.

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.

GLUT12 expression in human placenta in first trimester and term

The aim of this study was to characterize the expression of a novel glucose transporter protein GLUT12 in human placenta. GLUT12 mRNA expression was identified by RT-PCR in extracts from five normal term placentae and in extracts from cultured cells of the JAR, JEG-3 and HTR-8Svneo cell lines. In further studies, paraffin sections of first trimester tissue from chorionic villus sampling and term tissue obtained after delivery were analysed by immunohistology with a GLUT12 specific polyclonal antibody. GLUT12 immunoreactivity was expressed predominantly in the syncytiotrophoblast and in extra-villous trophoblast cells in first trimester tissues at 10, 11 and 12 weeks' gestation. In term tissue, however, GLUT12 staining was not detected in syncytiotrophoblast and was found predominantly in villous vascular smooth muscle cells and villous stromal cells. These results suggest that there is a dynamic spatial and temporal expression pattern for the novel glucose transporter GLUT12 in human placenta.

Influence of omega-3 fatty acids on the growth of human colon carcinoma in nude mice

The present study investigated the influence of dietary omega-3 fatty acid supplementation on the growth of human colon carcinoma xenograft in athymic nude mice. Four diets were fed to evaluate the effect of levels and types of fat on colon tumor growth. Animals were maintained on a standard diet modified by addition of fats containing omega-3 and omega-6 fatty acids to represent high and low fat intakes for 53 days. The final mean estimated tumor weight for the high fat corn oil (24%) fed group was 2,302 mg, whereas the low fat (8% corn oil) group was 1,681 mg. The final mean tumor weight of the high fat menhaden oil fed group was 782 mg representing a 66% decrease in growth compared to the high fat corn oil group and a decrease of 54% compared to the low corn oil fed group. The high fat golden algae oil fed group resulted in a mean final tumor weight of 223 mg representing a 90% inhibition of tumor growth relative to the high fat corn oil fed group and 87% inhibition of growth compared to the low fat corn oil fed group. These findings indicate that dietary omega-3 fatty acids possess significant tumor suppressing properties and that the primary tumor suppressing fatty acid is docosahexaenoic acid. Histopathologic examination of control and treated tumors and expression array analyses (human cytokine and apoptosis arrays) support the tumor growth inhibition data and provide evidence for discussion of possible mechanisms for the observed growth inhibition.