Hormonal regulation of neonatal weight: placental leptin and leptin receptors

Adipokines underlie the early origins of obesity and associated metabolic comorbidities in the offspring of women with pregestational obesity

Maternal pregestational obesity is a well-known risk factor for offspring obesity, metabolic syndrome, cardiovascular disease and type 2 diabetes. The mechanisms by which maternal obesity can induce alterations in fetal and later neonatal metabolism are not fully elucidated due to its complexity and multifactorial causes. Two adipokines, leptin and adiponectin, are involved in fetal and postnatal growth trajectories, and both are altered in women with pregestational obesity. The placenta synthesizes leptin, which goes mainly to the maternal circulation and in lesser amount to the developing fetus. Maternal pregestational obesity and hyperleptinemia are associated with placental dysfunction and changes in nutrient transporters which directly affect fetal growth and development. By the other side, the embryo can produce its own leptin from early in development, which is associated to fetal weight and adiposity. Adiponectin, an insulin-sensitizing adipokine, is downregulated in maternal obesity. High molecular weight (HMW) adiponectin is the most abundant form and with most biological actions. In maternal obesity lower total and HMW adiponectin levels have been described in the mother, paralleled with high levels in the umbilical cord. Several studies have found that cord blood adiponectin levels are related with postnatal growth trajectories, and it has been suggested that low adiponectin levels in women with pregestational obesity enhance placental insulin sensitivity and activation of placental amino acid transport systems, supporting fetal overgrowth. The possible mechanisms by which maternal pregestational obesity, focusing in the actions of leptin and adiponectin, affects the fetal development and postnatal growth trajectories in their offspring are discussed.

Role of insulin, adenosine, and adipokine receptors in the foetoplacental vascular dysfunction in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a disease of pregnancy associated with maternal and foetal hyperglycaemia and altered foetoplacental vascular function. Human foetoplacental microvascular and macrovascular endothelium from GDM pregnancy show increased maximal l-arginine transport capacity via the human cationic amino acid transporter 1 (hCAT-1) isoform and nitric oxide (NO) synthesis by the endothelial NO synthase (eNOS). These alterations are paralleled by lower maximal transport activity of the endogenous nucleoside adenosine via the human equilibrative nucleoside transporter 1 (hENT1) and activation of adenosine receptors. A causal relationship has been described for adenosine-activation of A_2A adenosine receptors, hCAT-1, and eNOS activity (i.e. the Adenosine/l-Arginine/Nitric Oxide, ALANO, signalling pathway). Insulin restores these alterations in GDM via activation of insulin receptor A (IR-A) form in the macrovascular but IR-A and IR-B forms in the microcirculation of the human placenta. Adipokines are secreted from adipocytes influencing the foetoplacental metabolic and vascular function. Various adipokines are dysregulated in GDM, with adiponectin and leptin playing major roles. Abnormal plasma concentration of these adipokines and the activation or their receptors are involved in the pathophysiology of GDM. However, involvement of adipokines, adenosine, and insulin receptors and membrane transporters in the aetiology of this disease of pregnancy is unknown. This review focuses on the pathophysiology of insulin and adenosine receptors and l-arginine and adenosine membranes transporters giving an overview of the key adipokines leptin and adiponectin in the foetoplacental vasculature in GDM. This article is part of a Special Issue entitled: Membrane Transporters and Receptors in Pregnancy Metabolic Complications edited by Luis Sobrevia.

Systemic and placental leptin and its receptors in pregnancies associated with obesity

This study aimed to gain new insights into both systemic and placental leptin and its receptors, with reference to the maternal prepregnancy body mass index (BMI). Thus, 84 women (29 lean, 24 overweight, and 31 obese) were recruited and maternal, cord blood, and placental tissues collected prior to term labor. Plasma levels were measured by enzyme-linked immunosorbent assay and for placenta, immunohistochemistry and messenger RNAs (mRNAs) were quantitated. We confirmed that maternal leptin increased linearly as the soluble receptor decreased with BMI (P = .001). Fetal leptin increased with maternal BMI (P = .02) and birth weight (P = .006) and was higher in female infants (P < .001). Placental mRNA levels of leptin and its receptors showed no change in BMI. However, we show a significant (P = .043) linear increase in leptin in the placental vascular endothelial cells with maternal obesity, while leptin in syncytiotrophoblast showed no statistical change. Leptin receptors localized to syncytiotrophoblast and intravillous macrophages and were unchanged with BMI.

The effect of ponderal index at birth on the relationships between common LEP and LEPR polymorphisms and adiposity in adolescents

This study examined the effect of ponderal index (PI) at birth on the relationships between eight common polymorphisms of the leptin (LEP) and leptin receptor (LEPR) genes and adiposity in adolescents. A total of 823 European adolescents (45.4% girls) aged 14.8 ± 1.4 years were genotyped for the LEP (rs2167270, rs12706832, rs10244329, rs2071045, and rs3828942) and LEPR (rs1137100, rs1137101, and rs8179183) polymorphisms. The PI was calculated from parental reports of birth weight and length. Fat mass index (FMI) was calculated. Analyses were adjusted for relevant confounders. An "adiposity-risk-allele score" based on genotypes at the three single-nucleotide polymorphisms (SNPs) associated with adolescents' FMI in adolescents within the lower tertile of PI was calculated. The LEP rs10244329 and rs3828942 polymorphisms were associated with higher FMI only in adolescents within the lower PI tertile (+0.55 kg/m(2) per minor T allele, P = 0.040, and +0.58 kg/m(2) per major G allele, P = 0.028, respectively). The LEPR rs8179183 polymorphism was significantly associated with higher FMI in adolescents within the lower PI tertile (+0.87 kg/m(2) per minor C allele, P = 0.006). After correction for multiple comparisons, only the association between the LEPR rs8179183 and FMI persisted. However, each additional risk allele conferred 0.53 kg/m(2) greater FMI in adolescents within the lower tertile of PI (P = 0.008). In conclusion, our results suggest that those adolescents born with lower PI could be more vulnerable to the influence of the LEP rs10244329 and rs3828942 polymorphisms and LEPR rs8179183 polymorphism on total adiposity content. Due to the relatively small sample size, these findings should be replicated in further larger population samples.

Anthropometry, carbohydrate and lipid metabolism in the East Flanders Prospective Twin Survey: linkage of candidate genes using two sib-pair based variance components analyses

Insulin resistance and obesity are underlying causes of type 2 diabetes and therefore much interest is focused on the potential genes involved. A series of anthropometric and metabolic characteristic were measured in 240 MZ and 112 DZ twin pairs recruited from the East Flanders Prospective Twin Survey. Microsatellite markers located close to ABCC8, ADIPOQ, GCK, IGF1, IGFBP1, INSR, LEP, LEPR, PPARgamma and the RETN gene were genotyped. Univariate single point variance components linkage analyses were performed using two methods: (1) the standard method, only comprising the phenotypic and genotypic data of the DZ twin pairs and (2) the extended method, also incorporating the phenotypic data of the MZ twin pairs. Suggestive linkages (LOD > 1) were observed between the ABCC8 marker and waist-to-hip ratio and HDL-cholesterol levels. Both markers flanking ADIPOQ showed suggestive linkage with triglycerides levels, the upstream marker also with body mass and HDL-cholesterol levels. The IGFBP1 marker showed suggestive linkage with fat mass, fasting insulin and leptin levels and the LEP marker showed suggestive linkage with birth weight. This study suggests that DNA variants in ABCC8, ADIPOQ, IGFBP1 and LEP gene region may predispose to type 2 diabetes. In addition, the two methods used to perform linkage analyses yielded similar results. This was however not the case for birth weight where chorionicity seems to be an important confounder.

Common SNPs in LEP and LEPR associated with birth weight and type 2 diabetes-related metabolic risk factors in twins

OBJECTIVE

Children born small for gestational age are at increased risk of developing type 2 diabetes in adulthood. The satiety signal leptin that regulates food intake and energy expenditure might be a possible molecular link, as umbilical cord leptin levels are positively correlated with birth weight. In the present study, we examined whether common single nucleotide polymorphisms (SNPs) in the leptin (LEP; 19G>A) gene and its receptor (LEPR; Q223R and K109R) are associated with birth weight and adult metabolic risk factors for type 2 diabetes in twins.

DESIGN

SNPs were genotyped in 396 monozygotic and 232 dizygotic twins (286 men and 342 women, mean age 25 years) recruited from the East Flanders Prospective Twin Survey. Data were analysed using linear mixed models.

RESULTS

The LEPR K109R SNP was associated with birth weight (KK, KR and RR (95% confidence interval, CI): 2511 (2465-2557), 2575 (2516-2635) and 2726 (2606-2845) gram; P(additive)=0.001). Also the LEPR Q223R SNP showed a significant association with weight at birth (QQ, QR and RR (95% CI): 2492 (2431-2554), 2545 (2495-2595) and 2655 (2571-2740) gram; P(additive)=0.003). Furthermore, an interaction between the LEPR K109R and the Q223R SNP on birth weight was observed (P=0.014). G allele carriers of the LEP 19G>A SNP had higher high-density lipoprotein (HDL) cholesterol levels compared to 19A homozygotes (GX vs AA (95% CI): 1.62 (1.58-1.66) vs 1.49 (1.40-1.58) mmol l(-1); P(recessive)=0.013).

CONCLUSIONS

This study indicates that leptin may act as a growth-promoting signal during fetal development, and suggests a possible role for the LEPR in explaining the inverse relationship between birth weight and the development of metabolic diseases in adulthood. Additionally, these results suggest that the LEP 19G>A SNP affect HDL cholesterol levels.

Leptin in pregnancy: an update

Leptin influences satiety, adiposity, and metabolism and is associated with mechanisms regulating puberty onset, fertility, and pregnancy in various species. Maternal hyperleptinemia is a hallmark of mammalian pregnancy, although both the roles of leptin and the mechanisms regulating its synthesis appear to be taxa specific. In pregnant humans and nonhuman primates, leptin is produced by both maternal and fetal adipose tissues, as well as by the placental trophoblast. Specific receptors in the uterine endometrium, trophoblast, and fetus facilitate direct effects of the polypeptide on implantation, placental endocrine function, and conceptus development. A soluble isoform of the receptor may be responsible for inducing maternal leptin resistance during pregnancy and/or may facilitate the transplacental passage of leptin for the purpose of directly regulating fetal development. The steroid hormones are linked to the regulation of leptin and the leptin receptor and probably interact with other pregnancy-specific, serum-borne factors to regulate leptin dynamics during pregnancy. In addition to its effects on normal conceptus development, leptin is linked to mechanisms affecting a diverse array of pregnancy-specific pathologies that include preeclampsia, gestational diabetes, and intrauterine growth restriction. Association with these anomalies and with mechanisms pointing to a fetal origin for a range of conditions affecting the individual's health in adult life, such as obesity, diabetes mellitus, and cardiovascular disease, reiterate the need for continued research dedicated to elucidating leptin's roles and regulation throughout gestation.

Relationship between serum concentrations of leptin, soluble leptin receptor, testosterone and IGF-I, and growth during the first year of postnatal life in the male rhesus monkey, Macaca mulatta

OBJECTIVES

Subnormal leptin levels in low birth weight infants may allow for catch-up growth during infancy. Scant data are available that relate growth with circulating leptin during normal infancy in primates. The current study objective was to examine the association between serum leptin, its soluble receptor (sOB-R), testosterone and IGF-I concentrations, and body weight during infancy in male rhesus monkeys.

DESIGN

Hormone levels were assessed longitudinally in animals (n = 7) from birth until 1 year of age.

RESULTS

Body weight increased during the first 6 months of life and was strongly correlated with rising IGF-I levels and, as IGF-I plateaued and then declined during the second half of the year, body weight gain decelerated. In contrast, leptin levels declined gradually with age during the first year of life in conjunction with increasing body weight. There was no association between body weight gain and serum leptin levels or between serum testosterone and leptin values. Since sOB-R levels also declined with leptin values, it does not appear that levels of bioavailable leptin changed during infancy.

CONCLUSIONS

The data do not support the contention that leptin regulates growth during infancy, but the close association between IGF-I levels and body weight suggested that this hormone may regulate growth in infant male monkeys. The failure to observe an association between serum testosterone and leptin concentrations suggested that leptin is not involved in the activation of the hypothalamic-pituitary -testicular axis during this developmental period.

Two Isoforms of the Leptin Receptor Are Enhanced in Pregnancy-Specific Tissues and Soluble Leptin Receptor Is Enhanced in Maternal Serum with Advancing Gestation in the Baboon1

Leptin is a polypeptide hormone produced by adipose and other endocrine tissues. Although it has been linked to receptor-mediated pathways that directly influence human conceptus development, mechanisms that regulate the leptin receptor in pregnancy-specific tissues remain unclear. Therefore, we assessed leptin-receptor ontogeny and regulation in the baboon (Papio sp.), a primate model for human pregnancy. Placentae, decidua, and amniochorion were collected from baboons in early (Days 54-63, n = 4), mid (Days 98-103, n = 4), and late (Days 159-165, n = 4) gestation. Regulation by estrogen was assessed by elimination of androgen precursors via removal of the fetus (fetectomy) at midgestation and collection of tissues in late gestation (n = 4; term, approximately 184 days). Maternal serum was sampled with advancing gestation, and the abundance of soluble leptin receptor (solLepR), a potential mediator of gestational hyperleptinemia, was determined. Two placental leptin-receptor isoforms (130 and 150 kDa) increased (P < 0.04 and P < 0.02, respectively) in abundance with advancing gestation. Similarly, the 130-kDa isoform increased approximately fourfold (P < 0.0025) in decidua and approximately 10-fold (P < 0.015) in amniochorion between early and late gestation. Following fetectomy, maternal serum estradiol levels declined approximately 85% (P < 0.03), and the 150-kDa placental leptin-receptor isoform was reduced by more than half (P < 0.002). Maternal serum solLepR concentrations were correlated with gestational age (r = 0.52, P < 0.01) and were unaffected by fetectomy. The presence of leptin-receptor isoforms in pregnancy-specific tissues further denoted leptin's potential to directly influence conceptus development, whereas the 130-kDa solLepR identified in maternal serum suggested a means to facilitate the hyperleptinemia typical of primate pregnancy. Although estrogen did not appear to be the principal regulator of solLepR, it and other factors linked to advancing gestation may be implicated in the regulation of leptin-receptor synthesis.

Leptin receptor expression increases in placenta, but not hypothalamus, during gestation in Mus musculus and Myotis lucifugus

In addition to effects on appetite and metabolism, the hormone leptin is required for reproduction in mammals. Maternal plasma leptin is increased above non-pregnant levels in all mammals thus far examined, including humans. The increase in plasma leptin appears to result in part from upregulation of adipose leptin secretion (e.g., in mice), or from production and secretion of leptin from the placenta (e.g., in humans and some bats). The placenta may also modulate maternal leptin levels via production of a plasma leptin-binding protein (mice, humans). Thus, the placenta plays a coordinating role in regulation of maternal leptin during pregnancy. In this study, the hypothesis that the placenta is also a target organ for leptin in diverse taxa was tested by examining the expression of leptin receptors (Ob-R) in placentae from species of distantly related mammalian taxa, Mus musculus (the laboratory mouse) and Myotis lucifugus (the little brown myotis, also called the little brown bat). A partial sequence of M. lucifugus Ob-R cDNA was first obtained and found to share approximately 78-88% homology at the nucleotide level with known mammalian Ob-R cDNAs. Using probes and primers designed from this sequence, receptor expression was detected in numerous tissues of M. lucifugus, including placenta, which expressed two major receptor isoforms as judged by molecular size. In both species, Ob-R mRNA expression in placenta significantly increased from early to late gestation. Expression of Ob-R mRNA was not affected by cAMP treatment in vitro. The increase in Ob-R mRNA expression in placenta was specific, since Ob-R mRNA expression did not change during gestation in either species in hypothalamus, the major site of the central actions of leptin. Thus, Ob-R is expressed in placenta throughout gestation in mice and bats, and its expression increases over the course of gestation, which raises the possibility that leptin may exert temporally distinct effects on placental growth or function throughout gestation. Because similar placenta-specific changes in leptin receptor expression occurred in species from distantly related mammalian taxa which collectively comprise approximately 70% of all known mammalian species, it is possible that placental actions of leptin are conserved across mammals, even in those species (such as the Swiss-Webster strain of mouse) in which the placenta does not itself produce leptin.

Maternal serum, amniotic fluid and cord leptin levels at term: their correlations with fetal weight

AIMS

To investigate the relationship between fetal weight and leptin levels in maternal serum, amniotic fluid and umbilical cord.

METHODS

Forty pregnant women presenting for antenatal care at early weeks of gestation were enrolled for the study. Maternal and cord blood samples for leptin measurement were obtained at birth. Amniotic fluid samples were recovered by amniotomy performed during labor. Maternal body mass index and placental weight were also recorded. Leptin measurement was carried out using the ELISA method. Spearman's correlation test was used for comparison of non-parametric data.

RESULTS

Leptin concentration in venous cord blood correlated significantly with birth weight and placental weight whereas maternal serum and amniotic fluid leptin levels did not show correlation with birth weight. There were no significant correlations between leptin levels in maternal serum, cord blood and amniotic fluid.

CONCLUSION

We conclude that lack of correlation between leptin levels in mother, cord and amniotic fluid suggest that these compartments may be non-communicating separate units or have different mechanisms regulating leptin synthesis or degradation, and that leptin in maternal blood and amniotic fluid may not have a direct effect on fetal growth but rather a different role in pregnancy.

Increased maternal plasma leptin in early pregnancy and risk of gestational diabetes mellitus

OBJECTIVE

Emerging evidence suggests that leptin, an adipocyte-derived hormone, may have independent direct effects on both insulin secretion and action, in addition to its well documented effects on appetite and energy expenditure. Some, but not all, previously published studies suggest that maternal leptin concentrations may be increased in pregnancies complicated by gestational diabetes mellitus (GDM). We examined the association between plasma leptin concentration and GDM risk.

METHODS

Women were recruited before 16 weeks of gestation and were followed up until delivery. Maternal plasma leptin concentrations (collected at 13 weeks of gestation) were measured by using immunoassay. We used generalized linear models to estimate relative risks and 95% confidence intervals.

RESULTS

GDM developed in 5.7% of the cohort (47 of 823). Elevated leptin concentrations were positively associated with GDM risk (P for trend <.001). After adjusting for maternal prepregnancy adiposity and other confounders, women with leptin concentrations of 31.0 ng/mL or higher experienced a 4.7-fold increased risk of GDM (95% confidence interval 1.2, 18.0) as compared with women who had concentrations of 14.3 ng/mL or lower. We noted a strong linear component of trend in risk of GDM with increasing maternal plasma leptin concentration. Each 10-ng/mL increase in the leptin concentration was associated with a 20% increase in GDM risk (relative risk 1.2; 95% confidence interval 1.0, 1.3).

CONCLUSIONS

Hyperleptinemia, independent of maternal adiposity, in early pregnancy appears to be predictive of an increased risk of GDM later in pregnancy. Additional larger prospective cohort studies are needed to confirm and more precisely assess the etiologic importance of hyperleptinemia in pregnancy.

LEVEL OF EVIDENCE

II-2

Modulation of susceptibility to weight gain and insulin resistance in low birthweight rats by treatment of their mothers with leptin during pregnancy and lactation

OBJECTIVES

To investigate whether administration of leptin to rats during pregnancy and lactation affects placental 11beta-hydroxysteroid dehydrogenase (11beta-HSD2) activity and the susceptibility of their offspring to weight gain and insulin resistance.

DESIGN

Pregnant rats fed on a low-protein diet were administered leptin or saline by subcutaneous minipump from day 14 of gestation and throughout lactation. A further group was fed a normal diet and given saline. After weaning, the offspring of each group were fed on a normal diet until 6 weeks of age and then half of each group was transferred to a high-fat diet until 12 months of age.

RESULTS

Plasma leptin levels were raised two-fold on days 16-18 of pregnancy in the leptin-treated dams, but, despite a constant rate of infusion, at parturition they dipped to control levels before rising again. The activity of placental 11beta-HSD2 was reduced by the low-protein diet; this reduction was prevented by treating the dams with leptin. The male offspring of the saline-treated dams gained more weight and had higher plasma leptin levels on the high fat than the chow diet, but the offspring of the leptin-treated dams did not. Fasting blood glucose and intraperitoneal glucose tolerance at 6 and 12 months of age was unaffected by the high-fat diet, but only the offspring of the leptin-treated dams achieved this control without raised insulin levels.

CONCLUSIONS

The rate of leptin clearance appears to increase at parturition. The administration of leptin to rats during late pregnancy and lactation makes their male offspring less susceptible to high-fat-diet-induced weight gain and insulin resistance.

Leptin distribution and metabolism in the pregnant rat: transplacental leptin passage increases in late gestation but is reduced by excess glucocorticoids

Leptin is essential for the establishment of pregnancy and appears to promote fetal growth, but the mechanisms regulating fetal leptin exposure remain unclear. In rodents, indirect evidence suggests that fetal leptin is partly derived from the maternal circulation via transplacental passage. Indeed, the placenta expresses mRNA for Ob-Ra, one of the short forms of the leptin receptor (Ob-R(S)) important in leptin transport, and this expression increases markedly in late pregnancy. Therefore, we determined the transplacental passage of maternal leptin to the fetus in the rat and whether this transport increases near term in association with a rise in placental expression of Ob-R(S) protein. Because of the proposed role of leptin in promoting fetal growth, we also assessed the effect of glucocorticoid-induced fetal growth retardation on placental leptin transport. Anesthetized rats received a constant infusion of (125)I-leptin via a jugular cannula before and at d 16 and 22 of pregnancy (term = d 23); plasma samples were obtained at 10, 20, 40, 60, 80, and 100 min, and fetuses and placentas were collected at the time of the final sample. The metabolic clearance rate of leptin fell (P < 0.01) from 3.08 +/- 0.23 ml/min per kg in nonpregnant rats to 2.36 +/- 0.13 ml/min per kg by d 22. Transplacental passage of (125)I-leptin, estimated from its concentration in the whole fetus relative to maternal plasma, increased 10-fold (P < 0.005) between d 16 and d 22 of pregnancy. Over this same period, Ob-R(S) protein expression in the placental labyrinth zone increased by almost 2-fold. Transplacental leptin passage was reduced (P < 0.05) by 77% after maternal dexamethasone treatment, whereas suppression of endogenous glucocorticoid synthesis (by metyrapone) increased (P < 0.05) the transfer of maternal leptin to the fetus by 55%. These data show that transplacental passage of maternal leptin is a significant source of fetal leptin and increases markedly during late pregnancy. Consistent with the proposed role of leptin as a fetal growth factor, transplacental leptin passage is reduced in association with glucocorticoid-induced fetal growth retardation.

Leptin concentrations in maternal serum and cord blood in diabetic and nondiabetic pregnancy

OBJECTIVE

The purpose of this study was to examine the relationships between maternal and cord leptin concentrations, maternal and neonatal outcomes, and measures of glycemic control in diabetic and nondiabetic pregnancy.

STUDY DESIGN

This was a prospective study of 60 type 1 diabetic and 50 nondiabetic pregnancies in a university teaching hospital. Serum leptin and hemoglobin A(1c) were measured serially throughout pregnancy; leptin, insulin, insulin-like growth factor-1, and C-peptide in venous cord blood were measured at delivery. Leptin was measured with the use of enzyme-linked immunosorbent assay. Data were analyzed with specific computer software.

RESULTS

Maternal leptin levels correlated with cord leptin levels in the nondiabetic group only. Cord leptin levels correlated with cord C-peptide, cord insulin-like growth factor-1, birth weight, birth weight corrected for gestational age, and neonatal anthropometry in both groups and with hemoglobin A(1c) in the diabetic group only. Cord leptin levels increased significantly with increasing birth weight corrected for gestational age but remained significantly higher at all birth weights in the diabetic group.

CONCLUSION

There are strong associations between cord leptin levels and other measures of fetal growth in both groups and with glycemic control in the diabetic group.

Umbilical cord and maternal blood leptin concentrations in intrauterine growth retardation

Leptin, the ob gene product, plays an important role in the regulation of body fat mass and weight. In previous studies, it was demonstrated that leptin is detectable in human fetal cord blood as early as at 18 weeks of gestation and that serum leptin concentrations are significantly reduced in small gestational age newborns. In the present study, we investigated whether umbilical and maternal serum leptin concentrations correlate with intrauterine growth retardation (IUGR). In addition, we aimed to determine the relationships between leptin concentration in the maternal and cord blood. We studied 40 newborn infants (21 female and 19 male; gestational age, 38-42 weeks) and their mothers. Of the infants studied, 10 had IUGR. Serum leptin concentrations were measured by radioimmunoassay. All newborns had detectable leptin concentrations. Leptin concentrations were significantly lower in newborns with IUGR and in their mothers (n = 10; 3.53 +/- 1.42 ng/ml, 6.75 +/- 1.47 ng/ml, respectively) than in infants experiencing normal growth and their mothers (n = 30; 5.58 +/- 2.98 ng/ml, 9.85 +/- 6.50 ng/ml, respectively) (p < 0.01 for newborns, p < 0.05 for mothers). There was no significant correlation between umbilical leptin concentration and maternal leptin concentration (r = 0.229; p = 0.155) in all study groups but, significantly, a correlation was observed in the group with IUGR (r = 0.736; p = 0.015). There were no significant correlations between both umbilical and maternal leptin concentrations and parity, delivery type and gestational age. There was a correlation between umbilical leptin concentration and birth weight of newborns (r = 0.383; p = 0.015) but no correlation with body mass index (BMI) of the newborns (r = 0.034; p = 0.834). Maternal leptin concentrations correlated with maternal weight and BMI (r=0.606; p=0.000, r=0.535; p=0.000, respectively). There was no correlation between maternal leptin concentrations and birth weight of the newborns (r=0.179; p=0.269) and with BMI of the newborns (r = 0.146; p = 0.367). There was no gender difference in leptin concentrations in the newborns (n=21; 5.50 +/- 3.37 ng/ml, for females; n = 19; 4.58 +/- 1.98 ng/ml for males) (p = 0.296). In summary, we have shown that IUGR is associated with a decreased leptin concentration in newborns and their mothers. The association between umbilical serum leptin and birth weight in this and other studies suggests a pivotal role of fetal leptin in regulating fetal growth and development.

Infants thinner at birth exhibit smaller kidneys for their size in late gestation in a sample of fetuses with appropriate growth

Fetal ultrasound measurements were employed to investigate the relationship between weight and ponderal index at birth and kidney size during the second (23 weeks) and third (32 weeks) trimesters of pregnancy in a sample of 25 normally growing fetuses. Kidney volume and kidney volume / fetal weight ratio at 32 weeks are significantly and positively related to both weight and ponderal index at birth, controlling for sex, gestational age at birth, and day of ultrasound measurement. A second-degree polynomial relationship approximates the predictability of kidney volume fetal weight ratio at 23 weeks to that at 32 weeks, demonstrating shifting growth rates in fetal organ and body growth relationships during midgestation. Sex and parental size are suggested as contributing to these patterns. Females have a surge in renal growth between 23 and 32 weeks to catch up to earlier growing males, and maternal weight significantly predicts incremental growth in kidney volume and the kidney volume / fetal weight ratio at 32 weeks of gestation. The observation that fetuses relatively thin at birth have relatively smaller kidneys for their size in late gestation suggests that the influence of maternal weight on birth outcome may act through organ growth.

Circulating concentrations of soluble leptin receptor: influence of menstrual cycle and diet therapy

Concentrations of the soluble leptin receptor (sOB-R) may be related to leptin resistance in obesity. We measured sOB-R concentrations in serum in 103 non-diabetic Japanese men and women. All subjects were grouped according to body mass index (BMI; in kg/m(2)). Serum sOB-R concentrations did not differ significantly between normal-weight (18.5 < or = BMI < 25.0) men and women, but were significantly higher in underweight subjects (BMI < 18.5) than in normal-weight subjects. In contrast, overweight (25 < or = BMI < 30) and obese (30 < or = BMI < 35.0, 35.0 < or = BMI < 40, and BMI > or = 40) subjects had significantly lower sOB-R concentrations than did normal-weight subjects. Serum sOB-R concentrations were inversely correlated with BMI and serum immunoreactive leptin concentrations. Very low-energy diet therapy for 4 wk significantly lowered serum immunoreactive leptin concentrations but did not significantly affect serum sOB-R concentrations. Serum sOB-R concentrations did not change significantly during the menstrual cycle. Our results showed that serum sOB-R concentrations decrease with increasing BMI and that sex hormones likely do not affect serum sOB-R concentrations in non-pregnant women. The reduction in serum sOB-R concentrations in overweight and obese persons may reflect downregulation of hypothalamic leptin receptor production as a result of an increase in circulating leptin and might be an important factor in leptin resistance.

Effect of iron deficiency on placental cytokine expression and fetal growth in the pregnant rat

Iron deficiency anemia is the most common nutritional disorder in the world. Anemia is especially serious during pregnancy, with deleterious consequences for both the mother and her developing fetus. We have developed a model to investigate the mechanisms whereby fetal growth and development are affected by maternal anemia. Weanling rats were fed a control or iron-deficient diet before and throughout pregnancy and were killed at Day 21. Dams on the deficient diet had lower hematocrits, serum iron concentrations, and liver iron levels. Similar results were recorded in the fetus, except that the degree of deficiency was markedly less, indicating compensation by the placenta. No effect was observed on maternal weight or the number and viability of fetuses. The fetuses from iron-deficient dams, however, were smaller than controls, with higher placental:fetal ratios and relatively smaller livers. Iron deficiency increased levels of tumor necrosis factor alpha (TNFalpha) only in the trophoblast giant cells of the placenta. In contrast, levels of type 1 TNFalpha receptor increased significantly in giant cells, labyrinth, cytotrophoblast, and fetal vessels. Leptin levels increased significantly in labyrinth and marginally (P = 0.054) in trophoblast giant cells. No change was observed in leptin receptor levels in any region of the placentas from iron-deficient dams. The data show that iron deficiency not only has direct effects on iron levels and metabolism but also on other regulators of growth and development, such as placental cytokines, and that these changes may, in part at least, explain the deleterious consequences of maternal iron deficiency during pregnancy.

Leptin in the ovine fetus correlates with fetal and placental size

OBJECTIVE

The purpose of this study was to detect the presence of leptin and its receptor in ovine fetal tissues and to examine the relationship between circulating leptin concentrations and fetal and placental weights on gestational day 138 (GD138) of ovine pregnancy (term, 145 days).

STUDY DESIGN

Pregnant sheep (n = 18) were instrumented on GD 110 to facilitate measurement and chronic reduction of uterine blood flow and produce intrauterine growth restriction. Four animals that served as controls were euthanized on GD 138 to obtain fetal tissues to determine the presence of ovine leptin and its receptor by reverse transcriptase-polymerase chain reaction. Seven instrumented animals were randomized into the control group, and 7 instrumented animals were randomized into the uterine blood flow restricted group (reduction equaled approximately 50% on GD 138). Maternal and fetal blood samples were obtained on day 138 to measure plasma leptin concentrations, and animals were euthanized for the determination of fetal morphometrics and placental weight.

RESULTS

Expression of RNA for ovine leptin and its receptor were observed in fetal liver, skeletal muscle, kidney, heart, and placenta. Fetal body weight, ponderal index, and placental weight were significantly decreased by approximately 40% in the blood flow restricted group as compared with controls. Fetal leptin concentrations were increased by 45% in the uteroplacental blood flow restricted group (P =.01). Maternal leptin concentrations were not significantly different between the 2 groups and did not correlate with fetal concentrations. Fetal leptin concentrations had an inverse relationship with uterine blood flow (r = -0.73; P =.004), fetal body weight (r = -0.78; P =.002), and placental weight (r = -0.68; P =.01).

CONCLUSION

Ovine fetal tissues express RNA for leptin and its receptor. Circulating leptin concentrations in the ovine intrauterine growth restriction fetus were significantly elevated on gestational day 138 compared with controls. Fetal leptin concentrations were inversely related to uterine blood flow and fetal and placental weight. These findings suggest that fetal leptin may be involved in an adaptive response to intrauterine growth restriction.

Leptin and leptin-binding activity in women with recurrent miscarriage: correlation with pregnancy outcome

BACKGROUND

Previous studies in humans and mice have suggested the importance of leptin in fetal growth. Recurrent miscarriage may be a result of abnormal placental and/or fetal development and therefore abnormal leptin levels may be associated with this form of pregnancy loss.

METHODS

Leptin and leptin-binding activity (LBA) were measured in blood obtained from women who had a history of recurrent miscarriage (n = 53) during weeks 5-6 and 7-8 of pregnancy, and the concentrations were correlated with subsequent pregnancy outcome.

RESULTS

Concentrations of leptin ranged from 1.4-62.8 ng/ml, but there was a strong correlation (r = 0.825, P < 0.001) between leptin values at weeks 5-6 and 7-8 in the same woman. Women who subsequently miscarried had significantly lower plasma leptin concentrations on both weeks 5-6 (13.34 +/- 2.1 ng/ml) (P < 0.05) and 7-8 (13.71 +/- 2.4 ng/ml) (P < 0.01) of pregnancy, than women who subsequently had a term birth (22.04 +/- 2.43 ng/ml week 5-6, 24.76 +/- 3.66 ng/ml week 7-8). LBA values ranged from 1-8.5% but there was no significant difference in LBA in blood obtained from women who subsequently miscarried or had a live birth.

CONCLUSIONS

The significantly lower concentrations of leptin in women who subsequently miscarried suggest that leptin may play a role in preventing miscarriage. However, as there was a considerable overlap between the values of leptin in women who subsequently miscarried, and those that had a live birth, these measurements are of limited use in the prediction of pregnancy outcome in these women.