Leptin and metabolic hormones in preterm newborns

Biomarkers and Biochemical Indicators to Evaluate Bone Metabolism in Preterm Neonates

The purpose of the present study was to evaluate the concentrations of some bone turnover markers in preterm neonates with uncomplicated clinical course in the first month of life. Samples from 13 preterm neonates were collected at three different times: at birth (T0) from umbilical cord blood (UCB); and at 15 (T1) and 30 (T2) days of life from peripheral blood (PB). The concentrations of calcium (Ca), phosphate (P), total alkaline phosphatase (ALP), Collagen Type 1 Amino-terminal Propeptide (PINP), osteocalcin (OC), Collagen Type 1 Carboxyl-Terminal Telopeptide (CTX) and Leptin were assessed. A statistically significant difference for ALP concentration at birth versus T1 and T2 was found. An evident increase in the median concentrations of CTX, OC and PINP from T0 to T2 were observed. A significant difference was also found for Leptin concentration at T0 compared to T1. In preterm infants, in the absence of acute or chronic medical conditions and without risk factors for metabolic bone disease (MBD) of prematurity, there is a significant increase in bone turnover markers during the first month of life. The knowledge of the variations in these markers in the first weeks of life, integrated by the variations in the biochemical indicators of bone metabolism, could help in recognizing any conditions at risk of developing bone diseases.

Association of umbilical cord insulin-like growth factor 1 levels with severe retinopathy in extremely preterm infants

BACKGROUND

The association between umbilical cord blood insulin-like growth factor 1 (IGF-1) levels and retinopathy of prematurity (ROP) remains unclear. This study aimed to investigate whether umbilical cord blood IGF-1 levels can predict the development of severe ROP in extremely preterm infants.

METHODS

This hospital-based retrospective cohort study included infants born at <37 weeks gestational age (GA) between 2019 and 2021 and then classified them into the two GA groups: extremely preterm, <28 weeks and preterm infants, 28-36 weeks. Extremely preterm infants were further subclassified into two groups according to the laser treatment as follows: the severe ROP (ROP-Tx) and ROP (No ROP-Tx) groups. Median umbilical cord blood IGF-1 values were compared between the groups. Perinatal risk factors were identified by univariate and multivariate analyses. Finally, umbilical cord IGF-1 cut-off values requiring ROP treatment with laser were determined by receiver operating characteristic (ROC) curve analyses.

RESULTS

A total of 205 infants were enrolled, with 32 being extremely preterm (ROP-Tx: n = 11; No ROP-Tx: n = 21) and 173 being preterm. IGF-1 levels were significantly lower in extremely preterm (13.5 ng/mL) than preterm infants (36 ng/mL, p < 0.001). In extremely preterm infants, IGF-1 levels were significantly lower in the ROP-Tx group than the No ROP-Tx group (10 vs. 19 ng/mL, respectively, p = 0.024). Only GA, umbilical cord blood IGF-1 levels, birth head circumference, and birth chest circumference were identified as risk factors by univariate analysis (p < 0.05). Multivariate analysis showed that only umbilical cord blood IGF-1 was an independent risk factor (odds ratio: 1.26, p = 0.021). ROC curves revealed an IGF-1 cut-off value of 14 ng/mL.

CONCLUSION

The need of laser treatment for ROP was found to be associated with low umbilical cord blood IGF-1 levels in extremely preterm infants. Umbilical cord blood IGF-1 can be used as a biomarker for the risk of developing severe ROP.

Percentile-Based Reference Values of Umbilical Cord Blood Insulin-like Growth Factor 1 in Japanese Newborns

We aimed to create percentile-based reference values of the umbilical cord blood insulin-like growth factor-1 (IGF-1) levels in Japanese newborns, as these values have not yet been established. A total of 259 newborns were classified into four gestational-age-at-birth (GA) groups: extremely preterm (<28 weeks); early preterm (28−33 weeks); late preterm (34−36 weeks); and term (≥37 weeks). They were further subclassified as small-for-gestational-age (SGA) or non-SGA. The 10th, 25th, 50th, 75th, and 90th percentiles of the umbilical cord blood IGF-1 levels were calculated and compared between the groups by using reference values of 9, 18, 33, 52, and 71 ng/mL, respectively. In the extremely preterm group, the IGF-1 levels were significantly lower than those in the early preterm, late preterm, and term groups (13.5, 24.0, 44.5, and 47.5 ng/mL, respectively; p < 0.001). The umbilical cord blood IGF-1 levels in the SGA newborns were significantly lower than those in the non-SGA newborns in all subgroups. In multivariate analyses, the GA and birth weight standard deviation scores were independent determinant factors for the umbilical cord blood IGF-1 levels. Thus, we established percentile-based reference values of umbilical cord blood IGF-1 in Japanese newborns; these reference values can be applied on the basis of the extent of prematurity and the SGA status.

Umbilical Cord Blood Adiponectin, Leptin, Insulin, and Ghrelin in Premature Infants and Their Association With Birth Outcomes

BACKGROUND

Premature/low-birth-weight infants are at significant risk of metabolic diseases in adulthood, which may be related to the levels of fetal adipokine. Here, we investigated the differences in the levels of umbilical cord blood adiponectin, leptin, insulin, and ghrelin in preterm and term infants and sought to elucidate the link between these hormones and fetal growth. We also evaluated the interrelationship among these metabolic hormones in both groups of newborns.

METHODS

A total of 149 mother-infant pairs (100 in the preterm group and 49 in the term group) were enrolled in the study. The preterm group was further subdivided according to birth weight (≤1,500, 1,501-2,000, 2,001-2,500, and >2,500 g), gestational age (<34 vs. ≥34 weeks), and appropriate for gestational age (AGA) vs. small for gestational age (SGA). The general condition of the mothers and the growth parameters of the newborns at birth were recorded.

RESULTS

The levels of adiponectin, leptin, and ghrelin were lower in the preterm group than those in the term group (p < 0.05). In the preterm group, the leptin levels of infants with gestational age ≥34 weeks were significantly higher than those of infants with gestational age <34 weeks (mean ln leptin = 0.63 vs. 0.36 ng/ml, p = 0.009). The levels of adiponectin were lower in the SGA group than those in the AGA group (mean ln adiponectin = 2.26 vs. 2.84 µg/ml, p = 0.001), whereas those of ghrelin displayed the opposite trend (mean ln ghrelin = 6.29 vs. 5.71 pg/ml, p < 0.001). Leptin was significantly correlated with insulin both in preterm infants with birth weight (BW) >2,000 g and in term infants. Umbilical cord blood leptin was positively correlated with the BW, birth length, and head circumference of newborns (r = 0.460, 0.311, and 0.310, respectively, all p < 0.05), whereas ghrelin was negatively correlated with the same parameters (r = -0.372, -0.415, and -0.373, respectively, all p > 0.05).

CONCLUSIONS

The lack of maturation of adipose tissue and the gastrointestinal tract by the fetus due to prematurity is associated with changes in the levels of cord blood adiponectin, leptin, and ghrelin. The dysregulation of these hormones in preterm infants may be a risk factor for fetal growth and future metabolic diseases.

Leptin and IGF-1 in relation to body composition and bone mineralization of preterm-born children from infancy to 8 years

OBJECTIVE

Preterm birth has been associated with altered body composition, especially increased fat mass (FM) and decreased bone mineralization, and leptin and IGF-1 have been suggested to be involved in the regulation of both. We aimed to study the interplay between leptin, IGF-1, FM and bone mineralization measured in infancy and childhood of children born preterm.

DESIGN

Observational study.

PATIENTS/SUBJECTS

Seventy-nine (40 boys) preterm-born children (gestational age ≤32 weeks and/or birth weight ≤1500 g) aged 8 years.

MEASUREMENTS

Serum leptin and IGF-1 were measured at term age, at 3- and 6-month corrected age (CA), and 8 years. Body composition (fat and lean mass) and bone parameters (bone area, mineral content and density) were measured by Dual-energy X-ray Absorptiometry (DXA) at term age, 6-month CA and 8 years.

RESULTS

Leptin was positively associated with FM at all time points and with bone parameters at term age and 6-month CA. IGF-1 was associated with body composition and bone density at most of the time points. Explained variation in bone mineralization increased significantly by adding bone area (BA) and height to the models.

CONCLUSIONS

During infancy and childhood, leptin and IGF-1 were associated with body composition in preterm-born children. In addition, leptin was associated with bone parameters in early infancy, but not in childhood. It is hypothesized that a complicated interplay between multiple pathways, which most likely changes over time, is involved in regulation of body composition and bone mineralization of preterm-born infants.

Modeling the impact of growth and leptin deficits on the neuronal regulation of blood pressure

The risk of hypertension is increased by intrauterine growth restriction (IUGR) and preterm birth. In the search for modifiable etiologies for this life-threatening cardiovascular morbidity, a number of pathways have been investigated, including excessive glucocorticoid exposure, nutritional deficiency and aberration in sex hormone levels. As a neurotrophic hormone that is intimately involved in the cardiovascular regulation and whose levels are influenced by glucocorticoids, nutritional status and sex hormones, leptin has emerged as a putative etiologic and thus a therapeutic agent. As a product of maternal and late fetal adipocytes and the placenta, circulating leptin typically surges late in gestation and declines after delivery until the infant consumes sufficient leptin-containing breast milk or accrues sufficient leptin-secreting adipose tissue to reestablish the circulating levels. The leptin deficiency seen in IUGR infants is a multifactorial manifestation of placental insufficiency, exaggerated glucocorticoid exposure and fetal adipose deficit. The preterm infant suffers from the same cascade of events, including separation from the placenta, antenatal steroid exposure and persistently underdeveloped adipose depots. Preterm infants remain leptin deficient beyond term gestation, rendering them susceptible to neurodevelopmental impairment and subsequent cardiovascular dysregulation. This pathologic pathway is efficiently modeled by placing neonatal mice into atypically large litters, thereby recapitulating the perinatal growth restriction-adult hypertension phenotype. In this model, neonatal leptin supplementation restores the physiologic leptin surge, attenuates the leptin-triggered sympathetic activation in adulthood and prevents leptin- or stress-evoked hypertension. Further pathway interrogation and clinical translation are needed to fully test the therapeutic potential of perinatal leptin supplementation.

Growth, metabolic markers, and cognition in 8-year old children born prematurely, follow-up of a randomized controlled trial with essential fatty acids

The study is a follow-up of a randomized, double-blinded, placebo-controlled trial of supplementation with docosahexaenoic acid (DHA) and arachidonic acid (AA) to 129 very low birth weight (VLBW; birth weight <1500 g) infants fed human milk. The main hypothesis was that supplementation would affect growth, metabolic markers, and cognitive function. The secondary aim was to describe predictors of metabolic markers and cognitive status at follow-up. Ninety-eight children met for 8-year follow-up with anthropometric measures, blood biomarkers, and cognitive testing. The intervention group had significantly lower insulin-like growth factor-1 (IGF-1) at 8 years, whereas no differences in growth or intelligence quotient (IQ) were found. For the total cohort, weight gain during first year of life was neither associated with BMI, metabolic markers, nor IQ at follow-up. Blood DHA at 8 years was positively associated with IQ.

CONCLUSIONS

The study is the first long-term follow-up of a randomized controlled trial with essential fatty acids investigating growth, metabolic factors, and IQ. IGF-1 levels were significantly lower in the intervention group at 8 years. First-year growth was not associated with BMI, metabolic markers, or IQ at follow-up. Current DHA status was a significant predictor of higher IQ at follow-up.

WHAT IS KNOWN

• Preterm children have increased risk of lower intelligence quotient (IQ), reduced growth, and abnormal metabolic status. • Early intake of docosahexaenoic acid (DHA) and arachidonic acid (AA), as well as early growth pattern, may influence both IQ and metabolic status. What is New: • Early intervention with DHA and AA led to reduced insulin-like growth factor-1 in blood at 8 years of age. • Weight gain during first year of life was neither associated with impaired metabolic markers nor improved IQ at follow-up. • Current DHA status was a significant predictor of higher IQ at 8 years, also when maternal education and birth weight were included in the model.

Response to IGF-1 Generation Test in Short Prepubertal Children Born Very Preterm or at Term

AIMS

To investigate whether short children born very preterm (<32 weeks of gestation) exhibit features of growth hormone (GH) resistance compared to term peers.

METHODS

We studied 26 prepubertal children (aged 7.0 ± 2.0 years) with short stature (height adjusted for parents' heights <10th percentile), who were born appropriate for gestational age and either very preterm (n = 11) or at term (n = 15). Children underwent insulin-like growth factor-1 (IGF-1) generation test via a daily recombinant human GH (rhGH) dose (0.05 mg/kg/day) over 4 consecutive days. Hormone and binding proteins were measured at baseline and day 5.

RESULTS

At baseline, preterm children had lower IGF-binding protein 1 (IGFBP-1; -22%; p = 0.049) and IGFBP-3 (-24%; p = 0.013) concentrations than term children. Preterm children also had insulin concentrations that tended to be 39% higher (p = 0.059) than term peers. After stimulation, IGF-1 and IGFBP-3 concentrations increased similarly in term and preterm groups, while GH-binding protein (GHBP) concentrations decreased in both groups. Preterm children had higher GHBP (+50%; p = 0.049), insulin (+86%; p = 0.005), and leptin (+107%; p = 0.020) but lower IGFBP-1 (-47%; p = 0.006) concentrations than term children following rhGH stimulation.

CONCLUSIONS

Preterm children who are short for genetic height potential show no evidence of GH resistance that would explain their short stature. However, there was indirect evidence of insulin resistance in the preterm children, as previously described in this group.

Markers of bone metabolism, serum leptin levels and bone mineral density in preterm babies

The prospective study assessed the influence of serum leptin levels on markers of bone metabolism and bone mineral density in 2-year-old infants born preterm. A total of 57 randomized preterm Caucasian newborns (32nd-37th week of gestation) were included in the study. Bone metabolism markers were measured every 6 months. The infants were monitored prospectively up to the age of 2 years. When the infants turned 2 years of age, they were investigated by dual energy X-ray absorptiometry (lumbar spine). The median cord blood leptin levels was 3.07 μg/L. The median leptin level during check-ups before 2 years of age was 9.96 μg/L. The other laboratory markers were within the normal ranges for that age. The bone mineral density reached, on average, 0.410 g/cm2. Lower leptin levels in the cord blood and in the serum of preterm infants do not influence bone mineral density during the first 2 years of life.

Adiponectin, leptin and insulin levels at birth and in early postnatal life in neonates with hypoxic ischemic encephalopathy

Background

Hypoxic ischemic encephalopathy (HIE) occurs in one to three per 1000 live full-term births. Fifteen to twenty percent will die in the postnatal period, and an additional 25 % will develop severe and permanent neuropsychological sequalae. The control of growth and nutritional status in the fetus and neonate is a complex mechanism, in which also hormones produced by adipose tissue, such as adiponectin and leptin are involved. The aim of this study was to measure the levels of adiponectin, leptin and insulin in neonates with HIE at birth and in early postnatal life and comparing them with normal healthy AGA and SGA neonates

Methods

This study carried out on 80 full-term neonates born in Minia university hospital during the period from May 2013 to December 2014. They were divided into group I included 25 neonates with HIE and group II included 55 normal healthy neonates (30 appropriate for gestational age (AGA) and 25 small for gestational age (SGA)). Weight, length, head circumference, body mass index (BMI), glucose, adiponectin, leptin and insulin levels were measured for all neonates. Adiponectin, leptin and insulin levels were compared between neonates with HIE and normal healthy neonates as well as between AGA and SGA neonates at birth, 2nd and 6th days of life.

Results

Adiponectin and leptin levels were significantly higher at birth then began to decrease during the first postnatal week in all neonates while insulin level increased during the same period. Serum adiponectin levels were significantly lower while serum leptin and insulin levels were significantly higher in neonates with HIE than healthy neonates. In all neonates, the serum adiponectin level was positively correlated at birth with weight, length, BMI and leptin levels but not with insulin level. In neonates with HIE, serum adiponectin level was not correlated with weight, BMI, leptin level or insulin level. In all neonates, the serum leptin level was positively correlated at birth with body weight, height and BMI. In neonates with HIE serum leptin levels were not correlated with weight, BMI or insulin level after birth. There were no correlations between either leptin or adiponectin serum levels or any of the studied parameters in neonates with HIE

Conclusions

Neonates who are suffering from HIE had lower serum levels of adiponectin and higher serum levels of leptin and insulin than normal healthy neonates at birth and during the early postnatal period. The decline of leptin and increased the insulin levels after birth in all neonates may be important for the stimulation of feeding behavior and the acquisition of energy homeostasis during the early postnatal life. Positive significant correlations between adiponectin, leptin, body weight and body mass indices were present in normal healthy neonates but not in neonates with HIE reflecting the effect of hypoxia on the regulatory mechanisms controlling the adipose tissue functions.

Late prematurity and adiposity in adolescents: Evidence from "Children of 1997" birth cohort

OBJECTIVE

The association of late prematurity with later adiposity is unclear, and the mediating role of infant growth is seldom studied. We assessed the association of late prematurity with markers of adiposity in adolescence and tested whether accelerated infant weight gain mediated the association.

METHODS

In the Chinese birth cohort "Children of 1997," we used multivariable linear regression to assess the adjusted association of late premature (n = 295), compared to term (n = 6874), births with markers of adiposity at 14 years. We tested whether any association was mediated by accelerated weight gain from birth to 12 months, i.e., a change in weight z-score ≥0.67.

RESULTS

Late premature births had greater body mass index (BMI) z-score (0.21, 95% confidence interval (CI) 0.07, 0.35), waist-hip ratio z-score (0.16, 95% CI 0.03, 0.29), and waist-height ratio z-score (0.27, 95% CI 0.14, 0.40) than term births in adolescence. The association of late prematurity with higher adolescent BMI, but not waist ratios, was mediated by accelerated infant weight gain.

CONCLUSIONS

Late prematurity was associated with higher BMI and waist ratios in adolescence, but only the association with BMI was mediated by infant weight gain, suggesting vulnerability to metabolic risk in late premature births may arise through multiple pathways.

Relationship between fat mass measured by dual-energy X-ray absorptiometry and leptin in preterm infants between term age and 6 months' corrected age

BACKGROUND/AIMS

In term subjects, fat mass (FM) is positively associated with leptin, whereas studies in preterm infants show conflicting results. However, none of these studies measured FM by dual-energy X-ray absorptiometry (DEXA). This study aims to relate FM measured by DEXA in relation to leptin and growth in preterm infants.

METHODS

In 139 preterm infants, weight (kg) and length (cm) were measured at birth, term age, and 6 months' corrected age (CA). FM (kg), measured by whole-body DEXA, and leptin (µg/l) were measured at term age and 6 months' CA.

RESULTS

At term age and 6 months' CA, FM was associated with leptin (β = 1.94, 95% CI: 1.51-2.36, and β = 0.37, 95% CI: 0.26-0.48, respectively; p < 0.001). Gain in weight standard deviation score (SDS) between term age and 6 months' CA was associated with FM and leptin at 6 months' CA (β = 0.24, 95% CI: 0.18-0.30, and β = 0.25, 95% CI: 0.16-0.33, respectively; p < 0.001).

CONCLUSION

In preterm infants, FM measured by DEXA is associated with leptin, which indicates that leptin is a marker of body FM during the first 6 months after term age. Gain in weight SDS between term age and 6 months' CA results in higher FM and higher leptin at 6 months' CA.

Prematurity and insulin sensitivity

Nowadays, an increased number of premature infants survive. The medical challenge is to reduce their postnatal morbidities with a special focus towards a decrease in metabolic risks. In this manuscript, we will examine available evidence of perinatal, infancy, and childhood consequences of prematurity on insulin sensitivity and glucose homeostasis. Moreover, we add some recent data on how nutritional intervention could modify these risks.

Adipokines in breast milk and preterm infants

Studies have shown that the early life environment affects feeding behaviour, food intake and energy balance in later life, suggesting there is a link between foetal and infant growth and the risk of metabolic disorders in adulthood. Although there is an evident epidemiological association between low birth weight and adult-onset diseases, the incidence of metabolic diseases in adulthood among people who were born prematurely is still unknown. Considerable advances have been made during the last years in the scientific knowledge of the benefits of early nutrition, such as breastfeeding, on health and well-being later in life. Nutritional researchers have focussed their attention on the biological characteristics of human breast milk, which represents the main source of nutrients in the first months of life for breastfed infants. Recently, leptin and ghrelin have been detected in the breast milk of mothers of term and preterm infants. Adiponectin and resistin, present in term human milk, have not been investigated in the breast milk of mothers of preterm infants. These hormones are involved in the regulation of energy balance and may have a role in the regulation of growth and development in the neonatal period and infancy, as well as long-term effects on metabolic programming. Leptin, adiponectin and resistin have been found at lower levels in pre-term infants compared with term newborns, whereas there seems to be no difference in ghrelin levels. Future research is necessary to clarify the role of hormones present in breast milk for identifying potential short- and long-term effects of breastfeeding on the health of children born prematurely.

Umbilical cord ghrelin in term and preterm newborns and its relation to metabolic hormones and anthropometric measurements

The aim of the study was to assess umbilical cord ghrelin level in term and preterm newborns and its relation to other metabolic hormones and anthropometric measurements. A cross sectional comparative study included 50 normal appropriate-for-gestational-age newborns (25 full-terms; 25 preterm). Assessment of anthropometric measurements, cord levels of ghrelin, leptin, insulin and glucose were done to all newborns. Umbilical cord ghrelin was detected in all newborns. There was no significant difference between term and preterm groups regarding ghrelin, insulin and glucose. Leptin was significantly lower in preterm than term group. Sex and mode of delivery had no effects regarding all studied variables. There was no overall correlation between ghrelin and gestational age, anthropometric measurements, leptin, insulin or glucose in all newborns. Preterm group demonstrated significant correlations between ghrelin and weight, body mass index and abdominal circumference. An overall significant correlation was found between leptin and gestational age and anthropometric measurements in all newborns. In preterm group leptin correlated with weight, length, subscapular skin-fold thickness and abdominal circumference. To conclude the umbilical cord ghrelin was relatively invariable at birth between 30 and 41 weeks gestation showing no gestational age-related variation, unlike leptin, which was lower in preterm group indicating increased adipose mass and placental maturation with increased gestational age.

Circulating levels of adiponectin in preterm infants

OBJECTIVE

To determine circulating levels of adiponectin in preterm infants and examine possible associations with anthropometric measurements, weight gain, and leptin and insulin levels.

DESIGN

Prospective study.

SETTING

A university hospital neonatal care unit.

STUDY POPULATION

62 preterm (mean (SD) gestational age 32.0 (2.1) weeks) and 15 full-term infants (reference group).

INTERVENTIONS

Blood samples taken at discharge (40.9 (14.8) days of life) from the preterm infants and at a comparable postnatal age in full-term infants. All infants were fed the same commercial formula, but in nine preterms the formula contained long-chain polyunsaturated fatty acids (LCPUFAs).

MAIN OUTCOME MEASURES

Serum levels of adiponectin, leptin and insulin. Associations of adiponectin levels were tested only in the preterm group.

RESULTS

Serum levels of adiponectin were lower in preterm (40.9 (14.8) microg/ml) than full-term infants (53.1 (16.0) microg/ml, p<0.01). However, after adjustment for body weight, the influence of prematurity on adiponectin levels was no longer significant. In preterm infants, adiponectin levels independently correlated with being born small for gestational age (SGA) (beta=-0.35, p=0.01), weight gain (beta=0.28, p=0.03) and LCPUFA-supplemented formula (beta=0.34, p=0.009). Serum adiponectin levels did not correlate with insulin or leptin levels. However, insulin levels were higher in preterm than in full-term infants after adjustment for body weight.

CONCLUSIONS

Adiponectin levels are lower in preterm infants at discharge than full-term infants probably due to decreased adiposity. The levels are influenced by being born SGA, weight gain and, possibly, by dietary LCPUFAs. The importance of these findings in the development of insulin or leptin resistance in children born prematurely needs to be further studied.

The contributions of plasma IGF-I, IGFBP-3 and leptin to growth in extremely premature infants during the first two years

We determined the contributions of IGF-I, IGFBP-3 and leptin to growth in extremely premature infants over the first two years. Weight (Wt), crown-to heel length (CHL), plasma IGF-I, IGFBP-3 and leptin were measured in infants (gestation 24-33 wk) at birth (n = 54), expected date of delivery (EDD) and 6, 12 and 24 mo post-EDD (n = 29). Area under the curve (AUC) for hormone levels was calculated over 4 periods: birth-EDD, EDD-200 d, EDD-350 d and EDD-700 d. IGFBP-3, but not IGF-I or leptin, on day 1 correlated with birth Wt SD scores (SDS) (r = 0.46, p = 0.002) and CHL SDS (r = 0.41, p = 0.01). Wt SDS at EDD correlated with AUC IGF-I, IGFBP-3 and leptin (birth-EDD), but leptin was the best predictor in multiple regression (r = 0.65, p < 0.0001). Wt at EDD + 700 d correlated with AUC leptin (EDD-700 d) (r = 0.62, p = 0.002). CHL SDS at EDD correlated with AUC IGFBP-3 and leptin (birth-EDD), but IGFBP-3 was the best predictor (r = 0.55, p < 0.0001). CHL at EDD + 700 d correlated with AUC IGF-I and IGFBP-3 (EDD-700 d), but IGFBP-3 was the best predictor (r = 0.47, p = 0.01). Wt and CHL at birth were associated with IGFBP-3 levels in these infants. Wt at EDD and EDD + 700 d was predicted by concurrent leptin output while linear growth at EDD and EDD + 700 d was predicted by IGFBP-3 output.

Prematurity and insulin sensitivity

Premature infants of low and extremely low birth weight represent a challenge for neonatal intensive care units and paediatricians. These neonates may be at increased risk of insulin resistance and diabetes perinatally and during childhood. During the first week of postnatal life, infants born prematurely are at risk of abnormalities in glucose homeostasis. Additionally, there are major differences in their glucose/insulin homeostasis compared with infants born at term. Preterm infants are at risk of hypoglycaemia, due to decreases in deposits of glycogen and fat that occur during the third trimester, and also to transient hyperinsulinaemia. Hyperglycaemia may also be observed in preterm infants during the perinatal period. These infants are unable to suppress glucose production within a large range of glucose and insulin concentrations, insulin secretory response is inappropriate, insulin processing is immature and there is an increased ratio of the glucose transporters Glut-1/Glut-2 in fetal tissues, which limits sensitivity and hepatocyte reaction to increments in glucose/insulin concentration during hyperglycaemia. In addition, increased concentrations of tumour necrosis factor alpha present in intrauterine growth retardation (IUGR) and induce insulin resistance. It has been proposed that the reduced insulin sensitivity may result from adaptation to an adverse in utero environment during a critical period of development. We have investigated postnatal insulin resistance in 60 children born with very low birth weight and either small for gestational age or at an appropriate size for gestational age. This study showed that IUGR, rather than low birth weight itself, was associated with increased fasting insulin levels. As poor fetal growth may be associated with the development of obesity, type 2 diabetes and the metabolic syndrome in later life, it is important that we continue to increase our understanding of the effects of IUGR on postnatal growth and metabolism.

Resistin in preterm and term newborns: relation to anthropometry, leptin, and insulin

This study aimed to investigate 1) the plasma resistin concentration at birth, 2) the relationship of resistin with leptin and insulin, and 3) the association of resistin with anthropometric indexes in newborn infants. Blood samples for hormonal assay were obtained from preterm and term newborns within the first 2 h of life and before milk feeding or energy intake. Although these infants required blood sampling for clinical reasons, all were proved to be noninfected. Plasma resistin was significantly higher in term than in preterm infants. It was also significantly correlated with serum leptin, and both hormones were significantly associated with gestational age and anthropometric indexes. Infants who were born vaginally were found to have significantly higher plasma resistin levels compared with those who were born by cesarean section. In the multivariate forward stepwise regression models, resistin was found to be significantly associated with the mode of delivery and gestational age or birth weight. The association among resistin, leptin, and anthropometric indexes suggested that both hormones might be gestation related. A high circulating resistin level at term gestation could be advantageous to the infant by promoting hepatic glucose production and preventing hypoglycemia after birth. Infants who were born vaginally had significantly higher plasma resistin levels, suggesting that this hormone might also be associated with stress or inflammation induced by the birth process.

Ghrelin in preterm and term newborns: relation to anthropometry, leptin and insulin

AIMS

This study aimed to investigate (i) the plasma ghrelin concentration at birth, (ii) the relationship of ghrelin with metabolic hormones, including leptin and insulin, and (iii) its association with anthropometric parameters, in appropriately grown preterm (23-36 weeks gestation) and term (37-42 weeks gestation) newborns.

PATIENTS AND METHODS

Blood samples for hormonal assay were obtained from preterm (n = 81) and term newborns (n = 40) within the first 2 h of life and before milk feeding or energy intake. The relationship between plasma ghrelin and other metabolic hormones or anthropometric parameters was evaluated.

RESULTS

Plasma ghrelin was detectable in all studied infants and the concentrations did not differ significantly between term and preterm infants [median (interquartile range): 1.21 (0.86-1.48) nmol/l vs. 1.04 (0.71-1.51) nmol/l, P = 0.52, respectively]. There was no overall significant correlation between plasma ghrelin and gestational age, anthropometric parameters and leptin or insulin. However, when term and preterm infants were analysed independently, plasma ghrelin was inversely correlated with birth weight (r = -0.31, P = 0.05) and body length (r = -0.33, P = 0.04) in the term infant group.

CONCLUSIONS

Our findings suggested that plasma ghrelin concentrations were relatively constant at birth, between 23 and 42 weeks gestation, and ghrelin secretion did not appear to undergo gestational age-related variations. An inverse relationship between plasma ghrelin and anthropometric indices in term infants raised the possibility that ghrelin might adopt its physiological role in regulating growth and metabolism at a late stage of gestation (> or = 37 weeks gestation). This phenomenon could be beneficial to term newborns by stimulating their appetite and maintaining an adequate blood sugar level at the most critical period when nutrients from mothers are abruptly terminated after birth.

Early postnatal growth in preterm infants and cord blood leptin

Although circulating leptin and insulin concentration is linked to intrauterine growth, fetal development and birth weight in full-term infants, there has been no enquiry into the influence of cord blood insulin and leptin for catch-up growth in preterm infants. The study evaluated the association of cord blood leptin with growth and weight gain of 96 premature babies during 6 months (corrected age). The temporal changes of anthropometric indexes over this period were calculated by repeated random regression (PROC MIXED) using SAS. Cord blood leptin was negatively associated with the rate of change in BMI (p=0.01) and length (p<0.001), from birth until 64 postnatal weeks. Insulin was positively associated with the change rate in BMI (p=0.03); however, this disappeared when adjusted for birth weight. For the first time, the association between lower leptin levels with greater catch up growth is shown for both BMI and length among preterm children. In conclusion, leptin levels at birth, but not insulin levels, predict growth rates.

Changes of leptin and metabolic hormones in preterm infants: a longitudinal study in early postnatal life

OBJECTIVES

Very little is known concerning the physiological role of leptin and growth in the early postnatal period and the association of leptin with other metabolic hormones in preterm infants. This study aims to investigate these relationships, and to explore the longitudinal and dynamic profile of leptin and metabolic hormones including insulin, ACTH, cortisol and FT4 in this category of patient. We also postulate that a rapid increase in body weight and body mass index in the first few weeks of life may be associated with a corresponding increase in serum leptin if the 'adipoinsular axis' is active at this stage.

DESIGN

A longitudinal study in a cohort of preterm infants < 34 weeks gestation for the first five weeks of postnatal life.

PATIENTS AND METHODS

Sixty-one preterm newborns < 34 weeks gestation were prospectively enrolled. Blood samples were collected in the morning when the newborns were 24 h of age (day 1), and on days 5, 14 and 35 of life. Serum leptin, insulin, cortisol, FT4, glucose and plasma ACTH concentrations were analysed using standard biochemical methods. Spearman's correlation coefficient was used to assess the inter-relationship of different metabolic hormones on the first day of life, and the relationship between metabolic hormones on day 1 and anthropometric or clinical parameters. The mixed-effects models were further used for analysing the multiple longitudinal measurements, and also for comparing the hormone concentrations between day 1 (baseline) and their corresponding levels on days 5, 14 and 35.

RESULTS

Serum leptin on day 1 (baseline) was significantly associated with serum insulin (r = 0.30, P < 0.05) and insulin:glucose ratio (r = 0.29, P < 0.05) in infants < 34 weeks gestation. Female preterm infants had significantly higher serum leptin (P < 0.05) and insulin (P < 0.05) levels than male infants. In addition, the duration between the last dose of antenatal dexamethasone and delivery significantly influenced the serum concentrations of leptin (r = - 0.27, P < 0.05), cortisol (r = 0.52, P < 0.001), plasma ACTH (r = 0.28, P < 0.05) and insulin:glucose ratio (r = - 0.27, P < 0.05) on the first day of life. Despite significant increase in body weight (P < 0.00001) and body mass index (P < 0.00001) by day 35 when compared to birth weight, no corresponding significant changes were observed for serum leptin, insulin and FT4. However, there was an increasing though statistically nonsignificant trend in serum leptin after day 14 of life.

CONCLUSION

This study characterized the longitudinal profile of leptin and metabolic hormones in preterm infants < 34 weeks gestation in the first 5 weeks of life. Serum leptin was significantly associated with serum insulin and insulin:glucose ratio supporting the hypothesis that an 'adipoinsular axis' exists and is likely to be functional before 34 weeks of gestation. Although a significant increase in body weight was demonstrated by day 35, no significant corresponding changes occurred with regard to serum leptin. We postulate that the limited quantity of adipose tissue at this stage of development might have contributed to this observation. Moreover, our results also showed that the duration between the last dose of antenatal corticosteroid and delivery could influence the postnatal concentrations of adipoinsular and pituitary-adrenal hormones. Thus, it is possible that antenatal dexamethasone might affect fetal growth and development via these neuroendocrine pathways in early intrauterine life.