Temporal manipulation of transferrin-receptor-1-dependent iron uptake identifies a sensitive period in mouse hippocampal neurodevelopment.

Iron is a necessary substrate for neuronal function throughout the lifespan, but particularly during development. Early life iron deficiency (ID) in humans (late gestation through 2-3 yr) results in persistent cognitive and behavioral abnormalities despite iron repletion. Animal models of early life ID generated using maternal dietary iron restriction also demonstrate persistent learning and memory deficits, suggesting a critical requirement for iron during hippocampal development. Precise definition of the temporal window for this requirement has been elusive due to anemia and total body and brain ID inherent to previous dietary restriction models. To circumvent these confounds, we developed transgenic mice that express tetracycline transactivator regulated, dominant negative transferrin receptor (DNTfR1) in hippocampal neurons, disrupting TfR1 mediated iron uptake specifically in CA1 pyramidal neurons. Normal iron status was restored by doxycycline administration. We manipulated the duration of ID using this inducible model to examine long-term effects of early ID on Morris water maze learning, CA1 apical dendrite structure, and defining factors of critical periods including parvalbmin (PV) expression, perineuronal nets (PNN), and brain-derived neurotrophic factor (BDNF) expression. Ongoing ID impaired spatial memory and resulted in disorganized apical dendrite structure accompanied by altered PV and PNN expression and reduced BDNF levels. Iron repletion at P21, near the end of hippocampal dendritogenesis, restored spatial memory, dendrite structure, and critical period markers in adult mice. However, mice that remained hippocampally iron deficient until P42 continued to have spatial memory deficits, impaired CA1 apical dendrite structure, and persistent alterations in PV and PNN expression and reduced BDNF despite iron repletion. Together, these findings demonstrate that hippocampal iron availability is necessary between P21 and P42 for development of normal spatial learning and memory, and that these effects may reflect disruption of critical period closure by early life ID.

Maternal executive function, infant feeding responsiveness and infant growth during the first 3 months.

BACKGROUND: There is limited research in young infants, particularly <3 months of age, on maternal feeding practices in spite of increasing evidence that early weight gain velocity is a determinant of later obesity risk. OBJECTIVE: To examine associations between maternal executive function (cognitive control over one's own behaviour), maternal feeding decisions and infant weight and adiposity gains. METHODS: We used a checklist to assess cues mothers use to decide when to initiate and terminate infant feedings at 2 weeks and 3 months of age (N = 69). Maternal executive function was assessed using the NIH Toolbox Cognition Battery subtests for executive function and infant body composition using air displacement plethysmography. RESULTS: Mothers with higher executive function reported relying on fewer non-satiety cues at 2 weeks of age (ß = -0.29, p = 0.037) and on more infant hunger cues at 3 months of age (ß = 0.31, p = 0.018) in their decisions on initiating and terminating feedings. Responsive feeding decisions, specifically the use of infant-based hunger cues at 3 months, in turn were associated with lower gains in weight-for-length (ß = -0.30, p = 0.028) and percent body fat (ß = -0.2, p = 0.091; non-covariate adjusted ß = -0.27, p = 0.029). CONCLUSIONS: These findings show both an association between maternal executive function and responsive feeding decisions and an association between responsive feeding decisions and infant weight and adiposity gains. The causal nature and direction of these associations require further investigation.

Eltrombopag, a thrombopoietin mimetic, crosses the blood-brain barrier and impairs iron-dependent hippocampal neuron dendrite development.

Essentials Potential neurodevelopmental side effects of thrombopoietin mimetics need to be considered. The effects of eltrombopag (ELT) on neuronal iron status and dendrite development were assessed. ELT crosses the blood-brain barrier and causes iron deficiency in developing neurons. ELT blunts dendrite maturation, indicating a need for more safety studies before neonatal use. SUMMARY: Background Thrombocytopenia is common in sick neonates. Thrombopoietin mimetics (e.g. eltrombopag [ELT]) might provide an alternative therapy for selected neonates with severe and prolonged thrombocytopenia, and for infants and young children with different varieties of thrombocytopenia. However, ELT chelates intracellular iron, which may adversely affect developing organs with high metabolic requirements. Iron deficiency (ID) is particularly deleterious during brain development, impairing neuronal myelination, dopamine signaling and dendritic maturation and ultimately impairing long-term neurological function (e.g. hippocampal-dependent learning and memory). Objective To determine whether ELT crosses the blood-brain barrier (BBB), causes neuronal ID and impairs hippocampal neuron dendrite maturation. Methods ELT transport across the BBB was assessed using primary bovine brain microvascular endothelial cells. Embryonic mouse primary hippocampal neuron cultures were treated with ELT or deferoxamine (DFO, an iron chelator) from 7 days in vitro (DIV) through 14 DIV and assessed for gene expression and neuronal dendrite complexity. Results ELT crossed the BBB in a time-dependent manner. 2 and 6 µm ELT increased Tfr1 and Slc11a2 (iron-responsive genes involved in neuronal iron uptake) mRNA levels, indicating neuronal ID. 6 µm ELT, but not 2 µm ELT, decreased BdnfVI, Camk2a and Vamp1 mRNA levels, suggesting impaired neuronal development and synaptic function. Dendrite branch number and length were reduced in 6 µm ELT-treated neurons, resulting in blunted dendritic arbor complexity that was similar to DFO-treated neurons. Conclusions Eltrombopag treatment during development may impair neuronal structure as a result of neuronal ID. Preclinical in vivo studies are warranted to assess ELT safety during periods of rapid brain development.

Antenatal betamethasone treatment has a persisting influence on infant HPA axis regulation.

OBJECTIVE: To examine the consequences of antenatal betamethasone (AB) exposure on postnatal stress regulation. STUDY DESIGN: Fourteen AB exposed infants born at 28-30 weeks' gestation were assessed in the NICU during postnatal week 1 and at 34 weeks postconception. Nine infants born at 34 weeks gestation without AB treatment were evaluated as a postconceptional age comparison group. Salivary cortisol, heart rate, and behavior were measured at baseline and in response to a heelstick blood draw. RESULTS: Repeated measures ANOVAs revealed that both groups displayed an increase in heart rate and behavioral distress in response to the stressor. The cortisol response, however, was blunted in AB-treated infants at both assessments. CONCLUSION: AB treatment has consequences for hypothalamic-pituitary-adrenal (HPA) axis regulation that persist for at least four to six weeks after birth, indicating that studies of long-term effects are warranted.

Abnormal shoulder girdle muscle tone in premature infants during their first 18 months of life.

To document the incidence of and neonatal factors associated with abnormal shoulder girdle muscle tone in premature infants at follow-up, we studied 125 consecutively admitted infants weighing less than 1,750 g treated in The Children's Hospital of Philadelphia intensive care nursery and subsequently seen in the Neonatal Follow-up Program up to 18 months of age. Fifty-seven infants (46%) displayed abnormal shoulder girdle muscle tone which presented clinically as scapular retractions. These infants had significantly lower birth weights (P less than .001) and gestational age (P less than .001) as well as a higher incidence of acute and chronic pulmonary disease (P less than 0.01) and CNS insults (P less than .05) when compared with infants without scapular retractions. The 57 infants with scapular retractions were further divided into two groups: 42 infants (74%) in whom scapular retractions were associated with generalized mild hypertonicity and 15 infants (26%) in whom scapular retractions compensated for trunk and neck hypotonicity. The infants with scapular retractions and hypotonicity had a significantly higher incidence of neonatal neurologic morbidity including seizures, major resuscitations, and birth asphyxia (P less than .01) when compared with the infants with scapular retractions and hypertonicity. Shoulder girdle tone abnormalities in the first year of life inhibit crawling, sitting, and object manipulation and, therefore, may manifest as delays in motor development. Identification of infants with significant neonatal risk factors for tone abnormalities is important to allow for earlier therapeutic intervention.

Abnormal truncal muscle tone as a useful early marker for developmental delay in low birth weight infants.

Thirty-four outborn premature infants of appropriate gestational ages with birth weights less than 1,750 g were seen in follow-up at 3, 6, 12, and 18 months, corrected age to assess the incidence of abnormalities of muscle tone and the relationship of the site of early abnormalities to 18-month developmental status. The incidence of abnormal tone was most common at 3 months and declined with increasing age. The percentages of infants with abnormal tone at 3, 6, 12, and 18 months, respectively, were: increased lower extremity tone--62%, 71%, 38%, 9%; decreased lower extremity tone--3%, 3%, 6%, 9%; increased truncal tone--41%, 15%, 6%, 0%; decreased truncal tone--21%, 18%, 15%, 6%. Infants with truncal hypertonicity at 3 months had significantly lower Bayley motor and mental scores at 18 months when compared with infants with normal truncal tone (P less than .05). However, infants with lower extremity hypertonicity at 3 months were no different developmentally at 18 months from infants with normal tone. Infants with truncal or lower extremity hypotonicity fared the worst developmentally (P less than .05). We conclude that there is a high incidence of abnormal muscle tone in premature infants up to 18 months of age and that early truncal tone abnormalities are associated with a worse developmental outcome.

American Academy of Pediatrics. Committee on Nutrition. Calcium requirements of infants, children, and adolescents.

This statement is intended to provide pediatric caregivers with advice about the nutritional needs of calcium of infants, children, and adolescents. It will review the physiology of calcium metabolism and provide a review of the data about the relationship between calcium intake and bone growth and metabolism. In particular, it will focus on the large number of recent studies that have identified a relationship between childhood calcium intake and bone mineralization and the potential relationship of these data to fractures in adolescents and the development of osteoporosis in adulthood. The specific needs of children and adolescents with eating disorders are not considered.

Identification and localization of divalent metal transporter-1 (DMT-1) in term human placenta.

The mechanism by which iron is transported from mother to fetus is incompletely understood. Whereas transferrin receptor (TfR) is responsible for iron uptake from maternal serum by the syncytiotrophoblast, the proteins responsible for intracytoplasmic transport and for delivery to the fetal serum remain unknown. The aim of this study was to determine whether the recently characterized endosomal membrane iron transporter, divalent metal ion transporter-1 (DMT-1), is expressed in human syncytiotrophoblast, and whether its cellular localization would support roles for cytoplasmic and placental-fetal iron transport. Six micron sections of frozen, term human placenta were assessed immunohistochemically using a polyclonal antibody to rat DMT-1 and a monoclonal antibody to human TfR. DMT-1 was found both in the cytoplasm and at the junction of the fetal (basal) membrane and fetal vessels, while TfR was localized predominantly to the maternal (apical) side of the syncytiotrophoblastic membrane. Double staining demonstrated no overlap between the two proteins on the apical membrane and minimal areas of overlap in the cytoplasm. We postulate that the syncytiotrophoblast takes up diferric transferrin from serum via TfR, subsequently incorporating the transferrin : TfR complex via endosomes. Subsequent transport of iron out of the endosome and across the basal membrane to the fetus may occur via DMT-1.

Increased N-glycosylation and reduced transferrin-binding capacity of transferrin receptor isolated from placentae of diabetic women.

Infants of diabetic mothers are frequently born iron deficient because their fetal iron demand exceeds placental iron transport capacity. Although transferrin receptor (TfR) expression is increased, binding to diferric transferrin is decreased proportionately to the severity of maternal disease. It is hypothesized that TfR isolated from diabetic placentae has altered N-glycosylation since proper glycosylation of N-linked oligosaccharides is important for normal TfR binding kinetics to diferric transferrin. TfR was obtained from syncytiotrophoblastic membranes of six diabetic and six non-diabetic human placentae. Competitive binding to 125I-transferrin demonstrated a higher Kd in the diabetic TfR (P = 0.04), directly correlated to cord serum C-peptide concentration (r = 0.81, P < 0.001). The molecular weight of the monomeric form of TfR prior to treatment with glycopeptidase F (PNG-F) was greater in the diabetic group (P < 0.001) was directly related to the Kd (r = 0.77, P = 0.002). Treatment with PNG-F eliminated the molecular weight difference between the two groups. Increased glycosylation of the N-linked oligosaccharides of TfR isolated from diabetic placentae may alter the three-dimensional structure or charge of the receptor, thus reducing its binding affinity for transferrin.

Increased placental iron regulatory protein-1 expression in diabetic pregnancies complicated by fetal iron deficiency.

Placental transferrin receptor (TfR) protein expression is increased in diabetic pregnancies that are complicated by low fetal iron stores, suggesting regulation of placental iron transport by fetoplacental iron status. In cell culture, iron homeostasis is regulated by coordinate stabilization of TfR mRNA and translation inactivation of ferritin mRNA by iron regulatory proteins (IRP-1 and -2) which bind to iron-responsive elements (IREs) on the respective mRNAs. Concentrations of IRP-1, IRP-2 and TfR mRNA were measured in 10 placentae obtained from diabetic and non-diabetic human pregnancies with a wide range of fetoplacental iron status. IRP-1 activity was present in human placenta and correlated closely with TfR mRNA concentration (r=0.82; P=0.007). IRP-2 activity and protein were not detected. In a second experiment, placentae were collected from 12 diabetic pregnancies, six with low fetal cord serum ferritin and placental non-heme iron concentrations, and six with normal iron status. IRP-1 activity and TfR Bmax for diferric transferrin were greater in the iron-deficient group (P<0.05). IRP-1 activity correlated inversely with cord serum ferritin (r=0.75; P<0.01) and placental non-heme iron (r=0.61; P=0.05) concentration. Placental IRP-1 activity is directly related to TfR mRNA concentration and is more highly expressed in iron-deficient placentae. The study provides direct in vivo evidence for IRP regulation of TfR expression in the human placenta.

Lower respiratory rates without decreases in oxygen consumption during neonatal synchronized intermittent mandatory ventilation.

OBJECTIVE: We tested the hypothesis that synchronization to patient effort during intermittent mandatory ventilation (SIMV), when compared to conventional unsynchronized intermittent mandatory ventilation (IMV), will decrease energy expenditure, as reflected by decreased oxygen consumption (VO2). DESIGN: We used a four-period crossover design. Each patient was studied over four 30-min continuous time intervals. Patients were randomized to receive initially IMV or SIMV, then crossed over such that each patient was treated twice with each modality. Data were analyzed using an analysis of variance technique. SETTING: Patients were receiving treatment in the newborn intensive care unit of Children's Hospital, St. Paul. PATIENTS: We studied 17 patients, who ranged from 23 to 37 weeks gestation, were < or = 14 days old, and had study weights from 623 to 3015 g. All were mechanically ventilated for hyaline membrane disease. MEASUREMENTS AND RESULTS: We measured and compared VO2, carbon dioxide consumption (VCO2), minute ventilation (VE), total respiratory rate, heart rate, arterial blood pressure, and arterial oxygen saturation (SaO2) values during IMV and SIMV. Total respiratory rate fell significantly during SIMV (73 +/- 26 during IMV, 57 +/- 17 during SIMV, p < 0.01) in spite of no significant change in VO2 (0.6 +/- 0.16% fall in VO2 during SIMV) or VCO2 (4.2 +/- 0.19% increase in VCO2 during SIMV) values. Moreover, there were no significant differences in heart rate, blood pressure, VE, or SaO2 values with either form of therapy. CONCLUSIONS: Though total respiratory rate fell, these data do not support the hypothesis that SIMV significantly reduces respiratory rate by decreasing oxygen consumption and carbon dioxide production during infant mechanical ventilation. Rather, the marked fall in respiratory rate may be due to a more efficient respiratory pattern.

A system approach to pharmacodynamics. Plasma iron mobilization by endogenous erythropoietin in the sheep fetus; evidence of threshold response in spontaneous hypoxemia.

At present, nearly all infants with birth weights of < 1 kg receive blood transfusions for treatment of clinical signs of tissue hypoxia resulting from anemia of prematurity. In contrast to the successful use of recombinant human erythropoietin (rhEp) in adults, treatment of anemic neonates with rhEp to stimulate red cell production and reduce the need for transfusions that pose serious infectious and immunologic risk has not been effective. The present study investigates the pharmacodynamics (PD) of endogenous erythropoietin (Ep) in sheep fetuses to determine possible causes for the poor rhEp response in early development. The dynamic relationship between plasma Ep and plasma iron resulting from spontaneous hypoxemic episodes is investigated by PD system analysis. The erythropoietic effect of Ep is measured in terms of the mobilization of plasma iron needed in the production on new erythrocytes. A hysteresis minimization approach is employed to determine the intrinsic PD dose-response relationship (transduction) of Ep. The dose-response relationship shows a well-defined threshold level that has to be exceeded before Ep begins to show a significant effect on plasma iron. It is postulated that the threshold mechanism may serve a useful purpose during early development by reducing the risk of the fetus developing a pathological degree of polycythemia and hyperviscosity in the relatively hypoxemic fetal environment. At the same time, the threshold serves the purpose of providing a needed response to more severe pathologic hypoxemic episodes. The occurrence of anemia during subsequent postnatal life when PaO2 levels increase markedly may be the inevitable, but unfortunate corollary of a continuation of this mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle proteolysis and weight loss in a neonatal rat model of sepsis syndrome.

Our hypothesis is that nitrogen loss in septic neonates is caused by increased muscle proteolysis. Sprague-Dawley rat pups (P7) were injected intraperitoneally with NaCl or 4 mg/kg/BW lipopolysaccharide (LPS) and then sacrificed at 2, 4, 24, and 48 hr. Sepsis syndrome was confirmed by elevated serum tumor necrosis factor (24.6 ng/mL +/- 18.4 [LPS] and < 1.0 ng/mL [controls]; p < .05). Proteolysis in gastrocnemius/soleus muscle was analyzed by quantitation of tissue tyrosine loss. The neonatal rats injected with LPS had significant media tyrosine release at 24 hr compared to the controls (0.39 +/- 0.14 versus 0.25 +/- 0.11 micromol tyrosine/g muscle; p < .05). At 48 hr, LPS-induced muscle tyrosine release ceased (0.24 +/- 0.04 [control] versus 0.23 +/- 0.03 micromol tyrosine/g muscle [LPS]). After 48 hr, gastrocnemius/soleus weight was less in the LPS-injected rats (50.5 +/- 4.8 to 31.2 +/- 4.0 g; p < .0001). Similar changes were not seen in the extensor digitorum longus, suggesting that some muscles were relatively preserved. Also, LPS resulted in significant weight loss. We conclude that selective muscle proteolysis contributes to nitrogen loss in neonatal sepsis. Although proteolysis abates by 48 hr, short-term injury results in significant muscle-mass deficit.

Transient hyperammonemia of the newborn: a vascular complication of prematurity?

Transient hyperammonemia of the newborn is an overwhelming disease manifested by hyperammonemic coma in ill premature infants. A summary of evidence is presented supporting the hypothesis that this syndrome is a vascular complication caused by shunting of blood away from the portal circulation of the liver into the systemic circulation with subsequent lack of ammonia removal. Alternative, nontraditional approaches of investigation and therapy targeting the hepatic portal circulation should be explored in patients with transient hyperammonemia of the newborn.

Routine use of dexamethasone for the prevention of postextubation respiratory distress.

We evaluated the routine use of dexamethasone for the prevention of postextubation respiratory distress by entering 60 ventilated infants into a prospective, randomized, blinded study. Thirty minutes before extubation, 30 infants were given a single dose of intravenous dexamethasone (0.25 mg/kg), and 30 infants received saline placebo. Infants were intubated orotracheally for at least 48 hours following a single intubation and were maintained on low ventilator settings (F10(2) less than 0.35, intermittent mandatory ventilation [IMV] less than 6, positive end-expiratory pressure [PEEP] less than 4) at least 12 hours before extubation. Following extubation, all infants weighing less than 1500 g were routinely placed on nasal continuous positive airway pressure (NCPAP). There was no difference between the two groups in postextubation Downes' score, serum pH, PCO2, or oxygen requirement at 30 minutes, 6 hours, and 24 hours. Respiratory acidosis occurred in one steroid-treated patient and in two placebo-treated infants. Stridor occurred in four infants in each group. No infant developed postextubation lobar atelectasis or required reintubation. We conclude that prophylactic administration of dexamethasone does not improve the immediate postextubation course of infants following a single intubation and that its routine use at the time of extubation is not indicated.

Effect of sepsis syndrome on neonatal protein and energy metabolism.

OBJECTIVE: It was our hypothesis that septic illness would alter both protein and energy metabolism in neonates, with elevations of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-1 beta (IL-1 beta) serving as markers for these effects. STUDY DESIGN: A total of 31 infants with suspected sepsis were enrolled into four groups: septic, sick-nonseptic, healthy-nonseptic, and recovered septic infants. Degree of illness, oxygen consumption, nitrogen balance, urine 3-methylhistidine/creatinine (MeH/Cr), and TNF-alpha, IL-6, IL-1 beta, and C-reactive protein (CRP) were measured. RESULTS: Oxygen consumption increased, while nitrogen balance decreased and MeH/Cr increased with increasing degree of illness. Nitrogen balance improved on recovery from sepsis. IL-6 and CRP levels were elevated in septic infants compared with sick-nonseptic and healthy infants. CONCLUSION: Neonates experience a hypermetabolic response with increased nitrogen loss during septic illness, proportional to the degree of illness. Increased delivery of protein substrate may be nutritionally advantageous to the septic neonate.

The effects of illness on neonatal metabolism and nutritional management.

In summary, careful attention to nutrient delivery in the IUGR infant is important to prevent and treat neonatal metabolic derangements and to improve postnatal growth. Carbohydrates are the essential fuel in the first days of life, to prevent hypoglycemia. Subsequent delivery of protein and fat helps rectify reduced muscle and fat stores and promotes weight gain. Calcium supplementation to prevent further bone demineralization and iron supplementation to replete iron stores may be necessary. Of special interest is that the neurologic outcome of these infants appears linked to the rate of catch-up growth. The rate of postnatal head growth depends on many perinatal and neonatal risk factors, and is a strong predictor of early developmental outcome in low-birthweight infants. Insufficient energy delivery beyond 2 weeks postnatal age in SGA premature infants results in failure to initiate subsequent catch-up head growth, with consequently smaller head circumferences at 1-year follow-up.

Nutritional assessment of the neonate.

Application of nutritional assessment techniques during the neonatal period provides the clinician with a strategy for evaluating the adequacy of macronutrient intake. To this end, the MAC:HC ratio and ponderal index appear to be more sensitive than birth weight in identifying newborns at risk for morbidity from fetal growth aberrations. In longitudinal assessment of postnatal growth the clinician is faced with several choices of anthropometric and/or biochemical techniques, either singly or in combination, to identify specific problems concerning protein energy nutritional status. Measurements of weight, length, and head and mid arm circumferences may be used both as static and dynamic assessments, but are more valid indicators when considered in relation to each other. Short-term biochemical markers, such as prealbumin, are more useful than albumin in assessing the effect of recent changes in protein intake. At the present time other biochemical tests are not helpful in the daily management of protein energy nutrition in infancy.

Health, growth, and use of community services in NICU graduates at early school age.

PURPOSE: To examine outcomes related to health, growth, and use of community health and education services in children ages 6 to 8 years who received newborn intensive care because of prematurity or perinatal complications. METHOD: Parents of 81 children who had received neonatal intensive care at a Midwest US tertiary care center completed a mailed questionnaire. Three birth weight groups (very low birth weight [VLBW] < 1500 g, n = 35; low birth weight [LBW] 1501-2500 g, n = 24, and normal birth weight [NBW] > 2500 g, n = 22) were compared regarding growth, health, and use of community-based services using descriptive statistics and one-way analysis of variance. FINDINGS: VLBW and NBW groups had more ongoing health concerns. Growth patterns were similar in all groups. VLBW and NBW groups demonstrated greater use of community-based services, and service use increased at school age. CONCLUSIONS: Comprehensive systems are needed for follow-up of high-risk infants to detect and refer problems early. Neonatal histories must be tracked throughout childhood. Seriously ill term NBW infants are at risk for later morbidity and require follow-up similar to that provided for VLBW children.

Assessment of large and small for gestational age newborn infants using growth curves.

Abnormal fetal growth patterns are associated with higher rates of neonatal morbidity. Measurement of anthropometric parameters immediately after birth, prior to the onset of potential neonatal symptoms, allows the physician to make an assessment as to which infants are at high risk. In general, a two-tiered approach will allow the physician to make the distinction between high- and low-risk infants. First, the standard one-factor anthropometrics--weight, length, and occipitofrontal head circumference--are plotted on curves that are appropriate for the population. In the vast majority of cases, these measurements give enough information regarding neonatal risk. When the standard measurements conflict with the clinical history or are disproportionate, the use of specialty one-factor anthropometrics, and especially two-factor body proportion assessments represent the second tier of assessment that can give greater insights into the etiology of abnormal fetal growth and can further define the groups at risk for neonatal sequelae.