Reticulocyte enrichment of zinc protoporphyrin/heme discriminates impaired iron supply during early development

Biomarkers of Brain Dysfunction in Perinatal Iron Deficiency

Iron deficiency in the fetal and neonatal period (perinatal iron deficiency) bodes poorly for neurodevelopment. Given its common occurrence and the negative impact on brain development, a screening and treatment strategy that is focused on optimizing brain development in perinatal iron deficiency is necessary. Pediatric societies currently recommend a universal iron supplementation strategy for full-term and preterm infants that does not consider individual variation in body iron status and thus could lead to undertreatment or overtreatment. Moreover, the focus is on hematological normalcy and not optimal brain development. Several serum iron indices and hematological parameters in the perinatal period are associated with a risk of abnormal neurodevelopment, suggesting their potential use as biomarkers for screening and monitoring treatment in infants at risk for perinatal iron deficiency. A biomarker-based screening and treatment strategy that is focused on optimizing brain development will likely improve outcomes in perinatal iron deficiency.

Anemia, Iron Supplementation, and the Brain

The developing brain is particularly vulnerable to extrinsic environmental events such as anemia and iron deficiency during periods of rapid development. Studies of infants with postnatal iron deficiency and iron deficiency anemia clearly demonstrated negative effects on short-term and long-term brain development and function. Randomized interventional trials studied erythropoiesis-stimulating agents and hemoglobin-based red blood cell transfusion thresholds to determine how they affect preterm infant neurodevelopment. Studies of red blood cell transfusion components are limited in preterm neonates. A biomarker strategy measuring brain iron status and health in the preanemic period is desirable to evaluate treatment options and brain response.

Impact and interactions between risk factors on the iron status of at-risk neonates

OBJECTIVE

Examine interactions between perinatal risk factors for congenital iron deficiency (ID) using two cohorts.

STUDY DESIGN

Iron status in a composite 767-member cord blood cohort and a NICU cohort of 257 infants < 33 weeks of gestation or small for gestational age (SGA). Risks for ID were examined. Cord ferritin levels < 84 µg/L defined congenital ID. Serum ferritin < 70 µg/L defined infantile ID at one-month.

RESULTS

31% of the cord cohort had congenital ID; risks summative (p < 0.0015). 16% of the NICU cohort had infantile ID; risks not summative. However, 32% had ID if the ferritin threshold was 100 µg/L. Being both preterm (p < 0.0001) and SGA (p < 0.05) negatively impacted cord iron status. Maternal hypertension was a novel predictor of iron status (p = 0.023 in preterm cord; p < 0.0025 in NICU).

CONCLUSION

Summing risks in term and understanding compounding risks in preterm infants can improve screening and management of ID in at-risk infants.

Cord Blood Erythropoietin and Hepcidin Reflect Lower Newborn Iron Stores due to Maternal Obesity during Pregnancy

OBJECTIVE

Obesity during pregnancy impedes fetal iron endowment. In adults, both iron depletion and hypoxia stimulate erythropoietin (Epo) production, while hepcidin, the primary iron regulator, is inhibited by Epo and stimulated by obesity. To understand this relationship in fetuses, we investigated obesity, inflammation, and fetal iron status on fetal Epo and hepcidin levels.

STUDY DESIGN

Epo, hepcidin, C-reactive protein (CRP), and ferritin levels were measured in 201 newborns of 35 to 40 weeks' gestation with historical risk factors for a low fetal iron endowment, including half with maternal obesity.

RESULTS

Epo was unrelated to fetal size, but Epo was directly related to maternal body mass index (BMI; kg/m²) (p < 0.03) and CRP (p < 0.0005) at delivery. Epo levels were twice as likely to be elevated (≥50 IU/L) while comparing the lowest quartile of ferritin with the upper three quartiles (p < 0.01). Hepcidin was directly related to ferritin (p < 0.001) and indirectly related to maternal BMI (p < 0.015), but BMI became nonsignificant when undergoing multivariate analysis. Hepcidin was unrelated to Epo.

CONCLUSION

Although some of the fetal responses involving Epo were similar to adults, we did not find a hepcidin-Epo relationship like that of adults, where fetal liver is the site of both hepcidin and Epo production.

Maternal Perceived Stress during Pregnancy Increases Risk for Low Neonatal Iron at Delivery and Depletion of Storage Iron at One Year

OBJECTIVE

To investigate the impact of maternal stress during pregnancy on newborn iron and stage 1 iron deficiency at 1 year of age.

STUDY DESIGN

In total, 245 mothers and their newborn infants (52% male; 72% white) were recruited at the Meriter Hospital Birthing Center on the basis of known risk factors for iron deficiency. Umbilical cord blood hemoglobin and zinc protoporphyrin/heme (ZnPP/H) were determined to evaluate erythrocyte iron and plasma ferritin was determined to reflect storage iron. Mothers retrospectively reported stress experienced previously during pregnancy on a 25-item questionnaire. Blood was also was collected from 79 infants who were breastfed at 1 year of age.

RESULTS

Maternal recall of distress and health concerns during pregnancy correlated with cord blood ZnPP/H indices (r = 0.21, P < .01), even in the absence of major traumatic events. When concurrent with other known risks for iron deficiency, including maternal adiposity, socioeconomic status, and race, maternal stress had a summative effect, lowering cord blood iron. At 1 year, 24% of infants who were breastfed had moderate iron deficiency (plasma ferritin <12 µg/L). Higher cord blood ZnPP/H was predictive of this moderate iron deficiency (95% CI 0.26-1.47, P = .007). When coincident with maternal reports of gestational stress, the likelihood of low plasma ferritin at 1 year increased 36-fold in breastfed infants as compared with low-stress pregnancies (95% CI 1.33-6.83, P = .007).

CONCLUSIONS

Maternal recall of stress during pregnancy was associated with lower iron stores at birth. High cord blood ZnPP/H, reflecting low erythrocyte iron, was correlated with the likelihood of stage 1 iron deficiency at 1 year, when rapid growth can deplete storage iron in breastfed infants.

Maternal Obesity Affects Inflammatory and Iron Indices in Umbilical Cord Blood

OBJECTIVE

To determine the impact of maternal obesity and gestational weight gain across pregnancy on fetal indices of inflammation and iron status.

STUDY DESIGN

Eighty-five healthy term newborns delivered via elective cesarean were categorized by 2 maternal body mass index (BMI) thresholds; above or below 30 kg/m(2) or above or below 35 kg/m(2). Umbilical cord plasma levels of C-reactive protein, interleukin (IL)-6, tumor necrosis factor (TNF)-α, ferritin, and hepcidin were assayed. Cytokines released by phytohemagglutinin-stimulated umbilical cord mononuclear cells (MNCs) were assayed.

RESULTS

Maternal class II obesity, defined as BMI of 35 kg/m(2) and above, predicted higher C-reactive protein and TNF-α in umbilical cord plasma (P < .05 for both), and also proinflammatory cytokines (IL-1β, IL-6, and TNF-α) from stimulated MNC (P < .05 for all). The rise in plasma TNF-α and MNC TNF-α was not linear but occurred when the threshold of BMI 35 kg/m(2) was reached (P < .005, P < .06). Poorer umbilical cord iron indices were associated with maternal obesity. When ferritin was low, IL-6 was higher (P < .04), but this relationship was present primarily when maternal BMI exceeded 35 kg/m(2) (P < .03). Ferritin was correlated with hepcidin (P < .0001), but hepcidin was unrelated to either maternal BMI or inflammatory indices.

CONCLUSIONS

Class II obesity and above during pregnancy is associated with fetal inflammation in a threshold fashion. Although maternal BMI negatively impacted fetal iron status, hepcidin, related to obesity in adults, was related to iron status and not obesity in fetuses. Pediatricians should be aware of these relationships.

Impact of Growth Restriction and Other Prenatal Risk Factors on Cord Blood Iron Status in Prematurity

OBJECTIVE

To determine whether prenatal risk factors (RFs) that predict cord blood iron status in term newborns also predict iron status of premature newborns.

STUDY DESIGN

Cord blood iron indices from 80 preterm newborns were compared with historical and demographic RFs for developing iron deficiency if born at term.

RESULT

The presence of multiple RFs did not incrementally interfere with cord iron status in preterm newborns. Poorer iron status accompanied being small for gestational age in prematurity, but other RFs, including diabetes, had relatively little impact.

CONCLUSION

Growth-restricted preterm newborns are at risk for poor iron endowment, likely due to uteroplacental insufficiency. Other RFs were less impactful on iron status of premature newborns than in term newborns, likely reflecting that disruptive effects of RFs are more impactful in the third trimester. Understanding RFs for poor iron endowment is important for clinical recognition and treatment of premature babies.

Dietary-induced gestational iron deficiency inhibits postnatal tissue iron delivery and postpones the cessation of active nephrogenesis in rats

Gestational iron deficiency (ID) can alter developmental programming through impaired nephron endowment, leading to adult hypertension, but nephrogenesis is unstudied. Iron status and renal development during dietary-induced gestational ID (<6 mg Fe kg-1 diet from Gestational Day 2 to Postnatal Day (PND) 7) were compared with control rats (198 mg Fe kg-1 diet). On PND2-PND10, PND15, PND30 and PND45, blood and tissue iron status were assessed. Nephrogenic zone maturation (PND2-PND10), radial glomerular counts (RGCs), glomerular size density and total planar surface area (PND15 and PND30) were also assessed. Blood pressure (BP) was measured in offspring. ID rats were smaller, exhibiting lower erythrocyte and tissue iron than control rats (PND2-PND10), but these parameters returned to control values by PND30-PND45. Relative kidney iron (µg g-1 wet weight) at PND2-PND10 was directly related to transport iron measures. In ID rats, the maturation of the active nephrogenic zone was later than control. RGCs, glomerular size, glomerular density, and glomerular planar surface area were lower than control at PND15, but returned to control by PND30. After weaning, the kidney weight/rat weight ratio (mg g-1) was heavier in ID than control rats. BP readings at PND45 were lower in ID than control rats. Altered kidney maturation and renal adaptations may contribute to glomerular size, early hyperfiltration and long-term renal function.

Maternal pregnancy weight gain and cord blood iron status are associated with eosinophilia in infancy

OBJECTIVE

Allergic disease is multifactorial in origin. Because iron nutrition affects immune responses and maternal pregnancy weight gain impairs fetal iron delivery while increasing fetal demands for growth, the study examined maternal pregnancy weight gain, newborn iron status and an index of atopic disease, infant eosinophilia.

STUDY DESIGN

Within a larger prospective study of healthy newborns at risk for developing iron deficiency anemia, umbilical cord iron indicators were compared to infant eosinophil counts.

RESULT

Infants who developed eosinophilia exhibited higher cord reticulocyte-enriched zinc protoporphyrin/heme ratio, P<0.05 and fewer cord ferritin values in the highest (best) quartile, P<0.05. If cord ferritin was in the upper three quartiles, the negative predictive value for infant eosinophilia was 90%. High maternal pregnancy weight gain predicted infant eosinophil counts, P<0.04, and contributed to cord ferritin predicting eosinophilia, P<0.003.

CONCLUSION

Poor fetal iron status may be an additional risk factor for infant eosinophilia.

Neonatal iron status is impaired by maternal obesity and excessive weight gain during pregnancy

OBJECTIVE

Maternal iron needs increase sixfold during pregnancy, but obesity interferes with iron absorption. We hypothesized that maternal obesity impairs fetal iron status.

STUDY DESIGN

Three hundred and sixteen newborns with risk factors for infantile iron deficiency anemia (IDA) were studied to examine obesity during pregnancy and neonatal iron status. Erythrocyte iron was assessed by cord blood hemoglobin (Hb), zinc protoporphyrin/heme (ZnPP/H) and reticulocyte-ZnPP/H, and storage iron by serum ferritin.

RESULT

Women with body mass index (BMI) ⩾ 30 kg m(-)(2), as compared with non-obese women, delivered larger offspring with higher reticulocyte-ZnPP/H and lower serum ferritin concentrations (P<0.05 for both). With increasing BMI, the estimated body iron was relatively lower (mg kg(-)(1)) and the ratio of total Hb-bound iron (mg) per total body iron (mg) increased. Maternal diabetes compromised infant iron status, but multivariate analysis demonstrated that obesity was an independent predictor.

CONCLUSION

Obesity during pregnancy and excessive weight gain are independent risk factors for iron deficiency in the newborn.

Endogenous siderophore 2,5-dihydroxybenzoic acid deficiency promotes anemia and splenic iron overload in mice

Eukaryotes produce a siderophore-like molecule via a remarkably conserved biosynthetic pathway. 3-OH butyrate dehydrogenase (BDH2), a member of the short-chain dehydrogenase (SDR) family of reductases, catalyzes a rate-limiting step in the biogenesis of the mammalian siderophore 2,5-dihydroxybenzoic acid (2,5-DHBA). Depletion of the mammalian siderophore by inhibiting expression of bdh2 results in abnormal accumulation of intracellular iron and mitochondrial iron deficiency in cultured mammalian cells, as well as in yeast cells and zebrafish embryos We disrupted murine bdh2 by homologous recombination to analyze the effect of bdh2 deletion on erythropoiesis and iron metabolism. bdh2 null mice developed microcytic anemia and tissue iron overload, especially in the spleen. Exogenous supplementation with 2,5-DHBA alleviates splenic iron overload in bdh2 null mice. Additionally, bdh2 null mice exhibit reduced serum iron. Although BDH2 has been proposed to oxidize ketone bodies, we found that BDH2 deficiency did not alter ketone body metabolism in vivo. In sum, our findings demonstrate a key role for BDH2 in erythropoiesis.

Impact of multiple prenatal risk factors on newborn iron status at delivery

BACKGROUND

Maternal anemia and several complications of pregnancy can affect fetal iron acquisition.

AIM

Because it is unknown whether the effects of demographic and maternal risk factors (RF) are summative, we examined cord iron status in newborns with multiple RF for acquiring iron deficiency.

METHODS

Cord blood indices from healthy control newborns with and without RF for newborn or infant iron deficiency were studied.

RESULTS

Newborns with greater RF had poorer erythrocyte and storage iron status. Poorest status was seen if mothers with comorbid obesity and diabetes delivered large-for-gestation newborns. Findings highlight the importance of identifying RF.

Ovine uterine space restriction alters placental transferrin receptor and fetal iron status during late pregnancy

BACKGROUND

Fetal growth restriction is reported to be associated with impaired placental iron transport. Transferrin receptor (TfR) is a major placental iron transporter in humans but has not been studied in sheep. TfR is regulated by both iron and nitric oxide (NO), the molecule produced by endothelial nitric oxide synthase (eNOS). We hypothesized that limited placental development downregulates both placental TfR and eNOS expression, thereby lowering fetal tissue iron.

METHODS

An ovine surgical uterine space restriction (USR) model, combined with multifetal gestation, tested the extremes of uterine and placental adaptation. Blood, tissues, and placentomes from non-space restricted (NSR) singletons were compared with USR fetuses at gestational day (GD) 120 or 130.

RESULTS

When expressed proportionate to fetal weight, liver iron content did not differ, whereas renal iron was higher in USR vs. NSR fetuses. Renal TfR protein expression did not differ, but placental TfR expression was lower in USR fetuses at GD130. Placental levels of TfR correlated to eNOS. TfR was localized throughout the placentome, including the hemophagous zone, implicating a role for TfR in ovine placental iron transport.

CONCLUSION

Fetal iron was regulated in an organ-specific manner. In USR fetuses, NO-mediated placental adaptations may prevent the normal upregulation of placental TfR at GD130.

Iron deficiency and renal development in the newborn rat

Iron is essential for fetal organ development, but the effect of isolated iron deficiency on nephrogenesis is unknown. Human premature infants are at risk for disrupted nephrogenesis because glomerular development is incomplete until 36-wk gestation. We modeled the effects of iron on postnatal glomerulogenesis in four groups of immature rats from P4 to P12: dam fed controls (DF), dam fed with sham gastrostomy surgery (DF + SS), iron-deficiency anemia (IDA), fed iron-deficient formula through gastrostomy apart from the dam, and IDA plus simultaneous enteral iron rescue (IDA+Fe). Hematocrit, plasma ferritin, and body and kidney tissue iron contents were measured. Tissue was examined. Rats grew similarly, but IDA rats exhibited lower hematocrit, plasma ferritin, and body and kidney iron contents than DF, DF + SS, or IDA + Fe. IDA exhibited 1.7 fewer radial glomerular counts (RGCs), 26% reduced glomerular density, and 29% less planar glomerular surface area than DF, with partial improvement in IDA + Fe. Compared with DF or DF + SS, we observed elevated plasma CRP levels and tubulointerstitial fibrosis in the IDA and IDA + Fe groups. IDA reduced glomerular density, glomerular surface area, and promoted fibrosis. Iron substantially rescued renal growth and development, supporting the critical role of iron in late nephrogenesis.