Iron Needs of Preterm Infant

Michael K. Georgieff M.D.Professor of Pediatrics and Child Development

Head, Division of Neonatology

Director, Center for Neurobehavioral Development

University of Minnesota

Overview• Iron Deficiency: Scope of Problem

• Basic Principles of Nutrient-Brain Interactions

• Role of Iron in the Developing Brain

• Risk of Iron Deficiency in Neonates– Human

• Preterm– Rodent

• Risk of Iron Overload in Neonates

• Iron Dosing/Monitoring Recommendations

Why Worry About Iron Deficiency?

• 2 billion people world-wide are iron deficient (WHO)– 30-50% of pregnant women

• Every cell/organ system needs iron for proper development and subsequent function

• Iron deficiency anemia is associated with clinical symptoms– Due to tissue level ID– Symptoms occur prior to anemia

• Main reason to worry is the effect on the developing brain– Cognitive and motor effects– Some temporary (while ID), others long-term (after iron repletion)

Early Nutrition and Brain Development:General Principles

Positive or negative nutrient effects

on brain development

Based on…

Timing, Dose and Duration of Exposure

Kretchmer, Beard, Carlson, 1996

Nutrient-Brain-Behavior Relationships

• Various brain regions/processes have different developmental trajectories

• The vulnerability of a brain region to a nutrient is based on

– When nutrient deficit/overload is likely to occur

– Brain’s requirement for that nutrient at that time

• Behavioral changes must map onto those brain structures altered by the nutrient effect

Fetus Late Infancy/Toddler Pubertal

Thompson & Nelson, 2001

Fetus Late Infancy/Toddler Pubertal

Iron: A Critical Nutrient for the Developing Brain

– Delta 9-desaturase, glial cytochromes control oligodendrocyte production of myelin

• Iron Deficiency=> Hypomyelination

– Cytochromes mediate oxidative phosphorylation and determine neuronal and glial energy status

• Iron Deficiency=> Impaired neuronal growth, differentiation, electrophysiology

– Tyrosine Hydroxylase involved in monamine neurotransmitter and receptor synthesis (dopamine, serotonin, norepi)

• Iron Deficiency=> Altered neurotransmitter regulation

Iron: A Significant Risk to the Developing Brain

• Potent oxidant stressor

– Role in Fenton reaction to create reactive oxygen species

• Iron overload associated with neurodegenerative disorders in adults

– S/P acute hypoxic-ischemic reperfusion injury

– Parkinson’s, Alzheimer’s diseases

• Fetus/premature infant at high risk for iron toxicity

– Underdeveloped anti-oxidant systems

– Low Total Iron Binding Capacity

The U-shaped Nutrition Risk Curve

Risk

Adequacy OverloadDeficiency

Dose

Iron and the U-shaped Nutrition Risk Curve

Risk

Adequacy OverloadDeficiency

Dose

Neonatal Iron Deficiency

Fetal Iron: Endowment and Distribution

• Fetuses have 75mg of elemental iron per kilogram body weight during 3rd trimester

– Term infant: 250mg

– 24 weeker (500g): 37.5 mg

• Majority is in the RBCs (55mg/kg)

• Liver storage pools are relatively large at term (12 mg/kg); serum ferritin >40 mcg/L

• Non-storage tissues, including brain, heart, skeletal muscle account for the rest (8 mg/kg)

What Can Negatively Affect Neonatal Iron Status?

• Decreased maternal iron supply– Fetus with very iron deficient mother (Hgb<8.5)– Common (>30%) in developing countries– No studies of newborn brain iron status

• Decreased placental iron transfer during gestation– Prematurity

• Iron accreted during third trimester

• Generally negative iron balance during NICU stay

– IUGR due to maternal hypertension during pregnancy• 50% affected

• 75,000 infants per year in US• 32% decrease in brain iron concentration (Georgieff et al, 1995)

Term Infants: What Can Negatively Affect Neonatal Iron Status?

• Diabetes Mellitus during pregnancy

– Chronically hypoxic fetus (IDM)=> Increased erythropoeisis

– 65% affected

– 150,000 infants per year in US

– 40% decrease in brain iron concentration (Petry et al, 1992)

• Basic principle:

Iron prioritized to RBCs over brain &

other organs when Fe demand> Fe supply

Preterm Infants: Risk for Iron Deficiency at Birth

Preterm Infants Are Born with Lower Iron Stores

0

50

100

150

200

250

300

350

400

20 25 30 35 40 45

Gestational Age (wks)

Serum Ferritin (mcgs/L)

Table 1. Percentiles for term and preterm infants.

Percentile

Gestational Age

5%

25% 50% 75% 95%

Term (≥37 w ),ks n =308 40 84 134 200 309 Pre- (<Term 37 w ),ks n = 149

35 80 115 170 267

Cord serum ferritin percentiles for term and preterm infants

1) Neonates have 75 mg Fe/Kg weight

2) 24 weeks EGA= 38mg Fe

3) 40 weeks EGA= 225mg Fe

4) 20-30% of preterms are IUGR

5) 50% of IUGRs have ferritin <5%ile

Siddappa et al., Neonatology, 2007

Preterm Infants: Risk for Negative Iron Balance During Hospitalization

Factors that Determine Preterm Infant Iron Balance in the NICU

Negative Iron Balance• Low Endowment (IUGR)• Phlebotomy Losses• Iron Rx at 2 months• Iron Rx < 2mg/kg/d• rhEpo Rx• Rapid Postnatal Growth

Positive Iron Balance• Older gestation & AGA• RBC Transfusion• Iron Rx at 2 weeks• Iron Rx @ 2-4 mg/kg/d• Iron Rx @ 6mg/kd/d c rhEpo• Parenteral Iron• Slow Postnatal Growth Rate

1) Preterm infants have elevated ZnPP at 34 weeks PCA (Winzerling &Kling)

2) Does anemia of prematurity have an iron deficiency component?

Preterm Infants: Risk of ID/IDA after Discharge

Iron Status after NICU Discharge

0

5

10

15

20

25

30

35

HB < 11 HB > 11

2 mos CGA Hemoglobin in <1750g Preterms

sTFR<8, ferritin>20sTFR>8, ferritin<20

Lower total body iron stores & higher serum TfR at 2 mos of age

Shah et al, PAS 2006

Up to 69% ID at follow-up if in hospital iron therapy delayed until 2 months postnatal age

Hall et al, 1993

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Neurobehavioral Risks of Early ID

Neurobehavioral Sequelae of Perinatal ID• Behavioral abnormalities

– Term infants with low neonatal iron stores have poorer school age neurodevelopment (Tamura et al, 2002)

– Iron deficient infants born to IDA mothers have altered temperament (Wachs et al, 2005)

– Preterm infants with lowest quartile of ferritin concentration at discharge have abnormal neurologic reflexes (Armony-Sivan, 2004)

– Preterm infants with low ferritins have slower central nerve conduction speeds (Amin, 2010)

• Electrophysiologic abnormalities– Term IDM with ferritin concentrations <35 mcg/L have impaired

auditory recognition memory processing (Siddappa et al, 2004)

Assessing Memory Function in ID Newborn Infants

(How do we do this and why?)

Mom: “Hi Baby”

Stranger: “Hi Baby”

Event related potentials (ERPs) in infants

Iron Sufficient Iron Deficient

Siddappa et al., 2004, Pediatr. Res.

Perinatal Iron Deficiency: What is the Biology?

Early Postnatal ID: Myelin Effects in the Rat

• Altered fatty acid profile in myelin fraction

• Decreased myelin proteins, including myelin basic protein

• Decreased oligodendrocyte proliferation

• Transcripts for myelin basic protein affected – short term (while ID) – long term (at P180 after iron repletion)

• Likely accounts for ABR findings in premies (Amin et al, 2010)

Neurotransmitter Effects in the Rat

• Effects on monoamines, esp dopamine, known since late 1970’s (Yehuda, Youdim, Beard)

• While ID: Decreased DAT, D1R, D2R • Regional differences- Large effects in striatum

– Changes related to timing and severity

– Behavioral effects include hesitancy, wariness

• Likely accounts for reduced engagement and altered temperament in ID newborns (Wachs et al, 2005)

Hippocampal Effects• Short and long-term genomic changes (ES Carlson et al, 2007)

– Dendrite structure, synaptic efficacy, oxidative metabolism • Reduced energy status (M deUngria et al, 2000)

• Altered dendrite morphology (ES Carlson et al, 2009)*

• Long-term suppression of BDNF and its receptor (P Tran et al, 2009)

• Reduced LTP (long-term potentiation) (LA Jorgenson et al, 2005)

• Reduced learning and memory– Morris Water Maze (B Felt and B Lozoff, 1996)

– Radial Arm Maze (AT Schmidt et al, 2007)

• Likely accounts for recognition memory deficits (Siddappa et al, 2004)

Sufficient Deficient

Excess Iron

Brain Iron Overload:Which Infants are at Risk?

• Birth Asphyxiated Newborns

– Increased free (non-protein bound) iron in cord blood (Perrone et al, 2002)

– Increased NPBI and thio-barbituric-acid-reactive species (TBARS) in plasma suggesting increased lipid peroxidation (Yu et al, 2003)

– Plasma NPBI >15.2mcmol/L is 100% sensitive and specific for neurologic impairment (Buonocore et al, 2003)

– NPBI elevated in CSF and correlated with oxidized proteins and Sarnat stage (Ogihara et al., 2003)

• Preterm Infants

– Parenteral iron (Pollak et al, 2001)

– RBC transfusion (with hemolysis)

– Relationship between RBC transfusions and other “oxidant diseases” (e.g. BPD, ROP)

Inder et al, 1997; Cooke et al, 1997

Human studies have not assessed specific neurodevelopment as a function of area of iron overload

Brain Iron Overload:Which Infants are at Risk?

Concerns About Excess Iron in the Term Neonate

• Newborn term infants with highest quartile of cord blood ferritin concentration have poorer outcome than middle quartiles (Tamura et al, 2002)– But not as bad as lowest quartile– High ferritin; iron or inflammation?

• Infants with high normal hemoglobins at 6-9 months receiving formula with 12 mg Fe/L have lower IQs at age 10 (Lozoff et al, 2008 PAS abstract)– Not true for infants with normal or low hemoglobins

How well regulated is enteral iron uptake in the neonate?» Term

» Preterm

Early Iron Overload: Animal Models • Free iron=>Reactive oxygen species

– Astrocyte dysfunction

– NMDA receptor impairment

– Damaged mitochondrial DNA

– Peroxidation of immature myelin sheaths

• Increased perivascular iron deposition in neonatal rat brain following severe hypoxia-ischemia (Palmer et al, 1999)

– Within hours of neonatal stroke

– Long term iron deposition and neuronal loss

– Protective effect of iron chelators • Palmer et al, 1994

Iron Supplements and Memory in IS Rodents

• Increasing levels of high dose (2.5 to 30 mg/kg/d) iron administration to iron sufficient neonatal rats results in worse memory performance as adults (Schroder et al, 2001)

– Dose responsive increase in brain iron content

– No specific regional structural/functional assessment (e.g. LTP)

Iron Overload: Summary

• There are plenty of theoretical reasons based on animal studies to be concerned

• Further research needs to explore this potential link in human infants, especially treatment of iron sufficient infants with supplemental iron

– Reviews by Buonocoare (2003) and Gressens (2002)

Iron Dosing

Treatment and Monitoring Iron Status in the Preterm Infant

• Current AAP dosing recommendations appear appropriate for preterms in NICU

– 2-4 mg/kg/day enteral iron• 4mg/kg if <30 weeks

• 2-3 mg/kg if >30 weeks

– 6 mg/kg/day if on rhEpo

• Post-discharge recommendations (2.25 mg/kg/d) appear low and should be increased to 3.3 mg/kg/d

• Consider monitoring ferritin at birth, at discharge and at follow-up (along with hemoglobin & indices)

Iron Dosing for Neonates and Infants• Term AGA• Term SGA• Preterm >30 w EGA• Preterm <30 w EGA• Preterm on rhEpo• Preterm; ferritin <35

• 1 mg/kg daily• 2 mg/kg daily• 2 mg/kg daily • 4 mg/kg daily• 6 mg/kg daily• +2 mg/kg daily

Conundrums in preterms: 1. Anemic, no retics, ferritin >3502. Breastfed infants

Monitoring Iron Status

• AAP recommends hemoglobin screening at 9 months of age– Earlier screening for premies, SGAs– sTfR, ZnPP, MCV might screen pre-anemia

• sTfR, ZnPP not available everywhere, lacking standards for < 12 month olds

• Ferritin is good pre-anemic screen– But, infant cannot have acute illness (acute phase reactant)

• NHANES and CDC testing sTfR/Heme ratio

Summary

• Iron has an important role in late gestational and early postnatal brain development

• Iron is regulated within a narrow range

• Iron deficiency and iron overload present risks to developing brain

• Risks can be global or regionally specific

• Abnormal behaviors in ID “map onto” regional brain areas at risk

Acknowledgements

• U of Minnesota– Raghu Rao– Lyric Jorgenson– Erik Carlson– Adam Schmidt– Jane Wobken– Tracy deBoer– Charles Nelson

• At HCMC& U of Minnesota– Asha Siddappa

• NICHD

• NINDS

• Jack Widness (U of Iowa)

• Betty Leibold (U of Utah)

• Rick Eisenstein (U of Wisconsin)

• Jim Connor, John Beard (Penn State)

• Betsy Lozoff, Barb Felt (U of Michigan)

• Raye-Ann deRegnier, Malika Shah (Northwestern U)