Gestational and lactational iron deficiency alters the developing striatal metabolome and associated behaviors in young rats

Long-term brain and behavioral consequences of early iron deficiency

Early iron deficiency not only affects brain and behavioral function during the period of iron deficiency, it persists long after treatment. The mechanisms include long-term alterations in dopamine metabolism, myelination, and hippocampal structure and function. Recent studies have demonstrated long-term genomic changes, which suggests the regulation of brain function is fundamentally altered.

Severe postnatal iron deficiency alters emotional behavior and dopamine levels in the prefrontal cortex of young male rats

Iron deficiency in early human life is associated with abnormal neurological development. The objective of this study was to evaluate the effect of postnatal iron deficiency on emotional behavior and dopaminergic metabolism in the prefrontal cortex in a young male rodent model. Weanling, male, Sprague-Dawley rats were fed standard nonpurified diet (220 mg/kg iron) or an iron-deficient diet (2-6 mg/kg iron). After 1 mo, hematocrits were 0.42 ± 0.0043 and 0.16 ± 0.0068 (mean ± SEM; P < 0.05; n = 8), liver nonheme iron concentrations were 2.3 ± 0.24 and 0.21 ± 0.010 μmol/g liver (P < 0.05; n = 8), and serum iron concentrations were 47 ± 5.4 and 23 ± 7.1 μmol/L (P < 0.05; n = 8), respectively. An elevated plus maze was used to study emotional behavior. Iron-deficient rats displayed anxious behavior with fewer entries and less time spent in open arms compared to control rats (0.25 ± 0.25 vs. 1.8 ± 0.62 entries; 0.88 ± 0.88 vs. 13 ± 4.6 s; P < 0.05; n = 8). Iron-deficient rats also traveled with a lower velocity in the elevated plus maze (1.2 ± 0.15 vs. 1.7 ± 0.12 cm/s; P < 0.05; n = 8), behavior that reflected reduced motor function as measured on a standard accelerating rotarod device. Both the time on the rotarod bar before falling and the peak speed attained on rotarod by iron-deficient rats were lower than control rats (156 ± 12 vs. 194 ± 12 s; 23 ± 1.5 vs. 28 ± 1.6 rpm; P < 0.05; n = 7-8). Microdialysis experiments showed that these behavioral effects were associated with reduced concentrations of extracellular dopamine in the prefrontal cortex of the iron-deficient rats (79 ± 7.0 vs. 110 ± 14 ng/L; P < 0.05; n = 4). Altered dopaminergic signaling in the prefrontal cortex most likely contributes to the anxious behavior observed in young male rats with severe iron deficiency.

Responses of HSC70 expression in diencephalon to iron deficiency anemia in rats

A powdered diet containing 100 or 3 ppm Fe was fed to rats starting at the age of 3 weeks. The voluntary activity level was checked using a wheel in the cage during the 17th week after the beginning of supplementation. Significantly less activity was seen in the 3 ppm Fe group during both light and dark periods. After 20 weeks, the blood and diencephalon were sampled from both groups. Lower hematocrit and blood hemoglobin content was observed in the 3 ppm Fe group. The level of 70 kDa heat shock cognate (HSC70) expression was greater in the diencephalon of the 3 ppm Fe group. In addition, the distribution of HSC70 was determined by proximity ligation assay. More HSC70-positive as well as total cells were noted in several areas of the diencephalon of the iron-deficient rats. The altered expression and distribution of HSC70 might play some role in the neurological changes.

Fetal and neonatal iron deficiency causes volume loss and alters the neurochemical profile of the adult rat hippocampus

OBJECTIVE

Perinatal iron deficiency results in persistent hippocampus-based cognitive deficits in adulthood despite iron supplementation. The objective of the present study was to determine the long-term effects of perinatal iron deficiency and its treatment on hippocampal anatomy and neurochemistry in formerly iron-deficient young adult rats.

METHODS

Perinatal iron deficiency was induced using a low-iron diet during gestation and the first postnatal week in male rats. Hippocampal size was determined using volumetric magnetic resonance imaging at 8 weeks of age. Hippocampal neurochemical profile, consisting of 17 metabolites indexing neuronal and glial integrity, energy reserves, amino acids, and myelination, was quantified using high-field in vivo (1)H NMR spectroscopy at 9.4T (N = 11) and compared with iron-sufficient control group (N = 10).

RESULTS

The brain iron concentration was 56% lower than the control group at 7 days of age in the iron-deficient group, but had recovered completely at 8 weeks. The cross-sectional area of the hippocampus was decreased by 12% in the formerly iron-deficient group (P = 0.0002). The hippocampal neurochemical profile was altered: relative to the control group, creatine, lactate, N-acetylaspartylglutamate, and taurine concentrations were 6-29% lower, and glutamine concentration 18% higher in the formerly iron-deficient hippocampus (P < 0.05).

DISCUSSION

Perinatal iron deficiency was associated with reduced hippocampal size and altered neurochemistry in adulthood, despite correction of brain iron deficiency. The neurochemical changes suggest suppressed energy metabolism, neuronal activity, and plasticity in the formerly iron-deficient hippocampus. These anatomic and neurochemical changes are consistent with previous structural and behavioral studies demonstrating long-term hippocampal dysfunction following perinatal iron deficiency.

Early iron deficiency has brain and behavior effects consistent with dopaminergic dysfunction

To honor the late John Beard's many contributions regarding iron and dopamine biology, this review focuses on recent human studies that test specific hypotheses about effects of early iron deficiency on dopamine system functioning. Short- and long-term alterations associated with iron deficiency in infancy can be related to major dopamine pathways (mesocortical, mesolimbic, nigrostriatal, tuberohypophyseal). Children and young adults who had iron deficiency anemia in infancy show poorer inhibitory control and executive functioning as assessed by neurocognitive tasks where pharmacologic and neuroimaging studies implicate frontal-striatal circuits and the mesocortical dopamine pathway. Alterations in the mesolimbic pathway, where dopamine plays a major role in behavioral activation and inhibition, positive affect, and inherent reward, may help explain altered social-emotional behavior in iron-deficient infants, specifically wariness and hesitance, lack of positive affect, diminished social engagement, etc. Poorer motor sequencing and bimanual coordination and lower spontaneous eye blink rate in iron-deficient anemic infants are consistent with impaired function in the nigrostriatal pathway. Short- and long-term changes in serum prolactin point to dopamine dysfunction in the tuberohypophyseal pathway. These hypothesis-driven findings support the adverse effects of early iron deficiency on dopamine biology. Iron deficiency also has other effects, specifically on other neurotransmitters, myelination, dendritogenesis, neurometabolism in hippocampus and striatum, gene and protein profiles, and associated behaviors. The persistence of poorer cognitive, motor, affective, and sensory system functioning highlights the need to prevent iron deficiency in infancy and to find interventions that lessen the long-term effects of this widespread nutrient disorder.

The role of iron in learning and memory

Iron deficiency (ID) is the most common nutrient deficiency, affecting 2 billion people and 30% of pregnant women and their offspring. Early life ID affects at least 3 major neurobehavioral domains, including speed of processing, affect, and learning and memory, the latter being particularly prominent. The learning and memory deficits occur while the infants are iron deficient and persist despite iron repletion. The neural mechanisms underlying the short- and long-term deficits are being elucidated. Early ID alters the transcriptome, metabolome, structure, intracellular signaling pathways, and electrophysiology of the developing hippocampus, the brain region responsible for recognition learning and memory. Until recently, it was unclear whether these effects are directly due to a lack of iron interacting with important transcriptional, translational, or post-translational processes or to indirect effects such as hypoxia due to anemia or stress. Nonanemic genetic mouse models generated by conditionally altering expression of iron transport proteins specifically in hippocampal neurons in late gestation have led to a greater understanding of iron's role in learning and memory. The learning deficits in adulthood likely result from interactions between direct and indirect effects that contribute to abnormal hippocampal structure and plasticity.

Maternal iron supplementation attenuates the impact of perinatal copper deficiency but does not eliminate hypotriiodothyroninemia nor impaired sensorimotor development

Copper, iron and iodine/thyroid hormone (TH) deficiencies disrupt brain development. Neonatal Cu deficiency causes Fe deficiency and may impact thyroidal status. One purpose of these studies was to determine the impact of improved iron status following Cu deficiency by supplementing the diet with iron. Cu deficiency was produced in pregnant Holtzman [Experiment 1 (Exp. 1)] or Sprague-Dawley [Experiment 2 (Exp. 2)] rats using two different diets. In Exp. 2, dietary Fe content was increased from 35 to 75 mg/kg according to NRC guidelines for reproduction. Cu-deficient (CuD) Postnatal Day 24 (P24) rats from both experiments demonstrated lower hemoglobin, serum Fe and serum triiodothyronine (T3) concentrations. However, brain Fe was lower only in CuD P24 rats in Exp. 1. Hemoglobin and serum Fe were higher in Cu adequate (CuA) P24 rats from Exp. 2 compared to Exp. 1. Cu- and TH-deficient rats from Exp. 2 exhibited a similar sensorimotor functional deficit following 3 months of repletion. Results suggest that Cu deficiency may impact TH status independent of its impact on iron biology. Further research is needed to clarify the individual roles for Cu, Fe and TH in brain development.

Brain iron metabolism and its perturbation in neurological diseases

Metal ions are of particular importance in brain function, notably iron. A broad overview of iron metabolism and its homeostasis both at the cellular level (involving regulation at the level of mRNA translation) and the systemic level (involving the peptide 'hormone' hepcidin) is presented. The mechanisms of iron transport both across the blood-brain barrier and within the brain are then examined. The importance of iron in the developing foetus and in early life is underlined. We then review the growing corpus of evidence that many neurodegenerative diseases (NDs) are the consequence of dysregulation of brain iron homeostasis. This results in the production of reactive oxygen species, generating reactive aldehydes, which, together with further oxidative insults, causes oxidative modification of proteins, manifested by carbonyl formation. These misfolded and damaged proteins overwhelm the ubiquitin/proteasome system, accumulating the characteristic inclusion bodies found in many NDs. The involvement of iron in Alzheimer's disease and Parkinson's disease is then examined, with emphasis on recent data linking in particular interactions between iron homeostasis and key disease proteins. We conclude that there is overwhelming evidence for a direct involvement of iron in NDs.

Hippocampus specific iron deficiency alters competition and cooperation between developing memory systems

Iron deficiency (ID) is the most common gestational micronutrient deficiency in the world, targets the fetal hippocampus and striatum and results in long-term behavioral abnormalities. These structures primarily mediate spatial and procedural memory, respectively, in the rodent but have interconnections that result in competition or cooperation during cognitive tasks. We determined whether ID-induced impairment of one alters the function of the other by genetically inducing a 40% reduction of hippocampus iron content in late fetal life in mice and measuring dorsal striatal gene expression and metabolism and the behavioral balance between the two memory systems in adulthood. Slc11a2^hipp/hipp mice had similar striatum iron content, but 18% lower glucose and 44% lower lactate levels, a 30% higher phosphocreatine:creatine ratio, and reduced iron transporter gene expression compared to wild type (WT) littermates, implying reduced striatal metabolic function. Slc11a2^hipp/hipp mice had longer mean escape times on a cued task paradigm implying impaired procedural memory. Nevertheless, when hippocampal and striatal memory systems were placed in competition using a Morris Water Maze task that alternates spatial navigation and visual cued responses during training, and forces a choice between hippocampal and striatal strategies during probe trials, Slc11a2^hipp/hipp mice used the hippocampus-dependent response less often (25%) and the visual cued response more often (75%) compared to WT littermates that used both strategies approximately equally. Hippocampal ID not only reduces spatial recognition memory performance but also affects systems that support procedural memory, suggesting an altered balance between memory systems.

Effects of early malnutrition on mental system, metabolic syndrome, immunity and the gastrointestinal tract

The notion of how malnutrition early in life affects ontogenesis has evolved considerably since the mid-1960s. Since then, there have been many studies on the effects of early malnutrition. Nutritional and metabolic exposure during critical periods in early human and animal development may have long-term programming effects in adulthood. This is supported by evidence from epidemiological studies, numerous animal models and clinical intervention trials. In this paper, we review the effects of early malnutrition on cognitive function, metabolic syndrome, immunity and the gastrointestinal tract, as well as possible underlying mechanisms, and consider diarrhoeal disease and poor cognitive function as examples for understanding the interrelation of the harmful effects caused by early malnutrition. Previous studies on early malnutrition have mainly concentrated on humans and rats. Therefore, the main aim of the present review was to give animal scientists a clear understanding of the harmful effects of early malnutrition on animal growth and animal production, and to help identify appropriate feeding techniques to prevent early malnutrition.

Maternal iron deficiency alters essential fatty acid and eicosanoid metabolism and increases locomotion in adult guinea pig offspring

Iron deficiency (ID) is the most prevalent worldwide nutritional deficiency. Groups at risk of developing ID anemia are infants and pregnant women, even in industrialized countries. Our goal in this study was to evaluate the long-term consequences of maternal ID on the offspring's fatty acid and eicosanoid metabolism, behavior, and spatial memory. Female guinea pigs consumed iron-sufficient (IS) and -deficient (ID) diets for 14 d before mating and throughout pregnancy and lactation. Dietary iron restriction resulted in ID in pregnant females. On postnatal d 9, all offspring (ID and IS) were weaned to the IS diet and at 42 d, all offspring were iron replete. Locomotion was tested in pups on postnatal d 24 and 40 and spatial memory from d 25 to 40. Pups from the ID group were significantly more active in the open field at both times of testing, whereas spatial memory, tested in a Morris water maze, was comparable in both groups. On postnatal d 42, liver, RBC, and brain fatty acid composition were measured. Dihomogammalinolenic [20:3(n-6)], docosapentaenoic [22:5(n-3)], and docosahexaenoic [22:6(n-3)] acid contents were significantly higher in brain phospholipids of offspring born to ID dams. Prostaglandin E(2) and F(2alpha) concentrations were also significantly higher in brains of offspring born to ID dams. This demonstrates that moderate ID during gestation and lactation results in alterations of brain fatty acid and eicosanoid metabolism and perturbation in behavior in adult offspring.

Copper deficiency alters the neurochemical profile of developing rat brain

Copper deficiency is associated with impaired brain development and mitochondrial dysfunction. Perinatal copper deficiency was produced in Holtzman rats. In vivo proton NMR spectroscopy was used to quantify 18 cerebellar and hippocampal metabolites on postnatal day 21 (P21). Copper status was evaluated in male copper-adequate (CuA) and copper-deficient (CuD) brothers at P19 and at P23, 2 days following NMR experiments, by metal and in vitro metabolite data. Compared to CuA pups, CuD pups had lower ascorbate concentration in both brain regions, confirming prior HPLC data. Both regions of CuD rats also had lower N-acetylaspartate levels consistent with delayed development or impaired mitochondrial function similar to prior work demonstrating elevated lactate and citrate. For other metabolites, the P21 neurochemical profile of CuD rats was remarkably similar to CuA rats but uniquely different from iron-deficient or chronic hypoxia models. Further research is needed to determine the neurochemical consequences of copper deficiency.

The role of iron in neurocognitive development

In this article we present a review of the current literature relating iron and iron deficiency to psychological and neurobiological outcomes in both humans and experimental animals. In particular, we focus on the role of iron during gestation and infancy and the possible impact on neurobehavioral development in the short and long term. In the context of reviewing this literature, the following questions are addressed: (1) What are the neural mechanisms that are directly influenced by iron and iron deficiency? (2) Does iron play a true causal role in determining these outcomes? (3) Is there a sensitive period during which iron deficiency is most harmful?

Sleep and neurofunctions throughout child development: lasting effects of early iron deficiency

Iron-deficiency anemia (IDA) continues to be the most common single nutrient deficiency in the world. Infants are at particular risk due to rapid growth and limited dietary sources of iron. An estimated 20% to 25% of the world's infants have IDA, with at least as many having iron deficiency without anemia. High prevalence is found primarily in developing countries, but also among poor, minority, and immigrant groups in developed ones. Infants with IDA test lower in mental and motor development assessments and show affective differences. After iron therapy, follow-up studies point to long-lasting differences in several domains. Neurofunctional studies showed slower neural transmission in the auditory system despite 1 year of iron therapy in IDA infants; they still had slower transmission in both the auditory and visual systems at preschool age. Different motor activity patterning in all sleep-waking states and several differences in sleep states organization were reported. Persistent sleep and neurofunctional effects could contribute to reduced potential for optimal behavioral and cognitive outcomes in children with a history of IDA.

The role of iron in neurodevelopment: fetal iron deficiency and the developing hippocampus

Iron is a ubiquitous nutrient that is necessary for normal neurodevelopment. Gestational conditions that compromise fetal iron status include maternal iron deficiency, smoking, diabetes mellitus and hypertension. The iron-deficient neonate has altered recognition memory function and temperament while iron-deficient. The memory deficits persist even after iron repletion. Animal models demonstrate that early iron deficiency affects neuronal and glial energy metabolism, monoamine metabolism and myelination, consistent with behavioural findings in human infants. Of particular recent interest are genomic changes in transcripts coding for signal transduction, dendritic structure and energy metabolism induced by early iron deficiency that last well into adulthood in spite of iron treatment. Early iron sufficiency is critical for long-term neurological health.

Why iron deficiency is important in infant development

Infants who experience iron deficiency during the first 6-12 mo of life are likely to experience persistent effects of the deficiency that alter functioning in adulthood. A lack of sufficient iron intake may significantly delay the development of the central nervous system as a result of alterations in morphology, neurochemistry, and bioenergetics. Depending on the stage of development at the time of iron deficiency, there may be an opportunity to reverse adverse effects, but the success of repletion efforts appear to be time dependent. Publications in the past several years describe the emerging picture of the consequences of iron deficiency in both human and animal studies. The mechanisms for iron accumulation in the brain and perhaps redistribution are being understood. The data in human infants are consistent with altered myelination of white matter, changes in monoamine metabolism in striatum, and functioning of the hippocampus. Rodent studies also show effects of iron deficiency during gestation and lactation that persist into adulthood despite restoration of iron status at weaning. These studies indicate that gestation and early lactation are likely critical periods when iron deficiency will result in long-lasting damage.

Iron injection restores brain iron and hemoglobin deficits in perinatal copper-deficient rats

Copper (Cu) deficiency during perinatal development in rats is associated with anemia, lower plasma iron (Fe), and brain Fe. Experiments were conducted to inject Fe dextran into Cu-deficient (Cu-) rat pups to attempt to reverse these conditions. Previous work with older Cu- rats did not reverse anemia following Fe injection. Dams began Cu-adequate (Cu+) or Cu- dietary treatments starting at embryonic d 7 and lasting through weaning. In Expt. 1, pups from each dietary treatment were given a single dose of Fe, 20 mg Fe/kg, or saline (S) at postnatal d 11 (P11). Plasma Fe and hemoglobin were higher in the Fe-injected groups at P13. Brain Fe deficit and brain transferrin receptor enhancement were eliminated in the Cu- group injected with Fe compared with Cu-S pups, supporting an association between low plasma Fe and low brain Fe. In Expt. 2, Fe treatment was increased to 45 mg Fe/kg. Four injections were given between P5 and P18 (total dose, 5-7 mg Fe). At P20, Fe concentrations in 4 brain regions (cortex, cerebellum, medulla/pons, and hypothalamus) generally were higher in all groups than in Cu-S pups. At P25, impaired vibrissae-elicited foot placement was evident in Cu-S rats and was not improved by Fe injection. However, at P26, the brain Fe deficit in Cu-S pups was eliminated by Fe injection. Fe injections in Cu- pups raised plasma Fe, brain Fe, and hemoglobin but did not reverse low cytochrome c oxidase or abnormal striatal behavior.

Iron deficiency alters expression of genes implicated in Alzheimer disease pathogenesis

Neonatal brain iron deficiency occurs after insufficient maternal dietary iron intake, maternal hypertension, and maternal diabetes mellitus and results in short and long-term neurologic and behavioral deficits. Early iron deficiency affects the genomic profile of the developing hippocampus that persists despite iron repletion. The purpose of the present study was threefold: 1) quantitative PCR confirmation of our previous microarray results, demonstrating upregulation of a network of genes leading to beta-amyloid production and implicated in Alzheimer disease etiology in iron-deficient anemic rat pups at the time of hippocampal differentiation; 2) investigation of the potential contributions of iron deficiency anemia and iron treatment to this differential gene expression in the hippocampus; and 3) investigation of these genes over a developmental time course in a mouse model where iron deficiency is limited to hippocampus, is not accompanied by anemia and is not repletable. Quantitative PCR confirmed altered regulation in 6 of 7 Alzheimer-related genes (Apbb1, C1qa, Clu, App, Cst3, Fn1, Htatip) in iron-deficient rats relative to iron-sufficient controls at P15. Comparison of untreated to treated iron-deficient animals at this age suggested the strong role of iron deficiency, not treatment, in the upregulation of this gene network. The non-anemic hippocampal iron-deficient mouse demonstrated upregulation of all 7 genes in this pathway from P5 to P25. Our results suggest a role for neonatal iron deficiency in dysregulation of genes that may set the stage for long-term neurodegenerative disease and that this may occur through a histone modification mechanism.

Docosahexaenoic acid-dependent iron accumulation in oligodendroglia cells protects from hydrogen peroxide-induced damage

Iron, a transition metal and essential nutrient, is a typical pro-oxidant forming free radicals, lipid peroxides and causing cell damage when added at high (> or = 50 microM) concentrations to oligodendroglia-like OLN-93 cells that have been enriched for 3 days with 10 microM docosahexaenoic acid (DHA, 22 : 6 n-3). At low (5 microM) iron concentrations lipid peroxides were still formed, but cells turned resistant to 250 microM H2O2, a secondary genotoxic stress. This has been attributed most likely to a time-dependent (16 h preconditioning) increase of cellular antioxidant enzyme activities i.e., glutathione peroxidase (38%) and glutathione reductase (26%). DHA but not arachidonic acid (20 : 4 n-6) supplements induced 3-fold increase in gene expression of divalent metal transporter-1, a transporter protein presumably responsible for the increase in intracellular iron. Elevated iron levels triggered a transient scrambling of membrane lipid asymmetry as evident by an accelerated ethanolamine phosphoglyceride translocation to the outer cell surface. Ethanolamine phosphoglyceride reorientation is proposed to activate certain signaling cascades leading to changes in nuclear transcription, a reaction that could represent a mechanism of preconditioning. These findings may have important implications for understanding the interactive role of iron and DHA in nutritional deficiencies, losses of polyunsaturated fatty acids in the aging brain or excessive iron accumulation in degenerative disorders.

Iron deficiency and child development

Iron deficiency is widespread in infants and young children, especially in developing countries. Animal models provide convincing evidence that, despite iron repletion, iron deficiency during the brain growth spurt alters metabolism and neurotransmission, myelination, and gene and protein profiles. In the human, there is compelling evidence that 6- to 24-month-old infants with iron-deficiency anemia are at risk for poorer cognitive, motor, social-emotional, and neurophysiologic development in the short- and long-term outcome. In contrast to inconsistent developmental effects of iron therapy for iron-deficient infants, recent large, randomized trials of iron supplementation in developing countries uniformly show benefits of iron, especially on motor development and social-emotional behavior. These results indicate that adverse effects can be prevented and/or reversed with iron earlier in development or before iron deficiency becomes severe or chronic. New findings also point to the need for more attention to the developmental effects of prenatal iron deficiency.