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Iron is necessary for life but also a potent pro-oxidant implicated in the pathogenesis of age-related diseases. We sought to determine if iron levels change with age and by sex in various tissues from several commonly studied mouse strains. Brain, liver, heart, retina, and retinal pigment epithelium (RPE)/choroid were dissected from male and female mice of young adult (2-6 month old) and aged (16-19 month old) C57BL/6, DBA/2J, and BALB/c mice. Iron was quantified through a chromagen-based spectrophotometric method or through atomic absorption spectrophotometry for increased sensitivity. Brain, liver, and heart iron increased by 30-70% in aged vs. young adult groups of all strains, while retina and RPE/choroid iron had variable age-related changes. Significant gender differences were observed in BALB/c and DBA/2J strains. Males had as much as 2- to 3-fold more brain, RPE/choroid, and retinal iron, while females had as much as 2- to 3-fold more liver iron. There was no significant gender difference observed in heart iron. The different profiles of change between gender and among strains suggest that hormones and genetics influence iron regulation with aging. Future manipulation of iron levels in mice will test the role of iron in aging and disease, and the data reported herein will be essential in directing such manipulations.

Iron is one of the essential micronutrients, and as such, is required for growth, development, and normal cellular functioning. In contrast to some other micronutrients such as water-soluble vitamins, there is a significant danger of toxicity if excessive amounts of iron accumulate in the body. A finely tuned feedback control system functions to limit this excessive accumulation by limiting absorption of iron. This chapter will discuss systemic and brain iron homeostasis.

The iron status of African-American infants continues to be subject to debate. We characterized the iron status of 198 9-month-old inner-city infants (94% fed iron-fortified formula) using a comprehensive panel of measures and assessing lead and inflammation markers. The proportion with iron deficiency was calculated based on three approaches (> or = 2 abnormal iron measures with or without anemia for MCV model--NHANES II, ferritin model--NHANES III, or Sweden/Honduras study) and a promising new measure-body iron, calculated from ferritin and transferrin receptor (TfR). There were no sex differences for any iron measure. Hb < 110 g/l was observed in 25%; Hb < or = 105 g/l in 10.1%. Free erythrocyte protoporphyrin (FEP) values were elevated without elevated lead concentrations or an inflammatory response: mean FEP = 86.6 microg/dl red blood cells [75.5 micromol/mol heme]; 52.3% were > 80 microg/dl (1.42 micromol/l), almost half of which were accompanied by a second abnormal iron measure. The estimated prevalence of iron deficiency was 14.4, 5.3, and 2.5% for the MCV model, ferritin model, and Sweden/Honduras cutoffs, respectively, and 4.1% for body iron < 0 mg/kg. Regulation of iron storage is immature at < 1 year of age, making estimates of iron deficiency that depend on ferritin, including body iron, suspect in this age period. Thus, the "true" prevalence of iron deficiency could not be established with confidence due to major differences in the results, depending on the guidelines used. Functional indicators of poor iron status in young infants are urgently needed., ((c) 2006 Wiley-Liss, Inc.)

Iron accumulates in the Alzheimer's disease (AD) brain and is directly associated with beta-amyloid pathology. The proton transverse relaxation rate (R(2)) has a strong linear relationship with iron concentrations in healthy brain tissue; however, an independent test of this relationship has not been extended to AD brain tissue. In this study in vitro single spin-echo (SE) measurements were made on tissue samples from four human AD brains using a 4.7T MRI research scanner. R(2) values were calculated for 14 cortical and subcortical gray matter (GM) and white matter (WM) regions. Atomic absorption spectroscopy was used to measure iron concentrations in the corresponding excised brain regions. Significant positive linear correlations were observed between R(2) values and iron concentrations in GM regions assessed across individual tissue samples and data averaged by brain region. With the use of a predictive model for R(2), a threshold iron concentration of 55 microg Fe/g wet tissue was determined above which R(2) appears to be dominated by the affects of iron in AD brain tissue. High-field MRI may therefore be a useful research tool for assessing brain iron changes associated with AD.

Oxidative stress is believed to be important in physiological aging and age-related diseases. Iron is a potent pro-oxidant implicated in several age-related diseases. While serum ferritin, as an estimate of body stores of iron, has been shown to increase with age, few studies have directly addressed the effect of age on human neural tissue iron levels. We used atomic absorption spectrophotometry to assess quantitatively iron levels within the eye structures, retina and retinal pigment epithelium/choroid of normal human eyes of various ages and of both sexes. We found that retinal iron increases with age, similar to serum ferritin levels. Women had more retinal iron than men at all ages, suggesting that there may be gender-specific influences on iron regulation.

Several observations suggest that iron is an essential factor in myelination and oligodendrocyte biology. However, the specific role of iron in these processes remains to be elucidated. This role could be as an essential cofactor in metabolic processes or as a transcriptional or translational regulator. In this study, we used animals models each with a unique defect in iron availability, storage, or transfer to test the hypothesis that disruptions in these mechanisms affect myelinogenesis and myelin composition. Disruption of iron availability either by limiting dietary iron or by altering iron storage capacity resulted in a decrease in myelin proteins and lipids but not the iron content of myelin. Among the integral myelin proteins, proteolipid protein was most consistently affected, suggesting that limiting iron to oligodendrocytes results not only in hypomyelination but also in a decrease in myelin compaction. Mice deficient in transferrin must receive transferrin injections beginning at birth to remain viable, and these mice had increases in all of the myelin components and in the iron content of the myelin. This finding indicates that the loss of endogenous iron mobility in oligodendrocytes could be overcome by application of exogenous transferrin. Overall, the results of this study demonstrate how myelin composition can be affected by loss of iron homeostasis and reveal specific chronic changes in myelin composition that may affect behavior and attempts to rescue myelin deficits.

Thy-1 is a cell adhesion molecule that plays a regulatory role in the vesicular release of neurotransmitters. The objective of this study is to examine the relationship between iron status and Thy1 expression in neuronal systems of varying complexity. Pheochromocytoma cell (PC12) cells were used to explore whether there was a direct relation between cellular iron status and Thy1 expression. Iron chelation significantly decreased expression of Thy1 in PC12 cells in a dose and time dependent manner. Transferrin receptor expression was increased with iron chelation demonstrating that a global decrease in protein synthesis could not account for the Thy1 changes. We also examined brain homogenates from adult rats that were nursed by dams on an iron deficient (ID) diet and found a significant decrease in Thy1 compared to control rats. Finally, the substantia nigra from individuals with Restless Legs Syndrome reportedly has lower than normal amounts of iron. Therefore, we examined this brain region from individuals with the clinical diagnosis of primary Restless Legs syndrome (RLS) and found the concentration of Thy1 was less than half that of controls. The results of these studies support the novel concept that there is a relationship between Thy1 and iron and point to a novel mechanism by which iron deficiency can affect brain function. They also indicate a possible mechanism by which iron deficiency compromises dopaminergic transmission in RLS, providing a potentially important link between decreased brain iron and the responsiveness to levodopa and iron supplementation treatment in RLS.

The distribution of brain iron is heterogeneous, but the mechanism by which these regional differences are achieved and maintained is unknown. In this study, the authors test two hypotheses related to brain iron transport. The first is that there is regional variability in the profile of proteins associated with iron transport and storage in the brain microvasculature. The second hypothesis is that the iron status of the brain will dictate the response of the protein profile in the microvasculature to changes in systemic iron status. The profile analysis consists of transferrin (iron transport), ferritin (iron storage), transferrin receptor (iron uptake), and divalent metal transporter 1 (release of iron from endosomes). An additional protein involved in cellular iron efflux, ferroportin, was not detected in brain microvasculature. The results show that there are significantly higher levels of these proteins in the microvasculature from each area of the brain compared to a whole brain homogenate, but no regional differences within the microvasculature. The levels of ferritin observed in the microvasculature indicate that the microvascular endothelial cells have significant iron storage capacity. There are no significant changes in the regional protein profiles in response to systemic iron manipulation when brain iron status was normal. In contrast, in Belgrade rats, whose brain is iron deficient, the expression of both divalent metal transporter 1 and transferrin receptor was increased compared with control in almost all brain regions examined, but not transferrin or ferritin. These findings indicate that regional brain iron heterogeneity is not maintained by differences in microvascular iron-management protein levels. The results also indicate that brain iron status dictates the response of the microvascular protein profile to systemic iron manipulation.

Iron deficiency anemia in early life is related to altered behavioral and neural development. Studies in human infants suggest that this is an irreversible effect that may be related to changes in chemistry of neurotransmitters, organization and morphology of neuronal networks, and neurobiology of myelination. The acquisition of iron by the brain is an age-related and brain-region-dependent process with tightly controlled rates of movement of iron across the blood-brain barrier. Dopamine receptors and transporters are altered as are behaviors related to this neurotransmitter. The growing body of evidence suggests that brain iron deficiency in early life has multiple consequences in neurochemistry and neurobiology.

Several neurodegenerative disorders such as Parkinson's Disease (PD) and Alzheimer's Disease (AD) are associated with elevated brain iron accumulation relative to the amount of ferritin, the intracellular iron storage protein. The accumulation of more iron than can be adequately stored in ferritin creates an environment of oxidative stress. We developed a heavy chain (H) ferritin null mutant in an attempt to mimic the iron milieu of the brain in AD and PD. Animals homozygous for the mutation die in utero but the heterozygotes (+/-) are viable. We examined heterozygous and wild-type (wt) mice between 6 and 8 months of age. Macroscopically, the brains of +/- mice were well formed and did not differ from control brains. There was no evidence of histopathology in the brains of the heterozygous mice. Iron levels in the brain of the +/- and wild-type (+/+) mice were similar, but +/- mice had less than half the levels of H-ferritin. The other iron management proteins transferrin, transferrin receptor, light chain ferritin, Divalent Metal Transporter 1, ceruloplasmin, were increased in the +/- mice compared to +/+ mice. The relative amounts of these proteins in relation to the iron concentration are similar to that found in AD and PD. Thus, we hypothesized that the brains of the heterozygote mice should have an increase in indices of oxidative stress. In support of this hypothesis, there was a decrease in total superoxide dismutase (SOD) activity in the heterozygotes coupled with an increase in oxidatively modified proteins. In addition, apoptotic markers Bax and caspase-3 were detected in neurons of the +/- mice but not in the wt. Thus, we have developed a mouse model that mimics the protein profile for iron management seen in AD and PD that also shows evidence of oxidative stress. These results suggest that this mouse may be a model to determine the role of iron mismanagement in neurodegenerative disorders and for testing antioxidant therapeutic strategies., (Copyright 2002 Wiley-Liss, Inc.)

Quantitative genetic analysis of hepatic and splenic iron levels in recombinant inbred mice yielded a quantitative trait locus that was found to coincide with the genomic locale encompassing the tumor necrosis factor receptor 2 gene (Tnfr2). When fed an iron-enriched diet, mice nullizygous with respect to Tnfr2, but not the Tnfr1 gene, showed a significant increase in splenic non-heme iron levels. This result contrasted with mice deficient in the hemochromatosis protein, HFE, which demonstrated a significant increase in normally high hepatic iron levels, but no change in splenic iron, when fed an iron-enriched chow. Both Tnfr2 knockout and HFE knockout mice fed an iron-enriched diet failed to demonstrate intestinal epithelial cell iron following the application of the Perls' stain, as compared to both Tnfr1 knockout and normal control mice. Moreover, intestinal intraepithelial lymphocytes (IELs) isolated from HFE knockout mice did not show an increase in TNF expression following challenge with the iron-enriched diet, in contrast to normal controls. These results suggest that HFE and TNFR2 are both involved in regulating iron deposition in tissues and that the regulation occurs at the level of the intestine through IEL-orchestrated production of TNF following the binding to TNFR2. These data suggest that HFE and TNFR2 may contribute to a common pathway of the iron stores regulator insuring the controlled efflux of gut iron.

Iron accumulation in the brain occurs in a number of neurodegenerative diseases. Two new iron transport proteins have been identified that may help elucidate the mechanism of abnormal iron accumulation. The Divalent Metal Transporter 1 (DMT1), is responsible for iron uptake from the gut and transport from endosomes. The Metal Transport Protein 1 (MTP1) promotes iron export. In this study we determined the cellular and regional expression of these two transporters in the brains of normal adult and Belgrade rats. Belgrade rats have a defect in DMT1 that is associated with lower levels of iron in the brain. In the normal rat, DMT1 expression is highest in neurons in the striatum, cerebellum, thalamus, ependymal cells lining the third ventricle, and vascular cells throughout the brain. The staining in the ependymal cells and endothelial cells suggests that DMT1 has an important role in iron transport into the brain. In Belgrade rats, there is generalized decrease in immunodetectable DMT1 compared to normal rats except in the ependymal cells. This decrease in immunoreactivity, however, was absent on immunoblots. The immunoblot analysis indicates that this protein did not upregulate to compensate for the chronic defect in iron transport. MTP1 staining is found in most brain regions. MTP1 expression in the brain is robust in pyramidal neurons of the cerebral cortex but is not detected in the vascular endothelial cells and ependymal cells. MTP1 staining in Belgrade rats was decreased compared to normal, but similar to DMT1 this decrease was not corroborated by immunoblotting. These results indicate that DMT1 and MTP1 are involved in brain iron transport and this involvement is regionally and cellularly specific., (Copyright 2001 Wiley-Liss, Inc.)

Iron regulatory proteins (IRPs) are proteins involved in the regulation of intracellular iron homeostasis that bind to specific mRNA structures termed iron responsive elements (IREs). Because the target mRNAs for the IRPs are both cytosolic and membrane associated, we hypothesize that movement of IRPs between the cytosolic and the membrane associated subcellular fractions occurs in response to intracellular iron changes. We tested this hypothesis in a cell culture model, using mouse fibroblast cells (NIH 3T3) and macrophage cells (J774), and in a rat model of early iron deficiency and excess. This presented the first opportunity to examine IRP binding activity in rat brain during states of dietary iron deficiency and excess. Binding activity for IRPs was demonstrated in both membrane and cytosolic fractions in the cell lines and the rat brain homogenates. Although IRP binding activity is predominantly located in the cytosol (90%), there was increased IRP/IRE binding activity in both cytosolic and membrane fractions when the cells were treated with deferoxamine, and decreased binding activity after treatment with iron. In the rat study, brain cortex, hippocampus and striatum homogenates had more IRP binding activity in iron-deficient rats and less in iron-supplemented rats in a region- and time-specific manner. The intracellular distribution of IRPs also changed between the cytosolic and membrane fractions of the brain homogenates in conjunction with changes in iron. These in vivo studies are consistent with the cell culture analyses showing intracellular redistribution of IRPs as a function of iron status. The results of these experiments extend our understanding of cytoplasmic mRNA binding protein activity and raise questions regarding the mechanism by which mRNA binding proteins can locate their target mRNAs within cells. The elucidation of this mechanism will have a significant impact on our understanding of eukaryotic gene regulation.

Objective: To examine the effects of resistance training on hematological and selected indices of iron status in 17 women aged 54-71 years and 18 men aged 56-69 years., Design: Tests and evaluations were done before and after all subjects participated in a resistance-training program twice weekly for 12 weeks., Results: The resistance training was effective as evidenced by increases in skeletal muscle strength of 20 +/- 9% and 23 +/- 13% for the men and women, respectively. Hematological parameters and serum iron concentrations were within normal clinical ranges and were unchanged by resistance training for both the men and the women. Total iron binding capacity (TIBC) and transferrin saturation were also unaffected by resistance training in the women but were significantly affected in the men. The men showed a decreased TIBC (p < .0001) and an increased transferrin saturation (p = .050). Serum ferritin concentrations decreased significantly in the women (p = .041) but were unchanged in the men. Transferrin receptor concentrations were unaffected by resistance training in the women but increased significantly in the men (p = .030)., Conclusions: With resistance training, iron status of older men and women changes in a sex specific way.

The estimated prevalence of iron deficiency in the world suggests that there should be widespread negative consequences of this nutrient deficiency in both developed and developing countries. In considering the reality of these estimates, the Belmont Conference seeks to reconsider the accepted relationships of iron status to physiological, biochemical and neurological outcomes. This review focuses on the biological processes that we believe are the basis for alterations in the immune system, neural systems, and energy metabolism and exercise. The strength of evidence is considered in each of the domains and the large gaps in knowledge of basic biology or iron-dependent processes are identified. Iron is both an essential nutrient and a potential toxicant to cells; it requires a highly sophisticated and complex set of regulatory approaches to meet the demands of cells as well as prevent excess accumulation. It is hoped that this review of the more basic aspects of the biology of iron will set the stage for subsequent in-depth reviews of the relationship of iron to morbidity, mortality and functioning of iron-deficient individuals and populations.

Iron deficiency in children is associated with retardation in growth and cognitive development, and the effects on cognition may be irreversible, even with treatment. Excessive iron has also been associated with neurological disease, especially in reference to the increased iron content in the brains of Alzheimer's disease and Parkinson's disease patients. This study evaluated the effects of dietary iron deficiency and excess iron on physical activity in rats. The animal model used is developmentally sensitive and permits control of the timing as well as the duration of the nutritional insult. Hence, to study the effects of early, late and long-term iron deficiency or excess iron (supplementation), rats were either made iron deficient or supplemented on postnatal day (PND) 10-21, PND 21-35 and PND 10-35. Some iron-deficient rats were iron repleted between PND 21-35. Different measures of motor activity were taken at PND 14, 17, 20, 27 and 34. Iron-deficient and iron-supplemented rats showed decreased activity and stereotypic behavior; this was apparent for any onset and duration of the nutritional insult. Recovery from iron deficiency did not normalize these functional variables, showing that the deleterious effects of early iron deficiency persist despite subsequent adequate treatment. This study demonstrates that iron deficiency in early life leads to irreversible behavioral changes. The biological bases for these behavioral alterations are not readily apparent, because iron therapy rapidly reverses the iron losses in all brain regions.

In the context of a larger study examining the interaction of vitamin A (VA) status and age on immune function, we examined age-related changes in hematologic and iron status variables in male Lewis rats. Animals were fed a nutritionally adequate purified diet containing either 0.35 (marginal), 4.0 (control) or 50 (supplemented) mg retinol equivalents (as retinyl palmitate) per kg of diet from the time of weaning until killing at 8-10 (middle-aged) or 20-22 (old) mo of age. Neither VA nor VA and age interaction effects were significant for most iron variables examined. After controlling for body weight, old rats had significantly lower hemoglobin, hematocrit and plasma iron than middle-aged rats. This decrease in hematologic and transport iron variables was not accompanied by a shift of iron into other storage compartments. Old rats also had significantly lower total iron content and iron concentration in liver, spleen and bone marrow. Hemosiderin iron in marrow smears correlated significantly (r = 0.43-0.76, P: < 0.05) with chemical estimates of iron in storage, transport and functional pools. Old rats also tended to have less stained iron in femur marrow smears. Thus, body iron in functional, transport and storage compartments, namely the liver, spleen and bone marrow, were significantly lower in old than in middle-aged rats. Although iron stores and status are usually considered to increase with advancing age, our data show a consistent pattern of lower hematologic and storage iron variables in old than in middle-aged Lewis rats. Future research is indicated to understand the biology and functional consequences of the observed age-associated decline in body iron.

The prevalence of iron deficiency anemia is likely to be higher in athletic populations and groups, especially in younger female athletes, than in healthy sedentary individuals. In anemic individuals, iron deficiency often not only decreases athletic performance but also impairs immune function and leads to other physiologic dysfunction. Although it is likely that dietary choices explain much of a negative iron balance, evidence also exists for increased rates of red cell iron and whole-body iron turnover. Other explanations of decreased absorption and increased sweat or urine losses are unlikely. The young female athlete may want to consider use of low-dose iron supplements under medical and dietary supervision to prevent a decline in iron status during training.

The rat has been widely used as a model for the study of iron deficiency (ID), but the differences in the timing of development of humans and rats must be taken into account to derive appropriate conclusions from the animal model. This study was designed to evaluate the effects of dietary ID and iron excess on rat brain iron and the iron metabolism proteins, transferrin (Tf), transferrin receptor (TfR) and ferritin. The experimental design is developmentally sensitive and permits control of the timing as well as the duration of the nutritional insult. Iron-deficient and iron-supplemented (SU) rats between postnatal day (PND) 10 and 21, PND 21 and 35 and PND 10 and 35 were used to study the effects of early, late, and long-term iron deficiency and supplementation. Some ID rats were iron repleted between PND 21 and 35. These experiments demonstrated several new findings: 1) Early ID/SU (PND 10-21) altered brain iron, TfR, Tf and ferritin concentration in many regions different from those observed in the later period (PND 21-35). 2) Two weeks of iron repletion were adequate for correcting the overall Fe concentration of the brain and of individual brain regions, although larger amounts of iron were necessary to fully normalize iron and its regulatory proteins. 3) Long-term ID/SU resulted accordingly in the continued decrease or increase in brain iron concentration in some brain regions and not others. In conclusion, brain regions regulate their iron concentration in response to local needs when faced with alterations in systemic iron delivery.

Hypotransferrinemia (hpx/hpx) is a genetic defect in mice resulting in <1% of normal plasma transferrin (Tf) concentrations; heterozygotes for this mutation (+/hpx) have low circulating Tf concentrations. These mice provide a unique opportunity to examine the role of Tf in Fe and Mn transport in the brain. Twenty weanling wild-type BALB/cJ mice, 15 +/hpx mice, and 12 hpx/hpx mice of both sexes were injected i.v. with either 54MnCl(2) or 59FeCl(3) either 1 h or 1 week before killing at 12 weeks of age. Total brain counts of 54Mn and 59Fe were measured, and regional brain distributions were assessed by autoradiography. Hypotransferrinemia did not affect total brain Mn uptake. However, 1 week after i.v. injection, hpx/hpx mice had less 54Mn in forebrain structures including cerebral cortex, corpus callosum, striatum, and substantia nigra. The +/hpx mice had the highest total brain 59Fe accumulation 1 h after i.v. injection. A striking effect of regional distribution of 59Fe was noted 1 week after injection; in hpx/hpx mice, 59Fe was located primarily in choroid plexus, whereas in +/+ and +/hpx mice 59Fe was widely distributed, with relatively high amounts in cerebral cortex and cerebellum. We interpret these data to mean that Tf is necessary for the transport of Fe but not Mn across the blood-brain barrier, and that there is a Tf-independent uptake mechanism for iron in the choroid plexus. Additionally, these data suggest that endogenous synthesis of Tf is necessary for Fe transport from the choroid plexus.

The metals iron (Fe) and manganese (Mn) are essential for normal functioning of the brain. This review focuses on recent developments in the literature pertaining to Fe and Mn transport. These metals are treated together because they appear to share several transport mechanisms. In addition, several neurological diseases such as Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease are all associated with Fe mismanagement in the brain, particularly in the striatum and basal ganglia. Similarly, Mn accumulation in brain also appears to target the same brain regions. Therefore, stringent regulation of the concentration of these metals in the brain is essential. The homeostatic mechanisms for these metals must be understood in order to design neurotoxicity prevention strategies., (Copyright 1999 Wiley-Liss, Inc.)

Objectives: To stimulate novel sustainable solutions to the problem of the nutritional iron deficiency, we asked: How does Nature insure proper iron nutrition of embryos and neonatal animals? Estimates of iron deficiency world-wide are 30% of the population, with women and children at the greatest risk. Recent studies linking iron deficiency with impeded cognitive development emphasizes the enormity of the impact of iron deficiency. Sustainable solutions to the problem of dietary iron deficiency have been elusive., Results: Data for storage iron was examined in seeds, developing plants, embryos and developing animals. In all cases, the common source of stored iron for development was ferritin. The protein component of ferritin concentrates iron billions of times above the solubility of the free metal ion. High conservation of ferritin sequences in bacteria, plants and animals and the specificity of ferritin bioavailability either added extrinsically or intrinsically enriched in a selected soybean cultivar, showed high efficacy in curing dietary iron deficiency in the rat model. Older data on ferritin were reevaluated in light of contemporary knowledge., Conclusions: Enhancement of natural seed ferritin content by biotechnology and breeding has the potential for a sustainable solution to the problem of global dietary iron deficiency.

Chromium competes with iron for binding to transferrin, and high-dose chromium supplementation has been hypothesized to adversely affect iron status. This study examined the effects of chromium picolinate supplementation on hematologic indexes and selected indexes of iron status in 18 men aged 56-69 y who participated in an introductory resistive training program. The men were randomly assigned (double-blind design) to groups (n = 9) that consumed either 17.8 mumol Cr/d (924 micrograms Cr/d) as chromium picolinate or a low-chromium placebo for 12 wk while engaging in resistive training twice weekly (3 sets of 8-12 repetitions at 80% of one repetition maximum for 5 exercises). Hematocrit, hemoglobin, red blood cell (erythrocyte) count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, red blood cell distribution width, platelet count, and mean platelet volume were within normal clinical ranges and were unchanged by either chromium picolinate supplementation or resistive training. Resistive training decreased total-iron-binding capacity from 38.4 +/- 9.3 to 27.3 +/- 5.6 mumol/L (P < 0.0001) and increased transferrin saturation from 35.7 +/- 16.3% to 45.4 +/- 16.9% (P = 0.050). Chromium picolinate supplementation did not influence these responses. Serum iron concentrations and serum ferritin concentrations were unchanged by either resistive training or chromium picolinate supplementation. These data suggest that high-dose chromium picolinate supplementation for 12 wk did not influence hematologic indexes or indexes of iron metabolism or status in older men. The decrease in total-iron-binding capacity and increase in transferrin saturation (%) with resistive training are largely opposite to changes associated with iron depletion and suggest a novel effect of resistive training on iron transport.

For several decades, very-low-energy diets (VLEDs) have been used by obese individuals to achieve weight loss. During the weight loss, patients often have dramatic drops in circulating thyroid hormone concentrations and experience cold intolerance. Because poor iron status is known to alter thermogenesis, we investigated the possibility that iron intake interacts with energy intake during weight loss in obese individuals. The effects on indicators of iron and thyroid status of increasing the iron content of a VLED from 18 to 27 mg/d during 12 wk of a VLED were compared with the effects on the same indicators of increasing energy intake from 1752 kJ(420 kcal) to 3347 kJ(800 kcal)/d. Although all VLED groups initially had 30% declines in plasma transferrin saturation, increases in plasma ferritin concentrations, and decreases in plasma thyroid hormone concentrations, patients who received iron supplementation had significantly higher circulating concentrations of triiodothyronine and thyroxine at the end of the VLED than did patients who received only the recommended dietary allowance of iron. The patients who received iron supplementation also had a more rapid return of iron indicators to normal values over the course of the VLED. The transitory fall in iron delivery to bone marrow was not associated with anemia. These data suggest that higher thyroid hormone concentrations can be maintained during VLEDs that provide higher iron intakes.

Iron dysregulation in the brain is thought to contribute to the oxidative damage seen in neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. A role for iron in the oxidative stress thought to contribute to normal ageing is less certain. To better characterize the role of iron in normal ageing, the concentrations of iron, transferrin, ferritin, and protein carbonyl groups are measured in nine separate regions of Fischer 344 rats. The largest (approximately 30%) age-related increases in brain iron concentration are seen in the temporal cortex, medial septum, and cerebellum. Ferritin concentration in these same brain regions increases 50 to 250% with age, while protein carbonyl concentration is only -27 to +4%, of young rats. These results indicate that an increase in the major iron-binding protein ferritin compensates for any age-related increase in iron concentration, and suggest that the increased ferritin is cytoprotective, serving to prevent the accumulation of protein carbonyl groups (a principal product of metal-catalysed oxidation of proteins).

Poor temperature regulation in both human and animal models has been associated with iron deficiency anemia. The review examines the evidence for causality in both animals and humans, as well as provides an overview of temperature regulation in homeotherms. A number of investigations conclude that anemia is a central component of the inability of iron-deficient individuals to temperature regulate when they are cold stressed. This is apparently due to effects both on heat production and heat loss rates. The former is related to poor thyroid function in iron deficiency and the latter to the competing demands for tissue oxygenation vs. decreased flood flow to minimize heat losses to the environment. Future research needs are outlined that require integration of endocrinology, physiology, and nutrition disciplines.

Despite its abundance in the earth's crust, iron deficiency is a serious health issue in many parts of the world. Although fundamental observations about iron metabolism and the significance of iron nutriture were first noted some time ago, the molecular mechanisms involved in iron metabolism are just now being defined.

Myelination is an essential component of normal development in the brain. Thus, the factors which influence the onset of myelination need to be identified and monitored during development to insure adequate myelination. These factors may also play a role in remyelination attempts which occur as a result of demyelinating diseases. One factor known to be involved in myelination is iron. In this study, the cellular deposition of iron and the intracellular iron storage protein ferritin are examined in the brains of 1-month-old piglets. Ferritin consists of 2 subunits (H and L chains) which occur in different ratios in different organs. The subunits are functionally distinct so their pattern of expression at the cellular level reveals information about the iron requirement of the cell and utilization versus storage. The H subunit of ferritin is expressed in abundance in oligodendrocytes within white-matter tracts whereas the L subunit in this region is found only in endothelial cells of blood vessels. H-ferritin-positive cells occur in clearly defined patches which are scattered throughout the white-matter tracts. The cellular distribution of iron is identical to that of H ferritin. H-ferritin-positive cells are identified as oligodendrocytes on the basis of immunofluorescent colocalization with CNPase. Also, some of the H-ferritin-positive cells are positive for myelin basic protein. However, the distribution of CNPase-positive cells is more even in the white matter than the patches of H-ferritin/iron-positive cells. The relationship between H-ferritin- and CNPase-positive cells indicates that the former are oligodendrocytes, but also reveals a subset of oligodendrocytes in the white matter. The results of this study provide insight into how the intracellular iron is managed in oligodendrocytes. The factors which initiate iron uptake and ferritin expression in a select population of oligodendrocytes, and the relationship of this select population to myelinogenesis and myelin maintenance, have yet to be identified.

The impact of long-term (6-month) moderate exercise on the iron status of previously sedentary women was determined by randomly assigning 62 college-age women into one of the following four groups: 1) 50 mg.d-1 iron supplement, low iron diet (N = 16); 2) Placebo, free choice diet (N = 13); 3) Meat supplement to achieve 15 mg.d-1 iron intake (N = 13); and 4) Control, free choice diet (N = 20). All groups except the Control group exercised 3 d.wk-1 at 60%-75% of their heart rate reserve. VO2max was measured at baseline and week 24. Blood was sampled at baseline and every 4 wk thereafter for 24 wk to measure iron status and to elucidate the causes for alterations in iron status. Subjects had depleted iron stores throughout the study as indicated by their serum ferritin levels (< 15 ng.ml-1). Serum iron, total iron binding capacity and transferrin saturation were not compromised with exercise. Mean hemoglobin level in the Placebo/Ex group was significantly (P < 0.05) lower than the 50 Fe/Ex and the Meat/Ex groups by week 24. However, changes in serum albumin, haptoglobin, and erythropoietin data from the study cannot explain these changes.

To study the iron, transferrin, and ferritin distribution at subcellular levels in response to acute dietary iron deficiency, we tested the hypothesis that early post-weaning iron deficiency can change iron and iron regulatory protein concentrations in rat brain. Male Sprague-Dawley rats were fed diets containing either 2 or 35 micrograms iron/g for 2, 3 or 4 wk starting at 21 d of age. Brain iron, transferrin and ferritin concentrations in cytosolic and microsomal fractions of either whole brain or pons and cerebellum were then determined. After 14 d of dietary iron restriction, brain iron concentrations were 50% lower in the microsomal fraction and 30% lower in cytosol compared with controls. Brain cytosolic transferrin concentration almost doubled in the same animals. Brain ferritin concentration in fractions from rats fed the iron-deficient diet for 14 d was lower than in controls, but then remained fairly constant. Absolute brain weight and total brain protein contents were unaffected by iron restriction. This study extends previous research by demonstrating that the brain responds to changes in body iron status with a change in transferrin concentration. If the dietary restriction is quite severe, this adaptation is insufficient. This study also notes that brain ferritin decreases with decreasing body iron status, though it was less responsive than nonheme iron in liver. The concept that iron enters the brain through a highly regulated endocytotic process at the blood brain barrier, that undoubtedly involves the regulation of transferrin receptors in capillary endothelial cell, is supported by our observation of elevated transferrin concentrations in brain of iron-deficient rats.

To differentiate iron-deficiency anemia and anemia associated with chronic inflammatory diseases in elderly women, subsets of laboratory, dietary, and functional assessment variables were obtained by using discriminant analysis. Fifty-one subjects (70-79 y of age) were classified into one of four groups on the basis of the presence of iron deficiency and chronic inflammatory disease. Iron deficiency was defined on the basis of a significant response in hemoglobin concentration after iron supplementation. The discriminating subset of laboratory tests consisted of measures for serum ferritin, plasma transferrin receptors, and erythrocyte sedimentation rate. The discriminant function classified subjects into iron-deficient, anemia of chronic disease, or a category in which the two coexist, with an error rate of 18.6%. The addition of other variables (dietary iron and functional assessment information) did not appreciably improve the classification. The results of these three key laboratory tests may help to identify functional iron deficiency in the presence of chronic inflammation.

We examined changes in iron status in 25 female varsity collegiate swimmers over the course of a competitive season via weekly capillary blood sampling. We also studied the effectiveness of moderate iron supplementation (39 mg/day) in preventing expected changes in iron status via a double-blinded crossover design. On entry into the study, 17 of the swimmers had depleted iron stores (plasma ferritin < 12 micrograms/L) and 5 were anemic (Hb < 120 g/L). After 5 wk of placebo treatment, hemoglobin decreased (> or = 6 g/L) in 44% and increased in 12% of the subjects. After 5 wk of iron supplementation, hemoglobin decreased in 16% and increased in 24% of the subjects. Likewise, after placebo treatment, plasma ferritin decreased (> or = 5 micrograms/L) in 24% and increased in 4% of the subjects, whereas iron supplementation resulted in decreases in 4% and increases in 68% of the subjects. In the absence of iron supplementation, hemoglobin levels decreased despite mean dietary iron intakes of 16.3 mg/day. These results show that moderate iron supplementation is effective in preventing decline in the iron status of female collegiate swimmers during a competitive season, but a higher dose of iron may be necessary to reverse their iron-deficient state.

This review has a focus on the distribution and function of iron in human brain and appropriate animal models. Data are presented on the consequences of abnormalities of iron status with regard to neural development, neurotransmitter metabolism, and cognition.

The location and function of iron in the central nervous system are reviewed with particular emphasis on human biology. Iron is distributed to different cell types in the brain in a heterogeneous fashion through the action of transferrin, transferrin receptors, and the metabolic needs of those cells. The function of this iron and its storage is documented in states of growth and development as well as during pathological states associated with aging. The information relating this biology to current observations of attention deficits in iron-deficient humans is also reviewed.

A recent prospective three-year follow-up study of 1931 men in Finland demonstrated a significant 2.2-fold greater risk of acute myocardial infarct in 42- to 60-year-old men who had serum ferritin concentrations above 200 micrograms/dL. However, the mean plasma ferritin concentration in this population was high and the prevalence of hemochromatosis was unknown; these issues mitigate the suggestion that high-normal iron stores leads to heart disease.

Day-to-day variability in biochemical indicators of iron status in well-hydrated and healthy women 70-79 y old (n = 10) was determined. Venous blood was collected on 4 nonconsecutive days during a 2-wk period. Analytical (sigma 2 rep) and biological (sigma 2 fd) variance components were computed based on a previously established scheme in younger adults. These two variance components were summed to obtain the total day-to-day variability (sigma 2 fd). Our results indicate that biological variation contributed most to the intraindividual variation. We calculated that sampling once for most iron indexes and twice for plasma transferrin receptors in elderly individuals is adequate to accurately determine these indexes whereas serum iron and transferrin saturation, indexes with high CVfd, require seven and eight measurements, respectively. These data, compared with previously published data in younger adults, demonstrate that aging is associated with a decreased variation in some indexes of iron status such as serum ferritin.

It is well established that iron, which is of considerable importance for normal neurological function, is highly regulated in all organ systems. However, until recently, iron regulation in the nervous system has received little attention. This study quantitatively compares the levels of the major iron-regulatory proteins, transferrin and ferritin, and iron itself in three cerebral cortical regions of the human brain from material collected at autopsy. Three groups were studied: 1) normal adult (under 65 yr of age), 2) aged (greater than 65), and 3) Alzheimer's disease. Normally, transferrin is more abundant in white matter than in gray matter. Ferritin is approximately 10x more abundant than transferrin throughout the brain regions examined and is evenly distributed, as is iron, in the gray and white matter. In Alzheimer's disease transferrin is consistently decreased particularly in the white matter of the various cerebral cortical regions examined whereas the iron and ferritin changes are inconsistent. The observations in this study are consistent with our general hypothesis that iron homeostasis is disrupted in the aging brain and the alterations in iron-regulatory proteins are exacerbated in Alzheimer's disease. The decrease in transferrin levels could indicate a decreased mobility and subsequent utilization of iron in the brain. Such a decrease in iron availability could play a significant role in neuronal degeneration and increased peroxidative damage known to occur in Alzheimer's disease.

We evaluated the day-to-day variation of four iron-status indices: hemoglobin (Hb), hematocrit (Hct), plasma ferritin (PF), and plasma iron (PI). Finger-prick blood samples were collected for 31 consecutive days in 20 healthy men and women. Replicate (sigma 2rep) and day-to-day (sigma 2day) variance components were estimated. Day-to-day variation in the iron-status measures was similar between men and women except for PF, for which the variation was greater in women. The CVs for a single future determination for Hb, Hct, PF, and PI were 4.6%, 3.0%, 15.2%, and 26.7% for males and 4.4%, 3.2%, 26.8%, and 29.0% for females, respectively. Three to 10 independent measurements are required to accurately determine PF and PI whereas one is adequate for Hb and Hct. Thus, day-to-day biological variation is a major component of the variability in these iron-status indicators and must be considered when assessing iron status.

Iron bioavailability in a variety of legumes was determined by radioisotopic measurements of iron absorption in human subjects. Soybeans, black beans, lentils, mung beans, and split peas were prepared as soups, labeled by the extrinsic tag method, and served to fasting subjects. Mean percentage absorption was uniformly low, ranging from 0.84 to 1.91%. Differences in absorption between the means were not statistically significant. The results indicate that these five commonly eaten legumes are all poor sources of dietary iron.

Dual radioiron tags were used to measure both heme and nonheme iron absorption simultaneously from meat-containing meals in 76 healthy male volunteers. Partial substitution of beef with soy flour reduced the availability of nonheme iron but improved the percentage absorption of heme iron significantly (27 to 59% rise). In contradistinction three other powerful inhibitors of nonheme iron absorption, bran, tea, and desferrioxamine, had no appreciable effect on heme. Ascorbic acid (100 mg and 1000 mg in separate experiments) improved nonheme iron uptake markedly but also failed to alter the assimilation of heme. These studies demonstrate that the deleterious effects on iron nutrition of substituting soy protein for beef are partially offset by improved availability of the remaining heme iron as well as by an increase in the nonheme iron content of the meal.

In view of evidence that nutritional status of iron and vitamin A may affect the other nutrient's metabolism, we used model-based compartmental analysis to examine effects of iron deficiency on whole-body vitamin A dynamics in rats. Weanling male Sprague-Dawley rats were fed the AIN93G diet with 2.5 nmol retinyl palmitate/g and either 45 [control (CN)] or 4 microg/g Fe [iron-deficient (ID)] for 8 wk. ID rats consumed food ad libitum; CN rats were food-restricted so that their body weights were the same as ID rats. Two rats/group were killed; liver vitamin A was determined and used for vitamin A balance calculations. [(3)H]Retinol-labeled plasma was administered intravenously to remaining rats, and 27 serial blood samples were collected for 7 wk. At killing, plasma vitamin A was 0.52+/-0.12 (ID, n = 5) vs. 1.34+/-0.12 micromol/L (CN, n = 6; P<0.001), and liver vitamin A was 809+/-94 (ID) vs. 112+/-24 nmol (CN, P<0.001). Plasma tracer data were fit to a three- or four-compartment model using the Simulation, Analysis and Modeling computer program and kinetic parameters were calculated. Vitamin A transfer rate between the retinyl ester storage pool [14+/-3 (ID) vs. 24+/-4 nmol/d (CN), P<0.05] and plasma was lower in ID rats. Vitamin A remained longer in the body [44+/-11 (ID) vs. 22+/-3 d (CN), P<0.05]. Adjusted mean disposal rate was lower in ID (10.0) than CN rats (19.9 nmol/d), as was estimated vitamin A absorption efficiency [58% (ID) vs. 76% (CN)]. Our results suggest that iron deficiency inhibits mobilization of vitamin A stores and may decrease the absorption and irreversible utilization of vitamin A. [ABSTRACT FROM AUTHOR]

Iron deficiency anemia is associated with lower plasma thyroid hormone concentrations in rodents and, in some studies, in humans. The objective of this project was to determine if plasma triiodothyronine (T3) and thyroxine (T4) kinetics were affected by iron deficiency. Studies were done at a near-thermoneutral temperature (30 degrees C), and a cool environmental temperature (15 degrees C), to determine plasma T3 and T4 kinetics as a function of dietary iron intake and environmental need for the hormones. Weanling male Sprague-Dawley rats were fed either a low Fe diet [iron-deficient group (ID), <5 microg/g Fe] or a control diet [control group (CN), 35 microg/g Fe] at each temperature for 7 wk before the tracer kinetic studies. An additional ID group receiving exogenous thyroid hormone replacement was also used at the cooler temperature. For T4, the disposal rate was >60% lower (89 +/- 6 vs. 256 +/- 53 pmol/h, P < 0.001) in ID rats than in controls at 30 degrees C, and approximately 40% lower (192 +/- 27 vs. 372 +/- 26 pmol/h, P < 0.01) in ID rats at 15 degrees C. Exogenous T4 replacement in a cohort of ID rats at 15 degrees C normalized the T4 concentration and the disposal rate. For T3, the disposal rate was significantly lower in ID rats in a cool environment (92 +/- 11 vs. 129 +/- 11 pmol/h, P < 0.01); thyroxine replacement again normalized the T3 disposal rate (126 +/- 12 pmol/h). Neither liver nor brown fat thyroxine 5'-deiodinase activities were sufficiently different to explain the lower T3 disposal rates in iron deficiency. Thus, plasma thyroid hormone kinetics in iron deficiency anemia are corrected by simply providing more thyroxine. This suggests a central regulatory defect as the primary lesion and not peripheral alterations. [ABSTRACT FROM AUTHOR]