Cellular Iron Distribution Research Articles

Altered cellular distribution of iron in rat cerebral cortex during the oestrous cycle

Iron levels in blood, liver and the substantia nigra fluctuate during the oestrous cycle but it is not known whether the cellular distribution also changes. This study shows that during dioestrus, when serum levels of oestradiol are low, the amount of histochemically detectable iron in the cerebral cortex is significantly lower than in proestrus when oestradiol levels are highest. During dioestrus iron is concentrated within neurones, and the transition to proestrus is associated with a shift in iron localisation from neurones to vascular endothelial cells and oligodendrocytes. These data raise the possibility that changes in the concentration of serum oestrogen (or other reproductive hormones) during the oestrous cycle can influence the intercellular transport of iron in the brain.

Iron metabolism in mice with partial frataxin deficiency.

Friedreich ataxia (FRDA), the most common autosomal recessive inherited ataxic disorder, is the consequence of deficiency of the mitochondrial protein frataxin, typically caused by homozygous intronic GAA expansions in the corresponding gene. The yeast frataxin homologue (yfh1p) is required for cellular respiration. Yfh1p appears to regulate mitochondrial iron homeostasis and protect from free radical toxicity. Complete loss of frataxin in knockout mice leads to early embryonic lethality, indicating an important role for frataxin during development. Heterozygous littermates with partial frataxin deficiency are apparently healthy and have no obvious phenotype. Here we evaluate iron metabolism and sensitivity to dietary and parenteral iron loading in heterozygote frataxin knockout mice (Fx(+/-)). Iron concentrations in the liver, heart, pancreas and spleen, and cellular iron distribution patterns were compared between wild type and Fx(+/-) mice. Response to parenteral iron challenge was not different between Fx(+/-) mice and wild type littermates, while sporadic iron deposits were observed in the hearts of dietary iron-loaded Fx(+/-) mice. Finally, we evaluated the effect of partial frataxin deficiency on susceptibility to cardiac damage in the mouse model of hereditary hemochromatosis (HH), the Hfe knockout mice. HH, an iron overload disease, is one of the most frequent genetic diseases in populations of European origin. By breeding Hfe(-/-) with Fx(+/-) mice, we obtained compound mutant mice lacking both Hfe and one frataxin allele. Sparse iron deposits in areas of mild to moderate cardiac fibrosis were found in the majority of these mice. However, they did not develop any neurological symptoms. Our studies indicate an association between frataxin deficiency, iron deposits and cardiac fibrosis, but no obvious association between iron accumulation and neurodegeneration similar to FRDA could be detected in our model. In addition, these results suggest that frataxin mutations may have a modifier role in HH, that predisposes to cardiomyopathy.

Quantitative model for the interecho time dependence of the CPMG relaxation rate in iron-rich gray matter.

A quantitative model is proposed for computing the dependence on the interecho time of the NMR relaxation rate in iron-rich gray matter obtained with a Carr-Purcell-Meiboom-Gill sequence. The model consists of representing oligodendrocytes as identical magnetic spheres arranged in a spatially random pattern, and in approximating water diffusion as isotropic and unrestricted. Predictions of the model are calculated numerically using a Monte Carlo technique and, for the weak field limit, using an analytic formula. The model is shown to provide a good fit to experimental measurements of in vitro samples of monkey brain at field levels of 1.0 T and 1.5 T. These field levels are not sufficient to fully determine the model parameters, but it is argued that this may be possible at 3.0 T. The model is potentially of value for multiple-spin-echo MRI studies of iron-related neurodegenerative disorders, such as Parkinson's disease. In particular, the model can be applied to correlate MRI data with the cellular distribution of iron in gray matter. Magn Reson Med 46:159-165, 2001.

Cellular distribution of iron in the brain of the Belgrade rat

In this study, we investigated the cellular distribution of iron in the brain of Belgrade rats. These rats have a mutation in Divalent Metal Transporter 1, which has been implicated in iron transport from endosomes. The Belgrade rats have iron-positive pyramidal neurons, but these are fewer in number and less intensely stained than in controls. In the white matter, iron is normally present in patches of intensely iron-stained oligodendrocytes and myelin, but there is dramatically less iron staining in the Belgrade rat. Those oligodendrocytes that stained for iron did so strongly and were associated with blood vessels. Astrocytic iron staining was seen in the cerebral cortex for both normal rats and Belgrade rats, but the iron-stained astrocytes were less numerous in the mutants. Iron staining in tanycytes, modified astrocytes coursing from the third ventricle to the hypothalamus, was not affected in the Belgrade rat, but was affected by diet. The results of this study indicate that Divalent Metal Transporter 1 is important to iron transport in the brain. Iron is essential in the brain for basic metabolic processes such as heme formation, neurotransmitter production and ATP synthesis. Excess brain iron is associated with a number of common neurodegenerative diseases. Consequently, elucidating the mechanisms of brain iron delivery is critical for understanding the role of iron in pathological conditions.

Nuclear microprobe analysis of iodine and iron distributions in tumor cells exposed to the anthracycline 4′-iodo-4′-deoxydoxorubicin

In this study, we performed nuclear microprobe analysis on cultured human ovarian cancer cells exposed to pharmacological concentrations of 4′-iodo-4′-deoxydoxorubicin (IDX), an anthracycline anticancer drug. We observed that iodine and iron cellular distributions were strongly correlated, suggesting intracellular iron chelation by the anthracycline. The average cellular iron concentration did not change during drug exposure, but the cellular distribution of iron was modified following the preferential nuclear localization of iodine, as determined by single cell microanalysis. These results are important for understanding the cellular pharmacology of anthracyclines. They suggest that iron cellular delocalization and its subsequent nuclear accumulation may participate to the overall cytotoxicity of IDX, and more generally to anthracycline antitumor activity.

The distribution of iron in the brain: A phylogenetic analysis using iron histochemistry

Histochemical procedures can be used to detect the cellular distribution of iron in the brain. The objective of the present study was to determine if the cellular distribution of iron enrichment is conserved between animals on different branches of the phylogenetic tree. This information can facilitate our understanding of the role of iron enrichment in cells of the brain. The animals studied were the mouse, rat, chicken, frog, fish and fly. In order to optimize the detection of iron, two histochemical staining methods and three fixatives per staining method were examined for each species. The results indicated that there was no single cell type that displayed iron enrichment in each of the species examined. In three out of five species in the phylum chordata, iron was enriched in oligodendrocytes; the exceptions to this were the fish and frog, which had iron enrichment in neurons but not oligodendrocytes. Iron was enriched in ependymal cells and endothelial cells in four out of the five species in the phylum chordata with the fish and the mouse being the respective exceptions. Myelin was stained in the mouse and rat, and microglia were occasionally observed in the rat and chicken. Astrocyte staining was not observed in any of the species examined. In the fly third instar larvae, iron enrichment was found in border glia and in neuropil. The absence of a conserved staining pattern between species suggests that iron enrichment probably does not play a role in the main functions that have been attributed to those cells that were stained. These findings, taken together with previously published data on the distribution of ferritin and transferrin, suggests that iron-enriched cells serve as stores of iron for the brain.

The expression of ferritin subunits and iron in oligodendrocytes in neonatal porcine brains.

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.

Cellular management of iron in the brain

All organs including the brain contain iron, and the proteins involved in iron uptake (transferrin and transferrin receptor) and intracellular storage (ferritin). However, because the brain resides behind a barrier and has a heterogeneous population of cells, there are aspects of its iron management that are unique. Iron management, the timely delivery of appropriate amounts of iron, is crucial to normal brain development and function. Mismanagement of cellular iron can result not only in decreased metabolic activity but increased vulnerability to oxidative damage. There is regional specificity in cell deposition of iron and the iron regulatory proteins. However, the sequestration of iron in the brain seems primarily the responsibility of oligodendrocytes, as these cells contain most of the stainable iron in the brain. Transferrin, the iron-mobilizing protein, is also found predominantly in these cells. The transferrin receptor is abundantly expressed on blood vessels, large neurons in the cortex, striatum, and hippocampus, and is also present on oligodendrocytes and astrocytes. Ferritin, the intracellular iron storage protein, consists of 2 subunits which are functionally distinct, and we provide evidence in this report that the cellular distribution of the ferritin subunits is also distinct. In addition, changes in the cellular distribution of iron and its associated regulatory proteins occur in Alzheimer's disease. Neuritic plaques contain relatively large amounts of stainable iron, and the surrounding cells robustly immunostain for ferritin and the transferrin receptor. Analysis of the cellular distribution of iron indicates the different levels of requirement of iron in the brain by different cell types and should ultimately elucidate how cells acquire and maintain this essential component of oxidative metabolism. In addition, changes in the ability of cells to deliver and manage iron may provide insight into altered metabolic activity with age and disease as well as identify cell populations at risk for iron-induced oxidative stress.

Cellular distribution of iron, transferrin, and ferritin in the hypotransferrinemic (Hp) mouse brain

Hypotransferrinemic (Hp) mice have a point mutation or small deletion in the transferrin (Tf) gene, resulting in defective splicing of precursor Tf mRNA. Hp animals produce < 1% of normal Tf levels and require supplemental serum or purified Tf for survival. Because of the lack of endogenous brain Tf, we examined regional and cellular distributions of iron and iron regulatory proteins (Tf and ferritin) in selected brain regions of Hp mice. The regional distribution of iron, Tf, and ferritin in Hp brain was similar to normal except for the pattern of iron staining in hippocampus. The cellular distribution of iron, ferritin, and Tf was similar between Hp and normal animals. The predominant cell type staining for Tf and iron was oligodendrocytes. Qualitative observations suggest that the number of cells staining for iron was similar between Hp and normal mice, whereas the number of Hp Tf-positive cells was reduced. Ferritin immunostaining was similar in both cases. However, ferritin-positive cells were predominantly astrocytes, an observation unique to mice among species studied previously. Western blot analysis revealed that Tf present in Hp brain was of exogenous origin (from supplemental injections). Presumably, Tf transports the iron found in Hp oligodendrocytes. These data demonstrate that, despite reduced endogenous Hp brain Tf, iron and plasma Tf migrate or are transported to the appropriate cells (oligodendrocytes), bringing into question the role of endogenous brain Tf in extracellular iron transport.

Iron and chronic viral hepatitis: emerging evidence for an important interaction.

Iron is an essential element for cell survival; it serves as a cofactor for essential enzymes in oxidative metabolism and (in the form of heme) as the major oxygen transporter in most forms of life on earth. Both deficiency and excess of iron often lead to disease. Iron is necessary for the proliferation of microorganisms and neoplastic cells. The presence of iron overload facilitates infection, as evidenced by the increased risk of persons with hemochromatosis to certain infections and by the fact that patients with lesser amounts of hepatic iron appear to respond better to interferon therapy for chronic viral hepatitis than those with larger amounts of hepatic iron. Viral hepatitis is a common cause of morbidity and mortality. Recent studies suggest that there is a key link between iron metabolism and the pathophysiology of viral hepatitis. The lobular and cellular distribution of iron in the liver may be as important as the total quantity of iron present. Whether iron removal will prove useful in the long-term management of chronic viral hepatitis is an issue in need of further well-designed, randomized, controlled trials.

A histochemical study of iron, transferrin, and ferritin in Alzheimer's diseased brains.

Immunohistochemical and histochemical staining were performed on Alzheimer's diseased brain tissue obtained at autopsy. The iron-regulatory proteins transferrin and ferritin as well as iron are, in general, found predominantly in oligodendrocytes similar to that previously reported for normal brain tissue. However, in the vicinity of senile plaques, the staining pattern is altered for both proteins and iron. Transferrin is homogenously distributed around the senile plaques and is apparently extracellular. In addition, transferrin is found in astrocytes in the cerebral cortical white matter of the Alzheimer's tissue rather than its normal distribution in oligodendrocytes. A robust ferritin immunoreaction accompanies senile plaques and many blood vessels in the Alzheimer's brain tissue. Although many ferritin-positive oligodendrocytes are present in the Alzheimer's tissue, most of the ferritin-containing cells associated with senile plaques and blood vessels are microglia. Iron can also be demonstrated in the senile plaques. The iron reaction product is observed both diffusely in proximity of the plaques and in cells associated with the plaques. These data strongly suggest a disruption in brain iron homeostasis in Alzheimer's disease as demonstrated by alterations in the normal cellular distribution of iron and the proteins responsible for iron regulation. These data will contribute to understanding both the potential for oxidative damage and the potential for metal neurotoxicity in Alzheimer's disease.

Comparative techniques for determining cellular iron distribution in brain tissues.

Iron is essential for a number of normal brain functions and accumulates in high concentrations in specific regions of the brain. In pathological states, it may further accumulate in these and other areas that are typically low in iron content. The contribution of excess iron to potential central nervous system damage through its ability to donate an electron and to promote oxygen free radical formation has made the nature, location, extent, and process of iron deposition in the brain important areas of investigation. Nevertheless, there is relatively little information currently available on the cellular and subcellular distribution of iron in the central nervous system in either normal or diseased states. We describe and compare a number of the currently available techniques by which iron can be detected within the cellular components of the brain. Histochemical approaches, primarily in the form of the Perls' stain, yields information only on iron in its ferric state and is a relatively insensitive technique. Electron microscopy with x-ray spectrometry can provide positive identification of iron but has limitations regarding morphological verification of the specific cells being probed and also has a relatively high lowest detection limit. Secondary ion mass spectrometry and proton-induced x-ray spectrometry are both expensive, highly complex techniques with greater detection sensitivity, but they have problems identifying the cellular components being analyzed. Finally, laser microprobe mass analysis combines histological localization and identification of probe sites in plastic-embedded histological sections with detection limits in the single part per million range.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered cellular distribution of iron in the central nervous system of myelin deficient rats

Under normal conditions, iron is found predominantly in oligodendrocytes, the myelin producing cell, in the rat brain. A genetic mutant strain of rats known as myelin deficient rats is examined in the present study because their number of oligodendrocytes is decreased and those oligodendrocytes present are structurally abnormal. The levels of iron in the liver (major site of iron storage) and in the pons-cerebellum did not differ statistically between the myelin deficient rats and the littermate control rats, whereas only half of the iron normally found in the cerebrum-midbrain was present in the myelin deficient rat. Histologically, iron was found predominantly in oligodendrocytes in the littermate control rats, as expected. In the myelin deficient rat, iron staining was confined to astrocytes and microglia. The results of this study strongly suggest that iron uptake into the brain continues in the absence of normal oligodendrocytes and myelin. Furthermore, these data suggest that iron metabolism can be substantially altered, as indicated by the accumulation of iron in astrocytes and microglia, when normal or near normal levels of iron are quantitatively demonstrated. The response of astrocytes and microglia to sequester the iron (presumably through phagocytosis) in the absence of invasive damage represents, to our knowledge, a new functional observation for these cells. Based on these observations it is clear that iron histochemistry in combination with quantitative analysis is necessary to interpret data regarding iron physiology, at least in neurobiology, and iron accumulation by astrocytes and microglia may provide clues of altered iron metabolism despite normal iron levels.

Iron Localization in Pea Plants

Iron chlorosis has often been ascribed to iron inactivation, immobilization, or precipitation within the plant (6, 7, 14, 18, 20). This argument has rested on the assumption that there is no correlation between the chlorophyll content and the iron content of chlorotic plants. Since more recent findings do not support this assumption (1, 11, 12, 13), it is difficult to assess suggestions that chlorosis is the result of iron precipitation in xylem elements (14, 18), nodes (10), high-pH tissue such as phloem or bundle sheaths (20), or translocating tissues in general (7,9, 19). If the total iron content of a leaf is related to its chlorophyll content, there is no reason to claim localized regions of high iron represent precipitation or inactivation. Before ascribing chlorosis to iron immobilization, more should be known about some fundamental aspects of its transport and distribution in normal, green plants. A previous study (5) described some of the factors governing iron transport. As a continuation of that study, the localization of absorbed iron was examined by various radioautographic techniques, some of which permitted cellular localization of soluble as well as insoluble iron. These radioautographic results are presented here. While corroborating previous evidence showing the metabolic involvement of root cells in iron transport (5), the radioautographic results shed new light on the cellular distribution of iron in non-chlorotic plants.