Recent advances in iron oxide nanocrystal technology for medical imaging

Superparamagnetic iron oxide particles (SPIO and USPIO) have a variety of applications in molecular and cellular imaging. Most of the recent research has concerned cellular imaging with imaging of in vivo macrophage activity. According to the iron oxide nanoparticle composition and size which influence their biodistribution, several clinical applications are possible: detection liver metastases, metastatic lymph nodes, inflammatory and/or degenerative diseases. USPIO are investigated as blood pool agents with T1 weighted sequence for angiography, tumour permeability and tumour blood volume or steady-state cerebral blood volume and vessel size index measurements using T2 weighted sequences. Stem cell migration and immune cell trafficking, as well as targeted iron oxide nanoparticles for molecular imaging studies, are at the stage of proof of concept, mainly in animal models.

A novel mammalian iron-regulated protein involved in intracellular iron metabolism

We have isolated and characterized a novel iron-regulated gene that is homologous to the divalent metal transporter 1 family of metal transporters. This gene, termed metal transporter protein (mtp1), is expressed in tissues involved in body iron homeostasis including the developing and mature reticuloendothelial system, the duodenum, and the pregnant uterus. MTP1 is also expressed in muscle and central nervous system cells in the embryo. At the subcellular level, MTP1 is localized to the basolateral membrane of the duodenal epithelial cell and a cytoplasmic compartment of reticuloendothelial system cells. Overexpression of MTP1 in tissue culture cells results in intracellular iron depletion. In the adult mouse, MTP1 expression in the liver and duodenum are reciprocally regulated. Iron deficiency induces MTP1 expression in the duodenum but down-regulates expression in the liver. These data indicate that MTP1 is an iron-regulated membrane-spanning protein that is involved in intracellular iron metabolism.

Superparamagnetic iron oxide: pharmacokinetics and toxicity

The pharmacokinetics (distribution, metabolism, bioavailability, excretion) and toxicity (acute and subacute toxicity, mutagenicity) of a superparamagnetic iron oxide preparation (AMI-25), currently used in clinical trials, were evaluated by 59Fe radiotracer studies, measurements of relaxation times, the ability to reverse iron deficiency anemia, histologic examination, and laboratory parameters. One hour after administration of AMI-25 to rats (18 mumol Fe/kg; 1 mg Fe/kg), 82.6 +/- 0.3% of the administered dose was sequestered in the liver and 6.2 +/- 7.6% in the spleen. Peak concentrations of 59Fe were found in liver after 2 hr and in the spleen after 4 hr. 59Fe slowly cleared from liver (half-life, 3 days) and spleen (half-life, 4 days) and was incorporated into hemoglobin of erythrocytes in a time-dependent fashion. The half-time of the T2 effect on liver and spleen (24-48 hr) was shorter than the 59Fe clearance, indicating metabolism of AMI-25 into other forms of iron. IV administration of AMI-25 (30 mg Fe/kg) corrected iron-deficiency anemia and showed bioavailability similar to that of commercially available IV iron preparations within 7 days. No acute or subacute toxic effects were detected by histologic or serologic studies in rats or beagle dogs who received a total of 3000 mumol Fe/kg, 150 times the dose proposed for MR imaging of the liver. Our results indicate that AMI-25 is a fully biocompatible potential contrast agent for MR.

Iron uptake, translocation, and regulation in higher plants

Iron is essential for the survival and proliferation of all plants. Higher plants have developed two distinct strategies to acquire iron, which is only slightly soluble, from the rhizosphere: the reduction strategy of nongraminaceous plants and the chelation strategy of graminaceous plants. Key molecular components-including transporters, enzymes, and chelators-have been clarified for both strategies, and many of these components are now thought to also function inside the plant to facilitate internal iron transport. Transporters for intracellular iron trafficking are also being clarified. A majority of genes encoding these components are transcriptionally regulated in response to iron availability. Recent research has uncovered central transcription factors, cis-acting elements, and molecular mechanisms regulating these genes. Manipulation of these molecular components has produced transgenic crops with enhanced tolerance to iron deficiency or with increased iron content in the edible parts.

Ultrasmall superparamagnetic iron oxide: characterization of a new class of contrast agents for MR imaging

An ultrasmall superparamagnetic iron oxide (USPIO) preparation was developed that is small enough to migrate across the capillary wall, a prerequisite in the design of targetable particulate pharmaceuticals. Seventy percent of particles were smaller than 10 nm; 26%, smaller than 5 nm. The blood half-life of USPIO in rats was 81 minutes, considerably longer than that of larger superparamagnetic iron oxide preparations such as AMI-25 (6 minutes). Electron microscopy demonstrated that USPIO particles transmigrate the capillary wall by means of vesicular transport and through interendothelial junctions. Twenty-four hours after intravenous administration, 3.6% of the injected dose per gram of tissue was found in lymph nodes, 2.9% per gram in bone marrow, 6.3% per gram in liver, and 7.1% per gram in spleen. The major potential applications for USPIO are as (a) an intravenous contrast agent for the lymphatic system, (b) a bone marrow contrast agent, (c) a long-half-life perfusion agent for brain and heart, and (d) the magnetic moiety in organ-targeted superparamagnetic contrast agents for magnetic resonance imaging.

The quantitative assessment of body iron

Current initiatives to reduce the high prevalence of nutritional iron deficiency have highlighted the need for reliable epidemiologic methods to assess iron status. The present report describes a method for estimating body iron based on the ratio of the serum transferrin receptor to serum ferritin. Analysis showed a single normal distribution of body iron stores in US men aged 20 to 65 years (mean +/- 1 SD, 9.82 +/- 2.82 mg/kg). A single normal distribution was also observed in pregnant Jamaican women (mean +/- 1 SD, 0.09 +/- 4.48 mg/kg). Distribution analysis in US women aged 20 to 45 years indicated 2 populations; 93% of women had body iron stores averaging 5.5 +/- 3.35 mg/kg (mean +/- 1 SD), whereas the remaining 7% of women had a mean tissue iron deficit of 3.87 +/- 3.23 mg/kg. Calculations of body iron in trials of iron supplementation in Jamaica and iron fortification in Vietnam demonstrated that the method can be used to calculate absorption of the added iron. Quantitative estimates of body iron greatly enhance the evaluation of iron status and the sensitivity of iron intervention trials in populations in which inflammation is uncommon or has been excluded by laboratory screening. The method is useful clinically for monitoring iron status in those who are highly susceptible to iron deficiency.

Clinically applicable labeling of mammalian and stem cells by combining superparamagnetic iron oxides and transfection agents

PURPOSE

To label mammalian and stem cells by combining commercially available transfection agents (TAs) with superparamagnetic iron oxide (SPIO) magnetic resonance (MR) imaging contrast agents.

MATERIALS AND METHODS

Three TAs were incubated with ferumoxides and MION-46L in cell culture medium at various concentrations. Human mesenchymal stem cells, mouse lymphocytes, rat oligodendrocyte progenitor CG-4 cells, and human cervical carcinoma cells were incubated 2-48 hours with 25 microg of iron per milliliter of combined TAs and SPIO. Cellular labeling was evaluated with T2 relaxometry, MR imaging of labeled cell suspensions, and Prussian blue staining for iron assessment. Proliferation and viability of mesenchymal stem cells and human cervical carcinoma cells labeled with a combination of TAs and ferumoxides were evaluated.

RESULTS

When ferumoxides-TA or MION-46L-TA was used, intracytoplasmic particles stained with Prussian blue stain were detected for all cell lines with a labeling efficiency of nearly 100%. Limited or no uptake was observed for cells incubated with ferumoxides or MION-46L alone. For TA-SPIO-labeled cells, MR images and relaxometry findings showed a 50%-90% decrease in signal intensity and a more than 40-fold increase in T2s. Cell viability varied from 103.7% +/- 9 to 123.0% +/- 9 compared with control cell viability at 9 days, and cell proliferation was not affected by endosomal incorporation of SPIO nanoparticles. Iron concentrations varied with ferumoxides-TA combinations and cells with a maximum of 30.1 pg +/- 3.7 of iron per cell for labeled mesenchymal stem cells.

CONCLUSION

Magnetic labeling of mammalian cells with use of ferumoxides and TAs is possible and may enable cellular MR imaging and tracking in experimental and clinical settings.

Lactoferrin: molecular structure and biological function

Lactoferrin is an 80-kDa, iron-binding glycoprotein present in milk and, to a lesser extent, in exocrine fluids such as bile and tears. It consists of a single-chain polypeptide with two gobular lobes and is relatively resistant to proteolysis. The complete cDNAs for lactoferrin from human milk, neutrophils, and bovine milk have been reported, and recombinant proteins have been produced. Owing to its iron-binding properties, lactoferrin has been proposed to play a role in iron uptake by the intestinal mucosa and to act as a bacteriostatic agent by withholding iron from iron-requiring bacteria. Its presence in neutrophils and its release during inflammation suggest that lactoferrin is also involved in phagocytic killing and immune responses. Additionally, lactoferrin may function in ways not related to iron-binding, e.g. as a growth factor and as a bactericidal agent. This review attempts to evaluate these proposed functions and their biological significance in more detail.

The transferrin receptor part I: Biology and targeting with cytotoxic antibodies for the treatment of cancer

The transferrin receptor (TfR) is a cell membrane-associated glycoprotein involved in the cellular uptake of iron and in the regulation of cell growth. Iron uptake occurs via the internalization of iron-loaded transferrin (Tf) mediated by the interaction with the TfR. In addition, the TfR may also contain other growth regulatory properties in certain normal and malignant cells. The elevated levels of TfR in malignancies, its relevance in cancer, and the extracellular accessibility of this molecule make it an excellent antigen for the treatment of cancer using antibodies. The TfR can be targeted by monoclonal antibodies specific for the extracellular domain of the receptor. In this review, we summarize advancements in the basic physiology of the TfR including structure, function, and expression. We also discuss the efficacy of targeting the TfR using cytotoxic antibodies that inhibit cell growth and/or induce apoptosis in targeted malignant cells.

Characterization of biophysical and metabolic properties of cells labeled with superparamagnetic iron oxide nanoparticles and transfection agent for cellular MR imaging

PURPOSE

To evaluate the effect of using the ferumoxides-poly-l-lysine (PLL) complex for magnetic cell labeling on the long-term viability, function, metabolism, and iron utilization of mammalian cells.

MATERIALS AND METHODS

PLL was incubated with ferumoxides for 60 minutes, incompletely coating the superparamagnetic iron oxide (SPIO) through electrostatic interactions. Cells were coincubated overnight with the ferumoxides-PLL complex, and iron uptake, cell viability, apoptosis indexes, and reactive oxygen species formation were evaluated. The disappearance or the life span of the detectable iron nanoparticles in cells was also evaluated. The iron concentrations in the media also were assessed at different time points. Data were expressed as the mean +/- 1 SD, and one-way analysis of variance and the unpaired Student t test were used to test for significant differences.

RESULTS

Intracytoplasmic nanoparticles were stained with Prussian blue when the ferumoxides-PLL complex had magnetically labeled the human mesenchymal stem and HeLa cells. The long-term viability, growth rate, and apoptotic indexes of the labeled cells were unaffected by the endosomal incorporation of SPIO, as compared with these characteristics of the nonlabeled cells. In nondividing human mesenchymal stem cells, endosomal iron nanoparticles could be detected after 7 weeks; however, in rapidly dividing cells, intracellular iron had disappeared by five to eight divisions. A nonsignificant transient increase in reactive oxygen species production was seen in the human mesenchymal stem and HeLa cell lines. Labeled human mesenchymal stem cells did not differentiate to other lineage. A significant increase in iron concentration was observed in both the human mesenchymal stem and HeLa cell media at day 7.

CONCLUSION

Magnetic cellular labeling with the ferumoxides-PLL complex had no short- or long-term toxic effects on tumor or stem cells.

Current understanding of iron homeostasis

Iron is an essential trace element, but it is also toxic in excess, and thus mammals have developed elegant mechanisms for keeping both cellular and whole-body iron concentrations within the optimal physiologic range. In the diet, iron is either sequestered within heme or in various nonheme forms. Although the absorption of heme iron is poorly understood, nonheme iron is transported across the apical membrane of the intestinal enterocyte by divalent metal-ion transporter 1 (DMT1) and is exported into the circulation via ferroportin 1 (FPN1). Newly absorbed iron binds to plasma transferrin and is distributed around the body to sites of utilization with the erythroid marrow having particularly high iron requirements. Iron-loaded transferrin binds to transferrin receptor 1 on the surface of most body cells, and after endocytosis of the complex, iron enters the cytoplasm via DMT1 in the endosomal membrane. This iron can be used for metabolic functions, stored within cytosolic ferritin, or exported from the cell via FPN1. Cellular iron concentrations are modulated by the iron regulatory proteins (IRPs) IRP1 and IRP2. At the whole-body level, dietary iron absorption and iron export from the tissues into the plasma are regulated by the liver-derived peptide hepcidin. When tissue iron demands are high, hepcidin concentrations are low and vice versa. Too little or too much iron can have important clinical consequences. Most iron deficiency reflects an inadequate supply of iron in the diet, whereas iron excess is usually associated with hereditary disorders. These disorders include various forms of hemochromatosis, which are characterized by inadequate hepcidin production and, thus, increased dietary iron intake, and iron-loading anemias whereby both increased iron absorption and transfusion therapy contribute to the iron overload. Despite major recent advances, much remains to be learned about iron physiology and pathophysiology.

Targeted gene disruption reveals an essential role for ceruloplasmin in cellular iron efflux

Aceruloplasminemia is an autosomal recessive disorder of iron metabolism. Affected individuals evidence iron accumulation in tissue parenchyma in association with absent serum ceruloplasmin. Genetic studies of such patients reveal inherited mutations in the ceruloplasmin gene. To elucidate the role of ceruloplasmin in iron homeostasis, we created an animal model of aceruloplasminemia by disrupting the murine ceruloplasmin (Cp) gene. Although normal at birth, Cp(-/-) mice demonstrate progressive accumulation of iron such that by one year of age all animals have a prominent elevation in serum ferritin and a 3- to 6-fold increase in the iron content of the liver and spleen. Histological analysis of affected tissues in these mice shows abundant iron stores within reticuloendothelial cells and hepatocytes. Ferrokinetic studies in Cp(+/+) and Cp(-/-) mice reveal equivalent rates of iron absorption and plasma iron turnover, suggesting that iron accumulation results from altered compartmentalization within the iron cycle. Consistent with this concept, Cp(-/-) mice showed no abnormalities in cellular iron uptake but a striking impairment in the movement of iron out of reticuloendothelial cells and hepatocytes. Our findings reveal an essential physiologic role for ceruloplasmin in determining the rate of iron efflux from cells with mobilizable iron stores.

Efficient magnetic cell labeling with protamine sulfate complexed to ferumoxides for cellular MRI

Recently, there have been several reports using various superparamagnetic iron oxide (SPIO) nanoparticles to label mammalian cells for monitoring their temporal and spatial migration in vivo by magnetic resonance imaging (MRI). The purpose of this study was to evaluate the efficiency and toxicity of labeling cells using 2 commercially available Food and Drug Administration (FDA)-approved agents, ferumoxides, a suspension of dextran-coated SPIO used as an MRI contrast agent, and protamine sulfate, conventionally used to reverse heparin anticoagulation but also used ex vivo as a cationic transfection agent. After labeling of human mesenchymal stem cells (MSCs) and hematopoietic (CD34+) stem cells and other mammalian cells with ferumoxides-protamine sulfate complexes (FE-Pro), cellular toxicity, functional capacity, and quantitative cellular iron incorporation were determined. FE-Pro-labeled cells demonstrated no short- or long-term toxicity, changes in differentiation capacity of the stem cells, or changes in phenotype when compared with unlabeled cells. Efficient labeling with FE-Pro was observed with iron content per cell varying between 2.01 +/- 0.1 pg for CD34+ cells and 10.94 +/- 1.86 pg for MSCs with 100% of cells labeled. Cell labeling using these agents should facilitate the translation of this method to clinical trials for evaluation of trafficking of infused or transplanted cells by MRI.

Iron requirements in pregnancy and strategies to meet them

Iron requirements are greater in pregnancy than in the nonpregnant state. Although iron requirements are reduced in the first trimester because of the absence of menstruation, they rise steadily thereafter; the total requirement of a 55-kg woman is approximately 1000 mg. Translated into daily needs, the requirement is approximately 0.8 mg Fe in the first trimester, between 4 and 5 mg in the second trimester, and >6 mg in the third trimester. Absorptive behavior changes accordingly: a reduction in iron absorption in the first trimester is followed by a progressive rise in absorption throughout the remainder of pregnancy. The amounts that can be absorbed from even an optimal diet, however, are less than the iron requirements in later pregnancy and a woman must enter pregnancy with iron stores of >/=300 mg if she is to meet her requirements fully. This is more than most women possess, especially in developing countries. Results of controlled studies indicate that the deficit can be met by supplementation, but inadequacies in health care delivery systems have limited the effectiveness of larger-scale interventions. Attempts to improve compliance include the use of a supplement of ferrous sulfate in a hydrocolloid matrix (gastric delivery system, or GDS) and the use of intermittent supplementation. Another approach is intermittent, preventive supplementation aimed at improving the iron status of all women of childbearing age. Like all supplementation strategies, however, this approach has the drawback of depending on delivery systems and good compliance. On a long-term basis, iron fortification offers the most cost-effective option for the future.

Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate

The dose-dependent inhibitory effect of sodium phytate on iron absorption was studied in man by serving wheat rolls containing no phytates and rolls to which various amounts (seven dose levels between 2 and 250 mg expressed as phytate phosphorus) were added just before serving. Fe in the two kinds of rolls was labeled with two radioisotopes of Fe (55Fe, 59Fe) and the rolls were served on alternate days. The inhibition of Fe absorption was strongly related to the amount of phytate added; 2 mg inhibited absorption by 18%, (p less than 0.001), 25 mg by 64% (p less than 0.001), and 250 mg by 82% (p less than 0.001). The addition of ascorbic acid significantly counteracted the inhibition whereas the corresponding effect of meat was less well defined and only seen at the highest phytate level. The marked inhibition of Fe absorption by phytates and the significant counteracting effect of ascorbic acid have wide nutritional implications.

Ultrasmall superparamagnetic iron oxide: an intravenous contrast agent for assessing lymph nodes with MR imaging

An ultrasmall superparamagnetic iron oxide (USPIO) preparation was evaluated as a potential intravenous contrast agent for lymph nodes. Relaxation time measurements and magnetic resonance (MR) imaging were performed in rats with normal lymph nodes and in rats with lymph node metastases. In normal animals, lymph node relaxation times decreased maximally within 24-48 hours after intravenous administration of USPIO. Twenty-four hours after administration, the T2 of normal lymph nodes had decreased from 74 msec +/- 2.2 to 30 msec +/- 0.7 (USPIO, 40 mumol of iron per kilogram) or 15 msec +/- 0.0 (200 mumol Fe/kg), whereas the T2 of metastatic nodes did not change. MR imaging of the animal model of nodal metastases confirmed the hypothesis that intravenously administered USPIO decreases signal intensity of normal but not metastatic nodes. A single intravenous administration of USPIO may allow detection of nodal metastases on the basis of signal intensity characteristics rather than the currently used, insensitive size characteristics.

Bioavailability of iron, zinc, and other trace minerals from vegetarian diets

Iron and zinc are currently the trace minerals of greatest concern when considering the nutritional value of vegetarian diets. With elimination of meat and increased intake of phytate-containing legumes and whole grains, the absorption of both iron and zinc is lower with vegetarian than with nonvegetarian, diets. The health consequences of lower iron and zinc bioavailability are not clear, especially in industrialized countries with abundant, varied food supplies, where nutrition and health research has generally supported recommendations to reduce meat and increase legume and whole-grain consumption. Although it is clear that vegetarians have lower iron stores, adverse health effects from lower iron and zinc absorption have not been demonstrated with varied vegetarian diets in developed countries, and moderately lower iron stores have even been hypothesized to reduce the risk of chronic diseases. Premenopausal women cannot easily achieve recommended iron intakes, as modified for vegetarians, with foods alone; however, the benefit of routine iron supplementation has not been demonstrated. It may be prudent to monitor the hemoglobin of vegetarian children and women of childbearing age. Improved assessment methods are required to determine whether vegetarians are at risk of zinc deficiency. In contrast with iron and zinc, elements such as copper appear to be adequately provided by vegetarian diets. Although the iron and zinc deficiencies commonly associated with plant-based diets in impoverished nations are not associated with vegetarian diets in wealthier countries, these nutrients warrant attention as nutritional assessment methods become more sensitive and plant-based diets receive greater emphasis.

Highly efficient endosomal labeling of progenitor and stem cells with large magnetic particles allows magnetic resonance imaging of single cells

Tracking transplanted stem cells using magnetic resonance imaging (MRI) could offer biologic insight into homing and engraftment. Ultrasmall dextran-coated iron oxide particles have previously been developed for uptake into cells to allow MRI tracking. We describe a new application of much larger, micron-scale, iron oxide magnetic particles with enhanced MR susceptibility, which enables detection of single cells at resolutions that can be achieved in vivo. In addition, these larger particles possess a fluorophore for histologic confirmation of cell distribution. We demonstrate highly efficient, nontoxic, endosomal uptake of these particles into hematopoietic CD34+ cells and mesenchymal stem cells documented by confocal and electron microscopy. Labeled cells retain biologic activity with preservation of colony-forming ability and differentiation capacity. MRI studies could detect labeled CD34+ cells and mesenchymal stem cells (MSCs) at single cell resolution. This appears to be a promising tool for serial noninvasive monitoring of in vivo cell homing and localization using MRI.

Iron and hydrogen peroxide detoxification properties of DNA-binding protein from starved cells. A ferritin-like DNA-binding protein of Escherichia coli

The DNA-binding proteins from starved cells (Dps) are a family of proteins induced in microorganisms by oxidative or nutritional stress. Escherichia coli Dps, a structural analog of the 12-subunit Listeria innocua ferritin, binds and protects DNA against oxidative damage mediated by H(2)O(2). Dps is shown to be a Fe-binding and storage protein where Fe(II) oxidation is most effectively accomplished by H(2)O(2) rather than by O(2) as in ferritins. Two Fe(2+) ions bind at each of the 12 putative dinuclear ferroxidase sites (P(Z)) in the protein according to the equation, 2Fe(2+) + P(Z) --> [(Fe(II)(2)-P](FS)(Z+2) + 2H(+). The ferroxidase site (FS) bound iron is then oxidized according to the equation, [(Fe(II)(2)-P](FS)(Z+2) + H(2)O(2) + H(2)O --> [Fe(III)(2)O(2)(OH)-P](FS)(Z-1) + 3H(+), where two Fe(II) are oxidized per H(2)O(2) reduced, thus avoiding hydroxyl radical production through Fenton chemistry. Dps acquires a ferric core of approximately 500 Fe(III) according to the mineralization equation, 2Fe(2+) + H(2)O(2) + 2H(2)O --> 2Fe(III)OOH((core)) + 4H(+), again with a 2 Fe(II)/H(2)O(2) stoichiometry. The protein forms a similar ferric core with O(2) as the oxidant, albeit at a slower rate. In the absence of H(2)O(2) and O(2), Dps forms a ferrous core of approximately 400 Fe(II) by the reaction Fe(2+) + H(2)O + Cl(-) --> Fe(II)OHCl((core)) + H(+). The ferrous core also undergoes oxidation with a stoichiometry of 2 Fe(II)/H(2)O(2). Spin trapping experiments demonstrate that Dps greatly attenuates hydroxyl radical production during Fe(II) oxidation by H(2)O(2). These results and in vitro DNA damage assays indicate that the protective effect of Dps on DNA most likely is exerted through a dual action, the physical association with DNA and the ability to nullify the toxic combination of Fe(II) and H(2)O(2). In the latter process a hydrous ferric oxide mineral core is produced within the protein, thus avoiding oxidative damage mediated by Fenton chemistry.

Regulation of the Iron Homeostatic Hormone Hepcidin

Iron is required for many biological processes but is also toxic in excess; thus, body iron balance is maintained through sophisticated regulatory mechanisms. The lack of a regulated iron excretory mechanism means that body iron balance is controlled at the level of absorption from the diet. Iron absorption is regulated by the hepatic peptide hormone hepcidin. Hepcidin also controls iron release from cells that recycle or store iron, thus regulating plasma iron concentrations. Hepcidin exerts its effects through its receptor, the cellular iron exporter ferroportin. Important regulators of hepcidin, and therefore of systemic iron homeostasis, include plasma iron concentrations, body iron stores, infection and inflammation, and erythropoiesis. Disturbances in the regulation of hepcidin contribute to the pathogenesis of many iron disorders: hepcidin deficiency causes iron overload in hereditary hemochromatosis and nontransfused β-thalassemia, whereas overproduction of hepcidin is associated with iron-restricted anemias seen in patients with chronic kidney disease, chronic inflammatory diseases, some cancers, and inherited iron-refractory iron deficiency anemia. This review summarizes our current understanding of the molecular mechanisms and signaling pathways involved in the control of hepcidin synthesis in the liver, a principal determinant of plasma hepcidin concentrations.

A novel approach to temporary stenting: degradable cardiovascular stents produced from corrodible metal-results 6-18 months after implantation into New Zealand white rabbits

OBJECTIVE

To determine whether corrodible materials may be safely used as biodegradable cardiovascular implants.

DESIGN

Corrodible iron stents (> 99.8% iron) were produced from pure iron and laser cut with a stent design similar to a commercially available permanent stent (PUVA-AS16). A total of 16 NOR-I stents were implanted into the native descending aorta of 16 New Zealand white rabbits (mean luminal diameter at the implantation site 3.4 mm, balloon diameter to vessel diameter ratio 1.13).

RESULTS

No thromboembolic complications and no adverse events occurred during the follow up of 6-18 months. All stents were patent at repeat angiography after 6 (n = 9), 12 (n = 5), and 18 months (n = 2) with no significant neointimal proliferation, no pronounced inflammatory response, and no systemic toxicity.

CONCLUSIONS

This initial in vivo experience suggests that degradable iron stents can be safely implanted without significant obstruction of the stented vessel caused by inflammation, neointimal proliferation, or thrombotic events.

Iron, hemochromatosis, and hepatocellular carcinoma

Hereditary hemochromatosis (HH) is associated with an increased risk for hepatocellular carcinoma (HCC). The risk previously had been estimated to be as high as 200-fold increased. Recent studies suggest that the risk for HCC in HFE -associated HH may be much lower and occurs predominantly in patients with cirrhosis at the time of diagnosis. The risk for HCC also is increased among patients with African iron overload and possibly in other iron-loading disorders such as homozygous beta thalassemia. The greatly increased iron stores in the liver observed in these disorders can stimulate carcinogenesis via both direct and indirect pathways. The prevalence of HCC also appears to be higher among patients with end-stage liver disease undergoing liver transplantation. It is not clear whether mildly to moderately increased hepatic iron stores or HFE mutations are associated independently with an increased risk for HCC among patients with other types of liver disease. In this article, the incidence and prevalence of HCC in patients with HH and other liver diseases associated with iron overload are discussed as well as the possible mechanisms for the increased risk for hepatic carcinogenesis in these disorders.

Long-term biocompatibility of a corrodible peripheral iron stent in the porcine descending aorta

Currently there are no biodegradable stents available for treatment of vascular obstructions in patients with congenital heart defects. This study was performed to evaluate the safety of a corrodible stent produced from pure iron in a peripheral stent design (6-12mm diameter) in a slotted tube design similar to a commercially available 316-L stent which served as control. Both stents were implanted into the descending aorta of 29 minipigs with an overstretch injury without technical problems. Two animals died after the implantation not related to the iron stent. The remaining 27 minipigs were followed for 1-360 days. Histomorphometry and quantitative angiography showed no difference with regard to the amount of neointimal proliferation between 316-L and iron stents. Histopathological examination of heart, lung, spleen, liver, kidney and para-aortic lymphatic nodes demonstrated no signs of iron overload or iron-related organ toxicity. Adjacent to the iron stent struts, there was no evidence for local toxicity due to corrosion products. We conclude that iron is a suitable metal for the production of a large-size degradable stent with no local or systemic toxicity. A faster degradation rate, however, is desirable and further studies have to focus on the modification of the composition and design of the stent to expedite the degradation process.

Nutritive metal uptake in teleost fish

Transition metals are essential for health, forming integral components of proteins involved in all aspects of biological function. However, in excess these metals are potentially toxic, and to maintain metal homeostasis organisms must tightly coordinate metal acquisition and excretion. The diet is the main source for essential metals, but in aquatic organisms an alternative uptake route is available from the water. This review will assess physiological, pharmacological and recent molecular evidence to outline possible uptake pathways in the gills and intestine of teleost fish involved in the acquisition of three of the most abundant transition metals necessary for life; iron, copper, and zinc.