Mechanisms and regulation of intestinal iron absorption

Attenuation of ferroptosis as a potential therapeutic target for neuropsychiatric manifestations of post-COVID syndrome

Coronavirus disease-19 (COVID-19), caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), is associated with the persistence of pre-existing or the emergence of new neurological and psychiatric manifestations as a part of a multi-system affection known collectively as "post-COVID syndrome." Cognitive decline is the most prominent feature among these manifestations. The underlying neurobiological mechanisms remain under intense investigation. Ferroptosis is a form of cell death that results from the excessive accumulation of intracellular reactive iron, which mediates lipid peroxidation. The accumulation of lipid-based reactive oxygen species (ROS) and the impairment of glutathione peroxidase 4 (GPX4) activity trigger ferroptosis. The COVID-19-associated cytokine storm enhances the levels of circulating pro-inflammatory cytokines and causes immune-cell hyper-activation that is tightly linked to iron dysregulation. Severe COVID-19 presents with iron overload as one of the main features of its pathogenesis. Iron overload promotes a state of inflammation and immune dysfunction. This is well demonstrated by the strong association between COVID-19 severity and high levels of ferritin, which is a well-known inflammatory and iron overload biomarker. The dysregulation of iron, the high levels of lipid peroxidation biomarkers, and the inactivation of GPX4 in COVID-19 patients make a strong case for ferroptosis as a potential mechanism behind post-COVID neuropsychiatric deficits. Therefore, here we review the characteristics of iron and the attenuation of ferroptosis as a potential therapeutic target for neuropsychiatric post-COVID syndrome.

Enlightening the mechanism of ferroptosis in epileptic heart

Epilepsy is a chronic neurological degenerative disease with a high incidence, affecting all age groups. Refractory Epilepsy (RE) occurs in approximately 30-40% of cases with a higher risk of sudden unexpected death in epilepsy (SUDEP). Recent studies have shown that spontaneous seizures developed in epilepsy can be related to an increase in oxidative stress and reactive oxygen derivatives (ROS) production. Increasing ROS concentration causes lipid peroxidation, protein oxidation, destruction of nuclear genetic material, enzyme inhibition, and cell death by a mechanism known as "ferroptosis" (Fts). Inactivation of glutathione peroxidase 4 (GPX4) induces Fts, while oxidative stress is linked with increased intracellular free iron (Fe+2) concentration. Fts is also a non-apoptotic programmed cell death mechanism, where a hypoxia-inducible factor 1 alpha (HIF-141) dependent hypoxic stress-like condition appears to occur with accumulation of iron and cytotoxic ROS in affected cells. Assuming convulsive crises as hypoxic stress, repetitive convulsive/hypoxic stress can be an effective inducer of the "epileptic heart" (EH), which is characterized by altered autonomic function and a high risk of malignant or fatal bradycardia. We previously reported that experimental recurrent seizures induce cardiomyocyte Fts associated with SUDEP. Furthermore, several genes related to Fts and hypoxia have recently been identified in acute myocardial infarction. An emerging theme from recent studies indicates that inhibition of GPX4 through modulating expression or activities of the xCT antiporter system (SLC7A11) governs cell sensitivity to oxidative stress from ferroptosis. Furthermore, during hypoxia, an increased expression of stress transcriptional factor ATF3 can promote Fts induced by erastin in a HIF-141-dependent manner. We propose that inhibition of Fts with ROS scavengers, iron chelators, antioxidants, and transaminase inhibitors could provide a therapeutic effect in epilepsy and improve the prognosis of SUDEP risk by protecting the heart from ferroptosis.

Hepcidin-guided screen-and-treat interventions for young children with iron-deficiency anaemia in The Gambia: an individually randomised, three-arm, double-blind, controlled, proof-of-concept, non-inferiority trial

BACKGROUND

Iron deficiency is the most prevalent nutritional disorder worldwide. Iron supplementation has modest efficacy, causes gastrointestinal side-effects that limit compliance, and has been associated with serious adverse outcomes in children across low-income settings. We aimed to compare two hepcidin-guided screen-and-treat regimens designed to reduce overall iron dosage by targeting its administration to periods when children were safe and ready to receive iron supplementation, with WHO's recommendation of universal iron supplementation.

METHODS

We conducted an individually randomised, three-arm, double-blind, controlled, proof-of-concept, non-inferiority trial in 12 rural communities across The Gambia. Eligible participants were children aged 6-23 months with anaemia. Participants were randomly assigned (1:1:1) to either the WHO recommended regimen of one sachet of multiple micronutrient powder (MMP) daily containing 12·0 mg iron as encapsulated ferrous fumarate (control group); to MMP with 12·0 mg per day iron for the next 7 days if plasma hepcidin concentration was less than 5·5 μg/L, or to MMP without iron for the next 7 days if plasma hepcidin concentration was at least 5·5 μg/L (12 mg screen-and-treat group); or to MMP with 6·0 mg per day iron for the next 7 days if plasma hepcidin concentration was less than 5·5 μg/L, or to MMP without iron for the next 7 days if plasma hepcidin concentration was at least 5·5 μg/L (6 mg screen-and-treat group). Randomisation was done by use of a permuted block design (block size of 9), with stratification by haemoglobin and age, using computer-generated numbers. Participants and the research team (except for the data manager) were masked to group allocation. The primary outcome was haemoglobin concentration, with a non-inferiority margin of -5 g/L. A per-protocol analysis, including only children who had consumed at least 90% of the supplements (ie, supplement intake on ≥75 days during the study), was done to assess non-inferiority of the primary outcome at day 84 using a one-sided t test adjusted for multiple comparisons. Safety was assessed by use of ex-vivo growth tests of Plasmodium falciparum in erythrocytes and three species of sentinel bacteria in plasma samples from participants. This trial is registered with the ISRCTN registry, ISRCTN07210906.

FINDINGS

Between April 23, 2014, and Aug 7, 2015, we prescreened 783 children, of whom 407 were enrolled into the study: 135 were randomly assigned to the control group, 136 to the 12 mg screen-and-treat group, and 136 to the 6 mg screen-and-treat group. 345 (85%) children were included in the per-protocol population: 115 in the control group, 116 in the 12 mg screen-and-treat group, and 114 in the 6 mg screen-and-treat group. Directly observed adherence was high across all groups (control group 94·8%, 12 mg screen-and-treat group 95·3%, and 6 mg screen-and-treat group 95·0%). 82 days of iron supplementation increased mean haemoglobin concentration by 7·7 g/L (95% CI 3·2 to 12·2) in the control group. Both screen-and-treat regimens were significantly less efficacious at improving haemoglobin (-5·6 g/L [98·3% CI -9·9 to -1·3] in the 12 mg screen-and-treat group and -7·8 g/L [98·3% CI -12·2 to -3·5] in the 6 mg screen-and-treat group) and neither regimen met the preset non-inferiority margin of -5 g/L. The 12 mg screen-and-treat regimen reduced iron dosage to 6·1 mg per day and the 6 mg screen-and-treat regimen reduced dosage to 3·0 mg per day. 580 adverse events were observed in 316 participants, of which eight were serious adverse events requiring hospitalisation mainly due to diarrhoeal disease (one [1%] participant in the control group, three [2%] in the 12 mg screen-and-treat group, and four [3%] in the 6 mg screen-and-treat group). The most common causes of non-serious adverse events (n=572) were diarrhoea (145 events [25%]), upper respiratory tract infections (194 [34%]), lower respiratory tract infections (62 [11%]), and skin infections (122 [21%]). No adverse events were deemed to be related to the study interventions.

INTERPRETATION

The hepcidin-guided screen-and-treat strategy to target iron administration succeeded in reducing overall iron dosage, but was considerably less efficacious at increasing haemoglobin and combating iron deficiency and anaemia than was WHO's standard of care, and showed no differences in morbidity or safety outcomes.

FUNDING

Bill & Melinda Gates Foundation and UK Medical Research Council.

Intraamniotic Administration (Gallus gallus) of Genistein Alters Mineral Transport, Intestinal Morphology, and Gut Microbiota

Genistein is an isoflavone naturally present in numerous staple food crops, such as soybeans and chickpeas. This study utilized the Gallus gallus intraamniotic administration procedure to assess genistein administration effects on trace mineral status, brush border membrane (BBM) functionality, intestinal morphology, and intestinal microbiome in vivo. Eggs were divided into five groups with 1 mL injection of the following treatments: no-injection, DI H₂O, 5% inulin, and 1.25% and 2.5% genistein (n = 8 per group). Upon hatch, blood, cecum, small intestine, and liver were collected for assessment of hemoglobin, intestinal microflora alterations, intestinal morphometric assessment, and mRNA gene expression of relevant iron and zinc transporter proteins, respectively. This study demonstrated that intraamniotic administration of 2.5% genistein increased villus surface area, number of acidic goblet cells, and hemoglobin. Additionally, genistein exposure downregulated duodenal cytochrome B (DcytB) and upregulated hepcidin expression. Further, genistein exposure positively altered the composition and function of the intestinal microbiota. Our results suggest a physiological role for genistein administration in improving mineral status, favorably altering BBM functionality and development, positively modulating the intestinal microbiome, as well as improving physiological status.

Low Level of Dietary Organic Trace Elements Improve the Eggshell Strength, Trace Element Utilization, and Intestinal Function in Late-Phase Laying Hens

This study was conducted to evaluate the effects of organic trace elements (Cu, Fe, Zn, and Mn) on performance, egg quality, trace elements utilization, and intestinal function in late-phase laying hens. A total of 1,080 laying hens (Hy-line brown, 65 weeks old) were randomly assigned to four treatments with six replications of 45 layers each. The basal diet was prepared without adding exogenous trace elements. The control group was fed with a basal diet supplemented with 600 mg/kg of inorganic trace elements. The three treatment groups were fed basal diets supplemented with 300, 450, and 600 mg/kg organic trace elements (OTE300, 450, and 600), respectively. The results showed that there was no significant difference in growth performance among all treatments. However, OTE450 significantly improved the eggshell strength of laying hens (p < 0.05), but had no significant effects on haugh unit, egg yolk weight, eggshell weight, and eggshell thickness, compared with other groups. Moreover, compared with the control group, OTE450 significantly increased the contents of copper, iron, and zinc in serum (p < 0.05). Meanwhile, all of the trace elements had a lower deposition in the feces in organic trace elements groups (p < 0.05). Histological analysis showed that the addition of organic trace elements could significantly improve the villus height and villus concealment ratio (p < 0.05). In addition, the messenger RNA (mRNA) and protein expressions of divalent metal transporter 1 (DMT1), zinc transporter 1 (ZnT-1), and ferroportin 1 (FPN1) were the highest in the OTE450 group. In conclusion, OTE450 could improve egg quality, intestinal function, and trace element utilization efficiency. Thus, this study provides a theoretical basis for the application of low levels of organic trace elements in laying hens.

Injectable Thermosensitive Hydrogels for a Sustained Release of Iron Nanochelators

Deferoxamine (DFO) is an FDA-approved iron-chelating agent which shows good therapeutic efficacy, however, its short blood half-life presents challenges such as the need for repeated injections or continuous infusions. Considering the lifelong need of chelating agents for iron overload patients, a sustained-release formulation that can reduce the number of chelator administrations is essential. Here, injectable hydrogel formulations prepared by integrating crosslinked hyaluronic acid into Pluronic F127 for an extended release of DFO nanochelators are reported. The subcutaneously injected hydrogel shows a thermosensitive sol-gel transition at physiological body temperature and provides a prolonged release of renal clearable nanochelators over 2 weeks, resulting in a half-life 47-fold longer than that of the nanochelator alone. In addition, no chronic toxicity of the nanochelator-loaded hydrogel is confirmed by biochemical and histological analyses. This injectable hydrogel formulation with DFO nanochelators has the potential to be a promising formulation for the treatment of iron overload disorders.

New Cases of Hypochromic Microcytic Anemia Due to Mutations in the SLC11A2 Gene and Functional Characterization of the G75R Mutation

Divalent metal-iron transporter 1 (DMT1) is a mammalian iron transporter encoded by the SLC11A2 gene. DMT1 has a vital role in iron homeostasis by mediating iron uptake in the intestine and kidneys and by recovering iron from recycling endosomes after transferrin endocytosis. Mutations in SLC11A2 cause an ultra-rare hypochromic microcytic anemia with iron overload (AHMIO1), which has been described in eight patients so far. Here, we report two novel cases of this disease. The first proband is homozygous for a new SLC11A2 splicing variant (c.762 + 35A > G), becoming the first ever patient reported with a SLC11A2 splicing mutation in homozygosity. Splicing studies performed in this work confirm its pathogenicity. The second proband harbors the previously reported DMT1 G75R mutation in homozygosis. Functional studies with the G75R mutation in HuTu 80 cells demonstrate that this mutation results in improper DMT1 accumulation in lysosomes, which correlates with a significant decrease in DMT1 levels in patient-derived lymphoblast cell lines (LCLs). We also suggest that recombinant erythropoietin would be an adequate therapeutic approach for AHMIO1 patients as it improves their anemic state and may possibly contribute to mobilizing excessive hepatic iron.

Association between obesity and iron deficiency (Review)

Obesity is a risk factor for several comorbidities and complications, including iron deficiency anemia. Iron deficiency anemia is a serious global public health problem, with a worldwide prevalence. The high prevalence of obesity in combination with iron deficiency incidence observed in different age and sex categories suggests an association between obesity and iron status. Obesity may disrupt iron homeostasis, resulting in iron deficiency anemia. The association between obesity and iron deficiency may be due to increased hepcidin levels mediated by chronic inflammation. Hepcidin is a small peptide hormone that functions as a negative regulator of intestinal iron absorption. Significant body weight loss in overweight and obese individuals decreases chronic inflammation and serum hepcidin levels, resulting in improved iron status due to increased iron absorption. However, further randomized controlled trials are required to confirm this effect.

Iron metabolism is disturbed and anti-copper treatment improves but does not normalize iron metabolism in Wilson's disease

Wilson's disease (WD) is a rare hereditary disorder of copper metabolism. Some data suggest that iron metabolism is disturbed in WD and this may affect the course of the disease. The current study aimed to determine whether anti-copper treatment could affect iron metabolism in WD. One hundred thirty-eight WD patients and 102 controls were examined. Serum ceruloplasmin and copper were measured by colorimetric enzyme assay or atomic adsorption spectroscopy, respectively. Routine and non-routine parameters of iron metabolism were measured by standard laboratory methods or enzyme immunoassay, respectively. WD patients, both newly diagnosed and treated, had less serum copper and ceruloplasmin than controls (90.0, 63.0, 22.0 mg/dL, respectively, p < 0.001); in the treated patients blood copper and ceruloplasmin were lower than in untreated patients (p < 0.001). Untreated patients (n = 39) had a higher median blood iron (126.0 vs 103.5 ug/dL, p < 0.05), ferritin (158.9 vs 47.5 ng/mL, p < 0.001), hepcidin (32, 6 vs 12.1 ng/mL, p < 0.001) and sTfR (0.8 vs. 0.7 ug/mL, p < 0.001) and lower blood transferrin (2.4 vs. 2.7 g/L, p < 0.001), TIBC (303.0 vs 338.0 ug/dL, p < 0.001), hemoglobin (13.1 vs 13.9 g/dL, p < 0.01) and RBC (4.3 vs. 4.6, p < 0.002) than controls. Treated patients (n = 99) had a significantly lower median iron (88.0 vs. 126.0 ug/dL, p < 0.001), ferritin (77.0 vs. 158.9 ng/mL, p < 0.005) and hepcidin (16.7 vs. 32.6 ng/mL, p < 001) and higher transferrin (2.8 vs. 2.4 g/L, p < 0.005), TIBC (336.0 vs 303.0 ug/dL, p < 0.001), RBC (4.8 vs. 4.3 M/L, p < 0.001) and hemoglobin (14.4 vs. 13.1 g/dL, p < 0.001) than untreated; the median iron (p < 0.005) was lower, and ferritin (p < 0.005), RBC (p < 0.005) and hepcidin (p < 0.002) were higher in them than in the control group. Changes in copper metabolism are accompanied by changes in iron metabolism in WD. Anti-copper treatment improves but does not normalize iron metabolism.

Difference in iron metabolism may partly explain sex-related variability in the manifestation of Wilson's disease

BACKGROUND/AIM

Wilson's disease (WD) is a hereditary disorder characterized by abnormal metabolism of copper. For unknown reasons, the clinical picture of this disease appears to be sex-dependent. Because the metabolism of copper and iron is interrelated, we aimed to evaluate whether the variability in the clinical picture of WD could be explained by the sex difference in iron metabolism.

METHODS

A total of 138 WD patients were examined in this study: 39 newly diagnosed, treatment naive patients and 99 individuals already treated with decoppering drugs. The serum concentration of ceruloplasmin (Cp) and copper were measured using an enzymatic colorimetric assay and by atomic absorption spectroscopy, respectively. The parameters of iron metabolism were determined by using standard laboratory methods and enzyme immunoassays.

RESULTS

In the treatment naive group men had a higher median serum concentration of ferritin (290.5 vs. 81.0 ng/mL, p < 10^-4), and hepcidin (Hepc) (55.4 vs. 22.8 ng/mL, p < 10^-3) compared to women, and tended to have higher concentration of iron, hemoglobin (HGB) and number of red blood cells (RBC). In the treated group men had higher median ferritin (122.0 vs. 46.0 ng/mL, p < 10^-4), Hepc (23.5 vs. 10.8 ng/mL, p < 10^-4), iron (102.5 vs. 68.0 μg/dL, p < 10^-4), HGB (15.0 vs. 13.2 g/dL, p < 10^-4), and RBC (5.0 vs. 4.5 M/L, p < 10^-4) than women.

CONCLUSION

Iron metabolism differs between men and women with WD, which may partly explain the sex difference noted in the disease manifestation.

Gamma Aminobutyric Acid Increases Absorption of Glycine-Bound Iron in Mice with Iron Deficiency Anemia

Iron deficiency is a leading cause of anemia. Amino acids are known to promote the absorption of both soluble and insoluble iron. The bioavailability of organic iron is higher than that of inorganic iron. Therefore, the aim of this study was to evaluate the iron absorption of glycine-bound iron (an organic iron) and a combination of glycine-bound iron and gamma aminobutyric acid (GABA) in mice with iron deficiency anemia (IDA). Mice were fed an iron-deficient diet for 3 weeks, followed by oral administration of GABA, inorganic iron, glycine-bound iron, or GABA plus glycine-bound iron for 5 weeks. Ferritin storage in the spleen was measure by immunohistochemistry (IHC). Iron deposition in the liver and spleen tissues was analyzed using atomic absorption spectrometry. Expression levels of iron absorption-related genes were measured by quantitative real-time polymerase chain reaction (qPCR). Iron absorption was enhanced in the glycine-bound iron-treated group compared with the inorganic iron-treated group. Hemoglobin, serum Fe, ferritin, and liver iron levels did not increase in mice treated with GABA alone. However, mice administered GABA in combination with glycine-bound iron showed higher iron absorption than those administered organic iron alone. Our results indicate that glycine-bound iron in combination with GABA might exert a synergistic effect on iron absorption and bioavailability, suggesting that the addition of GABA to existing iron supplements might increase their effectiveness for treating IDA.

Inherited iron overload disorders

Hereditary iron overload includes several disorders characterized by iron accumulation in tissues, organs, or even single cells or subcellular compartments. They are determined by mutations in genes directly involved in hepcidin regulation, cellular iron uptake, management and export, iron transport and storage. Systemic forms are characterized by increased serum ferritin with or without high transferrin saturation, and with or without functional iron deficient anemia. Hemochromatosis includes five different genetic forms all characterized by high transferrin saturation and serum ferritin, but with different penetrance and expression. Mutations in HFE, HFE2, HAMP and TFR2 lead to inadequate or severely reduced hepcidin synthesis that, in turn, induces increased intestinal iron absorption and macrophage iron release leading to tissue iron overload. The severity of hepcidin down-regulation defines the severity of iron overload and clinical complications. Hemochromatosis type 4 is caused by dominant gain-of-function mutations of ferroportin preventing hepcidin-ferroportin binding and leading to hepcidin resistance. Ferroportin disease is due to loss-of-function mutation of SLC40A1 that impairs the iron export efficiency of ferroportin, causes iron retention in reticuloendothelial cell and hyperferritinemia with normal transferrin saturation. Aceruloplasminemia is caused by defective iron release from storage and lead to mild microcytic anemia, low serum iron, and iron retention in several organs including the brain, causing severe neurological manifestations. Atransferrinemia and DMT1 deficiency are characterized by iron deficient erythropoiesis, severe microcytic anemia with high transferrin saturation and parenchymal iron overload due to secondary hepcidin suppression. Diagnosis of the different forms of hereditary iron overload disorders involves a sequential strategy that combines clinical, imaging, biochemical, and genetic data. Management of iron overload relies on two main therapies: blood removal and iron chelators. Specific therapeutic options are indicated in patients with atransferrinemia, DMT1 deficiency and aceruloplasminemia.

Effect of dietary inclusion of 1% or 3% of native chicory inulin on the large intestinal mucosa proteome of growing pigs

Native chicory inulin is one of the promising alternatives to replace antibiotic growth promoters in young animals. Several potential mechanisms of prebiotic action have been proposed, such as modification of the intestinal microbiota composition leading to improved epithelial integrity and gut mucosal immunity of the host. The current study was focused on inulin effect on the large intestinal proteome and its implications for gut barrier functions. Therefore, we used proteomic techniques to determine changes in the large intestinal mucosa proteome of growing pigs after 40-day supplementation with native chicory inulin. The experiment was performed on 24 piglets fed from the 10th day of life an unsupplemented cereal-based diet or inulin-enriched diets (1% or 3%) with an average degree of polymerisation ≥ 10. At the age of 50 days, animals were sacrificed and tissue samples were collected from the cecum, and proximal and distal colon. Feeding diets supplemented with both levels of native inulin increased cecal and colonic expression of molecular chaperones, protein foldases and antioxidant proteins, which are collectively responsible for maintaining mucosal cell integrity as well as protecting against endotoxins and reactive oxygen species. This may confirm the beneficial effect of inulin on the gut health in growing pigs.

Iron-oxide minerals in the human tissues

Iron is critically important and highly regulated trace metal in the human body. However, in its free ion form, it is known to be cytotoxic; therefore, it is bound to iron storing protein, ferritin. Ferritin is a key regulator of body iron homeostasis able to form various types of minerals depending on the tissue environment. Each mineral, e.g. magnetite, maghemite, goethite, akaganeite or hematite, present in the ferritin core carry different characteristics possibly affecting cells in the tissue. In specific cases, it can lead to disease development. Widely studied connection with neurodegenerative conditions is widely studied, including Alzheimer disease. Although the exact ferritin structure and its distribution throughout a human body are still not fully known, many studies have attempted to elucidate the mechanisms involved in its regulation and pathogenesis. In this review, we try to summarize the iron uptake into the body. Next, we discuss the known occurrence of ferritin in human tissues. Lastly, we also examine the formation of iron oxides and their involvement in brain functions.

Iron treatment of pregnant sows in a Danish herd without iron deficiency anemia did not improve sow and piglet hematology or stillbirth rate

Background

Anemia characterized by low hemoglobin concentration (HbC) is common in indoor housed pregnant sows. Iron is essential for hemoglobin synthesis and a number of metabolic processes including DNA synthesis and regulation of enzyme systems. In sows, anemia has been linked to lower HbC in piglets and increased occurrence of stillbirths. Therefore, the main objective of this study was to evaluate the effect of iron injection on hematology of pregnant sows and their offspring. Other objectives were to evaluate the effect of this injection on the probability of stillbirths and to study the tolerability of injected iron.

Results

A sow herd with bi-weekly batch farrowing was selected for the study and 100 sows at mid-gestation were randomly assigned to either a treatment (FeT) or a control (FeC) group. At the time of recruitment to the study (baseline), 46% of the sows in the herd were anemic with a HbC less than 103 g/L. However, none of the anemic sows had iron deficiency anemia on erythrocyte characterization. HbC decreased numerically during gestation in both the FeT (− 2.48 g/L) and FeC (− 2.99 g/L) groups but the decrease was insignificant between the groups (P = 0.79). Likewise, the change from baseline to farrowing and from baseline to post-farrowing in other hematologic variables was similar for both groups. The percentage of transferrin saturation was not statistically different between groups (P = 0.14). There was a batch effect (week of breeding) in most of the hematologic variables. The probability of stillbirth in the two groups did not differ (P = 0.94). None of the hematologic variables in piglets was significantly different between the two groups. The sows tolerated the iron injection well.

Conclusions

Intramuscular injection of two doses of 2500 mg iron 2 weeks apart at mid-gestation did neither change hematologic variables in sows nor in the piglets at farrowing. Similarly, iron treatment did not reduce the probability of stillbirths among the offspring. The sows recruited in this study tolerated the iron injections well. Further characterization of erythrocytes did not support that sows had iron deficiency anemia at baseline. Therefore, further studies on animals with well-defined anemia and with focus on the iron regulating hormone hepcidin are recommended.

Iron Homeostasis in Healthy Kidney and its Role in Acute Kidney Injury

Iron is required for key aspects of cellular physiology including mitochondrial function and DNA synthesis and repair. However, free iron is an aberration because of its ability to donate electrons, reduce oxygen, and generate reactive oxygen species. Iron-mediated cell injury or ferroptosis is a central player in the pathogenesis of acute kidney injury. There are several homeostatic proteins and pathways that maintain critical balance in iron homeostasis to allow iron's biologic functions yet avoid ferroptosis. Hepcidin serves as the master regulator of iron homeostasis through its ability to regulate ferroportin-mediated iron export and intracellular H-ferritin levels. Hepcidin is a protective molecule in acute kidney injury. Drugs targeting hepcidin, H-ferritin, and ferroptosis pathways hold great promise to prevent or treat kidney injury. In this review we discuss iron homeostasis under physiological and pathologic conditions and highlight its importance in acute kidney injury.

Effect of duck egg white peptide-ferrous chelate on iron bioavailability in vivo and structure characterization

BACKGROUND

In order to utilize the industrial by-product 'salted duck egg white' as novel iron additives, the effects of desalted duck egg white peptides-ferrous chelate (DPs-Fe) on the promotion of iron uptake and the structure were investigated.

RESULTS

Different doses of DPs-Fe were given and iron sulfate (FeSO₄ ) was used as a positive control. After three weeks, hemoglobin (Hb), hematocrit (HCT), red blood cells (RBCs), mean corpuscular volume (MCV), serum iron (SI) and serum ferritin (SF) in iron-deficiency anemia (IDA) rats could be significantly (P < 0.05) increased to the normal levels by DPs-Fe. The gene expressions of divalent metal transporter 1 (DMT1), ferroportin 1 (FPN1) and Hepcidin could be regulated by DPs-Fe. Additionally, DPs-Fe was formed during the chelation process and the structure was characterized. Eight crucial iron-chelating peptides of duck egg white peptides (DPs) were identified by HPLC-ESI-MS/MS, such as Pro-Val-Glu-Glu and Arg-Ser-Ser. It indicated that Glu, Asp, Lys, His, Ser, Cys residues might play crucial roles in the chelating of DPs with iron.

CONCLUSION

DPs-Fe could be a potential iron supplement, and the Glu, Asp, Lys, His played important roles in binding iron and promoting iron uptake. This research expands the understanding of iron uptake by DPs and provides an opportunity for recycling a discarded processing byproduct. © 2018 Society of Chemical Industry.

Sport Nutrigenomics: Personalized Nutrition for Athletic Performance

An individual's dietary and supplement strategies can influence markedly their physical performance. Personalized nutrition in athletic populations aims to optimize health, body composition, and exercise performance by targeting dietary recommendations to an individual's genetic profile. Sport dietitians and nutritionists have long been adept at placing additional scrutiny on the one-size-fits-all general population dietary guidelines to accommodate various sporting populations. However, generic "one-size-fits-all" recommendations still remain. Genetic differences are known to impact absorption, metabolism, uptake, utilization and excretion of nutrients and food bioactives, which ultimately affects a number of metabolic pathways. Nutrigenomics and nutrigenetics are experimental approaches that use genomic information and genetic testing technologies to examine the role of individual genetic differences in modifying an athlete's response to nutrients and other food components. Although there have been few randomized, controlled trials examining the effects of genetic variation on performance in response to an ergogenic aid, there is a growing foundation of research linking gene-diet interactions on biomarkers of nutritional status, which impact exercise and sport performance. This foundation forms the basis from which the field of sport nutrigenomics continues to develop. We review the science of genetic modifiers of various dietary factors that impact an athlete's nutritional status, body composition and, ultimately athletic performance.

New Perspectives on Iron Uptake in Eukaryotes

All eukaryotic organisms require iron to function. Malfunctions within iron homeostasis have a range of physiological consequences, and can lead to the development of pathological conditions that can result in an excess of non-transferrin bound iron (NTBI). Despite extensive understanding of iron homeostasis, the links between the “macroscopic” transport of iron across biological barriers (cellular membranes) and the chemistry of redox changes that drive these processes still needs elucidating. This review draws conclusions from the current literature, and describes some of the underlying biophysical and biochemical processes that occur in iron homeostasis. By first taking a broad view of iron uptake within the gut and subsequent delivery to tissues, in addition to describing the transferrin and non-transferrin mediated components of these processes, we provide a base of knowledge from which we further explore NTBI uptake. We provide concise up-to-date information of the transplasma electron transport systems (tPMETSs) involved within NTBI uptake, and highlight how these systems are not only involved within NTBI uptake for detoxification but also may play a role within the reduction of metabolic stress through regeneration of intracellular NAD(P)H/NAD(P)⁺ levels. Furthermore, we illuminate the thermodynamics that governs iron transport, namely the redox potential cascade and electrochemical behavior of key components of the electron transport systems that facilitate the movement of electrons across the plasma membrane to the extracellular compartment. We also take account of kinetic changes that occur to transport iron into the cell, namely membrane dipole change and their consequent effects within membrane structure that act to facilitate transport of ions.

Bacteria-Carried Iron Oxide Nanoparticles for Treatment of Anemia

The efficiency of maghemite nanoparticles for the treatment of anemia was sensibly higher when nanoparticles were incorporated onto the probiotic bacterium Lactobacillus fermentum (MNP-bacteria) than when administrated as uncoated nanoparticles (MNP). Plasma iron and hemoglobin, intestine expression of divalent metal transporter 1 (DMT1) and duodenal Cytochrome b (DcytB), as well as hepatic expression of the hormone hepcidin were fully restored to healthy levels after administration of MNP-bacteria but not of MNP. A magnetic study on biodistribution and biodegradation showed accumulation of maghemite nanoparticles in intestine lumen when MNP-bacteria were administrated. In contrast, MNP barely reached intestine. In vivo MRI studies suggested the internalization of MNP-bacteria into enterocytes, which did not occur with MNP. Transmission electronic microscopy confirmed this internalization. The collective analysis of results point out that L. fermentum is an excellent carrier to overcome the stomach medium and drive maghemite nanoparticles to intestine, where iron absorption occurs. Due the probiotic ability to adhere to the gut wall, MNP-bacteria internalize into the enterocyte, where maghemite nanoparticles are delivered, providing an adequate iron level into enterocyte. This paper advances a new route for effective iron absorption in the treatment of anemia.

Iron in neurodegenerative disorders: being in the wrong place at the wrong time?

Brain iron deposits have been reported consistently in imaging and histologic examinations of patients with neurodegenerative disorders. While the origins of this finding have not been clarified yet, it is speculated that impaired iron homeostasis or deficient transport mechanisms result in the accumulation of this highly toxic metal ultimately leading to formation of reactive oxygen species and cell death. On the other hand, there are also those who support that iron is just an incidental finding, a by product of neuronal loss. A literature review has been performed in order to present the key findings in support of the iron hypothesis of neurodegeneration, as well as to identify conditions causing or resulting from iron overload and compare and contrast their features with the most prominent neurodegenerative disorders. There is an abundance of experimental and observational findings in support of the hypothesis in question; however, as neurodegeneration is a rare incident of commonly encountered iron-associated disorders of the nervous system, and this metal is found in non-neurodegenerative disorders as well, it is possible that iron is the result or even an incidental finding in neurodegeneration. Understanding the underlying processes of iron metabolism in the brain and particularly its release during cell damage is expected to provide a deeper understanding of the origins of neurodegeneration in the years to come.

Effect of different sources and levels of iron in the diet of sows on iron status in neonatal pigs

This study was conducted to determine the effects of maternal dietary supplementation of ferrous glycine chelate (Fe-Gly) and ferrous sulfate monohydrate (FeSO₄·H₂O) on the relative organ weight, tissue iron contents, red blood cells (RBC), hemoglobin concentration (HGB) and hematocrit (HCT) in blood, as well as ferritin (Fn), serum iron (SI), and total iron binding capacity (TIBC) in serum of newborn piglets. Forty-five sows (Landrace × Large white, mean parity 3 to 4, no significant differences in BW) were randomly allotted to 9 treatments (n = 5 sows/treatment): control (basal diet with no Fe supplementation), the basal diet supplemented with 50, 80, 110 or 140 mg Fe/kg as Fe-Gly, and the basal diet supplemented with 50, 80, 110 or 140 mg Fe/kg as FeSO₄·H₂O. The neonatal piglets (n = 45) were used to determine the relative organ weight, tissue iron contents and blood biochemical indices. Compared with the control, the relative weight of spleen and kidney were significantly increased (P < 0.05) in the Fe-Gly groups. The iron contents in liver, spleen, kidney and femur were also found increased (P < 0.05) in the Fe-Gly groups. The RBC (d 1 and 21), HGB (d 1 and 21) and HCT (d 1 and 21) in blood and Fn (d 1) and SI (d 1 and 21) significantly increased (P < 0.05), but the TIBC (d 1 and 21) in serum decreased (P < 0.05) in the Fe-Gly groups. Moreover, the kidney relative weight, iron content in liver, spleen, kidney and femur, RBC (d 1) and HGB (d 21) in blood, and SI (d 1) in the Fe-Gly groups increased (P < 0.05) compared with the FeSO₄·H₂O treatment. Linear and quadratic responses of the kidney relative weight, the iron content in liver, spleen, kidney and femur, RBC (d 1 and 21), HGB (d 1 and 21) and HCT (d 1 and 21) in whole blood, SI (d 1) and TIBC (d 1 and 21) in the Fe-Gly groups were observed (P < 0.05). Linear responses of Fn (d 1 and 21) and SI (d 21) in the Fe-Gly groups, and spleen relative weight, HCT (d 1), Fn (d 1) and TIBC (d 1 and 21) in the FeSO₄·H₂O groups were observed (P < 0.05). These finding suggest that Fe-Gly supplemented at the level of 110 mg/kg in the diet of sows in this experiment is superior to other forms of supplementation, based on HGB concentration, the relative organ weight, tissue iron contents and blood biochemical indices of piglets.

Pathogenesis, Diagnostics, and Treatment of Hereditary Haemochromatosis: A 150 Year-Long Understanding of an Iron Overload Disorder

Haemochromatosis is an iron overload disorder that can be inherited or acquired and when diagnosis is delayed, disease progression and death can occur. Iron overload was first described by the French internist Armand Trousseau in 1865 in an article on diabetes in which alterations in skin pigmentations were reported. Some years later, the German pathologist Friedrich Daniel von Recklinghausen coined the term ‘haemochromatosis’ for a metabolic disorder characterised by excess deposition of iron in the tissue. This disorder affects 1 in 200 subjects of Caucasians of Northern European descent. The systemic excess iron build-up condition quickly gained an intense clinical interest. Haemochromatosis can lead to severe pathological symptoms in multiple organs, including the liver, bones, spleen, heart, pancreas, joints, and reproductive organs. With the progress of the disease, hepatic damage predominates. Polymorphisms in several independent genes can lead to haemochromatosis. However, the most widely known haemochromatosis-associated and studied ones are genetic variants in the HFE gene, located on the short arm of human chromosome 6. Early detection and phlebotomy prior to the onset of fibrosis/cirrhosis can reduce morbidity and normalise life expectancy. Consequently, phlebotomy has been accepted for decades as a standard treatment for the reduction of iron load. Nowadays, other methods, such as erythrocytapheresis, therapeutic application of iron chelators and proton pump inhibitors, or hepcidin-targeted therapy, are discussed as alternative personalised treatments of hereditary haemochromatosis. This review focusses on the pathogenesis, diagnosis, and therapy of haemochromatosis.

The DMT1 IVS4+44C>A polymorphism and the risk of iron deficiency anemia in children with celiac disease

BACKGROUND

Iron deficiency anemia in celiac disease is related to impaired duodenal mucosal uptake, due to villous atrophy. Iron enters the enterocytes through an apical divalent metal transporter, DMT1. Different DMT1 transcripts have been identified, depending on the presence of an iron-responsive element that allows DMT1 up-regulation during iron starvation. An intronic DMT1 polymorphism, IVS4+44C>A, has been associated with metal toxicity, and the CC-carriers show high iron levels.

AIMS

This study investigates the association between DMT1 IVS4+44C>A and anemia in a cohort of 387 Italian celiac children, and the functional role of the polymorphism.

METHODS AND RESULTS

By association analysis, we found that DMT1 IVS4+44-AA genotype confers a four-fold risk of developing anemia, despite of atrophy degree. By analysis of mRNA from gastroesophageal biopsies, we found that total DMT1 is significantly upregulated in presence of mild, but not severe, atrophy, independently from IVS4+44C>A variant, and in normal but not in atrophic CC-biopsies. Moreover, we found that A-allele is associated to preferential expression of the DMT1 transcripts lacking the iron-responsive element, thus limiting the DMT1 overexpression that normally occurs to respond to iron starvation.

DISCUSSION

Possibly, the IVS4+44-AA-related dysregulation of the iron-induced changes in DMT1 expression is not able to impair iron absorption in physiological condition. However, if exacerbated by the concomitant massive loss of functional absorbing tissue paralleling worsened stages of villus atrophy, it might be ineffective in counteracting iron deficiency, despite of DMT1 overexpression.

CONCLUSION

We suggest, for the first time, that celiac disease may unmask the contribution of the DMT1 IVS4+44C>A polymorphism to the risk of anemia.

Oral nucleic acid therapy using multicompartmental delivery systems

Nucleic acid-based therapeutics has the potential for treating numerous diseases by correcting abnormal expression of specific genes. Lack of safe and efficacious delivery strategies poses a major obstacle limiting clinical advancement of nucleic acid therapeutics. Oral route of drug administration has greater delivery challenges, because the administered genes or oligonucleotides have to bypass degrading environment of the gastrointestinal (GI) tract in addition to overcoming other cellular barriers preventing nucleic acid delivery. For efficient oral nucleic acid delivery, vector should be such that it can protect encapsulated material during transit through the GI tract, facilitate efficient uptake and intracellular trafficking at desired target sites, along with being safe and well tolerated. In this review, we have discussed multicompartmental systems for overcoming extracellular and intracellular barriers to oral delivery of nucleic acids. A nanoparticles-in-microsphere oral system-based multicompartmental system was developed and tested for in vivo gene and small interfering RNA delivery for treating colitis in mice. This system has shown efficient transgene expression or gene silencing when delivered orally along with favorable downstream anti-inflammatory effects, when tested in a mouse model of intestinal bowel disease. WIREs Nanomed Nanobiotechnol 2018, 10:e1478. doi: 10.1002/wnan.1478 This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Nonabsorbable Iron Binding Polymers Prevent Dietary Iron Absorption for the Treatment of Iron Overload

Chronic iron overload is a serious condition that develops as a consequence of long-term accumulation of iron, eventually overwhelming iron storage systems and causing oxidative stress and subsequent organ damage. Current pharmaceuticals used to treat iron overload typically suffer from toxicities leading to relatively high rates of adverse events. To address this need, we designed a new class of nonabsorbable iron binding polymers (IBPs) that bind and sequester iron within the gastrointestinal (GI) tract. IBPs were synthesized by cross-linking polyallylamine containing various amounts of conjugated 2,3-dihydroxybenzoic acid (DHBA). In vitro studies indicated that IBPs possessed high affinity, substantial binding capacity, and excellent selectivity toward iron. Moreover, in vivo studies demonstrated that IBPs showed no signs of side effects in mice and increased fecal iron excretion when compared to a similar dose of cross-linked polyallylamine. IBPs are a novel, nonabsorbed oral therapeutic agent that may ultimately prevent iron absorption as a safe alternative to iron chelation therapies for patients with hemochromatosis or other iron overload diseases.

Regulation of the divalent metal ion transporter via membrane budding

The release of extracellular vesicles (EVs) is important for both normal physiology and disease. However, a basic understanding of the targeting of EV cargoes, composition and mechanism of release is lacking. Here we present evidence that the divalent metal ion transporter (DMT1) is unexpectedly regulated through release in EVs. This process involves the Nedd4-2 ubiquitin ligase, and the adaptor proteins Arrdc1 and Arrdc4 via different budding mechanisms. We show that mouse gut explants release endogenous DMT1 in EVs. Although we observed no change in the relative amount of DMT1 released in EVs from gut explants in Arrdc1 or Arrdc4 deficient mice, the extent of EVs released was significantly reduced indicating an adaptor role in biogenesis. Furthermore, using Arrdc1 or Arrdc4 knockout mouse embryonic fibroblasts, we show that both Arrdc1 and Arrdc4 are non-redundant positive regulators of EV release. Our results suggest that DMT1 release from the plasma membrane into EVs may represent a novel mechanism for the maintenance of iron homeostasis, which may also be important for the regulation of other membrane proteins.

Iron acquisition in Leishmania and its crucial role in infection

Iron is an essential cofactor for many basic metabolic pathways in pathogenic microbes and their hosts. It is also dangerous as it can catalyse the production of reactive free radicals. This dual character makes the host can either limit iron availability to invading microbes or exploit iron to induce toxicity to pathogens. Successful pathogens, including Leishmania species, must possess mechanisms to circumvent host's iron limitation and iron-induced toxicity in order to survive. In this review, we discuss the regulation of iron metabolism in the setting of infection and delineate the iron acquisition strategies used by Leishmania parasites and their subversions to host iron metabolism to overcome host's iron-related defences.

Novel insights into iron regulation and requirement in marine medaka Oryzias melastigma

Iron (Fe) is an essential trace element for marine fish. However, our knowledge of Fe requirements at different development stages of marine fish is still limited. Here, we reported the efficient Fe absorption strategies adopted by larval fish under different dietary Fe supplementary levels (i.e., 0-640 mg/kg). Biokinetically, the larval fish controlled their dietary Fe assimilation efficiency (AE, 1.6-18.5%), and enhanced their waterborne Fe uptake (ca. 2.5 fold change of uptake rate constant) once the dietary Fe was deficient (i.e., 27.4 mg Fe/kg feed). Transcriptionally, the expression of hepcidin1 (hep1; Fe regulator; i.e., 2.3-15.7 fold change) in larval fish was positively correlated with the Fe supplementary levels. Comparatively, the female adult fish were poor in assimilating the added Fe source (i.e., ferric form) with similar life-sustainable levels of Fe (i.e., 0.046-0.12 μg/g/d assimilated for Fe supplementary levels of 27.4, 162 and 657 mg Fe/kg feed). The overall feeding experiments suggested that dietary net Fe flux sufficient for the normal growth of larval medaka was 0.71-1.75 μg/g/d (i.e., 83.9 mg Fe/kg feed), consistent with the modeled value (i.e., 1.09-2.16 μg/g/d). In female adults, the estimated essential net Fe flux was 0.88-0.90 μg/g/d.

Disturbance of ion environment and immune regulation following biodistribution of magnetic iron oxide nanoparticles injected intravenously

Although it is expected that accumulation of metal oxide nanoparticles that can induce redox reaction in the biological system may influence ion homeostasis and immune regulation through generation of free radicals, the relationship is still unclear. In this study, mice received magnetic iron oxide nanoparticles (M-FeNPs, 2 and 4 mg/kg) a single via the tail vein, and their distribution in tissues was investigated over time (1, 4, and 13 weeks). In addition, we evaluated the effects on homeostasis of redox reaction-related elements, the ion environment and immune regulation. The iron level in tissues reached at the maximum on 4 weeks after injection and M-FeNPs the most distributed in the spleen at 13 weeks. Additionally, levels of redox reaction-related elements in tissues were notably altered since 1 week post-injection. While levels of K(+) and Na(+) in tissue tended to decrease with time, Ca(2+) levels reached to the maximum at 4 weeks post-injection. On 13 weeks post-injection, the increased percentages of neutrophils and eosinophils, the enhanced release of LDH, and the elevated secretion of IL-8 and IL-6 were clearly observed in the blood of M-FeNP-treated mice compared to the control. While expression of antigen presentation related-proteins and the maturation of dendritic cells were markedly inhibited following distribution of M-FeNPs, the expression of several chemokines, including CXCR2, CCR5, and CD123, was enhanced on the splenocytes of the treated groups. Taken together, we suggest that accumulation of M-FeNPs may induce adverse health effects by disturbing homeostasis of the immune regulation and ion environment.

Transition metals activate TFEB in overexpressing cells

Exposure of cells to micromolar Cu activates recombinant transcription factor EB (TFEB), leading to expression of the lysosomal network genes. Whereas TFEB overexpression has a cytoprotective effect under moderate Cu exposure, it enhances oxidative stress and mitochondrial damage caused by high levels of Cu.

Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach.

Influence of lead on repetitive behavior and dopamine metabolism in a mouse model of iron overload

Exposures to lead (Pb) are associated with neurological problems including psychiatric disorders and impaired learning and memory. Pb can be absorbed by iron transporters, which are up-regulated in hereditary hemochromatosis, an iron overload disorder in which increased iron deposition in various parenchymal organs promote metal-induced oxidative damage. While dysfunction in HFE (High Fe) gene is the major cause of hemochromatosis, the transport and toxicity of Pb in Hfe-related hemochromatosis are largely unknown. To elucidate the relationship between HFE gene dysfunction and Pb absorption, H67D knock-in Hfe-mutant and wild-type mice were given drinking water containing Pb 1.6 mg/ml ad libitum for 6 weeks and examined for behavioral phenotypes using the nestlet-shredding and marble-burying tests. Latency to nestlet-shredding in Pb-treated wild-type mice was prolonged compared with non-exposed wild-types (p < 0.001), whereas Pb exposure did not alter shredding latency in Hfe-mutant mice. In the marble-burying test, Hfe-mutant mice showed an increased number of marbles buried compared with wild-type mice (p = 0.002), indicating more repetitive behavior upon Hfe mutation. Importantly, Pb-exposed wild-type mice buried more marbles than non-exposed wild-types, whereas the number of marbles buried by Hfe-mutant mice did not change whether or not exposed to Pb. These results suggest that Hfe mutation could normalize Pb-induced behavioral alteration. To explore the mechanism of repetitive behavior caused by Pb, western blot analysis was conducted for proteins involved in brain dopamine metabolism. The levels of tyrosine hydroxylase and dopamine transporter increased upon Pb exposure in both genotypes, whereas Hfe-mutant mice displayed down-regulation of the dopamine transporter and dopamine D1 receptor with D2 receptor elevated. Taken together, our data support the idea that both Pb exposure and Hfe mutation increase repetitive behavior in mice and further suggest that these behavioral changes could be associated with altered dopaminergic neurotransmission, providing a therapeutic basis for psychiatric disorders caused by Pb toxicity.

Alterations in gut microflora populations and brush border functionality following intra-amniotic daidzein administration

Daidzein is an isoflavone found primarily in soybean and various soy-based products such as tofu.

A novel model for brain iron uptake: introducing the concept of regulation

Neurologic disorders such as Alzheimer's, Parkinson's disease, and Restless Legs Syndrome involve a loss of brain iron homeostasis. Moreover, iron deficiency is the most prevalent nutritional concern worldwide with many associated cognitive and neural ramifications. Therefore, understanding the mechanisms by which iron enters the brain and how those processes are regulated addresses significant global health issues. The existing paradigm assumes that the endothelial cells (ECs) forming the blood-brain barrier (BBB) serve as a simple conduit for transport of transferrin-bound iron. This concept is a significant oversimplification, at minimum failing to account for the iron needs of the ECs. Using an in vivo model of brain iron deficiency, the Belgrade rat, we show the distribution of transferrin receptors in brain microvasculature is altered in luminal, intracellular, and abluminal membranes dependent on brain iron status. We used a cell culture model of the BBB to show the presence of factors that influence iron release in non-human primate cerebrospinal fluid and conditioned media from astrocytes; specifically apo-transferrin and hepcidin were found to increase and decrease iron release, respectively. These data have been integrated into an interactive model where BBB ECs are central in the regulation of cerebral iron metabolism.

Marginally excessive iron loading transiently blocks mucosal iron uptake in iron-deficient rats

Regular "mucosal block" is characterized by decreased uptake of a normal iron load 3-72 h after the administration of excess iron (generally 10 mg) to iron-deficient animals. We found that short-acting mucosal block could be induced by much lower iron concentration and much shorter induction time than previously reported, without affecting levels of gene expression. A rapid endocytic mechanism was reported to decrease intestinal iron absorption after a high iron load, but the activating iron load and the time to decreased absorption were undetermined. We assessed the effects of 30-2,000 μg iron load on iron uptake in the duodenal loop of iron-deficient and iron-sufficient rats under anesthesia. One hour later, mucosal cellular iron uptake in iron-deficient rats administered 30 μg iron was 76.1%, decreasing 25% to 50.7% in rats administered 2,000 μg iron. In contrast, iron uptake by iron-sufficient rats was 63% (range 60.3-65.5%) regardless of iron load. Duodenal mucosal iron concentration was significantly lower in iron-deficient than in iron-sufficient rats. Iron levels in portal blood were consistently higher in iron-deficient rats regardless of iron load, in contrast to the decreased iron uptake on the luminal side. Iron loading blocked mucosal uptake of marginally excess iron (1,000 μg), with a greater effect at 15 min than at 30 min. The rapid induction of short-acting mucosal block only in iron-deficient rats suggests DMT1 internalization.

Pathophysiology of the Belgrade rat

The Belgrade rat is an animal model of divalent metal transporter 1 (DMT1) deficiency. This strain originates from an X-irradiation experiment first reported in 1966. Since then, the Belgrade rat’s pathophysiology has helped to reveal the importance of iron balance and the role of DMT1. This review discusses our current understanding of iron transport homeostasis and summarizes molecular details of DMT1 function. We describe how studies of the Belgrade rat have revealed key roles for DMT1 in iron distribution to red blood cells as well as duodenal iron absorption. The Belgrade rat’s pathology has extended our knowledge of hepatic iron handling, pulmonary and olfactory iron transport as well as brain iron uptake and renal iron handling. For example, relationships between iron and manganese metabolism have been discerned since both are essential metals transported by DMT1. Pathophysiologic features of the Belgrade rat provide us with a unique and interesting animal model to understand iron homeostasis.

Appropriate nutrient supplementation in celiac disease

Reduced levels of iron, folate, vitamin B12, vitamin D, zinc, and magnesium are common in untreated celiac disease (CD) patients probably due to loss of brush border proteins and enzymes needed for the absorption of these nutrients. In the majority of patients, removal of gluten from the diet leads to histological recovery and normalization of iron, vitamin, and mineral levels. Iron deficiency anemia is the most common extra-intestinal sign of CD and usually resolves with adherence to a gluten-free diet. However, deficiencies of both folate and vitamin B12 may persist in some patients on a gluten-free diet, thus requiring vitamin supplementation to improve subjective health status. Similarly, exclusion of gluten from the diet does not always normalize bone mineral density; in these cases, supplementation of vitamin D and calcium is recommended. Resolution of mucosal inflammation may not be sufficient to abrogate magnesium deficiency. Since gluten-free cereal products have a lower magnesium content as compared with gluten-containing counterparts, a magnesium-enriched diet should be encouraged in CD patients. In this article we discuss the frequency and clinical relevance of nutrient deficiency in CD and whether and when nutrient supplementation is needed.

Prion protein regulates iron transport by functioning as a ferrireductase

Prion protein (PrPC) is implicated in the pathogenesis of prion disorders, but its normal function is unclear. We demonstrate that PrPC is a ferrireductase (FR), and its absence causes systemic iron deficiency in PrP knock-out mice (PrP-/-). When exposed to non-transferrin-bound (NTB) radioactive-iron (59FeCl3) by gastric-gavage, PrP-/- mice absorb significantly more 59Fe from the intestinal lumen relative to controls, indicating appropriate systemic response to the iron deficiency. Chronic exposure to excess dietary iron corrects this deficiency, but unlike wild-type (PrP+/+) controls that remain iron over-loaded, PrP-/- mice revert back to the iron deficient phenotype after 5 months of chase on normal diet. Bone marrow (BM) preparations of PrP-/- mice on normal diet show relatively less stainable iron, and this phenotype is only partially corrected by intraperitoneal administration of excess iron-dextran. Cultured PrP-/- BM-macrophages incorporate significantly less NTB-59Fe in the absence or presence of excess extracellular iron, indicating reduced uptake and/or storage of available iron in the absence of PrPC. When expressed in neuroblastoma cells, PrPC exhibits NAD(P)H-dependent cell-surface and intracellular FR activity that requires the copper-binding octa-peptide-repeat region and linkage to the plasma membrane for optimal function. Incorporation of NTB-59Fe by neuroblastoma cells correlates with FR activity of PrPC, implicating PrPC in cellular iron uptake and metabolism. These observations explain the correlation between PrPC expression and cellular iron levels, and the cause of iron imbalance in sporadic-Creutzfeldt-Jakob-disease brains where PrPC accumulates as insoluble aggregates.

Differential iron-bioavailability with relation to nutrient compositions in polished rice among selected Chinese genotypes using Caco-2 cell culture model

Genotypic variation of iron bioavailability and the relationship between iron bioavailability and nutrient composition in polished rice among 11 rice genotypes were assessed using an in vitro digestion/Caco-2 cell model. The results indicated that significant differences in iron bioavailability were detected among tested rice genotypes, with a 3-fold range, suggesting a possibility of selecting high bioavailable iron by plant breeding. Although iron bioavailability was not significantly correlated with Fe concentration in polished rice among tested rice genotypes, the results also indicated that most of the iron dense genotypes showed relatively high ferritin formation in Caco-2 cell and transported iron. Additionally, iron bioavailability in polished rice was enhanced by addition of ascorbic acid, with a much wider range of Fe bioavailability variation in polished rice with addition of ascorbic acid than that without addition of ascorbic acid. The positive relationship between iron bioavailability in polished rice and cysteine concentration (R = 0.669) or sulfur (S) concentration (R = 0.744) among tested rice genotypes, suggests that cysteine and sulfur concentration in polished rice could be used as an indicator for high iron bioavailability.

Advantages and disadvantages of the animal models v. in vitro studies in iron metabolism: a review

Iron deficiency is the most common nutritional deficiency in the world. Special molecules have evolved for iron acquisition, transport and storage in soluble, nontoxic forms. Studies about the effects of iron on health are focused on iron metabolism or nutrition to prevent or treat iron deficiency and anemia. These studies are focused in two main aspects: (1) basic studies to elucidate iron metabolism and (2) nutritional studies to evaluate the efficacy of iron supplementation to prevent or treat iron deficiency and anemia. This paper reviews the advantages and disadvantages of the experimental models commonly used as well as the methods that are more used in studies related to iron. In vitro studies have used different parts of the gut. In vivo studies are done in humans and animals such as mice, rats, pigs and monkeys. Iron metabolism is a complex process that includes interactions at the systemic level. In vitro studies, despite physiological differences to humans, are useful to increase knowledge related to this essential micronutrient. Isotopic techniques are the most recommended in studies related to iron, but their high cost and required logistic, making them difficult to use. The depletion-repletion of hemoglobin is a method commonly used in animal studies. Three depletion-repletion techniques are mostly used: hemoglobin regeneration efficiency, relative biological values (RBV) and metabolic balance, which are official methods of the association of official analytical chemists. These techniques are well-validated to be used as studies related to iron and their results can be extrapolated to humans. Knowledge about the main advantages and disadvantages of the in vitro and animal models, and methods used in these studies, could increase confidence of researchers in the experimental results with less costs.

Heme carrier protein 1 transports heme and is involved in heme-Fe metabolism

Heme-Fe is an important source of dietary iron in humans; however, the mechanism for heme-Fe uptake by enterocytes is poorly understood. Heme carrier protein 1 (HCP1) was originally identified as mediating heme-Fe transport although it later emerged that it was a folate transporter. We asked what happened to heme-Fe and folate uptake and the relative abundance of hcp1 and ho1 mRNA in Caco-2 cells after knockdown by transfection with HCP1-directed short hairpin (sh)RNA. Control Caco-2 cells were cultured in bicameral chambers with 0–80 μM heme-Fe for selected times. Intracellular Fe and heme concentration increased in Caco-2 cells reflecting higher external heme-Fe concentrations. Maximum Fe, heme, and heme oxygenase 1 (HO1) expression and activity were observed between 12 and 24 h of incubation. Quantitative RT-PCR for hcp1 revealed that its mRNA decreased at 20 μM heme-Fe while ho1 mRNA and activity increased. When shRNA knocked down hcp1 mRNA, heme-55Fe uptake and [3H]folate transport mirrored the mRNA decrease, ho1 mRNA increased, and flvcr mRNA was unchanged. These data argue that HCP1 is involved in low-affinity heme-Fe uptake not just in folate transport.