Recent advances in iron metabolism and related disorders

Cadmium alters whole animal ionome and promotes the re-distribution of iron in intestinal cells of Caenorhabditis elegans

The chronic exposure of humans to the toxic metal cadmium (Cd), either occupational or from food and air, causes various diseases, including neurodegenerative conditions, dysfunction of vital organs, and cancer. While the toxicology of Cd and its effect on the homeostasis of biologically relevant elements is increasingly recognized, the spatial distribution of Cd and other elements in Cd toxicity-caused diseases is still poorly understood. Here, we use Caenorhabditis elegans as a non-mammalian multicellular model system to determine the distribution of Cd at the tissue and cellular resolution and its effect on the internal levels and the distribution of biologically relevant elements. Using inductively coupled plasma-mass spectrophotometry (ICP-MS), we show that exposure of worms to Cd not only led to its internal accumulation but also significantly altered the C. elegans ionome. Specifically, Cd treatment was associated with increased levels of toxic elements such as arsenic (As) and rubidium (Rb) and a decreased accumulation of essential elements such as zinc (Zn), copper (Cu), manganese (Mn), calcium (Ca), cobalt (Co) and, depending on the Cd-concentration used in the assay, iron (Fe). We regarded these changes as an ionomic signature of Cd toxicity in C. elegans. We also show that supplementing nematode growth medium with Zn but not Cu, rescues Cd toxicity and that mutant worms lacking Zn transporters CDF-1 or SUR-7, or both are more sensitive to Cd toxicity. Finally, using synchrotron X-Ray fluorescence Microscopy (XRF), we showed that Cd significantly alters the spatial distribution of mineral elements. The effect of Cd on the distribution of Fe was particularly striking: while Fe was evenly distributed in intestinal cells of worms grown without Cd, in the presence of Cd, Fe, and Cd co-localized in punctum-like structures in the intestinal cells. Together, this study advances our understanding of the effect of Cd on the accumulation and distribution of biologically relevant elements. Considering that C. elegans possesses the principal tissues and cell types as humans, our data may have important implications for future therapeutic developments aiming to alleviate Cd-related pathologies in humans.

Ferroptosis: Biological Rust of Lipid Membranes

Significance: Iron is an essential element required for growth and proper functioning of the body. However, an excess of labile ferrous iron increases the risk of oxidative stress-induced injury due to the high reactivity of the unpaired reactive electrons of both ferrous iron and oxygen. This high reactivity can be exemplified in the outside world by one of its consequences, rust formation. In cells, this redox-active iron is involved in the formation of lipid radicals. Recent Advances: Defect or insufficient membrane-protective mechanisms can result in iron-catalyzed excessive lipid peroxidation and subsequent cell death, now conceptualized as ferroptosis. Growing reports propose the detrimental role of iron and ferroptosis in many experimental disease models such as ischemia-reperfusion, acute and chronic organ injuries. Critical Issues: This review first provides a snapshot of iron metabolism, followed by a brief introduction of the molecular mechanisms of ferroptosis, as an iron-dependent lipid peroxidation-driven mode of cell death. Upon describing how iron dysbiosis affects ferroptosis induction, we elaborate on the detrimental role of the iron-ferroptosis axis in several diseases. Future Directions: Despite compelling findings suggesting a role of ferroptosis in experimental animal models, the exact contribution of ferroptosis in human contexts still needs further investigation. Development of reliable ferroptosis biomarkers will be an important step in characterizing ferroptosis in human disease. This can provide therapeutic opportunities aiming at targeting ferroptosis in human diseases. Antioxid. Redox Signal. 35, 487-509.

A simplified diagnostic pathway for the differential diagnosis of iron deficiency anaemia and anaemia of chronic disease

INTRODUCTION

Iron deficiency anaemia (IDA) and anaemia of chronic disease (ACD) are common causes of anaemia with similar clinical and laboratory features. IDA is caused by low iron stores while ACD is due to iron-restricted erythropoiesis occurring in inflammatory states. Differential diagnosis requires analysis of multiple biochemical and haematological parameters. IDA can occur simultaneously to ACD (mixed aetiology). It is essential that true iron deficiency is identified, as these patients will require iron therapy. This preliminary study investigated whether hepcidin, the master regulator of iron homeostasis, in conjunction with reticulocyte haemoglobin equivalent (RetHe) has the potential to differentiate IDA from ACD, and to exclude IDA in patients with mixed aetiology.

METHODS

Hepcidin concentration (measured using a commercially available ELISA method), RetHe, and iron parameters along with C-reactive protein (CRP) were analysed in 77 Gastroenterology patients with anaemia in a secondary care setting.

RESULTS

Receiver operator characteristic (ROC) analysis showed that hepcidin at an optimal cut-off concentration of <6ng/ml could identify IDA with a sensitivity and specificity of 88.9% and 90.6% respectively and could distinguish ACD from IDA with both a sensitivity and specificity of 100% at a cut-off of >46ng/ml. Identifying true IDA in mixed aetiology patients could be achieved by RetHe analysis and applying an optimal cut-off of <30pg.

CONCLUSION

Hepcidin, in conjunction with RetHe, offers a new simplified diagnostic pathway for differential diagnosis of IDA and ACD, thereby reducing the diagnostic turnaround time and allowing appropriate treatment of patients with a true iron deficiency.

TfR1 Extensively Regulates the Expression of Genes Associated with Ion Transport and Immunity

Transferrin receptor 1 (TfR1), encoded by the TFRC gene, is the gatekeeper of cellular iron uptake for cells. A variety of molecular mechanisms are at work to tightly regulate TfR1 expression, and abnormal TfR1 expression has been associated with various diseases. In the current study, to determine the regulation pattern of TfR1, we cloned and overexpressed the human TFRC gene in HeLa cells. RNA-sequencing (RNA-seq) was used to analyze the global transcript levels in overexpressed (OE) and normal control (NC) samples. A total of 1669 differentially expressed genes (DEGs) were identified between OE and NC. Gene ontology (GO) analysis was carried out to explore the functions of the DEGs. It was found that multiple DEGs were associated with ion transport and immunity. Moreover, the regulatory network was constructed on basis of DEGs associated with ion transport and immunity, highlighting that TFRC was the node gene of the network. These results together suggested that precisely controlled TfR1 expression might be not only essential for iron homeostasis, but also globally important for cell physiology, including ion transport and immunity.

Safety of intravenous ferric carboxymaltose versus oral iron in patients with nondialysis-dependent CKD: an analysis of the 1-year FIND-CKD trial

Background. The evidence base regarding the safety of intravenous (IV) iron therapy in patients with chronic kidney disease (CKD) is incomplete and largely based on small studies of relatively short duration.

Methods. FIND-CKD (ClinicalTrials.gov number NCT00994318) was a 1-year, open-label, multicenter, prospective study of patients with nondialysis-dependent CKD, anemia and iron deficiency randomized (1:1:2) to IV ferric carboxymaltose (FCM), targeting higher (400–600 µg/L) or lower (100–200 µg/L) ferritin, or oral iron. A post hoc analysis of adverse event rates per 100 patient-years was performed to assess the safety of FCM versus oral iron over an extended period.

Results. The safety population included 616 patients. The incidence of one or more adverse events was 91.0, 100.0 and 105.0 per 100 patient-years in the high ferritin FCM, low ferritin FCM and oral iron groups, respectively. The incidence of adverse events with a suspected relation to study drug was 15.9, 17.8 and 36.7 per 100 patient-years in the three groups; for serious adverse events, the incidence was 28.2, 27.9 and 24.3 per 100 patient-years. The incidence of cardiac disorders and infections was similar between groups. At least one ferritin level ≥800 µg/L occurred in 26.6% of high ferritin FCM patients, with no associated increase in adverse events. No patient with ferritin ≥800 µg/L discontinued the study drug due to adverse events. Estimated glomerular filtration rate remained the stable in all groups.

Conclusions. These results further support the conclusion that correction of iron deficiency anemia with IV FCM is safe in patients with nondialysis-dependent CKD.

Strategy of Metal-Polymer Composite Stent To Accelerate Biodegradation of Iron-Based Biomaterials

The new principle and technique to tune biodegradation rates of biomaterials is one of the keys to the development of regenerative medicine and next-generation biomaterials. Biodegradable stents are new-generation medical devices applied in percutaneous coronary intervention, etc. Recently, both corrodible metals and degradable polymers have drawn much attention in biodegradable stents or scaffolds. It is, however, a dilemma to achieve good mechanical properties and appropriate degradation profiles. Herein, we put forward a metal-polymer composite strategy to achieve both. Iron stents exhibit excellent mechanical properties but low corrosion rate in vivo. We hypothesized that coating of biodegradable aliphatic polyester could accelerate iron corrosion due to the acidic degradation products, etc. To demonstrate the feasibility of this composite material technique, we first conducted in vitro experiments to affirm that iron sheet corroded faster when covered by polylactide (PLA) coating. Then, we fabricated three-dimensional metal-polymer stents (MPS) and implanted the novel stents in the abdominal aorta of New Zealand white rabbits, setting metal-based stents (MBS) as a control. A series of in vivo experiments were performed, including measurements of residual mass and radial strength of the stents, histological analysis, micro-computed tomography, and optical coherence tomography imaging at the implantation site. The results showed that MPS could totally corrode in some cases, whereas iron struts of MBS in all cases remained several months after implantation. Corrosion rates of MPS could be easily regulated by adjusting the composition of PLA coatings.

Parameters influencing in-hospital mortality in patients hospitalized in intensive cardiac care unit: is there an influence of anemia and iron deficiency?

We investigated the incidence and prognostic value of anemia as well as of the iron status in non-selected patients admitted to an intensive cardiac care unit (ICCU). 392 patients (mean age 70 ± 13.8 years, 43% women), 168 with acute coronary syndromes (ACS), 122 with acute decompensated heart failure, and 102 with other acute cardiac disorders were consecutively, prospectively assessed. The biomarkers of iron status-serum iron concentration (SIC), total iron binding capacity (TIBC), and transferrin saturation (TSAT) together with standard clinical, biochemical and echocardiographic variables-were analyzed. In-hospital mortality was 3.8% (15 patients). The prevalences of anemia (according to WHO criteria), and iron deficiency (ID) were 64 and 63%, respectively. The level of biomarkers of iron status, but not anemia, was lower in patients who died (p < 0.05). Anemia was less frequent in patients with ACS as compared to the remaining ICCU population (p = 0.019). The analysis by logistic regression indicated the highest risk of death for age [odds ratio (OD) 1.38, 95% CI 1.27-1.55], SIC (OR 0.85, 95% CI 0.78-0.94), TIBC (OR 0.95, 95% CI 0.91-0.98), left ventricle ejection fraction (OR 0.85, 95% CI 0.77-0.93), as well as hospitalization for non-ACS (OR 0.25, 95% CI 0.14-0.46), (p < 0.05). The risk of death during hospitalization tended to increase with decreasing levels of TIBC (p = 0.49), as well as with the absence of ACS (p = 0.54). The incidence of anemia and ID in heterogeneous ICCU patients is high. Parameters of the iron status, but not anemia per se, independently influence in-hospital mortality. The prevalence of anemia is higher in non-ACS patients, and tends to worsen the prognosis.

Fe-bLf nanoformulation targets survivin to kill colon cancer stem cells and maintains absorption of iron, calcium and zinc

Aim: To validate the anticancer efficacy of alginate-enclosed, chitosan-conjugated, calcium phosphate, iron-saturated bovine lactoferrin (Fe-bLf) nanocarriers/nanocapsules (NCs) with improved sustained release and ability to induce apoptosis by downregulating survivin, as well as cancer stem cells. Materials & methods: The stability, nanotoxicity of the modified nanoformulation was evaluated and their anticancer efficacy was re-examined. Their mechanism of internalization was studied and we identified the role of various miRNAs in absorption of these NCs/iron in various body parts of mice. We determined the effect of these NCs on survivin, stem cell markers, red blood cell count, iron, calcium and zinc concentration in mice, determined the antiangiogenic properties of these NCs and studied their effect on cancer stem-like cells. Results: Spherical NCs (396.1 ± 27.2 nm) exceedingly reduced viability of Caco-2 cells (32 ± 2.83%). The NCs also showed effective internalization and reduction of cancer stem cell markers in triple-positive CD133, survivin and CD44 cancer stem-like cells. Mice treated with the NCs showed no nanotoxicity and did not develop any tumors in xenograft colon cancer models. We found that the serum iron, zinc and calcium absorption were increased. DMT1, LRP, transferrin and lactoferrin receptors were responsible for internalization of the NCs. Different miRNAs were responsible for iron regulation in different organs. Interestingly, NCs inhibited survivin and its different isoforms. Conclusion: Our results confirmed that NCs internalized and changed the expression of selected miRNAs that further enhanced their uptake. The NCs activated both extrinsic, as well as intrinsic apoptotic pathways to induce apoptosis by targeting survivin in cancer cells and cancer stem cells, without inducing any nonspecific nanotoxicity. Apart from inhibiting angiogenesis and stem cell markers, NCs also maintained iron and calcium levels.

Original submitted 4 May 2014; Revised submitted 25 June 2014

Clinical significance of microcytosis in patients with primary myelofibrosis

Microcytosis is a relatively frequent finding in primary myelofibrosis (PMF); however its prognostic significance is unknown. We identified factors associated with microcytosis in PMF and measured its impact on outcomes. Among 725 patients with PMF, 140 (19%) showed microcytosis. In multivariate analysis, factors associated with microcytosis were absence of prior therapy, low iron, low transferrin saturation (satTF), and splenomegaly. Among 375 untreated patients, low satTF and splenomegaly were associated with microcytosis. Overall, microcytosis was associated with a higher risk of transformation to leukemia (p=0.03), but not shorter leukemia-free survival. Microcytosis in PMF may be related to dysregulation of iron homeostasis.

Preliminary investigation of bottlenose dolphins (Tursiops truncatus) for hfe gene-related hemochromatosis

Hemochromatosis (iron storage disease) has been reported in diverse mammals including bottlenose dolphins (Tursiops truncatus). The primary cause of excessive iron storage in humans is hereditary hemochromatosis. Most human hereditary hemochromatosis cases (up to 90%) are caused by a point mutation in the hfe gene, resulting in a C282Y substitution leading to iron accumulation. To evaluate the possibility of a hereditary hemochromatosis-like genetic predisposition in dolphins, we sequenced the bottlenose dolphin hfe gene, using reverse transcriptase-PCR and hfe primers designed from the dolphin genome, from liver of affected and healthy control dolphins. Sample size included two case animals and five control animals. Although isotype diversity was evident, no coding differences were identified in the hfe gene between any of the animals examined. Because our sample size was small, we cannot exclude the possibility that hemochromatosis in dolphins is due to a coding mutation in the hfe gene. Other potential causes of hemochromatosis, including mutations in different genes, diet, primary liver disease, and insulin resistance, should be evaluated.

Iron metabolism: from health to disease

BACKGROUND

Iron is vital for almost all living organisms by participating in a wide range of metabolic processes. However, iron concentration in body tissues must be tightly regulated since excessive iron may lead to microbial infections or cause tissue damage. Disorders of iron metabolism are among the most common human diseases and cover several conditions with varied clinical manifestations.

METHODS

An extensive literature review on the basic aspects of iron metabolism was performed, and the most recent findings on this field were highlighted as well.

RESULTS

New insights on iron metabolism have shed light into its real complexity, and its role in both healthy and pathological states has been recognized. Important discoveries about the iron regulatory machine and imbalances in its regulation have been made, which may lead in a near future to the development of new therapeutic strategies against iron disorders. Besides, the toxicity of free iron and its association with several pathologies has been addressed, although it requires further investigations.

CONCLUSION

This review will provide students in the fields of biochemistry and health sciences a brief and clear overview of iron physiology and toxicity, as well as imbalances in the iron homeostasis and associated pathological conditions.

Nucleotide/Tb3+ coordination polymer as a luminescent nanosensor: synthesis and sensing of iron(ii) in human serum

Lanthanide ions and nucleotides were used to design and prepare a kind of responsive luminescent nanosensor for iron ions through a self-assembly process.

Rescuing hepatocytes from iron-catalyzed oxidative stress using vitamins B1 and B6

In the following rescue experiments, iron-mediated hepatocyte oxidative stress cytotoxicity was found to be prevented if vitamin B1 or B6 was added 1h after treatment with iron. The role of iron in catalyzing Fenton-mediated oxidative damage has been implicated in iron overload genetic diseases, carcinogenesis (colon cancer), Alzheimer's disease and complications associated with the metabolic syndrome through the generation of reactive oxygen species (ROS). The objectives of this study were to interpret the cytotoxic mechanisms and intracellular targets of oxidative stress using "accelerated cytotoxicity mechanism screening" techniques (ACMS) and to evaluate the rescue strategies of vitamins B1 and B6. Significant cytoprotection by antioxidants or ROS scavengers indicated that iron-mediated cytotoxicity could be attributed to reactive oxygen species. Of the B6 vitamers, pyridoxal was best at rescuing hepatocytes from iron-catalyzed lipid peroxidation (LPO), protein oxidation, and DNA damage, while pyridoxamine manifested greatest protection against ROS-mediated damage. Thiamin (B1) decreased LPO, mitochondrial and protein damage and DNA oxidation. Together, these results indicate that added B1 and B6 vitamins protect against the multiple targets of iron-catalyzed oxidative damage in hepatocytes. This study provides insight into the search for multi-targeted natural therapies to slow or retard the progression of diseases associated with Fenton-mediated oxidative damage.