Iron release from macrophages after erythrophagocytosis is up-regulated by ferroportin 1 overexpression and down-regulated by hepcidin

Influencing factors of clinical efficacy of roxadustat among hemodialysis patients

OBJECTIVE

To explore independent influencing factors for clinical efficacy of roxadustat in hemodialysis patients.

METHODS

Hemodialysis patients treated with roxadustat were enrolled. The plasma trough concentrations of roxadustat were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A multiple logistic regression model was established to determine the factors that affect clinical efficacy of roxadustat in patients undergoing hemodialysis.

RESULTS

A total of 67 hemodialysis patients were enrolled in the study. The results showed that age, blood trough concentration of roxadustat, and baseline hemoglobin (Hb) level were independent factors of clinical efficacy of roxadustat (OR = 1.06, p = .025 for age; OR = 1.001, p = .037 for plasma concentration; and OR = 0.941, p = .003 for baseline Hb), with an AUC score of 0.859.

CONCLUSIONS

Age, blood trough concentration of roxadustat, and baseline Hb level were independent influencing factors of the response to roxadustat in hemodialysis patients.

Pharmacokinetics, pharmacodynamics, and tolerability of an aqueous formulation of rusfertide (PTG-300), a hepcidin mimetic, in healthy volunteers: A double-blind first-in-human study

OBJECTIVES

Rusfertide is a potent peptide mimetic of hepcidin being investigated for the treatment of polycythemia vera. This randomized, placebo-controlled, double-blind study evaluated the safety, pharmacokinetics, and pharmacodynamics of single and repeated subcutaneous doses of an aqueous formulation of rusfertide in healthy adult males.

METHODS

Subjects received single doses of 1, 3, 10, 20, 40, or 80 mg rusfertide or placebo. A separate cohort of subjects received two doses of 40 mg rusfertide or placebo 1 week apart. Blood samples for pharmacokinetics and pharmacodynamics were collected, and adverse events, clinical laboratory tests, 12-lead electrocardiograms, and vital signs were monitored.

RESULTS

Rusfertide was well tolerated. There were no serious or severe treatment-emergent adverse events, and no patterns of clinically important adverse events, or laboratory, vital sign, or electrocardiogram abnormalities. Mean maximum rusfertide plasma concentration (Cmax) and area under the concentration-time curve increased with dose, but less than dose proportionally. Median time to Cmax was 2-4.5 h for 40 and 80 mg rusfertide and 8-24 h for lower doses. Apparent clearance and half-life increased with dose. Single doses of rusfertide 1-80 mg were associated with dose-dependent decreases in serum iron and transferrin-iron saturation.

CONCLUSIONS

Rusfertide was well tolerated and showed dose-dependent pharmacokinetics and pharmacodynamics.

Apolipoprotein E deficiency leads to the polarization of splenic macrophages towards M1 phenotype by increasing iron content

Apolipoprotein E (ApoE) plays a crucial role in iron homeostasis in the body, while macrophages are the principal cells responsible for handling iron in mammals. However, it is unknown whether ApoE can affect the functional subtypes and the iron handling capacity of splenic macrophages (SM). Here, we investigated the effects of ApoE deficiency (ApoE-/-) on the polarization and iron content of SM and its potential mechanisms. ApoE-/- was found to induce a significant increase in the expressions of M1 marker genes CD86, IL-1β, IL-6, IL-12, TNF-α and iNOS and a reduction in M2 marker genes CD206, Arg-1, IL-10 and Ym-1 in SM of mice aged 28 weeks, Meanwhile, ApoE-/- caused a significant increase in iron content and expression of ferritin, transferrin receptor 1 (TfR1), iron regulatory protein 1 (IRP1) and heme oxygenase-1 (HO-1) and a reduction in ferroportin1 (Fpn1) in spleen and/or SM of mice aged 28 weeks. It was concluded that ApoE-/- can increase iron content through increased iron uptake mediated by TfR/ IRPs and decreased iron release mediated by Fpn1, leading to polarization of the SM to M1 phenotype.

Novel TMPRSS6 variants and their impact on iron-refractory iron deficiency anaemia in pregnancy: A North Indian genotype phenotype study

Iron-refractory iron deficiency anaemia (IRIDA) is a rare autosomal recessive disorder, distinguished by hypochromic microcytic anaemia, low transferrin levels and inappropriately elevated hepcidin (HEPC) levels. It is caused by mutations in TMPRSS6 gene. Systematic screening of 500 pregnant women with iron deficiency anaemia having moderate to severe microcytosis with no other causes of anaemia were enrolled to rule out oral iron refractoriness. It identified a final cohort of 10 (2.15% prevalence) individuals with IRIDA phenotype. Haematological and biochemical analysis revealed significant differences between iron responders and iron non-responders, with iron non-responders showing lower haemoglobin, red blood cell count, serum iron and serum ferritin levels, along with elevated HEPC (9.47 ± 2.75 ng/mL, p = 0.0009) and erythropoietin (4.58 ± 4.07 µ/mL, p = 0.0196) levels. Genetic sequencing of the TMPRSS6 gene in this final cohort identified 10 novel variants, including seven missense and three frame-shift mutations, with four missense variants showing high functional impact defining the IRIDA phenotype. Structural analysis revealed significant damage caused by two variants (p.L83R and p.S235R). This study provides valuable insights into IRIDA among pregnant women in the Indian subcontinent, unveiling its underlying causes of unresponsiveness, genetic mechanisms and prevalence. Furthermore, research collaboration is essential to validate these findings and develop effective treatments.

A Large Proportion of the Neonatal Iron Pool Is Acquired from the Gestational Diet in a Murine Model

BACKGROUND

Iron is crucial for growth and development, but excess iron is harmful. Neonatal mice have elevated concentrations of circulating iron, but the source of this iron is unclear. This lack of understanding makes it difficult to optimize early life iron balance.

OBJECTIVES

Identify the origins of neonatal tissue-specific iron pools using dietary manipulation and cross-fostering murine models.

METHODS

To determine whether tissue-specific neonatal iron was primarily acquired during gestation or after birth, pups born to iron-sufficient or iron-deficient dams were cross-fostered, and tissues were harvested at postnatal days 3-5 to measure iron content. A separate set of female mice were fed a diet enriched with the stable iron isotope 57 (57Fe) for 4 generations to replace naturally abundant liver iron isotope 56 (56Fe) stores with 57Fe. To quantify the proportions of neonatal iron acquired during gestation, pups born to dams with 56Fe or 57Fe stores were cross-fostered, and tissues were harvested at postnatal day 3-5 to determine 56Fe:57Fe ratios by inductively coupled plasma mass spectrometry. Finally, to quantify the proportion of neonatal iron acquired from the maternal diet, female mice with 56Fe or 57Fe stores switched diets upon mating, and pup tissues were harvested on P0 to determine 56Fe:57Fe ratios by inductively coupled plasma mass spectrometry.

RESULTS

Perinatal iron deficiency resulted in smaller pups, and gestational iron deficiency resulted in lower neonatal serum and liver iron. Cross-fostering between dams with 56Fe and 57Fe stores demonstrated that ≤70% of neonatal serum, liver, and brain iron were acquired during gestation. Dietary manipulation experiments using dams with 56Fe and 57Fe stores showed that over half of neonatal serum, liver, and brain iron were from the dam's gestational diet rather than preconception iron stores.

CONCLUSIONS

This study provides quantitative values for the sources of neonatal iron, which may inform approaches to optimize neonatal iron status.

Ferroptosis: principles and significance in health and disease

Ferroptosis, an iron-dependent form of cell death characterized by uncontrolled lipid peroxidation, is governed by molecular networks involving diverse molecules and organelles. Since its recognition as a non-apoptotic cell death pathway in 2012, ferroptosis has emerged as a crucial mechanism in numerous physiological and pathological contexts, leading to significant therapeutic advancements across a wide range of diseases. This review summarizes the fundamental molecular mechanisms and regulatory pathways underlying ferroptosis, including both GPX4-dependent and -independent antioxidant mechanisms. Additionally, we examine the involvement of ferroptosis in various pathological conditions, including cancer, neurodegenerative diseases, sepsis, ischemia-reperfusion injury, autoimmune disorders, and metabolic disorders. Specifically, we explore the role of ferroptosis in response to chemotherapy, radiotherapy, immunotherapy, nanotherapy, and targeted therapy. Furthermore, we discuss pharmacological strategies for modulating ferroptosis and potential biomarkers for monitoring this process. Lastly, we elucidate the interplay between ferroptosis and other forms of regulated cell death. Such insights hold promise for advancing our understanding of ferroptosis in the context of human health and disease.

Isobavachin attenuates osteoclastogenesis and periodontitis-induced bone loss by inhibiting cellular iron accumulation and mitochondrial biogenesis

As bone-resorbing cells rich in mitochondria, osteoclasts require high iron uptake to promote mitochondrial biogenesis and maintain a high-energy metabolic state for active bone resorption. Given that abnormal osteoclast formation and activation leads to imbalanced bone remodeling and osteolytic bone loss, osteoclasts may be crucial targets for treating osteolytic diseases such as periodontitis. Isobavachin (IBA), a natural flavonoid compound, has been confirmed to be an inhibitor of receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation from bone marrow-derived macrophages (BMMs). However, its effects on periodontitis-induced bone loss and the potential mechanism of its anti-osteoclastogenesis effect remain unclear. Our study demonstrated that IBA suppressed RANKL-induced osteoclastogenesis in BMMs and RAW264.7 cells and inhibited osteoclast-mediated bone resorption in vitro. Transcriptomic analysis indicated that iron homeostasis and reactive oxygen species (ROS) metabolic process were enriched among the differentially expressed genes following IBA treatment. IBA exerted its anti-osteoclastogenesis effect by inhibiting iron accumulation in osteoclasts. Mechanistically, IBA attenuated iron accumulation in RANKL-induced osteoclasts by inhibiting the mitogen-activated protein kinase (MAPK) pathway to upregulate ferroportin1 (Fpn1) expression and promote Fpn1-mediated intracellular iron efflux. We also found that IBA inhibited mitochondrial biogenesis and function, and reduced RANKL-induced ROS generation in osteoclasts. Furthermore, IBA attenuated periodontitis-induced bone loss by reducing osteoclastogenesis in vivo. Overall, these results suggest that IBA may serve as a promising therapeutic strategy for bone diseases characterized by osteoclastic bone resorption.

Why cells need iron: a compendium of iron utilisation

Iron deficiency is globally prevalent, causing an array of developmental, haematological, immunological, neurological, and cardiometabolic impairments, and is associated with symptoms ranging from chronic fatigue to hair loss. Within cells, iron is utilised in a variety of ways by hundreds of different proteins. Here, we review links between molecular activities regulated by iron and the pathophysiological effects of iron deficiency. We identify specific enzyme groups, biochemical pathways, cellular functions, and cell lineages that are particularly iron dependent. We provide examples of how iron deprivation influences multiple key systems and tissues, including immunity, hormone synthesis, and cholesterol metabolism. We propose that greater mechanistic understanding of how cellular iron influences physiological processes may lead to new therapeutic opportunities across a range of diseases.

The role of TMPRSS6 gene polymorphism in iron resistance iron deficiency anaemia (IRIDA): a systematic review

Iron resistance iron deficiency anaemia is a rare autosomal recessive disorder characterized by hypochromic microcytic anaemia, low transferrin saturation and inappropriately high hepcidin levels. The aetiology of this condition is rooted in genetic variations within the transmembrane serine protease 6 (TMPRSS6) genes, responsible for encoding matriptase-2, a pivotal negative regulator of hepcidin. We conducted a systematic search across four electronic databases, yielding 538 articles in total out of which 25 were finally included and were preceded further, aiming to prognosticate prevalent single nucleotide polymorphisms (SNPs) and detrimental genetic alterations. This review aims to elucidate the effects of various SNPs and pathogenic mutations on both haematological and biochemical parameters, as well as their potential interethnic correlation. Employing bioinformatics tools, we subjected over 100 SNPs to scrutiny, discerning their potential functional ramifications. We found rs1373272804, rs1430692214 and rs855791 variants to be most frequent and were having a significant impact on haematological and biochemical profile. We found that individuals of European ancestry were more prone to have these variants compared to other ethnic groups. In conclusion, this review not only sheds light on the association of TMPRSS6 polymorphism in iron resistance iron deficiency anaemia (IRIDA), but also highlights the critical need for further investigations involving larger sample size and more diverse ethnic groups around the globe. These future studies will be vital for gaining a stronger and more reliable understanding of how these genetic differences are linked to the development of IRIDA.

Upregulation of ATP6V0D2 benefits intracellular survival of Leishmania donovani in erythrocytes-engulfing macrophages

Visceral leishmaniasis (VL) is the most severe type of leishmaniasis which is caused by infection of Leishmania donovani complex. In the BALB/c mouse model of VL, multinucleated giant cells (MGCs) with heavy parasite infection consist of the largest population of hemophagocytes in the spleen of L. donovani-infected mice, indicating that MGCs provide the parasites a circumstance beneficial for their survival. Although ATP6V0D2 is a demonstrated factor inducing the formation of hemophagocytic MGCs during L. donovani infection, functions of this protein in shaping the infection outcome in macrophages remain unclear. Here we evaluated the influence of upregulated ATP6V0D2 on intracellular survival of the parasites. L. donovani infection-induced hemophagocytosis of normal erythrocytes by macrophages was suppressed by RNAi-based knockdown of Atp6v0d2. The knockdown of Atp6v0d2 did not improve the survival of amastigotes within macrophages when the cells were cultured in the absence of erythrocytes. On the other hand, reduced intracellular survival of amastigotes in macrophages by the knockdown was observed when macrophages were supplemented with antibody-opsonized erythrocytes before infection. There, increase in cytosolic labile iron pool was observed in the L. donovani-infected knocked-down macrophages. It suggests that ATP6V0D2 plays roles not only in upregulation of hemophagocytosis but also in iron trafficking within L. donovani-infected macrophages. Superior access to iron in macrophages may be how the upregulated expression of the molecule brings benefit to Leishmania for their intracellular survival in the presence of erythrocytes.

Access and utilization of host-derived iron by Leishmania parasites

Iron is involved in many biochemical processes including oxygen transport, ATP production, DNA synthesis and antioxidant defense. The importance of iron also applies to Leishmania parasites, an intracellular protozoan pathogen causing leishmaniasis. Leishmania are heme-auxotrophs, devoid of iron storage proteins and the heme synthesis pathway. Acquisition of iron and heme from the surrounding niche is thus critical for the intracellular survival of Leishmania inside the host macrophages. Moreover, Leishmania parasites are also exposed to oxidative stress within phagolysosomes of macrophages in mammalian hosts, and they need iron superoxide dismutase for overcoming this stress. Therefore, untangling the strategy adopted by these parasites for iron acquisition and utilization can be good targets for the development of antileishmanial drugs. Here, in this review, we will address how Leishmania parasites acquire and utilize iron and heme during infection to macrophages.

Iron metabolism in colorectal cancer: a balancing act

BACKGROUND

Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the second deadliest malignancy worldwide. Current dietary habits are associated with increased levels of iron and heme, both of which increase the risk of developing CRC. The harmful effects of iron overload are related to the induction of iron-mediated pro-tumorigenic pathways, including carcinogenesis and hyperproliferation. On the other hand, iron deficiency may also promote CRC development and progression by contributing to genome instability, therapy resistance, and diminished immune responses. In addition to the relevance of systemic iron levels, iron-regulatory mechanisms in the tumor microenvironment are also believed to play a significant role in CRC and to influence disease outcome. Furthermore, CRC cells are more prone to escape iron-dependent cell death (ferroptosis) than non-malignant cells due to the constitutive activation of antioxidant genes expression. There is wide evidence that inhibition of ferroptosis may contribute to the resistance of CRC to established chemotherapeutic regimens. As such, ferroptosis inducers represent promising therapeutic drugs for CRC.

CONCLUSIONS AND PERSPECTIVES

This review addresses the complex role of iron in CRC, particularly in what concerns the consequences of iron excess or deprivation in tumor development and progression. We also dissect the regulation of cellular iron metabolism in the CRC microenvironment and emphasize the role of hypoxia and of oxidative stress (e.g. ferroptosis) in CRC. Finally, we underline some iron-related players as potential therapeutic targets against CRC malignancy.

Ferroptosis in Neurological Disease

Iron accumulation in the CNS occurs in many neurological disorders. It can contribute to neuropathology as iron is a redox-active metal that can generate free radicals. The reasons for the iron buildup in these conditions are varied and depend on which aspects of iron influx, efflux, or sequestration that help maintain iron homeostasis are dysregulated. Iron was shown recently to induce cell death and damage via lipid peroxidation under conditions in which there is deficient glutathione-dependent antioxidant defense. This form of cell death is called ferroptosis. Iron chelation has had limited success in the treatment of neurological disease. There is therefore much interest in ferroptosis as it potentially offers new drugs that could be more effective in reducing iron-mediated lipid peroxidation within the lipid-rich environment of the CNS. In this review, we focus on the molecular mechanisms that induce ferroptosis. We also address how iron enters and leaves the CNS, as well as the evidence for ferroptosis in several neurological disorders. Finally, we highlight biomarkers of ferroptosis and potential therapeutic strategies.

The effects of soil intake on the growth performance, rumen microbial community and tissue mineral deposition of German Mutton Merino sheep

Soil ingestion by livestock is common in grazing ecosystems, but few studies have been conducted to assess its effect on the animal organism. The topic is worthy of attention because these potential effects are likely to be enriched in the food chain and interfere with animal and human health. In this study, we present an indoor feeding trial conducted based on a completely randomized design to comprehensively evaluate the effects of simulated soil ingestion during grazing on nutrient digestibility, rumen fermentation, and microflora, and mineral deposition in the organs and tissues of sheep. Eighteen Mutton Merino crossbred sheep (42.7 ± 2.34 kg) were randomly allotted to three treatments and fed diets containing 0% (Control), 5% (SOIL5), and 10% (SOIL10) for 62 d, including a 7-d metabolism trial. It was found that soil intake altered the rumen fermentation in sheep, as evidenced by a decrease in total volatile fatty acids (VFA) and acetate concentrations in rumen fluid of 50.6% and 51.3%, respectively (p < 0.01), with soil proportion in the diet increased from 0% to 10%. Soil ingestion also reduced the species richness of rumen bacteria, with the relative abundance of Bacteroidetes decreasing significantly (p < 0.01), while that of Firmicutes and Proteobacteria increased considerably (p < 0.05). In terms of mineral elements deposition, higher levels of iron (Fe) were detected in the spleen and liver, and a higher concentration of copper (Cu) and zinc (Zn) in the liver were found in sheep fed a diet containing 5% soil compared to the other two groups (p < 0.05). Moreover, the concentrations of lead (Pb) in the liver and kidney, and arsenic (As) in the heart were also clearly increased after ingestion of soil (p < 0.05). Our findings indicate that although soil intake had no significant effect on the growth performance of sheep, it altered ruminal fermentation and increased the risk of excessive Fe, Pb, and As in their organism. This study supplies a theoretical basis for risk assessment of soil ingestion in grazing livestock.

Myeloid Hif2α is not essential to maintain systemic iron homeostasis

Dietary consumption serves as the primary source of iron uptake, and erythropoiesis acts as a major regulator of systemic iron demand. In addition to intestinal iron absorption, macrophages play a crucial role in recycling iron from senescent red blood cells. The kidneys are responsible for the production of erythropoietin (Epo), which stimulates erythropoiesis, whereas the liver plays a central role in producing the iron-regulatory hormone hepcidin. The transcriptional regulator hypoxia-inducible factor (HIF)2α has a central role in the regulation of Epo, hepcidin, and intestinal iron absorption and therefore plays a crucial role in coordinating the tissue crosstalk to maintain systemic iron demands. However, the precise involvement of Hif2α in macrophages in terms of iron homeostasis remains uncertain. Our study demonstrates that deleting Hif2α in macrophages does not disrupt the expression of iron transporters or basal erythropoiesis. Mice lacking Hif2α in myeloid cells exhibited no discernible differences in hemodynamic parameters, including hemoglobin concentrations and erythrocyte count, when compared with littermate controls. This similarity was observed under conditions of both dietary iron deficiency and acute erythropoietic demand. Notably, we observed a significant increase in the expression of iron transporters in the duodenum during iron deficiency, indicating heightened iron absorption. Therefore, our findings suggest that the disruption of Hif2α in myeloid cells does not significantly impact systemic iron homeostasis under normal physiologic conditions. However, its disruption induces adaptive physiologic changes in response to elevated iron demand, potentially serving as a mechanism to sustain increased erythropoietic demand.

Effects of hypoxia-inducible factor prolyl hydroxylase inhibitors versus erythropoiesis-stimulating agents on iron metabolism and inflammation in patients undergoing dialysis: A systematic review and meta-analysis

Aims

This study aimed to evaluate the effects of hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF-PHIs) on iron metabolism and inflammation in dialysis-dependent chronic kidney disease (DD-CKD) patients.

Methods

PubMed, Embase, Web of Science, Cochrane Library, and ClinicalTrials.gov websites were searched for randomized controlled trials (RCTs) investigating HIF-PHIs versus ESAs for DD-CKD patients.

Key findings

Twenty studies with 14,737 participants were included in the meta-analysis, which demonstrated no significant difference in the effect of transferrin saturation and ferritin between HIF-PHIs and the ESAs group (MD, 0.65; 95%CI, -0.45 to 1.75; very low certainty; SMD, -0.03; 95% CI, -0.13 to 0.07; low certainty). However, HIF-PHIs significantly increased the iron (MD, 2.30; 95% CI, 1.40 to 3.20; low certainty), total iron-binding capacity (SMD, 0.82; 95% CI, 0.66 to 0.98; low certainty), and transferrin (SMD, 0.90; 95%CI, 0.74 to 1.05; moderate certainty) levels when compared with the ESAs group. In contrast, the hepcidin level and dosage of intravenous iron were significantly decreased in the HIF-PHIs group compared with the ESAs group (MD, -15.06, 95%CI, -21.96 to -8.16; low certainty; MD, -18.07; 95% CI, -30.05 to -6.09; low certainty). The maintenance dose requirements of roxadustat were independent of baseline CRP or hsCRP levels with respect to the effect on inflammation.

Significance

HIF-PHIs promote iron utilization and reduce the use of intravenous iron therapy. Furthermore, HIF-PHIs, such as roxadustat, maintain the erythropoietic response independent of the inflammatory state. Thus, HIF-PHIs may be an alternative treatment strategy for anemia in DD-CKD patients, where ESA is hyporesponsive due to iron deficiency and inflammation.

A Novel Hepcidin Mutation

BACKGROUND

The bioactive peptide hormone hepcidin-25 regulates iron levels by inhibiting iron transport to plasma via ferroportin. Hepcidin-25 is synthesized in the liver where the 84 amino acids pro-hepcidin is cleaved into the bioactive hepcidin-25. A patient admitted to the hospital presented with infertility and fatigue.

METHODS

Genomic DNA was purified from whole blood using the Maxwell 16 system (Promega). MLPA analysis was performed to detect large genomic rearrangements using the SALSA MLPA kit # P347, Hemochromatosis (MRC Holland, Holland). Plasma hepcidin measurements were performed using liquid chromatography/tandem mass spectrometry (LC-MS/MS).

RESULTS

A novel HAMP mutation (homozygous one base deletion in c.215delG, p.Cys72Serfs*?) was detected. The deletion in nucleotide 215 causes a frameshift altering the predicted protein sequence from cysteine13 in mature peptide. Whether this leads to nonsense mediated decay of the mRNA or synthesis of an aberrant peptide in unknown, but bioactive hepcidin-25 was undetectable in plasma. The patient had massive iron overload with ferritin up to 8360 µg/L. He was anaemic with a Hb at 7.0 mmol/L (11.3 g/dL) and suffered from hypogonadotropic hypogonadism with a total testosterone of 1.2 nmol/l . Continued treatment with venesection and gonadotropins led to reduced fatigue, reduction in iron overload, a normalized Hb and improvement of semen quality.

CONCLUSION

A novel hepcidin mutation was detected in a patient with massive iron overload, fatigue and hypogonadotropic hypogonadism.

Iron cycle disruption by heme oxygenase-1 activation leads to a reduced breast cancer cell survival

Heme oxygenase-1 (HO-1), which catalyzes heme degradation releasing iron, regulates several processes related to breast cancer. Iron metabolism deregulation is also connected with several tumor processes. However the regulatory relationship between HO-1 and iron proteins in breast cancer remains unclear. Using human breast cancer biopsies, we found that high HO-1 levels significantly correlated with low DMT1 levels. Contrariwise, high HO-1 levels significantly correlated with high ZIP14 and prohepcidin expression, as well as hemosiderin storage. At mRNA level, we found that high HO-1 expression significantly correlated with low DMT1 expression but high ZIP14, L-ferritin and hepcidin expression. In in vivo experiments in mice with genetic overexpression or pharmacological activation of HO-1, we detected the same expression pattern observed in human biopsies. In in vitro experiments, HO-1 activation induced changes in iron proteins expression leading to an increase of hemosiderin, ROS levels, lipid peroxidation and a decrease of the growth rate. Such low growth rate induced by HO-1 activation was reversed when iron levels or ROS levels were reduced. Our findings demonstrate an important role of HO-1 on iron homeostasis in breast cancer. The changes in iron proteins expression when HO-1 is modulated led to the iron accumulation deregulating the iron cell cycle, and consequently, generating oxidative stress and low viability, all contributing to impair breast cancer progression.

Mechanism of Ca2+ transport by ferroportin

Ferroportin (Fpn) is a transporter that releases ferrous ion (Fe²⁺) from cells and is important for homeostasis of iron in circulation. Export of one Fe²⁺ by Fpn is coupled to import of two H⁺ to maintain charge balance. Here, we show that human Fpn (HsFpn) binds to and mediates Ca²⁺ transport. We determine the structure of Ca²⁺-bound HsFpn and identify a single Ca²⁺ binding site distinct from the Fe²⁺ binding sites. Further studies validate the Ca²⁺ binding site and show that Ca²⁺ transport is not coupled to transport of another ion. In addition, Ca²⁺ transport is significantly inhibited in the presence of Fe²⁺ but not vice versa. Function of Fpn as a Ca²⁺ uniporter may allow regulation of iron homeostasis by Ca²⁺.

“Ferrocrinology”—Iron Is an Important Factor Involved in Gluco- and Lipocrinology

“Ferrocrinology” is the term used to describe the study of iron effects on the functioning of adipose tissue, which together with muscle tissue makes the largest endocrine organ in the human body. By impairing exercise capacity, reducing AMP-activated kinase activity, and enhancing insulin resistance, iron deficiency can lead to the development of obesity and type 2 diabetes mellitus. Due to impaired browning of white adipose tissue and reduced mitochondrial iron content in adipocytes, iron deficiency (ID) can cause dysfunction of brown adipose tissue. By reducing ketogenesis, aconitase activity, and total mitochondrial capacity, ID impairs muscle performance. Another important aspect is the effect of ID on the impairment of thermogenesis due to reduced binding of thyroid hormones to their nuclear receptors, with subsequently impaired utilization of norepinephrine in tissues, and impaired synthesis and distribution of cortisol, which all make the body’s reactivity to stress in ID more pronounced. Iron deficiency can lead to the development of the most common endocrinopathy, autoimmune thyroid disease. In this paper, we have discussed the role of iron in the cross-talk between glucocrinology, lipocrinology and myocrinology, with thyroid hormones acting as an active bystander.

Reprogramming of pancreatic adenocarcinoma immunosurveillance by a microbial probiotic siderophore

There is increasing evidence suggesting the role of microbiome alterations in relation to pancreatic adenocarcinoma and tumor immune functionality. However, molecular mechanisms of the interplay between microbiome signatures and/or their metabolites in pancreatic tumor immunosurveillance are not well understood. We have identified that a probiotic strain (Lactobacillus casei) derived siderophore (ferrichrome) efficiently reprograms tumor-associated macrophages (TAMs) and increases CD8 + T cell infiltration into tumors that paralleled a marked reduction in tumor burden in a syngeneic mouse model of pancreatic cancer. Interestingly, this altered immune response improved anti-PD-L1 therapy that suggests promise of a novel combination (ferrichrome and immune checkpoint inhibitors) therapy for pancreatic cancer treatment. Mechanistically, ferrichrome induced TAMs polarization via activation of the TLR4 pathway that represses the expression of iron export protein ferroportin (FPN1) in macrophages. This study describes a novel probiotic based molecular mechanism that can effectively induce anti-tumor immunosurveillance and improve immune checkpoint inhibitors therapy response in pancreatic cancer.

Can Iron Play a Crucial Role in Maintaining Cardiovascular Health in the 21st Century?

In the 21st century the heart is facing more and more challenges so it should be brave and iron to meet these challenges. We are living in the era of the COVID-19 pandemic, population aging, prevalent obesity, diabetes and autoimmune diseases, environmental pollution, mass migrations and new potential pandemic threats. In our article we showed sophisticated and complex regulations of iron metabolism. We discussed the impact of iron metabolism on heart diseases, treatment of heart failure, diabetes and obesity. We faced the problems of constant stress, climate change, environmental pollution, migrations and epidemics and showed that iron is really essential for heart metabolism in the 21st century.

Caffeine Decreases Hepcidin Expression to Alleviate Aberrant Iron Metabolism under Inflammation by Regulating the IL-6/STAT3 Pathway

Caffeine is well-known as a psychostimulant, and it can also be beneficial in numerous diseases such as diabetes and different types of cancer. Previous studies have shown that caffeine can have a protective role in bacterial infection-induced inflammation and hyperoxia-mediated pulmonary inflammation. Hepcidin, which is regulated by the IL-6/STAT3 inflammation pathway, is a peptide hormone that maintains systemic iron homeostasis. We hypothesized that caffeine's effects on inflammation may also influence hepcidin production and therefore systemic iron metabolism. To this end, we treated 2-month-old mice with caffeine by daily intragastric administration for 7 days, administering intraperitoneal LPS after the final caffeine treatment. Twelve hours after LPS treatment the mice were euthanized, and tissues were collected. We found that caffeine decreased hepatic hepcidin expression and attenuated LPS-induced hepatic hepcidin overexpression. IL-6 expression and STAT3 phosphorylation were also reduced upon caffeine administration. Additionally, hepatic and splenic FPN1 levels increased after caffeine treatment, leading to lower iron levels in liver and spleen tissues and higher iron levels in serum. Caffeine also prevented the increase in spleen weight and decrease in body weight after LPS treatment. Together, our findings suggest that caffeine decreases hepcidin expression via inhibiting inflammation and the activation of the IL-6/STAT3 pathway, thus presenting an attractive, potential therapeutic for the treatment of anemia of inflammation.

Dysregulation of Iron Homeostasis in the Central Nervous System and the Role of Ferroptosis in Neurodegenerative Disorders

Significance: Iron accumulation occurs in the central nervous system (CNS) in a variety of neurological conditions as diverse as spinal cord injury, stroke, multiple sclerosis, Parkinson's disease, and others. Iron is a redox-active metal that gives rise to damaging free radicals if its intracellular levels are not controlled or if it is not properly sequestered within cells. The accumulation of iron occurs due to dysregulation of mechanisms that control cellular iron homeostasis. Recent Advances: The molecular mechanisms that regulate cellular iron homeostasis have been revealed in much detail in the past three decades, and new advances continue to be made. Understanding which aspects of iron homeostasis are dysregulated in different conditions will provide insights into the causes of iron accumulation and iron-mediated tissue damage. Recent advances in iron-dependent lipid peroxidation leading to cell death, called ferroptosis, has provided useful insights that are highly relevant for the lipid-rich environment of the CNS. Critical Issues: This review examines the mechanisms that control normal cellular iron homeostasis, the dysregulation of these mechanisms in neurological disorders, and more recent work on how iron can induce tissue damage via ferroptosis. Future Directions: Quick and reliable tests are needed to determine if and when ferroptosis contributes to the pathogenesis of neurological disorders. In addition, there is need to develop better druggable agents to scavenge lipid radicals and reduce CNS damage for neurological conditions for which there are currently few effective treatments. Antioxid. Redox Signal. 37, 150-170.

Shigella iron-binding proteins: An insight into molecular physiology, pathogenesis, and potential target vaccine development

Shigella is a well-known etiological agent responsible for intestinal infection among children, the elderly, and immunocompromised people ranging from mild to severe cases. Shigellosis remains endemic in Malaysia and yet there is no commercial vaccine available to eradicate the disease. Iron is an essential element for the survival of Shigella within the host. Hence, it is required for regulating metabolic mechanisms and virulence determinants. Alteration of iron status in the extracellular environment directly triggers the signal in enteropathogenic bacterial, providing information that they are in a hostile environment. To survive in an iron-limited environment, molecular regulation of iron-binding proteins plays a vital role in facilitating the transportation and utilization of sufficient iron sources. Given the importance of iron molecules for bacterial survival and pathogenicity, this review summarizes the physiological role of iron-binding proteins in bacterial survival and their potential use in vaccine and therapeutic developments.

Hemoglobin Endocytosis and Intracellular Trafficking: A Novel Way of Heme Acquisition by Leishmania

Leishmania species are causative agents of human leishmaniasis, affecting 12 million people annually. Drugs available for leishmaniasis are toxic, and no vaccine is available. Thus, the major thrust is to identify new therapeutic targets. Leishmania is an auxotroph for heme and must acquire heme from the host for its survival. Thus, the major focus has been to understand the heme acquisition process by the parasites in the last few decades. It is conceivable that the parasite is possibly obtaining heme from host hemoprotein, as free heme is not available in the host. Current understanding indicates that Leishmania internalizes hemoglobin (Hb) through a specific receptor by a clathrin-mediated endocytic process and targets it to the parasite lysosomes via the Rab5 and Rab7 regulated endocytic pathway, where it is degraded to generate intracellular heme that is used by the parasite. Subsequently, intra-lysosomal heme is initially transported to the cytosol and is finally delivered to the mitochondria via different heme transporters. Studies using different null mutant parasites showed that these receptors and transporters are essential for the survival of the parasite. Thus, the heme acquisition process in Leishmania may be exploited for the development of novel therapeutics.

Crosstalk between Heme Oxygenase-1 and Iron Metabolism in Macrophages: Implications for the Modulation of Inflammation and Immunity

Heme oxygenase-1 (HO-1) is an enzyme that catalyzes the degradation of heme, releasing equimolar amounts of carbon monoxide (CO), biliverdin (BV), and iron. The anti-inflammatory and antioxidant properties of HO-1 activity are conferred in part by the release of CO and BV and are extensively characterized. However, iron constitutes an important product of HO-1 activity involved in the regulation of several cellular biological processes. The macrophage-mediated recycling of heme molecules, in particular those contained in hemoglobin, constitutes the major mechanism through which living organisms acquire iron. This process is finely regulated by the activities of HO-1 and of the iron exporter protein ferroportin. The expression of both proteins can be induced or suppressed in response to pro- and anti-inflammatory stimuli in macrophages from different tissues, which alters the intracellular iron concentrations of these cells. As we discuss in this review article, changes in intracellular iron levels play important roles in the regulation of cellular oxidation reactions as well as in the transcriptional and translational regulation of the expression of proteins related to inflammation and immune responses, and therefore, iron metabolism represents a potential target for the development of novel therapeutic strategies focused on the modulation of immunity and inflammation.

Macrophage-mediated delivery of Fe3O4-nanoparticles: a generalized strategy to deliver iron to Tumor Microenvironment

Background：Iron are used to alter macrophage phenotypes and induce tumor cell death. Iron oxide nanoparticles can induce macrophage polarization into the M1 phenotype, which inhibits tumor growth and can dissociate into iron ions in macrophages. Objective：In this study, we proposed to construct high expression of Ferroportin1 macrophages as carriers to deliver Fe3O4-nanoparticles and iron directly to tumor sites.

METHODS

Three sizes of Fe3O4-nanoparticles with gradient concentrations were used. The migration ability of iron-carrying macrophages was confirmed by an in vitro migration experiment and monocyte chemoattractant protein-1 detection. The release of iron from macrophages was confirmed by determining their levels in the cell culture supernatant, and we constructed a high expression of ferroportin strain of macrophage lines to increase intracellular iron efflux by increasing membrane transferrin expression. Fe3O4-NPs in Ana-1 cells were degraded in lysosomes, and the amount of iron released was correlated with the expression of ferroportin1.

RESULTS

After Fe3O4-nanoparticles uptake by macrophages, not only polarized macrophages into M1 phenotype, but the nanoparticles also dissolved in the lysosome and iron were released out of the cell. FPN1 has known as the only known Fe transporter, we use Lentiviral vector carrying FPN1 gene transfected into macrophages, has successfully constructed Ana-1-FPN1 cells, and maintains high expression of FPN1. Ana-1-FPN1 cells increases intracellular iron release. Fe3O4-nanoparticles loaded engineered Ana-1 macrophages can act as a "reservoir" of iron.

CONCLUSION

Our study provides proof of strategy for Fe3O4-NPs target delivery to the tumor microenvironment. Moreover, increase of intracellular iron efflux by overexpression of FPN1, cell carriers can act as a reservoir for iron, providing the basis for targeted delivery of Fe3O4-NPs and iron ions in vivo.

The Role of Iron in Staphylococcus aureus Infection and Human Disease: A Metal Tug of War at the Host—Microbe Interface

Iron deficiency anemia can be treated with oral or intravenous Fe supplementation. Such supplementation has considerable effects on the human microbiome, and on opportunistic pathogenic micro-organisms. Molecular understanding of the control and regulation of Fe availability at the host-microbe interface is crucial to interpreting the side effects of Fe supplementation. Here, we provide a concise overview of the regulation of Fe by the opportunistic pathogen Staphylococcus aureus. Ferric uptake regulator (Fur) plays a central role in controlling Fe uptake, utilization and storage in order to maintain a required value. The micro-organism has a strong preference for heme iron as an Fe source, which is enabled by the Iron-regulated surface determinant (Isd) system. The strategies it employs to overcome Fe restriction imposed by the host include: hijacking host proteins, replacing metal cofactors, and replacing functions by non-metal dependent enzymes. We propose that integrated omics approaches, which include metalloproteomics, are necessary to provide a comprehensive understanding of the metal tug of war at the host-microbe interface down to the molecular level.

Photomedicine based on heme-derived compounds

Photoimaging and phototherapy have become major platforms for the diagnosis and treatment of various health complications. These applications require a photosensitizer (PS) that is capable of absorbing light from a source and converting it into other energy forms for detection and therapy. While synthetic inorganic materials such as quantum dots and gold nanorods have been widely explored for their medical diagnosis and photodynamic (PDT) and photothermal (PTT) therapy capabilities, translation of these technologies has lagged, primarily owing to potential cytotoxicity and immunogenicity issues. Of the various photoreactive molecules, the naturally occurring endogenous compound heme, a constituent of red blood cells, and its derivatives, porphyrin, biliverdin and bilirubin, have shown immense potential as noteworthy candidates for clinically translatable photoreactive agents, as evidenced by previous reports. While porphyrin-based photomedicines have attracted significant attention and are well documented, research on photomedicines based on two other heme-derived compounds, biliverdin and bilirubin, has been relatively lacking. In this review, we summarize the unique photoproperties of heme-derived compounds and outline recent efforts to use them in biomedical imaging and phototherapy applications.

The microbiota regulates hematopoietic stem cell fate decisions by controlling iron availability in bone marrow

Host microbiota crosstalk is essential for the production and functional modulation of blood-cell lineages. Whether, and if so how, the microbiota influences hematopoietic stem cells (HSCs) is unclear. Here, we show that the microbiota regulates HSC self-renewal and differentiation under stress conditions by modulating local iron availability in the bone marrow (BM). In microbiota-depleted mice, HSC self-renewal was enhanced during regeneration, while the commitment toward differentiation was dramatically compromised. Mechanistically, microbiota depletion selectively impaired the recycling of red blood cells (RBCs) by BM macrophages, resulting in reduced local iron levels without affecting systemic iron homeostasis. Limiting iron availability in food (in vivo) or in culture (ex vivo), or by CD169⁺ macrophage depletion, enhanced HSC self-renewal and expansion. These results reveal an intricate interplay between the microbiota, macrophages, and iron, and their essential roles in regulating critical HSC fate decisions under stress.

Hemosiderin Accumulation in Liver Decreases Iron Availability in Tachycardia-Induced Porcine Congestive Heart Failure Model

Despite advances in the management of iron deficiency in heart failure (HF), the mechanisms underlying the effects of treatment remain to be established. Iron distribution and metabolism in HF pathogenesis need to be clarified. We used a porcine tachycardia-induced cardiomyopathy model to find out how HF development influences hepatic and myocardial iron storing, focusing on ferritin, the main iron storage protein. We found that cumulative liver congestion (due to the decrease of heart function) overwhelms its capacity to recycle iron from erythrocytes. As a consequence, iron is trapped in the liver as poorly mobilized hemosiderin. What is more, the ferritin-bound Fe³⁺ (reflecting bioavailable iron stores), and assembled ferritin (reflecting ability to store iron) are decreased in HF progression in the liver. We demonstrate that while HF pigs show iron deficiency indices, erythropoiesis is enhanced. Renin–angiotensin–aldosterone system activation and hepatic hepcidin suppression might indicate stress erythropoiesisinduced in HF. Furthermore, assembled ferritin increases but ferritin-bound Fe³⁺ is reduced in myocardium, indicating that a failing heart increases the iron storage reserve but iron deficiency leads to a drop in myocardial iron stores. Together, HF in pigs leads to down-regulated iron bioavailability and reduced hepatic iron storage making iron unavailable for systemic/cardiac needs.

Iron homeostasis and organismal aging

Iron is indispensable for normal body functions across species because of its critical roles in red blood cell function and many essential proteins and enzymes required for numerous physiological processes. Regulation of iron homeostasis is an intricate process involving multiple modulators at the systemic, cellular, and molecular levels. Interestingly, emerging evidence has demonstrated that many modulators of iron homeostasis contribute to organismal aging and longevity. On the other hand, the age-related dysregulation of iron homeostasis is often associated with multiple age-related pathologies including bone resorption and neurodegenerative diseases such as Alzheimer's disease. Thus, a thorough understanding on the interconnections between systemic and cellular iron balance and organismal aging may help decipher the etiologies of multiple age-related diseases, which could ultimately lead to developing therapeutic strategies to delay aging and treat various age-related diseases. Here we present the current understanding on the mechanisms of iron homeostasis. We also discuss the impacts of aging on iron homeostatic processes and how dysregulated iron metabolism may affect aging and organismal longevity.

Embryonal erythropoiesis and aging exploit ferroptosis

Ferroptosis is a form of regulated cell necrosis, as a consequence of Fe(II)-dependent lipid peroxidation. Although ferroptosis has been linked to cancer cell death, neurodegeneration and reperfusion injury, physiological roles of ferroptosis have not been elucidated to date mostly due to the lack of appropriate methodologies. Here, we show that 4-hydroxy-2-nonenal (HNE)-modified proteins detected by a HNEJ-1 mouse monoclonal antibody is a robust immunohistochemical technology to locate ferroptosis in tissues in combination with morphological nuclear information, based on various models of ferroptosis, including erastin-induced cysteine-deprivation, conditional Gpx4 knockout and Fe(II)-dependent renal tubular injury, as well as other types of regulated cell death. Specificity of HNEJ-1 with ferroptosis was endorsed by non-selective identification of HNE-modified proteins in an Fe(II)-dependent renal tubular injury model. We further comprehensively searched for signs of ferroptosis in different developmental stages of Fischer-344 rats from E9.5-2.5 years of age. We observed that there was a significant age-dependent increase in ferroptosis in the kidney, spleen, liver, ovary, uterus, cerebellum and bone marrow, which was accompanied by iron accumulation. Not only phagocytic cells but also parenchymal cells were affected. Epidermal ferroptosis in ageing SAMP8 mice was significantly promoted by high-fat or carbohydrate-restricted diets. During embryogenesis of Fischer-344 rats, we found ferroptosis in nucleated erythrocytes at E13.5, which disappeared in enucleated erythrocytes at E18.5. Administration of a ferroptosis inhibitor, liproxstatin-1, significantly delayed erythrocyte enucleation. Therefore, our results demonstrate for the first time the involvement of ferroptosis in physiological processes, such as embryonic erythropoiesis and aging, suggesting the evolutionally acquired mechanism and the inevitable side effects, respectively.

Hepcidin induces intestinal calcium uptake while suppressing iron uptake in Caco-2 cells

Abnormal calcium absorption and iron overload from iron hyperabsorption can contribute to osteoporosis as found in several diseases, including hemochromatosis and thalassemia. Previous studies in thalassemic mice showed the positive effects of the iron uptake suppressor, hepcidin, on calcium transport. However, whether this effect could be replicated in other conditions is not known. Therefore, this study aimed to investigate the effects of hepcidin on iron and calcium uptake ability under physiological, iron uptake stimulation and calcium uptake suppression. To investigate the potential mechanism, effects of hepcidin on the expression of iron and calcium transporter and transport-associated protein in Caco-2 cells were also determined. Our results showed that intestinal cell iron uptake was significantly increased by ascorbic acid together with ferric ammonium citrate (FAC), but this phenomenon was suppressed by hepcidin. Interestingly, hepcidin significantly increased calcium uptake under physiological condition but not under iron uptake stimulation. While hepcidin significantly suppressed the expression of iron transporter, it had no effect on calcium transporter expression. This indicated that hepcidin-induced intestinal cell calcium uptake did not occur through the stimulation of calcium transporter expression. On the other hand, 1,25(OH)₂D₃ effectively induced intestinal cell calcium uptake, but it did not affect intestinal cell iron uptake or iron transporter expression. The 1,25(OH)₂D₃-induced intestinal cell calcium uptake was abolished by 12 mM CaCl₂; however, hepcidin could not rescue intestinal cell calcium uptake suppression by CaCl₂. Taken together, our results showed that hepcidin could effectively and concurrently induce intestinal cell calcium uptake while reducing intestinal cell iron uptake under physiological and iron uptake stimulation conditions, suggesting its therapeutic potential for inactive calcium absorption, particularly in thalassemic patients or patients who did not adequately respond to 1,25(OH)₂D₃.

Inflammation and Oxidative Stress: Potential Targets for Improving Prognosis After Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) has a high mortality rate and causes long-term disability in many patients, often associated with cognitive impairment. However, the pathogenesis of delayed brain dysfunction after SAH is not fully understood. A growing body of evidence suggests that neuroinflammation and oxidative stress play a negative role in neurofunctional deficits. Red blood cells and hemoglobin, immune cells, proinflammatory cytokines, and peroxidases are directly or indirectly involved in the regulation of neuroinflammation and oxidative stress in the central nervous system after SAH. This review explores the role of various cellular and acellular components in secondary inflammation and oxidative stress after SAH, and aims to provide new ideas for clinical treatment to improve the prognosis of SAH.

The role of iron homeostasis in remodeling immune function and regulating inflammatory disease

The essential trace element iron regulates a wide range of biological processes in virtually all living organisms. Because both iron deficiency and iron overload can lead to various pathological conditions, iron homeostasis is tightly regulated, and understanding this complex process will help pave the way to developing new therapeutic strategies for inflammatory disease. In recent years, significant progress has been made with respect to elucidating the roles of iron and iron-related genes in the development and maintenance of the immune system. Here, we review the timing and mechanisms by which systemic and cellular iron metabolism are regulated during the inflammatory response and during infectious disease, processes in which both the host and the pathogen compete for iron. We also discuss the evidence and implications that immune cells such as macrophages, T cells, and B cells require sufficient amounts of iron for their proliferation and for mediating their effector functions, in which iron serves as a co-factor in toll-like receptor 4 (TLR4) signaling, mitochondrial respiration, posttranslational regulation, and epigenetic modification. In addition, we discuss the therapeutic implications of targeting ferroptosis, iron homeostasis and/or iron metabolism with respect to conferring protection against pathogen infection, controlling inflammation, and improving the efficacy of immunotherapy.

Treatment of Iron Deficiency Anemia in CKD and End-Stage Kidney Disease

Iron deficiency is common in individuals with chronic kidney disease and plays a major role in the development of anemia. Oral and intravenous iron agents are both available to replete iron in patients with chronic kidney disease diagnosed with iron deficiency. The choice of which agent to use is most often dictated by goals of therapy, tolerability, convenience, and response to prior therapy. Diminished absorption of iron in the gastrointestinal tract and a high incidence of gastrointestinal adverse effects can reduce the efficacy of oral iron agents, necessitating the use of i.v. iron formulations to treat iron deficiency anemia, particularly in patients requiring kidney replacement therapy. Newer oral agents may help to overcome these limitations and help treat iron deficiency in those not requiring kidney replacement therapy. Recent studies have provided new evidence that more aggressive repletion of iron in patients with chronic kidney disease requiring kidney replacement therapy may provide benefits with respect to anemia management and hard clinical outcomes such as cardiovascular disease and survival.

The Multiple Facets of Iron Recycling

The production of around 2.5 million red blood cells (RBCs) per second in erythropoiesis is one of the most intense activities in the body. It continuously consumes large amounts of iron, approximately 80% of which is recycled from aged erythrocytes. Therefore, similar to the “making”, the “breaking” of red blood cells is also very rapid and represents one of the key processes in mammalian physiology. Under steady-state conditions, this important task is accomplished by specialized macrophages, mostly liver Kupffer cells (KCs) and splenic red pulp macrophages (RPMs). It relies to a large extent on the engulfment of red blood cells via so-called erythrophagocytosis. Surprisingly, we still understand little about the mechanistic details of the removal and processing of red blood cells by these specialized macrophages. We have only started to uncover the signaling pathways that imprint their identity, control their functions and enable their plasticity. Recent findings also identify other myeloid cell types capable of red blood cell removal and establish reciprocal cross-talk between the intensity of erythrophagocytosis and other cellular activities. Here, we aimed to review the multiple and emerging facets of iron recycling to illustrate how this exciting field of study is currently expanding.

The Association between Hepcidin and Iron Status in Children and Adolescents with Obesity

Introduction

Iron deficiency (ID) is the most common nutritional deficiency found in pediatric practice. A higher prevalence of ID may be found in children with obesity. Obesity is a chronic low-grade inflammatory condition. It is postulated that inflammation increases hepcidin, a regulator of iron homeostasis. The aim of this study was to investigate the associations between iron status, hepcidin, and BMI-standard deviation score (BMI-SDS) in children with and without obesity.

Methods

A cross-sectional study of Thai children with obesity (5 to 15 years old) versus age- and sex-matched, nonobese controls was conducted. A total of 63 children with obesity and 27 controls were enrolled. Complete blood count, serum iron, ferritin, transferrin saturation, and total iron binding capacity were analyzed. Serum hepcidin-25 was assayed using a hepcidin ELISA Kit (Human Hepc25).

Results

There were 63 children with obesity, the median age (IQR) being 10 (9–13) years, and 27 controls. The median (IQR) BMI-SDS of the obese group was 2.3 (2.0–2.6) vs. −0.5 ((−1.3)−0.4) of the control group. ID was diagnosed in 27 children in the obese group (42.9%); 4 of the children with obesity and ID had anemia. Serum hepcidin-25 levels of the children with ID vs. without ID in the obese group were not significantly different (median (IQR) 25 (12.9–49.2) and 26.4 (12.6–43.6), respectively) but both of them were significantly higher than controls (19.7 (8.3–25.5) ng/ml, p = 0.04). BMI-SDS was positively correlated with hepcidin-25 (r = 0.28, p = 0.001).

Conclusion

Prevalence of iron deficiency in Thai children with obesity and serum hepcidin-25 was higher than controls. Further study in a larger population, preferably with interventions such as weight loss program, is warranted to clarify this association.

Phagosome-Bacteria Interactions from the Bottom Up

When attempting to propagate infections, bacterial pathogens encounter phagocytes that encase them in vacuoles called phagosomes. Within phagosomes, bacteria are bombarded with a plethora of stresses that often lead to their demise. However, pathogens have evolved numerous strategies to counter those host defenses and facilitate survival. Given the importance of phagosome-bacteria interactions to infection outcomes, they represent a collection of targets that are of interest for next-generation antibacterials. To facilitate such therapies, different approaches can be employed to increase understanding of phagosome-bacteria interactions, and these can be classified broadly as top down (starting from intact systems and breaking down the importance of different parts) or bottom up (developing a knowledge base on simplified systems and progressively increasing complexity). Here we review knowledge of phagosomal compositions and bacterial survival tactics useful for bottom-up approaches, which are particularly relevant for the application of reaction engineering to quantify and predict the time evolution of biochemical species in these death-dealing vacuoles. Further, we highlight how understanding in this area can be built up through the combination of immunology, microbiology, and engineering.

Marginally reduced maternal hepatic and splenic ferroportin under severe nutritional iron deficiency in pregnancy maintains systemic iron supply

The demand for iron is high in pregnancy to meet the increased requirements for erythropoiesis. Even pregnant females with initially iron‐replete stores develop iron‐deficiency anemia, due to inadequate iron absorption. In anemic females, the maternal iron supply is dedicated to maintaining iron metabolism in the fetus and placenta. Here, using a mouse model of iron deficiency in pregnancy, we show that iron recycled from senescent erythrocytes becomes a predominant source of this microelement that can be transferred to the placenta in females with depleted iron stores. Ferroportin is a key protein in the molecular machinery of cellular iron egress. We demonstrate that under iron deficiency in pregnancy, levels of ferroportin are greatly reduced in the duodenum, placenta and fetal liver, but not in maternal liver macrophages and in the spleen. Although low expression of both maternal and fetal hepcidin predicted ferroportin up‐regulation in examined locations, its final expression level was very likely correlated with tissue iron status. Our results argue that iron released into the circulation of anemic females is taken up by the placenta, as evidenced by high expression of iron importers on syncytiotrophoblasts. Then, a substantial decrease in levels of ferroportin on the basolateral side of syncytiotrophoblasts, may be responsible for the reduced transfer of iron to the fetus. As attested by the lowest decrease in iron content among analyzed tissues, some part is retained in the placenta. These findings confirm the key role played by ferroportin in tuning iron turnover in iron‐deficient pregnant mouse females and their fetuses.

Oral Administration of Ginger-Derived Lipid Nanoparticles and Dmt1 siRNA Potentiates the Effect of Dietary Iron Restriction and Mitigates Pre-Existing Iron Overload in Hamp KO Mice

Intestinal iron transport requires an iron importer (Dmt1) and an iron exporter (Fpn1). The hormone hepcidin regulates iron absorption by modulating Fpn1 protein levels on the basolateral surface of duodenal enterocytes. In the genetic, iron-loading disorder hereditary hemochromatosis (HH), hepcidin production is low and Fpn1 protein expression is elevated. High Fpn1-mediated iron export depletes intracellular iron, causing a paradoxical increase in Dmt1-mediated iron import. Increased activity of both transporters causes excessive iron absorption, thus initiating body iron loading. Logically then, silencing of intestinal Dmt1 or Fpn1 could be an effective therapeutic intervention in HH. It was previously established that Dmt1 knock down prevented iron-loading in weanling Hamp (encoding hepcidin) KO mice (modeling type 2B HH). Here, we tested the hypothesis that Dmt1 silencing combined with dietary iron restriction (which may be recommended for HH patients) will mitigate iron loading once already established. Accordingly, adult Hamp KO mice were switched to a low-iron (LFe) diet and (non-toxic) folic acid-coupled, ginger nanoparticle-derived lipid vectors (FA-GDLVs) were used to deliver negative-control (NC) or Dmt1 siRNA by oral, intragastric gavage daily for 21 days. The LFe diet reduced body iron burden, and experimental interventions potentiated iron losses. For example, Dmt1 siRNA treatment suppressed duodenal Dmt1 mRNA expression (by ~50%) and reduced serum and liver non-heme iron levels (by ~60% and >85%, respectively). Interestingly, some iron-related parameters were repressed similarly by FA-GDLVs carrying either siRNA, including 59Fe (as FeCl3) absorption (~20% lower), pancreatic non-heme iron (reduced by ~65%), and serum ferritin (decreased 40-50%). Ginger may thus contain bioactive lipids that also influence iron homeostasis. In conclusion, the combinatorial approach of FA-GDLV and Dmt1 siRNA treatment, with dietary iron restriction, mitigated pre-existing iron overload in a murine model of HH.

Rapid removal of phagosomal ferroportin in macrophages contributes to nutritional immunity

Nutrient sequestration is an essential facet of host innate immunity. Macrophages play a critical role in controlling iron availability through expression of the iron transport protein ferroportin (FPN), which extrudes iron from the cytoplasm to the extracellular milieu. During phagocytosis, the limiting phagosomal membrane, which derives from the plasmalemma, can be decorated with FPN and, if functional, will move iron from the cytosol into the phagosome lumen. This serves to feed iron to phagocytosed microbes and would be counterproductive to the many other known host mechanisms working to starve microbes of this essential metal. To understand how FPN is regulated during phagocytosis, we expressed FPN as a green fluorescent protein-fusion protein in macrophages and monitored its localization during uptake of various phagocytic targets, including Staphylococcus aureus, Salmonella enterica serovar Typhimurium, human erythrocytes, and immunoglobulin G opsonized latex beads. We find that FPN is rapidly removed, independently of Vps34 and PI(3)P, from early phagosomes and does not follow recycling pathways that regulate transferrin receptor recycling. Live-cell video microscopy showed that FPN movement on the phagosome is dynamic, with punctate and tubular structures forming before FPN is trafficked back to the plasmalemma. N-ethylmaleimide-sensitive factor, which disrupts soluble NSF attachment protein receptor (SNARE)-mediated membrane fusion and trafficking, prevented FPN removal from the phagosome. Our data support the hypothesis that removal of FPN from the limiting phagosomal membrane will, at the cellular level, ensure that iron cannot be pumped into phagosomes. We propose this as yet another mechanism of host nutritional immunity to subvert microbial growth.

Acute Hemolysis and Heme Suppress Anti-CD40 Antibody-Induced Necro-Inflammatory Liver Disease

Clearance of red blood cells and hemoproteins is a key metabolic function of macrophages during hemolytic disorders and following tissue injury. Through this archetypical phagocytic function, heme is detoxified and iron is recycled to support erythropoiesis. Reciprocal interaction of heme metabolism and inflammatory macrophage functions may modify disease outcomes in a broad range of clinical conditions. We hypothesized that acute hemolysis and heme induce acute anti-inflammatory signals in liver macrophages. Using a macrophage-driven model of sterile liver inflammation, we showed that phenylhydrazine (PHZ)-mediated acute erythrophagocytosis blocked the anti-CD40 antibody-induced pathway of macrophage activation. This process attenuated the inflammatory cytokine release syndrome and necrotizing hepatitis induced by anti-CD40 antibody treatment of mice. We further established that administration of heme-albumin complexes specifically delivered heme to liver macrophages and replicated the anti-inflammatory effect of hemolysis. The anti-inflammatory heme-signal was induced in macrophages by an increased intracellular concentration of the porphyrin independently of iron. Overall, our work suggests that induction of heme-signaling strongly suppresses inflammatory macrophage function, providing protection against sterile liver inflammation.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Treatment of anemia in difficult-to-manage patients with chronic kidney disease

The management of anemia of chronic kidney disease (CKD) is often challenging. In particular, for patients with underlying inflammation, comorbid type 2 diabetes or cancer, those hospitalized, and recipients of a kidney transplant, the management of anemia may be suboptimal. Responsiveness to iron and/or erythropoiesis-stimulating agents, the mainstay of current therapy, may be reduced and the risk of adverse reactions to treatment is increased in these difficult-to-manage patients with anemia of CKD. This review discusses the unique patient and disease characteristics leading to complications and suboptimal treatment response. New treatment options in clinical development, such as hypoxia-inducible factor-prolyl hydroxylase (HIF-PH) inhibitors, may be particularly useful for difficult-to-treat patients. In clinical studies, HIF-PH inhibitors provided increased hemoglobin levels and improved iron utilization in anemic patients with non-dialysis-dependent and dialysis-dependent CKD, and preliminary data suggest that HIF-PH inhibitors may be equally effective in patients with or without underlying inflammation. The availability of new treatment options, including HIF-PH inhibitors, may improve treatment outcomes in difficult-to-manage patients with anemia of CKD.

Hemolysis transforms liver macrophages into antiinflammatory erythrophagocytes

During hemolysis, macrophages in the liver phagocytose damaged erythrocytes to prevent the toxic effects of cell-free hemoglobin and heme. It remains unclear how this homeostatic process modulates phagocyte functions in inflammatory diseases. Using a genetic mouse model of spherocytosis and single-cell RNA sequencing, we found that erythrophagocytosis skewed liver macrophages into an antiinflammatory phenotype that we defined as MarcohiHmoxhiMHC class IIlo erythrophagocytes. This phenotype transformation profoundly mitigated disease expression in a model of an anti-CD40-induced hyperinflammatory syndrome with necrotic hepatitis and in a nonalcoholic steatohepatitis model, representing 2 macrophage-driven sterile inflammatory diseases. We reproduced the antiinflammatory erythrophagocyte transformation in vitro by heme exposure of mouse and human macrophages, yielding a distinctive transcriptional signature that segregated heme-polarized from M1- and M2-polarized cells. Mapping transposase-accessible chromatin in single cells by sequencing defined the transcription factor NFE2L2/NRF2 as a critical driver of erythrophagocytes, and Nfe2l2/Nrf2 deficiency restored heme-suppressed inflammation. Our findings point to a pathway that regulates macrophage functions to link erythrocyte homeostasis with innate immunity.