Role of hepcidin in the setting of hypoferremia during acute inflammation

Inflammation-driven NF-κB signaling represses ferroportin transcription in macrophages via HDAC1 and HDAC3

ABSTRACT

Anemia of inflammation is a prevalent comorbidity in patients with chronic inflammatory disorders. Inflammation causes hypoferremia and iron-restricted erythropoiesis by limiting ferroportin (FPN)-mediated iron export from macrophages that recycle senescent erythrocytes. Macrophage cell surface expression of FPN is reduced by hepcidin-induced degradation and/or by repression of FPN (Slc40a1) transcription via cytokine and Toll-like receptor (TLR) stimulation. Although the mechanisms underlying hepcidin-mediated control of FPN have been extensively studied, those inhibiting Slc40a1 messenger RNA (mRNA) expression remain unknown. We applied targeted RNA interference and pharmacological screens in macrophages stimulated with the TLR2/6 ligand FSL1 and identified critical signaling regulators of Slc40a1 mRNA repression downstream of TLRs and NF-κB signaling. Interestingly, the NF-κB regulatory hub is equally relevant for Slc40a1 mRNA repression driven by the TLR4 ligand lipopolysaccharide, the cytokine tumor necrosis factor β/lymphotoxin-alpha (LTA), and heat-killed bacteria. Mechanistically, macrophage stimulation with heat-killed Staphylococcus aureus recruits the histone deacetylases (HDACs) HDAC1 and HDAC3 to the antioxidant response element (ARE) located in the Slc40a1 promoter. Accordingly, pretreatment with a pan-HDAC inhibitor abrogates Slc40a1 mRNA repression in response to inflammatory cues, suggesting that HDACs act downstream of NF-κB to repress Slc40a1 transcription. Consistently, recruitment of HDAC1 and HDAC3 to the Slc40a1 ARE after stimulation with heat-killed S aureus is dependent on NF-κB signaling. These results support a model in which the ARE integrates the transcriptional responses of Slc40a1 triggered by signals from redox, metabolic, and inflammatory pathways. This work identifies the long-sought mechanism of Slc40a1 transcriptional downregulation upon inflammation, paving the way for therapeutic interventions at this critical juncture.

In defence of ferroptosis

Rampant phospholipid peroxidation initiated by iron causes ferroptosis unless this is restrained by cellular defences. Ferroptosis is increasingly implicated in a host of diseases, and unlike other cell death programs the physiological initiation of ferroptosis is conceived to occur not by an endogenous executioner, but by the withdrawal of cellular guardians that otherwise constantly oppose ferroptosis induction. Here, we profile key ferroptotic defence strategies including iron regulation, phospholipid modulation and enzymes and metabolite systems: glutathione reductase (GR), Ferroptosis suppressor protein 1 (FSP1), NAD(P)H Quinone Dehydrogenase 1 (NQO1), Dihydrofolate reductase (DHFR), retinal reductases and retinal dehydrogenases (RDH) and thioredoxin reductases (TR). A common thread uniting all key enzymes and metabolites that combat lipid peroxidation during ferroptosis is a dependence on a key cellular reductant, nicotinamide adenine dinucleotide phosphate (NADPH). We will outline how cells control central carbon metabolism to produce NADPH and necessary precursors to defend against ferroptosis. Subsequently we will discuss evidence for ferroptosis and NADPH dysregulation in different disease contexts including glucose-6-phosphate dehydrogenase deficiency, cancer and neurodegeneration. Finally, we discuss several anti-ferroptosis therapeutic strategies spanning the use of radical trapping agents, iron modulation and glutathione dependent redox support and highlight the current landscape of clinical trials focusing on ferroptosis.

Iron scavenging and myeloid cell polarization

Myeloid cells that populate all human organs and blood are a versatile class of innate immune cells. They are crucial for sensing and regulating processes as diverse as tissue homeostasis and inflammation and are frequently characterized by their roles in either regulating or promoting inflammation. Recent studies in cultured cells and mouse models highlight the role of iron in skewing the functional properties of myeloid cells in tissue damage and repair. Here, we review certain emerging concepts on how iron influences and determines myeloid cell polarization in the context of its uptake, storage, and metabolism, including in conditions such as multiple sclerosis (MS), sickle cell disease, and tumors.

Rocaglamide regulates iron homeostasis by suppressing hepcidin expression

The anemia of inflammation (AI) is characterized by the presence of inflammation and abnormal elevation of hepcidin. Accumulating evidence has proved that Rocaglamide (RocA) was involved in inflammation regulation. Nevertheless, the role of RocA in AI, especially in iron metabolism, has not been investigated, and its underlying mechanism remains elusive. Here, we demonstrated that RocA dramatically suppressed the elevation of hepcidin and ferritin in LPS-treated mice cell line RAW264.7 and peritoneal macrophages. In vivo study showed that RocA can restrain the depletion of serum iron (SI) and transferrin (Tf) saturation caused by LPS. Further investigation showed that RocA suppressed the upregulation of hepcidin mRNA and downregulation of Fpn1 protein expression in the spleen and liver of LPS-treated mice. Mechanistically, this effect was attributed to RocA's ability to inhibit the IL-6/STAT3 pathway, resulting in the suppression of hepcidin mRNA and subsequent increase in Fpn1 and TfR1 expression in LPS-treated macrophages. Moreover, RocA inhibited the elevation of the cellular labile iron pool (LIP) and reactive oxygen species (ROS) induced by LPS in RAW264.7 cells. These findings reveal a pivotal mechanism underlying the roles of RocA in modulating iron homeostasis and also provide a candidate natural product on alleviating AI.

The microbiota and the host organism switch between cooperation and competition based on dietary iron levels

The microbiota significantly impacts digestive epithelium functionality, especially in nutrient processing. Given the importance of iron for both the host and the microbiota, we hypothesized that host-microbiota interactions fluctuate with dietary iron levels. We compared germ-free (GF) and conventional mice (SPF) fed iron-containing (65 mg/Kg) or iron-depleted (<6 mg/Kg) diets. The efficacy of iron privation was validated by iron blood parameters. Ferritin and Dmt1, which represent cellular iron storage and transport respectively, were studied in tissues where they are abundant: the duodenum, liver and lung. When the mice were fed an iron-rich diet, the microbiota increased blood hemoglobin and hepcidin and the intestinal ferritin levels, suggesting that the microbiota helps iron storage. When iron was limiting, the microbiota inhibited the expression of the intestinal Dmt1 transporter, likely via the pathway triggered by Hif-2α. The microbiota assists the host in storing intestinal iron when it is abundant and competes with the host by inhibiting Dmt1 in conditions of iron scarcity. Comparison between duodenum, liver and lung indicates organ-specific responses to microbiota and iron availability. Iron depletion induced temporal changes in microbiota composition and activity, reduced α-diversity of microbiota, and led to Lactobacillaceae becoming particularly more abundant after 60 days of privation. By inoculating GF mice with a simplified bacterial mixture, we show that the iron-depleted host favors the gut fitness of Bifidobacterium longum.

Dynamics of iron metabolism in patients with bloodstream infections: a time-course clinical study

The close relationship between infectious diseases and iron metabolism is well known, but a more detailed understanding based on current knowledge may provide new insights into the diagnosis and treatment of infectious diseases, considering the growing threat of antibiotic-resistant bacteria. This study investigated adult patients with bloodstream infections, temporal changes, and relationships between blood levels of iron and related markers, including hepcidin and lipocalin-2 (LCN2). We included 144 samples from 48 patients (mean age 72 years, 50% male), with 30 diagnosed with sepsis. During the acute phase of infection, blood levels of hepcidin and LCN2 increased rapidly, whereas iron levels decreased, with values in 95.8% of cases below the normal range (40-188 μg/dL). Later, hepcidin and LCN2 decreased significantly during the recovery phase, and the decreased iron concentrations were restored. In the case of persistent inflammation, iron remained decreased. Acute LCN2 levels were significantly higher in patients with sepsis (p < 0.01). Hypoferremia induced by increased hepcidin would reduce iron in the environment of extracellular pathogens, and the increased LCN2 would inhibit siderophores, resulting in the prevention of the pathogen's iron acquisition in each manner during the acute phase of bloodstream infection.

Hepcidin deficiency in mice impairs white adipose tissue browning possibly due to a defect in de novo adipogenesis

The role of iron in the two major sites of adaptive thermogenesis, namely the beige inguinal (iWAT) and brown adipose tissues (BAT) has not been fully understood yet. Body iron levels and distribution is controlled by the iron regulatory peptide hepcidin. Here, we explored iron homeostasis and thermogenic activity in brown and beige fat in wild-type and iron loaded Hepcidin KO mice. Hepcidin-deficient mice displayed iron overload in both iWAT and BAT, and preferential accumulation of ferritin in stromal cells compared to mature adipocytes. In contrast to BAT, the iWAT of Hepcidin KO animals featured with defective thermogenesis evidenced by an altered beige signature, including reduced UCP1 levels and decreased mitochondrial respiration. This thermogenic modification appeared cell autonomous and persisted after a 48 h-cold challenge, a potent trigger of thermogenesis, suggesting compromised de novo adipogenesis. Given that WAT browning occurs in both mice and humans, our results provide physiological results to interrogate the thermogenic capacity of patients with iron overload disorders.

Is iron deficiency caused by BMPR2 mutations or dysfunction in pulmonary arterial hypertension patients?

Iron deficiency is common in idiopathic and heritable pulmonary arterial hypertension patients (I/HPAH). A previous report suggested a dysregulation of the iron hormone hepcidin, which is controlled by BMP/SMAD signaling involving the bone morphogenetic protein receptor 2 (BMPR-II). Pathogenic variants in the BMPR2 gene are the most common cause of HPAH. Their effect on patients' hepcidin levels has not been investigated. The aim of this study was to assess whether iron metabolism and regulation of the iron regulatory hormone hepcidin was disturbed in I/HPAH patients with and without a pathogenic variant in the gene BMPR2 compared to healthy controls. In this explorative, cross-sectional study hepcidin serum levels were quantified by enzyme-linked immunosorbent assay. We measured iron status, inflammatory parameters and hepcidin modifying proteins such as IL6, erythropoietin, and BMP2, BMP6 in addition to BMPR-II protein and mRNA levels. Clinical routine parameters were correlated with hepcidin levels. In total 109 I/HPAH patients and controls, separated into three groups, 23 BMPR2 variant-carriers, 56 BMPR2 noncarriers and 30 healthy controls were enrolled. Of these, 84% had iron deficiency requiring iron supplementation. Hepcidin levels were not different between groups and corresponded to the degree of iron deficiency. The levels of IL6, erythropoietin, BMP2, or BMP6 showed no correlation with hepcidin expression. Hence, iron homeostasis and hepcidin regulation was largely independent from these parameters. I/HPAH patients had a physiologically normal iron regulation and no false elevation of hepcidin levels. Iron deficiency was prevalent albeit independent of pathogenic variants in the BMPR2 gene.

Monocyte MRI Relaxation Rates Are Regulated by Extracellular Iron and Hepcidin

Many chronic inflammatory conditions are mediated by an increase in the number of monocytes in peripheral circulation, differentiation of monocytes to macrophages, and different macrophage subpopulations during pro- and anti-inflammatory stages of tissue injury. When hepcidin secretion is stimulated during inflammation, the iron export protein ferroportin is targeted for degradation on a limited number of cell types, including monocytes and macrophages. Such changes in monocyte iron metabolism raise the possibility of non-invasively tracking the activity of these immune cells using magnetic resonance imaging (MRI). We hypothesized that hepcidin-mediated changes in monocyte iron regulation influence both cellular iron content and MRI relaxation rates. In response to varying conditions of extracellular iron supplementation, ferroportin protein levels in human THP-1 monocytes decreased two- to eightfold, consistent with paracrine/autocrine regulation of iron export. Following hepcidin treatment, ferroportin protein levels further decreased two- to fourfold. This was accompanied by an approximately twofold increase in total transverse relaxation rate, R₂*, compared to non-supplemented cells. A positive correlation between total cellular iron content and R₂* improved from moderate to strong in the presence of hepcidin. These findings suggest that hepcidin-mediated changes detected in monocytes using MRI could be valuable for in vivo cell tracking of inflammatory responses.

A crosstalk between hepcidin and IRE/IRP pathways controls ferroportin expression and determines serum iron levels in mice

The iron hormone hepcidin is transcriptionally activated by iron or inflammation via distinct, partially overlapping pathways. We addressed how iron affects inflammatory hepcidin levels and the ensuing hypoferremic response. Dietary iron overload did not mitigate hepcidin induction in lipopolysaccharide (LPS)-treated wild type mice but prevented effective inflammatory hypoferremia. Likewise, LPS modestly decreased serum iron in hepcidin-deficient Hjv^-/- mice, model of hemochromatosis. Synthetic hepcidin triggered hypoferremia in control but not iron-loaded wild type animals. Furthermore, it dramatically decreased hepatic and splenic ferroportin in Hjv^-/- mice on standard or iron-deficient diet, but only triggered hypoferremia in the latter. Mechanistically, iron antagonized hepcidin responsiveness by inactivating IRPs in the liver and spleen to stimulate ferroportin mRNA translation. Prolonged LPS treatment eliminated ferroportin mRNA and permitted hepcidin-mediated hypoferremia in iron-loaded mice. Thus, de novo ferroportin synthesis is a critical determinant of serum iron and finetunes hepcidin-dependent functional outcomes. Our data uncover a crosstalk between hepcidin and IRE/IRP systems that controls tissue ferroportin expression and determines serum iron levels. Moreover, they suggest that hepcidin supplementation therapy is more efficient when combined with iron depletion.

Evaluation of liver specific ionizable lipid nanocarrierin the delivery of siRNA

Hepcidin, a key regulator of iron homeostasis, has been implicated in the pathogenesis of various iron-related diseases. Although small interfering RNA (siRNA) are potent to modulate the expression of hepcidin, their bioavailability remains a major issue. The β-galactopyranoside-conjugated liposomes (GAL-liposome) targeting liver synthesized hepcidin were prepared by thin lipid film hydration method to encapsulate siRNA and the conjugation of β-galactopyranoside to the lipid nanocarrier was achieved by covalent chemistry. The prepared siRNA loaded GAL-lip were spherical with around 50 nm radius in size as observed by HR-TEM. The zeta potential and polydispersity index of the prepared liposomes were -19.9±0.96 mV and 0.44±0.05, respectively. The encapsulation efficiency as determined by dialysis bag method was around 91.76±1.74%. The cell viability and cellular uptake analysis was examined in HepG2 cells by MTT assay and flow cytometry, respectively. The stability and cumulative release of siRNA was also assessed. The hepcidin mRNA expression on administration of siRNA loaded GAL-lip was determined in HepG2 cells and in lipopolysaccharide-induced mice model followed by examining itsin vivo biodistribution by fluorescence microscopy. The results suggested thatsiRNA loaded GAL-lip reduced the hepcidin levels, thus, highlighting a novel ligand conjugated ionizable lipid-based nanocarrier for inducing RNA interference.

H-Ferritin Produced by Myeloid Cells Is Released to the Circulation and Plays a Major Role in Liver Iron Distribution during Infection

During infections, the host redistributes iron in order to starve pathogens from this nutrient. Several proteins are involved in iron absorption, transport, and storage. Ferritin is the most important iron storage protein. It is composed of variable proportions of two peptides, the L- and H-ferritins (FTL and FTH). We previously showed that macrophages increase their expression of FTH1 when they are infected in vitro with Mycobacterium avium, without a significant increase in FTL. In this work, we investigated the role of macrophage FTH1 in M. avium infection in vivo. We found that mice deficient in FTH1 in myeloid cells are more resistant to M. avium infection, presenting lower bacterial loads and lower levels of proinflammatory cytokines than wild-type littermates, due to the lower levels of available iron in the tissues. Importantly, we also found that FTH1 produced by myeloid cells in response to infection may be found in circulation and that it plays a key role in iron redistribution. Specifically, in the absence of FTH1 in myeloid cells, increased expression of ferroportin is observed in liver granulomas and increased iron accumulation occurs in hepatocytes. These results highlight the importance of FTH1 expression in myeloid cells for iron redistribution during infection.

Upregulation of Local Hepcidin Contributes to Iron Accumulation in Alzheimer's Disease Brains

BACKGROUND

Accumulation of iron is a consistent feature of Alzheimer's disease (AD) brains. The underlying cause, however, remains debatable.

OBJECTIVE

To explore whether local hepcidin synthesized by brain cells contributes to iron accumulation in AD brains.

METHODS

Brain tissue from the cingulate cortex of 33 cases of AD pre-assigned to Braak stage I-VI, 6 cases of non-dementia, and 15 cases of non-AD dementia were analyzed for transcriptional upregulation of hepcidin by RT-qPCR and RT-PCR. Change in the expression of ferritin, ferroportin (Fpn), microglial activation marker Iba1, IL-6, and TGFβ2 was determined by western blotting. Total tissue iron was determined by colorimetry.

RESULTS

Significant transcriptional upregulation of hepcidin was observed in Braak stage III-VI relative to Braak stage I and II, non-AD dementia, and non-dementia samples. Ferritin was increased in Braak stage V, and a significant increase in tissue iron was evident in Braak stage III-VI. The expression of Iba1 and IL-6 was also increased in Braak stage III-VI relative to Braak stage I and II and non-AD dementia samples. Amyloid-β plaques were absent in most Braak stage I and II samples, and present in Braak stage III-VI samples with few exceptions.

CONCLUSION

These observations suggest that upregulation of brain hepcidin is mediated by IL-6, a known transcriptional activator of hepcidin. The consequent downregulation of Fpn on neuronal and other cells results in accumulation of iron in AD brains. The increase in hepcidin is disease-specific, and increases with disease progression, implicating AD-specific pathology in the accumulation of iron.

Effect of lipopolysaccharide on peripheral tissue and hypothalamic expression of metabolic and inflammatory markers in mice fed high-fat diets with distinct 18-carbon fatty acid composition

Physiological and metabolic effects of fatty acids are determined by their degree of saturation and chain length. Effects of 18-carbon fatty acids with various degrees of saturation on inflammatory, oxidative, and neuropeptide gene transcription, especially in the hypothalamus, in response to LPS-induced acute inflammation have not been well studied. We conducted this study to test whether diets with distinct 18-carbon fatty acid differentially affect inflammatory and metabolic response to LPS exposure in the hypothalamus, liver, and muscle tissues. Four experimental diets were fed for 4 weeks to male C57BL/6J mice, and a terminal 4-h lipopolysaccharide (LPS) injection was administered. Diets included a control diet (CON) containing 5.6% kcal fat from lard and 4.4% kcal fat from soybean oil, and three high-fat diets (HFD) containing 25% kcal fat from lard and 20% kcal fat from either shea butter (SHB; saturated fatty acid-rich fat), olive oil (OLO; monounsaturated fatty acid-rich oil), or soybean oil (SBO; polyunsaturated fatty acid-rich fat). Compared to CON, HFD-fed mice had higher weight gain and body fat accumulation. The SBO group had lowest Cpt1b expression in the liver, and OLO group had the lowest Pomc and the highest Lepr expression in the hypothalamus. LPS challenge increased pro-inflammatory cytokine mRNA expression in the brain and peripheral tissues. However, the diets did not exert distinguishable effects on LPS-induced inflammatory responses. Therefore, saturation degree of 18-carbon fatty acids may not play a critical role in their effects on inflammatory and metabolic indicators in response to acute inflammation induced by LPS.

Distinct iron homeostasis in C57BL/6 and Balb/c mouse strains

C57BL/6 (BL6) and Balb/c mice exhibit prototypical Th1- and Th2-dominant immune predispositions, respectively. Iron is a proinflammatory metal ion; however, limited information is documented on the differences in iron homeostasis between BL6 and Balb/c strains. The objective of this study was to investigate the extent to which strain-level differences in these mice dictates the regulation of iron homeostasis during physiologic and inflammatory conditions. At basal levels, Balb/c mice displayed significantly higher levels of iron in systemic circulation and tissue compared to BL6 mice. Moreover, Balb/c mice had greater iron absorption as indicated by higher gene expressions of duodenal DcytB, DMT1, Fpn, SFT, and Heph. Similarly, hepatic Tf, TfR1, TfR2, and DMT1 expressions were augmented in Balb/c mice. Interestingly, there was no change in hepatic Hamp expression between the two strains, suggesting that the disparity in their maintenance of iron is independent of hepcidin. Additionally, the basal levels of intracellular labile iron pool in Balb/c intestinal epithelial cells, and bone marrow-derived macrophages and neutrophils, were higher compared to BL6 mice. When mice were challenged with lipopolysaccharide, the acute inflammatory response in BL6 mice was more pronounced than in Balb/c mice, as indicated by the more rapid development of hypoferremia and upregulation of serum IL-6 and TNF-α levels in BL6 mice. In conclusion, this study underscores that iron homeostasis is distinct between BL6 and Balb/c strains under both physiologic and inflammatory conditions.

The hypoferremic response to acute inflammation is maintained in thalassemia mice even under parenteral iron loading

Background

Hepcidin controls iron homeostasis by inducing the degradation of the iron efflux protein, ferroportin (FPN1), and subsequently reducing serum iron levels. Hepcidin expression is influenced by multiple factors, including iron stores, ineffective erythropoiesis, and inflammation. However, the interactions between these factors under thalassemic condition remain unclear. This study aimed to determine the hypoferremic and transcriptional responses of iron homeostasis to acute inflammatory induction by lipopolysaccharide (LPS) in thalassemic (Hbb^th3/+) mice with/without parenteral iron loading with iron dextran.

Methods

Wild type and Hbb^th3/+ mice were intramuscularly injected with 5 mg of iron dextran once daily for two consecutive days. After a 2-week equilibration, acute inflammation was induced by an intraperitoneal injection of a single dose of 1 µg/g body weight of LPS. Control groups for both iron loading and acute inflammation received equal volume(s) of saline solution. Blood and tissue samples were collected at 6 hours after LPS (or saline) injection. Iron parameters and mRNA expression of hepcidin as well as genes involved in iron transport and metabolism in wild type and Hbb^th3/+ mice were analyzed and compared by Kruskal–Wallis test with pairwise Mann–Whitney U test.

Results

We found the inductive effects of LPS on liver IL-6 mRNA expression to be more pronounced under parenteral iron loading. Upon LPS administration, splenic erythroferrone (ERFE) mRNA levels were reduced only in iron-treated mice, whereas, liver bone morphogenetic protein 6 (BMP6) mRNA levels were decreased under both control and parenteral iron loading conditions. Despite the altered expression of the aforementioned hepcidin regulators, the stimulatory effect of LPS on hepcidin mRNA expression was blunt in iron-treated Hbb^th3/+ mice. Contrary to the blunted hepcidin response, LPS treatment suppressed FPN1 mRNA expression in the liver, spleen, and duodenum, as well as reduced serum iron levels of Hbb^th3/+ mice with parenteral iron loading.

Conclusion

Our study suggests that a hypoferremic response to LPS-induced acute inflammation is maintained in thalassemic mice with parenteral iron loading in a hepcidin-independent manner.

Central Nervous System Inflammation Induced by Lipopolysaccharide Up-Regulates Hepatic Hepcidin Expression by Activating the IL-6/JAK2/STAT3 Pathway in Mice

It is known that lipopolysaccharide (LPS) triggers inflammatory response after intracerebroventricular (ICV) injection and elevates the expression of hepcidin through the interleukin 6/janus kinase 2/transducer and activator of the transcription 3 (IL-6/JAK2/STAT3) signaling pathway in the brain. This study was conducted to determine whether LPS ICV injection can regulate peripheral hepatic hepcidin expression and iron metabolism. Here, we studied the hepcidin expression in the liver, as well as serum iron and transferrin saturation, after LPS ICV injection. We also demonstrated the role of the IL-6/JAK2/STAT3 pathway in hepcidin expression in the livers of IL-6 knockout (IL-6–/– mice) and IL-6+/+ mice. AG490 was used to verify the effect of the IL-6/JAK2/STAT3 pathway on hepatic hepcidin expression. Our present study demonstrated that LPS ICV injection up-regulated hepatic hepcidin expression. This finding provides further evidence for highlighting the importance of the central inflammation on hepatic hepcidin expression and peripheral iron metabolism.

A role for hepcidin in the anemia caused by Trypanosoma brucei infection

Trypanosomiasis is a parasitic disease affecting both humans and animals in the form of Human African Trypanosomiasis and Nagana disease, respectively. Anemia is one of the most common symptoms of trypanosomiasis, and if left unchecked can cause severe complications and even death. Several factors have been associated with the development of this anemia, including dysregulation of iron homeostasis, but little is known about the molecular mechanisms involved. Here, using murine models, we study the involvement of hepcidin, the key regulator of iron metabolism and an important player in the development of anemia of inflammation. Our data show two stages for the progression of anemia, to which hepcidin contributes a first stage when anemia develops, with a likely cytokine-mediated stimulation of hepcidin and subsequent limitation in iron availability and erythropoiesis, and a second stage of recovery, where the increase in hepcidin then declines due to the reduced inflammatory signal and increased production of erythroid regulators by the kidney, spleen and bone marrow, thus leading to an increase in iron release and availability, and enhanced erythropoiesis. In agreement with this, in hepcidin knockout mice, anemia is much milder and its recovery is complete, in contrast to wild-type animals which have not fully recovered from anemia after 21 days. Besides all other factors known to be involved in the development of anemia during trypanosomiasis, hepcidin clearly makes an important contribution to both its development and recovery.

C-FGF23 peptide alleviates hypoferremia during acute inflammation

Hypoferremia results as an acute phase response to infection and inflammation aiming to reduce iron availability to pathogens. Activation of toll-like receptors (TLR), the key sensors of the innate immune system, induces hypoferremia mainly through the rise of the iron hormone hepcidin. Conversely, stimulation of erythropoiesis suppresses hepcidin expression via induction of the erythropoietin-responsive hormone erythroferrone. Iron deficiency stimulates transcription of the osteocyte- secreted protein FGF23. Here we hypothesized that induction of FGF23 in response to TLR4 activation is a potent contributor to hypoferremia and, thus, impairment of its activity may alleviate hypoferremia induced by lipopolysaccharide (LPS), a TLR 4 agonist. We used the C-terminal tail of FGF23 to impair endogenous full-length FGF23 signaling in wildtype mice, and investigated its impact on hypoferremia. Our data show that FGF23 is induced as early as pro-inflammatory cytokines in response to LPS, followed by upregulation of hepcidin and downregulation of erythropoietin (Epo) expression in addition to decreased serum iron and transferrin saturation. Further, LPS-induced hepatic and circulating hepcidin were significantly reduced by FGF23 signaling disruption. Accordingly, iron sequestration in liver and spleen caused by TLR4 activation was completely abrogated by FGF23 signaling inhibition, resulting in alleviation of serum iron and transferrin saturation deficit. Taken together, our studies highlight for the first time that inhibition of FGF23 signaling alleviates LPS-induced acute hypoferremia.

Bacterial Lipopolysaccharides Suppress Erythroblastic Islands and Erythropoiesis in the Bone Marrow in an Extrinsic and G- CSF-, IL-1-, and TNF-Independent Manner

Anemia of inflammation (AI) is the second most prevalent anemia after iron deficiency anemia and results in persistent low blood erythrocytes and hemoglobin, fatigue, weakness, and early death. Anemia of inflammation is common in people with chronic inflammation, chronic infections, or sepsis. Although several studies have reported the effect of inflammation on stress erythropoiesis and iron homeostasis, the mechanisms by which inflammation suppresses erythropoiesis in the bone marrow (BM), where differentiation and maturation of erythroid cells from hematopoietic stem cells (HSCs) occurs, have not been extensively studied. Here we show that in a mouse model of acute sepsis, bacterial lipopolysaccharides (LPS) suppress medullary erythroblastic islands (EBIs) and erythropoiesis in a TLR-4- and MyD88-dependent manner with concomitant mobilization of HSCs. LPS suppressive effect on erythropoiesis is indirect as erythroid progenitors and erythroblasts do not express TLR-4 whereas EBI macrophages do. Using cytokine receptor gene knock-out mice LPS-induced mobilization of HSCs is G-CSF-dependent whereas LPS-induced suppression of medullary erythropoiesis does not require G- CSF-, IL- 1-, or TNF-mediated signaling. Therefore suppression of medullary erythropoiesis and mobilization of HSCs in response to LPS are mechanistically distinct. Our findings also suggest that EBI macrophages in the BM may sense innate immune stimuli in response to acute inflammation or infections to rapidly convert to a pro-inflammatory function at the expense of their erythropoietic function.

The Availability of Iron Is Involved in the Murine Experimental Toxoplasma gondii Infection Outcome

Iron is an important constituent of our environment, being necessary for both mammalian and pathogenic protozoa survival. Iron-containing proteins exert a wide range of biological processes such as biodegradation and biosynthesis, as well as immune function, fetal development, and physical and mental well-being. This work aimed to investigate the effect of iron deprivation in Toxoplasma gondii infection outcome. C57BL/6 mice were orally infected with T. gondii and treated with an iron chelator, deferoxamine, or supplemented with iron (ferrous sulfate), and the parasitism as well as immunological and histological parameters were analyzed. It was observed that the infection increased iron accumulation in the organs, as well as systemically, and deferoxamine treatment diminished the iron content in serum samples and intestine. The deferoxamine treatment decreased the parasitism and inflammatory alterations in the small intestine and lung. Additionally, they partially preserved the Paneth cells and decreased the intestinal dysbiosis. The ferrous sulfate supplementation, despite not significantly increasing the parasite load in the organs, increased the inflammatory alterations in the liver. Together, our results suggest that iron chelation, which is commonly used to treat iron overload, could be a promising medicine to control T. gondii proliferation, mainly in the small intestine, and consequently inflammation caused by infection.

Iron Administration, Infection, and Anemia Management in CKD: Untangling the Effects of Intravenous Iron Therapy on Immunity and Infection Risk

Patients with chronic kidney disease (CKD) are at increased risk for infection, attributable to immune dysfunction, increased exposure to infectious agents, loss of cutaneous barriers, comorbid conditions, and treatment-related factors (eg, hemodialysis and immunosuppressant therapy). Because iron plays a vital role in pathogen reproduction and host immunity, it is biologically plausible that intravenous iron therapy and/or iron deficiency influence infection risk in CKD. Available data from preclinical experiments, observational studies, and randomized controlled trials are summarized to explore the interplay between intravenous iron and infection risk among patients with CKD, particularly those receiving maintenance hemodialysis. The current evidence base, including data from a recent randomized controlled trial, suggests that proactive judicious use of intravenous iron (in a manner that minimizes the accumulation of non-transferrin-bound iron) beneficially replaces iron stores while avoiding a clinically relevant effect on infection risk. In the absence of an urgent clinical need, intravenous iron therapy should be avoided in patients with active infection. Although serum ferritin concentration and transferrin saturation can help guide clinical decision making about intravenous iron therapy, definition of an optimal iron status and its precise determination in individual patients remain clinically challenging in CKD and warrant additional study.

Regulation of tissue iron homeostasis: the macrophage "ferrostat"

Iron is an essential element for multiple fundamental biological processes required for life; yet iron overload can be cytotoxic. Consequently, iron concentrations at the cellular and tissue level must be exquisitely governed by mechanisms that complement and fine-tune systemic control. It is well appreciated that macrophages are vital for systemic iron homeostasis, supplying or sequestering iron as needed for erythropoiesis or bacteriostasis, respectively. Indeed, recycling of iron through erythrophagocytosis by splenic macrophages is a major contributor to systemic iron homeostasis. However, accumulating evidence suggests that tissue-resident macrophages regulate local iron availability and modulate the tissue microenvironment, contributing to cellular and tissue function. Here, we summarize the significance of tissue-specific regulation of iron availability and highlight how resident macrophages are critical for this process. This tissue-dependent regulation has broad implications for understanding both resident macrophage function and tissue iron homeostasis in health and disease.

Twenty Years of Ferroportin Disease: A Review or An Update of Published Clinical, Biochemical, Molecular, and Functional Features

Iron overloading disorders linked to mutations in ferroportin have diverse phenotypes in vivo, and the effects of mutations on ferroportin in vitro range from loss of function (LOF) to gain of function (GOF) with hepcidin resistance. We reviewed 359 patients with 60 ferroportin variants. Overall, macrophage iron overload and low/normal transferrin saturation (TSAT) segregated with mutations that caused LOF, while GOF mutations were linked to high TSAT and parenchymal iron accumulation. However, the pathogenicity of individual variants is difficult to establish due to the lack of sufficiently reported data, large inter-assay variability of functional studies, and the uncertainty associated with the performance of available in silico prediction models. Since the phenotypes of hepcidin-resistant GOF variants are indistinguishable from the other types of hereditary hemochromatosis (HH), these variants may be categorized as ferroportin-associated HH, while the entity ferroportin disease may be confined to patients with LOF variants. To further improve the management of ferroportin disease, we advocate for a global registry, with standardized clinical analysis and validation of the functional tests preferably performed in human-derived enterocytic and macrophagic cell lines. Moreover, studies are warranted to unravel the definite structure of ferroportin and the indispensable residues that are essential for functionality.

Protective Role of Hepcidin in Polymicrobial Sepsis and Acute Kidney Injury

Background: Acute kidney injury (AKI) portends worse prognosis following sepsis, with limited available interventions. Host iron acquisition by pathogens and systemic inflammatory response are key events in the pathogenesis of sepsis. In sepsis, hepcidin induces iron sequestration to limit iron availability to pathogens. Hepcidin is also known to limit inflammation. Since its role in pathophysiology of sepsis-associated AKI is unknown, we investigated the effect of exogenous hepcidin in endotoxin- and peritonitis-induced pathology and AKI.

Methods: C57BL/6 mice were treated with saline or 50–100 µg of hepcidin, pre- and post-LPS injection, or cecal ligation and puncture (CLP, model of peritonitis). Splenectomized mice were challenged with LPS, with and without hepcidin. Mice were euthanized at 24 h after LPS injection and at different time points after CLP. Systemic inflammation and renal injury markers were assessed. Direct effect of hepcidin on renal tubular and endothelial cells was evaluated using endotoxin-induced cytotoxic serum. Role of heavy chain ferritin (H-ferritin) in mediating hepcidin-induced anti-inflammatory effect on LPS stimulated macrophages was evaluated with siRNA studies.

Results: Twenty-four hours pretreatment with hepcidin significantly reduced LPS-induced AKI. Hepcidin ameliorated LPS-induced increase in serum TNFα and renal Cox-2, and prevented loss in PGC1α and cytochrome c oxidase activity. This was associated with reduced glomerular injury and preserved mitochondrial structure. Hepcidin did not exert direct protection on the renal parenchymal cells but reduced endotoxin-induced serum cytotoxicity to mitigate renal injury. Splenectomy reduced LPS-induced early inflammation and AKI, independent of hepcidin, indicating the importance of systemic inflammation. Higher splenic H-ferritin in hepcidin-treated animals was associated with reduced splenocytes apoptosis and inflammation. Hepcidin reduced LPS-induced IL-6 secretion in macrophages in H-ferritin dependent manner. Hepcidin significantly reduced CLP-induced AKI, and mortality (20% hepcidin treated vs 80% PBS treated). Importantly hepcidin reduced bacteremia and AKI even when administered after onset of sepsis.

Conclusion: We demonstrate a protective role of hepcidin in endotoxin- and peritonitis-induced pathologies and AKI, exerted primarily through its anti-inflammatory effects, and antibacterial property. Macrophage H-ferritin plays an important role in hepcidin-mediated protection against endotoxin-induced inflammation. We uncover a novel prophylactic and therapeutic role of hepcidin in sepsis-associated bacteremia, AKI, and mortality.

Lipocalin 24p3 Induction in Colitis Adversely Affects Inflammation and Contributes to Mortality

Recognition of microorganism associated molecular patterns by epithelial cells elicits signaling cascades resulting in the production of host defense proteins. Lipocalin 24p3 is purported to be one such protein. 24p3 binds prokaryotic and eukaryotic siderophores and by sequestering iron laden bacterial siderophores it was believed to restrict bacterial replication. As such mice deficient for 24p3 are susceptible to systemic infections. However, it is not clear whether deficiency of 24p3 on the gut mucosa contributes to inflammation. In line with 24p3's function as a bacteriostat, it would be reasonable to assume that deficiencies in the control of intestinal flora from 24p3 absence play a role in inflammatory intestinal diseases. Surprisingly, we show 24p3 is a contributor of inflammation and 24p3 deficiency protects mice from dextran sodium sulfate (DSS)-induced colitis. 24p3 was found to be a negative regulator of platelet-derived growth factor (PDGF), which helps maintain the integrity of the gut mucosa. Neutralization of PDGF-BB abrogated resistance of 24p3 null mice to DSS confirming the direct link between 24p3 and PDGF-BB. Finally, iron handling in wild-type and 24p3-null mice upon DSS treatment also differed. In summary, differential iron levels and enhanced expression of PDGF-BB in 24p3 null mice confers resistance to DSS.

An intimate crosstalk between iron homeostasis and oxygen metabolism regulated by the hypoxia-inducible factors (HIFs)

Oxygen and iron are among the most abundant elements and have significant roles in human biology. Iron is essential for oxygen transport and is a component of molecular O₂-carrying proteins, such as hemoglobin and myoglobin. Iron is also a constituent of redox enzymes and can occupy multiple oxidation states. An elaborate system has evolved to stringently regulate the concentrations of both, free iron and oxygen, in various sites of the body. The final destination for iron and oxygen in the cells is the mitochondria. The mitochondria require substantial amounts of iron for heme synthesis and maturation of iron-sulfur clusters, and oxygen, as the electron acceptor in oxidative phosphorylation. Therefore, the balance between the control of iron availability and the physiology of hypoxic responses is critical for maintaining cell homeostasis. Several lines of study have clearly demonstrated that the transcription factors, hypoxia-inducible factors (HIFs), play a central role in cellular adaptation to critically low oxygen levels in both normal and compromised tissues. It has also been shown that several target genes of HIFs are involved in iron homeostasis, reflecting the molecular links between oxygen homeostasis and iron metabolism. Furthermore, HIF activation is modulated by intracellular iron, through regulation of hydroxylase activity, which requires iron as a cofactor. In addition, HIF-2α translation is controlled by iron regulatory protein (IRP) activity, providing another level of interdependence between iron and oxygen homeostasis.

Iron deficiency anaemia: experiences and challenges

Iron deficiency remains the largest nutritional deficiency worldwide and the main cause of anaemia. Severe iron deficiency leads to anaemia known as iron deficiency anaemia (IDA), which affects a total of 1·24 billion people, the majority of whom are children and women from resource-poor countries. In sub-Saharan Africa, iron deficiency is frequently exacerbated by concomitant parasitic and bacterial infections and contributes to over 120 000 maternal deaths a year, while it irreparably limits the cognitive development of children and leads to poor outcomes in pregnancy.Currently available iron compounds are cheap and readily available, but constitute a non-physiological approach to providing iron that leads to significant side effects. Consequently, iron deficiency and IDA remain without an effective treatment, particularly in populations with high burden of infectious diseases. So far, despite considerable investment in the past 25 years in nutrition interventions with iron supplementation and fortification, we have been unable to significantly decrease the burden of this disease in resource-poor countries.If we are to eliminate this condition in the future, it is imperative to look beyond the strategies used until now and we should make an effort to combine community engagement and social science approaches to optimise supplementation and fortification programmes.

The opposing effects of acute inflammation and iron deficiency anemia on serum hepcidin and iron absorption in young women

Hepatic hepcidin synthesis is stimulated by inflammation but inhibited during iron deficiency anemia (IDA). In humans, the relative strength of these opposing signals on serum hepcidin and the net effect on iron absorption and systemic iron recycling is uncertain. In this prospective, 45-day study, in young women (n=46; age 18-49 years) with or without IDA, we compared iron and inflammation markers, serum hepcidin and erythrocyte iron incorporation from ⁵⁷Fe-labeled test meals, before and 8, 24 and 36 hours (h) after influenza/DPT vaccination as an acute inflammatory stimulus. Compared to baseline, at 24-36 h after vaccination: 1) interleukin-6 increased 2-3-fold in both groups (P<0.001); 2) serum hepcidin increased >2-fold in the non-anemic group (P<0.001), but did not significantly change in the IDA group; 3) serum iron decreased in the non-anemic group (P<0.05) but did not change in the IDA group; and 4) erythrocyte iron incorporation did not change in either of the two groups, but was approximately 2-fold higher in the IDA group both before and after vaccination (P<0.001). In this study, mild acute inflammation did not increase serum hepcidin in women with IDA, suggesting low iron status and erythropoietic drive offset the inflammatory stimulus on hepcidin expression. In non-anemic women, inflammation increased serum hepcidin and produced mild hypoferremia, but did not reduce dietary iron absorption, suggesting iron-recycling macrophages are more sensitive than the enterocyte to high serum hepcidin during inflammation. The study was registered as a prospective observational trial at clinicaltrials.gov identifier: 02175888 The study was funded by the International Atomic Energy Agency.

Novel Liposome Eencapsulated Guanosine Di Phosphate based Therapeutic Target against Anemia of Inflammation

Hepcidin, master regulator of iron homeostasis, causes anemia under infectious and inflammatory conditions by reducing intestinal absorption of iron with decreased release of iron from macrophages and liver despite adequate iron stores leading to Anemia of Inflammation (AI). Many therapeutic trials have been carried out but none have been effective due to its adverse effects. In present study, we discover that Guanosine 5'-diphosphate (GDP) encapsulated in lipid vesicle (NH+) was found to inhibit NF-ҝB activation by limiting phosphorylation and degradation of IҝBα, thus, attenuating IL-6 secretion from macrophage cells. Moreover, the suppressed IL-6 levels down regulated JAK2/STAT3 pathway with decrease inflammation-mediated Hamp mRNA transcription (HepG2) and increase iron absorption (Caco2) in HepG2/Caco2 co-culture model. Analogous results were obtained in acute and chronic AI mice model thus, correcting haemoglobin level. These results proved NH + GDP as novel therapeutic agent to overcome limitations and suggests it as potential drug to ameliorate AI.

The Dual Role of Hepcidin in Brain Iron Load and Inflammation

Hepcidin is the major regulator of systemic iron metabolism, while the role of this peptide in the brain has just recently been elucidated. Studies suggest a dual role of hepcidin in neuronal iron load and inflammation. This is important since neuronal iron load and inflammation are pathophysiological processes frequently associated with neurodegeneration. Furthermore, manipulation of hepcidin activity has recently been used to recover neuronal damage due to brain inflammation in animal models and cultured cells. Therefore, understanding the mechanistic insights of hepcidin action in the brain is important to uncover its role in treating neuronal damage in neurodegenerative diseases.

Hepcidin-mediated hypoferremic response to acute inflammation requires a threshold of Bmp6/Hjv/Smad signaling

Systemic iron balance is controlled by hepcidin, a liver hormone that limits iron efflux to the bloodstream by promoting degradation of the iron exporter ferroportin in target cells. Iron-dependent hepcidin induction requires hemojuvelin (HJV), a bone morphogenetic protein (BMP) coreceptor that is disrupted in juvenile hemochromatosis, causing dramatic hepcidin deficiency and tissue iron overload. Hjv^-/- mice recapitulate phenotypic hallmarks of hemochromatosis but exhibit blunted hepcidin induction following lipopolysaccharide (LPS) administration. We show that Hjv^-/- mice fail to mount an appropriate hypoferremic response to acute inflammation caused by LPS, the lipopeptide FSL1, or Escherichia coli infection because residual hepcidin does not suffice to drastically decrease macrophage ferroportin levels. Hfe^-/- mice, a model of milder hemochromatosis, exhibit almost wild-type inflammatory hepcidin expression and associated effects, whereas double Hjv^-/-Hfe^-/- mice phenocopy single Hjv^-/- counterparts. In primary murine hepatocytes, Hjv deficiency does not affect interleukin-6 (IL-6)/Stat, and only slightly inhibits BMP2/Smad signaling to hepcidin; however, it severely impairs BMP6/Smad signaling and thereby abolishes synergism with the IL-6/Stat pathway. Inflammatory induction of hepcidin is suppressed in iron-deficient wild-type mice and recovers after the animals are provided overnight access to an iron-rich diet. We conclude that Hjv is required for inflammatory induction of hepcidin and controls the acute hypoferremic response by maintaining a threshold of Bmp6/Smad signaling. Our data highlight Hjv as a potential pharmacological target against anemia of inflammation.

Modulation of Iron Metabolism in Response to Infection: Twists for All Tastes

Iron is an essential nutrient for almost all living organisms, but is not easily made available. Hosts and pathogens engage in a fight for the metal during an infection, leading to major alterations in the host’s iron metabolism. Important pathological consequences can emerge from the mentioned interaction, including anemia. Several recent reports have highlighted the alterations in iron metabolism caused by different types of infection, and several possible therapeutic strategies emerge, based on the targeting of the host’s iron metabolism. Here, we review the most recent literature on iron metabolism alterations that are induced by infection, the consequent development of anemia, and the potential therapeutic approaches to modulate iron metabolism in order to correct iron-related pathologies and control the ongoing infection.

The interrelationship between hepcidin, vitamin D, and anemia in children with acute infectious disease

BACKGROUND

Hepcidin is a master regulator of iron metabolism. Recently, it has been shown that vitamin D suppresses hepcidin expression. Our hypothesis was that hepcidin levels inversely correlate with vitamin D levels in anemic children during acute infection.

METHODS

A prospective study was performed on 90 patients (45 females, 45 males, mean age 7.3 ± 5 years) who were admitted to the pediatric ward. Sixty-two patients had infectious disease (32 with coexisting anemia, 30 without anemia), and 28 patients were hospitalized for noninfectious causes. Blood samples for IL-6, hepcidin, iron status parameters, and 25-hydroxyvitamin D (25-OHD) were obtained within 72 h after admission.

RESULTS

Serum concentrations of IL-6 and hepcidin were significantly higher and 25-OHD, iron, and transferrin were significantly lower in anemic children with infectious disease compared with controls. Children with a serum 25-OHD level < 20 ng/ml had significantly increased odds of having anemia than those with a level > 20 ng/ml (OR: 6.1, CI: 1.15-32.76). Correlation analyses found positive associations between hepcidin levels and ferritin (R² = 0.47, P < 0.001) and negative associations between hepcidin and transferrin (R² = 0.57, P < 0.001).

CONCLUSION

Higher IL-6 and lower 25-OHD levels may lead to higher hepcidin levels and subsequently to hypoferremia and anemia in children with acute infection.

Hepcidin protects grass carp (Ctenopharyngodon idellus) against Flavobacterium columnare infection via regulating iron distribution and immune gene expression

Columnaris disease (CD) caused by Flavobacterium columnare (F. columnare) is lack of knowledge on effective treatment measures. Bacterial pathogens require iron as an essential nutrient to infect the host. While hepcidin acts as a master regulator in iron metabolism, its contribution to host defense is emerging as complex and multifaceted. In vitro, recombinant Ctenopharyngodon idellus (C. idellus) hepcidin (CiHep) and synthetic CiHep both showed the ability to increase the expression of hepcidin and ferritin in C. idellus kidney cells, especially the recombinant CiHep. In vivo, recombinant CiHep improved the survival rate of C. idellus challenged with F. columnare. In addition, the fish fed diet containing recombinant CiHep (group H-1) had a higher survival rate than other pretreatment groups. The study showed that recombinant CiHep regulated iron metabolism causing iron redistribution, decreasing serum iron levels and increasing iron accumulation in the hepatopancreas. Moreover, the expression of iron-related genes was upregulated in various degrees at a different time except for group H-1. Immune-related genes were also evaluated, showing higher expression in the groups pretreated with CiHep at an early stage of infection. Of note, a clear upregulation of more immune genes occurred in the groups pretreated with recombinant CiHep than that pretreated with synthetic CiHep in the late stage of infection. In conclusion, the recombinant CiHep has a protective effect on the host response to bacterial pathogens. We speculate that hepcidin protects C. idellus against F. columnare infection via regulating the iron distribution and immune gene expression.

Efficacy of iron supplementation may be misinterpreted using conventional measures of iron status in iron-depleted, nonanemic women undergoing aerobic exercise training

Background: Despite its known detrimental effects, iron deficiency remains the most common micronutrient deficiency in the world. Many interventions that aim to improve iron status involve physically active populations. Intense aerobic exercise training negatively affects iron status; however, the impact of regular moderate aerobic exercise on the effectiveness of iron supplementation remains unclear.Objective: This study aimed to determine whether aerobic training modifies the assessment of the effectiveness of iron supplementation in improving conventional iron status measures.Design: Seventy-two iron-depleted, nonanemic Chinese women [serum ferritin (sFer) <25 μg/L and hemoglobin >110 g/L] were included in an 8-wk, partially blinded, randomized controlled trial with a 2 × 2 factorial design including iron supplements (42 mg elemental Fe/d) or placebo and aerobic training (five 25-min sessions/wk at 75-85% of maximum heart rate) or no training. Linear mixed models were used to evaluate the relation between supplement type, training, and changes in iron status over time, measured by sFer, hemoglobin, soluble transferrin receptor (sTfR), and estimated total body iron.Results: After treatment, both the iron-supplemented trained and untrained groups showed significantly improved sFer, sTfR, and body iron values compared with either of the placebo groups. Similarly, trained participants had significantly higher aerobic fitness measures than untrained participants. Training modified the sFer response to supplementation (training by supplement interaction, P = 0.07), with the iron-supplemented trained group having significantly lower sFer than the iron-supplemented untrained group at week 8 (mean ± SD: 31.8 ± 13.5 and 47.6 ± 15.7 μg/L, respectively; P = 0.042), whereas there was no significant difference between the placebo trained and untrained groups (21.3 ± 12.2 and 20.3 ± 7.0 μg/L, respectively; P = 1.00).Conclusions: Regular aerobic training reduces the apparent effectiveness of iron supplementation in improving sFer and calls into question whether conventional measures of iron status accurately reflect iron metabolism in physically active, nonanemic women. This trial was registered at clinicaltrials.gov as NCT03002090.

Iron and inflammation - the gut reaction

Anemia is a frequent complication of many inflammatory disorders, including inflammatory bowel disease. Although the pathogenesis of this problem is multifactorial, a key component is the abnormal elevation of the hormone hepcidin, the central regulator of systemic iron homeostasis. Investigations over the last decade have resulted in important insights into the role of hepcidin in iron metabolism and the mechanisms that lead to hepcidin dysregulation in the context of inflammation. These insights provide the foundation for novel strategies to prevent and treat the anemia associated with inflammatory diseases.

Pulmonary Iron Homeostasis in Hepcidin Knockout Mice

Pulmonary iron excess is deleterious and contributes to a range of chronic and acute inflammatory diseases. Optimal lung iron concentration is maintained through dynamic regulation of iron transport and storage proteins. The iron-regulatory hormone hepcidin is also expressed in the lung. In order to better understand the interactions between iron-associated molecules and the hepcidin-ferroportin axis in lung iron balance, we examined lung physiology and inflammatory responses in two murine models of systemic iron-loading, either hepcidin knock-out (Hepc KO) or liver-specific hepcidin KO mice (Hepc KOliv), which do (Hepc KOliv) or do not (Hepc KO) express lung hepcidin. We have found that increased plasma iron in Hepc KO mice is associated with increased pulmonary iron levels, consistent with increased cellular iron uptake by pulmonary epithelial cells, together with an increase at the apical membrane of the cells of the iron exporter ferroportin, consistent with increased iron export in the alveoli. Subsequently, alveolar macrophages (AM) accumulate iron in a non-toxic form and this is associated with elevated production of ferritin. The accumulation of iron in the lung macrophages of hepcidin KO mice contrasts with splenic and hepatic macrophages which contain low iron levels as we have previously reported. Hepc KOliv mice with liver-specific hepcidin deficiency demonstrated same pulmonary iron overload profile as the Hepc KO mice, suggesting that pulmonary hepcidin is not critical in maintaining local iron homeostasis. In addition, the high iron load in the lung of Hepc KO mice does not appear to enhance acute lung inflammation or injury. Lastly, we have shown that intraperitoneal LPS injection is not associated with pulmonary hepcidin induction, despite high levels of inflammatory cytokines. However, intranasal LPS injection stimulates a hepcidin response, likely derived from AM, and alters pulmonary iron content in Hepc KO mice.

AMPK is not required for the effect of metformin on the inhibition of BMP6-induced hepcidin gene expression in hepatocytes

The biguanide metformin is used for its antidiabetic effect for many years but how metformin acts remains poorly understood and controversial. AMP-activated protein kinase (AMPK), a protein kinase that plays a key role in maintaining energy homeostasis, is assumed to be one of the prime targets of metformin. However, since our demonstration that AMPK is not required for the beneficial effects of metformin on the control of glycemia, the list of AMPK-independent actions of metformin is rapidly increasing. Given the conflicting results on the effects of metformin we sought, using our genetic mouse models deficient in the catalytic subunits of AMPK, to determine whether this kinase is involved in the effects of metformin on the expression of the iron-regulatory hormone hepcidin, as recently proposed. Here we demonstrate, using different approaches, either isolated hepatocytes that lack AMPK, or direct AMPK activators, that, AMPK activation is not necessary for metformin to inhibit BMP6-induced hepcidin gene expression. These results may shed new lights on the increasingly recognized AMPK-independent metformin's molecular action, an important area of current research.

Hepcidin-(In)dependent Mechanisms of Iron Metabolism Regulation during Infection by Listeria and Salmonella

During bacterial infection, the pathogenic agent and the host battle for iron, due to its importance for fundamental cellular processes. However, iron redistribution and sequestration during infection can culminate in anemia. Although hepcidin has been recognized as the key regulator of iron metabolism, in some infections its levels remain unaffected, suggesting the involvement of other players in iron metabolism deregulation. In this work, we use a mouse model to elucidate the main cellular and molecular mechanisms that lead to iron redistribution during infection with two different pathogens: Listeria monocytogenes and Salmonella enterica serovar Typhimurium. Both infections clearly impacted iron metabolism, causing iron redistribution, decreasing serum iron levels, decreasing the saturation of transferrin, and increasing iron accumulation in the liver. Both infections were accompanied by the release of proinflammatory cytokines. However, when analyzing iron-related gene expression in the liver, we observed that hepcidin was induced by S Typhimurium but not by L. monocytogenes In the latter model, the downregulation of hepatic ferroportin mRNA and protein levels suggested that ferroportin plays a major role in iron redistribution. On the other hand, S Typhimurium infection induced the expression of hepcidin mRNA, and we show here, for the first time in vivo, that this induction is Toll-like receptor 4 (TLR4) dependent. In this work, we compare several aspects of iron metabolism alterations induced by two different pathogens and suggest that hepcidin-(in)dependent mechanisms contribute to iron redistribution upon infection.

Iron Loading Exaggerates the Inflammatory Response to the Toll-like Receptor 4 Ligand Lipopolysaccharide by Altering Mitochondrial Homeostasis

BACKGROUND

Perioperative and critically ill patients are often exposed to iron (in the form of parenteral-iron administration or blood transfusion) and inflammatory stimuli, but the effects of iron loading on the inflammatory response are unclear. Recent data suggest that mitochondrial reactive oxygen species have an important role in the innate immune response and that increased mitochondrial reactive oxygen species production is a result of dysfunctional mitochondria. We tested the hypothesis that increased intracellular iron potentiates lipopolysaccharide-induced inflammation by increasing mitochondrial reactive oxygen species levels.

METHODS

Murine macrophage cells were incubated with iron and then stimulated with lipopolysaccharide. C57BL/6 wild-type mice were intraperitoneally injected with iron and then with lipopolysaccharide. Markers of inflammation and mitochondrial superoxide production were examined. Mitochondrial homeostasis (the balance between mitochondrial biogenesis and destruction) was assessed, as were mitochondrial mass and the proportion of nonfunctional to total mitochondria.

RESULTS

Iron loading of mice and cells potentiated the inflammatory response to lipopolysaccharide. Iron loading increased mitochondrial superoxide production. Treatment with MitoTEMPO, a mitochondria-specific antioxidant, blunted the proinflammatory effects of iron loading. Iron loading increased mitochondrial mass in cells treated with lipopolysaccharide and increased the proportion of nonfunctional mitochondria. Iron loading also altered mitochondrial homeostasis to favor increased production of mitochondria.

CONCLUSIONS

Acute iron loading potentiates the inflammatory response to lipopolysaccharide, at least in part by disrupting mitochondrial homeostasis and increasing the production of mitochondrial superoxide. Improved understanding of iron homeostasis in the context of acute inflammation may yield innovative therapeutic approaches in perioperative and critically ill patients.

Lipocalin 2: An Emerging Player in Iron Homeostasis and Inflammation

Lipocalin 2 (Lcn2), an innate immune protein, has emerged as a critical iron regulatory protein during physiological and inflammatory conditions. As a bacteriostatic factor, Lcn2 obstructs the siderophore iron-acquiring strategy of bacteria and thus inhibits bacterial growth. As part of host nutritional immunity, Lcn2 facilitates systemic, cellular, and mucosal hypoferremia during inflammation, in addition to stabilizing the siderophore-bound labile iron pool. In this review, we summarize recent advances in understanding the interaction between Lcn2 and iron, and its effects in various inflammatory diseases. Lcn2 exerts mostly a protective role in infectious and inflammatory bowel diseases, whereas both beneficial and detrimental functions have been documented in neurodegenerative diseases, metabolic syndrome, renal disorders, skin disorders, and cancer. Further animal and clinical studies are necessary to unveil the multifaceted roles of Lcn2 in iron dysregulation during inflammation and to explore its therapeutic potential for treating inflammatory diseases.

A Red Carpet for Iron Metabolism

200 billion red blood cells (RBCs) are produced every day, requiring more than 2 × 10¹⁵ iron atoms every second to maintain adequate erythropoiesis. These numbers translate into 20 mL of blood being produced each day, containing 6 g of hemoglobin and 20 mg of iron. These impressive numbers illustrate why the making and breaking of RBCs is at the heart of iron physiology, providing an ideal context to discuss recent progress in understanding the systemic and cellular mechanisms that underlie the regulation of iron homeostasis and its disorders.

Iron- and Hepcidin-Independent Downregulation of the Iron Exporter Ferroportin in Macrophages during Salmonella Infection

Retention of iron in tissue macrophages via upregulation of hepcidin (HAMP) and downregulation of the iron exporter ferroportin (FPN) is thought to participate in the establishment of anemia of inflammation after infection. However, an upregulation of FPN has been proposed to limit macrophages iron access to intracellular pathogens. Therefore, we studied the iron homeostasis and in particular the regulation of FPN after infection with Salmonella enterica serovar Typhimurium in mice presenting tissue macrophages with high iron (AcB61), basal iron (A/J and wild-type mice), or low iron (Hamp knock out, Hamp^-/-) levels. The presence of iron in AcB61 macrophages due to extravascular hemolysis and strong erythrophagocytosis activity favored the proliferation of Salmonella in the spleen and liver with a concomitant decrease of FPN protein expression. Despite systemic iron overload, no or slight increase in Salmonella burden was observed in Hamp^-/- mice compared to controls. Importantly, FPN expression at both mRNA and protein levels was strongly decreased during Salmonella infection in Hamp^-/- mice. The repression of Fpn mRNA was also observed in Salmonella-infected cultured macrophages. In addition, the downregulation of FPN was associated with decreased iron stores in both the liver and spleen in infected mice. Our findings show that during Salmonella infection, FPN is repressed through an iron and hepcidin-independent mechanism. Such regulation likely provides the cellular iron indispensable for the growth of Salmonella inside the macrophages.

Modelling Systemic Iron Regulation during Dietary Iron Overload and Acute Inflammation: Role of Hepcidin-Independent Mechanisms

Systemic iron levels must be maintained in physiological concentrations to prevent diseases associated with iron deficiency or iron overload. A key role in this process plays ferroportin, the only known mammalian transmembrane iron exporter, which releases iron from duodenal enterocytes, hepatocytes, or iron-recycling macrophages into the blood stream. Ferroportin expression is tightly controlled by transcriptional and post-transcriptional mechanisms in response to hypoxia, iron deficiency, heme iron and inflammatory cues by cell-autonomous and systemic mechanisms. At the systemic level, the iron-regulatory hormone hepcidin is released from the liver in response to these cues, binds to ferroportin and triggers its degradation. The relative importance of individual ferroportin control mechanisms and their interplay at the systemic level is incompletely understood. Here, we built a mathematical model of systemic iron regulation. It incorporates the dynamics of organ iron pools as well as regulation by the hepcidin/ferroportin system. We calibrated and validated the model with time-resolved measurements of iron responses in mice challenged with dietary iron overload and/or inflammation. The model demonstrates that inflammation mainly reduces the amount of iron in the blood stream by reducing intracellular ferroportin transcription, and not by hepcidin-dependent ferroportin protein destabilization. In contrast, ferroportin regulation by hepcidin is the predominant mechanism of iron homeostasis in response to changing iron diets for a big range of dietary iron contents. The model further reveals that additional homeostasis mechanisms must be taken into account at very high dietary iron levels, including the saturation of intestinal uptake of nutritional iron and the uptake of circulating, non-transferrin-bound iron, into liver. Taken together, our model quantitatively describes systemic iron metabolism and generated experimentally testable predictions for additional ferroportin-independent homeostasis mechanisms.

The importance of iron in many physiological processes relies on its ability to participate in reduction-oxidation reactions. This property also leads to potential toxicity if concentrations of free iron are not properly managed by cells and tissues. Multicellular organisms therefore evolved intricate regulatory mechanisms to control systemic iron levels. A central regulatory mechanism is the binding of the hormone hepcidin to the iron exporter ferroportin, which controls the major fluxes of iron into blood plasma. Here, we present a mathematical model that is fitted and validated against experimental data to simulate the iron content in different organs following dietary changes and/or inflammatory states, or genetic perturbation of the hepcidin/ferroportin regulatory system. We find that hepcidin mediated ferroportin control is essential, but not sufficient to quantitatively explain several of our experimental findings. Thus, further regulatory mechanisms had to be included in the model to reproduce reduced serum iron levels in response to inflammation, the preferential accumulation of iron in the liver in the case of iron overload, or the maintenance of physiological serum iron concentrations if dietary iron levels are very high. We conclude that hepcidin-independent mechanisms play an important role in maintaining systemic iron homeostasis.

Hepcidin regulation in the anemia of inflammation

PURPOSE OF REVIEW

Anemia is prevalent in patients with infections and other inflammatory conditions. Induction of the iron regulatory hormone hepcidin has been implicated in the pathogenesis of anemia of inflammation. This review outlines recent discoveries in understanding how hepcidin and its receptor ferroportin are regulated, how they contribute to anemia of inflammation, and how this knowledge may help guide new diagnostic and therapeutic strategies for this disease.

RECENT FINDINGS

IL-6 is a primary driver for hepcidin induction in many models of anemia of inflammation, but the SMAD1/5/8 pathway also contributes, likely via Activin B and SMAD-STAT3 interactions at the hepcidin promoter. Hepcidin has an important functional role in many, but not all forms of anemia of inflammation, although hepcidin-independent mechanisms also contribute. In certain populations, hepcidin assays may help target therapy with iron or erythropoiesis-stimulating agents to patients who may benefit most. New therapies targeting the hepcidin-ferroportin axis have shown efficacy in preclinical and early clinical studies.

SUMMARY

Recent studies confirm an important role for the hepcidin-ferroportin axis in the development of anemia of inflammation, but also highlight the diverse and complex pathogenesis of this disorder depending on the underlying disease. Hepcidin-based diagnostic and therapeutic strategies offer promise to improve anemia treatment, but more work is needed in this area.