Iron overload alters innate and T helper cell responses to Candida albicans in mice

The influence of iron nutrition on the development of intestine and immune cell divergency in neonatal pigs

BACKGROUND

Appropriate iron supplementation is essential for neonatal growth and development. However, there are few reports on the effects of iron overload on neonatal growth and immune homeostasis. Thus, the aim of this study was to investigate the effects of iron nutrition on neonatal growth and intestinal immunity by administering different levels of iron to neonatal pigs.

RESULTS

We found that iron deficiency and iron overload resulted in slow growth in neonatal pigs. Iron deficiency and iron overload led to down-regulation of jejunum intestinal barrier and antioxidant marker genes, and promoted CD8+ T cell differentiation in jejunum and mesenteric lymph nodes (MLN) of pigs, disrupting intestinal health. Moreover, iron levels altered serum iron and tissue iron status leading to disturbances in redox state, affecting host innate and adaptive immunity.

CONCLUSIONS

These findings emphasized the effect of iron nutrition on host health and elucidated the importance of iron in regulating redox state and immunity development. This study provided valuable insights into the regulation of redox state and immune function by iron metabolism in early life, thus contributing to the development of targeted interventions and nutritional strategies to optimize iron nutrition in neonates.

Regulatory and pathogenic mechanisms in response to iron deficiency and excess in fungi

Iron is an essential element for all eukaryote organisms because of its redox properties, which are important for many biological processes such as DNA synthesis, mitochondrial respiration, oxygen transport, lipid, and carbon metabolism. For this reason, living organisms have developed different strategies and mechanisms to optimally regulate iron acquisition, transport, storage, and uptake in different environmental responses. Moreover, iron plays an essential role during microbial infections. Saccharomyces cerevisiae has been of key importance for decrypting iron homeostasis and regulation mechanisms in eukaryotes. Specifically, the transcription factors Aft1/Aft2 and Yap5 regulate the expression of genes to control iron metabolism in response to its deficiency or excess, adapting to the cell's iron requirements and its availability in the environment. We also review which iron-related virulence factors have the most common fungal human pathogens (Aspergillus fumigatus, Cryptococcus neoformans, and Candida albicans). These factors are essential for adaptation in different host niches during pathogenesis, including different fungal-specific iron-uptake mechanisms. While being necessary for virulence, they provide hope for developing novel antifungal treatments, which are currently scarce and usually toxic for patients. In this review, we provide a compilation of the current knowledge about the metabolic response to iron deficiency and excess in fungi.

Understanding How Minerals Contribute to Optimal Immune Function

Sufficient mineral supply is vital not only for the innate immune system but also for the components of the adaptive immune defense, which encompass defense mechanisms against pathogens and the delicate balance of pro- and anti-inflammatory regulation in the long term. Generally, a well-balanced diet is capable of providing the necessary minerals to support the immune system. Nevertheless, specific vulnerable populations should be cautious about obtaining adequate amounts of minerals such as magnesium, zinc, copper, iron, and selenium. Inadequate levels of these minerals can temporarily impair immune competence and disrupt the long-term regulation of systemic inflammation. Therefore, comprehending the mechanisms and sources of these minerals is crucial. In exceptional circumstances, mineral deficiencies may necessitate supplementation; however, excessive intake of supplements can have adverse effects on the immune system and should be avoided. Consequently, any supplementation should be approved by medical professionals and administered in recommended doses. This review emphasizes the crucial significance of minerals in promoting optimal functioning of the immune system. It investigates the indispensable minerals required for immune system function and the regulation of inflammation. Moreover, it delves into the significance of maintaining an optimized intake of minerals from a nutritional standpoint.

Serum IL-6 level and nutrition status as potential predictors of clinical leprosy development among household contacts in the endemic areas

Background

Leprosy is a chronic infectious disease that can lead to severe life-long disabilities. Close contacts of leprosy patients have a higher risk of acquiring the disease. Nevertheless, there is a lack of reliable markers to predict Mycobacterium leprae infection. We aim to identify new potential markers for developing clinical leprosy among contacts.

Methods

Serum levels of IL-6, IL-8, IL-10, hemoglobin, ferritin and transferrin saturation were measured in 67 multibacillary leprosy (MB) patients, 65 household contacts (HC) of MB patients, and 127 endemic controls (EC). By means of multivariate logistic regression and ROC analyses, we analyze baseline variables and laboratory parameters that showed significant differences between MB with HC and EC groups and obtained the respective areas under the curve (AUC). Optimal cut-off value of the associated cytokines was also determined.

Results

Elevated IL-6 level was observed in MB compared to HC and EC (p=0.022 and 0.0041, respectively). Anemia and iron deficiency were also higher in MB group compared to HC or EC (p<0.001). Likewise, we observed an increased risk of having MB leprosy in underweight HC [OR 2.599 (0.991; 6.820)] and underweight EC [2.176 (1.010; 4.692)]. Further analysis with ROC showed that high serum IL-6 level, underweight, anemia, and iron deficiency can discriminate leprosy from their household contacts [AUC 0.843 (95% CI 0.771-0.914); p=0.000; optimal cut-off value of IL-6 = 9.14 pg/ml].

Conclusions

Our results suggest that serum IL-6 and nutrition status could serve as potential prognostic markers for the development of clinical leprosy in infected individuals.

The impact of metal availability on immune function during infection

Nutrient transition metals are required cofactors for many proteins to perform functions necessary for life. As such, the concentration of nutrient metals is carefully maintained to retain critical biological processes while limiting toxicity. During infection, invading bacterial pathogens must acquire essential metals, such as zinc, manganese, iron, and copper, from the host to colonize and cause disease. To combat this, the host exploits the essentiality and toxicity of nutrient metals by producing factors that limit metal availability, thereby starving pathogens or accumulating metals in excess to intoxicate the pathogen in a process termed 'nutritional immunity'. As a result of inflammation, a heterogeneous environment containing both metal-replete and -deplete niches is created, in which nutrient metal availability may have an underappreciated role in regulating immune cell function during infection. How the host manipulates nutrient metal availability during infection, and the downstream effects that nutrient metals and metal-sequestering proteins have on immune cell function, are discussed in this review.

Baseline iron status and presence of anaemia determine the course of systemic Salmonella infection following oral iron supplementation in mice

BACKGROUND

Iron deficiency anaemia (IDA) is a major health concern. However, preventive iron supplementation in regions with high burden of infectious diseases resulted in an increase of infection related morbidity and mortality.

METHODS

We fed male C57BL/6N mice with either an iron deficient or an iron adequate diet. Next, they received oral iron supplementation or placebo followed by intraperitoneal infection with Salmonella Typhimurium (S.Tm).

FINDINGS

We found that mice with IDA had a poorer clinical outcome than mice on an iron adequate diet. Interestingly, iron supplementation of IDA mice resulted in higher bacterial burden in organs and shortened survival. Increased transferrin saturation and non-transferrin bound iron in the circulation together with low expression of ferroportin facilitated the access of the pathogen to iron and promoted bacterial growth. Anaemia, independent of iron supplementation, was correlated with reduced neutrophil counts and cytotoxic T cells. With iron supplementation, anaemia additionally correlated with increased splenic levels of the cytokine IL-10, which is suggestive for a weakened immune control to S.Tm infection.

INTERPRETATION

Supplementing iron to anaemic mice worsens the clinical course of bacterial infection. This can be traced back to increased iron delivery to bacteria along with an impaired anti-microbial immune response. Our findings may have important implications for iron supplementation strategies in areas with high endemic burden of infections, putting those individuals, who potentially profit most from iron supplementation for anaemia, at the highest risk for infections.

FUNDING

Financial support by the Christian Doppler Laboratory for Iron Metabolism and Anemia Research.

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.

Regulation of Th1 T Cell Differentiation by Iron via Upregulation of T Cell Immunoglobulin and Mucin Containing Protein-3 (TIM-3)

Iron plays an important role in host–pathogen interactions, in being an essential element for both pathogen and host metabolism, but also by impacting immune cell differentiation and anti-microbial effector pathways. Iron has been implicated to affect the differentiation of T lymphocytes during inflammation, however, so far the underlying mechanism remained elusive. In order to study the role of iron in T cell differentiation we here investigated how dietary iron supplementation affects T cell function and outcome in a model of chronic infection with the intracellular bacterium Salmonella enterica serovar typhimurium (S. Typhimurium). Iron loading prior to infection fostered bacterial burden and, unexpectedly, reduced differentiation of CD4⁺ T helper cells type 1 (Th1) and expression of interferon-gamma (IFNγ), a key cytokine to control infections with intracellular pathogens. This effect could be traced back to iron-mediated induction of the negative immune checkpoint regulator T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), expressed on the surface of this T cell subset. In vitro experiments demonstrated that iron supplementation specifically upregulated mRNA and protein expression of TIM-3 in naïve Th cells in a dose-depdendent manner and hindered priming of those T cells towards Th1 differentiation. Importantly, administration of TIM-3 blocking antibodies to iron-loaded mice infected with S. Typhimurium virtually restored Th1 cell differentiation and significantly improved bacterial control. Our data uncover a novel mechanism by which iron modulates CD4⁺ cell differentiation and functionality and hence impacts infection control with intracellular pathogens. Specifically, iron inhibits the differentiation of naive CD4⁺ T cells to protective IFNγ producing Th1 lymphocytes via stimulation of TIM-3 expression. Finally, TIM-3 may serve as a novel drug target for the treatment of chronic infections with intracellular pathogens, specifically in iron loading diseases.

The Iron Curtain: Macrophages at the Interface of Systemic and Microenvironmental Iron Metabolism and Immune Response in Cancer

Macrophages fulfill central functions in systemic iron metabolism and immune response. Infiltration and polarization of macrophages in the tumor microenvironment is associated with differential cancer prognosis. Distinct metabolic iron and immune phenotypes in tumor associated macrophages have been observed in most cancers. While this prompts the hypothesis that macroenvironmental manifestations of dysfunctional iron metabolism have direct associations with microenvironmental tumor immune response, these functional connections are still emerging. We review our current understanding of the role of macrophages in systemic and microenvironmental immune response and iron metabolism and discuss these functions in the context of cancer and immunometabolic precision therapy approaches. Accumulation of tumor associated macrophages with distinct iron pathologies at the invasive tumor front suggests an "Iron Curtain" presenting as an innate functional interface between systemic and microenvironmental iron metabolism and immune response that can be harnessed therapeutically to further our goal of treating and eliminating cancer.

Iron in immune cell function and host defense

The control over iron availability is crucial under homeostatic conditions and even more in the case of an infection. This results from diverse properties of iron: first, iron is an important trace element for the host as well as for the pathogen for various cellular and metabolic processes, second, free iron catalyzes Fenton reaction and is therefore producing reactive oxygen species as a part of the host defense machinery, third, iron exhibits important effects on immune cell function and differentiation and fourth almost every immune activation in turn impacts on iron metabolism and spatio-temporal iron distribution. The central importance of iron in the host and microbe interplay and thus for the course of infections led to diverse strategies to restrict iron for invading pathogens. In this review, we focus on how iron restriction to the pathogen is a powerful innate immune defense mechanism of the host called "nutritional immunity". Important proteins in the iron-host-pathogen interplay will be discussed as well as the influence of iron on the efficacy of innate and adaptive immunity. Recently described processes like ferritinophagy and ferroptosis are further covered in respect to their impact on inflammation and infection control and how they impact on our understanding of the interaction of host and pathogen.

Iron Supplementation Interferes With Immune Therapy of Murine Mammary Carcinoma by Inhibiting Anti-Tumor T Cell Function

Iron is both, an essential compound for many metabolic processes, and iron deficiency can impact on the proliferation of cells including lymphocytes but also tumor cells. On the other hand, excess iron-catalyzed radical formation can induce cellular toxicity which has been previously demonstrated for T cells in hereditary iron overload. Despite these interconnections, little is known on the effects of clinically approved intravenous iron supplements for curing cancer-related anemia, on T cell differentiation, tumor proliferation, anti-tumor T cell responses and, of clinical importance, on efficacy of cancer immunotherapies. Herein, we analyzed the effects of intravenous iron supplementation on T cell function and on the effectiveness of anti-cancer chemotherapy with IL-2/doxorubicin or immunotherapy with checkpoint-inhibitor anti-PD-L1 in C57Bl/6N female mice with implanted E0771 mammary carcinomas. We found that iron application resulted to an increased availability of iron in the tumor microenvironment and stimulation of tumor growth. In parallel, iron application inhibited the activation, expansion and survival of cytotoxic CD8⁺ T cells and of CD4⁺ T helper cells type 1 and significantly reduced the efficacy of the investigated anti-cancer treatments. Our results indicate that iron administration has a tumor growth promoting effect and impairs anti-cancer responses of tumor infiltrating T lymphocytes along with a reduced efficacy of anti-cancer therapies. Iron supplementation in cancer patients, especially in those treated with immunotherapies in a curative setting, may be thus used cautiously and prospective studies have to clarify the impact of such intervention on the outcome of patients.

Chromosomal segments may explain the antibody response cooperation for canine leishmaniasis pathogenesis

Visceral leishmaniasis (VL) is marked by hyperactivation of a humoral response secreting high quantity of immunoglobulins (Igs) that are inaccessible to intracellular parasites. Here we investigated the contributions of the antibody response to the canine leishmaniasis pathogenesis. Using correlation and genome-wide association analysis, we investigated the relationship of anti-Leishmania infantum immunoglobulin classes levels with parasite burden, clinical response, renal/hepatic biochemical, and oxidative stress markers in dogs from endemic areas of VL. Immunoglobulin G (IgG) and IgA were positively correlated with parasite burden on lymph node and blood. Increased IgG, IgA and IgE levels were associated with severe canine leishmaniasis (CanL) whereas IgM was elevated in uninfected exposed dogs. Correlations of IgM, IgG and IgA with creatinine, urea, AST and ALT levels in the serum were suggested an involvement of those Igs with renal and hepatic changes. The correlogram of oxidative radicals and antioxidants revealed a likely relationship of IgM, IgG and IgA with oxidative stress and lipid peroxidation in the blood, suggested as mechanisms mediating tissue damage and CanL worsening. The gene mapping on chromosomal segments associated with the quantitative variation of immunoglobulin classes identified genetic signatures involved with reactive oxygen species generation, phagolysosome maturation and rupture, free iron availability, Th1/Th2 differenciation and, immunoglobulin clearance. The findings demonstrated the roles of the antibody response as resistance or susceptibility markers and mediators of CanL pathogenesis. In addition we pinpointed candidate genes as potential targets for the therapy against the damage caused by exacerbated antibody response and parasitism in VL.

Iron in infection and immunity

Iron is an essential micronutrient for virtually all living cells. In infectious diseases, both invading pathogens and mammalian cells including those of the immune system require iron to sustain their function, metabolism and proliferation. On the one hand, microbial iron uptake is linked to the virulence of most human pathogens. On the other hand, the sequestration of iron from bacteria and other microorganisms is an efficient strategy of host defense in line with the principles of 'nutritional immunity'. In an acute infection, host-driven iron withdrawal inhibits the growth of pathogens. Chronic immune activation due to persistent infection, autoimmune disease or malignancy however, sequesters iron not only from infectious agents, autoreactive lymphocytes and neoplastic cells but also from erythroid progenitors. This is one of the key mechanisms which collectively result in the anemia of chronic inflammation. In this review, we highlight the most important interconnections between iron metabolism and immunity, focusing on host defense against relevant infections and on the clinical consequences of anemia of inflammation.

Linkage of alterations in systemic iron homeostasis to patients' outcome in sepsis: a prospective study

Background

Sepsis, a dysregulated host response following infection, is associated with massive immune activation and high mortality rates. There is still a need to define further risk factors and laboratory parameters predicting the clinical course. Iron metabolism is regulated by both, the body’s iron status and the immune response. Iron itself is required for erythropoiesis but also for many cellular and metabolic functions. Moreover, iron availability is a critical determinant in infections because it is an essential nutrient for most microbes but also impacts on immune function and intravascular oxidative stress. Herein, we used a prospective study design to investigate the putative impact of serum iron parameters on the outcome of sepsis.

Methods

Serum markers of iron metabolism were measured in a prospective cohort of 61 patients (37 males, 24 females) with sepsis defined by Sepsis-3 criteria in a medical intensive care unit (ICU) and compared between survivors and non-survivors. Regulation of iron parameters in patients stratified by focus of infection and co-medication as well as association of the markers with sepsis severity scores and survival were investigated with linear and logistic regression corrected for sex and age effects.

Results

Positive correlations of increased serum iron and ferritin concentrations upon ICU admission with the severity of organ failure (SOFA score) and with mortality were observed. Moreover, high TF-Sat, elevated ferritin and serum iron levels and low transferrin concentrations were associated with reduced survival. A logistic regression model consisting of SOFA and transferrin saturation (SOFA–TF-Sat) had the best predictive power for survival in septic ICU patients. Of note, administration of blood transfusions prior to ICU admission resulted in increased TF-Sat and reduced survival of septic patients.

Conclusions

Our study could show an important impact of serum iron parameters on the outcome of sepsis. Furthermore, we identified transferrin saturation as a stand-alone predictor of sepsis survival and as a parameter of iron metabolism which may in a combined model improve the prediction power of the SOFA score.

Trial registration

The study was carried out in accordance with the recommendations of the Declaration of Helsinki on biomedical research. The study was approved by the institutional ethics review board of the Medical University Innsbruck (study AN2013-0006).

Type I Interferon Response Dysregulates Host Iron Homeostasis and Enhances Candida glabrata Infection

Type I interferons (IFNs-I) fulfil multiple protective functions during pathogenic infections, but they can also cause detrimental effects and enhance immunopathology. Here, we report that IFNs-I promote the dysregulation of iron homeostasis in macrophages during systemic infections with the intracellular pathogen Candida glabrata, leading to fungal survival and persistence. By engaging JAK1, IFNs-I disturb the balance of the transcriptional activator NRF2 and repressor BACH1 to induce downregulation of the key iron exporter Fpn1 in macrophages. This leads to enhanced iron accumulation in the phagolysosome and failure to restrict fungal access to iron pools. As a result, C. glabrata acquires iron via the Sit1/Ftr1 iron transporter system, facilitating fungal intracellular replication and immune evasion. Thus, IFNs-I are central regulators of iron homeostasis, which can impact infection, and restricting iron bioavailability may offer therapeutic strategies to combat invasive fungal infections.

New insights into the pathogenesis of leprosy: contribution of subversion of host cell metabolism to bacterial persistence, disease progression, and transmission

Chronic infection by the obligate intracellular pathogen Mycobacterium leprae may lead to the development of leprosy. Of note, in the lepromatous clinical form of the disease, failure of the immune system to constrain infection allows the pathogen to reproduce to very high numbers with minimal clinical signs, favoring transmission. The bacillus can modulate cellular metabolism to support its survival, and these changes directly influence immune responses, leading to host tolerance, permanent disease, and dissemination. Among the metabolic changes, upregulation of cholesterol, phospholipids, and fatty acid biosynthesis is particularly important, as it leads to lipid accumulation in the host cells (macrophages and Schwann cells) in the form of lipid droplets, which are sites of polyunsaturated fatty acid-derived lipid mediator biosynthesis that modulate the inflammatory and immune responses. In Schwann cells, energy metabolism is also subverted to support a lipogenic environment. Furthermore, effects on tryptophan and iron metabolisms favor pathogen survival with moderate tissue damage. This review discusses the implications of metabolic changes on the course of M. leprae infection and host immune response and emphasizes the induction of regulatory T cells, which may play a pivotal role in immune modulation in leprosy.

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

Prevention of Adult Colitis by Oral Ferric Iron in Juvenile Mice Is Associated with the Inhibition of the Tbet Promoter Hypomethylation and Gene Overexpression

Iron is an essential nutrient needed for physiological functions, particularly during the developmental period of the early childhood of at-risk populations. The purpose of this study was to investigate, in an experimental colitis, the consequences of daily oral iron ingestion in the early period on the inflammatory response, the spleen T helper (Th) profiles and the associated molecular mechanisms. Juvenile mice orally received microencapsulated ferric iron or water for 6 weeks. On adult mice, we induced a sham or experimental trinitrobenzene sulfonic acid (TNBS) moderate colitis during the last week of the experiment before sacrificing the animals 7 days later. The severity of the gut inflammation was assessed by macroscopic damage scores (MDS) and the myeloperoxidase activity (MPO). Th profiles were evaluated by the examination of the splenic gene expression of key transcription factors of the Th differentiation (Tbet, Gata3, Foxp3 and RORγ) and the methylation of their respective promoter. While TNBS-induced colitis was associated with a change of the Th profile (notably an increase in the Tbet/Gata3 ratio in the spleen), the colitis-inhibition induced by ferric iron was associated with a limitation of the splenic Th profiles perturbation. The inhibition of the splenic Tbet gene overexpression was associated with an inhibition of promoter hypomethylation. In summary, mice treated by long-term oral ferric iron in the early period of life exhibited an inhibition of colitis associated with the inhibition of the splenic Tbet promoter hypomethylation and gene overexpression.

Chronic use of oral iron supplements is associated with poor clinical outcomes in patients with gram-negative bacteremia

An unabsorbed dietary iron supplementation can modify the colonic microbiota equilibrium and favor the growth of pathogenic strains over barrier strains. Nevertheless, the impact of oral iron supplements (OIS) use on the clinical outcomes of patients with gram-negative bacteremia (GNB) has not been evaluated. To explore the impact of OIS on the outcomes of patients with GNB. A retrospective study conducted in a tertiary hospital including patients with GNB during 2011-2016. The entire cohort was divided into chronic OIS users (study group) and nonusers (control group). The two groups were compared for the study outcomes, septic shock at presentation, length of hospital stay (LOS), and short-term mortality. The study cohort included 232 patients; 44 patients in the study group and 188 in the control one. There was no any significant difference in demographic and comorbidities characteristics between the two groups. Escherichia coli comprised the majority of bacteria (69%), while the urinary tract was the main source of the bacteremia. OIS alone and after adjustment was significantly associated with septic shock at presentation (OR = 2, CI95% [1.03-5], p = 0.04 and OR = 5, CI95% [1.4-15], p = 0.01, respectively). By multivariate analysis, OIS was significantly associated with 30-day mortality (OR = 3, CI95% [1.05-7], p = 0.04), but had no impact on LOS (16 + 23 vs. 12 + 15, p = 0.9). There is a significant association between chronic OIS exposure and increased adverse outcomes in patients with GNB. These findings might have important clinical implications.

Established and Emerging Concepts to Treat Imbalances of Iron Homeostasis in Inflammatory Diseases

Inflammation, being a hallmark of many chronic diseases, including cancer, inflammatory bowel disease, rheumatoid arthritis, and chronic kidney disease, negatively affects iron homeostasis, leading to iron retention in macrophages of the mononuclear phagocyte system. Functional iron deficiency is the consequence, leading to anemia of inflammation (AI). Iron deficiency, regardless of anemia, has a detrimental impact on quality of life so that treatment is warranted. Therapeutic strategies include (1) resolution of the underlying disease, (2) iron supplementation, and (3) iron redistribution strategies. Deeper insights into the pathophysiology of AI has led to the development of new therapeutics targeting inflammatory cytokines and the introduction of new iron formulations. Moreover, the discovery that the hormone, hepcidin, plays a key regulatory role in AI has stimulated the development of several therapeutic approaches targeting the function of this peptide. Hence, inflammation-driven hepcidin elevation causes iron retention in cells and tissues. Besides pathophysiological concepts and diagnostic approaches for AI, this review discusses current guidelines for iron replacement therapies with special emphasis on benefits, limitations, and unresolved questions concerning oral versus parenteral iron supplementation in chronic inflammatory diseases. Furthermore, the review explores how therapies aiming at curing the disease underlying AI can also affect anemia and discusses emerging hepcidin antagonizing drugs, which are currently under preclinical or clinical investigation.

Iron in the Tumor Microenvironment-Connecting the Dots

Iron metabolism and tumor biology are intimately linked. Iron facilitates the production of oxygen radicals, which may either result in iron-induced cell death, ferroptosis, or contribute to mutagenicity and malignant transformation. Once transformed, malignant cells require high amounts of iron for proliferation. In addition, iron has multiple regulatory effects on the immune system, thus affecting tumor surveillance by immune cells. For these reasons, inconsiderate iron supplementation in cancer patients has the potential of worsening disease course and outcome. On the other hand, chronic immune activation in the setting of malignancy alters systemic iron homeostasis and directs iron fluxes into myeloid cells. While this response aims at withdrawing iron from tumor cells, it may impair the effector functions of tumor-associated macrophages and will result in iron-restricted erythropoiesis and the development of anemia, subsequently. This review summarizes our current knowledge of the interconnections of iron homeostasis with cancer biology, discusses current clinical controversies in the treatment of anemia of cancer and focuses on the potential roles of iron in the solid tumor microenvironment, also speculating on yet unknown molecular mechanisms.

Iron and innate antimicrobial immunity-Depriving the pathogen, defending the host

The acute-phase response is triggered by the presence of infectious agents and danger signals which indicate hazards for the integrity of the mammalian body. One central feature of this response is the sequestration of iron into storage compartments including macrophages. This limits the availability of this essential nutrient for circulating pathogens, a host defence strategy known as 'nutritional immunity'. Iron metabolism and the immune response are intimately linked. In infections, the availability of iron affects both the efficacy of antimicrobial immune pathways and pathogen proliferation. However, host strategies to withhold iron from microbes vary according to the localization of pathogens: Infections with extracellular bacteria such as Staphylococcus aureus, Streptococcus, Klebsiella or Yersinia stimulate the expression of the iron-regulatory hormone hepcidin which targets the cellular iron-exporter ferroportin-1 causing its internalization and blockade of iron egress from absorptive enterocytes in the duodenum and iron-recycling macrophages. This mechanism disrupts both routes of iron delivery to the circulation, contributes to iron sequestration in the mononuclear phagocyte system and mediates the hypoferraemia of the acute phase response subsequently resulting in the development of anaemia of inflammation. When intracellular microbes are present, other strategies of microbial iron withdrawal are needed. For instance, in macrophages harbouring intracellular pathogens such as Chlamydia, Mycobacterium tuberculosis, Listeria monocytogenes or Salmonella Typhimurium, ferroportin-1-mediated iron export is turned on for the removal of iron from infected cells. This also leads to reduced iron availability for intra-macrophage pathogens which inhibits their growth and in parallel strengthens anti-microbial effector pathways of macrophages including the formation of inducible nitric oxide synthase and tumour necrosis factor. Iron plays a key role in infectious diseases both as modulator of the innate immune response and as nutrient for microbes. We need to gain a more comprehensive understanding of how the body can differentially respond to infection by extra- or intracellular pathogens. This knowledge may allow us to modulate mammalian iron homeostasis pharmaceutically and to target iron-acquisition systems of pathogens, thus enabling us to treat infections with novel strategies that act independent of established antimicrobials.

Iron at the Centre of Candida albicans Interactions

Iron is an absolute requirement for both the host and most pathogens alike and is needed for normal cellular growth. The acquisition of iron by biological systems is regulated to circumvent toxicity of iron overload, as well as the growth deficits imposed by iron deficiency. In addition, hosts, such as humans, need to limit the availability of iron to pathogens. However, opportunistic pathogens such as Candida albicans are able to adapt to extremes of iron availability, such as the iron replete environment of the gastrointestinal tract and iron deficiency during systemic infection. C. albicans has developed a complex and effective regulatory circuit for iron acquisition and storage to circumvent iron limitation within the human host. As C. albicans can form complex interactions with both commensal and pathogenic co-inhabitants, it can be speculated that iron may play an important role in these interactions. In this review, we highlight host iron regulation as well as regulation of iron homeostasis in C. albicans. In addition, the review argues for the need for further research into the role of iron in polymicrobial interactions. Lastly, the role of iron in treatment of C. albicans infection is discussed.

Association between baseline serum hepcidin levels and infection in kidney transplant recipients: Potential role for iron overload

BACKGROUND

The liver-synthesized peptide hepcidin is a key regulator of iron metabolism and correlates with total iron stores. We analyzed the association between pre-transplant hepcidin-25 levels and infection after kidney transplantation (KT).

METHODS

Serum hepcidin-25 levels were measured at baseline by high-sensitivity ELISA in 91 patients undergoing KT at our institution between December 2011 and March 2013. The impact of this biomarker on the incidence of post-transplant infection (excluding lower urinary tract infection) during the first year was assessed by Cox regression.

RESULTS

Mean hepcidin-25 level was 82.3 ± 67.4 ng/mL and strongly correlated with serum ferritin (Spearman's rho = 0.703; P < .001). There were no significant differences in hepcidin-25 levels between patients with or without overall infection (96.4 ± 67.5 vs 72.6 ± 66.7 ng/mL; P = .101). Such difference was evident for opportunistic (128.9 ± 75.0 vs 73.0 ± 62.3 ng/mL; P = .003) and, to a lesser extent, surgical-site infection (107.5 ± 73.3 vs 76.5 ± 65.2 ng/mL; P = .087). Patients with hepcidin-25 levels ≥72.5 ng/mL had higher 12-month cumulative incidence of overall infection (51.2% vs 29.2%; P = .032). After multivariate adjustment, hepcidin-25 ≥72.5 ng/mL acted as an independent risk factor for overall (adjusted hazard ratio [aHR] 3.86; 95% confidence interval [CI] 1.49-9.96; P = .005) and opportunistic infection (aHR 4.32; 95% CI 1.18-15.75; P = .027).

CONCLUSION

Elevated baseline serum hepcidin-25 levels were associated with increased risk of infection after KT, suggesting a role for iron overload in the individual susceptibility to post-transplant infection.

Genetic and Dietary Iron Overload Differentially Affect the Course of Salmonella Typhimurium Infection

Genetic and dietary forms of iron overload have distinctive clinical and pathophysiological features. HFE-associated hereditary hemochromatosis is characterized by overwhelming intestinal iron absorption, parenchymal iron deposition, and macrophage iron depletion. In contrast, excessive dietary iron intake results in iron deposition in macrophages. However, the functional consequences of genetic and dietary iron overload for the control of microbes are incompletely understood. Using Hfe^+/+ and Hfe^-/- mice in combination with oral iron overload in a model of Salmonella enterica serovar Typhimurium infection, we found animals of either genotype to induce hepcidin antimicrobial peptide expression and hypoferremia following systemic infection in an Hfe-independent manner. As predicted, Hfe^-/- mice, a model of hereditary hemochromatosis, displayed reduced spleen iron content, which translated into improved control of Salmonella replication. Salmonella adapted to the iron-poor microenvironment in the spleens of Hfe^-/- mice by inducing the expression of its siderophore iron-uptake machinery. Dietary iron loading resulted in higher bacterial numbers in both WT and Hfe^-/- mice, although Hfe deficiency still resulted in better pathogen control and improved survival. This suggests that Hfe deficiency may exert protective effects in addition to the control of iron availability for intracellular bacteria. Our data show that a dynamic adaptation of iron metabolism in both immune cells and microbes shapes the host-pathogen interaction in the setting of systemic Salmonella infection. Moreover, Hfe-associated iron overload and dietary iron excess result in different outcomes in infection, indicating that tissue and cellular iron distribution determines the susceptibility to infection with specific pathogens.

Molecular pathogenesis and clinical consequences of iron overload in liver cirrhosis

BACKGROUND

The liver, as the main iron storage compartment and the place of hepcidin synthesis, is the central organ involved in maintaining iron homeostasis in the body. Excessive accumulation of iron is an important risk factor in liver disease progression to cirrhosis and hepatocellular carcinoma. Here, we review the literature on the molecular pathogenesis of iron overload and its clinical consequences in chronic liver diseases.

DATA SOURCES

PubMed was searched for English-language articles on molecular genesis of primary and secondary iron overload, as well as on their association with liver disease progression. We have also included literature on adjuvant therapeutic interventions aiming to alleviate detrimental effects of excessive body iron load in liver cirrhosis.

RESULTS

Excess of free, unbound iron induces oxidative stress, increases cell sensitivity to other detrimental factors, and can directly affect cellular signaling pathways, resulting in accelerated liver disease progression. Diagnosis of liver cirrhosis is, in turn, often associated with the identification of a pathological accumulation of iron, even in the absence of genetic background of hereditary hemochromatosis. Iron depletion and adjuvant therapy with antioxidants are shown to cause significant improvement of liver functions in patients with iron overload. Phlebotomy can have beneficial effects on liver histology in patients with excessive iron accumulation combined with compensated liver cirrhosis of different etiology.

CONCLUSION

Excessive accumulation of body iron in liver cirrhosis is an important predictor of liver failure and available data suggest that it can be considered as target for adjuvant therapy in this condition.

Iron acquisition in Leishmania and its crucial role in infection

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

Increased IL-17 and TGF-β serum levels in peripheral blood of patients with β-thalassemia major: implication for continual transfusions role in T helper17-mediated proinflammatory responses

BACKGROUND/AIM

Recent studies have shown that IL-17-producing CD4+ T helper (Th17) cells play an important role in proinflammatory processes. In this report we analyzed IL-17, IL-21, and TGF-β serum levels in the peripheral blood of Iranian beta-thalassemia major patients that clinically exhibited splenectomy and iron overload.

MATERIALS AND METHODS

Blood samples were collected from 43 beta-thalassemia patients and 43 healthy individuals with no history of malignancies or autoimmune disorders. Then serum levels of IL-17, IL-21, and TGF-β were measured by enzyme linked immunosorbent assay (ELISA).

RESULTS

The levels of IL-17 (P = 0.005) and TGF-β (P < 0.001) were significantly higher in the thalassemia patients compared to the healthy control. No significant differences in the level of serum IL-21 was observed between the patients and controls. There were no significant differences in serum levels of IL-17, IL-21, and TGF-β between patients with high or low serum levels of ferritin.

CONCLUSION

Multiple blood transfusions cause constant immune stimulation, as a result of repeated exposure to new alloantigens. This might have significant effects on the stimulation of cytokine producing cells in those patients and cytokine profile can be used as a related marker for assessing disease severity and consequently therapeutic intervention.

Contrasting regulation of macrophage iron homeostasis in response to infection with Listeria monocytogenes depending on localization of bacteria

Due to its multiple roles for the proliferation and pathogenicity of many microbes on the one hand and via modulation of immune effector functions on the other hand the control over iron homeostasis is thought to play a decisive role in the course of infections. Diversion of cellular iron traffic is considered as an important defense mechanism of macrophages to reduce metal availability for intracellular bacteria residing in the phagosome. However, evidence is lacking whether such alterations of iron homeostasis also become evident upon infection with bacteria gaining access to the cytosol like Listeria monocytogenes. Here we show that infection of macrophages with L. monocytogenes triggers the expression of the major cellular iron exporter ferroportin1 and induces cellular iron egress. As the growth of Listeria within macrophages is promoted by iron, stimulation of ferroportin1 functionality limits the availability of the metal for Listeria residing in the cytoplasm, whereas ferroportin1 degradation upon hepcidin treatment increases intracellular bacterial growth. In parallel to an increase of ferroportin1 expression, infected macrophages induce anti-microbial immune effector mechanisms such as TNFα formation or NO expression which are aggravated upon iron deficiency. These adaptive changes of iron homeostasis and immune response pathways are only found in macrophages infected with Listeria which express listeriolysin O and are therefore able to escape from the phagosome to the cytoplasm. Listeriolysin O deficient Listeria which are restricted to the phagosome are even killed by excess iron which may be based on "iron intoxification" via macrophage radical formation, because iron supplementation in that setting is paralleled by increased ROS formation. Our results indicate that ferroportin1 mediated iron export is a nutritional immune effector pathway to control infection with Listeria residing in the cytoplasm, whereas a different strategy is observed in mutant Listeria restricted to the phagosome, where iron remains in the macrophages likewise contributing to ROS mediated intoxification of bacteria.

Oxidative stress and age-related changes in T cells: is thalassemia a model of accelerated immune system aging?

Iron overload in β-thalassemia major occurs mainly due to blood transfusion, an essential treatment for β-thalassemia major patients, which results in oxidative stress. It has been thought that oxidative stress causes elevation of immune system senescent cells. Under this condition, cells normally enhance in aging, which is referred to as premature immunosenescence. Because there is no animal model for immunosenescence, most knowledge on the immunosenescence pattern is based on induction of immunosenescence. In this review, we describe iron overload and oxidative stress in β-thalassemia major patients and how they make these patients a suitable human model for immunosenescence. We also consider oxidative stress in some kinds of chronic virus infections, which induce changes in the immune system similar to β-thalassemia major. In conclusion, a therapeutic approach used to improve the immune system in such chronic virus diseases, may change the immunosenescence state and make life conditions better for β-thalassemia major patients.

The Iron age of host-microbe interactions

Microbes exert a major impact on human health and disease by either promoting or disrupting homeostasis, in the latter instance leading to the development of infectious diseases. Such disparate outcomes are driven by the ever-evolving genetic diversity of microbes and the countervailing host responses that minimize their pathogenic impact. Host defense strategies that limit microbial pathogenicity include resistance mechanisms that exert a negative impact on microbes, and disease tolerance mechanisms that sustain host homeostasis without interfering directly with microbes. While genetically distinct, these host defense strategies are functionally integrated, via mechanisms that remain incompletely defined. Here, we explore the general principles via which host adaptive responses regulating iron (Fe) metabolism impact on resistance and disease tolerance to infection.

Receipt of Intravenous Iron and Clinical Outcomes among Hemodialysis Patients Hospitalized for Infection

BACKGROUND AND OBJECTIVES

Anemia guidelines for CKD recommend withholding intravenous iron in the setting of active infection, although no data specifically support this recommendation. This study aimed to examine the association between intravenous iron and clinical outcomes among hemodialysis patients hospitalized for infection.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a retrospective observational cohort study using data from the US Renal Data System of 22,820 adult Medicare beneficiaries on in-center hemodialysis who had received intravenous iron in the 14 days preceding their first hospitalization for bacterial infection in 2010. In multivariable analyses, the association between receipt of intravenous iron at any point from the day of hospital admission to discharge and all-cause 30-day mortality, mortality in 2010, length of hospital stay, and readmission for infection or death within 30 days of discharge was evaluated.

RESULTS

There were 2463 patients (10.8%) who received intravenous iron at any point from the day of admission to discharge. Receipt of intravenous iron was not associated with age, dialysis vintage, or comorbidities. There were 2618 deaths within 30 days of admission and 6921 deaths in 2010 (median follow-up 173 days; 25th and 75th percentiles, 78-271 days). The median length of stay was 7 days (25th and 75th percentiles, 5-12 days). Receipt of intravenous iron was not associated with higher 30-day mortality (odds ratio, 0.86; 95% confidence interval [95% CI], 0.74 to 1.00), higher mortality in 2010 (hazard ratio, 0.92; 95% CI, 0.85 to 1.00), longer mean length of stay (10.1 days [95% CI, 9.7 to 10.5] versus 10.5 days [95% CI, 10.3 to 10.7]; P=0.05), or readmission for infection or death within 30 days of discharge (odds ratio, 1.08; 95% CI, 0.96 to 1.22) compared with no receipt of intravenous iron.

CONCLUSIONS

This analysis does not support withholding intravenous iron upon admission for bacterial infection in hemodialysis patients, although clinical trials are required to make definitive recommendations.

The Labile Side of Iron Supplementation in CKD

The practice of intravenous iron supplementation has grown as nephrologists have gradually moved away from the liberal use of erythropoiesis-stimulating agents as the main treatment for the anemia of CKD. This approach, together with the introduction of large-dose iron preparations, raises the future specter of inadvertent iatrogenic iron toxicity. Concerns have been raised in original studies and reviews about cardiac complications and severe infections that result from long-term intravenous iron supplementation. Regarding the iron preparations specifically, even though all the currently available preparations appear to be relatively safe in the short term, little is known regarding their long-term safety. In this review we summarize current knowledge of iron metabolism with an emphasis on the sources and potentially harmful effects of labile iron, highlight the approaches to identifying labile iron in pharmaceutical preparations and body fluids and its potential toxic role as a pathogenic factor in the complications of CKD, and propose methods for its early detection in at-risk patients.

Iron at the interface of immunity and infection

Both, mammalian cells and microbes have an essential need for iron, which is required for many metabolic processes and for microbial pathogenicity. In addition, cross-regulatory interactions between iron homeostasis and immune function are evident. Cytokines and the acute phase protein hepcidin affect iron homeostasis leading to the retention of the metal within macrophages and hypoferremia. This is considered to result from a defense mechanism of the body to limit the availability of iron for extracellular pathogens while on the other hand the reduction of circulating iron results in the development of anemia of inflammation. Opposite, iron and the erythropoiesis inducing hormone erythropoietin affect innate immune responses by influencing interferon-gamma (IFN-γ) mediated (iron) or NF-kB inducible (erythropoietin) immune effector pathways in macrophages. Thus, macrophages loaded with iron lose their ability to kill intracellular pathogens via IFN-γ mediated effector pathways such as nitric oxide (NO) formation. Accordingly, macrophages invaded by the intracellular bacterium Salmonella enterica serovar Typhimurium increase the expression of the iron export protein ferroportin thereby reducing the availability of iron for intramacrophage bacteria while on the other side strengthening anti-microbial macrophage effector pathways via increased formation of NO or TNF-α. In addition, certain innate resistance genes such as natural resistance associated macrophage protein function (Nramp1) or lipocalin-2 exert part of their antimicrobial activity by controlling host and/or microbial iron homeostasis. Consequently, pharmacological or dietary modification of cellular iron trafficking enhances host resistance to intracellular pathogens but may increase susceptibility to microbes in the extracellular compartment and vice versa. Thus, the control over iron homeostasis is a central battlefield in host–pathogen interplay influencing the course of an infectious disease in favor of either the mammalian host or the pathogenic invader.

Iron and infection in hemodialysis patients

Intravenous iron is an important component of the treatment of anemia of end-stage renal disease (ESRD), but it is biologically plausible that iron could increase the risk of infection through impairment of neutrophil and T-cell function and promotion of microbial growth. Any such increase in risk would be particularly important because infection is a significant cause of mortality and morbidity in dialysis patients. The overall evidence favors an association between iron and infection in hemodialysis patients, but the optimal iron management strategy to minimize infection risk has yet to be identified. There is a need for further research on this topic, particularly in light of increased utilization of intravenous iron following implementation of the bundled ESRD reimbursement system.

The complex interplay of iron metabolism, reactive oxygen species, and reactive nitrogen species: insights into the potential of various iron therapies to induce oxidative and nitrosative stress

Production of minute concentrations of superoxide (O2(*-)) and nitrogen monoxide (nitric oxide, NO*) plays important roles in several aspects of cellular signaling and metabolic regulation. However, in an inflammatory environment, the concentrations of these radicals can drastically increase and the antioxidant defenses may become overwhelmed. Thus, biological damage may occur owing to redox imbalance-a condition called oxidative and/or nitrosative stress. A complex interplay exists between iron metabolism, O2(*-), hydrogen peroxide (H2O2), and NO*. Iron is involved in both the formation and the scavenging of these species. Iron deficiency (anemia) (ID(A)) is associated with oxidative stress, but its role in the induction of nitrosative stress is largely unclear. Moreover, oral as well as intravenous (iv) iron preparations used for the treatment of ID(A) may also induce oxidative and/or nitrosative stress. Oral administration of ferrous salts may lead to high transferrin saturation levels and, thus, formation of non-transferrin-bound iron, a potentially toxic form of iron with a propensity to induce oxidative stress. One of the factors that determine the likelihood of oxidative and nitrosative stress induced upon administration of an iv iron complex is the amount of labile (or weakly-bound) iron present in the complex. Stable dextran-based iron complexes used for iv therapy, although they contain only negligible amounts of labile iron, can induce oxidative and/or nitrosative stress through so far unknown mechanisms. In this review, after summarizing the main features of iron metabolism and its complex interplay with O2(*-), H2O2, NO*, and other more reactive compounds derived from these species, the potential of various iron therapies to induce oxidative and nitrosative stress is discussed and possible underlying mechanisms are proposed. Understanding the mechanisms, by which various iron formulations may induce oxidative and nitrosative stress, will help us develop better tolerated and more efficient therapies for various dysfunctions of iron metabolism.

Estrogen-dependent changes in serum iron levels as a translator of the adverse effects of estrogen during infection: a conceptual framework

Elevated levels of estrogen often associate with increased susceptibility to infection. This has been attributed to the ability of estrogen to concomitantly enhance the growth and virulence of pathogens and suppress host immunity. But the exact mechanism of how estrogen mediates such effects, especially in cases where the pathogen and/or the immune components in question do not express estrogen receptors, has yet to be elucidated. Here we propose that translating the adverse effects of estrogen during infection is dependent to a significant degree upon its ability to manipulate iron homeostasis. For elevated levels of estrogen alter the synthesis and/or activity of several factors involved in iron metabolism including hypoxia inducible factor 1α (HIF-1α) and hepcidin among others. This leads to the inhibition of hepcidin synthesis in hepatocytes and the maintenance of ferroportin (FPN) integrity on the surface of iron-releasing duodenal enterocytes, hepatocytes, and macrophages. Intact FPN permits the continuous efflux of dietary and stored iron into the circulation, which further enhances pathogen growth and virulence on the one hand and suppresses host immunity on the other. This new conceptual framework may help explain a multitude of disparate clinical and experimental observations pertinent to the relationship between estrogen and infection.

Fungal iron availability during deep seated candidiasis is defined by a complex interplay involving systemic and local events

Nutritional immunity – the withholding of nutrients by the host – has long been recognised as an important factor that shapes bacterial-host interactions. However, the dynamics of nutrient availability within local host niches during fungal infection are poorly defined. We have combined laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS), MALDI imaging and immunohistochemistry with microtranscriptomics to examine iron homeostasis in the host and pathogen in the murine model of systemic candidiasis. Dramatic changes in the renal iron landscape occur during disease progression. The infection perturbs global iron homeostasis in the host leading to iron accumulation in the renal medulla. Paradoxically, this is accompanied by nutritional immunity in the renal cortex as iron exclusion zones emerge locally around fungal lesions. These exclusion zones correlate with immune infiltrates and haem oxygenase 1-expressing host cells. This local nutritional immunity decreases iron availability, leading to a switch in iron acquisition mechanisms within mature fungal lesions, as revealed by laser capture microdissection and qRT-PCR analyses. Therefore, a complex interplay of systemic and local events influences iron homeostasis and pathogen-host dynamics during disease progression.

Microbial pathogens must assimilate essential micronutrients to establish infections. During bacterial infection, mammals limit the availability of micronutrients to inhibit the growth of the pathogen – a phenomenon termed ‘nutrient immunity.’ Nutrient immunity has not been examined during disseminated candidiasis. Yet micronutrient assimilation, and iron assimilation in particular, is required for fungal virulence, and life-threatening disseminated fungal infections are recognised as a major medical threat for patients with compromised immune systems. We show that nutrient immunity operates during disseminated Candida albicans infections in mice. Over time immune cells congregate around the fungal lesions in the kidney cortex, driving nutrient immunity and reducing iron availability for the pathogen. The fungus responds by tuning its iron assimilation strategies to the reduced iron levels. Paradoxically, iron levels increase in other parts of the kidney as Candida infections progress. We show that the fungal infection disturbs global iron homeostasis in the host by perturbing red blood cell recycling in the spleen and this is associated with increased iron storage in the kidney medulla. Therefore, fungal infection exerts system-wide effects upon iron homeostasis in the mammalian host, whilst triggering local nutrient immunity to limit the infection.

Nitric oxide-mediated regulation of ferroportin-1 controls macrophage iron homeostasis and immune function in Salmonella infection

NOS2-derived nitric oxide drives ferroportin-1–mediated iron export in Salmonella-infected macrophages, thus limiting bacterial growth.

Nitric oxide (NO) generated by inducible NO synthase 2 (NOS2) affects cellular iron homeostasis, but the underlying molecular mechanisms and implications for NOS2-dependent pathogen control are incompletely understood. In this study, we found that NO up-regulated the expression of ferroportin-1 (Fpn1), the major cellular iron exporter, in mouse and human cells. Nos2^−/− macrophages displayed increased iron content due to reduced Fpn1 expression and allowed for an enhanced iron acquisition by the intracellular bacterium Salmonella typhimurium. Nos2 gene disruption or inhibition of NOS2 activity led to an accumulation of iron in the spleen and splenic macrophages. Lack of NO formation resulted in impaired nuclear factor erythroid 2-related factor-2 (Nrf2) expression, resulting in reduced Fpn1 transcription and diminished cellular iron egress. After infection of Nos2^−/− macrophages or mice with S. typhimurium, the increased iron accumulation was paralleled by a reduced cytokine (TNF, IL-12, and IFN-γ) expression and impaired pathogen control, all of which were restored upon administration of the iron chelator deferasirox or hyperexpression of Fpn1 or Nrf2. Thus, the accumulation of iron in Nos2^−/− macrophages counteracts a proinflammatory host immune response, and the protective effect of NO appears to partially result from its ability to prevent iron overload in macrophages

Iron deficiency and susceptibility to infections: evaluation of the clinical evidence

Iron is a fundamental nutrient for human and microbial life. We sought to examine the association of iron deficiency versus normal iron status with the susceptibility to infections. A systematic search in the PubMed and Scopus databases was performed to identify relevant clinical studies. Six studies (including a total of 1,422 participants) met the inclusion criteria: four prospective cohort (859 participants), one retrospective case-control (115 participants), and one retrospective cohort study (448 participants). Intensive care unit (ICU)-acquired and postoperative infections were more common in patients with iron deficiency than among those with normal iron status in two studies, while no difference was reported in another study. In one study examining pregnant women with normal mean iron values, higher soluble transferrin receptor values independently predicted vaginosis-like microflora. Iron deficiency anemia was an independent predictor of respiratory tract infections in one study, and postoperative urinary tract infections were more common in patients with iron deficiency anemia in another. The limited available evidence suggests that individuals with iron deficiency and those with iron deficiency anemia may be more susceptible to infections than patients with normal iron status. Future studies should elucidate further these findings.

Iron overload favors the elimination of Leishmania infantum from mouse tissues through interaction with reactive oxygen and nitrogen species

Iron plays a central role in host-parasite interactions, since both intervenients need iron for survival and growth, but are sensitive to iron-mediated toxicity. The host's iron overload is often associated with susceptibility to infection. However, it has been previously reported that iron overload prevented the growth of Leishmania major, an agent of cutaneous leishmaniasis, in BALB/c mice. In order to further clarify the impact of iron modulation on the growth of Leishmania in vivo, we studied the effects of iron supplementation or deprivation on the growth of L. infantum, the causative agent of Mediterranean visceral leishmaniasis, in the mouse model. We found that dietary iron deficiency did not affect the protozoan growth, whereas iron overload decreased its replication in the liver and spleen of a susceptible mouse strain. The fact that the iron-induced inhibitory effect could not be seen in mice deficient in NADPH dependent oxidase or nitric oxide synthase 2 suggests that iron eliminates L. infantum in vivo through the interaction with reactive oxygen and nitrogen species. Iron overload did not significantly alter the mouse adaptive immune response against L. infantum. Furthermore, the inhibitory action of iron towards L. infantum was also observed, in a dose dependent manner, in axenic cultures of promastigotes and amastigotes. Importantly, high iron concentrations were needed to achieve such effects. In conclusion, externally added iron synergizes with the host's oxidative mechanisms of defense in eliminating L. infantum from mouse tissues. Additionally, the direct toxicity of iron against Leishmania suggests a potential use of this metal as a therapeutic tool or the further exploration of iron anti-parasitic mechanisms for the design of new drugs.

Leishmania are important vector-borne protozoan pathogens that cause different forms of disease, ranging from cutaneous self-healing lesions to life-threatening visceral infection. L. infantum is the most common species causing visceral leishmaniasis in Europe and the Mediterranean basin. Iron plays a critical role in host-pathogen interactions. Both the microorganism and its host need iron for growth. However, iron may promote the formation of toxic reactive oxygen species, which contribute to pathogen elimination, but also to host tissue pathology. We investigated the effect of manipulating host iron status on the outcome of L. infantum infection, using the mouse as an experimental model. We found that dietary iron deprivation had no effect on L. infantum growth, and iron-dextran injection decreased the multiplication of L. infantum in mouse organs. The fact that this anti-parasitic effect of iron was not observed in mice genetically deficient in superoxide and nitric oxide synthesis pathways indicates that iron is likely to act in synergy with reactive oxygen and nitrogen species produced by the host's macrophages. This work clearly shows that iron supplementation improves the host's capacity to eliminate L. infantum parasites and suggests that iron may be further explored as a therapeutic tool to fight this type of infection.

Anaemia in inflammatory rheumatic diseases

Anaemia is frequently observed in patients with inflammatory rheumatic diseases. Depending on its severity, anaemia negatively affects cardiovascular performance, physical activity and the quality of life of patients. However, anaemia is considered to be a symptom of the underlying inflammatory disease and, thus, neglected as a complex medical condition that warrants specific diagnosis and treatment. Although inflammation-induced alterations in iron homeostasis and erythropoiesis have a dominant role in the pathogenesis of this type of anaemia, multiple other factors such as chronic blood loss, haemolysis, disease and treatment-associated adverse effects or vitamin deficiencies can also take part in the development of anaemia. Accordingly, the prevalence of anaemia is positively associated with the severity of the underlying disease. This Review will summarize epidemiological data on anaemia in inflammatory rheumatic diseases, along with a detailed description of underlying pathophysiological pathways, available diagnostic tools and practical diagnostic strategies. Discussion of established and newly emerging treatment regimens, as well as the need for further research in this clinically relevant field, will also be included.

Insights into the pathophysiology of iron metabolism in Pythium insidiosum infections

Pythium insidiosum causes life-threatening disease in mammals. Animals with pythiosis usually develop anemia, and most human patients are reported to have thalassemia and the major consequence of thalassemia, iron overload. Therefore, this study evaluated the iron metabolism in rabbits experimentally infected with P. insidiosum. Ten infected rabbits were divided into two groups: one groups received a placebo, and the other was treated with immunotherapy. Five rabbits were used as negative controls. The hematological and biochemical parameters, including the iron profile, were evaluated. Microcytic hypochromic anemia was observed in the infected animals, and this condition was more accentuated in the untreated group. The serum iron level was decreased, whereas the transferrin level was increased, resulting in low saturation. The level of stainable iron in hepatocytes was markedly decreased in the untreated group. A high correlation was observed between the total iron binding capacity and the lesion size, and this correlation likely confirms the affinity of P. insidiosum for iron. The data from this study corroborate the previous implications of iron in the pathogenesis of pythiosis in humans and animals.

Iron inhibits activation-induced cytidine deaminase enzymatic activity and modulates immunoglobulin class switch DNA recombination

Immunoglobulin (Ig) class switch DNA recombination (CSR) and somatic hypermutation (SHM) are critical for the maturation of the antibody response. Activation-induced cytidine deaminase (AID) initiates CSR and SHM by deaminating deoxycytidines (dCs) in switch (S) and V(D)J region DNA, respectively, to generate deoxyuracils (dUs). Processing of dUs by uracil DNA glycosylase (UNG) yields abasic sites, which are excised by apurinic/apyrimidinic endonucleases, eventually generating double strand DNA breaks, the obligatory intermediates of CSR. Here, we found that the bivalent iron ion (Fe(2+), ferrous) suppressed CSR, leading to decreased number of switched B cells, decreased postrecombination Iμ-C(H) transcripts, and reduced titers of secreted class-switched IgG1, IgG3, and IgA antibodies, without alterations in critical CSR factors, such as AID, 14-3-3γ, or PTIP, or in general germline I(H)-S-C(H) transcription. Fe(2+) did not affect B cell proliferation or plasmacytoid differentiation. Rather, it inhibited AID-mediated dC deamination in a dose-dependent fashion. The inhibition of intrinsic AID enzymatic activity by Fe(2+) was specific, as shown by lack of inhibition of AID-mediated dC deamination by other bivalent metal ions, such as Zn(2+), Mn(2+), Mg(2+), or Ni(2+), and the inability of Fe(2+) to inhibit UNG-mediated dU excision. Overall, our findings have outlined a novel role of iron in modulating a B cell differentiation process that is critical to the generation of effective antibody responses to microbial pathogens and tumoral cells. They also suggest a possible role of iron in dampening AID-dependent autoimmunity and neoplastic transformation.

Ferric citrate CYP2E1-independently promotes alcohol-induced apoptosis in HepG2 cells via oxidative/nitrative stress which is attenuated by pretreatment with baicalin

In the case of alcoholic liver injury, an iron overload is always present. Both alcohol and iron can individually induce oxidative stress in liver. However, the combined effect of physiological concentrations of alcohol and iron on oxidative stress in hepatocytes remains unknown. Baicalin has been demonstrated to be an antioxidant or iron chelator in animal experiments. In this study, we investigated the injury to hepatocytes CYP2E1-independently induced by the combination of alcohol and iron and the protective effect of baicalin. Compared with cells treated with ethanol alone, ferric citrate enhanced the accumulation of reactive oxygen and nitrogen species, increased the occurrence of protein carbonylation/nitration and the levels of 4-hydroxy-2-nonenal, changed the distribution of iNOS, and eventually resulted in apoptosis. However, pretreatment with baicalin inhibited the oxidative stress induced by the combination of alcohol and iron, mainly by chelating iron. Our findings therefore suggest that iron could CPY2E1-independently enhance the oxidative stress induced by alcohol, which probably contributes to the pathogenesis of alcoholic liver disease. Baicalin is a promising phytomedicine for preventing alcoholic liver disease.