Iron in infection and immunity

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

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

Comparative Proteomic Analysis of Membrane Vesicles from Clinical C. acnes Isolates with Differential Antibiotic Resistance

Purpose

Cutibacterium acnes (C. acnes) is closely associated with the pathogenesis of acne, and antibiotics targeting C. acnes have been widely used for decades. However, antibiotic resistance has been increasing rapidly. Membrane vesicles (MVs) have been found to play important roles in antibiotic resistance in some bacteria. We aimed to explore the mechanism of antibiotic resistance and the virulence components within C. acnes-derived MVs.

Materials and Methods

We isolated clinical C. acnes strains from the lesions of acne patients who were sensitive or resistant to the antibiotics erythromycin and clindamycin. We analyzed the proteome of MVs from four sensitive C. acnes isolates and three resistant isolates by LC-MS/MS.

Results

We identified 543 proteins within the MVs of clinical C. acnes strains. Several lipases, NlpC/P60, CAMP factor, and Hta domain protein were detected as virulence factors in the C. acnes-derived MVs. The levels of two lipases and FtsZ were significantly higher in resistant C. acnes-derived MVs compared with sensitive strains (p < 0.05).

Conclusion

According to the implications of this study, improper antibiotic use might not only increase antibiotic resistance in C. acnes but could also further alter the cutaneous lipid composition and aggravate host inflammation, thus resulting in worse clinical manifestations in acne patients. This study re-emphasizes that the improper use of antibiotics should be treated more seriously in clinical practice. Furthermore, to combat multidrug resistance in C. acnes, this study suggests that FtsZ inhibitors could be useful.

The Effects of Vitamins and Micronutrients on Helicobacter pylori Pathogenicity, Survival, and Eradication: A Crosstalk between Micronutrients and Immune System

Helicobacter pylori as a class I carcinogen is correlated with a variety of severe gastroduodenal diseases; therefore, H. pylori eradication has become a priority to prevent gastric carcinogenesis. However, due to the emergence and spread of multidrug and single drug resistance mechanisms in H. pylori, as well as serious side effects of currently used antibiotic interventions, achieving successful H. pylori eradication has become exceedingly difficult. Recent studies expressed the intention of seeking novel strategies to improve H. pylori management and reduce the risk of H. pylori-associated intestinal and extragastrointestinal disorders. For which, vitamin supplementation has been demonstrated in many studies to have a tight interaction with H. pylori infection, either directly through the regulation of the host inflammatory pathways or indirectly by promoting the host immune response. On the other hand, H. pylori infection is reported to result in micronutrient malabsorption or deficiency. Furthermore, serum levels of particular micronutrients, especially vitamin D, are inversely correlated to the risk of H. pylori infection and eradication failure. Accordingly, vitamin supplementation might increase the efficiency of H. pylori eradication and reduce the risk of drug-related adverse effects. Therefore, this review aims at highlighting the regulatory role of micronutrients in H. pylori-induced host immune response and their potential capacity, as intrinsic antioxidants, for reducing oxidative stress and inflammation. We also discuss the uncovered mechanisms underlying the molecular and serological interactions between micronutrients and H. pylori infection to present a perspective for innovative in vitro investigations, as well as novel clinical implications.

Identification of an Iron Metabolism-Related lncRNA Signature for Predicting Osteosarcoma Survival and Immune Landscape

Background: Long noncoding RNAs (lncRNAs) act as epigenetic regulators in the process of ferroptosis and iron metabolism. This study aimed to identify an iron metabolism-related lncRNA signature to predict osteosarcoma (OS) survival and the immune landscape.

Methods: RNA-sequencing data and clinical information were obtained from the TARGET dataset. Univariate Cox regression and LASSO Cox analysis were used to develop an iron metabolism-related lncRNA signature. Consensus clustering analysis was applied to identify subtype-based prognosis-related lncRNAs. CIBERSORT was used to analyze the difference in immune infiltration and the immune microenvironment in the two clusters.

Results: We identified 302 iron metabolism-related lncRNAs based on 515 iron metabolism-related genes. The results of consensus clustering showed the differences in immune infiltration and the immune microenvironment in the two clusters. Through univariate Cox regression and LASSO Cox regression analysis, we constructed an iron metabolism-related lncRNA signature that included seven iron metabolism-related lncRNAs. The signature was verified to have good performance in predicting the overall survival, immune-related functions, and immunotherapy response of OS patients between the high- and low-risk groups.

Conclusion: We identified an iron metabolism-related lncRNA signature that had good performance in predicting survival outcomes and showing the immune landscape for OS patients. Furthermore, our study will provide valuable information to further develop immunotherapies of OS.

Bacterial and Viral Co-Infection in the Intestine: Competition Scenario and Their Effect on Host Immunity

Bacteria and viruses are both important pathogens causing intestinal infections, and studies on their pathogenic mechanisms tend to focus on one pathogen alone. However, bacterial and viral co-infections occur frequently in clinical settings, and infection by one pathogen can affect the severity of infection by another pathogen, either directly or indirectly. The presence of synergistic or antagonistic effects of two pathogens in co-infection can affect disease progression to varying degrees. The triad of bacterial–viral–gut interactions involves multiple aspects of inflammatory and immune signaling, neuroimmunity, nutritional immunity, and the gut microbiome. In this review, we discussed the different scenarios triggered by different orders of bacterial and viral infections in the gut and summarized the possible mechanisms of synergy or antagonism involved in their co-infection. We also explored the regulatory mechanisms of bacterial–viral co-infection at the host intestinal immune interface from multiple perspectives.

Drug Repositioning in Friedreich Ataxia

Friedreich ataxia is a rare neurodegenerative disorder caused by insufficient levels of the essential mitochondrial protein frataxin. It is a severely debilitating disease that significantly impacts the quality of life of affected patients and reduces their life expectancy, however, an adequate cure is not yet available for patients. Frataxin function, although not thoroughly elucidated, is associated with assembly of iron-sulfur cluster and iron metabolism, therefore insufficient frataxin levels lead to reduced activity of many mitochondrial enzymes involved in the electron transport chain, impaired mitochondrial metabolism, reduced ATP production and inefficient anti-oxidant response. As a consequence, neurons progressively die and patients progressively lose their ability to coordinate movement and perform daily activities. Therapeutic strategies aim at restoring sufficient frataxin levels or at correcting some of the downstream consequences of frataxin deficiency. However, the classical pathways of drug discovery are challenging, require a significant amount of resources and time to reach the final approval, and present a high failure rate. Drug repositioning represents a viable alternative to boost the identification of a therapy, particularly for rare diseases where resources are often limited. In this review we will describe recent efforts aimed at the identification of a therapy for Friedreich ataxia through drug repositioning, and discuss the limitation of such strategies.

Dual RNA sequencing reveals dendritic cell reprogramming in response to typhoidal Salmonella invasion

Salmonella enterica represent a major disease burden worldwide. S. enterica serovar Typhi (S. Typhi) is responsible for potentially life-threatening Typhoid fever affecting 10.9 million people annually. While non-typhoidal Salmonella (NTS) serovars usually trigger self-limiting diarrhoea, invasive NTS bacteraemia is a growing public health challenge. Dendritic cells (DCs) are key professional antigen presenting cells of the human immune system. The ability of pathogenic bacteria to subvert DC functions and prevent T cell recognition contributes to their survival and dissemination within the host. Here, we adapted dual RNA-sequencing to define how different Salmonella pathovariants remodel their gene expression in tandem with that of infected DCs. We find DCs harness iron handling pathways to defend against invading Salmonellas, which S. Typhi is able to circumvent by mounting a robust response to nitrosative stress. In parallel, we uncover the alternative strategies invasive NTS employ to impair DC functions.

The protein kinase Ire1 has a Hac1-independent essential role in iron uptake and virulence of Candida albicans

Protein kinases play central roles in virtually all signaling pathways that enable organisms to adapt to their environment. Microbial pathogens must cope with severely restricted iron availability in mammalian hosts to invade and establish themselves within infected tissues. To uncover protein kinase signaling pathways that are involved in the adaptation of the pathogenic yeast Candida albicans to iron limitation, we generated a comprehensive protein kinase deletion mutant library of a wild-type strain. Screening of this library revealed that the protein kinase Ire1, which has a conserved role in the response of eukaryotic cells to endoplasmic reticulum stress, is essential for growth of C. albicans under iron-limiting conditions. Ire1 was not necessary for the activity of the transcription factor Sef1, which regulates the response of the fungus to iron limitation, and Sef1 target genes that are induced by iron depletion were normally upregulated in ire1Δ mutants. Instead, Ire1 was required for proper localization of the high-affinity iron permease Ftr1 to the cell membrane. Intriguingly, iron limitation did not cause increased endoplasmic reticulum stress, and the transcription factor Hac1, which is activated by Ire1-mediated removal of the non-canonical intron in the HAC1 mRNA, was dispensable for Ftr1 localization to the cell membrane and growth under iron-limiting conditions. Nevertheless, expression of a pre-spliced HAC1 copy in ire1Δ mutants restored Ftr1 localization and rescued the growth defects of the mutants. Both ire1Δ and hac1Δ mutants were avirulent in a mouse model of systemic candidiasis, indicating that an appropriate response to endoplasmic reticulum stress is important for the virulence of C. albicans. However, the specific requirement of Ire1 for the functionality of the high-affinity iron permease Ftr1, a well-established virulence factor, even in the absence of endoplasmic reticulum stress uncovers a novel Hac1-independent essential role of Ire1 in iron acquisition and virulence of C. albicans.

Causal effect of iron status on lung function: A Mendelian randomization study

Background

The association between systemic iron status and lung function was conflicting in observational studies. We aim to explore the potential causal relationships between iron status and the levels of lung function using the two-sample Mendelian randomization (MR) design.

Methods

Genetic instruments associated with iron status biomarkers were retrieved from the Genetics of Iron Status (GIS) consortium (N = 48,972). Summary statistics of these genetic instruments with lung function were extracted from a meta-analysis of UK Biobank and SpiroMeta consortium (N = 400,102). The main analyses were performed using the inverse-variance weighted method, and complemented by multiple sensitivity analyses.

Results

Based on conservative genetic instruments, MR analyses showed that genetically predicted higher iron (beta: 0.036 per 1 SD increase, 95% confidence interval (CI): 0.016 to 0.056, P = 3.51 × 10^-4), log10-transformed ferritin (beta: 0.081, 95% CI: 0.047 to 0.116, P = 4.11 × 10^-6), and transferrin saturation (beta: 0.027, 95% CI: 0.015 to 0.038, P = 1.09 × 10^-5) were associated with increased forced expiratory volume in 1 s (FEV1), whereas higher transferrin was associated with decreased FEV1 (beta: -0.036, 95% CI: -0.064 to -0.008, P = 0.01). A significant positive association between iron status and forced vital capacity (FVC) was also observed. However, there is no causal association between iron status and FEV1-to-FVC ratio (P = 0.10). Similar results were obtained from the liberal instruments analyses and multiple sensitivity analyses.

Conclusion

Our study provided strong evidence to support that higher iron status is causally associated with higher levels of FEV1 and FVC, but has no impact on airway obstruction, confirming iron status as an important target for lung function management.

Anemia in Pediatric Kidney Transplant Recipients-Etiologies and Management

Posttransplant anemia (PTA) is a common complication of pediatric kidney transplantation, with a prevalence ranging from 22 to 85%. PTA is categorized as early (within 6 months posttransplant) and late (>6 months posttransplant). Early PTA is typically associated with surgical blood losses and iron deficiency. Late PTA primarily results from graft dysfunction; however, iron deficiency, drug toxicity, and posttransplant inflammation also play a role. PTA is more severe compared with the anemia in glomerular-filtration-rate matched patients with native chronic kidney disease. Treatment of PTA is directed toward the underlying cause. Erythropoiesis stimulating agents (ESA) are effective; however, their use is limited in the transplant setting. Timely diagnosis and treatment of PTA are vital to prevent long-term adverse outcomes in pediatric transplant recipients.

Storm of a rare opportunistic life threatening mucormycosis among post COVID-19 patients: A tale of two pathogens

Mucormycosis is a rare but life-threatening opportunistic fungal infection caused by a group of molds that belong to Zygomycetes of the order Mucorales. These fungi are found in the environment such as soil, decaying vegetation, and organic matters. Sporangiospores present in the environment enter the human body through inhalation or direct skin inoculation by trauma or ingestion and result in pulmonary, cutaneous, and gastrointestinal mucormycosis, respectively, in immunocompromised hosts. Patients with uncontrolled diabetes, hematological malignancies, high-dose glucocorticoid therapy, iron overload, and organ transplantation are at high risk of acquiring mucormycosis. The second wave of severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2] affected India severely with the highest number of cases and deaths compared to all other countries. Additionally, the country was affected by emergence of rare but life-threatening mucormycosis. Currently, many coronavirus disease 2019 patients with underlying risk factors such as uncontrolled diabetes, high-dose steroid therapy, and exposure to mechanical ventilation have developed mucormycosis. Inhalation is the most common mode of transmission that results in colonization of sporangiospores in the nose. In immunocompromised host, sporangiospores germinate, and subsequently form hyphae. These hyphae invade into tissues, and produce tissue infarction, necrosis, and thrombosis. Angioinvasion causes hematogenous dissemination to many organs, predominantly to brain, that result in rhino-orbital-cerebral mucormycosis. Clinical characteristics, radio imaging, fungal culture, histopathology, and molecular techniques are the key diagnostic methods. Surgical intervention and aggressive antifungal therapy are the main management strategies. Amphotericin B is the drug of choice for treatment of mucormycosis, whereas posaconazole or isavuconazole is used for step-down therapy and salvage therapy.

A detrimental role of NLRP6 in host iron metabolism during Salmonella infection

Maintaining host iron homeostasis is an essential component of nutritional immunity responsible for sequestrating iron from pathogens and controlling infection. Nucleotide-oligomerization domain-like receptors (NLRs) contribute to cytoplasmic sensing and antimicrobial response orchestration. However, it remains unknown whether and how NLRs may regulate host iron metabolism, an important component of nutritional immunity. Here, we demonstrated that NLRP6, a member of the NLR family, has an unconventional role in regulating host iron metabolism that perturbs host resistance to bacterial infection. NLRP6 deficiency is advantageous for maintaining cellular iron homeostasis in both macrophages and enterocytes through increasing the unique iron exporter ferroportin-mediated iron efflux in a nuclear factor erythroid-derived 2–related factor 2 (NRF2)-dependent manner. Additional studies uncovered a novel mechanism underlying NRF2 regulation and operating through NLRP6/AKT interaction and that causes a decrease in AKT phosphorylation, which in turn reduces NRF2 nuclear translocation. In the absence of NLRP6, increased AKT activation promotes NRF2/KEAP1 dissociation via increasing mTOR-mediated p62 phosphorylation and downregulates KEAP1 transcription by promoting FOXO3A phosphorylation. Together, our observations provide new insights into the mechanism of nutritional immunity by revealing a novel function of NLRP6 in regulating iron metabolism, and suggest NLRP6 as a therapeutic target for limiting bacterial iron acquisition.

What's metal got to do with it? Transition metals in Clostridioides difficile infection

The enteric pathogen Clostridioides difficile overcomes barriers to colonization imposed by the microbiota and host immune response to induce disease. To navigate the dynamic gut environment, C. difficile must respond to dietary and host-mediated fluctuations in transition metal availability. Transition metals are required trace nutrients that foster inter-microbial competition when limited, inhibit bacterial growth through host sequestration, or induce toxicity in excess. This review highlights recent evidence that transition metals influence multiple stages of C. difficile colonization and that C. difficile initiates a coordinated response to maintain metal-dependent homeostasis. Further exploration of the mechanisms of C. difficile metal sensing and nutrient competition with the microbiota will be necessary for the therapeutic manipulation of the gut environment during C. difficile infection.

Characteristics of macrophages from myelodysplastic syndrome microenvironment

Myelodysplastic syndrome (MDS) is a heterogeneous group of clonal hematopoietic neoplasms. The progression of malignancy is closely associated with immune regulation. Macrophages are indispensable tissue components and have been proposed to play a role in the pathophysiology of hematopoietic malignancies. However, the specific role of macrophages in the development of MDS remains unclear. Here, we investigated the characteristics and phenotypic evolution of macrophages from patients with MDS. Macrophages from patients with MDS expressed CD68, CD86 and CD163. Furthermore, MDS macrophages exhibited more M2-related characteristics. Moreover, a number of phenotype-associated genes in MDS macrophages exhibited diverse responses to iron overload or iron chelation upon stimulation by ferric chloride or deferoxamine (DFO, an iron chelator). Ferric chloride polarized MDS macrophages to exhibit more M1-related characteristics, a phenomenon that could be partially reversed by DFO. Therefore, this study reveals the characteristics and phenotypic evolution of MDS macrophages and broadens the knowledge of macrophage plasticity in hematopoietic malignancies.

COVID-19 vaccination in patients with heart failure: a position paper of the Heart Failure Association of the European Society of Cardiology

Patients with heart failure (HF) who contract SARS‐CoV‐2 infection are at a higher risk of cardiovascular and non‐cardiovascular morbidity and mortality. Regardless of therapeutic attempts in COVID‐19, vaccination remains the most promising global approach at present for controlling this disease. There are several concerns and misconceptions regarding the clinical indications, optimal mode of delivery, safety and efficacy of COVID‐19 vaccines for patients with HF. This document provides guidance to all healthcare professionals regarding the implementation of a COVID‐19 vaccination scheme in patients with HF. COVID‐19 vaccination is indicated in all patients with HF, including those who are immunocompromised (e.g. after heart transplantation receiving immunosuppressive therapy) and with frailty syndrome. It is preferable to vaccinate against COVID‐19 patients with HF in an optimal clinical state, which would include clinical stability, adequate hydration and nutrition, optimized treatment of HF and other comorbidities (including iron deficiency), but corrective measures should not be allowed to delay vaccination. Patients with HF who have been vaccinated against COVID‐19 need to continue precautionary measures, including the use of facemasks, hand hygiene and social distancing. Knowledge on strategies preventing SARS‐CoV‐2 infection (including the COVID‐19 vaccination) should be included in the comprehensive educational programmes delivered to patients with HF.

Leishmaniasis and Trace Element Alterations: a Systematic Review

Leishmaniasis is a worldwide prevalent parasitic infection caused by different species of the genus Leishmania. Clinically, the disease divided into three main forms, including visceral leishmaniasis (VL), cutaneous leishmaniasis (CL), and mucocutaneous leishmaniasis (MCL). There is no vaccine for human leishmaniasis and their treatment is challenging. Trace elements (TEs) alteration, including the selenium (Se), zinc (Zn), copper (Cu), ron (Fe), and magnesium (Mg) have been detected in patients with CL and VL as well as canine leishmaniasis. Because TEs play a pivotal role in the immune system, and host immune responses have crucial roles in defense against leishmaniasis, this systematic review aimed to summarize data regarding TEs alteration in human and animal leishmaniasis as well as the role of these elements as an adjuvant for treatment of leishmaniasis. In a setting of systematic review, we found 29 eligible articles (any date until October 1, 2020) regarding TEs in human CL (N = 12), human VL (N = 4), canine leishmaniasis (N = 3), and treatment of leishmaniasis based on TEs (N = 11), which one study examined the TEs level both in CL and VL patients. Our analysis demonstrated a significantly decreased level of Fe, Zn, and Se among human CL and canine leishmaniasis, and Zn and Fe in patients with VL. In contrast, an increased level of Cu in CL patients and Cu and Mg in VL patients and canine leishmaniasis was observed. Treatment of CL based zinc supplementation revealed enhancement of wound healing and diminished scar formation in human and experimentally infected animals. The results of this systematic review indicate that the TEs have important roles in leishmaniasis, which could be assessed as a prognosis factor in this disease. It is suggested that TEs could be prescribed as an adjuvant for the treatment of CL and VL patients.

Nifedipine Potentiates Susceptibility of Salmonella Typhimurium to Different Classes of Antibiotics

The calcium channel blocker nifedipine induces cellular iron export, thereby limiting the availability of the essential nutrient iron for intracellular pathogens, resulting in bacteriostatic activity. To study if nifedipine may exert a synergistic anti-microbial activity when combined with antibiotics, we used the mouse macrophage cell line RAW267.4, infected with the intracellular bacterium Salmonella Typhimurium, and exposed the cells to varying concentrations of nifedipine and/or ampicillin, azithromycin and ceftriaxone. We observed a significant additive effect of nifedipine in combination with various antibiotics, which was not observed when using Salmonella, with defects in iron uptake. Of interest, increasing intracellular iron levels increased the bacterial resistance to treatment with antibiotics or nifedipine or their combination. We further showed that nifedipine increases the expression of the siderophore-binding peptide lipocalin-2 and promotes iron storage within ferritin, where the metal is less accessible for bacteria. Our data provide evidence for an additive effect of nifedipine with conventional antibiotics against Salmonella, which is partly linked to reduced bacterial access to iron.

Autoimmunity to phosphatidylserine and anemia in African Trypanosome infections

Anemia caused by trypanosome infection is poorly understood. Autoimmunity during Trypanosoma brucei infection was proposed to have a role during anemia, but the mechanisms involved during this pathology have not been elucidated. In mouse models and human patients infected with malaria parasites, atypical B-cells promote anemia through the secretion of autoimmune anti-phosphatidylserine (anti-PS) antibodies that bind to uninfected erythrocytes and facilitate their clearance. Using mouse models of two trypanosome infections, Trypanosoma brucei and Trypanosoma cruzi, we assessed levels of autoantibodies and anemia. Our results indicate that acute T. brucei infection, but not T. cruzi, leads to early increased levels of plasma autoantibodies against different auto antigens tested (PS, DNA and erythrocyte lysate) and expansion of atypical B cells (ABCs) that secrete these autoantibodies. In vitro studies confirmed that a lysate of T. brucei, but not T. cruzi, could directly promote the expansion of these ABCs. PS exposure on erythrocyte plasma membrane seems to be an important contributor to anemia by delaying erythrocyte recovery since treatment with an agent that prevents binding to it (Annexin V) ameliorated anemia in T. brucei-infected mice. Analysis of the plasma of patients with human African trypanosomiasis (HAT) revealed high levels of anti-PS antibodies that correlated with anemia. Altogether these results suggest a relation between autoimmunity against PS and anemia in both mice and patients infected with T. brucei.

Seasonal patterns of malaria, genital infection, nutritional and iron status in non-pregnant and pregnant adolescents in Burkina Faso: a secondary analysis of trial data

Background

Adolescents are considered at high risk of developing iron deficiency. Studies in children indicate that the prevalence of iron deficiency increased with malaria transmission, suggesting malaria seasonally may drive iron deficiency. This paper examines monthly seasonal infection patterns of malaria, abnormal vaginal flora, chorioamnionitis, antibiotic and antimalarial prescriptions, in relation to changes in iron biomarkers and nutritional indices in adolescents living in a rural area of Burkina Faso, in order to assess the requirement for seasonal infection control and nutrition interventions.

Methods

Data collected between April 2011 and January 2014 were available for an observational seasonal analysis, comprising scheduled visits for 1949 non-pregnant adolescents (≤19 years), (315 of whom subsequently became pregnant), enrolled in a randomised trial of periconceptional iron supplementation. Data from trial arms were combined. Body Iron Stores (BIS) were calculated using an internal regression for ferritin to allow for inflammation. At recruitment 11% had low BIS (< 0 mg/kg). Continuous outcomes were fitted to a mixed-effects linear model with month, age and pregnancy status as fixed effect covariates and woman as a random effect. Dichotomous infection outcomes were fitted with analogous logistic regression models.

Results

Seasonal variation in malaria parasitaemia prevalence ranged between 18 and 70% in non-pregnant adolescents (P < 0.001), peaking at 81% in those who became pregnant. Seasonal variation occurred in antibiotic prescription rates (0.7–1.8 prescriptions/100 weekly visits, P < 0.001) and chorioamnionitis prevalence (range 15–68%, P = 0.026). Mucosal vaginal lactoferrin concentration was lower at the end of the wet season (range 2–22 μg/ml, P < 0.016), when chorioamnionitis was least frequent. BIS fluctuated annually by up to 53.2% per year around the mean BIS (5.1 mg/kg², range 4.1–6.8 mg/kg), with low BIS (< 0 mg/kg) of 8.7% in the dry and 9.8% in the wet seasons (P = 0.36). Median serum transferrin receptor increased during the wet season (P < 0.001). Higher hepcidin concentration in the wet season corresponded with rising malaria prevalence and use of prescriptions, but with no change in BIS. Mean Body Mass Index and Mid-Upper-Arm-Circumference values peaked mid-dry season (both P < 0.001).

Conclusions

Our analysis supports preventive treatment of malaria among adolescents 15–19 years to decrease their disease burden, especially asymptomatic malaria. As BIS were adequate in most adolescents despite seasonal malaria, a requirement for programmatic iron supplementation was not substantiated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-11819-0.

Hepcidin regulation in Kenyan children with severe malaria and non-typhoidal Salmonella bacteremia

Malaria and invasive non-typhoidal Salmonella (NTS) are life-threatening infections that often co-exist in African children. The iron-regulatory hormone hepcidin is highly upregulated during malaria and controls the availability of iron, a critical nutrient for bacterial growth. We investigated the relationship between Plasmodium falciparum malaria and NTS bacteremia in all pediatric admissions aged <5 years between August 1998 and October 2019 (n=75,034). We then assayed hepcidin and measures of iron status in five groups: (1) children with concomitant severe malarial anemia (SMA) and NTS (SMA+NTS, n=16); and in matched children with (2) SMA (n=33); (3) NTS (n=33); (4) cerebral malaria (CM, n=34); and (5) community-based children. SMA and severe anemia without malaria were associated with a 2-fold or more increased risk of NTS bacteremia, while other malaria phenotypes were not associated with increased NTS risk. Children with SMA had lower hepcidin/ferritin ratios (0.10; interquartile range [IQR]: 0.03-0.19) than those with CM (0.24; IQR: 0.14-0.69; P=0.006) or asymptomatic malaria (0.19; IQR: 0.09-0.46; P=0.01) indicating suppressed hepcidin levels. Children with SMA+NTS had lower hepcidin levels (9.3 ng/mL; IQR: 4.7-49.8) and hepcidin/ferritin ratios (0.03; IQR: 0.01-0.22) than those with NTS alone (105.8 ng/mL; IQR: 17.3-233.3; P=0.02 and 0.31; IQR: 0.06-0.66; P=0.007, respectively). Since hepcidin degrades ferroportin on the Salmonella-containing vacuole, we hypothesize that reduced hepcidin in children with SMA might contribute to NTS growth by modulating iron availability for bacterial growth. Further studies are needed to understand how the hepcidin-ferroportin axis might mediate susceptibility to NTS in severely anemic children.

Desferrioxamine B-Mediated Pre-Clinical In Vivo Imaging of Infection by the Mold Fungus Aspergillus fumigatus

Fungal infections are a serious threat, especially for immunocompromised patients. Early and reliable diagnosis is crucial to treat such infections. The bacterially produced siderophore desferrioxamine B (DFO-B) is utilized by a variety of microorganisms for iron acquisition, while mammalian cells lack the uptake of DFO-B chelates. DFO-B is clinically approved for a variety of long-term chelation therapies. Recently, DFO-B-complexed gallium-68 ([68Ga]Ga-DFO-B) was shown to enable molecular imaging of bacterial infections by positron emission tomography (PET). Here, we demonstrate that [68Ga]Ga-DFO-B can also be used for the preclinical molecular imaging of pulmonary infection caused by the fungal pathogen Aspergillus fumigatus in a rat aspergillosis model. Moreover, by combining in vitro uptake studies and the chemical modification of DFO-B, we show that the cellular transport efficacy of ferrioxamine-type siderophores is impacted by the charge of the molecule and, consequently, the environmental pH. The chemical derivatization has potential implications for its diagnostic use and characterizes transport features of ferrioxamine-type siderophores.

A Novel Ferroptosis-Related Prognostic Signature Reveals Macrophage Infiltration and EMT Status in Bladder Cancer

Bladder cancer (BC) belongs to one of the most common and highly heterogeneous malignancies. Ferroptosis is a newly discovered regulated cell death (RCD), characterized by accumulation of toxic lipid peroxides, and plays a crucial role in tumor progression. Here, we conducted a comprehensive analysis on the transcriptomics data of ferroptosis-related genes in BC based on The Cancer Genome Atlas (TCGA) and three Gene Expression Omnibus (GEO) datasets. In our study, a 6-gene signature was identified based on the potential prognostic ferroptotic regulatory genes. Furthermore, our signature revealed a good independent prognostic ability in BC. Patients with low-risk score exhibited higher FGFR3 mutation rates while high risk score had a positive association with higher RB1 mutation rates. Meanwhile, higher proportions of macrophages were observed in high BC risk group simultaneously with four methods. Unexpectedly, the risk score showed a significant positive correlation with epithelial-mesenchymal transition (EMT) status. Functional assays indicated that CRYAB and SQLE knockdown was associated with attenuated invasion capacity. Our study revealed a ferroptosis-related risk model for predicting prognostic and BC progression. Our results indicate that targeting ferroptosis may be a therapeutic strategy for BC.

Iron loading induces cholesterol synthesis and sensitizes endothelial cells to TNFα-mediated apoptosis

In plasma, iron is normally bound to transferrin, the principal protein in blood responsible for binding and transporting iron throughout the body. However, in conditions of iron overload when the iron-binding capacity of transferrin is exceeded, non-transferrin-bound iron (NTBI) appears in plasma. NTBI is taken up by hepatocytes and other parenchymal cells via NTBI transporters and can cause cellular damage by promoting the generation of reactive oxygen species. However, how NTBI affects endothelial cells, the most proximal cell type exposed to circulating NTBI, has not been explored. We modeled in vitro the effects of systemic iron overload on endothelial cells by treating primary human umbilical vein endothelial cells (HUVECs) with NTBI (ferric ammonium citrate [FAC]). We showed by RNA-Seq that iron loading alters lipid homeostasis in HUVECs by inducing sterol regulatory element-binding protein 2-mediated cholesterol biosynthesis. We also determined that FAC increased the susceptibility of HUVECs to apoptosis induced by tumor necrosis factor-α (TNFα). Moreover, we showed that cholesterol biosynthesis contributes to iron-potentiated apoptosis. Treating HUVECs with a cholesterol chelator hydroxypropyl-β-cyclodextrin demonstrated that depletion of cholesterol was sufficient to rescue HUVECs from TNFα-induced apoptosis, even in the presence of FAC. Finally, we showed that FAC or cholesterol treatment modulated the TNFα pathway by inducing novel proteolytic processing of TNFR1 to a short isoform that localizes to lipid rafts. Our study raises the possibility that iron-mediated toxicity in human iron overload disorders is at least in part dependent on alterations in cholesterol metabolism in endothelial cells, increasing their susceptibility to apoptosis.

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.

Peroxiredoxin Asp f3 Is Essential for Aspergillus fumigatus To Overcome Iron Limitation during Infection

Aspergillus fumigatus is an important fungal pathogen that causes allergic reactions but also life-threatening infections. One of the most abundant A. fumigatus proteins is Asp f3. This peroxiredoxin is a major fungal allergen and known for its role as a virulence factor, vaccine candidate, and scavenger of reactive oxygen species. Based on the hypothesis that Asp f3 protects A. fumigatus against killing by immune cells, we investigated the susceptibility of a conditional aspf3 mutant by employing a novel assay. Surprisingly, Asp f3-depleted hyphae were killed as efficiently as the wild type by human granulocytes. However, we identified an unexpected growth defect of mutants that lack Asp f3 under low-iron conditions, which explains the avirulence of the Δaspf3 deletion mutant in a murine infection model. A. fumigatus encodes two Asp f3 homologues which we named Af3l (Asp f3-like) 1 and Af3l2. Inactivation of Af3l1, but not of Af3l2, exacerbated the growth defect of the conditional aspf3 mutant under iron limitation, which ultimately led to death of the double mutant. Inactivation of the iron acquisition repressor SreA partially compensated for loss of Asp f3 and Af3l1. However, Asp f3 was not required for maintaining iron homeostasis or siderophore biosynthesis. Instead, we show that it compensates for a loss of iron-dependent antioxidant enzymes. Iron supplementation restored the virulence of the Δaspf3 deletion mutant in a murine infection model. Our results unveil the crucial importance of Asp f3 to overcome nutritional immunity and reveal a new biological role of peroxiredoxins in adaptation to iron limitation.

Cell Line Platforms Support Research into Arthropod Immunity

Simple Summary

Many insect and tick species are serious pests, because insects damage crop plants and, along with ticks, transmit a wide range of human and animal diseases. One way of controlling these pests is by impairing their immune system, which protects them from bacterial, fungal, and viral infections. An important tool for studying immunity is using long-lasting cell cultures, known as cell lines. These lines can be frozen and thawed at will to be used in automated tests, and they provide consistent results over years. Questions that can be asked using cell lines include: How do insects or ticks recognize when they have been infected and by what organism? What kinds of defensive strategies do they use to contain or kill infectious agents? This article reviews research with insect or tick cell lines to answer these questions, as well as other questions relating to immunity. This review also discusses future research strategies for working with cell lines.

Abstract

Innate immune responses are essential to maintaining insect and tick health and are the primary defense against pathogenic viruses, bacteria, and fungi. Cell line research is a powerful method for understanding how invertebrates mount defenses against pathogenic organisms and testing hypotheses on how these responses occur. In particular, immortal arthropod cell lines are valuable tools, providing a tractable, high-throughput, cost-effective, and consistent platform to investigate the mechanisms underpinning insect and tick immune responses. The research results inform the controls of medically and agriculturally important insects and ticks. This review presents several examples of how cell lines have facilitated research into multiple aspects of the invertebrate immune response to pathogens and other foreign agents, as well as comments on possible future research directions in these robust systems.

Pharmacological Targeting of BMP6-SMAD Mediated Hepcidin Expression Does Not Improve the Outcome of Systemic Infections With Intra-Or Extracellular Gram-Negative Bacteria in Mice

Introduction

Hepcidin is the systemic master regulator of iron metabolism as it degrades the cellular iron exporter ferroportin. In bacterial infections, hepcidin is upregulated to limit circulating iron for pathogens, thereby increasing iron retention in macrophages. This mechanism withholds iron from extracellular bacteria but could be of disadvantage in infections with intracellular bacteria. We aimed to understand the role of hepcidin in infections with intra- or extracellular bacteria using different hepcidin inhibitors.

Methods

For the experiments LDN-193189 and oversulfated heparins were used, which interact with the BMP6-SMAD pathway thereby inhibiting hepcidin expression. We infected male C57BL/6N mice with either the intracellular bacterium Salmonella Typhimurium or the extracellular bacterium Escherichia coli and treated these mice with the different hepcidin inhibitors.

Results

Both inhibitors effectively reduced hepcidin levels in vitro under steady state conditions and upon stimulation with the inflammatory signals interleukin-6 or lipopolysaccharide. The inhibitors also reduced hepcidin levels and increased circulating iron concentration in uninfected mice. However, both compounds failed to decrease liver- and circulating hepcidin levels in infected mice and did not affect ferroportin expression in the spleen or impact on serum iron levels. Accordingly, both BMP-SMAD signaling inhibitors did not influence bacterial numbers in different organs in the course of E.coli or S.Tm sepsis.

Conclusion

These data indicate that targeting the BMP receptor or the BMP-SMAD pathway is not sufficient to suppress hepcidin expression in the course of infection with both intra- or extracellular bacteria. This suggests that upon pharmacological inhibition of the central SMAD-BMP pathways during infection, other signaling cascades are compensatorily induced to ensure sufficient hepcidin formation and iron restriction to circulating microbes.

Aerobactin-Mediated Iron Acquisition Enhances Biofilm Formation, Oxidative Stress Resistance, and Virulence of Yersinia pseudotuberculosis

Aerobactin is a citrate-hydroxamate siderophore that is critical for the virulence of pathogenic enteric bacteria. However, although the aerobactin-producing iucABCD-iutA operon is distributed widely in the genomes of Yersinia species, none of the pathogenic Yersinia spp. was found to produce aerobactin. Here, we showed that the iucABCD-iutA operon in the food-borne enteric pathogen Yersinia pseudotuberculosis YPIII is a functional siderophore system involved in iron acquisition. The expression of the operon was found to be directly repressed by the ferric uptake regulator (Fur) in an iron concentration-dependent manner. In addition, we demonstrated that the aerobactin-mediated iron acquisition contributes to bacterial growth under iron-limited conditions. Moreover, we provided evidence that aerobactin plays important roles in biofilm formation, resistance to oxidative stress, ROS removal, and virulence of Y. pseudotuberculosis. Overall, our study not only uncovered a novel strategy of iron acquisition in Y. pseudotuberculosis but also highlighted the importance of aerobactin in the pathogenesis of Y. pseudotuberculosis.

Antifungal Siderophore Conjugates for Theranostic Applications in Invasive Pulmonary Aspergillosis Using Low-Molecular TAFC Scaffolds

Invasive pulmonary aspergillosis (IPA) is a life-threatening form of fungal infection, primarily in immunocompromised patients and associated with significant mortality. Diagnostic procedures are often invasive and/or time consuming and existing antifungals can be constrained by dose-limiting toxicity and drug interaction. In this study, we modified triacetylfusarinine C (TAFC), the main siderophore produced by the opportunistic pathogen Aspergillus fumigatus (A. fumigatus), with antifungal molecules to perform antifungal susceptibility tests and molecular imaging. A variation of small organic molecules (eflornithine, fludioxonil, thiomersal, fluoroorotic acid (FOA), cyanine 5 (Cy5) with antifungal activity were coupled to diacetylfusarinine C (DAFC), resulting in a "Trojan horse" to deliver antifungal compounds specifically into A. fumigatus hyphae by the major facilitator transporter MirB. Radioactive labeling with gallium-68 allowed us to perform in vitro characterization (distribution coefficient, stability, uptake assay) as well as biodistribution experiments and PET/CT imaging in an IPA rat infection model. Compounds chelated with stable gallium were used for antifungal susceptibility tests. [Ga]DAFC-fludioxonil, -FOA, and -Cy5 revealed a MirB-dependent active uptake with fungal growth inhibition at 16 µg/mL after 24 h. Visualization of an A. fumigatus infection in lungs of a rat was possible with gallium-68-labeled compounds using PET/CT. Heterogeneous biodistribution patterns revealed the immense influence of the antifungal moiety conjugated to DAFC. Overall, novel antifungal siderophore conjugates with promising fungal growth inhibition and the possibility to perform PET imaging combine both therapeutic and diagnostic potential in a theranostic compound for IPA caused by A. fumigatus.

Epigenomic regulation by labile iron

Iron is an essential micronutrient metal for cellular functions but can generate highly reactive oxygen species resulting in oxidative damage. For these reasons its uptake and metabolism is highly regulated. A small but dynamic fraction of ferrous iron inside the cell, termed intracellular labile iron, is redox-reactive and ready to participate multiples reactions of intracellular enzymes. Due to its nature its determination and precise quantification has been a roadblock. However, recent progress in the development of intracellular labile iron probes are allowing the reevaluation of our current understanding and unmasking new functions. The role of intracellular labile iron in regulating the epigenome was recently discovered. This chapter examine how intracellular labile iron can modulate histone and DNA demethylation and how its pool can mediate a signaling pathway from cAMP serving as a sensor of the metabolic needs of the cells.

The possible effects of iron loss from bloodletting on mortality from pneumonia in the nineteenth century

OBJECTIVE

To estimate iron losses and disease severity following 19th century bloodletting in patients with pneumonia.

STUDY DESIGN AND SETTING

Benefits of bloodletting in pneumonia patients were contested during the 19th century. Although large blood volumes during infection were removed there was no systematic data collection assessing efficacy and knowledge of iron composition of blood was rudimentary. This observational analysis of historical data quantifies iron losses in pneumonia cases in relation to disease severity.

RESULTS

Based on one detailed case series average blood volume removed for survivors was 830 mL (range 114-2272 mL), and mean recovery times were shorter in patients bled within 2 days of illness (P < 0.001). Average iron removed was 446 mg with phlebotomy done ≤2 days of illness presentation and 347 mg after >2 days of illness (P = 0.012). Across several European hospitals average case fatality in pneumonia patients receiving phlebotomy was higher than in those treated without phlebotomy (19.9% vs. 12.8%, OR 1.55, 95% CI 1.38-1.74, P < 0.001).

CONCLUSION

Variable efficacy for bloodletting could at least in part be explained by altered iron status.

Interplay between central carbon metabolism and metal homeostasis in mycobacteria and other human pathogens

Bacterial nutrition is a fundamental aspect of pathogenesis. While the host environment is in principle nutrient-rich, hosts have evolved strategies to interfere with nutrient acquisition by pathogens. In turn, pathogens have developed mechanisms to circumvent these restrictions. Changing the availability of bioavailable metal ions is a common strategy used by hosts to limit bacterial replication. Macrophages and neutrophils withhold iron, manganese, and zinc ions to starve bacteria. Alternatively, they can release manganese, zinc, and copper ions to intoxicate microorganisms. Metals are essential micronutrients and participate in catalysis, macromolecular structure, and signalling. This review summarises our current understanding of how central carbon metabolism in pathogens adapts to local fluctuations in free metal ion concentrations. We focus on the transcriptomics and proteomics data produced in studies of the iron-sparing response in Mycobacterium tuberculosis, the etiological agent of tuberculosis, and consequently generate a hypothetical model linking trehalose accumulation, succinate secretion and substrate-level phosphorylation in iron-starved M. tuberculosis. This review also aims to highlight a large gap in our knowledge of pathogen physiology: the interplay between metal homeostasis and central carbon metabolism, two cellular processes which are usually studied separately. Integrating metabolism and metal biology would allow the discovery of new weaknesses in bacterial physiology, leading to the development of novel and improved antibacterial therapies.

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.

Iron Deficiency in Obesity and after Bariatric Surgery

Iron deficiency (ID) is particularly frequent in obese patients due to increased circulating levels of acute-phase reactant hepcidin and adiposity-associated inflammation. Inflammation in obese subjects is closely related to ID. It induces reduced iron absorption correlated to the inhibition of duodenal ferroportin expression, parallel to the increased concentrations of hepcidin. Obese subjects often get decreased inflammatory response after bariatric surgery, accompanied by decreased serum hepcidin and therefore improved iron absorption. Bariatric surgery can induce the mitigation or resolution of obesity-associated complications, such as hypertension, insulin resistance, diabetes mellitus, and hyperlipidemia, adjusting many parameters in the metabolism. However, gastric bypass surgery and sleeve gastrectomy can induce malabsorption and may accentuate ID. The present review explores the burden and characteristics of ID and anemia in obese patients after bariatric surgery, accounting for gastric bypass technique (Roux-en-Y gastric bypass-RYGB) and sleeve gastrectomy (SG). After bariatric surgery, obese subjects' iron status should be monitored, and they should be motivated to use adequate and recommended iron supplementation.

Iron deficiency: a modern primer to diagnosis and management

PURPOSE OF REVIEW

Iron deficiency with anemia (IDA) and without anemia remain a diagnostic and management challenge. Iron deficiency has a broad spectrum of causes, including gastrointestinal malignancy. The purpose of this review is to summarize the value and limitations of current methods to diagnose iron deficiency and underline the relevance of contemporaneous evidence to guide the pretest probability of gastrointestinal disease.

RECENT FINDINGS

A number of biomarkers for iron deficiency exist, and all have their caveats. Serum ferritin remains the most pragmatic means of diagnosing iron deficiency. Hepcidin holds future promise as a marker of iron status during inflammatory states. Men and postmenopausal women with IDA have the highest overall prevalence of gastrointestinal malignancy (∼11%), while premenopausal women with IDA (<1.5%) and those with iron deficiency without anemia (<0.5%) have a very low risk. Noninvasive investigation with fecal immunochemical test and fecal calprotectin hold promise to guide further investigations in lower risk groups.

SUMMARY

Confirmation of iron deficiency remains a challenge. Appropriate risk stratification is the key to guiding judicious gastrointestinal investigation. Use of noninvasive tests may play an important role in lower risk groups. Risk prediction tools applicable to relevant populations are required.

Iron Metabolism in the Tumor Microenvironment: Contributions of Innate Immune Cells

Cells of the innate immune system are a major component of the tumor microenvironment. They play complex and multifaceted roles in the regulation of cancer initiation, growth, metastasis and responses to therapeutics. Innate immune cells like neutrophils and macrophages are recruited to cancerous tissues by chemotactic molecules released by cancer cells and cancer-associated stromal cells. Once they reach the tumor, they can be instructed by a network of proteins, nucleic acids and metabolites to exert protumoral or antitumoral functions. Altered iron metabolism is a feature of cancer. Epidemiological studies suggest that increased presence of iron and/or iron binding proteins is associated with increased risks of cancer development. It has been shown that iron metabolism is involved in shaping the immune landscapes in inflammatory/infectious diseases and cancer-associated inflammation. In this article, we will dissect the contribution of macrophages and neutrophils to dysregulated iron metabolism in malignant cells and its impact on cancer growth and metastasis. The mechanisms involved in regulating the actions of macrophages and neutrophils will also be discussed. Moreover, we will examine the effects of iron metabolism on the phenotypes of innate immune cells. Both iron chelating and overloading agents are being explored in cancer treatment. This review highlights alternative strategies for management of iron content in cancer cells by targeting the iron donation and modulation properties of macrophages and neutrophils in the tumor microenvironment.

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.

Prion Protein on Human Leukocytes Is Reduced in Iron Deficiency - Possible Implications for Age-related Macular Degeneration?

MATERIALS AND METHODS

Patients presenting to the department of ophthalmology of the Medical University of Graz for reasons unrelated to prion diseases were enrolled. Parameters of iron metabolism, including ferritin and soluble transferrin receptor were measured by routine laboratory tests. Serum prion protein was determined by enzyme-linked immunosorbent assay. Surface prion protein on CD14⁺ monocytes and CD4⁺ T cells was analyzed by fluorescence activated cell sorting.

RESULTS

95 patients were enrolled. Soluble transferrin receptor correlated significantly with prion protein levels on CD14⁺POM1⁺ monocytes (P = .001, r = -0.7) and on CD4⁺POM1⁺ T cells (P = .01, r = -0.62).

CONCLUSION

Our findings suggest a connection between the physiological function of the prion protein and iron metabolism in humans.

The versatile biochemistry of iron in macrophage effector functions

Macrophages are mononuclear phagocytes with remarkable polarization ability that allow them to have tissue-specific functions during development, homeostasis, inflammatory and infectious disease. One particular trophic factor in the tissue environment is iron, which is intimately linked to macrophage effector functions. Macrophages have a well-described role in the control of systemic iron levels, but their activation state is also depending on iron-containing proteins/enzymes. Haemoproteins, dioxygenases and iron-sulphur (Fe-S) enzymes are iron-binding proteins that have bactericidal, metabolic and epigenetic-related functions, essential to shape the context-dependent macrophage polarization. In this review, I describe mainly pro-inflammatory macrophage polarization focussing on the role of iron biochemistry in selected haemoproteins and Fe-S enzymes. I show how iron, as part of haem or Fe-S clusters, participates in the cellular control of pro-inflammatory redox reactions in parallel with its role as enzymatic cofactor. I highlight a possible coordinated regulation of haemoproteins and Fe-S enzymes during classical macrophage activation. Finally, I describe tryptophan and α-ketoglutarate metabolism as two essential effector pathways in macrophages that use diverse iron biochemistry at different enzymatic steps. Through these pathways, I show how iron participates in the regulation of essential metabolites that shape macrophage function.

Responses of Intestinal Microbiota and Immunity to Increasing Dietary Levels of Iron Using a Piglet Model

Iron is an essential metal for both animals and microbiota. In general, neonates and infants of humans and animals are at the risk of iron insufficiency. However, excess dietary iron usually causes negative impacts on the host and microbiota. This study aimed to investigate overloaded dietary iron supplementation on growth performance, the distribution pattern of iron in the gut lumen and the host, intestinal microbiota, and intestine transcript profile of piglets. Sixty healthy weaning piglets were randomly assigned to six groups: fed on diets supplemented with ferrous sulfate monohydrate at the dose of 50 ppm (Fe50 group), 100 ppm (Fe100 group), 200 ppm (Fe200 group), 500 ppm (Fe500 group), and 800 ppm (Fe800), separately, for 3 weeks. The results indicated that increasing iron had no significant effects on growth performance, but increased diarrheal risk and iron deposition in intestinal digesta, tissues of intestine and liver, and serum. High iron also reduced serum iron-binding capacity, apolipoprotein, and immunoglobin A. The RNA-sequencing analysis revealed that iron changed colonic transcript profile, such as interferon gamma-signal transducer and activator of transcription two-based anti-infection gene network. Increasing iron also shifted colonic and cecal microbiota, such as reducing alpha diversity and the relative abundance of Clostridiales and Lactobacillus reuteri and increasing the relative abundance of Lactobacillus and Lactobacillus amylovorus. Collectively, this study demonstrated that high dietary iron increased diarrheal incidence, changed intestinal immune response-associated gene expression, and shifted gut microbiota. The results would enhance our knowledge of iron effects on the gut and microbiome in piglets and further contribute to understanding these aspects in humans.

Impact of bacterial infections on erythropoiesis

INTRODUCTION

The importance of iron is highlighted by the many complex metabolic pathways in which it is involved. A sufficient supply is essential for the effective production of 200 billion erythrocytes daily, a process called erythropoiesis.

AREAS COVERED

During infection, the human body can withhold iron from pathogens, mechanism termed nutritional immunity. The subsequent disturbances in iron homeostasis not only impact on immune function and infection control, but also negatively affect erythropoiesis. The complex interplay between iron, immunity, erythropoiesis and infection control on the molecular and clinical level are highlighted in this review. Diagnostic algorithms for correct interpretation and diagnosis of the iron status in the setting of infection are presented. Therapeutic concepts are discussed regarding effects on anemia correction, but also toward their role on the course of infection.

EXPERT OPINION

In the setting of infection, anemia is often neglected and its impact on the course of diseases is incompletely understood. Clinical expertise can be improved in correct diagnosing of anemia and disturbances of iron homeostasis. Systemic studies are needed to evaluate the impact of specific therapeutic interventions on anemia correction on the course of infection, but also on patients' cardiovascular performance and quality of life.

Persisting alterations of iron homeostasis in COVID-19 are associated with non-resolving lung pathologies and poor patients' performance: a prospective observational cohort study

BACKGROUND

Severe coronavirus disease 2019 (COVID-19) is frequently associated with hyperinflammation and hyperferritinemia. The latter is related to increased mortality in COVID-19. Still, it is not clear if iron dysmetabolism is mechanistically linked to COVID-19 pathobiology.

METHODS

We herein present data from the ongoing prospective, multicentre, observational CovILD cohort study (ClinicalTrials.gov number, NCT04416100), which systematically follows up patients after COVID-19. 109 participants were evaluated 60 days after onset of first COVID-19 symptoms including clinical examination, chest computed tomography and laboratory testing.

RESULTS

We investigated subjects with mild to critical COVID-19, of which the majority received hospital treatment. 60 days after disease onset, 30% of subjects still presented with iron deficiency and 9% had anemia, mostly categorized as anemia of inflammation. Anemic patients had increased levels of inflammation markers such as interleukin-6 and C-reactive protein and survived a more severe course of COVID-19. Hyperferritinemia was still present in 38% of all individuals and was more frequent in subjects with preceding severe or critical COVID-19. Analysis of the mRNA expression of peripheral blood mononuclear cells demonstrated a correlation of increased ferritin and cytokine mRNA expression in these patients. Finally, persisting hyperferritinemia was significantly associated with severe lung pathologies in computed tomography scans and a decreased performance status as compared to patients without hyperferritinemia.

DISCUSSION

Alterations of iron homeostasis can persist for at least two months after the onset of COVID-19 and are closely associated with non-resolving lung pathologies and impaired physical performance. Determination of serum iron parameters may thus be a easy to access measure to monitor the resolution of COVID-19.

TRIAL REGISTRATION

ClinicalTrials.gov number: NCT04416100.

Fungal iron homeostasis with a focus on Aspergillus fumigatus

To maintain iron homeostasis, fungi have to balance iron acquisition, storage, and utilization to ensure sufficient supply and to avoid toxic excess of this essential trace element. As pathogens usually encounter iron limitation in the host niche, this metal plays a particular role during virulence. Siderophores are iron-chelators synthesized by most, but not all fungal species to sequester iron extra- and intracellularly. In recent years, the facultative human pathogen Aspergillus fumigatus has become a model for fungal iron homeostasis of siderophore-producing fungal species. This article summarizes the knowledge on fungal iron homeostasis and its links to virulence with a focus on A. fumigatus. It covers mechanisms for iron acquisition, storage, and detoxification, as well as the modes of transcriptional iron regulation and iron sensing in A. fumigatus in comparison to other fungal species. Moreover, potential translational applications of the peculiarities of fungal iron metabolism for treatment and diagnosis of fungal infections is addressed.

Intake of acrylamide at the dietary relevant concentration causes splenic toxicity in adult zebrafish

Acrylamide (AA) has recently been recognized as an immediate hazardous chemical compound owing to its various toxicities and unavoidable contamination of certain daily foods prepared at a high temperature. AA in foods is thus a worldwide concern; however, its toxicity at the dietary relevant concentration has yet to be experimentally elucidated. To determine whether dietary AA intake causes adverse health effects, adult zebrafish were fed a diet containing AA at a relevant dose for one month. Although AA-fed zebrafish showed no superficial abnormalities, their spleen was severely swollen. Therefore, their spleen was analyzed histologically and pathologically and the changes in cytokine expression in their spleen were also examined. Based on our findings, the intake of AA-containing food caused splenic damages, including cyst formation, hemorrhage, and inflammation, which were accompanied by immune responses as indicated by the appearance of a melanomacrophage center, activation of macrophages, and upregulation of major inflammatory cytokines in the spleen. Collectively, for the first time, we provided experimental evidence of the splenic toxicity caused by dietary AA intake.

How Severe Anaemia Might Influence the Risk of Invasive Bacterial Infections in African Children

Severe anaemia and invasive bacterial infections are common causes of childhood sickness and death in sub-Saharan Africa. Accumulating evidence suggests that severely anaemic African children may have a higher risk of invasive bacterial infections. However, the mechanisms underlying this association remain poorly described. Severe anaemia is characterized by increased haemolysis, erythropoietic drive, gut permeability, and disruption of immune regulatory systems. These pathways are associated with dysregulation of iron homeostasis, including the downregulation of the hepatic hormone hepcidin. Increased haemolysis and low hepcidin levels potentially increase plasma, tissue and intracellular iron levels. Pathogenic bacteria require iron and/or haem to proliferate and have evolved numerous strategies to acquire labile and protein-bound iron/haem. In this review, we discuss how severe anaemia may mediate the risk of invasive bacterial infections through dysregulation of hepcidin and/or iron homeostasis, and potential studies that could be conducted to test this hypothesis.

Prevalence and Predictive Value of Anemia and Dysregulated Iron Homeostasis in Patients with COVID-19 Infection

Infections with SARS-CoV-2 can result in severe clinical manifestations. As such patients present with systemic inflammation, we studied the prevalence and predictive value of anemia of inflammation (AI) or functional iron deficiency (FID), originating from immune-mediated alterations of iron homeostasis. Within this retrospective analysis of 259 hospitalized patients with COVID-19, we found that, upon admission, 24.7% were anemic, with the majority suffering from AI (68.8%). Anemia was associated with a significantly higher in-hospital mortality (OR 3.729 (95%CI 1.739-7.995), p = 0.001) but not an increased frequency of intensive care unit (ICU) admission or need for mechanical ventilation. FID was present in 80.0% of patients upon admission, linked to more advanced inflammation and associated with significantly longer hospital stay. Notably, a ferritin/transferrin ratio > 10 predicted a five-fold higher risk of ICU admission and an eight-fold higher risk of the need for mechanical ventilation. Anemia and alterations of iron homeostasis are highly prevalent in hospitalized COVID-19 patients. Iron metabolism biomarkers and hemoglobin can contribute to risk stratification of patients, as initial anemia is associated with increased mortality, whereas alterations of iron homeostasis with a higher ferritin/transferrin ratio reflect more advanced inflammation and predicts subsequent insufficient pulmonary oxygenation with the need for ICU admission and mechanical ventilation.

Mutation accumulation and horizontal gene transfer in Escherichia coli colonizing the gut of old mice

The ecology and environment of the microbes that inhabit the mammalian intestine undergoes several changes as the host ages. Here, we ask if the selection pressure experienced by a new strain colonizing the aging gut differs from that in the gut of young adults. Using experimental evolution in mice after a short antibiotic treatment, as a model for a common clinical situation, we show that a new colonizing E. coli strain rapidly adapts to the aging gut via both mutation accumulation and bacteriophage-mediated horizontal gene transfer (HGT). The pattern of evolution of E. coli in aging mice is characterized by a larger number of transposable element insertions and intergenic mutations compared to that in young mice, which is consistent with the gut of aging hosts harboring a stressful and iron limiting environment.

Iron homeostasis disorder in piglet intestine

Intestinal iron homeostasis is like the Zhong-Yong in traditional Chinese culture, which is a dynamic balance between Yin and Yang.