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

Two HbpA-like proteins HbpA1 and HbpA2 from Actinobacillus pleuropneumoniae protect bacteria from sulfur source limitation, oxidative and cold stresses, but not essential to virulence

Porcine pleuropneumonia is one of the respiratory diseases that pigs are susceptible to Actinobacillus pleuropneumoniae (A. pleuropneumoniae), poses a great threat to the global pig industry. Glutathione (GSH) is an important sulfur source, cellular antioxidant and virulence determinant of many pathogenic bacteria. In this study, roles of two HbpA-like proteins HbpA1 and HbpA2 of A. pleuropneumoniae were analyzed. A. pleuropneumoniae mutants without HbpA2 were basically unable to grow in chemically defined medium (CDM) with GSH as the sole sulfur source and had significantly reduced oxidative tolerance; whereas mutation in hbpA1 led to reduced survival under low-temperature environments. Neither HbpA1 nor HbpA2 affects utilization of heme. These two HbpA-like proteins are not associated with the virulence of A. pleuropneumoniae. Our results reveal the correlation of A. pleuropneumoniae HbpA1 and HbpA2 in GSH utilization, highlight the roles of HbpA1 in the cold stress resistance and HbpA2 in the anti-oxidative response. GSH limitation is not a way to attenuate colonization and pathogenicity of A. pleuropneumoniae.

Stealing survival: Iron acquisition strategies of Mycobacteriumtuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), faces iron scarcity within the host due to immune defenses. This review explores the importance of iron for Mtb and its strategies to overcome iron restriction. We discuss how the host limits iron as an innate immune response and how Mtb utilizes various iron acquisition systems, particularly the siderophore-mediated pathway. The review illustrates the structure and biosynthesis of mycobactin, a key siderophore in Mtb, and the regulation of its production. We explore the potential of targeting siderophore biosynthesis and uptake as a novel therapeutic approach for TB. Finally, we summarize current knowledge on Mtb's iron acquisition and highlight promising directions for future research to exploit this pathway for developing new TB interventions.

Donor-Specific Blood Transfusion in Lung Transplantation

Lung transplantation is still hindered by a high rate of chronic rejection necessitating profound immunosuppression with its associated complications. Donor-specific blood transfusion is a pre-transplant strategy aimed at improving graft acceptance. In contrast with standard stored blood or donor-specific regulatory T cells transfusions, this approach utilizes fresh whole blood from the donor prior to allograft transplantation, encompassing all cell types and plasma. The precise mechanisms underlying donor-specific blood transfusion-induced tolerance remain incompletely understood. Associations with regulatory/helper T cells, modulation of mononuclear phagocytic cells or microchimerism have been suggested. While numerous (pre-)clinical studies have explored its application in solid organ transplants like liver, kidney, and intestine, limited attention has been given to the setting of lung transplantation. This comprehensive review summarizes existing knowledge on the mechanisms and outcomes of donor-specific blood transfusion in solid organ transplants both in preclinical and clinical settings. We also address the potential benefits and risks associated with donor-specific blood transfusion in the field of lung transplantation, offering insights into future research directions.

Biofilm Microenvironment Activated Antibiotic Adjuvant for Implant-Associated Infections by Systematic Iron Metabolism Interference

Hematoma, a risk factor of implant-associated infections (IAIs), creates a Fe-rich environment following implantation, which proliferates the growth of pathogenic bacteria. Fe metabolism is a major vulnerability for pathogens and is crucial for several fundamental physiological processes. Herein, a deferiprone (DFP)-loaded layered double hydroxide (LDH)-based nanomedicine (DFP@Ga-LDH) that targets the Fe-rich environments of IAIs is reported. In response to acidic changes at the infection site, DFP@Ga-LDH systematically interferes with bacterial Fe metabolism via the substitution of Ga3+ and Fe scavenging by DFP. DFP@Ga-LDH effectively reverses the Fe/Ga ratio in Pseudomonas aeruginosa, causing comprehensive interference in various Fe-associated targets, including transcription and substance metabolism. In addition to its favorable antibacterial properties, DFP@Ga-LDH functions as a nano-adjuvant capable of delaying the emergence of antibiotic resistance. Accordingly, DFP@Ga-LDH is loaded with a siderophore antibiotic (cefiderocol, Cefi) to achieve the antibacterial nanodrug DFP@Ga-LDH-Cefi. Antimicrobial and biosafety efficacies of DFP@Ga-LDH-Cefi are validated using ex vivo human skin and mouse IAI models. The pivotal role of the hematoma-created Fe-rich environment of IAIs is highlighted, and a nanoplatform that efficiently interferes with bacterial Fe metabolism is developed. The findings of the study provide promising guidance for future research on the exploration of nano-adjuvants as antibacterial agents.

Impact of Iron Supplementation on Hospital Length of Stay for Pneumonia or Skin and Skin Structure Infections: A Retrospective Cohort Study

Objectives: Pathogenic organisms utilize iron to survive and replicate and have evolved many processes to extract iron from human hosts. The goal of this study was to elucidate the impact of iron supplementation given in the setting of acute infection. Methods: This was a retrospective cohort study of Veterans Affairs patients who received intravenous antibiotics for pneumonia or skin and skin structure infections. Five-thousand subjects were included in each of the 2 cohorts: iron-receiving and non-iron-receiving. Data was analyzed using Fischer's Exact test if categorical and independent t-tests if continuous. Primary and secondary objectives analyzed with Cox proportional hazard regression and outcome rates estimated utilizing Kaplan-Meier method. Results: Five-thousand patients were included in each cohort. The iron cohort was significantly older (Mean-years: Iron = 71.6, No-iron = 68.9; mean-difference = 2.7, P < .0001) with reduced renal function (Mean-eGFR[mL/min/1.73 m²]: Iron = 67.2, No-iron = 77.4; mean-difference = 10.2, P < .0001). For the primary outcome, the iron cohort had a significantly longer mean length of hospital stay (10.4 days) compared to the no-iron cohort (8.7 days) (mean difference 1.7 days, P < .0001). Secondary outcome analysis showed the iron cohort received intravenous antibiotics for longer (Iron = 8.2 days, No-iron = 7.1 days; mean-difference = 1.1 days, P < .0001) with a higher proportion of 30-day readmissions (Iron = 15.6%, No-iron = 12.8%; proportion difference = 2.8%, P < .0001). No significant difference was found between cohort proportions for 30-day mortality (Iron = 12.7%, No-iron = 11.3%, proportion difference = 1.4%, P = .052). Conclusions: Baseline characteristic differences between cohorts is representative of patients who would be expected to require iron replacement therapy. Given the magnitude of primary and secondary-outcomes, further studies controlling for these factors would be warranted.

Targeting iron-metabolism:a potential therapeutic strategy for pulmonary fibrosis

Iron homeostasisis is integral to normal physiological and biochemical processes of lungs. The maintenance of iron homeostasis involves the process of intake, storage and output, dependening on iron-regulated protein/iron response element system to operate tightly metabolism-related genes, including TFR1, DMT1, Fth, and FPN. Dysregulation of iron can lead to iron overload, which increases the virulence of microbial colonisers and the occurrence of oxidative stress, causing alveolar epithelial cells to undergo necrosis and apoptosis, and form extracellular matrix. Accumulated iron drive iron-dependent ferroptosis to exacerbated pulmonary fibrosis. Notably, the iron chelator deferoxamine and the lipophilic antioxidant ferritin-1 have been shown to attenuate ferroptosis and inhibit lipid peroxidation in pulmonary fibrosis. The paper summarises the regulatory mechanisms of dysregulated iron metabolism and ferroptosis in the development of pulmonary fibrosis. Targeting iron metabolism may be a potential therapeutic strategy for the prevention and treatment of pulmonary fibrosis.

Effects of oral or parenteral iron supplementation on haematological parameters, blood iron status and growth in newborn calves fed milk replacer

BACKGROUND

This study aimed to assess the influence of early life iron supplementation on the haematological parameters of calves fed milk replacer on a high plane of nutrition.

METHODS

Thirty calves were allocated to receive either a sham treatment (CON), injection of 1000 mg Fe3+ (INJ) or oral administration of 1050 mg Fe3+ (ORAL), all administered less than 1 hour after birth. Blood was obtained before treatment, on days 1, 3, 5 and 7 of life and once weekly until week 9. Samples were analysed for haemoglobin (Hb), packed cell volume (PCV) and estimated transferrin saturation (%TSAT).

RESULTS

The Hb and PCV of calves in the INJ and ORAL groups were above the values of those in the CON group throughout the study. Hb and PCV of the CON group remained within the reference range for calves. The %TSAT exceeded reported ranges in the ORAL group in the first week. Values for the CON group were below the INJ and ORAL groups throughout the entire study. Average daily gain did not differ between treatments.

LIMITATIONS

The sample size was insufficient to assess the influence of iron supplementation on disease development. Furthermore, the study was set in a controlled environment and not performed under field conditions.

CONCLUSIONS

Oral and subcutaneous iron administration had similar effects on haematological development but resulted in numerically different transferrin saturation. Control animals showed lower Hb and PCV but did not develop overt anaemia.

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.

Key players in the regulation of iron homeostasis at the host-pathogen interface

Iron plays a crucial role in the biochemistry and development of nearly all living organisms. Iron starvation of pathogens during infection is a striking feature utilized by a host to quell infection. In mammals and some other animals, iron is essentially obtained from diet and recycled from erythrocytes. Free iron is cytotoxic and is readily available to invading pathogens. During infection, most pathogens utilize host iron for their survival. Therefore, to ensure limited free iron, the host's natural system denies this metal in a process termed nutritional immunity. In this fierce battle for iron, hosts win over some pathogens, but others have evolved mechanisms to overdrive the host barriers. Production of siderophores, heme iron thievery, and direct binding of transferrin and lactoferrin to bacterial receptors are some of the pathogens' successful strategies which are highlighted in this review. The intricate interplay between hosts and pathogens in iron alteration systems is crucial for understanding host defense mechanisms and pathogen virulence. This review aims to elucidate the current understanding of host and pathogen iron alteration systems and propose future research directions to enhance our knowledge in this field.

Identification of antibacterial activity of LEAP2 from Antarctic icefish Chionodraco hamatus

Liver-expressed antimicrobial peptide 2 (LEAP2) is a small peptide, which is consisted of signal peptide, pro-peptide and the bioactive mature peptide. Mature LEAP2 is an antibacterial peptide with four highly conserved cysteines forming two intramolecular disulfide bonds. Chionodraco hamatus, an Antarctic notothenioid fish that lives in the coldest water, has white blood unlike most fish of the world. In this study, the LEAP2 coding sequence was cloned from C. hamatus, including a 29 amino acids signal peptide and mature peptide of 46 amino acids. High levels of LEAP2 mRNA were detected in the skin and liver. Mature peptide was obtained by chemical synthesis in vitro, displayed selective antimicrobial activities against Escherichia coli, Aeromonas hydrophila, Staphylococcus aureus and Streptococcus agalactiae. Liver-expressed antimicrobial peptide 2 showed bactericidal activity by destroying the cell membrane integrity and robustly combined with bacterial genomic DNA. In addition, overexpression of the Tol-LEAP2-EGFP in zebrafish larva showed stronger antimicrobial activity in C. hamatus than in zebrafish, accompanied by lower bacterial load and expression of pro-inflammatory factors. This is the first demonstration of the antimicrobial activity of LEAP2 from C. hamatus, which is of useful value in improving resistance to pathogens.

Uropathogenic Escherichia coli (UPEC)-Associated Urinary Tract Infections: The Molecular Basis for Challenges to Effective Treatment

Urinary tract infections (UTIs) are among the most common bacterial infections, especially among women and older adults, leading to a significant global healthcare cost burden. Uropathogenic Escherichia coli (UPEC) are the most common cause and accounts for the majority of community-acquired UTIs. Infection by UPEC can cause discomfort, polyuria, and fever. More serious clinical consequences can result in urosepsis, kidney damage, and death. UPEC is a highly adaptive pathogen which presents significant treatment challenges rooted in a complex interplay of molecular factors that allow UPEC to evade host defences, persist within the urinary tract, and resist antibiotic therapy. This review discusses these factors, which include the key genes responsible for adhesion, toxin production, and iron acquisition. Additionally, it addresses antibiotic resistance mechanisms, including chromosomal gene mutations, antibiotic deactivating enzymes, drug efflux, and the role of mobile genetic elements in their dissemination. Furthermore, we provide a forward-looking analysis of emerging alternative therapies, such as phage therapy, nano-formulations, and interventions based on nanomaterials, as well as vaccines and strategies for immunomodulation. This review underscores the continued need for research into the molecular basis of pathogenesis and antimicrobial resistance in the treatment of UPEC, as well as the need for clinically guided treatment of UTIs, particularly in light of the rapid spread of multidrug resistance.

Increasing serum iron levels and their role in the risk of infectious diseases: a Mendelian randomization approach

OBJECTIVES

Increased iron stores have been associated with elevated risks of different infectious diseases, suggesting that iron supplementation may increase the risk of infections. However, these associations may be biased by confounding or reverse causation. This is important, since up to 19% of the population takes iron supplementation. We used Mendelian randomization (MR) to bypass these biases and estimate the causal effect of iron on infections.

METHODS

As instrumental variables, we used genetic variants associated with iron biomarkers in two genome-wide association studies (GWASs) of European ancestry participants. For outcomes, we used GWAS results from the UK Biobank, FinnGen, the COVID-19 Host Genetics Initiative or 23andMe, for seven infection phenotypes: 'any infections', combined, COVID-19 hospitalization, candidiasis, pneumonia, sepsis, skin and soft tissue infection (SSTI) and urinary tract infection (UTI).

RESULTS

Most of our analyses showed increasing iron (measured by its biomarkers) was associated with only modest changes in the odds of infectious outcomes, with all 95% odds ratios confidence intervals within the 0.88 to 1.26 range. However, for the three predominantly bacterial infections (sepsis, SSTI, UTI), at least one analysis showed a nominally elevated risk with increased iron stores (P <0.05).

CONCLUSION

Using MR, we did not observe an increase in risk of most infectious diseases with increases in iron stores. However for bacterial infections, higher iron stores may increase odds of infections. Hence, using genetic variation in iron pathways as a proxy for iron supplementation, iron supplements are likely safe on a population level, but we should continue the current practice of conservative iron supplementation during bacterial infections or in those at high risk of developing them.

An Overview of Selected Bacterial Infections in Cancer, Their Virulence Factors, and Some Aspects of Infection Management

In cancer development and its clinical course, bacteria can be involved in etiology and secondary infection. Regarding etiology, various epidemiological studies have revealed that Helicobacter pylori can directly impact gastric carcinogenesis. The Helicobacter pylori-associated virulence factor cytotoxin-associated gene A perhaps plays an important role through different mechanisms such as aberrant DNA methylation, activation of nuclear factor kappa B, and modulation of the Wnt/β-catenin signaling pathway. Many other bacteria, including Salmonella and Pseudomonas, can also affect Wnt/β-catenin signaling. Although Helicobacter pylori is involved in both gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma, its role in the latter disease is more complicated. Among other bacterial species, Chlamydia is linked with a diverse range of diseases including cancers of different sites. The cellular organizations of Chlamydia are highly complex. Interestingly, Escherichia coli is believed to be associated with colon cancer development. Microorganisms such as Escherichia coli and Pseudomonas aeruginosa are frequently isolated from secondary infections in cancer patients. In these patients, the common sites of infection are the respiratory, gastrointestinal, and urinary tracts. There is an alarming rise in infections with multidrug-resistant bacteria and the scarcity of suitable antimicrobial agents adversely influences prognosis. Therefore, effective implementation of antimicrobial stewardship strategies is important in cancer patients.

Improved engineering of Pseudomonas aeruginosa to study the adaptation of pyoverdine production under intra- or inter- specific bacterial competition

Pseudomonas aeruginosa (PA) is a common cause of chronic infections, particularly feared by cystic fibrosis patients. PA colonizes the lung where it adapts to the local environment, and/or to treatments by drugs. This genotypic and phenotypic adaptation, in turns, influences its interaction with its environment, like bacteria from the microbiota. As an example, to access iron, PA produces and secretes two siderophores, pyoverdine and pyochelin that are iron chelators scavenging iron from the environment and bringing it back into the bacterial cells. Siderophores production depends on the level of iron starvation, on the presence of other bacteria, etc. this latter component being less well investigated. Even if studies on bacterial interactions, and their evolution, have been increasing since several years, we are still facing a lack of tools, for example, to specifically follow the growth of PA isolates in such competitive environments. We thus improved a cloning method to gain time in the cloning steps, to lower the polar effects, and to accurately follow the interactions of any PA isolate with other bacteria. For that, a fluorescent reporter gene was inserted between two genes, the glutamine-fructose-6-phosphate transaminase (glmS) and PA5548. This reporter was efficiently produced either from an inducible or a house-keeping promoter, and its expression did not lead to polar effects. We used this strain to study intra and inter-specific bacterial competitions for iron between different lung pathogens. We thus grew wild-type PA together either with an isogenic PA ΔpvdS variant, that does not produce the most efficient siderophore pyoverdine, or with Klebsiella pneumoniae or Acinetobacter baumanii, two other lung pathogens. We finally monitored the effect of the loss of pvdS on the competition between PA and the other bacterial species. These studies enabled us to differentiate intra from inter specific competitions, both arising in the lung environment, and pinpoint the importance of the bacterial specie for the adaptation of pyoverdine production.

The Siderophore Ferricrocin Mediates Iron Acquisition in Aspergillus fumigatus

The opportunistic fungal pathogen Aspergillus fumigatus utilizes two high-affinity iron uptake mechanisms, termed reductive iron assimilation (RIA) and siderophore-mediated iron acquisition (SIA). The latter has been shown to be crucial for virulence of this fungus and is a target for development of novel strategies for diagnosis and treatment of fungal infections. So far, research on SIA in this mold focused mainly on the hyphal stage, revealing the importance of extracellular fusarinine-type siderophores in iron acquisition as well as of the siderophore ferricrocin in intracellular iron handling. The current study aimed to characterize iron acquisition during germination. High expression of genes involved in biosynthesis and uptake of ferricrocin in conidia and during germination, independent of iron availability, suggested a role of ferricrocin in iron acquisition during germination. In agreement, (i) bioassays indicated secretion of ferricrocin during growth on solid media during both iron sufficiency and limitation, (ii) ferricrocin was identified in the supernatant of conidia germinating in liquid media during both iron sufficiency and limitation, (iii) in contrast to mutants lacking all siderophores, mutants synthesizing ferricrocin but lacking fusarinine-type siderophores were able to grow under iron limitation in the absence of RIA, and (iv) genetic inactivation of the ferricrocin transporter Sit1 decreased germination in the absence of RIA. Taken together, this study revealed that ferricrocin has not only an intracellular role but also functions as an extracellular siderophore to support iron acquisition. The iron availability-independent ferricrocin secretion and uptake during early germination indicate developmental, rather than iron regulation. IMPORTANCE Aspergillus fumigatus is one of the most common airborne fungal pathogens for humans. Low-molecular-mass iron chelators, termed siderophores, have been shown to play a central role in iron homeostasis and, consequently, virulence of this mold. Previous studies demonstrated the crucial role of secreted fusarinine-type siderophores, such as triacetylfusarinine C, in iron acquisition, as well as of the ferrichrome-type siderophore ferricrocin in intracellular iron storage and transport. Here, we demonstrate that ferricrocin is also secreted to mediate iron acquisition during germination together with reductive iron assimilation. During early germination, ferricrocin secretion and uptake were not repressed by iron availability, indicating developmental regulation of this iron acquisition system in this growth phase.

Ferritinophagy-mediated iron competition in RUTIs: Tug-of-war between UPEC and host

Uropathogenic Escherichia coli (UPEC) is the main pathogen of recurrent urinary tract infections (RUTIs). Urinary tract infection is a complicated interaction between UPEC and the host. During infection, UPEC can evade the host's immune response and retain in bladder epithelial cells, which requires adequate nutritional support. Iron is the first necessary trace element in life and a key nutritional factor, making it an important part of the competition between UPEC and the host. On the one hand, UPEC grabs iron to satisfy its reproduction, on the other hand, the host relies on iron to build nutritional immunity defenses against UPEC. Ferritinophagy is a selective autophagy of ferritin mediated by nuclear receptor coactivator 4, which is not only a way for the host to regulate iron metabolism to maintain iron homeostasis, but also a key point of competition between the host and UPEC. Although recent studies have confirmed the role of ferritinophagy in the progression of many diseases, the mechanism of potential interactions between ferritinophagy in UPEC and the host is poorly understood. In this paper, we reviewed the potential mechanisms of ferritinophagy-mediated iron competition in the UPEC-host interactions. This competitive relationship, like a tug-of-war, is a confrontation between the capability of UPEC to capture iron and the host's nutritional immunity defense, which could be the trigger for RUTIs. Therefore, understanding ferritinophagy-mediated iron competition may provide new strategies for exploring effective antibiotic alternative therapies to prevent and treat RUTIs.

The small RNA PrrH of Pseudomonas aeruginosa regulates hemolysis and oxidative resistance in bloodstream infection

Small regulatory RNAs (sRNAs) regulate multiple physiological functions in bacteria, and sRNA PrrH can regulate iron homeostasis and virulence. However, the function of PrrH in Pseudomonas aeruginosa (P. aeruginosa) bloodstream infection (BSI) is largely unknown. The aim of this study was to investigate the role of PrrH in P. aeruginosa BSI model. First, P. aeruginosa PAO1 was co-cultured with peripheral blood cells for 6 h qRT-PCR results showed a transient up-regulation of PrrH expression at 1 h. Simultaneously, the expression of iron uptake genes fpvA, pvdS and phuR was upregulated. In addition, the use of iron chelator 2,2'-dipyridyl to create low-iron conditions caused up-regulation of PrrH expression, a result similar to the BSI model. Furthermore, the addition of FeCl3 was found to decrease PrrH expression. These results support the hypothesis that the expression of PrrH is regulated by iron in BSI model. Then, to clarify the effect of PrrH on major cells in the blood, we used PrrH mutant, overexpressing and wild-type strains to act separately on erythrocytes and neutrophils. On one hand, the hemolysis assay revealed that PrrH contributes to the hemolytic activity of PAO1, and its effect was dependent on the T3SS system master regulator gene exsA, yet had no association with the hemolytic phospholipase C (plcH), pldA, and lasB elastase genes. On the other hand, PrrH mutant enhanced the oxidative resistance of PAO1 in the neutrophils co-culture assay, H2O2-treated growth curve and conventional plate spotting assays. Furthermore, the katA was predicted to be a target gene of PrrH by bioinformatics software, and then verified by qPCR and GFP reporter system. In summary, dynamic changes in the expression of prrH are iron-regulated during PAO1 bloodstream infection. In addition, PrrH promotes the hemolytic activity of P. aeruginosa in an exsA-dependent manner and negatively regulates katA to reduce the oxidative tolerance of P. aeruginosa.

Identification of Multiple Iron Uptake Mechanisms in Enterococcus faecalis and Their Relationship to Virulence

Among the unfavorable conditions bacteria encounter within the host is restricted access to essential trace metals such as iron. To overcome iron deficiency, bacteria deploy multiple strategies to scavenge iron from host tissues, with abundant examples of iron acquisition systems being implicated in bacterial pathogenesis. Yet the mechanisms utilized by the major nosocomial pathogen Enterococcus faecalis to maintain intracellular iron balance are poorly understood. In this study, we conducted a systematic investigation to identify and characterize the iron acquisition mechanisms of E. faecalis and to determine their contribution to virulence. Bioinformatic analysis and literature surveys revealed that E. faecalis possesses three conserved iron uptake systems. Through transcriptomics, we discovered two novel ABC-type transporters that mediate iron uptake. While inactivation of a single transporter had minimal impact on the ability of E. faecalis to maintain iron homeostasis, inactivation of all five systems (Δ5Fe strain) disrupted intracellular iron homeostasis and considerably impaired cell growth under iron deficiency. Virulence of the Δ5Fe strain was generally impaired in different animal models but showed niche-specific variations in mouse models, leading us to suspect that heme can serve as an iron source to E. faecalis during mammalian infections. Indeed, heme supplementation restored growth of Δ5Fe under iron depletion and virulence in an invertebrate infection model. This study revealed that the collective contribution of five iron transporters promotes E. faecalis virulence and that the ability to acquire and utilize heme as an iron source is critical to the systemic dissemination of E. faecalis.

Anemia and iron deficiency in cancer patients: the role of intravenous iron supplements (a literature review)

Anemia in patients with malignancies is a common disorder that has a markedly negative impact on quality of life and overall prognosis. The pathogenesis of anemia is complex and multifactorial, depending on the type and stage of malignancy, nutritional status, renal function, age and gender, cytostatic drug, dose, and chemotherapeutic regimen, with iron deficiency often being the main and potentially treatable factor for anemia. In cancer patients, it can be caused by various concomitant mechanisms, including bleeding (e.g., in malignant gastrointestinal tumors or after surgery), malnutrition, medication, and hepcidin-induced iron sequestration in macrophages, with subsequent iron-deficient erythropoiesis. The variety of clinical manifestations of anemia makes it challenging to establish universal criteria to develop optimal treatments. Current therapy for anemia in malignant tumors includes replacement therapy with an iron supplement, erythropoiesis-stimulating agents (erythropoietins), and blood transfusions. However, blood transfusions should be minimized due to the high risks and costs. Therapy with an iron supplement is an effective approach to correcting the iron deficiency. It can increase the efficacy of erythropoiesis-stimulating drugs and reduce the need for blood transfusions. Published guidelines suggest the wide use of intravenous iron supplements. This article discusses possible approaches to treating iron deficiency in cancer patients in various clinical settings. We build on current guidelines and emphasize the need for further research in this area.

Impact of allogeneic red blood cell transfusion on prognosis in soft tissue sarcoma patients. A single-centre study

BACKGROUND

Perioperatively administered (leukocyte reduced) allogeneic red blood cell transfusions (lrRBCTs) may lead to transfusion-related immunomodulation and reduced overall survival (OS) in cancer patients. Herein, the effect of lrRBCT on local recurrence (LR), distant metastasis (DM), and OS in soft tissue sarcoma (STS) patients was analysed.

METHODS

Retrospective study on 432 STS patients (mean age: 60.0 ± 17.8 years; 46.1% female), surgically treated at a tertiary tumour centre. Uni- and multivariate survival models were calculated to analyse impact of perioperative lrRBCTs on LR, DM, OS.

RESULTS

Perioperatively, 75 patients (17.4%) had received lrRBCTs. Older patients, deep, large, lower limb STS rather required lrRBCTs (all p < 0.05). No significant association between lrRBCT administration and LR- (p = 0.582) or DM-risk (p = 0.084) was observed. LrRBCT was associated with worse OS in univariate analysis (HR: 2.222; p < 0.001), with statistical significance lost upon multivariate analysis (HR: 1.658; p = 0.059; including age, histology, size, grading, amputation, depth). Adding preoperative haemoglobin in subgroup of 220 patients with laboratory parameters revealed significant negative impact of low haemoglobin on OS (p = 0.014), whilst effect of lrRBCT was further diminished (p = 0.167).

CONCLUSION

Unfavourable prognostic factors prevail in STS patients requiring lrRBCTs. Low haemoglobin levels rather than lrRBCT seem to reduce OS.

A zero-sum game or an interactive frame? Iron competition between bacteria and humans in infection war

ABSTRACT

Iron is an essential trace element for both humans and bacteria. It plays a vital role in life, such as in redox reactions and electron transport. Strict regulatory mechanisms are necessary to maintain iron homeostasis because both excess and insufficient iron are harmful to life. Competition for iron is a war between humans and bacteria. To grow, reproduce, colonize, and successfully cause infection, pathogens have evolved various mechanisms for iron uptake from humans, principally Fe 3+ -siderophore and Fe 2+ -heme transport systems. Humans have many innate immune mechanisms that regulate the distribution of iron and inhibit bacterial iron uptake to help resist bacterial invasion and colonization. Meanwhile, researchers have invented detection test strips and coupled antibiotics with siderophores to create tools that take advantage of this battle for iron, to help eliminate pathogens. In this review, we summarize bacterial and human iron metabolism, competition for iron between humans and bacteria, siderophore sensors, antibiotics coupled with siderophores, and related phenomena. We also discuss how competition for iron can be used for diagnosis and treatment of infection in the future.

Computational Modeling of Macrophage Iron Sequestration during Host Defense against Aspergillus

Iron is essential to the virulence of Aspergillus species, and restricting iron availability is a critical mechanism of antimicrobial host defense. Macrophages recruited to the site of infection are at the crux of this process, employing multiple intersecting mechanisms to orchestrate iron sequestration from pathogens. To gain an integrated understanding of how this is achieved in aspergillosis, we generated a transcriptomic time series of the response of human monocyte-derived macrophages to Aspergillus and used this and the available literature to construct a mechanistic computational model of iron handling of macrophages during this infection. We found an overwhelming macrophage response beginning 2 to 4 h after exposure to the fungus, which included upregulated transcription of iron import proteins transferrin receptor-1, divalent metal transporter-1, and ZIP family transporters, and downregulated transcription of the iron exporter ferroportin. The computational model, based on a discrete dynamical systems framework, consisted of 21 3-state nodes, and was validated with additional experimental data that were not used in model generation. The model accurately captures the steady state and the trajectories of most of the quantitatively measured nodes. In the experimental data, we surprisingly found that transferrin receptor-1 upregulation preceded the induction of inflammatory cytokines, a feature that deviated from model predictions. Model simulations suggested that direct induction of transferrin receptor-1 (TfR1) after fungal recognition, independent of the iron regulatory protein-labile iron pool (IRP-LIP) system, explains this finding. We anticipate that this model will contribute to a quantitative understanding of iron regulation as a fundamental host defense mechanism during aspergillosis.

IMPORTANCE Invasive pulmonary aspergillosis is a major cause of death among immunosuppressed individuals despite the best available therapy. Depriving the pathogen of iron is an essential component of host defense in this infection, but the mechanisms by which the host achieves this are complex. To understand how recruited macrophages mediate iron deprivation during the infection, we developed and validated a mechanistic computational model that integrates the available information in the field. The insights provided by this approach can help in designing iron modulation therapies as anti-fungal treatments.

The gut commensal bacterium Enterococcus faecalis LX10 contributes to defending against Nosema bombycis infection in Bombyx mori

BACKGROUND

Microsporidia, a group of obligate intracellular fungal-related parasites, have been used as efficient biocontrol agents for agriculture and forestry pests due to their host specificity and transovarial transmission. They mainly infect insect pests through the intestinal tract, but the interactions between microsporidia and the gut microbiota of the host have not been well demonstrated.

RESULTS

Based on the microsporidia-Bombyx mori model, we report that the susceptibility of silkworms to exposure to the microsporidium Nosema bombycis was both dose and time dependent. Comparative analyses of the silkworm gut microbiome revealed substantially increased abundance of Enterococcus belonging to Firmicutes after N. bombycis infection. Furthermore, a bacterial strain (LX10) was obtained from the gut of B. mori and identified as Enterococcus faecalis based on 16S rRNA sequence analysis. E. faecalis LX10 reduced the N. bombycis spore germination rate and the infection efficiency in vitro and in vivo, as confirmed by bioassay tests and histopathological analyses. In addition, after simultaneous oral feeding with E. faecalis LX10 and N. bombycis, gene (Akirin, Cecropin A, Mesh, Ssk, DUOX and NOS) expression, hydrogen peroxide and nitric oxide levels, and glutathione S-transferase (GST) activity showed different degrees of recovery and correction compared with those under N. bombycis infection alone. Finally, the enterococcin LX protein was identified from sterile LX10 fermentation liquid based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.

CONCLUSION

Altogether, the results revealed that E. faecalis LX10 with anti-N. bombycis activity might play an important role in protecting silkworms from microsporidia. Removal of these specific commensal bacteria with antibiotics and utilization of transgenic symbiotic systems may effectively improve the biocontrol value of microsporidia. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Association of Abnormal Iron Status with the Occurrence and Prognosis of Peritoneal Dialysis-Related Peritonitis: A Longitudinal Data-Based 10-Year Retrospective Study

This retrospective study investigated the effect of iron status on peritonitis by analyzing longitudinal iron parameters in peritoneal dialysis (PD) patients. Patients who received PD at our center from 1 January 2006 to 31 December 2015 were included and followed up until 31 December 2017. According to the joint quartiles of baseline transferrin saturation and ferritin, iron status was categorized as reference iron status (RIS), absolute iron deficiency (AID), functional iron deficiency (FID), and high iron status (HIS). Generalized estimating equations and Cox regression models with time-dependent covariates were used. A total of 1258 PD patients were included; 752 (59.8%) were male, with a mean (±standard deviation) age of 47.4 (±14.9) years. During a median follow-up period of 35.5 (interquartile range, 18.4–60.0) months, 450 (34.3%) patients had 650 episodes of peritonitis. By analyzing longitudinal data, patients with AID were independently positively associated with the occurrence (adjusted odds ratio (AOR) = 1.45) and treatment failure of peritonitis (adjusted hazard ratio (AHR) = 1.85). Patients with HIS were positively associated with the treatment failure of peritonitis (AHR = 2.70). Longitudinal AID and HIS were associated with the episodes and poor prognosis of peritonitis. Active clinical monitoring and correction of iron imbalance in patients with PD are needed.

Iron deficiency anemia associated factors and early childhood caries in Qingdao

Background

Iron deficiency anemia (IDA) has been shown to be related to early childhood caries (ECC). However, data on the relationship, if any, between IDA-associated factors and ECC remain scant. This study aimed to explore the interplay between IDA-associated factors and ECC.

Methods

This study randomly sampled a total of 1598 children in Qingdao city, and analyzed the severity of ECC using decayed-missing-filled teeth index, while the rate of caries was analyzed following the WHO recommendations. The correlation between IDA and ECC was analyzed by both the chi-square test and Mann–Whitney U test. In addition, we designed an electronic questionnaire and employed the disordered multi-classification logistic regression to interrogate the relationship between the IDA-associated factors and ECC.

Results

Children with IDA had higher rates and severe ECC than those without IDA (p < 0.001). Children who were breastfed until 2 years old had a higher risk of IDA and ECC, compared to those who were not {OR 3.453 (1.681–7.094)}. Compared with children who had no history of IDA at the age of 2 years or below, those with IDA history had a higher risk of IDA and ECC {OR 8.762 (3.648–21.041)}. In addition, children who had a maternal history of IDA at pregnancy were at a higher risk of IDA and ECC compared to those who had no IDA history at pregnancy {OR 4.913 (2.934–8.226)}. Our data showed that children from a family with an annual income lower than 50,000 Renminbi (RMB) had a higher risk of IDA and ECC compared to those with an annual family income higher than 200,000 RMB {OR 3.421 (1.505–7.775)}. On the other hand, compared with children taking iron supplements, children who did not were at a higher risk of ECC and IDA {OR 5.602 (1.858–16.896)}.

Conclusion

Factors such as low family income, history of IDA in children aged 2 years or younger, IDA history during pregnancy, children breastfed until 2 years old, and those not taking iron supplements were significantly associated with the occurrence of ECC and IDA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02127-z.

Ingestion, Immunity, and Infection: Nutrition and Viral Respiratory Tract Infections

Respiratory infections place a heavy burden on the health care system, particularly in the winter months. Individuals with a vulnerable immune system, such as very young children and the elderly, and those with an immune deficiency, are at increased risk of contracting a respiratory infection. Most respiratory infections are relatively mild and affect the upper respiratory tract only, but other infections can be more serious. These can lead to pneumonia and be life-threatening in vulnerable groups. Rather than focus entirely on treating the symptoms of infectious disease, optimizing immune responsiveness to the pathogens causing these infections may help steer towards a more favorable outcome. Nutrition may have a role in such prevention through different immune supporting mechanisms. Nutrition contributes to the normal functioning of the immune system, with various nutrients acting as energy sources and building blocks during the immune response. Many micronutrients (vitamins and minerals) act as regulators of molecular responses of immune cells to infection. It is well described that chronic undernutrition as well as specific micronutrient deficiencies impair many aspects of the immune response and make individuals more susceptible to infectious diseases, especially in the respiratory and gastrointestinal tracts. In addition, other dietary components such as proteins, pre-, pro- and synbiotics, and also animal- and plant-derived bioactive components can further support the immune system. Both the innate and adaptive defense systems contribute to active antiviral respiratory tract immunity. The initial response to viral airway infections is through recognition by the innate immune system of viral components leading to activation of adaptive immune cells in the form of cytotoxic T cells, the production of neutralizing antibodies and the induction of memory T and B cell responses. The aim of this review is to describe the effects of a range different dietary components on anti-infective innate as well as adaptive immune responses and to propose mechanisms by which they may interact with the immune system in the respiratory tract.

A review on bacterial redox dependent iron transporters and their evolutionary relationship

Iron is an essential yet toxic micronutrient and its transport across biological membranes is tightly regulated in all living organisms. One such iron transporter, the Ftr-type permeases, is found in both eukaryotic and prokaryotic cells. These Ftr-type transporters are required for iron transport, predicted to form α-helical transmembrane structures, and conserve two ArgGluxxGlu (x = any amino acid) motifs. In the yeast Ftr transporter (Ftr1p), a ferroxidase (Fet3p) is required for iron transport in an oxidation coupled transport step. None of the bacterial Ftr-type transporters (EfeU and FetM from E. coli; cFtr from Campylobacter jejuni; FtrC from Brucella, Bordetella, and Burkholderia spp.) contain a ferroxidase protein. Bioinformatics report predicted periplasmic EfeO and FtrB (from the EfeUOB and FtrABCD systems) as novel cupredoxins. The Cu²⁺ binding and the ferrous oxidation properties of these proteins are uncharacterized and the other two bacterial Ftr-systems are expressed without any ferroxidase/cupredoxin, leading to controversy about the mode of function of these transporters. Here, we review published data on Ftr-type transporters to gain insight into their functional diversity. Based on original bioinformatics data presented here evolutionary relations between these systems are presented.

Battle for Metals: Regulatory RNAs at the Front Line

Metal such as iron, zinc, manganese, and nickel are essential elements for bacteria. These nutrients are required in crucial structural and catalytic roles in biological processes, including precursor biosynthesis, DNA replication, transcription, respiration, and oxidative stress responses. While essential, in excess these nutrients can also be toxic. The immune system leverages both of these facets, to limit bacterial proliferation and combat invaders. Metal binding immune proteins reduce the bioavailability of metals at the infection sites starving intruders, while immune cells intoxicate pathogens by providing metals in excess leading to enzyme mismetallation and/or reactive oxygen species generation. In this dynamic metal environment, maintaining metal homeostasis is a critical process that must be precisely coordinated. To achieve this, bacteria utilize diverse metal uptake and efflux systems controlled by metalloregulatory proteins. Recently, small regulatory RNAs (sRNAs) have been revealed to be critical post-transcriptional regulators, working in conjunction with transcription factors to promote rapid adaptation and to fine-tune bacterial adaptation to metal abundance. In this mini review, we discuss the expanding role for sRNAs in iron homeostasis, but also in orchestrating adaptation to the availability of other metals like manganese and nickel. Furthermore, we describe the sRNA-mediated interdependency between metal homeostasis and oxidative stress responses, and how regulatory networks controlled by sRNAs contribute to survival and virulence.

Transcriptional Differences Guided Discovery and Genetic Identification of Coprogen and Dimerumic Acid Siderophores in Metarhizium robertsii

Siderophores are small molecular iron chelators and participate in the multiple cellular processes in fungi. In this study, biosynthesis gene clusters of coprogens and dimerumic acids were identified by transcriptional level differences of genes related to iron deficiency conditions in Metarhizium robertsii. This leads to the characterization of new coprogen metachelin C (1) and five known siderophores metachelin A (2), metachelin A-CE (3), metachelin B (4), dimerumic acid 11-mannoside (5), and dimerumic acid (6). The structure of metachelin C (1) was elucidated by NMR spectroscopy and HR-ESI-MS analysis. Genetic deletions of mrsidA, and mrsidD abolished the production of compounds 1–6 that implied their involvement in the biosynthesis of coprogen and dimerumic acid. Interestingly, NRPS gene mrsidD is responsible for biosynthesis of both coprogen and dimerumic acid, thus we proposed plausible biosynthetic pathways for the synthesis of coprogen and dimerumic acid siderophores. Therefore, our study provides the genetic basis for understanding the biosynthetic pathway of coprogen and dimerumic acid in Metarhizium robertsii.

Prevalence of childhood anaemia in Brazil: still a serious health problem: a systematic review and meta-analysis

OBJECTIVE

To estimate the prevalence of anaemia in Brazilian children up to 83·9 months old.

DESIGN

Systematic review and meta-analysis, using databases PubMed, Scopus, SciELO, Lilacs, Google Scholar, Periódicos Capes, Arca, Biblioteca Virtual em Saúde, Microsoft Academic Search and Cochrane Library using search terms: anaemia, prevalence, child and Brazil. PROSPERO Registration number: CRD42020208818.

SETTING

Cross-sectional, cohort, case-control and intervention studies published between 2007 and 2020 were searched, excluding those who assessed children with an illness or chronic condition. The main outcome was anaemia prevalence. Random effects models based on the inverse variance method were used to estimate pooled prevalence measures. Sensitivity analyses removed studies with high contribution to overall heterogeneity.

PARTICIPANTS

From 6790 first screened, 134 eligible studies were included, totalling 46 978 children aged zero to 83·9 months analysed, with adequate regions representativeness.

RESULTS

Pooled prevalence of anaemia was 33 % (95 % CI 30, 35). Sensitivity analyses showed that withdrawal of studies that contributed to high heterogeneity did not influence national average prevalence.

CONCLUSIONS

Childhood anaemia is still a serious public health problem in Brazil, exposing 33 % of Brazilian children to the anaemia repercussions. The main limitation of the study is the estimation of national prevalence based on local surveys, but a large number of studies were included, with representation in all regions of the country, giving strength to the results. In Brazil, more public policies are needed to promote supplementation, fortification and access to healthy eating to reduce the high level of anaemia among children.

HCV-Induced Immunometabolic Crosstalk in a Triple-Cell Co-Culture Model Capable of Simulating Systemic Iron Homeostasis

Iron is crucial to the regulation of the host innate immune system and the outcome of many infections. Hepatitis C virus (HCV), one of the major viral human pathogens that depends on iron to complete its life cycle, is highly skilled in evading the immune system. This study presents the construction and validation of a physiologically relevant triple-cell co-culture model that was used to investigate the input of iron in HCV infection and the interplay between HCV, iron, and determinants of host innate immunity. We recorded the expression patterns of key proteins of iron homeostasis involved in iron import, export and storage and examined their relation to the iron regulatory hormone hepcidin in hepatocytes, enterocytes and macrophages in the presence and absence of HCV. We then assessed the transcriptional profiles of pro-inflammatory cytokines Interleukin-6 (IL-6) and interleukin-15 (IL-15) and anti-inflammatory interleukin-10 (IL-10) under normal or iron-depleted conditions and determined how these were affected by infection. Our data suggest the presence of a link between iron homeostasis and innate immunity unfolding among liver, intestine, and macrophages, which could participate in the deregulation of innate immune responses observed in early HCV infection. Coupled with iron-assisted enhanced viral propagation, such a mechanism may be important for the establishment of viral persistence and the ensuing chronic liver disease.

The intracellular phase of extracellular respiratory tract bacterial pathogens and its role on pathogen-host interactions during infection

PURPOSE OF REVIEW

An initial intracellular phase of usually extracellular bacterial pathogens displays an important strategy to hide from the host's immune system and antibiotics therapy. It helps the bacteria, including bacterial pathogens of airway diseases, to persist and eventually switch to a typical extracellular infection. Several infectious diseases of the lung are life-threatening and their control is impeded by intracellular persistence of pathogens. Thus, molecular adaptations of the pathogens to this niche but also the host's response and potential targets to interfere are of relevance. Here we discuss examples of historically considered extracellular pathogens of the respiratory airway where the intracellular survival and proliferation is well documented, including infections by Staphylococcus aureus, Bordetella pertussis, Haemophilus influenzae, Pseudomonas aeruginosa, and others.

RECENT FINDINGS

Current studies focus on bacterial factors contributing to adhesion, iron acquisition, and intracellular survival as well as ways to target them for combatting the bacterial infections.

SUMMARY

The investigation of common and specific mechanisms of pathogenesis and persistence of these bacteria in the host may contribute to future investigations and identifications of relevant factors and/or bacterial mechanisms to be blocked to treat or improve prevention strategies.

Ferritin H deficiency deteriorates cellular iron handling and worsens Salmonella typhimurium infection by triggering hyperinflammation

Iron is an essential nutrient for mammals as well as for pathogens. Inflammation-driven changes in systemic and cellular iron homeostasis are central for host-mediated antimicrobial strategies. Here, we studied the role of the iron storage protein ferritin H (FTH) for the control of infections with the intracellular pathogen Salmonella enterica serovar Typhimurium by macrophages. Mice lacking FTH in the myeloid lineage (LysM-Cre+/+Fthfl/fl mice) displayed impaired iron storage capacities in the tissue leukocyte compartment, increased levels of labile iron in macrophages, and an accelerated macrophage-mediated iron turnover. While under steady-state conditions, LysM-Cre+/+Fth+/+ and LysM-Cre+/+Fthfl/fl animals showed comparable susceptibility to Salmonella infection, i.v. iron supplementation drastically shortened survival of LysM-Cre+/+Fthfl/fl mice. Mechanistically, these animals displayed increased bacterial burden, which contributed to uncontrolled triggering of NF-κB and inflammasome signaling and development of cytokine storm and death. Importantly, pharmacologic inhibition of the inflammasome and IL-1β pathways reduced cytokine levels and mortality and partly restored infection control in iron-treated ferritin-deficient mice. These findings uncover incompletely characterized roles of ferritin and cellular iron turnover in myeloid cells in controlling bacterial spread and for modulating NF-κB and inflammasome-mediated cytokine activation, which may be of vital importance in iron-overloaded individuals suffering from severe infections and sepsis.

The critical roles of iron during the journey from fetus to adolescent: Developmental aspects of iron homeostasis

Iron is indispensable for human life. However, it is also potentially toxic, since it catalyzes the formation of harmful oxidative radicals in unbound form and may facilitate pathogen growth. Therefore, iron homeostasis needs to be tightly regulated. Rapid growth and development require large amounts of iron, while (especially young) children are vulnerable to infections with iron-dependent pathogens due to an immature immune system. Moreover, unbalanced iron status early in life may have effects on the nervous system, immune system and gut microbiota that persist into adulthood. In this narrative review, we assess the critical roles of iron for growth and development and elaborate how the body adapts to physiologically high iron demands during the journey from fetus to adolescent. As a first step towards the development of clinical guidelines for the management of iron disorders in children, we summarize the unmet needs regarding the developmental aspects of iron homeostasis.

Dr. NO and Mr. Toxic - the versatile role of nitric oxide

Nitric oxide (NO) is present in various organisms from humans, to plants, fungus and bacteria. NO is a fundamental signaling molecule implicated in major cellular functions. The role of NO ranges from an essential molecule to a potent mediator of cellular damages. The ability of NO to react with a broad range of biomolecules allows on one hand its regulation and a gradient concentration and on the other hand to exert physiological as well as pathological functions. In humans, NO is implicated in cardiovascular homeostasis, neurotransmission and immunity. However, NO can also contribute to cardiovascular diseases (CVDs) or septic shock. For certain denitrifying bacteria, NO is part of their metabolism as a required intermediate of the nitrogen cycle. However, for other bacteria, NO is toxic and harmful. To survive, those bacteria have developed processes to resist this toxic effect and persist inside their host. NO also contributes to maintain the host/microbiota homeostasis. But little is known about the impact of NO produced during prolonged inflammation on microbiota integrity, and some pathogenic bacteria take advantage of the NO response to colonize the gut over the microbiota. Taken together, depending on the environmental context (prolonged production, gradient concentration, presence of partners for interaction, presence of oxygen, etc.), NO will exert its beneficial or detrimental function. In this review, we highlight the dual role of NO for humans, pathogenic bacteria and microbiota, and the mechanisms used by each organism to produce, use or resist NO.

Iron Acquisition Systems of Gram-negative Bacterial Pathogens Define TonB-Dependent Pathways to Novel Antibiotics

Iron is an indispensable metabolic cofactor in both pro- and eukaryotes, which engenders a natural competition for the metal between bacterial pathogens and their human or animal hosts. Bacteria secrete siderophores that extract Fe3+ from tissues, fluids, cells, and proteins; the ligand gated porins of the Gram-negative bacterial outer membrane actively acquire the resulting ferric siderophores, as well as other iron-containing molecules like heme. Conversely, eukaryotic hosts combat bacterial iron scavenging by sequestering Fe3+ in binding proteins and ferritin. The variety of iron uptake systems in Gram-negative bacterial pathogens illustrates a range of chemical and biochemical mechanisms that facilitate microbial pathogenesis. This document attempts to summarize and understand these processes, to guide discovery of immunological or chemical interventions that may thwart infectious disease.

Hypoferritinemia and iron deficiency in youth with pediatric acute-onset neuropsychiatric syndrome

BACKGROUND

Pediatric acute-onset neuropsychiatric syndrome (PANS) is an abrupt debilitating psychiatric illness. We anecdotally observed hypoferritinemia and iron deficiency in a subset of patients with PANS, prompting this study.

METHODS

In this IRB-approved prospective cohort study, we included patients seen at the Stanford PANS Clinic who met study criteria. The prevalence of hypoferritinemia (using cut-offs of 7 ng/ml in children ≤ 15 years and 18 ng/ml in adolescents > 15 years) and iron deficiency was estimated. Differences in patients with and without hypoferritinemia during PANS flare were explored.

RESULTS

Seventy-nine subjects (mean age of PANS onset of 8.7 years) met study criteria. Hypoferritinemia was observed in 27% and three quarters occurred during a PANS flare. Compared to patients without hypoferritinemia during PANS flare, patients with hypoferritinemia had worse global impairment, more comorbid inflammatory diseases, and exhibited a chronic course of PANS illness. The estimated prevalence of iron deficiency was 3-8% in the PANS cohort, 1.4-2.0-fold higher than in the age- and sex-matched U.S.

POPULATION

More stringent ferritin level cut-offs than the comparison CDC dataset were used.

CONCLUSION

Hypoferritinemia and iron deficiency appear to be more common in PANS patients. More research is needed to confirm and understand this association.

IMPACT

Our study suggests hypoferritinemia and iron deficiency are more common in patients with pediatric acute-onset neuropsychiatric syndrome (PANS) than in the sex- and age-matched US population. Hypoferritinemia was commonly observed during a disease flare but not associated with dietary or demographic factors. In patients with PANS and iron deficiency, clinicians should consider possibility of inflammation as the cause especially if iron deficiency cannot be explained by diet and blood loss. Future research should include larger cohorts to corroborate our study findings and consider examining the iron dynamics on MRI brain imaging in order to better understand the pathophysiology of PANS.

"Limiting access to iron decreases infection of Atlantic salmon SHK-1 cells with bacterium Piscirickettsia salmonis"

BACKGROUND

Vertebrate hosts limit the availability of iron to microbial pathogens in order to nutritionally starve the invaders. The impact of iron deficiency induced by the iron chelator deferoxamine mesylate (DFO) was investigated in Atlantic salmon SHK-1 cells infected with the facultative intracellular bacterium Piscirickettsia salmonis.

RESULTS

Effects of the DFO treatment and P. salmonis on SHK-1 cells were gaged by assessing cytopathic effects, bacterial load and activity, and gene expression profiles of eight immune biomarkers at 4- and 7-days post infection (dpi) in the control group, groups receiving single treatments (DFO or P. salmonis) and their combination. The chelator appears to be well-tolerated by host cells, while it had a negative impact on the number of bacterial cells and associated cytotoxicity. DFO alone had minor effects on gene expression of SHK-1 cells, including an early activation of IL-1β at 4 dpi. In contrast to few moderate changes induced by single treatments (either infection or chelator), most genes had highest upregulation in the infected groups receiving DFO. The mildest induction of hepcidin-1 (antimicrobial peptide precursor and regulator of iron homeostasis) was observed in cells exposed to DFO alone, followed by P. salmonis infected cells while the addition of DFO to infected cells further increased the mRNA abundance of this gene. Transcripts encoding TNF-α (immune signaling) and iNOS (immune effector) showed sustained increase at both time points in this group while cathelicidin-1 (immune effector) and IL-8 (immune signaling) were upregulated at 7 dpi. The stimulation of protective gene responses seen in infected cultures supplemented with DFO coincided with the reduction of bacterial load and activity (judged by the expression of P. salmonis 16S rRNA), and damage to cultured host cells.

CONCLUSION

The absence of immune gene activation under normal iron conditions suggests modulation of host responses by P. salmonis. The negative effect of iron deficiency on bacteria likely allowed host cells to respond in a more protective manner to the infection, further decreasing its progression. Presented findings encourage in vivo exploration of iron chelators as a promising strategy against piscirickettsiosis.

Flipside of the Coin: Iron Deficiency and Colorectal Cancer

Iron deficiency, with or without anemia, is the most frequent hematological manifestation in individuals with cancer, and is especially common in patients with colorectal cancer. Iron is a vital micronutrient that plays an essential role in many biological functions, in the context of which it has been found to be intimately linked to cancer biology. To date, however, whereas a large number of studies have comprehensively investigated and reviewed the effects of excess iron on cancer initiation and progression, potential interrelations of iron deficiency with cancer have been largely neglected and are not well-defined. Emerging evidence indicates that reduced iron intake and low systemic iron levels are associated with the pathogenesis of colorectal cancer, suggesting that optimal iron intake must be carefully balanced to avoid both iron deficiency and iron excess. Since iron is vital in the maintenance of immunological functions, insufficient iron availability may enhance oncogenicity by impairing immunosurveillance for neoplastic changes and potentially altering the tumor immune microenvironment. Data from clinical studies support these concepts, showing that iron deficiency is associated with inferior outcomes and reduced response to therapy in patients with colorectal cancer. Here, we elucidate cancer-related effects of iron deficiency, examine preclinical and clinical evidence of its role in tumorigenesis, cancer progression and treatment response. and highlight the importance of adequate iron supplementation to limit these outcomes.

Hepcidin and Ferritin Predict Microbial Etiology in Community-Acquired Pneumonia

Background

Iron is crucial for survival and growth of microbes. Consequently, limiting iron availability is a human antimicrobial defense mechanism. We explored iron and iron-related proteins as potential biomarkers in community-acquired pneumonia and hypothesized that infection-induced changes in these potential biomarkers differ between groups of pathogens and could predict microbial etiology.

Methods

Blood samples from a prospective cohort of 267 patients with community-acquired pneumonia were analyzed for hepcidin, ferritin, iron, transferrin, and soluble transferrin receptor at admission, clinical stabilization, and a 6-week follow-up. A total of 111 patients with an established microbiological diagnosis confined to 1 microbial group (atypical bacterial, typical bacterial, or viral) were included in predictive analyses.

Results

High admission levels of ferritin predicted atypical bacterial versus typical bacterial etiology (odds ratio [OR], 2.26; 95% confidence interval [CI], 1.18–4.32; P = .014). Furthermore, hepcidin and ferritin predicted atypical bacterial versus viral etiology (hepcidin: OR = 3.12, 95% CI = 1.34–7.28, P = .008; ferritin: OR = 2.38, 95% CI = 1.28–4.45, P = .006). The findings were independent of C-reactive protein and procalcitonin.

Conclusions

Hepcidin and ferritin are potential biomarkers of microbial etiology in community-acquired pneumonia.

Iron-withdrawing anti-infectives for new host-directed therapies based on iron dependence, the Achilles' heel of antibiotic-resistant microbes

The iron dependence of antibiotic-resistant microbes represents an Achilles' heel that can be exploited broadly. The growing global problem of antibiotic resistance of microbial pathogens wherein microbes become resistant to the very antibiotics used against them during infection is linked not only to our health uses but also to agribusiness practices and the changing environment. Here we review mechanisms of microbial iron acquisition and host iron withdrawal defense, and the influence of iron withdrawal on the antimicrobial activity of antibiotics. Antibiotic-resistant microbes are unaltered in their iron requirements, but iron withdrawal from microbes enhances the activities of various antibiotics and importantly suppresses outgrowth of antibiotic-exposed resistant microbial survivors. Of the three therapeutic approaches available to exploit microbial iron susceptibility, including (1) use of gallium as a non-functional iron analogue, (2) Trojan horse conjugates of microbial siderophores carrying antibiotics, and (3) new generation iron chelators, purposely designed as anti-microbials, the latter offers various advantages. For instance, these novel anti-microbial chelators overcome the limitations of conventional clinically-used hematological chelators which display host toxicity and are not useful antimicrobials. 3-Hydroxypyridin-4-one-containing polymeric chelators appear to have the highest potential. DIBI (developmental code name) is a well-developed lead candidate, being a low molecular weight, water-soluble copolymer with enhanced iron binding characteristics, strong anti-microbial and anti-inflammatory activities, low toxicity for animals and demonstrated freedom from microbial resistance development. DIBI has been shown to enhance antibiotic efficacy for antibiotic-resistant microbes during infection, and it also prevents recovery growth and resistance development during microbe exposure to various antibiotics. Because DIBI bolsters innate iron withdrawal defenses of the infected host, it has potential to provide a host-directed anti-infective therapy.

Associations between prenatal and postnatal lead exposure and preschool children humoral and cellular immune responses

Studies have shown that lead exposure affected the immune function, but few studies have examined the relationships between in utero lead exposure, a sensitive period that is important for immune development, and later immune responses. To investigate the effects of prenatal and childhood lead exposure on the preschool-aged children's immune responses, a prospective birth cohort study was established in Wuhan, China, in which lead concentrations were analyzed in maternal urine during the third trimester and in plasma samples from children aged about 3 years. We assessed immune responses by measuring immune cytokines in the children's plasma (n = 326) and peripheral blood T lymphocyte subsets (n = 394) at 3 years of age. Each unit increase in maternal urinary lead concentration (μg/g creatinine) was associated with reduced IL-10 (β = -5.93%, 95%CI: -11.82%, -0.03%) and reduced IL-4 levels (β = -5.62%, 95%CI: -10.44%, -0.80%). Lead in children's plasma (μg/L) was associated with significant increase in TNF-α (β = 10.78%, 95%CI: 3.97%, 17.59%). No statistically significant relationship of childhood lead exposure with T lymphocyte subsets was observed. The study suggested prenatal and childhood lead exposure was associated with changes in preschool children's plasma cytokine levels.

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.

The pathogen Pseudomonas aeruginosa optimizes the production of the siderophore pyochelin upon environmental challenges

Siderophores are iron chelators produced by bacteria to access iron, an essential nutrient. The pathogen Pseudomonas aeruginosa produces two siderophores, pyoverdine and pyochelin, the former with a high affinity for iron and the latter with a lower affinity. Furthermore, the production of both siderophores involves a positive auto-regulatory loop: the presence of the ferri-siderophore complex is essential for their large production. Since pyochelin has a lower affinity for iron it was hard to consider the role of pyochelin in drastic competitive environments where the host or the environmental microbiota produce strong iron chelators and may inhibit iron chelation by pyochelin. We showed here that the pyochelin pathway overcomes this difficulty through a more complex regulating mechanism for pyochelin production than previously described. Indeed, in the absence of pyoverdine, and thus higher difficulty to access iron, the bacteria are able to produce pyochelin independently of the presence of ferri-pyochelin. The regulation of the pyochelin pathway appeared to be more complex than expected with a more intricate tuning between repression and activation. Consequently, when the bacteria cannot produce pyoverdine they are able to produce pyochelin even in the presence of strong iron chelators. Such results support a more complex and varied role for this siderophore than previously described, and complexify the battle for iron during P. aeruginosa infection.

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.

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.

The possible mechanisms of action of 4-aminoquinolines (chloroquine/hydroxychloroquine) against Sars-Cov-2 infection (COVID-19): A role for iron homeostasis?

The anti-malarial drugs chloroquine (CQ) and primarily the less toxic hydroxychloroquine (HCQ) are currently used to treat autoimmune diseases for their immunomodulatory and anti-thrombotic properties. They have also been proposed for the treatment of several viral infections, due to their anti-viral effects in cell cultures and animal models, and, currently, for the treatment of coronavirus disease 2019 (COVID-19), the pandemic severe acute respiratory syndrome caused by coronavirus 2 (Sars-Cov-2) infection that is spreading all over the world. Although in some recent studies a clinical improvement in COVID-19 patients has been observed, the clinical efficacy of CQ and HCQ in COVID-19 has yet to be proven with randomized controlled studies, many of which are currently ongoing, also considering pharmacokinetics, optimal dosing regimen, therapeutic level and duration of treatment and taking into account patients with different severity degrees of disease. Here we review what is currently known on the mechanisms of action of CQ and HCQ as anti-viral, anti-inflammatory and anti-thrombotic drugs and discuss the up-to-date experimental evidence on the potential mechanisms of action of CQ/HCQ in Sars-Cov2 infection and the current clinical knowledge on their efficacy in the treatment of COVID-19 patients. Given the role of iron in several human viral infections, we also propose a different insight into a number of CQ and HCQ pharmacological effects, suggesting a potential involvement of iron homeostasis in Sars-Cov-2 infection and COVID-19 clinical course.

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.