Sepsis: the critical role of iron

Understanding the clinical and molecular basis of thyroid orbitopathy: a review of recent evidence

Thyroid eye disease (TED) is an autoimmune orbital inflammatory disease which ranges from mild to severe. Tissue remodeling, fibrosis and fat proliferation cause changes in the orbital tissues which can affect esthetics and visual function. In its severe form, it is sight threatening, debilitating, and disfiguring and may lead to social stigma, the embarrassment about which has an impact on the quality of life of those affected and the family members. The pathogenesis of TED, which is influenced by genetic, immunological, and environmental factors, is complex and not fully elucidated. However, it remains unknown what factors determine the severity of the disease. Recent research has revealed a number of diagnostic and prognostic biomarkers of this disease. In this overview of TED, we focus on new insights and perspectives regarding biological agents that may provide a basis for new treatment modalities.

Is a Lower Dose of More Bioavailable Iron (18-mg Ferrous Bisglycinate) Noninferior to 60-mg Ferrous Sulfate in Increasing Ferritin Concentrations While Reducing Gut Inflammation and Enteropathogen Detection in Cambodian Women? A Randomized Controlled Noninferiority Trial

BACKGROUND

Global guidelines recommend untargeted iron supplementation for women in regions of anemia prevalence ≥40%, such as Cambodia. However, the potential harms of untargeted iron on the gut have not been rigorously studied in women and likely vary depending on iron dose and form.

OBJECTIVES

We investigated if a lower dose of a highly bioavailable iron amino acid chelate was as effective as the standard dose of iron salts in increasing ferritin concentrations and whether any differences were observed in gut inflammation or enteropathogen detection.

METHODS

A double-blind, randomized placebo-controlled noninferiority trial was conducted in Cambodia. Nonpregnant women (n = 480, 18-45 y) were randomly assigned to 60-mg ferrous sulfate, 18-mg ferrous bisglycinate, or placebo for 12 wk. Nonfasting blood and stool specimens were collected at baseline and 12 wk. Ferritin and fecal calprotectin were measured with an ELISA. A molecular assay was used to detect 11 enteropathogens in a random subset of n = 100 women. Generalized linear mixed-effects models were used to estimate the adjusted mean difference in ferritin concentrations at 12 wk (primary outcome), as compared with our 'a priori' noninferiority margin of 20 μg/L.

RESULTS

Baseline anemia and iron deficiency prevalence was low (17% and 6%, respectively). The adjusted mean difference in ferritin concentrations between the iron groups was 14.6 (95% confidence interval [CI]: 7.6, 21.6) μg/L. Mean ferritin concentration at 12 wk was higher in the ferrous sulfate (99 [95% CI: 95, 103] μg/L, P < 0.001) than in ferrous bisglycinate (84 [95% CI: 80, 88] μg/L) and placebo groups (78 [95% CI: 74, 82] μg/L). No differences in fecal calprotectin concentrations or enteropathogen detection were observed across groups at 12 wk.

CONCLUSIONS

Ferrous bisglycinate (18-mg) was not as effective as ferrous sulfate (60-mg) in increasing ferritin concentrations and did not differentially influence biomarkers of gut health in this predominantly iron-replete population of Cambodian women. This trial was registered at clinicaltrials.gov registry as NCT04017598.

Dysregulated Iron Homeostasis as Common Disease Etiology and Promising Therapeutic Target

Iron is irreplaceably required for animal and human cells as it provides the activity center for a wide variety of essential enzymes needed for energy production, nucleic acid synthesis, carbon metabolism and cellular defense. However, iron is toxic when present in excess and its uptake and storage must, therefore, be tightly regulated to avoid damage. A growing body of evidence indicates that iron dysregulation leading to excess quantities of free reactive iron is responsible for a wide range of otherwise discrete diseases. Iron excess can promote proliferative diseases such as infections and cancer by supplying iron to pathogens or cancer cells. Toxicity from reactive iron plays roles in the pathogenesis of various metabolic, neurological and inflammatory diseases. Interestingly, a common underlying aspect of these conditions is availability of excess reactive iron. This underpinning aspect provides a potential new therapeutic avenue. Existing hematologically used iron chelators to take up excess iron have shown serious limitations for use but new purpose-designed chelators in development show promise for suppressing microbial pathogen and cancer cell growth, and also for relieving iron-induced toxicity in neurological and other diseases. Hepcidin and hepcidin agonists are also showing promise for relieving iron dysregulation. Harnessing iron-driven reactive oxygen species (ROS) generation with ferroptosis has shown promise for selective destruction of cancer cells. We review biological iron requirements, iron regulation and the nature of iron dysregulation in various diseases. Current results pertaining to potential new therapies are also reviewed.

Association between age and the host response in critically ill patients with sepsis

BACKGROUND

The association of ageing with increased sepsis mortality is well established. Nonetheless, current investigations on the influence of age on host response aberrations are largely limited to plasma cytokine levels while neglecting other pathophysiological sepsis domains like endothelial cell activation and function, and coagulation activation. The primary objective of this study was to gain insight into the association of ageing with aberrations in key host response pathways and blood transcriptomes in sepsis.

METHODS

We analysed the clinical outcome (n = 1952), 16 plasma biomarkers providing insight in deregulation of specific pathophysiological domains (n = 899), and blood leukocyte transcriptomes (n = 488) of sepsis patients stratified according to age decades. Blood transcriptome results were validated in an independent sepsis cohort and compared with healthy individuals.

RESULTS

Older age was associated with increased mortality independent of comorbidities and disease severity. Ageing was associated with lower endothelial cell activation and dysfunction, and similar inflammation and coagulation activation, despite higher disease severity scores. Blood leukocytes of patients ≥ 70 years, compared to patients < 50 years, showed decreased expression of genes involved in cytokine signaling, and innate and adaptive immunity, and increased expression of genes involved in hemostasis and endothelial cell activation. The diminished expression of gene pathways related to innate immunity and cytokine signaling in subjects ≥ 70 years was sepsis-induced, as healthy subjects ≥ 70 years showed enhanced expression of these pathways compared to healthy individuals < 50 years.

CONCLUSIONS

This study provides novel evidence that older age is associated with relatively mitigated sepsis-induced endothelial cell activation and dysfunction, and a blood leukocyte transcriptome signature indicating impaired innate immune and cytokine signaling. These data suggest that age should be considered in patient selection in future sepsis trials targeting the immune system and/or the endothelial cell response.

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.

Is untargeted iron supplementation harmful when iron deficiency is not the major cause of anaemia? Study protocol for a double-blind, randomised controlled trial among non-pregnant Cambodian women

INTRODUCTION

The WHO recommends daily oral iron supplementation for 12 weeks in women and adolescents where anaemia prevalence is greater than 40%. However, if iron deficiency is not a major cause of anaemia, then, at best, untargeted iron supplementation is a waste of resources; at worst, it could cause harm. Further, different forms of iron with varying bioavailability may present greater risks of harm.

METHODS AND ANALYSIS

A 12-week three-arm, double-blind, randomised controlled supplementation trial was conducted in Cambodia to determine if there is potential harm associated with untargeted iron supplementation. We will recruit and randomise 480 non-pregnant women (ages 18-45 years) to receive one of three interventions: 60 mg elemental iron as ferrous sulfate (the standard, commonly used form), 18 mg ferrous bisglycinate (a highly bioavailable iron amino acid chelate) or placebo. We will measure ferritin concentrations (to evaluate non-inferiority between the two forms of iron), as well as markers of potential harm in blood and stool (faecal calprotectin, gut pathogen abundance and DNA damage) at baseline and 12 weeks. Mixed-effects generalised linear models will be used to assess the effect of iron on ferritin concentration and markers of potential harm at 12 weeks.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the University of British Columbia Clinical Research Ethics Board (H18-02610), the Children's and Women's Health Centre of British Columbia Research Ethics Board (H18-02610) and the National Ethics Committee for Health Research in Cambodia (273-NECHR). Findings will be published in peer-reviewed journals, presented to stakeholders and policymakers globally and shared within participants' communities.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Registry (NCT04017598).

Thyroid-Gut-Axis: How Does the Microbiota Influence Thyroid Function?

A healthy gut microbiota not only has beneficial effects on the activity of the immune system, but also on thyroid function. Thyroid and intestinal diseases prevalently coexist-Hashimoto's thyroiditis (HT) and Graves' disease (GD) are the most common autoimmune thyroid diseases (AITD) and often co-occur with Celiac Disease (CD) and Non-celiac wheat sensitivity (NCWS). This can be explained by the damaged intestinal barrier and the following increase of intestinal permeability, allowing antigens to pass more easily and activate the immune system or cross-react with extraintestinal tissues, respectively. Dysbiosis has not only been found in AITDs, but has also been reported in thyroid carcinoma, in which an increased number of carcinogenic and inflammatory bacterial strains were observed. Additionally, the composition of the gut microbiota has an influence on the availability of essential micronutrients for the thyroid gland. Iodine, iron, and copper are crucial for thyroid hormone synthesis, selenium and zinc are needed for converting T4 to T3, and vitamin D assists in regulating the immune response. Those micronutrients are often found to be deficient in AITDs, resulting in malfunctioning of the thyroid. Bariatric surgery can lead to an inadequate absorption of these nutrients and further implicates changes in thyroid stimulating hormone (TSH) and T3 levels. Supplementation of probiotics showed beneficial effects on thyroid hormones and thyroid function in general. A literature research was performed to examine the interplay between gut microbiota and thyroid disorders that should be considered when treating patients suffering from thyroid diseases. Multifactorial therapeutic and preventive management strategies could be established and more specifically adjusted to patients, depending on their gut bacteria composition. Future well-powered human studies are warranted to evaluate the impact of alterations in gut microbiota on thyroid function and diseases.

The impact of maternal and early life malnutrition on health: a diet-microbe perspective

BACKGROUND

Early-life malnutrition may have long-lasting effects on microbe-host interactions that affect health and disease susceptibility later in life. Diet quality and quantity in conjunction with toxin and pathogen exposure are key contributors to microbe-host physiology and malnutrition. Consequently, it is important to consider both diet- and microbe-induced pathologies as well as their interactions underlying malnutrition.

MAIN BODY

Gastrointestinal immunity and digestive function are vital to maintain a symbiotic relationship between the host and microbiota. Childhood malnutrition can be impacted by numerous factors including gestational malnutrition, early life antibiotic use, psychological stress, food allergy, hygiene, and exposure to other chemicals and pollutants. These factors can contribute to reoccurring environmental enteropathy, a condition characterized by the expansion of commensal pathobionts and environmental pathogens. Reoccurring intestinal dysfunction, particularly during the critical window of development, may be a consequence of diet-microbe interactions and may lead to life-long immune and metabolic programming and increased disease risk. We provide an overview of the some key factors implicated in the progression of malnutrition (protein, fat, carbohydrate, iron, vitamin D, and vitamin B12) and discuss the microbiota during early life that may contribute health risk later in life.

CONCLUSION

Identifying key microbe-host interactions, particularly those associated with diet and malnutrition requires well-controlled dietary studies. Furthering our understanding of diet-microbe-host interactions will help to provide better strategies during gestation and early life to promote health later in life.

[Characterization of anemic syndrome in cancer patients with sepsis in the early postoperative period.]

A study of the main indicators of red blood (RBC, HGB, HCT, MCV, MCH) and the concentration of EPO, sTfR in 9 cancer patients with anemic syndrome (AS) against sepsis was carried out. Among them, patients with chronic disease anemia (ACh), with normocytic, normochromic characteristics of red blood cells and low hematocrit predominated. In 2 patients, microcytosis and erythrocyte hypochromia were noted, the concentration of sTfR was significantly higher than normal (0.9 ± 0.07 μg / ml), amounted to 2.7 μg / ml in one of them and 1.9 μg / ml in the other, which testified to t iron deficiency erythropoiesis (IDE) on the background of the ACh,. In 7 patients with ACh without IDE, sTfR values were within the normal range (0.1-1.2) μg / ml, the median was 0.5 μg/ml. In all patients with sepsis, the production of EPO was inadequate for the severity of the AS, to a lesser extent in patients with IDE. The average EPO production in the group was 19.4 ± 5.1 (7.7-52.8) mU / ml, median = 12.1 mE / ml. Further studies of EPO, sTfR are planned in order to determine their role in therapeutic tactics in the correction of AS in cancer patients with sepsis.

Role of neuroendocrine modulation and biochemistry in the sepsis in Piaractus mesopotamicus

Sepsis is a systemic process with multifactorial pathophysiology that affects most animal species. It is responsible for high rates of morbidity and mortality. This work aimed to study the biochemical and neuroendocrine changes of the sepsis process in Piaractus mesopotamicus after Aeromonas hydrophila inoculation analyzing changes in blood leukocyte and differences in neuroendocrine-biochemical modulation using RNA-seq. Fish showed hypercortisolemia, inhibition of glucose absorption, followed by hypocortisolemia and then hyperglycemia. Thyroid hormones (T₃ and T₄) showed immediate decrease in serum and T₄ increased 6 h post-inoculation (HPI). Sepsis-induced hormonal alterations triggered changes in the metabolic pathways increasing protein and lipid catabolism, use of transient anaerobic glycolysis and liver injury. A reference transcriptome was constructed based on blood leukocytes from P. mesopotamicus. The assembly resulted in total 266,272 contigs with a N50 of 2786 bp. There was a reorganization of plasma membrane of leukocytes at the beginning of the septic process with increased expression of neuroendocrine receptors and with continuous flow of neurotransmitters, hormones and solutes with compensatory regulation at 6 HPI. Three and nine HPI seemed to be critical, the expression of a number of transcription factors was increased, including the modulatory DEGs related to glucocorticoid and thyroid hormones induced and suppressed (FDR < 0.05). Neuroendocrine modulation can regulate leukocytes and biochemical parameters of peripheral blood, being important sources for the study of the pathophysiology of sepsis. These finding highlights the importance of further studies focusing on biochemical-neuroendocrine changes in blood leukocytes and systemic sepsis.

Impact of pregravid obesity on maternal and fetal immunity: Fertile grounds for reprogramming

Maternal pregravid obesity results in several adverse health outcomes during pregnancy, including increased risk of gestational diabetes, preeclampsia, placental abruption, and complications at delivery. Additionally, pregravid obesity and in utero exposure to high fat diet have been shown to have detrimental effects on fetal programming, predisposing the offspring to adverse cardiometabolic, endocrine, and neurodevelopmental outcomes. More recently, a deeper appreciation for the modulation of offspring immunity and infectious disease-related outcomes by maternal pregravid obesity has emerged. This review will describe currently available animal models for studying the impact of maternal pregravid obesity on fetal immunity and review the data from clinical and animal model studies. We also examine the burden of pregravid obesity on the maternal-fetal interface and the link between placental and systemic inflammation. Finally, we discuss future studies needed to identify key mechanistic underpinnings that link maternal inflammatory changes and fetal cellular reprogramming events.

Comprehensive identification of Vibrio vulnificus genes required for growth in human serum

Vibrio vulnificus can be a highly invasive pathogen capable of spreading from an infection site to the bloodstream, causing sepsis and death. To survive and proliferate in blood, the pathogen requires mechanisms to overcome the innate immune defenses and metabolic limitations of this host niche. We created a high-density transposon mutant library in YJ016, a strain representative of the most virulent V. vulnificus lineage (or phylogroup) and used transposon insertion sequencing (TIS) screens to identify loci that enable the pathogen to survive and proliferate in human serum. Initially, genes underrepresented for insertions were used to estimate the V. vulnificus essential gene set; comparisons of these genes with similar TIS-based classification of underrepresented genes in other vibrios enabled the compilation of a common Vibrio essential gene set. Analysis of the relative abundance of insertion mutants in the library after exposure to serum suggested that genes involved in capsule biogenesis are critical for YJ016 complement resistance. Notably, homologues of two genes required for YJ016 serum-resistance and capsule biogenesis were not previously linked to capsule biogenesis and are largely absent from other V. vulnificus strains. The relative abundance of mutants after exposure to heat inactivated serum was compared with the findings from the serum screen. These comparisons suggest that in both conditions the pathogen relies on its Na⁺ transporting NADH-ubiquinone reductase (NQR) complex and type II secretion system to survive/proliferate within the metabolic constraints of serum. Collectively, our findings reveal the potency of comparative TIS screens to provide knowledge of how a pathogen overcomes the diverse limitations to growth imposed by serum.

High Serum Iron level is Associated with Increased Mortality in Patients with Sepsis

Iron is an essential nutrient for bacterial survival and thus higher iron levels may precipitate bacterial infections. We investigated the association between the serum iron level and prognosis in patients with sepsis by using the single-centre Medical Information Mart for Intensive Care III (MIMIC-III) database. Sepsis patients with iron parameters measured on ICU admission were included and stratified according to quartiles of serum iron levels. A total of 1,891 patients diagnosed with sepsis according to the Sepsis-3 criteria were included in this study, 324 of whom were septic shock. After adjusting for confounding variables, higher iron quartile was associated with an increase in 90-day mortality in the Cox regression analysis. Moreover, a stepwise increase in the risk of 90-day mortality was observed as the quartiles of serum iron levels increased in the patients with sepsis. In conclusion, higher serum iron levels were independently associated with increased 90-day mortality in this large cohort of patients with sepsis.

Influence of Carnicor, Venofer, and Sevelamer on the levels of genotoxic damage in end-stage renal disease patients

End-stage renal disease (ESRD) patients present high levels of phosphorus and calcium products in serum, which contribute to the development of vascular calcification and cardiovascular disease, and to low iron stores and carnitine deficiency. For these reasons, ESRD patients are generally supplemented with different medicines. Some of the most common treatments include the use of Carnicor, Venofer, and Sevelamer drugs. Carnicor is used as a source of L-carnitine, acting as antioxidant and neuroprotector. Venofer is used to reduce the deficit of iron. Sevelamer is used to treat hyperphosphatemia. To determine the potential harmful genotoxic effects of these drugs, a group of 214 patients included in a hemodialysis program with different intakes of Carnicor, Venofer, and Sevelamer were evaluated. The levels of basal and oxidative DNA damage, as well as chromosomal damage, were measured in all individuals using the comet and the micronucleus assays, respectively. Our results indicate that Carnicor administration was associated with low but significant increases in the frequency of basal DNA damage and micronuclei. Environ. Mol. Mutagen. 59:302-311, 2018. © 2018 Wiley Periodicals, Inc.

The effects of iron fortification and supplementation on the gut microbiome and diarrhea in infants and children: a review

In infants and young children in Sub-Saharan Africa, iron-deficiency anemia (IDA) is common, and many complementary foods are low in bioavailable iron. In-home fortification of complementary foods using iron-containing micronutrient powders (MNPs) and oral iron supplementation are both effective strategies to increase iron intakes and reduce IDA at this age. However, these interventions produce large increases in colonic iron because the absorption of their high iron dose (≥12.5 mg) is typically <20%. We reviewed studies in infants and young children on the effects of iron supplements and iron fortification with MNPs on the gut microbiome and diarrhea. Iron-containing MNPs and iron supplements can modestly increase diarrhea risk, and in vitro and in vivo studies have suggested that this occurs because increases in colonic iron adversely affect the gut microbiome in that they decrease abundances of beneficial barrier commensal gut bacteria (e.g., bifidobacteria and lactobacilli) and increase the abundance of enterobacteria including entropathogenic Escherichia coli These changes are associated with increased gut inflammation. Therefore, safer formulations of iron-containing supplements and MNPs are needed. To improve MNP safety, the iron dose of these formulations should be reduced while maximizing absorption to retain efficacy. Also, the addition of prebiotics to MNPs is a promising approach to mitigate the adverse effects of iron on the infant gut.

Protecting the Newborn and Young Infant from Infectious Diseases: Lessons from Immune Ontogeny

Infections in the first year of life are common and often severe. The newborn host demonstrates both quantitative and qualitative differences to the adult in nearly all aspects of immunity, which at least partially explain the increased susceptibility to infection. Here we discuss how differences in susceptibility to infection result not out of a state of immaturity, but rather reflect adaptation to the particular demands placed on the immune system in early life. We review the mechanisms underlying host defense in the very young, and discuss how specific developmental demands increase the risk of particular infectious diseases. In this context, we discuss how this plasticity, i.e. the capacity to adapt to demands encountered in early life, also provides the potential to leverage protection of the young against infection and disease through a number of interventions.

Fluorescence High-Throughput Screening for Inhibitors of TonB Action

Gram-negative bacteria acquire ferric siderophores through TonB-dependent outer membrane transporters (TBDT). By fluorescence spectroscopic hgh-throughput screening (FLHTS), we identified inhibitors of TonB-dependent ferric enterobactin (FeEnt) uptake through Escherichia coli FepA (EcoFepA). Among 165 inhibitors found in a primary screen of 17,441 compounds, we evaluated 20 in secondary tests: TonB-dependent ferric siderophore uptake and colicin killing and proton motive force-dependent lactose transport. Six of 20 primary hits inhibited TonB-dependent activity in all tests. Comparison of their effects on [⁵⁹Fe]Ent and [¹⁴C]lactose accumulation suggested several as proton ionophores, but two chemicals, ebselen and ST0082990, are likely not proton ionophores and may inhibit TonB-ExbBD. The facility of FLHTS against E. coli led us to adapt it to Acinetobacter baumannii We identified its FepA ortholog (AbaFepA), deleted and cloned its structural gene, genetically engineered 8 Cys substitutions in its surface loops, labeled them with fluorescein, and made fluorescence spectroscopic observations of FeEnt uptake in A. baumannii Several Cys substitutions in AbaFepA (S279C, T562C, and S665C) were readily fluoresceinated and then suitable as sensors of FeEnt transport. As in E. coli, the test monitored TonB-dependent FeEnt uptake by AbaFepA. In microtiter format with A. baumannii, FLHTS produced Z' factors 0.6 to 0.8. These data validated the FLHTS strategy against even distantly related Gram-negative bacterial pathogens. Overall, it discovered agents that block TonB-dependent transport and showed the potential to find compounds that act against Gram-negative CRE (carbapenem-resistant Enterobacteriaceae)/ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens. Our results suggest that hundreds of such chemicals may exist in larger compound libraries.IMPORTANCE Antibiotic resistance in Gram-negative bacteria has spurred efforts to find novel compounds against new targets. The CRE/ESKAPE pathogens are resistant bacteria that include Acinetobacter baumannii, a common cause of ventilator-associated pneumonia and sepsis. We performed fluorescence high-throughput screening (FLHTS) against Escherichia coli to find inhibitors of TonB-dependent iron transport, tested them against A. baumannii, and then adapted the FLHTS technology to allow direct screening against A. baumannii This methodology is expandable to other drug-resistant Gram-negative pathogens. Compounds that block TonB action may interfere with iron acquisition from eukaryotic hosts and thereby constitute bacteriostatic antibiotics that prevent microbial colonization of human and animals. The FLHTS method may identify both species-specific and broad-spectrum agents against Gram-negative bacteria.

Iron Fortification of Foods for Infants and Children in Low-Income Countries: Effects on the Gut Microbiome, Gut Inflammation, and Diarrhea

Iron deficiency anemia (IDA) is common among infants and children in Sub-Saharan Africa and is a leading contributor to the global burden of disease, as well as a hindrance to national development. In-home iron fortification of complementary foods using micronutrient powders (MNPs) effectively reduces the risk for IDA by ensuring that the iron needs of infants and young children are met without changing their traditional diet. However, the iron dose delivered by MNPs is high, and comparable on a mg iron per kg body weight to the supplemental doses (2 mg/kg) typically given to older children, which increases diarrhea risk. In controlled studies, iron-containing MNPs modestly increase risk for diarrhea in infants; in some cases, the diarrhea is severe and may require hospitalization. Recent in vitro and in vivo studies provide insights into the mechanism of this effect. Provision of iron fortificants to school-age children and iron-containing MNPs to weaning infants decreases the number of beneficial ‘barrier’ commensal gut bacteria (e.g., bifidobacteria), increases the enterobacteria to bifidobacteria ratio and abundances of opportunistic pathogens (e.g., pathogenic Escherichia coli), and induces gut inflammation. Thus, although iron-containing MNPs are highly effective in reducing IDA, they may increase gastrointestinal morbidity in infants, and safer formulations are needed.

Redox therapy in neonatal sepsis: reasons, targets, strategy, and agents

Neonatal sepsis is one of the most fulminating conditions in neonatal intensive care units. Antipathogen and supportive care are administered routinely, but do not deliver satisfactory results. In addition, the efforts to treat neonatal sepsis with anti-inflammatory agents have generally shown to be futile. The accumulating data imply that intracellular redox changes intertwined into neonatal sepsis redox cycle represent the main cause of dysfunction of mitochondria and cells in neonatal sepsis. Our aim here is to support the new philosophy in neonatal sepsis treatment, which involves the integration of mechanisms that are responsible for cellular dysfunction and organ failure, the recognition of the most important targets, and the selection of safe agents that can stop the neonatal sepsis redox cycle by hitting the hot spots. Redox-active agents that could be beneficial for neonatal sepsis treatment according to these criteria include lactoferrin, interleukin 10, zinc and selenium supplements, ibuprofen, edaravone, and pentoxifylline.

Iron fortification adversely affects the gut microbiome, increases pathogen abundance and induces intestinal inflammation in Kenyan infants

BACKGROUND

In-home iron fortification for infants in developing countries is recommended for control of anaemia, but low absorption typically results in >80% of the iron passing into the colon. Iron is essential for growth and virulence of many pathogenic enterobacteria. We determined the effect of high and low dose in-home iron fortification on the infant gut microbiome and intestinal inflammation.

METHODS

We performed two double-blind randomised controlled trials in 6-month-old Kenyan infants (n=115) consuming home-fortified maize porridge daily for 4 months. In the first, infants received a micronutrient powder (MNP) containing 2.5 mg iron as NaFeEDTA or the MNP without iron. In the second, they received a different MNP containing 12.5 mg iron as ferrous fumarate or the MNP without the iron. The primary outcome was gut microbiome composition analysed by 16S pyrosequencing and targeted real-time PCR (qPCR). Secondary outcomes included faecal calprotectin (marker of intestinal inflammation) and incidence of diarrhoea. We analysed the trials separately and combined.

RESULTS

At baseline, 63% of the total microbial 16S rRNA could be assigned to Bifidobacteriaceae but there were high prevalences of pathogens, including Salmonella Clostridium difficile, Clostridium perfringens, and pathogenic Escherichia coli. Using pyrosequencing, +FeMNPs increased enterobacteria, particularly Escherichia/Shigella (p=0.048), the enterobacteria/bifidobacteria ratio (p=0.020), and Clostridium (p=0.030). Most of these effects were confirmed using qPCR; for example, +FeMNPs increased pathogenic E. coli strains (p=0.029). +FeMNPs also increased faecal calprotectin (p=0.002). During the trial, 27.3% of infants in +12.5 mgFeMNP required treatment for diarrhoea versus 8.3% in -12.5 mgFeMNP (p=0.092). There were no study-related serious adverse events in either group.

CONCLUSIONS

In this setting, provision of iron-containing MNPs to weaning infants adversely affects the gut microbiome, increasing pathogen abundance and causing intestinal inflammation.

TRIAL REGISTRATION NUMBER

NCT01111864.

Change of hemopexin level is associated with the severity of sepsis in endotoxemic rat model and the outcome of septic patients

PURPOSE

The purpose of the study is to uncover the role of hemopexin (HPX) as anti-inflammatory mediator in animals and humans.

MATERIALS AND METHODS

We injected rats with 5 and 10 mg/kg of lipopolysaccharide to induce low- and high-grade endotoxemia (LGE and HGE), respectively, and we measured serum levels of tumor necrosis factor α, interleukin 6, and HPX at 0, 1, 3, and 6 hours after the injection. In a clinical study, we measured the initial serum HPX concentrations of septic shock patients. We evaluated the correlation between HPX levels and sepsis severity in rats and the predictive value of the HPX level for 28-day mortality of patients.

RESULTS

In rats, serum interleukin 6 and tumor necrosis factor α concentrations were lower in LGE than in HGE, whereas the HPX level in HGE at 6 hours was significantly lower than in LGE (0.88, interquartile range [0.79-1.00] vs 1.33, interquartile range [1.29-1.49] mg/mL, P= .002). In patients, the initial serum HPX level in nonsurvivors was significantly lower than in survivors (0.75 vs 1.02 mg/mL, P< .001). Multivariate logistic regression analysis revealed that HPX exhibited independent prognostic value for 28-day mortality, and its levels were closely related to Acute Physiology and Chronic Health Evaluation II scores.

CONCLUSIONS

Low serum HPX levels are related to sepsis severity and could indicate poor prognosis for septic shock patients.

Physiological and proteomic analysis of Escherichia coli iron-limited chemostat growth

Iron bioavailability is a major limiter of bacterial growth in mammalian host tissue and thus represents an important area of study. Escherichia coli K-12 metabolism was studied at four levels of iron limitation in chemostats using physiological and proteomic analyses. The data documented an E. coli acclimation gradient where progressively more severe iron scarcity resulted in a larger percentage of substrate carbon being directed into an overflow metabolism accompanied by a decrease in biomass yield on glucose. Acetate was the primary secreted organic by-product for moderate levels of iron limitation, but as stress increased, the metabolism shifted to secrete primarily lactate (∼70% of catabolized glucose carbon). Proteomic analysis reinforced the physiological data and quantified relative increases in glycolysis enzyme abundance and decreases in tricarboxylic acid (TCA) cycle enzyme abundance with increasing iron limitation stress. The combined data indicated that E. coli responds to limiting iron by investing the scarce resource in essential enzymes, at the cost of catabolic efficiency (i.e., downregulating high-ATP-yielding pathways containing enzymes with large iron requirements, like the TCA cycle). Acclimation to iron-limited growth was contrasted experimentally with acclimation to glucose-limited growth to identify both general and nutrient-specific acclimation strategies. While the iron-limited cultures maximized biomass yields on iron and increased expression of iron acquisition strategies, the glucose-limited cultures maximized biomass yields on glucose and increased expression of carbon acquisition strategies. This study quantified ecologically competitive acclimations to nutrient limitations, yielding knowledge essential for understanding medically relevant bacterial responses to host and to developing intervention strategies.

Transfusion of older stored blood worsens outcomes in canines depending on the presence and severity of pneumonia

BACKGROUND

In experimental pneumonia we found that transfused older blood increased mortality and lung injury that was associated with increased in vivo hemolysis and elevated plasma cell-free hemoglobin (CFH), non-transferrin-bound iron (NTBI), and plasma labile iron (PLI) levels. In this study, we additionally analyze identically treated animals that received lower or higher bacterial doses.

STUDY DESIGN AND METHODS

Two-year-old purpose-bred beagles (n = 48) challenged intrabronchially with Staphylococcus aureus (0 [n = 8], 1.0 × 10(9) [n = 8], 1.25 × 10(9) [n = 24], and ≥1.5 × 10(9) [n = 8] colony-forming units/kg) were exchange transfused with either 7- or 42-day-old canine universal donor blood (80 mL/kg in four divided doses).

RESULTS

The greater increases in CFH with older blood over days after exchange proved relatively independent of bacterial dose. The lesser increases in CFH observed with fresher blood were bacterial dose dependent potentially related to bacterial hemolysins. Without bacterial challenge, levels of CFH, NTBI, and PLI were significantly higher with older versus fresher blood transfusion but there was no significant measurable injury. With higher-dose bacterial challenge, the elevated NTBI and PLI levels declined more rapidly and to a greater extent after transfusion with older versus fresher blood, and older blood was associated with significantly worse shock, lung injury, and mortality.

CONCLUSION

The augmented in vivo hemolysis of transfused older red blood cells (RBCs) appears to result in excess plasma CFH and iron release, which requires the presence of established infection to worsen outcome. These data suggest that transfused older RBCs increase the risks from infection in septic subjects.

Heme catabolism by heme oxygenase-1 confers host resistance to Mycobacterium infection

Heme oxygenases (HO) catalyze the rate-limiting step of heme degradation. The cytoprotective action of the inducible HO-1 isoform, encoded by the Hmox1 gene, is required for host protection against systemic infections. Here we report that upregulation of HO-1 expression in macrophages (M) is strictly required for protection against mycobacterial infection in mice. HO-1-deficient (Hmox1(-/-)) mice are more susceptible to intravenous Mycobacterium avium infection, failing to mount a protective granulomatous response and developing higher pathogen loads, than infected wild-type (Hmox1(+/+)) controls. Furthermore, Hmox1(-/-) mice also develop higher pathogen loads and ultimately succumb when challenged with a low-dose aerosol infection with Mycobacterium tuberculosis. The protective effect of HO-1 acts independently of adaptive immunity, as revealed in M. avium-infected Hmox1(-/-) versus Hmox1(+/+) SCID mice lacking mature B and T cells. In the absence of HO-1, heme accumulation acts as a cytotoxic pro-oxidant in infected M, an effect mimicked by exogenous heme administration to M. avium-infected wild-type M in vitro or to mice in vivo. In conclusion, HO-1 prevents the cytotoxic effect of heme in M, contributing critically to host resistance to Mycobacterium infection.

Bench-to-bedside review: sepsis - from the redox point of view

The pathogenesis of sepsis and its progression to multiple organ dysfunction syndrome and septic shock have been the subject of investigations for nearly half a century. Controversies still exist with regard to understanding the molecular pathophysiology of sepsis in relation to the complex roles played by reactive oxygen species, nitric oxide, complements and cytokines. In the present review we categorise the key turning points in sepsis development and outline the most probable sequence of events leading to cellular dysfunction and organ failure under septic conditions. We have applied an integrative approach in order to fuse current state-of-the-art knowledge about redox processes involving hydrogen peroxide, nitric oxide, superoxide, peroxynitrite and hydroxyl radical, which lead to mitochondrial respiratory dysfunction. Finally, from this point of view, the potential of redox therapy targeting sepsis is discussed.

The role of EPR spectroscopy in studies of the oxidative status of biological systems and the antioxidative properties of various compounds

In this era of intense study of free radicals and antioxidants, electron paramagnetic resonance (EPR) is arguably the best-suited technique for such research, particularly when considering biochemical and biological systems. No attempt was made to cover all the topics of EPR application but instead attention was restricted to two areas that are both novel and received less attention in previous reviews. In the first section, the application of EPR in assessing the oxidative status of various biological systems, using endogenous stabile paramagnetic species, such as the ascorbyl radical, semiquinone, melanin, and oxidized pigments, is addressed. The second section covers the use of EPR in the emerging field of antioxidant development, using EPR spin-trapping and spin-probing techniques. In both sections, in addition to giving an overview of the available literature, examples (mostly from the authors? recent work) are also presented in sufficient detail to illustrate how to explore the full potential of EPR. This review aims at encouraging biologists, chemists and pharmacologists interested in the redox metabolism of living systems, free radical chemistry or antioxidative properties of new drugs and natural products to take advantage of this technique for their investigations.

The effects of iron fortification on the gut microbiota in African children: a randomized controlled trial in Cote d'Ivoire

BACKGROUND

Iron is essential for the growth and virulence of many pathogenic enterobacteria, whereas beneficial barrier bacteria, such as lactobacilli, do not require iron. Thus, increasing colonic iron could select gut microbiota for humans that are unfavorable to the host.

OBJECTIVE

The objective was to determine the effect of iron fortification on gut microbiota and gut inflammation in African children.

DESIGN

In a 6-mo, randomized, double-blind, controlled trial, 6-14-y-old Ivorian children (n = 139) received iron-fortified biscuits, which contained 20 mg Fe/d, 4 times/wk as electrolytic iron or nonfortifoed biscuits. We measured changes in hemoglobin concentrations, inflammation, iron status, helminths, diarrhea, fecal calprotectin concentrations, and microbiota diversity and composition (n = 60) and the prevalence of selected enteropathogens.

RESULTS

At baseline, there were greater numbers of fecal enterobacteria than of lactobacilli and bifidobacteria (P < 0.02). Iron fortification was ineffective; there were no differences in iron status, anemia, or hookworm prevalence at 6 mo. The fecal microbiota was modified by iron fortification as shown by a significant increase in profile dissimilarity (P < 0.0001) in the iron group as compared with the control group. There was a significant increase in the number of enterobacteria (P < 0.005) and a decrease in lactobacilli (P < 0.0001) in the iron group after 6 mo. In the iron group, there was an increase in the mean fecal calprotectin concentration (P < 0.01), which is a marker of gut inflammation, that correlated with the increase in fecal enterobacteria (P < 0.05).

CONCLUSIONS

Anemic African children carry an unfavorable ratio of fecal enterobacteria to bifidobacteria and lactobacilli, which is increased by iron fortification. Thus, iron fortification in this population produces a potentially more pathogenic gut microbiota profile, and this profile is associated with increased gut inflammation. This trial was registered at controlled-trials.com as ISRCTN21782274.

Electron Paramagnetic Resonance - A Powerful Tool of Medical Biochemistry in Discovering Mechanisms of Disease and Treatment Prospects

In pathophysiological conditions related to oxidative stress, the application of selected antioxidants could have beneficial effects on human health. Electron paramagnetic resonance (EPR) spectroscopy is a technique that provides unique insight into the redox biochemistry, due to its ability to: (i) distinguish and quantify different reactive species, such as hydroxyl radical, superoxide, carbon centered radicals, hydrogen atom, nitric oxide, ascorbyl radical, melanin, and others; (ii) evaluate the antioxidative capacity of various compounds, extracts and foods; (iii) provide information on other important parameters of biological systems. A combination of EPR spectroscopy and traditional biochemical methods represents an efficient tool in the studies of disease mechanisms and antioxidative therapy prospects, providing a more complete view into the redox processes in the human organism.

Iron deficiency and infection

Iron deficiency is the most common micronutrient deficiency in the world. Children, particularly infants living in developing countries are highly vulnerable to infectious diseases. Therefore, understanding the relationship between iron deficiency and infection is of great importance. Iron deficiency is associated with impairment of innate (natural) immunity and cell mediated immunity, thereby contributing to increased risk of infections. The iron acquisition by the microbes and their virulence is determined by various host and microbial mechanisms. Altering these mechanisms might provide modes of future therapy for infectious diseases.

Serum hepcidin concentration in chronic haemodialysis patients: associations and effects of dialysis, iron and erythropoietin therapy

BACKGROUND

Hepcidin, a liver-derived peptide induced by iron overload and inflammation, is a major regulator of iron homeostasis. As hepcidin decreases gastrointestinal iron absorption and recirculation from monocytes, over-expression is associated with the development of anaemia.

METHODS

We studied the associations between circulating hepcidin levels and various laboratory parameters related to anaemia and/or inflammation in 20 patients on chronic haemodialysis. Furthermore, we determined the impact of dialysis and iron and/or erythropoietin (rhEpo) supplementation therapy on hepcidin serum concentrations. The patients were withheld from iron and rhEpo for 2 weeks before study entry. Hepcidin was measured by liquid chromatography-mass spectrometry (LC-MS/MS); serum iron and haematological parameters, cytokines and pro-hepcidin by commercially available enzyme-linked immunosorbent assays (ELISA) or standard automated methods.

RESULTS

While hepcidin levels at baseline were not correlated to pro-hepcidin, interleukin-6 or transforming growth factor-beta concentrations, we found significant associations with reticulocyte count (r = -0.55; P = 0.015), serum iron (r = 0.7; P = 0.004) and ferritin levels (r = 0.63; P = 0.004) and transferrin saturation (r = 0.69, P = 0.001). Dialysis using either a high or a low flux biocompatible dialyser resulted in a significant decrease of hepcidin concentrations, which returned to pre-dialysis values before the next dialysis session. When studying the effects of anaemia treatment, we observed a significant reduction of hepcidin levels following administration of rhEpo but not iron.

CONCLUSIONS

Hepcidin levels in stable haemodialysis patients appear to reflect systemic iron load, but not inflammation. Due to the negative association between reticulocyte counts and hepcidin, the reduction of circulating hepcidin concentrations by dialysis and/or rhEpo treatment may positively affect erythropoiesis.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Spin-trapping of oxygen free radicals in chemical and biological systems: new traps, radicals and possibilities

The choice of the spin-trap that is to be applied in any EPR study represents the crossroad between a comprehensive investigation and an "ordinary" quantification of production of radicals. So, the scope of our study was to compare the performance of different spin-traps for qualitative analysis of radical-generating systems, and their ability to recognize previously unnoticed radicals. In addition, we present a brief account of the difficulties involved in the detection of oxygen-centered radicals in chemical and biological systems accompanied by the rationale for using the EPR spin-trapping technique in quantitative studies of such reactive species. Certain technical aspects of EPR experiments related to efficient trapping of free radicals in biochemical systems are also discussed. As an example we present here results obtained using EPR spectroscopy and the spin-trap DEPMPO, which show that the Fenton reaction, as well as various biological systems generate a previously unappreciated hydrogen (*H) atom.

Ferritin levels in children with severe sepsis and septic shock

AIM

To evaluate serum ferritin level in children with severe sepsis and septic shock and its association with mortality.

METHOD

A cohort study of 36 children aged 1 month-16 years with severe sepsis or septic shock requiring intensive care was conducted. Serum ferritin levels were measured at the time of diagnosis of sepsis and a ferritin index (FI=observed serum ferritin divided by the upper limit of normal ferritin for age and gender) was calculated.

RESULTS

The median age (range) of the children was 6 (2-100) months. Ferritin was <200 ng/mL in 13 children, 200-500 ng/mL in 11 children and >500 ng/mL in 12 children. The mortality associated with these groups was 23%, 9% and 58%, respectively. A ferritin>500 ng/mL was associated with a 3.2 (1.3-7.9) relative risk of death (p=0.01). FI of 1.7 was the best cutoff value for identifying those who died. In a logistic regression analysis, ferritin level and PRISM were independently associated with mortality.

CONCLUSIONS

Ferritin is raised in children with septic shock and high ferritin level is associated with poorer outcome.

2-aminoadipic acid is a marker of protein carbonyl oxidation in the aging human skin: effects of diabetes, renal failure and sepsis

We hypothesized that the epsilon-amino group of lysine residues in longlived proteins oxidatively deaminates with age forming the carbonyl compound, allysine (alpha-aminoadipic acid-delta-semialdehyde), which can further oxidize into 2-aminoadipic acid. In the present study, we measured both products in insoluble human skin collagen from n=117 individuals of age range 10-90 years, of which n=61 and n=56 were non-diabetic and diabetic respectively, and a total of n=61 individuals had either acute or chronic renal failure. Allysine was reduced by borohydride into 6-hydroxynorleucine and both products were measured in acid hydrolysates by selective ion monitoring gas chromatography (GC)-MS. The results showed that 2-aminoadipic acid (P<0.0001), but not 6-hydroxynorleucine (P=0.14), significantly increased with age reaching levels of 1 and 0.3 mmol/mol lysine at late age respectively. Diabetes in the absence of renal failure significantly (P<0.0001) increased 2-aminoadipic acid up to <3 mmol/mol, but not 6-hydroxynorleucine (levels<0.4 mmol/mol, P=0.18). Renal failure even in the absence of diabetes markedly increased levels reaching up to <0.5 and 8 mmol/mol for 6-hydroxynorleucine and 2-aminoadipic acid respectively. Septicaemia significantly (P<0.0001) elevated 2-aminoadipic acid in non-diabetic, but not diabetic individuals, and mildly correlated with other glycoxidation markers, carboxymethyl-lysine and the methylglyoxal-derived products, carboxyethyl-lysine, argpyrimidine and MODIC (methylglyoxal-derived imidazolium cross-link). These results provide support for the presence of metal-catalysed oxidation (the Suyama pathway) in diabetes and the possible activation of myeloperoxidase during sepsis. We conclude that 2-aminoadipic acid is a more reliable marker for protein oxidation than its precursor, allysine. Its mechanism of formation in each of these conditions needs to be elucidated.

Host-pathogen interactions: the role of iron

Iron is essential for both host and pathogen, and complex systems of acquisition and utilization have evolved in competition. Our increasing knowledge of the basic mechanisms of homeostasis and their adaptation during deficiency, overload, and infection indicate that iron is a key regulator of host pathogen interactions. This review concentrated on the clinical and public health aspects of the interaction between the iron acquisition mechanisms of select pathogens of public health importance with host iron homeostasis. Knowledge of these interactions is essential in assessing likely morbidity responses to supplementation.

Erythropoietic response to two epoetin alfa regimens in critically ill patients: a pilot study

STUDY OBJECTIVE

To compare the erythropoietic responses and tolerability of two recombinant human erythropoietin (EPO) regimens.

DESIGN

Prospective, open-label, multicenter study.

SETTING

Three multidisciplinary intensive care units in Québec, Canada.

PATIENTS

Sixty critically ill patients.

INTERVENTION

The first 30 patients received EPO 40,000 U/week (group A); the next 30 received 40,000 U twice/week (group B).

MEASUREMENTS AND MAIN RESULTS

Percent change from baseline in reticulocyte count and hemoglobin concentration were evaluated in both groups on study days 7 and 14. The numbers of adverse events were also compared between the two groups. No statistically significant differences were found in the results between the two groups.

CONCLUSION

Although the study had limitations, it suggested that EPO 40,000 U twice/week did not increase or sustain stimulation of the erythropoietic response compared with EPO 40,000 U/week in critically ill patients.

Iron-withholding strategy in innate immunity

The knowledge of how organisms fight infections has largely been built upon the ability of host innate immune molecules to recognize microbial determinants. Although of overwhelming importance, pathogen recognition is but only one of the facets of innate immunity. A primitive yet effective antimicrobial mechanism which operates by depriving microbial organisms of their nutrients has been brought into the forefront of innate immunity once again. Such a tactic is commonly referred to as the iron-withholding strategy of innate immunity. In this review, we introduce various vertebrate iron-binding proteins and their invertebrate homologues, so as to impress upon readers an obscured arm of innate immune defense. An excellent comprehension of the mechanics of innate immunity paves the way for the possibility that novel antimicrobial therapeutics may emerge one day to overcome the prevalent antibiotic resistance in bacteria.

Sortases and the art of anchoring proteins to the envelopes of gram-positive bacteria

The cell wall envelopes of gram-positive bacteria represent a surface organelle that not only functions as a cytoskeletal element but also promotes interactions between bacteria and their environment. Cell wall peptidoglycan is covalently and noncovalently decorated with teichoic acids, polysaccharides, and proteins. The sum of these molecular decorations provides bacterial envelopes with species- and strain-specific properties that are ultimately responsible for bacterial virulence, interactions with host immune systems, and the development of disease symptoms or successful outcomes of infections. Surface proteins typically carry two topogenic sequences, i.e., N-terminal signal peptides and C-terminal sorting signals. Sortases catalyze a transpeptidation reaction by first cleaving a surface protein substrate at the cell wall sorting signal. The resulting acyl enzyme intermediates between sortases and their substrates are then resolved by the nucleophilic attack of amino groups, typically provided by the cell wall cross bridges of peptidoglycan precursors. The surface protein linked to peptidoglycan is then incorporated into the envelope and displayed on the microbial surface. This review focuses on the mechanisms of surface protein anchoring to the cell wall envelope by sortases and the role that these enzymes play in bacterial physiology and pathogenesis.