Hemochromatosis and Vibrio vulnificus wound infections

Hypoferremia of inflammation: Innate host defense against infections

Iron is an essential nutrient for microbes, plants and animals. Multicellular organisms have evolved multiple strategies to control invading microbes by restricting microbial access to iron. Hypoferremia of inflammation is a rapidly-acting organismal response that prevents the formation of iron species that would be readily accessible to microbes. This review takes an evolutionary perspective to explore the mechanisms and host defense function of hypoferremia of inflammation and its clinical implications.

[Oral microbiota and liver]

The liver has many important biological functions for the body, as it is involved in the storage and distribution of nutrients (carbohydrates to glycogen, lipids to triglycerides), the digestion of fats, the synthesis of blood proteins, and the detoxification of alcohol and drugs. The liver can be affected by various diseases such as viral or drug-induced hepatitis, fibrosis and cirrhosis, in which damaged hepatocytes are progressively replaced by scar tissue.

Clinical features and treatment outcomes of Vibrio vulnificus infection in the coastal city of Ningbo, China

Background

Vibrio vulnificus is a gram-negative, opportunistic pathogen common to warm waters worldwide. Human V. vulnificus infection is rare and typically affects those residing in coastal areas during the summer months, but it causes rapid deterioration and is fatal.

Methods

The medical records of six patients with sepsis caused by V. vulnificus infection who were treated at the First Affiliated Hospital of Ningbo University from 2020 to 2022 were retrospectively reviewed. The patient demographics, clinical symptoms, laboratory test results, treatments, and outcomes are summarized.

Results

Vibrio vulnificus infection was confirmed by blood or pus culture, 16S ribosomal DNA sequencing, and metagenomic next-generation sequencing. All six patients were male with pre-existing liver diseases and two reported consuming seafood before the onset of symptoms. Of the six patients, four succumbed to the disease, two recovered, and one underwent leg amputation.

Conclusion

Vibrio vulnificus infection progresses rapidly and is highly fatal, thus prompt and aggressive treatment is necessary. Vibrio vulnificus infection should be considered in older (>40 years) patients with a history of liver disease and recent consumption of seafood or exposure to seawater, especially those residing in coastal areas during the summer months.

EASL Clinical Practice Guidelines on haemochromatosis

Haemochromatosis is characterised by elevated transferrin saturation (TSAT) and progressive iron loading that mainly affects the liver. Early diagnosis and treatment by phlebotomy can prevent cirrhosis, hepatocellular carcinoma, diabetes, arthropathy and other complications. In patients homozygous for p.Cys282Tyr in HFE, provisional iron overload based on serum iron parameters (TSAT >45% and ferritin >200 μg/L in females and TSAT >50% and ferritin >300 μg/L in males and postmenopausal women) is sufficient to diagnose haemochromatosis. In patients with high TSAT and elevated ferritin but other HFE genotypes, diagnosis requires the presence of hepatic iron overload on MRI or liver biopsy. The stage of liver fibrosis and other end-organ damage should be carefully assessed at diagnosis because they determine disease management. Patients with advanced fibrosis should be included in a screening programme for hepatocellular carcinoma. Treatment targets for phlebotomy are ferritin <50 μg/L during the induction phase and <100 μg/L during the maintenance phase.

Role of Iron and Iron Overload in the Pathogenesis of Invasive Fungal Infections in Patients with Hematological Malignancies

Iron is an essential trace metal necessary for the reproduction and survival of fungal pathogens. The latter have developed various mechanisms to acquire iron from their mammalian hosts, with whom they participate in a continuous struggle for dominance over iron. Invasive fungal infections are an important problem in the treatment of patients with hematological malignancies, and they are associated with significant morbidity and mortality. The diagnosis of invasive clinical infections in these patients is complex, and the treatment, which must occur as early as possible, is difficult. There are several studies that have shown a possible link between iron overload and an increased susceptibility to infections. This link is also relevant for patients with hematological malignancies and for those treated with allogeneic hematopoietic stem cell transplantation. The role of iron and its metabolism in the virulence and pathogenesis of various invasive fungal infections is intriguing, and so far, there is some evidence linking invasive fungal infections to iron or iron overload. Clarifying the possible association of iron and iron overload with susceptibility to invasive fungal infections could be important for a better prevention and treatment of these infections in patients with hematological malignancies.

A Rare Case of Aeromonas Hydrophila Infection in a Patient With Hereditary Hemochromatosis

Hereditary hemochromatosis (HH) is a genetic disorder characterized by abnormal iron metabolism, which leads to elevated serum iron levels and iron tissue deposition. This can suppress immunity and increase pathogen virulence, increasing the susceptibility to serious infections. We present a case of a 76-year-old man with a history of HH, who was later found to have pancreatic adenocarcinoma. He underwent a pancreaticoduodenectomy that was complicated by an unusual Aeromonas hydrophila septicemia that leads to death. It is important for physicians to appreciate the potential for highly unusual and life-threatening infections in the management of patients with HH.

Pathological mechanisms of abnormal iron metabolism and mitochondrial dysfunction in systemic lupus erythematosus

Introduction: Systemic lupus erythematosus [SLE] is a chronic, autoimmune condition characterized by the formation of autoantibodies directed against nuclear components and by oxidative stress. Recently, a number of studies have demonstrated the essential role of iron in the immune response and there is growing evidence that abnormal iron homeostasis can occur in the chronic inflammatory state seen in SLE. Not only is iron vital for hematopoiesis, it is also important for a number of other key physiological processes, in particular in maintaining healthy mitochondrial function.Areas covered: In this review, we highlight the latest understanding with regards to how patients with SLE may be at risk of cellular iron depletion as a result of both absolute and functional iron deficiency. Furthermore, we aim to explain the latest evidence of mitochondrial dysfunction in the pathogenesis of the disease.Expert opinion: Growing evidence suggests that both abnormal iron homeostasis and subsequent mitochondrial dysfunction can impair effector immune cell function. Through a greater understanding of these abnormalities, therapeutic options that directly target iron and mitochondria may ultimately represent novel treatment targets that may translate into clinical care of patients with SLE in the near future.

Infections in Cirrhosis: A Guide for the Clinician

Cirrhosis contributes significantly to morbidity and mortality worldwide. Infections in patients with cirrhosis are common and significantly impact health-related quality of life. As our understanding of immune dysfunction associated with cirrhosis grows and as rates of drug-resistant organisms increase, the management of infections in cirrhosis has become increasingly nuanced. In this review, we discuss the current understanding of cirrhosis-associated immune deficiency, review the most common infections in patients with cirrhosis, and highlight techniques for the general clinician in the prevention and treatment of infections in this high-risk population.

Prognostic Factors of Mortality in Vibrio vulnificus Sepsis and Soft Tissue Infections: Meta-Analysis

Background: Vibrio vulnificus is a rare but life-threatening infection that effects the population near warm coastal areas. This infection could be fulminant and rapidly progress to severe sepsis and necrotizing soft tissue infection. Early diagnosis and treatment are critical to saving patients' lives. With multiple studies reporting discrepancies in prognostic factors and different treatment protocols, we aimed through this meta-analysis to assess these factors and protocols and the impact on the outcome of the infection. Materials and Methods: In accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic search of PubMed, Embase, and Cochrane Library databases by two independent reviewers was reported. Studies evaluating prognostic factors and treatment outcomes of Vibrio vulnificus infections were included. Comprehensive Meta-Analysis, version 3.0 was used. Results: Two hundred eleven studies were identified. Of those, eight studies met our inclusion criteria. The following factors on presentation were associated with higher mortality rates; concomitant liver disease (odds ratio [OR], 4.38; 95% confidence interval [CI], 2.43-7.87; p < 0.001), renal disease (OR, 3.90; 95% CI, 1.37-11.12; p = 0.011), septic shock (OR, 2.82; 95% CI, 1.84-4.31; p < 0.001), higher Acute Physiology and Chronic Health Evaluation (APACHE) II score (OR, 3.40; 95% CI, 2.26-5.12; p < 0.001), elevated band cells count (OR, 2.61; 95% CI, 1.13-6.0; p = 0.024), hypoalbuminemia (OR, 3.41; 95% CI, 1.58-7.35; p = 0.002), and infection involving multiple limbs (OR, 4.36; 95% CI, 1.72-11.07; p = 0.002). Interestingly, different antibiotic regimens did not have any impact on outcomes, however, delayed surgical intervention after the first 12 or 24 hours was associated with higher mortality rates (OR, 2.64; 95% CI, 1.39-5.0; p = 0.003 and OR, 2.99; 95% CI, 1.54-5.78; p = 0.001, respectively). Conclusion: The presence of liver or renal disease, higher APACHE II scores, septic shock, hypoalbuminemia, or elevated band cell on presentation should alert the physician to the higher risk of mortality. Different antibiotic regimens did not impact the outcomes in these patients and delayed surgical intervention is associated with worsening of mortality.

Managing Genetic Hemochromatosis: An Overview of Dietary Measures, Which May Reduce Intestinal Iron Absorption in Persons With Iron Overload

Genetic hemochromatosis causes iron overload by excess absorption of dietary iron, due to a decreased expression of hepcidin. The objective was to elaborate dietary recommendations that can reduce intestinal iron absorption in hemochromatosis patients, based on our present knowledge of the iron contained in nutrients and the mechanisms of iron uptake. This is a narrative review. Literature search in PubMed and Google Scholar of papers dealing with iron absorption from the diet was conducted. Most important proposed dietary recommendations are: 1) Choose a varied vegetarian, semi-vegetarian or flexitarian diet. A “veggie-lacto-ovo-poultry-pescetarian” diet seems optimal. Avoid iron enriched foods and iron supplements. 2) Eat many vegetables and fruits, at least 600 g per day. Choose protein rich pulses and legumes (e.g., kidney- and soya beans). Fresh fruits should be eaten between meals. 3) Abstain from red meat from mammals and choose the lean, white meat from poultry. Avoid processed meat, offal and blood containing foods. Eat no more than 200 g meat from poultry per week. Choose fish, eggs, vegetables and protein rich legumes the other days. Eat fish two to four times a week as main course, 350 - 500 g fish per week, of which half should be fat fish. 4) Choose whole grain products in cereals and bread. Avoid iron enriched grains. Choose non-sourdough, yeast-fermented bread with at least 50% whole grain. 5) Choose vegetable oils, and low-fat dairy products. 6) Eat less sugar and salt. Choose whole foods and foods with minimal processing and none or little added sugar or salt. 7) Quench your thirst in water. Drink green- or black tea, coffee, or low-fat milk with the meals, alternatively water or non-alcoholic beer. Fruit juices must be consumed between meals. Abstain from alcoholic beverages. Drink soft drinks, non-alcoholic beer, or non-alcoholic wine instead. These advices are close to the official Danish dietary recommendations in 2021. In the management of hemochromatosis, dietary modifications that lower iron intake and decrease iron bioavailability may provide additional measures to reduce iron uptake from the foods and reduce the number of phlebotomies. However, there is a need for large, prospective, randomized studies that specifically evaluate the effect of dietary interventions.

Critical Role for Molecular Iron in Coxiella burnetii Replication and Viability

Coxiella burnetii, the causative agent of Query (Q) fever in humans, is a highly infectious obligate intracellular bacterium. Following uptake into a host cell, C. burnetii replicates within a phagolysosome-derived compartment referred to as the Coxiella-containing vacuole (CCV). During infection, C. burnetii exhibits tropism for tissues related to iron storage and recycling (e.g., the liver and splenic red pulp), suggesting that pathogen physiology is linked to host iron metabolism. Iron has been described to have a limited role in C. burnetii virulence regulation, despite evidence that C. burnetii -infected host cells increase expression of transferrin receptors, thereby suggesting that active iron acquisition by the bacterium occurs upon infection. Through the use of host cell-free culture, C. burnetii was separated from the host cell in order to directly assess the role of different forms of iron in C. burnetii replication and viability, and therefore virulence. Results indicate that C. burnetii tolerates molecular iron over a broad concentration range (i.e., ∼0.001 to 1 mM) and undergoes gross loss of viability upon iron starvation. C. burnetii protein synthesis and energy metabolism, however, occur nearly uninhibited under iron concentrations not permissive to replication. Despite the apparent absence of genes related to acquisition of host-associated iron-containing proteins, C. burnetii replication is supported by hemoglobin, transferrin, and ferritin, likely due to release of iron from such proteins under acidic conditions. Moreover, chelation of host iron pools inhibited pathogen replication during infection of cultured cells.IMPORTANCE Host organisms restrict the availability of iron to invading pathogens in order to reduce pathogen replication. To counteract the host's response to infection, bacteria can rely on redundant mechanisms to obtain biologically diverse forms of iron during infection. C. burnetii appears specifically dependent on molecular iron for replication and viability and exhibits a response to iron akin to bacteria that colonize iron-rich environments. Physiological adaptation of C. burnetii to the unique acidic and degradative environment of the CCV is consistent with access of this pathogen to molecular iron.

Innate Nutritional Immunity

Iron (Fe) is an essential micronutrient for both microbes and their hosts. The biologic importance of Fe derives from its inherent ability to act as a universal redox catalyst, co-opted in a variety of biochemical processes critical to maintain life. Animals evolved several mechanisms to retain and limit Fe availability to pathogenic microbes, a resistance mechanism termed "nutritional immunity." Likewise, pathogenic microbes coevolved to deploy diverse and efficient mechanisms to acquire Fe from their hosts and in doing so overcome nutritional immunity. In this review, we discuss how the innate immune system regulates Fe metabolism to withhold Fe from pathogenic microbes and how strategies used by pathogens to acquire Fe circumvent these resistance mechanisms.

Vibrio vulnificus infection: a persistent threat to public health

Vibrio vulnificus is a gram-negative bacterium that can cause serious, potentially fatal infections. V. vulnificus causes three distinct syndromes: an overwhelming primary septicemia caused by consuming contaminated seafood, wound infections acquired when an open wound is exposed to contaminated warm seawater, and gastrointestinal tract-limited infections. Case-fatality rates are higher than 50% for primary septicemia, and death typically occurs within 72 hours of hospitalization. Risk factors for V. vulnificus infection include chronic liver disease, alcoholism, and hematological disorders. When V. vulnificus infection is suspected, appropriate antibiotic treatment and surgical interventions should be performed immediately. Third-generation cephalosporin with doxycycline, or quinolone with or without third-generation cephalosporin, may be potential treatment options for patients with V. vulnificus infection.

Tuning the Anti(myco)bacterial Activity of 3-Hydroxy-4-pyridinone Chelators through Fluorophores

Controlling the sources of Fe available to pathogens is one of the possible strategies that can be successfully used by novel antibacterial drugs. We focused our interest on the design of chelators to address Mycobacterium avium infections. Taking into account the molecular structure of mycobacterial siderophores and considering that new chelators must be able to compete for Fe(III), we selected ligands of the 3-hydroxy-4-pyridinone class to achieve our purpose. After choosing the type of chelating unit it was also our objective to design chelators that could be monitored inside the cell and for that reason we designed chelators that could be functionalized with fluorophores. We didn’t realize at the time that the incorporation a fluorophore, to allow spectroscopic detection, would be so relevant for the antimycobacterial effect or to determine the affinity of the chelators towards biological membranes. From a biophysical perspective, this is a fascinating illustration of the fact that functionalization of a molecule with a particular label may lead to a change in its membrane permeation properties and result in a dramatic change in biological activity. For that reason we believe it is interesting to give a critical account of our entire work in this area and justify the statement “to label means to change”. New perspectives regarding combined therapeutic approaches and the use of rhodamine B conjugates to target closely related problems such as bacterial resistance and biofilm production are also discussed.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

Haemochromatosis

Haemochromatosis is defined as systemic iron overload of genetic origin, caused by a reduction in the concentration of the iron regulatory hormone hepcidin, or a reduction in hepcidin-ferroportin binding. Hepcidin regulates the activity of ferroportin, which is the only identified cellular iron exporter. The most common form of haemochromatosis is due to homozygous mutations (specifically, the C282Y mutation) in HFE, which encodes hereditary haemochromatosis protein. Non-HFE forms of haemochromatosis due to mutations in HAMP, HJV or TFR2 are much rarer. Mutations in SLC40A1 (also known as FPN1; encoding ferroportin) that prevent hepcidin-ferroportin binding also cause haemochromatosis. Cellular iron excess in HFE and non-HFE forms of haemochromatosis is caused by increased concentrations of plasma iron, which can lead to the accumulation of iron in parenchymal cells, particularly hepatocytes, pancreatic cells and cardiomyocytes. Diagnosis is noninvasive and includes clinical examination, assessment of plasma iron parameters, imaging and genetic testing. The mainstay therapy is phlebotomy, although iron chelation can be used in some patients. Hepcidin supplementation might be an innovative future approach.

Barrier-tissue macrophages: functional adaptation to environmental challenges

Macrophages are found throughout the body, where they have crucial roles in tissue development, homeostasis and remodeling, as well as being sentinels of the innate immune system that can contribute to protective immunity and inflammation. Barrier tissues, such as the intestine, lung, skin and liver, are exposed constantly to the outside world, which places special demands on resident cell populations such as macrophages. Here we review the mounting evidence that although macrophages in different barrier tissues may be derived from distinct progenitors, their highly specific properties are shaped by the local environment, which allows them to adapt precisely to the needs of their anatomical niche. We discuss the properties of macrophages in steady-state barrier tissues, outline the factors that shape their differentiation and behavior and describe how macrophages change during protective immunity and inflammation.

Macrophages and Iron Metabolism

Macrophages exert multiple important roles in iron metabolism. As scavengers, splenic and hepatic macrophages phagocytize and degrade senescent and damaged erythrocytes to recycle iron, predominantly for the production of hemoglobin in new erythrocytes. Splenic red pulp macrophages are specialized for iron recycling, with increased expression of proteins for the uptake of hemoglobin, breakdown of heme, and export of iron. Iron release from macrophages is closely regulated by the interaction of hepcidin, a peptide hormone produced by hepatocytes, with the macrophage iron exporter ferroportin. As regulators and effectors of antimicrobial host defense, macrophages employ multiple mechanisms to contain microbial infections by depriving microbes of iron. Macrophages also have an important trophic role in the bone marrow, supporting efficient erythropoiesis.

The hemochromatosis protein HFE 20 years later: An emerging role in antigen presentation and in the immune system

Introduction

Since its discovery, the hemochromatosis protein HFE has been primarily defined by its role in iron metabolism and homeostasis, and its involvement in the genetic disease termed hereditary hemochromatosis (HH). While HH patients are typically afflicted by dysregulated iron levels, many are also affected by several immune defects and increased incidence of autoimmune diseases that have thereby implicated HFE in the immune response. Growing evidence has supported an immunological role for HFE with recent studies describing HFE specifically as it relates to MHC I antigen presentation.

Methods/Results

Here, we present a comprehensive overview of the relationship between iron metabolism, HFE, and the immune system to better understand the origin and cause of immune defects in HH patients. We further describe the role of HFE in MHC I antigen presentation and its potential to impair autoimmune responses in homeostatic conditions, a mechanism which may be exploited by tumors to evade immune surveillance.

Conclusion

Overall, this increased understanding of the role of HFE in the immune response sets the stage for better treatment and management of HH and other iron‐related diseases, as well as of the immune defects related to this condition.

"Pumping iron"-how macrophages handle iron at the systemic, microenvironmental, and cellular levels

Macrophages reside in virtually every organ. First arising during embryogenesis, macrophages replenish themselves in the adult through a combination of self-renewal and influx of bone marrow-derived monocytes. As large phagocytic cells, macrophages participate in innate immunity while contributing to tissue-specific homeostatic functions. Among the key metabolic tasks are senescent red blood cell recycling, free heme detoxification, and provision of iron for de novo hemoglobin synthesis. While this systemic mechanism involves the shuttling of iron between spleen, liver, and bone marrow through the concerted function of defined macrophage populations, similar circuits appear to exist within the microenvironment of other organs. The high turnover of iron is the prerequisite for continuous erythropoiesis and tissue integrity but challenges macrophages’ ability to maintain cellular iron homeostasis and immune function.

This review provides a brief overview of systemic, microenvironmental, and cellular aspects of macrophage iron handling with a focus on exciting and unresolved questions in the field.

Diabetes in HFE Hemochromatosis

Diabetes in whites of European descent with hemochromatosis was first attributed to pancreatic siderosis. Later observations revealed that the pathogenesis of diabetes in HFE hemochromatosis is multifactorial and its clinical manifestations are heterogeneous. Increased type 2 diabetes risk in HFE hemochromatosis is associated with one or more factors, including abnormal iron homeostasis and iron overload, decreased insulin secretion, cirrhosis, diabetes in first-degree relatives, increased body mass index, insulin resistance, and metabolic syndrome. In p.C282Y homozygotes, serum ferritin, usually elevated at hemochromatosis diagnosis, largely reflects body iron stores but not diabetes risk. In persons with diabetes type 2 without hemochromatosis diagnoses, serum ferritin levels are higher than those of persons without diabetes, but most values are within the reference range. Phlebotomy therapy to achieve iron depletion does not improve diabetes control in all persons with HFE hemochromatosis. The prevalence of type 2 diabetes diagnosed today in whites of European descent with and without HFE hemochromatosis is similar. Routine iron phenotyping or HFE genotyping of patients with type 2 diabetes is not recommended. Herein, we review diabetes in HFE hemochromatosis and the role of iron in diabetes pathogenesis in whites of European descent with and without HFE hemochromatosis.

Prevalence of Biofilm Formation and Wide Distribution of Virulence Associated Genes among Vibrio spp. Strains Isolated from the Monastir Lagoon, Tunisia

In the current study, 65 Vibrio spp. were isolated from the Monastir lagoon water, were characterized phenotypically and genotypically. In addition, we looked for the presence of three Vibrio parahaemolyticus virulence genes (tlh, trh and tdh) and ten Vibrio cholerae virulence genes (ctxA, vpi, zot, ace, toxR, toxT, tosS, toxRS, tcpA and cpP). We also investigated the antibiotic susceptibilities and the adherence ability of the identified strains to abiotic material and to biotic surfaces. The cytotoxicity activity against HeLa and Vero cell lines were also carried out for all tested strains. All Vibrio isolates were identified to the species level and produced several hydrolytic exoenzymes. The results also revealed that all strains were expressing high rates of resistance to tested antibiotics. The minimum inhibitory concentration (MIC) values showed that tetracycline and chloramphenicol were the most effective antibiotics against the tested bacteria. Vibrio alginolyticus and V. cholerae species were the most adhesive strains to both biotic and abiotic surfaces. Besides, V. alginolyticus isolates has the high levels of recombination of genes encoding V. cholerae and V. parahaemolyticus virulence factors. In vitro cytotoxic activities of several Vibrio extracellular product were also observed among HeLa and Vero cells.

Metabolic crosstalk between host and pathogen: sensing, adapting and competing

Our understanding of bacterial pathogenesis is dominated by the cell biology of the host-pathogen interaction. However, the majority of metabolites that are used in prokaryotic and eukaryotic physiology and signalling are chemically similar or identical. Therefore, the metabolic crosstalk between pathogens and host cells may be as important as the interactions between bacterial effector proteins and their host targets. In this Review we focus on host-pathogen interactions at the metabolic level: chemical signalling events that enable pathogens to sense anatomical location and the local physiology of the host; microbial metabolic pathways that are dedicated to circumvent host immune mechanisms; and a few metabolites as central points of competition between the host and bacterial pathogens.

Iron homeostasis in host defence and inflammation

Iron is an essential trace element for multicellular organisms and nearly all microorganisms. Although iron is abundant in the environment, common forms of iron are minimally soluble and therefore poorly accessible to biological organisms. Microorganisms entering a mammalian host face multiple mechanisms that further restrict their ability to obtain iron and thereby limit their pathogenicity. Iron levels also modulate host defence, as iron content in macrophages regulates their cytokine production. Here, we review recent advances that highlight the role of systemic and cellular iron-regulating mechanisms in protecting hosts from infection, emphasizing aspects that are applicable to human health and disease.

Strategies of Vibrio parahaemolyticus to acquire nutritional iron during host colonization

Iron is an essential element for the growth and development of virtually all living organisms. As iron acquisition is critical for the pathogenesis, a host defense strategy during infection is to sequester iron to restrict the growth of invading pathogens. To counteract this strategy, bacteria such as Vibrio parahaemolyticus have adapted to such an environment by developing mechanisms to obtain iron from human hosts. This review focuses on the multiple strategies employed by V. parahaemolyticus to obtain nutritional iron from host sources. In these strategies are included the use of siderophores and xenosiderophores, proteases and iron-protein receptor. The host sources used by V. parahaemolyticus are the iron-containing proteins transferrin, hemoglobin, and hemin. The implications of iron acquisition systems in the virulence of V. parahaemolyticus are also discussed.

Individuality, phenotypic differentiation, dormancy and 'persistence' in culturable bacterial systems: commonalities shared by environmental, laboratory, and clinical microbiology

For bacteria, replication mainly involves growth by binary fission. However, in a very great many natural environments there are examples of phenotypically dormant, non-growing cells that do not replicate immediately and that are phenotypically 'nonculturable' on media that normally admit their growth. They thereby evade detection by conventional culture-based methods. Such dormant cells may also be observed in laboratory cultures and in clinical microbiology. They are usually more tolerant to stresses such as antibiotics, and in clinical microbiology they are typically referred to as 'persisters'. Bacterial cultures necessarily share a great deal of relatedness, and inclusive fitness theory implies that there are conceptual evolutionary advantages in trading a variation in growth rate against its mean, equivalent to hedging one's bets. There is much evidence that bacteria exploit this strategy widely. We here bring together data that show the commonality of these phenomena across environmental, laboratory and clinical microbiology. Considerable evidence, using methods similar to those common in environmental microbiology, now suggests that many supposedly non-communicable, chronic and inflammatory diseases are exacerbated (if not indeed largely caused) by the presence of dormant or persistent bacteria (the ability of whose components to cause inflammation is well known). This dormancy (and resuscitation therefrom) often reflects the extent of the availability of free iron. Together, these phenomena can provide a ready explanation for the continuing inflammation common to such chronic diseases and its correlation with iron dysregulation. This implies that measures designed to assess and to inhibit or remove such organisms (or their access to iron) might be of much therapeutic benefit.

Individuality, phenotypic differentiation, dormancy and 'persistence' in culturable bacterial systems: commonalities shared by environmental, laboratory, and clinical microbiology

For bacteria, replication mainly involves growth by binary fission. However, in a very great many natural environments there are examples of phenotypically dormant, non-growing cells that do not replicate immediately and that are phenotypically 'nonculturable' on media that normally admit their growth. They thereby evade detection by conventional culture-based methods. Such dormant cells may also be observed in laboratory cultures and in clinical microbiology. They are usually more tolerant to stresses such as antibiotics, and in clinical microbiology they are typically referred to as 'persisters'. Bacterial cultures necessarily share a great deal of relatedness, and inclusive fitness theory implies that there are conceptual evolutionary advantages in trading a variation in growth rate against its mean, equivalent to hedging one's bets. There is much evidence that bacteria exploit this strategy widely. We here bring together data that show the commonality of these phenomena across environmental, laboratory and clinical microbiology. Considerable evidence, using methods similar to those common in environmental microbiology, now suggests that many supposedly non-communicable, chronic and inflammatory diseases are exacerbated (if not indeed largely caused) by the presence of dormant or persistent bacteria (the ability of whose components to cause inflammation is well known). This dormancy (and resuscitation therefrom) often reflects the extent of the availability of free iron. Together, these phenomena can provide a ready explanation for the continuing inflammation common to such chronic diseases and its correlation with iron dysregulation. This implies that measures designed to assess and to inhibit or remove such organisms (or their access to iron) might be of much therapeutic benefit.

Nramp1 and Other Transporters Involved in Metal Withholding during Infection

During the course of infection, many natural defenses are set up along the boundaries of the host-pathogen interface. Key among these is the host response to withhold metals to restrict the growth of invading microbes. This simple act of nutritional warfare, starving the invader of an essential element, is an effective means of limiting infection. The physiology of metal withholding is often referred to as "nutritional immunity," and the mechanisms of metal transport that contribute to this host response are the focus of this review.

Metal limitation and toxicity at the interface between host and pathogen

Metals are required cofactors for numerous fundamental processes that are essential to both pathogen and host. They are coordinated in enzymes responsible for DNA replication and transcription, relief from oxidative stress, and cellular respiration. However, excess transition metals can be toxic due to their ability to cause spontaneous, redox cycling and disrupt normal metabolic processes. Vertebrates have evolved intricate mechanisms to limit the availability of some crucial metals while concurrently flooding sites of infection with antimicrobial concentrations of other metals. To compete for limited metal within the host while simultaneously preventing metal toxicity, pathogens have developed a series of metal regulatory, acquisition, and efflux systems. This review will cover the mechanisms by which pathogenic bacteria recognize and respond to host-induced metal scarcity and toxicity.

Systemic iron homeostasis

The iron hormone hepcidin and its receptor and cellular iron exporter ferroportin control the major fluxes of iron into blood plasma: intestinal iron absorption, the delivery of recycled iron from macrophages, and the release of stored iron from hepatocytes. Because iron losses are comparatively very small, iron absorption and its regulation by hepcidin and ferroportin determine total body iron content. Hepcidin is in turn feedback-regulated by plasma iron concentration and iron stores, and negatively regulated by the activity of erythrocyte precursors, the dominant consumers of iron. Hepcidin and ferroportin also play a role in host defense and inflammation, and hepcidin synthesis is induced by inflammatory signals including interleukin-6 and activin B. This review summarizes and discusses recent progress in molecular characterization of systemic iron homeostasis and its disorders, and identifies areas for further investigation.

The skin: a mirror to the gut

INTRODUCTION

This review discusses the diseases with involvement of both skin and gut. GI manifestations of vesicobullous disorders and systemic diseases and syndromes involving skin and gut, dermatologic manifestations of inflammatory bowel disease (IBD), polyposis syndromes, and GI malignancies have been discussed. Diagnostic and treatment approaches towards these disorders are summarized.

CONCLUSIONS

Interaction of the skin and gut has always been an area of inquisitiveness. Gastrointestinal (GI) tract can be involved in dermatological disorders or GI diseases can have a dermatological manifestation.

Macrophages and systemic iron homeostasis

As a principal aspect of their scavenging function, splenic and hepatic macrophages phagocytize and degrade senescent and damaged erythrocytes to recover iron, mainly for the production of hemoglobin in new erythrocytes but also for other carriers and enzymes requiring iron. Splenic red pulp macrophages are specialized for iron recycling with increased expression of proteins for the uptake of hemoglobin, breakdown of heme and the export of iron. In humans, recycling macrophages contribute the majority of the iron flux into extracellular fluid, exceeding the contribution of dietary iron absorption and release of stored iron from hepatocytes. Iron release from macrophages is closely regulated by the interaction of hepcidin, a peptide hormone produced by hepatocytes, with the macrophage iron exporter ferroportin. In addition to their homeostatic role, macrophages employ multiple mechanisms to contain microbial infections by depriving microbes of iron. This review discusses the iron-scavenging function of macrophages in the context of iron homeostasis and host defense.

Metal ion acquisition in Staphylococcus aureus: overcoming nutritional immunity

Transition metals are essential nutrients to virtually all forms of life, including bacterial pathogens. In Staphylococcus aureus, metal ions participate in diverse biochemical processes such as metabolism, DNA synthesis, regulation of virulence factors, and defense against oxidative stress. As an innate immune response to bacterial infection, vertebrate hosts sequester transition metals in a process that has been termed "nutritional immunity." To successfully infect vertebrates, S. aureus must overcome host sequestration of these critical nutrients. The objective of this review is to outline the current knowledge of staphylococcal metal ion acquisition systems, as well as to define the host mechanisms of nutritional immunity during staphylococcal infection.

Host iron withholding demands siderophore utilization for Candida glabrata to survive macrophage killing

The fungal pathogen Candida glabrata has risen from an innocuous commensal to a major human pathogen that causes life-threatening infections with an associated mortality rate of up to 50%. The dramatic rise in the number of immunocompromised individuals from HIV infection, tuberculosis, and as a result of immunosuppressive regimens in cancer treatment and transplant interventions have created a new and hitherto unchartered niche for the proliferation of C. glabrata. Iron acquisition is a known microbial virulence determinant and human diseases of iron overload have been found to correlate with increased bacterial burden. Given that more than 2 billion people worldwide suffer from iron deficiency and that iron overload is one of the most common single-gene inherited diseases, it is important to understand whether host iron status may influence C. glabrata infectious disease progression. Here we identify Sit1 as the sole siderophore-iron transporter in C. glabrata and demonstrate that siderophore-mediated iron acquisition is critical for enhancing C. glabrata survival to the microbicidal activities of macrophages. Within the Sit1 transporter, we identify a conserved extracellular SIderophore Transporter Domain (SITD) that is critical for siderophore-mediated ability of C. glabrata to resist macrophage killing. Using macrophage models of human iron overload disease, we demonstrate that C. glabrata senses altered iron levels within the phagosomal compartment. Moreover, Sit1 functions as a determinant for C. glabrata to survive macrophage killing in a manner that is dependent on macrophage iron status. These studies suggest that host iron status is a modifier of infectious disease that modulates the dependence on distinct mechanisms of microbial Fe acquisition.

Candida glabrata is a major human pathogen due to its low susceptibility to conventional antifungal drugs and the dramatic increase in the number of immunocompromised individuals suffering from HIV AIDS, cancer, and diabetes. Iron overload is one of the most common genetically inherited diseases and reports suggest increased susceptibility of these patients to bacterial infection. The ability of microorganisms to obtain iron from their environment is a major determinant in their fitness and hence in their ability to cause infectious disease. Here we demonstrate that the siderophore iron carrier is critical for C. glabrata survival after ingestion by mouse and human macrophage immune effector cells. Through the generation of macrophage models of human iron overload disease we demonstrate that ingested C. glabrata cells sense altered macrophage iron levels, and that the Sit1 siderophore-iron transporter functions as a critical determinant in the ability of C. glabrata to survive macrophage killing in a manner that is dependent on macrophage iron status. Our results reveal a role for siderophore-iron as a source of iron during C. glabrata infection, suggest additional therapeutic intervention strategies, and support a pivotal contribution for a common human iron overload disease in the mechanisms used for Fe acquisition in C. glabrata.

War-Fe-re: iron at the core of fungal virulence and host immunity

Iron acquisition is a bona fide virulence determinant. The successful colonization of the mammalian host requires that microorganisms overcome the Fe aridity of this milieu in which the levels of circulating Fe are maintained exceedingly low both through the compartmentalization of this nutrient within cells as well as the tight binding of Fe to host circulating proteins and ligands. Microbes notoriously employ multiple strategies for high affinity Fe acquisition from the host that rely either on the expression of receptors for host Fe-binding proteins and ligands, its reduction by cell surface reductases or the utilization of siderophores, small organic molecules with very high affinity for Fe(3+). This review will discuss the multiple mechanisms deployed by fungal pathogens in Fe acquisition focusing on the role of siderophore utilization in virulence as well as host immune strategies of iron withholding and emerging clinical evidence that human disorders of Fe homeostasis can act as modifiers of infectious disease.

A comprehensive review of Vibrio vulnificus: an important cause of severe sepsis and skin and soft-tissue infection

Vibrio vulnificus is a halophilic Gram-negative bacillus found worldwide in warm coastal waters. The pathogen has the ability to cause primary sepsis in certain high-risk populations, including patients with chronic liver disease, immunodeficiency, iron storage disorders, end-stage renal disease, and diabetes mellitus. Most reported cases of primary sepsis in the USA are associated with the ingestion of raw or undercooked oysters harvested from the Gulf Coast. The mortality rate for patients with severe sepsis is high, exceeding 50% in most reported series. Other clinical presentations include wound infection and gastroenteritis. Mild to moderate wound infection and gastroenteritis may occur in patients without obvious risk factors. Severe wound infection is often characterized by necrotizing skin and soft-tissue infection, including fasciitis and gangrene. V. vulnificus possesses several virulence factors, including the ability to evade destruction by stomach acid, capsular polysaccharide, lipopolysaccharide, cytotoxins, pili, and flagellum. The preferred antimicrobial therapy is doxycycline in combination with ceftazidime and surgery for necrotizing soft-tissue infection.

How I treat hemochromatosis

Hemochromatosis is a common genetic disorder in which iron may progressively accumulate in the liver, heart, and other organs. The primary goal of therapy is iron depletion to normalize body iron stores and to prevent or decrease organ dysfunction. The primary therapy to normalize iron stores is phlebotomy. In this opinion article, we discuss the indications for and monitoring of phlebotomy therapy to achieve iron depletion, maintenance therapy, dietary and pharmacologic maneuvers that could reduce iron absorption, and the role of voluntary blood donation.