Iron acquisition from Pseudomonas aeruginosa siderophores by human phagocytes: an additional mechanism of host defense through iron sequestration?

A compensatory RNase E variation increases Iron Piracy and Virulence in multidrug-resistant Pseudomonas aeruginosa during Macrophage infection

During chronic cystic fibrosis (CF) infections, evolved Pseudomonas aeruginosa antibiotic resistance is linked to increased pulmonary exacerbations, decreased lung function, and hospitalizations. However, the virulence mechanisms underlying worse outcomes caused by antibiotic resistant infections are poorly understood. Here, we investigated evolved aztreonam resistant P. aeruginosa virulence mechanisms. Using a macrophage infection model combined with genomic and transcriptomic analyses, we show that a compensatory mutation in the rne gene, encoding RNase E, increased pyoverdine and pyochelin siderophore gene expression, causing macrophage ferroptosis and lysis. We show that iron-bound pyochelin was sufficient to cause macrophage ferroptosis and lysis, however, apo-pyochelin, iron-bound pyoverdine, or apo-pyoverdine were insufficient to kill macrophages. Macrophage killing could be eliminated by treatment with the iron mimetic gallium. RNase E variants were abundant in clinical isolates, and CF sputum gene expression data show that clinical isolates phenocopied RNase E variant functions during macrophage infection. Together these data show how P. aeruginosa RNase E variants can cause host damage via increased siderophore production and host cell ferroptosis but may also be targets for gallium precision therapy.

Recent Developments in Drug Delivery for Treatment of Tuberculosis by Targeting Macrophages

Tuberculosis (TB) is among the greatest public health and safety concerns in the 21st century, Mycobacterium tuberculosis, which causes TB, infects alveolar macrophages and uses these cells as one of its primary sites of replication. The current TB treatment regimen, which consist of chemotherapy involving a combination of 3-4 antimicrobials for a duration of 6-12 months, is marked with significant side effects, toxicity, and poor compliance. Targeted drug delivery offers a strategy that could overcome many of the problems of current TB treatment by specifically targeting infected macrophages. Recent advances in nanotechnology and material science have opened an avenue to explore drug carriers that actively and passively target macrophages. This approach can increase the drug penetration into macrophages by using ligands on the nanocarrier that interact with specific receptors for macrophages. This review encompasses the recent development of drug carriers specifically targeting macrophages actively and passively. Future directions and challenges associated with development of effective TB treatment is also discussed.

Synthesis and in vitro analysis of novel gallium tetrakis(4-methoxyphenyl)porphyrin and its long-acting nanoparticle as a potent antimycobacterial agent

Bacterial heme uptake pathways offer a novel target for antimicrobial drug discovery. Recently, gallium (Ga) porphyrin complexes were found to be effective against mycobacterial heme uptake pathways. The goal of the current study is to build on this foundation and develop a new Ga(III) porphyrin and its nanoparticles, formulated by a single emulsion-evaporation technique to inhibit the growth of Mycobacterium avium complex (MAC) with enhanced properties. Gallium 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin chloride (GaMeOTP) was synthesized from 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin and GaCl₃. GaMeOTP showed enhanced antimicrobial activity against MAC104 and some clinical M. avium isolates. The synthesized Ga(III) porphyrin antimicrobial activity resulted in the overproduction of reactive oxygen species. Our study also demonstrated that F127 nanoparticles encapsulating GaMeOTP exhibited a smaller size than GaTP nanoparticles and a better duration of activity in MAC-infected macrophages compared to the free GaMeOTP. The nanoparticles were trafficked to endosomal compartments within MAC-infected macrophages, likely contributing to the antimicrobial activity of the drug.

Advancement of Gallium and Gallium-Based Compounds as Antimicrobial Agents

With the abuse and misuse of antibiotics, antimicrobial resistance has become a challenging issue in the medical system. Iatrogenic and non-iatrogenic infections caused by multidrug-resistant (MDR) pathogens pose serious threats to global human life and health because the efficacy of traditional antibiotics has been greatly reduced and the resulting socio-economic burden has increased. It is important to find and develop non-antibiotic-dependent antibacterial strategies because the development of new antibiotics can hardly keep pace with the emergence of resistant bacteria. Gallium (III) is a multi-target antibacterial agent that has an excellent antibacterial activity, especially against MDR pathogens; thus, a gallium (III)-based treatment is expected to become a new antibacterial strategy. However, some limitations of gallium ions as antimicrobials still exist, including low bioavailability and explosive release. In recent years, with the development of nanomaterials and clathrates, the progress of manufacturing technology, and the emergence of synergistic antibacterial strategies, the antibacterial activities of gallium have greatly improved, and the scope of application in medical systems has expanded. This review summarizes the advancement of current optimization for these key factors. This review will enrich the knowledge about the efficiency and mechanism of various gallium-based antibacterial agents and provide strategies for the improvement of the antibacterial activity of gallium-based compounds.

Gallium Porphyrin and Gallium Nitrate Synergistically Inhibit Mycobacterial Species by Targeting Different Aspects of Iron/Heme Metabolism

There is an urgent need for new effective and safe antibiotics active against pathogenic mycobacterial species. Gallium (Ga) nitrate (Ga(NO₃)₃) and Ga porphyrin (GaPP) have each been shown to inhibit the growth of a variety of mycobacterial species. The Ga(III) ion derived from Ga(NO₃)₃ has the potential to disrupt the mycobacterial Fe(III) uptake mechanisms and utilization, including replacing iron (Fe) in the active site of enzymes, resulting in the disruption of function. Similarly, noniron metalloporphyrins such as heme mimetics, which can be transported across the bacterial membrane via heme-uptake pathways, would potentially block the acquisition of iron-containing heme and bind to heme-utilizing proteins, making them nonfunctional. Given that they likely act on different aspects of mycobacterial Fe metabolism, the efficacy of combining Ga(NO₃)₃ and GaPP was studied in vitro against Mycobacterium avium, Mycobacterium abscessus, and Mycobacterium tuberculosis (M. tb). The combination was then assessed in vivo in a murine pulmonary infection model of M. abscessus. We observed that Ga(NO₃)₃ in combination with GaPP exhibited synergistic inhibitory activity against the growth of M. avium, M. tb, and M. abscessus, being most active against M. abscessus. Activity assays indicated that Ga(NO₃)₃ and GaPP inhibited both catalase and aconitase at high concentrations. However, the combination showed a synergistic effect on the aconitase activity of M. abscessus. The Ga(NO₃)₃/GaPP combination via intranasal administration showed significant antimicrobial activity in mice infected with M. abscessus. M. abscessus CFU from the lungs of the Ga(NO₃)₃/GaPP-treated mice was significantly less compared to that of nontreated or single Ga(III)-treated mice. These findings suggest that combinations of different Ga(III) compounds can synergistically target multiple iron/heme-utilizing mycobacterial enzymes. The results support the potential of combination Ga therapy for development against mycobacterial pathogens.

Intraspecies Signaling between Common Variants of Pseudomonas aeruginosa Increases Production of Quorum-Sensing-Controlled Virulence Factors

The opportunistic pathogen Pseudomonas aeruginosa damages hosts through the production of diverse secreted products, many of which are regulated by quorum sensing (QS). The lasR gene, which encodes a central QS regulator, is frequently mutated in clinical isolates from chronic infections, and loss of LasR function (LasR-) generally impairs the activity of downstream QS regulators RhlR and PqsR. We found that in cocultures containing LasR+ and LasR- strains, LasR- strains hyperproduce the RhlR/RhlI-regulated antagonistic factors pyocyanin and rhamnolipids in diverse models and media and in different strain backgrounds. Diffusible QS autoinducers produced by the wild type were not required for this effect. Using transcriptomics, genetics, and biochemical approaches, we uncovered a reciprocal interaction between wild-type and lasR mutant pairs wherein the iron-scavenging siderophore pyochelin produced by the lasR mutant induced citrate release and cross-feeding from the wild type. Citrate, a metabolite often secreted in low iron environments, stimulated RhlR signaling and RhlI levels in LasR-but not in LasR+ strains. These studies reveal the potential for complex interactions between recently diverged, genetically distinct isolates within populations from single chronic infections.IMPORTANCE Coculture interactions between lasR loss-of-function and LasR+ Pseudomonas aeruginosa strains may explain the worse outcomes associated with the presence of LasR- strains. More broadly, this report illustrates how interactions within a genotypically diverse population, similar to those that frequently develop in natural settings, can promote unpredictably high virulence factor production.

Review of Potential Pseudomonas Weaponry, Relevant to the Pseudomonas-Aspergillus Interplay, for the Mycology Community

Pseudomonas aeruginosa is one of the most prominent opportunistic bacteria in airways of cystic fibrosis patients and in immunocompromised patients. These bacteria share the same polymicrobial niche with other microbes, such as the opportunistic fungus Aspergillus fumigatus. Their inter-kingdom interactions and diverse exchange of secreted metabolites are responsible for how they both fare in competition for ecological niches. The outcomes of their contests likely determine persistent damage and degeneration of lung function. With a myriad of virulence factors and metabolites of promising antifungal activity, P. aeruginosa products or their derivatives may prove useful in prophylaxis and therapy against A. fumigatus. Quorum sensing underlies the primary virulence strategy of P. aeruginosa, which serves as cell–cell communication and ultimately leads to the production of multiple virulence factors. Understanding the quorum-sensing-related pathogenic mechanisms of P. aeruginosa is a first step for understanding intermicrobial competition. In this review, we provide a basic overview of some of the central virulence factors of P. aeruginosa that are regulated by quorum-sensing response pathways and briefly discuss the hitherto known antifungal properties of these virulence factors. This review also addresses the role of the bacterial secretion machinery regarding virulence factor secretion and maintenance of cell–cell communication.

Incidence of Peritonitis in Chronic Peritoneal Dialysis Patients Infused with Intravenous Iron Dextran

Background

The Dialysis Outcomes Quality Initiative (DOQI) guidelines, published in 1997, emphasize the need for careful monitoring of iron stores and for provision of adequate iron replacement therapy to achieve target goals of hemoglobin concentration in end-stage renal disease (ESRD) patients, especially those treated with recombinant erythropoietin (rHuEPO). Intravenous iron dextran (IVID) therapy, which has long been used in hemodialysis patients, is increasingly being used in chronic peritoneal dialysis (CPD) patients. In 1997, we began using this form of iron therapy for our CPD patients. However, because considerable data exists to show a relationship between iron metabolism and acute infections, we questioned whether IVID infusion placed our patients at greater risk for peritonitis, the leading cause of death and patient dropout from CPD therapy.

Objective

To evaluate the relationship between iron and infection, we studied episodes of peritonitis in CPD patients who were infused with IVID.

Design

In a retrospective study of adult CPD patients who received IVID during 1998, we investigated the occurrence of peritonitis episodes and the spectrum of causative organisms. Patients with a hemoglobin level of < 12.5 g/dL who also had a ferritin level < 100 ng/mL or a transferrin saturation level < 20% (or both) and who did not respond to oral iron therapy, were administered between 0.5 g and 1.0 g of IVID in an outpatient hospital setting. We calculated the expected and observed number of peritonitis episodes in these patients within 30, 60, and 90 days after infusion of IVID.

Results

During the study period, 56 patients received 77 doses of IVID, with 14 patients requiring 2 or more infusions. Of the 77 doses, 71 were given as a 1-g bolus. The IVID was well tolerated by all patients. Within 90 days of IVID administration, 14 patients developed peritonitis: 6 episodes occurred within 30 days, 7 episodes occurred between 31 and 60 days, and 1 episode occurred between 61 and 90 days after the IVID dosing. The peritonitis rate for patients not receiving IVID was 1 episode per 13.7 patient-months. Taking this rate as the “expected” rate, the expected number of episodes of peritonitis for the study population was 5.6 episodes within 30 days, 11.2 episodes within 60 days, and 16.8 episodes within 90 days following IVID administration. The difference between the expected and observed rates of peritonitis in patients who were dosed with IVID was not statistically different. The spectrum of organisms seen in the peritonitis episodes in the study population was not significantly different from that seen in the peritonitis episodes in our CPD unit population.

Conclusions

There is evidence that IVID infusion therapy can improve anemia and reduce rHuEPO requirements in CPD patients, usually without adverse reaction and without exposing patients to an increased risk of peritonitis. More research is needed in the area of potential increased risk of infection in ESRD patients who are ( 1 ) infused with large doses of IVID, and ( 2 ) iron-overloaded.

Metal binding ability of microbial natural metal chelators and potential applications

Metallophores can chelate many different metal and metalloid ions next to iron, make them valuable for many applications.

Dual Inhibition of Klebsiella pneumoniae and Pseudomonas aeruginosa Iron Metabolism Using Gallium Porphyrin and Gallium Nitrate

Iron- and heme-uptake pathways and metabolism are promising targets for the development of new antimicrobial agents, as their disruption would lead to nutritional iron starvation and inhibition of bacterial growth. Salts of gallium(III) (Ga), an iron mimetic metal, disrupt iron-dependent biological processes by binding iron-utilizing proteins and competing with iron for uptake by bacterial siderophore-mediated iron uptake systems. Ga porphyrins, heme mimetic complexes, disrupt heme-utilizing hemoproteins. Because Ga(NO₃)₃ and Ga porphyrin disrupt different pathways of bacterial ion acquisition and utilization, we hypothesized that if used in combination, they would result in enhanced antimicrobial activity. Antimicrobial activity of Ga porphyrins (Ga protoporphyrin, GaPP, or Ga mesoporphyrin, GaMP) alone and in combination with Ga(NO₃)₃ were evaluated against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, and methicillin-resistant Staphylococcus aureus (MRSA) under iron-limited conditions. The Ga porphyrin/Ga(NO₃)₃ combination demonstrated substantial synergism against K. pneumoniae, P. aeruginosa, and MRSA. Time-kill assays revealed that the synergistic combination of GaPP/Ga(NO₃)₃ was bacteriostatic against K. pneumoniae and MRSA and bactericidal against P. aeruginosa. The GaPP/Ga(NO₃)₃ combination significantly disrupted K. pneumoniae and P. aeruginosa biofilms on plasma-coated surfaces and increased the survival of Caenorhabditis elegans infected with K. pneumoniae or P. aeruginosa. When assessing the antibacterial activity of the Ga(III)/antibiotic combinations, GaPP/colistin and Ga(NO₃)₃/colistin combinations also showed synergistic activity against K. pneumoniae and P. aeruginosa. Our results demonstrate that GaPP and Ga(NO₃)₃ have significant synergistic effects against several important human bacterial pathogens through dual inhibition of iron and heme metabolism.

Gallium nanoparticles facilitate phagosome maturation and inhibit growth of virulent Mycobacterium tuberculosis in macrophages

New treatments and novel drugs are required to counter the growing problem of drug-resistant strains of Mycobacterium tuberculosis (M.tb). Our approach against drug resistant M.tb, as well as other intracellular pathogens, is by targeted drug delivery using nanoformulations of drugs already in use, as well as drugs in development. Among the latter are gallium (III) (Ga)-based compounds. In the current work, six different types of Ga and rifampin nanoparticles were prepared in such a way as to enhance targeting of M.tb infected-macrophages. They were then tested for their ability to inhibit growth of a fully pathogenic strain (H37Rv) or a non-pathogenic strain (H37Ra) of M.tb. Encapsulating Ga in folate- or mannose-conjugated block copolymers provided sustained Ga release for 15 days and significantly inhibited M.tb growth in human monocyte-derived macrophages. Nanoformulations with dendrimers encapsulating Ga or rifampin also showed promising anti-tuberculous activity. The nanoparticles co-localized with M.tb containing phagosomes, as measured by detection of mature cathepsin D (34 kDa, lysosomal hydrogenase). They also promoted maturation of the phagosome, which would be expected to increase macrophage-mediated killing of the organism. Delivery of Ga or rifampin in the form of nanoparticles to macrophages offers a promising approach for the development of new therapeutic anti-tuberculous drugs.

Prolonged-acting, multi-targeting gallium nanoparticles potently inhibit growth of both HIV and mycobacteria in co-infected human macrophages

Human immunodeficiency virus (HIV) infection and Mycobacterium tuberculosis (TB) are responsible for two of the major global human infectious diseases that result in significant morbidity, mortality and socioeconomic impact. Furthermore, severity and disease prevention of both infections is enhanced by co-infection. Parallel limitations also exist in access to effective drug therapy and the emergence of resistance. Furthermore, drug-drug interactions have proven problematic during treatment of co-incident HIV and TB infections. Thus, improvements in drug access and simplified treatment regimens are needed immediately. One of the key host cells infected by both HIV and TB is the mononuclear phagocyte (MP; monocyte, macrophage and dendritic cell). Therefore, we hypothesized that one way this can be achieved is through drug-targeting by a nanoformulated drug that ideally would be active against both HIV and TB. Accordingly, we validated macrophage targeted long acting (sustained drug release) gallium (Ga) nanoformulation against HIV-mycobacterium co-infection. The multi-targeted Ga nanoparticle agent inhibited growth of both HIV and TB in the macrophage. The Ga nanoparticles reduced the growth of mycobacterium and HIV for up to 15 days following single drug loading. These results provide a potential new approach to treat HIV-TB co-infection that could eventually lead to improved clinical outcomes.

Granulocyte-macrophage colony stimulatory factor enhances the pro-inflammatory response of interferon-γ-treated macrophages to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an opportunistic pathogen that can cause severe infections at compromised epithelial surfaces, such those found in burns, wounds, and in lungs damaged by mechanical ventilation or recurrent infections, particularly in cystic fibrosis (CF) patients. CF patients have been proposed to have a Th2 and Th17-biased immune response suggesting that the lack of Th1 and/or over exuberant Th17 responses could contribute to the establishment of chronic P. aeruginosa infection and deterioration of lung function. Accordingly, we have observed that interferon (IFN)-γ production by peripheral blood mononuclear cells from CF patients positively correlated with lung function, particularly in patients chronically infected with P. aeruginosa. In contrast, IL-17A levels tended to correlate negatively with lung function with this trend becoming significant in patients chronically infected with P. aeruginosa. These results are in agreement with IFN-γ and IL-17A playing protective and detrimental roles, respectively, in CF. In order to explore the protective effect of IFN-γ in CF, the effect of IFN-γ alone or in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF), on the ability of human macrophages to control P. aeruginosa growth, resist the cytotoxicity induced by this bacterium or promote inflammation was investigated. Treatment of macrophages with IFN-γ, in the presence and absence of GM-CSF, failed to alter bacterial growth or macrophage survival upon P. aeruginosa infection, but changed the inflammatory potential of macrophages. IFN-γ caused up-regulation of monocyte chemoattractant protein-1 (MCP-1) and TNF-α and down-regulation of IL-10 expression by infected macrophages. GM-CSF in combination with IFN-γ promoted IL-6 production and further reduction of IL-10 synthesis. Comparison of TNF-α vs. IL-10 and IL-6 vs. IL-10 ratios revealed the following hierarchy in regard to the pro-inflammatory potential of human macrophages infected with P. aeruginosa: untreated < treated with GM-CSF < treated with IFN-γ < treated with GM-CSF and IFN-γ.

Role of lung iron in determining the bacterial and host struggle in cystic fibrosis

Cystic fibrosis (CF) is the most common lethal genetic disorder in Caucasian populations. It is a multiorgan system disease that affects the lungs, gastrointestinal tract, liver, and pancreas. The majority of morbidity and mortality in CF relates to chronic airway infection with a variety of bacterial species, commencing in very early infancy, which results in lung destruction and ultimately organ failure ( 41 , 43 ). This review focuses on iron homeostasis in the CF lung and its role in determining the success and chronicity of Pseudomonas aeruginosa infection. There have been previous excellent reviews regarding iron metabolism in the lower respiratory tract and mechanisms of P. aeruginosa iron acquisition, and we direct readers to these articles for further background reading ( 31 , 53 , 58 , 77 , 96 ). In this review, we have brought the “two sides of the coin” together to provide a holistic overview of the relationship between host and bacterial iron homeostasis and put this information into the context of current understanding on infection in the CF lung.

Is there a causal relationship between the receipt of blood transfusions and the development of chronic lung disease of prematurity?

The number and total volume of blood transfusions received by premature babies is, after gestational age and birth weight a good predictor of the likelihood of developing chronic lung disease of prematurity (CLD) and retinopathy of prematurity (ROP). Oxidative damage, inflammation and pulmonary infections are also strongly associated with the development of CLD. It is currently not clear whether there is a causal relationship between the receipt of blood transfusions and oxidative damage, infection, inflammation and CLD in these babies. Strong arguments may be made both for and against a causal relationship. The babies who receive blood transfusions are usually smaller than those who do not, and are ventilated, often with high oxygen levels, for a longer period of time. The longer the baby is on a ventilator the more likely it is to develop pulmonary infection and inflammation. All these factors will promote free radical production and oxidative damage irrespective of the receipt of blood transfusion. This would argue against a causal relationship. On the other hand, an argument may be presented which is based on iron promoted free radical generation, infection and fibrosis consequent to the breakdown of haeme released from transfused erythrocytes. Haeme is broken down by haeme oxygenase (HO) to iron, CO and bilirubin. Under normal circumstances the products of HO activity are beneficial to the organism, but when HO activity is excessive, the products are potentially damaging. Free iron, (in the Fe2+ form) if not sequestered with protein or urate, will generate highly toxic free radicals via the Fenton and Heber-Wiess reactions, predispose the tissue to infection and promote fibrosis. The iron chelating ability of the premature baby appears to be limited so that it would be difficult to deal with any increase in free iron production. Free iron will in turn induce HO activity leading to a potentially serious positive feedback process. The lung is particularly sensitive to iron induced HO activity. In addition, HO activity may be enhanced by other events occurring in the premature lung such as the production of proinflammatory cytokines and the reduced level of glutathione. Thus, the possibility of a causal relationship clearly exists and needs to be examined. This can be attempted by measuring the products of HO activity in relation to the receipt of blood transfusions.

Gallium-Inducible Transferrin-Independent Iron Acquisition Is a Property of Many Cell Types: Possible Role of Alterations in the Plasma Membrane

BACKGROUND

We have previously shown that human myeloid cell types can acquire large amounts of iron (Fe)3+ from low-molecular-weight chelates by a process that is independent of adenosine triphosphate and dramatically increased by gallium (Ga) and other multivalent cationic metals.

METHODS

To provide further insight into the mechanism responsible and its relevance to other cellular systems, we investigated Fe acquisition from nitrilotriacetic acid (NTA) by several myeloid and nonmyeloid cell lines in the presence and absence of Ga.

RESULTS

Most nonmyeloid cells examined exhibited similar ability to acquire Fe from NTA. Ga increased the apparent maximum velocity (Vmax), with minimal changes in apparent Michaelis constant (Km), of all cell lines. Both erythrocytes and erythrocyte ghosts acquired Fe from NTA, which increased with Ga exposure, analogous to nucleated cells. However, liposomes made from phospholipids did not exhibit Ga-inducible Fe association. Enzymes that modify surface proteins and carbohydrates did not alter HL-60 cell Fe acquisition. Modifying HL-60 membrane fatty acid content had only a minimal effect. Ga exposure did not change membrane potential or fluidity. However, electron microscopy suggested that Ga alters plasma membrane physical properties.

CONCLUSION

Multivalent cations appear to induce changes in cell membranes that may alter their interaction with Fe3+ and probably other multivalent cations.

Fungal susceptibility to zinc deprivation

Calprotectin is a neutrophil-derived antimicrobial protein that competes with microorganisms for zinc. The zinc-specific effect of calprotectin against Candida albicans appears to be related to this organism's marked susceptibility to deprivation of this metal. However, it is not known whether this susceptibility is particular to C albicans or whether it is a characteristic of pathogenic fungi in general. As a means of deciding between these 2 possibilities, we undertook the study reported here to compare the susceptibility to zinc deprivation of 6 other pathogenic fungal species in addition to that of C albicans . We tested the effect of metals in reversing growth inhibition of the 7 fungi against abscess-fluid supernatant (a source of calprotectin) and 3 chemical chelators. Data were expressed as the concentration of metal required to bring about 50% restoration of growth. Zinc was found to be much more potent than the other metals tested in reversing growth inhibition of all the organisms by human abscess fluid and all 3 chemical chelators. Copper and manganese also had some effect. In some cases, chelator stability constants were higher for other metals than for zinc; in particular, although diethylenetriaminopentaacetic acid has a stability constant for iron almost 10(10) times greater than that for zinc, zinc was more effective than iron in reversing growth inhibition by this chelator against all of the organisms. These results suggest that marked susceptibility to zinc deprivation is a general characteristic of pathogenic fungi.

Intracellular chelation of iron by bipyridyl inhibits DNA virus replication: ribonucleotide reductase maturation as a probe of intracellular iron pools

The efficient replication of large DNA viruses requires dNTPs supplied by a viral ribonucleotide reductase. Viral ribonucleotide reductase is an early gene product of both vaccinia and herpes simplex virus. For productive infection, the apoprotein must scavenge iron from the endogenous, labile iron pool(s). The membrane-permeant, intracellular Fe(2+) chelator, 2,2'-bipyridine (bipyridyl, BIP), is known to sequester iron from this pool. We show here that BIP strongly inhibits the replication of both vaccinia and herpes simplex virus, type 1. In a standard plaque assay, 50 microm BIP caused a 50% reduction in plaque-forming units with either virus. Strong inhibition was observed only when BIP was added within 3 h post-infection. This time dependence was observed also in regards to inhibition of viral late protein and DNA synthesis by BIP. BIP did not inhibit the activity of vaccinia ribonucleotide reductase (RR), its synthesis, nor its stability indicating that BIP blocked the activation of the apoprotein. In parallel with its inhibition of vaccinia RR activation, BIP treatment increased the RNA binding activity of the endogenous iron-response protein, IRP1, by 1.9-fold. The data indicate that the diiron prosthetic group in vaccinia RR is assembled from iron taken from the BIP-accessible, labile iron pool that is sampled also by ferritin and the iron-regulated protein found in the cytosol of mammalian cells.

Effect of metals on Candida albicans growth in the presence of chemical chelators and human abscess fluid

Calprotectin is a calcium- and zinc-binding protein that is present in abscess fluid supernatants and appears to inhibit microbial growth through competition for zinc. In the present study, growth inhibition by chemical chelators was compared with that produced by human abscess fluid to determine whether other chelators, perhaps with different metal specificities, would have the same or different patterns of metal reversibility as abscess fluid. Zinc was found to be more potent than the other metals tested in reversing C. albicans growth inhibition by human abscess fluid and three chemical chelators, even though in some cases the stability constants of certain of these chelators were higher for other metals. For example, in the presence of the chelator diethylenetriaminopentaacetic acid, zinc stimulated Candida growth at a 10-fold lower concentration than did iron, even though this chelator has a stability constant for iron that is almost 10(10) higher than that for zinc. These results suggest that the zinc specificity of calprotectin's C. albicans growth inhibition can best be explained by the marked sensitivity of this organism to zinc deprivation rather than by selective binding of this metal by the protein.