Biosynthesis of novel desferrioxamine derivatives requires unprecedented crosstalk between separate NRPS-independent siderophore pathways

Iron is essential to many biological processes but its poor solubility in aerobic environments restricts its bioavailability. To overcome this limitation, bacteria have evolved a variety of strategies, including the production and secretion of iron-chelating siderophores. Here, we describe the discovery of four series of siderophores from Streptomyces ambofaciens ATCC23877, three of which are unprecedented. MS/MS-based molecular networking revealed that one of these series corresponds to acylated desferrioxamines (acyl-DFOs) recently identified from S. coelicolor. The remaining sets include tetra- and penta-hydroxamate acyl-DFO derivatives, all of which incorporate a previously undescribed building block. Stable isotope labeling and gene deletion experiments provide evidence that biosynthesis of the acyl-DFO congeners requires unprecedented crosstalk between two separate non-ribosomal peptide synthetase (NRPS)-independent siderophore (NIS) pathways in the producing organism. Although the biological role(s) of these new derivatives remain to be elucidated, they may confer advantages in terms of metal chelation in the competitive soil environment due to the additional bidentate hydroxamic functional groups. The metabolites may also find application in various fields including biotechnology, bioremediation, and immuno-PET imaging.IMPORTANCEIron-chelating siderophores play important roles for their bacterial producers in the environment, but they have also found application in human medicine both in iron chelation therapy to prevent iron overload and in diagnostic imaging, as well as in biotechnology, including as agents for biocontrol of pathogens and bioremediation. In this study, we report the discovery of three novel series of related siderophores, whose biosynthesis depends on the interplay between two NRPS-independent (NIS) pathways in the producing organism S. ambofaciens-the first example to our knowledge of such functional cross-talk. We further reveal that two of these series correspond to acyl-desferrioxamines which incorporate four or five hydroxamate units. Although the biological importance of these novel derivatives is unknown, the increased chelating capacity of these metabolites may find utility in diagnostic imaging (for instance, 89Zr-based immuno-PET imaging) and other applications of metal chelators.

Chelating Effect of Siderophore Desferrioxamine-B on Uranyl Biomineralization Mediated by Shewanella putrefaciens

In contaminated water and soil, little is known about the role and mechanism of the biometabolic molecule siderophore desferrioxamine-B (DFO) in the biogeochemical cycle of uranium due to complicated coordination and reaction networks. Here, a joint experimental and quantum chemical investigation is carried out to probe the biomineralization of uranyl (UO22+, referred to as U(VI) hereafter) induced by Shewanella putrefaciens (abbreviated as S. putrefaciens) in the presence of DFO and Fe3+ ion. The results show that the production of mineralized solids {hydrogen-uranium mica [H2(UO2)2(PO4)2·8H2O]} via S. putrefaciens binding with UO22+ is inhibited by DFO, which can both chelate preferentially UO22+ to form a U(VI)-DFO complex in solution and seize it from U(VI)-biominerals upon solvation. However, with Fe3+ ion introduced, the strong specificity of DFO binding with Fe3+ causes re-emergence of biomineralization of UO22+ {bassetite [Fe(UO2)2(PO4)2·8(H2O)]} by S. putrefaciens, owing to competitive complexation between Fe3+ and UO22+ for DFO. As DFO possesses three hydroxamic functional groups, it forms hexadentate coordination with Fe3+ and UO22+ ions via these functional groups. The stability of the Fe3+-DFO complex is much higher than that of U(VI)-DFO, resulting in some DFO-released UO22+ to be remobilized by S. putrefaciens. Our finding not only adds to the understanding of the fate of toxic U(VI)-containing substances in the environment and biogeochemical cycles in the future but also suggests the promising potential of utilizing functionalized DFO ligands for uranium processing.

Effects of iron concentration and DFB (Desferrioxamine-B) on transcriptional profiles of an ecologically relevant marine bacterium

Research into marine iron cycles and biogeochemistry has commonly relied on the use of chelators (including siderophores) to manipulate iron bioavailability. To test whether a commonly used chelator, desferrioxamine B (DFB) caused effects beyond changing the iron-status of cells, cultures of the environmentally relevant marine heterotrophic bacterium, Ruegeria pomeroyii, were grown in media with different concentrations of iron and/or DFB, resulting in a gradient of iron availability. To determine how cells responded, transcriptomes were generated for cells from the different treatments and analyzed to determine how cells reacted to these to perturbations. Analyses were also performed to look for cellular responses specific to the presence of DFB in the culture medium. As expected, cells experiencing different levels of iron availability had different transcriptomic profiles. While many genes related to iron acquisition were differentially expressed between treatments, there were many other genes that were also differentially expressed between different sample types, including those related to the uptake and metabolism of other metals as well as genes related to metabolism of other types of molecules like amino acids and carbohydrates. We conclude that while DFB certainly altered iron availability to cells, it also appears to have had a general effect on the homeostasis of other metals as well as influenced metabolic processes outside of metal acquisition.

Amelioration effects of the soybean lecithin-gallic acid complex on iron-overload-induced oxidative stress and liver damage in C57BL/6J mice

CONTEXT

Gallic acid (GA) and lecithin showed important roles in antioxidant and drug delivery, respectively. A complex synthesized from GA and soybean lecithin (SL-GAC), significantly improved bioavailability of GA and pharmacological activities. However, the antioxidant activity of SL-GAC and its effect on iron-overload-induced liver injury remains unexplored.

OBJECTIVE

This study investigates the antioxidant properties of SL-GAC in vitro and in mice, and its remediating effects against liver injury by iron-overloaded.

MATERIALS AND METHODS

In vitro, free radical scavenging activity, lipid peroxidation inhibition, and ferric reducing power of SL-GAC were measured by absorbance photometry. In vivo, C57BL/6J mice were randomized into 4 groups: control, iron-overloaded, iron-overloaded + deferoxamine, and iron-overloaded + SL-GAC. Treatments with deferoxamine (150 mg/kg/intraperitioneally) and SL-GAC (200 mg/kg/orally) were given to the desired groups for 12 weeks, daily. Iron levels, oxidative stress, and biochemical parameters were determined by histopathological examination and molecular biological techniques.

RESULTS

In vitro, SL-GAC showed DPPH and ABTS free radicals scavenging activity with IC₅₀ values equal to 24.92 and 128.36 μg/mL, respectively. In C57BL/6J mice, SL-GAC significantly reduced the levels of serum iron (22.82%), liver iron (50.29%), aspartate transaminase (25.97%), alanine transaminase (38.07%), gamma glutamyl transferase (42.11%), malondialdehyde (19.82%), total cholesterol (45.96%), triglyceride (34.90%), ferritin light chain (18.51%) and transferrin receptor (27.39%), while up-regulated the levels of superoxide dismutase (24.69%), and glutathione (11.91%).

CONCLUSIONS

These findings encourage the use of SL-GAC to treat liver injury induced by iron-overloaded. Further in vivo and in vitro studies are needed to validate its potential in clinical medicine.

Ferroptosis inhibitor improves cardiac function more effectively than inhibitors of apoptosis and necroptosis through cardiac mitochondrial protection in rats with iron-overloaded cardiomyopathy

Iron overload cardiomyopathy (IOC) is the leading cause of death in cases of iron overload in patients. Previous studies demonstrated that iron overload led to cardiomyocyte dysfunction and death through multiple pathways including apoptosis, necroptosis and ferroptosis. However, the dominant cell death pathway in the iron-overloaded heart needs clarification. We tested the hypothesis that ferroptosis, an iron-dependent cell death, plays a dominant role in IOC, and ferroptosis inhibitor exerts greater efficacy than inhibitors of apoptosis and necroptosis on improving cardiac function in iron-overloaded rats. Iron dextran was injected intraperitoneally into male Wistar rats for four weeks to induce iron overload. Then, the rats were divided into 5 groups: treated with vehicle, apoptosis inhibitor (z-VAD-FMK), necroptosis inhibitor (Necrostatin-1), ferroptosis inhibitor (Ferrostatin-1) or iron chelator (deferoxamine) for 2 weeks. Cardiac function, mitochondrial function, apoptosis, necroptosis and ferroptosis were determined. The increased expression of apoptosis-, necroptosis- and ferroptosis-related proteins, were associated with impaired cardiac and mitochondrial function in iron-overloaded rats. All cell death inhibitors attenuated cardiac apoptosis, necroptosis and ferroptosis in iron-overloaded rats. Ferrostatin-1 was more effective than the other drugs in diminishing mitochondrial dysfunction and Bax/Bcl-2 ratio. Moreover, both Ferrostatin-1 and deferoxamine reversed iron overload-induced cardiac dysfunction as indicated by restored left ventricular ejection fraction and E/A ratio, whereas z-VAD-FMK and Necrostatin-1 only partially improved this parameter. These results indicated that ferroptosis could be the predominant form of cardiomyocyte death in IOC, and that inhibiting ferroptosis might be a potential novel treatment for IOC.

[Effect of sodium alginate-g-deferoxamine/chitosan microspheres on osteogenic differentiation of rat bone mesenchymal stem cells]

PURPOSE

To explore the effect of sodium alginate-g-deferoxamine/chitosan (SA-g-DFO/CS) microspheres on proliferation and osteogenic differentiation of rat bone mesenchymal stem cells (BMSCs).

METHODS

A kind of SA-g-DFO/CS microsphere was developed through electrostatic interaction between porous chitosan microspheres and sodium alginate chemically grafted on the surface of DFO. Its morphology, porosity rate, pore size and sustained release of DFO in vitro were examined. Rat BMSCs were isolated and co-cultured with microspheres in osteogenic differentiation medium. MTT assay was used to study the influence of cell proliferation, and Calcein-AM/PI staining was used to observe the cell viability. Alkaline phosphatase (ALP) activity assay was conducted. PCR was used to detect the expression of genes related to angiogenesis and osteogenesis. Statistical analysis was performed using SPSS 22.0 software package.

RESULTS

The SA-g-DFO/CS porous microspheres were successfully prepared with a sustained re6lease of DFO. Compared with SA/CS microspheres, the SA-g-DFO/CS microspheres were conducive to cell proliferation and differentiation, with the increases in expression level of ALP, related angiogenesis genes HIF-1α, VEGF and osteogenesis genes COLI, OCN.

CONCLUSIONS

The SA-g-DFO/CS porous microspheres can provide a new choice for the development of alveolar bone regeneration.

Siderophore Synthetase DesD Catalyzes N-to-C Condensation in Desferrioxamine Biosynthesis

Desferrioxamine siderophores are assembled by the nonribosomal-peptide-synthetase-independent siderophore (NIS) synthetase enzyme DesD via ATP-dependent iterative condensation of three N1-hydroxy-N1-succinyl-cadaverine (HSC) units. Current knowledge of NIS enzymology and the desferrioxamine biosynthetic pathway does not account for the existence of most known members of this natural product family, which differ in substitution patterns of the N- and C-termini. The directionality of desferrioxamine biosynthetic assembly, N-to-C versus C-to-N, is a longstanding knowledge gap that is limiting further progress in understanding the origins of natural products in this structural family. Here, we establish the directionality of desferrioxamine biosynthesis using a chemoenzymatic approach with stable isotope incorporation and dimeric substrates. We propose a mechanism where DesD catalyzes the N-to-C condensation of HSC units to establish a unifying biosynthetic paradigm for desferrioxamine natural products in Streptomyces.

Transcriptomic analysis of the effect of deferoxamine exposure on the growth, photosynthetic activity and iron transfer of Microcystis aeruginosa

Deferoxamine (DFB) is a trihydroxamic acid siderophore that chelates with iron (Fe) to form iron-siderophore complexes. The existence of siderophores in nature changes the form of iron and affects the absorption and utilization of iron by organisms. However, the relationship between siderophores and the growth of Cyanobacteria is largely unknown. In this study, the cellular and transcriptomic responses to the addition of DFB were investigated. A high concentration of DFB (12 mg/L) significantly inhibited the growth of Cyanobacteria cells, reduced photosynthetic activity, and induced the production of peroxidase, with the highest inhibition rate of algal growth of 74.82%. These indexes were also affected for the low (3 mg/L) and medium concentration (6 mg/L) groups, but this difference is closely related to the growth stage of Cyanobacteria cells. This may be due to competition between the cell-associated iron-binding part/system and the extracellular Fe (Ⅲ)-DFB ligand. Transcriptome results showed that most of the genes involved in iron uptake and transport were down-regulated, and only the fur gene encoding the iron uptake regulator protein was significantly up-regulated. Most genes related to photosynthesis, glycolysis, and fatty acid metabolism were also down-regulated, while the obvious up-regulation of a few genes may be a complex regulation in response to the down-regulation of most genes. These findings will provide important insights into the effects of siderophores on iron bioavailability in algae.

Deferoxamine Interference in Fibro-inflammation: Additional Action in Control of Obese Adipose Tissue Dysfunction

INTRODUCTION

Several studies demonstrated that deferoxamine, an iron chelator, can improve inflammatory alterations in adipose tissue induced by obesity. Obesity alterations in adipose tissue are also associated with tissue remodeling, and deferoxamine has anti-fibrosis action previously described in sites like the skin and liver.

METHODS

In this work, we analyzed deferoxamine effects on adipose tissue fibro-inflammation during obesity induced by diet in mice. in vitro approaches with fibroblasts and macrophages were also carried out to elucidate deferoxamine activity.

RESULTS

Our results demonstrated that in addition to exerting anti-inflammatory effects, reducing the cytokine production in adipose tissue of obese mice and by human monocyte differentiated in macrophage in vitro, deferoxamine can alter metalloproteinases expression and extracellular matrix production in vivo and in vitro.

CONCLUSION

Deferoxamine could be an alternative to control fibro-inflammation in obese adipose tissue, contributing to the metabolic improvements previously described.

Characterization of a broadly specific cadaverine N-hydroxylase involved in desferrioxamine B biosynthesis in Streptomyces sviceus

N-hydroxylating flavin-dependent monooxygenases (FMOs) are involved in the biosynthesis of hydroxamate siderophores, playing a key role in microbial virulence. Herein, we report the first structural and kinetic characterization of a novel alkyl diamine N-hydroxylase DesB from Streptomyces sviceus (SsDesB). This enzyme catalyzes the first committed step in the biosynthesis of desferrioxamine B, a clinical drug used to treat iron overload disorders. X-ray crystal structures of the SsDesB holoenzyme with FAD and the ternary complex with bound NADP+ were solved at 2.86 Å and 2.37 Å resolution, respectively, providing a structural view of the active site environment. SsDesB crystallized as a tetramer and the structure of the individual protomers closely resembles the structures of homologous N-hydroxylating FMOs from Erwinia amylovora (DfoA), Pseudomonas aeruginosa (PvdA), and Aspergillus fumigatus (SidA). Using NADPH oxidation, oxygen consumption, and product formation assays, kinetic parameters were determined for various substrates with SsDesB. SsDesB exhibited typical saturation kinetics with substrate inhibition at high concentrations of NAD(P)H as well as cadaverine. The apparent kcat values for NADPH in steady-state NADPH oxidation and oxygen consumption assays were 0.28 ± 0.01 s-1 and 0.24 ± 0.01 s-1, respectively. However, in product formation assays used to measure the rate of N-hydroxylation, the apparent kcat for NADPH (0.034 ± 0.008 s-1) was almost 10-fold lower under saturating FAD and cadaverine concentrations, reflecting an uncoupled reaction, and the apparent NADPH KM was 33 ± 24 μM. Under saturating FAD and NADPH concentrations, the apparent kcat and KM for cadaverine in Csaky assays were 0.048 ± 0.004 s-1 and 19 ± 9 μM, respectively. SsDesB also N-hydroxylated putrescine, spermidine, and L-lysine substrates but not alkyl (di)amines that were branched or had fewer than four methylene units in an alkyl chain. These data demonstrate that SsDesB has wider substrate scope compared to other well-studied ornithine and lysine N-hydroxylases, making it an amenable biocatalyst for the production of desferrioxamine B, derivatives, and other N-substituted products.

Desferrioxamine Supports Metabolic Function in Primary Human Macrophages Infected With Mycobacterium tuberculosis

Tuberculosis is the single biggest infectious killer in the world and presents a major global health challenge. Antimicrobial therapy requires many months of multiple drugs and incidences of drug resistant tuberculosis continues to rise. Consequently, research is now focused on the development of therapies to support the function of infected immune cells. HIF1α-mediated induction of aerobic glycolysis is integral to the host macrophage response during infection with Mtb, as this promotes bacillary clearance. Some iron chelators have been shown to modulate cellular metabolism through the regulation of HIF1α. We examined if the iron chelator, desferrioxamine (DFX), could support the function of primary human macrophages infected with Mtb. Using RT-PCR, we found that DFX promoted the expression of key glycolytic enzymes in Mtb-infected primary human MDMs and human alveolar macrophages. Using Seahorse technology, we demonstrate that DFX enhances glycolytic metabolism in Mtb-stimulated human MDMs, while helping to enhance glycolysis during mitochondrial distress. Furthermore, the effect of DFX on glycolysis was not limited to Mtb infection as DFX also boosted glycolytic metabolism in uninfected and LPS-stimulated cells. DFX also supports innate immune function by inducing IL1β production in human macrophages during early infection with Mtb and upon stimulation with LPS. Moreover, using hypoxia, Western blot and ChIP-qPCR analyses, we show that DFX modulates IL1β levels in these cells in a HIF1α-mediated manner. Collectively, our data suggests that DFX exhibits potential to enhance immunometabolic responses and augment host immune function during early Mtb infection, in selected clinical settings.

Magnetite nanoparticles coated with oleic acid: accumulation in hepatopancreatic cells of the mangrove crab Ucides cordatus

The field of nanotechnology had enormous developments, resulting in new methods for the controlled synthesis of a wide variety of nanoscale materials with unique properties. Efficient methods such as thermal decomposition for efficient size control have been developed in recent years for the synthesis of oleic acid (OA)-coated magnetite (Fe₃O₄) nanoparticles (MNP-OA). These nanostructures can be a source of pollution when emitted in the aquatic environment and could be accumulated by vulnerable marine species such as crustaceans. In this work, we synthesized and characterized MNP-OA of three different diameters (5, 8, and 12 nm) by thermal decomposition. These nanoparticles were remarkably stable after treatment with high affinity iron chelators (calcein, fluorescent desferrioxamine, and fluorescent apotransferrin); however, they displayed pro-oxidant activity after being challenged with ascorbate under two physiological buffers. Free or nanoparticle iron displayed low toxicity to four types of hepatopancreatic cells (E, R, F, and B) of the mangrove crab Ucides cordatus; however, they were promptly bioavailable, posing the risk of ecosystem disruption due to the release of excess nutrients.

Uncovering production of specialized metabolites by Streptomyces argillaceus: Activation of cryptic biosynthesis gene clusters using nutritional and genetic approaches

Sequencing of Streptomyces genomes has revealed they harbor a high number of biosynthesis gene cluster (BGC), which uncovered their enormous potentiality to encode specialized metabolites. However, these metabolites are not usually produced under standard laboratory conditions. In this manuscript we report the activation of BGCs for antimycins, carotenoids, germicidins and desferrioxamine compounds in Streptomyces argillaceus, and the identification of the encoded compounds. This was achieved by following different strategies, including changing the growth conditions, heterologous expression of the cluster and inactivating the adpAa or overexpressing the abrC3 global regulatory genes. In addition, three new carotenoid compounds have been identified.

Actinobacteria phylogenomics, selective isolation from an iron oligotrophic environment and siderophore functional characterization, unveil new desferrioxamine traits

Desferrioxamines are hydroxamate siderophores widely conserved in both aquatic and soil-dwelling Actinobacteria. While the genetic and enzymatic bases of siderophore biosynthesis and their transport in model families of this phylum are well understood, evolutionary studies are lacking. Here, we perform a comprehensive desferrioxamine-centric (des genes) phylogenomic analysis, which includes the genomes of six novel strains isolated from an iron and phosphorous depleted oasis in the Chihuahuan desert of Mexico. Our analyses reveal previously unnoticed desferrioxamine evolutionary patterns, involving both biosynthetic and transport genes, likely to be related to desferrioxamines chemical diversity. The identified patterns were used to postulate experimentally testable hypotheses after phenotypic characterization, including profiling of siderophores production and growth stimulation of co-cultures under iron deficiency. Based in our results, we propose a novel des gene, which we term desG, as responsible for incorporation of phenylacetyl moieties during biosynthesis of previously reported arylated desferrioxamines. Moreover, a genomic-based classification of the siderophore-binding proteins responsible for specific and generalist siderophore assimilation is postulated. This report provides a much-needed evolutionary framework, with specific insights supported by experimental data, to direct the future ecological and functional analysis of desferrioxamines in the environment.

67Ga-labeled deferoxamine derivatives for imaging bacterial infection: Preparation and screening of functionalized siderophore complexes

INTRODUCTION

Deferoxamine (DFO) is a siderophore that bacteria use to scavenge iron and could serve as a targeting vector to image bacterial infection where current techniques have critical limitations. [⁶⁷Ga]-DFO, which is a mimetic of the corresponding iron complex, is taken up by bacteria in culture, however in vivo it clears too rapidly to allow for imaging of infection. In response, we developed several new DFO derivatives to identify those that accumulate in bacteria, and at sites of infection, and that could potentially have improved pharmacokinetics.

METHODS

A library of DFO derivatives was synthesized by functionalizing the terminal amine group of DFO using three different carbamate-forming reactions. Uptake of [⁶⁷Ga]-DFO and the ⁶⁷Ga-labeled derivatives by bacteria and the biodistribution of lead compounds were studied.

RESULTS

⁶⁷Ga-labeled DFO derivatives were prepared and isolated in >90% radiochemical yield and >95% radiochemical purity. The derivatives had significant but slower uptake rates in Staphylococcus aureus than [⁶⁷Ga]-DFO (6% to 60% of the control rate), with no uptake for the most lipophilic derivatives. Biodistribution studies in mice with a S. aureus infection in one thigh revealed that the ethyl carbamate derivative had an excellent infected-to-non-infected ratio (11:1), but high non-specific localization in the gall bladder, liver and small intestine.

CONCLUSIONS

The work reported shows that it is possible to functionalize DFO-type siderophores and retain active uptake of the ⁶⁷Ga-labeled complexes by bacteria. Novel ⁶⁷Ga-labeled DFO derivatives were specifically taken up by S. aureus and selected derivatives demonstrated in vivo localization at sites of infection. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: ⁶⁷Ga-labeled DFO derivatives were actively transported by bacteria using the iron-siderophore pathway, suggesting that it is possible to develop siderophore-based radiopharmaceuticals for imaging bacterial infection.

New Deferoxamine Glycoconjugates Produced upon Overexpression of Pathway-Specific Regulatory Gene in the Marine Sponge-Derived Streptomyces albus PVA94-07

Activation of silent biosynthetic gene clusters in Streptomyces bacteria via overexpression of cluster-specific regulatory genes is a promising strategy for the discovery of novel bioactive secondary metabolites. This approach was used in an attempt to activate a cryptic gene cluster in a marine sponge-derived Streptomyces albus PVA94-07 presumably governing the biosynthesis of peptide-based secondary metabolites. While no new peptide-based metabolites were detected in the recombinant strain, it was shown to produce at least four new analogues of deferoxamine with additional acyl and sugar moieties, for which chemical structures were fully elucidated. Biological activity tests of two of the new deferoxamine analogues revealed weak activity against Escherichia coli. The gene knockout experiment in the gene cluster targeted for activation, as well as overexpression of certain genes from this cluster did not have an effect on the production of these compounds by the strain overexpressing the regulator. It seems plausible that the production of such compounds is a response to stress imposed by the production of an as-yet unidentified metabolite specified by the cryptic cluster.

Synthesis of siderophores by plant-associated metallotolerant bacteria under exposure to Cd(2.)

Rhizosphere and endophytic bacteria are well known producers of siderophores, organic compounds that chelate ferric iron (Fe(3+)), and therefore play an important role in plant growth promotion in metalliferous areas, thereby improving bioremediation processes. However, in addition to their primary function in iron mobilization, siderophores also have the capacity to chelate other heavy metals, such as Al(3+), Zn(2+), Cu(2+), Pb(2+) and Cd(2+), that can affect homeostasis and the heavy metal tolerance of microorganisms. The main goal of our study was to select the most efficient siderophore-producing bacterial strains isolated from the roots (endophytes) and rhizosphere of Betula pendula L. and Alnus glutinosa L. growing at two heavy metal contaminated sites in southern Poland. Siderophore biosynthesis of these strains in the presence of increasing concentrations of Cd(2+) (0, 0.5, 1, 2 and 3 mM) under iron-deficiency conditions was analysed using spectrophotometric chemical tests for hydroxamates, catecholates and phenolates, as well as the separation of bacterial siderophores by HPLC and characterization of their structure by UHPLC-QTOF/MS. We proved that (i) siderophore-producing bacterial strains seems to be more abundant in the rhizosphere (47%) than in root endophytes (18%); (ii) the strains most effective at siderophore synthesis belonged to the genus Streptomyces and were able to secrete three types of siderophores under Cd(2+) stress: hydroxamates, catecholates and phenolates; (iii) in general, the addition of Cd(2+) enhanced siderophore synthesis, particularly ferrioxamine B synthesis, which may indicate that siderophores play a significant role in tolerance to Cd(2+) in Streptomyces sp.

Deferoxamine attenuates lipopolysaccharide-induced inflammatory responses and protects against endotoxic shock in mice

To examine the role of the intracellular labile iron pool (LIP) in the induction of inflammatory responses, we investigated the anti-inflammatory effect of the iron chelator deferoxamine (DFO) on lipopolysaccharide (LPS)-induced inflammatory responses in RAW264.7 macrophage cells and endotoxic shock in mice in the present study. Our data showed that DFO significantly decreased LPS-induced LIP and ROS upregulation. We then found that DFO inhibited phosphorylation of MAP kinases such as ERK and p38 and also inhibited the activation of NF-κB induced by LPS. Furthermore, the production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), nitric oxide (NO) and prostaglandin E2 (PGE2) induced by LPS was inhibited by DFO in RAW264.7 macrophages. Administration of DFO significantly decreased the mortality and improved the survival of septic mice with lethal endotoxemia in LPS-injected mice. These results demonstrate that iron plays a pivotal role in the induction of inflammatory responses and against septic shock. DFO has effective inhibitory effect on the production of inflammatory mediators via suppressing activation of MAPKs and NF-κB signaling pathways; it also has a protective effect on LPS-induced endotoxic shock in mice. Our findings open doors to further studies directed at exploring a new class of drugs against septic shock or other inflammatory diseases by modulating cellular chelatable iron.

Organic extracts from African dust storms stimulate oxidative stress and induce inflammatory responses in human lung cells through Nrf2 but not NF-κB

The health impact of the global African dust event (ADE) phenomenon in the Caribbean has been vaguely investigated. Heavy metals in ADE and non-ADE extracts were evaluated for the formation of reactive oxygen species (ROS) and antioxidant capacity by cells using, deferoxamine mesylate (DF) and N-acetyl-l-cysteine (NAC). Results show that ADE particulate matter 2.5 (PM2.5) induces ROS and stimulates oxidative stress. Pre-treatment with DF reduces ROS in ADE and Non-ADE extracts and in lung cells demonstrating that heavy metals are of utmost importance. Glutathione-S-transferase and Heme Oxygenase 1 mRNA levels are induced with ADE PM and reduced by DF and NAC. ADE extracts induced Nrf2 activity and IL-8 mRNA levels significantly more than Non-ADE. NF-κB activity was not detected in any sample. Trace elements and organic constituents in ADE PM2.5 enrich the local environment load, inducing ROS formation and activating antioxidant-signaling pathways increasing pro-inflammatory mediator expressions in lung cells.

Direct evidence of iron uptake by the Gram-positive siderophore-shuttle mechanism without iron reduction

Iron is an essential element for all organisms, and microorganisms produce small molecule iron-chelators, siderophores, to efficiently acquire Fe(III). Gram-positive bacteria possess lipoprotein siderophore-binding proteins (SBPs) on the membrane. Some of the SBPs bind both apo-siderophores (iron-free) and Fe-siderophore (iron-chelated) and only import Fe-siderophores. When the SBP initially binds an apo-siderophore, the SBP uses the Gram-positive siderophore-shuttle mechanism (the SBPs exchange Fe(III) from a Fe-siderophore to the apo-siderophore bound to the protein) and/or displacement mechanism (the apo-siderophore bound to the SBP is released and a Fe-siderophore is then bound to the protein) to import the Fe-siderophore. Previously, we reported that the Bacillus cereus SBP, YxeB, exchanges Fe(III) from a ferrioxamine B (FO) to a desferrioxamine B (DFO) bound to YxeB using the siderophore-shuttle mechanism although the iron exchange was indirectly elucidated. Synthetic Cr-DFO (inert metal FO analog) and Ga-DFO (nonreducible FO analog) are bound to YxeB and imported via YxeB and the corresponding permeases and ATPase. YxeB exchanges Fe(III) from FO and Ga(III) from Ga-DFO to DFO bound to the protein, indicating that the metal-exchange occurs without metal reduction. YxeB also binds DFO derivatives including acetylated DFO (apo-siderophore) and acetylated FO (AcFO, Fe-siderophore). The iron from AcFO is transferred to DFO when bound to YxeB, giving direct evidence of iron exchange. Moreover, YxeB also uses the displacement mechanism when ferrichrome (Fch) is added to the DFO:YxeB complex. Uptake by the displacement mechanism is a minor pathway compared to the shuttle mechanism.

Accessibility of humic-associated Fe to a microbial siderophore: implications for bioavailability

Microorganisms in aerobic, circum-neutral environments are challenged to acquire sufficient nutrient Fe due to low solubilities of Fe oxides. To overcome this challenge, many aerobic microbes produce low molecular weight (MW) organic ligands, or siderophores, with extremely high Fe-binding affinities. This research expands the existing understanding of siderophore-mediated Fe acquisition from minerals by examining the effects of the siderophore desferrioxamine B (DFOB) on Fe removal from aquatic humic substances (XAD-8-isolated) and other organic matter (OM) isolates (reverse osmosis, RO; and "transphilic", XAD-4) from several rivers including the Suwannee River (GA, USA). Analysis of samples by asymmetrical flow field-flow fractionation (AsFlFFF) with in-line ICP-MS and UV-vis detectors showed that Fe was naturally abundant and primarily associated with intermediate to high MW OM. An excess of DFOB (relative to naturally present Fe) removed ∼ 75% of Fe and shifted the OM MW distribution to lower MWs, perhaps due to removal of "bridging" Fe, although additional mechanistic study of MW shifts is needed. Removal of other OM-associated metals (e.g., Al, Cu, Zn) by DFOB was minimal for all but a few samples. Fe bound to humic substances and other more "transphilic" organic components therefore should be considered readily bioavailable to aerobic, siderophore-producing microorganisms.

Bisucaberin B, a linear hydroxamate class siderophore from the marine bacterium Tenacibaculum mesophilum

A siderophore, named bisucaberin B, was isolated from Tenacibaculum mesophilum bacteria separated from a marine sponge collected in the Republic of Palau. Using spectroscopic and chemical methods, the structure of bisucaberin B (1) was clearly determined to be a linear dimeric hydroxamate class siderophore. Although compound 1 is an open form of the known macrocyclic dimer bisucaberin (2), and was previously described as a bacterial degradation product of desferrioxamine B (4), the present report is the first description of the de novo biosynthesis of 1. To the best of our knowledge, compound 1 is the first chemically characterized siderophore isolated from a bacterium belonging to the phylum Bacteroidetes.

Uptake, distribution, and velocity of organically complexed plutonium in corn (Zea mays)

Lysimeter experiments and associated simulations suggested that Pu moved into and through plants that invaded field lysimeters during an 11-year study at the Savannah River Site. However, probable plant uptake and transport mechanisms were not well defined, so more detailed study is needed. Therefore, experiments were performed to examine movement, distribution, and velocity of soluble, complexed Pu in corn. Corn was grown and exposed to Pu using a "long root" system in which the primary root extended through a soil pot and into a hydroponic container. To maintain solubility, Pu was complexed with the bacterial siderophore DFOB (Desferrioxamine B) or the chelating agent DTPA (diethylenetriaminepentaacetic acid). Corn plants were exposed to nutrient solutions containing Pu for periods of 10 min to 10 d. Analysis of root and shoot tissues permitted concentration measurement and calculation of uptake velocity and Pu retardation in corn. Results showed that depending on exposure time, 98.3-95.9% of Pu entering the plant was retained in the roots external to the xylem, and that 1.7-4.1% of Pu entered the shoots (shoot fraction increased with exposure time). Corn Pu uptake was 2-4 times greater as Pu(DFOB) than as Pu(2)(DTPA)(3). Pu(DFOB) solution entered the root xylem and moved 1.74 m h(-1) or greater upward, which is more than a million times faster than Pu(III/IV) downward movement through soil during the lysimeter study. The Pu(DFOB) xylem retardation factor was estimated to be 3.7-11, allowing for rapid upward Pu transport and potential environmental release.

Chemical syntheses and in vitro antibacterial activity of two desferrioxamine B-ciprofloxacin conjugates with potential esterase and phosphatase triggered drug release linkers

Two desferrioxamine B-ciprofloxacin conjugates with 'trimethyl-lock' based linkers that are designed to release the antibiotic after esterase or phosphatase-mediated hydrolysis were synthesized. The potential esterase-sensitive conjugate 13 displayed moderate to good antibacterial activities against selected ferrioxamine-utilizing bacteria, although the activities were lower than the parent drug ciprofloxacin. However, the potential phophatase-sensitive conjugate 23 was inactive against the same panel of organisms tested. These properties appeared to be related to the activating efficiency of the linker by the enzyme and to the outer membrane protein recognition of the chemically modified siderophore used in the conjugate.

Iron homeostasis and fire blight susceptibility in transgenic pear plants overexpressing a pea ferritin gene

The bacterial pathogen Erwinia amylovora causes the devastating disease known as fire blight in some rosaceous plants including apple and pear. One of the pathogenicity factors affecting fire blight development is the production of a siderophore, desferrioxamine, which overcomes the limiting conditions in plant tissues and also protects bacteria against active oxygen species. In this paper we examine the effect of an iron chelator protein encoded by the pea ferritin gene on the fire blight susceptibility of pear (Pyrus communis). Transgenic pear clones expressing this gene controlled either by the constitutive promoter CaMV 35S or by the inducible promoter sgd24 promoter were produced. The transgenic clones produced were analysed by Q-RT-PCR to determine the level of expression of the pea transgene. A pathogen-inducible pattern of expression of the pea transgene was observed in sgd24-promoter transformants. Adaptation to iron deficiency in vitro was tested in some transgenic clones and different iron metabolism parameters were measured. No strong effect on iron and chlorophyll content, root reductase activity and fire blight susceptibility was detected in the transgenic lines tested. No transformants showed a significant reduction in susceptibility to fire blight in greenhouse conditions when inoculated with E. amylovora.

Mechanisms for the shuttling of plasma non-transferrin-bound iron (NTBI) onto deferoxamine by deferiprone

In iron overload conditions, plasma contains non-transferrin bound iron species, collectively referred to as plasma NTBI. These include iron citrate species, some of which are protein bound. Because NTBI is taken into tissues susceptible to iron loading, its removal by chelation is desirable but only partial using standard deferoxamine (DFO) therapy. Speciation plots suggest that, at clinically achievable concentrations, deferiprone (DFP) will shuttle iron onto DFO to form feroxamine (FO), but whether NTBI chelation by DFO is enhanced to therapeutically relevant rates by DFP is unknown. As FO is highly stable, kinetic measurements of FO formation by high-performance liquid chromatography or by stopped-flow spectrometry are achievable. In serum from thalassemia major patients supplemented with 10 microM DFO, FO formation paralleled NTBI removal but never exceeded 50% of potentially available NTBI; approximately one third of NTBI was chelated rapidly but only 15% of the remainder at 20 h. Addition of DFP increased the magnitude of the slower component, with increments in FO formation equivalent to complete NTBI removal by 8 h. This shuttling effect was absent in serum from healthy control subjects, indicating no transferrin iron removal. Studies with iron citrate solutions also showed biphasic chelation by DFO, the slow component being accelerated by the addition of DFP, with optimal enhancement at 30 microM. Physiological concentrations of albumin also enhanced DFO chelation from iron citrate, and the co-addition of DFP further accelerated this effect. We conclude that at clinically relevant concentrations, DFP enhances plasma NTBI chelation with DFO by rapidly accessing and shuttling NTBI fractions that are otherwise only slowly available to DFO.

Studies on iron stores built up by an iron-poly (sorbitol-gluconic acid) complex, Ferastral, in man. Preliminary report

The characteristics of iron stores built up by a new parenteral iron-poly (sorbitol-gluconic acid) complex, Ferastral, have been studied in iron depleted non-anemic blood donors. The results from studies on the first three subjects are presented. The availability of this storage iron for the chelator, desferrioxamine, was found to be in the same range as normal iron stores. The pattern of distribution in reticulo-endothelial cells of the bone marrow could not be differentiated from natural storage iron. No visible iron could be detected in liver parenchymal cells 40 days after iron administration. The results from these preliminary studies suggests normal bioavailability of this material for Hb-synthesis. The absence of iron in liver parenchymal cells might be explained by the short time interval between the iron administration and the fine needle aspiration biopsy.

Effects of the microbial siderophore DFO-B on Pb and Cd speciation in aqueous solution

This study investigates the complexation environments of aqueous Pb and Cd in the presence of the trihydroxamate microbial siderophore, desferrioxamine-B (DFO-B) as a function of pH. Complexation of aqueous Pb and Cd with DFO-B was predicted using equilibrium speciation calculation. Synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy at Pb L(III) edge and Cd K edge was used to characterize Pb and Cd-DFO-B complexes at pH values predicted to best represent each of the metal-siderophore complexes. Pb was not found to be complexed measurably by DFO-B at pH 3.0, but was complexed by all three hydroxamate groups to form a totally "caged" hexadentate structure at pH 7.5-9.0. At the intermediate pH value (pH 4.8), a mixture of Pb-DFOB complexes involving binding of the metal through one and two hydroxamate groups was observed. Cd, on the other hand, remained as hydrated Cd2+ at pH 5.0, occurred as a mixture of Cd-DFOB and inorganic species at pH 8.0, and was bound by three hydroxamate groups from DFO-B at pH 9.0. Overall, the solution species observed with EXAFS were consistent with those predicted thermodynamically. However, Pb speciation at higher pH values differed from that predicted and suggests that published constants underestimate the binding constant for complexation of Pb with all three hydroxamate groups of the DFO-B ligand. This molecular-level understanding of metal-siderophore solution coordination provides physical evidence for complexes of Pb and Cd with DFO-B, and is an important first step toward understanding processes at the microbial- and/or mineral-water interface in the presence of siderophores.

Mutation of Streptomyces griseoflavus in order to obtain high yield desferrioxamine producing fused cells

Streptomyces griseoflavus PTCC 1130 was mutated by UV irradiation. Two mutants were obtained (C7031 and S7011). These two mutants were able to produce desferioxamine. Desferrioxamine was extracted from the culture broth of the two mutated strains and the thin layer chromatogram of the products showed the R(F) values of 0.461, 0.463 and 0.456 for S7011, C7031 and the standard, respectively. The protoplasts of mutated Streptomyces griseoflavus were isolated and fused together. Total numbers of 58 fusions were obtained and only 17 fusions showed significant resistance to sodium azide and crystal violet. In terms of production of desferrioxamine only fusion PF9 and PF10 increased 68.3 and 81.8% desferrioxamine production as compared to parent strain (PTCC 1130), respectively.

Characterization of the ferrioxamine uptake system of Nitrosomonas europaea

The chemolithoautotroph Nitrosomonas europaea has two genes predicted to encode outer-membrane (OM) ferrioxamine transporters. Expression of the ferrioxamine uptake system required induction, as shown by the shorter lag phase in ferrioxamine-containing cultures when ferrioxamine-exposed cells were used as an inoculum. The two OM ferrioxamine siderophore transporters encoded by foxA(1) (NE1097) and foxA(2) (NE1088) were produced only in cells grown in Fe-limited ferrioxamine-containing medium. The inactivation of foxA(1), singly or in combination with foxA(2), prevented growth in Fe-limited medium containing excess desferrioxamine (DFX). The foxA(2)-disrupted single mutant grew poorly in the regular Fe-limited (0.2 microM) medium with 10 microM DFX, but grew well when the Fe level was raised to 1.0 microM with 10 microM DFX. For efficient acquisition of Fe-loaded ferrioxamine, N. europaea needs both ferrioxamine transporters FoxA(1) and FoxA(2). FoxA(1) probably regulates its own production, and it controls the production of FoxA(2) as well.

Chelators at the cancer coalface: desferrioxamine to Triapine and beyond

The importance of iron and copper in cancer biology has been well established. Iron plays a fundamental role in cellular proliferation and copper has been shown to be a significant cofactor for angiogenesis. Early observations with the chelator used for the treatment of iron overload, desferrioxamine, showed that it had promise as an anticancer agent. These results sparked great interest in the possibility of developing more effective iron chelators for cancer therapy. The recent entry into clinical trials of the iron-binding drug, Triapine, provides evidence of the potential of this antitumor strategy. Likewise, chelators originally designed to treat disorders of copper overload, such as penicillamine, trientine, and tetrathiomolybdate, have also emerged as potential anticancer drugs, as they are able to target the key angiogenic cofactor, copper. In this review, we will discuss the development of these and other chelators that show potential as anticancer agents.

Non-transferrin-bound iron reaches mitochondria by a chelator-inaccessible mechanism: biological and clinical implications

Non-transferrin-bound iron, commonly found in the plasma of iron-overloaded individuals, permeates into cells via pathways independent of the transferrin receptor. This may lead to excessive cellular accumulation of labile iron followed by oxidative damage and eventually organ failure. Mitochondria are the principal destination of iron in cells and a primary site of prooxidant generation, yet their mode of acquisition of iron is poorly understood. Using fluorescent probes sensitive to iron or to reactive oxygen species, targeted to cytosol and/or to mitochondria, we traced the ingress of labile iron into these compartments by fluorescence microscopy and quantitative fluorimetry. We observed that 1) penetration of non-transferrin-bound iron into the cytosol and subsequently into mitochondria occurs with barely detectable delay and 2) loading of the cytosol with high-affinity iron-binding chelators does not abrogate iron uptake into mitochondria. Therefore, a fraction of non-transferrin-bound iron acquired by cells reaches the mitochondria in a nonlabile form. The physiological role of occluded iron transfer might be to confer cells with a “safe and efficient cytosolic iron corridor” to mitochondria. However, such a mechanism might be deleterious in iron-overload conditions, because it could lead to surplus accumulation of iron in these critical organelles.

BNIP3 is an RB/E2F target gene required for hypoxia-induced autophagy

Hypoxia and nutrient deprivation are environmental stresses governing the survival and adaptation of tumor cells in vivo. We have identified a novel role for the Rb tumor suppressor in protecting against nonapoptotic cell death in the developing mouse fetal liver, in primary mouse embryonic fibroblasts, and in tumor cell lines. Loss of pRb resulted in derepression of BNip3, a hypoxia-inducible member of the Bcl-2 superfamily of cell death regulators. We identified BNIP3 as a direct target of pRB/E2F-mediated transcriptional repression and showed that pRB attenuates the induction of BNIP3 by hypoxia-inducible factor to prevent autophagic cell death. BNIP3 was essential for hypoxia-induced autophagy, and its ability to promote autophagosome formation was enhanced under conditions of nutrient deprivation. Knockdown of BNIP3 reduced cell death, and remaining deaths were necrotic in nature. These studies identify BNIP3 as a key regulator of hypoxia-induced autophagy and suggest a novel role for the RB tumor suppressor in preventing nonapoptotic cell death by limiting the extent of BNIP3 induction in cells.

Growth stimulation of Brevibacterium sp. by siderophores

AIMS

To assess which types of siderophores are typically produced by Brevibacterium and how siderophore production and utilization traits are distributed within this genus.

METHODS AND RESULTS

During co-cultivation experiments it was found that growth of B. linens Br5 was stimulated by B. linens NIZO B1410 by two orders of magnitude. The stimulation was caused by the production of hydroxamate siderophores by B. linens NIZO B1410 that enabled the siderophore-auxotrophic strain Br5 to grow faster under the applied iron-limited growth conditions. Different patterns of siderophore production and utilization were observed within the genus Brevibacterium. These patterns did not reflect the phylogenetic relations within the group as determined by partial 16S rDNA sequencing. Most Brevibacterium strains were found to utilize hydroxamate siderophores.

CONCLUSIONS

Brevibacteria can produce and utilize siderophores although certain strains within this genus are siderophore-auxotrophic.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is reported for the first time that brevibacteria produce and utilize siderophores. This knowledge can be utilized to stimulate growth of auxotrophic strains under certain conditions. Enhancing the growth rate of Brevibacterium is of importance for the application of this species, for example, for cheese manufacturing or for industrial production of enzymes or metabolites.

The iron- and cAMP-regulated gene SIT1 influences ferrioxamine B utilization, melanization and cell wall structure in Cryptococcus neoformans

The mechanisms by which pathogens sense and transport iron are important during infection, because of the low availability of free iron in the mammalian host. Iron is a key nutritional cue for the pathogen Cryptococcus neoformans, because it influences expression of the polysaccharide capsule that is the major virulence factor of the fungus. In this study, C. neoformans mutants were constructed with a defect in the iron-regulated gene SIT1 that encodes a putative siderophore iron transporter. Analysis of mutants in serotype A and D strains demonstrated that SIT1 is required for the use of siderophore-bound iron, and for growth in a low-iron environment. The sit1 mutants also showed changes in melanin formation and cell wall density, and it was found that mutants defective in protein kinase A, which is known to influence melanization and capsule formation, showed elevated SIT1 transcripts in both the serotype A and the serotype D backgrounds. Finally, the mutants were tested for virulence in a murine model of cryptococcosis, and it was found that SIT1 was not required for virulence. Overall, these studies establish links between iron acquisition, melanin formation and cAMP signalling in C. neoformans.

Huntingtin inclusion bodies are iron-dependent centers of oxidative events

Recently, we reported that the transient expression of huntingtin exon1 polypeptide containing polyglutamine tracts of various sizes (httEx1-polyQ) in cell models of Huntington disease generated an oxidative stress whose intensity was CAG repeat expansion-dependent. Here, we have analyzed the intracellular localization of the oxidative events generated by the httEx1-polyQ polypeptides. Analysis of live COS-7 cells as well as neuronal SK-N-SH and PC12 cells incubated with hydroethidine or dichlorofluorescein diacetate revealed oxidation of these probes at the level of the inclusion bodies formed by httEx1-polyQ polypeptides. The intensity and frequency of the oxidative events among the inclusions were CAG repeat expansion-dependent. Electron microscopic analysis of cell sections revealed the presence of oxidation-dependent morphologic alterations in the vicinity of httEx1-polyQ inclusion bodies. Moreover, a high level of oxidized proteins was recovered in partially purified inclusions. We also report that the iron chelator deferroxamine altered the structure, localization and oxidative potential of httEx1-polyQ inclusion bodies. Hence, despite the fact that the formation of inclusion bodies may represent a defense reaction of the cell to eliminate httEx1 mutant polypeptide, this phenomenon appears inherent to the generation of iron-dependent oxidative events that can be deleterious to the cell.

Transcriptional regulation of the desferrioxamine gene cluster of Streptomyces coelicolor is mediated by binding of DmdR1 to an iron box in the promoter of the desA gene

Streptomyces coelicolor and Streptomyces pilosus produce desferrioxamine siderophores which are encoded by the desABCD gene cluster. S. pilosus is used for the production of desferrioxamine B which is utilized in human medicine. We report the deletion of the desA gene encoding a lysine decarboxylase in Streptomyces coelicolor A3(2). The DeltadesA mutant was able to grow on lysine as the only carbon and nitrogen source but its desferrioxamine production was blocked, confirming that the L-lysine decarboxylase encoded by desA is a dedicated enzyme committing L-lysine to desferrioxamine biosynthesis. Production of desferrioxamine was restored by complementation with the whole wild-type desABCD cluster, but not by desA alone, because of a polar effect of the desA gene replacement on expression of the downstream des genes. The transcription pattern of the desABCD cluster in S. coelicolor showed that all four genes were coordinately induced under conditions of iron deprivation. The transcription start point of the desA gene was identified by primer extension analysis at a thymine located 62 nucleotides upstream of the translation start codon. The -10 region of the desA promoter overlaps the 19-nucleotide palindromic iron box sequence known to be involved in iron regulation in Streptomyces. Binding of DmdR1 divalent metal-dependent regulatory protein to the desA promoter region of both S. coelicolor and S. pilosus was shown using electrophoretic mobility-shift assays, validating the conclusion that iron regulation of the desABCD cluster is mediated by the regulatory protein DmdR1. We conclude that the genes involved in desferrioxamine production are under transcriptional control exerted by the DmdR1 regulator in the presence of iron and are expressed under conditions of iron limitation.

Coenzyme Q(10) provides neuroprotection in iron-induced apoptosis in dopaminergic neurons

The exact molecular mechanism of progressive loss of neuromelanin containing nigrostriatal dopaminergic neurons in Parkinson's disease (PD) remains unknown, yet evidence suggests that iron might play an important role in PD pathology. In this study we have determined the neuroprotective role of coenzyme Q(10) (CoQ(10)) in ironinduced apoptosis in cultured human dopaminergic (SK-N-SH) neurons, in metallothionein gene- manipulated mice, and in alpha-synuclein knockout (alpha-synko) mice with a primary objective to assess a possible therapeutic and anti-inflammatory potential for CoQ(10) in PD. Iron-induced mitochondrial damage and apoptosis were characterized by reactive oxygen species production, increased metallothionein and glutathione synthesis, caspase- 3 activation, NF-kappaB induction, and decreased Bcl-2 expression, without any significant change in Bax expression. Lower concentrations of FeSO4 (1-10 microM) induced perinuclear aggregation of mitochondria, whereas higher concentrations (100-250 microM) induced CoQ(10) depletion, plasma membrane perforations, mitochondrial damage, and nuclear DNA condensation and fragmentation. FeSO(4)-induced deleterious changes were attenuated by pretreatment with CoQ(10) and by deferoxamine, a potent iron chelator, in SK-N-SH cells. 1-Methyl, 4-phenyl, 1,2,3,6- tetrahydropyridine (MPTP)-induced striatal release of free iron, and NF-kappaB expression were significantly increased; whereas ferritin and melanin synthesis were significantly reduced in the substantia nigra pars compacta (SNpc) of MT(dko) mice as compared with control(wt) mice, MT(trans) mice, and alpha-synko mice. CoQ(10) treatment inhibited MPTP-induced NF-kappaB induction in all of the genotypes. These data suggest that glutathione and metallothionein synthesis might be induced as an attempt to combat iron-induced oxidative stress, whereas exogenous administration of CoQ(10) or of metallothionein induction might provide CoQ(10)-mediated neuroprotection in PD.

Histidine-induced injury to cultured liver cells, effects of histidine derivatives and of iron chelators

The amino acid histidine is an excellent buffer and is therefore included in several organ preservation solutions used in transplantation medicine. However, when used at concentrations as in these solutions, histidine has a marked injurious potential. Therefore, we here assessed the mechanism of histidine-induced cell injury and searched for ways to use the buffering power of histidine but avoid histidine toxicity. When cultured hepatocytes were incubated in HTK solution or in modified Krebs-Henseleit buffer containing 198 mM L-histidine at 37 degrees C, most cells lost viability within 3 h (LDH release 86 +/- 7% and 89 +/- 5%, respectively). This injury was accompanied by marked lipid peroxidation, and was strongly inhibited by hypoxia, by the antioxidants trolox, butylated hydroxytoluene and N-acetylcysteine and by the membrane-permeable iron chelators 2,2'-dipyridyl, 1,10-phenanthroline, LK 614, LK 616 and deferoxamine. Thus, histidine-induced cell injury appears to be mediated by an iron-dependent formation of reactive oxygen species. D-Histidine, imidazol and L-histidine methyl ester also elicited marked injury, while the N-substituted derivatives Nalpha-acetyl-L-histidine and tert-butyl-oxycarbonylhistidine and histidine-containing dipeptides showed almost no toxicity. Histidine toxicity, its iron dependence and the superiority of Nalpha-acetyl-L-histidine were also evident during/after cold (4 degrees C) incubations. Therefore, we suggest the addition of iron chelators to histidine-containing solutions, and/or replacing histidine with Nalpha-acetyl-L-histidine in organ preservation solutions.

Identification of siderophores ofPseudomonas stutzeri

We have identified two types of siderophores produced by Pseudomonas, one of which has never before been found in the genus. Twelve strains of Pseudomonas stutzeri belonging to genomovars 1, 2, 3, 4, 5, and 9 produced proferrioxamines, the hydroxamate-type siderophores. Pseudomonas stutzeri JM 300 (genomovar 7) and DSM 50238 (genomovar 8) and Pseudomonas balearica DSM 6082 produced amonabactins, catecholate-type siderophores. The major proferrioxamines detected were the cyclic proferrioxamines E and D2. Pseudomonas stutzeri KC also produced cyclic (X1and X2) and linear (G1and G2a-c) proferrioxamines. Our data indicate that the catecholate-type siderophores belong to amonabactins P 750, P 693, T 789, and T 732. A mutant of P. stutzeri KC (strain CTN1) that no longer produced the secondary siderophore pyridine-2,6-dithiocarboxylic acid continued to produce all other siderophores in its normal spectrum. Siderophore profiles suggest that strain KC (genomovar 9) belongs to the proferrioxamine-producing P. stuzeri. Moreover, a putative ferrioxamine outer membrane receptor gene foxA was identified in strain KC, and colony hybridization showed the presence of homologous receptor genes in all P. stutzeri and P. balearica strains tested.Key words: siderophore, Pseudomonas stutzeri, ferrioxamine, amonabactin.

Critical role of methionine-722 in the stimulation of human brain G-proteins and neurotoxicity induced by London familial Alzheimer's disease (FAD) mutated V717G-APP(714-723)

We have demonstrated earlier that V717G-APP(714-723), the membrane fragment of the V717G ("London") familial Alzheimer's disease (FAD) mutant of amyloid precursor protein (APP), is a potent stimulator of G-proteins in human brain membranes. In this study, we tested the hypothesis that Met-722 in the V717G-APP(714-723) peptide (P2) plays a critical role in the P2-induced oxidative stimulation of G-proteins in the human temporal cortex membranes and in the neurotoxicity of the peptide in differentiated PC12 and cerebellar granular cells. We found that 10 microM P3, the Met-722 sulfoxide analog of P2, produced a twofold lower stimulation of G-proteins ([(35)S]-GTPgammaS binding) in control temporal cortex membranes compared with 10 microM P2. The stimulatory effect of 10 microM P4, the Met-722 sulfone analog of P2, was 2.5-fold lower than the effect of P2. In Alzheimer's disease (AD) temporal cortex, the P3 and P4 stimulation of G-proteins was slightly weaker than the P2 stimulation. Substitution of the Met-722 S-atom in P2 by -CH(2)- group (P5) led to the disappearance of P2 stimulatory effect on G-proteins. Glutathione (GSH), melatonin (Mel), desferrioxamine (DFO) and 17-beta-estradiol (17betaE) significantly reduced P2 stimulatory effect on G-proteins in human brain. Only DFO and Mel were able to reduce the moderate stimulation of G-proteins by P3, whereas none of the tested antioxidants influenced the weak stimulation by P4. P2 at 100 microM induced a 40% decrease in PC12 cell viability as revealed by MTT assay, the effect being significantly higher than that of P3 or P4, whereas P1 (wild-type APP(714-723)) did not affect cell viability. Trypan Blue exclusion assay demonstrated that 10 microM P2 and P3 induced 3.8- and 3.5-fold death in the cerebellar granular cells as compared with the respective control values. P1 and P4 at 10 microM induced 1.7- and 2.3-fold increase in cell death, respectively. Treatment of the cerebellar granular cells with pertussis toxin decreased the high neurotoxicity of P2 and P3, whereas the low toxicity of P1 and P4 was not influenced. These results support the hypothesis that the G-protein stimulatory effect and neurotoxicity of "London"-mutated V717G-APP(714-723) (P2) and its Met-722 oxidized analogs involve oxidative-dependent and oxidative-independent mechanisms and the oxidation state of Met-722 plays a critical role in determining the mechanism.

Multiple biosynthetic and uptake systems mediate siderophore-dependent iron acquisition in Streptomyces coelicolor A3(2) and Streptomyces ambofaciens ATCC 23877

Siderophore-mediated iron acquisition has been well studied in many bacterial pathogens because it contributes to virulence. In contrast, siderophore-mediated iron acquisition by saprophytic bacteria has received relatively little attention. The independent identification of the des and cch gene clusters that direct production of the tris-hydroxamate ferric iron-chelators desferrioxamine E and coelichelin, respectively, which could potentially act as siderophores in the saprophyte Streptomyces coelicolor A3(2), has recently been reported. Here it is shown that the des cluster also directs production of desferrioxamine B in S. coelicolor and that very similar des and cch clusters direct production of desferrioxamines E and B, and coelichelin, respectively, in Streptomyces ambofaciens ATCC 23877. Sequence analyses of the des and cch clusters suggest that components of ferric-siderophore uptake systems are also encoded within each cluster. The construction and analysis of a series of mutants of S. coelicolor lacking just biosynthetic genes or both the biosynthetic and siderophore uptake genes from the des and cch clusters demonstrated that coelichelin and desferrioxamines E and B all function as siderophores in this organism and that at least one of these metabolites is required for growth under defined conditions even in the presence of significant quantities of ferric iron. These experiments also demonstrated that a third siderophore uptake system must be present in S. coelicolor, in addition to the two encoded within the cch and des clusters, which show selectivity for coelichelin and desferrioxamine E, respectively. The ability of the S. coelicolor mutants to utilize a range of exogenous xenosiderophores for iron acquisition was also examined, showing that the third siderophore-iron transport system has broad specificity for tris-hydroxamate-containing siderophores. Together, these results define a complex system of multiple biosynthetic and uptake pathways for siderophore-mediated iron acquisition in S. coelicolor and S. ambofaciens.

FoxB of Pseudomonas aeruginosa functions in the utilization of the xenosiderophores ferrichrome, ferrioxamine B, and schizokinen: evidence for transport redundancy at the inner membrane

Expression of the inner membrane protein FoxB (PA2465) of Pseudomonas aeruginosa in mutants of Sinorhizobium meliloti that are defective in the utilization of ferrichrome, ferrioxamine B, and schizokinen resulted in the restoration of siderophore utilization. Mutagenesis of foxB in P. aeruginosa did not abolish siderophore utilization, suggesting that the function is redundant.

Neisseria gonorrhoeae requires expression of TonB and the putative transporter TdfF to replicate within cervical epithelial cells

Neisseria gonorrhoeae has evolved a repertoire of iron acquisition systems that facilitate essential iron uptake in the human host. Acquisition of iron requires both the energy-harnessing cytoplasmic membrane protein, TonB, as well as specific outer membrane TonB-dependent transporters (TdTs.) Survival within host epithelial cells is important to the pathogenesis of gonococcal disease and may contribute to the persistence of infection. However, the mechanisms by which gonococci acquire iron within this intracellular niche are not currently understood. In this study, we investigated the survival of gonococcal strain FA1090 within ME180 human cervical epithelial cells with respect to high affinity iron acquisition. Intracellular survival was dependent upon iron supplied by the host cell. TonB was expressed in the host cell environment and this protein was critical to gonococcal intracellular survival. Furthermore, expression of the characterized outer membrane transporters TbpA, FetA and LbpA and putative transporters TdfG, TdfH and TdfJ were not necessary for intracellular survival. Conversely, intracellular survival was dependent on expression of the putative transporter, TdfF. Expression of TdfF was detected in the presence of epithelial cell culture media containing fetal bovine serum. Expression was further modulated by iron availability. To our knowledge, this study is the first to demonstrate the specific requirement for a single iron transporter in the survival of a bacterial pathogen within host epithelial cells.

Identification of genes involved in siderophore transport inStreptomyces coelicolorA3(2)

The potential iron siderophore transporter genes have been determined from the genome sequence of Streptomyces coelicolor A3(2). One of these gene clusters, cdtABC, was disrupted and characterized to determine its role in the uptake of the siderophores produced by S. coelicolor. Resistance to the siderophore-like antibiotics, salmycin and albomycin, was tested in the parent and cdtABC mutant, showing that the parent, but not the mutant, was sensitive to salmycin, while both were resistant to albomycin. Ferrioxamine competition assays against salmycin suggest that the uptake of salmycin is via a ferrioxamine transport system. However, Fe-55 ferrioxamine B uptake experiments did not reveal any difference between the parent and mutant. This suggests that CdtABC specifically transports salmycin, while ferrioxamine uptake maybe substituted by another transport system.

Targeting the hypoxia inducible factor pathway with mitochondrial uncouplers

Hypoxia inducible factor-1 (HIF-1) is central to most adaptation responses of tumors to hypoxia, and consists of a hypoxia inducible HIF-1alpha or -2alpha subunit, and a constitutively expressed HIF-1beta subunit. Previously, mitochondrial uncouplers, rottlerin and FCCP, were shown to increase the rate of cellular O(2 )consumption. In this study, we determined that mitochondrial uncouplers, rottlerin and FCCP, significantly decreased hypoxic as well as normoxic HIF-1 transcriptional activity which was in part mediated by down-regulation of the oxygen labile HIF-1alpha and HIF-2alpha protein levels in PC-3 and DU-145 prostate cancer cells. Our results also revealed that mitochondrial uncouplers decreased the expression of HIF target genes, VEGF and VEGF receptor-2. Taken together, our results indicate that functional mitochondria are important in HIF-1alpha and HIF-2alpha protein stability and transcriptional activity during normoxia as well as in hypoxia, and that mitochondrial uncouplers may be useful in the inhibition of HIF pathway in tumors.

The heterologous siderophores ferrioxamine B and ferrichrome activate signaling pathways in Pseudomonas aeruginosa

Pseudomonas aeruginosa secretes two siderophores, pyoverdine and pyochelin, under iron-limiting conditions. These siderophores are recognized at the cell surface by specific outer membrane receptors, also known as TonB-dependent receptors. In addition, this bacterium is also able to incorporate many heterologous siderophores of bacterial or fungal origin, which is reflected by the presence of 32 additional genes encoding putative TonB-dependent receptors. In this work, we have used a proteomic approach to identify the inducing conditions for P. aeruginosa TonB-dependent receptors. In total, 11 of these receptors could be discerned under various conditions. Two of them are only produced in the presence of the hydroxamate siderophores ferrioxamine B and ferrichrome. Regulation of their synthesis is affected by both iron and the presence of a cognate siderophore. Analysis of the P. aeruginosa genome showed that both receptor genes are located next to a regulatory locus encoding an extracytoplasmic function sigma factor and a transmembrane sensor. The involvement of this putative regulatory locus in the specific induction of the ferrioxamine B and ferrichrome receptors has been demonstrated. These results show that P. aeruginosa has evolved multiple specific regulatory systems to allow the regulation of TonB-dependent receptors.

The ABC transporter Abcg2/Bcrp: role in hypoxia mediated survival

ABC (ATP-binding cassette) transporters have diverse roles in many cellular processes. These diverse roles require the presence of conserved membrane spanning domains and nucleotide binding domains. Bcrp (Abcg2) is a member of the ATP binding cassette family of plasma membrane transporters that was originally discovered for its ability to confer drug resistance in tumor cells. Subsequent studies showed Bcrp expression in normal tissues and high expression in primitive stem cells. Bcrp expression is induced under low oxygen conditions consistent with its high expression in tissues exposed to low oxygen environments. Moreover, Bcrp interacts with heme and other porphyrins. This finding and its regulation by hypoxia suggests it may play a role in protecting cells/tissue from protoporphyrin accumulation under hypoxia. These observations are strengthened by the fact that porphyrins accumulate in tissues of the Bcrp knockout mouse. It is possible that humans with loss of function Bcrp alleles may be more susceptible to porphyrin-induced phototoxicity. We propose that Bcrp plays a role in porphyrin homoeostasis and regulates survival under low oxygen conditions.