The decline in cellular iron is crucial for differentiation in keratinocytes

Iron is a vital metal for most biological functions in tissues, and its concentration is exquisitely regulated at the cellular level. During the process of differentiation, keratinocytes in the epidermis undergo a noticeable reduction in iron content. Conversely, psoriatic lesions, characterized by disruptions in epidermal differentiation, frequently reveal an excessive accumulation of iron within keratinocytes that have undergone differentiation. In this study, we clarified the significance of attenuated cellular iron content in the intricate course of epidermal differentiation. We illustrated this phenomenon through the utilization of hinokitiol, an iron chelator derived from the heartwood of Taiwanese hinoki, which forcibly delivers iron into cells independent of the intrinsic iron-regulation systems. While primary cultured keratinocytes readily succumbed to necrotic cell death by this iron chelator, mild administration of the hinokitiol-iron complex modestly disrupts the process of differentiation in these cells. Notably, keratinocyte model cells HaCaT and anaplastic skin rudiments exhibit remarkable resilience against the cytotoxic impact of hinokitiol, and the potent artificial influx of iron explains a suppressive effect selectively on epidermal differentiation. Moreover, the augmentation of iron content induced by the overexpression of divalent metal transporter 1 culminates in the inhibition of differentiation in HaCaT cells. Consequently, the diminution in cellular iron content emerges as an important determinant influencing the trajectory of keratinocyte differentiation.

Quantifiable and Inexpensive Cell-Free Fluorescent Method to Confirm the Ability of Novel Compounds to Chelate Iron

Cancer cells require large amounts of iron to maintain their proliferation. Iron metabolism is considered a hallmark of cancer, making iron a valid target for anti-cancer approaches. The development of novel compounds and the identification of leads for further modification requires that proof of mechanism assays be carried out. There are many assays to evaluate the impact on proliferation; however, the ability to chelate iron is an important and sometimes overlooked end-point measure due to the high costs of equipment and the challenge to quickly and reproducibly quantify the strength of chelation. Here, we describe a quantifiable and inexpensive cell-free fluorescent method to confirm the ability of novel compounds to chelate iron. Our assay relies on the commercially available inexpensive fluorescent dye Calcein, whose fluorescence can be quantified on most fluorescent microtiter plate readers. Calcein is a weak iron chelator, and its fluorescence is quenched when it binds Fe2+/3+; fluorescence is restored when a novel chelator outcompetes Calcein for bound Fe2+/3+. The removal of fluorescent quenching and the resulting increase in fluorescence allows the chelation ability of a novel putative chelator to be determined. Therefore, we offer an inexpensive, high-throughput assay that allows the rapid screening of novel candidate chelator compounds.

Deferasirox: A comprehensive drug profile

Deferasirox is an iron-chelating drug developed by Novartis company for treatment of diseases accompanied by chronic iron overload; such as β-thalassemia or sickle cell diseases. Owing to its advantages such as high affinity, specificity and wide therapeutic window, it is considered as first line treatment. The current chapter describes the physicochemical characteristics, mode of action, pharmacokinetics, therapeutic applications and synthetic methods for deferasirox. Moreover, it includes Fourier transform infrared spectrometry (FTIR) and nuclear magnetic resonance spectroscopy (NMR) analysis for its functional groups. In addition, the selected analytical methods are summarized to aid the analysts in their routine analysis of deferasirox.

Growth of Acinetobacter baumannii impacted by iron chelation

Acinetobacter baumannii (AB) has become multidrug-resistant (MDR) in recent years, and, currently, there are limited effective treatment options. Nutrient metals (e.g. iron) are essential to the metabolic functions of AB. This study examined the impact of iron chelation on the growth of AB in vitro and in vivo. Susceptible and MDR-AB bloodstream isolates (n = 9) were recovered from different patients between 2011 and 2018. Clonal diversity was ascertained by Fourier-transform infrared spectroscopy. In vitro bacterial densities were measured over 20 h to determine growth profiles. Variable amounts of a chelating agent [deferiprone (DFP)] were added to create a concentration gradient. Galleria mellonella larvae were inoculated with an isolate, with and without DFP. Quantitative culture was used to ascertain the bacterial burden of aggregate larvae immediately and 4 h post-infection. Increasing concentrations of DFP caused a transient and concentration-dependent hindrance to in vitro growth, compared to the no-treatment group. In vivo bacterial burden immediately post-infection in both groups was comparable. After 4 h, the burden was much higher in the control group comparatively (8.7 and 6.7 log CFU g-1). These results support that micro-nutrient limitation has the potential of being a novel approach for treating high-risk infections due to MDR-AB.

Bioactive nutraceutical ligands and their efficiency to chelate elemental iron of varying dynamic oxidation states to mitigate associated clinical conditions

The natural bioactive or nutraceuticals exhibit several health benefits, including anti-inflammatory, anti-cancer, metal chelation, antiviral, and antimicrobial activity. The inherent limitation of nutraceuticals or bioactive ligand(s) in terms of poor pharmacokinetic and other physicochemical properties affects their overall therapeutic efficiency. The excess of iron in the physiological compartments and its varying dynamic oxidation state [Fe(II) and Fe(III)] precipitates various clinical conditions such as non-transferrin bound iron (NTBI), labile iron pool (LIP), ferroptosis, cancer, etc. Though several natural bioactive ligands are proposed to chelate iron, the efficiency of bioactive ligands is limited due to poor bioavailability, denticity, and other related physicochemical properties. The present review provides insight into the relevance of studying the dynamic oxidation state of iron(II) and iron(III) in the physiological compartments and its clinical significance for selecting diagnostics and therapeutic regimes. We suggested a three-pronged approach, i.e., diagnosis, selection of therapeutic regime (natural bioactive), and integration of novel drug delivery systems (NDDS) or nanotechnology-based principles. This systematic approach improves the overall therapeutic efficiency of natural iron chelators to manage iron overload-related clinical conditions.

Canonical Wnt signaling works downstream of iron overload to prevent ferroptosis from damaging osteoblast differentiation

Excessive iron has emerged in a large population of patients suffering from degenerative or hematological diseases with a common outcome, osteoporosis. However, its underlying mechanism remains to be clarified in order to formulate effective prevention and intervention against the loss of bone-forming osteoblasts. We show herein that increased intracellular iron by ferric ammonium citrate (FAC) mimicking the so-called non-transferrin bound iron concentrations leads to ferroptosis and impaired osteoblast differentiation. FAC upregulates the expression of Trfr and DMT1 genes to increase iron uptake, accumulating intracellular labile ferrous iron for iron overload status. Then, the excessive ferrous iron generates reactive oxygen species (ROS) and lipid peroxidation products (LPO), causing ferroptosis with its typical mitochondrial morphological changes, such as shrinkaged and condensed membrane with diminution and loss of crista and outer membrane rupture. We further examined that ferroptosis is the main cause responsible for FAC-disrupted osteoblast differentiation, although apoptosis and senescence are concurrently induced as well. Mechanistically, we revealed that iron dose-dependently down-regulates the expression of Wnt target genes and inhibits the transcription of Wnt reporter TopFlash construct, so as to inhibit the canonical Wnt signaling. Wnt agonist, ferroptosis inhibitor, or antioxidant melatonin reverses iron-inhibited canonical Wnt signaling to restore osteoblast differentiation by reducing ROS and LPO production to prevent ferroptosis notably without reducing iron overload. This study proposes a working model against excessive iron-induced osteoporosis: iron chelator deferoxamine or the above three drugs prevent ferroptosis, restore traditional Wnt signaling to maintain osteoblast differentiation no matter whether iron overload is removed or not. Additionally, iron chelator should be used to a suitable extent because iron itself is necessary for osteogenic differentiation.

Implications of the Mn:ligand ratio for Mn uptake by Glycine max L. plants fertilized with heptagluconate and gluconate complexes

BACKGROUND

The environmental risk of the application of synthetic chelates has furthered the implementation of biodegradable complexes to correct manganese (Mn)-deficient plants. This study used the biodegradable ligands of heptagluconate (G7) and gluconate (G6) to test the influence of the Mn2+ :ligand ratio on their fertilizers' capacity to provide Mn to plants. The efficacy of these complexes to correct Mn-deficient soybean was evaluated in hydroponics and calcareous soil conditions and compared with the synthetic chelate EDTA (ethylenediaminetetraacetic acid).

RESULTS

This study demonstrated that G7 was a biodegradable alternative to EDTA for supplying Mn, maintaining an adequate nutritional balance compared with G6, which reduced iron (Fe) uptake by the plants. The efficacy of the Mn complexes depended on both the ligand and the Mn:ligand ratio, with the 1:1 and 1:2 molar ratios of Mn2+ :G7 being the most effective complexes in the short term on the basis of their chemical structure and stability.

CONCLUSION

The Mn2+ :G7 (1:1 and 1:2) complexes were found to be effective Mn sources for plant nutrition due to their chemical structures providing adequate stability in alkaline solution and their fast-action effect. © 2021 Society of Chemical Industry.

Leonardite iron humate and synthetic iron chelate mixtures in Glycine max nutrition

BACKGROUND

The aim of this work was to study the possible synergic effect between mixtures with iron leonardite humate (L/Fe3+ ) and synthetic chelates iron (Ch/Fe3+ : o,oEDDHA /Fe3+ or HBED/Fe3+ ), and to reevaluate the classical chelate shuttle-effect model. Different molar ratios of L/Fe3+ :Ch/Fe3+ , different doses, and different sampling times were used in hydroponic and soil experiments using soybean (Glycine max) as a model Strategy I crop in calcareous conditions. Ligand competition between the humate and chelating agents was also examined.

RESULTS

Iron humate participates in the chelate shuttle mechanism, providing available Fe to the chelating agent and then to the plants, showing a slight synergic effect. After a few days, the contribution of the chelates to the Fe nutrition decreases substantially, but the contribution of the humates is maintained.

CONCLUSIONS

The most efficient ratio was two parts of iron humates and one part of iron chelate. In particular, HBED/Fe3+ was the most suitable iron chelate because its lasting effect fits the iron humate long-term effect better. The soluble iron in soil increased and the shoot-to-root iron translocation improved due to a synergic effect by a shuttle effect exerted by iron chelate in the mixture. © 2021 Society of Chemical Industry.

The Role of GSH in Intracellular Iron Trafficking

Evidence is reviewed for the role of glutathione in providing a ligand for the cytosolic iron pool. The possibility of histidine and carnosine forming ternary complexes with iron(II)glutathione is discussed and the physiological significance of these interactions considered. The role of carnosine in muscle, brain, and kidney physiology is far from established and evidence is presented that the iron(II)-binding capability of carnosine relates to this role.

Potential Antioxidant and Angiotensin I-converting Enzyme Inhibitory Activity in Crust of Dry-aged Beef

Antioxidant activity, angiotensin I-converting enzyme (ACE) inhibitory activity, and protein profile of crust (the dried surface of dry-aged beef) were evaluated compared to unaged, wet-, and dry-aged beef. Antioxidant activity was determined using 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-di-(3-ethylbenzthiazoline sulfonate) radical scavenging activities, ferric reducing antioxidant power, and ferrous ion chelating activity. The crust samples showed the greatest (P < 0.05) ACE inhibitory and antioxidant activity resulting from the three different mechanisms of action (radical scavenging, non-radical redox potential activity, and metal chelating) among the treatments. Small molecular weight protein bands and small peptides (<3 kDa) indicating potent bioactivity were evident in the myofibrillar protein profile of crust samples. The lowest (P < 0.05) ACE inhibitory activity was observed in unaged beef. The results indicate that crust could be utilized in various areas as a functional ingredient possessed antioxidant and ACE inhibitory activity instead of being discarded. In addition, dry aging can use for generation of functional ingredient from beef as the regime.

Siderophore (from Synechococcus sp. PCC 7002)-Chelated Iron Promotes Iron Uptake in Caco-2 Cells and Ameliorates Iron Deficiency in Rats

Siderophores are iron chelators with low molecular weight secreted by microorganisms. Siderophores have the potential to become natural iron fortifiers. To explore the feasibility of the application of Synechococcus sp. PCC7002-derived siderophores as iron fortifiers, Synechococcus sp. PCC7002, as a carrier, was fermented to produce siderophores. The absorption mechanism and anemia intervention effect of siderophores-chelated iron (SCI) were studied through the polarized Caco-2 Cell monolayers and the rat model of iron-deficiency anemia, respectively. The results indicated that siderophores (from Synechococcus sp. PCC7002) had an enhancing effect on iron absorption in polarized Caco-2 cell monolayers. The main absorption site of SCI was duodenum with pH 5.5, and the absorption methods included endocytosis and DMT1, with endocytosis being dominant. The effect of sodium phytate on SCI was less than that of ferrous sulfate. Therefore, SCI could resist inhibitory iron absorption factors in polarized Caco-2 cell monolayers. SCI showed significantly higher relative bioavailability (133.58 ± 15.42%) than ferrous sulfate (100 ± 14.84%) and ferric citrate (66.34 ± 8.715%) in the rat model. Food intake, hemoglobin concentration, and hematocrit and serum iron concentration of rats improved significantly after Fe-repletion. Overall, this study indicated that siderophores derived from Synechococcus sp. PCC7002 could be an effective and feasible iron nutritive fortifier.

Cyanobacterial Siderophores-Physiology, Structure, Biosynthesis, and Applications

Siderophores are low-molecular-weight metal chelators that function in microbial iron uptake. As iron limits primary productivity in many environments, siderophores are of great ecological importance. Additionally, their metal binding properties have attracted interest for uses in medicine and bioremediation. Here, we review the current state of knowledge concerning the siderophores produced by cyanobacteria. We give an overview of all cyanobacterial species with known siderophore production, finding siderophores produced in all but the most basal clades, and in a wide variety of environments. We explore what is known about the structure, biosynthesis, and cycling of the cyanobacterial siderophores that have been characterized: Synechobactin, schizokinen and anachelin. We also highlight alternative siderophore functionality and technological potential, finding allelopathic effects on competing phytoplankton and likely roles in limiting heavy-metal toxicity. Methodological improvements in siderophore characterization and detection are briefly described. Since most known cyanobacterial siderophores have not been structurally characterized, the application of mass spectrometry techniques will likely reveal a breadth of variation within these important molecules.

Effect of duck egg white peptide-ferrous chelate on iron bioavailability in vivo and structure characterization

BACKGROUND

In order to utilize the industrial by-product 'salted duck egg white' as novel iron additives, the effects of desalted duck egg white peptides-ferrous chelate (DPs-Fe) on the promotion of iron uptake and the structure were investigated.

RESULTS

Different doses of DPs-Fe were given and iron sulfate (FeSO₄ ) was used as a positive control. After three weeks, hemoglobin (Hb), hematocrit (HCT), red blood cells (RBCs), mean corpuscular volume (MCV), serum iron (SI) and serum ferritin (SF) in iron-deficiency anemia (IDA) rats could be significantly (P < 0.05) increased to the normal levels by DPs-Fe. The gene expressions of divalent metal transporter 1 (DMT1), ferroportin 1 (FPN1) and Hepcidin could be regulated by DPs-Fe. Additionally, DPs-Fe was formed during the chelation process and the structure was characterized. Eight crucial iron-chelating peptides of duck egg white peptides (DPs) were identified by HPLC-ESI-MS/MS, such as Pro-Val-Glu-Glu and Arg-Ser-Ser. It indicated that Glu, Asp, Lys, His, Ser, Cys residues might play crucial roles in the chelating of DPs with iron.

CONCLUSION

DPs-Fe could be a potential iron supplement, and the Glu, Asp, Lys, His played important roles in binding iron and promoting iron uptake. This research expands the understanding of iron uptake by DPs and provides an opportunity for recycling a discarded processing byproduct. © 2018 Society of Chemical Industry.

Siderophores: From natural roles to potential applications

Siderophores are secondary metabolites produced by different organisms in order to scavenge iron from their surrounding environment making this essential element available to the cell. Presenting high affinity for ferric iron, siderophores are secreted out to form soluble ferric complexes that can be taken up by the organisms. Siderophores present complex chemistry that allows them to form the strongest iron-chelating complexes. Interest in this field is always up to date and new siderophores are found with new roles and applications. For example, siderophores participate to the mobilization of iron and other elements and are involved in virulence processes. Recently, a strong relation between siderophores and oxidative stress tolerance has been also highlighted. Their application in medicine has been widely studied as well as in agriculture. However, new fields are paying attention to the use of siderophores as green-iron chelators. In particular, siderophores have been proposed for the preservation of cultural heritage.

Antioxidants Potential of the Filamentous Fungi (Mucor circinelloides)

Three important strains of Mucorcircinelloides grown in complete and minimal media for specified period (72 h, 120 h and 168 h) under submerged fermentation conditions were investigated for their potential antioxidants/secondary metabolite production. All mycelial extracts demonstrated effective antioxidant activities in terms of β-carotene/linoleic acid bleaching, radical scavenging, reduction of metal ions and chelating abilities against ferrous ions. Different extraction methods and solvent systems affected the recovery yield and antioxidant activities of the extracts significantly (p ≤ 0.05). Ethanolic extracts were found to be rich source of antioxidant components and subsequently more effective in antioxidant properties. Fermentation period and media used also significantly affected (p ≤ 0.05) the antioxidant production and the resulting antioxidant properties. The (ethanolic) extracts of all the strains from late exponential growth phase (120 h) showed highest antioxidant production with topmost reducing, chelating and radical scavenging capabilities. Strain MC277.49 was found to be the highest producer of antioxidants followed by MC108.16 and WJ11. Phenolic compounds were detected significantly in higher (p ≤ 0.05) amount succeeded by the condensed tannins and flavonoids. Total phenol content of each extract was attributed to overall antioxidant capacity. Submerged fermentation with nutritional stress conditions were found to be excellent way of producing surplus amount of natural antioxidants/secondary metabolites with their vast potential commercial application in food and pharmaceutical industries.

Antioxidant and Anti-Inflammatory Activities of Hydrolysates and Peptide Fractions Obtained by Enzymatic Hydrolysis of Selected Heat-Treated Edible Insects

This study investigated the effect of heat treatment of edible insects on antioxidant and anti-inflammatory activities of peptides obtained by in vitro gastrointestinal digestion and absorption process thereof. The antioxidant potential of edible insect hydrolysates was determined as free radical-scavenging activity, ion chelating activity, and reducing power, whereas the anti-inflammatory activity was expressed as lipoxygenase and cyclooxygenase-2 inhibitory activity. The highest antiradical activity against DPPH• (2,2-diphenyl-1-picrylhydrazyl radical) was noted for a peptide fraction from baked cricket Gryllodes sigillatus hydrolysate (IC50 value 10.9 µg/mL) and that against ABTS•+ (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical) was the highest for raw mealworm Tenebrio molitor hydrolysate (inhibitory concentration (IC50 value) 5.3 µg/mL). The peptides obtained from boiled locust Schistocerca gregaria hydrolysate showed the highest Fe2+ chelation ability (IC50 value 2.57 µg/mL); furthermore, the highest reducing power was observed for raw G. sigillatus hydrolysate (0.771). The peptide fraction from a protein preparation from the locust S. gregaria exhibited the most significant lipoxygenase and cyclooxygenase-2 inhibitory activity (IC50 value 3.13 µg/mL and 5.05 µg/mL, respectively).

Effect of three safeners on sulfur assimilation and iron deficiency response in barley (Hordeum vulgare) plants

BACKGROUND

Safeners are agrochemicals used in agriculture to protect crops from herbicide injuries. They act by stimulating herbicide metabolism. As graminaceous plants, to cope with iron (Fe) deficiency, activate sulfur (S) metabolism and release huge amounts of Fe-chelating compounds, or phytosiderophores (PSs), we investigated, in barley plants (Hordeum vulgare, L.) grown in Fe deficiency, the effects of three safeners on two enzymes of S assimilation, cysteine (Cys) and glutathione (GSH), and PS release. Finally, we monitored the root Fe content in plants treated with the most effective safener.

RESULTS

Generally, all the safeners activated S metabolism and increased Cys and GSH contents. In addition, the safened plants excreted higher levels of PSs. Given that mefenpyr-diethyl (Mef) was the most effective in causing these effects, we assessed the Fe concentration in Mef-treated barley and found higher Fe levels than those in untreated plants.

CONCLUSION

The three safeners, in different ways but specifically, activated S reductive metabolism and regulated Cys and GSH contents, PS release rate and Fe content (Mef-treated barley). The results of this research provide new indications of the biochemical and physiological mechanisms involved in the safening action. © 2016 Society of Chemical Industry.

Siderophore Cephalosporin Cefiderocol Utilizes Ferric Iron Transporter Systems for Antibacterial Activity against Pseudomonas aeruginosa

Cefiderocol (S-649266) is a novel parenteral siderophore cephalosporin conjugated with a catechol moiety at the third-position side chain. The in vitro activity of cefiderocol against Pseudomonas aeruginosa was enhanced under iron-depleted conditions, whereas that of ceftazidime was not affected. The monitoring of [thiazole-14C]cefiderocol revealed the increased intracellular accumulation of cefiderocol in P. aeruginosa cells incubated under iron-depleted conditions compared with those incubated under iron-sufficient conditions. Cefiderocol was shown to have potent chelating activity with ferric iron, and extracellular iron was efficiently transported into P. aeruginosa cells in the presence of cefiderocol as well as siderophores, while enhanced transport of extracellular ferric iron was not observed when one of the hydroxyl groups of the catechol moiety of cefiderocol was replaced with a methoxy group. We conclude that cefiderocol forms a chelating complex with iron, which is actively transported into P. aeruginosa cells via iron transporters, resulting in potent antibacterial activity of cefiderocol against P. aeruginosa.

Antioxidant activities of protein hydrolysates obtained from the housefly larvae

The housefly is an important resource insect and the housefly larvae are ideal source of food additives. The housefly larvae protein hydrolysates were obtained by enzymatic hydrolysis by alcalase and neutral proteinase. Their antioxidant activities were investigated, including the superoxide and hydroxyl radicalscavenging activity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, reducing power and metal chelating activity. The antioxidant activities of both hydrolysates increased with their increasing concentrations. The alcalase hydrolysate (AH) showed higher scavenging activities against hydroxyl radical and superoxide anion radical at low concentrations and higher metal-chelating activity than the neutral proteinase hydrolysate (NPH). The NPH exhibited higher scavenging activity against DPPH free radical and higher reducing power than the AH. Both hydrolysates showed more than 50% superoxide anion radical-scavenging activity at 10 μg/mL. These results indicate that both housefly larvae protein hydrolysates display high antioxidant activities and they could serve as potential natural antioxidant food additives.

Identification of Phenolic Compounds from Seed Coats of Differently Colored European Varieties of Pea (Pisum sativum L.) and Characterization of Their Antioxidant and In Vitro Anticancer Activities

To date little has been done on identification of major phenolic compounds responsible for anticancer and antioxidant properties of pea (Pisum sativum L.) seed coat extracts. In the present study, phenolic profile of the seed coat extracts from 10 differently colored European varieties has been determined using ultrahigh-performance liquid chromatography-linear trap quadrupole orbitrap mass spectrometer technique. Extracts of dark colored varieties with high total phenolic content (up to 46.56 mg GAE/g) exhibited strong antioxidant activities (measured by 2,2-diphenyl-1-picrylhydrazyl or DPPH assay, and ferric ion reducing and ferrous ion chelating capacity assays) which could be attributed to presence of gallic acid, epigallocatechin, naringenin, and apigenin. The aqueous extracts of dark colored varieties exert concentration-dependent cytotoxic effects on all tested malignant cell lines (human colon adenocarcinoma LS174, human breast carcinoma MDA-MB-453, human lung carcinoma A594, and myelogenous leukemia K562). Correlation analysis revealed that intensities of cytotoxic activity of the extracts strongly correlated with contents of epigallocatechin and luteolin. Cell cycle analysis on LS174 cells in the presence of caspase-3 inhibitor points out that extracts may activate other cell death modalities besides caspase-3-dependent apoptosis. The study provides evidence that seed coat extracts of dark colored pea varieties might be used as potential cancer-chemopreventive and complementary agents in cancer therapy.

Microbial siderophores and their potential applications: a review

Siderophores are small organic molecules produced by microorganisms under iron-limiting conditions which enhance the uptake of iron to the microorganisms. In environment, the ferric form of iron is insoluble and inaccessible at physiological pH (7.35-7.40). Under this condition, microorganisms synthesize siderophores which have high affinity for ferric iron. These ferric iron-siderophore complexes are then transported to cytosol. In cytosol, the ferric iron gets reduced into ferrous iron and becomes accessible to microorganism. In recent times, siderophores have drawn much attention due to its potential roles in different fields. Siderophores have application in microbial ecology to enhance the growth of several unculturable microorganisms and can alter the microbial communities. In the field of agriculture, different types of siderophores promote the growth of several plant species and increase their yield by enhancing the Fe uptake to plants. Siderophores acts as a potential biocontrol agent against harmful phyto-pathogens and holds the ability to substitute hazardous pesticides. Heavy-metal-contaminated samples can be detoxified by applying siderophores, which explicate its role in bioremediation. Siderophores can detect the iron content in different environments, exhibiting its role as a biosensor. In the medical field, siderophore uses the "Trojan horse strategy" to form complexes with antibiotics and helps in the selective delivery of antibiotics to the antibiotic-resistant bacteria. Certain iron overload diseases for example sickle cell anemia can be treated with the help of siderophores. Other medical applications of siderophores include antimalarial activity, removal of transuranic elements from the body, and anticancer activity. The aim of this review is to discuss the important roles and applications of siderophores in different sectors including ecology, agriculture, bioremediation, biosensor, and medicine.

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.

Multifunctional iron bound lactoferrin and nanomedicinal approaches to enhance its bioactive functions

Lactoferrin (Lf), an iron-binding protein from the transferrin family has been reported to have numerous functions. Even though Lf was first isolated from milk, it is also found in most exocrine secretions and in the secondary granules of neutrophils. Antimicrobial and anti-inflammatory activity reports on lactoferrin identified its significance in host defense against infection and extreme inflammation. Anticarcinogenic reports on lactoferrin make this protein even more valuable. This review is focused on the structural configuration of iron-containing and iron-free forms of lactoferrin obtained from different sources such as goat, camel and bovine. Apart for emphasizing on the specific beneficial properties of lactoferrin from each of these sources, the general antimicrobial, immunomodulatory and anticancer activities of lactoferrin are discussed here. Implementation of nanomedicinial strategies that enhance the bioactive function of lactoferrin are also discussed, along with information on lactoferrin in clinical trials.

High-performance liquid chromatography method for ferric iron chelators using a post-column reaction with Calcein Blue

Iron (Fe) is an essential element for higher plants, which take it up from the soil at the root surface and transport it to shoots through the xylem. Fe(III) chelators, such as organic acids and phytosiderophores, play important roles in the acquisition and transportation of Fe(III). Therefore, a selective and sensitive method for analyzing Fe(III) chelators is required to study the many Fe-related physiological mechanisms in plants. A novel analytical approach employing a high-performance liquid chromatography post-column method with fluorescence detection was developed to separate and detect Fe(III) chelators. This method takes advantage of the quenching of the fluorescence of Calcein Blue (CB) that occurs with the formation of an Fe(III)-CB complex and the dequenching that occurs with the release of CB as a result of competition for Fe(III) between CB and an Fe(III) chelator. This simple experimental method does not require complicated pretreatments and can selectively detect Fe(III) chelators according to their Fe(III)-chelating ability. The detection limit for citric acid using this method was 72pmol. Furthermore, this method can also detect unknown Fe(III) chelators that exhibit a high affinity for Fe(III). The method was evaluated with xylem sap of barley, which was shown to contain several Fe(III) chelators.

Spectroscopic, potentiometric and theoretical studies of novel imino-phenolate chelators for Fe(III)

The present study was targeted to explore the binding properties of two strong chelators for Fe(III) based on tripodal-iminophenolate moiety. Complexation behavior of the tripodal systems cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({2-[(2-hydroxy-benzylidene)-amino]-ethyl}-amide (CYCOENSAL, L(1)) and cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({3-[(2-hydroxy-benzylidene)-amino]-propyl}-amide (CYCOPNSAL, L(2)) is described. Three protonation constants obtained are assigned for three hydroxyl groups of aromatic ring were employed for the evaluation of the formation constants of the metal complexes. Both ligands liberate three protons each forming monomeric complexes of type FeLH3, FeLH2, FeLH and FeL (L=L(1) and L(2)). The first species FeLH3 depicted at low pH, where the ligands were coordinated through three imine nitrogen and other species form subsequently from FeLH3 in steps upon deprotonation and coordination of the phenolic oxygen giving encapsulated tris(phenolate) complexes. The probable structures of the metal complexes formed in solution were proposed through molecular modeling calculations. L(2) was observed to be highly selective towards Fe(III) as compared to L(1).

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.

Antioxidant potential and oxidative DNA damage preventive activity of unexplored endemic species of Curcuma

Free radical scavenging activity, ferrous ion chelating capacity, reducing power and genoprotective effect of the aqueous leaf extracts of four unexplored endemic Curcuma spp. (C. vamana, C. neilgherrensis, C. mutabilis, C. haritha) were found to be dose-dependent and were highest in C. vamana. DNA protection property of the extracts was evaluated against H202/UV-induced oxidative damage. DNA-methyl green displacement assay showed that these extracts were free of DNA intercalating compounds. Further, hemolysis assay also showed that the extracts were non-toxic to human erythrocytes. The results highlight C. vamana as a promising source for herbal preparations possessing high antioxidant potential and genoprotective activity.

Reduction-based iron uptake revisited: on the role of secreted iron-binding compounds

With the exception of the grasses, plants rely on a reduction-based iron (Fe) uptake system that is compromised by high soil pH, leading to severe chlorosis and reduced yield in crop plants. We recently reported that iron deficiency triggers the production of secondary metabolites that are beneficial for Fe uptake in particular at high external pH when iron is present but not readily available. The exact function of these metabolites, however, remains enigmatic. Here, we speculate on the mechanism by which secondary metabolites secreted by roots from Fe-deficient plants improve Fe acquisition. We suggest that the production and excretion of Iron Binding Compounds (IBCs) constitute an integrative, pH-insensitive component of the reduction-based iron uptake strategy in plants.

A teleostean counterpart of ferritin M subunit from rock bream (Oplegnathus fasciatus): an active constituent in iron chelation and DNA protection against oxidative damage, with a modulated expression upon pathogen stress

Ferritins are biological iron chelators that can sequestrate excess iron to maintain iron homeostasis in the body. Ferritins basically consist of 2 types of subunits, designated as H and L. However, another new subunit, ferritin "M" which possesses characteristic features of both the H and L subunits, was recently identified in lower vertebrates, mostly in fish. In this study, a ferritin M-like subunit from rock bream (Oplegnathus fasciatus) (RbFerM) was characterized at the molecular level, and its transcriptional profile was analyzed in healthy fish, as well as in pathogen- and mitogen-stimulated fish. Furthermore, its functional properties were evaluated using the recombinant protein. The complete coding sequence of RbFerM was 528 bp in length, encoding a 176-amino acid peptide with a calculated molecular mass of 20 kDa. In silico analysis of RbFerM revealed that it has features similar to both the mammalian ferritin subunits, H and L. Phylogenetic analysis depicted the higher evolutionary proximity of RbFerM with its fish counterparts. Quantitative real time polymerase chain reaction (PCR) analysis detected a ubiquitous transcriptional profile of RbFerM in selected tissues of rock bream, in which more pronounced expression was observed in blood and liver tissues. Significant transcriptional inductions of RbFerM were detected in liver tissues upon lipopolysaccharides (LPS), Edwardsiella tarda, Streptococcus iniae, and rock bream irido virus (RBIV) exposures in time-course immune-challenge experiments. The purified recombinant protein of RbFerM demonstrated detectable iron chelating activity that varied with the temperature. Moreover, the recombinant RbFerM rendered a detectable protection effect against iron (II) and H2O2-mediated DNA damage.

Studies of interaction between terbium(III)-deferasirox and double helix DNA by spectral and electrochemical methods

DNA binding studies of terbium(III)-deferasirox (Tb3+-DFX) complex were monitored to understand the reaction mechanism and introduce a new probe for the assay of DNA. In the present work, UV absorption spectrophotometry, fluorescence spectroscopy, circular dichroism (CD), cyclic voltammetry (CV) and viscosity measurement were employed to study the interactions of Tb3+-DFX with calf thymus DNA (ctDNA). The binding of Tb3+-DFX complex to ctDNA showed a hyperchromic effect in the absorption spectra and the increase in fluorescence quenching effect (amount) of Tb3+-DFX complex in the presence of ctDNA. The binding constants (Kb) for the complex with ctDNA were estimated to be 1.8×10(4) M(-1) through UV absorption spectrophotometry and fluorescence spectroscopy. Upon addition of the complex, clear decreases were observed in the viscosity of ctDNA. The CD spectra indicated that there are certain detectable conformational changes in the DNA double helix when the complex was added. The CV method showed that both anodic and cathodic peak potentials of Tb3+-DFX complex showed negative shifts on the addition of the ctDNA. Further, competitive methylene blue binding studies with fluorescence spectroscopy have shown that the complex can bind to ctDNA through nonintercalative mode. The experimental results suggest that Tb3+-DFX complex binds to DNA via groove binding and/or electrostatic binding mode.

Phytochemical contents and enzyme inhibitory and antioxidant properties of Anethum graveolens L. (dill) samples cultivated under organic and conventional agricultural conditions

Inhibitory effect of the n-hexane, dichloromethane, ethyl acetate, and ethanol extracts from Anethum graveolens L. (dill) cultivated under organic (AG-O) and conventional (AG-C) conditions was tested against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and tyrosinase at 200 μg mL⁻¹. Their antioxidant activity was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), N,N-dimethyl-p-phenylendiamine (DMPD), and nitric oxide (NO) radical scavenging assays as well as ferric ion-chelation capacity, ferric-(FRAP), and phosphomolybdenum-reducing antioxidant power (PRAP). The phytochemical analyses have been performed on both of the plant samples. GC-MS analysis pointed out that α-phellandrene was the main component in both of the essential oils in varying amounts (47.75% for AG-O and 27.94% for AG-C), while oleic acid was the dominant in the fruit oils of two samples (36.39% for AG-O and 53.87% for AG-C). HPLC analysis showed that both of the extracts contained rosmarinic acid as the major phenolic acid. The extracts inhibited BChE at moderate level, while the ethanol extracts exerted remarkable NO scavenging effect. The results emphasize that cultivation conditions may have effect on bioactivity and phytochemical content on plant samples.

Towards high-siderophore-content foods: optimisation of coprogen production in submerged cultures of Penicillium nalgiovense

BACKGROUND

Fungal siderophores are likely to possess atheroprotective effects in humans, and therefore studies are needed to develop siderophore-rich food additives or functional foods to increase the siderophore uptake in people prone to cardiovascular diseases. In this study the siderophore contents of mould-ripened cheeses and meat products were analysed and the coprogen production by Penicillium nalgiovense was characterised.

RESULTS

High concentrations of hexadentate fungal siderophores were detected in penicillia-ripened Camembert- and Roquefort-type cheeses and also in some sausages. In one sausage fermented by P. nalgiovense, the siderophore content was comparable to those found in cheeses. Penicillium nalgiovense produced high concentrations of coprogen in submerged cultures, which were affected predominantly by the available carbon and nitrogen sources under iron starvation. Considerable coprogen yields were still detectable in the presence of iron when the fermentation medium was supplemented with the iron chelator Na₂-EDTA or when P. nalgiovense was co-cultivated with Saccharomyces cerevisiae.

CONCLUSION

These data may be exploitable in the future development of high-siderophore-content foods and/or food additives. Nevertheless, the use of P. nalgiovense fermentation broths for these purposes may be limited by the instability of coprogen in fermentation media and by the β-lactam production by the fungus.

Antioxidant activities of buttermilk proteins, whey proteins, and their enzymatic hydrolysates

The oxygen radical absorbance capacities (ORAC) and metal chelating capacities (MCC) of protein concentrates prepared from buttermilk and cheese whey by ultrafiltration were compared with those of skim milk protein. Samples were also heat-denatured and hydrolyzed by pepsin for 2 h followed by trypsin for 3 h. The highest MCC was obtained for hydrolyzed skim milk protein. ORAC values ranged from 554.4 to 1319.6 μmol Trolox equivalents/g protein, with the highest value obtained for hydrolyzed buttermilk protein. Liquid-phase isoelectric focusing (IEF) of this hydrolysate yielded peptide fractions with lower ORAC values. LC-MS analysis of the hydrolyzed skim milk and buttermilk proteins and IEF fractions of the latter showed that peptides derived from milk fat globule membrane proteins, primarily butyrophilin, could be responsible for the superior antioxidant activity of buttermilk. These results suggest overall that hydrolyzed buttermilk protein could be used as a source of natural antioxidants.

Substituent effects on desferrithiocin and desferrithiocin analogue iron-clearing and toxicity profiles

Desferrithiocin (DFT, 1) is a very efficient iron chelator when given orally. However, it is severely nephrotoxic. Structure-activity studies with 1 demonstrated that removal of the aromatic nitrogen to provide desazadesferrithiocin (DADFT, 2) and introduction of either a hydroxyl group or a polyether fragment onto the aromatic ring resulted in orally active iron chelators that were much less toxic than 1. The purpose of the current study was to determine if a comparable reduction in renal toxicity could be achieved by performing the same structural manipulations on 1 itself. Accordingly, three DFT analogues were synthesized. The iron-clearing efficiency and ferrokinetics were evaluated in rats and primates; toxicity assessments were carried out in rodents. The resulting DFT ligands demonstrated a reduction in toxicity that was equivalent to that of the DADFT analogues and presented with excellent iron-clearing properties.

Unique iron coordination in iron-chelating molecule vibriobactin helps Vibrio cholerae evade mammalian siderocalin-mediated immune response

Iron is essential for the survival of almost all bacteria. Vibrio cholerae acquires iron through the secretion of a catecholate siderophore called vibriobactin. At present, how vibriobactin chelates ferric ion remains controversial. In addition, the mechanisms underlying the recognition of ferric vibriobactin by the siderophore transport system and its delivery into the cytoplasm specifically have not been clarified. In this study, we report the high-resolution structures of the ferric vibriobactin periplasmic binding protein ViuP and its complex with ferric vibriobactin. The holo-ViuP structure reveals that ferric vibriobactin does not adopt the same iron coordination as that of other catecholate siderophores such as enterobactin. The three catechol moieties donate five, rather than six, oxygen atoms as iron ligands. The sixth iron ligand is provided by a nitrogen atom from the second oxazoline ring. This kind of iron coordination results in the protrusion of the second catechol moiety and renders the electrostatic surface potential of ferric vibriobactin less negatively polarized compared with ferric enterobactin. To accommodate ferric vibriobactin, ViuP has a deeper subpocket to hold the protrusion of the second catechol group. This structural characteristic has not been observed in other catecholate siderophore-binding proteins. Biochemical data show that siderocalin, which is part of the mammalian innate immune system, cannot efficiently sequester ferric vibriobactin in vitro, although it can capture many catecholate siderophores with high efficiency. Our findings suggest that the unique iron coordination found in ferric vibriobactin may be utilized by some pathogenic bacteria to evade the siderocalin-mediated innate immune response of mammals.

Quality, antioxidative ability, and cell proliferation-enhancing activity of fermented black soybean broths with various supplemental culture medium

The fermented soybean-based foods have played an important role in traditional diets around the world for many centuries, and Bacillus subtilis is typically used in the fermentation of soybean-based foods. The fermentation process may improve not only the flavor but also the nutritional value of food, and substances produced in this fermented broth were affected by many factors including culture medium and the selected soybeans. In this study, we use 3 potential culture mediums in the fermentation of black soybean and the fermented black soybean broths were used for the examination of amino acid composition, total phenolics content, flavonoids and anthocyanins contents, the antioxidant properties, and cytotoxicity. Our results indicated that the fermented black soybean broth, fermentation III, have the most abundant essential amino acid (79.77 mg/g), phenolics (19.33 mg/g), flavonoids (46.01 mg/g), and anthocyanins (1.06 mg/g). Besides, all of the fermented black soybean broths exhibited the significant antioxidative abilities with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging effect, reducing power and ferrous ion chelating effect. In addition, the fermented black soybean broths demonstrated the cell proliferation-enhancing activity in Detroit 551 cells. The cells were augmented up to the maximum value of 183.6% (compared with control) at 10 mg/mL of the fermentation I. Therefore, the different supplemental culture medium fermented black soybean broths may be used as a functional ingredient in the products of nutritional drinks and health foods.

PRACTICAL APPLICATION

The present study illustrated the potential of various supplemental culture medium fermented black soybean broths in the application of functional ingredient for nutritional drinks and health foods.

Immune interference in Mycobacterium tuberculosis intracellular iron acquisition through siderocalin recognition of carboxymycobactins

The innate immune system antibacterial protein Siderocalin (Scn) binds ferric carboxymycobactin (CMB) and also several catecholate siderophores. Although the recognition of catecholates by Scn has been thoroughly investigated, the binding interactions of Scn with the full spectrum of CMB isoforms have not been studied. Here we show that Scn uses different binding modes for the limited subset of bound CMB isoforms, resulting in a range of binding affinities that are much weaker than other siderophore targets of Scn. Understanding the binding interaction between Scn and CMBs provides clues for the influence of Scn on mycobacterial iron acquisition.

Iron deficiency enhances bioactive phenolics in lemon juice

BACKGROUND

This study was designed to describe the phenolic status of lemon juice obtained from fruits of lemon trees differing in iron (Fe) nutritional status. Three types of Fe(III) compound were used in the experiment, namely a synthetic chelate and two complexes derived from natural polymers of humic and lignine nature.

RESULTS

All three Fe(III) compounds were able to improve the Fe nutritional status of lemon trees, though to different degrees. This Fe(III) compound effect led to changes in the polyphenol content of lemon juice. Total phenolics were decreased (∼33% average decrease) and, in particular, flavanones, flavones and flavonols were affected similarly.

CONCLUSION

Iron-deficient trees showed higher phenolic contents than Fe(III) compound-treated trees, though Fe deficiency had negative effects on the yield and visual quality of fruits. However, from a human nutritional point of view and owing to the health-beneficial properties of their bioavailable phenolic compounds, the nutritional quality of fruits of Fe-deficient lemon trees in terms of phenolics was higher than that of fruits of Fe(III) compound-treated lemon trees. Moreover, diosmetin-6,8-di-C-glucoside in lemon juice can be used as a marker for correction of Fe deficiency in lemon trees.

Immunomodulatory and antioxidant potential of Lactobacillus exopolysaccharides

BACKGROUND

Immunomodulation by probiotic microorganisms has become a topic of increasing interest in food microbiology. Polysaccharides are broadly used in the food industry as gelling, thickening, stabilizing, or emulsifying agents. Some probiotics such as lactic acid bacteria also produce exopolysaccharides that stimulate macrophage production of cytokines. The aim of this study was to characterize the effects of exopolysaccharides of Lactobacillus paracasei subsp. paracasei NTU 101 (101EP) and Lactobacillus plantarum NTU 102 (102EP) exopolysaccharides on antioxidant activity and immunomodulation in vitro.

RESULTS

The sugar composition (including arabinose, galactose, glucose, fructose, mannose, and maltose) of 101EP and 102EP was quantified by high-performance anion-exchange chromatography. Cytokine production (including IL-6, TNF-α, and IL-1β) was induced by 101EP and 102EP in Raw 264.7 in a dose-dependent manner (5-500 µg mL(-1) ). 101EP and 102EP also demonstrated potential antioxidant properties (1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, chelation of ferrous ions, inhibition of linoleic acid peroxidation, and reducing power) in vitro.

CONCLUSION

101EP and 102EP stimulate cell proliferation and may be useful as a mild immune modulator of macrophages.

The effects of metabolite molecules produced by drinking water-isolated bacteria on their single and multispecies biofilms

The elucidation of the mechanisms by which diverse species survive and interact in drinking water (DW) biofilm communities may allow the identification of new biofilm control strategies. The purpose of the present study was to investigate the effects of metabolite molecules produced by bacteria isolated from DW on biofilm formation. Six opportunistic bacteria, viz. Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata and Staphylococcus sp. isolated from a drinking water distribution systems (DWDS) were used to form single and multispecies biofilms in the presence and absence of crude cell-free supernatants produced by the partner bacteria. Biofilms were characterized in terms of mass and metabolic activity. Additionally, several physiological aspects regulating interspecies interactions (sessile growth rates, antimicrobial activity of cell-free supernatants, and production of iron chelators) were studied to identify bacterial species with biocontrol potential in DWDS. Biofilms of Methylobacterium sp. had the highest growth rate and M. mucogenicum biofilms the lowest. Only B. cepacia was able to produce extracellular iron-chelating molecules. A. calcoaceticus, B. cepacia, Methylobacterium sp. and M. mucogenicum biofilms were strongly inhibited by crude cell-free supernatants from the other bacteria. The crude cell-free supernatants of M. mucogenicum and S. capsulata demonstrated a high potential for inhibiting the growth of counterpart biofilms. Multispecies biofilm formation was strongly inhibited in the absence of A. calcoaceticus. Only crude cell-free supernatants produced by B. cepacia and A. calcoaceticus had no inhibitory effects on multispecies biofilm formation, while metabolite molecules of M. mucogenicum showed the most significant biocontrol potential.

Accumulation and distribution of iron, cadmium, lead and nickel in cucumber plants grown in hydroponics containing two different chelated iron supplies

Cucumber plants grown in hydroponics containing 10 μM Cd(II), Ni(II) and Pb(II), and iron supplied as Fe(III) EDTA or Fe(III) citrate in identical concentrations, were investigated by total-reflection X-ray fluorescence spectrometry with special emphasis on the determination of iron accumulation and distribution within the different plant compartments (root, stem, cotyledon and leaves). The extent of Cd, Ni and Pb accumulation and distribution were also determined. Generally, iron and heavy-metal contaminant accumulation was higher when Fe(III) citrate was used. The accumulation of nickel and lead was higher by about 20% and 100%, respectively, if the iron supply was Fe(III) citrate. The accumulation of Cd was similar. In the case of Fe(III) citrate, the total amounts of Fe taken up were similar in the control and heavy-metal-treated plants (27-31 μmol/plant). Further, the amounts of iron transported from the root towards the shoot of the control, lead- and nickel-contaminated plants were independent of the iron(III) form. Although Fe mobility could be characterized as being low, its distribution within the shoot was not significantly affected by the heavy metals investigated.

Iron-sulfur proteins are the major source of protein-bound dinitrosyl iron complexes formed in Escherichia coli cells under nitric oxide stress

Protein-bound dinitrosyl iron complexes (DNICs) have been observed in prokaryotic and eukaryotic cells under nitric oxide (NO) stress. The identity of proteins that bind DNICs, however, still remains elusive. Here we demonstrate that iron-sulfur proteins are the major source of protein-bound DNICs formed in Escherichia coli cells under NO stress. Expression of recombinant iron-sulfur proteins, but not proteins without iron-sulfur clusters, almost doubles the amount of protein-bound DNICs formed in E. coli cells after NO exposure. Purification of recombinant proteins from the NO-exposed E. coli cells further confirms that iron-sulfur proteins, but not proteins without iron-sulfur clusters, are modified, forming protein-bound DNICs. Deletion of the iron-sulfur cluster assembly proteins IscA and SufA to block the [4Fe-4S] cluster biogenesis in E. coli cells largely eliminates the NO-mediated formation of protein-bound DNICs, suggesting that iron-sulfur clusters are mainly responsible for the NO-mediated formation of protein-bound DNICs in cells. Furthermore, depletion of the "chelatable iron pool" in wild-type E. coli cells effectively removes iron-sulfur clusters from proteins and concomitantly diminishes the NO-mediated formation of protein-bound DNICs, indicating that iron-sulfur clusters in proteins constitute at least part of the chelatable iron pool in cells.

Towards a knowledge-based correction of iron chlorosis

Iron (Fe) deficiency-induced chlorosis is a major nutritional disorder in crops growing in calcareous soils. Iron deficiency in fruit tree crops causes chlorosis, decreases in vegetative growth and marked fruit yield and quality losses. Therefore, Fe fertilizers, either applied to the soil or delivered to the foliage, are used every year to control Fe deficiency in these crops. On the other hand, a substantial body of knowledge is available on the fundamentals of Fe uptake, long and short distance Fe transport and subcellular Fe allocation in plants. Most of this basic knowledge, however, applies only to Fe deficiency, with studies involving Fe fertilization (i.e., with Fe-deficient plants resupplied with Fe) being still scarce. This paper reviews recent developments in Fe-fertilizer research and the state-of-the-art of the knowledge on Fe acquisition, transport and utilization in plants. Also, the effects of Fe-fertilization on the plant responses to Fe deficiency are reviewed. Agronomical Fe-fertilization practices should benefit from the basic knowledge on plant Fe homeostasis already available; this should be considered as a long-term goal that can optimize fertilizer inputs, reduce grower's costs and minimize the environmental impact of fertilization.

The root-hairless barley mutant brb used as model for assessment of role of root hairs in iron accumulation

Main components of Strategy II mechanism for Fe uptake are secretion of chelating compounds, phytosiderophores, and specific uptake of Fe(III)-phytosiderophores complex. Since the amount of phytosiderophores secreted correlates positively with plant ability to cope with Fe shortage, a role of root hairs in enhancing root capability to store phytosiderophores under Fe stress might be envisaged. In this study the root-hairless mutant of barley (Hordeum vulgare L.) brb (bald root barley) and the wild-type genotype (cv. Pallas) were compared with respect to their capacity to respond to Fe shortage in nutrient solution. Plants were grown with Fe(III)-EDTA at 0, 0.02 and 0.08 mM, in order to reproduce severe or moderate Fe deficiency, and adequate Fe nutritional status, respectively. Analysis was performed after 11 and 14 days considering leaf Fe content, phytosiderophores release and accumulation in root tips, and ⁵⁹Fe uptake. Biomass accumulation and chlorophyll content were not reduced in mutant plants as compared to wild-type ones; leaf Fe content was similar in both genotypes after 14 days of growth. Accumulation and release of phytosiderophores showed a similar trend in both genotypes when subjected to Fe limitation. Furthermore, no significant difference between the two genotypes was observed when ⁵⁹Fe uptake was measured. Results seem to support the idea that the presence of root hairs and their increased production in response to low-Fe availability, while causing major modifications of root geometry, did not necessarily lead neither to an effect on growth nor on Fe uptake and accumulation in barley plants.

Acquisition of iron by alkaliphilic bacillus species

The biochemical and molecular mechanisms used by alkaliphilic bacteria to acquire iron are unknown. We demonstrate that alkaliphilic (pH > 9) Bacillus species are sensitive to artificial iron (Fe³+) chelators and produce iron-chelating molecules. These alkaliphilic siderophores contain catechol and hydroxamate moieties, and their synthesis is stimulated by manganese(II) salts and suppressed by FeCl₃ addition. Purification and mass spectrometric characterization of the siderophore produced by Caldalkalibacillus thermarum failed to identify any matches to previously observed fragmentation spectra of known siderophores, suggesting a novel structure.

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.