Complexation of desferricoprogen with trivalent Fe, Al, Ga, In and divalent Fe, Ni, Cu, Zn metal ions: effects of the linking chain structure on the metal binding ability of hydroxamate based siderophores

Pathophysiology and Molecular Imaging of Diabetic Foot Infections

Diabetic foot infection is the leading cause of non-traumatic lower limb amputations worldwide. In addition, diabetes mellitus and sequela of the disease are increasing in prevalence. In 2017, 9.4% of Americans were diagnosed with diabetes mellitus (DM). The growing pervasiveness and financial implications of diabetic foot infection (DFI) indicate an acute need for improved clinical assessment and treatment. Complex pathophysiology and suboptimal specificity of current non-invasive imaging modalities have made diagnosis and treatment response challenging. Current anatomical and molecular clinical imaging strategies have mainly targeted the host's immune responses rather than the unique metabolism of the invading microorganism. Advances in imaging have the potential to reduce the impact of these problems and improve the assessment of DFI, particularly in distinguishing infection of soft tissue alone from osteomyelitis (OM). This review presents a summary of the known pathophysiology of DFI, the molecular basis of current and emerging diagnostic imaging techniques, and the mechanistic links of these imaging techniques to the pathophysiology of diabetic foot infections.

Pathophysiology and Molecular Imaging of Diabetic Foot Infections

Diabetic foot infection is the leading cause of non-traumatic lower limb amputations worldwide. In addition, diabetes mellitus and sequela of the disease are increasing in prevalence. In 2017, 9.4% of Americans were diagnosed with diabetes mellitus (DM). The growing pervasiveness and financial implications of diabetic foot infection (DFI) indicate an acute need for improved clinical assessment and treatment. Complex pathophysiology and suboptimal specificity of current non-invasive imaging modalities have made diagnosis and treatment response challenging. Current anatomical and molecular clinical imaging strategies have mainly targeted the host's immune responses rather than the unique metabolism of the invading microorganism. Advances in imaging have the potential to reduce the impact of these problems and improve the assessment of DFI, particularly in distinguishing infection of soft tissue alone from osteomyelitis (OM). This review presents a summary of the known pathophysiology of DFI, the molecular basis of current and emerging diagnostic imaging techniques, and the mechanistic links of these imaging techniques to the pathophysiology of diabetic foot infections.

Deferoxamine B: A Natural, Excellent and Versatile Metal Chelator

Deferoxamine B is an outstanding molecule which has been widely studied in the past decade for its ability to bind iron and many other metal ions. The versatility of this metal chelator makes it suitable for a number of medicinal and analytical applications, from the well-known iron chelation therapy to the most recent use in sensor devices. The three bidentate hydroxamic functional groups of deferoxamine B are the centerpiece of its metal binding ability, which allows the formation of stable complexes with many transition, lanthanoid and actinoid metal ions. In addition to the ferric ion, in fact, more than 20 different metal complexes of deferoxamine b have been characterized in terms of their chemical speciation in solution. In addition, the availability of a terminal amino group, most often not involved in complexation, opens the way to deferoxamine B modification and functionalization. This review aims to collect and summarize the available data concerning the complex-formation equilibria in solutions of deferoxamine B with different metal ions. A general overview of the progress of its applications over the past decade is also discussed, including the treatment of iron overload-associated diseases, its clinical use against cancer and neurodegenerative disorders and its role as a diagnostic tool.

A Friendly Complexing Agent for Spectrophotometric Determination of Total Iron

Iron, one of the most common metals in the environment, plays a fundamental role in many biological as well as biogeochemical processes, which determine its availability in different oxidation states. Its relevance in environmental and industrial chemistry, human physiology, and many other fields has made it necessary to develop and optimize analysis techniques for accurate determination. Spectrophotometric methods are the most frequently applied in the analytical determination of iron in real samples. Taking advantage of the fact that desferrioxamine B, a trihydroxamic acid used since the 1970s in chelation therapy for iron overload treatment, forms a single stable 1:1 complex with iron in whichever oxidation state it can be found, a smart spectrophotometric method for the analytical determination of iron concentration was developed. In particular, the full compliance with the Lambert-Beer law, the range of iron concentration, the influence of pH, and the interference of other metal ions have been taken into account. The proposed method was validated in terms of LoD, LoQ, linearity, precision, and trueness, and has been applied for total iron determination in natural water certified material and in biological reference materials such as control human urine and control serum.

Matching and adjusting energy band structures of Pd-modified sulphides (ZnS, In2S3 and CuS) and improving the photocatalytic activity of CO2 photoreduction

A series of Pd-modified sulphide photocatalysts (ZnS-PdX%, In₂S₃-PdX% and CuS-PdX%) for the photoreduction of CO₂ were synthesised via a simple hydrothermal method. Here, the introduction of the -S-Pd-S- surface species onto the surface of the sulphides extended the visible light absorption, prolonged the lifetime of photogenerated electrons and suppressed the recombination of the photocarriers. Additionally, the match between the band structure and the redox potential for the photoreduction of CO₂ was improved. As a result, the photocatalytic activity of ZnS-Pd1.5%, In₂S₃-Pd1.5% and CuS-Pd1.5% was enhanced when compared with the results from ZnS, In₂S₃ and CuS photocatalysts. Also, ZnS-Pd1.5%, In₂S₃-Pd1.5% and CuS-Pd1.5% showed different photocatalytic activities due to differences in the matching relationships between the band structure and the redox potential. In this paper, extensive details on adjusting and matching the energy band structures, as well as viable methods for improving photocatalytic performance, are provided.

The effects of structurally different siderophores on the organelles of Pinus sylvestris root cells

Siderophores are a driver of Pinus sylvestris root responses to metabolites secreted by pathogenic and mycorrhizal fungi. Structurally different siderophores regulate the uptake of Fe by microorganisms and may play a key role in the colonization of plants by beneficial or pathogenic fungi. Siderophore action, however, may be dependent on the distribution of Fe within cells. Here, the involvement of siderophores in determining the changes of organelle morphology and element composition of some cellular fractions of root cells in Pinus sylvestris to trophically diverse fungi was investigated. Changes in the morphology and concentrations of different elements within organelles of root cells in response to three structurally different siderophores were examined by transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. Weak development of mitochondrial cristae and the deposition of backup materials in plastids occurred in the absence of Fe in the structures of triacetylfusarinine C and ferricrocin. In response to metabolites of both pathogenic and mycorrhizal fungi, Fe accumulated mainly in the cell walls and cytoplasm. Fe counts increased in all of the analyzed organelles in response to applications of ferricrocin and triacetylfusarinine C. Chelation of Fe within the structure of siderophores prevents the binding of exogenous Fe, decreasing the abundance of Fe in the cell wall and cytoplasm. The concentrations of N, P, K, Ca, Mn, Cu, Mg, and Zn also increased in cells after applications of ferricrocin and triacetylfusarinine C, while the levels of these elements decreased in the cell wall and cytoplasm when Fe was present within the structure of the siderophores. These results provide insight into the siderophore-driven response of plants to various symbionts.

Yeast Chemogenomic Profiling Reveals Iron Chelation To Be the Principle Cell Inhibitory Mode of Action of Gossypol

Gossypol is an inhibitor of eukaryotic cells with an undetermined mode of action. Here we show that the chemogenomic profile of gossypol is strikingly similar to that of the iron chelators deferasirox and desferricoprogen. Iron import channels Fet1 and Fet3 are prominent in all three profiles. Furthermore, yeast inhibited by gossypol and deferasirox is rescued by the addition of Fe²⁺. We propose that Fe²⁺ chelation is in fact the principle mode of action of gossypol.

Quantitative SPECT imaging and biodistribution point to molecular weight independent tumor uptake for some long-circulating polymer nanocarriers

Polymeric nanocarriers are promising entities for cancer diagnosis and therapy. The aim of such nanocarriers is to selectively accumulate in cancerous tissue that is difficult to visualize or treat. The passive accumulation of a nanocarrier in a tumor through extravasation is often attributed to the enhanced permeation and retention (EPR) effect and the size and shape of the nanocarrier. However, the tumor microenvironment is very heterogeneous and the intratumoral pressure is usually high, leading to different opinions about how the EPR of nanocarriers through the irregular vasculature of a tumor leads to accumulation. In order to investigate this topic, we studied methods for the determination of pharmacokinetic parameters, biodistribution and the tumor uptake of nanocarriers. More specifically, we used non-invasive quantitative Single-Photon Emission Computed Tomography/Computed Tomography (qSPECT/CT) imaging of hyperbranched polyglycerols (HPGs) to explore the specific biodistribution and tumor uptake of six model nanocarriers in Rag2m mice. We were interested to see if a distinct molecular weight (MW) of nanocarriers (HPG 25, 50, 100, 200, 300, 500 kDa) is favoured by the tumor. To trace the model nanocarriers, HPGs were covalently linked to the strong chelator desferrioxamine (DFO), and radiolabeled with the gamma emitter 67Ga (EC = 100%, E γ = 185 keV (21.4%), 300 keV (16.6%), half-life = 3.26 d). Without the need for blood collection, but instead using qSPECT/CT imaging inside the heart, the blood circulation half-lives of the 67Ga labeled HPGs were determined and increased from 9.9 ± 2.9 to 47.8 ± 7.9 hours with increasing polymer MW. Total tumor accumulation correlated positively with the circulation time of the HPGs. Comparing the tumor-to-blood ratio dynamically revealed how blood and tumor concentrations of the nanocarrier change over time and when equilibrium is reached. The time of equilibrium is size-dependent and increases with molecular weight. Furthermore, the data indicate that for larger MWs, nanocarrier uptake and retention by the tumor is size independent. Further studies are necessary to advance our understanding of the interplay between MW and nanoparticle accumulation in tumors.

Mn(II)/Mn(III) and Fe(III) binding capability of two Aspergillus fumigatus siderophores, desferricrocin and N', N″, N‴-triacetylfusarinine C

Manganese(II) and manganese(III) complexes of the exocyclic desferricrocin (H3DFCR) and endocyclic triacetylfusarinine C (H3TAF) in solution have been studied by using pH-potentiometry, UV-Vis spectrophotometry, relaxometry and cyclic voltammetry. A comparison between the present results and the corresponding ones for the open-chain analogues, desferrioxamine B (DFB) and desferricoprogen (DFC), shows (i) The dissociation processes of H3DFCR occur in the expected pH-range (pH7-10.5), but hydrogen bonding is assumed to be responsible for a quite low proton dissociation constant (pK=4.18) of H3TAF and also an unusually high one (10.59). (ii) Moderate stability complexes with 1:1 Mn(II) to ligand ratio are formed with all four siderophores. (iii) The coordination of the three hydroxamates of a siderophore takes place in stepwise processes, except the case of desferricrocin, with which, large-extent overlapping of the processes occurs. (iv) Out of the four tris-chelated [ML] type complexes, the complex of DFCR is the most compact, as it is indicated by the relaxivity values. (v) Following the stoichiometric oxidation of the Mn(II)-siderophore complexes at pH≥9, tris-chelated Mn(III) complexes are formed. To make a comparison between the stability of the Mn(III) and the corresponding Fe(III) complexes of DFCR and TAF, the determination of the stability of the Fe(III) complexes under our condition has also been performed, by using UV-Vis spectrophotometry. Comparable stability of the corresponding complexes was found. (vi) Correlation study of the stability constants resulted in estimation of the constant of the Mn(III) monohydroxo complex, for which there was no data in the literature under our conditions.

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.

Proton and iron binding by the cyanobacterial toxin microcystin-LR

Microcystins (MCs) are a group of hepatotoxins produced by cyanobacteria that have not had their functional role or the environmental factors that trigger production clearly determined. One suggestion is that microcystins are siderophores (i.e., ligands with an extremely high affinity with iron, typically with stability constants substantially greater than 10(25)). In this work, we explore proton and iron binding with microcystin-LR (MC-LR). Using UV-visible spectroscopy and a HPLC peak retention time-based method, the two acid dissociation constants associated with the carboxylic groups of MC-LR were determined to be: pKa₁ = 2.17 and pKa₂ = 3.96. Cyclic voltammetry provides evidence for the formation of at least two Fe(III)-MC-LR complexes, with the Fe(III) reduction peak significantly shifted to more reducing potentials in the presence of MC-LR. These complexes have been interpreted as a rapidly formed initial complex (Complex 1) and a more stable, and slower forming, Complex 2. The stability constant for Fe(III)-MC-LR (Complex 2) was estimated to be approximately 10(13) in 60% v/v MeOH/water at 0.1 M ionic strength. The electrochemical experiments provide no evidence for the formation of a complex between Fe(2+) and MC-LR. Given that most MC-LR is released only upon cell lysis, and coupled with the moderate strength of the stability constant with Fe(III) determined in this study, it appears unlikely that that MC-LR is an extracellular siderophore. If MC-LR is involved in iron regulation in cyanobacteria, it is more likely as a shuttle for iron across the cell membrane or in intracellular processes.

Gold-deferrioxamine nanometric interface for selective recognition of Fe(III) using square wave voltammetry and electrochemical impedance spectroscopy methods

Deferrioxamine, a bacterial hydroxamic siderophore having high binding affinity for Fe(III), is used in its immobilized form, as self-assembled monolayer on Au, for accumulation and recognition of Fe(III) from the solution phase. The accumulated Fe(III) is detected via both active mode based on faradaic reduction current of Fe(III), and inactive mode based on impedimetric effect of accumulated Fe(III) against redox reaction of a suitable probe. Appropriate electrochemical techniques, square wave voltammetry and electrochemical impedance spectroscopy, are used for the transduction of analytical signals obtained by this sensor. Then, the parameters influencing the sensor response are optimized. In the best conditions, a linear response, from 1.0×10(-10) to 1.0×10(-7)M Fe(III) in logarithmic scale with a detection limit of 2.0×10(-11)M, and mean relative standard deviation of 1.7% for n=4 is observed. The results show that the sensor can be used for determination of Fe(III) in the presence of various inorganic ions and biological species. Validity of the method and applicability of the sensor are successfully tested by determination of Fe(III) in various real samples including plant tissue (corn leaves), industrial alloy (Ferrotitanium), and pharmaceutical samples (Venofer(®) ampoule, Ironorm(®) capsule, and V.M. Protein(®) powder).

Optimization of coprogen production in Neurospora crassa

Coprogen production of Neurospora crassa was dependent on glucose, aspartate and iron contents as well as on initial pH of the culture media. Surplus iron and acidic pH hindered the production of coprogen as well as the transcription of the sid1 gene (NCU07117) encoding putative L-ornithine-N5-monooxygenase, the first enzyme in the coprogen biosynthetic pathway. High glucose (40 g/l) and aspartate (21 g/l) concentrations were beneficial for coprogen synthesis, but neither glucose nor aspartate affected the sid1 transcription. Moreover, efficient coprogen production was observed after glucose had been consumed, which suggested that N. crassa accumulated iron even in non-growing, carbon-starving cultures.

Potential mobilization of platinum-group elements by siderophores in surface environments

The emission of platinum-group elements (PGEs) from catalytic converters has led to increased environmental abundances of Pt, Pd, and Rh; however, little is known about the environmental effects and fate of these metals. Organic ligands found in soils have the potential to increase the mobility of PGEs and potentially increase the bioavailability of the metals. Here, we assessed the abilities of microbially produced iron-chelating ligands (siderophores) to complex with the PGEs. Batch experiments using the synthetic siderophore desferrioxamine-B (DFO-B) and powdered metal or oxide forms of Pt, Pd, or Rh showed that DFO-B enhances the solubility of Pt and Pd due to the formation of Pt- and Pd-DFO-B aqueous complexes, with estimated minimum stability constants on the order of 10(17-18) and 10(20-24), respectively. Dissolution rates for Pd are comparable to other mineral dissolution rates with DFO-B. DFO-B had little to no effect on the dissolution of Rh metal or Rh2O3. Our results indicate that siderophores have the potential to increase the mobility of Pt and Pd in environments with limited activities of free trivalent cations. These results have implications for the fate of catalytic converter-emitted Pt and Pd, and support the need for further Pt and Pd toxicity and bioaccumulation studies.