Iron chelating agents for iron overload diseases

Although iron is an essential element for life, an excessive amount may become extremely toxic both for its ability to generate reactive oxygen species, and for the lack in humans of regulatory mechanisms for iron excretion. Chelation therapy has been introduced in clinical practice in the seventies of last century to defend thalassemic patients from the effects of iron overload and, in spite of all its limitations, it has dramatically changed both life expectancy and quality of life of patients. It has to be considered that the drugs in clinical use present some disadvantages too, this makes urgent new more suitable chelating agents. The requirements of an iron chelator have been better and better defined over the years and in this paper they will be discussed in detail. As a final point the most interesting ligands studied in the last years will be presented

Titolazioni chelometriche con EDTA: considerazioni sul grafico di Reilley

Theory and procedure on which Reilley curve is based are discussed; it defines the minimum pH for an effective metal titration with EDTA. This curve, widely reported in Analytical Chemistry textbooks, was originally presented in an implicit way by Reilley, who assumed a 106 conditional constant for 0.01 M metal concentration. We report here the conditional constants necessary for 99, 99.9 and 99.99 complex formation percentage at various analytical concentration. An updated Reilley plot is furthermore presented, which takes into consideration all formation constants at 20°C reported till 1998 for EDTA complexes

The Involvement of amino acid side chains in shielding the nickel coordination site: an NMR study

Coordination of proteins and peptides to metal ions is known to affect their properties, often by a change in their structural organization. Side chains of the residues directly involved in metal binding or very close to the coordination centre may arrange themselves around it, in such a way that they can, for instance, disrupt the protein functions or stabilize a metal complex by shielding it from the attack of water or other small molecules. The conformation of these side chains may be crucial to different biological or toxic processes. In our research we have encountered such behaviour in several cases, leading to interesting results for our purposes. Here we give an overview on the structural changes involving peptide side chains induced by Ni(II) coordination. In this paper we deal with a number of peptides, deriving from proteins containing one or more metal coordinating sites, which have been studied through a series of NMR experiments in their structural changes caused by Ni(II) complexation. Several peptides have been included in the study: short sequences from serum albumin (HSA), Des-Angiotensinogen, the 30-amino acid tail of histone H4, some fragments from histone H2A and H2B, the initial fragment of human protamine HP2 and selected fragments from prion and Cap43 proteins. NMR was the election technique for gathering structural information. Experiments performed for this purpose included 1D ¹H and ¹³C, and 2D HSQC, COSY, TOCSY, NOESY and ROESY acquisitions, which allowed the calculation of the Ni(II) complexes structural models

Novel DFO-functionalized mesoporous silica for iron sensing. Part 2. Experimental detection of free iron concentration (pFe) in urine samples.

Successful in vivo chelation treatment of iron(III) overload pathologies requires that a significant fraction of the administered drug actually chelates the toxic metal. Increased mobilization of the iron(III) in experiments on animals or humans, most often evaluated from urinary output, is usually used as an assessment tool for chelation therapy. Alternatively, the efficiency of a drug is estimated by calculating the complexing ability of a chelating agent towards Fe(III). The latter is calculated by the pFe value, defined as the negative logarithm of the concentration of the free metal ion in a solution containing 10 μM total ligand and 1 μM total metal at a physiological pH of 7.4. In theory, pFe has to be calculated taking into account all the complexation equilibria involving the metal and the possible ligands. Nevertheless, complexation reactions in complex systems such as serum and urine may hardly be accurately modelled by computer software. The experimental determination of the bioavailable fraction of iron(III) in biological fluids would therefore be of the utmost relevance in the clinical practice. The efficiency of the therapy could be more easily estimated as well as the course of overload pathologies. In this context, the aim of the present work was the development of a sensor to assess the free iron directly in biological fluids (urine) of patients under treatment with chelating agents. In the proposed device (DFO-MS), the strong iron chelator deferoxamine (DFO) is immobilized on the MCM-41 mesoporous silica. The characterization of the iron(III) sorption on DFO-MS was undertaken, firstly in 0.1 M KNO3, then directly in urine samples, in order to identify the sorption mechanism. The stoichiometry of the reaction in the solid phase was found to be: with an exchange constant (average value) of log βex = 40(1). The application of DFO-MS to assess pFe in SPU (Simulating Pathology Urine) samples was also considered. The results obtained were very promising for a future validation and subsequent application of the sensor in samples of patients undergoing chelation therapy

Synthesis and Mass Spectrometry Analysis of Mimosine-Containing Peptides

AbstractNon-proteinogenic amino acids are widely explored group of compounds due to their chemical properties and great potential of application in the combinatorial chemistry, medicinal investigation etc. Therefore the synthetic methods of their incorporation to the peptide chain are required. l-Mimosine, (S)-α-amino-β-(3-hydoxy-4-oxo-1,4-dihydropyridin-1-yl)-propanoic acid), is a plant amino acid, known to induce apoptosis in human pancreatic cancer xenografts. Here we present our investigations on the synthesis of mimosine-containing peptide and their ESI-MS/MS analysis. We successfully applied Fmoc-protected mimosine a with a free hydroxy ketone group for efficient peptide synthesis in the presence of HATU as a coupling reagent without the formation of side products. Additionally the tandem mass spectrometry analysis revealed the characteristic loss of the heterocyclic ring from mimosine residue side chain. The described method allows insertion of mimosine residue at any endo-position within a peptide sequence. The obtained results may be useful in the synthesis and mass spectrometry analysis of various mimosine-containing peptides

DFO@EVOH and 3,4-HP@EVOH: Towards New Polymeric Sorbents for Iron(III)

The paper presents the synthesis and preliminary characterization of two novel solid-phase sorbents for iron(III), resulting from the functionalization of ethylene-vinyl alcohol copolymer (EVOH) with deferoxamine, DFO (DFO@EVOH), and a novel tripodal 3-hydroxy-4-pyridinone, named 3,4-HP (3,4-HP@EVOH). DFO and 3,4-HP have been covalently bonded to EVOH, using carbonyldiimidazole as a coupling agent. Before their use as Fe(III) sorbents, they were warm-pressed to obtain a thin film. Polymers have been characterized by conventional physico-chemical techniques; furthermore, the sorption properties towards Fe(III) were investigated. The physico-chemical characterization of the new solid-state devices demonstrates the effective linkage of the two receptors on the polymeric support. Despite a relatively low sorption capacity for both materials, the stoichiometry and the complexation constants of Fe(III)/DFO@EVOH and Fe(III)/3,4-HP@EVOH are in pretty good agreement with those obtained for the same ligands in aqueous solutions

Chelating Agents in Soil Remediation: A New Method for a Pragmatic Choice of the Right Chelator

Soil pollution by metal ions constitutes one of the most significant environmental problems in the world, being the ecosystems of extended areas wholly compromised. The remediation of soils is an impelling necessity, and different methodologies are used and studied for reaching this goal. Among them, the application of chelating agents is one of the most promising since it could allow the removal of metal ions while preserving the most meaningful properties of the original soils. The research in this field requires the joined contribute of different expertise spanning from biology to chemistry. In this work, we propose a parsimonious and pragmatic approach for screening among a range of potential chelating agents. This methodology, the Nurchi's method, is based on an extension of the Reilley procedure for EDTA titrations. This allows forecasting the binding ability of chelating agents toward the target polluting metal ions and those typically found in soils, based on the knowledge of the related protonation and complex formation constants. The method is thoroughly developed, and then tested by application to some representative cases. Its use and relevance in biomedical and industrial applications is also discussed

A speciation study on the perturbing effects of iron chelators on the homeostasis of essential metal ions

A number of reports have appeared in literature calling attention to the depletion of essential metal ions during chelation therapy on beta-thalassaemia patients. We present a speciation study to determine how the iron chelators used in therapy interfere with the homeostatic equilibria of essential metal ions. This work includes a thorough analysis of the pharmacokinetic properties of the chelating agents currently in clinical use, of the amounts of iron, copper and zinc available in plasma for chelation, and of all the implied complex formation constants. The results of the study show that a significant amount of essential metal ions is complexed whenever the chelating agent concentration exceeds the amount necessary to coordinate all disposable iron-a frequently occurring situation during chelation therapy. On the contrary, copper and zinc do not interfere with iron chelation, except for a possible influence of copper on iron speciation during deferiprone treatment

Thermodynamic Study of Oxidovanadium(IV) with Kojic Acid Derivatives: A Multi-Technique Approach

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VIVO2+, constitute the precondition for the development of new insulinmimetic and anticancer compounds. In the present work, we examined the VIVO2+ complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VIVO2+ ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species