The present status of chelating agents in medicine

Efficiently suppress of ferroptosis using deferoxamine nanoparticles as a new method for retinal ganglion cell protection after traumatic optic neuropathy

Traumatic optic neuropathy (TON) is the major contributor to optic nerve damage, where the retinal ganglion cells (RGCs) are substantially lost. However, the underlying pathological mechanisms for these conditions remain largely elusive. Present work conducted a study on TON rat model, where the iron-dependent cyclooxygenase-2 (COX-2) overexpression and lipid peroxidation were observed in RGCs, suggesting ferroptosis, an iron-dependent non-apoptotic cell death, is involved in TON-induced death of RGCs. Hence, the newly formulated hyaluronic acid (HA)-based deferoxamine (DFO) nanoparticles (DFO-NPs) were intravitreally administrated in the rat model. It was hypothesized that the effective delivery of DFO, iron chelator, to the RGCs might rescue RGC ferroptosis from TON-induced injury. Also, since DFO is poor in bioavailability and of very short half-life in vivo, its safe and efficient intravitreal delivery is critical. Therefore, DFO-NPs were prepared by chemical grafting DFO onto HA molecules, and then crosslinking them in microemulsion bubbles for nanoparticles formulation. The nanoparticles were highly accumulated around the ganglionic cells and DFO uptake was increased in RGCs, accompanied by the significantly inhibited the overexpression of COX-2 and inactivation of glutathione peroxidase 4 (GPX4). These results indicate that DFO-NPs acted as an effective ferroptosis inhibitor, for the prevention of TON-induced RGC death. The current study provides new insights into the underlying mechanism of TON-induced RGC death, which may help to explore a novel strategy for the treatment of TON.

Zinc: Multidimensional Effects on Living Organisms

Zinc is a redox-inert trace element that is second only to iron in abundance in biological systems. In cells, zinc is typically buffered and bound to metalloproteins, but it may also exist in a labile or chelatable (free ion) form. Zinc plays a critical role in prokaryotes and eukaryotes, ranging from structural to catalytic to replication to demise. This review discusses the influential properties of zinc on various mechanisms of bacterial proliferation and synergistic action as an antimicrobial element. We also touch upon the significance of zinc among eukaryotic cells and how it may modulate their survival and death through its inhibitory or modulatory effect on certain receptors, enzymes, and signaling proteins. A brief discussion on zinc chelators is also presented, and chelating agents may be used with or against zinc to affect therapeutics against human diseases. Overall, the multidimensional effects of zinc in cells attest to the growing number of scientific research that reveal the consequential prominence of this remarkable transition metal in human health and disease.

Transferrin receptor 1 is a cellular receptor for human heme-albumin

Iron is essential for living cells. Uptake of iron-loaded transferrin by the transferrin receptor 1 (CD71, TFR) is a major but not sufficient mechanism and an alternative iron-loaded ligand for CD71 has been assumed. Here, we demonstrate that CD71 utilizes heme-albumin as cargo to transport iron into human cells. Binding and endocytosis of heme-albumin via CD71 was sufficient to promote proliferation of various cell types in the absence of transferrin. Growth and differentiation of cells induced by heme-albumin was dependent on heme-oxygenase 1 (HO-1) function and was accompanied with an increase of the intracellular labile iron pool (LIP). Import of heme-albumin via CD71 was further found to contribute to the efficacy of albumin-based drugs such as the chemotherapeutic Abraxane. Thus, heme-albumin/CD71 interaction is a novel route to transport nutrients or drugs into cells and adds to the emerging function of CD71 as a scavenger receptor.

Brell, Berg et al find that iron enters cells not only through iron-transferrin uptake by the transferrin receptor (CD71) but also through uptake of heme-albumin by this receptor and that heme-albumin stimulates proliferation in a manner dependent on heme oxygenase 1. This study presents a new route for iron uptake in mammalian cells.

A new approach to evaluate toxic metal transport in a catchment

Competitive sorption and desorption of Cd²⁺, Pb²⁺, and Hg²⁺ onto riverbank and sediment samples of an area impacted by pyritic residue in a Southern Brazilian catchment were evaluated. Although these ions are considered poorly mobile, a new approach has been proposed to assess their behavior and associated risk. In this sense, factorial design and three-dimensional surface methodology are proposed to describe the competitive sorption behavior of the metal ion in the environmental matrix, as well as an innovative mobilization factor (MF) to describe the desorption rate from the integration of the normalized difference of sorption-desorption fluorescence peaks. Sorption was carried out with a central composite factorial design (2³) to estimate simultaneous effects of independent variables. Three-dimensional surface analysis indicated increasing Cd²⁺ equilibrium concentration (C_eq) with Hg²⁺ and Pb²⁺ initial concentration (C_i), showing synergistic effect and low Cd²⁺ affinity to the solid phase. Statistical analysis presented [Formula: see text] as a significant variable for cadmium and lead dynamics, although [Formula: see text] was also significant for Hg²⁺ releasing to the liquid phase. After integrating the sorption and desorption fluorescence peaks, the MF for Cd²⁺, Pb²⁺, and Hg²⁺ was around 0.2, 0.5, and 0.1 in riverbank sediment, and 0.3, 0.9, and 0.1 in sediment, respectively. Hence, consistent ion mobilization along the river was observed, with Pb²⁺ mobilizing 9 and 6 times more than Hg²⁺ and Cd²⁺, respectively. The transport of ions such as Pb²⁺ and Hg²⁺, usually considered immobile, has indeed occurred, causing contamination through the watershed and increasing environmental risk. Graphical Abstract A new approach to determine toxic metal mobilization factor in a river catchment.

Lactoferrin in Aseptic and Septic Inflammation

Lactoferrin (Lf), a cationic glycoprotein able to chelate two ferric irons per molecule, is synthesized by exocrine glands and neutrophils. Since the first anti-microbial function attributed to Lf, several activities have been discovered, including the relevant anti-inflammatory one, especially associated to the down-regulation of pro-inflammatory cytokines, as IL-6. As high levels of IL-6 are involved in iron homeostasis disorders, Lf is emerging as a potent regulator of iron and inflammatory homeostasis. Here, the role of Lf against aseptic and septic inflammation has been reviewed. In particular, in the context of aseptic inflammation, as anemia of inflammation, preterm delivery, Alzheimer’s disease and type 2 diabetes, Lf administration reduces local and/or systemic inflammation. Moreover, Lf oral administration, by decreasing serum IL-6, reverts iron homeostasis disorders. Regarding septic inflammation occurring in Chlamydia trachomatis infection, cystic fibrosis and inflammatory bowel disease, Lf, besides the anti-inflammatory activity, exerts a significant activity against bacterial adhesion, invasion and colonization. Lastly, a critical analysis of literature in vitro data reporting contradictory results on the Lf role in inflammatory processes, ranging from pro- to anti-inflammatory activity, highlighted that they depend on cell models, cell metabolic status, stimulatory or infecting agents as well as on Lf iron saturation degree, integrity and purity.

Iron and Alzheimer's Disease: From Pathogenesis to Therapeutic Implications

As people age, iron deposits in different areas of the brain may impair normal cognitive function and behavior. Abnormal iron metabolism generates hydroxyl radicals through the Fenton reaction, triggers oxidative stress reactions, damages cell lipids, protein and DNA structure and function, and ultimately leads to cell death. There is an imbalance in iron homeostasis in Alzheimer's disease (AD). Excessive iron contributes to the deposition of β-amyloid and the formation of neurofibrillary tangles, which in turn, promotes the development of AD. Therefore, iron-targeted therapeutic strategies have become a new direction. Iron chelators, such as desferoxamine, deferiprone, deferasirox, and clioquinol, have received a great deal of attention and have obtained good results in scientific experiments and some clinical trials. Given the limitations and side effects of the long-term application of traditional iron chelators, alpha-lipoic acid and lactoferrin, as self-synthesized naturally small molecules, have shown very intriguing biological activities in blocking Aβ-aggregation, tauopathy and neuronal damage. Despite a lack of evidence for any clinical benefits, the conjecture that therapeutic chelation, with a special focus on iron ions, is a valuable approach for treating AD remains widespread.

Targeted Brain Delivery of Rabies Virus Glycoprotein 29-Modified Deferoxamine-Loaded Nanoparticles Reverses Functional Deficits in Parkinsonian Mice

Excess iron deposition in the brain often causes oxidative stress-related damage and necrosis of dopaminergic neurons in the substantia nigra and has been reported to be one of the major vulnerability factors in Parkinson's disease (PD). Iron chelation therapy using deferoxamine (DFO) may inhibit this nigrostriatal degeneration and prevent the progress of PD. However, DFO shows very short half-life in vivo and hardly penetrates the blood brain barrier (BBB). Hence, it is of great interest to develop DFO formulations for safe and efficient intracerebral drug delivery. Herein, we report a polymeric nanoparticle system modified with brain-targeting peptide rabies virus glycoprotein (RVG) 29 that can intracerebrally deliver DFO. The nanoparticle system penetrates the BBB possibly through specific receptor-mediated endocytosis triggered by the RVG29 peptide. Administration of these nanoparticles significantly decreased iron content and oxidative stress levels in the substantia nigra and striatum of PD mice and effectively reduced their dopaminergic neuron damage and as reversed their neurobehavioral deficits, without causing any overt adverse effects in the brain or other organs. This DFO-based nanoformulation holds great promise for delivery of DFO into the brain and for realizing iron chelation therapy in PD treatment.

Interaction of 5'-Guanosine Monophosphate with Organotin(IV) Moieties: Synthesis, Structural Characterization, and Anti-Inflammatory Activity

Reaction(s) of 5'-guanosine monophosphate (5'GMP) with di- and triorganotin(IV) chloride(s) led to formation of organotin(IV) derivatives of general formulae, [R2Sn(5'-GMP)·H2O] n and [(R'3Sn)2(5'-GMP)·H2O] n , where R = Me, n-Bu, and Ph; R' = Me, i-Pr, n-Bu, and Ph; (5'-GMP)(2-) = 5'-guanosine monophosphate. An attempt has been made to prove the structures of the resulting derivatives on the basis of FT-IR, multinuclear (1)H, (13)C, and (119)Sn NMR and (119)Sn Mössbauer spectroscopic studies. These investigations suggest that both di- and triorganotin(IV)-5'-guanosine monophosphates are polymeric in which (5'-GMP)(2-) is bonded through phosphate group resulting in a distorted trigonal bipyramidal geometry around tin. The ribose conformation in all of the derivatives is C3'-endo, except diphenyltin(IV) and tri-i-propyltin(IV) derivatives where it is C2'-endo. All of the studied derivatives exhibited mild-to-moderate anti-inflammatory activity (~15.64-20.63% inhibition) at 40 mg kg(-1) dose and LD50 values > 400 mg kg(-1) in albino rats.

Intranasal deferoxamine reverses iron-induced memory deficits and inhibits amyloidogenic APP processing in a transgenic mouse model of Alzheimer's disease

Increasing evidence indicates that a disturbance of normal iron homeostasis and an amyloid-β (Aβ)-iron interaction may contribute to the pathology of Alzheimer's disease (AD), whereas iron chelation could be an effective therapeutic intervention. In the present study, transgenic mice expressing amyloid precursor protein (APP) and presenilin 1 and watered with high-dose iron served as a model of AD. We evaluated the effects of intranasal administration of the high-affinity iron chelator deferoxamine (DFO) on Aβ neuropathology and spatial learning and memory deficits created in this AD model. The effects of Fe, DFO, and combined treatments were also evaluated in vitro using SHSY-5Y cells overexpressing the human APP Swedish mutation. In vivo, no significant differences in the brain concentrations of iron, copper, or zinc were found among the treatment groups. We found that high-dose iron (deionized water containing 10 mg/mL FeCl(3)) administered to transgenic mice increased protein expression and phosphorylation of APP695, enhanced amyloidogenic APP cleavage and Aβ deposition, and impaired spatial learning and memory. Chelation of iron via intranasal administration of DFO (200 mg/kg once every other day for 90 days) inhibited iron-induced amyloidogenic APP processing and reversed behavioral alterations. DFO treatment reduced the expression and phosphorylation of APP protein by shifting the processing of APP to the nonamyloidogenic pathway, and the reduction was accompanied by attenuating the Aβ burden, and then significantly promoted memory retention in APP/PS1 mice. The effects of DFO on iron-induced amyloidogenic APP cleavage were further confirmed in vitro. Collectively, the present data suggest that intranasal DFO treatment may be useful in AD, and amelioration of iron homeostasis is a potential strategy for prevention and treatment of this disease.

Nanoparticle and iron chelators as a potential novel Alzheimer therapy

Current therapies for Alzheimer disease (AD) such as the acetylcholinesterase inhibitors and the latest NMDA receptor inhibitor, Namenda, provide moderate symptomatic delay at various stages of the disease, but do not arrest the disease progression or bring in meaningful remission. New approaches to the disease management are urgently needed. Although the etiology of AD is largely unknown, oxidative damage mediated by metals is likely a significant contributor since metals such as iron, aluminum, zinc, and copper are dysregulated and/or increased in AD brain tissue and create a pro-oxidative environment. This role of metal ion-induced free radical formation in AD makes chelation therapy an attractive means of dampening the oxidative stress burden in neurons. The chelator desferrioxamine, FDA approved for iron overload, has shown some benefit in AD, but like many chelators, it has a host of adverse effects and substantial obstacles for tissue-specific targeting. Other chelators are under development and have shown various strengths and weaknesses. Here, we propose a novel system of chelation therapy through the use of nanoparticles. Nanoparticles conjugated to chelators show unique ability to cross the blood-brain barrier (BBB), chelate metals, and exit through the BBB with their corresponding complexed metal ions. This method may provide a safer and more effective means of reducing the metal load in neural tissue, thus attenuating the harmful effects of oxidative damage and its sequelae. Experimental procedures are presented in this chapter.

Metal chelators coupled with nanoparticles as potential therapeutic agents for Alzheimer's disease

Alzheimer's disease (AD) is a devastating neuro-degenerative disorder characterized by the progressive and irreversible loss of memory followed by complete dementia. Despite the disease's high prevalence and great economic and social burden, an explicative etiology or viable cure is not available. Great effort has been made to better understand the disease's pathogenesis, and to develop more effective therapeutic agents. However, success is greatly hampered by the presence of the blood-brain barrier that limits a large number of potential therapeutics from entering the brain. Nanoparticle-mediated drug delivery is one of the few valuable tools for overcoming this impediment and its application as a potential AD treatment shows promise. In this review, the current studies on nanoparticle delivery of chelation agents as possible therapeutics for AD are discussed because several metals are found excessive in the AD brain and may play a role in the disease development. Specifically, a novel approach involving transport of iron chelation agents into and out of the brain by nanoparticles is highlighted. This approach may provide a safer and more effective means of simultaneously reducing several toxic metals in the AD brain. It may also provide insights into the mechanisms of AD pathophysiology, and prove useful in treating other iron-associated neurodegenerative diseases such as Friedreich's ataxia, Parkinson's disease, Huntington's disease and Hallervorden-Spatz Syndrome. It is important to note that the use of nanoparticle-mediated transport to facilitate toxicant excretion from diseased sites in the body may advance nanoparticle technology, which is currently focused on targeted drug delivery for disease prevention and treatment. The application of nanoparticle-mediated drug transport in the treatment of AD is at its very early stages of development and, therefore, more studies are warranted.

Nanoparticle and other metal chelation therapeutics in Alzheimer disease

Current therapies for Alzheimer disease (AD) such as the anticholinesterase inhibitors and the latest NMDA receptor inhibitor, Namenda, provide moderate symptomatic delay at various stages of disease, but do not arrest disease progression or supply meaningful remission. As such, new approaches to disease management are urgently needed. Although the etiology of AD is largely unknown, oxidative damage mediated by metals is likely a significant contributor since metals such as iron, aluminum, zinc, and copper are dysregulated and/or increased in AD brain tissue and create a pro-oxidative environment. This role of metal ion-induced free radical formation in AD makes chelation therapy an attractive means of dampening the oxidative stress burden in neurons. The chelator desferioxamine, FDA approved for iron overload, has shown some benefit in AD, but like many chelators, it has a host of adverse effects and substantial obstacles for tissue-specific targeting. Other chelators are under development and have shown various strengths and weaknesses. In this review, we propose a novel system of chelation therapy through the use of nanoparticles. Nanoparticles conjugated to chelators show a unique ability to cross the blood-brain barrier (BBB), chelate metals, and exit through the BBB with their corresponding complexed metal ions. This method may prove to be a safe and effective means of reducing the metal load in neural tissue thus staving off the harmful effects of oxidative damage and its sequelae.

The metallobiology of Alzheimer's disease

The cause of Alzheimer's disease (AD) is closely related to the aggregation of a normal protein, beta-amyloid (Abeta), within the neocortex. Recently, evidence has been gathered to suggest that Abeta precipitation and toxicity in AD are caused by abnormal interactions with neocortical metal ions, especially Zn, Cu and Fe. However, Abeta might also participate in normal metal-ion homeostasis. An inevitable, age-dependent rise in brain Cu and Fe might hypermetallate the Abeta peptide, causing the catalysis of H(2)O(2) production that mediates the toxicity and auto-oxidation of Abeta. The greater incidence of AD in females could be due to greater constitutive activity of the synaptic Zn transporter ZnT3, and attenuated binding of metal ions to the rodent homologue of Abeta might explain why these animals are spared Alzheimer's pathology. Compounds that interdict metal-ion binding to Abeta dissolve brain deposits in vitro and one such compound, clioquinol, inhibits Abeta deposition in the Tg2576 mouse model for AD and could be useful clinically. These insights could also apply to other degenerative disorders in which metal-ion-protein interactions have been implicated.

Metal complexing agents as therapies for Alzheimer's disease

Modern research approaches into drug development for Alzheimer's disease (AD) target beta-amyloid (Abeta) accumulation in the brain. The main approaches attempt to prevent Abeta production (secretase inhibitors) or to clear Abeta (vaccine). However, there is now compelling evidence that Abeta does not spontaneously aggregate, but that there is an age-dependent reaction with excess brain metal (copper, iron and zinc), which induces the protein to precipitate into metal-enriched masses (plaques). The abnormal combination of Abeta with Cu or Fe induces the production of hydrogen peroxide, which may mediate the conspicuous oxidative damage to the brain in AD. We have developed metal-binding compounds that inhibit the in vitro generation of hydrogen peroxide by Abeta, as well as reverse the aggregation of the peptide in vitro and from human brain post-mortem specimens. Most recently, one of the compounds, clioquinol (CQ; a USP antibiotic) was given orally for 9 weeks to amyloid-bearing transgenic mice, and succeeded in markedly inhibiting Abeta accumulation. On the basis of these results, CQ is being tested in clinical trials.

The effect of hexaaza- and hexathia-macrocyclic ligands on transition metal cytotoxicity in human hepatoma-derived cultured cells

The effect of macrocyclic ligands on cytotoxic concentrations of the transition metal ions of copper, zinc, and cadmium was investigated. For this purpose, a hexaaza- [3,6,9,17,20,23-hexaazatricyclo[23.3.1.1(11,15)] triaconta-1(29),11(30),12,14,25,27-hexaene (L2)] and hexathia-chelating ligand [1,4,7,10,13,16-hexathiacyclooctadecane (L3)] were used in the human hepatoma-derived HepG2 cell line. The cytotoxicity was measured by the neutral red uptake inhibition assay. First, the NI50 of the ligands, i.e., the concentration of the ligand inducing a 50% inhibition in neutral red uptake compared to control cells, was determined. In several metal/ligand combination experiments, the effects for L2 were difficult to interpret, whereas for L3 in combination with copper ions, a severe increase -- and for zinc ions, a significant decrease of cell toxicity -- relative to the metal control was observed. To further examine the different effects observed with L3 in combination with, respectively, Cu2+ and Zn2+, the glutathione (GSH) content was measured. The relative GSH content decreased as the concentration of L3 increased. It was proposed that the increased toxicity of the combination Cu(2+)/L3 could be caused by the depletion of GSH and a subsequent inability to scavenge the produced reactive oxygen species (ROS). This hypothesis was supported by experiments during which vitamin E or C was added to the Cu(2+)/L3 system.

Metal chelation as a potential therapy for Alzheimer's disease

Alzheimer's disease is a rapidly worsening public health problem. The current lack of effective treatments for Alzheimer's disease makes it imperative to find new pharmacotherapies. At present, the treatment of symptoms includes use of acetylcholinesterase inhibitors, which enhance acetylcholine levels and improve cognitive functioning. Current reports provide evidence that the pathogenesis of Alzheimer's disease is linked to the characteristic neocortical amyloid-beta deposition, which may be mediated by abnormal metal interaction with A beta as well as metal-mediated oxidative stress. In light of these observations, we have considered the development of drugs that target abnormal metal accumulation and its adverse consequences, as well as prevention or reversal of amyloid-beta plaque formation. This paper reviews recent observations on the possible etiologic role of A beta deposition, its redox activity, and its interaction with transition metals that are enriched in the neocortex. We discuss the effects of metal chelators on these processes, list existing drugs with chelating properties, and explore the promise of this approach as a basis for medicinal chemistry in the development of novel Alzheimer's disease therapeutics.

Structure-activity relationship of macrocyclic and linear gadolinium chelates: investigation of transmetallation effect on the zinc-dependent metallopeptidase angiotensin-converting enzyme

Transmetallation between commercially available solutions of gadolinium (Gd) chelates and the zinc (Zn)-dependent angiotensin-converting enzyme (ACE) was investigated. In vitro, the strongest inhibitions were observed for the linear Gd complexes, Gd diethylenetriamine pentaacetic acid (DTPA) bis-methylamide (BMA) (IC50 = .016 +/- .006 mmol/l) and Gd-DTPA (IC50 = .350 +/- .034 mmol/l). The two macrocycles Gd tetraazacyclododecane tetraacetic acid (DOTA) and Gd-HP-DO3A were similar and 400 times less active than Gd-DTPA-BMA. These effects were mainly due to the presence of free ligand for DTPA and calcium (Ca) chelate in the case of DTPA-BMA because the addition of Zn2+ in the same quantities suppresses their inhibitory effects. In vivo, these two solutions of linear Gd chelates significantly inhibited ACE activity (Gd-DTPA: (67 +/- 9% versus baseline; and Gd-DTPA-BMA: 73 +/- 2% versus baseline at the clinical dose of .1 mmol/kg), whereas no significant effect was observed for the two macrocyclic chelates Gd-DOTA and Gd-HP-DO3A. Formulating the Gd chelate solution with either an excess of free ligand or Ca chelate (to decrease Gd3+ release) in the case of linear Gd chelate may have deleterious biologic consequences.

Complexation of copper(I) by thioamino acids. Implications for copper speciation in blood plasma

There is mounting evidence that Cu(I) is the most important oxidation state of copper in many physiological systems. Research into Cu(I)-thioamino acid complex formation serves not only to improve the chelation therapy for treating copper intoxication but may also provide a better understanding of many facets of normal copper metabolism. Formation constants for the ternary mixed ligand complexes of Cu(I) with cysteine (Cys), glutathione (GSH) and penicillamine (Pen) are reported here for the first time. Potentiometric titrations, using techniques specially developed for the stabilization of aqueous Cu(I), were performed at 25 degrees C in 1.00 M (Na)Cl. It was found that precipitation severely limits the experimentally accessible pH range and, consequently, the computer analysis of the binary metal-ligand systems; however, it is also found that this is less of a problem when two different ligands are present. This latter fact permitted better models of the binary systems to be developed. The formation constants of Cu(I)-thioamino acids determined in this work were used in an improved computer simulation of copper speciation in blood plasma which, for the first time, incorporates redox equilibria.

Probing the chloroquine resistance locus of Plasmodium falciparum with a novel class of multidentate metal(III) coordination complexes

The malaria organism Plasmodium falciparum detoxifies heme released during degradation of host erythrocyte hemoglobin by sequestering it within the parasite digestive vacuole as a polymer called hemozoin. Antimalarial agents such as chloroquine appear to work by interrupting the heme polymerization process, but their efficacy has been impaired by the emergence of drug-resistant organisms. We report here the identification of a new class of antimalarial compounds, hexadentate ethylenediamine-N, N'-bis[propyl(2-hydroxy-(R)-benzylimino)]metal(III) complexes [(R)-ENBPI-M(III)] and a corresponding ((R)-benzylamino)] analog [(R)-ENBPA-M(III)], a group of lipophilic monocationic leads amenable to metallopharmaceutical development. Racemic mixtures of Al(III), Fe(III), or Ga(III) but not In(III) (R)-ENBPI metallo-complexes killed intraerythrocytic malaria parasites in a stage-specific manner, the R = 4,6-dimethoxy-substituted ENBPI Fe(III) complex being most potent (IC50 approximately 1 microM). Inhibiting both chloroquine-sensitive and -resistant parasites, potency of these imino complexes correlated in a free metal-independent manner with their ability to inhibit heme polymerization in vitro. In contrast, the reduced (amino) 3-MeO-ENBPA Ga(III) complex (MR045) was found to be selectively toxic to chloroquine-resistant parasites in a verapamil-insensitive manner. In 21 independent recombinant progeny of a genetic cross, susceptibility to this agent mapped in perfect linkage with the chloroquine resistance phenotype suggesting that a locus for 3-MeO-ENBPA Ga(III) susceptibility was located on the same 36-kilobase segment of chromosome 7 as the chloroquine resistance determinant. These compounds may be useful as novel probes of chloroquine resistance mechanisms and for antimalarial drug development.

Aluminum chelation: chemistry, clinical, and experimental studies and the search for alternatives to desferrioxamine

This review focuses on aluminum (Al) chelation, its chemistry and biology. The toxicology and biology of Al in mammalian organisms are briefly reviewed to introduce the problems associated with excessive Al exposure and accumulation and the challenges facing an effective Al chelator. The basics of Al chelation chemistry are considered to help the reader understand the Al chelation chemical literature. The chemical properties of Al enable prediction of effective functional groups for Al chelation. A compilation of distribution coefficients between octanol and aqueous phases (Do/a) for chelators and their complexes with Al shows the effect of complexation on lipophilicity. A compilation of stability constants for Al.chelator complexes illustrates the role of oxygen in ligands that form stable complexes. The history of clinical Al chelation therapy is reviewed, with emphasis on desferrioxamine (DFO), which has been extensively used since 1980. The beneficial and adverse effects and limitations of DFO use in end-stage renal-diseased patients, in patients with neurodegenerative disorders, including Alzheimer's disease, and in animal models of Al intoxication are presented. The methods to evaluate potential Al chelators in vitro, in vivo, and using computer modeling are discussed. The Al chelation literature is reviewed by the chemical class of chelators, including fluoride, carboxylic acids, amino acids, catechols, polyamino carboxylic acids, phenyl carboxylic acids, the hydroxypyridinones, and hydroxamic acids.

Cytotoxic and cytostatic activity of copper(II) complexes. Importance of the speciation for the correct interpretation of the in vitro biological results

The cytotoxicity of some copper(II) compounds against the mouse cancer cell line B16, murine L929, human KB cells, and fibroblasts was investigated. All the copper(II) systems tested were shown to have pronounced toxicity against transformed cells and a cytostatic effect against untransformed cells, i.e., human fibroblasts. A careful speciation of the actual in vitro conditions reveals that copper(II) is essentially present as mixed complexes formed with the amino acids of the culture medium, [Cu(glutamine)(histidine)] being the main species. It was found that the cytotoxic activity is related to the amount of copper(II) contained in the tested compounds.

Evaluation of the iron chelation potential of hydrazones of pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde using the hepatocyte in culture

A range of new analogues of the promising iron chelator pyridoxal isonicotinoyl hydrazone was prepared and assessed for activity in reducing hepatocyte iron, mechanism of action and potential in iron-chelation therapy. A total of 45 compounds were synthesized by condensation of aromatic aldehydes (pyridoxal, salicylaldehyde and 2-hydroxy-1-naphthylaldehyde) with various acid hydrazides prepared by systematic substitutions on the benzene ring or by the replacement of the ring with an acetyl, pyridyl, furoyl or thiophene moiety. The effects of these compounds on 59Fe uptake and intracellular distribution in hepatocytes in culture and on 59Fe mobilization from prelabeled hepatocytes were assessed. Toxicity, lipophilicity and the ability to chelate plasma transferrin-bound 59Fe were also evaluated. Several compounds were much more active than pyridoxal isonicotinoyl hydrazone and may have clinical potential. These included pyridoxal benzoyl hydrazone, pyridoxal p-methoxybenzoyl hydrazone, pyridoxal m-fluorobenzoyl hydrazone and pyridoxal 2-pyridyl hydrazone. All were more effective at reducing iron uptake than mobilizing hepatocyte iron; they also may act primarily on the transit iron pool rather than on storage iron. Other compounds (e.g., salicylaldehyde p-t-butyl-benzoyl hydrazone) redistributed ferritin-59Fe to different intracellular sites but had little net effect on hepatocyte iron levels.

New developments in therapeutic chelating agents as antidotes for metal poisoning

An examination of the studies on therapeutic chelating agents that have been carried out during the last decade reveals that extensive efforts have been made to develop compounds superior to those previously available for the treatment of acute and chronic intoxication by many metals. These metals include primarily iron, plutonium, cadmium, lead, and arsenic, but also many other elements for which acute and chronic intoxication is less common. These studies have revealed the importance of several additional factors of importance in the design of such compounds and have led to many new compounds of considerable clinical promise. An additional development has been the introduction of previously developed chelating agents for use with certain metals on a broader scale.

The mobilization of intracellular cadmium by butyl and amyl esters of meso-2,3-dimercaptosuccinic acid

The esters of the general structure, [CH(SH)COOR]2, i.e., Di-BDMS, R = CH2CH(CH3)2; Ds-BDMS, R = CH(CH3)CH2CH3; Di-ADMS, R = CH2CH2CH(CH3)2; and D3-ADMS, R = CH(CH2CH3)2 from the reaction of meso-2,3-dimercaptosuccinic acid with isobutyl, sec-butyl, isoamyl, and 3-amyl alcohols, respectively, have been prepared, characterized, and examined as chelating agents for the removal of cadmium from its aged intracellular deposits. All of these compounds depleted cadmium from such deposits and significantly reduced the whole body levels of cadmium. In the case of three (Ds-BDMS, Di-BDMS, and Di-ADMS) of these compounds, the reductions achieved are equal to or greater than that produced by 2,3-dimercapto-1-propanol (BAL) under similar circumstances. None of these compounds caused any redistribution of cadmium to the brain, and two of them (Di-BDMS and Di-ADMS) caused a very much larger reduction in the liver levels of cadmium than BAL. None was as effective as BAL in reducing kidney levels of cadmium. These compounds are not soluble in water and are administered as solutions in peanut oil. A comparison of the behavior of these compounds with others which have been reported to be effective in reducing body burdens of cadmium in chronic cadmium intoxication reveals that they are among the most effective. An analysis of the manner in which mobilizing efficacy changes with structure indicates that higher, purely alkyl analogs are not expected to be superior to these compounds, though other structural variations may be.

Effects of macromolecular chelators on intestinal cadmium absorption in mice

Suppression of absorption by macromolecular chelators have been successful with several metals. In this paper a series of immobilized chelators ranging from DTPA to S-containing soft bases have been synthetized and investigated for ability to suppress intestinal uptake of 109Cd2+ in mice. Dextran-0-ethyl-mercaptan, xanthates derived from polysaccharides and polyvinyl alcohol, dithiocarbamates of polyethylene imine and aminoethyl cellulose, and DTPA immobilized on aminopropyl silica were all ineffective. DTPA immobilized on aminoethyl cellulose even enhanced the intestinal uptake. The macromolecular chelators were without extensive effect on organ distribution of absorbed cadmium, except for dithiocarbamate immobilized on polyethylene imine, which enhanced the deposition of cadmium in several organs including the brain. Although the results are discouraging, they indicate that design and synthesis of immobilized vicinal dithio compounds may represent an avenue for development of non-absorbable chelators with high affinity for cadmium.

Iron chelators of the pyridoxal isonicotinoyl hydrazone class. III. Formation constants with calcium(II), magnesium(II) and zinc(II)

Formation constants for the calcium(II), magnesium(II) and zinc(II) complexes of the orally effective iron chelator, pyridoxal isonicotinoyl hydrazone (PIH) and three analogues, pyridoxal benzoyl hydrazone (PBH), pyridoxal p-methoxybenzoyl hydrazone (PpMBH) and pyridoxal m-fluorobenzoyl hydrazone (PmFBH) have been determined by potentiometry at 25 degrees C and I = 0.1 M [KNO3]. The four ligands bind calcium(II) weakly and magnesium(II) only slightly more strongly, as a 1:1 complex which is formed at pH greater than 8. The chelation of zinc(II) for all the ligands studied was greater than that for calcium(II) and magnesium(II), with complexation generally becoming significant at about pH 5. Thus, chelation of zinc(II) but not calcium(II) or magnesium(II) at physiological pH, 7.4 may be expected. Calculated values of the concentration of uncomplexed metal ion indicate that the selectivity of these ligands towards Fe(III) is comparable to that of the clinically used chelator desferrioxamine.

Metal ion-tetracycline interactions in biological fluids. Part 5. Formation of zinc complexes with tetracycline and some of its derivatives and assessment of their biological significance

A series of studies was previously devoted to the dependence of the bioavailability of various tetracyclines on their coordination with calcium and magnesium ions. Several clinical investigations have also shown zinc to interfere with the gastrointestinal absorption of the drug in humans. On the other hand, the administration of tetracycline to rats was reported to result in the increase of the elimination rate of zinc, which could originate in zinc-tetracycline interactions in blood plasma. Formation constants for zinc complexes with tetracycline, oxytetracycline, doxycycline, minocycline, chlortetracycline and demethylchlortetracycline were thus determined at 37 degrees C in NaCl 0.15 mol. dm-3 aqueous medium. Computer simulations were then carried out to investigate the drug influence on the distribution of the low-molecular-weight fraction of zinc in human blood plasma. Zinc-tetracycline interactions in the gastrointestinal fluid were also simulated, using clinical data relative to fasting subjects as taken from the literature. No significant effect can be expected from tetracyclines on the distribution of zinc in plasma at the usual therapeutic levels. However, zinc-tetracycline interactions have been found to be determining factors for the bioavailabilities of the metal as well as of the antibiotic in the gastrointestinal fluid.

Copper and inflammation--a possible rationale for the pharmacological manipulation of inflammatory disorders

Acute and chronic inflammations are characterized, among other features, by changes in the metabolism of copper and by a widespread responsiveness to the therapy with copper-containing molecules. The exact map of inflammation-induced copper movements as well as the role played by the metal in the pathogenesis of inflammatory disorders are, however, far from being clear, and this is especially true in the case of chronic processes. Nevertheless the present knowledge suggests that the "copper approach' may provide a new way for coping with the problem of anti-inflammatory/anti-arthritic therapies. The administration of exogenous copper, and the in vivo manipulation of the endogenous metal levels are proposed as two possible therapeutic strategies, not necessarily mutually exclusive. For a better understanding of the value of such an approach, further research work is needed, especially to attain a more detailed know-how on the involved chemical forms, distribution and functions of copper in both normal as well as inflamed organisms.