Cellular zinc content is a major determinant of iron chelator-induced apoptosis of thymocytes

Efficacy of the iron-chelating agent, deferiprone, in patients with Parkinson's disease: A systematic review and meta-analysis

INTRODUCTION

Several studies have reported iron accumulation in the basal ganglia to be associated with the development of Parkinson's Disease (PD). Recently, a few trials have examined the efficacy of using the iron-chelating agent Deferiprone (DFP) for patients with PD. We conducted this meta-analysis to summarize and synthesize evidence from published randomized controlled trials about the efficacy of DFP for PD patients.

METHODS

A comprehensive literature search of four electronic databases was performed, spanning until February 2023. Relevant RCTs were selected, and their data were extracted and analyzed using the RevMan software. The primary outcome was the change in the Unified Parkinson's Disease Rating Scale (UPDRS-III).

RESULTS

Three RCTs with 431 patients were included in this analysis. DFP did not significantly improve UPDRS-III score compared to placebo (Standardized mean difference -0.06, 95% CI [-0.69, 0.58], low certainty evidence). However, it significantly reduced iron accumulation in the substantia nigra, putamen, and caudate as measured by T2*-weighted MRI (with high certainty evidence).

CONCLUSION

Current evidence does not support the use of DFP in PD patients. Future disease-modification trials with better population selection, adjustment for concomitant medications, and long-term follow up are recommended.

Design and Synthesis of Poly(2,2'-Bipyridyl) Ligands for Induction of Cell Death in Cancer Cells: Control of Anticancer Activity by Complexation/Decomplexation with Biorelevant Metal Cations

Chelation therapy is a medical procedure for removing toxic metals from human organs and tissues and for the treatment of diseases by using metal-chelating agents. For example, iron chelation therapy is designed not only for the treatment of metal poisoning but also for some diseases that are induced by iron overload, cancer chemotherapy, and related diseases. However, the use of such metal chelators needs to be generally carried out very carefully, because of the side effects possibly due to the non-specific complexation with intracellular metal cations. Herein, we report on the preparation and characterization of some new poly(bpy) ligands (bpy: 2,2'-bipyridyl) that contain one-three bpy ligand moieties and their anticancer activity against Jurkat, MOLT-4, U937, HeLa S3, and A549 cell lines. The results of MTT assays revealed that the tris(bpy) and bis(bpy) ligands exhibit potent activity for inducing the cell death in cancer cells. Mechanistic studies suggest that the main pathway responsible for the cell death by these poly(bpy) ligands is apoptotic cell death. It was also found that the anticancer activity of the poly(bpy) ligands could be controlled by the complexation (anticancer activity is turned OFF) and decomplexation (anticancer activity is turned ON) with biorelevant metal cations. In this paper, these results will be described.

Hydroxypyrone derivatives in drug discovery: from chelation therapy to rational design of metalloenzyme inhibitors

The versatile structural motif of hydroxypyrone is found in natural products and can be easily converted into hydroxypyridone and hydroxythiopyridone analogues. The favourable toxicity profile and ease of functionalization to access a vast library of compounds make them an ideal structural scaffold for drug design and discovery. This versatile scaffold possesses excellent metal chelating properties that can be exploited for chelation therapy in clinics. Deferiprone [1,2-dimethyl-3-hydroxy-4(1H)-one] was the first orally active chelator to treat iron overload in thalassemia major. Metal complexes of hydroxy-(thio)pyr(id)ones have been investigated as magnetic resonance imaging contrast agents, and anticancer and antidiabetic agents. In recent years, this compound class has demonstrated potential in discovering and developing metalloenzyme inhibitors. This review article summarizes recent literature on hydroxy-(thio)pyr(id)ones as inhibitors for metalloenzymes such as histone deacetylases, tyrosinase and metallo-β-lactamase. Different approaches to the design of hydroxy-(thio)pyr(id)ones and their biological properties against selected metalloenzymes are discussed.

High Antiproliferative Activity of Hydroxythiopyridones over Hydroxypyridones and Their Organoruthenium Complexes

Hydroxypyr(id)ones are a pharmaceutically important class of compounds that have shown potential in diverse areas of drug discovery. We investigated the 3-hydroxy-4-pyridones 1a-1c and 3-hydroxy-4-thiopyridones 1d-1f as well as their Ru(η⁶-p-cymene)Cl complexes 2a-2f, and report here the molecular structures of 1b and 1d as determined by X-ray diffraction analysis. Detailed cell biological investigations revealed potent cytotoxic activity, in particular of the 3-hydroxy-4-thiopyridones 1d-1f, while the Ru complexes of both compound types were less potent, despite still showing antiproliferative activity in the low μM range. The compounds did not modulate the cell cycle distribution of cancer cells but were cytostatic in A549 and cytotoxic in NCI-H522 non-small lung cancer cells, among other effects on cancer cells.

Morphological Profiling Identifies a Common Mode of Action for Small Molecules with Different Targets

Unbiased morphological profiling of bioactivity, for example, in the cell painting assay (CPA), enables the identification of a small molecule's mode of action based on its similarity to the bioactivity of reference compounds, irrespective of the biological target or chemical similarity. This is particularly important for small molecules with nonprotein targets as these are rather difficult to identify with widely employed target-identification methods. We employed morphological profiling using the CPA to identify compounds that are biosimilar to the iron chelator deferoxamine. Structurally different compounds with different annotated cellular targets provoked a shared physiological response, thereby defining a cluster based on their morphological fingerprints. This cluster is based on a shared mode of action and not on a shared target, that is, cell-cycle modulation in the S or G2 phase. Hierarchical clustering of morphological fingerprints revealed subclusters that are based on the mechanism of action and could be used to predict target-related bioactivity.

The Pathopharmacological Interplay between Vanadium and Iron in Parkinson's Disease Models

Parkinson's disease (PD) pathology is characterised by distinct types of cellular defects, notably associated with oxidative damage and mitochondria dysfunction, leading to the selective loss of dopaminergic neurons in the brain's substantia nigra pars compacta (SNpc). Exposure to some environmental toxicants and heavy metals has been associated with PD pathogenesis. Raised iron levels have also been consistently observed in the nigrostriatal pathway of PD cases. This study explored, for the first time, the effects of an exogenous environmental heavy metal (vanadium) and its interaction with iron, focusing on the subtoxic effects of these metals on PD-like oxidative stress phenotypes in Catecholaminergic a-differentiated (CAD) cells and PTEN-induced kinase 1 (PINK-1)B9Drosophila melanogaster models of PD. We found that undifferentiated CAD cells were more susceptible to vanadium exposure than differentiated cells, and this susceptibility was modulated by iron. In PINK-1 flies, the exposure to chronic low doses of vanadium exacerbated the existing motor deficits, reduced survival, and increased the production of reactive oxygen species (ROS). Both Aloysia citrodora Paláu, a natural iron chelator, and Deferoxamine Mesylate (DFO), a synthetic iron chelator, significantly protected against the PD-like phenotypes in both models. These results favour the case for iron-chelation therapy as a viable option for the symptomatic treatment of PD.

Deferiprone: Pan-selective Histone Lysine Demethylase Inhibition Activity and Structure Activity Relationship Study

Deferiprone (DFP) is a hydroxypyridinone-derived iron chelator currently in clinical use for iron chelation therapy. DFP has also been known to elicit antiproliferative activities, yet the mechanism of this effect has remained elusive. We herein report that DFP chelates the Fe2+ ion at the active sites of selected iron-dependent histone lysine demethylases (KDMs), resulting in pan inhibition of a subfamily of KDMs. Specifically, DFP inhibits the demethylase activities of six KDMs - 2A, 2B, 5C, 6A, 7A and 7B - with low micromolar IC50s while considerably less active or inactive against eleven KDMs - 1A, 3A, 3B, 4A-E, 5A, 5B and 6B. The KDM that is most sensitive to DFP, KDM6A, has an IC50 that is between 7- and 70-fold lower than the iron binding equivalence concentrations at which DFP inhibits ribonucleotide reductase (RNR) activities and/or reduces the labile intracellular zinc ion pool. In breast cancer cell lines, DFP potently inhibits the demethylation of H3K4me3 and H3K27me3, two chromatin posttranslational marks that are subject to removal by several KDM subfamilies which are inhibited by DFP in cell-free assay. These data strongly suggest that DFP derives its anti-proliferative activity largely from the inhibition of a sub-set of KDMs. The docked poses adopted by DFP at the KDM active sites enabled identification of new DFP-based KDM inhibitors which are more cytotoxic to cancer cell lines. We also found that a cohort of these agents inhibited HP1-mediated gene silencing and one lead compound potently inhibited breast tumor growth in murine xenograft models. Overall, this study identified a new chemical scaffold capable of inhibiting KDM enzymes, globally changing histone modification profiles, and with specific anti-tumor activities.

Zinc Status in Beta Thalassemia Major Patients

Beta thalassemia is a common monogenic hereditary hemoglobinopathy which is associated with compound complications. Zinc deficiency, which is commonly observed in thalassemia patients, is also associated with multiple health complications. The objective of this study was to determine the zinc status and its effect on the growth and immune functions of young beta thalassemia major patients. The study included 40 patients in comparison with age- and sex-matched 30 healthy individuals as controls. The patients were interviewed for socio-demographic variables, and their medical histories were obtained from the hospital files. Serum concentrations of zinc and ferritin, height, and body mass indices (BMI) were calculated. Mean serum zinc level in beta thalassemia major patients was 44.7 ± 24.2 μg/dl whereas in the control group it was 63.3 ± 30.3μg/dl. The mean serum zinc level is significantly low in beta thalassemia major patients with respect to the control group. The gender, age, duration of blood transfusion, blood transfusion volume, mean pretransfusion hemoglobin concentration, deferasirox dose, and serum ferritin level bear no relationship with serum zinc level of the beta thalassemia major patients. Zinc level showed no significant correlation with z-scores of stature, sitting height index, BMI, and frequency of recent infections of patients. Although zinc deficiency is common in beta thalassemia major patients, it was found to have no significant effect on physical growth and frequency of infections. Further studies are recommended to investigate zinc status of beta thalassemia major patients.

Eltrombopag: a powerful chelator of cellular or extracellular iron(III) alone or combined with a second chelator

Eltrombopag (ELT) is a thrombopoietin receptor agonist reported to decrease labile iron in leukemia cells. Here we examine the previously undescribed iron(III)-coordinating and cellular iron-mobilizing properties of ELT. We find a high binding constant for iron(III) (log β₂=35). Clinically achievable concentrations (1 µM) progressively mobilized cellular iron from hepatocyte, cardiomyocyte, and pancreatic cell lines, rapidly decreasing intracellular reactive oxygen species (ROS) and also restoring insulin secretion in pancreatic cells. Decrements in cellular ferritin paralleled total cellular iron removal, particularly in hepatocytes. Iron mobilization from cardiomyocytes exceeded that obtained with deferiprone, desferrioxamine, or deferasirox at similar iron-binding equivalents. When combined with these chelators, ELT enhanced cellular iron mobilization more than additive (synergistic) with deferasirox. Iron-binding speciation plots are consistent with ELT donating iron to deferasirox at clinically relevant concentrations. ELT scavenges iron citrate species faster than deferasirox, but rapidly donates the chelated iron to deferasirox, consistent with a shuttling mechanism. Shuttling is also suggested by enhanced cellular iron mobilization by ELT when combined with the otherwise ineffective extracellular hydroxypyridinone chelator, CP40. We conclude that ELT is a powerful iron chelator that decreases cellular iron and further enhances iron mobilization when combined with clinically available chelators.

Chemical features of in use and in progress chelators for iron overload

An excessive amount of iron may become extremely toxic both for its ability to generate reactive oxygen species, and for the lack of regulatory mechanisms for iron excretion in humans. Chelation therapy has been introduced in clinical practice in the 1970's to defend thalassemia patients from the effects of iron overload and it has dramatically changed both life expectancy and quality of life. The disadvantages of the drugs in clinical use make the research for new, more suitable iron chelating agents, urgent. This review defines the requirements of an iron chelator, then points out the principal chemical features of the iron chelators in use. Finally, a survey on the last ten years of the literature relative to iron chelators is done, and the most interesting ligands are presented, with particular emphasis to those that reached clinical trials.

3-Hydroxypyridinone derivatives as metal-sequestering agents for therapeutic use

Although iron is one of the most important metal ions for living organisms, it becomes toxic when in excess or misplaced. This review presents a glance at representative examples of hydroxypyridinone-based chelators, which have been recently developed as potential clinically useful drugs for metal overload diseases, mostly associated with excess of iron but also other hard metal-ions. It also includes a detailed discussion on the factors assisting chelator design strategy toward fulfillment of the most relevant biochemical properties of hydroxypyridinone chelators, highlighting structure-activity relationships and a variety of potential clinical applications, beyond chelatotherapy. This study appears as a response to the growing interest on metal chelation therapy and opens new perspectives of possible applications in future medicine.

Zinc(II) and copper(II) complexes with hydroxypyrone iron chelators

High stability of the complexes formed at physiological pH is one of the basic requisites that a good iron chelator must possess. At the same time the chelating agent must be selective toward iron, i.e., the stability of iron complexes must be significantly higher than that of the complexes formed with essential metal ions, in order that these last ones do not perturb iron chelation. In the frame of our research on iron chelators we have designed and synthesized a series of tetradentate derivatives of kojic acid, and examined their binding properties toward Fe(3+) and Al(3+). In this paper, for a characterization of the behavior of the proposed iron chelating agents in biological fluids, their complex formation equilibria with copper(II) and zinc(II) ions have been fully characterized together with a speciation study, showing the degree at which the iron chelators interfere with the homeostatic equilibria of these two essential metal ions.

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 β-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.

Characterization of Zinc Influx Transporters (ZIPs) in Pancreatic β Cells: ROLES IN REGULATING CYTOSOLIC ZINC HOMEOSTASIS AND INSULIN SECRETION

Zinc plays an essential role in the regulation of pancreatic β cell function, affecting important processes including insulin biosynthesis, glucose-stimulated insulin secretion, and cell viability. Mutations in the zinc efflux transport protein ZnT8 have been linked with both type 1 and type 2 diabetes, further supporting an important role for zinc in glucose homeostasis. However, very little is known about how cytosolic zinc is controlled by zinc influx transporters (ZIPs). In this study, we examined the β cell and islet ZIP transcriptome and show consistent high expression of ZIP6 (Slc39a6) and ZIP7 (Slc39a7) genes across human and mouse islets and MIN6 β cells. Modulation of ZIP6 and ZIP7 expression significantly altered cytosolic zinc influx in pancreatic β cells, indicating an important role for ZIP6 and ZIP7 in regulating cellular zinc homeostasis. Functionally, this dysregulated cytosolic zinc homeostasis led to impaired insulin secretion. In parallel studies, we identified both ZIP6 and ZIP7 as potential interacting proteins with GLP-1R by a membrane yeast two-hybrid assay. Knock-down of ZIP6 but not ZIP7 in MIN6 β cells impaired the protective effects of GLP-1 on fatty acid-induced cell apoptosis, possibly via reduced activation of the p-ERK pathway. Therefore, our data suggest that ZIP6 and ZIP7 function as two important zinc influx transporters to regulate cytosolic zinc concentrations and insulin secretion in β cells. In particular, ZIP6 is also capable of directly interacting with GLP-1R to facilitate the protective effect of GLP-1 on β cell survival.

Polymeric nanocarriers for the treatment of systemic iron overload

Desferrioxamine (DFO), deferiprone (L1) and desferasirox (ICL-670) are clinically approved iron chelators used to treat secondary iron overload. Although iron chelators have been utilized since the 1960s and there has been much improvement in available therapy, there is still the need for new drug candidates due to limited long-term efficacy and drug toxicity. Moreover, all currently approved iron chelators are of low molecular weight (MW) (<600 Da) and the objectives reported for the “ideal” chelator of low MW, including possessing the ability to promote iron excretion without causing toxic side effects, has proven difficult to realize in practice. With prolonged iron chelator use, patients may develop toxicities or become insensitive. In contrast, the limited research that has been geared towards developing higher MW, polymeric, long circulating iron chelators has shown promise. The inherent potential of polymeric iron chelators toward longer plasma half-lives and reduction in toxicity provides optimism and may be a significant addition to the currently available low MW iron chelators. This article reviews knowledge pertaining to this theme, highlights some unique advantages that these nanomedicines have in treating systemic iron overload as well as their potential utility in the treatment of other disease states.

Polymeric nanocarriers for the treatment of systemic iron overload

Desferrioxamine (DFO), deferiprone (L1) and desferasirox (ICL-670) are clinically approved iron chelators used to treat secondary iron overload. Although iron chelators have been utilized since the 1960s and there has been much improvement in available therapy, there is still the need for new drug candidates due to limited long-term efficacy and drug toxicity. Moreover, all currently approved iron chelators are of low molecular weight (MW) (<600 Da) and the objectives reported for the "ideal" chelator of low MW, including possessing the ability to promote iron excretion without causing toxic side effects, has proven difficult to realize in practice. With prolonged iron chelator use, patients may develop toxicities or become insensitive. In contrast, the limited research that has been geared towards developing higher MW, polymeric, long circulating iron chelators has shown promise. The inherent potential of polymeric iron chelators toward longer plasma half-lives and reduction in toxicity provides optimism and may be a significant addition to the currently available low MW iron chelators. This article reviews knowledge pertaining to this theme, highlights some unique advantages that these nanomedicines have in treating systemic iron overload as well as their potential utility in the treatment of other disease states.

The relative contribution of calcium, zinc and oxidation-based cross-links to the stiffness of Arion subfuscus glue

Metal ions are present in many different biological materials, and are capable of forming strong cross-links in aqueous environments. The relative contribution of different metal-based cross-links was measured in the defensive glue produced by the terrestrial slug Arion subfuscus. This glue contains calcium, magnesium, zinc, manganese, iron and copper. These metals are essential to the integrity of the glue and to gel stiffening. Removal of all metals caused at least a 15-fold decrease in the storage modulus of the glue. Selectively disrupting cross-links involving hard Lewis acids such as calcium reduced the stiffness of the glue, while disrupting cross-links involving borderline Lewis acids such as zinc did not. Calcium is the most common cation bound to the glue (40 mmol l(-1)), and its charge is balanced primarily by sulphate at 82-84 mmol l(-1). Thus these ions probably play a primary role in bringing polymers together directly. Imine bonds formed as a result of protein oxidation also contribute substantially to the stiffness of the glue. Disrupting these bonds with hydroxylamine caused a 33% decrease in storage modulus of the glue, while stabilizing them by reduction with sodium borohydride increased the storage modulus by 40%. Thus a combination of metal-based bonds operates in this glue. Most likely, cross-links directly involving calcium play a primary role in bringing together and stabilizing the polymer network, followed by imine bond formation and possible iron coordination.

Yttrium decreases the intracellular Zn2+ concentration in rat thymocytes by attenuating a temperature-sensitive Zn2+ influx

Yttrium is used in the production of various electronic devices because the alloy it contains enhances or modifies the properties of other elements. In order to study the cytotoxic action of yttrium, the effect of yttrium chloride (YCl(3)) on the intracellular Zn(2+) level was examined in rat thymocytes using a flow cytometer with FluoZin-3-AM and propidium iodide. The application of YCl(3) significantly decreased the intensity of the FluoZin-3 fluorescence, suggesting a decrease in the intracellular Zn(2+) level or quenching of the FluoZin-3 fluorescence by Y(3+). However, since Y(3+) did not attenuate the FluoZin-3 fluorescence under cell-free conditions, the latter suggestion was ruled out. Rat thymocytes possess a temperature-sensitive membrane pathway that carries Zn(2+) into the cells. The application of YCl(3) attenuated the FluoZin-3 fluorescence augmented by externally applied ZnCl(2) in a concentration-dependent manner. This suggested that Y(3+) inhibited the Zn(2+) influx, resulting in the decrease in the intracellular Zn(2+) level. Yttrium may induce dyshomeostasis of intracellular Zn(2+), leading to some cytotoxic actions.

Nanomolar concentrations of zinc pyrithione increase cell susceptibility to oxidative stress induced by hydrogen peroxide in rat thymocytes

Zinc pyrithione is used as an antifouling agent. However, the environmental impacts of zinc pyrithione have recently been of concern. Zinc induces diverse actions during oxidative stress; therefore, we examined the effect of zinc pyrithione on rat thymocytes suffering from oxidative stress using appropriate fluorescent probes. The cytotoxicity of zinc pyrithione was not observed when the cells were incubated with 3 μM zinc pyrithione for 3 h. However, zinc pyrithione at nanomolar concentrations (10 nM or more) significantly increased the lethality of cells suffering from oxidative stress induced by 3 mM H(2)O(2). The application of zinc pyrithione alone at nanomolar concentrations increased intracellular Zn(2+) level and the cellular content of superoxide anions, and decreased the cellular content of nonprotein thiols. The simultaneous application of nanomolar zinc pyrithione and micromolar H(2)O(2) synergistically increased the intracellular Zn(2+) level. Therefore, zinc pyrithione at nanomolar concentrations may exert severe cytotoxic action on cells simultaneously exposed to chemicals that induce oxidative stress. If so, zinc pyrithione leaked from antifouling materials into surrounding environments would be a risk factor for aquatic ecosystems. Alternatively, zinc pyrithione under conditions of oxidative stress may become more potent antifouling ingredient.

Coordinate expression and localization of iron and zinc transporters explain iron-zinc interactions during uptake in Caco-2 cells: implications for iron uptake at the enterocyte

Iron and zinc have diverse and important physiological functions. Yet, the mechanism of their absorption at the intestine remains controversial and is confounded by the fact that many studies have shown, to varying extents, that they inhibit the absorption of each other. We have studied the expression of iron and zinc transporters and storage proteins, and their regulation, in Caco-2 cells, an established enterocyte model, under normal culture conditions and under conditions of iron and zinc depletion and supplementation using a combination of immunoblotting, confocal microscopy and reverse transcriptase polymerase chain reaction. We show that divalent metal transporter-1 (DMT-1) delocalizes from the plasma membrane upon iron or zinc depletion, but its apical abundance increases with zinc supplementation. This translocation of DMT-1 coincides with an increase in iron uptake upon zinc supplementation, as previously reported by us. FPN-1 expression increases upon zinc supplementation and decreases with iron or zinc depletion, effluxing the excess sequestered iron and thus maintaining cellular iron homeostasis. Zinc influx transporters Zip-1 and Zip-14 and efflux transporters ZnT-1 and ZnT-4 are coordinately regulated under conditions of zinc supplementation and depletion to ensure cellular zinc homeostasis. We have previously reported that iron uptake can entail two transporters and that zinc noncompetitively inhibits iron uptake in Caco-2 cells. We now provide evidence that this inhibition is independent of DMT-1 and that Zip-14 may be a relevant iron transporter. These new observations provide experimental support to this two-transporter model of iron uptake and give mechanistic insight to iron-zinc interactions during uptake at the enterocyte.

Deficiency of calcium and magnesium induces apoptosis via scavenger receptor BI

AIMS

Cells undergo apoptosis in stressed status such as in intracellular calcium overload or extracellular calcium/magnesium deficiency. The mechanisms of how deficiency of the divalent metal ions induces apoptosis remain to be defined. Scavenger receptor BI (SR-BI) is a high density lipoprotein (HDL) receptor. Recent studies demonstrated that SR-BI is a stress response molecule which induces apoptosis upon serum deprivation. In this study, we assessed our hypothesis that the deficiency of calcium/magnesium induces apoptosis via SR-BI apoptotic pathway.

MAIN METHODS

We employed CHO cell lines expressing vector and SR-BI to test the effect of SR-BI on apoptosis induced by deficiency of calcium, magnesium and zinc in culture medium. The regain of different metal ions in deficient medium was also performed, respectively. Cell death was detected by morphological changes and quantified by LDH cytotoxicity assay. Apoptosis was also assessed by DNA ladder assay and DNA condensation assay. The SR-BIC323G mutant cells which lack the apoptotic activity of SR-BI were employed to verify the SR-BI-dependent effect on calcium/magnesium induced apoptosis.

KEY FINDINGS

The deficiency of calcium/magnesium induced cell apoptosis in CHO-SR-BI cells, but not in CHO-vector cells. Moreover, no apoptotic cell death was observed in SR-BIC323G mutant cells, indicating that the deficiency of divalent metal ions induces apoptosis in a SR-BI-dependent manner. Furthermore, the restoration of calcium or magnesium, but not zinc, protected CHO-SR-BI cells from apoptotic cell death, in a dose-dependent fashion.

SIGNIFICANCE

These findings extend our understanding about how calcium and magnesium deficiency induces apoptosis.

Toxicity of Non-protein Amino Acids to Humans and Domestic Animals

Non-protein amino acids are common in plants and are present in widely consumed animal feeds and human foods such as alfalfa ( Medicago sativa), which contains canavanine, and lentil ( Lens culinaris), which contains homoarginine. Some occur in wild species that are inadvertently harvested with crop species. Some nonprotein amino acids and metabolites can be toxic to humans, e.g. Lathyrus species contain a neurotoxic oxalyl-amino acid. Some potential toxins may be passed along a food chain via animal intermediates. The increased interest in herbal medicines in the Western countries will increase exposure to such compounds.

Desferrioxamine (DFX) induces apoptosis through the p38-caspase8-Bid-Bax pathway in PHA-stimulated human lymphocytes

Desferrioxamine (DFX) induces apoptosis in human lymphocytes, although the mechanism leading to cell death is unclear. Therefore, we investigated the signaling pathways implicated in DFX-induced apoptosis in lymphocytes. DFX treatment activated caspase-9, caspase-3, and caspase-8. DFX-induced apoptosis was inhibited by both z-IETD-fmk and z-DEVD-fmk. DFX treatment also enhanced caspase-8 activity, Bid cleavage, and the conformational activation of Bax. DFX treatment activated two MAPKs, p38 and JNK, and induced the phosphorylation of two proteins in the p38 pathway, MKK3 and MKK6. DFX treatment also increased the phosphorylation of two downstream targets of p38, ATF-2 and MAPKAPK2, indicating that DFX promotes p38 activity. In addition, the selective p38 inhibitor SB203580 suppressed DFX-induced apoptosis and caspase-8 activation, whereas the JNK inhibitor, SP600125, and the ERK inhibitor, PD98059, had no effect. Our results suggest that DFX-induced apoptosis is mediated by the p38 pathway and a caspase-8-dependent Bid-Bax pathway in human lymphocytes.

Effect of an oral iron chelator or iron-deficient diets on uroporphyria in a murine model of porphyria cutanea tarda

Porphyria cutanea tarda is a liver disease characterized by elevated hepatic iron and excessive production of uroporphyrin (URO). Phlebotomy is an effective treatment that probably acts by reducing hepatic iron. Here we used Hfe(-/-) mice to compare the effects on hepatic URO accumulation of two different methods of hepatic iron depletion: iron chelation using deferiprone (L1) versus iron-deficient diets. Hfe(-/-) mice in a 129S6/SvEvTac background were fed 5-aminolevulinic acid (ALA), which results in hepatic URO accumulation, and increasing doses of L1 in the drinking water. Hepatic URO accumulation was completely prevented at low L1 doses, which partially depleted hepatic nonheme iron. By histological assessment, the decrease in hepatic URO accumulation was associated with greater depletion of iron from hepatocytes than from Kupffer cells. The L1 treatment had no effect on levels of hepatic cytochrome P4501A2 (CYP1A2). L1 also effectively decreased hepatic URO accumulation in C57BL/6 Hfe(-/-) mice treated with ALA and a CYP1A2 inducer. ALA-treated mice maintained on defined iron-deficient diets, rather than chow diets, did not develop uroporphyria, even when the animals were iron-supplemented either directly in the diet or by iron dextran injection.

CONCLUSION

The results suggest that dietary factors other than iron are involved in the development of uroporphyria and that a modest depletion of hepatocyte iron by L1 is sufficient to prevent URO accumulation.

The role of metals in molluscan adhesive gels

Several gastropod molluscs produce glues that are interesting because they are dilute gels and yet they produce strong adhesion. Specific glue proteins have been identified that play a central role in this adhesion, possibly by crosslinking other polymers in the gel. This study investigates the role of metals in the action of these glue proteins. Atomic absorption spectrometry showed that glue from the slug Arion subfuscus contains substantial quantities of zinc (46±7 p.p.m. and 189±80 p.p.m. in two different sets of experiments) and also iron, copper and manganese (2–7 p.p.m.). Iron-specific staining demonstrates that iron is bound specifically to the 15 kDa glue protein. Several approaches were used to show that these metals have important functional effects. Adding iron or copper to dissolved glue causes the proteins to precipitate rapidly, although zinc has no effect. Removing iron and related transition metals with a chelator during secretion of the glue causes a sixfold increase in the solubility of the glue. Once the glue has set, however, removing these metals has no effect. Finally, the gel-stiffening activity of the glue proteins was measured in the presence and absence of the chelator. The chelator eliminated the gel-stiffening effect of the proteins, suggesting that transition metals were necessary for the proteins to act on the gel. Thus, the glue contains transition metals and these metals play an essential role in glue function.

Desferrioxamine (DFX) has genotoxic effects on cultured human lymphocytes and induces the p53-mediated damage response

Desferrioxamine (DFX), which is an iron chelator, mimics hypoxia by enhancing HIF1-alpha accumulation and upregulating inflammatory mediators. DFX is usually beneficial, with preventive effects related primarily to its ability to scavenge reactive oxygen species. However, toxic effects on skeletal and ocular organs have been reported. The cytokinesis block micronucleus test and alkaline single-cell gel (Comet) assay were used to evaluate the genotoxic effects of DFX on human blood lymphocytes. Cultured human lymphocytes treated with 130microM DFX for various periods of time showed significant differences in the incidence of micronucleated binucleate cells, as well as in the length and moment of the comet tail. Western blot analysis using antibodies to proteins involved in the p53-mediated response to DNA damage revealed that p53 was accumulated and DNA damage checkpoint kinases were activated in lymphocytes treated with DFX. On the other hand, the p53 downstream target proteins p21 and bax were not affected, which indicates that DFX does not promote the transactivational activity of p53. Apoptosis assays demonstrated DFX-induced apoptosis of lymphocytes via the caspase cascade. The observed increase in the sub-G1 fraction and enhanced caspase-3 activity indicate that DFX can promote apoptosis in human lymphocytes, and these results were confirmed by protein immunoblot analysis. As apoptotic cell death is preceded by the collapse of the mitochondrial membrane potential, we also measured the mitochondrial membrane potential (Deltapsi(m)) using DiOC6, which is a fluorescent membrane potential probe. The fluorescence intensity of DiOC6 in lymphocytes was significantly reduced in a time-dependent manner after DFX treatment. Taken together, these results indicate that DFX activates p53-mediated checkpoint signals and induces apoptosis via mitochondrial damage in human peripheral blood lymphocytes.

Plasticity of neuroendocrine-thymus interactions during ontogeny and ageing: role of zinc and arginine

Thymic re-growth and reactivation of thymic functions may be achieved in old animals by different endocrinological or nutritional manipulations such as, (a) treatment with melatonin, (b) implantation of a growth hormone (GH) secreting tumour cell line (GH3 cells) or treatment with exogenous GH, (c) castration or treatment with exogenous luteinizing hormone-releasing hormone (LHRH), (d) treatment with exogenous thyroxin or triiodothyronine, and (e) nutritional interventions such as arginine or zinc supplementation. These data strongly suggest that thymic involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of these interactions in old age that is responsible for age-associated immune-neuroendocrine dysfunctions. The targets involved in hormones-induced thymic reconstitution may directly or indirectly involve hormone receptors, cytokines, arginine, and a trace element such as zinc, which is pivotal for the efficiency of neuroendocrine-immune network during the whole life of an organism. The effect of GH, thyroid hormones, and LHRH may be due to specific hormone receptors on thymocytes and on thymic epithelial cells (TECs), which synthesize thymic peptides. Melatonin may also act through specific receptors on T-cells. In this context, the role of zinc, which turnover is reduced in old age, is pivotal because of its involvement through zinc fingers in the gene expression of hormone receptors. In addition, the effects of zinc are multifaceted: from the reactivation of zinc-dependent enzymes, to cell proliferation and apoptosis, to cytokines expression and to the reactivation of thymulin, which is a zinc-dependent thymic hormone required for intrathymic T-cell differentiation and maturation as well as for the homing of stem cells into the thymus. Zinc is also required for arginine action, via NO pathway. The role of zinc is therefore crucial in neuroendocrine-thymus interactions. According to data in animals and humans, the above reported endocrinological manipulations (GH, thyroid hormones, and melatonin) or arginine treatment may also act via zinc pool in restoring thymic activity in ageing allowing improvements on peripheral immune efficiency.

Mimosine attenuates serine hydroxymethyltransferase transcription by chelating zinc. Implications for inhibition of DNA replication

L-mimosine is a naturally occurring plant amino acid and iron chelator that arrests the cell cycle in the late G(1) phase, although its mechanism of action is not known. Some studies indicate that mimosine prevents the initiation of DNA replication, whereas other studies indicate that mimosine disrupts elongation of the replication fork by impairing deoxyribonucleotide synthesis by inhibiting the activity of the iron-dependent enzyme ribonucleotide reductase and the transcription of the cytoplasmic serine hydroxymethyltransferase gene (SHMT1). In this study, the mechanism for mimosine-induced inhibition of SHMT1 transcription was elucidated. A mimosine-responsive transcriptional element was localized within the first 50 base pairs of the human SHMT1 promoter by deletion analyses and gel mobility shift assays. The 50-base-pair sequence contains a consensus zinc-sensing metal regulatory element (MRE) at position -44 to -38, and mutation of the MRE attenuated mimosine-induced transcription repression. Mimosine treatment eliminated MRE- and Sp1-binding activity in nuclear extracts from MCF-7 cells but not in nuclear extracts from a mimosine-resistant cell line, MCF-7/2a. MCF-7 cells cultured in zinc-depleted medium for more than 16 days were viable and lacked cytoplasmic serine hydroxymethyltransferase protein, confirming that mimosine inhibits SHMT1 transcription by chelating zinc. The disruption of DNA-protein interactions by zinc chelation provides a general mechanism for the inhibitory effects of mimosine on nuclear processes, including replication and transcription. Furthermore, this study establishes that SHMT1 is a zinc-inducible gene, which provides the first mechanism for the regulation of folate-mediated one-carbon metabolism by zinc.

Role of zinc and iron chelation in apoptosis mediated by tachpyridine, an anti-cancer iron chelator

Tachpyridine (N,N',N"-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane; tachpyr) is a potent hexadentate iron chelator under preclinical investigation as a potential anti-cancer agent. Tachpyridine induces apoptosis in cultured cancer cells by triggering a mitochondrial pathway of cell death that is p53-independent. To explore the relationship between the chelation chemistry of tachpyridine and its biological activity, a sensitive and specific reversed-phase high-performance liquid chromatography (RP-HPLC) method was devised and used to measure tachpyr and its metal complexes in cells and tissue culture media. Major species identified in cells treated with tachpyr were tachpyr itself, [Zn(tachpyr)](2+), and iron coordinated to two partially oxidized species of tachpyridine, [Fe(tachpyr-ox-2)](2+), and [Fe(tachpyr-ox-4)](2+). The kinetics of intracellular accumulation of [Zn(tachpyr)](2+) and [Fe(tachpyr-ox-2)](2+) were markedly different: [Zn(tachpyr)](2+) rapidly reached plateau levels, whereas intracellular levels of [Fe(tachpyr-ox-2)](2+) and free tachpyr rose steadily. At the last timepoint measured, 9% of total cellular iron and 13% of total cellular zinc were bound by tachpyridine. Taken together, [Zn(tachpyr)](2+), [Fe(tachpyr-ox-2)](2+), and free tachpyr accounted for virtually all of the tachpyr added, indicating that iron and zinc are the principal metals targeted by tachpyridine in cells. Consistent with these findings, activation of the apoptotic caspases 9 and 3 was blocked in cells pre-treated with either iron or zinc. Pretreatment with either of these metals also completely protected cells from the cytotoxic effects of tachpyridine. These results demonstrate a link between metal depletion and chelator cytotoxicity, and suggest that intracellular chelation of zinc as well as iron may play a role in the cytotoxicity of tachpyridine.