scholarly journals Polyphosphate Functions In Vivo as an Iron Chelator and Fenton Reaction Inhibitor

mBio ◽  
2020 ◽  
Vol 11 (4) ◽  
Author(s):  
François Beaufay ◽  
Ellen Quarles ◽  
Allison Franz ◽  
Olivia Katamanin ◽  
Wei-Yun Wholey ◽  
...  
Keyword(s):  
Hydroxyl Radicals ◽  
Fenton Reaction ◽  
Iron Homeostasis ◽  
Iron Chelator ◽  
Iron Chelators ◽  
Iron Stress ◽  
Fenton Chemistry ◽  
Free Iron ◽  
Cellular Iron

ABSTRACT Maintaining cellular iron homeostasis is critical for organismal survival. Whereas iron depletion negatively affects the many metabolic pathways that depend on the activity of iron-containing enzymes, any excess of iron can cause the rapid formation of highly toxic reactive oxygen species (ROS) through Fenton chemistry. Although several cellular iron chelators have been identified, little is known about if and how organisms can prevent the Fenton reaction. By studying the effects of cisplatin, a commonly used anticancer drug and effective antimicrobial, we discovered that cisplatin elicits severe iron stress and oxidative DNA damage in bacteria. We found that both of these effects are successfully prevented by polyphosphate (polyP), an abundant polymer consisting solely of covalently linked inorganic phosphates. Subsequent in vitro and in vivo studies revealed that polyP provides a crucial iron reservoir under nonstress conditions and effectively complexes free iron and blocks ROS formation during iron stress. These results demonstrate that polyP, a universally conserved biomolecule, plays a hitherto unrecognized role as an iron chelator and an inhibitor of the Fenton reaction. IMPORTANCE How do organisms deal with free iron? On the one hand, iron is an essential metal that plays crucial structural and functional roles in many organisms. On the other hand, free iron is extremely toxic, particularly under aerobic conditions, where iron rapidly undergoes the Fenton reaction and produces highly reactive hydroxyl radicals. Our study now demonstrates that we have discovered one of the first physiologically relevant nonproteinaceous iron chelators and Fenton inhibitors. We found that polyphosphate, a highly conserved and ubiquitous inorganic polyanion, chelates iron and, through its multivalency, prevents the interaction of iron with peroxide and therefore the formation of hydroxyl radicals. We show that polyP provides a crucial iron reservoir for metalloproteins under nonstress conditions and effectively chelates free iron during iron stress. Importantly, polyP is present in all cells and organisms and hence is likely to take on this crucial function in both prokaryotic and eukaryotic cells.

scholarly journals Polyphosphate Functions In Vivo as Iron Chelator and Fenton Inhibitor

2020 ◽  
Author(s):  
Francois Beaufay ◽  
Ellen Quarles ◽  
Allison Franz ◽  
Olivia Katamanin ◽  
Wei-Yun Wholey ◽  
...  
Keyword(s):  
Fenton Reaction ◽  
Oxidative Dna Damage ◽  
Iron Homeostasis ◽  
Iron Chelator ◽  
Iron Stress ◽  
Fenton Chemistry ◽  
Cellular Iron ◽  
Covalently Linked

AbstractMaintaining cellular iron homeostasis is critical for organismal survival. Whereas iron depletion negatively affects the many metabolic pathways that depend on the activity of iron-containing enzymes, any excess of iron can cause the rapid formation of highly toxic reactive oxygen species (ROS) through Fenton chemistry. Although several cellular iron chelators have been identified, little is known about if and how organisms can prevent the Fenton reaction. By studying the effects of cisplatin, a commonly used anticancer drug and effective antimicrobial, we discovered that cisplatin elicits severe iron stress and oxidative DNA damage in bacteria. We found that both of these effects are successfully prevented by polyphosphate (polyP), an abundant polymer consisting solely of covalently linked inorganic phosphates. Subsequent in vitro and in vivo studies revealed that polyP provides a crucial iron reservoir under non-stress conditions, and effectively complexes free iron and blocks ROS formation during iron stress. These results demonstrate that polyP, a universally conserved biomolecule, plays a hitherto unrecognized role as an iron chelator and an inhibitor of the Fenton reaction.

Cellular Iron Homeostasis and Therapeutic Implications of Iron Chelators in Cancer

2014 ◽  
Vol 15 (12) ◽  
pp. 1125-1140 ◽  
Author(s):  
Mohsin Raza ◽  
Sankalpa Chakraborty ◽  
Monjoy Choudhury ◽  
Prahlad Ghosh ◽  
Alo Nag
Keyword(s):  
Iron Homeostasis ◽  
Iron Chelators ◽  
Therapeutic Implications ◽  
Cellular Iron ◽  
Cellular Iron Homeostasis

scholarly journals CBIO-10. REDUCED IRON EXPORT FUNCTIONS IN A CELL INTRINSIC MANNER TO DRIVE GLIOBLASTOMA GROWTH

2020 ◽  
Vol 22 (Supplement_2) ◽  
pp. ii17-ii17
Author(s):  
Katie Troike ◽  
Erin Mulkearns-Hubert ◽  
Daniel Silver ◽  
James Connor ◽  
Justin Lathia
Keyword(s):  
Tumor Cells ◽  
Iron Uptake ◽  
Iron Homeostasis ◽  
Iron Status ◽  
Tumor Grade ◽  
Hfe Gene ◽  
Iron Release ◽  
Female Patients ◽  
Cellular Iron

Abstract Glioblastoma (GBM), the most common primary malignant brain tumor in adults, is characterized by invasive growth and poor prognosis. Iron is a critical regulator of many cellular processes, and GBM tumor cells have been shown to modulate expression of iron-associated proteins to enhance iron uptake from the surrounding microenvironment, driving tumor initiation and growth. While iron uptake has been the central focus of previous investigations, additional mechanisms of iron regulation, such as compensatory iron efflux, have not been explored in the context of GBM. The hemochromatosis (HFE) gene encodes a transmembrane glycoprotein that aids in iron homeostasis by limiting cellular iron release, resulting in a sequestration phenotype. We find that HFE is upregulated in GBM tumors compared to non-tumor brain and that expression of HFE increases with tumor grade. Furthermore, HFE mRNA expression is associated with significantly reduced survival specifically in female patients with GBM. Based on these findings, we hypothesize that GBM tumor cells upregulate HFE expression to augment cellular iron loading and drive proliferation, ultimately leading to reduced survival of female patients. To test this hypothesis, we generated Hfe knockdown and overexpressing mouse glioma cell lines. We observed significant alterations in the expression of several iron handling genes with Hfe knockdown or overexpression, suggesting global disruption of iron homeostasis. Additionally, we show that knockdown of Hfe in these cells increases apoptosis and leads to a significant impairment of tumor growth in vivo. These findings support the hypothesis that Hfe is a critical regulator of cellular iron status and contributes to tumor aggression. Future work will include further exploration of the mechanisms that contribute to these phenotypes as well as interactions with the tumor microenvironment. Elucidating the mechanisms by which iron effulx contributes to GBM may inform the development of next-generation targeted therapies.

scholarly journals A Novel Star Like Eight-Arm Polyethylene Glycol-Deferoxamine Conjugate for Iron Overload Therapy

Pharmaceutics ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 329
Author(s):  
Bohong Yu ◽  
Yinxian Yang ◽  
Qi Liu ◽  
Aiyan Zhan ◽  
Yang Yang ◽  
...  
Keyword(s):  
Polyethylene Glycol ◽  
Iron Overload ◽  
Iron Chelator ◽  
Iron Chelators ◽  
Iron Binding ◽  
Binding Ability ◽  
Amide Bonds ◽  
Plasma Half Life ◽  
Iron Chelator Deferoxamine

The traditional iron chelator deferoxamine (DFO) has been widely used in the treatment of iron overload disease. However, DFO has congenital disadvantages, including a very short circular time and non-negligible toxicity. Herein, we designed a novel multi-arm conjugate for prolonging DFO duration in vivo and reducing cytotoxicity. The star-like 8-arm-polyethylene glycol (8-arm-PEG) was used as the macromolecular scaffold, and DFO molecules were bound to the terminals of the PEG branches via amide bonds. The conjugates displayed comparable iron binding ability to the free DFO. Furthermore, these macromolecule conjugates could significantly reduce the cytotoxicity of the free DFO, and showed satisfactory iron clearance capability in the iron overloaded macrophage RAW 246.7. The plasma half-life of the 8-arm-PEG-DFO conjugate was about 190 times than that of DFO when applied to an intravenously administered rat model. In conclusion, research indicated that these star-like PEG-based conjugates could be promising candidates as long circulating, less toxic iron chelators.

Calcein and the Labile Iron Pool.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1546-1546
Author(s):  
Shan Soe-Lin ◽  
Joan L. Buss ◽  
Evelyn Tang ◽  
Prem Ponka
Keyword(s):  
Iron Homeostasis ◽  
Iron Chelator ◽  
Acetoxymethyl Ester ◽  
Iron Regulatory Proteins ◽  
Labile Iron Pool ◽  
Cellular Iron ◽  
Labile Iron ◽  
The Difference ◽  
Iron Pool ◽  
Cellular Iron Homeostasis

Abstract The labile iron pool is a putative cytosolic compartment of loosely bound, redox-active, chelator-accessible iron. Iron contained within this pool is thought to influence the activity of iron regulatory proteins (IRPs), which bind to iron response elements (IRE) during low iron conditions; this association blocks the translation of ferritin mRNA, and stabilizes transferrin receptor mRNA. High levels of labile iron have been shown to promote oxidative stress. As this pool has such profound effects upon cellular iron homeostasis, there has been great interest in the development of methods to measure labile iron. Calcein, a fluorescent iron chelator, has been widely used to monitor the labile iron pool. When the non-fluorescent acetoxymethyl ester moiety (calcein-AM), enters cells, it is immediately cleaved by cytosolic esterases to its cell-impermeable, fluorescent calcein form. Iron binding to calcein quenches its fluorescence, which can subsequently be recovered following the loss of its iron to a stronger chelator. The difference in fluorescence between the bound and unbound calcein forms is thought to be proportional to the labile iron pool itself. While this method has been commonly exploited, it is unknown whether calcein may over-estimate the size of the labile pool by stripping iron from sources where it may be loosely bound, or by intercepting iron during its passage from one compartment to another. Although it is believed that calcein exerts very little direct influence on cellular iron homeostasis and acts only as a passive sensor of labile iron, some recent evidence from our lab indicates that this may not be the case. We have observed that incubation with calcein results in the activation of IRP-2 and stabilization of HIF-1α, a potent physiological regulator governing the expression of genes involved in oxygen sensing and iron metabolism. Furthermore, we have found that the size of the labile iron pool as measured by calcein was proportional to the amount of calcein loaded in HeLa and K562 cell lines. These findings suggest that calcein may be able to perturb cellular iron homeostasis, and may not accurately reflect the size of the labile iron pool. While calcein may still be used for comparative purposes under identically controlled conditions, its usefulness as a quantifying agent should be regarded with caution.

Effects of Phenyl-1-Pyridin-2yl-Ethanone (PPY)-Based Iron Chelators on the Formation of Methemoglobin

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 4823-4823
Author(s):  
Nowah K. A. Afangbedji ◽  
Namita Kumari ◽  
Dymtro Kowalskyy ◽  
Sergei Nekhai
Keyword(s):  
Antitumor Activity ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Iron Chelator ◽  
Redox Activity ◽  
Iron Chelators ◽  
Human Red Blood Cells ◽  
Anti Hiv ◽  
Hiv 1

Abstract Background Iron chelators are used in the treatment of iron overload related diseases and are currently receiving a major attention as potential antitumor drugs. In recent studies, the antitumor activity of thiosemicarbazones-class of iron chelator, including Di-2-pyridilketone-4,4- dimethyl-3-thiosemicarbazone (Dp44mT) has been investigated in over 20 phase I and II clinical trials [1, 2,3]. Iron chelators were also considered as anti-HIV-1 agents. However, the main obstacle to using iron chelators in vivois the deleterious side effect of methemoglobinemia induced by some iron chelators that are able to scavenge electrons from the heme-bound iron in hemoglobin. In our previous studies, we developed novel phenyl-1-pyridin-2yl-ethanone (PPY)-based iron chelators that we showed to increase IKBα expression, modulate CDK2 and CDK9 activities and inhibit HIV-1 [4]. Objective Our objective was to test the effect of PPYeT iron chelator for methemoglobin induction. The methemoglobin induction effect was compared with several additional iron chelators including Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT) and PPY analogues. Methods Fluorometric analysis was carried out in promonocytic THP-1 cells to evaluate the ability of our novel PPYeT iron chelator to reduce labile iron pool (LIP). The effect of PPYet on LIP was compared to the effect to SIH. Subsequently, spectrophotometric analysis was used to measure and quantify the production of methemoglobin in human red blood cells lysates and in isolated intact human red blood cells treated with PPYeT and various other iron chelators including DP44mT and DP4mT. Results PPYeT significantly reduced LIP in THP-1 cells overloaded with iron comparing to the cells treated with SIH. In RBC lysates and in intact RBC, PPYeT treatment showed notably lesser production of methemoglobin in comparison to DP44mT and DP4mT chelators. In RBC lysates, PPYeT produced about four-fold less methemoglobin than Dp44mT and ten-fold less than Dp4mT. Conclusion The novel compound, PPYeT, shows a remarkably low ability to catalyze the formation of methemoglobin in human RBC lysates and also in intact RBCs as compared to Dp44mT. These findings indicate that PPYeT may be useful for future in vivo studies as it produces less methemoglobinemia. Further studies will evaluate the effect PPYeT as anti-cancer or anti HIV-1 inhibitor in vivo. Acknowledgments This work was supported by NIH Research Grants 1P50HL118006, 1R01HL125005, and 5G12MD007597. The content is solely the responsibility of the authors and does not necessarily represent the official view of NHLBI, NIMHD or NIH. References 1. Richardson, D. R.; Sharpe, P. C.; Lovejoy, D. B.; Senaratne, D.; Kalinowski, D. S.; Islam, M.; Bernhardt, P. V. Dipyridyl Thiosemicarbazone Chelators with Potent and Selective Antitumor Activity Form Iron Complexes with Redox Activity. Journal of Medicinal Chemistry. 2006, 49, 6510−6521 2-Yuan, J.; Lovejoy, D. B.; Richardson, D. R. Novel Di-2-pyridylDerived Iron Chelators with Marked and Selective Antitumor Activity: In Vitro and in Vivo Assessment. Blood2004, 104, 1450−1458. 3-Whitnall, M.; Howard, J.; Ponka, P.; Richardson, D. R. A Class of Iron Chelators with a Wide Spectrum of Potent Antitumor Activity that Overcomes Resistance to Chemotherapeutics. Proceedings of National Academy of Science. U. S. A.2006, 103, 14901−14906. 4. Kumari N, Iordanskiy S, Kovalskyy D, Breuer D, Niu X, Lin X, Xu M, Gavrilenko K, Kashanchi F, Dhawan S et al: Phenyl-1-Pyridin-2yl-ethanone-based iron chelators increase IkappaB-alpha expression, modulate CDK2 and CDK9 activities, and inhibit HIV-1 transcription. Antimicrob Agents Chemother 2014, 58(11):6558-6571. Disclosures No relevant conflicts of interest to declare.

scholarly journals Nitric oxide–mediated regulation of ferroportin-1 controls macrophage iron homeostasis and immune function in Salmonella infection

2013 ◽  
Vol 210 (5) ◽  
pp. 855-873 ◽  
Author(s):  
Manfred Nairz ◽  
Ulrike Schleicher ◽  
Andrea Schroll ◽  
Thomas Sonnweber ◽  
Igor Theurl ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Iron Homeostasis ◽  
Molecular Mechanisms ◽  
Iron Acquisition ◽  
Iron Chelator ◽  
Related Factor ◽  
Cellular Iron ◽  
Splenic Macrophages ◽  
Ferroportin 1 ◽  
Pathogen Control

Nitric oxide (NO) generated by inducible NO synthase 2 (NOS2) affects cellular iron homeostasis, but the underlying molecular mechanisms and implications for NOS2-dependent pathogen control are incompletely understood. In this study, we found that NO up-regulated the expression of ferroportin-1 (Fpn1), the major cellular iron exporter, in mouse and human cells. Nos2−/− macrophages displayed increased iron content due to reduced Fpn1 expression and allowed for an enhanced iron acquisition by the intracellular bacterium Salmonella typhimurium. Nos2 gene disruption or inhibition of NOS2 activity led to an accumulation of iron in the spleen and splenic macrophages. Lack of NO formation resulted in impaired nuclear factor erythroid 2-related factor-2 (Nrf2) expression, resulting in reduced Fpn1 transcription and diminished cellular iron egress. After infection of Nos2−/− macrophages or mice with S. typhimurium, the increased iron accumulation was paralleled by a reduced cytokine (TNF, IL-12, and IFN-γ) expression and impaired pathogen control, all of which were restored upon administration of the iron chelator deferasirox or hyperexpression of Fpn1 or Nrf2. Thus, the accumulation of iron in Nos2−/− macrophages counteracts a proinflammatory host immune response, and the protective effect of NO appears to partially result from its ability to prevent iron overload in macrophages

The Iron Chelator L1 Potentiates Oxidative DNA Damage in Iron-Loaded Liver Cells

Blood ◽  
1998 ◽  
Vol 92 (2) ◽  
pp. 632-638 ◽  
Author(s):  
Louise Cragg ◽  
Robert P. Hebbel ◽  
Wesley Miller ◽  
Alex Solovey ◽  
Scott Selby ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Dna Damage ◽  
Iron Overload ◽  
Oxidative Dna Damage ◽  
Iron Chelator ◽  
Liver Cells ◽  
Iron Chelators

Abstract Iron-mediated carcinogenesis is thought to occur through the generation of oxygen radicals. Iron chelators are used in attempts to prevent the long term consequences of iron overload. In particular, 1,2-dimethyl-3-hydroxypyrid-4-one (L1), has shown promise as an effective chelator. Using an established hepatocellular model of iron overload, we studied the generation of iron-catalyzed oxidative DNA damage and the influence of iron chelators, including L1, on such damage. Iron loading of HepG2 cells was found to greatly exacerbate hydrogen peroxide–mediated DNA damage. Desferrithiocin was protective against iron/hydrogen peroxide–induced DNA damage; deferoxamine had no effect. In contrast, L1 exposure markedly potentiated hydrogen peroxide–mediated oxidative DNA damage in iron-loaded liver cells. However, when exposure to L1 was maintained during incubation with hydrogen peroxide, L1 exerted a protective effect. We interpret this as indicating that L1's potential toxicity is highly dependent on the L1:iron ratio. In vitro studies examining iron-mediated ascorbate oxidation in the presence of L1 showed that an L1:iron ratio must be at least 3 to 1 for L1 to inhibit the generation of free radicals; at lower concentrations of L1 increased oxygen radical generation occurs. In the clinical setting, such potentiation of iron-catalyzed oxidative DNA damage at low L1:iron ratios may lead to long-term toxicities that might preclude administration of L1 as an iron chelator. Whether this implication in fact extends to the in vivo situation will have to be verified in animal studies.

scholarly journals Disrupted iron homeostasis causes dopaminergic neurodegeneration in mice

2016 ◽  
Vol 113 (13) ◽  
pp. 3428-3435 ◽  
Author(s):  
Pavle Matak ◽  
Andrija Matak ◽  
Sarah Moustafa ◽  
Dipendra K. Aryal ◽  
Eric J. Benner ◽  
...  
Keyword(s):  
Transferrin Receptor ◽  
Dopaminergic Neurons ◽  
Iron Homeostasis ◽  
Motor Deficits ◽  
Metabolic Switch ◽  
Dopaminergic Neurodegeneration ◽  
Cellular Iron ◽  
Transferrin Receptor 1 ◽  
The Unfolded Protein Response

Disrupted brain iron homeostasis is a common feature of neurodegenerative disease. To begin to understand how neuronal iron handling might be involved, we focused on dopaminergic neurons and asked how inactivation of transport proteins affected iron homeostasis in vivo in mice. Loss of the cellular iron exporter, ferroportin, had no apparent consequences. However, loss of transferrin receptor 1, involved in iron uptake, caused neuronal iron deficiency, age-progressive degeneration of a subset of dopaminergic neurons, and motor deficits. There was gradual depletion of dopaminergic projections in the striatum followed by death of dopaminergic neurons in the substantia nigra. Damaged mitochondria accumulated, and gene expression signatures indicated attempted axonal regeneration, a metabolic switch to glycolysis, oxidative stress, and the unfolded protein response. We demonstrate that loss of transferrin receptor 1, but not loss of ferroportin, can cause neurodegeneration in a subset of dopaminergic neurons in mice.

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