Assessment of Chelatable Mitochondrial Iron by Using Mitochondrion-Selective Fluorescent Iron Indicators with Different Iron-Binding Affinities

Fpa (YlaN) is an iron(II) binding protein that functions to relieve Fur-mediated repression of gene expression in Staphylococcus aureus

Iron (Fe) is a trace nutrient required by nearly all organisms. As a result of the demand for Fe and the toxicity of non-chelated cytosolic ionic Fe, regulatory systems have evolved to tightly balance Fe acquisition and usage while limiting overload. In most bacteria, including the mammalian pathogen Staphylococcus aureus, the ferric uptake regulator (Fur) is the primary transcriptional regulator controlling the transcription of genes that code for Fe uptake and utilization proteins. Fpa (formerly YlaN) was demonstrated to be essential in Bacillus subtilis unless excess Fe is added to the growth medium, suggesting a role in Fe homeostasis. Here, we demonstrate that Fpa is essential in S. aureus upon Fe deprivation. Null fur alleles bypassed the essentiality of Fpa. The absence of Fpa abolished the derepression of Fur-regulated genes during Fe limitation. Bioinformatic analyses suggest that fpa was recruited to Gram-positive bacteria and, once acquired, was maintained in the genome as it co-evolved with Fur. Consistent with a role for Fpa in alleviating Fur-dependent repression, Fpa and Fur interacted in vivo, and Fpa decreased the DNA-binding ability of Fur in vitro. Fpa bound Fe(II) in vitro using oxygen or nitrogen ligands with an association constant that is consistent with a physiological role in Fe homeostasis. These findings have led to a model wherein Fpa is an Fe(II) binding protein that influences Fur-dependent regulation through direct interaction.IMPORTANCEIron (Fe) is an essential nutrient for nearly all organisms. If Fe homeostasis is not maintained, Fe may accumulate in the cytosol, which can be toxic. Questions remain about how cells efficiently balance Fe uptake and usage to prevent overload. Iron uptake and proper metalation of proteins are essential processes in the mammalian bacterial pathogen Staphylococcus aureus. Understanding the gene products involved in the genetic regulation of Fe uptake and usage and the physiological adaptations that S. aureus uses to survive in Fe-depleted conditions provides insight into pathogenesis. Herein, we demonstrate that the DNA-binding activity of the ferric uptake regulator transcriptional repressor is alleviated under Fe limitation, but uniquely, in S. aureus, alleviation requires the presence of Fpa.

Ferroptosis in Osteoarthritis: Current Understanding

Osteoarthritis (OA) is a prevalent degenerative disease in elderly people that is characterized by cartilage loss and abrasion, leading to joint pain and dysfunction. The aetiology of OA is complicated and includes abnormal mechanical stress, a mild inflammatory environment, chondrocyte senescence and apoptosis, and changes in chondrocyte metabolism. Ferroptosis is a regulated cell death modality characterized by the excessive accumulation of lipid peroxidation and mitochondrial dysfunction. The role of ferroptosis in OA pathogenesis has aroused researchers' attention in the past two years, and there is mounting evidence indicating that ferroptosis is destructive. However, the impact of ferroptosis on OA and how the regulators of ferroptosis affect OA development are unclear. Here, we reviewed the current understanding of ferroptosis in OA pathogenesis and summarized several drugs and compounds targeting ferroptosis in OA treatment. The accumulation of intracellular iron, the trigger of Fenton reaction, the excessive production of ROS, the peroxidation of PUFA-PLs, and mitochondrial and membrane damage are involved in chondrocyte ferroptosis. System Xc - and GPX4 are the most important regulators that control ferroptosis. Several compounds, such as DFO and Fer-1, have been proven effective in preventing ferroptosis and slowing OA progression on animal models. Collectively, targeting ferroptosis shows great potential in treating OA.

Novel bioassays based on 3D-printed device for sensing of hypoxia and p53 pathway in 3D cell models

Cell-based assays are widely exploited for drug screening and biosensing, providing useful information about bioactivity of target analytes and complex biological samples. It is well recognized that 3D cell models are required to achieve highly valuable information, also from the perspective of replacing animal models. However, bioassays relying on 3D cell models are generally highly demanding in terms of facilities, equipment, and skilled personnel requirements. To reduce cost, increase sustainability, and provide a flexible 3D cell-based platform for bioassays, we here report a novel approach based on a 3D-printed microtissue device. To assess the suitability of this strategy for reporter gene technology, we selected to monitor two molecular pathways which were of interest in several applications, hypoxia signaling and the p53 pathway. The investigation of such pathways is highly relevant in fields spanning from drug screening to bioactivity monitoring for industrial by-product valorization. Microtissues of human hepatocarcinoma (HepG2) and human embryonic kidney (Hek293T) cell lines were obtained with a low-cost and sustainable chip platform and bioassays were developed to monitor the hypoxia-inducible factors (HIFs) and the p53 tumor suppressor pathway. HepG2 and Hek293T 3D cell models were genetically engineered to express the Luc2P from Photinus pyralis firefly either under the regulation of p53 or HIF response elements. The bioassays allowed quantitative assessment of hypoxia and tumoral activity with 1,10-phenanthroline for HIF and with doxorubicin for p53 pathway activation, respectively, showing good potential for applications of this sustainable and low-cost 3D-printed microfluidic platform for bioactivity analyses, drug screening, and precision medicine.

Role of ferroptosis in mitochondrial damage in diabetic retinopathy

Diabetic retinopathy is driven by oxidative stress-mitochondrial damage. Activation of ROS producing cytosolic NADPH oxidase 2 (Nox2) in diabetes precedes retinal mitochondrial damage, initiating a vicious cycle of free radicals. Elevated ROS levels peroxidize membrane lipids increasing damaging lipid peroxides (LPOs). While glutathione peroxidase 4 (GPx4) neutralizes LPOs, an imbalance in its generation-neutralization leads to ferroptosis, which is characterized by increased LPOs, free iron and decreased GPx4 activity. Mitochondria are rich in polyunsaturated fatty acids and iron and have mitochondrial isoform of GPx4. Our aim was to investigate mitochondrial ferroptosis in diabetic retinopathy, focusing on Nox2 mediated ROS production. Using human retinal endothelial cells, incubated in 5 mM or 20 mM D-glucose for 12-96 h, with or without Nox2 inhibitors (100 μM apocynin, 5 μM EHop-016 or 5 μM Gp91 ds-tat), or ferroptosis inhibitors (1 μM ferrostatin-1, 50 μM deferoxamine) or activator (0.1 μM RSL3), cytosolic and mitochondrial ROS, LPOs, iron, GPx4 activity, mitochondrial integrity (membrane permeability, oxygen consumption rate, mtDNA copy numbers) and cell death were quantified. High glucose significantly increased ROS, LPOs and iron levels and inhibited GPx4 activity in cytosol, and while Nox2 and ferroptosis inhibitors prevented glucose-induced increase in ferroptosis markers, mitochondrial damage and cell death, RSL3, further worsened them. Furthermore, high glucose also increased ferroptosis markers in the mitochondria, which followed their increase in the cytosol, suggesting a role of cytosolic ROS in mitochondrial ferroptosis. Thus, targeting Nox2-ferroptosis should help break down the self-perpetuating vicious cycle of free radicals, initiated by the damaged mitochondria, and could provide novel therapeutics to prevent/retard the development of diabetic retinopathy.

The Staphylococcus aureus small non-coding RNA IsrR regulates TCA cycle activity and virulence

Staphylococcus aureus has evolved mechanisms to cope with low iron (Fe) availability in host tissues. S. aureus uses the ferric uptake transcriptional regulator (Fur) to sense titers of cytosolic Fe. Upon Fe depletion, apo-Fur relieves transcriptional repression of genes utilized for Fe uptake. We demonstrate that an S. aureus Δfur mutant has decreased expression of acnA, which codes for the Fe-dependent enzyme aconitase. Decreased acnA expression prevented the Δfur mutant from growing with amino acids as sole carbon and energy sources. Suppressor analysis determined that a mutation in isrR, which produces a regulatory RNA, permitted growth by decreasing isrR transcription. The decreased AcnA activity of the Δfur mutant was partially relieved by an ΔisrR mutation. Directed mutation of bases predicted to facilitate the interaction between the acnA transcript and IsrR, decreased the ability of IsrR to control acnA expression in vivo and IsrR bound to the acnA transcript in vitro. IsrR also bound to the transcripts coding the alternate TCA cycle proteins sdhC, mqo, citZ, and citM. Whole cell metal analyses suggest that IsrR promotes Fe uptake and increases intracellular Fe not ligated by macromolecules. Lastly, we determined that Fur and IsrR promote infection using murine skin and acute pneumonia models.

Exploring the relationship between anastasis and mitochondrial ROS-mediated ferroptosis in metastatic chemoresistant cancers: a call for investigation

Ferroptosis induces significant changes in mitochondrial morphology, including membrane condensation, volume reduction, cristae alteration, and outer membrane rupture, affecting mitochondrial function and cellular fate. Recent reports have described the intrinsic cellular iron metabolism and its intricate connection to ferroptosis, a significant kind of cell death characterized by iron dependence and oxidative stress regulation. Furthermore, updated molecular insights have elucidated the significance of mitochondria in ferroptosis and its implications in various cancers. In the context of cancer therapy, understanding the dual role of anastasis and ferroptosis in chemoresistance is crucial. Targeting the molecular pathways involved in anastasis may enhance the efficacy of ferroptosis inducers, providing a synergistic approach to overcome chemoresistance. Research into how DNA damage response (DDR) proteins, metabolic changes, and redox states interact during anastasis and ferroptosis can offer new insights into designing combinatorial therapeutic regimens against several cancers associated with stemness. These treatments could potentially inhibit anastasis while simultaneously inducing ferroptosis, thereby reducing the likelihood of cancer cells evading death and developing resistance to chemotherapy. The objective of this study is to explore the intricate interplay between anastasis, ferroptosis, EMT and chemoresistance, and immunotherapeutics to better understand their collective impact on cancer therapy outcomes. We searched public research databases including google scholar, PubMed, relemed, and the national library of medicine related to this topic. In this review, we discussed the interplay between the tricarboxylic acid cycle and glycolysis implicated in modulating ferroptosis, adding complexity to its regulatory mechanisms. Additionally, the regulatory role of reactive oxygen species (ROS) and the electron transport chain (ETC) in ferroptosis has garnered significant attention. Lipid metabolism, particularly involving GPX4 and System Xc- plays a significant role in both the progression of ferroptosis and cancer. There is a need to investigate the intricate interplay between anastasis, ferroptosis, and chemoresistance to better understand cancer therapy clinical outcomes. Integrating anastasis, and ferroptosis into strategies targeting chemoresistance and exploring its potential synergy with immunotherapy represent promising avenues for advancing chemoresistant cancer treatment. Understanding the intricate interplay among mitochondria, anastasis, ROS, and ferroptosis is vital in oncology, potentially revolutionizing personalized cancer treatment and drug development.

Exploring the relationship between anastasis and mitochondrial ROS-mediated ferroptosis in metastatic chemoresistant cancers: a call for investigation

Ferroptosis induces significant changes in mitochondrial morphology, including membrane condensation, volume reduction, cristae alteration, and outer membrane rupture, affecting mitochondrial function and cellular fate. Recent reports have described the intrinsic cellular iron metabolism and its intricate connection to ferroptosis, a significant kind of cell death characterized by iron dependence and oxidative stress regulation. Furthermore, updated molecular insights have elucidated the significance of mitochondria in ferroptosis and its implications in various cancers. In the context of cancer therapy, understanding the dual role of anastasis and ferroptosis in chemoresistance is crucial. Targeting the molecular pathways involved in anastasis may enhance the efficacy of ferroptosis inducers, providing a synergistic approach to overcome chemoresistance. Research into how DNA damage response (DDR) proteins, metabolic changes, and redox states interact during anastasis and ferroptosis can offer new insights into designing combinatorial therapeutic regimens against several cancers associated with stemness. These treatments could potentially inhibit anastasis while simultaneously inducing ferroptosis, thereby reducing the likelihood of cancer cells evading death and developing resistance to chemotherapy. The objective of this study is to explore the intricate interplay between anastasis, ferroptosis, EMT and chemoresistance, and immunotherapeutics to better understand their collective impact on cancer therapy outcomes. We searched public research databases including google scholar, PubMed, relemed, and the national library of medicine related to this topic. In this review, we discussed the interplay between the tricarboxylic acid cycle and glycolysis implicated in modulating ferroptosis, adding complexity to its regulatory mechanisms. Additionally, the regulatory role of reactive oxygen species (ROS) and the electron transport chain (ETC) in ferroptosis has garnered significant attention. Lipid metabolism, particularly involving GPX4 and System Xc- plays a significant role in both the progression of ferroptosis and cancer. There is a need to investigate the intricate interplay between anastasis, ferroptosis, and chemoresistance to better understand cancer therapy clinical outcomes. Integrating anastasis, and ferroptosis into strategies targeting chemoresistance and exploring its potential synergy with immunotherapy represent promising avenues for advancing chemoresistant cancer treatment. Understanding the intricate interplay among mitochondria, anastasis, ROS, and ferroptosis is vital in oncology, potentially revolutionizing personalized cancer treatment and drug development.

Dibutyl phthalate exposure induced mitochondria-dependent ferroptosis by enhancing VDAC2 in zebrafish ZF4 cells

Dibutyl phthalate (DBP) contamination has raised global concern for decades, while its health risk with toxic mechanisms requires further elaboration. This study used zebrafish ZF4 cells to investigate the toxicity of ferroptosis with underlying mechanisms in response to DBP exposure. Results showed that DBP induced ferroptosis, characterized by accumulation of ferrous iron, lipid peroxidation, and decrease of glutathione peroxidase 4 levels in a time-dependent manner, subsequently reduced cell viability. Transcriptome analysis revealed that voltage-dependent anion-selective channel (VDAC) in mitochondrial outer membrane was upregulated in ferroptosis signaling pathways. Protecting mitochondria with a VDAC2 inhibitor or siRNAs attenuated the accumulation of mitochondrial superoxide and lipid peroxides, the opening of mitochondrial permeability transition pore (mPTP), and the overload of iron levels, suggesting VDAC2 oligomerization mediated the influx of iron into mitochondria that is predominant and responsible for mitochondria-dependent ferroptosis under DBP exposure. Furthermore, the pivotal role of activating transcription factor 4 (ATF4) was identified in the transcriptional regulation of vdac2 by ChIP assay. And the intervention of atf4b inhibited DBP-induced VDAC2 upregulation and oligomerization. Taken together, this study reveals that ATF4-VDAC2 signaling pathway is involved in the DBP-induced ferroptosis in zebrafish ZF4 cells, contributing to the in-depth understanding of biotoxicity and the ecological risk assessment of phthalates.

DMT1-dependent endosome-mitochondria interactions regulate mitochondrial iron translocation and metastatic outgrowth

Transient early endosome (EE)-mitochondria interactions can mediate mitochondrial iron translocation, but the associated mechanisms are still elusive. We showed that Divalent Metal Transporter 1 (DMT1) sustains mitochondrial iron translocation via EE-mitochondria interactions in triple-negative MDA-MB-231, but not in luminal A T47D breast cancer cells. DMT1 silencing increases labile iron pool (LIP) levels and activates PINK1/Parkin-dependent mitophagy in MDA-MB-231 cells. Mitochondrial bioenergetics and the iron-associated protein profile were altered by DMT1 silencing and rescued by DMT1 re-expression. Transcriptomic profiles upon DMT1 silencing are strikingly different between 2D and 3D culture conditions, suggesting that the environment context is crucial for the DMT1 knockout phenotype observed in MDA-MB-231 cells. Lastly, in vivo lung metastasis assay revealed that DMT1 silencing promoted the outgrowth of lung metastatic nodules in both human and murine models of triple-negative breast cancer cells. These findings reveal a DMT1-dependent pathway connecting EE-mitochondria interactions to mitochondrial iron translocation and metastatic fitness of breast cancer cells.

Ironing out the details: ferroptosis and its relevance to diabetic cardiomyopathy

Ferroptosis is a newly identified myocardial cell death mechanism driven by iron-dependent lipid peroxidation. The presence of elevated intramyocardial lipid levels and excessive iron in patients with diabetes suggest a predominant role of ferroptosis in diabetic cardiomyopathy. As myocardial cell death is a precursor of heart failure, and intensive glycemic control cannot abate the increased risk of heart failure in patients with diabetes, targeting myocardial cell death via ferroptosis is a promising therapeutic avenue to prevent and/or treat diabetic cardiomyopathy. This review provides updated and comprehensive molecular mechanisms underpinning ferroptosis, clarifies several misconceptions about ferroptosis, emphasizes the importance of ferroptosis in diabetes-induced myocardial cell death, and offers valuable approaches to evaluate and target ferroptosis in the diabetic heart. Furthermore, basic concepts and ideas presented in this review, including glutathione peroxidase-4-independent and mitochondrial mechanisms of ferroptosis, are also important for investigating ferroptosis in other diabetic organs, as well as nondiabetic and metabolically compromised hearts.

Ferritinophagy-mediated apoptosis and paraptosis induction involved MAPK and PI3K/AKT pathway in mechanism of an iron chelator

Melanoma cells were more resistant to ferroptosis with still poor therapy outcomes. Sensitizing melanoma cell to the ferroptosis inducer was a crucial strategy for treatment of melanoma. In the present study, 2,2'-di-pyridylketone hydrazone dithiocarbamate s-butyric acid (DpdtbA) displayed superior inhibitory activity than ferroptosis inducer Erastin in melanoma cells, which prompt us to explore the underlying mechanism. The analyses from flow cytometry and Western blot showed that the growth inhibition of DpdtbA against SK-MEL-28 and A375 cells involved apoptosis induction and G1 phase arrest. Surprisingly, the cytoplasmic vacuoles were found upon the treatment; transmission electron microscopy and endoplasmic reticulum (ER) staining revealed that the cytoplasmic vacuoles were in ER; while down-regulation of alix and requirement of protein synthesis suggested there was an occurrence of paraptosis. However, both NAC and 3-MA could significantly attenuate the cytoplasmic vacuolization and growth inhibition, hinting that both ROS and autophagy involved the paraptosis induction. The additional evidence revealed that there was an occurrence of continuous ferritinophagy, which was responsible for the ROS production. Downregulation of NCOA4 clearly attenuated the apoptosis and paraptosis induction. In addition, activation of MAPK involved regulation of paraptosis, but only ERK and JNK had role in the formation of cytoplasmic vacuoles and growth inhibition. Furthermore, a ROS dependent regulation of PI3K/AKT pathway was also involved. Taken together, our result firstly demonstrated that a continuous ferritinophagy contributed to the apoptosis and paraptosis induction, highlighting that the lysosomal labile iron pool had a crucial role in control of melanoma cell fate.

A Timm-Nissl multiplane microscopic atlas of rat brain zincergic terminal fields and metal-containing glia

The ability of Timm's sulphide silver method to stain zincergic terminal fields has made it a useful neuromorphological marker. Beyond its roles in zinc-signalling and neuromodulation, zinc is involved in the pathophysiology of ischemic stroke, epilepsy, degenerative diseases and neuropsychiatric conditions. In addition to visualising zincergic terminal fields, the method also labels transition metals in neuronal perikarya and glial cells. To provide a benchmark reference for planning and interpretation of experimental investigations of zinc-related phenomena in rat brains, we have established a comprehensive repository of serial microscopic images from a historical collection of coronally, horizontally and sagittally oriented rat brain sections stained with Timm's method. Adjacent Nissl-stained sections showing cytoarchitecture, and customised atlas overlays from a three-dimensional rat brain reference atlas registered to each section image are included for spatial reference and guiding identification of anatomical boundaries. The Timm-Nissl atlas, available from EBRAINS, enables experimental researchers to navigate normal rat brain material in three planes and investigate the spatial distribution and density of zincergic terminal fields across the entire brain.

Mitochondrial Genome Variants as a Cause of Mitochondrial Cardiomyopathy

Mitochondria are small double-membraned organelles responsible for the generation of energy used in the body in the form of ATP. Mitochondria are unique in that they contain their own circular mitochondrial genome termed mtDNA. mtDNA codes for 37 genes, and together with the nuclear genome (nDNA), dictate mitochondrial structure and function. Not surprisingly, pathogenic variants in the mtDNA or nDNA can result in mitochondrial disease. Mitochondrial disease primarily impacts tissues with high energy demands, including the heart. Mitochondrial cardiomyopathy is characterized by the abnormal structure or function of the myocardium secondary to genetic defects in either the nDNA or mtDNA. Mitochondrial cardiomyopathy can be isolated or part of a syndromic mitochondrial disease. Common manifestations of mitochondrial cardiomyopathy are a phenocopy of hypertrophic cardiomyopathy, dilated cardiomyopathy, and cardiac conduction defects. The underlying pathophysiology of mitochondrial cardiomyopathy is complex and likely involves multiple abnormal processes in the cell, stemming from deficient oxidative phosphorylation and ATP depletion. Possible pathophysiology includes the activation of alternative metabolic pathways, the accumulation of reactive oxygen species, dysfunctional mitochondrial dynamics, abnormal calcium homeostasis, and mitochondrial iron overload. Here, we highlight the clinical assessment of mtDNA-related mitochondrial cardiomyopathy and offer a novel hypothesis of a possible integrated, multivariable pathophysiology of disease.

A new fluorescent sensor mitoferrofluor indicates the presence of chelatable iron in polarized and depolarized mitochondria

Mitochondrial chelatable iron contributes to the severity of several injury processes, including ischemia/reperfusion, oxidative stress, and drug toxicity. However, methods to measure this species in living cells are lacking. To measure mitochondrial chelatable iron in living cells, here we synthesized a new fluorescent indicator, mitoferrofluor (MFF). We designed cationic MFF to accumulate electrophoretically in polarized mitochondria, where a reactive group then forms covalent adducts with mitochondrial proteins to retain MFF even after subsequent depolarization. We also show in cell-free medium that Fe²⁺ (and Cu²⁺), but not Fe³⁺, Ca²⁺, or other biologically relevant divalent cations, strongly quenched MFF fluorescence. Using confocal microscopy, we demonstrate in hepatocytes that red MFF fluorescence colocalized with the green fluorescence of the mitochondrial membrane potential (ΔΨ_m) indicator, rhodamine 123 (Rh123), indicating selective accumulation into the mitochondria. Unlike Rh123, mitochondria retained MFF after ΔΨ_m collapse. Furthermore, intracellular delivery of iron with membrane-permeant Fe³⁺/8-hydroxyquinoline (FeHQ) quenched MFF fluorescence by ∼80% in hepatocytes and other cell lines, which was substantially restored by the membrane-permeant transition metal chelator pyridoxal isonicotinoyl hydrazone. We also show FeHQ quenched the fluorescence of cytosolically coloaded calcein, another Fe²⁺ indicator, confirming that Fe³⁺ in FeHQ undergoes intracellular reduction to Fe²⁺. Finally, MFF fluorescence did not change after addition of the calcium mobilizer thapsigargin, which shows MFF is insensitive to physiologically relevant increases of mitochondrial Ca²⁺. In conclusion, the new sensor reagent MFF fluorescence is an indicator of mitochondrial chelatable Fe²⁺ in normal hepatocytes with polarized mitochondria as well as in cells undergoing loss of ΔΨ_m.

HIV-1 gp120-Induced Endolysosome de-Acidification Leads to Efflux of Endolysosome Iron, and Increases in Mitochondrial Iron and Reactive Oxygen Species

The HIV-1 coat protein gp120 continues to be implicated in the pathogenesis of HIV-1 associated neurocognitive disorder (HAND); a condition known to affect ~50% of people living with HIV-1 (PLWH). Autopsy brain tissues of HAND individuals display morphological changes to mitochondria and endolysosomes, and HIV-1 gp120 causes mitochondrial dysfunction including increased levels of reactive oxygen species (ROS) and de-acidification of endolysosomes. Ferrous iron is linked directly to ROS production, ferrous iron is contained in and released from endolysosomes, and PLWH have elevated iron and ROS levels. Based on those findings, we tested the hypothesis that HIV-1 gp120-induced endolysosome de-acidification and subsequent iron efflux from endolysosomes is responsible for increased levels of ROS. In U87MG glioblastoma cells, HIV-1 gp120 de-acidified endolysosomes, reduced endolysosome iron levels, increased levels of cytosolic and mitochondrial iron, and increased levels of cytosolic and mitochondrial ROS. These effects were all attenuated significantly by the endolysosome-specific iron chelator deferoxamine, by inhibitors of endolysosome-resident two-pore channels and divalent metal transporter-1 (DMT-1), and by inhibitors of mitochondria-resident DMT-1 and mitochondrial permeability transition pores. These results suggest that oxidative stress commonly observed with HIV-1 gp120 is downstream of its ability to de-acidify endolysosomes, to increase the release of iron from endolysosomes, and to increase the uptake of iron into mitochondria. Thus, endolysosomes might represent early and upstream targets for therapeutic strategies against HAND.

The Role of the Metabolism of Zinc and Manganese Ions in Human Cancerogenesis

Metal ion homeostasis is fundamental for life. Specifically, transition metals iron, manganese and zinc play a pivotal role in mitochondrial metabolism and energy generation, anti-oxidation defense, transcriptional regulation and the immune response. The misregulation of expression or mutations in ion carriers and the corresponding changes in Mn²⁺ and Zn²⁺ levels suggest that these ions play a pivotal role in cancer progression. Moreover, coordinated changes in Mn²⁺ and Zn²⁺ ion carriers have been detected, suggesting that particular mechanisms influenced by both ions might be required for the growth of cancer cells, metastasis and immune evasion. Here, we present a review of zinc and manganese pathophysiology suggesting that these ions might cooperatively regulate cancerogenesis. Zn and Mn effects converge on mitochondria-induced apoptosis, transcriptional regulation and the cGAS-STING signaling pathway, mediating the immune response. Both Zn and Mn influence cancer progression and impact treatment efficacy in animal models and clinical trials. We predict that novel strategies targeting the regulation of both Zn and Mn in cancer will complement current therapeutic strategies.

Defining Local Chemical Conditions in Magnetosomes of Magnetotactic Bacteria

Defining chemical properties of intracellular organelles is necessary to determine their function(s) as well as understand and mimic the reactions they host. However, the small size of bacterial and archaeal microorganisms often prevents defining local intracellular chemical conditions in a similar way to what has been established for eukaryotic organelles. This work proposes to use magnetite (Fe₃O₄) nanocrystals contained in magnetosome organelles of magnetotactic bacteria as reporters of elemental composition, pH, and redox potential of a hypothetical environment at the site of formation of intracellular magnetite. This methodology requires combining recent single-cell mass spectrometry measurements together with elemental composition of magnetite in trace and minor elements. It enables a quantitative characterization of chemical disequilibria of 30 chemical elements between the intracellular and external media of magnetotactic bacteria, revealing strong transfers of elements with active influx or efflux processes that translate into elemental accumulation (Mo, Se, and Sn) or depletion (Sr and Bi) in the bacterial internal medium of up to seven orders of magnitude relative to the extracellular medium. Using this concept, we show that chemical conditions in magnetosomes are compatible with a pH of 7.5-9.5 and a redox potential of -0.25 to -0.6 V.

Interconversion between [2Fe-2S] and [4Fe-4S] cluster glutathione complexes

We present here how different iron-sulfide-glutathione ratios, applied in in vitro conditions comparable to those present in the mitochondrial matrix, affect the speciation of iron-sulfur cluster glutathione complexes. An excess of sulfide with respect to iron ions promotes the formation of a tetranuclear [Fe^II₂Fe^III₂S₄(GS)₄]^2- complex, while an excess of iron ions favors the formation of a dinuclear [Fe^IIFe^IIIS₂(GS)₄]^3- complex. These two complexes establish an interconversion equilibrium. The latter might play a role in the composition of the mitochondrial labile iron pool potentially contributing to the regulation of cellular iron homeostasis.

Iron Overload, Oxidative Stress, and Ferroptosis in the Failing Heart and Liver

Iron accumulation is a key mediator of several cytotoxic mechanisms leading to the impairment of redox homeostasis and cellular death. Iron overload is often associated with haematological diseases which require regular blood transfusion/phlebotomy, and it represents a common complication in thalassaemic patients. Major damages predominantly occur in the liver and the heart, leading to a specific form of cell death recently named ferroptosis. Different from apoptosis, necrosis, and autophagy, ferroptosis is strictly dependent on iron and reactive oxygen species, with a dysregulation of mitochondrial structure/function. Susceptibility to ferroptosis is dependent on intracellular antioxidant capacity and varies according to the different cell types. Chemotherapy-induced cardiotoxicity has been proven to be mediated predominantly by iron accumulation and ferroptosis, whereas there is evidence about the role of ferritin in protecting cardiomyocytes from ferroptosis and consequent heart failure. Another paradigmatic organ for transfusion-associated complication due to iron overload is the liver, in which the role of ferroptosis is yet to be elucidated. Some studies report a role of ferroptosis in the initiation of hepatic inflammation processes while others provide evidence about an involvement in several pathologies including immune-related hepatitis and acute liver failure. In this manuscript, we aim to review the literature to address putative common features between the response to ferroptosis in the heart and liver. A better comprehension of (dys)similarities is pivotal for the development of future therapeutic strategies that can be designed to specifically target this type of cell death in an attempt to minimize iron-overload effects in specific organs.

Down the Iron Path: Mitochondrial Iron Homeostasis and Beyond

Cellular iron homeostasis and mitochondrial iron homeostasis are interdependent. Mitochondria must import iron to form iron–sulfur clusters and heme, and to incorporate these cofactors along with iron ions into mitochondrial proteins that support essential functions, including cellular respiration. In turn, mitochondria supply the cell with heme and enable the biogenesis of cytosolic and nuclear proteins containing iron–sulfur clusters. Impairment in cellular or mitochondrial iron homeostasis is deleterious and can result in numerous human diseases. Due to its reactivity, iron is stored and trafficked through the body, intracellularly, and within mitochondria via carefully orchestrated processes. Here, we focus on describing the processes of and components involved in mitochondrial iron trafficking and storage, as well as mitochondrial iron–sulfur cluster biogenesis and heme biosynthesis. Recent findings and the most pressing topics for future research are highlighted.

Mechanisms of Ferroptosis and Application to Head and Neck Squamous Cell Carcinoma Treatments

Many kinds of cancer cells are intrinsically sensitive to ferroptosis, and research interest regarding ferroptosis has been sparked by its significant role in many detrimental diseases. Ferroptosis is a novel type of iron-dependent cell death mediated by accumulation of reactive oxygen species and lipid peroxidation. Furthermore, a large number of small agents can induce ferroptosis in numerous kinds of cancer cells, including prostate cancer, pancreatic cancer, breast cancer, lymphomas, and renal cancer. These insights may help discover novel approaches for cancer therapeutic strategies; however, there is considerable uncertainty regarding ferroptosis in head and neck cancer (HNC). So far, no review of the current studies on this topic has been published. Therefore, we here elaborate the mechanisms of ferroptosis and summarize the latest findings regarding its role in HNC according to current literature. The respective findings shed light on the role of ferroptosis in HNC treatment with a number of important implications for future practice in HNC management, as outlined in this review.

Ferroptosis Is a Potential Novel Diagnostic and Therapeutic Target for Patients With Cardiomyopathy

Cardiomyocyte death is a fundamental progress in cardiomyopathy. However, the mechanism of triggering the death of myocardial cells remains unclear. Ferroptosis, which is the nonapoptotic, iron-dependent, and peroxidation-driven programmed cell death pathway, that is abundant and readily accessible, was not discovered until recently with a pharmacological approach. New researches have demonstrated the close relationship between ferroptosis and the development of many cardiovascular diseases, and several ferroptosis inhibitors, iron chelators, and small antioxidant molecules can relieve myocardial injury by blocking the ferroptosis pathways. Notably, ferroptosis is gradually being considered as an important cell death mechanism in the animal models with multiple cardiomyopathies. In this review, we will discuss the mechanism of ferroptosis and the important role of ferroptosis in cardiomyopathy with a special emphasis on the value of ferroptosis as a potential novel diagnostic and therapeutic target for patients suffering from cardiomyopathy in the future.

The misogyny of iron deficiency

Anaemia is common, particularly in women and the commonest underlying cause, iron deficiency, is often overlooked. Anaemia is associated with increased morbidity and mortality in patients undergoing anaesthesia; however, women are defined as being anaemic at a lower haemoglobin level than men. In this narrative review, we present the history of iron deficiency anaemia and how women's health has often been overlooked. Iron deficiency was first described as 'chlorosis' and a cause of 'hysteria' in women and initial treatment was by iron filings in cold wine. We present data of population screening demonstrating how common iron deficiency is, affecting 12-18% of apparently 'fit and healthy' women, with the most common cause being heavy menstrual bleeding; both conditions being often unrecognised. We describe a range of symptoms reported by women, that vary from fatigue to brain fog, hair loss and eating ice. We also describe experiments exploring the physical impact of iron deficiency, showing that reduced exercise performance is related to iron deficiency independent of haemoglobin concentration, as well as the impact of iron supplementation in women improving oxygen consumption and fitness. Overall, we demonstrate the need to single out women and investigate iron deficiency rather than accept the dogma of normality and differential treatment; this is to say, the need to change the current standard of care for women undergoing anaesthesia.

Development of Iron Sequester Antioxidant Quercetin@ZnO Nanoparticles with Photoprotective Effects on UVA-Irradiated HaCaT Cells

BACKGROUND

Solar ultraviolet radiation A (UVA, 320-400 nm) is a significant risk factor leading to various human skin conditions such as premature aging or photoaging. This condition is enhanced by UVA-mediated iron release from cellular iron proteins affecting huge populations across the globe.

PURPOSE

Quercetin-loaded zinc oxide nanoparticles (quercetin@ZnO NPs) were prepared to examine its cellular iron sequestration ability to prevent the production of reactive oxygen species (ROS) and inflammatory responses in HaCaT cells.

METHODS

Quercetin@ZnO NPs were synthesized through a homogenous precipitation method, and the functional groups were characterized by Fourier transform infrared (FTIR) spectroscopy, whereas scanning electron microscopy (SEM) described the morphologies of NPs. MTT and qRT-PCR assays were used to examine cell viability and the expression levels of various inflammatory cytokines. The cyclic voltammetry (CV) was employed to evaluate the redox potential of quercetin-Fe³⁺/quercetin-Fe²⁺ complexes.

RESULTS

The material characterization results supported the loading of quercetin molecules on ZnO NPs. The CV and redox potential assays gave Fe-binding capability of quercetin at 0.15 mM and 0.3 mM of Fe(NO₃)₃. Cytotoxicity assays using quercetin@ZnO NPs with human HaCaT cells showed no cytotoxic effects and help regain cell viability loss following UVA (150 kJ/m²).

CONCLUSION

Quercetin@ZnO NPs showed that efficient quercetin release action is UV-controlled, and the released quercetin molecules have excellent antioxidant, anti-inflammatory, and iron sequestration potential. Quercetin@ZnO NPs have superior biocompatibility to provide UVA protection and medication at once for antiphotoaging therapeutics.

Mitochondrial iron metabolism and its role in diseases

Iron is one of the most important elements for life, but excess iron is toxic. Intracellularly, mitochondria are the center of iron utilization requiring sufficient amounts to maintain normal physiologic function. Accordingly, disruption of iron homeostasis could seriously impact mitochondrial function leading to impaired energy state and potential disease development. In this review, we discuss mechanisms of iron metabolism including transport, processing, heme synthesis, iron-sulfur cluster biogenesis and storage. We highlight the vital role of mitochondrial iron in pathologic states including neurodegenerative disorders and sideroblastic anemia.

Ferroptosis and Cancer: Mitochondria Meet the "Iron Maiden" Cell Death

Ferroptosis is a new type of oxidative regulated cell death (RCD) driven by iron-dependent lipid peroxidation. As major sites of iron utilization and master regulators of oxidative metabolism, mitochondria are the main source of reactive oxygen species (ROS) and, thus, play a role in this type of RCD. Ferroptosis is, indeed, associated with severe damage in mitochondrial morphology, bioenergetics, and metabolism. Furthermore, dysregulation of mitochondrial metabolism is considered a biochemical feature of neurodegenerative diseases linked to ferroptosis. Whether mitochondrial dysfunction can, per se, initiate ferroptosis and whether mitochondrial function in ferroptosis is context-dependent are still under debate. Cancer cells accumulate high levels of iron and ROS to promote their metabolic activity and growth. Of note, cancer cell metabolic rewiring is often associated with acquired sensitivity to ferroptosis. This strongly suggests that ferroptosis may act as an adaptive response to metabolic imbalance and, thus, may constitute a new promising way to eradicate malignant cells. Here, we review the current literature on the role of mitochondria in ferroptosis, and we discuss opportunities to potentially use mitochondria-mediated ferroptosis as a new strategy for cancer therapy.

The effects of iron overload on mitochondrial function, mitochondrial dynamics, and ferroptosis in cardiomyocytes

Excessive iron accumulation in the heart can lead to iron overload cardiomyopathy (IOC), the leading cause of death in hemochromatosis patients. Current understanding regarding the mechanism by which iron overload causes a deterioration in cardiac performance, mitochondrial dysfunction, and impaired mitochondrial dynamics remains limited. Ferroptosis, a newly identified form of regulated cell death, has recently been revealed influencing the pathophysiological process of IOC. Nevertheless, the direct effect of cardiac iron overload on ferroptotic cell death is incompletely characterized. This review article comprehensively summarizes and discusses the effects of iron overload on cardiac mitochondrial function, cardiac mitochondrial dynamics, ferroptosis of cardiomyocytes, and left ventricular function in in vitro and in vivo reports. This review also provides relevant consistent and controversial information which can facilitate further mechanistic investigation into iron-induced cardiac dysfunction in the clinical setting in the near future.

Deferoxamine Enhanced Mitochondrial Iron Accumulation and Promoted Cell Migration in Triple-Negative MDA-MB-231 Breast Cancer Cells Via a ROS-Dependent Mechanism

In our previous study, Deferoxamine (DFO) increased the iron concentration by upregulating the expression levels of TfR1 and DMT1 and exacerbated the migration of triple-negative breast cancer cells. However, the mechanisms of iron distribution and utilization in triple-negative breast cancer cells with a DFO-induced iron deficiency are still unclear. In this study, triple-negative MDA-MB-231 and estrogen receptor (ER)-positive MCF-7 breast cancer cells were used to investigate the mechanisms of iron distribution and utilization with a DFO-induced iron deficiency. We found that the mitochondrial iron concentration was elevated in MDA-MB-231 cells, while it was decreased in MCF-7 cells after DFO treatment. The cellular and mitochondrial reactive oxygen species (ROS) levels increased in both breast cancer cell types under DFO-induced iron-deficient conditions. However, the increased ROS levels had different effects on the different breast cancer cell types: Cell viability was inhibited and apoptosis was enhanced in MCF-7 cells, but cell viability was maintained and cell migration was promoted in MDA-MB-231 cells through the ROS/NF-κB and ROS/TGF-β signaling pathways. Collectively, this study suggests that under DFO-induced iron-deficient conditions, the increased mitochondrial iron levels in triple-negative MDA-MB-231 breast cancer cells would generate large amounts of ROS to activate the NF-κB and TGF-β signaling pathways to promote cell migration.

The significance, trafficking and determination of labile iron in cytosol, mitochondria and lysosomes

The labile iron pool (LIP) is a pool of chelatable and redox-active iron, not only essential for a wide variety of metabolic process, but also as a catalyst in the Fenton reaction, causing the release of hazardous reactive oxygen species (ROS) with potential for inducing oxidative stress and cell damage. The cellular LIP represents the entirety of every heterogenous sub-pool of iron, not only present in the cytosol, but also in mitochondria, lysosomes and the nucleus, which have all been detected and characterized by various fluorescent methods. Accumulated evidence indicates that alterations in the intracellular LIP can substantially contribute to a variety of injurious processes and initiate pathological development. Herein, we present our understanding of the role of the cellular LIP. To fully review the LIP, firstly, the significance of cellular labile iron in different subcellular compartments is presented. And then, the trafficking processes of cellular labile iron between/in cytosol, mitochondria and lysosomes are discussed in detail. Then, the recent progress in uncovering and assessing the cellular LIP by fluorescent methods have been noted. Overall, this summary may help to comprehensively envision the important physiological and pathological roles of the LIP and shed light on profiling the LIP in a real-time and nondestructive manner with fluorescent methods. Undoubtedly, with the advent and development of iron biology, a better understanding of iron, especially the LIP, may also enhance treatments for iron-related diseases.

A mitochondria-targeted fluorescent probe for selective detection of mitochondrial labile Fe(ii)

Mitochondria are iron-rich organelles that are involved in the process of energy production through the electron-transporting system and heme synthesis. We developed a new mitochondria-targeted fluorescent probe, MtFluNox/Ac-MtFluNox, for Fe(ii) based on N-oxide chemistry, which we recently established as a Fe(ii)-selective fluorogenic switch. The deacetylated form MtFluNox showed a turn-on response towards Fe(ii) with high metal selectivity in cuvette experiments, and an imaging study using its cell-compatible analogue Ac-MtFluNox demonstrated mitochondria-specific fluorescence enhancement in response to Fe(ii) in living cells. Furthermore, the probe was able to detect endogenously accumulated Fe(ii) induced as a result of the inhibition of heme synthesis.

A coumarin-based fluorescent probe for monitoring labile ferrous iron in living systems

Labile Fe2+ has been considered to be a metabolically active and regulatory form of cellular iron. Monitoring the dynamic level of labile Fe2+ in biological systems is vital for evaluating the iron related biological processes and diseases as well as dissecting the exact physiological and pathophysiological functions of the labile Fe2+. Herein, we rationally constructed a coumarin-based fluorescent probe for sensing labile Fe2+ in living systems based on a novel Fe2+ meditated cyclization reaction strategy. The probe showed a highly selective and sensitive response to Fe2+, and the detection limit was determined to be 45 nM. Significantly, the probe displayed fast response to Fe2+, with the sensing reaction completed in 2 min, which is beneficial for real time sensing. The application of the probe for sensing different concentrations of labile Fe2+ in living cells has been conducted. In addition, the basal and endogenous levels of labile Fe2+ in living systems were also successfully monitored.

Iron Regulation: Macrophages in Control

Macrophages are sentinel cells of the innate immune system and have important functions in development, tissue homeostasis, and immunity. These phylogenetically ancient cells also developed a variety of mechanisms to control erythropoiesis and the handling of iron. Red pulp macrophages in the spleen, Kupffer cells in the liver, and central nurse macrophages in the bone marrow ensure a coordinated metabolism of iron to support erythropoiesis. Phagocytosis of senescent red blood cells by macrophages in the spleen and the liver provide a continuous delivery of recycled iron under steady-state conditions and during anemic stress. Central nurse macrophages in the bone marrow utilize this iron and provide a cellular scaffold and niche to promote differentiation of erythroblasts. This review focuses on the role of the distinct macrophage populations that contribute to efficient iron metabolism and highlight important cellular and systemic mechanisms involved in iron-regulating processes.

Mitochondrial Iron in Human Health and Disease

Mitochondria are an iconic distinguishing feature of eukaryotic cells. Mitochondria encompass an active organellar network that fuses, divides, and directs a myriad of vital biological functions, including energy metabolism, cell death regulation, and innate immune signaling in different tissues. Another crucial and often underappreciated function of these dynamic organelles is their central role in the metabolism of the most abundant and biologically versatile transition metals in mammalian cells, iron. In recent years, cellular and animal models of mitochondrial iron dysfunction have provided vital information in identifying new proteins that have elucidated the pathways involved in mitochondrial homeostasis and iron metabolism. Specific signatures of mitochondrial iron dysregulation that are associated with disease pathogenesis and/or progression are becoming increasingly important. Understanding the molecular mechanisms regulating mitochondrial iron pathways will help better define the role of this important metal in mitochondrial function and in human health and disease.

Tuning the Anti(myco)bacterial Activity of 3-Hydroxy-4-pyridinone Chelators through Fluorophores

Controlling the sources of Fe available to pathogens is one of the possible strategies that can be successfully used by novel antibacterial drugs. We focused our interest on the design of chelators to address Mycobacterium avium infections. Taking into account the molecular structure of mycobacterial siderophores and considering that new chelators must be able to compete for Fe(III), we selected ligands of the 3-hydroxy-4-pyridinone class to achieve our purpose. After choosing the type of chelating unit it was also our objective to design chelators that could be monitored inside the cell and for that reason we designed chelators that could be functionalized with fluorophores. We didn’t realize at the time that the incorporation a fluorophore, to allow spectroscopic detection, would be so relevant for the antimycobacterial effect or to determine the affinity of the chelators towards biological membranes. From a biophysical perspective, this is a fascinating illustration of the fact that functionalization of a molecule with a particular label may lead to a change in its membrane permeation properties and result in a dramatic change in biological activity. For that reason we believe it is interesting to give a critical account of our entire work in this area and justify the statement “to label means to change”. New perspectives regarding combined therapeutic approaches and the use of rhodamine B conjugates to target closely related problems such as bacterial resistance and biofilm production are also discussed.

Microbial Siderophore Enterobactin Promotes Mitochondrial Iron Uptake and Development of the Host via Interaction with ATP Synthase

Elucidating the benefits of individual microbiota-derived molecules in host animals is important for understanding the symbiosis between humans and their microbiota. The bacteria-secreted enterobactin (Ent) is an iron scavenging siderophore with presumed negative effects on hosts. However, the high prevalence of Ent-producing commensal bacteria in the human gut raises the intriguing question regarding a potential host mechanism to beneficially use Ent. We discovered an unexpected and striking role of Ent in supporting growth and the labile iron pool in C. elegans. We show that Ent promotes mitochondrial iron uptake and does so, surprisingly, by binding to the ATP synthase α subunit, which acts inside of mitochondria and independently of ATP synthase. We also demonstrated the conservation of this mechanism in mammalian cells. This study reveals a distinct paradigm for the "iron tug of war" between commensal bacteria and their hosts and an important mechanism for mitochondrial iron uptake and homeostasis.

Tryparedoxin peroxidase-deficiency commits trypanosomes to ferroptosis-type cell death

Tryparedoxin peroxidases, distant relatives of glutathione peroxidase 4 in higher eukaryotes, are responsible for the detoxification of lipid-derived hydroperoxides in African trypanosomes. The lethal phenotype of procyclic Trypanosoma brucei that lack the enzymes fulfils all criteria defining a form of regulated cell death termed ferroptosis. Viability of the parasites is preserved by α-tocopherol, ferrostatin-1, liproxstatin-1 and deferoxamine. Without protecting agent, the cells display, primarily mitochondrial, lipid peroxidation, loss of the mitochondrial membrane potential and ATP depletion. Sensors for mitochondrial oxidants and chelatable iron as well as overexpression of a mitochondrial iron-superoxide dismutase attenuate the cell death. Electron microscopy revealed mitochondrial matrix condensation and enlarged cristae. The peroxidase-deficient parasites are subject to lethal iron-induced lipid peroxidation that probably originates at the inner mitochondrial membrane. Taken together, ferroptosis is an ancient cell death program that can occur at individual subcellular membranes and is counterbalanced by evolutionary distant thiol peroxidases.

Plants, animals and fungi all belong to a group of organisms known as eukaryotes. Their cells host a variety of compartments, with each having a specific role. For example, mitochondria are tasked with providing the energy that powers most of the processes that keep the cell alive. Membranes delimit these compartments, as well as the cells themselves.

Iron is an element needed for chemical reactions that are essential for the cell to survive. Yet, the byproducts of these reactions can damage – ‘oxidize’ – the lipid molecules that form the cell’s membranes, including the one around mitochondria. Unless enzymes known as peroxidases come to repair the oxidized lipids, the cell dies in a process called ferroptosis. Scientists know that this death mechanism is programmed into the cells of humans and other complex eukaryotes.

However, Bogacz and Krauth-Siegel wanted to know if ferroptosis also exists in creatures that appeared early in the evolution of eukaryotes, such as the trypanosome Trypanosoma brucei. This single-cell parasite causes sleeping sickness in humans and a disease called nagana in horses and cattle. Before it infects a mammal, T. brucei goes through an ‘insect stage’ where it lives in the tsetse fly; there, it relies on its mitochondrion to produce energy.

Bogacz and Krauth-Siegel now show that if the parasites in the insect stage do not have a specific type of peroxidases, they die within a few hours. In particular, problems in the membranes of the mitochondrion stop the compartment from working properly. These peroxidases-free trypanosomes fare better if they are exposed to molecules that prevent iron from taking part in the reactions that can harm lipids. They also survive more if they are forced to create large amounts of an enzyme that relies on iron to protect the mitochondrion against oxidation. Finally, using drugs that prevent ferroptosis in human cells completely rescues these trypanosomes. Taken together, the results suggest that ferroptosis is an ancient cell death program which exists in T. brucei; and that, in the insect stage of the parasite's life cycle, this process first damages the mitochondrion.

This last finding could be particularly relevant because the role of mitochondria in ferroptosis in mammals is highly debated. Yet, most of the research is done in cells that do not rely on this cellular compartment to get their energy. During their life cycle, trypanosomes are either dependent on their mitochondria, or they can find their energy through other sources: this could make them a good organism in which to dissect the precise mechanisms of ferroptosis.

Fe(II) Ion Release during Endocytotic Uptake of Iron Visualized by a Membrane-Anchoring Fe(II) Fluorescent Probe

Iron is an essential transition metal species for all living organisms and plays various physiologically important roles on the basis of its redox activity; accordingly, the disruption of iron homeostasis triggers oxidative stress and cellular damage. Therefore, cells have developed sophisticated iron-uptake machinery to acquire iron while protecting cells from uncontrolled oxidative damage during the uptake process. To examine the detailed mechanism of iron uptake while controlling the redox status, it is necessary to develop useful methods with redox state selectivity, sensitivity, and organelle specificity to monitor labile iron, which is weakly bound to subcellular ligands. Here, we report the development of Mem-RhoNox to monitor local Fe(II) at the surface of the plasma membrane of living cells. The redox state-selective fluorescence response of the probe relies on our recently developed N-oxide strategy, which is applicable to fluorophores with dialkylarylamine in their π-conjugation systems. Mem-RhoNox consists of the N-oxygenated rhodamine scaffold, which has two arms, both of which are tethered with palmitoyl groups as membrane-anchoring domains. In an aqueous buffer, Ac-RhoNox, a model compound of Mem-RhoNox, shows a fluorescence turn-on response to the Fe(II) redox state-selectively. An imaging study with Mem-RhoNox and its derivatives reveals that labile Fe(II) is transiently generated during the major iron-uptake pathways: endocytotic uptake and direct transport. Furthermore, Mem-RhoNox is capable of monitoring endosomal Fe(II) in primary cultured neurons during endocytotic uptake. This report is the first example that identifies the generation of Fe(II) over the course of cellular iron-uptake processes.

Is There Still Any Role for Oxidative Stress in Mitochondrial DNA-Dependent Aging?

Recent deep sequencing data has provided compelling evidence that the spectrum of somatic point mutations in mitochondrial DNA (mtDNA) in aging tissues lacks G > T transversion mutations. This fact cannot, however, be used as an argument for the missing contribution of reactive oxygen species (ROS) to mitochondria-related aging because it is probably caused by the nucleotide selectivity of mitochondrial DNA polymerase γ (POLG). In contrast to point mutations, the age-dependent accumulation of mitochondrial DNA deletions is, in light of recent experimental data, still explainable by the segregation of mutant molecules generated by the direct mutagenic effects of ROS (in particular, of HO· radicals formed from H₂O₂ by a Fenton reaction). The source of ROS remains controversial, because the mitochondrial contribution to tissue ROS production is probably lower than previously thought. Importantly, in the discussion about the potential role of oxidative stress in mitochondria-dependent aging, ROS generated by inflammation-linked processes and the distribution of free iron also require careful consideration.

Activity-based sensing fluorescent probes for iron in biological systems

Iron is an essential nutrient for life, and its capacity to cycle between different oxidation states is required for processes spanning oxygen transport and respiration to nucleotide synthesis and epigenetic regulation. However, this same redox ability also makes iron, if not regulated properly, a potentially dangerous toxin that can trigger oxidative stress and damage. New methods that enable monitoring of iron in living biological systems, particularly in labile Fe²⁺ forms, can help identify its contributions to physiology, aging, and disease. In this review, we summarize recent developments in activity-based sensing (ABS) probes for fluorescence Fe²⁺ detection.

Mitochondrial ATP-Mg/phosphate carriers transport divalent inorganic cations in complex with ATP

The ATP-Mg/phosphate carriers (APCs) modulate the intramitochondrial adenine nucleotide pool size. In this study the concentration-dependent effects of Mg²⁺ and other divalent cations (Me²⁺) on the transport of [³H]ATP in liposomes reconstituted with purified human and Arabidopsis APCs (hAPCs and AtAPCs, respectively, including some lacking their N-terminal domains) have been investigated. The transport of Me²⁺ mediated by these proteins was also measured. In the presence of a low external concentration of [³H]ATP (12 μM) and increasing concentrations of Me²⁺, Mg²⁺ stimulated the activity (measured as initial transport rate of [³H]ATP) of hAPCs and decreased that of AtAPCs; Fe²⁺ and Zn²⁺ stimulated markedly hAPCs and moderately AtAPCs; Ca²⁺ and Mn²⁺ markedly AtAPCs and moderately hAPCs; and Cu²⁺ decreased the activity of both hAPCs and AtAPCs. All the Me²⁺-dependent effects correlated well with the amount of ATP-Me complex present. The transport of [¹⁴C]AMP, which has a much lower ability of complexation than ATP, was not affected by the presence of the Me²⁺ tested, except Cu²⁺. Furthermore, the transport of [³H]ATP catalyzed by the ATP/ADP carrier, which is known to transport only free ATP and ADP, was inhibited by all the Me²⁺ tested in an inverse relationship with the formation of the ATP-Me complex. Finally, direct measurements of Mg²⁺, Mn²⁺, Fe²⁺, Zn²⁺ and Cu²⁺ showed that they are cotransported with ATP by both hAPCs and AtAPCs. It is likely that in vivo APCs transport free ATP and ATP-Mg complex to different degrees, and probably trace amounts of other Me²⁺ in complex with ATP.

The Suf Iron-Sulfur Cluster Biosynthetic System Is Essential in Staphylococcus aureus, and Decreased Suf Function Results in Global Metabolic Defects and Reduced Survival in Human Neutrophils

Staphylococcus aureus remains a causative agent for morbidity and mortality worldwide. This is in part a result of antimicrobial resistance, highlighting the need to uncover novel antibiotic targets and to discover new therapeutic agents. In the present study, we explored the possibility that iron-sulfur (Fe-S) cluster synthesis is a viable antimicrobial target. RNA interference studies established that Suf (sulfur mobilization)-dependent Fe-S cluster synthesis is essential in S. aureus We found that sufCDSUB were cotranscribed and that suf transcription was positively influenced by sigma factor B. We characterized an S. aureus strain that contained a transposon inserted in the intergenic space between sufC and sufD (sufD*), resulting in decreased transcription of sufSUB Consistent with the transcriptional data, the sufD* strain had multiple phenotypes associated with impaired Fe-S protein maturation. They included decreased activities of Fe-S cluster-dependent enzymes, decreased growth in media lacking metabolites that require Fe-S proteins for synthesis, and decreased flux through the tricarboxylic acid (TCA) cycle. Decreased Fe-S cluster synthesis resulted in sensitivity to reactive oxygen and reactive nitrogen species, as well as increased DNA damage and impaired DNA repair. The sufD* strain also exhibited perturbed intracellular nonchelated Fe pools. Importantly, the sufD* strain did not exhibit altered exoprotein production or altered biofilm formation, but it was attenuated for survival upon challenge by human polymorphonuclear leukocytes. The results presented are consistent with the hypothesis that Fe-S cluster synthesis is a viable target for antimicrobial development.

Iron chelators inhibit the heme-degradation reaction by HutZ from Vibrio cholerae

The heme-degradation reaction by HutZ fromVibrio choleraeis inhibited by the iron chelators.

Mitochondria and Iron: current questions

INTRODUCTION

Mitochondria are cellular organelles that perform numerous bioenergetic, biosynthetic, and regulatory functions and play a central role in iron metabolism. Extracellular iron is taken up by cells and transported to the mitochondria, where it is utilized for synthesis of cofactors essential to the function of enzymes involved in oxidation-reduction reactions, DNA synthesis and repair, and a variety of other cellular processes. Areas covered: This article reviews the trafficking of iron to the mitochondria and normal mitochondrial iron metabolism, including heme synthesis and iron-sulfur cluster biogenesis. Much of our understanding of mitochondrial iron metabolism has been revealed by pathologies that disrupt normal iron metabolism. These conditions affect not only iron metabolism but mitochondrial function and systemic health. Therefore, this article also discusses these pathologies, including conditions of systemic and mitochondrial iron dysregulation as well as cancer. Literature covering these areas was identified via PubMed searches using keywords: Iron, mitochondria, Heme Synthesis, Iron-sulfur Cluster, and Cancer. References cited by publications retrieved using this search strategy were also consulted. Expert commentary: While much has been learned about mitochondrial and its iron, key questions remain. Developing a better understanding of mitochondrial iron and its regulation will be paramount in developing therapies for syndromes that affect mitochondrial iron.

Chemical tools for detecting Fe ions

Owing to its distinctive electrochemical properties with interconvertible multiple oxidation states, iron plays a significant role in various physiologically important functions such as respiration, oxygen transport, energy production, and enzymatic reactions. This redox activity can also potentially produce cellular damage and death, and numerous diseases are related to iron overload resulting from the dysfunction of the iron regulatory system. In this case, “free iron” or “labile iron,” which refers to iron ion weakly bound or not bound to proteins, causes aberrant production of reactive oxygen species. With the aim of elucidating the variation of labile iron involved in pathological processes, some chemical tools that can qualitatively and/or quantitatively monitor iron have been utilized to investigate the distribution, accumulation, and flux of biological iron species. Since iron ions show unique reactivity depending on its redox state, i.e., Fe²⁺ or Fe³⁺ (or transiently higher oxidative states), methods for the separate detection of iron species with different redox states are preferred to understand its physiological and pathological roles more in detail. The scope of this review article covers from classical chromogenic to newly emerging chemical tools for the detection of Fe ions. In particular, chemical tools applicable to biological studies will be presented.

Endosome-mitochondria interactions are modulated by iron release from transferrin

Using superresolution and quantitative fluorescence microscopy, Das et al. have revealed that iron-transferrin–containing endosomes directly interact with mitochondria, facilitating iron transfer in epithelial cells. Their findings further enrich the repertoire of organelle–organelle direct interactions to accomplish a functional significance.

Transient “kiss and run” interactions between endosomes containing iron-bound transferrin (Tf) and mitochondria have been shown to facilitate direct iron transfer in erythroid cells. In this study, we used superresolution three-dimensional (3D) direct stochastic optical reconstruction microscopy to show that Tf-containing endosomes directly interact with mitochondria in epithelial cells. We used live-cell time-lapse fluorescence microscopy, followed by 3D rendering, object tracking, and a distance transformation algorithm, to track Tf-endosomes and characterize the dynamics of their interactions with mitochondria. Quenching of iron sensor RDA-labeled mitochondria confirmed functional iron transfer by an interacting Tf-endosome. The motility of Tf-endosomes is significantly reduced upon interaction with mitochondria. To further assess the functional role of iron in the ability of Tf-endosomes to interact with mitochondria, we blocked endosomal iron release by using a Tf K206E/K534A mutant. Blocking intraendosomal iron release led to significantly increased motility of Tf-endosomes and increased duration of endosome–mitochondria interactions. Thus, intraendosomal iron regulates the kinetics of the interactions between Tf-containing endosomes and mitochondria in epithelial cells.