Iron metabolism and ferroptosis in human health and disease

Abstract

Iron is indispensable to most lifeforms, underpinning a myriad of physiological processes. Dysregulation of iron homeostasis underlies a broad spectrum of biological phenomena and pathological conditions. Notably, excessive iron overload acts as a key driver of ferroptosis, a unique form of regulated cell death. Consequently, through the lens of ferrology, targeted modulation of iron balance and ferroptosis has emerged as a compelling avenue for the prevention and treatment of major diseases. Herein, we review the molecular mechanisms governing iron homeostasis, the roles of iron metabolism disorders and ferroptosis in disease pathogenesis, and the latest breakthroughs in iron-regulated therapeutic agents.

Ferrology and the biological roles of iron

Iron is the most abundant element by mass on Earth, and is vital for a multitude of life forms, including microorganisms, plants, animals, and humans [1, 2]. During the early stages of evolution, iron has emerged as the preferred centre for enzymatic reactions and energy acquisition, which is likely attributable to its abundance and diverse valence states. Iron plays a critical role in redox reactions and mediates oxidative stress, which is considered a driving force in evolution [3]. Iron ions in different oxidation states (such as Fe²⁺ and Fe³⁺) are active components of many key proteins and enzymes. For example, haemoglobin and myoglobin bind oxygen in the form of Fe²+, while catalase and peroxidase utilise Fe³⁺ in redox reactions. These iron-containing proteins participate in numerous biological processes, including metabolism, biocatalysis, electron transport within the respiratory chain, oxygen transport, energy maintenance, and immune regulation [4–7].

Dysregulation of iron levels, whether elevated or diminished, can result in cellular and tissue damage, leading to various pathological conditions. Notably, ferroptosis, a unique form of programmed cell death associated with aberrant iron metabolism, is first reported in 2012 [8]. Disorders related to ferroptosis and iron metabolism are implicated in numerous human diseases, such as iron deficiency anaemia, haemochromatosis, cardiovascular and cerebrovascular diseases, various metabolic disorders, and many forms of cancer [9]. Consequently, the targeted regulation of iron ion homeostasis has emerged as an effective strategy for the prevention and treatment of numerous major diseases, with new clinical pharmacological agents being widely implemented [7].

We have proposed the term ‘ferrology’ to represent a novel interdisciplinary research domain focused on the element iron, which encompasses the examination of iron ions across various levels, from ‘molecule-cell-individual-population’ to the investigation of both individual and collective patterns throughout ‘the entire life cycle, multidimensional aspects, and interspecies interactions’ [10]. In this review, we first describe the molecular mechanisms governing iron homeostasis at the levels of systemic and cellular metabolism. We then review recent advancements in understanding the mechanisms underlying ferroptosis and imbalances in iron homeostasis in human diseases. Finally, we highlight the latest research developments concerning iron-regulated therapeutic agents and rational treatment strategies aimed at targeting ferroptosis.

The regulation of iron homeostasis

Iron homeostasis within the human body is regulated by a multifaceted system that encompasses absorption, transport, storage, utilisation, and excretion [11]. The regulation of iron homeostasis is tightly controlled at both the systemic (Fig. 1A) and the cellular level (Fig. 1B).

Fig. 1.

Circulating and cellular iron metabolism. A Circulating iron metabolism pathways. Dietary iron is primarily absorbed in the duodenum, with a significant portion of heme iron being recycled by macrophages. Excess iron is stored as a reserve in both the liver and macrophages. B Cellular iron metabolism pathways. Cells utilise various mechanisms for the uptake of different forms of iron. Non-heme iron can enter the cell in two distinct forms: transferrin-bound iron (TBI) and non-transferrin-bound iron (NTBI). The ferrous iron that enters the cytoplasm contributes to the LIP and is utilised in various biological processes, such as heme biosynthesis, or stored in ferritin. Iron stored in ferritin can be released back into the LIP through NCOA4-mediated autophagy, while FPN facilitates the excretion of iron from the LIP into the extracellular space. An increase in hepcidin secretion from the liver inhibits FPN, thereby reducing the release of iron from cells. LCN2, Lipocalin 2; SLC22A17, solute carrier family 22 member 17; TF, transferrin; TFR1, transferrin receptor protein 1; Cp, Ceruloplasmin; Heph, hephaestin; DCYTB, duodenal cytochrome b; SLC39A14, solute carrier family 39 member 14; DMT1, divalent metal transporter 1; HCP1, heme carrier protein 1; HO-1, heme oxygenase 1; STEAP3, six-transmembrane epithelial antigen of prostate 3; TRPLM, transient receptor potential mucolipin; LIP, labile iron pool; NCOA4, nuclear receptor coactivator 4; FPN, ferroportin; MFRN1, also known as SLC25A37; MFRN2, also known as SLC25A28; RNF217, E3 ubiquitin ligase; FLVCR1, feline leukaemia virus subgroup C receptor 1

Circulating iron metabolism

The significance of iron in biological systems is underscored by the existence of multiple pathways for cellular iron uptake in living organisms to facilitate the absorption of the various forms of iron. Humans cannot synthesize iron, and it must therefore be obtained from the diet. Dietary iron occurs in two forms: heme iron (Fe²⁺), which is found in animal products, like meat and seafood, and non-heme iron (Fe³⁺), which is found in plant foods, fortified foods, and animal products. The absorption mechanisms of heme iron and non-heme iron are not the same. Haemoglobin-bound iron is transported into the intestinal epithelial cells by heme carrier protein 1 (HCP1) that is localised to the intestinal mucosal epithelium. Under the action of haem oxygenase, the porphyrin ring of haemoglobin is opened, releasing Fe²⁺ [12]. In contrast, non-heme iron is found predominantly in an insoluble form as Fe³⁺. Firstly, it needs to be reduced to Fe²⁺ by gastric acid or the action of cytochrome b heme reductase 1 (duodenal cytochrome b, DCYTB), before it can be transported into the small intestinal villus cells by divalent cation transporter 1 (DMT1). The absorbed Fe²⁺ can be stored in cells in the form of ferritin or transported out of the cells by the action of iron exporter, ferroportin (FPN). Transferrin (Tf) in the blood is responsible for the transportation of iron and only binds Fe³⁺ with high affinity. Therefore, after Fe²⁺ is excreted, it is oxidized to Fe³⁺ by iron transport auxiliary proteins on the basolateral membrane or by ceruloplasmin, after which the generated pools of Fe³⁺ bind with Tf to enter the plasma, forming serum iron, or they are transferred to cells that require iron.

Most of the iron in the body is stored in the liver as ferritin (e.g., in hepatocytes or in Kupffer cells), with a small portion stored in the spleen (in macrophages), the intestines (via short-term storage in intestinal cells), and in the bone marrow; in all cases, the stored iron is released when needed [13]. The total amount of iron is 45 mg/kg in healthy men and 30 mg/kg in women [14]. Tf serves as a crucial iron transporter, responsible for the binding and transportation of free iron within the circulatory system. The transferrin receptor (TfR) functions as the primary receptor for cellular iron uptake, binding to iron-containing ligands to form Tf-Fe complexes, thereby initiating the process of iron uptake [15]. A significant portion of the absorbed iron is utilised by erythrocytes for the binding and transport of oxygen throughout the body. Approximately 20 mg/day of iron is recovered from haemoglobin following the phagocytosis of senescent erythrocytes by reticuloendothelial macrophages [16, 17]. FPN is an important protein that controls iron levels, releases free iron into the bloodstream, and is the only known cellular iron export protein. FPN activity is controlled by another protein produced in the liver called hepcidin, which reduces iron translocation by degrading FPN in the basement membranes of duodenocytes, macrophages, and hepatocytes, thereby lowering serum iron levels [18]. Hepcidin levels are mainly regulated by the bone morphogenetic protein (BMP)/Smad (small mothers against decapentaplegic) pathway and the interleukin 6 (IL-6)-signal transducer and activator of transcription 3 (STAT3) pathway [19]. The body lacks active iron excretion pathways, with only a small amount of iron excreted through gastrointestinal cells and the bile [20, 21]. Therefore, control of uptake through the hepcidin-FPN pathway is essential for the proper maintenance of iron homeostasis in the plasma [22].

Cellular iron metabolism

The maintenance of cellular iron homeostasis is achieved through the coordinated regulatory expression of ferritin and other proteins, including Tf. Cells possess TfRs that mediate iron metabolism. Iron is imported via endocytosis of Fe³⁺-loaded Tf, or via DMT1 for non-transferrin-bound iron (NTBI), and the zinc transporter protein, SLC39A14, and stored in the labile iron pool (LIP) or as ferritin [23]. Other transporters that are engaged in cellular heme transport include HCP1 and feline leukaemia virus group C cellular receptor 1 (FLVCR1). Tf interacts with its receptors (TfR1 and TfR2) to establish a tightly regulated feedback control mechanism. Iron regulatory proteins 1 and 2 (IRP1 and IRP2) monitor cytoplasmic iron concentrations and post-transcriptionally regulate the expression of genes involved in iron metabolism [24, 25]. The LIP enhances intracellular iron flux through the interactions of IRPs with iron-responsive elements (IREs) in the promoter of iron metabolism-related genes, thereby upregulating the transcription and ultimately the protein expression of iron-absorbing proteins, such as ferritin, TfR1, FPN, and DMT1. Specifically, when intracellular iron levels are low, IRPs bind to IREs, leading to an increase in TfR expression to elevate iron content while simultaneously inhibiting ferritin synthesis to reduce storage. Conversely, in response to elevated iron levels, IRPs lose their capacity to bind IREs, resulting in decreased iron uptake and increased iron storage.

Nuclear receptor coactivator 4 (NCOA4) functions as a cytoplasmic autophagy receptor that binds to ferritin, facilitating its degradation through ferritinophagy. This selective form of autophagy releases stored iron, which can then be utilised in biosynthetic pathways. Lipocalin 2 (LCN2), also known as neutrophil gelatinase-associated lipocalin (NGAL), is another iron-binding protein that can bind iron-containing complexes (such as catechol-iron complexes) and mediate iron endocytosis through interaction with SLC22A17 (an LCN2 transporter). Fe³⁺ is released from LCN2 and may be reduced to Fe²⁺ and transported to the cytoplasm, enabling efficient iron recycling by the cell. This high-affinity system operates independently of the transferrin pathway and plays a crucial role in iron recycling and under pathological conditions (such as inflammation and tumours) [26]. Mitochondrial ferritin (MTFN1) facilitates the import of cytoplasmic iron into the mitochondria for haemoglobin production, iron-sulfur cluster biosynthesis, or storage in mitochondrial ferritin (MtFt) [27]. Within the nucleus, iron serves as a critical component or factor for enzymes and factors involved in DNA repair, synthesis, and transcription [28].

Regulation of ferroptosis

Ferroptosis represents a distinct form of programmed cell death that diverges significantly from other established forms of cell death, including apoptosis, autophagy, and necrosis. The occurrence of ferroptosis is contingent upon the accumulation of intracellular iron and the process of lipid peroxidation. This form of cell death is modulated by a complex network of metabolic signalling pathways, with the primary metabolic pathways being those associated with iron-dependent and oxidation reactions, antioxidant systems, and lipid peroxidation (Fig. 2).

Fig. 2.

Molecular mechanisms of ferroptosis. The primary metabolic pathways involved in iron-induced ferroptosis encompass iron metabolism, amino acid metabolism, and lipid peroxidation metabolism. In the context of iron metabolism, processes such as ferritinophagy and the import/export of iron can initiate lipid peroxidation and ferroptosis through the Fenton reaction or Fenton-like reactions. Mitochondrial metabolism is integral to the process of ferroptosis. Amino acid metabolic pathways primarily involve cyst(e)ine/GSH/GPX4 axis and NAD(P)H/FSP1/CoQ₁₀ axis. Catabolism of glutamine, reduced availability of cysteine, and elevated extracellular concentrations of glutamate all influence the synthesis of glutathione, which ultimately initiates ferroptosis through a series of biochemical reactions. Within the NAD(P)H/FSP1/CoQ₁₀ system, the protective effect against ferroptosis conferred by FSP1 is attributed to its oxidoreductase activity, which facilitates the reduction of extra-mitochondrial CoQ₁₀ to its reduced form, CoQ₁₀H₂, utilising NAD(P)H as a cofactor. In the context of lipid peroxidative metabolism, free PUFA, such as AA or AdA, are metabolised by ACSL4-ACSL1, followed by the action of LPCAT3. This metabolic pathway is subsequently mediated by PEBP1, cytochrome POR, and ALOXs, thereby facilitating lipid peroxidation and the induction of ferroptosis. TFR1, transferrin receptor protein 1; STEAP3, six-transmembrane epithelial antigen of prostate 3; DMT1, divalent metal transporter 1; NRF2, nuclear factor erythroid 2-related factor 2; SLC25A28, also known as MFRN2, mitoferrin 2; CISD, CDGSH iron sulfur domain; ISCU, iron-sulfur cluster assembly; NFS1, cysteine desulfurase; NCOA4, nuclear receptor coactivator 4; HO-1, heme oxygenase 1; LIP, labile iron pool; GSH, glutathione; GSR, glutathione-disulfide reductase; GPX4, glutathione peroxidase 4; GSSG, glutathione disulfide; GTP, guanosine triphosphate; GCH1, GTP cyclohydrolase-1; GH₄, tetrahydrobiopterin; CoQ₁₀, coenzyme Q₁₀; CoQ₁₀H₂, ubiquinol; FSP1, ferroptosis suppressor protein-1; PUFAs, polyunsaturated fatty acids; AA, arachidonic acid; AdA, adrenic acid; ACSL, acyl-CoA synthetase long-chain family; LPCAT3, lysophosphatidylcholine acyltransferase 3; POR, P450 oxidoreductase; PEBP1, Phosphatidylethanolamine Binding Protein 1; ROS, reactive oxygen species; NAD(P)H, quinone oxidoreductase; ALOXs, arachidonate lipoxygenases

Iron-dependent and oxidation reaction

The initiation of ferroptosis requires an oxidative environment and is promoted by reactive oxygen species (ROS) from multiple sources. ROS is a general term for a class of chemically active molecules and ions with high oxidative activity, including superoxide anions (${\text{O}}_2^{·}$⁻), hydrogen peroxide (H₂O₂), lipid hydroperoxides (LOOH), hydroxyl radicals (HO·), and lipid alkoxyl radicals (LOR). Excessive Fe²⁺ in the LIP increases the production of ROS. Fe²⁺ acts as a catalyst, reducing H₂O₂ to ·OH and OH^-, and itself is oxidised to Fe³⁺. This reaction is called the Fenton reaction. When the LIP expands, the Fenton reaction, which triggers lipid peroxidation, makes cells more susceptible to ferroptosis [29, 30]. One important source of LIP expansion is the selective autophagic degradation of ferritin, which leads to the accumulation of iron in the cytoplasm in the form of Fe²⁺. NCOA4-mediated ferritinophagy has been shown to trigger ferroptosis by degrading ferritin and inducing iron overload [31]. Tf enhances cellular resistance to ferroptosis by regulating iron uptake, inhibiting ROS production, and reducing lipid peroxidation. On the other hand, when O₂-and H₂O₂ are present in the cytosol, Fe³⁺ can be converted to Fe²⁺, which is also known as the Haber–Weiss reaction and is the driving force of the Fenton reaction. Conversely, some mechanisms that inhibit LIP expansion have been discovered. Certain mitochondrial proteins involved in the biosynthesis of iron-sulfur clusters (ISCs), such as cysteine desulfurase NFS1, ISC proteins, CISD1, and CISD2, have been shown to negatively regulate ferroptosis by reducing the availability of Fe²⁺ [32–35]. For example, the protein products of the CISD1 and CISD2 genes, MitoNEET and NAF-1, respectively, act together to transport ISCs into mitochondria. Low expression levels of CISD1 and CISD2 limit the Fe³⁺ content in mitochondria, thereby inhibiting ferroptosis. Regulating the LIP can determine the fate of cells, and ferroptosis is iron-dependent.

In addition, mitochondria also produce a large amount of ROS during normal metabolism and the generation of cellular energy via the electron transport chain, leading to cell and tissue damage [36]. Fenton-like reactions involving other transition metals (such as Cu²⁺, Co²⁺, and Mn²⁺) can also catalyse similar reactions, including the production of OH^- and ⋅OH, thus promoting lipid peroxidation [37].

Antioxidant systems

The antioxidant system is an important barrier that intercepts ROS in biological processes and protects cells from ferroptosis. The glutathione peroxidase 4 (GPX4)-glutathione (GSH) system is considered one of the classic antioxidant systems against ferroptosis [38, 39]. GPX4 is an enzyme that can directly reduce LOOH to harmless lipid alcohol (LOH), which can inhibit the accumulation of lipid ROS. The antioxidant effect of GPX4 depends on the presence of GSH as a reducing agent, with two GSH reducing one LOOH. When GSH is depleted and GPX4 is inactivated, cells are unable to repair lipid peroxidation damage, and ferroptosis occurs. Therefore, the pathway regulating GPX4–GSH has become a regulator of ferroptosis. Firstly, the Xc⁻ system (solute carrier family 7 member 11 and family 3 member 2 (SLC7A11 and SLC3A2)) is responsible for taking up cystine to generate the substrate cysteine for the synthesis of GSH and is also involved in the formation of the GPX4 catalytic unit. Erastin, the first ferroptosis inducer discovered, targets SLC7A11, leading to GSH depletion and subsequent GPX4 inactivation, leading to ferroptosis [8]. Genetic depletion of Slc7a11 or Gpx4 in mouse embryonic fibroblasts leads to ferroptosis [40, 41]. In vivo, conditional deletion of Slc7a11 or Gpx4 in mice also leads to ferroptosis-like damage [42].

It should be noted that in certain cell types or cell lines, inhibition of GPX4 fails to induce ferroptosis, suggesting the existence of alternative mechanisms. Ferroptosis suppressing protein 1 (FSP1) protects cells from ferroptosis by acting as a redox enzyme that consumes NADH/NADPH to reduce coenzyme Q₁₀ (CoQ₁₀). It generates lipophilic radical trapping antioxidants (RTAs) to prevent the accumulation of lipid peroxides [43], while also indirectly regenerating another antioxidant, α-tocopherol, to capture free radicals and inhibit ferroptosis [44–46]. The FSP1-CoQ10-NAD(P)H pathway functions as an independent parallel system, synergising with GPX4 and GSH to inhibit lipid peroxidation and ferroptosis [44]. If this system is disrupted, such as by selective small-molecule inhibitors, like iFSP1, or by gene deletion, the loss of FSP1 function promotes ferroptosis. FSP1 can also effectively inhibit ferroptosis through the non-classical vitamin K oxidation–reduction cycle. Researchers have found that FSP1 can reduce vitamin K to VKH₂, which acts as an antioxidant to capture free radicals and inhibit lipid peroxidation [47]. Therefore, FSP1 is considered another major ferroptosis regulatory molecule besides GPX4, playing a crucial role in inhibiting ferroptosis.

Additionally, the GTP-cyclohydrolase 1 (GCH1)-antioxidant tetrahydrobiopterin (BH₄) pathway is a key GPX4-independent system that regulates ferroptosis [48]. The mechanism by which this pathway inhibits lipid peroxidation may be based on the direct antioxidant function of BH₄, selectively preventing the oxidation of phospholipids containing two unsaturated acyl chains [48]. BH₄ is synthesized from its precursor GTP, with GCH1 acting as the rate-limiting enzyme. The expression level of GCH1 largely determines the cell’s resistance to ferroptosis. Genetic or pharmacological inhibition of GCH1 leads to BH₄ deficiency, thereby promoting cellular progression toward peroxide accumulation and ferroptosis [49]. Conversely, overexpression of GCH1 selectively enhances BH₄ biosynthesis and reduces ROS production [50]. Additionally, BH₄ may prevent CoQ₁₀ depletion by alleviating oxidative stress and by promoting its synthesis by converting phenylalanine into tyrosine, which can further be converted into a CoQ₁₀ precursor (4HB), thereby reducing lipid peroxidation levels via CoQ₁₀. These mechanisms link the GCH1–BH₄ axis with the FSP1–CoQ₁₀ axis, thereby coordinating and precisely regulating ferroptosis.

Lipid peroxidation

Lipid peroxidation refers to the process by which various types of free radicals, such as oxygen free radicals, peroxy free radicals, and hydroxyl free radicals, abstract electrons from lipids, producing reactive intermediates capable of further reactions, thereby initiating a lipid peroxidation chain reaction. Lipid peroxides and peroxy radicals derived from polyunsaturated fatty acid chains are one of the executors of cellular ferroptosis [51]. Due to the high solubility of molecular oxygen, the generation of free radicals in biological membranes is extremely robust. Furthermore, membrane phospholipids bound to polyunsaturated fatty acids (PUFAs) are highly sensitive to free radical damage, leading to the accumulation of lipid peroxides (such as LOOH) [52]. The substrates for peroxidation reactions during ferroptosis are phospholipids with polyunsaturated fatty acid tails (PL-PUFAs), as they inherently possess intrinsic susceptibility to peroxidation reactions. In particular, phosphatidylethanolamine (PE)-containing arachidonic acid (AA) or adrenergic acid (AdA) have been identified as the primary substrate for oxidation in ferroptosis [51]. These PL-PUFAs are generated by enzymes, such as ACSL4 and LPCATs, which activate and incorporate free PUFAs into phospholipids. Once PL-PUFAs are incorporated into the membrane environment, iron-dependent enzymes and free iron utilise molecular oxygen (O₂) to catalyse peroxidation reactions, generating PL-PUFA-OOH. Iron-dependent enzymes known to drive ferroptosis include lipoxygenases (LOX), cyclooxygenases (COX), and cytochrome P450 oxidoreductases (POR) [53–56], all of which catalyse the formation of bioactive LOOH, which regulates cellular signalling. Additionally, the degradation byproducts of lipid peroxides (such as malondialdehyde and 4-hydroxy-2-nonenal) can damage various key biomolecules (including proteins and nucleic acids). This damage can alter the permeability and fluidity of cell membranes, ultimately leading to changes in cellular structure and function, and may trigger cell death [57, 58]. Dixon et al. found that monounsaturated fatty acids (MUFAs) can compete with PUFAs, such as AA, inhibiting the formation of specific lipid peroxides (PE-AA-OOH) [59]. Specifically, MUFAs react with coenzyme A (CoA) under the catalysis of ACSL3 to form the intermediate product MUFA-CoA, which is inserted into the fatty acid chain of phospholipids. This reaction limits the synthesis of PE-AA, reducing the concentration of lipid peroxides and peroxy radicals, thereby conferring resistance to ferroptosis. Generally, MUFAs, such as oleic acid (OA), are synthesised from saturated fatty acids (SFAs) by the rate-limiting enzyme stearoyl-CoA desaturase 1 (SCD1), which is thus the primary determinant of MUFA levels. Lipidomics analysis suggests that OA may competitively compete with AA and AdA for phospholipid uptake, thereby reducing the content of PLs associated with ferroptosis, such as PE or PC containing AA or AdA [60]. Therefore, unlike PUFAs, SCD1 and its products (i.e., MUFAs) have been confirmed to be potent inhibitors of ferroptosis [54, 59].

In summary, the three antioxidant systems Xc⁻-GSH-GPX4, FSP1-CoQ₁₀-NAD(P)H, and GCH1-BH₄ can scavenge lipid peroxides during ferroptosis. In addition to these mechanisms, there are other non-enzymatic antioxidants within cells that can directly interact with free radicals and scavenge them, thereby mitigating harmful lipid peroxidation and preventing ferroptosis. Some relevant examples include vitamins E and C, minerals (such as selenium and zinc), and metabolites (such as bilirubin and melatonin).

Iron homeostasis and ferroptosis in human diseases

Imbalances in iron homeostasis are significantly correlated with the onset and progression of various diseases. Given the critical role of iron in redox reactions, both elevated and diminished levels of iron can lead to tissue and cellular damage (Fig. 3).

Fig. 3.

The impact of iron deficiency, iron overload, and ferroptosis on human. IDA, iron deficiency anaemia; RLS, restless legs syndrome; PD, Parkinson’s disease; AD, Alzheimer’s disease; HH, hereditary haemochromatosis

Iron deficiency and human disease

Iron deficiency significantly impacts oxygen transport, cellular metabolism, growth, and immune function. The aetiology of iron deficiency encompasses both physiological and pathological factors. Physiological iron deficiency is typically linked to increased demand and inadequate absorption, while pathological iron deficiency may arise from iron malabsorption (such as gastric acid insufficiency or mutations in TMPRSS6) or chronic blood loss (due to tumours, gastrointestinal bleeding, or infections), among other causes [61–64]. Chronic inflammation, characterised by elevated levels of hepcidin and diminished iron absorption, also contributes to iron deficiency [19]. Iron deficiency exists on a continuum, ranging from iron depletion without anaemia to impaired erythropoiesis and anaemia [65]. Iron is a critical component of haemoglobin; thus, iron deficiency results in decreased haemoglobin synthesis and a reduced capacity for oxygen transport, ultimately leading to iron deficiency anaemia (IDA). The repercussions of iron deficiency extend beyond the erythrocyte profile, adversely affecting various immune cells. For instance, iron deficiency has been associated with impaired T-cell proliferation, inhibited macrophage differentiation, and diminished natural killer cell activity [66, 67]. Furthermore, iron deficiency disrupts mitochondrial function and its essential role in oxidative metabolism, ATP production (via the tricarboxylic acid cycle), and related enzymatic activities, leading to dysregulated cellular metabolism. Common manifestations of iron deficiency include fatigue, malaise, and lethargy, which reflect a generalised impairment of energy metabolism [68]. Notably, organs with high iron requirements and energy demands, such as the cardiovascular and nervous systems, are particularly affected [69, 70]. Iron deficiency heart failure is characterised by systemic iron depletion and impaired erythropoiesis, alongside disproportionate intracellular iron depletion in skeletal muscle and cardiac myocytes [71]. Iron also serves as a cofactor for tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, and for the dopamine D2 receptor, playing a crucial role in myelin synthesis for dopamine production in the brain [72]. Consequently, iron deficiency or impaired metabolism can lead to damage to nigrostriatal neurons and disruption of the dopamine system, which is a primary pathobiological factor in restless legs syndrome (RLS) [73, 74]. Additionally, iron deficiency in infants has been linked to slow cognitive rhythms and symptoms of attention-deficit-hyperactivity disorder (ADHD) during childhood and adolescence [75].

Iron overload and human disease

The body’s total iron stores may be increased due to several conditions, which collectively are referred to as iron overload disorders. Such elevations in systemic iron can cause damage to various organs, including the liver, pancreas, and heart. Genetic abnormalities or secondary illnesses caused by excessive blood transfusions, dyserythropoietic syndromes, persistent haemolysis, or iron supplementation can cause iron metabolism issues, which can manifest as primary or secondary iron overload conditions. Hereditary haemochromatosis (HH) is a genetic condition where iron levels slowly build up. The majority of HH cases arise from mutations in HFE, which encodes for a protein that regulates intracellular iron levels by both interacting with TfR and hepcidin. However, other forms of HH, known as non-HFE haemochromatosis, also share the trait of having low plasma hepatic phospholipid levels that are out of proportion to the body’s iron levels. Unwanted iron from the diet is absorbed in HH, resulting in iron overload of the liver and other organs [76, 77]. Iron-modulin insufficiency is a consequence of both HFE-associated and non-HFE-associated HH, and it causes splenic macrophages and small intestine cells to discharge more iron into the plasma. Elevated plasma iron levels, in turn, lead to an increase in iron transport into parenchymal cells, particularly hepatocytes, pancreatic cells, and cardiomyocytes, leading to organ iron overload. Frequent blood transfusions, exogenous iron consumption, and specific haematological conditions, such as sickle cell anaemia or thalassaemia, are linked to secondary iron overload. Iron excess is frequently linked to metabolic syndrome, alcoholic liver disease, and chronic hepatitis C virus infection [78]. In certain neurological conditions, iron buildup in particular tissues can also be seen. Friedreich’s ataxia is a common example, where iron synthesis and its incorporation into haemoglobin and the use of Fe-S clusters are hampered by a mitochondrial ataxin deficit [79]. The resulting buildup of iron damages mitochondria, causing the cerebellum, cardiomyocytes, and dorsal root ganglia to malfunction. Furthermore, iron accumulation is even higher in the substantia nigra in Parkinson’s disease (PD) and in anatomical regions affected by β-amyloid plaques and tau protein loading in Alzheimer’s disease (AD) suggesting iron overload as a key factor in the pathogenesis of common neurodegenerative diseases [80, 81].

Ferroptosis and human diseases

The accumulation of excess iron serves as the primary catalyst for ferroptosis, thereby increasing the vulnerability of various cell types to this form of cell death [82]. This process is significant in numerous biological and pathological contexts and is implicated in the onset and progression of a wide array of human diseases. The induction of ferroptosis not only serves to inhibit tumour proliferation but also holds promise for enhancing the efficacy of immunotherapy and addressing resistance to current cancer treatments. Certain organs that are rich in iron and lipids exhibit increased susceptibility to ferroptosis induction during the process of carcinogenesis, particularly in the context of glioblastoma, pancreatic cancer, and triple-negative breast cancer [83–85]. Despite the advancements in immunotherapy, challenges such as the presence of cold tumours and treatment resistance persist. The modulation of iron and lipid metabolic pathways to induce ferroptosis may provide a synergistic effect when combined with immunotherapeutic approaches [86]. In tumours, extracellular traps released by neutrophils (referred to as NETs) can shape the tumour microenvironment into an immunosuppressive context. A peptide-drug conjugate-based transformable iron nanochelator (TIN) has been shown to chelate Fe²⁺ to regulate the iron metabolism of neutrophils, thereby inhibiting NET formation. When TIN is used in combination with anti-PD-L1, it can significantly enhance the efficacy of immunotherapy, raising the tumour inhibition rate to 93.3% [87]. Furthermore, the activation of epithelial-mesenchymal transition (EMT) is recognized as a significant contributor to invasive growth and therapeutic resistance in various malignancies [88]. Cancer cells exhibiting mesenchymal traits are generally more prone to ferroptosis compared to their epithelial counterparts [89, 90].

Ferroptosis is implicated in various non-cancer disease contexts through its influence on iron metabolism and lipid peroxidation. In metabolic disorders, such as metabolic dysfunction-associated steatotic liver disease (MASLD), ferroptosis exacerbates lipid oxidation and contributes to tissue damage [91]. In autoimmune diseases, including systemic lupus erythematosus [92], ferroptosis induces oxidative stress and disrupts immune homeostasis. In hereditary conditions, such as HH, iron overload results in organ dysfunction. In cardiovascular diseases, particularly ischemia–reperfusion injury [93], ferroptosis is associated with the loss of cardiomyocytes and heightened inflammation. In neurodegenerative disorders, such as Parkinson’s disease [94], ferroptosis is a catalyst for neuronal degeneration and cell death. Furthermore, in musculoskeletal diseases, like osteoarthritis, ferroptosis adversely affects chondrocytes, leading to the progression of joint degeneration [95]. These mechanisms elucidate the pathological underpinnings of ferroptosis across a spectrum of diseases and suggest potential therapeutic targets.

Treatment strategies

The management of imbalances in iron homeostasis necessitates the implementation of distinct therapeutic strategies tailored to the underlying aetiology. Most conditions associated with iron deficiency can be effectively addressed by replenishing the body’s iron levels through various supplementation methods. Conversely, disorders characterised by iron overload may be treated using iron chelators or through therapeutic phlebotomy. Furthermore, conditions primarily influenced by ferroptosis can be mitigated by focusing on the regulation of iron homeostasis (utilizing iron chelators), as well as by modulating lipid and amino acid metabolic pathways.

Interventions for the management of dysregulated iron homeostasis

Most anaemias resulting from absolute iron deficiency can be effectively managed through iron supplementation therapy [96, 97]. Both intravenous and oral formulations have been developed for this purpose (Table 1). However, the efficacy of oral iron supplementation is often constrained by the iron regulatory system, which includes the ferromodulin-iron transporter protein, to mitigate the risk of iron overload. Bone morphogenetic protein 6 (BMP6) plays a crucial role in regulating ferromodulin expression, and targeting this pathway presents a promising therapeutic strategy [98]. Petzer et al. have reported that a fully human anti-BMP6 antibody (KY1070), whether administered as monotherapy or in conjunction with Darbepoetin alfa, may enhance the effectiveness of anaemia treatment in chronic disease [99]. Additionally, prolyl hydroxylase domain (PHD) inhibitors, such as the clinical drug Roxadustat (FG-4592), are capable of treating a variety of recalcitrant anaemia—including refractory anaemia, inflammatory anaemias, and chemotherapy-associated anaemias—by activating the HIF-2α axis [100]. Functional iron deficiency is commonly observed in chronic conditions, such as heart failure and chronic kidney disease [63, 101, 102]. Neomorphic oral iron preparations, such as Ferric maltol, have demonstrated improved tolerability and efficacy in patients with inactive inflammatory bowel disease [103, 104]. Furthermore, iron carboxymaltose therapy has been shown to significantly enhance exercise tolerance and quality of life in patients suffering from chronic heart failure [105]. The combination of ferrous sulphate and methylphenidate has proven effective in alleviating symptoms of ADHD in non-anaemic children with low serum ferritin levels [106]. The optimal approach for safe, effective, and precise iron supplementation continues to be a topic of ongoing debate.

Table 1.

Iron formulations

Iron preparation	Pros	Cons
Oral iron
Ferrous sulfate	Inexpensive, widely available	Tendency to cause gastrointestinal side effects, include nausea, vomiting and constipation, and these lead to frequent dose adjustments, change in prescription, non-adherence or treatment discontinuation
Ferrous gluconate
Ferrous fumarate
Ferrous ascorbate
Ferric formulations
IV iron
Iron sucrose (IS)	Hypoallergenic, easy to use, widely available	repeated infusions
Low-molecular-weight iron dextran (LD)	Quickly replenishes iron	Higher allergic reactions
Ferric gluconate	Hypoallergenic, Lower single dose for long-term use	low effect
Ferumoxytol	Hypoallergenic, Quickly replenishes iron	Expensive, may trigger adverse reactions in liver or kidney function
Ferric carboxymaltose (FCM)	Fast and efficient, low side effects and allergic reactions, widely available	High injection volume and monitoring
Iron isomaltoside	High efficiency and long-term stability, low side effects and allergic reactions	Long injection time

The iron metabolism system is characterised by the absence of a mechanism for the active excretion of iron, leading to the necessity of employing iron chelators or bloodletting as treatment options for iron overload-related diseases. In patients with primary hemochromatosis, bloodletting is the predominant therapeutic approach [107]. A variety of iron chelators have received approval for the management of iron overload and the associated organ damage resulting from secondary hemochromatosis. It is noteworthy that supplementation with iron-modulating agents does not effectively reduce hepatic iron stores and is anticipated to garner significant interest as a novel therapeutic strategy for addressing the pathogenesis of hemochromatosis [108, 109]. The novel oral iron chelator CN128 has exhibited superior efficacy and a reduced incidence of adverse effects in the treatment of β-thalassaemia following routine blood transfusions and is currently undergoing phase II clinical trials [110]. Furthermore, targeted interventions, including gene therapy, are being explored in clinical trials. VIT-2736, a targeted inhibitor of FPN, has been developed by Vifor Pharma for the treatment of β-thalassaemia and has recently completed a phase I clinical trial [111]. Additional therapeutic strategies, such as the use of proton pump inhibitors (e.g., esomeprazole) to limit intestinal iron absorption, are also under clinical investigation [112].

Therapeutic strategies for targeting ferroptosis

It has been over a decade since the term ferroptosis was first introduced, and as research has advanced, several clinical drugs and bioactive pharmacological agents have been identified as modulators of ferroptosis, including inhibitors (Table 2) [113–125] and inducers (Table 3) [126–140]. Iron-dependent cell death relies on lipid peroxidation of iron, ultimately leading to programmed cell death. This process can be counteracted through iron chelation, antioxidant effects, and modulation of iron-dependent cell death targets. Iron chelators, such as DFP, DFX, and DFO, have been shown to significantly reduce iron overload and serum iron levels in patients with thalassaemia [113–115]. DXZ is currently used clinically to alleviate cardiac toxicity caused by chemotherapy drugs, such as doxorubicin [116]. By further elucidating the pathogenic mechanism by which hepatic iron accumulation triggers ferroptosis through the c-Myc-Acsl4 regulatory axis, thereby accelerating the progression of metabolic-associated steatohepatitis (MASH), our research team identified a novel iron chelator, FOT1 (FerroTerminator1, formerly known as CN128), through drug screening, which can prevent and treat the onset and progression of MASH disease [117]. Antioxidants that act by scavenging lipid free radicals—including liproxstatin-1, ferrostatin-1, and α-tocopherol (vitamin E)—have been shown to significantly inhibit ferroptosis [118–120]. Many natural compounds possess intrinsic antioxidant activity due to their structural characteristics. For example, puerarin has been approved for use in treating cardiovascular diseases, while kaempferide and kaempferol can scavenge free radicals and thereby inhibit ferroptosis [121, 122]. The mitochondrial-targeted derivative of 2,2,6,6-tetramethylpiperidinooxy (TEMPO), Mito-TEMPO, can scavenge excess free radicals produced by mitochondria and is used as a ferroptosis inhibitor to study the occurrence of ferroptosis in mitochondria [123]. Additionally, ferroptosis can be inhibited by regulating targets such as GPX4 and ACSL4. For example, carvacrol upregulates GPX4 expression to slow the progression of lipid peroxidation, thereby inhibiting ferroptosis and showing potential for treating cerebral ischemia [124]. Thiazolidinedione compounds, clinically used as drugs for treating type 2 diabetes, have been found to selectively inhibit ACSL4, thereby inhibiting ferroptosis [125].

Table 2.

Ferroptosis inhibitors

Compound/drug	Target	Mechanism	Study [ref]
Deferiprone (DFP)	Free iron	Iron chelation	Morales et al., 2022 [113]
Deferasirox (DFX)	Free iron	Iron chelation	Antoine et al., 2016 [114]
Deferoxamine (DFO)	Free iron	Iron chelation	Kontoghiorghe et al., 2016 [115]
Dexrazoxane (DXZ)	Free iron	Cardiac iron chelation	Zhu et al., 2025 [116]
FerroTerminator1 (FOT1)	Inhibition of c-Myc-Acsl4	Suppresses ACSL4 expression to reduce iron accumulation in the liver	Tao et al., 2024 [117]
Liproxstatin-1	Lipid ROS	Blocks ACSL4 and ALOX15	Tong et al., 2023 [118]
Ferrostatin-1	Lipid ROS	Slows the accumulation of lipid hydroperoxides	Zilka et al., 2017 [119]
Vitamin E	LOX	15-lipoxygenase via reduction of the enzyme’s non-heme iron from its active Fe3+ state to an inactive Fe2+ state	Hinman et al., 2018 [120]
Puerarin	GPX4	Upregulates GPX4 expression and decrease intracellular Fe3+ and ROS content	Liu et al., 2018 [121]
Kaempferide/Kaempferol	Antioxidant system	Radical-scavenging, induces antioxidant response element-mediated transcriptional activity	Takashima et al., 2019 [122]
MitoTEMPO	Mitochondria	Scavenging of lipid peroxidation specifically in the mitochondria	Fang et al., 2019 [123]
Carvacrol	GPX4	Upregulates GPX4 expression and slows down lipid peroxidation	Guan et al., 2019 [124]
Thiazolidinedione	ACSL4	Inhibits ACSL4	Doll et al., 2017 [125]

Table 3.

Ferroptosis inducers

Compound/drug	Target	Mechanism	Study [ref]
Buthionine sulfoximine (BSO)	GSH	Inhibits γ-GCS activity and prevents GSH synthesis	Luo et al., 2021 [126]
Erastin	System Xc−	Inhibits cystine uptake	Yan et al., 2022 [127]
Imidazole ketone erastin (IKE)	System-Xc−	Inactivates GPX4 due to GSH depletion	Zhang et al., 2019 [128]
Cyst(e)inase	[Cys] depletion	Inactivates GPX4 due to GSH depletion	Cramer et al., 2017 [129]
Sorafenib	System-Xc−	Inhibits SLC7A11 activity	Louandre et al., 2013 [130]
Sulfasalazine(SAS)	System-Xc−	Inhibits the absorption of cystine by system xc-, causes GSH depletion	Gout et al., 2001 [131]
Acetaminophen	GSH	Reacts rapidly with GSH causing extensive GSH depletion	Lőrincz et al., 2015 [132]
RSL3	GPX4	Inhibits GPX4, ROS production	Sui et al., 2018 [133]
ML162	GPX4	Inactivates GPX4	Eaton et al., 2019 [134]
FIN56	GPX4	Direct degradation of GPX4 and consumption of CoQ10	Shimada et al., 2016 [135]
Withaferin A	GPX4	Inactivates GPX4 or targets Kelch-like ECH-associated protein 1	Hassannia et al., 2018 [136]
FINO2	Free iron	Increases iron overload and induces GPX4 degradation	Gaschleret al., 2018 [137]
Artemisinin derivatives	Keap1/Nrf2/Fe2+	Lowers cellular GSH levels and increases lipid ROS levels	Deng et al., 2025 [138] Roh et al., 2017 [139]
Ferumoxytol	ROS production	Acute myelocytic leukaemia (AML)	Trujillo-Alonso et al., 2019 [140]

Refractory cancers, such as pancreatic cancer, triple-negative breast cancer, and glioblastoma, as well as drug-resistant tumours, frequently demonstrate a high resistance to ferroptosis. Accumulating preclinical evidence indicates that the induction of ferroptosis may serve as a viable therapeutic strategy to combat tumour growth and enhance drug resistance. Ferroptosis can be triggered by GSH depletion, which can be achieved by inhibiting GSH biosynthesis (e.g., buthionine sulfoximine (BSO) inhibits γ-glutamylcysteine synthetas (γ-GCS)) or blocking the uptake of cysteine from the extracellular environment (e.g., erastin inhibits the Xc⁻ system) [126, 127]. Researchers introduced a ketone functional group into the erastin structure to obtain the carbonyl analog imidazole ketone erastin (IKE), which is more effective at inducing ferroptosis [128]. Cyst(e)inase is an artificial enzyme that can effectively promote GSH depletion in cells and increase intracellular lipid peroxidation levels. It has shown good efficacy in the treatment of malignant tumours, such as prostate cancer, breast cancer, and chronic lymphocytic leukaemia [129]. Several FDA-approved medications, such as sorafenib, salazosulfapyridine (SAS), and acetaminophen, have been demonstrated to induce ferroptosis in a variety of cancerous and non-cancerous cell types by inhibiting the system Xc⁻ or GSH [130–132]. The initial GPX4 inhibitors identified through high-throughput screening include RSL3 and ML162 [133, 134]. Although ML162 shares similar structural and biological characteristics with RSL3, it exhibits greater activity. FIN56, an inducer of ferroptosis derived from CIL56, promotes endogenous antioxidant activity by either facilitating the degradation of GPX4 or binding to and activating squalene synthase (SQS), which results in the depletion of CoQ₁₀ [135]. Withaferin A (WA) has been found to not only inhibit the activity of GPX4 in neuroblastoma but also activate heme oxygenase-1 to increase intracellular Fe³⁺ concentration, thereby inducing ferroptosis in neuroblastoma [136]. FINO₂, a 1,2-hydroxybenzoic acid inhibitor based on a 1,2-benzoic acid structure, is characterised as an organic peroxide with a 1,2-dioxane skeleton. It operates through a dual mechanism, inducing ferroptosis by directly promoting iron oxidation or indirectly inhibiting GPX4 activity [137]. Furthermore, artemisinin and its derivatives have been shown to effectively induce iron-dependent cell death in cancer cells [138]. A concentration of 50 µmol/L artesunate selectively induces cell death in head and neck cancer cells without affecting normal cells by activating an iron-dependent, ROS-accumulating ferroptosis pathway [139]. In addition, iron-based nanomedicines currently hold significant potential in the treatment of major diseases, such as malignant tumours, cardiovascular diseases, and neurological disorders. For example, ferumoxytol can selectively kill leukaemia cells with low FPN expression while exhibiting low toxicity to normal hematopoietic cells, demonstrating its potential for targeted leukaemia therapy [140].

Recently, our research group has identified the ferroptosis-related molecule SLC7A11 as playing a multifaceted role in the pathogenesis of metabolic dysfunction-associated fatty liver disease (MASLD), influencing cystine levels and disease progression [141]. Mechanistic studies have demonstrated that 5(S),15(S)-DiHETE-mediated ferroptosis signalling facilitates the degradation of hypoxia-inducible factor-1α (HIF1α). Therefore, targeting the HIF1α-c-MYC-PGC1β pathway enhances thermogenesis in beige adipose tissue, thereby providing a potential therapeutic strategy to mitigate obesity and metabolic disorders associated with high-fat diets [142]. In conclusion, while ferroptosis represents a promising area of research, the exploration of the mechanisms underlying the action of ferroptosis-related drugs in clinical applications remains a long-term endeavour.

Conclusions and perspective

Iron is integral to numerous essential biological processes, and disturbances in iron homeostasis can result in various pathological conditions. Ferroptosis is recognized as a specific mode of cell death that is closely associated with iron metabolism and is implicated in the progression of several major diseases, including cancer. In the context of cancer treatment, the induction of apoptosis through conventional therapeutic methods and immunotherapy has often been hindered by drug resistance, highlighting the urgent necessity to investigate alternative pathways of cell death. The induction of ferroptosis not only suppresses tumour growth but also enhances the efficacy of immunotherapeutic responses and mitigates resistance to existing cancer therapies. Enhancing the specificity of ferroptosis activators and regulating their dosage to minimize adverse effects on healthy tissues are anticipated to represent novel oncological therapeutic strategies. The application of nanocarriers can effectively encapsulate or adsorb ferroptosis modulators, thereby improving their solubility and delivery efficiency. With the rapid advancements in science and technology, the role of iron ions in life and health is increasingly recognized as being more profound and complex than previously anticipated. In addition, ferrology, as a new cross-cutting discipline for the study of iron, is not limited to the fields of biology and biomedicine. Continued promotion of research in ferrology and the establishment of this emerging disciplinary framework will significantly facilitate the interdisciplinary exchange within the field of iron research, further advancing the prevention and control of diseases and the maintenance of human health, thereby providing essential scientific support.

Authors’ contributions

The authors' responsibilities were as follows: MZ, YW: wrote the first draft of the manuscript; JM, FW: provided critical input on the manuscript; JM, FW: critically revised the manuscript by providing important intellectual content; and all authors: contributed significantly to the manuscript, agreed with respect to the content of the manuscript, and have read and approved the final version of this manuscript.

Funding

This study was supported by grants from the National Natural Science Foundation of China (82471593 to J.M., 32330047 to F.W.)

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This article does not contain any studies with human participants or animals performed by any of the authors.

Competing interests

The authors declare no competing interests.