Among the enzymatic pathways involved in ferroptosis, LOXs play a paramount role. The three families of lipid oxidase (cyclooxygenases [COX], cytochromes P450 [CYPs], lipoxygenases [LOXs]) can convert free PUFA into lipid oxides, but it is the LOXs family that has the most significant impact on ferroptosis (FENG and STOCKWELL, 2018). LOXs are enzymes containing non-heme iron and exhibit specificity for the oxidation of PUFAs (XIE et al., 2022). Studies have demonstrated that PEs derived from arachidonic acid (AA) and adrenal acid (AdA) serve as crucial substrates for lipid peroxidation in ferroptosis (DOLL et al., 2017; KAGAN et al., 2017).

The process begins with PEs linked to free AA and AdA, which are converted into AA CoA and AdA-CoA through acyl CoA synthase long-chain family 4 (ACSL4). Subsequently, under the catalytic action of lysophosphatidyl acyltransferase member 3 (LPCAT3), AA-PE and AdA-PE are formed. Finally, these compounds are further converted into PLOOH through the combined catalysis of unstable Fe and LOXs, consequently triggering lipid peroxidation and cell ferroptosis (CHEN et al., 2022). Notably, ACSL4 and LPCAT3 play pivotal roles as driving factors for ferroptosis. ACSL4 is considered a sensitive marker for ferroptosis, as cellular ferroptosis can be induced by glutathione peroxidase 4 (GPX4)−/−, while cells with simultaneous knockout of both GPX4 and ACSL4 can survive normally (CAPELLETTI et al., 2020). Nevertheless, there is still ongoing debate regarding the key LOX subtypes driving ferroptosis in this process (FORCINA and DIXON, 2019). Studies have revealed that the LOX-15 complex, in conjunction with PE binding protein 1 (FEBP1), acts as a specific catalyst for AA/AdA-PEs, leading to lipid peroxidation and promoting cell ferroptosis (STOYANOVSKY et al., 2019). Additionally, another study identified edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one, EDA) as an inhibitor of neuronal cell ferroptosis through downregulation of LOX-5 in neurons, thereby facilitating recovery after spinal cord injury (PANG et al., 2022).

Furthermore, investigations have demonstrated that the combination of nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (POR) and nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase (CYB5R1) allows electrons from NAD(P)H to react with O2, generating H2O2. Ultimately, this leads to the Fenton reaction with free iron ions, indirectly inducing lipid peroxidation and facilitating cell ferroptosis (YAN et al., 2021).

The GSH-GPX4 pathway plays a crucial role in inhibiting lipid peroxidation, and the traditional approach to inducing ferroptosis involves inhibiting the synthesis pathway of GSH. In this pathway, GSH serves as a key antioxidant, and its synthesis primarily relies on intracellular cysteine (Cys) uptake through System Xc-. Cys is then reduced to serve as the direct source for GSH. While the System Xc-is considered the main source of Cys (LOU et al., 2022), studies suggest that Cys can also be synthesized through the sulfur transfer pathway when the System Xc-is inhibited (SHIMADA and STOCKWELL, 2015). The System Xc- and sulfur transfer pathway work cooperatively in Cys synthesis (ZHENG and CONRAD, 2020). However, dysregulation of the System Xc-still leads to Cys deficiency and GSH depletion in cells (LI FJ. et al., 2022).

GPX4, the fourth member of the GPX family containing selenium, plays a crucial role in inhibiting lipid peroxidation. GPX4 contains eight nucleophilic amino acids, including selenocysteine (Sec) (SHA et al., 2021), which is essential for its function (LEI et al., 2019). The unique amino acid sequence and structure of GPX4 establish it as a key regulatory factor in inhibiting ferroptosis (TURCHI et al., 2020; WU et al., 2022). Specifically, GPX4 utilizes reduced GSH as a critical substrate to convert GSH into oxidative GSH (GSSG) and PLOOH into fatty alcohols (PLOH), thus inhibiting the process of lipid peroxidation. In the catalytic cycle of GSH-GPX4, the active group -SeH of GPX4 is oxidized to -SeOH by PLOOH. GSH can then reactivate GPX4 by reducing -SeOH, releasing GSSG while maintaining the activity of GPX4 (LI FJ. et al., 2022). Consequently, inhibiting GSH synthesis has been shown in numerous studies to impair the activity of GPX4 (CHEN et al., 2019; YANG et al., 2020; QIN et al., 2021; YANG et al., 2021).

Alongside the GPX4 pathway, other pathways contribute to ferroptosis inhibition, notably the FSP1-CoQ10-NAD(P)H pathway and the methoxyphenate pathway. Recent studies propose that the FSP1-mediated ferroptosis defense mechanism can function as an independent parallel system (BERSUKER et al., 2019). This mechanism effectively suppresses ferroptosis even in the absence of GPX4 due to genetic deletion. In the FSP1-CoQ10-NADPH pathway, ferroptosis inhibitory protein 1 (FSP1), previously known as flavoprotein apoptosis-inducing factor mitochondrial 2 (AIFM2), acts as a potent ferroptosis inhibitor by reducing coenzyme Q (CoQ10) on the cytoplasmic membrane to panthenol (CoQH2) (SANTORO, 2020). CoQ10 serves as a lipophilic free radical scavenger and antioxidant, protecting the plasma membrane from oxidative damage caused by free radicals. Additionally, CoQ10 acts as a mobile lipid-soluble electron carrier, preserving the normal energy conversion of mitochondrial respiratory chains (SANTORO, 2020).

Nicotinamide adenine dinucleotide phosphate (NADPH), functioning as a dehydrogenase cofactor, is an essential reducing agent for clearing lipid hydroperoxides (STOCKWELL et al., 2017). FSP1 reduces CoQ10 to CoQH2 through NAD(P)H, which directly inhibits lipid peroxidation or indirectly promotes the regeneration of tocopherol free radicals (vitamin E), a natural chain-breaking antioxidant. This process eliminates lipid free radicals, thereby inhibiting lipid peroxidation (KAGAN et al., 2017). CoQ10 plays a vital role in this pathway, and when CoQ10 synthesis is inhibited, it results in increased lipid peroxidation (SANTORO, 2020). Although the precise source of CoQ10 synthesis remains unclear, most CoQ10 is synthesized within the mitochondria. Recent research identified a mitochondrial defense mechanism against ferroptosis mediated by dihydroorotate dehydrogenase (DHODH). In the absence of GPX4 activity, DHODH upregulates CoQH2 production to inhibit ferroptosis (MAO et al., 2021). Furthermore, studies have revealed that tetrahydrobiopterin (BH4), facilitated by GTP cyclohydrolase 1 (GCH1), effectively inhibits ferroptosis as a free radical scavenger. BH4 can suppress lipid peroxidation by generating CoQH2. Thus, it is plausible that two independent sources of CoQ10 production exist within cells (KRAFT et al., 2020; SANTORO, 2020; SOULA et al., 2020).

The MVA pathway is another important pathway involved in ferroptosis inhibition. It has significant roles in both the FSP1-CoQ10-NAD(P)H pathway and the GSH-GPX4 pathway. The MVA pathway starts with acetyl CoA, which undergoes a series of reductase reactions, including 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR), leading to the production of MVA. Under the action of coenzymes like methylglutarate kinase (MVK), MVA further produces isoamyl pyrophosphate (IPP) (CHEN et al., 2020). IPP is an intermediate molecule in various biomolecules involved in the regulation of ferroptosis (ZHENG and CONRAD, 2020). For example, IPP can generate farnesyl pyrophosphate (FPP) through the activity of phosphofarnesyl synthase. Subsequently, FPP can be converted to squalene by squalene synthase (SQS). Squalene then undergoes cyclization by squalene cyclase to produce cholesterol. However, when SQS is inhibited, FPP bypasses the cholesterol synthesis pathway and instead converts to CoQ10 (CHEN et al., 2020), thereby inhibiting ferroptosis. Studies have demonstrated that FIN56, a known ferroptosis inducer, can activate SQS, leading to reduced CoQ10 synthesis (SHIMADA et al., 2016).

The MVA pathway also plays a crucial role in GPX4 synthesis. In the selenium-containing GPX4 synthesis pathway, the insertion of Sec is essential for GPX4 to exert its antioxidant activity. This process is facilitated by the catalytic integration effect of IPP (WU et al., 2022). FIN56, as a ferroptosis inducer, can inhibit the integration of Sec on the GPX4 catalytic subunit, thereby reducing the expression of GPX4’s antioxidant activity (OU et al., 2022).

The Gln metabolism pathway is another important pathway involved in the regulation of ferroptosis. Gln, a key amino acid in the human body, plays a crucial role in various biological processes and energy production within mitochondria, such as the tricarboxylic acid (TCA) cycle (KOPPULA et al., 2021). Gln is primarily taken up by cells through SLC1A5 and is then broken down by glutaminase (GLS) into glutamic acid. The converted glutamic acid enters the TCA cycle as α-ketoglutaric acid (α-KG) with the help of enzymes like glutamate (GLU) dehydrogenase (GLUD1) (LI S. et al., 2023), regulating lipid synthesis and the ferroptosis process (YAO et al., 2021). GLS, a key enzyme in Gln breakdown, consists of two subtypes: GLS1 and GLS2. Studies have demonstrated that GLS2 is the essential subtype for mitochondrial regulation of ferroptosis (GAO et al., 2015; SUZUKI et al., 2022). GLS2 facilitates the production of glutamic acid, which enters mitochondria and is further converted to α-KG by aspartate aminotransferase (GOT) and GLUD1. This process maintains energy metabolism and component transformation in the TCA cycle (YAO et al., 2021). The glutamic acid derived from Gln breakdown in the TCA cycle induces structural and functional changes in mitochondria, including depolarization of the mitochondrial membrane potential and reduced activity of the mitochondrial electron transfer chain. These changes contribute to the accumulation of lipid ROS, ultimately leading to ferroptosis (SONG et al., 2023). Therefore, modulation of the Gln metabolism pathway can regulate the sensitivity of cells to ferroptosis (KANG et al., 2019; SUZUKI et al., 2022).

Downregulation of solute carrier family 7 member 11 (SLC7A11), a component of System Xc-, has been shown to induce ferroptosis (CHEN et al., 2021). Recent studies have revealed that increased expression of SLC7A11 in tumor cells leads to excessive cystine uptake for GSH synthesis and loss of GLU (YAO et al., 2021), resulting in an imbalance in the Gln metabolism pathway. By inhibiting SLC7A11 or depriving cells of Cys, the glutamic acid produced from Gln breakdown can bypass System Xc- and enter the TCA cycle, leading to the accumulation of lipid ROS and ultimately triggers ferroptosis. Targeting this pathway provides new potential strategies for cancer treatment based on ferroptosis (KOPPULA et al., 2021).

As mentioned previously, ferroptosis is primarily triggered by iron-dependent lipid peroxidation. Iron ions are crucial for human physiological processes. Under normal conditions, systemic iron homeostasis relies on the coordinated expression of transferrin (TF), ferroportin 1 (FPN1), transferrin receptor 1 (TfR1), and liver-produced iron regulatory proteins (ROCHETTE et al., 2022). Two forms of iron ions exist in the human body: Fe²⁺ and Fe³⁺. When there is an imbalance in iron homeostasis, these ions participate in oxidation-reduction reactions, resulting in the production of peroxy free radicals and ultimately leading to ferroptosis (LOU et al., 2022).

During this process, extracellular Fe³⁺ binds to TF and is recognized by TfR1 before being internalized into the cell. Subsequently, within vesicles, prostate transmembrane epithelial 3 antigen antibody (STEAP3) facilitates the reduction of Fe³⁺ to Fe²⁺. The transported Fe²⁺ from the vesicles enters the cytoplasm either through divalent metal transporter 1 (DMT1) and zinc iron regulatory protein family 8/14 (ZIP8/14), or it binds to ferritin, storing it in unstable iron pools (LIPs). Free Fe²⁺ in the cytoplasm is susceptible to the Fenton reaction, leading to lipid peroxidation. Additionally, ferritin bound to Fe²⁺ in LIP undergoes autophagic degradation, releasing free Fe²⁺ mediated by nuclear receptor coactivator 4 (NCOA4) upon entering the lysosome (CHEN et al., 2022). This initiates the Fenton reaction and promotes lipid peroxidation. FPN serves as the sole protein responsible for transporting Fe²⁺ out of cells, thereby reducing intracellular Fenton reactions and inhibiting ferroptosis (SUN et al., 2022). Furthermore, studies have shown that Fe²⁺ exported via FPN can be converted to less oxidizing Fe³⁺ through the action of ceruloplasmin (CP). Depletion of CP leads to the accumulation of intracellular Fe²⁺, thus inducing ferroptosis (SHANG et al., 2020).

Moreover, unstable iron within LIP can bind to ferritin (including both ferritin light chain and ferritin heavy chain) and transform into Fe³⁺ for storage in lysosomes, effectively inhibiting lipid peroxidation. In instances of iron deficiency, iron bound to ferritin heavy chain (FTH) can be released into LIP with the aid of NCOA4. Free Fe²⁺ within LIP is crucial for mitochondrial function (FUJIMAKI et al., 2019). The influx of Fe²⁺ from unstable iron pools into mitochondria not only triggers the Fenton reaction leading to ferroptosis, but also serves as a substrate for Fe-S cluster synthesis. The stability of Fe-S clusters plays an indispensable role in maintaining the normal functioning of electron transfer chains (ETC.) and the TCA cycle (FANG et al., 2023). Damage to, ETC can also result in lipid peroxidation and subsequent ferroptosis within cells (JAVADOV, 2022; DONG et al., 2023).

The System Xc-pathway is facilitated by a chloride ion-dependent Glu/Cys transporter protein located on the plasma membrane. This protein consists of solute carrier family 7 member 11 (SLC7A11) and solute carrier family 3 member 2 (SLC3A2), which are interconnected by disulfide bonds (LI FJ. et al., 2022). System Xc-operates based on a concentration gradient of Glu/Cys both inside and outside the cell, allowing for Cys intake into the cell in a 1:1 ratio while Glu is excreted (ISHII et al., 1987; CONRAD and SATO, 2012; LI et al., 2020; WU X. et al., 2021). Several biomolecular synthesis processes occur following the uptake of Cys via System Xc-, leading to the synthesis of GSH. In this process, ingested Cys is catalyzed by thioredoxin reductase 1 (TrxR1) to convert it to Cys, which is then combined with glutamic acid (Glu) through the catalytic action of GLU Cys ligase (GCL) to form γ-glutacyl-L-Cys. Ultimately, this compound is directly utilized in the biosynthesis of GSH along with glycine, thereby inhibiting ferroptosis (LIN et al., 2020; LI FJ. et al., 2022; LIU et al., 2022). Among these steps, the transport of Cys through the amino acid transport system is primarily regulated by SLC7A11 (LI FJ. et al., 2022). Thus, inhibiting the expression of SLC7A11 can increase cellular sensitivity to ferroptosis (JENNIS et al., 2016; NISHIZAWA et al., 2020; WANG et al., 2020). Intracellular Cys can also be acquired through the sulfur transfer pathway and neutral amino acid transporters (CONRAD and SATO, 2012; HAYANO et al., 2016). This indicates that the induction of ferroptosis by targeting the Cys source is not limited to a singular pathway. However, when ferroptosis inducers like Erastin and its analogues inhibit System Xc- (SATO et al., 2018), intracellular Cys depletion still occurs, leading to reduced GSH synthesis and eventual lipid peroxidation. Therefore, targeting the System Xc-pathway is crucial in modulating GSH synthesis (SHAO et al., 2022) (Figure 2).

Neuroinflammation refers to the immune response of the central nervous system (CNS) mediated mainly by microglia and astrocytes in the hippocampus (LEE and HYUN, 2023). Microglia, known for their high iron content (UZUNGIL et al., 2022), have been implicated in depression associated with abnormal glial activation and iron overload, suggesting a potential connection between iron and neuroinflammation (ZENG et al., 2023). However, the precise mechanism by which iron overload disrupts neurotransmitter homeostasis and induces anxiety and depressive behaviors remains unclear (UZUNGIL et al., 2022).

Research has shown that signal transduction involving brain-derived neurotrophic factor (BDNF) plays a crucial role in synaptic plasticity in depression, and the downregulation of BDNF may contribute to neurotoxic effects (SHKUNDIN and HALARIS, 2023). In this context, Li et al. demonstrated that iron overload may downregulate BDNF via the iron urin BDNF pathway, leading to hippocampal nerve damage (LI J. et al., 2023). Furthermore, Gao et al. showed in a chronic unpredictable mild stress (CUMS) mouse model that iron deposition in microglia within the hippocampus is closely associated with neuronal degeneration and death (GAO W. et al., 2019). Additionally, Zeng et al. highlighted the significant role of Nrf2 as an anti-inflammatory factor in regulating iron deposition and neuroinflammatory responses in depression (ZENG et al., 2023). In a comparative study using hippocampal proteomics, Cao et al. observed distinct protein expression differences between normal mice and CUMS model mice, indicating pronounced activation of neuronal necrosis and iron deposition in the hippocampus, thus promoting the occurrence of depression (CAO et al., 2021). Recently, Zhang et al. discovered that expression levels of various inflammatory factors significantly increased in CUMS model mice, while treatment with the iron chelating agent deferoxamine (DFO) effectively reversed this neuropathological change (ZHANG W. et al., 2022). Collectively, these findings suggest a potential link between the neurotoxicity induced by iron overload and the development of depression.

Since the discovery of ferroptosis in 2012, mitochondria have been proposed to play a crucial role in regulating erastin-induced ferroptosis (FANG et al., 2023). Multiple membrane iron transporters (MFRNs) located on the mitochondrial membrane facilitate the distribution of iron within mitochondria and the cytoplasm. When mitochondrial iron overload occurs, it leads to the generation of a substantial amount of mtROS, resulting in cellular ferroptosis (FUHRMANN and BRÜNE, 2022). Two potential mechanisms for mitochondrial ferroptosis have been suggested (FANG et al., 2023). Firstly, an imbalance in mitochondrial iron homeostasis and an elevation in Fe²⁺ levels promote ROS production via the Fenton reaction, ultimately inducing cell ferroptosis. Secondly, as iron serves as a key regulator of oxidative phosphorylation (OXPHOS), disruption of iron metabolism can lead to impaired electron transfer, lipid peroxidation, and subsequent induction of ferroptosis. Mitochondria contain a significant amount of iron, primarily involved in heme synthesis, Fe-S cluster biosynthesis, and storage within mitochondrial-specific ferritin (FtMt), which maintains the structure and function of the electron transport chain (ETC.) and TCA cycle. Disturbances in iron metabolism can significantly cause structural changes and dysfunction of mitochondria (CHENG et al., 2022; DONG et al., 2023). ROS produced by mitochondrial dysfunctionis essential for ferroptosis induction (GAO M. et al., 2019). Numerous studies have demonstrated a close association between depression and oxidative stress, as well as disruptions in the, ETC within mitochondria (SONG et al., 2023; XU et al., 2023). In recent years, research has increasingly focused on the mechanism of ferroptosis in patients with depression. Adenosine triphosphate (ATP), predominantly produced by mitochondria, has been found to exhibit a positive correlation with the occurrence of depression (INCZEDY-FARKAS et al., 2014; CHANG et al., 2015; BRYMER et al., 2018; WANG et al., 2018). Kondo et al. further confirmed this relationship using magnetic resonance spectroscopy (MRS) (KONDO et al., 2011). When mitochondrial iron metabolism disorders occur, excessive free iron ions can impair the, ETC and subsequently inhibit ATP production (BATTAGLIA et al., 2020). Romano et al. reviewed the potential role of 4-HNE, a product of ferroptosis (CAPELLETTI et al., 2020), in the pathogenesis of mental disorders such as bipolar disorder and depression, along with lipid peroxidation (ROMANO et al., 2017). Mitochondria, being the primary source of cellular ROS, may also be involved in modulating depression via the ferroptosis signaling pathway (BANSAL and KUHAD, 2016). Based on the available evidence, disturbances in mitochondrial iron metabolism can contribute to the development of depression by influencing mitochondrial function and structure (ZUO et al., 2022; SONG et al., 2023).

The brain-gut axis (GBA) refers to a bidirectional signaling network involving the brain, gut, and gut microbiota. This network operates through neuroendocrine, immune regulation, and microbial molecules, connecting emotional and cognitive activities in the brain with physiological and pathological changes in the peripheral gut (KANIA et al., 2023). The occurrence of depression and bipolar disorder may be associated with intestinal microbiota and dysfunction in the bidirectional communication within the CNS (GÓRALCZYK-BIŃKOWSKA et al., 2022). Remarkably, imbalances in serum iron homeostasis can induce both intestinal microbiota imbalance and inflammation, leading to stress responses in the brain. Consequently, the expression of IL-6 is promoted, which triggers glial cells to release hemodulin, isolating excess iron in neurons. However, this process can unexpectedly induce oxidative stress response, resulting in neuronal damage (HOUSER and TANSEY, 2017; KANIA et al., 2023). Furthermore, studies have elucidated the potential connection between the IL-6-mediated signaling pathway and the pathogenesis of depression (TING et al., 2020). Additionally, as previously mentioned, iron overload may contribute to depression by downregulating the expression of BDNF (LI J. et al., 2023; SHKUNDIN and HALARIS, 2023). Recent research has demonstrated that alterations in gut microbiota distribution, according to the brain-gut axis mechanism, can modulate BDNF expression, thereby influencing the onset of depression (LIAQAT et al., 2022). Moreover, a meta-analysis revealed decreased levels of Corprococcus and Faecalibacterium bacteria in the intestines of individuals with depression compared to healthy individuals. Notably, intervention with probiotics resulted in improved depression symptoms. Taken together, these findings suggest that ferroptosis may inhibit the damage caused by neuroinflammation through cross talk among the brain-gut axis mechanism, gut microbiota, and CNS (WANG et al., 2023a; KANIA et al., 2023). Thus, it holds promise as a potential target for the diagnosis and treatment of depression.

Autophagy is a natural and RCD process that facilitates the degradation of damaged organelles, pathogens, and other biological components (such as proteins, lipids, DNA, and RNA) within cells. It serves as a survival mechanism in response to stress (LIU et al., 2020). The relationship between autophagy and ferroptosis remains unclear. Recent studies have proposed that ROS triggered by the ferroptosis inducer erastin can induce autophagy in cells, and autophagy, in turn, can regulate ferroptosis by degrading cellular ferritin (PARK and CHUNG, 2019). Zuo et al. demonstrated that oxidative stress, mediated by ROS, plays a crucial role in depression induction, and Nrf2 activation can mitigate oxidative stress by simultaneously regulating multiple potential mechanisms, including autophagy and ferroptosis (ZUO et al., 2022). Furthermore, mitochondrial autophagy has been found to be significant in depression (TRIPATHI et al., 2021), and Nrf2 activation can directly modulate mitochondrial autophagy (MURATA et al., 2015). From the perspective of ferroptosis, the ferroptosis pathway may also hold promise as a potential mechanism for treating depression (ZUO et al., 2022). Autopsy results from patients with depression revealed decreased levels of GSH and GPX in the brain (GAWRYLUK et al., 2011). Wigner et al. identified a potential association between GPX4 gene polymorphism and depression regulation (WIGNER et al., 2018). Additionally, it has been demonstrated that most genes involved in ferroptosis are directly or indirectly regulated by Nrf2 (HARADA et al., 2011; DODSON et al., 2019). Dang et al. investigated the effects of EDA and showed its ability to reduce oxidative stress and ferroptosis through the Silent information regulatory factor 2 homologous protein 1 (Sirt1)/Nrf2/Heme oxygenase-1 (HO-1)/Gpx4 pathway, thereby inhibiting the development of depression (DANG et al., 2022). These findings provide evidence of crosstalk between autophagy and ferroptosis in the pathological mechanism of depression, which may serve as a potential therapeutic avenue for depression.

Allicin, a prominent active compound in Chinese herbal garlic, has been found to possess neuroprotective effects (CHEN et al., 2014). Gao et al. demonstrated that Allicin can alleviate depressive behavior in the CSDS model mice by inhibiting NLRP3 inflammasomes. Increased concentration of DMT1 in hippocampal neurons during the chronic phase of inflammation indicates iron deposition, suggesting a potential link between Allicin and ferroptosis as one of the mechanisms for treating depression (GAO W. et al., 2019).

Saikosaponin B2 (SSB2), derived from the Chinese herbal medicine Radix Bupleuri, has a long history of being used to treat depression, as documented in the TCM classic “Taiping Huimin HeJiJu Fang” (YANG et al., 2017). The antidepressant and neuroprotective effects of Radix Bupleuri have been confirmed through modern research (TONG et al., 2024). Wang et al., using the CUMS mouse model and ferroptosis mouse model, demonstrated that SSB2 inhibits Toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) pathway-mediated ferroptosis to improve depression-induced microglia activation. This leads to inhibition of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. However, the therapeutic effect of SSB2 on depression is blocked when GPX4 is knocked out, indicating that SSB2 acts through a GPX4-dependent manner in mediating TLR4/NF-κB pathway, exerting its anti-ferroptosis and anti-neuroinflammatory roles (WANG et al., 2023b).

Lycium barbarum glycopeptide (LbGp), a carbohydrate conjugate composed of proteins and monosaccharides, is a major active component of Chinese herbal medicine Lycium barbarum (PENG et al., 2001). Recent studies have shown that goji berry polysaccharides effectively alleviate depression (FU et al., 2021; LI X. et al., 2022). Dai et al. observed in their study using chronic restraint stress (CRS) model mice that GPX4 knockout-induced ferroptosis disrupts cortical function, leading to increased depression and anxiety in mice. However, treatment with LbGp can attenuate the anxiety caused by ferroptosis by increasing superoxide dismutase (SOD) activity and inhibiting the elevation of GSH and MDA levels (DAI et al., 2023). Gallic acid (3,4,5-trihydroxybenzoic acid) is an active ingredient extracted from Chinese herbal medicine found in various plants, such as green tea and gallnuts (Al Zahrani et al., 2020). Recent studies have revealed that the phenolic hydroxyl group of gallic acid has the ability to clear ROS and disrupt the cycle of new free radicals, thereby exhibiting anti-inflammatory properties (TEIXEIRA et al., 2013). Yang et al. discovered that gallic acid can effectively treat depression development by inhibiting the P2X7 regulatory ferroptosis signaling pathway in chronic contractile injury (CCI) model rats and CUMS model rats. Inhibition of P2X7 expression leads to downregulation of TNF-α, NF-κB expression levels, and STAT3 phosphorylation. Consequently, the expression of GSH and GPX4 increases, which suppresses ROS accumulation and the generation of MDA, ultimately alleviating the pain and depressive symptoms in CCI and CUMS rats through the inhibition of ferroptosis (YANG R. et al., 2023). Silybin, another primary active ingredient derived from Chinese herbal medicine Silybin, has been shown to possess neuroprotective effects as well as antidepressant effects (SONG et al., 2018; LIU et al., 2021). Liu et al. discovered that silybin reduces neuroinflammation mediated by interferon gene stimulating factor (STING) by downregulating the ferroptosis signaling pathway. This leads to an improvement in depressive behavior in an Alzheimer’s disease mouse model. Hippocampal neurons (HT-22) treated with streptozotocin (STZ) exhibit dysregulation of the p53/SLC7A11/GSH/GPX4 pathway, resulting in excessive ROS accumulation and ferroptosis activation, which subsequently triggers the cellular immune response via the STING signaling pathway. This pathological mechanism induces the release of various inflammatory factors, leading to depressive behavior in mice. Silybin treatment can reverse this pathological change by inhibiting the ferroptosis signaling pathway (LIU et al., 2023) (Table 2).

Currently, there is limited research on the modulation of the ferroptosis signaling pathway in TCM prescriptions for treating depression. Recent studies employing metabolomics and nuclear MRS have revealed the potential antidepressant effects of Xiaoyao powder (consisting of Radix Bupleuri, Poria, Rhizoma Zingiberis Recens, Radix Angelicae Sinensis, Radix Paeoniae Alba, Rhizoma Atractylodis Macrocephalae, Radix Glycyrrhizae, and Herba Menthae Haplocalycis) on CUMS rats (LIU et al., 2019). Jiao et al. found that Xiaoyao powder ameliorates depression-like behavior in CUMS model mice by modulating the ferroptosis signaling pathway mediated by the hippocampus. The antidepressant mechanism of Xiaoyao powder may involve the upregulated expressionsof PEBP1 and extracellular regulatory protein kinase 1/2 (ERK1/2), and modulation of GPX4 within the ferroptosis signaling pathway. These findings suggest that Xiaoyao powder may alleviate depressive behavior in mice through mediating PEBP1-GPX4 interactions (JIAO et al., 2021).

Furthermore, Dihuang Yinzi (composed of Radix Rehmanniae Praeparata, Radix Ophiopogonis, Caulis Dendrobii, Fructus Corni, Fructus Schisandrae Chinensis, Herba Cistanches, Radix Morindae Officinalis, Radix Aconiti Lateralis Praeparata, Cortex Cinnamomi, Poria, Rhizoma Acori Tatarinowii, Radix Dolygalae, Herba Menthae, Rhizoma Zingiberis Recens, and Fructus Jujubae) has been found to possess neuroprotective effects (ZHANG et al., 2017). Moreover, Zhou et al. observed that Dihuang Yinzi can mitigate neural damage caused by post-stroke depression (PSD) in rats by regulating the ferroptosis signaling pathway. The active extract of Dihuang Yinzi modulates the P53/SLC7A11 pathway and upregulates the expression of SLC7A11 protein through promotion of P53 ubiquitination, consequently increasing GPX4 expression. This intervention effectively inhibits ferroptosis in PSD, improving depressive symptoms and cognitive impairment (YANG Z. et al., 2023).