Potential role of AhR in ischemia‑reperfusion injury and cancers: Focus on ferroptosis and lipid peroxidation signaling pathways (Review)

Introduction

The maintenance of redox homeostasis is dependent upon the levels of pro-oxidant active molecules and antioxidants (1). The disruption of this equilibrium plays a crucial role in the development and progression of numerous diseases (2). The accumulation of pro-oxidative reactive factors, including reactive oxygen species (ROS), reactive nitrogen species (RNS) and reactive lipids (RLS), leads to the oxidation of DNA, proteins and lipids, altering their structure, activity and physical properties, and resulting in oxidative stress and cellular dysfunction (3). ROS are among the most ubiquitous oxidants in cells and are capable of reacting with numerous substances to form superoxide (4). The reaction between ROS and polyunsaturated fatty acids (PUFAs) in plasma, cell membranes and organelle membranes is critical, leading to the production of lipid peroxides (5). RLS produced by lipid peroxidation, such as 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA), are closely associated with the onset and progression of numerous diseases, including cancer, diabetes, neurodegenerative disorders, cardiovascular diseases and ischemia/reperfusion (I/R) injury. Redox homeostasis therefore plays a critical role in the pathogenesis of multiple diseases.

The aryl hydrocarbon receptor (AhR) is a transcription factor intricately linked to redox homeostasis in a variety of inflammatory diseases (6). AhR is activated by a diverse array of exogenous and endogenous ligands and transcriptional regulates downstream target genes. This process consequently modulates the oxidative and antioxidant balance and a variety of cellular functions. AhR target genes, including the NAD(P)H dehydrogenase [quinone] 1 (NQO1), glutathione S-transferase (GST), UDP-glucuronosyltransferase 1-1 (UGT1A1), CYP1A1 and CYP1B1 genes, play a crucial role in regulating cellular redox homeostasis (7). Moreover, AhR plays a crucial role in the metabolism of exogenous substances and drugs, iron and heme metabolism, glutathione synthesis, and lipid metabolism (8,9). The dysregulation of AhR is observed in numerous disease processes, highlighting its essential role in cell survival, particularly under conditions of redox homeostasis imbalance.

AhR plays a multifaceted role in maintaining cell survival, and both AhR agonists and inhibitors have been shown to modulate cell survival or death, particularly in the context of tumor therapy (10-14). In 2003, Dixon et al (15) identified a novel form of cell death termed ferroptosis, characterized as an iron-dependent process triggered by lipid peroxidation. This pathway was initially discovered through the high-throughput screening of anti-neoplastic drugs (15). The ferroptosis-inducing drug, erastin, induces ferroptosis through the inhibition of the cystine/glutamate antiporter system xC-/xCT, which is essential for the synthesis of reduced glutathione, ultimately leading to the accumulation of toxic lipid peroxides (16). Transcriptome analysis conducted by Kwon et al (17) on pan-cancer cell lines revealed that the activity of transcription factors, including Nuclear factor erythroid 2-related factor 2 (NFE2L2/NRF2) and AhR, serves as a critical marker of erastin resistance. AhR plays a context-dependent role in modulating ferroptosis sensitivity across tumor cell lines (18,19). For instance, the siRNA-mediated knockdown of AhR increases erastin sensitivity in erastin-insensitive A549 cells, while reducing sensitivity in erastin-sensitive Calu1 cells, highlighting its dual role in ferroptosis resistance (17). Supporting this, Kou et al (19) and Peng et al (20) demonstrated that AhR expression levels were closely associated with erastin sensitivity in both A549 and BEAS-2B (human normal bronchial epithelial cells). Their research further identified the solute carrier family 7 member 11 (SLC7A11) antioxidant system as a key downstream effector of AhR (19,20). Despite these advancements, the precise molecular mechanisms underlying the involvement of AhR in ferroptosis remain to be fully elucidated.

AhR plays a pivotal role in modulating disease progression through the regulation of lipid peroxidation and ferroptosis across diverse pathological contexts (17,18). Beyond its established functions in tumors, AhR activation has been implicated in other diseases. For example, in I/R injury (liver, myocardium and kidneys), it exacerbates tissue damage by promoting lipid peroxidation and ferroptosis (21-24); AhR-mediated lipid peroxidation and ferroptosis have been implicated in neurodegenerative disorders, such as Alzheimer's disease (25); in intestinal inflammation, AhR induces ferroptosis in intestinal intraepithelial lymphocytes (natural TCRαβ+ CD8αα+ T-cells and TCRγδ+ CD8αα+ T-cells, as well as induced TCRαβ+ CD4+ and TCRαβ+ CD8αβ+ T-cells) (26); and in asthma pathogenesis, AhR modulates ferroptosis in lung epithelial cells (BEAS-2B) (27). Notably, AhR exhibits context-dependent roles in these processes. In I/R injury, AhR activation uniformly aggravates tissue damage. By contrast, its role in tumors is more intricate, displaying dual effects that vary by cell type and ligand specificity. While the AhR-ferroptosis axis has been extensively studied in tumors and I/R injury, its implications in inflammatory bowel disease, neurodegenerative diseases and lung diseases remain underexplored, representing critical gaps in current research.

Early studies have identified several key mechanisms underlying the context-dependent roles of AhR in response to diverse ligands or cellular environments (28). The differential effects of AhR activation may be attributed to the following factors: i) Ligand-specific receptor conformation. Distinct ligands, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the tryptophan metabolite, 6-formylindolo[3,2-b]carbazole (FICZ), induce unique conformational changes in AhR, affecting its interaction with the exenobiotic response element (XRE), the core DNA sequence regulating gene transcription in the AhR signaling pathway. ii) Ligand affinity and chemical properties: The binding stability and nuclear retention of AhR are determined by ligand characteristics (e.g., hydrophobicity, molecular size). High-affinity ligands prolong nuclear localization and sustained signaling, while low-affinity ligands (e.g., plant-derived metabolites) typically trigger transient activation. iii) Cofactor recruitment specificity: The AhR-AhR nuclear translocator (ARNT) complex recruits ligand-dependent cofactors, such as inflammation-related cofactors (e.g., NF-κB and STAT), metabolic regulators (e.g., glypican 1α and sterol regulatory element-binding protein 1), to direct the downstream responses. iv) Cell type and microenvironment dependency: Tissue-specific expression of cofactors results in the activation of different genes by the same ligand in different cells. For example, AhR may preferentially bind to IL-6 or IL-22 promoters in immune cells, while promoting CYP450 transcriptione in hepatocytes. Furthermore, ligands may remodel the chromatin accessibility of AhR, and at the same time, change the epigenetic state through metabolites. v) Species/tissues-specific AhR isoforms: AhR subtype expression (e.g., AhR1 and AhR2) induces differential responses across tissues or species.

Given that AhR target genes critically regulate redox homeostasis, its role in lipid peroxidation and ferroptosis varies by ligand context and disease setting, suggesting that targeted AhR modulation may have potential for use in various pathological conditions (Table I). Ferroptosis has emerged as a crucial pathological mechanism in diverse diseases, particularly in cancer and I/R injury, where its initiation is intricately linked to disruptions in redox homeostasis and excessive lipid peroxidation (29). This review specifically examines the therapeutic implications of targeting AhR-mediated lipid peroxidation and ferroptosis in these two clinically significant conditions. The present review focuses on the fundamental association between lipid peroxidation and ferroptosis, summarizing and critically analyzing the role and potential mechanisms of AhR in these processes. The present review aimed to enhance the understanding of AhR signaling in diseases pathogenesis and to explore novel therapeutic avenues targeting this pathway for disease intervention.

Table I Summary of AhR ligands and antagonists regulating lipid peroxidation and ferroptosis pathways.

Table I

Summary of AhR ligands and antagonists regulating lipid peroxidation and ferroptosis pathways.

Ligands or antagonists	Promotes/inhibits the AhR signaling pathway	Cell line/animal model	Target gene and signaling pathway	Influence of ferroptosis and lipid peroxidation	(Refs.)
CH223191	Inhibits	Mesenchymal stem cells (MSCS) in hepatic ischemia-reperfusion injury models	STAT3-HO-1/COX-2 pathway	Inhibits	(67)
CH223191	Inhibits	Hepatocytes of the mouse model of Metabolic Disaster-associated steatohepatitis (MASH)	Pten/Akt/β-catenin pathway	Inhibits	(24)
CH223191	Inhibits	Primary murine renal proximal tubular epithelial cells (RPTECs)	The cytochrome P450 superfamily	Inhibits	(21)
TCDD	Promotes	Prostate cancer (LNCap, 22Rv1)	NR4A1/SCD1 axis	Promotes	(18)
IDA	Promotes	Colorectal cancer cell lines and mouse models of colorectal cancer (HT29)	ALDH1A3-FSP1 axis	Inhibits	(91)
indirubin	Promotes	Mouse embryonic fibroblast (MEF) cell line induced by cysteine deprivation for ferroptosis	ATF4-SLC7A11 axis	Inhibits	(84)
SR1	Inhibits	Mouse embryonic fibroblast (MEF) cell line induced by cysteine deprivation for ferroptosis	ATF4-SLC7A11 axis	Promotes	(84)
DIM	Inhibits	Non-small cell lung cancer cell lines (A549, H1299)	NRF2-GPX4 axis	Promotes	(112)
I3P	Promotes	BEAS-2B	SLC7A11 axis	Inhibits	(20)
Benzopyrene	Promotes	Airway epithelial cells (AEC) of the mouse asthma model	cPLA2-ACSL4 axis	Promotes	(27)
Kyn	Promotes	Human lung cancer cell lines A549 and H1299 and mouse lung cancer cell lines	NRF2 pathway	Inhibits	(76)
Kyn	Promotes	Glioblastoma multiforme (GBM) cell line	FTO-SLC7A11 axis	Inhibits	(108)
NBP	Inhibits	In vitro ferroptosis models (HT22 cells, hippocampal sections and primary neurons) and in vivo controlled cortical shock mouse models	CYP1B1-ROS axis	Inhibits	(53)
IS	Promotes	MC3T3-E1 cell line and mouse models of chronic kidney disease	SLC7A11/GPX4 axis	Promotes	(81)
ILA	Promotes	Cardiotoxic (DIC) mice and DOX-treated H9C2 cells	NRF2 pathway	Inhibits	(107)
YH439	Promotes	Mouse hepatic stellate cells (mHSCs)	Mrp1	Promotes	(111)
Ethanol extract of Hibiscus (HS) calyx	Inhibits	Human keratinocytes HaCaT cells	FTH1, GPX4 and SLC7A11 pathway	Promotes	(113)

[i] IDA, trans-3-indoleacrylic acid; DIM, 3,3′-diindolemethane; I3P, indole 3-pyruvic acid; benzopyrene, indeno [1,2,3-cd] pyrene; NBP, butylphthalide; IS, indole sulfate ; ILA, indole-3-lactic acid; YH439, isopropyl-2-(1,3-dithiazole-2-subunit)2-[N-(4-methylthiazole-2-unit) carbamoyl] acetate; COX-2, cyclooxygenase-2; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; ALDH1A3, aldehyde dehydrogenase 1 family, member A3; FSP1, ferroptosis suppressor protein 1; ATF4, activating transcription factor 4; SLC7A11, solute carrier family 7 member 11; NRF2, nuclear factor erythroid 2-related factor 2; FTH1, ferritin heavy chain 1; GPX, glutathione peroxidase.

Association between lipid peroxidation and ferroptosis

Lipid peroxidation is an ubiquitous phenomenon observed in a wide array of disease conditions and serves as a critical triggering factor for ferroptosis. This process typically manifests as a free radical chain reaction, characterized by an overabundance of reactive species, such as ROS, RNS and RLS, along with the excessive accumulation of labile iron pools in cells (30). The primary event in lipid peroxidation involves the generation of labile hydroperoxides (LOOH) through the interaction of ROS with membrane PUFAs. LOOH compounds are highly susceptible to decomposition, leading to the formation of metabolically toxic by-products, MDA and 4-HNE, which are closely associated with iron-induced cell death (31). Furthermore, ferrous iron plays a crucial role as an initiator of ferroptosis (32). Ferrous iron can catalyze the conversion of hydrogen peroxide into hydroxyl radicals, which subsequently react with PUFAs to produce lipid peroxides, leading to cellular membrane damage and the onset of ferroptosis.

Lipid peroxides and their degradation products are controlled by intracellular antioxidant mechanisms (33). It has been found that the defense systems against ferroptosis primarily consist of glutathione (GSH)-dependent and GSH-independent antioxidant pathways. Reduced glutathione serves as a substrate for glutathione peroxidase 4 (GPX4), which catalyzes the reduction of lipid peroxides to non-toxic alcohol forms, thereby detoxifying these harmful compounds. Ferroptosis suppressor protein 1 (FSP1) utilizes NADPH to generate reduced coenzyme Q10, thereby shielding the cell membrane from damage induced by lipid peroxides. These two independent antioxidant defense systems exert stringent control over lipid peroxidation levels. Erastin and icFSP1 are specific inhibitors of both ferroptosis defense systems and have been used in the treatment of various diseases (34,35).

The induction of lipid peroxidation-mediated ferroptosis is critically influenced by three pivotal factors: The generation of reactive species, the concentration of the intracellular labile iron pool and the modulation of the antioxidant defense system (Fig. 1). These pathways are governed by multiple factors, many of which are transcriptionally regulated by AhR. For instance, stearoyl-CoA desaturase 1 regulates the metabolism of unsaturated fatty acids and reduces the oxidative vulnerability of PUFAs, thereby promoting lipid peroxide formation (36). Heme oxygenase 1 (HMOX1) regulates heme catabolism, releasing free iron that upregulates the levels of labile iron pools within cells (37). Cyclooxygenase-2 (COX-2) facilitates ROS production via multiple metabolic pathways, inducing lipid peroxidation and ferroptosis (38). The SLC7A1/GPX4 system, a GSH-dependent antioxidant mechanism, maintains intracellular redox homeostasis by promoting the synthesis of reduced GSH (39). FSP1, an antioxidant system independent of GSH, inhibits lipid peroxidation and ferroptosis by consuming NADPH and promoting the reduction of ubiquinone Q10 (34). NFE2L2/NRF2 is a master regulator of the cellular antioxidant response, promoting the transcription of numerous downstream antioxidant-related genes through binding to their antioxidant response elements (ARE) (40). CYP1B1, a member of the cytochrome P450 enzyme family, mediates metabolic processes that generate ROS, contributing to lipid peroxidation and ferroptosis (41). Other members of the cytochrome P450 enzyme family, including CYP1A1 and CYP1A2, have also been implicated in lipid peroxidation, although to the best of our knowledge, no studies to date have demonstrated a direct link between these enzymes and ferroptosis. Notably, the key factors regulating lipid peroxidation and ferroptosis are either target genes of AhR or are regulated by AhR target genes. This suggests that AhR may serve as a crucial regulatory node for lipid peroxidation and ferroptosis. Investigating the mechanisms by which AhR modulates ferroptosis and identifying the potential targets of AhR in this process holds significant promise for the development of novel therapeutic agents and the treatment of associated diseases.

Figure 1 Molecular mechanisms and key regulators of lipid peroxidation and ferroptosis. The initiation of ferroptosis is primarily driven by the accumulation of labile iron pools within cells, which originates from two main sources: Iron uptake mediated by transferrin receptor 1 and free iron release during heme metabolism catalyzed by heme oxygenase 1. In normal cells, free iron, polyunsaturated fatty acids, and ROS generate lipid hydroperoxides via the Fenton reaction. This process is predominantly modulated by GSH-dependent and non-GSH-dependent intracellular antioxidant systems. The GSH-dependent system facilitates the uptake of cystine, an essential precursor for reduced glutathione, through the SLC7A11/SLC3A2 isodimer, and subsequently consumes reduced GSH via GPX to detoxify lipid peroxides. FSP1, also known as AIFM2 or AMID, represents a recently identified core inhibitor of ferroptosis. It regulates the redox cycle of coenzyme Q10 through pathways independent of GSH and GPX4, thereby forming a secondary defense mechanism against lipid peroxidation. ATF4 and NRF2 function as the core transcription factors enabling cells to respond to oxidative stress and metabolic imbalance. Both ATF4 and NRF2 inhibit lipid peroxidation and confer resistance to ferroptosis by regulating distinct target gene networks. ROS, reactive oxygen species; GSH, glutathione; SLC7A11, solute carrier family 7 member 11; GPX, glutathione peroxidase; FSP1, ferroptosis suppressor protein 1; ATF4, activating transcription factor 4; NRF2, nuclear factor erythroid 2-related factor 2; CoQ10, coenzyme Q10; NADP+, nicotinamide adenine dinucleotide phosphate; PUFA, polyunsaturated fatty acid; MDA, malondialdehyde; 4-HNE, 4-hydroxynonenal; ARE, antioxidant response element.

AhR-mediated regulation of lipid peroxidation and ferroptosis

AhR orchestrates lipid peroxidation and ferroptosis through diverse molecular mechanisms, thereby critically influencing the pathogenesis of multiple diseases. The AhR-mediated regulation of lipoferroptosis includes the following: The regulation of the gene expression levels of pro-oxidant and antioxidant enzymes; the regulation of iron, heme and arachidonic acid metabolism; and the regulation of the ferroptosis defense system and synthesis of antioxidant compounds. Notably, AhR activation plays a dual role in lipid peroxidation-ferroptosis axis, with distinct regulatory effects depending on the specific ligands (42). This mechanistic plasticity, evidenced by ChIP-seq and microarray analyses across different cell lineages and developmental stage (43-46), positions AhR as both a potential therapeutic target and a challenge for precise pharmacological intervention.

AhR mediates lipid peroxidation and ferroptosis by regulating the transcription of pro-oxidant and antioxidant enzymes AhR activation by pro-oxidative ligands induces pro-oxidative enzymes expression, mediating lipid peroxidation and ferroptosis

AhR is a ligand-dependent transcription factor that can mediate both protective and pathological responses. Initially identified due to its involvement in the toxicity of dioxins such as TCDD, AhR predominantly resides in the cytoplasm in an inactive state, complexed with chaperone proteins, including HSP90, AIP and p23. Upon binding to TCDD, AhR translocates to the nucleus, dimerizes with ARNT, and binds to XRE in target gene enhancer regions (47). This classical AhR/ARNT pathway upregulates the expression of CYP1 family members, such as CYP1A1, CYP1A2 and CYP1B1 (48). These enzymes represent the most extensively studied target genes of the AhR/ARNT complex of the activation of the classic pathway of AhR. CYP450 enzymes, including CYP1, CYP2 and CYP3, catalyze metabolic reactions that facilitate the production of ROS (49). The upregulation of CYP1A1 and CYP1B1 promote lipid peroxidation and trigger ferroptosis, and both TCDD and benzo(a)pyrene promote lipid peroxidation via this pathway (50), while the AhR antagonist, CH223191, reverses this effect (51). Similarly, decabromodiphenyl ether (BDE-209) induces lipid peroxidation via the AhR-CYP1A1-ROS pathway (52).

Notably, AhR activation by natural ligands, such as dietary indole and sulforaphane, as well as other low-affinity AhR ligands, supports intestinal homeostasis and immune regulation. However, in chronic inflammatory bowel disease, dysregulated AhR signaling, driven by gut microbiota imbalances, exacerbates oxidative stress, lipid peroxidation and iron deficiency in intestinal epithelial lymphocytes, and this can potentially be mitigated by specific AhR inhibitors (26). Moreover, in neurological and hepatic contexts, butylphthalide mitigates traumatic brain injury-induced ferroptosis by inhibiting the AhR-CYP1B1-ROS pathway (53), while CYP1B1 drives ferroptosis in hepatocellular and cholangiocarcinoma (41). Collectively, these findings underscore the pivotal role of AhR in modulating lipid peroxidation and ferroptosis through pro-oxidant enzyme regulation.

Antioxidant AhR ligands induce antioxidant enzyme expression to regulate lipid peroxidation and ferroptosis

While pro-oxidative ligands, such as TCDD and benzo(a) pyrene induce lipid peroxidation via AhR activation, emerging evidence highlights the dual role of AhR in redox regulation. Natural exogenous AhR agonists, such as extracts from artichoke (Cynara scolymus), soybean, fig tree and Houttuynia cordata, mitigate ROS production, oxidative stress and lipid peroxidation by regulation of antioxidant enzyme target genes, such as NQO1, GST and UGT1A1 genes by AhR (54-56) (Fig. 2). Furthermore, the key antioxidant stress transcription factor NRF2 serves as a direct target for AhR signaling transduction. Notably, its promoter region containing multiple XRE (57), antioxidant enzymes such as NQO1, GST and UGT1A1 are also direct target genes of NRF2. This indicates that AhR regulates the NRF2 gene and thereby promotes the transcription of antioxidant enzymes. In summary, the activation or inhibition of AhR classic signaling using appropriate AhR ligands under various disease conditions can influence lipid peroxidation and ferroptosis levels by regulating the synthesis of pro-oxidant and antioxidant enzymes.

Figure 2 Oxidative and antioxidant AhR ligands regulate lipid peroxidation and ferroptosis via an oxidative-antioxidant bidirectional regulatory network. Exogenous pro-oxidative AhR ligands, such as the toxins TCDD and benzo[a]pyrene, bind to AhR, forming the AhR-ARNT complex that translocates into the nucleus. This complex subsequently binds to the XRE, initiating the transcription of various progenitor enzymes, including CYP1A1, CYP1B1, CYP1A2, COX-2 and NOX, then mediating ROS production, which in turn induces lipid peroxidation and ferroptosis. Conversely, natural AhR ligands derived from plant sources, such as snake tail grass, soybean, fig tree, and fish tail grass, activate the transcription of antioxidant enzymes (e.g., NQO1, GST and UGT1A1) through AhR signaling. This activation suppresses ROS production, thereby mitigating lipid peroxidation and inhibiting ferroptosis. AhR, aryl hydrocarbon receptor; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; ARNT, AhR nuclear translocator; NOX, nitrogen oxide; ROS, reactive oxygen species; NQO1, NAD(P) H dehydrogenase [quinone] 1; GST, glutathione S-transferase; UGT1A1, UDP-glucuronosyltransferase 1-1; HMOX1, heme oxygenase 1; IDO1, indoleamine 2,3-dioxygenase 1; SLC7A11, solute carrier family 7 member 11; COX-2, cyclooxygenase-2; ALDH1A3, aldehyde dehydrogenase 1 family, member A3.

AhR regulates lipid peroxidation and ferroptosis by modulating a range of metabolic pathways

Targeted lipid peroxidation and ferroptosis affect the pathogenesis of I/R injury

I/R injury represents a condition wherein tissue cells, following a period of ischemia, experience reperfusion, leading to an accelerated exacerbation of tissue damage. This pathological process, observed in multiple organs and diseases, results in massive ROS production in I/R injury (58). During I/R injury, various endogenous ligands of AhR, such as the tryptophan metabolite kynurenine (Kyn), are generated to sustain AhR activation, leading to CYP450-mediated ROS overproduction and exacerbating oxidative stress (59). The restoration of blood flow and subsequent reoxygenation during reperfusion frequently result in reperfusion injury, a condition increasingly recognized as being mediated by ferroptosis (60). Previous studies have indicated that ferroptosis is more likely to occur during the reperfusion phase rather than the ischemic phase in I/R injury (61). The endogenous mechanisms responsible for scavenging ROS are compromised following I/R, leading to ineffective ROS neutralization. I/R injury is characterized by a series of intracellular events, including excessive ROS production during reperfusion, lipid peroxidation and elevated intracellular iron levels (62). Lipid peroxidation and oxidative damage induced by ROS can result in cellular damage and death, which aligns with the hallmarks of ferroptosis. Ferroptosis inhibitors, such as Fer-1 and deferoxamine (DFO), can effectively prevent or mitigate the progression of I/R injury when administered prior to or during the I/R event. DFO is applied in coronary artery bypass grafting procedures. The intravenous administration of DFO has been shown to protect the myocardium from reperfusion injury and mitigate lipid peroxidation (63).

Targeting AhR-mediated arachidonic acid and heme metabolism to mitigate I/R injury

Emerging evidence highlights AhR as a crucial regulator in I/R injury affecting the liver, kidneys and myocardium (21-23,64). During the early phase of I/R injury, oxidative stress stimulates the production of oxyindole, a compound that has been demonstrated to be an effective AhR agonist and significantly activates AhR (65). Moreover, under the oxidative stress conditions associated with I/R injury, there is an increased presence of endogenous pro-oxidative ligands for AhR (66). These multiple pro-oxidative endogenous ligands may constitute a critical component in the pathophysiology of I/R injury. In a previous study, in two distinct mouse models of liver I/R injury, both the conventional ferroptosis inhibitor DFO and the AhR antagonist CH223191 were found to be effective in reversing ferroptosis and lipid peroxidation. Moreover, CH223191 demonstrated superior efficacy compared with DFO (67), suggesting that AhR activation is closely related to I/R injury. HMOX1 and COX-2 are pivotal enzymes in heme and arachidonic acid metabolism, respectively. Transcriptomic analysis revealed that the STAT3-HMOX1/COX-2 signaling pathway was inhibited following the administration of CH223191 (67). The activation of HMOX1 facilitates the release of free iron ions from heme, consequently elevating intracellular free iron levels (68). COX-2 also catalyzes the production of ROS, leading to oxidative stress and lipid peroxidation (38). Both HMOX1 and COX-2 genes play crucial roles in the induction of ferroptosis. Previous studies have demonstrated that AhR signaling exerts direct or indirect effects on the HMOX1/COX-2 signaling pathway via multiple mechanisms (69-72), and the AhR signaling pathway is intricately associated with the metabolism of arachidonic acid and heme (73).

A previous study demonstrated that targeting ferroptosis is a promising therapeutic approach to mitigate renal tubular cell injury in acute tubular necrosis induced by I/R (74). The administration of the AhR antagonist, CH223191, or the ferroptosis inhibitor, α-col, prior to the onset of reperfusion and reoxygenation injury has the potential to prevent the production of ROS, reduce lipid peroxidation and mitigate cellular iron toxicity. The underlying mechanism may involve the transcriptional regulation of AhR through indoleamine 2,3-dioxygenase (IDO)-mediated Kyn metabolism (21,66). The inhibition of AhR signaling has been shown to mitigate reperfusion injury in a rat model of cardiac I/R (23). Arachidonate 12/15-lipoxygenase-mediated arachidonic acid metabolism significantly contributes to myocardial I/R injury (75). Therefore, arachidonic acid metabolism mediated by AhR signaling may be a potential target for alleviating myocardial I/R injury.

These studies demonstrate that AhR plays a crucial role in I/R injury across various parenchymal organs. The underlying mechanisms may be associated with the metabolism of hemin and arachidonic acid. Oxidative stress induced by I/R injury results in the activation of AhR through endogenous pro-oxidative ligands, such as Kyn and oxyindole. IDO, as a key enzyme in tryptophan metabolism, can produce many endogenous ligands of AhR. IDO also serves as the target gene of AhR. Due to this particular cyclic activation characteristic, it will easily cause the continuous activation of AhR (76). Moreover, studies have shown that IDO plays a key role in I/R injury. The pharmacological inhibition of IDO by using 1-MT (IDO inhibitor) limits the production of Kyn, inhibits the activation of AhR, and subsequently the production of ROS. This effect can also be achieved by using the AhR antagonist, CH223191 (66,77). This indicates that it is of utmost importance to reduce the production of ROS induced by arachidonic acid and heme metabolism mediated by the continuous activation of AhR through targeting this circular pathway. The overproduction of these pro-oxidant ligands during I/R injury may contribute to continuous activation of AhR signaling. This activation subsequently mediates oxidative stress and lipid peroxidation, indicating that targeting AhR signaling may be a promising therapeutic strategy for mitigating reperfusion injury.

AhR affects lipid peroxidation and ferroptosis by regulating the levels of antioxidant active substances and ferroptosis defense system

In chronic kidney disease (CKD), AhR activation by indoxyl sulfate (IS) suppresses the antioxidant system via SLC7A11, and subsequently promotes lipid peroxidation and induces ferroptosis

SLC7A11 is a critical component of the cystine/glutamate antiporter, which is crucial for glutathione synthesis, and it exerts a significant negative regulatory influence on ferroptosis (78). The SLC7A11-GPX4-GSH-cysteine axis serves as the pivotal hub in the ferroptosis cascade (79). In patients with CKD, the accumulation of IS, a metabolite of tryptophan, as a result of impaired renal excretion, can result in various health-related complications (80). In a previous study, in a mouse model of CKD, IS induced ferroptosis in MC3T3-E1 cells by activating the AhR signaling pathway and mediating the inhibition of the SLC7A11-GPX4 antioxidant signaling pathway. This process inhibited the osteogenic differentiation of MC3T3-E1 cells and contributed to alveolar bone resorption in mice with CKD via ferroptosis (81). The inhibition of AhR activity can mitigate the osteotoxic effects induced by IS. However, the exact mechanisms through which AhR influences SLC7A11-GPX4 signaling to trigger ferroptosis in the context of IS activation remain elusive. A plausible explanation for this phenomenon is the interaction between AhR signaling and HIF-1α signaling. In patients with CKD, HIF-1α signaling is upregulated as a result of tissue hypoxia, which is caused by diminished erythropoietin synthesis (82). Research has demonstrated that the activation of HIF-1α signaling leads to the increased expression of SLC7A11 (83,84). AhR competes with HIF-1α for binding to ARNT, thereby competitively inhibiting the HIF-1α signaling pathway. This inhibition of SLC7A11 expression, mediated by the HIF-1α signaling pathway, may promote lipid peroxidation and ferroptosis.

Indole-3-pyruvate (I3P)-activated AhR upregulates SLC7A11 to suppress lipid peroxidation and ferroptosis in both BEAS-2B and non-small cell lung cancer (NSCLC) cells

In contrast to the previously described induction of ferroptosis by IS through the activation of the AhR-mediated inhibition of the SLC7A11-GPX4 antioxidant signaling pathway, the knockdown of AhR influences lipid peroxidation levels in both BEAS-2B and NSCLC cells. AhR affects the transcriptional regulation of SLC7A11. Notably, the pharmacological inhibition and genetic knockdown of AhR in BEAS-2B cells markedly increases erastin-induced ferroptosis. In PC9 cells, the promoter region of SLC7A11 harbors an AhR binding site. Furthermore, a comprehensive database search and analysis using JASPAR indicated that the promoter region of SLC7A11 contains specific XREs. The study also highlighted the role of I3P, an endogenous AhR agonist ligand and a tryptophan analog, in the development of a novel AhR receptor. The AhR-SLC7A11-GSH-GPX4 axis protects cells against ferroptosis via an AhR-dependent mechanism (19,20). These findings demonstrate that the activation of AhR signaling directly modulates the transcriptional expression of the antioxidant defense system, SLC7A11, thereby conferring resistance to ferroptosis in both BEAS-2B and NSCLC cells.

The AhR signaling pathway indirectly activates the SLC7A11 antioxidant system via activating transcription factor 4 (ATF4), thereby enhancing ferroptosis resistance in tumors

In addition to its direct influence on the transcriptional expression of SLC7A11, AhR signaling also indirectly transcriptionally regulates SLC7A11 by detecting lysosomal cysteine levels and inducing the adaptive expression of ATF4. ATF4 is crucial for cells adapting to adverse conditions of amino acid deprivation and mediates a variety of cellular phenotypic changes (85). The study by Swanda et al (86) revealed that lysosomal cysteine deficiency, sensed through the Kyn pathway of AhR, leads to adaptive ATF4 expression, which subsequently enhances SLC7A11 transcription and renders cells less susceptible to ferroptosis. The synthetic mRNA reagent, CysRx, was designed to convert cytosolic cysteine into lysosomal cysteine, thereby sensitizing tumor cells to ferroptosis by downregulating ATF4 expression. The AhR inhibitor stemregenin (SR1) was used to induce ferroptosis in cysteine-deficient cells, while the AhR activator indirubin fully rescued these cells from ferroptosis (86). Notably, this pathway regulates the transcriptional activity of ATF4 in the nucleus independently of the conventional integrated stress response and oxidative stress effects. These findings demonstrate that, apart from modulating cellular sensitivity to ferroptosis through the regulation of lysosomal cysteine levels, manipulating the AhR signaling pathway to induce ferroptosis in cancer cells is a promising therapeutic target.

Intestinal microbiota metabolites activate AhR to confer ferroptosis resistance in intestinal tumors through non-GSH antioxidant pathways

Gut commensal microbiota metabolites serve as a significant source of AhR agonists (87). FICZ, Kyn, indirubin, indole and I3P are endogenous ligands of AhR. Metabolites produced by the gut microbiota can be categorized into two main groups: Immunosuppressive metabolites, including short-chain fatty acids, tryptophan metabolites and bile acid metabolites; inflammatory metabolites, such as those activating the stimulator of interferon genes pathway and lipopolysaccharides (88). Immunosuppressive metabolites derived from the gut microbiota are inclined to inhibit ferroptosis (89), whereas inflammatory metabolites facilitate ferroptosis (90). Studies have shown that the anaerobic gut bacterium Streptococcus gastro metabolizes tryptophan to produce trans-3-indoleacrylic acid (IDA), which, upon activating AhR, regulates the expression of aldehyde dehydrogenase 1 family, member A3 (ALDH1A3) by binding with a high affinity region approximately 100 base pairs upstream of the ALDH1A3 transcription start site. This regulation occurs through ARNT-mediated nuclear translocation, indicating that when AhR is activated by IDA, it is recruited to the ALDH1A3 promoter (91). ALDH1A3, an aldehyde dehydrogenase which uses retinaldehyde as its substrate, is predominantly overexpressed in tumor cells (92), potentially due to the elevated levels of redox metabolism observed in tumor cells. ALDH1A3 plays a crucial role in the production of NADPH, which serves as the primary electron donor essential for reduction reactions and activates the classical FSP1, thereby inhibiting ferroptosis (34). This indicates that the intestinal microbiota metabolite IDA can enhance FSP1-mediated synthesis of reduced coenzyme Q10 via the AhR-ALDH1A3 pathway, leading to NADPH production, ferroptosis inhibition, and ultimately promoting the progression of colorectal cancer (91).

Previously, transcriptomic analysis revealed a significant association between AhR levels and erastin sensitivity (17). Given the influence of AhR activity on the sensitivity of various tumor cell lines to erastin, and the role of erastin as a specific inhibitor of SLC7A11, it was hypothesized that the bidirectional effect of AhR signaling on SLC7A11 may be attributed to context-dependent variations in AhR function. Investigating the association between AhR and erastin across diverse tumor cell lines and precisely modulating AhR activity to influence erastin-induced ferroptosis sensitivity is an area worth further exploration. Pharmacologically regulating AhR activity in conjunction with erastin to eradicate tumor cells and delay tumor progression represents a promising therapeutic strategy.

Potential applications of targeting AhR-mediated lipid peroxidation and ferroptosis in cancer and I/R injury therapy

Pharmacological modulation by inducing or inhibiting ferroptosis is a key potential approach for addressing drug-resistant cancers, ischemic organ damage, and a range of other diseases characterized by extensive lipid peroxidation (29). Previous studies have indicated that drug-resistant cancer cells, particularly those exhibiting a mesenchymal phenotype and propensity for metastasis, are highly vulnerable to ferroptosis (17,93). AhR modulates ferroptosis via multiple pathways, functioning as a promoter in specific conditions such as I/R injury and certain tumors (Fig. 3), while serving as a suppressor in bronchial epithelial cells and other tumor types (Fig. 4). This dual regulatory role of AhR in ferroptosis reflects its complex function. However, the role of AhR as either a promoter or inhibitor of ferroptosis in numerous diseases remains underexplored. A more comprehensive understanding of the regulatory mechanisms of AhR in ferroptosis could pave the way for novel therapeutic approaches and may provide profound insight into the fundamental mechanisms underlying ferroptosis.

Figure 3 The mechanism of AhR mediating lipid peroxidation-ferroptosis via CYP1, SLC7A11/GPX4 axis, or HMOX1 heme metabolism by different ligands in different disease states. AhR modulates the expression of diverse target genes across various contexts, consequently influences ferroptosis in distinct disease processes. IS triggers ferroptosis in MC3T3-E1 cells by activating the SLC7A11/GPX4 signaling pathway via AhR. In renal tubular epithelial cells and liver I/R injury, suppression of the AhR signaling pathway mitigates the extent of damage. Under the condition of oxidative stress of intestinal epithelial lymphocytes, inhibition of AhR signaling can alleviate intestinal epithelial lymphocytes ferroptosis by reducing ROS production. Butylphthalide exerts an inhibit effect on neuronal ferroptosis in traumatic brain injury by inhibiting the AhR-CYP1A-ROS axis. AhR, aryl hydrocarbon receptor; SLC7A11, solute carrier family 7 member 11; GPX, glutathione peroxidase; HMOX1, heme oxygenase 1; I/R, ischemia/reperfusion; ROS, reactive oxygen species.

Figure 4 The mechanism of AhR mediating lipid peroxidation-ferroptosis through the SLC7A11/GPX4 axis or the ALDH1A3/FSP1 axis under different ligand binding or cytosolic lysosomal cystine deficiency states. AhR modulates the expression of diverse target genes across different contexts, thereby influencing ferroptosis in various disease states. Specifically, lysosomal cystine deficiency triggers ATF4 expression via the AhR signaling pathway, leading to the activation of the SLC7A11/GPX4 antioxidant system, which in turn inhibits ferroptosis in tumors. I3P inhibits ferroptosis by activating the AhR-mediated SLC7A11/GPX4 axis antioxidant system in bronchial epithelial cells and non-small cell lung cancer. In colorectal cancer, intestinal metabolites regulate the IDA-AhR-ALDH1A3 pathway and affect the level of NADPH to promote the production of FSP1-mediated reduced ubiquinone, thereby inhibiting tumor cell ferroptosis and promoting tumor progression. AhR, aryl hydrocarbon receptor; SLC7A11, solute carrier family 7 member 11; ALDH1A3, aldehyde dehydrogenase 1 family, member A3; FSP1, ferroptosis suppressor protein 1; GPX, glutathione peroxidase; IDA, trans-3-indoleacrylic acid; ATF4, activating transcription factor 4; CoQ10, coenzyme Q10; NADP+, nicotinamide adenine dinucleotide phosphate.

Potential to mitigate hepatic, renal and myocardial I/R injury by targeting the AhR-mediated metabolism of arachidonic acid and heme

In models of I/R injury, ferroptosis is predominantly observed during the reperfusion phase, rather than the ischemic phase (94). Consistent with these observations, AhR is reactivated during the reperfusion phase of I/R injury, leading to an increase in intracellular ROS production and lipid peroxidation (21). Following I/R, the antioxidant system is significantly impaired, leading to the inefficient scavenging of ROS. The reperfusion of ischemic tissue results in an overproduction of ROS, which mediates I/R injury. Evidence suggests that I/R injury is associated with multiple cellular events, including excessive ROS production (62), lipid peroxidation, and increased intracellular iron concentrations (95). Lipid peroxidation and the generation of ROS contribute to cellular damage and mortality (21). These phenomena align with the characteristics of iron-dependent ferroptosis, and studies in both experimental models and clinical settings have demonstrated that iron chelators can mitigate I/R injury by inhibiting the initiation and progression of ferroptosis (21,63,66).

DFO, a widely used non-toxic iron chelator, has been shown to suppress lipid peroxidation-induced ferroptosis across diverse conditions. Beyond its role in inhibiting AhR, as detailed in the preceding section, the AhR antagonist, CH223191, has proven effective in reducing I/R injury in multiple organ systems, including the liver, kidneys and myocardium, as evidenced in various animal models (21,66,77). Previous studies have demonstrated that AhR is closely related to arachidonic acid metabolism, and various AhR ligands can regulate arachidonic acid metabolism in endothelial cells, hepatocytes, and cardiomyocytes (96-98). Moreover, the COX-2 pathway, lipoxygenase (LOX) pathway and CYP450 pathway in arachidonic acid metabolism play key roles in I/R injury (99) and are potential targets for the AhR-mediated relief of I/R injury. Additionally, heme metabolism is closely related to AhR, such as in I/R injury, atherosclerosis, and liver poisoning, and AhR can affect their occurrence and development through iron and heme metabolism (72,100). As a transcriptional regulator, AhR may also modulate ferroptosis via multiple potential pathways. AhR may alleviate I/R injury through ROS production mediated by CYP450 and COX-2 arachidonic acid metabolism, iron/heme metabolism mediated by STAT3/6 and HMOX1 and Kyn metabolism mediated by AhR. Notably, some studies have demonstrated that the application of CH223191 in hepatic I/R injury is more effective than DFO in alleviating hepatocyte I/R injury and ferroptosis (21,66,67). These findings suggest the feasibility of targeting the AhR signaling pathway with specific inhibitors to ameliorate I/R injury in parenchymal organs.

Inhibiting tumor progression by targeting the AhR-mediated CYP450/ROS axis, ferroptosis antioxidant defense system, heme metabolism and epithelial-mesenchymal transition (EMT)

Ferroptosis exerts a dual effect on tumor biology; targeting ferroptosis is a promising direct strategy for cancer cell eradication, while ferroptosis simultaneously contributes to tumor progression and immune response suppression (101). Similarly, AhR exhibits intricate roles in tumorigenesis and cancer therapy, exhibiting both pro-tumor and anti-tumor effects (102). The activation of AhR is also closely associated with tumor immunity (103), and these effects are contingent upon the specific tumor type and the involved ligand (18,91). In ferroptosis in cancer cells, AhR exhibits various effects, potentially associated with varying activation levels of the downstream transcription of AhR in distinct cell lines. For example, it was demonstrated that the activation level of CYP1A1 in the H358 lung cancer cell line was markedly higher compared with that in the Calu1 cell line. The disparity in the downstream transcriptional response of AhR to the same ligand across different tumor cell lines is likely a critical factor of the differential roles of AhR in ferroptosis within these cells (17). The mechanisms by which AhR inhibits tumor ferroptosis include the modulation of the SLC7A11/GPX4 axis and the enhancement of reduced NADPH production.

It has been shown that AhR-mediated CYP450 influences the extent of ferroptosis in neurons following traumatic brain injury (53). The stabilization of CYP1B1 protein may also play a crucial role in regulating ferroptosis in hepatocellular carcinoma and cholangiocarcinoma (41). However, to the best of our knowledge, there is currently no direct evidence demonstrating that AhR promotes ferroptosis in tumor cells via the transcriptional regulation of CYP450. Moreover, AhR activation in certain tumor cells has been hypothesized to be associated with a metastatic mesenchymal state, characterized by both metastatic and immunosuppressive properties (104). Mesenchyma-like tumor cells exhibit heightened sensitivity to ferroptosis inducers, which aligns with the dual role of ferroptosis in tumor biology. The AhR signaling pathway is intricately linked to heme and iron metabolism mediated by HMOX1. Previous research has demonstrated that tumor cells overexpressing AhR exhibit elevated basal levels of HMOX1 compared with wild-type cells (59), and a high HMOX1-mediated increase in the free iron pool level is a key mediator for the triggering of ferroptosis. A reasonable explanation for the close association between AhR and heme metabolism is that AhR signaling may indirectly mediate heme metabolism through the NRF2 signaling pathway. CYP450, EMT and heme metabolism may serve as key mechanisms underlying AhR-mediated ferroptosis in tumor cells.

The majority of drugs known to induce ferroptosis, such as sorafenib, sulfadiazine, FIN and 3-phenylquinazolinone, are systemic inhibitors of xCT, GPX4 and FSP1, which are regulated by AhR (19,81,88). Therefore, the modulation of AhR levels is anticipated to substantially enhance the efficacy of ferroptosis-inducing drugs. Both AhR gene silencing and stimulation with the exogenous ligand TCDD can induce ferroptosis and increase the sensitivity of tumor cells to erastin (17,18). Consequently, the strategic use of efficient AhR ligands, either alone or in combination with ferroptosis inducers, is a viable strategy for triggering ferroptosis in tumor cells.

The AhR agonists and inhibitors currently used in in cancer therapy include aminoflavone, ITE and SR1 (10,11,14,105). These compounds exhibit notable tumor-suppressive effects. The antitumor mechanism of ITE involves restoring tumor cell sensitivity to sorafenib. The antitumor effects of SR1 and aminoflavonone are partially mediated by ROS. These mechanisms may be facilitated through various potential pathways, such as those involving AhR-mediated CYP450, SLC7A11 and EMT. The application of these highly potent AhR ligands to modulate AhR signaling in conjunction with ferroptosis-inducing drugs is anticipated to yield enhanced antitumor efficacy.

Synopsis

AhR modulation combined with ferroptosis inducers triggers lipid peroxidation and ferroptosis in tumor cells

AhR-mediated lipid peroxidation-ferroptosis plays a critical role in various diseases, particularly in tumors and I/R injury. Silencing the AhR gene in NSCLC A549 cells was previously shown to enhance the antitumor efficacy of erastin (17). Another study elucidated the underlying mechanism, revealing that the activation of AhR in A549 cells mediates the transcription of SLC7A11, a well-established target of the antitumor activity of erastin (20). It is notable that the lung cancer cell line, A549, with the silencing of the AhR gene, promotes the antitumor effect of erastin (19). Conversely, in the lung cancer cell line, Calu1, the silencing of the AhR gene inhibited the antitumor effect of erastin (17). The underlying mechanisms for these discrepancies may resemble those observed in immune cells, where AhR preferentially binds to the IL-6 or IL-22 promoter. In hepatocytes, AhR is more inclined to promote the transcription of the CYP450 enzyme system. These divergent outcomes may be attributed to variations in AhR reactivity towards target genes across different cell lines and within different states of the same cell line. Such differences may involve multiple factors, including unsaturated fatty acid anabolism, EMT, heme/iron metabolism, transcriptional regulation of oxidative antioxidant enzymes and GSH-dependent/independent ferroptosis defense mechanisms. Moreover, the application of specific AhR agonists and inhibitors, including aminoflavone, ITE, SR1 and CH223191, in conjunction with ferroptosis inducers, is anticipated to augment the antitumor efficacy against targeted tumor cells.

Targeting AhR signaling via specific AhR ligands to control lipid peroxidation and ferroptosis in oxidative stress-driven diseases

While AhR plays a dual role in mediating ferroptosis in cancer cells, it mainly acts as a pro-oxidant to promote ferroptosis induced by lipid peroxidation in disease models, such as I/R injury, CKD and colitis. This phenomenon may be attributed to the pro-oxidative nature of the predominant AhR ligands in these contexts, including oxyindole, IS, TCDD and dioxins. Conversely, the antioxidant AhR ligand I3P maintains redox homeostasis by activating the AhR-mediated GSH-dependent ferroptosis defense system in BEAS-2B cells (20). I3P also exhibits antioxidant properties across various disease types (106). Similarly, ILA, another antioxidant AhR agonist ligand, has also been shown to exert an inhibitory effect on ferroptosis (107). These observations suggest that AhR-mediated lipid peroxidation-ferroptosis in non-neoplastic conditions may primarily depend on the specific ligand involved. During I/R injury, oxidative stress activates the tryptophan metabolic pathway, generating numerous endogenous AhR ligands, such as Kyn and FICZ. Kyn has been shown to promote tumor progression by inhibiting ferroptosis in an AhR-dependent manner in glioblastoma multiforme and lung cancer A549 cell lines (20,108). However, Kyn also demonstrates context-dependent effects: It induces ferroptosis in natural killer cells within the gastric cancer microenvironment independently of AhR, while inhibiting ferroptosis in Hela cells also via an AhR-independent mechanism (89,109). Notably, the key enzyme IDO produced by Kyn is the target gene of AhR, indicating that AhR is a central molecule mediating oxidative stress and affecting ferroptosis pathways (76). This highlights the complex and multifaceted association between AhR and ferroptosis, requiring the consideration of multiple factors. Targeting AhR signaling with specific ligands presents a potential therapeutic strategy across various diseases. A comprehensive ligand-AhR-disease database could guide this approach.

Therapeutic potential of novel AhR ligands: Mitigating toxicity through natural derivatives and engineered synthetics

Numerous ligands have demonstrated antitumor efficacy in cellular experiments or therapeutic effects in animal models. However, well-known AhR ligands, such as TCDD and benzo[a]pyrene may induce adverse effects. At present, a number of low-toxicity or non-toxic AhR ligands are under investigation and development, including indoles and flavonoids derived from natural plant metabolites, which are characterized by their favorable safety profiles. For instance, indole-3-carbinol exhibits both low toxicity and anti-cancer properties. As previously mentioned, a number of tryptophan derivatives/metabolites serve as endogenous AhR ligands (87). Recent findings indicate their potential in treating various inflammatory bowel diseases, although excessive levels may concurrently promote intestinal tumor progression (91).

Given the potent toxicity of traditional AhR ligands such as TCDD and the potential limitations of low-affinity natural ligands, synthesis AhR ligands represent a promising avenue. Compounds such as 6,2′,4′-trimethoxyflavone (TMF) retain AhR activation capabilities, but eliminate the chlorine atoms present in TCDD, reducing abnormal signaling. TMF also mimics structural features of endogenous ligands, such as the indole/carbazole scaffold of tryptophan metabolites, to enhance compatibility and incorporates formyl groups to facilitate metabolism and prevent long-term cellular accumulation. TMF has been shown to exert antitumor effects in liver cancer models (110). Similarly, YH439, a synthetic low-toxicity AhR ligand, demonstrated efficacy in alleviating hepatic fibrosis (111). 3,3′-diindolylmethane, a low-toxicity phytochemical from cruciferous vegetables, exhibits anti-hepatocellular carcinoma properties and can induce ferroptosis in hepatocytes (112). These findings underscore the substantial potential of both synthetic AhR ligands and natural plant-derived alternatives (113). Systematic investigations to discover or synthesize clinically applicable AhR ligands are highly promising. Furthermore, in diseases such as intestinal disorders, modulating the gut microbiota to regulate the production of endogenous AhR ligands provides an alternative therapeutic strategy worthy of attention.

In conclusion, the present review underscores the pivotal role of AhR in mediating disease onset and progression through ferroptosis across various diseases. Pharmacological inhibition of AhR signaling, particularly in I/R injury, can mitigate tissue damage. The pharmacological modulation of AhR signaling in specific tumor cell lines, either through activation or inhibition, can induce lipid peroxidation-ferroptosis directly or in combination with ferroptosis inducers, which provides a biological foundation for a promising therapeutic strategy against tumor progression (Fig. 5). Currently, research on AhR-regulated lipid peroxidation and ferroptosis in diseases is limited, with the majority of studies focusing on I/R injury in tumors or various organs. Exploring the role of AhR in lipid peroxidation and ferroptosis across different diseases and tissues, and implementing targeted regulation using natural low-toxicity or synthetic AhR ligands, holds substantial clinical potential.

Figure 5 Pharmacological targeting of AhR to modulate ferroptosis in cancer and I/R injury. AhR ligands regulate lipid peroxidation and ferroptosis through different molecular axes, demonstrating environment-dependent therapeutic potential. In parenchymal organs, such as the heart, liver and kidneys, AhR antagonists CH223191 and SR1 alleviate I/R injury by inhibiting the iron-stimulating pathway: CH223191 downregulates CYP1A-driven ROS amplification and COX-2-mediated inflammatory signals, while SR1 inhibits HMOX1-dependent iron release and IDO1-induced oxidative stress, jointly maintaining the redox balance of cells. In tumors, AhR is pharmacologically regulated through AhR ligands, such as aminoflavone, ITE, SR1 and CH223191, thereby influencing key molecules in various lipid peroxidation and ferroptosis processes, and further inducing ferroptosis in tumor cells or enhancing their sensitivity to erastin. This is expected to eliminate tumor cells, alleviate tumor progression and enhance the anti-tumor efficacy of iron deposition inducers. AhR, aryl hydrocarbon receptor; HMOX1, heme oxygenase 1; IDO1, indoleamine 2,3-dioxygenase 1; ROS, reactive oxygen species; COX-2, cyclooxygenase-2; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; NQO1, NAD(P)H dehydrogenase [quinone] 1; GST, glutathione S-transferase; UGT1A1, UDP-glucuronosyltransferase 1-1.

Conclusion and future perspectives

Current research demonstrates that AhR target genes regulate numerous key genes and mediators involved in ferroptosis, encompassing cellular antioxidant systems, oxidative/antioxidant enzymes, heme/iron metabolism and the arachidonic acid pathway. Notably, AhR can regulate the SLC7A11-GPX4 axis, a pivotal suppressor of ferroptosis. Moreover, AhR modulates ferroptosis through the GSH-independent FSP1 pathway. Consequently, targeting AhR represents a promising therapeutic strategy for diseases driven by lipid peroxidation and ferroptosis, such as cancer and I/R injury.

Availability of data and materials

Not applicable.

Authors' contributions

ZL, WL and XS designed the study. ZL completed the first draft of this manuscript. ZL, MH, SH and YZ collected the data from the literature and revised the manuscript. XS, WL and ZL designed the figures. YZ, WL and XS obtained funding. All authors have read and approved the final version of the manuscript. Data authentication is not applicable.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

Not applicable.

Funding

The present study was supported by the high-level talents scientific research start-up funds of the Affliated Hospital of Guangdong Medical University (grant no. GCC2022023) and the Zhanjiang Science and Technology Project (grant no. 2023A20709).

References