A recently discovered type of cell death, known as cuproptosis, results from an excessive accumulation of copper (Cu) within cells (1). Through enzymatic activity and nuclear magnetic resonance analysis, Tsvetkov et al (2) discovered that elesclomol targets ferredoxin 1 (FDX1) and induces Cu-dependent cell death. Elesclomol and disulfiram are examples of Cu ionophores that raise intracellular Cu levels (3). This increase causes oxidative stress and consequent cell death, which may have consequences for cancer treatment (3). Additionally, Cu ionophores contribute to Cu toxicity and cell death by interfering with protein lipoylation and mitochondrial respiration (3). Cuproptosis is a Cu-dependent cell death that differs from the well-known programmed cell death (PCD) (4). Typical modes of PCD include ferroptosis, necroptosis, autophagy, pyroptosis, apoptosis and neutrophil extracellular traps (5). However, cuproptosis has unique molecular mechanisms and signaling pathways that differentiate it from other forms of cell death, such as apoptosis, necroptosis and ferroptosis (6).

Cuproptosis results from disruptions to Cu homeostasis, which is dependent on the Cu transporter (7). Inflammation, oxidative stress and apoptosis are among the pathogenic processes in which cuproptosis is now known to be involved (8). Attention has recently been drawn to the part that Cu and Cu-induced cell death play in the etiology of cancer (9). Due to its immense potential for cancer therapy, cuproptosis has attracted a lot of attention from cancer research communities (9). Cu-based therapy inhibits the growth of malignancies and may make it possible to treat tumors that are resistant to chemotherapy (9). Cuproptosis is a highly investigated topic in the field of cancer research (8). In the setting of inflammatory bowel disease (IBD), cuproptosis has not been well studied (10). Additionally, numerous studies have now demonstrated that genes linked to cuproptosis are essential for the initiation, spread and prognosis of a wide range of malignancies, such as breast cancer, lung adenocarcinoma and uterine corpus endometrial carcinoma (11-14). Nevertheless, the precise function of genes linked to cuproptosis in ulcerative colitis (UC) (14) and Crohn's disease (CD) remains unclear. Current evidence indicates that these genes are involved in the pathophysiology of IBD (15). Despite this, limited clinical treatments target these genes in IBD, which justifies the search for new drugs that can cure IBD caused by cuproptosis-related genes. Consequently, the present review emphasizes the cuproptosis mechanism, related genes, their pathogenesis and their use as biomarkers for IBD, aiming to explore therapeutic strategies targeting these genes.

The type of cell death known as cuproptosis was discovered in 2022 and depends on the precise delivery of Cu ions to lipoylated tricarboxylic acid (TCA) cycle proteins (16). A study by Huo et al (17) showed that the creation of the Cu ionophore elesclomol causes cuproptosis in cardiomyocytes, implying that Cu ions may be involved in cuproptosis. Solute carrier family 31 member 1 (SLC31A1) importers and ATPase Cu transporting β (ATP7B) exporters of Cu modulate intracellular Cu²⁺ levels to regulate cuproptosis (18). The first three metal-binding domains and the Cu chaperone antioxidant 1 Cu chaperone (ATOX1), which transports Cu to ATP7B, are essential for controlling ATP7B activity (19). Notably, excess Cu causes cuproptosis through the TCA cycle's Cu-dependent aberrant oligomerisation of lipoylation proteins and subsequent reduction in iron-sulphur cluster protein levels, leading to proteotoxic stress and, eventually, cellular death (7,16). During the TCA cycle, Cu binds to acyl-CoA synthetase, causing cuproptosis (20). In the formation of the pyruvate dehydrogenase (PDH) complex, FDX1 stimulates the lipoacylation of dihydrolipoyl transacetylase (DLAT) and inhibits iron-sulfur cluster proteins by converting Cu²⁺ to Cu⁺, which results in cell death (7). Additionally, FDX1 interacts directly with lipoyl synthase (LIAS) to support its function in lipoylation of cellular proteins, which is necessary to keep cells viable in low-glucose environments (21). FDX1 is both a critical regulator of Cu ionophore-induced cell death and an upstream regulator of cellular protein lipoylation, a post-translational modification based on mitochondrial lipids that occurs spontaneously on four mitochondrial enzymes necessary for TCA cycle function (21).

In summary, the core regulatory axis of cuproptosis includes Cu increase, FDX1 stimulation, LIAS upregulation, and DLAT, as the executioner of cuproptosis. Elesclomol increases intracellular Cu levels (3), but FDX1 is a reductase that converts Cu²⁺ to a more hazardous Cu¹⁺ (22). Furthermore, FDX1 directly interacts with LIAS to facilitate its role in cellular protein lipoylation (21). LIAS enhances the lipoylation of DLAT, thereby altering DLAT and facilitating Cu binding to it (23). Finally, DLAT conducts cuproptosis by aggregation and oligomerization. Proteotoxic stress-induced cuproptosis results from this, as well as the decrease in iron-sulfur cluster protein levels (23). Fig. 1 illustrates the pathways in more detail.

Cuproptosis is a type of cell death triggered by excessive Cu accumulation within cells (1), and key regulatory genes include negative regulators [glutaminase (GLS), cyclin-dependent kinase inhibitor 2A (CDKN2A) and metal regulatory transcription factor 1] and positive regulators [FDX1, LIAS, lipoyltransferase 1, dihydrolipoamide dehydrogenase (DLD), DLAT, pyruvate dehydrogenase E1 subunit α1 (PDHA1) and pyruvate dehydrogenase E1 subunit β (PDHB)] (63,64), whilst ferroptosis, which is a non-apoptotic cell death that is iron-dependent, involves a deficiency in GSH or glutathione peroxidase 4 (GPX4) (65,66). The expression levels of GPX4 (67), FDX1, LIAS, DLAT, PDHA1 and DLD (15,68) in the inflamed gut are all decreased. Also, necroptosis is driven by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL), leading to cell expansion, membrane disintegration, leakage of intracellular content and cell death, along with inflammation (69). Deficiency in caspase-8 leads to activation of RIPK3 and MLKL (70,71). In the inflamed gut, RIPK3 and MLKL levels are increased when caspase-8 is reduced or deficient (70). Conversely, adaptor proteins such as TNF receptor-associated death domain protein (TRADD) and Fas-associated death domain protein, along with caspase-8 and caspase-10, are essential for apoptosis signaling through death receptors. Within the inflamed gut environment, the expression of Fas and Fas ligand (72), which are part of the extrinsic route, is increased, while in the intrinsic route of apoptosis, the expression of BAX and caspase 3 is increased (73). Pyroptosis is an inflammatory cell death triggered by inflammasomes; it degrades gasdermin D (GSDMD) and activates cytokines such as IL-1β and IL-18 (74,75). The pyroptosis effector is GSDMD (76). In the inflamed gut environment, GSDMD, as well as other markers of pyroptosis, such as NOD-like receptor family pyrin domain-containing 3 (NLRP3), IL-1β and caspase-1, are increased (77).

To summarize, in terms of core elements, cuproptosis depends on Cu ions, ferroptosis on iron, apoptosis on death receptors and caspase 8, necroptosis on RIPK1, RIPK3 and MLKL in the absence of caspase 8, and pyroptosis on GSDMD. Furthermore, cuproptosis does not require caspases but relies on lipoylation proteins, whereas apoptosis and pyroptosis require caspases. The morphological alterations in cuproptosis, as well as the genes involved, differ from other cell death processes. This suggests that therapeutic approaches for other types of cell death, such as ferroptosis, necroptosis, pyroptosis and apoptosis, may differ from cuprotosis due to distinct cell death pathways.

Although Table I (7,16,69,78-97) highlights the key differences between cuproptosis and other forms of cell death, there are also key overlapping features among them. Cuproptosis and ferroptosis, for example, share a link to GSH depletion. Notably, when comparing ferroptosis and cuproptosis, GSH works at the crossover point of the regulation network (98). Therefore, GSH depletion may lead to cuproptosis and ferroptosis. Additionally, the cystine-glutamate antiporter xCT allows free cystine to enter cells; however, plasma GSH-disulfide may be the primary source of cystine in the body (99). Reduced cystine and glutamine levels interfere with GSH synthesis in acute myeloid cells, which causes glutathione peroxidase-4 (GPX4), a cofactor that keeps lipid peroxidation homeostasis, to malfunction (100). Thus, blocking the cystine-glutamate antiporter xCT (SLC7A11/SLC3A2) may diminish GSH and GPX4 and, in the presence of elevated Cu levels, might lead to cuproptosis and ferroptosis. Additionally, SLC31A1 downregulation and mitochondrial Cu depletion in cardiac fibrosis (CF) are associated with lower Cu concentrations (101). SLC31A1 deficiency specific to fibroblasts increases mitochondrial Cu depletion, increases glycolysis, stimulates fibroblast proliferation and causes CF (104). This suggests that SLC31A1 upregulation may increase mitochondrial Cu accumulation, leading to cuproptosis. Lysine demethylase 5B (KDM5B) is activated by intracellular α-ketoglutarate buildup caused by SLC31A1-mediated cuproptosis (102). Activated KDM5B, in particular, demethylates H3K4me3 marks at the promoter of the ferroptosis regulator ferritin heavy chain 1 (FTH1), inhibiting transcription and making keratinocytes more susceptible to ferroptotic cell death, thereby increasing inflammatory tissue damage (102). These results demonstrate a basic pathogenic SLC31A1/KDM5B/FTH1 molecular axis that connects cuproptosis and dysregulated Cu metabolism to the execution of ferroptosis (102). Thus, cuproptosis and ferroptosis could overlap or intersect via SLC31A1, GSH depletion and the cystine-glutamate antiporter xCT (SLC7A11/SLC3A2).

Cuproptosis can also overlap with apoptosis in terms of mitochondrial damage. One of the roles of cytochrome c in living cells is to catalyze lipid peroxidation in the inner mitochondrial membrane, which triggers apoptosis (103). According to a previous study, Cu buildup in cardiomyocyte mitochondria causes mitochondrial damage, and exposure to cytochrome c causes apoptosis, further damaging the heart (104). Additionally, mitochondrial damage has been identified as a characteristic of cuproptosis (105). This implies that mitochondrial damage may occur in both cuproptosis and apoptosis. Furthermore, cuproptosis can coexist with apoptosis by producing ROS. Oxidative stress refers to elevated intracellular ROS levels that harm proteins, lipids and DNA (106). Overproduction of ROS overwhelms the cells' antioxidant defenses, resulting in either cell death or functional damage (107). Cu ionophores that increase intracellular Cu levels include disulfiram and elesclomol. This rise results in oxidative stress, which leads to cell death (3). This implies that ROS may overlap with the cuproptosis and apoptosis pathways. Finally, p53 activities may also overlap with cuproptosis and apoptosis. For instance, Cu buildup results in apoptosis, which appears to be mediated by p53 activation and DNA damage (108). At physiological concentrations, Cu can directly interact with p53 and prevent it from binding DNA (109), but high Cu levels in hepatocytes result in increased p53 mRNA and apoptotic cell death (110). p53 regulates a variety of metabolic pathways to help cells maintain metabolic homeostasis and adapt to stress (111). In Fanconi anemia hematopoietic stem cells, p53 inactivation inhibits the switch from glycolysis to OXPHOS (112), implying that p53 activation may stimulate this switch. Given that OXPHOS is an essential component of cuproptosis (46), p53 may play a role in regulating cuproptosis (51).

Cuproptosis and pyroptosis may overlap via the NLRP3 pathway. Cu exposure causes NLRP3-dependent cellular pyroptosis, which promotes inflammatory reactions and neurotoxicity (113). Cu has been shown to mediate macrophage pyroptosis and participate in the control of the inflammatory response through the NLRP3 inflammatory vesicle-initiation pathway (114). In a mouse model of acute inflammation that was pretreated with the Cu chelator TTM, serum caspase-1-dependent cellular factors were decreased, but caspase-1-independent cellular factors were unaffected (114,115). Dong et al (116) demonstrated that NLRP3, cleaved caspase-1, apoptosis-associated speck-like protein containing a CARD and IL-1β protein levels increased in a time-dependent manner when CuCl₂ and lipopolysaccharide were administered to primary microglia in non-mutant control mice. CuCl₂ exposure has been indicated to trigger NLRP3 activation-mediated inflammation and the resultant neurotoxicity in microglia (116). Additionally, hepatocyte toxicity is mediated by caspase-1-dependent cellular pyroptosis, which is triggered by excessive Cu exposure. CuSO-treated hepatocytes cocultured with N-acetylcysteine exhibited increased expression of the caspase-1 protein and mRNA levels of genes linked to Cu²⁺-induced pyroptosis. Treatment with the caspase-1 inhibitor Z-YVAD-FMK reduced Cu²⁺-induced increases in lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase activities, mitochondrial membrane potential and apoptotic activity. These findings suggest a link and signaling pathway interaction between pyroptosis and apoptosis caused by Cu exposure (116,117).

Cuproptosis and necroptosis may overlap due to the activation of the necroptosome. When cells are exposed to high levels of Cu, they allow MLKL infiltration and increase MLKL levels, triggering the formation of necroptosomes. This causes MLKL to translocate to the nucleus, where it regulates NF-kB transcriptional activity and provides components for MLKL pore assembly. Cu overload also activates downstream tumor necrosis factor (TNF)/TNF receptor regulators, such as cellular inhibitor of apoptosis 1/TRADD/RIPK1/TNF-receptor-associated factor-2 complexes that control NF-κB essential modulator (NEMO) and TAK1-binding protein 2/3 protein levels and inhibitor of NF-κBα activity, which in turn affects NF-κB transcription. Additionally, the linear ubiquitin chain assembly complex ligates linear chains to NEMO after being drawn to the activated TNF receptor complex by identifying ubiquitin chains produced by other E3 ubiquitin ligases. When the ubiquitin binding in ABIN and NEMO structural domain of NEMO in another IκB kinase (IKK) complex identifies the linear chains attached to NEMO, the IKK complex dimerizes, IKK2 is autophosphorylated and NF-κB is activated (118).

Cell death entails signaling pathways and molecularly specified effector processes (119), including necroptosis (120), apoptosis (121), ferroptosis (122,123) and pyroptosis (124,125). According to previous studies, elesclomol causes ROS-dependent apoptosis in cells (126-128). However, neither the cleavage of caspase 3 nor its activation, which is indicative of apoptosis, occurred in elesclomol-induced cell death (129). Similarly, when the two main apoptotic effectors, BAX and BAK1, were removed or cells were co-treated with pan-caspase inhibitors (Z-VAD-FMK and Boc-D-FMK), the ability of elesclomol to kill cells was preserved, demonstrating once again that Cu-induced cell death is distinct from apoptosis (16). Additionally, Cu ionophore-induced cell death was not prevented by treatment with inhibitors of other recognized cell death pathways, such as ferroptosis (ferrostatin-1), necroptosis (necrostatin-1) or oxidative stress (N-acetyl cysteine), indicating a process different from established cell death routes (16). As a result, treatment for cuproptosis-induced IBD may differ from other types of controlled cell death.

A long-term and recurrent inflammatory condition of the gut is known as IBD (130), with the two main types being CD and UC (131). Depending on the type, location and intensity of the ailment, symptoms may include diarrhea, bleeding, abdominal pain, fever and weight loss (132). It is considered that a patient's immune system, gut microbiota and genetic composition all significantly influence IBD (133). IBD is a prevalent ailment in Europe and America, and its incidence rate is increasing in Asia due to dietary changes (134). Although colorectal cancer (CRC) cases have been less common recently, patients with IBD are at a higher risk of developing CRC (135). The complications of IBD include a toxic megacolon (136), strictures (137), intestinal fibrosis (138), fistulas, abscesses and colitis-associated neoplasia (139). Balloon dilatation of strictures has been replaced by endoscopic stricturotomy, strictureplasty, stenting, fistulotomy, sinusotomy and neoplasia ablation as the methods for treating complications (139). These endoscopic procedures have made it possible to treat certain complications using minimally invasive procedures (139). Additionally, extra-intestinal manifestations (EIMs) of IBD are linked to intestinal activity and can negatively impact quality of life (140). EIMs usually impact the skin, joints and eyes, while the kidneys, liver and pancreas are less frequently affected (140). Studies have shown the efficacy of aminosalicylates (141,142), corticosteroids (143-145), immunomodulators (146-148), small molecule inhibitors (149,150) and biologics (151-155) in treating IBD.

Chelation therapy is the preferred method of treatment for Cu overload or poisoning (238). Cu chelators have been used at the cellular and organismal levels to study Cu acquisition, distribution and disposition (239). One of the most effective ways to maintain physiological Cu concentrations is by using Cu-chelating agents (240). Tetrathiomolybdate™, trientine (triethylenetetramine dihydrochloride), 5,7-dichloro-2[(dimethylamino)methyl]quinoline-8-ol, 2,3-dimercaptosuccinic acid and D-penicillamine [(S)-2-amino-3-mercapto-3-methylbutanoic acid] are the primary Cu-chelating agents (240). Numerous chelating medications have been shown to alter Cu levels by various processes. Specifically, tetrathiomolybdate encourages Cu biliary excretion, whereas penicillamine, trientine and dimercaptosuccinic acid produce complexes that are eliminated in the urine (240). As a result, using medications to help regulate Cu levels in IBD may help alleviate cuproptosis. Preclinical studies have shown that Cu chelators TM (241), TM + cetuximab (242) and disulfiram + oxaliplatin (243) can be used in treating breast cancer, head and neck carcinoma, and CRC, respectively. Additionally, other clinical trials or studies have also shown that trientine plus carboplatin and pegylated liposomal doxorubicin (244), bis-choline tetrathiomolybdate or trientine tetrahydrochloride (245,246), D-penicillamine with Cu sulfate (247), and TM combined with irinotecan, 5-fluorouracil and leucovorin (248) can be used to treat relapse of epithelial ovarian, tubal and peritoneal cancer, Wilson disease, glioblastoma multiforme and metastatic CRC, respectively. Nonetheless, research into Cu chelators and ionophores in the treatment of IBD is ongoing, and there is no concrete evidence that Cu chelators can control Cu levels in IBD. Notably, differentially expressed cuproptosis-related genes have been shown to contribute to the etiology of IBD. As a result, drugs that target these genes using molecular approaches may prevent IBD. For example, molecular docking and other techniques have been used to identify potential medications targeting cuproptosis genes in IBD and provide therapeutic benefit (10,68,221,227). These prospective medication breakthroughs could help prevent IBD in the future.

Cuproptosis is a recently discovered type of cell death that warrants further investigation. Studies have reported increased Cu levels in IBD, while others have found lower Cu levels in the same condition. As a result, more research is needed to determine the specific pathways by which dysregulated Cu contributes to the pathogenesis of IBD. Moreover, the availability of Cu-targeting medications for IBD is currently limited. Notably, Cu has been shown to play a dual role in IBD, having both beneficial and harmful effects, which complicates the targeting of Cu ions as a therapeutic approach.

According to the present review, the majority of cuproptosis-related genes have a role in IBD pathogenesis. However, most of these genes were found via bioinformatic analyses or public databases. Additionally, the complicated regulatory mechanisms of cuproptosis in IBD were also observed. The clinical and experimental data on cuproptosis in IBD are extremely scarce. A lack of raw sequencing data, which could lead to selection bias, and smaller sample sizes were also seen (10,68,227,228). Therefore, these findings provide additional clinical or experimental validation of cuproptosis-related gene expression levels in IBD pathogenesis. In addition, larger sample sizes are required for clinical investigations and well-designed prospective studies. Further research is needed to clarify the underlying mechanisms of cuproptosis genes in IBD. Also, prospective studies on cuproptosis dynamics during the transition from chronic inflammation to colitis-associated cancer are recommended. The use of molecular docking/methods, more IBD medications, natural products, stem cells and nanoparticles should be explored to target cuproptosis-related genes for therapeutic purposes. When it comes to natural products, stem cells and nanoparticles, these can help reduce the side effects of some IBD medications.

IBD is a chronic inflammatory disorder characterized by recurrent episodes and includes conditions such as UC and CD. Research has shown that IBD is associated with imbalances in Cu levels; while some studies indicate that Cu levels increase in patients with IBD, others report a decrease. Cu plays a complex role in IBD, complicating the development of effective therapeutic strategies. Recent studies have identified several cuproptosis-related genes that can serve as biomarkers in diagnosing and predicting the progression of IBD. These genes have also been linked to increased infiltration of immune cells. In response, emerging therapeutic approaches aim to regulate these cuproptosis-related genes. Researchers are exploring novel drugs through molecular docking and other methods to target these genes for treatment.