Copper Homeostasis and Cuproptosis in Neurological Disorders

Introduction

Neurological disorders, characterized by progressive degeneration of the structure and function of the nervous system, are becoming an increasingly significant global health challenge and burden.^1,2 The Global Burden of Disease (GBD) study in 2021 highlighted this phenomenon.³ With the ongoing global aging population, the prevalence of neurological diseases is expected to continue rising, placing an ever-growing strain on medical resources, family care, and public healthcare systems.^4,5 The nervous system is a central network that controls sensory, motor, cognitive, and memory functions, and is composed of large numbers of neurons and glial cells.⁶ Neurofilaments form a cytoskeletal network within neuronal axons, maintaining axonal structural integrity and influencing the velocity of signal conduction.⁷ Any abnormalities in neuronal structure or signal transmission may lead to impairments in sensory, motor, or cognitive functions.

Therapeutic strategies for neurological diseases face substantial challenges, and a wide range of approaches—including conventional pharmaceuticals, antioxidants, neuroprotective agents, and natural bioactive compounds derived from traditional medicinal plants—are being continuously developed and applied.⁸ For example, Shrivastava et al designed and synthesized a class of dual-target small-molecule compounds that simultaneously inhibit acetylcholinesterase (AChE) and β‑site amyloid precursor protein cleaving enzyme 1 (BACE1), demonstrating the feasibility of multi-target intervention in Alzheimer’s disease (AD).⁹

Disruption of copper (Cu) homeostasis has been identified as a key pathogenic mechanism in neurological disorders.¹⁰ Numerous studies have shown that dysregulation of copper homeostasis may impact the nervous system through mechanisms such as oxidative stress (OS), mitochondrial dysfunction, neuroinflammation, and protein misfolding.¹¹ The premature aging model, copper sulfate‐induced stress‐induced premature senescence (CuSO₄‑SIPS), has also confirmed copper’s critical role in age-related functional decline and the development of age-associated diseases.¹² As an essential trace element, copper is indispensable for the normal physiological activities of higher plants and animals.¹³ Human cells can only maintain optimal bioactivity within a narrow concentration range of copper ions.¹⁴ Copper homeostasis is delicately regulated through a complex network of copper-dependent proteins, ensuring precise intracellular distribution. Both copper deficiency and copper overload are detrimental to human health.¹⁵

In 2022, Tsvetkov et al first introduced the concept of cuproptosis.¹⁶ Unlike apoptosis, pyroptosis, or ferroptosis, cuproptosis is a newly identified form of programmed cell death triggered by copper ion overload.¹⁷ Its core mechanism involves excess copper binding to lipoylated proteins in the tricarboxylic acid (TCA) cycle, such as dihydrolipoamide S-acetyltransferase (DLAT) and dihydrolipoamide S-succinyltransferase (DLST), leading to abnormal aggregation of these lipoylated proteins. This disrupts the stability of iron–sulfur (Fe-S) cluster proteins in oxidative phosphorylation (OXPHOS), leading to disulfide bond–dependent aggregation of lipoylated proteins in the TCA cycle, resulting in destabilization or loss of iron-sulfur (Fe-S) cluster proteins and inducing proteotoxic stress.¹⁸ Notably, cuproptosis occurs only in cells with active mitochondrial OXPHOS, whereas glycolysis-dependent cells exhibit significant resistance.¹⁹

Lutsenko et al summarized and discussed the physiological functions, molecular mechanisms, and associated diseases of copper homeostasis in mammals.²⁰ Meng et al reviewed the mechanisms of copper metabolism and regulation in the AD brain and discussed the involvement of cuproptosis in the pathological processes of AD.²¹ Peng et al focused on stroke, examining the physiological roles of copper in stroke and its relationships with pathological processes such as cuproptosis and OS.²² Gao et al summarized current knowledge on copper metabolism, mechanisms of cuproptosis, copper-related cell death, and copper-associated neurological diseases.²³ Xu et al systematically summarized brain-specific copper homeostasis, detailing the roles of BBB transporters, glia-mediated copper buffering, and neuron-specific copper chaperones in maintaining cerebral copper balance.²⁴ This article provides an in-depth investigation of the mechanisms underlying copper metabolism and cuproptosis, without limitation to a single disease or neurodegenerative disorders, and comprehensively reviews the associations between dysregulation of copper homeostasis and a wide range of neurological diseases, including WD and MD that can manifest with neurological symptoms.

In addition to traditional chemical drugs and certain plant extracts that have shown beneficial effects in interventions for neurological diseases,^25,26 novel therapeutics based on the regulation of copper homeostasis have increasingly become a research focus. This article also compiles potential therapeutic agents targeting copper homeostasis mechanisms, with the aim of providing new perspectives for the prevention and treatment of neurological diseases.

Systemic Copper Metabolism

Copper is an essential trace element for nearly all living organisms. According to previous studies, copper is extensively utilized by organisms in various physiological processes mediated by copper-dependent enzymes.²⁷ Due to its potential toxicity, copper requires precise transport and homeostatic regulation²⁸ (Figure 1).

Figure 1 Systemic copper metabolism. Dietary Cu(II) is reduced to Cu(I) in the small intestine, where it is absorbed into intestinal epithelial cells. It is then transported into the portal circulation via ATP7A. In the bloodstream, copper binds to soluble carriers such as ceruloplasmin (CP), α2-macroglobulin, and human serum albumin (HSA), which deliver it to specific tissues or organs. Approximately 75% of copper entering the blood is taken up by the liver. In hepatocytes, copper is imported via CTR1. Within the liver, ATP7B has two major functions: it pumps copper into the Golgi apparatus for CP metalation and, under copper overload conditions, relocates to the apical membrane of bile canaliculi to excrete excess copper into bile, thereby maintaining copper homeostasis. Excess copper is mainly excreted via bile, with small amounts eliminated through urine, sweat, and other routes.

Dietary copper is absorbed in the stomach, duodenum, and small intestine.²⁹ In the intestinal lumen, Cu(II)(Cu²⁺) is reduced to Cu(I)(Cu⁺) by metalloreductases such as six-transmembrane epithelial antigen of the prostate (STEAP)³⁰ and duodenal cytochrome b (DCYTB).³¹ Cu(I) is then transported into intestinal epithelial cells via the apical high-affinity copper transporter 1 (CTR1/SLC31A1).³² Inside the enterocytes, copper is shuttled by the antioxidant 1 copper chaperone (ATOX1) to the basolateral membrane, where it is exported into the portal circulation by ATPase copper-transporting alpha (ATP7A).³³ In the bloodstream, copper binds to soluble carrier proteins such as albumin and α₂-macroglobulin for delivery to specific tissues and organs.³⁴

Approximately 75% of the copper entering the bloodstream is taken up by the liver.³⁵ Within hepatocytes, Cu(I) is internalized via CTR1. ATOX1 then delivers copper to ATP7A and ATPase copper-transporting beta (ATP7B) for incorporation into cuproenzymes. The copper chaperone for superoxide dismutase (CCS) transfers copper to superoxide dismutase 1 (SOD1), while the cytochrome c oxidase copper chaperone 17(COX17) delivers copper to cytochrome c oxidase (COX) in the mitochondria. Excess copper is stored by metallothionein (MT) or bound to glutathione (GSH).^15,36 ATP7B plays a dual role: it pumps copper into the Golgi apparatus for incorporation into ceruloplasmin (CP), which is then secreted into the bloodstream for systemic distribution, and under conditions of copper excess, ATP7B translocates to the canalicular membrane to excrete surplus copper into the bile, thus regulating systemic copper homeostasis.³⁷

The liver is the primary site for copper storage. Excess copper is mainly excreted via bile, with smaller amounts eliminated through urine, sweat, and desquamated tissues.³⁸ When dietary copper intake is high, copper absorption decreases while excretion increases; the opposite occurs when intake is low.³⁹ When copper levels in peripheral tissues and organs are insufficient to sustain normal physiological function, ATP7B located in the Golgi apparatus mobilizes stored copper from hepatocytes into the bloodstream, where it binds to plasma proteins and enters systemic circulation.⁴⁰

Cellular Copper Metabolism

Under normal physiological conditions, intracellular copper levels are tightly maintained within a narrow range by a complex network of proteins. This network includes cuproenzymes, copper chaperones, and membrane transporters, which work in coordination to regulate copper uptake, utilization, and efflux at the cellular level (Figure 2). Maintaining optimal copper concentrations is essential for cell survival—copper deficiency disrupts cellular respiration and metabolism, while copper excess impairs cell viability and may lead to cell death.⁴¹ Unlike traditional mechanisms of cell death, cuproptosis exhibits a strong dependence on mitochondria, particularly the TCA cycle.⁴²

Figure 2 Intracellular copper metabolism. Cu(II) is reduced to Cu(I) by STEAP on the cell membrane and then enters the cell via CTR1. SLC25A3 transports Cu(I) from the mitochondrial intermembrane space into the mitochondrial matrix and influences superoxide dismutase 1 (SOD1) activity. COX17 transfers Cu(I) to SCO1 and COX11, where COX11 delivers copper to COX1 and SCO1 transfers it to COX2, facilitating the metal center assembly of cytochrome c oxidase (CCO). ATOX1 transports copper and targets it to ATP7A/ATP7B located on the trans-Golgi network (TGN) membrane. ATP7A/ATP7B use ATP hydrolysis to drive transmembrane copper transport, delivering copper into the TGN for the metalation of enzymes such as ceruloplasmin (CP) and extracellular superoxide dismutase 3 (SOD3), which require copper as a cofactor. When cytosolic copper levels rise, ATP7A/ATP7B relocate from the TGN to the plasma membrane or intracellular secretory vesicles to export excess copper. Upon restoration of copper homeostasis, they return to the TGN to resume the transport cycle. ATOX1 can also shuttle copper into the nucleus, where it binds specific DNA promoter sequences to drive gene transcription. In the cytosol, CCS inserts Cu(I) into the copper-binding site of SOD1 and catalyzes the formation of the essential disulfide bond in SOD1.

Uptake

Cellular copper uptake primarily depends on the CTR1. Under copper-deficient conditions, Specificity Protein 1 (Sp1) is activated and promotes the transcriptional upregulation of the CTR1 gene.⁴³ Conversely, when copper is sufficient, copper ions suppress Sp1 activity and trigger the endocytosis and degradation of CTR1, thereby downregulating its expression and function.⁴⁴ Mammalian copper homeostasis is regulated through the Cu-Sp1-CTR1 tripartite model.⁴⁵

However, dietary copper mainly exists in the oxidized form Cu(II), which must first be reduced to Cu(I) by membrane-bound metalloreductases such as STEAP2, STEAP3, and STEAP4,^46,47 or by DCYTB,³¹ before it can be transported into the cell via CTR1. In any tissue expressing STEAP proteins (eg, intestine, liver, heart, prostate), Cu(II) can be reduced to Cu(I) and subsequently absorbed through the CTR1 channel. In intestinal epithelial cells, DCYTB and STEAP enzymes function in concert.⁴⁸

Divalent metal transporter 1 (DMT1), a member of the proton-coupled metal ion transporter family,⁴⁹ can mediate Cu(II) uptake when CTR1 is limited or absent, such as in intestinal epithelial cells, though it is less efficient in transporting copper.⁵⁰ In addition to CTR1 and DMT1, low-affinity Fe(II) transport protein (Fet4p)^51,52 and divalent metal ion transporter SMF1 (Smf1p)⁵³ can also transport Cu(II), but due to their low metal specificity, they are collectively referred to as low-affinity transporters.

In summary, Cu(II) is first reduced to Cu(I) by STEAP family proteins or DCYTB at the cell membrane, and then transported into cells via CTR1. In contrast, copper ions entering through DMT1, Fet4p, or Smf1p bypass the redox conversion step and are directly taken up in the Cu(II) form.

Utilization

In the cytoplasm, copper is transported by ATOX1 and targeted to the trans-Golgi network (TGN) membrane-bound transporters ATP7A and ATP7B.^54,55 ATP7A and ATP7B are P-type ATPases that contain six metal-binding domains (MBDs) and utilize ATP hydrolysis to drive the transmembrane transport of copper into the TGN.^56,57 This process facilitates the metallation of copper-dependent enzymes such as tyrosinase, CP, and superoxide dismutase 3 (SOD3).⁵⁸ Under normal copper levels, ATP7A/ATP7B are localized to the TGN, where they function in enzyme loading.⁵⁹ When cytoplasmic copper concentrations rise, ATP7A and ATP7B relocalize to the plasma membrane or intracellular secretory vesicles to export excess copper.⁵⁸ Once copper levels normalize, they return to the TGN to resume another transport cycle.

ATP7A primarily functions in tissues such as the intestine, placenta, and central nervous system (CNS), where it is responsible for delivering copper into the bloodstream.⁶⁰ In contrast, ATP7B plays a dominant role in the liver, preventing copper accumulation by excreting it into bile.⁶¹ This tissue-specific division of labor ensures proper copper distribution and homeostasis. Mutations in the ATP7A or ATP7B genes result in two distinct genetic disorders: Menkes disease (MD), characterized by copper deficiency,⁶² and Wilson disease (WD), characterized by copper toxicity.⁶³

Cytochrome c oxidase (COX, also known as complex IV) is a critical enzyme complex in the mitochondrial respiratory chain, essential for electron transfer and oxygen reduction, and plays a vital role in maintaining respiratory function.⁶⁴ solute carrier family 25 member 3 (SLC25A3) transports copper ions from the mitochondrial intermembrane space (IMS) into the matrix, which is crucial for the metallation of COX and influences the activity of SOD1.⁶⁵ The copper chaperone COX17 specifically transfers Cu(I) to synthesis of cytochrome c oxidase 1 (SCO1) and cytochrome c oxidase copper chaperone 11 (COX11), which assist in loading the copper centers of COX.^66,67

Mitochondrially encoded cytochrome c oxidase subunit I (COX1) and subunit II (COX2) are core components of COX, each containing distinct copper-binding sites—Cu_B and Cu_A, respectively.⁶⁸ COX11 delivers copper to the Cu_B site on COX1, while SCO1 transfers copper to the Cu_A site on COX2.⁶⁹ These two copper sites (Cu_A and Cu_B) form the catalytic core of COX,⁷⁰ playing complementary and essential roles in oxygen reduction and electron transport. Under copper-deficient conditions, cells prioritize mitochondrial copper homeostasis, underscoring its primary importance in overall cellular copper balance.⁷¹

In the cytoplasm, CCS receives copper from CTR1 and inserts Cu(I) into the copper-binding site of SOD1, catalyzing the formation of essential disulfide bonds to activate the enzyme.⁷² SOD1 is an antioxidant enzyme located in both the cytosol and IMS, and CCS also facilitates the maturation of SOD1 within the IMS.^73,74

In the nucleus, ATOX1 can also deliver copper ions, where it binds to specific DNA promoter sequences and promotes gene transcription.⁷⁵

Efflux

When intracellular copper levels become excessive, ATP7A and ATP7B relocate from the TGN to vesicular compartments, which subsequently fuse with the plasma membrane to excrete copper ions via exocytosis into the bile. This represents a major pathway for endogenous copper excretion.³⁷ Once copper concentrations return to physiological levels, these proteins relocalize back to the TGN.⁷⁶

According to a study by Gioilli et al, small copper carriers (SCCs) also play an important role in copper transport and homeostasis. SCCs can serve as an alternative copper efflux pathway, transferring copper from the liver and intestinal epithelial cells to other cells, and under conditions of copper overload, they may be excreted into the urine.⁷⁷

Copper Homeostasis Dysregulation

Copper Homeostasis and Oxidative Stress

Reactive oxygen species (ROS) are byproducts of aerobic metabolism. When intracellular ROS levels exceed the cellular antioxidant defense capacity, they induce oxidative stress (OS), leading to oxidative damage of biomolecules and ultimately resulting in cell death.⁷⁸ Excess copper can increase ROS production, causing OS, while also promoting structural and functional damage to mitochondria. Mitochondrial structural and functional damage, in turn, can feedback to further enhance ROS production, exacerbating oxidative injury.⁷⁹

Dysregulation of copper homeostasis can exert neurotoxicity by inducing OS. In cell models, part of the mechanism by which copper ion carriers induce astrocyte death involves excessive ROS generation, suggesting a role for OS in copper toxicity.⁸⁰ The use of the compound copper pyrithione (CPT) can also induce OS-mediated cytotoxicity, inhibiting neurite outgrowth.⁸¹ Copper deficiency increases the brain’s susceptibility to OS.⁸² Additionally, copper may enhance the ability of 6-hydroxydopamine (6-OHDA) to induce OS, further damaging dopaminergic neurons.⁸³

Copper Homeostasis and Inflammatory Response

Nuclear factor kappa‑light‑chain‑enhancer of activated B cells (NF-κB) is a nuclear transcription factor that normally exists in the cytoplasm in an inactive state by binding to inhibitor of NF-κB (IκB) proteins.⁸⁴ Excess copper can activate the IκB kinase complex, promoting phosphorylation and degradation of IκB proteins and thereby releasing the NF-κB complex. The released p65 subunit is phosphorylated and translocates to the nucleus, where it binds specific DNA sequences to initiate transcription of inflammatory factors such as tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6).^85,86

In BV2 microglial cells, copper can increase ROS levels, activate the NF-κB pathway, induce secretion of inflammatory factors by microglia, and impair mitophagy, ultimately leading to ferroptosis of dopaminergic neurons.⁸⁵ Copper-binding peptides can mitigate microglial inflammation by inhibiting the NF-κB pathway.⁸⁷ In addition, ROS-induced OS can activate the NLRP3 inflammasome, promoting caspase-1–dependent secretion of proinflammatory cytokines and inducing pyroptosis.^88,89

Copper Homeostasis and Mitochondrial Dysfunction

Mitochondria are double-membrane organelles present in all eukaryotic cells, responsible for aerobic respiration, and cooperate with the cytoskeleton to maintain cell morphology and function.⁹⁰ They also serve as critical sites for multiple metabolic pathways, including key reactions such as metal ion metabolism.⁹¹

In neurons and glial cells, excess copper can accumulate in the mitochondrial matrix, disrupting mitochondrial membrane potential and inhibiting alpha‑ketoglutarate dehydrogenase (KGDH) and pyruvate dehydrogenase (PDH) activities, leading to reduced mitochondrial pyruvate production.⁹² The use of antioxidants such as dihydrolipoic acid can attenuate this process and the subsequent cell death.⁹²

Additionally, copper can inhibit BNIP3-mediated mitophagy by downregulating the mitochondrial autophagy regulator BCL-2/adenovirus E1B 19kDa interacting protein 3 (BNIP3), which in traumatic brain injury (TBI) models manifests as exacerbated synaptic damage.⁹³ AMP-activated protein kinase (AMPK), a cellular energy sensor, is activated during mitochondrial inhibition to help maintain ATP levels. In the cerebellum of copper-deficient mice, mitochondrial dysfunction leads to energy deficiency, activating AMPK and promoting its phosphorylation, which subsequently phosphorylates acetyl‑CoA carboxylase (ACC) to inhibit fatty acid synthesis and conserve energy.⁹⁴

Copper Homeostasis and Synaptic Function

When copper is present in the synaptic cleft, it can directly or indirectly modulate the activity of neurotransmitter receptors, thereby affecting excitability.⁹⁵ In addition, copper may participate in the binding of synaptic vesicles to the cell membrane by regulating the interaction between α-synuclein (α-Syn) and synaptic vesicles.⁹⁶ Nam et al proposed that the synaptic cleft may contain three elements: Cu(I)/Cu(II), β-amyloid protein (Aβ), and neurotransmitters. Cu(I)/Cu(II) and neurotransmitters released during neuronal excitation are key components for modulating neurotransmitter receptor activation and maintaining signal transduction in the synapse, whereas under pathological conditions, Aβ may interact with these components to contribute to neurodegeneration.⁹⁷

Mechanism of Cuproptosis

Copper is an essential trace element in organisms, playing irreplaceable roles in maintaining mitochondrial respiration, enzyme activity, and protein function.⁹⁸ Cells can maintain normal activity only within an extremely narrow range of copper ion concentrations. Experiments using the MC3T3-E1 cell line (derived from the calvaria of a newborn mouse) showed that cells retain high activity only at copper concentrations of approximately 10⁻⁷-10⁻⁶ M, and even slight increases approach the toxicity threshold.^99,100 Dysregulation of copper homeostasis can induce mitochondrial morphological and functional abnormalities, leading to metabolic disorders and irreversible damage to the organism¹⁰¹ (Figure 3).

Figure 3 Mechanism of cuproptosis. Cu(II) is directly imported into the cell and mitochondria by the copper ionophore ELC. In mitochondria, FDX1 catalyzes the reduction of Cu(II) to Cu(I), accompanied by the generation of reactive oxygen species (ROS). FDX1 also interacts with LIAS to promote the lipoylation of DLAT. The lipoylated DLAT proteins interact with Cu(I) and subsequently aggregate. Additionally, Cu(I) disrupts iron–sulfur (Fe–S) cluster proteins, leading to their loss. Together, these effects induce cuproptosis. Cuproptosis causes the accumulation of key tricarboxylic acid (TCA) cycle components such as DLAT, DLST, NADH, and FADH2, reducing their activity and suppressing the electron transport chain (ETC), thereby decreasing ATP production.

Unlike OS induced by copper overload, cuproptosis occurs primarily in mitochondria and depends on the interaction between copper ions and mitochondrial metabolism.¹⁰² Moreover, multiple studies have shown that cuproptosis can proceed even in the presence of antioxidants such as N-acetylcysteine (NAC) or ferrostatin‑1, indicating that ROS are a concomitant rather than an essential driving factor.^79,103 ROS accumulation may also activate other programmed cell death pathways, including apoptosis and ferroptosis, but these are only concurrent phenomena and not central mechanisms of cuproptosis.¹⁰⁴ Furthermore, classical inhibitors of apoptosis, necrosis, pyroptosis, and ferroptosis (eg, caspase inhibitors, ferrostatin‑1) are ineffective against cuproptosis; only copper chelators or knockout of key genes such as FDX1 and lipoyltransferases can reverse cell fate.¹⁰⁵ These findings indicate that cuproptosis is a novel cell death mechanism completely independent of known programmed cell death pathways.

Mitochondrial Lipoylated Protein Aggregation

Under normal physiological conditions, copper uptake is mediated by CTR1, and copper efflux is regulated by ATP7A/ATP7B; however, under high copper load or in the presence of copper ionophores, these regulatory mechanisms fail to maintain copper homeostasis. Excess copper or exogenous copper ion carriers such as Elesclomol (ELC) can induce cuproptosis. ELC forms an Elesclomol-Cu(II) complex that transports Cu(II) from the extracellular space into the cytoplasm and mitochondria. Upon dissociation from the complex, Cu(II) undergoes repeated cycles of binding and release, leading to progressive accumulation of Cu(II) within mitochondria.^106,107

In the mitochondrial matrix, Ferredoxin 1 (FDX1), an Fe-S cluster reductase, serves as a critical regulator of cuproptosis and plays a dual role. FDX1 reduces Cu(II) to the more toxic Cu(I), a process that is particularly pronounced in cells highly dependent on OXPHOS.¹⁰⁸ FDX1 is an upstream regulator of protein lipoylation. By directly interacting with lipoic acid synthetase (LIAS), FDX1 promotes LIAS-mediated lipoylation of target proteins, increasing the lipoylation levels of TCA cycle-related enzymes such as DLAT, thereby providing a basis for the interaction between copper and these modified proteins and ultimately contributing to the initiation of the cuproptosis signaling pathway.¹⁰⁹ Knockout of FDX1 confers resistance to copper ionophore (such as ELC)-induced cell death, indicating that FDX1 is a key upstream regulator of cuproptosis.¹⁰⁸ A 2024 study on the drug disulfiram (DSF) showed that inhibition of FDX1 reduces copper ion accumulation and alleviates cuproptosis. Additionally, it mitigates ischemia-reperfusion-induced neuroinflammation through modulation of the heat shock protein 70 (HSP70)/toll-like receptor 4 (TLR4)/NLR family pyrin domain containing 3 (NLRP3) pathway, contributing to brain tissue protection.¹¹⁰

Lipoylation is a highly conserved post-translational modification in which lipoic acid is covalently attached to lysine residues of proteins, primarily occurring on key complexes of the mitochondrial TCA cycle and related metabolic pathways, including DLAT, DLST, dihydrolipoamide branched‑chain transacylase E2 (DBT), and glycine cleavage system protein H (GCSH).¹¹¹ Excess Cu(I) can bind to certain critical mitochondrial metabolic enzymes, causing their misfolding and aggregation into clumps, thereby obstructing energy metabolism and activating the cellular proteostasis machinery. Ultimately, the inability to clear these damaged proteins leads to mitochondrial instability, collapse of cellular function, and the occurrence of cuproptosis.^112,113

In in vitro experiments, FDX1 deletion causes mitochondrial proteins to lose lipoylation modifications and their Cu(II) binding sites, thereby reducing copper toxicity. However, because lipoylation is essential for the function of TCA cycle enzymes, FDX1 deletion impairs TCA metabolism, diminishes mitochondrial respiration and OXPHOS function, and markedly restricts cell growth under low-glucose conditions.¹⁰⁹

Loss of Iron-Sulfur Cluster Proteins

In cuproptosis, when a large amount of copper binds to lipoylated proteins, it not only induces aggregation of these proteins but also disrupts the stability of Fe-S cluster proteins, leading to their depletion and inactivation. Since Fe-S cluster proteins are extensively involved in the TCA cycle, electron transport, and nucleic acid repair, their loss exacerbates OXPHOS inefficiency, disrupts electron transport, increases ROS production, and causes widespread metabolic dysfunction.^16,114 The loss of Fe-S cluster proteins, together with lipoylated protein aggregation, synergistically triggers mitochondrial proteotoxic stress, further promoting cell death.¹¹⁵

The Relationship Among Copper Homeostasis, Cuproptosis, and Neurological Diseases

Alzheimer’s Disease

Alzheimer’s disease (AD) is one of the most common neurological disorders, clinically characterized by progressive cognitive impairments in visual, language, executive, behavioral, and motor domains.^116,117 The formation of extracellular Aβ plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein in the hippocampus and cerebral cortex are central to AD pathogenesis.¹¹⁸ According to the amyloid cascade hypothesis, abnormal processing of amyloid precursor protein (APP) during pathology leads to extracellular accumulation of Aβ, which triggers tau hyperphosphorylation and ultimately NFT formation.^119,120 Concurrently, Aβ aggregation induces neuroinflammation, oxidative stress (OS), and synaptic loss, culminating in neuronal death and cognitive decline.¹²¹

In AD patients, free copper levels (particularly in serum) are significantly elevated, resulting in diminished antioxidant defenses and mitochondrial dysfunction. Moreover, increased copper levels correlate with the rate of cognitive decline,^122,123 and serum copper levels positively associate with AD risk¹²⁴ (Figure 4).

Figure 4 Copper homeostasis and cuproptosis in Alzheimer’s disease (AD). IFN-γ disrupts copper homeostasis. Excess copper increases free radicals via the Fenton reaction, leading to oxidative stress (OS) and cell death. These radicals interact with Aβ and APP, promoting Aβ aggregation and ROS production. Copper accumulation reduces synaptic proteins (SYP, PSD-95) and neurotransmitters (5-HT, GABA), and inhibits BDNF production through the CREB/BDNF pathway, impairing synaptic plasticity. APP cleavage by α- and γ-secretase produces non-toxic P3, while BACE1 and γ-secretase generate Aβ40 and Aβ42. Copper promotes α-cleavage, whereas copper deficiency favors β-cleavage, worsening AD pathology. Microglia can clear Aβ or Aβ-antibody complexes, but excess copper impairs this function. In the hippocampus, copper elevates NO and LPO levels, damages antioxidant defenses, and disrupts neuronal function. Copper also induces tau hyperphosphorylation and aggregation.

Copper-induced OS may be one of the primary mechanisms underlying its neurotoxicity. Since copper in the brain can cycle between Cu(II) and Cu(I) oxidation states, it possesses redox activity and can readily catalyze the production of ROS, thereby exacerbating OS in the brain.¹²⁵ Excess copper generates large amounts of free radicals through the Fenton reaction, inducing oxidative damage and cell death, which leads to neurodegeneration.¹²⁶ The free radicals produced by the Fenton reaction are not only closely related to OS but can also directly interact with Aβ plaques and APP, promoting Aβ synthesis and aggregation.¹²⁷ Copper can also bind directly to Aβ plaques, catalyzing ROS generation; these ROS may cause oxidative damage to the Aβ peptides themselves as well as surrounding molecules such as proteins and lipids.¹²⁸ In the hippocampus, copper treatment significantly elevates levels of nitric oxide (NO) and lipid peroxidation products (LPO), impairs the antioxidant defense system, and consequently damages neural function.¹²⁹ Copper overload can disrupt critical mitochondrial enzymes such as COX, causing electron transport chain blockage, sharply increasing ROS production, activating cuproptosis, and ultimately inducing neuronal apoptosis or necrosis.¹³⁰ As the main energy supplier of cells, mitochondrial dysfunction not only increases neurotoxicity but also leads to synaptic loss and memory impairment.¹³¹

Hippocampal dysfunction typically occurs early in AD, accompanied by inhibition of long‑term potentiation (LTP) and synaptic dysfunction in patients’ brains. Excessive copper accumulation can downregulate presynaptic protein synaptophysin (SYP), postsynaptic density protein 95 (PSD-95), and neurotransmitters such as 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA) in mice.¹³² SYP expression correlates closely with the number of presynaptic vesicles, while PSD-95 supports and anchors postsynaptic receptors and regulates receptor-associated protein organization.¹³³ 5-HT and GABA are key neurotransmitters in the synaptic cleft involved in learning and memory processes.^134,135 These four molecules are all involved in higher brain functions within the synaptic system, indicating that copper can simultaneously affect presynaptic regulation, postsynaptic modulation, and neurotransmitter release, leading to synaptic transmission impairments. Moreover, brain-derived neurotrophic factor (BDNF), an important target of cAMP response element-binding protein (CREB),¹³⁶ regulates synaptic plasticity and participates in neuroprotection and neural regeneration.¹³⁷ Copper may inhibit the CREB/BDNF signaling pathway, reducing BDNF expression and thereby suppressing synaptic plasticity, which hinders memory formation and consolidation.¹³²

Persistent activation of microglia is closely related to abnormal copper homeostasis and is involved in AD pathology.¹³⁸ Microglia can phagocytose Aβ or Aβ-antibody complexes,¹³⁹ but excessive copper ions inhibit this phagocytic function. The inflammatory cytokine interferon-γ (IFN-γ) not only triggers and exacerbates inflammation but also disrupts copper homeostasis by altering the cytoplasmic relocalization of copper transporter ATP7A, increasing copper uptake and upregulating CTR1 expression.¹⁴⁰ This process may explain the fluctuating copper homeostasis observed in AD patients.

Furthermore, APP and tau proteins are critical in AD pathogenesis. APP acts as a receptor in the CNS, involved in synaptic growth, neuronal adhesion, axonal transport, and development.¹⁴¹ Under the action of α-secretase and γ-secretase, APP produces a non-toxic P3 fragment. However, cleavage by β-secretase (BACE1) and γ-secretase generates the longer peptides Aβ₄₀ and Aβ₄₂, which form amyloid plaques in the AD brain.^142,143 Increased copper levels promote the α-secretase-mediated non-toxic pathway, whereas copper deficiency promotes the BACE1-mediated toxic pathway, accelerating Aβ formation.¹⁴⁴ Tau protein, a neuron-specific microtubule-associated protein, normally maintains axonal microtubule stability. In AD, tau becomes hyperphosphorylated and dissociates from microtubules, causing axonal transport deficits and neuronal structural damage, ultimately triggering cell death.¹⁴⁵ ROS generation is an important trigger of tau hyperphosphorylation and filament aggregation. Excess copper promotes tau phosphorylation, while treatment with copper chelators can inhibit copper levels and markedly reduce tau phosphorylation.^146,147 Studies also suggest that reducing brain copper by limiting dietary copper intake may be a feasible strategy to regulate tau pathology in AD.¹⁴⁶

Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder after AD, with rapidly increasing global prevalence and mortality.¹⁴⁸ Clinically, it is characterized by bradykinesia, resting tremor, muscle rigidity, postural and gait abnormalities, often accompanied by cognitive impairment.¹⁴⁹ Pathologically, PD is marked by progressive loss of dopaminergic neurons in the substantia nigra-striatum region and the presence of α-Syn inclusions in neuronal cytoplasm, forming Lewy bodies and Lewy neurites.¹⁵⁰ α-Syn undergoes oligomerization and converts into β-sheet-rich protofibrils, forming cytotoxic amyloid aggregates.¹⁵¹ These aggregates coexist with mitochondrial dysfunction and decreased copper and GSH levels in brain regions, implicating OS and metabolic imbalance in PD pathology progression.¹⁵²

Studies show that copper levels are decreased in multiple brain regions of PD patients post-mortem, especially in the substantia nigra, as measured by inductively coupled plasma mass spectrometry (ICP-MS).¹⁵³ Synchrotron X-ray fluorescence microscopy and particle-induced X-ray emission analyses indicate a 55–65% reduction in copper in the substantia nigra and locus coeruleus of PD brains¹⁵⁴ (Figure 5). CP, the main copper carrier and ferroxidase in plasma, shows dysregulated function in PD patients. Reduced CP-bound copper may cause iron homeostasis disturbance, worsening neuronal injury.

Figure 5 Copper homeostasis and cuproptosis in Parkinson’s disease (PD). In PD, copper directly interacts with α-synuclein (α-Syn), promoting its aggregation into toxic oligomers. These complexes generate ROS and dopamine oxidation products, impair energy metabolism, and exacerbate neuronal damage. Intracellular GSH chelates copper and reduces its toxicity. When GSH is depleted, free copper increases, leading to elevated DLAT levels and loss of Fe–S cluster proteins, ultimately triggering copper-induced cell death. Copper bound to ceruloplasmin (CP) helps maintain iron homeostasis, which may protect neurons. CTR1 promotes α-Syn phosphorylation, contributing to dopaminergic neuron loss and PD progression. Overexpression of CTR1 may also deplete GSH and induce caspase-3-dependent cell death. Additionally, GSTM1-null and GSTT1-null genotypes may increase PD susceptibility.

In vitro studies demonstrate that Cu(II) effectively induces spontaneous oligomerization of α-Syn at micromolar concentrations, promoting formation of oligomers and protofibrils.^155,156 Binding of α-Syn with Cu(II) produces an N-terminal acetylated α-Syn-Cu(II) complex, exhibiting catechol oxidase and redox activity, catalyzing dopamine oxidation and ROS generation; this activity is further enhanced when membrane-bound.^157,158 Additionally, metabolic energy decline is closely linked to disrupted catecholamine metabolism in highly active catecholaminergic neurons (eg, dopaminergic neurons in the substantia nigra pars compacta and noradrenergic neurons in the locus coeruleus), which disrupts redox-active metals such as copper and iron homeostasis.¹⁵⁹ These mechanisms suggest α-Syn-Cu(II) exacerbates dopaminergic/noradrenergic neuronal dysfunction via OS and metabolic imbalance, contributing to PD pathology.

CTR1 is the primary high-affinity copper importer. In PD animal models, CTR1 deficiency significantly reduces α-Syn phosphorylation at S129, decreases dopaminergic neuron loss, and improves motor dysfunction.¹⁶⁰ Conversely, CTR1 overexpression or excess causes intracellular GSH depletion and caspase-3-dependent cell death, indicating that excessive copper can also induce neuronal injury.¹⁶¹ Decoppering treatment partially restores apoptosis levels and expression of copper death-related proteins,¹³² supporting a role for copper death mechanisms in PD.

Copper homeostasis is closely linked with GSH metabolism. Zhang et al used the high-efficiency GSH fluorescent probe R13 to find reduced GSH levels in PD mouse brains.¹⁶² Clinically, GSH levels are significantly decreased in the substantia nigra of PD patients.¹⁶³ GSH chelates Cu(I), blocking copper toxicity; however, GSH deficiency increases free Cu(I), disrupting Fe-S cluster proteins and inducing OS and cell death.¹⁶ From a genetic perspective, deletion polymorphisms in glutathione S-transferase Mu1 (GSTM1) and Theta1 (GSTT1) are associated with increased PD susceptibility,¹⁶⁴ emphasizing the importance of GSH metabolism in defending against copper toxicity. Supplementation with cysteine precursors (eg, 6-OHDA/xanthine induction schemes) enhances cellular GSH levels and restores neuronal vitality.^165,166 GSH deficiency may underlie copper-induced neurodegeneration, making modulation of GSH metabolism a potential PD therapeutic strategy.

Recent research links amorphous SOD1 aggregates with PD progression; these new SOD1-containing aggregates are amorphous and spherical, largely devoid of α-Syn but ubiquitin-positive, with copper as a structural and functional cofactor of SOD1, implicating copper deficiency in abnormal SOD1 aggregation.¹⁶⁷ Indeed, SOD1 immunoreactivity has been detected in Lewy bodies and Lewy neurites of the substantia nigra and locus coeruleus in PD brains.¹⁶⁸

In summary, copper homeostasis imbalance in PD manifests as localized copper deficiency rather than widespread copper toxicity, involving multiple mechanisms including α-Syn aggregation, catecholamine oxidation, GSH deficiency-induced metabolic imbalance, Fe-S protein dysfunction, and SOD1 aggregation. A complex network comprising CTR1, CP, GST, SOD1, and Fe–S cluster proteins underlies these processes. These findings provide a theoretical foundation for PD early diagnosis and therapeutic strategies targeting copper metabolism.

Huntington’s Disease

Huntington’s disease (HD) is a progressive neurodegenerative disorder with a genetic origin. The most common symptoms include loss of energy and initiative, poor perseverance and work quality, impaired judgment, decreased self-care ability, and emotional blunting; about half of studied patients exhibit emotional symptoms such as depression, anxiety, and irritability.¹⁶⁹ HD is an autosomal dominant hereditary disease caused by CAG repeat expansion mutations in the gene encoding huntingtin (HTT) protein located on the short arm of chromosome 4.¹⁷⁰ The N-terminus of the HTT protein contains a polyglutamine (polyQ) tract, and when the CAG repeats expand, a structurally defective mutated huntingtin (mHTT) protein is produced.¹⁷¹ This mHTT protein is prone to misfolding and forms β-sheet-rich aggregates and inclusions in the neuronal cytoplasm and nucleus.¹⁷² These abnormal aggregates disrupt cellular protein homeostasis, axonal transport, transcription, translation, mitochondrial, and synaptic functions.^173,174 Diagnosis is typically confirmed by detecting the number of CAG repeats (≥36 repeats, with ≥40 repeats being fully pathogenic) in the HTT gene of patients exhibiting clinical features.¹⁷⁵

Researchers have found abnormally high concentrations of copper in the striatum of both HD patients and HD mouse models, suggesting that copper may be involved in HD pathogenesis.¹⁷⁶ In Drosophila models, copper ions increase the formation of mHTT aggregates and enhance their neurotoxicity,¹⁷⁷ while copper chelators inhibit mHTT aggregate formation, further supporting the link between copper and HD pathogenesis.¹⁷⁸ Copper ions promote mHTT aggregate formation by binding to mHTT monomers and oligomers, lowering the nucleation energy barrier for aggregation.¹⁷⁶ In vitro studies show that copper ions selectively bind to the N-terminal fragment of HTT protein containing 17–68 glutamine residues, while other metal ions such as Fe³⁺ and Zn²⁺ show no significant binding affinity.¹⁷⁸ Excess copper in the brain inhibits key mitochondrial and energy metabolism dehydrogenases, including lactate dehydrogenase (LDH)¹⁷⁹ and succinate dehydrogenase (SDH),⁹² leading to energy metabolism imbalance. Neurons highly depend on lactate released by astrocytes as their primary energy substrate;¹⁸⁰ thus, copper inhibition of LDH directly disrupts lactate metabolism, further weakening neuronal energy supply and exacerbating HD neurodegeneration. Additionally, in Drosophila HD models, copper ions increase mHTT aggregate formation and enhance accumulation of sulfur-positive Aβ structures within mHTT aggregates, representing the toxic aggregation of mHTT and altering autophagy in the brain.¹⁷⁷ Studies also show that copper ions directly bind mHTT, increasing its aggregation propensity and β-sheet structure, thereby enhancing its cytotoxicity in neurons.¹⁷⁶

Mutant HTT disrupts nuclear pore proteins in the nuclear pore complex (NPC), impairing nucleocytoplasmic transport and causing cellular toxicity.¹⁸¹ Meanwhile, mHTT interacts with the mitochondrial protein dynamin-related protein 1 (DRP1), promoting mitochondrial fission, resulting in mitochondrial dysfunction and synaptic protein sequestration.¹⁸² Moreover, compared to healthy controls, levels of several ubiquitin-proteasome system (UPS) enzymes, including ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligase (E3), are altered in HD patients. Increased expression of these enzymes may affect proteasome-dependent degradation of mHTT or influence its solubility, aggregation, or assembly, thereby directly or indirectly impacting cellular pathways and stress responses involved in HD pathogenesis.¹⁸³ The UPS plays a crucial role in clearing aggregated mHTT protein.¹⁸⁴ Additionally, UPS participates in the translation and regulation of copper transport proteins and copper chaperones; however, since UPS contains copper-dependent enzyme components, it is itself influenced by copper levels.^184,185

Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a common neurological disorder characterized by the simultaneous degeneration of upper motor neurons in the motor cortex and lower motor neurons in the spinal cord and brainstem.¹⁸⁶ Most ALS cases (~90%) are sporadic without a family history, while a minority (~10%) represent rare autosomal dominant familial amyotrophic lateral sclerosis (FALS).¹⁸⁷ The exact etiology of sporadic amyotrophic lateral sclerosis (SALS) remains unclear; however, current consensus suggests it is a complex multistep disease triggered by a combination of genetic susceptibility, environmental exposures, and aging factors.¹⁸⁸ The primary cause of FALS is mutations in the SOD1 gene, which encodes a metalloprotein that forms a highly stable homodimer by binding copper and zinc ions. SOD1 mutations cause OS, mitochondrial dysfunction, electron transport disruption, and protein aggregation.^189,190

It is widely accepted that accumulation of misfolded conformers, oligomers, and aggregates of SOD1 in motor neurons is a core pathological mechanism of ALS. Due to disulfide bond disruption, SOD1 oligomers exhibit enhanced pro-oxidant activity and toxicity.¹⁹¹ Mutant SOD1 reduces protein folding stability by impairing metal binding and disulfide bond formation, leading to misfolding, aggregation, and eventual cytotoxicity.¹⁹² Copper is not only central to SOD1 enzymatic activity but is also crucial for its structural integrity and stability; abnormal copper metabolism may contribute to ALS pathogenesis by affecting SOD1 function or aggregation.^193,194 One of the earliest pathological features in mutant SOD1 is loss of metal at copper-binding sites.¹⁹⁵ Copper deficiency is common in mutant SOD1 cells, and aggregates are generally copper-deficient.¹⁹⁶ Moreover, copper levels in cerebrospinal fluid (CSF) from ALS patients are lower than controls, especially in spinal-onset ALS, where copper concentration significantly decreases.¹⁹⁷

Overexpression of COX in adult mice carrying mutant SOD1 results in impaired copper transport in the late stages of life, suggesting that age-related copper deficiency may be an important factor in the onset of SOD1-induced ALS.¹⁹⁸ Deficiency of metals such as copper and zinc promotes the exposure of hydrophobic residues in SOD1, which facilitates the formation and stabilization of toxic SOD1 oligomers. These oligomers exhibit high toxicity and pro-oxidant activity, representing a key pathological process leading to neuronal damage.¹⁹⁹ In addition, the disruption of copper binding and disulfide bond formation in SOD1 may contribute to the onset and progression of ALS.²⁰⁰ When SOD1 forms disulfide bonds before binding metal ions, it loses the ability to be recognized and activated by CCS, thereby blocking the copper supply from CCS and hindering the maturation of the disulfide bond in SOD1.²⁰¹

Conversely, abnormally elevated free copper levels may act as immune stimuli. Misallocated copper ions generate large amounts of free radicals via Fenton reactions, directly causing oxidative damage and inducing microglial release of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β).¹⁹⁴ Excess copper also activates NF-κB in astrocytes, amplifying inflammatory responses and further damaging motor neurons.¹⁹⁴ Indeed, in SOD1-ALS models, both copper deficiency (leading to protein dysfunction) and copper overload (triggering toxic inflammation) coexist and synergistically drive disease progression.¹⁹⁴

Mitochondrial dysfunction has been observed in ALS mouse models and patients,²⁰² representing a key hallmark of ALS neuropathology. Aberrant interaction between CCS and mutant SOD1 results in increased copper binding to SOD1, reducing copper transfer to mitochondria and causing accumulation of unstable SOD1, limiting ROS clearance, and ultimately leading to motor neuron toxicity.²⁰³ Overexpression of CCS accelerates disease progression in SOD1(G93A) transgenic mice (Gly93Ala mutation in the copper/zinc superoxide dismutase 1 gene), significantly reducing COX activity in late-stage disease.²⁰⁴ Furthermore, soluble misfolded mutant SOD1 deposits on mitochondrial intermembrane and outer membranes in ALS animals, which is a key mechanism underlying mitochondrial dysfunction.²⁰⁵

Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the CNS and a leading cause of neurological disability in young adults.²⁰⁶ MS is characterized by neuronal lesions formed in the brain and spinal cord, resulting in a range of clinical symptoms including visual impairment, limb weakness, sensory abnormalities, and ataxia.²⁰⁷ Key factors triggering MS include neuroinflammation, oligodendrocyte death, subsequent OS, and axonal demyelination.²⁰⁸ Cuprizone, a copper chelator, is used to induce an MS mouse model in which microglial activation, demyelination, and mitochondrial damage have been observed.²⁰⁹

Significantly elevated copper concentrations have been detected in the serum and CSF of MS patients. Upregulation of copper transport proteins in the CNS may contribute to astrocyte-mediated demyelination. Moreover, under neuroinflammatory conditions, copper homeostasis alterations mediated by tropomyosin receptor kinase B (TrkB) and upregulation of copper transporter CTR1 play critical roles in MS. These processes affect astrocyte copper uptake and release, ultimately inducing demyelination.²¹⁰ Additionally, increased expression of transient receptor potential melastatin 2 (TRPM2) has been observed in the cuprizone model. TRPM2 gene promotes cuprizone-induced demyelination, synaptic loss, microglial NLRP3 inflammasome activation, and production of pro-inflammatory cytokines, indicating a key role for TRPM2 in MS-associated neuroinflammation.²¹¹ However, excessively low divalent copper ion concentrations inhibit TRPM2 channel activity irreversibly,²¹² thereby contributing to MS pathological features.

SOD1 is an antioxidant and anti-inflammatory enzyme. Studies by Mezzaroba et al, Arakawa et al, and Rasoul et al have shown that OS induced by SOD1 deficiency plays an important role in tissue damage during MS progression.^213–215 However, excessive copper accumulation in vivo can cause copper toxicity and generate ROS under Fenton reaction conditions, leading to OS.²¹⁶ Therefore, copper is currently believed to contribute to MS by inducing oxidative damage, which plays a key role in the pathogenesis of demyelination and neurodegeneration.²¹⁵

Wilson Disease

Wilson disease (WD) is a non-traditional neurological disorder caused by various mutations in the ATP7B gene. It is characterized by impaired copper excretion into bile, leading to copper accumulation in the liver, while copper buildup in the brain may cause neuropsychiatric symptoms.²¹⁷ The most common neurological manifestations of WD are movement disorders, including tremor, ataxia, dystonia, parkinsonism, and chorea.^218,219 To date, over 600 pathogenic variants in ATP7B have been identified, with the most common being single nucleotide missense and nonsense mutations, followed by insertions/deletions, and more rarely, splice site mutations.²²⁰

ATP7B plays a dual critical role in the liver: on one hand, it transports copper to the TGN, where copper binds to CP and is excreted via bile; on the other hand, its dysfunction directly causes impaired copper excretion, leading to abnormal copper deposition in target organs.²²¹ When ATP7B is inactivated in WD patients, excess copper cannot enter bile and instead overflows into the bloodstream, depositing in various tissues including the brain. The accumulation of free copper triggers neurological lesions, manifesting as neurological symptoms and psychiatric disorders.^222,223 Simultaneously, ATP7B dysfunction causes loosely bound non-CP copper in the blood to bind to albumin and attack erythrocyte membranes, leading to coombs-negative hemolysis and potential hemolytic crises, ultimately resulting in anemia.²²⁴

Copper toxicity is considered the main cause of organ damage in WD patients. When cellular copper levels reach a critical threshold and exceed the binding capacity of MT and GSH, OS is induced, resulting in free radical damage to proteins, lipids, and nucleic acid structures. This ultimately causes cellular damage and membrane rupture.¹²⁶ Additionally, mitochondrial dysfunction has been observed in the livers of WD patients.²²⁵ Protein thiols are key targets of mitochondrial copper toxicity; copper accumulation in the liver attacks protein thiols, leading to mitochondrial dysfunction and subsequent hepatocellular injury in WD patients.²²⁶ GSH is a critical intracellular molecule protecting protein thiols from oxidation. Compared with liver mitochondria, brain mitochondria have lower total GSH levels, rendering them more sensitive to copper.²²⁶ Moreover, significantly elevated copper levels can be detected in nearly all brain regions of WD patients.²²⁷ Therefore, excessive copper accumulation may be a central pathological mechanism underlying the neurological damage and psychiatric abnormalities observed in WD.

Structural brain magnetic resonance imaging (MRI) scans of WD patients reveal marked changes in normal brain structures, including widespread lesions in the midbrain, globus pallidus, putamen, pons, cerebellum, and thalamus, as well as cortical atrophy.²²⁸ In the early disease stages, Alzheimer-type I and II astrocytes, along with morphologically abnormal astrocytes, can be observed in the basal ganglia of WD patients, representing typical neuropathological features of WD.²²⁹ Studies in WD mouse models have shown activated microglia and astrocytes in the striatum and corpus callosum regions, closely associated with demyelination and neuronal loss.²³⁰ Furthermore, astrocytes protect neurons from copper toxicity by sequestering excess copper ions.²²⁹ However, as the disease progresses, brain parenchymal copper levels increase significantly, astrocyte damage worsens, weakening their protective function, which further impairs neuronal physiology and ultimately leads to neuronal death.²³¹

Menkes Disease

Menkes disease (MD) is an X-linked recessive genetic disorder of copper metabolism caused by mutations in the copper transporter gene ATP7A. It primarily manifests as growth retardation and severe neurological impairments during infancy.²³² ATP7A plays a critical role in the TGN, facilitating intracellular copper transport.²³³ In MD, mutations in ATP7A impair copper export function on the basolateral membrane of intestinal epithelial cells, leading to defective copper transport in the intestine, resulting in abnormally low copper levels in blood, kidney, liver, and brain, while copper accumulates abnormally within intestinal epithelial cells.¹²⁶ Furthermore, COX deficiency has been observed in the brains of MD patients, which may be related to mutations in the SCO1 and SCO2 genes, essential for copper metallation of the Cu_A site.²³⁴ Therefore, mitochondrial dysfunction caused by reduced COX activity may contribute to neuronal degeneration in MD patients.

The normal physiological functions of copper-dependent enzymes are impaired in MD patients. Dopamine-β-hydroxylase (DBH), a key enzyme in noradrenergic neurons responsible for converting dopamine to norepinephrine, shows decreased activity.²³⁵ This reduction leads to a characteristic neurochemical pattern in patients’ plasma and CSF, namely elevated dopamine and its metabolites and decreased norepinephrine and its metabolites.^235–237 Clinically, this pattern can be used for newborn screening and early diagnosis of MD.²³⁵ In infants with MD, significantly increased levels of L-DOPA (L-3,4-dihydroxyphenylalanine, a precursor of catecholamines) have been detected in blood and CSF, indicating reduced DBH activity.²³⁸ Since DBH catalyzes the copper-dependent conversion of dopamine to norepinephrine, its dysfunction further reflects the copper deficiency-associated neurochemical disturbances in MD patients.²³⁹

Lysyl oxidase (LOX) is another copper-dependent enzyme catalyzing the initial oxidative deamination step in the crosslinking of collagen and elastin.²⁴⁰ In MD patients, LOX enzymatic activity is significantly decreased due to defective copper transport, leading to connective tissue abnormalities.²⁴¹ Related studies show that reduced plasma copper levels and copper transport defects in MD patients not only decrease LOX catalytic activity but also downregulate the mRNA expression of LOX and its substrate pro-elastin.^242,243

Occipital horn syndrome (OHS) is a mild variant of WD caused by ATP7A gene defects, characterized mainly by connective tissue abnormalities, including characteristic bony projections (occipital horns) at the attachment of the occipital muscles.²⁴⁴ This phenotype is closely associated with decreased copper-dependent LOX activity and can result in typical kinky hair, vascular tortuosity, and peripheral arterial aneurysms.²⁴⁵ Due to residual ATP7A function (~30%) that retains partial copper transport, neurological symptoms in OHS patients are relatively mild.²⁴⁶ Their serum copper and CP levels are lower than normal but higher than in classic WD, while elevated catecholamine levels in CSF indicate insufficient DBH activity consistent with the neurochemical abnormalities of classic MD.²³⁶

Stroke

Stroke is a common neurological disorder caused by acute focal injury to the CNS. It ranks as the second leading cause of death worldwide among adults, second only to ischemic heart disease, and is the third leading cause of disability.²⁴⁷ Stroke is typically classified as ischemic or hemorrhagic, with ischemic stroke being more prevalent.²⁴⁸ Elevated plasma copper levels increase susceptibility to stroke.²⁴⁹ Plasma copper is positively associated with a higher risk of ischemic stroke but inversely associated with hemorrhagic stroke risk.²⁵⁰ Another meta-analysis showed that serum copper levels were significantly higher in ischemic stroke patients compared to controls.²⁵¹ These studies collectively indicate that copper homeostasis imbalance is a potential risk factor for stroke.

Copper imbalance influences stroke through pathways including vascular regeneration, hyperlipidemia, OS, maturation of neuroprotective peptides, and inflammatory responses.

Endothelial progenitor cells (EPCs) are bone marrow–derived cells circulating in the blood that can differentiate into endothelial cells and participate in angiogenesis and tissue repair. Studies have shown that EPCs play a crucial role in the recovery process after ischemic brain injury by promoting vascular reperfusion, inhibiting apoptosis and inflammation in the ischemic penumbra, thereby improving neurological function.²⁵² However, copper overload significantly impairs EPC migration, adhesion, and tube formation by upregulating thrombospondin-1 (TSP-1) expression, while also weakening their antioxidant defenses. This leads to suppressed cerebral microvascular angiogenesis post-ischemia and exacerbates brain injury after stroke.^253,254

Additionally, a retrospective study based on the 2011–2016 NHANES database found that in women, serum copper levels positively correlated with total cholesterol and low-density lipoprotein low‑density lipoprotein (LDL). Each 1 µg/dL increase in copper was associated with approximately 0.11 mg/dL and 0.09 mg/dL increases in total cholesterol and LDL, respectively, suggesting copper may indirectly elevate stroke risk by increasing blood lipid levels. However, as this was a cross-sectional study, prospective research is needed to validate this mechanism.²⁵⁵

Copper also plays a critical role as an essential cofactor of SOD1, maintaining its antioxidant function. Dysregulated copper homeostasis may lead to reduced SOD1 activity or abnormal aggregation, enhancing OS and exacerbating neural damage.^193,194 Conversely, SOD1 overexpression in ischemia-reperfusion animal models significantly reduces superoxide anion production and overall ROS levels, promoting neural stem cell survival and partially mitigating ischemic stroke damage.²⁵⁶

Furthermore, copper is vital for the maturation of multiple neuropeptides, especially through the peptidylglycine α-amidating monooxygenase (PAM)-catalyzed C-terminal amidation pathway. Copper deficiency reduces PAM enzyme activity, resulting in neuropeptides such as neuropeptide Y (NPY) and corticotropin-releasing hormone (CRH) failing to form structurally mature C-terminal amidated forms.^257,258 These peptides are crucial in neuroprotection and inflammation regulation following stroke. NPY has been shown to exert anti-inflammatory effects, reduce infarct volume, and promote neural regeneration,^259,260 whereas CRH mediates stress-related inflammatory responses, modulating neuroinflammation during post-stroke pathology.²⁶¹

Drugs Related to Neurological Diseases

For human copper homeostasis and cuproptosis, therapeutic drugs for neurological diseases are continuously being developed, and several agents with potential efficacy require further investigation. These drugs mainly include copper chelators, copper ionophores, copper nanoparticles, and natural compounds (Table 1).

Table 1 Drugs Related to Nervous System Diseases

Copper Chelators

Copper chelators can bind excess copper ions, blocking their participation in redox reactions and thereby reducing ROS production and protein aggregation.³⁰¹ Determining the optimal timing for intervention with copper chelators is a major challenge, as the development and permeability of the blood-brain barrier (BBB) directly determine whether copper ions are sequestered in the bloodstream or delivered into neurons.³⁰² Most classical chelators have limited BBB penetration, preventing them from reaching brain tissue to exert their effects.³⁰³ For example, D-penicillamine (DPA) poorly crosses the BBB, cannot directly modulate intracellular copper homeostasis, and its therapeutic efficacy is therefore limited.³⁰⁴ Efforts to enhance BBB penetration by increasing compound hydrophobicity may lead to increased toxicity or altered clearance, creating a trade-off between hydrophilicity and hydrophobicity.

In addition, clioquinol (CQ) and its derivative 5,7-Dichloro-2-[(dimethylamino)methyl]quinolin-8-ol (PBT2), although able to penetrate the BBB due to their chemical properties, lack selectivity for copper ions. These chelators cannot distinguish between copper bound to essential metalloproteins and toxic copper associated with Aβ, resulting in uneven copper distribution in the nervous system and potentially exacerbating neural damage. Consequently, CQ and PBT2 have not achieved the expected efficacy in clinical trials.³⁰⁵ Therefore, developing copper chelators with high selectivity and good BBB permeability remains a significant challenge in the treatment of neurological diseases. Future research should focus on optimizing the molecular structures of chelators to enhance copper ion selectivity and BBB penetration, thereby achieving more effective therapeutic outcomes.

D-Penicillamine

D-penicillamine (DPA) is a thiol-containing α‑amino thiol and a degradation product of penicillin with high affinity for copper ions. In Drosophila melanogaster experiments, DPA significantly extended the survival of flies exposed to Cu(II), reversed Cu(II)-induced changes in oxidative stress (OS) markers—such as restoring total thiol (T-SH) and GSH levels—and reduced copper-induced alterations in AChE activity, demonstrating certain neuroprotective effects.³⁰⁶

DPA is an effective clinical treatment for WD. Both DPA and triethylenetetramine (trientine/TETA) mobilize copper in the liver and other tissues and promote its urinary excretion, reversing hepatic, neurological, and psychiatric symptoms in most WD patients.^263,267 However, a systematic meta-analysis found that although DPA is effective, it is associated with a relatively higher incidence of adverse reactions compared with zinc therapy. In clinical practice, trientine or zinc salts may be considered as alternative or adjunct therapies.²⁶⁸

DPA may also have potential effects in AD. A small-scale clinical trial showed that DPA could reduce OS markers in the serum of AD patients but did not significantly improve cognitive function or slow clinical progression.²⁶⁵ In animal models, intranasally administered DPA carriers demonstrated possible effects on Aβ deposition and improved cognitive performance, although extensive further validation is still required.²⁶⁶

Triethylenetetramine

Triethylenetetramine (trientine/TETA) is a polyamine-structured copper chelator that forms stable complexes with copper ions through its four nitrogen atoms, effectively reducing systemic copper levels. It is an oral drug used for the treatment of WD.²⁶⁹ Trientine acts similarly to DPA but has fewer side effects and a lower risk of neurological deterioration. It promotes urinary copper excretion and inhibits intestinal copper absorption.^270,307 Compared with DPA for restoring copper balance, trientine is particularly suitable for patients who are intolerant to penicillamine.³⁰⁸ Additionally, trientine can suppress in vivo inflammatory responses induced by hepatic radiofrequency ablation (RFA).³⁰⁹

Tetrathiomolybdate

Tetrathiomolybdate (TTM) has potent anti-copper properties. TTM forms stable ternary complexes with copper and proteins, reducing serum free copper levels.²⁷¹ By rapidly lowering serum copper, TTM can restore normal copper homeostasis within weeks without causing abnormal elevations in serum copper levels.²⁷¹ TTM is an effective clinical treatment for WD, significantly improving neurological symptoms, and the risk of neurological deterioration in WD patients treated with TTM is markedly lower than with TETA.^272,273 TTM may cause adverse effects such as anemia, leukopenia, and elevated transaminase levels, but these are generally reversible with dose adjustment or temporary discontinuation.¹⁰

There is experimental evidence that TTM has therapeutic effects in ALS animal models. TTM can remove copper ions from copper-thiolate clusters such as SOD1, reducing the amount of SOD1 aggregates. It prolongs survival in familial ALS mouse models (SOD1(G93A)), mitigates loss of motor neurons and axons, and prevents skeletal muscle atrophy.^274,275 In addition, TTM effectively lowers spinal cord copper levels and inhibits lipid peroxidation (LPO), thereby suppressing SOD1 enzymatic activity in SOD1(G93A) mice.²⁷⁵ However, there is currently insufficient clinical data to demonstrate clear efficacy in ALS patients.

Clioquinol

Clioquinol (CQ) is a hydrophobic small molecule capable of crossing the BBB and exhibiting moderate affinity for copper and zinc ions, showing therapeutic potential in several neurological disease models.

CQ’s chelation of copper and zinc effectively reduces spinal white matter damage and behavioral deficits in MS mouse models, markedly decreases microglial activation in experimental autoimmune encephalomyelitis mice, improves clinical symptoms, and lowers the incidence of spinal demyelination.²⁷⁶ In AD studies, CQ reduces ROS generation and LPO in yeast cells, decreases the toxicity of Aβ₄₂ (an isoform of Aβ), and restores GSH homeostasis disrupted by Aβ₄₂ through regulation of Yes-associated protein 1 (YAP1), thereby protecting cells from OS.²⁷⁷ In AD mouse models, CQ treatment increases soluble Aβ levels and reduces Aβ deposition in the brain.²⁷⁸ Intracellular Cu(I) accumulation is significantly reduced, and CQ also lowers endogenous phosphorylated tau in primary cortical neurons of mice.²⁷⁹

Diacetyl-Bis(4-Methylthiosemicarbazonato)copper(II)

Diacetyl-bis(4-methylthiosemicarbazonato)copper(II)(Cu(II)(atsm)) is an inflammation-modulating compound with potential therapeutic effects for ALS and PD.^282,310

In ALS, treatment with Cu(II)(atsm) after symptom onset is less effective than pre-symptomatic administration, but it can still improve motor function and survival.²⁸¹ In SOD1(G37R) mice (where glycine at residue 37 in SOD1 is replaced with arginine), Cu(II)(atsm) enhances copper delivery to metal-free (apo) SOD1, promoting its conversion to a more stable and less toxic holo-SOD1 form,²⁸⁰ inhibiting SOD1 activity and reducing aggregation of mutant SOD1 protein. Improvements in motor function and survival in SOD1(G37R) mice support Cu(II)(atsm) as a potential ALS therapeutic.²⁸¹

In PD models, Cu(II)(atsm) exhibits neuroprotective effects associated with reduced OS and decreased α-Syn aggregation.²⁸³ Cu(II)(atsm) also reduces Aβ levels in APP-CHO cells (Chinese hamster ovary cells overexpressing APP).³¹¹ Additionally, Cu(II)(atsm) serves as a tracer for positron emission tomography (PET) imaging. In animal models, Cu(II)(atsm) demonstrates neuroprotective potential, possibly by improving mitochondrial function and reducing OS to protect dopaminergic neurons.³¹² However, its clinical efficacy requires further validation.

Bis-Choline Tetrathiomolybdate

Bis-choline tetrathiomolybdate (WTX101) is a first-in-class oral copper-protein chelator for the treatment of WD that is currently undergoing clinical trials. WTX101 can directly remove excess copper from hepatic copper stores and form stable ternary complexes with copper and proteins such as serum albumin in the circulation, promoting biliary copper excretion.²⁸⁴

In a Phase II open-label study, WTX101 demonstrated the potential to rapidly reduce serum non‑ceruloplasmin‑bound copper (NCC) and improve certain pathological markers.²⁸⁵

Tetradentate Monoquinolines

Tetradentate monoquinoline 20 (TDMQ20) acts on the cholinergic system to regulate copper homeostasis in the brains of AD patients. TDMQ20 improves memory and cognitive function in AD rat models by inhibiting OS catalyzed by Cu‑Aβ complexes.^286,287 TDMQ20 efficiently crosses the BBB and is a potential therapeutic candidate for AD.²⁸⁸

Copper Ion Carriers

Elesclomol

Elesclomol (ELC) is a mitochondria-targeting copper ionophore and an inducer of OS. ELC targets mitochondria by forming a complex with copper and transporting it into the organelle, where ELC-Cu(II) is reduced to Cu(I), triggering ROS production.³¹³ Studies have shown that ELC has potential to improve MD, as it delivers copper to mitochondria and increases COX levels in the brain, mitigating detrimental neurological lesions and improving survival in mottled brindled mice, a severe MD mouse model.²⁸⁹

5,7-Dichloro-2-[(Dimethylamino)methyl]-8-Hydroxyquinoline

The CQ derivative 5,7-Dichloro-2-[(dimethylamino)methyl]quinolin-8-ol (PBT2) is similar to CQ, targeting metal-induced Aβ aggregation, but is more effective as a zinc/copper ionophore and has improved BBB permeability and solubility,²⁹⁰ showing potential benefits in AD treatment. In AD mouse models, PBT2 inhibits copper-induced Aβ accumulation, reduces interstitial Aβ levels and tau phosphorylation, and restores cognitive function.^291,292 PBT2 has undergone Phase II clinical trials in both AD and HD, demonstrating good safety but without clear clinical efficacy, indicating the need for further investigation.^293,305

Additionally, in PD animal models, 5,7-dichloro-2-[(ethylamino)methyl]-8-hydroxy-3-methylquinazolin-4(3H)-one (PBT434/ATH434) prevents α-Syn accumulation and protects the nigrostriatal dopaminergic circuitry and motor function.^294,314

Copper Nanoparticles

Nanoparticle delivery systems can cross the BBB and have the potential to transport DPA into the brain, preventing Aβ_1-42 accumulation and reducing metal ion buildup in CNS diseases.³¹⁵ Copper nanoparticles increase AChE and low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) levels, reduce Aβ in the brain and gut, and decrease tau protein in the rat brain.²⁹⁵

However, in animal studies, high intake of copper nanoparticles severely affects hepatic drug metabolism in rats by inhibiting the expression of multiple cytochrome P450 (CYP450) enzymes, increasing the risk of drug-drug interactions.³¹⁶ The combination of copper oxide nanoparticles (CuONPs) and furan synergistically enhances cardiovascular toxicity in zebrafish embryos.³¹⁷

For neurological diseases, the optimal type of copper nanoparticles and their mechanisms of action remain unclear. Copper nanoparticle-based drugs for clinical use in neurological disorders are yet to be developed.

Natural Compounds

Natural compounds are a treasure trove for humans, with diverse and often mysterious biological effects. Many medicinal plants and their natural constituents possess antioxidant, free radical–scavenging, and neuroprotective properties, demonstrating significant efficacy in preventing copper-induced neurotoxicity.

Luteolin, a plant flavonoid extracted from Artemisia species, exhibits neuroprotective effects in neurological diseases and traumatic brain injury (TBI).²⁹⁶ Luteolin exerts its effects by downregulating amyloid beta precursor protein (AβPP) expression, inhibiting Aβ_1-42 secretion, suppressing apoptosis, and modulating redox imbalance.³¹⁸ Another study showed that coordination and transfer of divalent copper ions significantly enhance luteolin’s free radical scavenging efficiency and antioxidant activity.³¹⁹

Apigenin, a low-toxicity flavonoid, antagonizes copper-mediated Aβ neurotoxicity and provides neuroprotection by alleviating OS, inhibiting ROS-induced signaling pathways, preventing apoptosis, and preserving mitochondrial function.²⁹⁹

Rutin, a glycoside and polyphenol, can cross the BBB and exhibits antioxidant properties. Rutin mitigates copper-induced brain injury—including cortical perforation layers and neuronal degeneration—by reducing OS and neuroinflammation.³⁰⁰

Resveratrol, a natural polyphenol found in various plants, modulates plasma copper and zinc levels and influences OS and antioxidant status in copper-deficient rats.³²⁰ Resveratrol improves memory and neuroinflammation through antioxidant, anti-inflammatory effects, reduction of Aβ-induced LPO, and regulation of cellular signaling pathways.²⁹⁷ Supplementation with resveratrol has shown some effects on cognitive and functional decline in AD patients.²⁹⁸ Additionally, resveratrol regulates cellular proteostasis by upregulating autophagy, thereby attenuating CuSO₄-induced senescence.¹² Another study reported that resveratrol effectively alleviates OS and hepatic-renal injury induced by CuONPs.³²¹

Conclusion and Future Perspectives

Copper is an essential element involved in oxidative metabolism and is indispensable for brain cell function. The storage and utilization of copper affect tissues and organs throughout the body. Copper-dependent protein networks—including copper reductases, copper chaperones, and membrane transporters—play critical regulatory roles in maintaining intracellular copper homeostasis. Disruption of copper homeostasis contributes significantly to the pathogenesis of various neurological disorders. Both copper overload and copper deficiency can affect the nervous system through multiple mechanisms, including the induction of oxidative stress (OS), mitochondrial dysfunction, interference with protein folding, and disturbance of metabolic balance, ultimately leading to neuronal dysfunction and death.

In recent years, the discovery of cuproptosis has expanded our understanding of copper-related pathological mechanisms. Unlike classical forms of cell death such as apoptosis, necrosis, or ferroptosis, cuproptosis is characterized by the aberrant binding of copper ions to lipoylated proteins, resulting in protein aggregation and loss of iron–sulfur cluster proteins, which trigger mitochondrial destabilization and metabolic collapse.

Copper dyshomeostasis is closely associated with numerous neurological diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), Wilson disease (WD), Menkes disease (MD), and stroke. The pathogenic mechanisms of copper metabolism abnormalities vary considerably among different diseases, encompassing both the toxic effects of copper overload and enzyme dysfunction or metabolic imbalance caused by copper deficiency. These two opposing states often coexist in different stages or regions of the same disease.

Copper death (cuproptosis) modulators hold potential for alleviating neurotoxicity and protecting neurons. Developing more precise molecular-targeted modulators—such as drugs affecting copper transporters, copper chaperones, or mitochondrial copper utilization—could provide neuroprotection by intervening in the core regulatory mechanisms of cuproptosis. This approach may form part of future therapeutic strategies but faces challenges, including poor BBB penetration, insufficient targeting, and the risk of inhibiting essential metalloprotein enzymes. Combining modulators with targeted delivery systems, such as brain-targeted nanoparticles, may enhance their efficacy and safety in the central nervous system (CNS), enabling more precise treatment. In the context of neurological drug development, all preclinical experiments on cuproptosis modulators should be conducted according to GLP standards to ensure scientific rigor and reliability of experimental design and data analysis. The research workflow should encompass key steps, including cell and animal models, drug administration, assessment of copper homeostasis, and measurement of cuproptosis activity, thereby providing a high-quality evidence base for the subsequent development of cuproptosis-targeted therapeutics.