Intestinal expression of metal transporters in Wilson's disease

Copper and Colorectal Cancer

Minerals constitute only 5% of the typical human diet but are vital for health and functionality. Copper, a trace element, is absorbed by the human gut at 30-40% from diets typical of industrialized countries. The liver produces metallothioneins, which store copper. Copper is crucial for mitochondrial respiration, pigmentation, iron transport, antioxidant defense, hormone production, and extracellular matrix biosynthesis. Copper deficiency, often caused by mutations in the ATP7A gene, results in Menkes disease, an X-linked recessive disorder. On the contrary, Wilson disease is characterized by toxic copper accumulation. Cuproptosis, a unique form of cell death regulated by copper, is a subtype of necrosis induced by enhanced mitochondrial metabolism and intracellular copper accumulation. This process can reduce the malignant potential of tumor cells by inhibiting glucose metabolism. Therapeutically, copper and its complexes have shown efficacy in malignancy treatments. The disruption of copper homeostasis and excessive cuproplasia are significant in colorectal cancer development and metastasis. Therefore, manipulating copper status presents a potential therapeutic target for colorectal cancer, using copper chelators to inhibit copper formation or copper ion carriers to promote cuproptosis. This review highlights the role of copper in human physiology and pathology, emphasizing its impact on colorectal cancer and potential therapeutic strategies. Future AI-based approaches are anticipated to accelerate the development of new compounds targeting cuproptosis and copper disruption in colorectal cancer.

Deadly excess copper

Higher eukaryotes' life is impossible without copper redox activity and, literally, every breath we take biochemically demonstrates this. However, this dependence comes at a considerable price to ensure target-oriented copper action. Thereto its uptake, distribution but also excretion are executed by specialized proteins with high affinity for the transition metal. Consequently, malfunction of copper enzymes/transporters, as is the case in hereditary Wilson disease that affects the intracellular copper transporter ATP7B, comes with serious cellular damage. One hallmark of this disease is the progressive copper accumulation, primarily in liver but also brain that becomes deadly if left untreated. Such excess copper toxicity may also result from accidental ingestion or attempted suicide. Recent research has shed new light into the cell-toxic mechanisms and primarily affected intracellular targets and processes of such excess copper that may even be exploited with respect to cancer therapy. Moreover, new therapies are currently under development to fight against deadly toxic copper.

Metabolic Derangement of Essential Transition Metals and Potential Antioxidant Therapies

Essential transition metals have key roles in oxygen transport, neurotransmitter synthesis, nucleic acid repair, cellular structure maintenance and stability, oxidative phosphorylation, and metabolism. The balance between metal deficiency and excess is typically ensured by several extracellular and intracellular mechanisms involved in uptake, distribution, and excretion. However, provoked by either intrinsic or extrinsic factors, excess iron, zinc, copper, or manganese can lead to cellular damage upon chronic or acute exposure, frequently attributed to oxidative stress. Intracellularly, mitochondria are the organelles that require the tightest control concerning reactive oxygen species production, which inevitably leaves them to be one of the most vulnerable targets of metal toxicity. Current therapies to counteract metal overload are focused on chelators, which often cause secondary effects decreasing patients' quality of life. New therapeutic options based on synthetic or natural antioxidants have proven positive effects against metal intoxication. In this review, we briefly address the cellular metabolism of transition metals, consequences of their overload, and current therapies, followed by their potential role in inducing oxidative stress and remedies thereof.

Missing heritability of Wilson disease: a search for the uncharacterized mutations

Wilson disease (WD), a copper metabolism disorder caused by mutations in ATP7B, manifests heterogeneous clinical features. Interestingly, in a fraction of clinically diagnosed WD patients, mutations in ATP7B appears to be missing. In this review we discuss the plausible explanations of this missing heritability and propose a workflow that can identify the hidden mutations. Mutation analyses of WD generally includes targeted sequencing of ATP7B exons, exon-intron boundaries, and rarely, the proximal promoter region. We propose that variants in the distal cis-regulatory elements and/or deep intronic variants that impact splicing might well represent the hidden mutations. Heterozygous del/ins that remain refractory to conventional PCR-sequencing method may also represent such mutations. In this review, we also hypothesize that mutations in the key copper metabolism genes, like, ATOX1, COMMD1, and SLC31A1, could possibly lead to a WD-like phenotype. In fact, WD does present overlapping symptoms with other rare genetic disorders; hence, the possibility of a misdiagnosis and thus adding to missing heritability cannot be excluded. In this regard, it seems that whole-genome analysis will provide a comprehensive and rapid molecular diagnosis of WD. However, considering the associated cost for such a strategy, we propose an alternative customized screening schema of WD which include targeted sequencing of ATP7B locus as well as other key copper metabolism genes. Success of such a schema has been tested in a pilot study.

Biochemical regulatory processes in the control of oxidants and antioxidants production in the brain of rats with iron and copper chronic overloads

Iron [Fe(II)] and copper [Cu(II)] overloads in rat brain are associated with oxidative stress and damage. The purpose of this research is to study whether brain antioxidant enzymes are involved in the control of intracellular redox homeostasis in the brain of rats male Sprague-Dawley rats (80-90 g) that received drinking water supplemented with either 1.0 g/L of ferrous chloride (n = 24) or 0.5 g/L cupric sulfate (n = 24) for 42 days. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and glutathione transferase (GT) activities in brain were determined by spectrophotometric methods and NO production by the content of nitrite concentration in the organ. Chronic treatment with Fe(II) and Cu(II) led to a significant decrease of nitrite content and SOD activity in brain. Activity of NADPH oxidase increased with Cu(II) treatment. Concerning Fe(II), catalase and GT activities increased in brain after 28 and 4 days of treatment, respectively. In the case of Cu(II), catalase activity decreased whereas GT activity increased after 2 and 14 days, respectively. The regulation of redox homeostasis in brain involves changes of the activity of these enzymes to control the steady state of oxidant species related to redox signaling pathways upon Cu and Fe overload. NO may serve to detoxify cells from superoxide anion and hydrogen peroxide with the concomitant formation of peroxynitrite. However, the latest is a powerful oxidant which leads to oxidative modifications of biomolecules. These results suggest a common pathway to oxidative stress and damage in brain for Cu(II) and Fe(II).

Copper Dyshomeostasis in Neurodegenerative Diseases-Therapeutic Implications

Copper is one of the most abundant basic transition metals in the human body. It takes part in oxygen metabolism, collagen synthesis, and skin pigmentation, maintaining the integrity of blood vessels, as well as in iron homeostasis, antioxidant defense, and neurotransmitter synthesis. It may also be involved in cell signaling and may participate in modulation of membrane receptor-ligand interactions, control of kinase and related phosphatase functions, as well as many cellular pathways. Its role is also important in controlling gene expression in the nucleus. In the nervous system in particular, copper is involved in myelination, and by modulating synaptic activity as well as excitotoxic cell death and signaling cascades induced by neurotrophic factors, copper is important for various neuronal functions. Current data suggest that both excess copper levels and copper deficiency can be harmful, and careful homeostatic control is important. This knowledge opens up an important new area for potential therapeutic interventions based on copper supplementation or removal in neurodegenerative diseases including Wilson's disease (WD), Menkes disease (MD), Alzheimer's disease (AD), Parkinson's disease (PD), and others. However, much remains to be discovered, in particular, how to regulate copper homeostasis to prevent neurodegeneration, when to chelate copper, and when to supplement it.

ATP7B knockout disturbs copper and lipid metabolism in Caco-2 cells

Intestinal cells control delivery of lipids to the body by adsorption, storage and secretion. Copper (Cu) is an important trace element and has been shown to modulate lipid metabolism. Mutation of the liver Cu exporter ATP7B is the cause of Wilson disease and is associated with Cu accumulation in different tissues. To determine the relationship of Cu and lipid homeostasis in intestinal cells, a CRISPR/Cas9 knockout of ATP7B (KO) was introduced in Caco-2 cells. KO cells showed increased sensitivity to Cu, elevated intracellular Cu storage, and induction of genes regulating oxidative stress. Chylomicron structural protein ApoB48 was significantly downregulated in KO cells by Cu. Apolipoproteins ApoA1, ApoC3 and ApoE were constitutively induced by loss of ATP7B. Formation of small sized lipid droplets (LDs) was enhanced by Cu, whereas large sized LDs were reduced. Cu reduced triglyceride (TG) storage and secretion. Exposure of KO cells to oleic acid (OA) resulted in enhanced TG storage. The findings suggest that Cu represses intestinal TG lipogenesis, while loss of ATP7B results in OA-induced TG storage.

Whole-exome sequencing identifies novel pathogenic variants across the ATP7B gene and some modifiers of Wilson's disease phenotype

BACKGROUND & AIMS

Wilson's disease (WD) is an autosomal recessive disorder associated with disease-causing alterations across the ATP7B gene, with highly variable symptoms and age of onset. We aimed to assess whether the clinical variability of WD relates to modifier genes.

METHODS

A total of 248 WD patients were included, of whom 148 were diagnosed after age of 17. Human exome libraries were constructed using AmpliSeq technology and sequenced using the IonProton platform.

RESULTS

ATP7B p.His1069Gln mutation was present in 215 patients, with 112 homozygotes and 103 heterozygotes. Three other mutations: p.Gln1351Ter, p.Trp779Ter and c.3402delC were identified in >10 patients. Among patients, 117 had a homozygous mutation, 101 were compound heterozygotes, 27 had one heterozygous mutation, and 3 other patients had no identifiable pathogenic variant of ATP7B. Sixteen mutations were novel, found as part of a compound mutation or as a sole, homozygous mutation. For disease phenotype prediction, age at diagnosis was a deciding factor, while frameshift allelic variants of ATP7B and being male increased the odds of developing a neurological phenotype. Rare allelic variants in ESD and INO80 increased and decreased chances for the neurological phenotype, respectively, while rare variants in APOE and MBD6 decreased the chances of WD early manifestation. Compound mutations contributed to earlier age of onset.

CONCLUSIONS

In a Polish population, genetic screening for WD may help genotype for four variants (p.His1069Gln, p.Gln1351Ter, p.Trp779Ter and c.3402delC), with direct sequencing of all ATP7B amplicons as a second diagnostic step. We also identified some allelic variants that may modify a WD phenotype.

Animal models of Wilson disease

Wilson disease (WD) is an autosomal recessive disorder of copper metabolism manifesting with hepatic, neurological and psychiatric symptoms. The limitations of the currently available therapy for WD (particularly in the management of neuropsychiatric disease), together with our limited understanding of key aspects of this illness (e.g. neurological vs. hepatic presentation) justify the ongoing need to study WD in suitable animal models. Four animal models of WD have been established: the Long-Evans Cinnamon rat, the toxic-milk mouse, the Atp7b knockout mouse and the Labrador retriever. The existing models of WD all show good similarity to human hepatic WD and have been helpful in developing an improved understanding of the human disease. As mammals, the mouse, rat and canine models also benefit from high homology to the human genome. However, important differences exist between these mammalian models and human disease, particularly the absence of a convincing neurological phenotype. This review will first provide an overview of our current knowledge of the orthologous genes encoding ATP7B and the closely related ATP7A protein in C. elegans, Drosophila and zebrafish (Danio rerio) and then summarise key characteristics of rodent and larger mammalian models of ATP7B-deficiency.

Oxidative damage to rat brain in iron and copper overloads

Increased cytosolic levels of Fe²⁺, Cu⁺and H₂O₂are central to the hypothesis that Fe and Cu toxicities are mediated by OH˙ formation and oxidative damage due to phospholipids and proteins oxidation.