Atp7b-/- mice as a model for studies of Wilson's disease

Profile of plasma microRNAs as a potential biomarker of Wilson's disease

BACKGROUND

Wilson's disease (WD) is a rare condition resulting from autosomal recessive mutations in ATP7B, a copper transporter, manifesting with hepatic, neurological, and psychiatric symptoms. Timely diagnosis and appropriate treatment yield a positive prognosis, while delayed identification and/or insufficient therapy lead to a poor outcome. Our aim was to establish a prognostic method for WD by characterising biomarkers based on circulating microRNAs.

METHODS

We conducted investigations across three cohorts: discovery, validation (comprising unrelated patients), and follow-up (revisiting the discovery cohort 3 years later). All groups were compared to age- and gender-matched controls. Plasma microRNAs were analysed via RNA sequencing in the discovery cohort and subsequently validated using quantitative PCR in all three cohorts. To assess disease progression, we examined the microRNA profile in Atp7b-/- mice, analysing serum samples from 6 to 44 weeks of age and liver samples at three time points: 20, 30, and 40 weeks of age.

RESULTS

In patients, elevated levels of the signature microRNAs (miR-122-5p, miR-192-5p, and miR-885-5p) correlated with serum activities of aspartate transaminase, alanine aminotransferase and gamma-glutamyl transferase. In Atp7b-/- mice, levels of miR-122-5p and miR-192-5p (miR-885-5p lacking a murine orthologue) increased from 12 weeks of age in serum, while exhibiting fluctuations in the liver, possibly attributable to hepatocyte regenerative capacity post-injury and the release of hepatic microRNAs into the bloodstream.

CONCLUSIONS

The upregulation of the signature miR-122-5p, miR-192-5p, and miR-885-5p in patients and their correlation with liver disease progression in WD mice support their potential as biomarkers of WD.

Aberrant copper metabolism and hepatic inflammation cause neurological manifestations in a mouse model of Wilson's disease

Pathogenic germline mutations in the P-type copper-transporting ATPase (ATP7B) gene cause Wilson's disease (WD), a hereditary disorder characterized by disrupted copper metabolism. The Arg778Leu (R778L) mutation in exon 8 is prevalent among individuals with WD in East Asia and is associated with more severe phenotypes. In this study, we generated a WD mouse model harboring R778L mutation (R778L mice) using CRISPR/Cas9. R778L mice exhibit a range of pathological characteristics resembling those of patients with WD and the same point mutations, including aberrant copper metabolism, pathological cellular injury, inflammation, and severe hepatic fibrosis. At 3-5 months of age, these mice started to display neurological deficits in motor coordination and cognitive dysfunction, accompanied by increased expression of inflammatory cytokines in the central nervous system. Microglia in the striatum and cortex exhibit significant activation, shorter processes, and decreased branch points. However, the Cu2+ levels in the brain tissue of R778L mice did not differ significantly from those of wild-type mice. Notably, inhibition of hepatic inflammation with PJ34 or siNfkb markedly alleviated the deficiencies in cognitive performance and improved locomotor activity in R778L mice. Thus, this study establishes a novel murine model to investigate the pathophysiology of WD, highlights the liver-brain crosstalk responsible for neurological manifestations in individuals with WD caused by the R778L point mutation, and demonstrates the potential of modulating liver inflammation as a therapeutic strategy for alleviating the neurological manifestations of WD.

Recent Development on Copper-Sensor and its Biological Applications: A Review

Metal ion recognition is one of the most prospective research topics in the field of chemical sensors due to its wide range of clinical, biological and environmental applications. In this context, hydrazones are well known compounds that exhibit metal sensing and several biological properties due to the presence of N=CH- bond. Some of the biological properties includes anti-cancer, anti-tumor, anti-oxidant, anti-microbial activities. Hydrazones are also used as a ligand to detect metal ion as well as to generate metal complexes that exhibit medicinal properties. Thus, in recent years, many attempts were made to develop novel ligands with enhanced metal sensing and medicinal properties. In this review, some of the recent development on the hydrazones and their copper complexes are covered from the last few years from 2015-2023. These includes significance of copper ions, synthesis, biological properties, mechanism and metal sensing properties of some of the copper complexes were discussed.

Copper Metabolism and Cuproptosis: Molecular Mechanisms and Therapeutic Perspectives in Neurodegenerative Diseases

Copper is an essential trace element, and plays a vital role in numerous physiological processes within the human body. During normal metabolism, the human body maintains copper homeostasis. Copper deficiency or excess can adversely affect cellular function. Therefore, copper homeostasis is stringently regulated. Recent studies suggest that copper can trigger a specific form of cell death, namely, cuproptosis, which is triggered by excessive levels of intracellular copper. Cuproptosis induces the aggregation of mitochondrial lipoylated proteins, and the loss of iron-sulfur cluster proteins. In neurodegenerative diseases, the pathogenesis and progression of neurological disorders are linked to copper homeostasis. This review summarizes the advances in copper homeostasis and cuproptosis in the nervous system and neurodegenerative diseases. This offers research perspectives that provide new insights into the targeted treatment of neurodegenerative diseases based on cuproptosis.

Insights Into the Role of Copper in Neurodegenerative Diseases and the Therapeutic Potential of Natural Compounds

Neurodegenerative diseases encompass a collection of neurological disorders originating from the progressive degeneration of neurons, resulting in the dysfunction of neurons. Unfortunately, effective therapeutic interventions for these diseases are presently lacking. Copper (Cu), a crucial trace element within the human body, assumes a pivotal role in various biological metabolic processes, including energy metabolism, antioxidant defense, and neurotransmission. These processes are vital for the sustenance, growth, and development of organisms. Mounting evidence suggests that disrupted copper homeostasis contributes to numerous age-related neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Wilson's disease (WD), Menkes disease (MD), prion diseases, and multiple sclerosis (MS). This comprehensive review investigates the connection between the imbalance of copper homeostasis and neurodegenerative diseases, summarizing pertinent drugs and therapies that ameliorate neuropathological changes, motor deficits, and cognitive impairments in these conditions through the modulation of copper metabolism. These interventions include Metal-Protein Attenuating Compounds (MPACs), copper chelators, copper supplements, and zinc salts. Moreover, this review highlights the potential of active compounds derived from natural plant medicines to enhance neurodegenerative disease outcomes by regulating copper homeostasis. Among these compounds, polyphenols are particularly abundant. Consequently, this review holds significant implications for the future development of innovative drugs targeting the treatment of neurodegenerative diseases.

Histological features of liver disease development in the Atp7b-/- mouse: a model of Wilson's disease

AIMS

Wilson's disease (WD) is caused by mutations in the ATP7B gene, resulting in copper accumulation and toxicity in liver and brain tissues. Due to the initial asymptomatic liver involvement, the progression of liver injuries in WD stays primarily unknown. Atp7b-/- knockout mice have been shown to be an appropriate model of WD for liver involvement.

METHODS

A total of 138 Atp7b-/- mice were included and separated into five groups according to age as follows: 6, 20, 39 and 50 weeks without treatment, and 50 weeks with copper chelator treatment from 39 to 50 weeks of age and compared with 101 wild-type (WT) mice at the same stages. The evolution of histological liver lesions was analysed and compared between groups.

RESULTS

Significant changes were observed in Atp7b-/- mice compared with WT. Copper deposits in hepatocytes appeared as early as 6 weeks but no significant increase over time was observed. Inflammation appeared as early as 6 weeks and progressed henceforth. Lobular and periportal acidophilic bodies appeared after 20 weeks. Significant atypia was also observed at 20 weeks and increased over time to reach a severe stage at 39 weeks. Fibrosis also became apparent at 20 weeks, progressing subsequently to precirrhotic stages at 50 weeks. Copper content, inflammation and fibrosis scores were significantly reduced in the treated group. No bile duct lesions or dysplastic changes were noted.

CONCLUSIONS

Copper accumulation leads to progressive changes in Atp7b-/- mice regarding inflammation, fibrosis and atypia. The severity of liver damage is lessened by chelation therapy.

A novel carbazole-based fluorometric and colorimetric sensor for the highly sensitive and specific detection of Cu2+ in aqueous solution

Based on the typical Suzuki coupling reaction and Schiff base reaction, a novel fluorescent molecular PCBW is synthesized and applied as a fluorescence and colorimetric sensor to detect Cu2+ in aqueous solution. The PCBW sensor presents the aggregation-caused quenching (ACQ) effect and at 1 × 10-5 mol L-1 it emits the strongest turquoise fluorescence in the DMSO-H2O system (fw = 40%). The sensor exhibits a 'turn-off' fluorescent characteristic by adding Cu2+, and its fluorescent intensity shows a reliable linear relationship with the Cu2+ concentration in the range of 0-6 × 10-6 mol L-1, with a detection limit of 1.19 × 10-8 mol L-1. Meanwhile, the PCBW sensor also exhibits the colorimetric sensing from colorless to light yellow. The sensor has good selectivity and anti-interference and its pH application range can be extended from 5 to 10. The intramolecular charge transfer (ICT) is speculated as the main fluorescence mechanism of PCBW. In addition, the sensor presents good reusability and is practicable to detect Cu2+ in diverse aqueous samples.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

Oxidation state-specific fluorescent copper sensors reveal oncogene-driven redox changes that regulate labile copper(II) pools

Copper is an essential metal nutrient for life that often relies on redox cycling between Cu(I) and Cu(II) oxidation states to fulfill its physiological roles, but alterations in cellular redox status can lead to imbalances in copper homeostasis that contribute to cancer and other metalloplasias with metal-dependent disease vulnerabilities. Copper-responsive fluorescent probes offer powerful tools to study labile copper pools, but most of these reagents target Cu(I), with limited methods for monitoring Cu(II) owing to its potent fluorescence quenching properties. Here, we report an activity-based sensing strategy for turn-on, oxidation state-specific detection of Cu(II) through metal-directed acyl imidazole chemistry. Cu(II) binding to a metal and oxidation state-specific receptor that accommodates the harder Lewis acidity of Cu(II) relative to Cu(I) activates the pendant dye for reaction with proximal biological nucleophiles and concomitant metal ion release, thus avoiding fluorescence quenching. Copper-directed acyl imidazole 649 for Cu(II) (CD649.2) provides foundational information on the existence and regulation of labile Cu(II) pools, including identifying divalent metal transporter 1 (DMT1) as a Cu(II) importer, labile Cu(II) increases in response to oxidative stress induced by depleting total glutathione levels, and reciprocal increases in labile Cu(II) accompanied by decreases in labile Cu(I) induced by oncogenic mutations that promote oxidative stress.

Prognostic value of cuproptosis-related genes signature and its impact on the reshaped immune microenvironment of glioma

Glioma is the most prevalent malignancy in the central nervous system. The impact of ion-induced cell death on malignant tumors’ development and immune microenvironment has attracted broad attention in recent years. Cuproptosis is a novel copper-dependent mechanism that could potentially regulate tumor cell death by targeting mitochondria respiration. However, the role of cuproptosis in gliomas remains unclear. In the present study, we investigated the relationships between the expression of cuproptosis-related genes (CRGs) and tumor characteristics, including prognosis and microenvironment of glioma, by analyzing multiple public databases and our cohort. Consensus clustering based on the expression of twelve CRGs stratified the glioma patients into three subgroups with significantly different prognosis and immune microenvironment landscapes. Reduced immune infiltration was associated with the less aggressive CRG cluster. A prognostic CRGs risk signature (CRGRS), based on eight critical CRGs, classified the patients into low- and high-risk groups in the training set and was endorsed by validation sets from multiple cohorts. The high-risk group manifested a shorter overall survival, and further survival analysis demonstrated that the CRGRS was an independent prognostic factor. The nomogram combining CRGRS and other clinicopathological factors exhibited good accuracy in predicting the prognosis of glioma patients. Moreover, analyses of tumor immune microenvironment indicated that higher CRGRS was correlated with increased immune cell infiltration but diminished immune function. Gliomas in the high-risk group exhibited higher expression of multiple immune checkpoints, including PD-1 and PD-L1, and a better predicted therapy response to immune checkpoint inhibitors. In conclusion, our study elucidated the connections between CRGs expression and the aggressiveness of gliomas, and the application of CRGRS derived a new robust model for prognosis evaluation of glioma patients. The correlations between the profiles of CRGs expression and immune tumor microenvironment illuminated prospects and potential indications of immunotherapy for glioma.

Novel Gene-Correction-Based Therapeutic Modalities for Monogenic Liver Disorders

The majority of monogenic liver diseases are autosomal recessive disorders, with few being sex-related or co-dominant. Although orthotopic liver transplantation (LT) is currently the sole therapeutic option for end-stage patients, such an invasive surgical approach is severely restricted by the lack of donors and post-transplant complications, mainly associated with life-long immunosuppressive regimens. Therefore, the last decade has witnessed efforts for innovative cellular or gene-based therapeutic strategies. Gene therapy is a promising approach for treatment of many hereditary disorders, such as monogenic inborn errors. The liver is an organ characterized by unique features, making it an attractive target for in vivo and ex vivo gene transfer. The current genetic approaches for hereditary liver diseases are mediated by viral or non-viral vectors, with promising results generated by gene-editing tools, such as CRISPR-Cas9 technology. Despite massive progress in experimental gene-correction technologies, limitations in validated approaches for monogenic liver disorders have encouraged researchers to refine promising gene therapy protocols. Herein, we highlighted the most common monogenetic liver disorders, followed by proposed genetic engineering approaches, offered as promising therapeutic modalities.

Copper induces cell death by targeting lipoylated TCA cycle proteins

Copper is an essential cofactor for all organisms, and yet it becomes toxic if concentrations exceed a threshold maintained by evolutionarily conserved homeostatic mechanisms. How excess copper induces cell death, however, is unknown. Here, we show in human cells that copper-dependent, regulated cell death is distinct from known death mechanisms and is dependent on mitochondrial respiration. We show that copper-dependent death occurs by means of direct binding of copper to lipoylated components of the tricarboxylic acid (TCA) cycle. This results in lipoylated protein aggregation and subsequent iron-sulfur cluster protein loss, which leads to proteotoxic stress and ultimately cell death. These findings may explain the need for ancient copper homeostatic mechanisms.

Low Molecular Weight Probe for Selective Sensing of PH and Cu2+ Working as Three INHIBIT Based Digital Comparator

A novel simple molecular chemosensor 2 was synthesized and examined for pH, cations and anions detection. At pH values higher than 10, probe 2 switches on a green emission where the excited state intramolecular proton transfer (ESIPT) is ceased. Also, the probe absorption spectrum shows a clear pH dependence, and the probe aqueous solution (ethanol/water = 1:2, borate buffer) responds selectively and sensitively through its fluorescence spectrum to the presence of Cu²⁺. Job's plot gave a 2:1 stoichiometry of Probe-2/Cu²⁺ complex, which responds to the presence of S^2- and H₂PO₄^- in aqueous solution (ethanol/water = 1:2, borate buffer) by its absorption and fluorescence spectra. In addition, probe 2 mimics a digital comparator based on three INHIBIT logic gates by different outputs using HO^- and H⁺ as inputs. Moreover, probe 2 also executes AND and NOT TRANSFER logic gates using Cu²⁺ and S^2- as inputs.

A highly selective fluorescence and absorption sensor for rapid recognition and detection of Cu2+ ion in aqueous solution and film

A fluorescence and absorption chemosensor (SAAT) based on 5-(hydroxymethyl)-salicylaldehyde (SA) and o-aminothiophenol (AT) was designed and synthesized. SAAT in DMSO-HEPES (20.0 mM, v/v, 1:99, pH=7.0) solution shows a highly selective and sensitive absorption and "on-off" fluorescence response to Cu²⁺ ions in aqueous solutions over all other competitive metal ions including Na⁺ , Ag⁺ , Ba²⁺ , Ca²⁺ , Cd²⁺ , Mg²⁺ , Zn²⁺ , Cr³⁺ , Al³⁺ , Hg²⁺ , K⁺ , Mn²⁺ , Ni²⁺ , Sr²⁺ , Tb³⁺ and Co²⁺ . SAAT exhibits ratiometric absorption sensing ability for Cu²⁺ ions. Importantly, SAAT also can sense Cu²⁺ ions by fluorescence quenching, the fluorescence intensity of SAAT showed a good linear relationship with Cu²⁺ concentration, and the detection limit of Cu²⁺ was 0.34 μM. The results of Job's plot, Benesi-Hildebrand plot, mass spectra, and DFT calculations confirmed that the selective absorption and fluorescence response were attributed to the formation of 1:1 complex between SAAT and Cu²⁺ . SAAT in test film can identify Cu²⁺ in water samples by the intuitive fluorescence color change under UV lamp. SAAT has great application value as a selective and sensitive chemosensor to discrimination and detection of Cu²⁺ ions.

CRISPR-targeted genome editing of human induced pluripotent stem cell-derived hepatocytes for the treatment of Wilson's disease

Background & Aims

Wilson’s disease (WD) is an autosomal recessive disorder of copper metabolism caused by loss-of-function mutations in ATP7B, which encodes a copper-transporting protein. It is characterized by excessive copper deposition in tissues, predominantly in the liver and brain. We sought to investigate whether gene-corrected patient-specific induced pluripotent stem cell (iPSC)-derived hepatocytes (iHeps) could serve as an autologous cell source for cellular transplantation therapy in WD.

Methods

We first compared the in vitro phenotype and cellular function of ATP7B before and after gene correction using CRISPR/Cas9 and single-stranded oligodeoxynucleotides (ssODNs) in iHeps (derived from patients with WD) which were homozygous for the ATP7B R778L mutation (ATP7B^R778L/R778L). Next, we evaluated the in vivo therapeutic potential of cellular transplantation of WD gene-corrected iHeps in an immunodeficient WD mouse model (Atp7b^-/-/ Rag2^-/-/ Il2rg^-/-; ARG).

Results

We successfully created iPSCs with heterozygous gene correction carrying 1 allele of the wild-type ATP7B gene (ATP7B^WT/-) using CRISPR/Cas9 and ssODNs. Compared with ATP7B^R778L/R778L iHeps, gene-corrected ATP7B^WT/- iHeps restored in vitro ATP7B subcellular localization, its subcellular trafficking in response to copper overload and its copper exportation function. Moreover, in vivo cellular transplantation of ATP7B^WT/- iHeps into ARG mice via intra-splenic injection significantly attenuated the hepatic manifestations of WD. Liver function improved and liver fibrosis decreased due to reductions in hepatic copper accumulation and consequently copper-induced hepatocyte toxicity.

Conclusions

Our findings demonstrate that gene-corrected patient-specific iPSC-derived iHeps can rescue the in vitro and in vivo disease phenotypes of WD. These proof-of-principle data suggest that iHeps derived from gene-corrected WD iPSCs have potential use as an autologous ex vivo cell source for in vivo therapy of WD as well as other inherited liver disorders.

Lay summary

Gene correction restored ATP7B function in hepatocytes derived from induced pluripotent stem cells that originated from a patient with Wilson’s disease. These gene-corrected hepatocytes are potential cell sources for autologous cell therapy in patients with Wilson’s disease.

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Correction of the ATP7B R778L mutation restored the subcellular localization of ATP7B in iHeps.

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The copper exportation capability of ATP7B was restored in gene-corrected iHeps.

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Gene-corrected iHeps reduced hepatic copper accumulation and copper-induced hepatic toxicity in mice with Wilson’s disease.

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Gene-corrected iHeps are potential ex vivo cell sources for therapy in Wilson’s disease.

Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn2+ and Colorimetric Chemosensors for Zn2+, Cu2+, and Ni2+ Ions

Metal ions play a very important role in environmental as well as biological fields. The detection of specific metal ions at a minute level caught much attention, and hence, several probes are available in the literature. Even though benzothiazole-based molecules have a special place in the medicinal field, only very few chemosensors are reported based on this moiety. The current work describes the design and synthesis of the benzothiazole-based chemosensor for a highly selective and sensitive detection of biologically important metal ions such as Zn2+, Cu2+, and Ni2+. The sensing studies of compound-1 showed a ratiometric as well as colorimetric response toward Zn2+, Cu2+, and Ni2+ ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Fe2+, Fe3+, Mg2+, K+, and Na+). Further, compound-1 exhibited ratiometric as well as turn-on-enhanced fluorescence response toward Zn2+ ions and turn off response for Cu2+ and Ni2+ ions. The Job plots revealed that the binding stoichiometry of compound-1 and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn2+, while it was 0.30 ppm and 0.34 ppm for Ni2+ and Cu2+, respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that compound-1 can be used as a powerful chemosensor for the detection of Zn2+, Cu2+, and Ni2+ ions. The bioimaging data illustrated that compound-1 is a very effective ratiometric sensor for Zn2+ ions in live cells.

Platinum-Based Interdigitated Micro-Electrode Arrays for Reagent-Free Detection of Copper

Water is a precious resource that is under threat from a number of pressures, including, for example, release of toxic compounds, that can have damaging effect on ecology and human health. The current methods of water quality monitoring are based on sample collection and analysis at dedicated laboratories. Recently, electrochemical-based methods have attracted a lot of attention for environmental sensing owing to their versatility, sensitivity and their ease of integration with cost effective, smart and portable readout systems. In the present work, we report on the fabrication and characterization of platinum-based interdigitated microband electrodes arrays, and their application for trace detection of copper. Using square wave voltammetry after acidification with mineral acids, a limit of detection of 0.8 μg/L was achieved. Copper detection was also undertaken on river water samples and compared with standard analytical techniques. The possibility of controlling the pH at the surface of the sensors—thereby avoiding the necessity to add mineral acids—was investigated. By applying potentials to drive the water splitting reaction at one comb of the sensor’s electrode (the protonator), it was possible to lower the pH in the vicinity of the sensing electrode. Detection of standard copper solutions down to 5 μg/L (ppb) using this technique is reported. This reagent free method of detection opens the way for autonomous, in situ monitoring of pollutants in water bodies.

Systemic deletion of Atp7b modifies the hepatocytes' response to copper overload in the mouse models of Wilson disease

Wilson disease (WD) is caused by inactivation of the copper transporter Atp7b and copper overload in tissues. Mice with Atp7b deleted either globally (systemic inactivation) or only in hepatocyte recapitulate various aspects of human disease. However, their phenotypes vary, and neither the common response to copper overload nor factors contributing to variability are well defined. Using metabolic, histologic, and proteome analyses in three Atp7b-deficient mouse strains, we show that global inactivation of Atp7b enhances and specifically modifies the hepatocyte response to Cu overload. The loss of Atp7b only in hepatocytes dysregulates lipid and nucleic acid metabolisms and increases the abundance of respiratory chain components and redox balancing enzymes. In global knockouts, independently of their background, the metabolism of lipid, nucleic acid, and amino acids is inhibited, respiratory chain components are down-regulated, inflammatory response and regulation of chromosomal replication are enhanced. Decrease in glucokinase and lathosterol oxidase and elevation of mucin-13 and S100A10 are observed in all Atp7b mutant strains and reflect the extent of liver injury. The magnitude of proteomic changes in Atp7b-/- animals inversely correlates with the metallothioneins levels rather than liver Cu content. These findings facilitate identification of WD-specific metabolic and proteomic changes for diagnostic and treatment.

Raposo MM. Optical Fiber Sensors for Biocide Monitoring: Examples, Transduction Materials, and Prospects

Antifouling biocides are toxic to the marine environment impacting negatively on the aquatic ecosystems. These biocides, namely, tributyltin (TBT) and Cu(I) compounds, are used to avoid biofouling; however, their toxicity turns TBT and Cu(I) monitoring an important health issue. Current monitoring methods are expensive and time-consuming. This review provides an overview of the actual state of the art of antifouling paints' biocides, including their impact and toxicity, as well as the reported methods for TBT and Cu(I) detection over the past decade. The principles of optical fiber sensors (OFS) applications, with focus on environmental applications, and the use of organic chemosensors in this type of sensors are debated. The multiplexing ability of OFS and their application on aquatic environments are also discussed.

Switching of C-C and C-N Coupling/Cleavage for Hypersensitive Detection of Cu2+ by a Catalytically Mediated 2-Aminoimidazolyl-Tailored Six-Membered Rhodamine Probe

A robust six-membered rhodamine spirocyclic probe 1 containing a versatile 2-aminoimidazolyl moiety was elaborately designed and synthesized via an attractive C-C and C-N coupling strategy to improve the performance in the detection of ultralow transition metal ions. Probe 1 allowed the highly hypersensitive detection of Cu²⁺ with a superior picomolar limit of detection (35 pM) and nanomolar naked-eye performance (80 nM) via the switching of C-C and C-N cleavage by a catalytic hydrolysis mode.

Liver transplantation as a rescue therapy for severe neurologic forms of Wilson disease

OBJECTIVE

To evaluate the effect of liver transplantation (LT) in patients with Wilson disease (WD) with severe neurologic worsening resistant to active chelation.

METHODS

French patients with WD who underwent LT for pure neurologic indication were retrospectively studied. Before LT and at the last follow-up, neurologic impairment was evaluated with the Unified Wilson's Disease Rating Scale (UWDRS) score, disability with the modified Rankin Scale (mRS) score, and hepatic function with the Model for End-stage Liver Disease score, together with the presence of a Kayser-Fleischer ring (KFR), brain MRI scores, and copper balance. The survival rate and disability at the last follow-up were the coprimary outcomes; evolution of KFR and brain MRI were the secondary outcomes. Prognosis factors were further assessed.

RESULTS

Eighteen patients had LT. All were highly dependent before LT (median mRS score 5). Neurologic symptoms were severe (median UWDRS score 105), dominated by dystonia and parkinsonism. The cumulated survival rate was 88.8% at 1 year and 72.2% at 3 and 5 years. At the last follow-up, 14 patients were alive. Their mRS and UWDRS scores improved (p < 0.0001 and p = 0.0003). Eight patients had a major improvement (78% decrease of the UWDRS score), 4 a moderate one (41% decrease), and 2 a stable status. KFR and brain MRI scores improved (p = 0.0007). Severe sepsis (p = 0.011) and intensive care unit admission (p = 0.001) before LT were significantly associated with death.

CONCLUSIONS

LT is a rescue therapeutic option that should be carefully discussed in selected patients with neurologic WD resistant to anticopper therapies (chelators or zinc salts) as it might allow patients to gain physical independency with a reasonable risk.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that for patients with WD with severe neurologic worsening resistant to active pharmacologic therapy, LT might decrease neurologic impairment.

A novel colorimetric and "turn-off" fluorescent probe based on catalyzed hydrolysis reaction for detection of Cu2+ in real water and in living cells

A novel and highly selective fluorescent 1,8-naphthalimide-based probe, 3, was designed and synthesized for rapid Cu²⁺ detection in a CH₃CN-H₂O (3:1, v/v, pH = 7.4) solution by means of a distinct hydrolysis mechanism via its Cu²⁺-promoting feature. Upon treatment with Cu²⁺, the fluorescence response of probe 3 at 550 nm abruptly decreased, which was visible to the naked eye, and this response was accompanied by a clear change of the color of the solution; the color changed from the original yellow color to colorless. This color change occurred due to the Cu²⁺-promoted hydrolysis of 3, which yielded a fluorescence-quenched product. It is inspiring that probe 3 exhibited excellent sensitivity, a short response time and strong anti-interference recognition. Compared with the allowable amount of Cu²⁺ (∼20 μM) in drinking water, the detection limit of 3 for Cu²⁺ is calculated to be 9.15 nM, which is much lower than the amount defined by standards. The probe can be successfully applied for the determination of Cu²⁺ in real aqueous samples. Furthermore, probe 3 can be used as a fluorescent sensor to detect Cu²⁺ in biological environments, demonstrating its low toxicity to organisms and good cell permeability in live cell imaging.

A long-lived Donor-Acceptor fluorescent probe for sequential detection of Cu2+ and biothiols

A new long-lived Donor-Acceptor (D-A) fluorophore based on carbazolyl dicyanobenzene was developed as an ON-OFF-ON multifunctional fluorescent probe 1 for sequential detection of Cu²⁺ and biothiols (Cys, Hcy and GSH). The fluorescence of probe 1 can be significantly and selectively quenched by Cu²⁺. Meanwhile, the fluorescence lifetime decreased from 2.1 μs to 18.5 ns. The limit of detection was determined to be 33.6 nM. Upon addition of biothiols (Cys, Hcy and GSH), the generated ensemble 1-Cu²⁺ displayed a "turn-on" fluorescent response at 555 nm and an obvious recovery in fluorescence lifetime and UV-vis absorption within 1 min. The limit of detection for Cys, Hcy and GSH were calculated by fluorescence titration experiments to be 0.19, 0.21 and 0.29 μM, respectively. The ensemble 1-Cu²⁺ was further successfully applied in bioimaging.

Comprehensive and comparative exploration of the Atp7b−/− mouse plasma proteome

Wilson's disease (WD) is a rare genetic disease caused by mutations in the ATP7B gene. In this study, we used MS-based proteomics to explore the plasma proteome of the Atp7b^−/− mouse, a genetic and phenotypic model for WD.

Liver Expression of a MiniATP7B Gene Results in Long-Term Restoration of Copper Homeostasis in a Wilson Disease Model in Mice

Gene therapy with an adeno-associated vector (AAV) serotype 8 encoding the human ATPase copper-transporting beta polypeptide (ATP7B) complementary DNA (cDNA; AAV8-ATP7B) is able to provide long-term copper metabolism correction in 6-week-old male Wilson disease (WD) mice. However, the size of the genome (5.2 kilobases [kb]) surpasses the optimal packaging capacity of the vector, which resulted in low-yield production; in addition, further analyses in WD female mice and in animals with a more advanced disease revealed reduced therapeutic efficacy, as compared to younger males. To improve efficacy of the treatment, an optimized shorter AAV vector was generated, in which four out of six metal-binding domains (MBDs) were deleted from the ATP7B coding sequence, giving rise to the miniATP7B protein (Δ57-486-ATP7B). In contrast to AAV8-ATP7B, AAV8-miniATP7B could be produced at high titers and was able to restore copper homeostasis in 6- and 12-week-old male and female WD mice. In addition, a recently developed synthetic AAV vector, AAVAnc80, carrying the miniATP7B gene was similarly effective at preventing liver damage, restoring copper homeostasis, and improving survival 1 year after treatment. Transduction of approximately 20% of hepatocytes was sufficient to normalize copper homeostasis, suggesting that corrected hepatocytes are acting as a sink to eliminate excess of copper. Importantly, administration of AAVAnc80-miniATP7B was safe in healthy mice and did not result in copper deficiency. Conclusion: In summary, gene therapy using an optimized therapeutic cassette in different AAV systems provides long-term correction of copper metabolism regardless of sex or stage of disease in a clinically relevant WD mouse model. These results pave the way for the implementation of gene therapy in WD patients.

An "off-on" fluorescent sensor for copper ion using graphene quantum dots based on oxidation of l-cysteine

A simple and highly efficient "off-on" fluorescent sensor based on grapheme quantum dots (GQDs) for Cu²⁺ was developed. In this sensing platform, the fluorescence of GQDs was quenched in the presence of 2,4-dinitrophenylcysteine (DNPC), which is the reaction product of 1-chloro-2,4-dinitrobenzene (CDNB) and l-cysteine, owing to the spectral overlap between the absorption of DNPC and the excitation of GQDs. In the presence of Cu²⁺, l-cysteine was catalytically oxidized to l-cystine by O₂, resulting in the reduction of DNPC. Thus, the fluorescence of GQDs was recovery. Based on this, the fluorescent detection of Cu²⁺ could be achieved. The proposed sensing strategy offered a selective identification of Cu²⁺ with a detection limit of 4.5 nM. Additionally, the practical application of this assay for Cu²⁺ determination in real water samples was also demonstrated.

Raposo MM, Martínez-Máñez R, Sancenón F. N,N-Diphenylanilino-heterocyclic aldehyde-based chemosensors for UV-vis/NIR and fluorescence Cu(ii) detection

Cu(ii) coordination with aldehyde-containing probes induced the appearance of NIR bands coupled with remarkable colour changes.

In Atp7b-/- Mice Modeling Wilson's Disease Liver Repopulation With Bone Marrow-Derived Myofibroblasts or Inflammatory Cells and Not Hepatocytes Is Deleterious

In Wilson's disease, Atp7b mutations impair copper excretion with liver or brain damage. Healthy transplanted hepatocytes repopulate the liver, excrete copper, and reverse hepatic damage in animal models of Wilson's disease. In Fah^-/- mice with tyrosinemia and α-1 antitrypsin mutant mice, liver disease is resolved by expansions of healthy hepatocytes derived from transplanted healthy bone marrow stem cells. This potential of stem cells has not been defined for Wilson's disease. In diseased Atp7b^-/- mice, we reconstituted bone marrow with donor cells expressing green fluorescent protein reporter from healthy transgenic mice. Mature hepatocytes originating from donor bone marrow were identified by immunostaining for green fluorescence protein and bile canalicular marker, dipeptidylpeptidase-4. Mesenchymal and inflammatory cell markers were used for other cells from donor bone marrow cells. Gene expression, liver tests, and tissues were analyzed for outcomes in Atp7b^-/- mice. After bone marrow transplantation in Atp7b^-/- mice, donor-derived hepatocytes containing bile canaliculi appeared within weeks. Despite this maturity, donor-derived hepatocytes neither divided nor expanded. The liver of Atp7b^-/- mice was not repopulated by donor-derived hepatocytes: Atp7b mRNA remained undetectable; liver tests, copper content, and fibrosis actually worsened. Restriction of proliferation in hepatocytes accompanied oxidative DNA damage. By contrast, donor-derived mesenchymal and inflammatory cells extensively proliferated. These contributed to fibrogenesis through greater expression of inflammatory cytokines. In Wilson's disease, donor bone marrow-derived cells underwent different fates: hepatocytes failed to proliferate; inflammatory cells proliferated to worsen disease outcomes. This will help guide stem cell therapies for conditions with proinflammatory or profibrogenic microenvironments.

Evaluation of the accuracy of exchangeable copper and relative exchangeable copper (REC) in a mouse model of Wilson's disease

Wilson's disease (WD) is caused by mutations in the ATP7B gene responsible for a toxic copper overload mainly in the liver and the central nervous system. Phenotypic heterogeneity may challenge the diagnostic confirmation. Exchangeable copper (CuEXC) has recently been proposed as a new marker of WD, and its ratio to the total serum copper (Cus), Relative Exchangeable Copper (REC = CuEXC/Cus), as a diagnostic marker. This study aimed to investigate whether this could be confirmed in Atp7b^-/- mice, an engineered WD animal model. Atp7b^-/- (n = 137) and wild type (WT; n = 101) mice were investigated under the same conditions at 6-8, 20, 39, or 50 weeks of age. Twenty-four Atp7b^-/- mice received D-penicillamine treatment from 39 to 50 weeks of age. Serum and liver [histology and intrahepatic copper (IHCu)] data were evaluated. In the WT group, all serum and liver data were normal. Atp7b^-/- livers developed a chronic injury from isolated moderate inflammation (6-8 weeks: 16/33 = 48%) to inflammatory fibrosis with cirrhosis (50 weeks: 25/25 = 100% and 16/25 = 64% respectively). Cus and CuEXC increased until week 39, whereas IHCu and REC were stable with increasing age and much higher than in WT mice (mean ± SD: 669 ± 269 vs. 13 ± 3 μg/g dry liver and 39 ± 12 vs. 11 ± 3%, respectively). A threshold value of 20% for REC provided a diagnostic sensitivity and specificity of 100%, regardless of sex, age, or the use of D-penicillamine. Eleven weeks of 100 mg/kg D-penicillamine reduced liver fibrosis (p = 0.001), IHCu (p = 0.026) and CuEXC (p = 0.175). In conclusion, this study confirms REC as a WD diagnostic marker in a mouse model of chronic liver disease caused by copper overload. Further studies are needed to assess the usefulness of CuEXC to monitor the evolution of WD, particularly during treatment.

Altered zinc balance in the Atp7b-/- mouse reveals a mechanism of copper toxicity in Wilson disease

Wilson disease (WD) is an autosomal recessive disorder caused by mutation in the ATP7B gene that affects copper transport in the body. ATP7B mutation damages copper transporter function, ultimately resulting in excessive copper accumulation and subsequent toxicity in both the liver and brain. Mechanisms of copper toxicity, however, are not well defined. The Atp7b-/- mouse model is well-characterized and presents a hepatic phenotype consistent with WD. In this study, we found that the untreated Atp7b-/- mice accumulate approximately 2-fold excess hepatic zinc compared to the wild type. We used targeted transcriptomics and proteomics to analyze the molecular events associated with zinc and copper accumulation in the Atp7b-/- mouse liver. Altered gene expression of Zip5 and ZnT1 zinc transporters indicated a transcriptional homeostatic response, while increased copper/zinc ratios associated with high levels of metallothioneins 1 and 2, indicated altered Zn availability in cells. These data suggest that copper toxicity in Wilson disease includes effects on zinc-dependent proteins. Transcriptional network analysis of RNA-seq data reveals an interconnected network of transcriptional activators with over-representation of zinc-dependent and zinc-responsive transcription factors. In the context of previous research, these observations support the hypothesis that mechanisms of copper toxicity include disruption of intracellular zinc distribution in liver cells. The translational significance of this work lies in oral zinc supplementation in treatment for WD, which is thought to mediate protective effects through the induction of metallothionein synthesis in the intestine. This work indicates broader impacts of altered zinc-copper balance in WD, including global transcriptional responses and altered zinc balance in the liver.

Apolipoprotein E deletion has no effect on copper-induced oxidative stress in the mice brain

The current study was designed to investigate effect of copper administration on oxidative damage to the brain in ApoE^−/− mice and to explore the putative neuroprotective effects rendered by apolipoprotein E (ApoE). Male C57BL/6 ApoE^−/− and wild-type mice were randomly assigned into four groups, ApoE^−/− mice wild-type mice treated with either copper or saline. Copper sulphate pentahydrate or saline (200 µl) were administered intragastrically daily for 12 weeks. Expression of malondialdehyde, superoxide dismutase (SOD), hemeoxygenase 1 (HO-1), and NAD(P)H: quinone oxidoreductase 1 (NQO1) were determined by a combination of biochemical assays. The concentration of copper in the brain of C57BL/6 mice and ApoE^−/− mice treated by copper significantly increased compared with mice treated by saline (P=0.0099 and P=0.0443). Compared with the C57BL/6 mice treated by copper, the level of the ApoE⁻/⁻ mice treated by copper was higher (P=0.018). TBARS and SOD activities or the expressions of NQO1 and HO-1 in the brain were not significantly different amongst the four experimental groups of mice. The relative value of NQO1/β-actin expression in the brain of the ApoE^−/− mice was similar in both saline and copper administration experimental groups. However, Western blot analysis showed that NQO1 expression was significantly higher in the ApoE^−/− mice brain treated with saline compared with saline treated wild-type mice (P=0.0449). ApoE does not function in protecting the brain from oxidative damage resulting from copper build-up in Wilson’s disease, but may play a role in regulating copper accumulation in the brain.

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.

Tuning the Color Palette of Fluorescent Copper Sensors through Systematic Heteroatom Substitution at Rhodol Cores

Copper is an essential nutrient for sustaining life, and emerging data have expanded the roles of this metal in biology from its canonical functions as a static enzyme cofactor to dynamic functions as a transition metal signal. At the same time, loosely bound, labile copper pools can trigger oxidative stress and damaging events that are detrimental if misregulated. The signal/stress dichotomy of copper motivates the development of new chemical tools to study its spatial and temporal distributions in native biological contexts such as living cells. Here, we report a family of fluorescent copper sensors built upon carbon-, silicon-, and phosphorus-substituted rhodol dyes that enable systematic tuning of excitation/emission colors from orange to near-infrared. These probes can detect changes in labile copper levels in living cells upon copper supplementation and/or depletion. We demonstrate the ability of the carbon-rhodol based congener, Copper Carbo Fluor 1 (CCF1), to identify elevations in labile copper pools in the Atp7a-/- fibroblast cell model of the genetic copper disorder Menkes disease. Moreover, we showcase the utility of the red-emitting phosphorus-rhodol based dye Copper Phosphorus Fluor 1 (CPF1) in dual-color, dual-analyte imaging experiments with the green-emitting calcium indicator Calcium Green-1 to enable simultaneous detection of fluctuations in copper and calcium pools in living cells. The results provide a starting point for advancing tools to study the contributions of copper to health and disease and for exploiting the rapidly growing palette of heteroatom-substituted xanthene dyes to rationally tune the optical properties of fluorescent indicators for other biologically important analytes.

Synthesis of near-infrared fluorescent rhodamines via an SNArH reaction and their biological applications

Seven rectilinearly π-extended NIR fluorescent rhodamines were synthesized via an intramolecular S_NAr^H reaction under mild conditions without any transition metal catalyst or extra oxidant.

Full-length cellular β-secretase has a trimeric subunit stoichiometry, and its sulfur-rich transmembrane interaction site modulates cytosolic copper compartmentalization

The β-secretase (BACE1) initiates processing of the amyloid precursor protein (APP) into Aβ peptides, which have been implicated as central players in the pathology of Alzheimer disease. BACE1 has been described as a copper-binding protein and its oligomeric state as being monomeric, dimeric, and/or multimeric, but the native cellular stoichiometry has remained elusive. Here, by using single-molecule fluorescence and in vitro cross-linking experiments with photo-activatable unnatural amino acids, we show that full-length BACE1, independently of its subcellular localization, exists as trimers in human cells. We found that trimerization requires the BACE1 transmembrane sequences (TMSs) and cytoplasmic domains, with residues Ala⁴⁶³ and Cys⁴⁶⁶ buried within the trimer interface of the sulfur-rich core of the TMSs. Our 3D model predicts that the sulfur-rich core of the trimeric BACE1 TMS is accessible to metal ions, but copper ions did not trigger trimerization. The results of functional assays of endogenous BACE1 suggest that it has a role in intracellular copper compartmentalization by transferring cytosolic copper to intracellular compartments, while leaving the overall cellular copper concentration unaltered. Adding to existing physiological models, our results provide novel insight into the atypical interactions between copper and BACE1 and into its non-enzymatic activities. In conclusion, therapeutic Alzheimer disease prevention strategies aimed at decreasing BACE1 protein levels should be regarded with caution, because adverse effects in copper homeostasis may occur.

Age-dependent changes of cerebral copper metabolism in Atp7b -/- knockout mouse model of Wilson's disease by [64Cu]CuCl2-PET/CT

Copper is a nutritional metal required for brain development and function. Wilson's disease (WD), or hepatolenticular degeneration, is an inherited human copper metabolism disorder caused by a mutation of the ATP7B gene. Many WD patients present with variable neurological and psychiatric symptoms, which may be related to neurodegeneration secondary to copper metabolism imbalance. The objective of this study was to explore the feasibility and use of copper-64 chloride ([⁶⁴C]CuCl₂) as a tracer for noninvasive assessment of age-dependent changes of cerebral copper metabolism in WD using an Atp7b ^-/- knockout mouse model of WD and positron emission tomography/computed tomography (PET/CT) imaging. Continuing from our recent study of biodistribution and radiation dosimetry of [⁶⁴C]CuCl₂ in Atp7b ^-/- knockout mice, PET quantitative analysis revealed low ⁶⁴Cu radioactivity in the brains of Atp7b ^-/- knockout mice at 7th weeks of age, compared with ⁶⁴Cu radioactivity in the brains of age- and gender-matched wild type C57BL/6 mice, at 24 h (h) post intravenous injection of [⁶⁴C]CuCl₂ as a tracer. Furthermore, age-dependent increase of ⁶⁴Cu radioactivity was detected in the brains of Atp7b ^-/- knockout mice from the 13th to 21th weeks of age, based on the data derived from a longitudinal [⁶⁴C]CuCl₂-PET/CT study of Atp7b ^-/- knockout mice with orally administered [⁶⁴Cu]CuCl₂ as a tracer. The findings of this study support clinical use of [⁶⁴Cu]CuCl₂-PET/CT imaging as a tool for noninvasive assessment of age-dependent changes of cerebral copper metabolism in WD patients presenting with variable neurological and psychiatric symptoms.

Reversal of liver fibrosis: From fiction to reality

In chronic liver diseases, an ongoing hepatocellular injury together with inflammatory reaction results in activation of hepatic stellate cells (HSCs) and increased deposition of extracellular matrix (ECM) termed as liver fibrosis. It can progress to cirrhosis that is characterized by parenchymal and vascular architectural changes together with the presence of regenerative nodules. Even at late stage, liver fibrosis is reversible and the underlying mechanisms include a switch in the inflammatory environment, elimination or regression of activated HSCs and degradation of ECM. While animal models have been indispensable for our understanding of liver fibrosis, they possess several important limitations and need to be further refined. A better insight into the liver fibrogenesis resulted in a large number of clinical trials aiming at reversing liver fibrosis, particularly in patients with non-alcoholic steatohepatitis. Collectively, the current developments demonstrate that reversal of liver fibrosis is turning from fiction to reality.

Demonstrating Potential of Cell Therapy for Wilson's Disease with the Long-Evans Cinnamon Rat Model

Wilson's disease (WD) is characterized by the inability to excrete copper (Cu) from the body with progressive tissue injury, especially in liver and brain. The molecular defect in WD concerns mutations in ATP7B gene leading to loss of Cu transport from the hepatocyte to the bile canaliculus. While drugs, e.g., Cu chelators, have been available for several decades, these must be taken lifelong, which can be difficult due to issues of compliance or side effects. Many individuals may require liver transplantation, which can also be difficult due to donor organ shortages. Therefore, achieving permanent cures via cell or gene therapy are of great interest for WD. Cell therapy is feasible because transplanted hepatocytes can integrate in liver parenchyma and restore deficient functions, including transport of Cu into bile. The availability of authentic animal models that recapitulate hepatic WD, especially the Long-Evans Cinnamon (LEC) rat, has advanced cell transplantation research in WD. We describe requirements for cell therapy in animal models with several standardized methods for studies to test or refine cell therapy strategies in WD.

Copper regulates cyclic-AMP-dependent lipolysis

Cell signaling relies extensively on dynamic pools of redox-inactive metal ions such as sodium, potassium, calcium and zinc, but their redox-active transition metal counterparts such as copper and iron have been studied primarily as static enzyme cofactors. Here we report that copper is an endogenous regulator of lipolysis, the breakdown of fat, which is an essential process in maintaining body weight and energy stores. Using a mouse model of genetic copper misregulation, in combination with pharmacological alterations in copper status and imaging studies in a 3T3-L1 white adipocyte model, we found that copper regulates lipolysis at the level of the second messenger, cyclic AMP (cAMP), by altering the activity of the cAMP-degrading phosphodiesterase PDE3B. Biochemical studies of the copper-PDE3B interaction establish copper-dependent inhibition of enzyme activity and identify a key conserved cysteine residue in a PDE3-specific loop that is essential for the observed copper-dependent lipolytic phenotype.