Effects of tetrathiomolybdate on copper metabolism in healthy volunteers and in patients with Wilson disease

BACKGROUND & AIMS

In Wilson disease (WD), copper accumulates in the liver and brain causing disease. Bis-choline tetrathiomolybdate (TTM) is a potent copper chelator that may be associated with a lower risk of inducing paradoxical neurological worsening than conventional therapy for neurologic WD. To better understand the mode of action of TTM, we investigated its effects on copper absorption and biliary excretion.

METHODS

In a double-blind randomized setting, hepatic 64Cu activity was examined after orally administered 64Cu by PET/CT in 16 healthy volunteers before and after seven days of TTM treatment (15 mg/d) or placebo. Oral 64Cu was administered one hour after the final TTM dose. Changes in hepatic 64Cu activity reflected changes in intestinal 64Cu uptake. Additionally, in four patients with WD, the distribution of 64Cu in venous blood, liver, gallbladder, kidney, and brain was followed after i.v. 64Cu dosing for up to 68 hours before and after seven days of TTM (15 mg/day), using PET/MRI. Increased gallbladder 64Cu activity was taken as evidence of increased biliary 64Cu excretion.

RESULTS

In healthy volunteers, TTM reduced intestinal 64Cu uptake by 82% 15 hours after the oral 64Cu dose. In patients with WD, gallbladder 64Cu activity was negligible before and after TTM, while TTM effectively retained 64Cu in the blood, significantly reduced hepatic 64Cu activity at all time-points and significantly reduced cerebral 64Cu activity two hours after the intravenous 64Cu dose.

CONCLUSIONS

While we did not show an increase in biliary excretion of 64Cu following TTM administration, we demonstrated that TTM effectively inhibited most intestinal 64Cu uptake and retained 64Cu in the blood stream, limiting the exposure of organs like the liver and brain to 64Cu.

IMPACT AND IMPLICATIONS

Bis-choline tetrathiomolybdate (TTM) is an investigational copper chelator being developed for the treatment of Wilson disease. In animal models of Wilson disease, TTM has been shown to facilitate biliary copper excretion. In the present human study, TTM surprisingly did not facilitate biliary copper excretion but instead reduced intestinal copper uptake to a clinically significant degree. Our study builds on our understanding of human copper metabolism and the mechanism of action of TTM.

Amyloid Targeting Red Emitting AIE Dots for Diagnostic and Therapeutic Application against Alzheimer's Disease

The emergence of neurodegenerative diseases is connected to several pathogenic factors, including metal ions, amyloidogenic proteins, and reactive oxygen species. Recent studies suggest that cytotoxicity is caused by the small, dynamic, and metastable nature of early stage oligomeric species. This work introduces a small molecule-based red-emitting probe with smart features such as increased reactivities against multiple targets, metal-free amyloid-β (Aβ), and metal-bound amyloid-β (Aβ), and most importantly, early stage oligomeric species which are associated with the most common and widespread type of dementia, Alzheimer's disease (AD). Theoretical analyses like molecular dynamics simulation and molecular docking were performed to confirm the reactivity of the molecule toward Aβ and found some excellent interactions between the molecule and the peptide. The in vitro and cellular studies demonstrated that this highly biocompatible molecule effectively reduces the structural damage to mitochondria while shielding cells from apoptosis, scavenges ROS (reactive oxygen species), and attenuates multifaceted amyloid toxicity.

Naturally-Occurring Tyrosinase Inhibitors Classified by Enzyme Kinetics and Copper Chelation

Currently, there are three major assaying methods used to validate in vitro whitening activity from natural products: methods using mushroom tyrosinase, human tyrosinase, and dopachrome tautomerase (or tyrosinase-related protein-2, TRP-2). Whitening agent development consists of two ways, melanin synthesis inhibition in melanocytes and downregulation of melanocyte stimulation. For melanin levels, the melanocyte cell line has been used to examine melanin synthesis with the expression levels of TRP-1 and TRP-2. The proliferation of epidermal surfaced cells and melanocytes is stimulated by cellular signaling receptors, factors, or mediators including endothelin-1, α-melanocyte-stimulating hormone, nitric oxide, histamine, paired box 3, microphthalmia-associated transcription factor, pyrimidine dimer, ceramide, stem cell factors, melanocortin-1 receptor, and cAMP. In addition, the promoter region of melanin synthetic genes including tyrosinase is upregulated by melanocyte-specific transcription factors. Thus, the inhibition of growth and melanin synthesis in gene expression levels represents a whitening research method that serves as an alternative to tyrosinase inhibition. Many researchers have recently presented the bioactivity-guided fractionation, discovery, purification, and identification of whitening agents. Melanogenesis inhibition can be obtained using three different methods: tyrosinase inhibition, copper chelation, and melanin-related protein downregulation. There are currently four different types of inhibitors characterized based on their enzyme inhibition mechanisms: competitive, uncompetitive, competitive/uncompetitive mixed-type, and noncompetitive inhibitors. Reversible inhibitor types act as suicide substrates, where traditional inhibitors are classified as inactivators and reversible inhibitors based on the molecule-recognizing properties of the enzyme. In a minor role, transcription factors can also be downregulated by inhibitors. Currently, the active site copper iron-binding inhibitors such as kojic acid and chalcone exhibit tyrosinase inhibitory activity. Because the tyrosinase catalysis site structure is important for the mechanism determination of tyrosinase inhibitors, understanding the enzyme recognition and inhibitory mechanism of inhibitors is essential for the new development of tyrosinase inhibitors. The present review intends to classify current natural products identified by means of enzyme kinetics and copper chelation to exhibit tyrosinase enzyme inhibition.

High-Affinity Cu(I)-Chelator with Potential Anti-Tumorigenic Action-A Proof-of-Principle Experimental Study of Human H460 Tumors in the CAM Assay

Human lung cancer ranks among the most frequently treated cancers worldwide. As copper appears critical to angiogenesis and tumor growth, selective removal of copper represents a promising strategy to restrict tumor growth. To this end, we explored the activity of the novel high-affinity membrane-permeant Cu(I) chelator PSP-2 featuring a low-zeptomolar dissociation constant. Using H460 human lung cancer cells, we generated small tumors on the chorioallantoic membrane of the chicken embryo (CAM assay) and studied the effects of topical PSP-2 application on their weight and vessel density after one week. We observed a significant angiosuppression along with a marked decrease in tumor weight under PSP-2 application compared to controls. Moreover, PSP-2 exposure resulted in lower ki67⁺ cell numbers at a low dose but increased cell count under a high dose. Moreover, HIF-1α⁺ cells were significantly reduced with low-dose PSP-2 exposure compared to high-dose and control. The total copper content was considerably lower in PSP-2 treated tumors, although statistically not significant. Altogether, PSP-2 shows promising potential as an anti-cancer drug. Nevertheless, further animal experiments and application to different tumor types are mandatory to support these initial findings, paving the way toward clinical trials.

Antioxidant Activity of Deferasirox and Its Metal Complexes in Model Systems of Oxidative Damage: Comparison with Deferiprone

Deferasirox is an orally active, lipophilic iron chelating drug used on thousands of patients worldwide for the treatment of transfusional iron overload. The essential transition metals iron and copper are the primary catalysts of reactive oxygen species and oxidative damage in biological systems. The redox effects of deferasirox and its metal complexes with iron, copper and other metals are of pharmacological, toxicological, biological and physiological importance. Several molecular model systems of oxidative damage caused by iron and copper catalysis including the oxidation of ascorbic acid, the peroxidation of linoleic acid micelles and the oxidation of dihydropyridine have been investigated in the presence of deferasirox using UV-visible and NMR spectroscopy. Deferasirox has shown antioxidant activity in all three model systems, causing substantial reduction in the rate of oxidation and oxidative damage. Deferasirox showed the greatest antioxidant activity in the oxidation of ascorbic acid with the participation of iron ions and reduced the reaction rate by about a 100 times. Overall, deferasirox appears to have lower affinity for copper in comparison to iron. Comparative studies of the antioxidant activity of deferasirox and the hydrophilic oral iron chelating drug deferiprone in the peroxidation of linoleic acid micelles showed lower efficiency of deferasirox in comparison to deferiprone.

Black tea polyphenol theaflavin as promising antioxidant and potential copper chelator

BACKGROUND

In this work, we investigated the antioxidant and copper chelating abilities of theaflavin, a polyphenol responsible for astringency, color, and sensation in black tea. Using voltammetric techniques, the analyses were conducted with disposable electrochemical printed carbon chips in conjunction with a portable hand-held potentiostat.

RESULTS

Voltammograms of theaflavin showed five separate oxidation peaks, corresponding to the oxidation of five individual functional groups. Electroanalytical data indicated that, after interaction with copper, theaflavin had higher antioxidant potential and was a better copper chelator than epigallocatechin gallate, a major polyphenol present in green tea and a well-known antioxidant. This could be attributed to the extra fused ring and larger number of OH groups in theaflavin.

CONCLUSIONS

Our findings introduce another natural compound as a potential nutraceutical in oxidation- and copper-modulated illnesses. This simple and fast approach would also be highly pertinent to the inspection of the health benefits of natural food products. To the best of our knowledge, this is the first report of the electrochemical analysis of Cu (II) chelation with theaflavin. © 2020 Society of Chemical Industry.

Recognition of antioxidants and photosensitizers in Dyssodia pinnata by EPR spectroscopy

INTRODUCTION

Previous studies report the isolation mainly of terthiophene derivatives and flavonoids from Dyssodia species. Terthiophenes are known as photosensitizers by their capacity to generate singlet oxygen (¹ O₂ ), and flavonoid antioxidant activity is recognized. These opposite properties could represent interesting options in photodynamic therapy.

OBJECTIVE

To determine the antioxidant and photosensitizer activities of extracts and isolates of Dyssodia pinnata by electron paramagnetic resonance (EPR).

METHODOLOGY

Extracts and isolates were evaluated as antioxidants by the interactions with copper ion (Cu²⁺ ) observed in EPR, and by the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and the thiobarbituric reactive substances (TBARS) methods. Their abilities as ¹ O₂ producers were also estimated by EPR.

RESULTS

Terthiophenes were obtained from hexane (DPH) and acetone (DPA) extracts, and flavonoids from DPA and methanol (DPM) extracts. The interaction with Cu²⁺ of extracts and isolated compounds of Dyssodia pinnata showed two effects in EPR: reduction and chelation; flavonoids exhibited both effects, while terthiophenes showed only reduction. DPA, DPM, and flavonoids were active in DPPH and TBARS assays. Quercetagetin-7-O-β-glucoside showed the highest antioxidant and chelating activities, 3-glycosidated flavonoids were less active. Upon irradiation extracts and terthiophenes induced ¹ O₂ formation.

CONCLUSION

Flavonoid reducing activity on Cu²⁺ and free radical scavenging capacity were related to the number of hydroxy groups and to the conjugation between the B and C rings. All tested flavonols showed a major complex with Cu²⁺ , with the most probable site of chelation between the 5-hydroxy and 4-oxo groups. Extracts and terthiophene derivatives showed photosensitizer activity. Thus, EPR is useful to evaluate free radical scavenging and pro-oxidant properties.

difficile-Infected Fecal Water

Probiotic supplementation plays a key role in maintaining intestinal homeostasis due to its ability to modulate gut microbiota. Although their potential as potent antioxidants have previously been explored, their ability to affect the redox status in the gut lumen of healthy subjects or those with gastrointestinal (GI) disorders remains unclear. In our study, we assessed the ability of single strain and multispecies probiotic supplementation to cause a change in the redox status of normal fecal water and in Clostridium (C.) difficile-infected fecal water using a simulated gastrointestinal model. Changes in redox status were assessed by ferric-reducing antioxidant power (FRAP), 2’,2’-diphenyl-1-picrylhydrazyl (DPPH), and iron and copper chelation assays. The findings from our study showed that in normal fecal water, probiotic supplements, apart from Lactobacillus (L.) rhamnosus R0011, showed a significant increase in iron chelation (p < 0.05), which was associated with lower FRAP and copper chelation. In C. difficile-infected fecal water, all probiotic supplements showed a significant increase in FRAP (p < 0.05) and were associated with increased copper chelation. The DPPH assay showed no treatment effect in either fecal water. These findings suggest that C. difficile mediates dysregulation of redox status, which is counteracted by probiotics through ferric-reducing ability and copper chelation.

Anti-melanogenic activity of ellagitannin casuarictin in B16F10 mouse melanoma cells

Ellagitannins such as casuarictin (CAS), isolated from clove extracts, have been shown to have superior benefits such as antioxidant and anti-inflammatory activity, but there have been no reports on their capacity to inhibit melanogenesis. Inhibition of melanogenesis by novel natural products has gained attention for cosmetic applications such as skin lightening. Here, we report the effects of CAS on melanogenesis in B16F10 mouse melanoma cells. Our results showed that CAS (30 µM) significantly inhibited intracellular melanogenesis while being nontoxic to B16F10 cells or to HaCaT cells at that concentration. CAS (30 μM) also inhibited intracellular tyrosinase activity as well as mushroom tyrosinase activity; possessed robust copper chelating ability comparable to that of 500 µM kojic acid; and downregulated MITF protein levels, all of which contribute to the inhibitory mechanisms underlying its anti-melanogenic activity. In summary, our results demonstrate that CAS might hold promise as a depigmenting agent for hyperpigmentation disorders.

Isolation and Identification of Tyrosinase-Inhibitory and Copper-Chelating Peptides from Hydrolyzed Rice-Bran-Derived Albumin

Rice-bran albumin (RBAlb), which shows higher tyrosinase-inhibitory activity than other protein fractions, was hydrolyzed with papain to improve the bioactivity. The obtained RBAlb hydrolysate (RBAlbH) was separated into 11 peptide fractions by RP-HPLC. Tyrosinase inhibition and copper chelation activities decreased with increasing retention times of the peptide fractions. RBAlbH fraction 1, which exhibited the greatest activity, contained 13 peptides whose sequences were determined by using LC-MS/MS. Most of the peptide sequences contained features of previously reported tyrosinase-inhibitory and metal-chelating peptides, especially peptide SSEYYGGEGSSSEQGYYGEG. RBAlbH fraction 1 showed more effective tyrosinase inhibition (IC50 = 1.31 mg/mL) than citric acid (IC50 = 9.38 mg/mL), but it was less effective than ascorbic acid (IC50 = 0.03 mg/mL, P ≤ 0.05). It showed copper-chelating activity (IC50 = 0.62 mg/mL) stronger than that of EDTA (IC50 = 1.06 mg/mL, P ≤ 0.05). These results suggest that RBAlbH has potential as a natural tyrosinase inhibitor and copper chelator for application in the food and cosmetic industries.

Unhindered copper uptake by glutaraldehyde-polyethyleneimine coatings in an artificial seawater model system with adsorbed swollen polysaccharides and competing ligand EDTA

Shortly after a surface is submerged in the sea, a conditioning film is generally formed by adsorption of organic molecules, such as polysaccharides. This could affect transport of molecules and ions between the seawater and the surface. An artificial seawater model system was developed to understand how adsorbed polysaccharides impact copper binding by glutaraldehyde-crosslinked polyethyleneimine coatings. Coating performance was also determined when competed against copper-chelating EDTA. Polysaccharide adsorption and copper binding and distribution were investigated using advanced analytical techniques, including depth-resolved time-of-flight secondary ion mass spectroscopy, grazing incidence X-ray absorption near-edge spectroscopy, quartz crystal microbalance with dissipation monitoring and X-ray photoelectron spectroscopy. In artificial seawater, the polysaccharides adsorbed in a swollen state that copper readily penetrated and the glutaraldehyde-polyethyleneimine coatings outcompeted EDTA for copper binding. Furthermore, the depth distribution of copper species was determined with nanometre precision. The results are highly relevant for copper-binding and copper-releasing materials in seawater.

Melatonin and its metabolites as copper chelating agents and their role in inhibiting oxidative stress: a physicochemical analysis

The copper sequestering ability of melatonin and its metabolites cyclic 3-hydroxymelatonin (3OHM), N(1) -acetyl-N(2) -formyl-5-methoxykynuramine (AFMK), and N(1) -acetyl-5-methoxykynuramine (AMK) was investigated within the frame of the Density Functional Theory. It was demonstrated that these compounds are capable of chelating copper ions, yielding stable complexes. The most likely chelation sites were identified. Two different mechanisms were modeled, the direct-chelation mechanism (DCM) and the coupled-deprotonation-chelation mechanism (CDCM). It is proposed that, under physiological conditions, CDCM would be the main chelation route for Cu(II). It was found that melatonin and its metabolites fully inhibited the oxidative stress induced by Cu(II)-ascorbate mixtures, via Cu(II) chelation. In the same way, melatonin, AFMK, and 3OHM also prevented the first step of the Haber-Weiss reaction, consequently turning off the ˙OH production via the Fenton reaction. Therefore, it is proposed that, in addition to the previously reported free radical scavenging cascade, melatonin is also involved in a concurrent 'chelating cascade', thereby contributing to a reduction in oxidative stress. 3OHM was identified as the most efficient of the studied compounds for that purpose, supporting the important role of this metabolite in the beneficial effects of melatonin against oxidative stress.