An improved Bathocuproine assay for accurate valence identification and quantification of copper bound by biomolecules

Experimental evidence of the anti-bacterial activity pathway of copper ion treatment on Mycobacterium avium subsp. paratuberculosis

Copper causes significant damage to the integrity of many bacteria, mainly at the DNA level, through its redox states, as well as its reactive oxygen species (ROS) generating capacity at the cellular level. But whether these mechanisms also apply to Mycobacterium avium subsp. paratuberculosis (MAP) is unknown. In the present study, we have evaluated whether copper ions produce damage at the DNA level of MAP, either through their redox states or through ROS production. MAP-spiked PBS was first supplemented with different copper chelators (2) and ROS antioxidants (3), followed by treatment with copper ions at 942 ppm. MAP DNA integrity (qPCR, magnetic phage separation) was then evaluated. We found that bathocuproine (BCS), as a chelator, and D-mannitol, as an antioxidant of hydroxyl radicals, had a significant protective effect (P < 0.05) on DNA molecules, and that EDTA, as a chelator, and D-mannitol, as an antioxidant had a significant positive effect (P < 0.05) on the viability of this pathogen in contrast to the control and other chelators and anti-oxidants used. In light of the reported findings, it may be concluded that copper ions within MAP cells are directly related to MAP DNA damage.

PredPromoter-MF(2L): A Novel Approach of Promoter Prediction Based on Multi-source Feature Fusion and Deep Forest

Promoters short DNA sequences play vital roles in initiating gene transcription. However, it remains a challenge to identify promoters using conventional experiment techniques in a high-throughput manner. To this end, several computational predictors based on machine learning models have been developed, while their performance is unsatisfactory. In this study, we proposed a novel two-layer predictor, called PredPromoter-MF(2L), based on multi-source feature fusion and ensemble learning. PredPromoter-MF(2L) was developed based on various deep features learned by a pre-trained deep learning network model and sequence-derived features. Feature selection based on XGBoost was applied to reduce fused features dimensions, and a cascade deep forest model was trained on the selected feature subset for promoter prediction. The results both fivefold cross-validation and independent test demonstrated that PredPromoter-MF(2L) outperformed state-of-the-art methods.

Dual roles of tau R peptides on Cu(II)/(I)-mediated reactive oxygen species formation

Metal dyshomeostasis plays a critical role in the reactive oxygen species (ROS) formation and protein misfolding and aggregation; hence, contributing to neurodegeneration. Tau protein plays a key role in normal cellular function by maintaining microtubule formation in brain. The role of metal ions on tau protein biochemistry has not been systematically evaluated, but earlier reports indicated that metal ions modulate the complex biochemistry of this protein and its peptides. Herein, we evaluated interactions of biologically-relevant Cu(II) ions with the four repeat peptides of tau protein (R1 through R4) and their role on the formation of ROS, Cu(II) to Cu(I) reduction, and ultimately, peptide aggregation. The role of R peptides on ROS formation was characterized in the absence and presence of biological reducing agent, ascorbate by using UV-Vis and fluorescence spectroscopy. In the presence of the reducing agent, all Cu(II)-peptide complexes reduced hydroxyl radical (OH·), while only Cu(II)-R3 complex depleted the hydrogen peroxide (H₂O₂). In the absence of a reducing agent, only Cu(II)-R2 and Cu(II)-R3 complexes, which contain Cys and His residues, produced OH· and H₂O₂. Only R2 and R3 peptides, but not R1 and R4, reduced Cu(II) to Cu(I). The aggregation propensities of R peptides were modulated by Cu(II) and ascorbate, and were imaged by transmission electron microscopy. All metallo-peptides were characterized predominantly as singly charged mononuclear complexes by mass spectrometry. The data indicate that Cu(II)-peptide complexes may act as pro-oxidants or antioxidants and exhibit unique aggregation propensities under specific environmental conditions, with implications in the biological setting.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer’s disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-β (Aβ) have been proposed as one of the major causes of the disease, the mechanism of clearing Aβ is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aβ in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

Doble role of bathocuproine disulfonic acid as multi-walled carbon nanotubes dispersing agent and copper preconcentration ligand: Analytical applications for the development of hydrogen peroxide and glucose electrochemical sensors

We are reporting a new strategy for preparing carbon nanotubes (CNTs)-based hydrogen peroxide and glucose amperometric sensors by taking advantage of the dual role of bathocuproine disulfonic acid (BCS) as dispersing agent of multi-walled carbon nanotubes (MWCNTs) and as ligand for the preconcentration of Cu(II). The platform was obtained by casting glassy carbon electrodes (GCE) with the dispersion of MWCNTs in BCS (MWCNTs-BCS) followed by the preconcentration of Cu(II) by surface complex formation at open circuit potential (GCE/MWCNTs-BCS/Cu). The resulting electrode was used for the sensitive amperometric quantification of hydrogen peroxide at 0.400 V catalyzed by the preconcentrated copper, with a linear range between 5.0 × 10^-7 and 7.4 × 10^-6 M, a sensitivity of 24.3 mA.M^-1, and a detection limit of 0.2 μM. The adsorption of GOx at GCE/MWCNTs-BCS/Cu followed by the immobilization of Nafion (Naf), allowed the construction of a sensitive and selective amperometric glucose biosensor with a linear range between 5.0 × 10^-6 M and 4.9 × 10^-4 M, a sensitivity of (477 ± 3) μA.M^-1 and a detection limit of 2 μM. The proposed (bio)sensors were successfully used for the quantification of hydrogen peroxide in enriched milk samples and glucose in milk and commercial beverages without any pretreatment.

The Glutathione/Metallothionein System Challenges the Design of Efficient O2 -Activating Copper Complexes

Copper complexes are of medicinal and biological interest, including as anticancer drugs designed to cleave intracellular biomolecules by O2 activation. To exhibit such activity, the copper complex must be redox active and resistant to dissociation. Metallothioneins (MTs) and glutathione (GSH) are abundant in the cytosol and nucleus. Because they are thiol-rich reducing molecules with high CuI affinity, they are potential competitors for a copper ion bound in a copper drug. Herein, we report the investigation of a panel of CuI /CuII complexes often used as drugs, with diverse coordination chemistries and redox potentials. We evaluated their catalytic activity in ascorbate oxidation based on redox cycling between CuI and CuII , as well as their resistance to dissociation or inactivation under cytosolically relevant concentrations of GSH and MT. O2 -activating CuI /CuII complexes for cytosolic/nuclear targets are generally not stable against the GSH/MT system, which creates a challenge for their future design.

Iron-Doping of Copper Oxide Nanoparticles Lowers Their Toxic Potential on C6 Glioma Cells

Copper oxide nanoparticles (CuO-NPs) are well known for their cytotoxicity which in part has been attributed to the release of copper ions from CuO-NPs. As iron-doping has been reported to reduce the susceptibility of CuO-NPs to dissolution, we have compared pure CuO-NPs and CuO-NPs that had been doped with 10% iron (CuO-Fe-NPs) for copper release and for their toxic potential on C6 glioma cells. Physicochemical characterization revealed that dimercaptosuccinate (DMSA)-coated CuO-NPs and CuO-Fe-NPs did not differ in their size or zeta potential. However, the redox activity and liberation of copper ions from CuO-Fe-NPs was substantially slower compared to that from CuO-NPs, as demonstrated by cyclic voltammetry and by the photometric quantification of the copper ion-bathocuproine complex, respectively. Exposure of C6 cells to these NPs caused an almost identical cellular copper accumulation and each of the two types of NPs induced ROS production and cell toxicity. However, the time- and concentration-dependent loss in cell viability was more severe for cells that had been treated with CuO-NPs compared to cells exposed to CuO-Fe-NPs. Copper accumulation and toxicity after exposure to either CuO-NPs or CuO-Fe-NPs was prevented in the presence of copper chelators, while neutralization of the lysosomal pH by bafilomycin A1 prevented toxicity without affecting cellular copper accumulation or ROS production. These data demonstrate that iron-doping does not affect cellular accumulation of CuO-NPs and suggests that the intracellular liberation of copper ions from CuO-NPs is slowed by the iron doping, which in turn lowers the cell toxic potential of iron-doped CuO-NPs.

Disulfiram causes selective hypoxic cancer cell toxicity and radio-chemo-sensitization via redox cycling of copper

Therapies for lung cancer patients initially elicit desirable responses, but the presence of hypoxia and drug resistant cells within tumors ultimately lead to treatment failure. Disulfiram (DSF) is an FDA approved, copper chelating agent that can target oxidative metabolic frailties in cancer vs. normal cells and be repurposed as an adjuvant to cancer therapy. Clonogenic survival assays showed that DSF (50-150 nM) combined with physiological levels of Cu (15 μM CuSO₄) was selectively toxic to H292 NSCLC cells vs. normal human bronchial epithelial cells (HBEC). Furthermore, cancer cell toxicity was exacerbated at 1% O₂, relative to 4 or 21% O₂. This selective toxicity of DSF/Cu was associated with differential Cu ionophore capabilities. DSF/Cu treatment caused a >20-fold increase in cellular Cu in NSCLCs, with nearly two-fold higher Cu present in NSCLCs vs. HBECs and in cancer cells at 1% O₂vs. 21% O₂. DSF toxicity was shown to be dependent on the retention of Cu as well as oxidative stress mechanisms, including the production of superoxide, peroxide, lipid peroxidation, and mitochondrial damage. DSF was also shown to selectively (relative to HBECs) enhance radiation and chemotherapy-induced NSCLC killing and reduce radiation and chemotherapy resistance in hypoxia. Finally, DSF decreased xenograft tumor growth in vivo when combined with radiation and carboplatin. These results support the hypothesis that DSF could be a promising adjuvant to enhance cancer therapy based on its apparent ability to selectively target fundamental differences in cancer cell oxidative metabolism.

Multi-walled carbon nanotubes functionalized with bathocuproinedisulfonic acid: analytical applications for the quantification of Cu(II)

This work reports the successful non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with bathocuproinedisulfonic acid (BCS) and the analytical application of the resulting dispersion (MWCNTs-BCS) to develop an electrochemical sensor for Cu(II) quantification. The sensor was obtained by casting glassy carbon electrodes (GCEs) with MWCNTs-BCS. The sensing mechanism was based on the open circuit preconcentration of Cu(II) at the electrode surface by complexation of Cu(II) through the phenanthroline ring nitrogen of the BCS that supports the MWCNTs, the reduction of the preconcentrated Cu(II), and final differential pulse voltammetry-anodic stripping in 0.020 M acetate buffer, pH 5.00. The sensitivity of the sensor was (2.73 ± 0.08) μA μM^-1, with a linear range between 5.0 × 10^-7 M and 6.0 × 10^-6 M, a detection limit of 0.15 μM (9.5 μg L^-1), and reproducibility of 6.2% using the same dispersion and 7.1% using three different MWCNTs-BCS dispersions. The quantification of Cu(II) was highly selective even in the presence of As³⁺, Cr³⁺, Cd²⁺, Ni²⁺, Pb²⁺, Co²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Rh, Ir, and Ru. The proposed sensor was successfully used for quantifying Cu(II) in tap water. Graphical abstract.