Na, K-ATPase as a Biological Target for Gold(III) Complexes: A Theoretical and Experimental Approach.

BACKGROUND: Gold-based complexes represent a new class of potential metallodrugs. Although their action mechanism is not entirely understood, it was shown that gold complexes inhibit some enzymes' activities. Among them, Na,K-ATPase is emerging as an essential target for various anticancer drugs. The functionalization of nanoparticles by gold(III) complexes could facilitate their delivery into the cells and enable the following of their distribution in the target tissues. OBJECTIVE: The paper presents an overview of Na,K-ATPase interaction with representative and structurally related cytotoxic gold(III) complexes. The results obtained by the employment of theoretical methods (DFT and docking studies) combined with the experimental approach involving a variety of nanotechnology-base techniques (UV/Vis, Raman and fluorescence spectroscopy, CD, AFM, DLS) are discussed. Detailed information was obtained on the enzyme's conformational and structural changes upon binding the gold(III) complexes. The experimentally determined reaction parameters (constants of dissociation and the reaction stoichiometry) were predicted theoretically. CONCLUSION: The presented results offer further support to the view that Na,K-ATPase may be a relevant biomolecular target for cytotoxic gold(III) compounds of medicinal interest.

Drug delivery systems based on nanoparticles and related nanostructures.

A new approach to drug design based on nanoparticles and related nanostructures for effective drug delivery, is of great importance in future medical treatment, especially for cancer therapy. Nanomaterials hold tremendous potential for increasing the efficiency of drug delivery, with a high degree of biocompatibility. Additionally, for biomedical applications, they must be biodegradable, have prolonged circulation half-life, not tend to aggregate or cause an inflammatory response in the body and to be cost-effective. The efficacy of such structures is highly dependent on their chemical properties as well as on shape, charge, size, surface modifications and loading method. Here we focused on the potential of using different kinds of nanoparticles and similar nanostructures loaded with various drugs in order to achieve specific targeting and controlled drug release. Thereby, computational modeling on NPs-based drug delivery could help in providing a better understanding of all parts of the delivery system. This review emphasizes recent advances in the usage of various types of nanoparticles and similar nanostructures for drug delivery, aiming to provide a critical review of less toxic and more effective treatment.

Conjugates of Gold Nanoparticles and Antitumor Gold(III) Complexes as a Tool for Their AFM and SERS Detection in Biological Tissue.

Citrate-capped gold nanoparticles (AuNPs) were functionalized with three distinct antitumor gold(III) complexes, e.g., [Au(N,N)(OH)2][PF6], where (N,N)=2,2'-bipyridine; [Au(C,N)(AcO)2], where (C,N)=deprotonated 6-(1,1-dimethylbenzyl)-pyridine; [Au(C,N,N)(OH)][PF6], where (C,N,N)=deprotonated 6-(1,1-dimethylbenzyl)-2,2'-bipyridine, to assess the chance of tracking their subcellular distribution by atomic force microscopy (AFM), and surface enhanced Raman spectroscopy (SERS) techniques. An extensive physicochemical characterization of the formed conjugates was, thus, carried out by applying a variety of methods (density functional theory-DFT, UV/Vis spectrophotometry, AFM, Raman spectroscopy, and SERS). The resulting gold(III) complexes/AuNPs conjugates turned out to be pretty stable. Interestingly, they exhibited a dramatically increased resonance intensity in the Raman spectra induced by AuNPs. For testing the use of the functionalized AuNPs for biosensing, their distribution in the nuclear, cytosolic, and membrane cell fractions obtained from human lymphocytes was investigated by AFM and SERS. The conjugates were detected in the membrane and nuclear cell fractions but not in the cytosol. The AFM method confirmed that conjugates induced changes in the morphology and nanostructure of the membrane and nuclear fractions. The obtained results point out that the conjugates formed between AuNPs and gold(III) complexes may be used as a tool for tracking metallodrug distribution in the different cell fractions.

Interaction of Au(iii) and Pt(ii) complexes with Na/K-ATPase: experimental and theoretical study of reaction stoichiometry and binding sites.

The present paper deals with investigation of the interaction between selected simple structure Au(iii) ([AuCl4]-, [AuCl2(dmso)2]+, [AuCl2(bipy)]+) and Pt(ii) ([PtCl2(dmso)2]) complexes with Na/K-ATPase as the target enzyme, using an experimental and theoretical approach. Reaction stoichiometries and binding constants for these enzyme/complex systems were determined, while kinetic measurements were used in order to reveal the type of inhibition. Based on the results obtained by quantum mechanical calculations (electrostatic surface potential (ESP), volume and surface of the complexes) the nature of the investigated complexes was characterized. By using the solvent accessible surface area (SASA) applied on specific inhibitory sites (ion channel and intracellular domains) the nature of these sites was described. Docking studies were used to determine the theoretical probability of the non-covalent metal binding site positions. Inhibition studies implied that all the investigated complexes decreased the activity of the enzyme while the kinetic analysis indicated an uncompetitive mode of inhibition for the selected complexes. Docking results suggested that the main inhibitory site of all these complexes is located in the ion translocation pathway on the extracellular side in the E2P enzyme conformation, similar to the case of cardiac glycosides, specific Na/K-ATPase inhibitors. Also, based on our knowledge, the hydrolyzed forms of [AuCl4]- and [PtCl2(dmso)2] complexes were investigated for the first time by theoretical calculations in this paper. Thereby, a new inhibitory site situated between the M2 and M4 helices was revealed. Binding in this site induces conformational changes in the enzyme domains and perturbs the E1-E2P conformational equilibrium, causing enzyme inhibition.

Sulphur-containing Amino Acids: Protective Role Against Free Radicals and Heavy Metals.

BACKGROUND: Sulphur is an abundant element in biological systems, which plays an important role in processes essential for life as a constituent of proteins, vitamins and other crucial biomolecules. The major source of sulphur for humans is plants being able to use inorganic sulphur in the purpose of sulphur-containing amino acids synthesis. Sulphur-containing amino acids include methionine, cysteine, homocysteine, and taurine. Methionine and cysteine are classified as proteinogenic, canonic amino acids incorporated in protein structure. Sulphur amino acids are involved in the synthesis of intracellular antioxidants such as glutathione and N-acetyl cysteine. Moreover, naturally occurring sulphur-containing ligands are effective and safe detoxifying agents, often used in order to prevent toxic metal ions effects and their accumulation in human body. METHODS: Literature search for peer-reviewed articles was performed using PubMed and Scopus databases, and utilizing appropriate keywords. RESULTS: This review is focused on sulphur-containing amino acids - methionine, cysteine, taurine, and their derivatives - glutathione and N-acetylcysteine, and their defense effects as antioxidant agents against free radicals. Additionally, the protective effects of sulphur-containing ligands against the toxic effects of heavy and transition metal ions, and their reactivation role towards the enzyme inhibition are described. CONCLUSION: Sulphur-containing amino acids represent a powerful part of cell antioxidant system. Thus, they are essential in the maintenance of normal cellular functions and health. In addition to their worthy antioxidant action, sulphur-containing amino acids may offer a chelating site for heavy metals. Accordingly, they may be supplemented during chelating therapy, providing beneficial effects in eliminating toxic metals.

The influence of oxo-bridged binuclear gold(III) complexes on Na/K-ATPase activity: a joint experimental and theoretical approach.

The in vitro effects of oxo-bridged binuclear gold(III) complexes, i.e., [(bipy2Me)2Au2(µ-O)2][PF6]2 (Auoxo6), Au2[(bipydmb-H)2(µ-O)][PF6] (Au2bipyC) and [Au2(phen2Me)2(µ-O)2](PF6)2 (Au2phen) on Na/K-ATPase, purified from the porcine cerebral cortex, were investigated. All three studied gold complexes inhibited the enzyme activity in a concentration-dependent manner achieving IC50 values in the low micromolar range. Kinetic analysis suggested an uncompetitive mode of inhibition for Auoxo6 and Au2bipyC, and a mixed type one for Au2phen. Docking studies indicated that the inhibitory actions of all tested complexes are related to E2-P enzyme conformation binding to ion channel and intracellular part between N and P sub-domain. In addition, Au2phen was able to inhibit the enzyme by interacting with its extracellular part as well. Toxic effects of the gold(III) complexes were evaluated in vitro by following lactate dehydrogenase activity in rat brain synaptosomes and incidence of micronuclei and cytokinesis-block proliferation index in cultivated human lymphocytes. All investigated complexes turned out to induce cytogenetic damage consisting of a significant decrease in cell proliferation and an increase in micronuclei in a dose-dependent manner. On the other hand, lactate dehydrogenase activity, an indicator of membrane integrity/viability, was not affected by Auoxo6 and Au2bipyC, while Au2phen slightly modified its activity.

Na/K-ATPase as a target for anticancer metal based drugs: insights into molecular interactions with selected gold(iii) complexes.

Na/K-ATPase is emerging as an important target for a variety of anticancer metal-based drugs. The interactions of Na/K-ATPase (in its E1 state) with three representative and structurally related cytotoxic gold(iii) complexes, i.e. [Au(bipy)(OH)2][PF6], bipy = 2,2'-bipyridine; [Au(pydmb-H)(CH3COO)2], pydmb-H = deprotonated 6-(1,1-dimethylbenzyl)-pyridine and [Au(bipydmb-H)(OH)][PF6], bipyc-H = deprotonated 6-(1,1-dimethylbenzyl)-2,2'-bipyridine, are investigated here in depth using a variety of spectroscopic methods, in combination with docking studies. Detailed information is gained on the conformational and structural changes experienced by the enzyme upon binding of these gold(iii) complexes. The quenching constants of intrinsic enzyme fluorescence, the fraction of Trp residues accessible to gold(iii) complexes and the reaction stoichiometries were determined in various cases. Specific hypotheses are made concerning the binding mode of these gold(iii) complexes to the enzyme and the likely binding sites. Differences in their binding behaviour toward Na/K-ATPase are explained on the ground of their distinctive structural features. The present results offer further support to the view that Na/K-ATPase may be a relevant biomolecular target for cytotoxic gold(iii) compounds of medicinal interest and may thus be involved in their overall mode of action.

A combined crystallographic analysis and ab initio calculations to interpret the reactivity of functionalized hexavanadates and their inhibitor potency toward Na(+)/K(+)-ATPase.

In vitro influence of five synthesized functionalized hexavanadates (V6) on commercial porcine cerebral cortex Na(+)/K(+)-ATPase activity has been studied. Dose dependent Na(+)/K(+)-ATPase inhibition was obtained for all investigated compounds. Calculated half maximal inhibitory concentration IC50 values, in mol/L, for Na(+)/K(+)-ATPase were 7.6×10(-5), 1.8×10(-5), 2.9×10(-5), 5.5×10(-5) for functionalized hexavanadates (V6) with tetrabutylammonium (TBA) [V6-CH3][TBA]2, [V6-NO2][TBA]2, [V6-OH][TBA]2 and [V6-C3][TBA]2 respectively. [V6-OH][Na]2 inhibited Na(+)/K(+)-ATPase activity up to 30% at maximal investigated concentration 1×10(-3)mol/L. This reactivity has been interpreted using a study of the non-covalent interactions of functionalized hexavanadate hybrids through Cambridge Structural Database (CSD) analysis. Bibliographic searching has led to 18 different structures and 99 contacts. We have observed that C-H⋯O contacts consolidate the structures. We have also performed density functional theory (DFT) calculations and have determined electrostatic potential values at the molecular surface on a series of functionalized V6. These results enlightened their chemical reactivity and their potential biological applications such as the inhibition of the ATPase.

In vitro evaluation of neurotoxicity potential and oxidative stress responses of diazinon and its degradation products in rat brain synaptosomes.

Although primary toxic action of organophosphorous insecticides is associated with acetylcholinesterase inhibition, later studies suggest that oxidative stress may be responsible for induced organophosphates toxicity. These studies mostly include thio forms, while the effects of their metabolites/degradation products have been less investigated. Therefore, this paper studies the toxic effects of diazinon degradation products, diazoxon and 2-isopropyl-6-methyl-4-pyrimidinol, and compares them with the toxic potential of the parent compound. The toxicity induced by various concentrations of the investigated compounds was in vitro evaluated by the activities of acetylcholinesterase, ATPases, antioxidant defense enzymes and lactate dehydrogenase, and malondialdehyde level in rat brain synaptosomes. Diazinon inhibited acetylcholinesterase and Na(+)/K(+)-ATPase in dose-dependent manner, while the inhibition of ecto-ATPase activity was less than 15% at all investigated concentrations. It did not demonstrate noteworthy prooxidative properties causing increase (up to 10%) in antioxidant enzymes activity and malondialdehyde level, as a marker of lipid peroxidation. Diazinon oxidation product, diazoxon was found as the most toxic investigated compound. Beside the expected strong inhibitory effect on acetylcholinesterase, it induced dose-dependent and almost complete inhibition of Na(+)/K(+)-ATPase and ecto-ATPase at the highest investigated concentration (0.1mM). Increasing diazoxon concentrations activated catalase (up to 30%), superoxide dismutase (up to 50%), glutathione peroxidase (up to 30%), and significantly increased malondialdehyde level (up to 50%). The investigated hydrolysis product of diazinon, 2-isopropyl-6-methyl-4-pyrimidinol did not remarkably alter the activities of acetylcholinesterase, Na(+)/K(+)-ATPase, catalase, glutathione peroxidase and lipid peroxidation level (up to about 10%). Although this diazinon metabolite has been known as non toxic, it induced superoxide dismutase stimulation up to 30%. Finally, even high concentrations of both diazinon and its metabolites did noticeably affect lactate dehydrogenase activity as a marker of synaptosomal integrity. The changes in investigated biochemical parameters in rat brain synaptosomes could serve as indicators of toxicity due to the exposure to thio organophosphates and/or their break-down products.

Inhibition of rat synaptic membrane Na⁺/K⁺-ATPase and ecto-nucleoside triphosphate diphosphohydrolases by 12-tungstosilicic and 12-tungstophosphoric acid.

The in vitro influence of Keggin structure polyoxotungstates, 12-tungstosilicic acid, H(4)SiW(12)O(40) (WSiA) and 12-tungstophosphoric acid, H(3)PW(12)O(40) (WPA), and monomer Na(2)WO(4) × 2H(2)O on rat synaptic plasma membrane (SPM) Na(+)/K(+)-ATPase and E-NTPDase activity was studied, whereas the commercial porcine cerebral cortex Na(+)/K(+)-ATPase served as a reference. Dose-dependent Na(+)/K(+)-ATPase inhibition was obtained for all investigated compounds. Calculated IC(50) (10 min) values, in mol/l, for SPM/commercial Na(+)/K(+)-ATPase, were: 3.4 × 10(-6)/4.3 × 10(-6), 2.9 × 10(-6)/3.1 × 10(-6) and 1.3 × 10(-3)/1.5 × 10(-3) for WSiA, WPA and Na(2)WO(4) × 2H(2)O, respectively. In the case of E-NTPDase, increasing concentrations of WSiA and WPA induced its activity reduction, while Na(2)WO(4) × 2H(2)O did not noticeably affect the enzyme activity at all investigated concentrations (up to 1 × 10(-3)mol/l). IC(50) (10 min) values, obtained from the inhibition curves, were (in mol/l): 4.1 × 10(-6) for WSiA and 1.6 × 10(-6) for WPA. Monolacunary Keggin anion was found as the main active molecular species present under physiological conditions (in the enzyme assays, pH 7.4), for the both polyoxotungstates solutions (1 mmol/l), using Fourier transform infrared (FT-IR) and micro-Raman spectroscopy. Additionally, commercial porcine cerebral cortex Na(+)/K(+)-ATPase was exposed to the mixture of Na(2)WO(4) × 2H(2)O and WSiA at different concentrations. Additive inhibition effect was achieved for lower concentrations of Na(2)WO(4) × 2H(2)O/WSiA (≤ 1 × 10(-3)/4 × 10(-6) mol/l), while antagonistic effect was obtained for all higher concentrations of the inhibitors.

Interaction of some Pd(II) complexes with Na+ / K+-ATPase: inhibition, kinetics, prevention and recovery.

The aim of this work was to investigate the influence of [PdCl4]2-, [PdCl(dien)]+ and [PdCl(Me4dien)]+ complexes on Na+ / K+-ATPase activity. The dose-dependent inhibition curves were obtained in all cases. IC50 values determined by Hill analysis were 2.25 x 10(-5) M, 1.21 x 10(-4) M and 2.36 x 10(-4) M, respectively. Na+ / K+-ATPase exhibited typical Michelis-Menten kinetics in the presence of Pd(II) complexes. Kinetic parameters (Vmax, Km) derived using Eadie-Hofstee transformation indicated a noncompetitive type of Na+ / K+-ATPase inhibition. The inhibitor constants (Ki) were determined from Dixon plots. The order of complex affinity for binding with Na+ / K+-ATPase, deducted from Ki values, was [PdCl4]2- > [PdCl(dien)]+ > [PdCl(Me4dien)]+. The results indicated that the potency of Pd(II) complexes to inhibit Na+/ K +-ATPase activity depended strongly on ligands of the related compound. Furthermore, the ability of SH-donor ligands, L-cysteine and glutathione, to prevent and recover the Pd(II) complexes-induced inhibition of Na+ / K+-ATPase was examined. The addition of 1 mM L-cysteine or glutathione to the reaction mixture before exposure to Pd(II) complexes prevented the inhibition by increasing the IC50 values by one order of magnitude. Moreover, the inhibited enzymatic activity was recovered by addition of SH-donor ligands in a concentration-dependent manner.