Reactions of oxygen free radicals with copper complexes in pyridine: differentiation between superoxide and hydroxyl radicals

Construction of an ultrasensitive non-enzymatic sensor to investigate the dynamic process of superoxide anion release from living cells

In this work, a novel non-enzymatic superoxide anion (O₂•^-) sensor was constructed based on Ag nanoparticles (NPs) / poly (amidoamine) (PAMAM) dendrimers and used to investigate the dynamic process of O₂•^- release from living cells. The AgNPs/PAMAM nanohybrids were characterized by transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The fabricated electrode exhibited excellent catalytic activity toward the reaction of O₂•^- with a super low detection limit (LOD) of 2.530 × 10^-13M (S/N = 3) and wide linear range of 8 orders of magnitude. It could fulfill the requirement of real-time measurement O₂•^- released from living cells. Furthermore, zymosan was chosen as the stimulant to induce O₂•^- generation from cancer cells (rat adrenal medulla pheochromocytoma cell (PC12)). The electrochemical experiment results indicated that the levels of intracellular O₂•^- depended on the amount of Zymosan. A large amount of O₂•^- generated in the living cells by added heavy stimulant could damage cells seriously. More importantly, a vitro simulation experiment confirmed the role of superoxide dismutase (SOD) for the first time because it could maintain the O₂•^- concentration at a normal physiological range. These findings are of great significance for evaluating the metabolic processes of O₂•^- in the biological system, and this work has the tremendous potential application in clinical diagnostics to assess oxidative stress.

A sensor for superoxide in aqueous and organic/aqueous media based on immobilized cytochrome c on binary self-assembled monolayers

A method for the electrochemical detection of superoxide radical was developed, based on cytochrome c (cyt c) immobilized on the binary self-assembled monolayers (SAMs) of thioctic acid (T-COOH) and thioctic amide (T-NH2) on gold electrode. The sensor works by electrochemically detecting cyt c reduced by the superoxide radical generated by a xanthine-XOD system. The electrochemical properties of immobilized cyt c were investigated in aqueous buffer and in a mixture of aqueous and organic solvents. The interaction of superoxide radical with the modified electrode was characterized in phosphate buffer solution (PBS) and in the mixtures of both PBS and dimethyl sulfoxide (DMSO) and PBS and glycerol (Gly). The results showed that the sensors responded immediately to superoxide radical in PBS and gave a steady-state anodic current within 10s during the generation of superoxide radical. In 40% DMSO and in 30% Gly solution, the current response reached a steady-state anodic current within 20s. The sensor could also be used to estimate superoxide dismutase (SOD).

Modulation of polymorphonuclear leukocyte responsiveness by copper (II)2 (niflumate)4

Antiinflammatory activities and modulations of PMNL responses produced by treatment with tetrakis-mu-2-[3-(trifluoromethyl)-phenyl]aminonicotinatodicopper (II) [Cu(II)2(niflumate)4] and niflumic acid were studied in isologous serum-induced rat pleurisy. Doses of 10 or 30 mg/kg (35 or 106 mumol/kg) of niflumic acid or Cu(II)2(niflumate)4 (8 or 23 mumol/kg) caused significant (p < 0.01) reductions in pleural exudate and number of polymorphonuclear leukocytes (PMNLs) in the exudate. While both doses of Cu(II)2(niflumate)4 produced significant dose-related reductions in both parameters, only the higher dose of niflumic acid produced a significant dose-related reduction in both parameters. Boyden chamber measurements of N-formyl-methionyl-leucyl-phenylalanine (f-MLP) chemotaxis by PMNLs incubated with 10 or 30 micrograms/ml niflumic acid (35 or 106 nmol/ml) or Cu(II)2(niflumate)4 (8 or 23 nmol/ml) were significantly (p < 0.01 to p < 0.001) decreased in dose-related fashions. Chemotaxis of PMNLs from pleuritic rats treated orally with 10 or 30 mg/kg niflumic acid or Cu(II)2(niflumate)4 was significantly (p < 0.001) inhibited by the larger dose of niflumic acid and both doses of Cu(II)2(niflumate)4. Opsonized zymosan (OZ)-stimulated chemiluminescence (CL) of PMNLs from pleuritic rats treated orally with these same doses of niflumic acid or Cu(II)2(niflumate)4 was only significantly (p < 0.05 or p < 0.01 respectively) decreased by the larger doses. Superoxide (O2-) production by these cells was significantly decreased by the larger dose of niflumic acid (p < 0.05) while both doses of Cu(II)2(niflumate)4 produced significant (p < 0.05 to p < 0.01) decreases.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactions of copper complexes with oxygen radicals generated by human neutrophils

The intensity of the chemiluminescence of unstimulated human neutrophils in the presence of luminol was used to investigate the effects of low-molecular-weight copper complexes at the cellular level. In different models (superoxide dismutase mimetic activity, inhibition of haematoporphyrin derivative/light-induced lysis of cells), the biological activity of the complexes exceeded the activity of the ligands alone.

EPR spectra of DMPO spin adducts of superoxide and hydroxyl radicals in pyridine

Electron spin resonance spectroscopy and the spin trapping technique were used to study the formation of the superoxide radical in pyridine. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was employed as a trapping agent. Superoxide radical was generated using chemical (potassium superoxide) and photochemical methods with anthralin, benzanthrone, rose bengal, 1,8-dihydroxyanthraquinone and zinc tetraphenylporphyrine as photoactive pigments. Hyperfine coupling (hf) constants for DMPO/O2.- were determined to be aN = 12.36 G, a beta H = 9.85, G, a gamma H = 1.34 G. The aN and a beta H hf constants are in good agreement with values calculated from a previously determined relationship between hf constants and solvent acceptor number (Reszka et al., (1992) Free Radical Res. Commun., in press). When concentrated hydrogen peroxide was added to DMPO in pyridine a similar EPR spectrum was observed. It is suggested that in this case the DMPO/.O2H adduct is formed by nucleophilic addition of H2O2 to DMPO to give a hydroxylamine, followed by oxidation to the respective nitroxide. The EPR spectrum observed when tetrapropylammonium hydroxide and H2O2 were added to DMPO in pyridine had hf couplings aN = 13.53 G, a beta H = 11.38 G, a gamma H = 0.79 G and it was assigned to a DMPO/.OH adduct. This assignment was based on similarity of this spectrum to the one produced by UV photolysis of hydrogen peroxide and DMPO in aqueous solution and subsequent transfer to pyridine.