Catalytic activity of a copper(II)-oxidized glutathione complex on aqueous superoxide ion dismutation

Redox-implications associated with the formation of complexes between copper ions and reduced or oxidized glutathione

Binding of copper by reduced glutathione (GSH) is generally seen as a mechanism to lower, if not abolish, the otherwise high electrophilicity and redox activity of its free ions. In recent years, however, this concept has been contradicted by new evidence revealing that, rather than stabilizing free copper ions, its binding to GSH leads to the formation of a Cu(I)-[GSH]2 complex capable of reducing molecular oxygen into superoxide. It is now understood that, under conditions leading to the removal of such radicals, the Cu(I)-[GSH]2 complex is readily oxidized into Cu(II)-GSSG. Interestingly, in the presence of a GSH excess, the latter complex is able to regenerate the superoxide-generating capacity of the complex it originated from, opening the possibility that a GSH-dependent interplay exists between the reduced and the oxidized glutathione forms of these copper-complexes. Furthermore, recent evidence obtained from experiments conducted in non-cellular systems and intact mitochondria indicates that the Cu(II)-GSSG complex is also able to function in a catalytic manner as an efficient superoxide dismutating- and catalase-like molecule. Here we review and discuss the most relevant chemical and biological evidence on the formation of the Cu(I)-[GSH]2 and Cu(II)-GSSG complexes and on the potential redox implications associated with their intracellular occurrence.

[Carbohydrate restriction in the larval diet causes oxidative stress in adult insects of Drosophila melanogaster]

The influence of 20 and 1% glucose and fructose, which were components of larval diet, on the level of oxidized proteins and lipids, low molecular mass antioxidant content as well as activities of antioxidant and associated enzymes in adult fruit fly Drosophila melanogaster were investigated. The restriction of carbohydrates in larval diet leads to oxidative stress in adult insects. It is supported by 40-50% increased content of protein carbonyl groups and by 60-70% decreased level of protein thiol groups as well as by a 4-fold increase of lipid peroxide content in 2-day-old flies of both sexes, developed on the diet with 1% carbohydrates. Oxidative stress, induced by carbohydrate restriction of the larval diet, caused the activation of antioxidant defence, differently exhibited in male and female fruit flies. Caloric restriction increased activity of superoxide dismutase and thioredoxin reductase associating only in males with 2-fold higher activity of NADPH-producing enzymes--glucose-6-phosphate dehydrogenase and isocitrate dehydrogenase. Carbohydrate restriction in the larval diet caused the increase of uric acid content, but the decrease in catalase activity in males. In females the values of these parameters were changed in opposite direction compared with males. The obtained results let us conclude the different involvement of low molecular mass antioxidants, glutathione and uric acid, and antioxidant enzyme catalase in the protection of male and female fruit fly macromolecules against oxidative damages, caused by calorie restriction of larval diet.

Whole genome gene expression analysis reveals casiopeína-induced apoptosis pathways

Copper-based chemotherapeutic compounds Casiopeínas, have been presented as able to promote selective programmed cell death in cancer cells, thus being proper candidates for targeted cancer therapy. DNA fragmentation and apoptosis-in a process mediated by reactive oxygen species-for a number of tumor cells, have been argued to be the main mechanisms. However, a detailed functional mechanism (a model) is still to be defined and interrogated for a wide variety of cellular conditions before establishing settings and parameters needed for their wide clinical application. In order to shorten the gap in this respect, we present a model proposal centered in the role played by intrinsic (or mitochondrial) apoptosis triggered by oxidative stress caused by the chemotherapeutic agent. This model has been inferred based on genome wide expression profiling in cervix cancer (HeLa) cells, as well as statistical and computational tests, validated via functional experiments (both in the same HeLa cells and also in a Neuroblastoma model, the CHP-212 cell line) and assessed by means of data mining studies.

Mechanism of copper-catalyzed oxidation of glutathione

The mechanism of copper-catalyzed glutathione oxidation was investigated using oxygen consumption, thiol depletion, spectroscopy and hydroxyl radical detection. The mechanism of oxidation has kinetics which appear biphasic. During the first reaction phase a stoichiometric amount of oxygen is consumed (1 mole oxygen per 4 moles thiol) with minimal .OH production. In the second reaction phase, additional (excess) oxygen is consumed at an increased rate and with significant hydrogen peroxide and .OH production. The kinetic and spectroscopic data suggest that copper forms a catalytic complex with glutathione (1 mole copper per 2 moles glutathione). Our proposed reaction mechanism assumes two parallel processes (superoxide-dependent and peroxide-dependent) for the first reaction phase and superoxide-independent for the second phase. Our current results indicate that glutathione, usually considered as an antioxidant, can act as prooxidant at physiological conditions and therefore can participate in cellular radical damage.

The inhibitory effects of 21 mimics of superoxide dismutase on luminol-mediated chemiluminescence emitted from PMA-stimulated polymorphonuclear leukocyte

Four groups comprising 21 superoxide dismutase (SOD) mimics synthesized by us were comparatively studied for their inhibitory effects on luminol-mediated chemiluminescence emitted from phorbol myristate acetate (PMA)-stimulated polymorphonuclear leukocyte (PMNL). Among these groups, 20-membered macrocyclic bicopper(II) complexes and 13-membered macrocyclic dioxotetramine copper(II) complexes exhibited relatively higher activities of scavenging reactive oxygen species (ROS) produced by PMA-stimulated PMNL as compared with polyamine Cu(II)-Zn(II) complexes and copper(II) complexes of bis-shiff-base. Moreover, distinctly different effects of SOD mimics in the biological system have been found even in the same group. It is suggested that the biological effects of some SOD mimics are related to their structures.

The superoxide dismutase-like activity of some copper(II) complexes derived from tridentate Schiff bases

Oxygen free radicals are the final or intermediate products of many metabolic reactions. Of greatest significance to the organism are superoxide anion radical (O2-.), hydrogen peroxide (H2O2), hydroxyl radical (.OH), singlet oxygen (1O2) etc. A proper ratio between both production and breakdown of oxy-radicals is essential for the maintenance of a dynamic equilibrium of vital processes. The superoxide dismutases protect cells against toxic influence of the superoxide. In addition, some square-pyramidally pentacoordinated copper(II) complexes, derived from tridentate Schiff bases of the N-salicylideneaminoalcanoate type, show remarkable SOD-like activity. A selected set of complexes of this type have been tested: potassium [aqua-(N-salicylideneglutamato) cuprate] (L- and D,L-form), potassium [(isothiocyanato)-(N-salicylideneglycinato) cuprate], potassium [(isothiocyanato)-(N-salicylidene-D,L-alaninato) cuprate], potassium [(isothiocyanato)-(N-salicylidene-beta-alaninato) cuprate] and potassium [(isocyanato)-(N-salicylideneglycinato) cuprate]. Our results suggest that the copper complexes are not only antioxidants, but may also possess anti-inflammatory, cytostatic and radioprotective properties.

Antioxidant activity of hemocyanin; a pulse radiolysis study

In order to determine the reactivity on hemocyanin from Androctonus australis, the reaction of superoxide anion has been investigated using pulse radiolysis. The kinetics of O2- decays have been studied in aqueous buffered media at various basic pH (8, 8.5 and 9), first in the absence and then in the presence of hemocyanin (in oxygenated solutions containing formate anion 0.16 mol.l-1). We have shown that, in the presence of hemocyanin, O2- decay is a first-order process whose apparent rate constant is proportional to protein concentration (10(-7) to 10(-6) mol.l-1) and pH independent between 8 to 9. A second-order rate constant of 3.5 +/- 0.1.10(7) mol-1.l.s-1, has been deduced for the catalytic rate constant of hemocyanin with O2-. Meanwhile, this activity is smaller than that described for free copper, eukaryotic Cu-Zn-SOD or some copper chelates. We have verified that apohemocyanin--the copper deprived protein--does not exhibit such an activity vs. SOD (superoxide dismutase).

Role of the superoxide anion in the oxidative activation of the new antitumor drug BD40: a radiolysis study

BD40, a new antitumor drug derived from 9-azaellipticine, is thought to have an oxygen-dependent metabolism in vivo. We have investigated the one-electron oxidation of this drug by gamma radiolysis using OH. free radicals as oxidants and the reaction of O2-. with the BD40 oxidized transient(s). The absorption spectrum of the one-electron oxidized free radical was determined by pulse radiolysis using OH. or N.3 as reactant. In the absence of O2 and O2-., the initial yield of disappearance of the drug is equal to 2.5 x 10(-7) mol J-1 independently of the initial concentration of the drug and of the dose rate. When BD40 is oxidized by OH. radicals in the presence of O2 and O2-., the yield is the same. This yield is halved if superoxide dismutase is present during irradiation. Superoxide anions do not react directly with the drug. Thus it is suggested that these radicals oxidize the BD40 free radical produced by oxidation with OH. Biological implications are discussed.

Protection of Chinese hamster ovary cells from paraquat-mediated cytotoxicity by a low molecular weight mimic of superoxide dismutase (DF-Mn)

Paraquat exerts a cytotoxic effect on Chinese hamster ovary cells in culture via the superoxide radical (O2-). We have described a superoxide dismutase (SOD) mimic based on manganese (DF-Mn) which consists of a one-to-one complex between desferrioxamine B (Desferal) and MnO2. It is a small molecular weight molecule, easy to prepare and possesses considerable stability. It is now shown to protect mammalian cells from paraquat toxicity. Thus, 20 microM DF-Mn affords up to complete protection against the cytotoxicity of 200 microM paraquat in Chinese hamster ovary cells. Desferrioxamine B or MnO2 alone gave no protection. MnCl2 or catalase provided little or no protection against the paraquat, respectively. Equivalent amounts of human Cu-Zn SOD in terms of activity, also provided no protection. Copper diisopropylsalicylate (CuDIPS) provided limited, yet significant, protection, but this is explained in terms other than SOD activity. Finally, at higher concentrations, purified human SOD, exerts a limited toxicity as well as a protective ability against paraquat (similar to DF-Mn) both of which are eliminated upon heat denaturation of the enzyme. It appears that the SOD mimic, DF-Mn, can enter mammalian cells and can protect against the cytotoxic effects of O2-.

Effects of paraquat on the green alga Dunaliella salina: protection by the mimic of superoxide dismutase, Desferal-Mn(IV)

Paraquat caused a time-, dose-, and light-dependent bleaching of the halophilic green alga Dunaliella salina. Sublethal levels of paraquat elicited increases in cell content of both superoxide dismutase and catalase, with changes in the pattern of electromorphs of these enzymes. Desferal-Mn(IV), which catalyzes the dismutation of O2- in vitro, protected against the toxic effect of paraquat. Desferal (desferoxamine mesylate) alone was toxic to D. salina, and the salts of Mn(II), Mn(III), and Mn(IV), in the absence of Desferal, did not protect. Desferal-Mn(IV) is green, but its absorbance was 15% or less than the peak absorbances due to the chlorophyll in D. salina under the conditions of exposure; hence, masking of incident light could not have been the basis of the protective effect of the complex. Incubation of the cells with Desferal-Mn(IV), for up to 8 h prior to the addition of paraquat, did not increase its protective action, and brief washing, following 30 min incubation with the complex, eliminated its protective effect. Neither catalase nor superoxide dismutase, added to the medium, provided protection against paraquat. These results support the view that Desferal-Mn(IV) gains entry into D. salina and protects against the lethal effect of paraquat by there catalyzing the dismutation of O2- into H2O2 + O2.