Claudio Olea-Azar

Synthesis and antitrypanosomal evaluation of E-isomers of 5-nitro-2-furaldehyde and 5-nitrothiophene-2-carboxaldehyde semicarbazone derivatives. Structure-activity relationships.

Several novel semicarbazone derivatives were prepared from 5-nitro-2-furaldehyde or 5-nitrothiophene-2-carboxaldehyde and semicarbazides bearing a spermidine-mimetic moiety. All derivatives presented the E-configuration, as determined by NMR-NOE experiments. These compounds were tested in vitro as potential antitrypanosomal agents, and some of them, together with the parent compounds, 5-nitro-2-furaldehyde and 5-nitrothiophene-2-carboxaldehyde semicarbazone derivatives, were also evaluated in vivo using infected mice. Structure-activity relationship studies were carried out using voltammetric response and lipophilic-hydrophilic balance as parameters. Two of the compounds (1 and 3) displayed the highest in vivo activity. A correlation was found between lipophilic-hydrophilic properties and trypanocidal activity, high R(M) values being associated with low in vivo effects.

Generation of superoxide radicals by copper–glutathione complexes: Redox-consequences associated with their interaction with reduced glutathione

The interaction between Cu(2+) ions and GSH molecules leads to the swift formation of the physiologically occurring Cu(I)-[GSH](2) complex. Recently, we reported that this complex is able to reduce molecular oxygen into superoxide in a reversible reaction. In the present study, by means of fluorescence, luminescence, EPR and NMR techniques, we investigated the superoxide-generating capacity of the Cu(I)-[GSH](2) complex, demonstrated the occurrence and characterized the chemical nature of the oxidized complex which is formed upon removing of superoxide radicals from the former reaction, and addressed some of the redox consequences associated with the interaction between the Cu(I)-[GSH](2) complex, its oxidized complex form, and an in-excess of GSH molecules. The interaction between Cu(I)-[GSH](2) and added GSH molecules led to an substantial exacerbation of the ability of the former to generate superoxide anions. Removal of superoxide from a solution containing the Cu(I)-[GSH](2) complex, by addition of Tempol, led to the formation and accumulation of Cu(II)-GSSG. Interaction between the latter complex and GSH molecules permitted the re-generation of the Cu(I)-[GSH](2) complex and led to a concomitant recovery of its superoxide-generating capacity. Some of the potential redox and biological implications arising from these interactions are discussed.

Platinum-based complexes of bioactive 3-(5-nitrofuryl)acroleine thiosemicarbazones showing anti-Trypanosoma cruzi activity.

Eight new platinum(II) complexes with 3-(5-nitrofuryl)acroleine thiosemicarbazones showing anti-trypanosomal activity were synthesized, characterized and in vitro evaluated. Most of the complexes showed IC(50) values in the micromolar range against two different strains of Trypanosoma cruzi, causative agent of Chagas disease (American Trypanosomiasis). In addition, most of the newly developed complexes, together with the analogous platinum 5-nitrofuraldehyde containing thiosemicarbazones previously reported, resulted more active than the reference trypanocidal drug nifurtimox on the infective trypomastigote form of the parasite. Their capacity to produce free radicals that could lead to parasite death was evaluated by ESR experiments in the parasite and by respiration measurements. Compounds were tested for their DNA interaction ability. Results showed that some of the compounds could act as dual inhibitors in the parasite, through production of toxic free radicals and interaction with DNA. All the results were compared with those previously reported for the free ligands, the analogous palladium(II) compounds and the previously reported series of platinum(II) compounds.

Complexation of morin with three kinds of cyclodextrin: A thermodynamic and reactivity study

Properties of inclusion complexes between morin (M) and beta-cyclodextrin (betaCD), 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) and Heptakis (2,6-O-di methyl) beta-cyclodextrin (DMbetaCD) such as aqueous solubility and the association constants of this complex have been determined. The water solubility of morin was increased by inclusion with cyclodextrins. The phase-solubility diagrams drawn from UV spectral measurements are of the A(L)-type. Also ORAC(FL) studies were done. An increase in the antioxidant reactivity is observed when morin form inclusion complex with the three cyclodextrin studied. Finally, thermodynamics studies of cyclodextrin complexes indicated that for DMbetaCD the inclusion is primarily enthalpy-driven process meanwhile betaCD and HPbetaCD are entropy-driven processes. This is corroborated by the different inclusion geometries obtained by 2D-NMR.

Cu(I)-glutathione complex: a potential source of superoxide radicals generation.

Cu(2+) ions and GSH molecules interact swiftly to form the complex Cu(I)-glutathione. We investigated the potential capacity of such complex to reduce molecular oxygen. The addition of SOD to a solution containing Cu(I)-glutathione led to a sustained decline of the basal oxygen level. Such effect was partially reverted by the addition of catalase. The complex was able to induce the reduction of cytochrome c and the oxidation of dyhydroethidium into 2-hydroxyethidium. Both effects were totally blocked by SOD. The ability of the complex to generate superoxide radicals was confirmed by EPR spin-trapping. Cu(I)-glutathione induces no oxidation of fluorescein, a hydroxyl radical-sensitive probe. We conclude that in solutions containing the complex, oxygen is continually reduced into superoxide, and that-in absence of interceptors-the latter radicals are quantitatively re-oxidized into molecular oxygen. We suggest that, by functioning as a continuous source of superoxide, the complex could potentially affect a broad range of susceptible biological targets.

Synthesis and Electrochemical and Biological Studies of Novel Coumarin–Chalcone Hybrid Compounds

A series of novel hydroxy-coumarin-chalcone hybrid compounds 2a-i has been synthesized by employing a simple and efficient methodology. An electrochemical characterization using cyclic voltammetry and ESR spectroscopy were carried out to characterize the oxidation mechanism for the target compounds. The antioxidant capacity and reactivity were determined by ORAC and ESR assays, respectively. Biological assays were assessed to evaluate the cytotoxicity and cytoprotection capacity against ROS/RNS on BAEC. The results revealed that all tested compounds present ORAC values that are much higher than other well-known antioxidant compounds such as quercetin and catechin. Compound 2e showed the highest ORAC value (14.1) and also presented a low oxidation potential, good scavenging capacity against hydroxyl radicals, low cytotoxicity, and high cytoprotective activity.

New organoruthenium complexes with bioactive thiosemicarbazones as co-ligands: potential anti-trypanosomal agents

In the search for new therapeutic tools against neglected diseases produced by trypanosomatid parasites, and particularly against African Trypanosomiasis, whose etiological agent is Trypanosoma brucei, organoruthenium compounds with bioactive nitrofuran containing thiosemicarbazones (L) as co-ligands were obtained. Four ruthenium(II) complexes with the formula [Ru(2)(p-cymene)(2)(L)(2)]X(2), where X = Cl or PF(6), were synthesized and the crystal structures of two of them were solved by X-ray diffraction methods. Two of the complexes show significant in vitro growth inhibition activity against Trypanosoma brucei brucei and are highly selective towards trypanosomal cells with respect to mammalian cells (J774 murine macrophages). These promising results make the title organoruthenium compounds good lead candidates for further developments towards potential antitrypanosomal organometallic drugs.

Ceramide-induced formation of ROS and ATP depletion trigger necrosis in lymphoid cells

In lymphocytes, Fas activation leads to both apoptosis and necrosis, whereby the latter form of cell death is linked to delayed production of endogenous ceramide and is mimicked by exogenous administration of long- and short-chain ceramides. Here molecular events associated with noncanonical necrotic cell death downstream of ceramide were investigated in A20 B lymphoma and Jurkat T cells. Cell-permeable, C6-ceramide (C6), but not dihydro-C6-ceramide (DH-C6), induced necrosis in a time- and dose-dependent fashion. Rapid formation of reactive oxygen species (ROS) within 30 min of C6 addition detected by a dihydrorhodamine fluorescence assay, as well as by electron spin resonance, was accompanied by loss of mitochondrial membrane potential. The presence of N-acetylcysteine or ROS scavengers like Tiron, but not Trolox, attenuated ceramide-induced necrosis. Alternatively, adenovirus-mediated expression of catalase in A20 cells also attenuated cell necrosis but not apoptosis. Necrotic cell death observed following C6 exposure was associated with a pronounced decrease in ATP levels and Tiron significantly delayed ATP depletion in both A20 and Jurkat cells. Thus, apoptotic and necrotic death induced by ceramide in lymphocytes occurs via distinct mechanisms. Furthermore, ceramide-induced necrotic cell death is linked here to loss of mitochondrial membrane potential, production of ROS, and intracellular ATP depletion.

1,2,5-Oxadiazole N-oxide derivatives as potential anti-cancer agents: synthesis and biological evaluation. Part IV

Several new 1,2,5-oxadiazole N-oxide derivatives and some deoxygenated analogues were synthesized to be tested as potential selective hypoxic cell cytotoxins. Compounds prepared were designed in order to gain insight into the mechanism of action of this kind of cytotoxin. Compounds were tested in oxia and hypoxia and they proved to be non-selective. 3-Cyano-N(2)-oxide-4-phenyl-1,2,5-oxadiazole showed the best cytotoxic activity in oxia. The cytotoxicity observed for these derivatives could be explained in terms of the electronic characteristics of the 1,2,5-oxadiazole substituents. Electrochemical and ESR studies were performed on the more cytotoxic derivative.

Potent in vitro anti-Trypanosoma cruzi activity of pyridine-2-thiol N-oxide metal complexes having an inhibitory effect on parasite-specific fumarate reductase.

In the search for new therapeutic tools against Chagas disease (American trypanosomiasis) palladium and platinum complexes of the bioactive ligand pyridine-2-thiol N-oxide were exhaustively characterized and evaluated in vitro. Both complexes showed high in vitro growth inhibition activity (IC50 values in the nanomolar range) against Trypanosoma cruzi, the causative agent of the disease. They were 39–115 times more active than the antitrypanosomal drug Nifurtimox. The palladium complex showed an approximately threefold enhancement of the activity compared with the parent compound. In addition, owing to their low unspecific cytotoxicity on mammalian cells, the complexes showed a highly selective antiparasite activity. To get an insight into the mechanism of action of these compounds, DNA, redox metabolism (intraparasite free-radical production) and two parasite-specific enzymes absent in the host, namely, trypanothione reductase and NADH-fumarate reductase, were evaluated as potential parasite targets. Additionally, the effect of metal coordination on the free radical scavenger capacity previously reported for the free ligand was studied. All the data strongly suggest that trypanocidal action of the complexes could mainly rely on the inhibition of the parasite-specific enzyme NADH-fumarate reductase.