Francisco O.N. da Silva

Novel ruthenium complexes as potential drugs for Chagas's disease: enzyme inhibition and in vitro/in vivo trypanocidal activity

Background and purpose:  The discovery of the pharmacological functions of nitric oxide has led to the development of NO donor compounds as therapeutic agents. A new generation of ruthenium NO donors, cis‐[Ru(NO)(bpy)2L]Xn, has been developed, and our aim was to show that these complexes are able to lyse Trypanosoma cruzi in vitro and in vivo.

Comparative Study on the Antioxidant and Anti-Toxoplasma Activities of Vanillin and Its Resorcinarene Derivative

A resorcinarene derivative of vanillin, resvan, was synthesized and characterized by spectroscopic techniques. We measured the cytotoxicity (in vivo and in vitro), antioxidant and anti-Toxoplasma activities of vanillin and the resorcinarene compound. Here we show that vanillin has a dose-dependent behavior with IC50 of 645 µg/mL through an in vitro cytotoxicity assay. However, we could not observe any cytotoxic response at higher concentrations of resvan (IC50 > 2,000 µg/mL). The in vivo acute toxicity assays of vanillin and resvan exhibited a significant safety margin indicated by a lack of systemic and behavioral toxicity up to 300 mg/kg during the first 30 min, 24 h or 14 days after administration. The obtained derivative showed greater antioxidative activity (84.9%) when comparing to vanillin (19.4%) at 1,000 μg/mL. In addition, vanillin presents anti-Toxoplasma activity, while resvan does not show that feature. Our findings suggest that this particular derivative has an efficient antioxidant activity and a negligible cytotoxic effect, making it a potential target for further biological investigations.

The ruthenium NO donor, [Ru(bpy)2(NO)SO3](PF6), inhibits inflammatory pain: involvement of TRPV1 and cGMP/PKG/ATP-sensitive potassium channel signaling pathway.

The activation of nitric oxide (NO) production is an analgesic mechanism shared by drugs such as morphine and diclofenac. Therefore, the controlled release of low amounts of NO seems to be a promising analgesic approach. In the present study, the antinociceptive effect of the ruthenium NO donor [Ru(bpy)2(NO)SO3](PF6) (complex I) was investigated. It was observed that complex I inhibited in a dose (0.3-10mg/kg)-dependent manner the acetic acid-induced writhing response. At the dose of 1mg/kg, complex I inhibited the phenyl-p-benzoquinone-induced writhing response and formalin- and complete Freunds adjuvant-induced licking and flinch responses. Additionally, complex I also inhibited transient receptor potential cation channel subfamily V member 1 (TRPV1)-dependent overt pain-like behavior induced by capsaicin. Complex I also inhibited the carrageenin-induced mechanical hyperalgesia and increase of myeloperoxidase activity (MPO) in paw skin samples. The inhibitory effect of complex I in the carrageenin-induced hyperalgesia, MPO activity and formalin was prevented by the treatment with ODQ, KT5823 and glybenclamide, indicating that complex I inhibits inflammatory hyperalgesia by activating the cGMP/PKG/ATP-sensitive potassium channel signaling pathway. The present study demonstrates the efficacy of a novel ruthenium NO donor and its analgesic mechanisms.

A novel and simple synthetic route for a piperazine derivative

Um novo derivado da piperazina, 5-oxopiperazinio-3-sulfonato monohidratado, foi produzido a partir de uma rota sintetica simples como resultado da adicao do ion bisulfito, HSO3-, ao anel e do ataque nucleofilico de moleculas de agua a moleculas de pirazina. O material isolado foi caracterizado por RMN, espectrometria de massa, infravermelho e difracao de raios-X.

Tetraammine ruthenate complexes: cationic SAMs for cytochrome c recognition

The redox process of the cyt c metalloprotein was assessed by the cationic SAMs formed with [Ru(CNPy)(NH3)4(1,4-dt)]2+ and [Ru(CNPy)(NH3)4(pyS)]2+ complexes on gold, where CNPy = 4-cyanopyridine, pyS = 4-mercaptopyridine and 1,4-dt = dithiane. The observed cyt c redox potentials are indicative of the native protein form. The voltammograms, however, were observed to be affected by the conformation of the modifiers, determined by SERS spectroscopy. The [Ru(CNPy)(NH3)4(pyS)]2+ complex, which exhibits trans conformation on the surface, presented a well-defined voltammogram. On the other hand, the gauche conformation of the [Ru(CNPy)(NH3)4(1,4-dt)]2+ SAM seems to make the assessment of the cyt c hET reaction difficult. The reductive desorption potentials, at -0.52 and -0.64 V vs Ag|AgCl|Cl- for the [Ru(CNPy)(NH3)4(1,4-dt)]2+ and [Ru(CNPy)(NH3)4(pyS)]2+ SAMs, respectively, are indicative of the bonding mode with the surface and the p withdrawing capability of the CNpy ligand.

Identification of mechanisms involved in the relaxation of rabbit cavernous smooth muscle by a new nitric oxide donor ruthenium compound

PURPOSE The aim of this study was to evaluate the relaxation in vitro of cavernous smooth muscle induced by a new NO donor of the complex nitrosil-ruthenium, named trans-[Ru(NH3)4(caffeine)(NO)]C13 (Rut-Caf) and sodium nitroprusside (SNP). MATERIALS AND METHODS The tissues, immersed in isolated bath systems, were pre-contracted with phenilephrine (PE) (1 µM) and then concentration-response curves (10 (-12) - 10(-4) M) were obtained. To clarify the mechanism of action involved, it was added to the baths ODQ (10 µM, 30 µM), oxyhemoglobin (10 µM), L-cysteine (100 µM), hydroxicobalamine (100 µM), glibenclamide, iberotoxin and apamine. Tissue samples were frozen in liquid nitrogen to measure the amount of cGMP and cAMP produced. RESULTS The substances provoked significant relaxation of the cavernous smooth muscle. Both Rut-Caf and SNP determined dose-dependent relaxation with similar potency (pEC50) and maximum effect (E(max)). The substances showed activity through activation of the soluble guanylyl cyclase (sGC), because the relaxations were inhibited by ODQ. Oxyhemoglobin significantly diminished the relaxation effect of the substances. L-cysteine failed to modify the relaxations caused by the agents. Hydroxicobalamine significantly diminished the relaxation effect of Rut-Caf. Glibenclamide significantly increased the efficacy of Rut-Caf (pEC50 4.09 x 7.09). There were no alterations of potency or maximum effect of the substances with the addition of the other ion channel blockers. Rut-Caf induced production of significant amounts of cGMP and cAMP during the relaxation process. CONCLUSIONS In conclusion, Rut-Caf causes relaxation of smooth muscle of corpus cavernosum by means of activation of sGC with intracellular production of cGMP and cAMP; and also by release of NO in the intracellular environment. Rut-Caf releases the NO free radical and it does not act directly on the potassium ion channels.

Photochemical and Electrochemical Study of the Release of Nitric Oxide from [Ru(bpy)2L(NO)](PF6)n Complexes (L = Imidazole, 1-Methylimidazole, Sulfite and Thiourea), Toward the Development of Therapeutic Photodynamic Agents

The development of NO photoreleaser compounds has important potential applications on medicine, particularly on preventing topic infections and controlling cancers. Due to these expectations, the photochemical release of nitric oxide from complexes of [Ru(bpy)2LX]n+, where L = imidazole, 1-methylimidazole, sulphite and thiourea and X = NO+ and NO2− was investigated employing spectroscopic and electrochemical techniques. The release of NO was confirmed by chronoamperometry using a NO selective electrode, while the other product, mainly [RuIIH2O], was detected by UV-Visible spectroscopy and electrochemical techniques for all complexes except for thiourea. The amount of NO released by these complexes upon irradiation was determined using a new developed method using square wave voltammetry.

A vanillin-based copper(II) metal complex with a DNA-mediated apoptotic activity

Vanillin (vanH) is the major component of vanilla and one of the most widely used flavoring agents. In this work the complex [Cu(phen)(van)2] was prepared and characterized by structural (X-ray), spectroscopic (IR, UV-Vis, EPR) and electrochemical techniques. This compound showed an octahedral geometry with an unusual arrangement of the vanillin ligands, where the methoxy groups of the vanillinate ions are coordinated opposite to each other. The compound promoted DNA cleavage in the presence of glutathione (GSH) and H2O2. At 40 μmol L−1 of complex with GSH (10 mmol L−1), there is a complete cleavage of DNA to nicked form II, while only at 10 μmol L−1 of this complex with H2O2 (1 mmol L−1) an extensive cleavage leading to form III took place. Additionally, we have evidences of superoxide generation upon reaction with GSH. Therefore, DNA fragmentation occurs likely through an oxidative pathway. MTT assays indicated that the complex is highly cytotoxic against three distinct cell lines: B16–F10 (IC50 = 3.39 ± 0.61 μmol L−1), HUH-7 (IC50 = 4.22 ± 0.31 μmol L−1) and 786-0 (IC50 = 10.38 ± 0.91 μmol L−1). Flow cytometry studies conducted with 786-0 cell line indicated cell death might occur by apoptosis. Cell cycle progression evaluated at 5 and 10 μmol L−1 resulted in a clear increase of 786-0 cells at G1 phase and depletion of G2/M, while higher doses showed an expressive increase of sub-G1 phase. Altogether, these results pointed out to a promising biological activity and potential as an anti-cancer agent.

CHROMATOGRAPHIC INVESTIGATION OF RUTHENIUM NITROSYL COMPLEX: NO INTERCONVERSION AND REACTIONS WITH BIOLOGICAL REDUCTANTS

One experimental strategy to prepare a nitrosyl metal complex is based on the acid-base conversion of NO2 into NO. Here, we employed UV-vis absorption and FTIR spectroscopies to investigate the reaction of cis-[Ru(NO2)(bpy)2(imN)]PF6 with H3O, which produced cis-[Ru(NO)(bpy)2(imN)](PF6)3 complex. Chromatographic studies were carried out and showed that immediately after nitrite complex was dissolved only one species was present with retention time(tR) of 6.81 minutes. Addition of H3O to nitrite complex led to the formation of one major peak with tR of 3.92 min supporting nitrosyl complex formation. The reaction of nitrosyl complex with cysteine was also monitored by HPLC and it showed clearly the formation and followed decrease of a peak at 3.38 minute with maximum absorption at 380 nm, consistent with an intermediate complex. Later, it was observed the appearance of a peak at 4.15 minute with absorption band at 470 nm. In contrast to the reaction with cysteine, methionine did not show the formation of any intermediate. The use of HPLC was an important tool to support mechanistic assumptions for nitrosyl reactions.