Roberto Santana da Silva

Nitric oxide donor trans‐[RuCl([15]aneN4)NO]2+ as a possible therapeutic approach for Chagas' disease

Background and purpose:u2002 Benznidazole (Bz) is the therapy currently available for clinical treatment of Chagas disease. However, many strains of Trypanosoma cruzi parasites are naturally resistant. Nitric oxide (NO) produced by activated macrophages is crucial to the intracellular killing of parasites. Here, we investigate the in vitro and in vivo activities against T. cruzi, of the NO donor, trans‐[RuCl([15]aneN4)NO]2+.

Endothelium negatively modulates the vascular relaxation induced by nitric oxide donor, due to uncoupling NO synthase.

Nitrosyl ruthenium complexes have been characterized as nitric oxide (NO) donors that induce relaxation in the denuded rat aorta. There are some differences in their vascular relaxation mechanisms compared with sodium nitroprusside. This study investigates whether the endothelium could interfere with the [Ru(terpy)(bdq)NO](3+)-TERPY-induced vascular relaxation, by analyzing the maximal relaxation (Emax) and potency (pD(2)) of TERPY. Vascular reactivity experiments showed that the endothelium negatively modulates (pD(2): 6.17+/-0.07) the TERPY relaxation in intact rat aortic rings compared with the denuded rat aorta (pD(2): 6.65+/-0.07). This effect is abolished by a non-selective NO-synthase (NOS) inhibitor L-NAME (pD(2): 6.46+/-0.10), by the superoxide anion (O(2)(-)) scavenger TIRON (pD(2): 6.49+/-0.08), and by an NOS cofactor BH(4) (pD(2): 6.80+/-0.10). The selective dye for O(2)(-) (DHE) shows that TERPY enhances O(2)(-) concentration in isolated endothelial cells (intensity of fluorescence (IF):11258.00+/-317.75) compared with the basal concentration (IF: 7760.67+/-381.50), and this enhancement is blocked by L-NAME (IF: 8892.33+/-1074.41). Similar results were observed in vascular smooth muscle cells (concentration of superoxide after TERPY: 2.63+/-0.17% and after TERPY+L-NAME: -4.63+/-0.14%). Considering that TERPY could induce uncoupling NOS, thus producing O(2)(-), we have also investigated the involvement of prostanoids in the negative modulation of the endothelium. The non-selective cyclooxygenase (COX) inhibitor indomethacin and the selective tromboxane (TXA(2)) receptor antagonist SQ29548 reduce the effect of the endothelium on TERPY relaxation (pD(2) INDO: 6.80+/-0.17 and SQ29548: 6.85+/-0.15, respectively). However, a selective prostaglandin F(2alpha) receptor antagonist (AH6809) does not change the endothelium effect. Moreover, TERPY enhances the concentration of TXA(2) stable metabolite (TXB(2)), but this effect is blocked by L-NAME and TIRON. The present findings indicate that TERPY induces uncoupling of eNOS, enhancing O(2)(-) concentration. This enhancement in O(2)(-) concentration induces COX activation, producing TXA(2), which negatively modulates the rat aorta relaxation induced by the NO donor TERPY.

Long-lasting hypotensive effect in renal hypertensive rats induced by nitric oxide released from a ruthenium complex.

Abstract: In this study, we investigated the effect of the ruthenium complex [Ru(terpy)(bdq)NO+]3+ (TERPY) on the arterial pressure from renal hypertensive 2 kidney-1 clip (2K-1C) rats, which was compared with sodium nitroprusside (SNP). The most interesting finding was that the intravenous bolus injection of TERPY (2.5, 5.0, 7 mg/kg) had a dose-dependent hypotensive effect only in 2K-1C rats. On the other hand, SNP (35 and 70 &mgr;g/kg) presented a similar hypotensive effect in both normotensive (2K) and 2K-1C although the effect of 70 &mgr;g/kg was >35 &mgr;g/kg. The injection of the nonselective NO-synthase inhibitor N&ohgr;-nitro-L-arginine methyl ester (L-NAME) increased the arterial pressure in 2K and 2K-1C rats with a similar magnitude. After infusion of L-NAME, the hypotensive effect induced by TERPY and SNP was potentiated in both 2K and in 2K-1C rats. The administration of the superoxide scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl increased the hypotensive effect induced by TERPY or SNP in both 2K and 2K-1C rats. The hypotensive effect induced by TERPY was longer than that produced by SNP. Taken together, our results show that the TERPY has a long-lasting hypotensive effect, which has a dose dependence and higher magnitude in 2K-1C compared with in 2K rats. In comparison with SNP, TERPY is less potent in inducing arterial pressure fall, but it presents a much longer hypotensive effect.

A new procedure to synthesize cis-[Ru(NH3)4L2]n+ species containing ruthenium(II) or ruthenium(III) using tetrammino (3,4-diolatobenzoato)ruthenium(II) as precursor☆

Abstract The preparation of [Ru(NH3)4(diox-COO)], where diox-COO is 3,4-diolatobenzoate, was achieved using pentamminechlororuthenium(III) chloride and 3,4-dihydroxybenzoic acid in basic medium. The neutral quinone complex is extremely soluble in water and easily purified by ion-exchange chromatography. The chemical or electrochemical reduction, in acidic medium, produces cis-[Ru(NH3)4(H2O)2]2+, indicating this dioxolene ruthenium complex to be a useful precursor to prepare cis-tetraammineruthenium(II) or ruthenium(III) species.

Function and Protein Expression of Potassium Channels in MesentericResistance Arteries Isolated from 2K-1C Hypertensive Rats

The present study aimed to evaluate the K+ channels activation in vascular relaxation induced by the nitric oxide (NO) donors ruthenium-derived complex (Terpy) and sodium nitroprusside (SNP), as well as its protein expression, on mesenteric resistance arteries (MRA) isolated from renal hypertensive rats (2K-1C) and sham-operated rats (Sham). The NO donors Terpy and SNP induced relaxation with similar efficacy in isolated MRA from both 2K-1C and Sham rats, although SNP was more potent than Terpy. The maximum relaxation induced by Terpy was decreased when the voltagegated potassium channels were blocked in MRA from Sham, but not in 2K-1C rat arteries. The blockade of ATP-sensitive (KATP), big and small conductance Ca2+-activated (SKCa) or inward rectifier (KIR) potassium channels decreased the maximum relaxation induced by Terpy in MRA from Sham and 2K-1C rats. However, the maximum relaxation induced by SNP was inhibited in Sham but not in 2K-1C rats when the big conductance calcium-activated potassium channel was blocked. However, it remained the same when the other potassium channels were blocked. The protein expression of the SKCa and KATP were not altered in 2K-1C hypertensive rat MRA whereas the expression of KV and BKCa were augmented in MRA from 2K-1C rats. Therefore, the potassium channels play different role on the relaxation induced by SNP and Terpy. The activation of different potassium channels and the protein expression of potassium channels may be differently modulated in arteries from 2K-1C hypertensive rats when compared to normotensive rats.

Structural, Spectroscopic, and Photochemical Investigation of an Octahedral NO-Releasing {RuNO}(7) Species.

[Ru(Me3[9]aneN3)(bpy)(NO)](BF4)2 ([1](BF4)2) was explored by single-crystal X-ray diffractometry, leading to the first crystal structure of an octahedral {RuNO}(7) complex. The metal resides on the center of a distorted octahedron, with dN-O and ∠Ru-N-O at 1.177(3) Å and 141.6(2)°, respectively. [1](BF4)2 can be stored indefinitely under argon. Solutions of [1](2+) show no signs of decomposition when protected from air and light. The electron paramagnetic resonance X-band spectrum at 85 K in vitrified acetonitrile (MeCN) shows signals consistent with an S = (1)/2 spin state, better described as Ru(II)NO(•) (g = [2.030, 1.993, 1.880] and A = [11.0, 30.4, 3.9]/10(-4) cm(-1)). In water, the {RuNO}(7) species reacts with O2 in a 1:4 stoichiometry. The reaction is first-order in both reactants with k = (1.9 ± 0.2) M(-1) s(-1) at 25 °C (ΔH(⧧) = 11.5 ± 0.3 kJ mol(-1); ΔS(⧧) = -189 ± 1 J K(-1) mol(-1)). Solutions of [1](2+) evolve NO when irradiated a 365 nm with ϕNO = 0.024 and 0.090 mol einstein(-1) in H2O and MeCN, respectively.

Synthesis, spectral and redox properties of tetraammine dioxolene ruthenium complexes

A series of species [RuIII(NH3)4(Cat-R)]n+ have been synthesized where Cat-R is a catecholate dianion having the substituent Rxa0=xa0CO2−, CO2H, OMe or H. These so-called parent species were characterized by their electronic spectra, FTIR, mass spectrum, cyclic voltammetry and EPR. Controlled potential reduction yields [RuII(NH3)4(Cat-R)](nxa0−xa01)+ while controlled potential oxidation yields [RuII(NH3)4(Q-R)](nxa0+xa01)+ (Q-Rxa0=xa0substituted quinone). Density Functional Theory (DFT) was primarily used to explore the electronic structures of these complexes. Application of the INDO semi-empirical model proved less useful. Time dependent density functional response theory was used to calculate the electronic spectra of the species with Rxa0=xa0H. The electronic spectra of the closed shell species are well reproduced by the calculations. The physical properties of these complexes indicate a charge delocalized system reminiscent of a delocalized organic molecule. The simple valence descriptions noted above are convenient to use but do not reflect the actual electronic structure. The electronic spectra of the parent species are temperature dependent. The visible region charge transfer band shifts by about 1500 cm−1 to higher energy in acidic media at liquid nitrogen temperature. This is interpreted in terms of solvent effects rather than valence tautomerism. The electrochemical properties of [RuIII(NH3)4(Cat-R)], in aqueous solution, reveal the first example of a reversible and stable Ru–quinone species in that medium. The pKa values for several dioxolene species, with Rxa0=xa0CO2−, are derived from a Pourbaix diagram.

NO Exchange for a Water Molecule Favorably Changes Iontophoretic Release of Ruthenium Complexes to the Skin

Ruthenium (Ru) complexes have been studied as promising anticancer agents. Ru nitrosyl complex (Ru-NO) is one which acts as a pro-drug for the release of nitric oxide (NO). The Ru-aqueous complex formed by the exchange of NO for a water molecule after NO release could also possess therapeutic effects. This study evaluates the influence of iontophoresis on enhancing the skin penetration of Ru-NO and Ru-aqueous and assesses its applicability as a tool in treating diverse skin diseases. Passive and iontophoretic (0.5 mA·cm−2) skin permeation of the complexes were performed for 4 h. The amount of Ru and NO in the stratum corneum (SC), viable epidermis (VE), and receptor solution was quantified while the influence of iontophoresis and irradiation on NO release from Ru-NO complex was also evaluated. Iontophoresis increased the amount of Ru-NO and Ru-aqueous recovered from the receptor solution by 15 and 400 times, respectively, as compared to passive permeation. Iontophoresis produced a higher accumulation of Ru-aqueous in the skin layers as compared to Ru-NO. At least 50% of Ru-NO penetrated the SC was stable after 4 h. The presence of Ru-NO in this skin layer suggests that further controlled release of NO can be achieved by photo-stimulation after iontophoresis.

FTOX002 A new vasodilator does not induce tolerance in rat aorta and cava vein.

The nitrite anion (NO2-) can be the major source of intravascular and tissue storage of nitric oxide (NO), important modulator of vascular tone and blood pressure control. The compound [RU(BPY)2(PY)NO2](PF6)], (RUBPY), releases NO inside the vascular smooth muscle cell in a tissue dependent manner. Long-term treatment with the patients with the NO donors such as nitroglycerin, leads to the development of tolerance characterized by the rapid loss of vasodilator effects. It is believed that the tolerance is a multifactorial process and it involves increased production of vascular reactive oxygen species (ROS), decreased activity of soluble guanylyl-cyclase (sGC) and increased expression and activity of phosphodiesterases. The tolerance may be due to endothelial dysfunction. Therefore, we have hypothesized that RuBPY would induce tolerance in veins and in intact endothelium rat aorta.

Evaluation of Nitrosyl Ruthenium Complexes Entrapped in an Oil-In- Water Emulsion as Vasodilator Agents

Several attempts have been made toward the production of oxide (NO)- releasing agents based on metallic complexes. However, many of these agents have been shown to undergo hydroxide electrophilic attack, thus generating the corresponding nitro species. Entrapped nitrosyl ruthenium species can be stabilized in an oil-in-water (o/w) emulsion and be further used for local NO delivery. This study describes the transdermal permeation of cis and trans- (RuCl(bpy)2NO)(PF6)2 complexes as NO-donor agents from a topically applied emulsion, with NO release rates of 0.042 ± 0.002 and 0.035 ± 0.003 � mol/cm 2 .h, respectively. In vitro skin permeation studies performed with the cis and trans- (RuCl(bpy)2(NO))(PF6)2 complexes in o/w emulsion showed that they tend to accumulate in the stratum corneum (SC) and viable skin, with spontaneous NO release occurring in the viable skin only. NO release was detected by using an NO- sensor when the complexes were in contact with the sonicated skin. The vascular responses to the NO released from the cis and trans-(RuCl(bpy)2(NO))(PF6)2 complexes in o/w emulsion were also evaluated by vasodilation experiments.