Reatividade do Nitrosilo Complexo de Ferro trans-[Fe(cyclam)(NO)Cl]Cl2

Abstract

Nitric oxide (NO), produced endogenously, is responsible for vasodilation of blood vessels and other physiological processes. The nitroxyl ion (NO-), a species generated by monoeletronic reduction of NO, has rised the interest of the scientific community due to its distinct biological activity of nitric oxide. Sodium nitroprusside (SNP) is part of a class of compounds that release NO, being the only metal complex used clinically, but there are problems associated with their use, including photosensitivity and release of cyanide. Therefore, alternative compounds including iron-based ones have been studied, such as trans-[Fe(cyclam)(NO)Cl]Cl2, whose studies of chemical reactivity as well as its precursor (trans-[Fe(cyclam)Cl2](PF6)), were investigated in this work. In addition, we evaluated the potential anticancer and microbicides these complexes. The nitrosyl complex showed the ability to release NO under physiological conditions and spontaneously when stimulated by light. The NO released by nitrosyl complex thermally and photochemically was probed by the reaction with selective traps at different. The half-life values (t1/2) for reaction of nitrosyl complex with cPTIO were 115 (k = 0.1 x 10-3 s-1) and 385 (k = 3.0 x 10-5 s-1) minutes to photochemical and thermal reactions, respectively, being well known that light accelerates the process of release. The photochemical test using myoglobin is indicated release of NO, however it was not possible to determine the rate of this reaction. The reaction of the complex with glutathione (GSH) was monitored by electron paramagnetic resonance (EPR) and suggested the production of HNO. Kinetic results for this reaction indicates that there is the formation of a reactive intermediate with band at 541 nm, likely the adduct trans-[Fe(cyclam)(Cl)N(O)SG]+. The rate constants indicate that the first intermediate rapidly forms (kobs = 2.79 s-1) and decays slowly (kobs = 7.17 x 10-5 s-1). The high stability of this intermediate can be related to its ability to engage in intramolecular interactions. Vasodilation assay showed that complex trans-[Fe(cyclam)(NO)Cl]2+ has vasodilating activity with EC50 = 910 nmol L-1. It was also found that the nitrosyl complex presented scavenging activity toward O2•⎯ ions, thus having antioxidant potential. Electrophoresis experiments employing plasmid DNA and the complex trans-[Fe(cyclam)Cl2]+ and trans-[Fe(cyclam)(NO)Cl]2+, showed nuclease activity stimulated by light (350 and 460 nm) or stimulated by biologically relevant agents (H2O2 and GSH). However, cell viability assays with cancer cells showed that both complexes have low cytotoxic activity, the complex trans-[Fe(cyclam)Cl2]+ and trans-[Fe(cyclam)(NO)Cl]2+, respectively, showed IC50 values equal to: 8.5 and 144.2 mol L-1 against strain B16-F10 cells, and 130.4 and 142.9 mol L-1 against HUH-7 cell line. Additionally, preliminary tests of bactericidal activity in Escherichia coli strains indicated that the compounds were effective at inhibiting bacterial growth. These studies support a synergistic action as releasing NO/HNO and vasodilating action, anticancer and microbicide, which deserve further pharmacological and biochemical investigations for a better description of the mechanisms of action.