Determinação Voltamétrica de Modulador Redox de Estresse Oxidativo à Base de Mn-Porfirina

Oxidative stress is a redox imbalance, characterized by excess of reactive species (O2●–, H2O2, ONOO–/ONOOH, ●NO2, ●OH) and is commonly associated with diseases, such as cancer, diabetes, and is chemia/reperfusion injuries.1 The enzymes superoxide dismutases(SOD) regulatethe in vivo O2●–levels and, thus,the overall oxidative stress conditions. Cationic Mn porphyrins (MnPs)are among the most potent SOD mimics for pre-clinical studies and are currently under phases I/II Clinical Trials in Canada and USA as redox active therapeutics. The activity of MnPs in vivo depends not only on its intrinsic catalytic potency, but also on its bioavailability, accumulation, and pharmaco kinetics, which demands, in turn,reliable and sensitive analytical methods for MnP quantification in biological milieu, such as UV-vis,2HPLC-fluorescence,3or HPLC-MS/MS3methods. Hereon we presenta voltammetric method for quantification of the prototypical Mn(III) porphyrin, meso-tetrakis (N-methylpyridinium-2-yl) porphyrin(MnTM-2-PyP5+), based on square-wave voltammetry (SWV). The voltammetric measurements were carried out using glassycarbon electrode,Ag/AgCl electrode, and platinum electrode as working, reference, and auxiliary electrodes, respectively, in 0.05 mol L-1phosphate buffer (pH 7.8) containing 0.1 mol L-1NaCl. SWV parameters were optimized (Es: 7 mV; f: 75 Hz ; amp: 75 mV),and theanalytical curve presented two linear regions depending on MnTM-2-PyP5+concentration range: (i) from 0.04 to0.11;(ii) from 0.3to10.10μmol L-1.The lower concentration range is represented by the equation: I (μA) = 0.376(μA) + [0.847(μA L μmol-1) x C(MnP, μmol L-1)], R2 = 0.9913.The limit of detection (LD) and the limit of quantification (LQ) were 0.02 and 0.06 μmol L-1,respectively. This LQis satisfactory, since it is within the LQ range found by other analytical methods(UV-vis: 0.7,2HPLC-fluorescence: 0.0013,3and HPLC-MS/MS:0.0005 μmolL-1)3;furthermore, the SWV-basedmethod is simple, fast,and of relatively low cost.