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Molecules 2013, 18(3), 2821-2839; doi:10.3390/molecules18032821

Apocynin: Chemical and Biophysical Properties of a NADPH Oxidase Inhibitor

1 Departamento de Análises Clínicas, Faculdade de Ciências Farmacêuticas, Unesp-Univ Estadual Paulista, Araraquara, SP 14801-902, Brazil 2 Departamento de Química Orgânica, Instituto de Química, Unesp-Univ Estadual Paulista, Araraquara, SP, 14800-900, Brazil 3 Departamento de Química, Faculdade de Ciências, Unesp-Univ Estadual Paulista, Bauru, SP 17033-360, Brazil
* Author to whom correspondence should be addressed.
Received: 16 January 2013 / Revised: 21 February 2013 / Accepted: 25 February 2013 / Published: 1 March 2013
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Apocynin is the most employed inhibitor of NADPH oxidase (NOX), a multienzymatic complex capable of catalyzing the one-electron reduction of molecular oxygen to the superoxide anion. Despite controversies about its selectivity, apocynin has been used as one of the most promising drugs in experimental models of inflammatory and neurodegenerative diseases. Here, we aimed to study the chemical and biophysical properties of apocynin. The oxidation potential was determined by cyclic voltammetry (Epa = 0.76V), the hydrophobicity index was calculated (logP = 0.83) and the molar absorption coefficient was determined (e275nm = 1.1 × 104 M−1 cm−1). Apocynin was a weak free radical scavenger (as measured using the DPPH, peroxyl radical and nitric oxide assays) when compared to protocatechuic acid, used here as a reference antioxidant. On the other hand, apocynin was more effective than protocatechuic acid as scavenger of the non-radical species hypochlorous acid. Apocynin reacted promptly with the non-radical reactive species H2O2 only in the presence of peroxidase. This finding is relevant, since it represents a new pathway for depleting H2O2 in cellular experimental models, besides the direct inhibition of NADPH oxidase. This could be relevant for its application as an inhibitor of NOX4, since this isoform produces H2O2 and not superoxide anion. The binding parameters calculated by fluorescence quenching showed that apocynin binds to human serum albumin (HSA) with a binding affinity of 2.19 × 104 M−1. The association did not alter the secondary and tertiary structure of HSA, as verified by synchronous fluorescence and circular dichroism. The displacement of fluorescent probes suggested that apocynin binds to site I and site II of HSA. Considering the current biomedical applications of this phytochemical, the dissemination of these chemical and biophysical properties can be very helpful for scientists and physicians interested in the use of apocynin.
Keywords: NADPH oxidase; apocynin; hydrogen peroxide; albumin; binding constant NADPH oxidase; apocynin; hydrogen peroxide; albumin; binding constant
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Petrônio, M.S.; Zeraik, M.L.; Fonseca, L.M.; Ximenes, V.F. Apocynin: Chemical and Biophysical Properties of a NADPH Oxidase Inhibitor. Molecules 2013, 18, 2821-2839.

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