Protocatechuic acid alkyl esters: hydrophobicity as a determinant factor for inhibition of NADPH oxidase.

This study presents the increased efficiency of NADPH oxidase inhibition produced by esterification of protocatechuic acid (P0). Alkyl esters bearing chain lengths of 4 (P4), 7 (P7) and 10 (P10) carbons were synthesized and their oxidation potential, hydrophobicity, antiradical activity, inhibition of superoxide anion (O2°(-)), and the abilities to affect hypochlorous acid (HOCl) production by leukocytes and inhibit myeloperoxidase (MPO) chlorinating activity were studied. The increased hydrophobicity (logP, 0.81-4.82) of the esters was not correlated with a significant alteration in their oxidation potential (0.222-0.298 V). However, except for P10, the esters were ~ 2-fold more effective than the acid precursor for the scavenging of DPPH and peroxyl radicals. The esters were strong inhibitors of O2°(-) released by activated neutrophils (PMNs) and peripheral blood mononuclear cells (PBMCs). A correlation was found between the carbon chain length and the relative inhibitory potency. P7, the most active ester, was ~ 10-fold more efficient as NADPH oxidase inhibitor than apocynin. The esters strongly inhibited the release of HOCl by PMNs, which was a consequence of the inhibition of NADPH oxidase activity in these cells. In conclusion, as effective inhibitors of NADPH oxidase, the esters of protocatechuic acid are promising drugs for treatment of chronic inflammatory diseases. Moreover, this is the first demonstration that, besides the redox active moiety, the hydrophobicity can also be a determinant factor for the design of NADPH oxidase inhibitors.

4'-Aminochalcones as novel inhibitors of the chlorinating activity of myeloperoxidase.

The excessive activation of neutrophils generates reactive oxygen species (ROS) and the secretion of primary granular enzymes, such as myeloperoxidase (MPO), which is implicated in numerous inflammatory diseases. The aim of this study was to evaluate chalcones as inhibitors of the chlorinating activity of MPO using in vitro and ex vivo assays. In addition to cytotoxic properties, the inhibition of respiratory burst, the scavenger capacity, and the oxidation potential were measured. 4'-Aminochalcone (1), 4'-amino-4- fluorochalcone (2), and 4'-amino-4-methylchalcone (3) exhibited potent inhibition of the chlorinating activity of MPO, as evaluated in a neutrophil system and a free cell system, to the following degree: (1) IC50 = 0.265 � 0.036 µmol L-1; (2) IC50 = 0.250 � 0.081 µmol L-1; and (3) IC50 = 0.250 � 0.012 µmol L-1. These values were similar to those for 5-fluorotryptamine (IC50 = 0.192 � 0.012 µmol L-1), a compound considered to be a potent MPO inhibitor. These aminochalcones were not toxic to neutrophils at concentrations below 100 µmol L- 1, as determined by the trypan blue exclusion assay. Compounds 1-3 presented a high oxidation potential (Epa1 ≉ 0.80 V), low scavenger capacity against DPPH• and HOCl, and low inhibition of respiratory burst. These data indicated that aminochalcones are potent inhibitors of MPO chlorinating activity, a new property for chalcone derivatives, given that they are neither antioxidant agents nor inhibitors of respiratory burst. In conclusion, the selected aminochalcones have potential as pharmacological agents for inflammatory diseases.