Abstract: Substances as resveratrol, quercetin, gallic acid, curcumin and their derivatives are among the most recognized natural antioxidants which are able to inhibit the production of Nitric Oxide (NO) by activated macrophages. Despite these antioxidants have very different molecular structures; they share the common and essential characteristic of to be phenolic compounds. For this reason, we studied the relative potency of commercial p-substituted phenols as inhibitors of the production of NO by LPS-stimulated macrophages. Our objective was to access the correlation between the reduction potential of the p-substituted phenols, which is directly influenced by the presence of electron-donating and electron-withdrawing substituents groups in the phenolic moiety, with the efficiency of inhibition. The production of NO by LPS-stimulated macrophages was measured by Griess`s assay. The compounds were not cytotoxic in the concentration used as determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. We found that p-hydroxyphenol, the compound with lower reduction potential, was the best inhibitor of the production of NO. On the other hand, compounds like p-nitrophenol and p-acetylphenol, bearing electron-withdrawing substituents groups and, consequently, higher reduction potential, were ineffective as NO inhibitor. We also compared natural antioxidants as quercetin (E� = 0.33 V), apocynin (E� = 0.66 V) and melatonin (E� = 0.95 V) and, again, quercetin, the substance with lower reduction potential, was the more efficient inhibitor.
Sandra Ananias , Iracilda Z. Carlos and V.F. Ximenes , 2008. p-Substituted Phenols as Inhibitors of Nitric Oxide Production by LPS-Activated Macrophages. Research Journal of Biological Sciences, 3: 673-677.