Radical Scavenging Activity of Phenol, m-Cresol, and Thymol

Objectives: Phenol, cresol and thymol are used as sedatives and disinfectants in dentistry. However, such a mechanism remains unclear. To clarify a possible link between the radical scavenging activity and the bioactivity, these compounds were compared for their scavenging activity of nitric oxide (NO), hydroxyl radical, superoxide and diphenylpicrylhydrazyl (DPPH) radicals. Methods: NO was produced by 1-hydroxy-2-oxo-3-(N-3-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC-7)(NO generator) and 2-(4-carboxylphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO)(a spin trap agent). Hydroxyl radical and superoxide were produced by the Fenton reaction and the hypoxanthine/xanthine oxidase reaction, respectively. These radical detection was assayed using an ESR spectroscopy. DPPH radical was determined at 540 nm using a visible-light absorbance spectroscopy. Results: The NO scavenging activity (EC50 mM) of phenol, cresol and thymol was 0.05, 0.05 and 0.09, respectively, whereas that of superoxide of corresponding phenols (superoxide desmutase (SOD) U/mg) was 0.1, 0.1 and <0.1, respectively. The hydroxyl radical scavenging activity of phenol was similar to that of cresol (EC50 mM, 1.10). That of thymol was not detected due to the high hydrophobicity. DPPH radical scavenging activity declined in the order of thymol>>cresol, phenol. The significant difference between thymol and phenol or cresol was observed in NO, superoxide, DPPH (p<0.01). Conclusion: Phenol compounds scavenged free radicals such superoxide, hydroxyl radical, NO and DPPH radicals.