A catechol antioxidant protocatechuic acid potentiates inflammatory leukocyte-derived oxidative stress in mouse skin via a tyrosinase bioactivation pathway

The modifying effects of topical application of a catechol antioxidant prot ocatechuic acid (PA) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammatory responses in mouse skin were investigated. Treatment with a hi gh dose (20,000 nmol) of PA, based on time of application, modifies inflamm atory responses in the skin of the B6C3F(1) mouse, a resistant strain to in flammatory response induction by TPA, but shows much higher tyrosinase expr ession than that of an albino mouse. The responsibility of a large amount o f PA-induced leukocyte infiltration to an inflamed region in a B6C3F(1) mou se is mon sensitive than that of an ICR albino mouse. When ICR mice were tr eated with TPA (1.6 nmol) twice weekly for 5 weeks to induce chronic inflam matory responses, pretreatment with 1600 nmol PA 30 min prior to each TPA t reatment significantly enhanced the inflammatory responses including edema formation, leukocyte infiltration, and the level of thiobarbituric acid-rea cting substances. The dose-dependency was closely parallel to the results o f a tumor promotion study of PA previously reported. Further, the treatment of PA alone resulted in tyrosinase-dependent contact hypersensitivity in I CR mouse skin. In addition, the in vitro study of cytotoxicity demonstrated that bioactivation by tyrosinase but not myeloperoxidase of PA significant ly enhanced cytotoxicity and intracellular glutathione consumption. We conc lude that the tyrosinase-derived reactive quinone intermediate(s) of PA, wh ich binds nucleophilic residues of proteins including sulfhydryl group and conjugates of which are recognized as haptens, was partially involved in al teration of the cellular immune functions including oxygen radical-generati ng leukocytes migration to inflamed regions. (C) 2001 Elsevier Science Inc.