Polyphenol oxidase/caffeic acid may reduce the allergenic properties of peanut allergens

Polyphenol oxidase (PPO) catalyzes the oxidation of tyrosine residues of proteins and, therefore, their cross-linking. Previously we demonstrated that cross-links produced by peroxidase (POD), which also catalyzes tyrosine oxidation, led to a reduction in the allergenic properties of peanut allergens.(11) We postulated in this study that PPO can also reduce the allergenic properties by cross-linking the allergens. Because caffeic acid, a phenolic compound, can cross-link proteins, its effect on peanut allergens was also examined. In the experiments, peanut extracts were treated with and without PPO, PPO/caffeic (pH 8, 37 degrees C for 1 h) and caffeic acid (pH 10.5, overnight), respectively. The samples were then analyzed for cross-links and IgE binding by SDS-PAGE, Western blots, and competitive inhibition ELISA. Results showed that, in all cases, cross-links and a decrease of the levels of two peanut major allergens, Ara h 1 and Ara h 2, were observed. Of the three treatments, PPO/caffeic was the most effective in reducing IgE binding or the allergenic properties of peanut allergens. The availability of tyrosine residues was also demonstrated in a POD-treated system, using a monoclonal antibody against dityrosine. We concluded that PPO/caffeic acid reduced the allergenic properties of Ara h 1 and Ara h 2 by cross-linking and decreasing the levels of allergens. (c) 2005 Society of Chemical Industry.