Direct evaluation of the antioxidant properties of salivary proline-rich proteins

Proline-rich proteins are associated with the formation of an acquired protein layer overlying the tooth enamel surface. Previous studies have described the antioxidant activity of salivary histatin against the hydroxyl radical from Fenton’s reaction, acting as the critical reactive oxygen species. However, the role of proline-rich proteins in mitigating the oxidative stress caused by reactive oxygen species in the oral cavity remains unclear. In this study, we investigated the antioxidant effects of proline-rich proteins 2 on direct reactive oxygen species using electron spin resonance spectroscopy. For the first time, we demonstrated that proline-rich proteins 2 exhibits antioxidant activity directly against the hydroxyl radical produced by hydrogen peroxide with ultraviolet. Considering that identical results were obtained when assaying 30 residues of proline-rich proteins 2, the direct antioxidant effects against the hydroxyl radical by proline-rich proteins 2 may be related to these specific 30 residues.