Peroxynitrite (ONOO-), formed from a reaction of superoxide and nitric oxide, is one of the most potent cytotoxic species that are known to oxidize cellular constituents including essential proteins, lipids, and DNA. ONOO- induces cellular and tissue injury, resulting in several human diseases such as Alzheimer's disease, atherosclerosis and stroke. Due to the lack of endogenous enzymes responsible for ONOO- scavenging activity, finding a specific ONOO- scavenger is of considerable importance. In this study, the ability of trypsin inhibitor (TI), isolated from sweet potato storage roots, to scavenge ˙ON and ONOO- were investigated. The data obtained show that TI generated a dose-dependent inhibition on production of nitrite and superoxide radicals. The IC50 value of TI on superoxide radical was 143.2 +- 4.29 .mu.g╱mL. And we used SOD activity staining to conform SOD activity of SPTI. SPTI also caused a dose-dependent inhibition of the oxidation of dihydrorhodamine 123 (DHR) by peroxynitrite. A calculated IC50 value of 809.1 +- 32.36 .mu.g╱mL was obtained on the inhibition of peroxynitrite radical. Spectrophotometric analyses revealed that TI suppressed the formation of ONOO--mediated tyrosine nitration through an electron donation mechanism. In further studies, TI also showed a significant ability of inhibiting nitration of bovine serum albumin (BSA) in a dose-dependent manner. In vivo TI inhibited LPS-induced nitrite production in macrophages in a concentration-dependent manner with an IC50 value of 932.8 +- 29.85 .mu.g╱mL. The present study suggested that TI had an efficient reactive nitrogen species scavenging ability. TI might be a potential effective NO and ONOO- scavenger useful for the prevention of the NO and ONOO- involved diseases.
