Phenolic antioxidants prevent peroxynitrite-derived collagen modification in vitro

To investigate the prevention of protein modification by food components, effects of natural antioxidants on in vitro modification of collagen by peroxynitrite were examined using a polyclonal antibody specific to 3-nitrotyrosine, To perform the assay with many samples at a time, the inhibitory effects of antioxidants were evaluated using an enzyme-linked immunosorbent assay. Polyphenols such as caffeic acid, curcumin, and flavonoids showed strong inhibitory effects on the formation of 3-nitrotyrosine in peroxynitrite-modified collagen. The inhibitory effects of caffeic acid and its related compounds on nitration of Tyr were then further investigated. Both caffeic acid, ferulic acid, and p-coumaric acid inhibited the modification, whereas cinnamic acid did not. By the treatment of p-coumaric acid with peroxynitrite, nitrated p-coumaric acid was detected in the reaction mixture using a liquid chromatograph-mass spectrometer (LC-MS). These results suggest that some phenolic antioxidants may prevent tissue injury by oxidants including peroxynitrite in vivo.