Inhibition in vitro linoleic acid peroxidation and haemolysis by caffeoyltryptophan

Abstract

Antioxidant activities of caffeoyltryptophan were investigated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging system, the superoxide anion generation system and the superoxide anion-mediated linoleic acid peroxidation system. At 10 μM, caffeoyltryptophan showed greater scavenging activity on DPPH than dl- α-tocopherol or ascorbic acid. DPPH radical scavenging activity of caffeoyltryptophan increased dose-dependently at concentrations ranging from 1 to 50 μM; 1 mol of caffeoyltryptophan reacted with ca 4 mol of radical. Caffeoyltryptophan caused 80% inhibition of superoxide anion generation at 50 μM. The inhibitory activity of caffeoyltryptophan was as strong as that of 5-caffeoylquinic acid. Caffeoyltryptophan inhibited the formation of conjugated diene from linoleic acid. The inhibitory activity increased in the order caffeic acid <5-caffeoylquinic acid < caffeoyltryptophan < dl- α-tocopherol. Effects on the in vitro haemolysis and peroxidation of mouse erythrocytes induced by H 2O 2 were also examined. Caffeoyltryptophan exhibited strong inhibitory activities; Tryptophan was ineffective in these systems. These data suggest that caffeoyltryptophan may be a natural antioxidant in the human diet and, as such, may intervene in toxicological processes that are mediated by radical mechanisms.