RESUMO
The ability of several indoleamines to scavenge free radicals is well documented. Our aim was to evaluate the ability of 0.01-3 mM tryptophan (Trp) and 0.1-5 mM 5-hydroxytryptophan (5-OH-Trp) to protect hepatic cell membranes against 0.1 mM FeCl(3) plus 0.1 mM ascorbic acid-induced lipid peroxidation and increases in membrane rigidity. Membrane fluidity was evaluated using fluorescence spectroscopy. Lipid and protein oxidation were estimated by quantifying malondialdehyde (MDA) plus 4-hydroxyalkenals (4-HDA) concentrations and carbonyl group content, respectively. Exposure to FeCl(3) plus ascorbic acid increased hepatic cell membrane rigidity, MDA + 4-HDA and carbonyl content. The presence of 5-OH-Trp, but not Trp, attenuated these changes. In the absence of oxidative stress, neither indoleamine modified fluidity, MDA + 4-HDA or carbonylation. These results suggest that C5 hydroxylation determines the ability of Trp to preserve membrane fluidity in the presence of oxidative stress.