Antioxidant effects of water- and lipid-soluble nitroxide radicals in liposomes.

Liposomes are today useful tools in different fields of science and technology. A lack of stability due to lipid peroxidation is the main problem in the extension of the use of these formulations. Recent investigative works have reported the protective effects of stable nitroxide radicals against oxidative processes in different media and under different stress conditions. Our group has focused its attention on the natural aging of liposomes and the protection provided by the water- and lipid-soluble nitroxide radicals 2,2,6,6-tetramethylpiperdine-1-oxyl (TEMPO) and doxylstearic acids (5-DSA, 12-DSA, and 16-DSA), respectively. Unilamellar liposomes were incubated under air atmosphere at 37 degrees C, both in the absence and in the presence of these radicals. Conjugated dienes, lipid hydroperoxides, TBARS, membrane fluidity, and nitroxide ESR signal intensity were followed as a function of time. Our results demonstrated that doxylstearic acids were more efficient than TEMPO in retarding lipid peroxidation at all the concentrations tested. The inhibition percentages, depending on the total nitroxide concentration, were not proportional to the lipid-water partition coefficient. Furthermore, time-course ESR signals showed a slower decrease for doxylstearic acids than for TEMPO. No significant differences were found among 5-DSA, 12-DSA, and 16-DSA. We concluded that the nitroxide radical efficiency as antioxidant directly depends on both nitroxide concentration and lipophilicity.

Oxidative stress and membrane fluidity in erythrocytes from patients with hemolytic uremic syndrome

In order to investigative the implications of oxidative disturbances in the hemolysis associated with the Hemolytic Uremic Syndrome (HUS), basal levels of lipid peroxidation products, the response to t-butyl hydroperoxide induced damage and membrane fluidity were assayed by the technique of electron spin resonance in erythrocytes spin labeled with 5-Doxyl stearic acid obtained from eight children with HUS, during the 1st, 2nd, 4th and 12 th weeks after diagnosis. During the acute phase of the disease, red blood cells (RBC) showed increased initial lipid peroxidation products, a higher susceptibility to oxidative insult and a lower membrane fluidity. All parameters reached control values the 12th week after diagnosis. The results suggest that in the acute phase of HUS, RBCs are exposed to an oxidative imbalance that could contribute to hemolysis directly through oxidative damage and/or by decreasing membrane fluidity.

Oxidative stress and membrane fluidity in erythrocytes from patients with hemolytic uremic syndrome

In order to investigative the implications of oxidative disturbances in the hemolysis associated with the Hemolytic Uremic Syndrome (HUS), basal levels of lipid peroxidation products, the response to t-butyl hydroperoxide induced damage and membrane fluidity were assayed by the technique of electron spin resonance in erythrocytes spin labeled with 5-Doxyl stearic acid obtained from eight children with HUS, during the 1st, 2nd, 4th and 12 th weeks after diagnosis. During the acute phase of the disease, red blood cells (RBC) showed increased initial lipid peroxidation products, a higher susceptibility to oxidative insult and a lower membrane fluidity. All parameters reached control values the 12th week after diagnosis. The results suggest that in the acute phase of HUS, RBCs are exposed to an oxidative imbalance that could contribute to hemolysis directly through oxidative damage and/or by decreasing membrane fluidity. (AU)