Assessment of lipid peroxidation associated with lung damage induced by oxidative stress. In vivo and in vitro studies.

The lung thiobarbituric acid-reactive substances (TBA-RS) content and the amount of ethane exhaled, two potential markers of the lipid peroxidation process, were measured in rats following intratracheal administration of chemicals stimulating the production of free radicals, i.e. paraquat, phorbol myristate acetate and ferrous ions. Five hours after treatment, autopsy revealed gross pulmonary damage but the lung TBA-RS and the ethane exhalation were not different from control animals. On the contrary, a large increase in ethane production was observed 2 hr after intraperitoneal administration of the hepatotoxic carbon tetrachloride. In vitro, incubation of lung and liver homogenates from control rats with ferrous iron led to the development of a lipid peroxidation process in both tissues but the accumulation of TBA-RS and ethane was much lower with homogenates from lung as compared to liver tissue. Those results suggest that the lung may be more resistant than the liver to the initiation and/or propagation of a lipid peroxidation process. The possibility that others markers than ethane and TBA-RS are more appropriate to detect this process in the lung must also be considered.

The role of vitamin E in the susceptibility of rat lung and liver microsomes to iron-stimulated peroxidation.

The production of thiobarbituric acid-reactive substances (TBA-RS) and ethane, two markers of the lipid peroxidation process, was evaluated in rat lung and liver microsomal membranes incubated in the presence of either ferrous ions or a mixture of ferric ions and ascorbate. Microsomal fractions isolated from lung tissue were more resistant than those isolated from the liver. Compared to Fe2+, the association of Fe3+/ascorbate seemed to be totally ineffective in stimulating peroxidation of lung microsomes. The fatty acid profile of lung and liver microsomal membranes could not be responsible for their different susceptibility to free radical degradation. The microsomal fraction isolated from lung showed a higher vitamin E concentration than the liver. The importance of vitamin E in protecting lung membranes was assessed by using lung and liver isolated from vitamin E-deficient and vitamin E-supplemented rats. For both lung and liver microsomal fractions an inverse relationship between vitamin E concentrations and the extent of lipid peroxidation was observed. However, although the vitamin E concentrations in lung and liver microsomes isolated from rats submitted to a vitamin E-deficient diet were not different, lung microsomes still exhibited a lower production of TBA-RS and ethane than liver. In addition to vitamin E, other factors must be involved to explain the resistance of lung microsomes to lipid peroxidation.

Effect of oxygen concentration on production of ethane and thiobarbituric acid-reactive substances by peroxidizing lung and liver homogenates and formation of ethanol by peroxidizing docosahexaenoic acid preparations under hyperoxic conditions.

The oxygen dependence of ethane formation was investigated in rat lung and liver homogenates, incubated in sealed flasks, in which the peroxidation was stimulated by the addition of ferrous ions. For both tissues, the production of ethane was maximal under a 20% oxygenated gas phase, while hyperoxic conditions led to a decreased ethane in the gas phase. The formation of thiobarbituric acid-reactive substances (TBA-RS), another marker of the lipid peroxidation process, in the homogenates of lung and liver was strongly stimulated at 100% compared to 20% oxygen. Experiments were also carried out on iron-stimulated peroxidation of pure docosahexaenoic acid preparations, which under air led to a large production of ethane. As for tissue homogenates, the TBA-RS content was increased in the presence of 100% oxygen. Those conditions, however, did not induce an increase in ethane production but led to the formation of ethanol. Therefore, the quenching of ethyl radical by molecular oxygen seems to be a very attractive hypothesis to explain the lack of increased ethane production in favor of ethanol when iron-induced lipid peroxidation was stimulated by oxygen.