Paraquat and NADPH-dependent lipid peroxidation in lung microsomes

Since there exists some controversy in the literature as to whether paraquat augments microsomal lipid peroxidation via superoxide anion (O2-), the role of paraquat and active oxygen species in NADPH-dependent lung microsomal lipid peroxidation was investigated. Incubation of buffered aerobic mixture of bovine lung microsome and NADPH, in the presence or absence of exogenously added iron, resulted in a progressive formation of lipid peroxides whose accumulation could be followed at 535 nm as malondialdehyde. Paraquat strongly inhibited this lipid peroxidation. Thus, malondialdehyde formation was 50% inhibited by 4 X 10(-5) M paraquat in the reaction mixture. The malondialdehyde color development by lipid peroxides was not affected by this concentration of paraquat. Lipid peroxidation was also strongly inhibited by singlet oxygen scavengers, e.g. dimethylfuran and diphenylfuran, and by catalase. Hydroxyl radical scavengers, e.g. mannitol, benzoate, and ethanol, had little effect in malondialdehyde production. Superoxide dismutase, which removes O2- efficiently, did not inhibit malondialdehyde production by lung microsomes and rather enhanced its formation. A scheme in which paraquat and active O2 species may be involved with microsomal lipid peroxidation is presented.