Effect of paraquat on the malondialdehyde level in rat liver microsomes (in vitro).
Toxicosis due to paraquat, a redox cycling xenobiotic, is still a subject of much debate. In the present study on lipid peroxidation, paraquat had a biphasic effect on the malondialdehyde (MDA) level in rat liver microsomes; stimulation at the initial stage (within 10 min) and depression at the later stage. Although paraquat increased the initial rate of NADPH oxidation dose-dependently, the rate was not necessarily parallel with the increase in the MDA level. The MDA level increased linearly up to 0.1 mM paraquat added, but then it attained a plateau. The stimulation obtained by paraquat within 10 min was absolutely dependent on exogenous Fe2+ ion and NADPH, and the stimulation was entirely SOD sensitive, while the iron-driven increase in MDA was 20% sensitive. Thus, there were different mechanisms between iron-driven lipid peroxidation and paraquat-modified peroxidation. Catalase increased the level, but mannitol, a scavenger of OH, had no effect. EPR spectra showed that superoxide was formed dose-dependently up to 0.1 mM paraquat and that it attained a plateau at the same as MDA level described above. From these results, we concluded that paraquat stimulates lipid peroxidation through a mechanism dependent on the superoxide complex involving Fe2+ ion.
Tomita
M
M
Department of Legal Medicine, Kawasaki Medical School, Kurashiki, Japan.
Okuyama
T
T
D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000378:metabolism; D066298:In Vitro Techniques; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism*; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010269:Paraquat / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013482:Superoxide Dismutase / Q000494:pharmacology; D013997:Time Factors
D005290:Ferric Compounds; D008315:Malondialdehyde; D009249:NADP; D013482:Superoxide Dismutase; D010269:Paraquat