Effects of aurothioglucose on iron-induced rat liver microsomal lipid peroxidation

Aurothioglucose (ATG), an inhibitor of selenium-dependent glutathione peroxidase activity, at a concentration of 100 microM, strongly increases lipid peroxidation of rat liver microsomes exposed to either ferrous ion (10 microM) or the combination of ferric ion (10 microM) and ascorbic acid (500 microM), in the presence of reduced glutathione (GSH, 800 microM). This effect was not achieved using heat-inactivated microsomes and was dependent on the presence of GSH. ATG did not affect the lag period associated with ascorbic acid/ferric ion-induced microsomal lipid peroxidation (previously attributed to an undefined GSH-dependent microsomal agent), but did increase the rate of peroxidation subsequent to the lag period. The potent GSH-dependent inhibition of microsomal lipid peroxidation by cytosol (10% of total volume) was completely reversed by ATG (100 microM). ATG similarly reversed an inhibition of phosphatidylcholine hydroperoxide-dependent liposomal peroxidation that has been attributed to phospholipid hydroperoxide glutathione peroxidase (PHGPX), an enzyme distinct from the classical glutathione that cannot utilize intact phospholipids. ATG inhibited, in addition to the classical selenium-dependent glutathione peroxidase, both cytosolic and microsomal (basal and N-ethyl maleimide-stimulated) glutathione S-transferase activities with greater than 80% inhibition achieved at 100 microM ATG. ATG, at concentrations up to 250 microM, did not inhibit PHGPX activity measured by the coupled-enzyme method in the presence of Triton X-100 (0.1%).(ABSTRACT TRUNCATED AT 250 WORDS)