Glutathione and antioxidants protect microsomes against lipid peroxidation and enzyme inactivation

The study investigated the relationship between lipid peroxidation and enzyme inactivation in rat hepatic microsomes and whether prior inactivation of aldehyde dehydrogenase (ALDH) exacerbated inactivation of other enzymes. In microsomes incubated with 2.5 μM iron as ferric sulfate and 50 μM ascorbate, ALDH, glucose-6-phosphate (G6Pase) and cytochrome P450 (Cyt-P450) levels decreased rapidly and concurrently with increased levels of thiobarbituric acid-reactive substances. Microsomal glutathioneS-transferase and nicotinamide adenine dinucleotide phosphate-cytochromec reductase were little affected during 1 hr of incubation. Addition of reduced glutathione partially protected, andN,N′-diphenyl-p-phenylenediamine and butylated hydroxytoluene completely protected microsomes against inactivation of ALDH, G6Pase and Cyt-P450, as well as lipid peroxidation induced by iron and ascorbate. ALDH was more susceptible than G6Pase to inactivation by iron and ascorbate, and was thus an excellent marker for oxidative stress. Inhibition of ALDH by cyanamide injection of rats exacerbated the inactivation of G6Pase in microsomes incubated with 0.1 mM, but not 25 μM 4-hydroxynonenal (4-HN). 4-HN did not stimulate lipid peroxidation. Thus, 4-HN may play a minor role in microsomal enzyme inactivation. In contrast, lipid, peroxyl radicals play an important role in microsomal enzyme inactivation, as evidenced by the prevention of both lipid peroxidation and enzyme inactivation by chain-breaking antioxidants.