Lipid peroxide formation in microsomes. Relationship of hydroxylation to lipid peroxide formation

Abstract

1. Aminopyrine strongly inhibits NADPH-induced lipid peroxide formation in rat liver microsomes, but ascorbate-induced peroxidation is inhibited to a smaller extent. 2. Aminopyrine oxidation is stimulated by Mg(2+) but inhibited by Ca(2+). Concentrated solutions (10mm) of iron-chelating agents inhibit aminopyrine oxidation, but the more dilute solutions (0.5mm) of chelators that block lipid peroxide formation do not inhibit aminopyrine oxidation. Microsomes prepared from sucrose-EDTA homogenates rapidly oxidize aminopyrine, but do not form lipid peroxide when incubated with ascorbate or NADPH. 3. Aminopyrine oxidation is strongly inhibited by p-chloromercuribenzoate, less by iodoacetamide and weakly by N-ethylmaleimide. The site of action of these compounds is considered to be a ferredoxin-type protein. GSH and cysteine also inhibit. 4. Other drugs oxidized by microsomes such as caffeine, phenobarbitone and hexobarbitone had either no or little effect on lipid peroxide formation, but codeine inhibited. 5. Most aliphatic hydrocarbons, alcohols, ketones and aldehydes did not affect lipid peroxide formation, but chloroform and carbon tetrachloride inhibited. 6. Many aromatic compounds inhibited lipid peroxide formation. Only aromatic acids were without any effect and phenols and amines were very strong inhibitors. 7. Induction of lipid peroxide formation in microsomes by incubation with ascorbate or NADPH or by treatment with ionizing radiation leads to a sharp decline in the ability of microsomes to oxidize aminopyrine or hydroxylate aniline. 8. It is considered that the two processes of hydroxylation and lipid peroxide formation are closely linked in microsomes. They probably depend on the same electron-transport chain, and peroxide formation, which involves membrane disintegration, may be part of the normal membrane remodelling process.

Protective influence of vitamin E on the antioxidant defence system in the whole blood and liver of normal and alloxan-induced diabetic rats

“…The level of reduced glutathione was determined using the method of Ellman (21). Free radical mediated damage was assessed by measurement of the extent of lipid peroxidation in terms of malondialdehyde (MDA) formed, essentially according to the method of Wills (22). Protein was determined by the method of Lowry et al (23).…”

Protictive effects of green tea and garlic on the morphological and oxidative stress changes of hippocampus in aged male and female albino rats

“…The samples were centrifuged at 2000g for 15 min for serum separation. Lipid peroxidation product (MDA) was measured by the method according to [16]. The activity of superoxide dismutase (SOD) was measured based on [17].…”

EFFECTS OF LYOPHILIZATION AND STORAGE OF RAT LIVER MICROSOMES ON ACTIVITY OF ANILINE HYDROXYLASE, CONTENTS OF CYTOCHROME b5 AND CYTOCHROME P-450 AND ANILINE-INDUCED P-450 DIFFERENCE SPECTRUM

“…Since activity of aniline hydroxylase was not recovered even when fresh soluble fraction was added, the loss of the activity of aniline hydroxylase during storage might be accompanied either with in activation of NADPH-cyt.c reductase or with change in membrane structure of endo plasmic reticulum. Recent observations of Wills (13) and the authors (14) that NADPH linked lipid peroxidation in liver microsomes produced an inactivation of drug metaboliz ing enzymes, and another one by Gram and Fouts (15) that significant lipid peroxidation was seen in the rat but negligible peroxidation occurred in the rabbit, may suggest that drug metabolizing enzymes in the rabbit liver are more stable than those in the rat. As previously described (14), addition of EDTA, a potent inhibitor of lipid peroxidation (16), prevented inactivation of ethyl morphine N-demethylase which occurs during incubation.…”