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Inhibition of hepatic microsomal lipid peroxidation by endogenous glycogen in the rat
1Department of Pharmacology and Toxicology, Rutgers University, Piscataway, NJ 08854.
Abstract:
The effect of endogenous glycogen on lipid peroxidation was examined in hepatic microsomes from rats. Microsomes were prepared to retain endogenous hepatic glycogen (Pg+) or to minimize it (Pg-). The indices of lipid peroxidation examined included the rate of NADPH-dependent formation of malondialdehyde (MDA) and the concomitant destruction of cytochrome P-450 and decline in the linearity of benzphetamine N-demethylase activity in microsomes. Cytochrome P-450 was destroyed during benzphetamine N-demethylation in microsomes with the loss being more extensive in Pg- than in Pg+. The destruction of cytochrome P-450 and the concomitant loss in linearity of benzphetamine N-demethylation in Pg- were prevented by added EDTA. Added linoleic acid hydroperoxide (LAHP) also caused a time-dependent loss of cytochrome P-450 in microsomes with the rate being greater in Pg- than in Pg+. The results show that glycogen inhibits hepatic microsomal lipid peroxidation and suggest that variations in glycogen content may contribute to disparities in in vitro oxidative activities between different microsomal samples. Such disparities may be minimized by the removal of glycogen during the preparation of microsomes and then supplementing the incubation mixtures with EDTA. The in vivo relevance of the observed antioxidant effect of glycogen is discussed in terms of the possible modulation by the polysaccharide of hepatotoxicity by agents whose effects may be mediated by lipid peroxidation.
Insights
Glycogen inhibits lipid peroxidation in rat liver microsomes. Removing glycogen during preparation minimizes oxidative damage and loss of cytochrome P-450, suggesting glycogen
Area of Science:
- Biochemistry
- Hepatology
- Toxicology
Background:
- Hepatic microsomes are crucial for drug metabolism and detoxification.
- Lipid peroxidation is a damaging process implicated in various liver diseases.
- Endogenous glycogen levels can vary, potentially affecting microsomal functions.
Purpose of the Study:
- To investigate the role of endogenous hepatic glycogen in modulating lipid peroxidation.
- To determine if glycogen content influences the stability of cytochrome P-450 and enzyme activity.
Main Methods:
- Preparation of rat hepatic microsomes with high (Pg+) and low (Pg-) endogenous glycogen content.
- Assay of NADPH-dependent malondialdehyde formation as an index of lipid peroxidation.
- Measurement of cytochrome P-450 destruction and benzphetamine N-demethylase activity.
- Evaluation of the effects of EDTA and linoleic acid hydroperoxide (LAHP).
Main Results:
- Microsomes with low glycogen (Pg-) exhibited more extensive cytochrome P-450 destruction and loss of enzyme activity compared to Pg+ microsomes.
- EDTA prevented P-450 destruction in Pg- microsomes, while LAHP accelerated P-450 loss more in Pg- than Pg+.
- Glycogen was shown to inhibit hepatic microsomal lipid peroxidation.
Conclusions:
- Endogenous glycogen acts as an inhibitor of hepatic microsomal lipid peroxidation.
- Variations in glycogen content can explain differences in in vitro microsomal oxidative activities.
- Optimized microsomal preparation (glycogen removal, EDTA addition) can minimize oxidative disparities and may have in vivo relevance for hepatotoxicity.