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Formation of liver microsomal MDA-protein adducts in mice with chronic dietary iron overload
1Division of Gastroenterology, School of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
Abstract:
Lipid peroxidation has been proposed to be a major mechanism involved in the pathophysiology of hepatic iron overload. Hepatic microsomal lipid peroxidation has been demonstrated in animals with dietary iron overload, and major products of lipid peroxidation with known cytotoxicity, such as malondialdehyde (MDA), may be involved in iron-induced hepatocellular injury by covalent binding to microsomal proteins. This investigation examined whether DBA/2Ibg mice fed a diet enriched with ferrocene-iron for 16 weeks, results in hepatic lipid peroxidation, and if liver microsomes contain proteins adducted by MDA. Chronic iron feeding to mice resulted in a severe hepatic iron overload with hepatic stores of iron 12-fold greater than those measured in control mice and a three-fold increase in hepatic concentrations of MDA, indicating the occurrence of iron-induced lipid peroxidation in vivo. Hepatic collagen content was increased by over three-fold (p < 0.05) in iron-fed mice as compared to control animals, suggesting increased fibrogenesis. Using rabbit antiserum specific for MDA amine protein adducts and immunoprecipitation-Western blotting, we documented formation of 10 liver microsomal proteins adducted by MDA in iron overload mice (approximate molecular weights; 214, 140, 129, 121, 103, 83, 62, 60, 48, and 43-kD). Control mice did not exhibit positive immunostaining for these protein adducts. The incubation of synthetic MDA with liver microsomes isolated from untreated mice demonstrated formation of MDA-adducted proteins with molecular weights comparable to those detected following in vivo iron overload. The data from this animal study are the first to demonstrate that lipid-derived aldehydes produced from hepatic iron overload in vivo, covalently bind and hence, chemically modify numerous proteins in microsomes. These data suggest that MDA modified proteins in microsomes may play a role in a sequence of events that lead to cell injury during metal-induced liver damage.
Insights
Iron overload in mice causes lipid peroxidation, increasing malondialdehyde (MDA) and leading to MDA-protein adducts in liver microsomes. This suggests MDA-modified proteins contribute to liver injury in hepatic iron overload.
Area of Science:
- Biochemistry
- Hepatology
- Toxicology
Background:
- Hepatic iron overload is linked to lipid peroxidation.
- Malondialdehyde (MDA), a cytotoxic lipid peroxidation product, may cause hepatocellular injury through protein binding.
Purpose of the Study:
- To investigate if chronic iron feeding induces hepatic lipid peroxidation and MDA-protein adducts in mice.
- To determine the role of MDA-modified proteins in iron-induced liver damage.
Main Methods:
- DBA/2Ibg mice were fed an iron-enriched diet for 16 weeks.
- Hepatic iron and MDA concentrations were measured.
- Immunoprecipitation-Western blotting was used to detect MDA-protein adducts in liver microsomes.
Main Results:
- Iron feeding caused severe hepatic iron overload and a three-fold increase in hepatic MDA.
- Increased hepatic collagen content suggested enhanced fibrogenesis.
- Ten distinct liver microsomal proteins were found to be adducted by MDA in iron-overloaded mice.
Conclusions:
- Chronic iron overload induces lipid peroxidation and the formation of MDA-protein adducts in mouse liver microsomes.
- These MDA-modified proteins may contribute to hepatocellular injury in hepatic iron overload.
- This study provides the first in vivo evidence of lipid-derived aldehydes covalently binding to microsomal proteins during iron overload.