Lipid peroxide formation in microsomes. The role of non-haem iron

Abstract

1. Metal ion-chelating agents such as EDTA, o-phenanthroline or desferrioxamine inhibit lipid peroxide formation when rat liver microsomes prepared from homogenates made in pure sucrose are incubated with ascorbate or NADPH. 2. Microsomes treated with metal ion-chelating agents do not form peroxide on incubation unless inorganic iron (Fe(2+) or Fe(3+)) in a low concentration is added subsequently. No other metal ion can replace inorganic iron adequately. 3. Microsomes prepared from sucrose homogenates containing EDTA (1mm) do not form lipid peroxide on incubation with ascorbate or NADPH unless Fe(2+) is added. Washing the microsomes with sucrose after preparation restores most of the capacity to form lipid peroxide. 4. Lipid peroxide formation in microsomes prepared from sucrose is stimulated to a small extent by inorganic iron but to a greater extent if adenine nucleotides, containing iron compounds as a contaminant, are added. 5. The iron contained in normal microsome preparations exists in haem and in non-haem forms. One non-haem component in which the iron may be linked to phosphate is considered to be essential for both the ascorbate system and NADPH system that catalyse lipid peroxidation in microsomes.

Hepatic lipid peroxidation in vivo in rats with chronic iron overload.

“…These are not mutually exclusive theories as lipid peroxidation may mediate the loss of lysosomal membrane integrity. Although ionic iron (Fe2+, Fe3+) in vitro can initiate lipid peroxidation in isolated hepatocellular organelles (11)(12)(13)(14)(15)(16)(17)(18), evidence that chronic iron overload results in hepatic lipid peroxidation in vivo has been limited to two reports in which increased malonic dialdehyde (MDA)l was demonstrated in liver of rats that had received parenteral iron dextran (19,20 Preparation of hepatic mitochondrial fraction. Experimental and control rats from each group were treated identically as above except that the homogenizing solution was 0.25 M sucrose, 0.003 M EDTA, pH 7.4.…”

Haem oxygenase shows pro-oxidant activity in microsomal and cellular systems: implications for the release of low-molecular-mass iron

“…However, the initiation process, and the role of iron complexes in this, have remained topics of debate because both enzymic and non-enzymic components are involved [27][28][29]. The participation of HO in microsomal LPO seems likely from the results that we obtained.…”

“…Two types of microsomal LPO have been identified : a nonenzymic process, induced by ascorbate and EDTA-Fe(III), and an enzymic process, which is NADPH-dependent [27][28][29]43]. NADPH-dependent LPO is catalysed by NADPH : cytochrome P450 reductase.…”

Renin release and lipid peroxidation by ascorbic acid in the renin granule fraction of rat kidney cortex.

“…It is known that iron components, probably inorganic iron ions, are essential for the formation of lipid peroxides in the presence of ascorbic acid. The requirement for an iron ion appears to be specific, and no other metal ions can replace it (25). The role of ascorbic acid is thought to maintain iron ions in their reduced form (26).…”