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Lipid peroxidation of human granulocytes (PMN) and monocytes by iron complexes
I M Hoepelman1, W A Bezemer, E van Doornmalen
1Department of Internal Medicine, University Hospital Utrecht, The Netherlands.
Abstract:
Because the phagocytic function of non-stimulated human polymorphonuclear granulocytes (PMN) is impaired after incubation with either polynuclear Fe(III) or Fe(II), we decided to study lipid peroxidation of PMN and monocytes by these iron complexes. Lipid peroxidation was assessed by measuring thiobarbituric acid reactive substances and fluorescent compounds. In this study we report that monocytes, isolated in the standard way (EDTA-mediated detachment), release significantly more thiobarbituric acid reactive substances after incubation with iron than PMN. Monocytes, however, isolated without EDTA release the same amount after incubation with iron as PMN. The iron complexes shown to impair phagocyte function also stimulated the peroxidation of membrane lipids. Ascorbic acid in high concentrations enhanced iron-induced lipid peroxidation. Lipid peroxidation induced by ferrous ascorbate (1:20) could be inhibited by catalase, the iron chelators deferoxamine and transferrin, and the hydroxyl radical scavenger thiourea. Mononuclear complexes (ferric citrate 1:20) did not impair granulocyte function and did not induce lipid peroxidation. Our results suggest that impaired phagocyte function in patients with iron overload may be due to non-transferrin bound iron-mediated peroxidation of membrane lipids. However, the lowest amount of ferrous ascorbate (1:20) capable of inducing lipid peroxidation (50 microM) was significantly higher than that which impaired phagocyte function (10 microM).
Insights
Iron complexes impair phagocyte function by stimulating lipid peroxidation in monocytes and polymorphonuclear granulocytes (PMN). This peroxidation may explain impaired function in iron overload, though iron levels differ for peroxidation versus function impairment.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Phagocytic function of human polymorphonuclear granulocytes (PMN) is impaired by iron complexes.
- Lipid peroxidation is a potential mechanism affecting cellular function.
Purpose of the Study:
- To investigate the effect of polynuclear iron complexes on lipid peroxidation in human PMN and monocytes.
- To explore the role of non-transferrin bound iron in impaired phagocyte function.
Main Methods:
- Lipid peroxidation assessed by measuring thiobarbituric acid reactive substances and fluorescent compounds.
- Incubation of PMN and monocytes with various iron complexes (Fe(II), Fe(III), ferrous ascorbate, ferric citrate).
- Assessment of inhibition of lipid peroxidation using catalase, deferoxamine, transferrin, and thiourea.
Main Results:
- Monocytes isolated using EDTA released more thiobarbituric acid reactive substances upon iron incubation compared to PMN.
- Iron complexes impairing phagocyte function also stimulated membrane lipid peroxidation.
- Ferrous ascorbate-induced lipid peroxidation was inhibited by catalase, iron chelators, and a hydroxyl radical scavenger.
- Mononuclear iron complexes did not impair granulocyte function or induce lipid peroxidation.
Conclusions:
- Non-transferrin bound iron-mediated peroxidation of membrane lipids may contribute to impaired phagocyte function in iron overload.
- Specific iron concentrations required for lipid peroxidation differ from those impairing phagocyte function.