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Iron induces lipid peroxidation in cultured macrophages, increases their ability to oxidatively modify LDL, and
Abstract:
The present study demonstrates for the first time that iron ions can induce lipid peroxidation in intact macrophages without causing cell death. Macrophage lipid peroxidation increases cell-mediated oxidation of LDL, enhances the release of interleukin 1 and inhibits the release of apolipoprotein E from the macrophages. When cultured macrophages were exposed to ferrous ions (50 microM FeSO4) for 4 h at 37 degrees C, cellular lipid peroxidation (measured by analyses of malondialdehyde (MDA), conjugated dienes (CD), and lipid peroxides (PD)) increased 2-4-fold in comparison with non-treated cells. This process was iron-dose dependent, reached its maximum after 4 h of incubation, and was accompanied by 68% and 53% reductions in the content of the cellular linoleic (18:2), and arachidonic acid (20:4), respectively, and by 29% and 36% reductions of cellular vitamin E and vitamin A, respectively. Cell viability (measured by trypan blue exclusion, by [3H]thymidine incorporation into DNA, by analysis of the release of lactate dehydrogenase (LDH) or [3H]adenine), and cell morphology (studied by scanning electron microscopy) were not significantly affected by the iron-induced oxidative stress. Manitol and dimethylthiourea (DMTU), but not catalase or superoxide dismutase (SOD), significantly inhibited iron-induced cellular lipid peroxide formation, suggesting that hydroxyl radical, but not superoxides or hydrogen peroxides, mediated the iron-induced cellular lipid peroxidation. Incubation of LDL (0.2 mg of protein/ml) with oxidized macrophages resulted in LDL lipids peroxidation, as evidenced by an 8-fold increase in the LDL associated MDA in comparison with LDL that was incubated under similar conditions with non-oxidized macrophages. Furthermore, oxidation of LDL by oxidized macrophages in the presence of copper ions (10 microM CuSO4) was 2-fold higher in comparison with oxidation of LDL by non-oxidized macrophages. The release of apolipoprotein E from oxidized macrophages decreased by 50%, whereas macrophage release of beta-glucuronidase and of interleukin-1 beta increased by 83% and by a factor of 6, respectively. This study demonstrates for the first time that iron ions induce oxidation of the cellular polyunsaturated fatty acids in intact macrophages and that this cellular lipid peroxidation can subsequently induce LDL oxidation.
Insights
Iron ions induce lipid peroxidation in macrophages without cell death, promoting LDL oxidation and altering cytokine release. This study reveals iron
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Macrophages play a crucial role in immune responses and lipid metabolism.
- Oxidative stress, particularly from iron, is implicated in various diseases.
- Understanding iron-induced cellular changes is vital for disease pathogenesis research.
Purpose of the Study:
- To investigate the effects of iron ions on lipid peroxidation in intact macrophages.
- To determine the downstream consequences of iron-induced macrophage lipid peroxidation on LDL oxidation and cytokine release.
- To elucidate the reactive oxygen species involved in iron-mediated lipid peroxidation.
Main Methods:
- Cultured macrophages exposed to ferrous ions (FeSO4).
- Measurement of lipid peroxidation markers (MDA, CD, PD), fatty acids, and vitamins.
- Assessment of cell viability and morphology.
- Analysis of LDL oxidation and cytokine release (interleukin-1, apolipoprotein E).
- Inhibition studies using antioxidants (mannitol, DMTU, catalase, SOD).
Main Results:
- Iron ions significantly increased macrophage lipid peroxidation without affecting cell viability.
- Reduced levels of cellular polyunsaturated fatty acids and vitamins E and A were observed.
- Iron-induced lipid peroxidation enhanced LDL oxidation and increased interleukin-1 release while decreasing apolipoprotein E release.
- Hydroxyl radical, not superoxide or hydrogen peroxide, was identified as the mediator.
Conclusions:
- Iron ions induce lipid peroxidation in intact macrophages, leading to subsequent LDL oxidation.
- This process alters macrophage function, impacting inflammatory responses and lipoprotein metabolism.
- The findings highlight a novel mechanism linking iron overload to oxidative stress and cardiovascular risk.