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Effect of iron on the stability of macrophage lysosomes
Abstract:
Mouse peritoneal macrophages exposed to 60 microM Fe3+ in culture showed a pronounced decline in survival rate and an enhanced capacity for lipid peroxidation, as estimated by the formation of malondialdehyde. The iron-exposed cells contain secondary lysosomes loaded with iron as demonstrated by transmission electron microscopy, energy dispersive X-ray micro-analysis and the sulphide-silver method. The macrophages concentrated within their lysosomes the weak base acridine orange (AO) when the latter was added to the medium in a low concentration (1:10(5)). When cells were viewed under continuous illumination with short wave blue light in a fluorescence microscope, AO-exposed cells initially showed a brilliant red granular fluorescence and subsequently a progressive redistribution of AO into the cell sap and the nucleus with resultant green fluorescence. This redistribution of AO was associated with the disappearance of the normal granular reaction product pattern of the lysosomal marker enzyme acid phosphatase (AP), as demonstrated with a Gomori-type reaction, and later with cell death. The redistribution of AO and AP from the lysosomal vacuome to the cell sap under the influence of blue light occurred markedly more rapidly in macrophages containing iron loaded lysosomes than in control cells. The findings indicate that the presence of iron in lysosomes decreases the proton-retaining ability of their bordering membranes, possibly by way of enhanced metal (iron) catalyzed lipid peroxidation. It appears that leakage of AO signifies destabilization of the lysosomal membrane.
Insights
Iron overload in macrophages damages lysosomes, increasing lipid peroxidation and cell death. This study shows iron impairs lysosomal membranes, leading to leakage and reduced cell survival.
Area of Science:
- Cell Biology
- Biochemistry
- Toxicology
Background:
- Lysosomes are critical for cellular waste disposal and homeostasis.
- Iron overload is implicated in various pathologies, but its specific effects on lysosomal function are not fully understood.
- Lysosomal membrane integrity is essential for preventing cellular damage.
Purpose of the Study:
- To investigate the impact of iron (Fe3+) exposure on mouse peritoneal macrophages.
- To determine the role of iron in lysosomal function and membrane stability.
- To elucidate the mechanisms underlying iron-induced macrophage cell death.
Main Methods:
- Primary mouse peritoneal macrophages were cultured and exposed to Fe3+.
- Lipid peroxidation was assessed by malondialdehyde formation.
- Iron localization in lysosomes was confirmed using transmission electron microscopy, energy dispersive X-ray micro-analysis, and sulphide-silver staining.
- Acridine orange (AO) redistribution and acid phosphatase (AP) activity were monitored under blue light to assess lysosomal function and membrane integrity.
Main Results:
- Fe3+ exposure significantly reduced macrophage survival and increased lipid peroxidation.
- Iron-loaded macrophages exhibited secondary lysosomes containing high iron concentrations.
- Blue light induced a rapid redistribution of AO and loss of AP activity in iron-loaded macrophages compared to controls.
- This redistribution correlated with lysosomal membrane destabilization and eventual cell death.
Conclusions:
- Iron accumulation within macrophage lysosomes compromises lysosomal membrane integrity.
- Iron-catalyzed lipid peroxidation likely contributes to lysosomal membrane destabilization.
- Lysosomal membrane leakage, indicated by AO redistribution, is a key event in iron-induced macrophage toxicity.