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Disruption of erythrocyte membranal organization by superoxide
Abstract:
Human erythrocyte ghosts were covalently labeled with 4-maleimide-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance (EPR) spectrometry revealed two major binding environments representing strongly (S) and weakly (W) immobilized species. The disorder parameter, W/S, determined from the respective peak amplitudes, was shown to be irreversibly elevated following treatment of the labeled ghosts with superoxide, indicating an increase in membrane fluidity. Labeled ghosts reduced with ascorbate showed no nitroxide EPR signals. However, following exposure of these membranes to superoxide, the nitroxide spectrum returned with a W/S ratio of 25. In contrast, the disorder parameter for spin-labeled ghosts decreased following exposure to hydroxyl radicals suggesting decreased fluidity, as a result of lipid peroxidation. This effect could be prevented by the inclusion of mannitol. These changes in membrane fluidity and/or protein mobility observed by EPR are compared with previous results obtained by other methods and provide additional evidence for physiologic alterations initiated by superoxide.
Insights
Superoxide increases human erythrocyte membrane fluidity, as shown by electron paramagnetic resonance (EPR) of spin-labeled ghosts. Hydroxyl radicals decrease fluidity, indicating lipid peroxidation, which mannitol can prevent.
Area of Science:
- Biochemistry
- Biophysics
- Membrane Biology
Background:
- Human erythrocyte membranes are crucial for cellular integrity and function.
- Understanding membrane dynamics is key to comprehending cellular responses to oxidative stress.
- Electron paramagnetic resonance (EPR) spectrometry is a powerful tool for probing molecular motion and membrane fluidity.
Purpose of the Study:
- To investigate the effects of superoxide and hydroxyl radicals on human erythrocyte membrane fluidity.
- To utilize spin-labeling and EPR spectrometry to quantify changes in membrane dynamics.
- To explore the role of antioxidants like mannitol in mitigating radical-induced membrane damage.
Main Methods:
- Covalent labeling of human erythrocyte ghosts with a nitroxide spin probe (4-maleimide-2,2,6,6-tetramethylpiperidinooxyl).
- Analysis of spin-labeled membranes using electron paramagnetic resonance (EPR) spectrometry.
- Quantification of membrane fluidity using the disorder parameter (W/S ratio) derived from EPR spectra.
- Treatment of labeled membranes with superoxide and hydroxyl radicals, with and without mannitol.
Main Results:
- Superoxide treatment irreversibly increased the W/S ratio, indicating enhanced membrane fluidity.
- Ascorbate reduction abolished nitroxide signals, but subsequent superoxide exposure restored them with a W/S ratio of 25.
- Hydroxyl radical exposure decreased the W/S ratio, suggesting reduced fluidity due to lipid peroxidation.
- Mannitol effectively prevented the decrease in membrane fluidity caused by hydroxyl radicals.
Conclusions:
- EPR-based spin labeling provides sensitive detection of oxidative stress-induced changes in erythrocyte membrane fluidity.
- Superoxide appears to increase membrane fluidity, while hydroxyl radicals induce lipid peroxidation and decrease fluidity.
- Mannitol demonstrates a protective effect against hydroxyl radical-induced membrane damage.