Erythrocytes reduce extracellular ascorbate free radicals using intracellular ascorbate as an electron donor

Area of Science:

• Biochemistry
• Cell Biology
• Redox Biology

Background:

• Ascorbate (vitamin C) is a vital antioxidant readily oxidized by ascorbate oxidase.
• Oxidation of ascorbate generates ascorbate radicals, which can disproportionate into ascorbate and dehydroascorbic acid.
• Understanding cellular mechanisms that protect ascorbate is crucial for combating oxidative stress.

Purpose of the Study:

• To investigate the role of intracellular ascorbate in protecting extracellular ascorbate from oxidation.
• To elucidate the mechanism by which erythrocytes influence ascorbate stability.
• To determine if erythrocytes possess a plasma membrane redox system for ascorbate protection.

Main Methods:

• Utilized electron spin resonance (ESR) spectroscopy to measure extracellular ascorbate radical levels.
• Quantified changes in ascorbate and dehydroascorbic acid concentrations in erythrocyte suspensions.
• Conducted control experiments to rule out alternative explanations like cell leakage or oxygen depletion.

Main Results:

• Increased intracellular ascorbate concentrations reduced extracellular ascorbate oxidation in a dose-dependent manner.
• Electron spin resonance spectroscopy confirmed decreased extracellular ascorbate radical levels with higher intracellular ascorbate.
• Intracellular ascorbate radicals were detected upon exposure to high extracellular radical levels, and dehydroascorbic acid efflux was observed.

Conclusions:

• Intracellular ascorbate directly inhibits extracellular ascorbate oxidation, independent of cell leakage or oxygen levels.
• Erythrocytes employ a plasma membrane redox system to transfer electrons from intracellular ascorbate to extracellular ascorbate radicals.
• This cellular redox system effectively protects extracellular ascorbate from oxidative degradation, preserving antioxidant capacity.