Reductive metabolism of ascorbic acid in the central nervous system

Area of Science:

• Biochemistry
• Neuroscience

Background:

• Ascorbic acid (vitamin C) is a vital antioxidant in the central nervous system.
• Its regeneration is crucial for maintaining cellular function.
• The specific enzymes involved in ascorbic acid recycling in the CNS were not fully elucidated.

Purpose of the Study:

• To investigate the presence and activity of semidehydroascorbate reductase (SDAR) and dehydroascorbate reductase (DHAR) in mammalian CNS tissues.
• To determine the primary enzyme responsible for ascorbic acid regeneration in the brain and spinal cord.

Main Methods:

• Enzyme assays were performed on rat and feline brain and feline spinal cord tissues.
• Activity of SDAR was measured using NADH oxidase and NADH-dependent ascorbyl radical quenching.
• Subcellular fractionation was used to localize SDAR within rat cerebrum.

Main Results:

• Semidehydroascorbate reductase (SDAR) was detected in all examined rat and feline CNS tissues.
• SDAR activity was highest in rat cerebrum and lowest in feline spinal cord.
• SDAR activity correlated with local ascorbic acid levels and was predominantly found in a large granular fraction.
• Dehydroascorbate reductase (DHAR) was not detectable in any of the studied tissues.

Conclusions:

• Semidehydroascorbate reductase (SDAR) is the principal enzyme responsible for regenerating reduced ascorbic acid in the central nervous system.
• These findings highlight SDAR's critical role in maintaining the antioxidant capacity of the brain and spinal cord.