Vitamin C degradation products and pathways in the human lens

Area of Science:

• Biochemistry
• Oxidative Stress Research
• Protein Chemistry

Background:

• Vitamin C (ascorbic acid) and its degradation products contribute to protein modification via non-enzymatic glycation.
• Advanced glycation end products (AGEs) form from these reactions, potentially damaging proteins.
• Understanding vitamin C degradation pathways in vivo is crucial due to its high concentration in specific tissues like the lens.

Purpose of the Study:

• To investigate the in vivo degradation pathways of vitamin C in the human lens.
• To quantify specific vitamin C oxidation and degradation products within different lens protein fractions.
• To identify the major dicarbonyl compounds involved in vitamin C-related protein modification in the eye.

Main Methods:

• Human lenses were analyzed for vitamin C degradation products, including dehydroascorbic acid, 2,3-diketogulonic acid, 3-deoxythreosone, xylosone, and threosone.
• O-phenylenediamine was used to trap both free and protein-bound adducts.
• Analysis was performed on protein-free fractions, water-soluble proteins (WSP), and water-insoluble proteins (WIP).

Main Results:

• All five investigated vitamin C degradation products were found in the protein-free fraction and WSP.
• 3-deoxythreosone was the most abundant dicarbonyl in WSP and showed a positive correlation with age.
• In WIP, 3-deoxythreosone was significantly more abundant (∼20-fold) than threosone, with only these two detected.

Conclusions:

• 3-deoxythreosone is identified as the major vitamin C degradation product bound to human lens proteins.
• This finding provides in vivo evidence supporting a non-oxidative pathway of dehydroascorbate degradation via erythrulose as a primary route for vitamin C breakdown.
• The accumulation of 3-deoxythreosone in the lens may contribute to age-related protein damage.