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Ascorbic acid and glucose oxidation by ultraviolet A-generated oxygen free radicals
A Giangiacomo1, P R Olesen, B J Ortwerth
1Mason Institute of Ophthalmology, University of Missouri, Columbia 65212, USA.
Investigative Ophthalmology & Visual Science
|July 1, 1996
Summary
Ascorbic acid (ASA) readily oxidizes under glycation conditions and UVA light, unlike glucose. This suggests ASA, not glucose, is the primary glycating agent in aging human lenses.
Area of Science:
- Biochemistry
- Ophthalmology
- Oxidative Stress
Background:
- Glycation reactions are implicated in lens aging and cataract formation.
- Ascorbic acid (ASA) and glucose are present in the human lens.
- Understanding their relative reactivity is crucial for lens health research.
Purpose of the Study:
- To compare the oxidation rates of ASA and glucose.
- To investigate oxidation under conditions mimicking in vitro glycation.
- To assess oxidation induced by UVA-generated free radicals in the presence of lens proteins.
Main Methods:
- Oxidation rates were measured using spectrophotometry and chromatography.
- UVA irradiation was used to generate reactive oxygen species with human lens proteins as sensitizers.
- The roles of specific reactive oxygen species were determined using scavengers like superoxide dismutase and catalase.
Main Results:
- ASA oxidized rapidly in buffer, an effect inhibited by metal chelators and lens proteins.
- Glucose showed negligible oxidation under all tested conditions.
- UVA irradiation oxidized ASA significantly faster (10^3 times) than glucose, with superoxide anion and singlet oxygen being key oxidants.
Conclusions:
- In vitro glycation conditions and UVA-induced radicals preferentially oxidize ASA over glucose.
- ASA is a more likely primary glycating agent in the aging normal lens.
- These findings have implications for understanding age-related changes in the lens.