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The hydroxyl radical in lens nuclear cataractogenesis
1Cell Biology Group, the Heart Research Institute, Camperdown, New South Wales, 2050, Australia.
The Journal of Biological Chemistry
|October 24, 1998
Summary
Age-related cataracts are linked to increased protein hydroxylation, particularly DOPA, in the eye lens. This oxidative modification, driven by hydroxyl radicals, may explain cataract development.
Area of Science:
- Biochemistry
- Ophthalmology
- Molecular Biology
Background:
- Cataract is a leading cause of blindness, with age-related (senile) cataract being the most common form.
- The precise mechanisms driving cataract formation remain largely unknown.
- Understanding the molecular changes in the lens is crucial for addressing vision impairment.
Purpose of the Study:
- To investigate the role of protein oxidation in the development of nuclear cataracts.
- To identify specific oxidized amino acid residues and their abundance in cataractous lenses.
- To elucidate the primary mechanisms responsible for protein oxidation in the aging lens.
Main Methods:
- Analysis of protein-bound amino acid residues in human lens proteins from normal and cataractous eyes.
- Quantification of hydroxylated amino acids, including DOPA, tyrosine isomers, hydroxyvaline, hydroxyleucine, and dityrosine.
- Comparison of in vivo oxidation patterns with in vitro oxidation models using different reactive oxygen species and light exposure.
Main Results:
- Nuclear cataracts show a significant increase (up to 15-fold for DOPA) in protein-bound hydroxylated amino acids compared to normal lenses.
- The relative abundance of oxidized amino acids follows the pattern: DOPA > o-/m-tyrosine > 3-hydroxyvaline/5-hydroxyleucine > dityrosine.
- Nigrescent cataracts exhibit extremely high levels of hydroxylated amino acids.
- Oxidation patterns align with hydroxyl radical or metal-dependent oxidation, not hypochlorite or tyrosyl radical oxidation.
- Photoxidation with 310 nm light does not produce the observed hydroxylated aliphatic amino acids.
Conclusions:
- Extensive hydroxylation of crystallin proteins, likely mediated by hydroxyl radicals via Fenton-like reactions, is strongly associated with nuclear cataractogenesis.
- This post-translational modification appears to be a dominant in vivo oxidation pathway contributing to cataract formation.
- The findings provide a molecular explanation for key features of age-related nuclear cataracts.