Comparison of Non-Tryptophan Fluorophores in Protein-Free Extract of Brunescent and Non-Brunescent Human Cataract

Abstract

Purpose: To investigate whether any of the fluorophores in the human lens nuclei might be responsible for human brunescent cataract formation. Methods: Human lens nuclei (non-brunescent, from 13; brunescent, from 8) were obtained after extracapsular cataract extraction in nondiabetic patients. Protein-free extract, prepared by filtrating the water-soluble fraction of each nucleus through a centrifugal ultrafilter (molecular weight < 5,000), was analytically separated by high-performance liquid chromatography. Results: No significant differences between non-brunescent and brunescent nuclei were observed in the concentrations (mean ± SD) of 3-hydroxykynurenine O-β-glucoside (0.67 ± 0.38 vs. 0.85 ± 0.62 μmol/g wet weight), 4-(2-amino-3-hydroxyphenyl)-4-oxobutanoic acid O-glucoside (4.1 × 10 5 ± 2.9 × 10 5 vs. 6.3 × 10 5 ± 5.0 × 10 5 area unit/g wet weight), and kynurenine (0.016 ± 0.011 vs. 0.029 ± 0.021 μmol/g wet weight). A novel fluorophore that has not been identified so far was significantly present more in brunescent than in non-brunescent nuclei (brunescent: 1.5 × 10 5 ± 1.0 × 10 5 vs. non-brunescent: 2.6 × 10 3 ± 6.3× 10 3 area unit/g wet weight, P < .01). Digestion of the protein-free extract with β-glucosidase eliminated the peak corresponding to the novel unidentified fluorophore. Conclusion: The present results imply a novel protein-unbound fluorophore, presumably a β-glucoside, might possibly be involved in brunescent cataract formation.