Comparison of non-tryptophan fluorophores in protein-free extract of brunescent and non-brunescent human cataract.

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-beta-glucoside (0.67 +/- 0.38 vs. 0.85 +/- 0. 62 micromol/g wet weight), 4-(2-amino-3-hydroxyphenyl)-4-oxobutanoic acid O-glucoside (4.1 x 10(5) +/- 2.9 x 10(5) vs. 6.3 x 10(5) +/- 5. 0 x 10(5) area unit/g wet weight), and kynurenine (0.016 +/- 0.011 vs. 0.029 +/- 0.021 micromol/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 x 10(5) +/- 1.0 x 10(5) vs. non-brunescent: 2.6 x 10(3) +/- 6.3 x 10(3) area unit/g wet weight, P <.01). Digestion of the protein-free extract with beta-glucosidase eliminated the peak corresponding to the novel unidentified fluorophore. CONCLUSION The present results imply a novel protein-unbound fluorophore, presumably a beta-glucoside, might possibly be involved in brunescent cataract formation.