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Lenticular Levels of Amino Acids and Free UV Filters Differ Significantly between Normals and Cataract Patients

¹From the Australian Cataract Research Foundation, University of Wollongong, Wollongong, New South Wales, Australia; and the ²Department of Chemistry, Macquarie University, Sydney, New South Wales, Australia.

PURPOSE. To determine the levels of free UV filters and selected amino acids in cataract lenses compared with normal lenses.

METHODS. Indian cataract lenses (n = 39) and normal lenses (n = 6) were examined by HPLC to quantify levels of UV filter compounds, the UV filter precursor amino acid tryptophan (Trp), as well as tyrosine (Tyr) and uric acid.

RESULTS. The levels of the two major primate UV filters, 3-hydroxykynurenine glucoside (3OHKG) and 4-(2-amino-3-hydroxyphenyl)-4-oxobutanoic acid glucoside (AHBG), in cataract lenses were markedly decreased compared with levels in normal lenses. By contrast, the levels of Trp were greatly increased. Mean Trp concentrations were an order of magnitude higher than in normal lenses, with 86% of dark-colored cataract lens nuclei having Trp concentrations greater than the mean level in the normal lenses. The concentrations of Tyr were also higher in cataract lenses. The levels of Kyn, however, were unchanged, and the uric acid levels were substantially lower.

CONCLUSIONS. The levels of the free UV filter compounds 3OHKG and AHBG, and also of Trp, Tyr, and uric acid were different in cataract lenses compared to normal lenses. These data suggest that the metabolism of a large proportion of patients with cataract may be substantially different than in persons with normal lenses. Although the mechanism of such metabolic defects are unknown, the authors speculate that an amino acid transporter system may be upregulated in patients with cataract. Because kynurenine levels in cataract were not significantly different from those of normal lenses, there may be a defect in the lenticular UV filter pathway at one, or both, of the steps that convert kynurenine to 3OHKG.

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