Tryptophan and kynurenine levels in lenses of Wistar and accelerated-senescence OXYS rats

PURPOSE: To determine the levels of kynurenine (KN) and its metabolic precursor tryptophan (Trp) in lenses of accelerated-senescence OXYS (cataract model) and Wistar (control) rats at ages from 1 day to 24 months. METHODS: Protein-free lens extracts were prepared from Wistar and senescent-accelerated OXYS rat lenses. The presence and levels of KN and Trp were determined using high performance liquid chromatography (HPLC) analysis and mass spectrometric measurements. All statistical calculations were made using the software package Statistica 6.0, using factor dispersion analysis and Newman-Keuls post-hoc test for comparison of group mean values. RESULTS: The levels of KN, which plays the role of a molecular Ultraviolet (UV) filter in the human lens, and its metabolic precursor Trp in the rat lens significantly depend on the rat strain and age. During the first 20 days after birth, before the first signs of cataract in OXYS rats, there is a strong difference in the content of both Trp and KN between Wistar and OXYS lenses. This difference becomes insignificant in lenses of 1 month and older. The levels of Trp and KN in young lenses are higher than that in lenses of 1 month and older for both strains. CONCLUSIONS: The presented results demonstrate that the KN pathway of Trp catabolism does not play a significant role in cataract development in the rat lens at the stages of cataract manifestation; however, in the first 3 weeks of postnatal development, the interstrain difference in KN and Trp levels is very strong. The obtained results show a correlation between the low level of KN and the high level of Trp at the stage of lens maturation and future cataractogenesis, and suggest an imbalance in the KN pathway of Trp catabolism in potentially cataractous lenses.