Abstract
Abstract: :
Purpose: To study the distribution of free cysteine (CSH) and glutathion (GSH) pools and their association with protein-S-S-cysteine (PSSC) and protein-S-S-glutathion(PSSG) formation in various types of cataractous lenses. Methods: Patients were examined for cataracts and the lenses were classified by LOCSIII method before extraction. The extracted lenses (nuclear portions) were classified into: mature (3), nuclear (3), cortical (2), posterior subcapsular (PSC) (2), nuclear posterior subcapsular (NPSC) (3) and mixed cataracts (4). Eight age-matched donor lenses from the Nebraska Lions Eye Bank were used as controls. Each sample was divided into inner cortical-outer nuclear (designated as cortical) and the inner nuclear portions (designated as nuclear). Half of each divided sample was used for free CSH and GSH analysis by HPLC method. The other half was qualified for PSSC and PSSG by Dionex LC. Results: In normal lenses, GSH and PSSG levels were much higher than that of CSH and PSSC. The levels of CSH and GSH were higher in the cortical than the nuclear region while the distributions of the bound form were reversed. Both CSH and GSH decreased significantly with a corresponding increase in PSSC and PSSG after the development of cataracts. CSH and GSH pools were almost nil in the mature cataract, which also showed a highest level of nuclear PSSC and a lowest level of cortical PSSG. Nuclear and cortical CSH were well conserved in cataracts that involved the nucleus (eg. mature, nuclear, NPSC and mixed cataracts) while the PSSC levels in both regions were above the normal lenses. In contrast, the cortical and PSC cataracts in which the nucleus was not involved showed lower levels of nuclear and cortical PSSC than that of normal lenses. Pure nuclear and NPSC cataracts also displayed the highest level of protein thiolation, particularly in the nuclear region. Their PSSG pools were the highest among all cataracts and the PSSC increase correlated with cataract severity. Conclusion: The six types of cataracts displayed different changes in the free and bound GSH and CSH. The data suggests that cataracts with nuclear involvement may have a different mechanism of formation compared to cataracts with cortical involvement.
Keywords: 525 protein modifications-post translational • 338 cataract • 504 oxidation/oxidative or free radical damage