Reduced glutathione level and GSH-dependent enzyme activities in corticonuclear blocks of lenses in patients with senile cataract

Abstract

Introduction: Reduced compound glutathione (GSH) in the lens has the function to protect the thiol group of lens proteins, and as a substrate of glutathione peroxidase (GPx) and glutathione S-transferase (GST). Protein containing thiol groups is significant for the normal function of lens epithelium, i.e. enzymes Na-K-ATP-ase, thus influencing cell permeability. The relationship GSH/GSSG (oxidized glutathione) is normally high in the lens and other ocular tissue owing to the glutathioneredox cycle, which is localized in the lens epithelium and cortex surface. Objective: The aim of the study was to investigate non-enzymic factors of the antioxidant protection of non-protein and protein tiol, as well as to determine glutathione-dependent enzyme activity in the corticonuclear blocks of lenses in patients with senile cataract. Methods: Biochemical studies of lens were carried on 101 patients with senile cataract. According to cataract maturity degree, the patients were classified into two groups: senile incipient cataract (N=41) and mature senile cataract (N=60). GSH concentration was determined by Ellman's reagent. GPx activity was assayed with cumene hydroperoxide, and that of glutathione S-transferase by follow-up of glutathione conjugation and 1-chloro-2.4-dinitrobenzene rates. Results: A significantly higher GSH concentration was found in the corticonuclear blocks of lenses with initial as related to mature cataract (p<0.001).The activity of enzyme GPx and GST was considerably higher in the corticonuclear blocks of lenses with initial cataract (p<0.001).With cataract progression, the quantity of available GSH, necessary for GPx and GST functioning, declined, so that the activity of these enzymes was also significantly decreased in mature cataract. Conclusion: The determined lower GSH concentration and antioxidant enzyme activity in corticonuclear blocks of lenses, particularly in cataract with a nuclear component, indicate the weakened antioxidant response of lens tissue during the development of senile cataract.