Correlation of Nuclear Color and Opalescence with Protein S-thiolation in Human Lenses

Abstract

Human lens nuclei were collected during routine cataract surgery and used to study the role of oxidation in cataract formation and brunescence. This study focused on the comparison of the intensities of nuclear opacity and pigmentation (brunescence) with the changes in free glutathione (GSH) and the three species of protein-thiol mixed disulfides: protein-S-S-glutathione (PSSG), protein-S S-cysteine (PSSC) and protein-S-S-γ-glutamylcysteine (PSSGC). Eighty-one freshly excised human lens nuclei from a population with a mean age of 77 were used. The nuclear color was graded using the CCRG system, ranging from yellow to dark brown. The nuclear cataract opalescence of these lenses was also graded using the LOCS II system, ranging from LOCS II NO-1 to NO-4. Three normal human lenses (average age of 88 yr) were also included in the study as controls. The nuclear samples were each analyzed for free GSH and protein-thiol mixed disulfides, respectively. It was found that nuclear GSH decreased as the nuclear color increased from yellow to dark brown (from 0.73±0.13 to 0.13±0.03 μmole g wet wt−1) and as the nuclear opalescence increased from NO.1 to NO.4 (from 0.80±0.19 to 0.20±0.01 μmole g wet wt−1). All these values were lower than that of GSH in normal controls (1.43±0.59 μmole g wet wt−1). Levels of both PSSG and PSSC progressively increased, however, as the nuclear color intensified. PSSG increased from 0.29±0.05 to 0.91±0.11 μmole g wet wt−1while PSSC increased from 0.13±0.04 to 0.41± 0.06 μmole g wet wt−1. PSSGC concentration progressively increased with increases in both nuclear pigmentation (from 0.05±0.01 to 0.23±0.05 μmole g wet wt−1) and nuclear opacity (from 0.02±0.00 to 0.20±0.02 μmole g wet wt−1). In comparison, normal controls had lower levels of all three mixed disulfide species: PSSG, 0.22±0.06; PSSC, 0.08±0.02; PSSGC, 0.02±0.06 μmole g wet wt−1, respectively. The correlation of lens nuclear color and opalescence intensity with nuclear protein S-thiolation indicates that protein-thiol mixed disulfides may play an important role in cataractogenesis and development of brunescence in human lenses.