Further studies on the dynamic changes of glutathione and protein-thiol mixed disulfides in H2O2 induced cataract in rat lenses: distributions and effect of aging.

To further investigate the role of protein-thiol mixed disulfides in cataractogenesis, an in vitro H2O2 cataract model was used with rat lenses to study the effect of aging, and the dynamic changes in the cortex, nucleus and the lens protein fractions. A group of lenses was exposed to H2O2-containing media (0.6 mM) for 1 to 3 days so that cortical cataract was induced gradually. Another group of lenses was first subjected to H2O2 exposure for one day and then recovered in the oxidant-free media for one or two days. These lenses were examined for the distribution of free glutathione and protein-thiol mixed disulfides (protein-glutathione and protein-cysteine) in the cortical and nuclear regions as well as in the water soluble and water insoluble fractions. Similar to the results reported earlier, the glutathione depletion in the whole lens occurred immediately and extensively during the 3-day H2O2 exposure. This loss was evenly distributed in the cortical and nuclear fractions. The level of protein-glutathione increased rapidly and continued throughout the 3 days. Most of the accumulation was found in the cortex and in both lens protein fractions. The protein-cysteine modification responded more slowly and less to oxidative stress. The delayed formation occurred mainly in the nucleus and in both lens protein fractions. In the recovery group, glutathione depletion was less drastic in the cortical and nuclear regions, but the elevated protein-glutathione in both regions and both protein fractions spontaneously decreased to its respective basal level within 1 day. Protein-cysteine on the other hand remained quite high, and in some cases it continued to rise in the absence of oxidation. Aging showed little effect on the response of rat lenses to oxidative stress. Similar patterns in glutathione and protein-thiol mixed disulfides occurred in both age groups (1, 23 months) and in both chronic oxidative stress and recovery conditions.