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.