Effect of pigmentation on glutathione redox cycle antioxidant defense in whole as well as different regions of human cataractous lens.

'Reactive oxygen species', generated within the lens, are implicated in the deepening of nuclear pigmentation leading to browning of the human cataractous lens. The present study, which was carried out in senile brunescent cataracts, deals with changes in the antioxidant glutathione redox cycle defense system during the progression of browning (yellow to brown) in different regions of the human lens. A significant reduction in the levels of reduced glutathione was noted in the cortical and nuclear regions of the brown lens as compared to yellow lens, despite normal glutathione reductase activity. The rate limiting enzyme of the hexosemonophosphate shunt pathway, glucose 6-phosphate dehydrogenase, and the important oxidant scavenger enzyme, glutathione peroxidase, showed significant changes in opposite directions (glucose 6-phosphate dehydrogenase increased and glutathione peroxidase decreased), only in the cortical region of the brown lens as compared to yellow lens. The significance of the present findings in relation to the overall biochemical mechanisms underlying browning of the lens tissue in human cataracts is discussed.