Non-invasive techniques in the study of cataract development at the metabolic and protein molecular level.

Abstract

Metabolic changes may precede changes in lens protein structure and cataract opacification. Since many of the effects associated with cataract are oxidative in nature, changes in the redox state may be caused by alterations in the level of various metabolic intermediates such as ATP and NAD(P)H. Abnormal levels of H2O2 have been found in the aqueous fluid of cataract patients. Lenses have been treated with 1 mM-H2O2 in organ culture as a cataract model. H2O2 in this system uncouples Na+, K+-ATPase. This metabolic stress has been further evaluated non-invasively by 31P NMR to show that H2O2 can reduce ATP levels without any immediate effects on visual transparency. However, further treatment by this oxidant leads to definitive visual changes in lens clarity. These changes may be due to further changes in structural lens proteins caused by denaturation and aggregation induced by H2O2. The effects of H2O2 on isolated lens proteins is being examined in molecular detail by NMR to ascertain how the lens proteins become denatured in solution. The relevance of the H2O2 model to cataract formation can only be evaluated by using several non-invasive techniques beyond NMR, and then critically comparing the model systems with human cataract tissue samples.