Zinc content of human retinal pigment epithelium decreases with age and macular degeneration, but superoxide dismutase activity increases

Abstract

We previously reported an age-related decline of catalase activity and metallothionein (MT) in human retinal pigment epithelium (RPE) isolated from donor eyes. MT content and catalase activity also were shown to decrease in RPE cells cultured in zinc-deficient medium. We now sought to determine whether zinc content and superoxide dismutase activity change with age and signs of macular degenerative disease in isolated human RPE. Eyes from 57 donors were graded with respect to disease by the presence or absence of visible drusen and macular pigment changes. RPE was collected from macular and peripheral regions. Tissues from 39 donors were separated into soluble and pigment granule fractions and zinc content determined by flame atomic absorption spectroscopy. RPE from 18 separate donors was used for SOD activity analysis. Total RPE zinc was 9% lower in eyes from donors >70 years of age compared to that from donors <age 70. Soluble macular zinc was 45% less in eyes >age 70 and showed a greater decline in the soluble fraction of macular RPE in eyes with signs of macular disease. Total SOD activity increased significantly (P < .05) with donor age. We conclude that zinc content decreased dramatically in the soluble fraction of macular RPE with age and signs of macular degeneration. Total SOD activity correlated negatively with changes in zinc content. It remains to be determined whether the age-related decline in macular zinc is causal with respect to previously observed decreases in cellular MT and catalase. © 1996 Wiley-Liss, Inc.