Lysosomal enzyme cytochemistry of human RPE, Bruch's membrane and drusen

Abstract

Twenty-five human eyes of various ages from eye bank donors and surgical enucleations were obtained for ultrastructural cytochemical demonstration of acid phosphatase (AcPase) and arylsulfatase B (ASB) in the retinal pigment epithelium (RPE) and Bruch's membrane. Results with post-mortem (less than 10 hr) tissues were comparable to those of fresh specimens. Vigorous reactivity was demonstrated in lysosomes of RPE and choriocapillary endothelium but no reactive sites were found in Bruch's membrane, although many lysosome-like dense bodies occurred in eyes greater than 20 yr of age. Granular drusen of 30-70-yr-olds contained no reactive bodies. In eyes greater than 80 years old blebs of RPE basal cytoplasm protruding into Bruch's membrane contained reactive lysosomes. We conclude that the RPE ordinarily does not extrude or exocytose active lysosomes (ie, phagolysosomes, other secondary lysosomes, residual bodies, lipofuscin) or lysosomal enzymes. Aged RPE, however, extrudes cytoplasm with active lysosomes into Bruch's membrane. The possible impact of this process on the extracellular connective tissue is discussed, particularly with regard to age-related deterioration of Bruch's membrane and neovascularization.