[Mechanism of the inhibition of lysosomal functions in the retinal pigment epithelium by lipofuscin retinoid component A2-E].
BACKGROUND
Excessive accumulation of lipofuscin in the retinal pigment epithelium with age and in various hereditary and degenerative retinal diseases, is of pathogenetic significance. We have shown that the major lipofuscin fluorophor A2-E (N-retinylidene-N-retinylethanolamine) affects the lysosomal degradation of human RPE cells and damages the cellular metabolism by phototoxic properties. Herein we sought to determine mechanisms for the inhibitory effect on lysosomal function apart from pH elevation.


METHODS
Potter-Elvejem homogenates of RPE cells were used to measure the activity of 24 lysosomal enzymes before and after incubation with A2-E.


RESULTS
This is the first time that RPE cells have been screened for a large spectrum of lysosomal hydrolases including proteases, lipidases, glycosidases, nucleases, sulfatases and phosphatases. The activities of these hydrolases were readily detectable in cultured RPE cells. Incubation of RPE cell homogenates even with high A2-E concentrations (up to 10 microM) did not affect the activity of isolated lysosomal enzymes.


CONCLUSIONS
The results suggest that a direct inhibition of lysosomal enzyme activity would not explain the inhibitory effect on lysosomal degradation. A2-E increases the acidic intralysosomal pH thereby probably hindering pH-dependent lysosomal enzymatic activities. The understanding of the inhibitory effects of A2-E on RPE cell metabolism may contribute to new approaches for treatment of retinal diseases with excessive lipofuscin accumulation such as ARMD or M. Stargardt.
Schütt
F
F
Universitäts-Augenklinik, Im Neuenheimer Feld 400, 69120 Heidelberg.
Bergmann
M
M
Kopitz
J
J
Holz
F G
FG
D000367:Age Factors; D000368:Aged; D002478:Cells, Cultured; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000378:metabolism; D006868:Hydrolysis; D008062:Lipofuscin / Q000378:metabolism*; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology*; D008268:Macular Degeneration / Q000209:etiology / Q000378:metabolism; D010787:Photosensitivity Disorders / Q000209:etiology; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012164:Retinal Diseases / Q000209:etiology / Q000378:metabolism; D012176:Retinoids / Q000009:adverse effects / Q000494:pharmacology*
D008062:Lipofuscin; D012176:Retinoids; D006867:Hydrolases