Fig. 3.

Lipofuscin-mediated photooxidative damage results in lysosomal membrane permeabilization with cytosolic leakage of lysosomal enzymes. a Intact lysosomes (red) and nuclei (green) were visualized in ARPE-19 cells by means on acridine orange staining. b Lysosomal membrane permeabilization resulted in a loss of lysosomal staining that was quantified by flow cytometry. c Digitonin effect on ARPE-19 cells was titrated for maximum plasma membrane permeabilization (release of cytosolic LDH) and at the same time minimal lysosomal membrane permeabilization (release of lysosomal acid phosphatase, AP). d A digitonin concentration of 20 μg/ml was selected for separation of cytosolic and lysosomal cellular fractions, and cytosolic leakage of lysosomal enzymes was assessed by analyzing the activity of lysosomal marker enzyme acid phosphatase in the cytosolic fractions. Scale bar, 50 μm