title: Kinetic studies on phagocytosis and lysosomal digestion of rod outer segments by human retinal pigment epithelial cells in vitro.
abstract: Using novel methodology, this study describes the kinetics of rod outer segment (ROS) phagocytosis and digestion by human retinal pigment epithelial (RPE) cells in vitro and examines the effect of certain lysosomal enzyme inhibitors on ROS digestion in these cells. Human RPE cells displayed saturation of phagocytosis with respect to both ROS concentration and time. While surface-binding and ingestion phases of ROS phagocytosis saturated after 24-36 h, the rate of ROS digestion reached a maximal level within 24 h. Increasing the concentration of zinc in the culture medium from 1.9 to 100 microM had no significant effect on ROS digestion. The effects of swainsonine (an alpha-mannosidase inhibitor), pepstatin (an aspartic protease inhibitor), and leupeptin (a cysteine protease inhibitor) were also examined. At 6 h, ROS digestion was reduced 27.3 +/- 15.3% by swainsonine, 69.4 +/- 20.9% by pepstatin, and 77.0 +/- 14.4% by leupeptin. The effect of these inhibitors declined with increasing time. This study is the first to demonstrate the functional importance of cysteine and aspartic proteases in the digestion of ROS by RPE cells in vitro.
authors.affiliation: Department of Surgery, University of Western Australia, Nedlands.
authors.forename: C J
authors.initials: CJ
authors.lastname: Kennedy
authors.forename: P E
authors.initials: PE
authors.lastname: Rakoczy
authors.forename: T A
authors.initials: TA
authors.lastname: Robertson
authors.forename: J M
authors.initials: JM
authors.lastname: Papadimitriou
authors.forename: I J
authors.initials: IJ
authors.lastname: Constable
mesh_terms: D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D007976:Leupeptins / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D008361:Mannosidases / Q000037:antagonists & inhibitors; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D010436:Pepstatins / Q000494:pharmacology; D010587:Phagocytosis; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D017026:Swainsonine / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology; D043323:alpha-Mannosidase
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D010436:Pepstatins; C014195:Streptomyces pepsin inhibitor; D008361:Mannosidases; D043323:alpha-Mannosidase; D016282:Aspartic Acid Endopeptidases; D015032:Zinc; C032854:leupeptin; D017026:Swainsonine; C031375:pepstatin