title: Enzymatic digestion increases permeability of the outer blood-retinal barrier for high-molecular-weight substances.
abstract: BACKGROUND
  The purpose of the study was to investigate whether lysosomal enzymes can participate in damaging the outer blood-retinal barrier and to examine the role of glycosaminoglycans in maintaining the barrier function for high-molecular-weight substances.
  
  
  METHODS
  The ciliary artery was cannulated in freshly enucleated pig eyes. Perfusion was performed with buffer (controls), with heparinase (substrate: heparan sulfate), or with lysosomal enzymes freshly prepared from pig retinal pigment epithelium at 36 degrees C, followed by perfusion with the tracer native ferritin (NF) or the marker cationized ferritin (CF). The eyes were examined by electron microscopy.
  
  
  RESULTS
  In controls treated with buffer alone, NF was found in high concentration in the lumina of the choroidal capillaries; however, little NF was found in Bruch's membrane (BsM). The tracer did not penetrate to any extent beyond BsM. In eyes digested with heparinase or lysosomal enzymes, significantly higher numbers of tracer molecules were found in BsM. Furthermore, NF penetrated BsM and was apparent in the subretinal space and also inside retinal pigment epithelial cells, probably due to pinocytosis.
  
  
  CONCLUSIONS
  The results indicate that heparan sulfate proteoglycan is important for the maintenance of the outer blood-retinal barrier and that lysosomal proteases may participate in damaging this barrier, causing increased permeability to high-molecular-weight substances.
authors.affiliation: University Eye Clinic, Basel, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Prünte
authors.forename: H L
authors.initials: HL
authors.lastname: Kain
mesh_terms: D000818:Animals; D001813:Blood-Retinal Barrier / Q000187:drug effects*; D016570:Bruch Membrane / Q000378:metabolism / Q000648:ultrastructure; D002196:Capillaries / Q000378:metabolism / Q000648:ultrastructure; D002199:Capillary Permeability / Q000187:drug effects*; D002829:Choroid / Q000098:blood supply; D002924:Ciliary Body / Q000098:blood supply; D005293:Ferritins / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000494:pharmacology*; D019763:Heparin Lyase; D006497:Heparan Sulfate / Q000502:physiology; D011133:Polysaccharide-Lyases / Q000494:pharmacology*; D012160:Retina / Q000378:metabolism / Q000648:ultrastructure; D013552:Swine
chemical_list: D005293:Ferritins; D006026:Glycoside Hydrolases; D019763:Heparin Lyase; D006497:Heparan Sulfate; D011133:Polysaccharide-Lyases; C010297:polycationic ferritin