Mapping the blood vessels with paracellular permeability in the retinas of diabetic rats.
OBJECTIVE
Diabetic retinopathy increases the permeability of the blood-retinal barrier, but the specific vessels that become permeable have not been identified. Both transcellular and paracellular pathways of vascular solute flux have been proposed. This study was conducted to test the hypothesis that paracellular flux contributes to increased retinal vascular permeability after VEGF treatment or diabetes, and to map the types of vessels that became permeable.


METHODS
Regions of paracellular flux were identified by perfusion with fluorescent concanavalin A (ConA). Rats were injected intravitreally with VEGF or made diabetic with streptozotocin (STZ). After specified times, the rats were perfused with fixative followed by ConA, which binds to the basement membrane but not the luminal surface of endothelial cells. With this approach, ConA labels only blood vessels with paracellular permeability. Retinas were also labeled by immunofluorescence for the tight junction proteins occludin and claudin-5 and examined by confocal microscopy.


RESULTS
ConA labeling increased in the superficial arterioles and postcapillary venules, 2 weeks after the onset of diabetes. After 1 month, ConA labeling dramatically increased and extended to the capillaries of the outer plexiform layer. There was an inverse relationship between occludin immunoreactivity and ConA binding, but no change in claudin-5 immunoreactivity was detected. Injection of VEGF gave similar results.


CONCLUSIONS
Diabetes and VEGF increase paracellular vascular permeability in the retina, associated with redistribution of occludin. This permeability begins in the superficial arterioles and postcapillary venules and progresses to the capillary bed.
Barber
Alistair J
AJ
Department of Ophthalmology, The Penn State Retina Research Group, The Ulerich Ophthalmology Research Center, Penn State College of Medicine, Hershey, PA 17033, USA.
Antonetti
David A
DA
D000818:Animals; D001813:Blood-Retinal Barrier / Q000502:physiology*; D002199:Capillary Permeability / Q000502:physiology*; D062507:Claudin-5; D003208:Concanavalin A / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism / Q000503:physiopathology*; D003930:Diabetic Retinopathy / Q000378:metabolism / Q000503:physiopathology*; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000378:metabolism; D007150:Immunohistochemistry; D007267:Injections; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D062793:Occludin; D051381:Rats; D017207:Rats, Sprague-Dawley; D012171:Retinal Vessels / Q000378:metabolism / Q000503:physiopathology*; D042461:Vascular Endothelial Growth Factor A / Q000008:administration & dosage; D014822:Vitreous Body
D062507:Claudin-5; C491510:Cldn5 protein, rat; D008565:Membrane Proteins; D062793:Occludin; C568987:Ocln protein, rat; D042461:Vascular Endothelial Growth Factor A; C042784:fluorescein isothiocyanate-concanavalin A; D003208:Concanavalin A; D016650:Fluorescein-5-isothiocyanate