Corticosteroids inhibit VEGF-induced vascular leakage in a rabbit model of blood–retinal and blood–aqueous barrier breakdown

• Published in: Experimental eye research Vol. 80; no. 2; pp. 249 - 258
• Main Authors: Edelman, Jeffrey L., Lutz, David, Castro, Marisol R.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-02-2005
• Subjects: Animals; Anti-Inflammatory Agents - therapeutic use; Blood-Aqueous Barrier - drug effects; Blood-Retinal Barrier - drug effects; blood–aqueous barrier; blood–retinal barrier; Calcium - metabolism; corticosteroid; dexamethasone; Dexamethasone - therapeutic use; Dose-Response Relationship, Drug; Endothelium, Vascular - drug effects; Endothelium, Vascular - metabolism; Female; Fluorescein Angiography; fluorophotometry; Fundus Oculi; Glucocorticoids - therapeutic use; indomethacin; intravitreal; Macular Edema - chemically induced; Macular Edema - physiopathology; Macular Edema - prevention & control; rabbit; Rabbits; Recombinant Proteins - pharmacology; Tomography, Optical Coherence; triamcinolone acetonide; Triamcinolone Acetonide - therapeutic use; vascular endothelial growth factor; Vascular Endothelial Growth Factor A - antagonists & inhibitors; Vascular Endothelial Growth Factor A - pharmacology; dexamethasone; fluorophotometry; triamcinolone acetonide; vascular endothelial growth factor; rabbit; corticosteroid; blood–aqueous barrier; intravitreal; blood–retinal barrier; indomethacin
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2004.09.013

Recent clinical studies show that a single intravitreal injection of the corticosteroid triamcinolone acetonide (TAA) may reduce edematous retinal swelling and improve visual acuity in patients with diabetic macular edema (DME). In addition, clinical and experimental studies strongly suggest that blood–retinal barrier breakdown in diabetes is induced by vascular endothelial growth factor (VEGF). These results suggest that corticosteroids may modulate VEGF-mediated responses
in vivo. To test this hypothesis directly, the current study evaluated the effects of TAA and dexamethasone (DEX) in a newly developed rabbit model of VEGF-induced blood–retinal barrier and blood–aqueous (iris) barrier breakdown.
VEGF
165 or vehicle was injected intravitreally in female Dutch Belt rabbits, and scanning ocular fluorophotometry was used to non-invasively measure fluorescein leakage from retinal and iris vasculature. VEGF-induced retinal vasculopathy was further assessed with fundus imaging, fluorescein angiography, and ocular coherence tomography. For pharmacologic studies, rabbits were treated with either DEX (2
mg
kg
−1 daily, s.c.), TAA (2 or 4
mg, intravitreal), indomethacin (20
mg
kg
−1 daily, s.c.), or vehicle (s.c. or intravitreal). Human umbilical vein endothelial cells (HUVEC) were loaded with the fluorescent Ca
2+ indicator dye fluo-4 and treated with dexamethasone (0·1–10
μ
m) or vehicle for either 2 or 24
hr prior to stimulation with 10
ng
ml
−1 VEGF
165.
VEGF injected intravitreally induced a time and dose-dependent breakdown of the blood–retinal and blood–aqueous barriers. Maximal vascular leakage was measured at 48
hr after intravitreal injection with a dose of 500
ng VEGF. Other effects of VEGF included prominent retinal vasodilation, vessel tortuousity, fluorescein leakage from retinal vessels, and inner retinal edema. These VEGF-mediated responses are transient and approach baseline by 1 week. VEGF-induced blood–retinal and blood–aqueous barrier breakdown was completely blocked by the corticosteroid DEX administered systemically for 3 days. In contrast, the non-steroidal anti-inflammatory drug, indomethacin, had no effect. In a separate study with VEGF injected intravitreally at six different time points over 5 months, a single intravitreal 2
mg dose of TAA completely blocked VEGF-induced retinal and iris leakage for 45 days. VEGF/VEGF receptor-2-mediated Ca
2+ mobilization in endothelial cells was not affected by 2 or 24
hr pretreatment with dexamethasone.
These results indicate that one mechanism by which corticosteroids block blood–ocular barrier breakdown and edema is via their modulation of signaling or effector proteins downstream of the VEGF receptor.