Nonsteroidal anti-inflammatory drugs prevent early diabetic retinopathy via TNF-alpha suppression

Leukocyte adhesion to the diabetic retinal vasculature results in blood-retinal barrier breakdown, capillary nonperfusion, and endothelial cell injury and death. Intercellular adhesion molecule-1 (ICAM-1) and the leukocyte integrin CD18 are required for these processes. Diabetes was induced in Long Evans rats, resulting in a two- to threefold increase in retinal leukocyte adhesion. Following one week of diabetes, neutrophil CD11a, CD11b, and CD18 expression was increased significantly, as were retinal ICAM-1 levels. Animals were treated with aspirin, a cyclooxygenase 2 (COX-2) inhibitor (meloxicam), or a soluble tumor necrosis factor alpha (TNF-alpha) receptor/Fc construct (TNFR-Fc, etanercept). High-dose aspirin, etanercept, and high-dose meloxicam each reduced leukocyte adhesion and suppressed blood-retinal barrier breakdown. High-dose aspirin also reduced the expression of CD11a, CD11b, and CD18, whereas meloxicam and etanercept did not. High-dose aspirin, etanercept, and high-dose meloxicam each reduced retinal ICAM-1 expression. Aspirin and meloxicam both lowered retinal TNF-alpha levels. Notably, aspirin, meloxicam, and etanercept did not change retinal vascular endothelial growth factor levels. High-dose aspirin, etanercept and high-dose meloxicam, each suppressed the retinal expression of eNOS and the DNA-binding capacity of retinal nuclear factor-kappaB. High-dose aspirin also suppressed Erk kinase activity, which is involved in CD18 up-regulation. Taken together, these data identify COX-2 and TNF-alpha as operative in the early signature pathologies of diabetic retinopathy, a newly recognized inflammatory disease.