Increased Angiopoietin-1 and -2 levels in human vitreous are associated with proliferative diabetic retinopathy

Background Diabetic retinopathy is a frequent complication of diabetes mellitus and a leading cause of blindness in adults. The objective of this study was to elucidate the diabetic retinopathy pathophysiology in more detail by comparing protein alterations in human vitreous of different diabetic retinopathy stages. Methods Vitreous samples were obtained from 116 patients undergoing pars plana vitrectomy. Quantitative immunoassays were performed of angiogenic factors (VEGF-A, PIGF, Angiopoietin- 1, Angiopoietin-2, Galectin-1) as well as cytokines (IL-1β, IL-8, IFN-γ, TNF-α, CCL3) in samples from control patients (patients who don't suffer from diabetes; n = 58) as well as diabetes mellitus patients without retinopathy (n = 25), non-proliferative diabetic retinopathy (n = 12), and proliferative diabetic retinopathy patients (n = 21). In addition, correlation analysis of protein levels in vitreous samples and fasting glucose values of these patients as well as correlation analyses of protein levels and VEGF-A were performed. Results We detected up-regulated levels of VEGF-A (p = 0.001), PIGF (p<0.001), Angiopoietin-1 (p = 0.005), Angiopoietin-2 (p<0.001), IL-1β (p = 0.012), and IL-8 (p = 0.018) in proliferative diabetic retinopathy samples. Interestingly, we found a strong positive correlation between Angiopoietin-2 and VEGF-A levels as well as a positive correlation between Angiopoietin-1 and VEGF-A. Conclusion This indicated that further angiogenic factors, besides VEGF, but also pro-inflammatory cytokines are involved in disease progression and development of proliferative diabetic retinopathy. In contrast, factors other than angiogenic factors seem to play a crucial role in non- proliferative diabetic retinopathy development. A detailed breakdown of the pathophysiology contributes to future detection and treatment of the disease.