Assessment of Neurotrophins and Inflammatory Mediators in Vitreous of Patients With Diabetic Retinopathy

PURPOSE. To assess vitreous levels of inflammatory cytokines and neurotrophins (NTs) in diabetic retinopathy (DR) and elucidate their potential roles. METHODS. A prospective study was performed on 50 vitreous samples obtained from patients with DR (n = 22) and the nondiabetic controls (n = 28). All patients were candidates for vitrectomy. Inflammatory cytokine and NT levels were determined with ELISA. Potential source and role of NTs was determined by using human retinal Muller glia and mouse photoreceptor cells and challenging them with TNF-alpha or IL-1 beta, followed by detection of NTs and cell death. RESULTS. Vitreous NT levels of all DR patients were significantly higher than those of nondiabetic controls (nerve growth factor [NGF, P = 0.0001], brain-derived neurotrophic factor [BDNF, P = 0.009], neurotrophin-3 [NT-3, P < 0.0001], neurotrophin-4 [NT-4, P = 0.0001], ciliary neurotrophic factor [CNTF, P = 0.0001], and glial cell-derived neurotrophic factor [GDNF, P = 0.008]). Similarly, the levels of inflammatory mediators IL-1 beta (P < 0.0001), IL-6 (P = 0.0005), IL-8 (P < 0.0001), and TNF-alpha (P < 0.0001) were also higher in eyes with DR. Interestingly, inflammatory cytokine and NT levels, particularly TNF-alpha (P < 0.05), IL-8 (P < 0.004), NT-3 (P = 0.012), NGF (P = 0.04), GDNF (P = 0.005), and CNTF (P = 0.002), were higher in eyes with nonproliferative diabetic retinopathy (NPDR) than in eyes with active proliferative diabetic retinopathy (PDR). Cytokine stimulation of Muller glia resulted in production of NTs, and GDNF treatment reduced photoreceptor cell death in response to inflammation and oxidative stress. CONCLUSIONS. Together, our study demonstrated that patients with DR have higher levels of both inflammatory cytokines and NTs in their vitreous. Muller glia could be the potential source of NTs under inflammatory conditions to exert neuroprotection.