Intravitreal Concentration of Pigment-Epithelium Derived Growth Factor (PEDF) in Eyes with Proliferative Diabetic Retinopathy

Abstract

Abstract: : Purpose: To investigate the relation between intravitreal concentrations of PEDF and the type of diabetes present in the patient with proliferative diabetic retinopathy. Methods: Vitreous samples were collected from 30 diabetic patients undergoing vitreous surgery for proliferative diabetic retinopathy. PEDF levels were estimated by sandwich ELISA using a biotin conjugated antibody and HRP conjugated avidin for detection. Rabbit α-PEDF was coated on 96 well Immulon flat bottom microtiter plate in 0.1 M NaHCO₃ overnight at 4°C. The wells were blocked with 10% fetal bovine serum in PBS pH 7.4 for 2 hours at 37°C. PEDF protein standards and vitreous samples were loaded as 100 µl aliquots into wells and the plate was kept overnight at 4°C. Detection consisted of a secondary mouse polyclonal α-PEDF followed by a biotin conjugated rat α-mouse IgG and HRP conjugated avidin. Each step of detection was conducted with plate agitation at room temperature for 1-2 hours and the plate was washed 5 times between steps. TMB peroxidase substrate system was pipetted into all wells and allowed to reach fully developed color, before terminating the reaction with 1 M H₃PO₄. The plates were read in an automated microplate reader at 450 nm. Results: The mean PEDF value in the vitreous for eyes with type1 diabetes was 3.7 ng/well, while that of the eyes with type2 diabetes was 7.9 ng/well. The mean age and sex distribution for both diabetic groups were comparable (P>0.05). The visual acuity change after vitrectomy was not statistically different for the two groups (P>0.05). However the PEDF levels for Type1 diabetic eyes were significantly higher as compared to the eyes with Type2 diabetes (P<0.05). Conclusions: PEDF levels were higher in vitreous of patients having Type2 diabetes (potential for less severe diabetic retinopathy) than patients with Type1 diabetes. Estimation of PEDF levels in the vitreous could be of prognostic and therapautic significance due to its anti-angiogenic protective value in patients with diabetic retinopathy.

Keywords: diabetic retinopathy • vitreous • retina