Isolated Hyperglycemia Does Not Affect Intraocular Growth Factors In Humans

Abstract

Abstract: : Purpose:Intraocular concentration of Pigment epithelium–derived factor (PEDF) is decreased in proliferative diabetic retinopathy. However, regulation of PEDF in early stages of diabetes is unclear yet. We thus investigated vitreous levels of PEDF and VEGF in diabetes patients without diabetic retinopathy. Methods:We obtained 47 vitreous samples of 47 patients undergoing pars plana vitrectomy due to macular hole, epiretinal gliosis or rhegmatogenous retinal detachment. 40 nondiabetic control patients and 7 patients with type 2 diabetes but without signs of diabetic retinopathy were compared. A polyclonal PEDF–specific antibody was produced by immunisation of rabbits with recombinant PEDF expressed in HEK293 cells. Vitreous levels were determined by Western blot with this ab and additionally with a commercial monoclonal ab (Chemicon, Temecula). VEGF was measured by ELISA (R&D Systems, Minneapolis). Albumin levels were measured by standard techniques. Statistical analysis was performed by Mann–Whitney–U–test or Chi–Square test. All results are provided as mean ± SEM. Results:Diabetes patients had a higher mean fasting glucose and HbA1c as expected (7.5±1.9mmol/L, 7.6±0.9% vs. 5.5±0.7mmol/L (p<0.001), 5.9±0.6% (p<0.001), respectively). None of the diabetes patients had any sign of diabetic retinopathy. PEDF Western blot yielded one specific band at the predicted size of 49 kDa. This band disappeared after preincubation of the first antibody with recombinant PEDF (competition), thus showing specificity of the band. PEDF was found in comparable concentrations as in previous studies. However, there was no significant difference between both groups (3.73±0,22µg/mL in controls vs. 3.50±0.56µg/mL in the diabetic group; p=0.757). We also did not find different levels of VEGF in diabetes patients without diabetic retinopathy. VEGF was detectable in 13 [7.78 pg/mL(median)] controls and in one diabetic patient (5.7 pg/mL, p=0.349) Albumin concentration was 0.29 ± 0.06 mg/mL in controls and not statistically different from the diabetics with (0.24 ± 0.08, p=1.0) mg/mL. Conclusions:We conclude that intraocular concentrations of VEGF and PEDF are not changed in stages of hyperglycemia without existing diabetic retinopathy. Thus, growth factor changes are late in the pathogenesis of diabetic retinopathy and may require additional stimuli such as hypoxia or blood–retina barrier breakdown.

Keywords: diabetic retinopathy • vitreous • growth factors/growth factor receptors