The hyperglycemia-induced early retinal pigment epithelium dysfunction is mediated by vascular endothelial growth factor

Abstract

 

Purpose

 

Diabetes-associated vision loss is often attributed to the accumulation of fluid within the layers of the neurosensory retina. Numerous studies focused on vascular endothelial growth factor (VEGF)-induced retinal vessel leakage as the principal source of this fluid. However, we have recently shown that VEGF also impairs fluid removal by the retinal pigment epithelium (RPE). Here, we investigated whether VEGF is critical to RPE fluid resorption in a hyperglycemic rat model.

 

Methods

 

Hyperglycemia was induced in Brown-Norway rats by streptozotocin (STZ, 65 mg/kg intravitreally in citrate buffer). Optical coherence tomography and angiography was performed at STZ treatment and 1, 4, and 9 weeks post-injection. The resorption of subretinal saline blebs (1 μL) was monitored for 30 min and the rate was determined from the change of bleb volume. At 4 weeks post STZ, selected animals (hyperglycemics and controls) received 1 mL of 25 μg intravitreal Avastin or vehicle (saline). Data were collected for > 4 animals in each group.

 

Results

 

At 4 weeks post-STZ injection, RPE fluid resorption was 5.6±1.2 (µL/cm²*h) compared to 6.5±1.5 (µL/cm²*h) in control animals. But by 9 weeks, hyperglycemic animals exhibited a significant reduction in resorption (2.4±0.6 µL/cm²*h vs. 7.6±0.4 µL/cm²*h in controls; p < 0.05). One injection of intravitreal Avastin significantly increased resorption (4.6±0.3 µL/cm2*h; p < 0.05) when compared to vehicle-treated hyperglycemic rats (8.9±1.2 µL/cm2*h). Avastin treatment in non-glycemic rats (6.8±1.1 µlL/cm2*h) did not significantly alter RPE fluid resorption compared to sham-injected or vehicle-injected animals.

 

Conclusions

 

Our studies demonstrate that RPE fluid resorption from the retina declines rapidly (to 39% of normal in 9 weeks) in hyperglycemia. These changes are observed before cataracts or vascular complications develop. The reduction in fluid resorption is associated with the release of VEGF, as Avastin partially restored (to 61% of normal) the function of the tissue. These experiments establish the RPE as a key player in the pathogenesis of macular edema, and indicate the utility of tissue specific treatments to prevent the accumulation of retinal fluid in diabetes.  

 

Fluid resorption in hyperglycemic Brown Norway rats vs. controls at 9 weeks post STZ injection. Selected animals received a 1× dose of 25 μg intravitreal (1 μL) Avastin at week 4.