Abstract
Purpose:
We have previously reported that metformin, an anti-diabetic drug, has anti-angiogenic and anti-inflammatory effects directly on human retinal vascular endothelial cells (hRVECs). This study investigates if metformin also protects retinal vascular permeability from inflammatory insult induced by tumor necrosis factor-α (TNFα) in vitro and in vivo.
Methods:
Primary hRVECs were grown in transwell to form monolayer and then challenged with TNFα with or without metformin treatment. Transwell permeability to FITC-dextran was assayed. The integrity of endothelial cell adhesion was determined by immunofluorescent staining of VE-cadherin and occludin. C57BL/6 mice with 50 ng intravitreal TNFα injection were treated with daily oral metformin or BSS vehicle 3 days before TNFα challenge for 10 days. Retinal vascular permeability was examined by quantifying albumin extravasation into the retinal parenchyma.
Results:
TNFα at 2.5 and 5.0 ng/ml induced a dose-dependent increase of hRVEC monolayer permeability to FITC-dextran. Metformin 5 mM pretreatment completely blocked 2.5 ng/ml TNFα effect and significantly attenuate 5.0 ng/ml TNFα effect (p < 0.05). Immunofluorescent staining of VE-cadherin and occludin revealed that metformin pretreatment dose-dependently prevented TNFα-induced disruptions of hRVEC monolayer integrity. In vivo study showed that TNFα intravitreal injection led to a 3-fold remarkable increase of retinal albumin level, indicating a severe breakdown of blood-retinal barrier. In contrast, metformin treated animals had a normal retinal albumin level in the BSS injected control group (n = 5, p < 0.05).
Conclusions:
These in vitro and in vivo results demonstrate that metformin protects the integrity of the retinal vascular endothelial cell barrier function from TNFα-induced inflammatory insult. It indicates that metformin may provide additional benefit to control retinal vascular hyperpermeability in the conditions such as diabetic retinopathy and other inflammatory retinal diseases.