Aqueous Humor Cytokines and Total Retinal Blood Flow in Patients with Type 2 Diabetes and Non-Proliferative Diabetic Retinopathy

Abstract

Purpose: Altered retinal blood flow (RBF) is a common feature of diabetic retinopathy (DR), yet the mechanism for this vascular disruption is not well understood. RBF disturbance may be linked to diabetes-induced upregulation of locally produced hemodynamic, angiogenic and inflammatory factors. This study aims to correlate aqueous humor (AH) biomarkers and total RBF (TRBF) in patients with Type 2 diabetes with early non-proliferative DR (NPDR).

Methods: 17 healthy controls and 16 diabetic patients with NPDR scheduled for routine cataract surgery were recruited into the study. AH was collected prior to cataract extraction to measure concentrations of hemodynamic factors (Endothelin-1 (ET-1), Insulin), angiogenic factors (Vascular endothelial growth factor (VEGF), Fibroblast growth factor (FGF-1)) and inflammatory signals (E-selectin, Interleukins-8 (IL-8), Transforming growth factor beta 1 (TGFβ1)). Multiplex immunoassays of the AH samples were analyzed using the BioPlex 200 system (Bio-Rad Laboratories, Inc., Hercules, CA, USA). 4 weeks post-surgery, 6 images were acquired to assess TRBF using the prototype RTVue^TM Doppler FD-OCT (Optovue, Inc., Fremont, CA) and a double circular scan protocol. Forearm blood was also collected to determine glycosylated hemoglobin (A1c).

Results: AH levels of ET-1, IL-8, TGFβ1 were significantly higher (p=0.040, p=0.030 and p<0.001, respectively) and FGF-1 was lower (p= 0.045) in patients with NPDR compared to controls. E-selectin was only detectable in patients with NPDR (mean 18.47 ± 32.78 pg/ml), but was below detection in controls. TRBF was reduced in the NPDR group compared to controls (32.96 ± 8.88 vs. 42.29 ± 7.13 ul/min, p=0.002). AH levels of TGFβ1 and FGF-1 were correlated with TRBF (r=-0.577, p=0.010 and r= 0.394, p=0.034, respectively). Forearm A1c was elevated in the NPDR group compared to controls (7.1 vs. 5.4 %, p<0.001) and was associated with TRBF (r=-0.413, p=0.021). There were no differences in insulin or in VEGF levels between groups (p>0.05).

Conclusions: Our results show that ET-1, IL-8, TGF β1 and E-selectin were increased in the AH of patients with NPDR. Additionally, lower TRBF is associated with higher AH TGFβ1 and lower FGF-1 in patients with and without NPDR. This study identifies a link between AH biomarkers and retinal vascular disorders in diabetes.