Abstract
Nearly all patients with type 1 diabetes and 60% of those with type 2 diabetes develop diabetic retinopathy (DR). Thus, there is an urgent need to identify new therapeutic targets to prevent or at least to minimize microvascular dysfunction associated with DR. Activation of the renin-angiotensin system (RAS) contributes to breakdown of blood-retinal barrier (BRB) and neovascularization in DR. Clinical studies underscored RAS as a promising therapeutic target to treat DR. Although, blockade of RAS has reduced the incidence of DR in clinical studies, it did not reduce the progression of DR. Cytochrome-P450 metabolizes arachidonic acid to the pro-angiogenic and -permeability mediators, epoxyeicosatrienoic acids (EETs) which are metabolized by the soluble epoxide hydrolase (sEH) to inactive products. Our experiments demonstrated that:
1.) Angiotensin II (Ang II) increases retinal expression of sEH by 2.8 fold (2.84 ± 1.1 vs. 1 ± 0.08, P < 0.05, n = 4), which is blunted by angiotensin receptor-1 (AT1) inhibition;
2.) both sEH blockade and knockout (KO), which accumulate EETs, enhance Ang II-induced BRB injury as shown by 1.58 fold increase in retinal albumin leakage (1.58 ± 0.4 vs. 1 ± 0.13, P < 0.05, n = 4) and 2.8 fold (2.8 ± 1.7 vs. 1 ± 0.09, P < 0.05, n = 4), respectively. These results were confirmed by fluorescein angiogram analysis;
3.) Administration of synthetic 11,12-EET enhances intravitreal Ang II-induced retinal albumin leakage by 2.2 fold (2.2 ± 0.5 vs. 1 ± 0.18, P < 0.05, n = 4); and
4.) sEH KO potentiates diabetes (STZ)-induced retinal damage. This was associated with upregulation of retinal vascular endothelial growth factor (VEGF) and glucose transporter-1 (GLUT-1).
In conclusion, our data demonstrate that in DR, activation of retinal AT1 triggers a compensatory mechanism by increasing retinal sEH that decreases EETs production. Thus, the use of combined EETs blockade with AT1 blocker holds the promise, as a new therapeutic strategy to prevent or reduce DR.
Disclosure
M. Al-Shabrawey: None. A. Ibrahim: None. A.M. Tawfik: None. M.H. Wang: None.
Funding
American Heart Association (SE00144); National Institutes of Health (R01EY023315 to M.A-S.)