Abstract
Purpose: :
Angiotensin II blockade is being evaluated as a treatment for diabetic retinopathy. We examined whether aldosterone, a down-stream product of angiotensin II and a potent stimulator of fibrovascular pathology, influences retinopathy of prematurity (ROP) and diabetic retinopathy.
Methods: :
Bovine retinal endothelial cells (BRECs) and bovine retinal pericytes (BRPs) were cultured with aldosterone for 2 hours. ROP was induced in Sprague Dawley rats (80%/20% O2 postnatal day (P)0-11, room air P12-18). Shams were in room air. ROP groups were 1) control, 2) mineralocorticoid receptor (MR) antagonist, spironolactone (Sp, 20mg/kg/day, gavage), 3) angiotensin type 1 receptor blockade (AT1-RB, gavage), valsartan (Val, 40mg/kg/day, gavage), 4) 1% NaCl (low salt, drinking water), 5) 1% NaCl+Sp, 6) 1% NaCl+Val, 7) aldosterone (0.75microg/hr, pump), 8) aldosterone-salt, 9) aldosterone-salt+Sp and 10) aldosterone-salt+Val. Treatments were between P12-18 with 7-10 rats/group. Adult rat groups were 1) non-diabetic control, 2) streptozotocin diabetes control, 3) diabetic+MR antagonist, eplerenone (100mg/kg/day, gavage) and 4) diabetic+Val (40mg/kg/day, gavage). Rats were treated for 1 week with 9 rats/group. Blood vessels were quantitated in the inner retina (6 paraffin 3 micron sections, 60 microns apart) and leukostasis in whole retina following in vivo perfusion with ConcanavalinA. Vascular endothelial growth factor (VEGF), monocyte chemoattractant protein-1 (MCP-1) and aldosterone synthase were measured by real-time PCR, and MR by immunohistochemistry.
Results: :
MR immunolabelling was detected in neurons, glia, BRECs and BRPs. In BRECs, aldosterone induced MR translocation, proliferation and tubulogenesis. These findings translated into ROP, where aldosterone-salt was pro-angiogenic and Sp and Val, anti-angiogenic. VEGF mRNA was reduced with Val but not Sp. Leukocytes and MCP-1 are implicated in vascular remodeling in the retina. In ROP, leukostasis and MCP-1 mRNA were increased with aldosterone-salt and reduced with Sp and Val. Similarly, in diabetes, leukostasis was reduced with eplerenone and Val. Aldosterone synthase mRNA was expressed in retina and up-regulated by low salt and hyperglycaemia and down-regulated by AT1-RB and MR antagonism.
Conclusions: :
To our knowledge we make the first report of a functional retinal aldosterone system and identify a previously unrecognised pathogenic role for aldosterone in ROP and diabetic retinopathy. These findings indicate that MR antagonism may be relevant when considering therapies for ischemic retinopathies which target the renin-angiotensin system.
Keywords: neovascularization • inflammation • retinopathy of prematurity