An Endothelin Type A Receptor Antagonist Reverses Upregulated VEGF and ICAM-1 Levels in Streptozotocin-Induced Diabetic Rat Retina

Abstract

Diabetic retinopathy, a cause of blindness, is often associated with the upregulation of vascular endothelial growth factor (VEGF) in the retina. Recently, leukocyte adhesion (leukostasis) is claimed for the occlusion of retinal capillary vascularity, which ultimately assists in the progression of diabetic retinopathy. In addition, intercellular adhesion molecule-1 (ICAM-1), a representative factor for leukostasis, is increased in diabetic retina. Endothelin (ET)-1, a potent vasoconstrictor peptide, is closely linked to the pathogenesis of diabetic retinopathy. Different therapeutic interventions concerning VEGF have already been proposed to prevent diabetic retinopathy. However, no study has yet reported concerning the effects of ET-1 receptor antagonist on the upregulated VEGF and ICAM-1 in morphologically intact diabetic retina. The current study investigated the effect of ET(A) receptor antagonist (TA-0201; 1 mg kg(-1) day(-1)) on the expressions of VEGF and ICAM-1 in rat diabetic retina. Diabetes was induced by intraperitoneal injection of streptozotocin (70 mg/kg) in Sprague-Dawley rats, whereas control rats (Cont) received only citrate buffer. After 1 week, the streptozotocin-administered rats were randomly divided into two groups: ET(A) receptor antagonist-treated group (DM+TA-0201) and saline-treated group (DM+vehicle). After the treatment for 4 weeks, the retina was removed from the eyeball. In DM+vehicle group, the VEGF expression of retina was significantly increased (33.5 pg/mg) in comparison with that in the Cont group (25.1 pg/mg), and the upregulation of VEGF was reversed in DM+TA-0201 group (26.9 pg/mg), a phenomenon consistent with the change in VEGF mRNA levels. The expression of retinal ICAM-1 was increased in DM+vehicle group (55.1 pg/mg) compared with Cont group (43.8 pg/mg), and ET antagonism completely blocked this increase (43.8 pg/mg). Moreover, an increased leukostasis by 3.3-fold in DM+vehicle retina was returned to the control level by ET antagonism. In the current study, there was no obvious retinal morphological alteration from both the hematoxylin and eosin staining and the FITC-dextran angiography. Thus, ET(A) receptor antagonist might be useful in preventing the progression of diabetic retinopathy, as evidenced by suppressing the increase in VEGF and ICAM-1 levels as well as leukostasis in morphologically intact diabetic retina.

Pharmacology of Macitentan, an Orally Active Tissue-Targeting Dual Endothelin Receptor Antagonist

“…Prevention of VEGF increase by macitentan in the retina of diabetic rats indicates potential antiedema activity since VEGF increases vascular permeability and is involved in early stage of retinal damage in this model (Cukiernik et al, 2004). Our results are also in line with a previous study in the same animal model, using another dual ET receptor antagonist, SB209670 (Masuzawa et al, 2006). Macitentan, by decreasing VEGF in diabetic rats, might therefore possess particular antiedema and antipermeability properties.…”

“…Urinary ET-1 levels correlate with the severity of nephropathy in diabetic patients (Lee et al, 1994) and glomerular ET-1, not its receptors, is increased in STZ rats (Fukui et al, 1993). Accumulating evidence point to a role for ET-1 in renal cells proliferation and matrix turnover since ET-1 closely interacts with several growth factors such as transforming growth factor-␤ and VEGF (Schrijvers et al, 2004;Masuzawa et al, 2006). Hence, ET-1 transgenic mice with only slightly elevated tissue ET-1 concentrations develop glomerulosclerosis, interstitial fibrosis, renal cysts, and a progressive decline in glomerular filtration rate (Hocher et al, 1997).…”

Endothelin antagonism normalizes VEGF signaling and cardiac function in STZ-induced diabetic rat hearts

“…It should be noted that, at this diabetic stage, there was no morphological abnormality in retina. However, retinal VEGF expression was increased ϳ35%, which was significantly normalized by the blockade of ET receptors (31,32). Although the VEGF expression level in the whole kidney was not significantly upregulated, renal NO levels declined but were reversed by SB-209670 (unpublished observation).…”

Melatonin prevents retinal oxidative stress and vascular changes in diabetic rats

“…For the assays, retina samples were placed in a cold phosphate-buffered saline (diluted ratio 1 : 5; pH 7.2) and homogenized with a mechanic homogenizator as described by Masuzawa et al 10 Aliquots of homogenates were then centrifuged at 10 000 g for 30 min and the supernatants were analyzed for the investigations. Enzyme-linked immunosorbent assay (ELISA) was performed for determinations of retinal VEGF, HIF-1a, PEDF, and nitrotyrosine.…”