Alleviating effects of α-melanocyte-stimulating hormone on retinal vessel leakage in diabetic rats

Abstract

Background The primary pathogenic basis of diabetic retinopathy (DR) is microangiopathy and inflammatory procedure. Studies showed that α-melanocyte stimulating hormone (α-MSH) can play anti-oxidative stress and anti-apoptosis effects on retina via intravitreal injection and therefore mend blood-retinal barrier (BRB). However, experiment has not yet proved its mechanism. Objective This study was to investigate the protective effects of α-MSH on retinal vessel in diabetic rats. Methods Ninety clean SD rats were assigned to the normal control group, diabetes mellitus (DM) model group and α-MSH group. DM models were established by streptozocin (STZ) injection via tail vein in the rats of the DM model group and the α-MSH group, and sodium citrate buffer was injected in the same way in the normal control group. α-MSH of 3 μl (3.3 μg/μl) was intravitreally injected 1 week and 3 weeks after modeling in the rats of the α-MSH group, and normal saline solution was used in the same way in the normal control group; while no operation was performed in the DM model group. In the fifth week after modeling, Evans blue at the dose of 30 mg/ml (45 mg/kg) was injected via tail vein of rats, and retinal mount was prepared 2 hours later to examine the morphology of retinal vessels under the fluorescent microscope. The blood samples were collected from inner canthus vein for the assessment of leakage amount of Evans blue. The rat retinas were isolated after perfusion of sodium citrate buffer via the left ventricle for the observation of choroidal and retinal vessel ultrastructure by transmission electron microscopy (TEM). The relative expressions of intercellular cell adhesion molecule-1 (ICAM-1) mRNA, tumor necrosis factor-α (TNF-α), occluding mRNA and vascular endothelial growth factor (VEGF) mRNA were detected by quantitative real-time PCR. Results The body weight was lighter and the water intake was higher in the DM rats than those in the normal control rats. The blood glucose levels in the DM model group were (29.69±4.77) mmol/L at the third day and (24.64±2.72) mmol/L in the fifth week following the injection of STZ, respectively. An amount of Evans blue leaked from vessels in the rat retina of DM model group, but the retinal vessels were intact in the rats of the α-MSH group and the normal control group. The leakage amount was (10.04±8.18)μl/(g·h) in the DM model group, which was significantly more than that of (2.62±3.73)μl/(g·h) in the α-MSH group and (3.10±1.13)μl/(g·h) in the normal control group at the fifth week after modeling (P=0.035, 0.041). The ultrastructure of choriodal and retinal vessels was almost normal in the α-MSH group and the normal control group, but the swelling of choriodal vascular endothelial cells and vacuolar-like changes of the retinal pigment epithelium (RPE) were found in the DM model group. In addition, the relative expression levels of ICAM-1 mRNA and TNF-α mRNA were significantly elevated, but those of occludin mRNA were significantly declined in the DM model group compared with the α-MSH group and the normal control group (all at P<0.05). No significant difference was found in the relative expression level of VEGF mRNA among the three groups (F=0.791, P=0.466). Conclusions α-MSH ameliorates retinal vascular leakage in STZ-induced diabetic rats after intravitreal injection by improving ultrastructure of choroid and retinal vessels, down-regulating the expression of proinflammatory factors and up-regulating tight junction component in retina. Key words: α-Melanocyte-stimulating hormone; Diabetic retinopathy/therapy; Intercellular adhesion molecule-1; Tumor necrosis factor-α; Occludin; Vascular endothelial growth factor; Blood-retina barrier; Rats, Sprague Dawley