The Dipeptide Arg–Gln Inhibits Retinal Neovascularization in the Mouse Model of Oxygen Induced Retinopathy (OIR)

Abstract

Abstract: : Purpose: Vascular endothelial growth factor (VEGF) plays an important role in retinopathy of prematurity (ROP). Amino acid deprivation increases VEGF expression and glutamine has been shown to reverse this increase in VEGF. Very low birthweight infants (VLBW) are deprived of the usual quantity of glutamine they would be receiving from their mothers had they remained in utero. A multicenter trial of enteral replacement of glutamine suggested decreased intraventricular hemorrhage and periventricular leukomalacia, two problems often associated with ROP(1). VLBW infants with necrotizing enterocolitis (NEC) have low plasma arginine and a trial of arginine replacement has been shown to decrease NEC. Arginine replacement stimulates immune function, nitric oxide generation, and growth hormone production in these infants. Critically ill infants have demonstrated efficacy and safety of both amino acid supplements separately and in this study we asked whether the dipeptide containing both glutamine and arginine, arginyl–glutamine, could inhibit retinal neovascularization in the mouse model of OIR that mimics ROP. Methods: 7–day old pups and their mothers were exposed to 75% oxygen for 5 days. After hyperoxia the animals received twice–daily injections intraperitoneally of either the dipeptide (Arg–Gln, n=18) or the control peptide (Ala–Gly n=18) or were uninjected (n=18). At day 17, the animals were perfused with fluorescein–dextran and killed. Wholemounts of the retinas from one set of eyes were prepared and examined, and the retinas of the contralateral eyes were embedded, sectioned and stained for counting neovascular nuclei extending beyond the internal limiting membrane into the vitreous. Results: Angiography of retinal whole mounts showed reduction of neovascular tufts in animals treated with Arg–Gln compared to Ala–Gly or control animals. Quantification of the extra retinal neovascular nuclei showed that treatment with Arg–Gln resulted in an 83% reduction in retinal neovascularization (p= 0.0018). Ala–Gly had no effect on neovascularization (p=0.44). Conclusions:The dipeptide Arg–Gln inhibited retinal neovascularization in the OIR model. Both glutamine and arginine have beneficial effects in VLBW infants; the dipeptide of these two amino acids is safe and may be beneficial in the prevention of ROP. 1. Vaughn P, Thomas P, Clark R, Neu J. Enteral glutamine supplementation and morbidity in low birth weight infants. J Pediatr 2003;142(6):662–8.

Keywords: retinal neovascularization • retinopathy of prematurity • vascular cells