Degeneration of Retinal Pigment Epithelium Induced by Intravitreous Administration of Spermidine in Rats

Abstract

Purpose: : The degeneration of retinal pigment epithelial (RPE) cells is a crucial event in dry age-related macular degeneration (dry AMD) and gyrate atrophy (GA). Spermidine, a metabolite of ornithine, is shown to inhibit the growth of RPE cells in vitro. The purposes of this study were to elucidate the mechanism underlying spermidine-induced RPE cell death in vitro and to investigate the effect of spermidine on the morphology, electroretinogram (ERG) and barrier function of rat retina in vivo.

Methods: : Cultured ARPE-19 cells were treated with spermidine (250 µM) in the presence or absence of N-acetylcysteine (NAC), an antioxidant or aldehyde dehydrogenase (ALDH), a metabolic enzyme for acrolein. Cell viability was assessed by MTS assay 24 hours after the treatment. In in vivo study, spermidine (10, 20 and 30 nmol/eye) was administrated intravitreously into adult Brown Norway rats. The scotopic ERG was measured 2 and 6 days after administration. The permeability of the blood-retinal barrier (BRB) was measured by vitreous fluorophotometry, and then eyes were enucleated, and subjected to histological examinations 1, 3 and 7 days after administration.

Results: : Both NAC and ALDH significantly inhibited the spermidine-induced cell death of ARPE-19. Morphologically, the intravitreous injection of spermidine induced vacuolization, atrophy and reduction of RPE cells of rats, and then caused the disruption of photoreceptor outer segments in a time and dose-dependent manner. In contrast, spermidine did not affect the structure of the inner retina. Regarding the function of retina, spermidine significantly decreased the amplitude of ERG a- and b-waves at day 6, and prominently increased the permeability of outer BRB at day 7.

Keywords: retinal pigment epithelium • retinal degenerations: cell biology • oxidation/oxidative or free radical damage