Suppression of <i>N</i>-Methyl-<i>N</i>-Nitrosourea-Induced Retinal Damage in Mice by Oligonol, an Oligomerized Polyphenol Formulation

Oligonol is a lychee fruit-derived functional food that contains oligomerized polyphenol compounds.Oligonol exhibits a number of beneficial biological effects, primarily due to its antioxidant activity.Retinitis pigmentosa (RP) is an inherited chronic degenerative disease affecting retinal photoreceptor cells.There is currently no effective therapy capable of stopping or reversing the progression of the disease.In RP, apoptosis of photoreceptor cells resulting from oxidative damage is considered to be the final common pathway.In this report, we present an evaluation of the suppressive activity of Oligonol against N-methyl-N-nitrosourea (MNU)-induced retinal damage in mice, which is a commonly used animal model of RP.Both intraperitoneal and oral administration of Oligonol reduced the loss of photoreceptor cells 7 days after MNU injection, as evaluated by histological staining.Photoreceptor cells derived from MNU-treated mice exhibited increased TUNELpositive staining, suggesting increased DNA fragmentation, a hallmark of apoptosis.Oligonol treatment reduced the number of TUNEL-positive cells.Additionally, Oligonol suppressed MNUinduced retinal production of 8-hydroxydeoxyguanosine (8-OHdG), a marker of oxidative stress.Moreover, Oligonol attenuated the MNU-induced decrease in the visual activity of mice, as evaluated by the visual cliff test.Oligonol, therefore, effectively suppresses NMU-induced retinal degeneration.