Diosmin protects rat retina from ischemia/reperfusion injury

Abstract

Objective: Diosmin, a natural flavone glycoside, possesses antioxidant activity and has been used to alleviate ischemia/reperfusion (I/R) injury. The aim of this study was to clarify whether the administration of diosmin has a protective effect against I/R injury induced using the high intraocular pressure (IOP) model in rat retina, and to determine the possible antioxidant mechanisms involved.

Methods: Retinal I/R injury was induced in the rats by elevating the IOP to 110 mmHg for 60 min. Diosmin (100 mg/kg) or vehicle solution was administered intragastrically 30 min before the onset of ischemia and then daily after I/R injury until the animals were sacrificed. The levels of malondialdehyde (MDA) and the activities of total-superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in the retinal tissues were determined 24 h after I/R injury. At 7 days post-I/R injury, electroretinograms (ERGs) were recorded, and the density of surviving retinal ganglion cells (RGCs) was estimated by counting retrograde tracer-labeled cells in whole-mounted retinas. Retinal histological changes were also examined and quantified using light microscopy.

Results: Diosmin significantly decreased the MDA levels and increased the activities of T-SOD, GSH-Px, and CAT in the retina of rats compared with the ischemia group (P<0.05), and suppressed the I/R-induced reduction in the a- and b-wave amplitudes of the ERG (P<0.05). The thickness of the entire retina, inner nuclear layer, inner plexiform layer, and outer retinal layer and the number of cells in the ganglion cell layer were significantly less after I/R injury (P<0.05), and diosmin remarkably ameliorated these changes on retinal morphology. Diosmin also attenuated the I/R-induced loss of RGCs of the rat retina (P<0.05).

Conclusion: Diosmin protected the retina from I/R injury, possibly via a mechanism involving the regulation of oxidative parameters.

FIG. 1.

Changes in the level of MDA and the activities of T-SOD, GSH-Px, and CAT in the retina 24 h after I/R (n=8). The level of MDA in the MV group was significantly higher than that in both SV and SD groups (P<0.05); the level of MDA in the MD group was significantly lower than that in the MV group (P<0.05) (A). The activities of T-SOD, GSH-Px, and CAT in the MV group were significantly lower than those in both SV and SD groups (P<0.05); the activities in the MD group was significantly higher than those in the MV group (P<0.05) (B–D). *P<0.05. I/R, ischemia/reperfusion; MDA, malondialdehyde; T-SOD, total-superoxide dismutase; GSH-Px, glutathione peroxidase; CAT, catalase; SV, sham+vehicle; MV, model+vehicle; MD, model+diosmin; SD, sham+diosmin.

FIG. 2.

Representative photographs of retrogradely labeled retinas in the 4 groups (A). The density of surviving RGCs in the MV group was significantly lower than that in both SV and SD groups (P<0.05) (n=6) (B); the density of surviving RGCs in the MD group was significantly higher than that in the MV group (P<0.05) (n=6) (B). *P<0.05. RGCs, retinal ganglion cells.

FIG. 3.

Representative photographs of ERG records in the 4 groups (A). The responses to a light flash (2.5 cds/m²) from a photic stimulator were amplified, and the pre-amplifier bandwidth was set at 0.3–300 Hz. The ERG was recorded 7 days after I/R injury, and the a- and b-wave amplitudes were measured. Data are expressed as the mean±standard deviation (n=6) (B). *P<0.05. ERG, electroretinogram.

FIG. 4.

Representative photographs of the rat retinas in the 4 groups 7 days after I/R (n=8). In both SV and SD groups, the GCL and INL were obvious and well organized. Seven days after I/R, the INL in the MV group was obviously thinner, and the number of GCL cells was significantly decreased, whereas in the MD group, the retina was more normal in structure, with a thicker INL than in the MV group. GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; OPL, outer plexiform layer; ONL, outer nuclear layer. Scale bar=20 μm.