Intravitreous delivery of the corticosteroid fluocinolone acetonide attenuates retinal degeneration in S334ter-4 rats

Abstract

Purpose: To study the neuroprotective properties of low-dose, sustained-release intravitreous fluocinolone acetonide (FA) in transgenic S334ter-4 rats.

Methods: S334ter-4 rats aged 4 weeks were divided into four groups: 0.5 microg/d FA-loaded intravitreous drug delivery implant (IDDI); 0.2 microg/d FA-loaded IDDI; inactive IDDI; and unoperated controls. Electroretinography (ERG) was performed before surgery and every 2 weeks after surgery for 8 weeks. When the rats were 12 weeks of age, outer nuclear layer (ONL) and inner nuclear layer (INL) thicknesses were measured. Microglial cell counts were obtained from retinal wholemounts labeled for Iba-1.

Results: At the end of the study, unoperated and inactive IDDI-implanted rats demonstrated 50% to 60% reductions in ERG amplitudes compared with those recorded at 4 weeks (P < 0.001 for both groups). FA 0.2-microg/d animals demonstrated 15% amplitude attenuation, while FA 0.5-microg/d animals showed 30% reduction. ONL thickness in FA 0.2-microg/d-treated eyes was 25.8% +/- 2.3% higher than in control group eyes (P < 0.001) and 30.0% +/- 2.1% higher than in inactive IDDI-implanted eyes (P < 0.001). In FA 0.5-microg/d-treated eyes, ONL thickness was 22.4% +/- 2.8% higher than in control group eyes (P < 0.001) and 22.3% +/- 3.7% higher than in inactive IDDI-implanted eyes (P < 0.01). No statistically significant difference was observed between the two control groups. No statistically significant difference between the two FA-treated groups was found. FA-treated groups demonstrated significantly fewer activated microglial cells than control groups.

Conclusions: Chronic intravitreous infusion of FA preserves ONL cell morphology and ERG a- and b-wave amplitudes and reduces retinal neuroinflammation in S334ter rats. Based on these findings, the synthetic corticosteroid FA may promise a therapeutic role in patients with retinal degeneration.

Figure 1.

Intravitreal drug delivery implant placed next to a ruler with 1-mm divisions.

Figure 2.

Representative ERG traces among four experimental groups of S334ter-4 rats throughout the study course. Week designations correspond to animals' ages.

Figure 3.

Mean (±SE) ERG a-wave and b-wave amplitudes in treated (OD) and untreated (OS) eyes of S334ter-4 rats throughout the study course among four experimental groups. (A) ERG a-wave amplitudes for the right (OD, treated) eyes. (B) ERG a-wave amplitudes for the left (OS, untreated) eyes. (C) ERG b-wave amplitudes for the right (OD, treated) eyes. (D) ERG b-wave amplitudes for the left (OS, untreated) eyes. (A) *P < 0.05; **P < 0.001. (C) *P < 0.01; **P < 0.0001, compared with both inactive IDDI-treated and unoperated control eyes for the end time point ERG measurements. Week designations correspond to animals' ages.

Figure 4.

Mean (±SE) ERG a-wave and b-wave implicit times in treated (OD) and untreated (OS) eyes of S334ter-4 rats throughout the study course among four experimental groups. (A) ERG a-wave implicit times for the right (OD, treated) eyes. (B) ERG a-wave implicit times for the left (OS, untreated) eyes. (C) ERG b-wave implicit times for the right (OD, treated) eyes. (D) ERG b-wave implicit times for the left (OS, untreated) eyes. (C) *P < 0.001; **P < 0.0001, compared with both inactive IDDI-treated and unoperated control eyes for the end time point ERG measurements. Week designations correspond to animals' ages.

Figure 5.

Micrographs (200×) of representative retinal histologic sections (hematoxylin and eosin staining) among four experimental groups of 12-week S334ter-4 rats.

Figure 6.

Mean (±SE) retinal ONL and INL thicknesses among four experimental groups of 12-week S334ter-4 rats. *P < 0.01; **P < 0.00001, compared with both inactive IDDI-treated and unoperated control eyes.

Figure 7.

Mean measurements of ONL thickness along transverse retinal sections from the optic nerve head to the ora serrata of 12-week S334ter-4 rats among four experimental groups.

Figure 8.

Photomicrograph (400×) of Iba-1–labeled microglial cells within different retinal layers of 12-week S334ter-4 rats among four experimental groups.

Figure 9.

Mean (±SE) Iba-1–labeled microglial cell counts at the level of different retinal layers among four experimental groups of 12-week S334ter-4 rats. *P < 0.00001 compared with both inactive IDDI-treated and unoperated control eyes.