Retinal function and morphology in the rabbit eye after intravitreal injection of the TNF alpha inhibitor adalimumab.

AIM: To study the effects of the tumor necrosis factor alpha inhibitor adalimumab on rabbit retina after injection into the vitreous body. METHODS: Forty-eight rabbits of mixed strain (9-12 months old, weighing ≈ 3.5 kg) were randomized into four groups. Adalimumab was injected at one of two concentrations (1.25 mg or 2.5 mg) into the eyes of two groups, and balanced salt solution into the eyes of the third group. The fourth group acted as controls. Full-field electroretinography (ffERG) was performed before injection and 1 and 6 weeks post-injection. At 6 weeks post-injection the rabbits were euthanized and the sectioned retinas were studied. Retinal histology was studied with hematoxylin-eosin staining. Immunohistochemical analysis was performed on rods, cones, rod bipolar cells, horizontal cells, amacrine cells and Müller cells. RESULTS: No significant difference in ffERG amplitudes or implicit times was observed between the four groups at any time point. Histological and immunohistochemical findings were similar in all groups. CONCLUSIONS: Injection of adalimumab into the vitreous body of healthy rabbits, at doses up to 2.5 mg, does not appear to be toxic to the rabbit retina.

Intravitreal injection of triamcinolone acetonide into healthy rabbit eyes alters retinal function and morphology.

AIM: To study the effects of intravitreally injected triamcinolone acetonide (TA) and/or its preservative benzyl alcohol (BA) in healthy rabbit retina. METHODS: Forty-eight rabbits (aged 4 months, body weight ≈3 kg) were randomized into four groups (n = 12). They were examined with electroretinography (ERG) prior to drug exposure, and then injected intravitreally with a combination of TA and BA, TA without BA, BA alone or a balanced saline solution (BSS). The electroretinograms were assessed 1 week and 7 weeks post-injection. The rabbits were euthanized and the sectioned retinas were studied. Immunohistochemical analysis was performed on rods, cones, rod bipolar cells, horizontal cells, amacrine cells and Müller cells. RESULTS: Rabbits injected with BA showed a significantly lower rod-mediated b-wave amplitude than the controls 1 week after injection. TA-injected rabbits demonstrated significantly higher a- and b-wave amplitudes in the total retinal response than the controls 1 week post-injection. The rabbits injected with TA + BA demonstrated a significantly higher b-wave amplitude in the total retinal response than the controls 1 week after injection. The significantly higher a-wave amplitude in the total retinal response remained in the TA-injected rabbits 7 weeks after injection. Immunohistochemistry revealed that protein kinase C alpha (PKC α) was down-regulated in both the perikarya and the axons of bipolar cells in histological sections from rabbit retina injected with TA + BA, BA and TA. CONCLUSIONS: Intravitreal injection of the preservative BA reduces the isolated rod-mediated retinal response in the rabbit, transiently and selectively. Intravitreal injection of TA increases the total retinal response in the rabbit up to seven weeks after injection. The effects observed are not only limited to retinal function, but also include changes in the expression of PKC α in rod bipolar cells, indicating drug-related interference with normal retinal physiology in the healthy rabbit eye.

Retinal function and morphology in rabbit after intravitreal injection of VEGF inhibitors.

PURPOSE/AIM: To explore changes in morphology and function in the rabbit retina after intravitreal high-dose injection of three commonly used VEGF inhibitors. MATERIALS AND METHODS: Forty-eight rabbits of mixed strain (6 months of age, body weight ≈ 3 kg) were randomized into four groups (n = 12). They were examined with full-field electroretinography (ERG) and with multifocal electroretinography (mf ERG) prior to drug exposure. The rabbits were then injected intravitreally with bevacizumab, ranibizumab, pegaptanib, or with a balanced saline solution. The dose of VEGF inhibitor was chosen to achieve a vitreous concentration approximately three times higher than the one clinically used in the adult human eye. ERG was then performed 8 weeks postinjection, and mf ERG 9 weeks postinjection. After 9 weeks, the rabbits were sacrificed and the sectioned retina was studied. Immunohistochemical analysis was performed of rods, cones, rod bipolar cells, horizontal cells, and amacrine cells. RESULTS: Rabbits injected with VEGF inhibitors all showed significantly lower amplitude of the dark-adapted b-wave rod-mediated response to dim light, compared to the rabbits injected with BSS. The a wave (reflecting photoreceptor function) in the response to single flash white light was however not affected. Immunohistochemistry revealed a significant reduction in PKC labeling of rod bipolar cells in pegaptanib and ranibizumab injected eyes whereas bevacizumab injected eyes displayed normal PKC labeling. No apparent morphological change was seen with markers for remaining retinal cells. CONCLUSIONS: Our results indicate that the use of high-dose intravitreal VEGF inhibitors in the rabbit eye affects rod-mediated retinal function and PKC expression in rod bipolars cells for at least 9 weeks after drug administration. The three VEGF inhibitors influence the retina slightly differently. These results are important for the understanding of drug action and when devising therapeutical strategies in new areas such as retinopathy of prematurity where vitreous volume is significantly lower compared to the adult eye.

Rifabutin accumulates in the lens and reduces retinal function in the rabbit eye.

PURPOSE: To study the toxicology of rifabutin in the rabbit eye with emphasis on retinal function and histopathology. METHODS: Seven rabbits received a daily dose of rifabutin during 15 months. Six rabbits receiving only the vehicle were used as controls. Repeated standardized full-field electroretinograms (ERG) were assessed. After discontinuing treatment, the rabbits were killed and the cornea, the lens, and the sectioned retina was studied. Immunhistochemistry directed against vimentin, glial fibrillaryacidic protein (GFAP), protein kinase C (PKC), and peanut agglutinin (PNA) was performed. RESULTS: Rifabutin was detected in serum of the treated rabbits. During treatment, the full-field ERG demonstrated significantly reduced b-wave amplitudes in the total rod-cone response as well as in the isolated rod and cone response compared with the recordings before treatment. The control rabbits did not demonstrate a reduction of the ERG amplitudes. The treated rabbits developed a discoloration of the lens, not seen in the control group. No retinal pathology was demonstrated using immunohistochemical methods. CONCLUSION: Rifabutin causes a discoloration of the lens and reduces both rod and cone function in rabbits, but does not alter retinal morphology. Previous reports on ocular side effects caused by rifabutin are supported by the results of this study.