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, 11 (1), 25-30

Safety Threshold of Intravitreal Clonidine in Rabbit's Eyes


Safety Threshold of Intravitreal Clonidine in Rabbit's Eyes

Homayoun Nikkhah et al. Int J Ophthalmol.


Aim: To determine the safe dose of intravitreal clonidine (IVC), a potential drug for neuroprotection and angiogenesis inhibition in rabbits.

Methods: A total of 28 rabbits were divided into four groups. Three groups received IVC with concentrations of 15 (Group A), 25 (Group B), and 50 (Group C) µg/0.1 mL and the control group (Group D) received 0.1 mL balanced salt solution (BSS). To investigate IVC safety, electroretinography (ERG) was performed at baseline, then at 1, 4 and 8wk after injection. After last ERG, all rabbits were euthanized, their eyes were enucleated and subjected to routine histopathological evaluation, immunohistochemistry for glial fibrillary acidic protein (GFAP) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) test.

Results: Based on ERG, histopathology, GFAP and TUNEL assay findings, 15 µg IVC was determined as the safe dose in rabbit eyes. While, the results of routine histopathology and TUNEL assay were unremarkable in all groups, toxic effects attributed to 25 and 50 µg IVC were demonstrated by ERG and GFAP tests.

Conclusion: Totally 15 µg clonidine is determined as the safe dose for intravitreal injection in rabbits. Contribution of IVC in neuroprotection and inhibition of angiogenesis deserve more studies.

Keywords: TUNEL assay; clonidine; electroretinography; glial fibrillary acidic protein; intravitreal injection.


Figure 1
Figure 1. Representative unremarkable neurosensory retina with intravitreal injection of 15 µg (B1), 25 µg (C1), and 50 µg (D1) clonidine as compared to the BSS-injected (A1) eyes (hematoxylin & eosin stain, magnification ×400). Note non-significant GFAP immunoreactivity of the retina in a representative eye injected with 15 µg (B2) clonidine and BSS (A2) and significant retinal GFAP immunoreactivity in a representative eye injected with 25 µg (C2) and 50 µg (D2) clonidine (magnification ×400).
Figure 2
Figure 2. Determination of the apoptotic effects of 15, 25, and 50 µg of intravitreal clonidine injections on rabbit retinas by using TUNEL assay
Positive control is a section of retinoblastoma with viable tumor cells (see R in A) surrounded by apoptotic cells and negative control was not treated by TUNEL reaction mixture (B). Results indicated that none of examined clonidine concentrations 15 µg (C), 25 µg (D), and 50 µg (E) imposed apoptotic effects on the treated groups when compared to the control (F) (all images magnification ×400).

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