Effect of Systemic Administration of FK506 in a Rat Model of Retinal Detachment

Abstract

Purpose: : Recent studies showed the immunosuppressive agent FK506 to be neuroprotective in animal injury models. FK506 has also been reported to influence apoptosis by various mechanisms. We investigated its action on photoreceptor apoptosis in a rat model of retinal detachment.

Methods: : Retinal detachments were created in the eyes of Brown Norway rats by injecting 10% hyaluronic acid into the subretinal space using a transvitreal approach. FK506 (tacrolimus) (5 mg/kg/day) diluted in PBS was administered by gastric gavage one day prior to the induction of retinal detachment, the day of the induction and for the two following days (n = 6). Control animals received same volume of PBS (0.5cc) by gastric gavage one day prior to the induction of retinal detachment, the day of the induction and for the two following days (n = 3). Additional controls included animals that did not undergo retinal detachment and were either treated with FK506 (n=2) or received PBS (n=2). All eyes were enucleated 72 hours after retinal detachment induction, embedded in paraffin and 14µm sections obtained. DNA fragmentation was examined using terminal dUTP–biotin nick end–labeling (TUNEL). TUNEL–positive cells were counted by a masked observer and an average obtained from three adjacent standardized fields in two serial sections.

Results: : Pyknotic nuclei in the outer nuclear layer (ONL) and disruption of the outer segments were noted in the area of the detachment. TUNEL–positive cells were present in the ONL only in the areas of retinal detachment. Animals treated with FK506 were noted to have fewer TUNEL–positive cells compared to the eyes of control animals: 130.13 ± 54.3 vs. 195.5 ± 25.04 (mean ± SD). There was a 35% reduction in the mean number of TUNEL–positive cells in the treated group (p <0.05, Student's one–tailed t–test). Eyes that did not undergo retinal detachment showed normal morphology whether or not the animal received FK506, and no morphological signs of toxicity were noted in the eyes of treated animals.

Conclusions: : These data suggest that systemic administration of the therapeutic agent FK506 may inhibit photoreceptor apoptosis associated with retinal detachment.

Keywords: retinal detachment • photoreceptors • apoptosis/cell death