Time Course of Inflammation and Apoptosis in a Scopolamine–Induced Dry Eye Rat Model

Abstract

Purpose: : Dry eye syndrome is due to tear secretion deficiency or excessive tear evaporation leading to tear film instability. The aim of this study was to evaluate the time course of inflammation and apoptosis in a scopolamine–induced dry eye rat model.

Methods: : Osmotic pumps continuously delivering scopolamine (12.5mg/d) were implanted subcutaneously in female Lewis rats for 1, 2, 3, 7, 10, 17 and 28 days. During the treatment, the corneal status was assessed by fluorescein impregnation and tears were collected for prostaglandin E2 (PGE2) immunoassay. At the end of the treatment period, the animals were sacrificed and the ocular tissues and the lacrimal glands were excised. MHCII and mucin MUC5AC were immunostained on tissue cryosections. Apoptosis was detected using the TUNEL technique and active caspase 3 immunostaining. Lipids were extracted from the lacrimal glands for fatty acid analysis.

Results: : Every dry eye rat cornea exhibited keratitis after a 17–day treatment period whereas no clinical signs were observed in control animals. Apoptosis was detected mainly at the early time points (1 and 2–day treatment periods) compared to the late time points (from 10 days of treatment) but seemed to be caspase 3 independent. The number of goblet cells on the conjunctival epithelium was highly decreased after 1, 2, 10 days of treatment and more. MHCII was detected on the conjunctival epithelium and sub–epithelium of dry eye animals mainly after 7 days of treatment. Both arachidonic acid in the lacrimal glands and PGE2 in tears were increased in dry eye animals (maximum of +56% for arachidonic acid with a 10–day treatment period).

Conclusions: : Altogether these results show that in this scopolamine–induced dry eye rat model, apoptosis occurs at the early time points although inflammation is detected mainly after one week of treatment.

Keywords: cornea: tears/tear film/dry eye • conjunctiva • inflammation