Objective To investigate the effect and mechanism of EGF eyedrop in treating dry eye on the mouse models induced by topical administration of Benzalkonium Chloride (BAC).
Method 24 BALB/c mice were enrolled in the study, 18 of which were treated with topical administration of 0.20% BAC twice a day to establish the dry eye condition and others were used as normal control. Based on the consistency of tear film break-up time, corneal fluorescein staining score, inflammation index and phenol red thread tear test, 18 mice were evenly divided into three groups when the dry eye models were set up on day(D)14. Dry eye group was the blank control and sacrificed immediately. Solvent-treated and EGF-treated groups were topically administered with solvents of EGF, 200 ng/ml EGF solutions three times a day respectively. Tear film break-up time, corneal fluorescein staining score, inflammation index and phenol red thread tear test were evaluated in solvent-treated and EGF-treated groups on D2, 4 and 6 during the treatment and global specimens were collected on D6. Sections of 24 mice were stained by periodic acid-schiff (PAS) assay, and labeled with Ki-67, EGFR, MUC1 antibody. The EGFR expression and the phosphorylation of ERK of the cornea were observed by western blot. TUNEL assay was used to measure the apoptosis of different groups.
Result No differences of clinical evaluations were detected at the baseline (D0) of dry eye group, solvent-treated group and EGF-treated group. Comparing to solvent-treated group, BUT of EGF-treated group was significantly lengthened on D2 and D6 (p<0.05, p<0.01), while score of fluorescein staining was smaller on D4 and D6 (p<0.001, p<0.01). No significant difference was detected at any time points in inflammation index or phenol red thread tear test. Confocal immunofluorescent staining showed EGFR expression on the epithelial cell membranes decreased in the dry eye condition and great improvement was noticed in EGF-treated group, which was consistent with western blot outcomes. Immunohistochemical staining of Ki-67 and TUNEL assay indicated the EGF promoted proliferation and inhibited apoptosis of corneal epithelium in dry eye via the phosphorylation of ERK. The density of goblet cells in the conjunctival fornix and MUC1 expression of corneal epithelium were impaired in dry eye condition and recovered after the treatment of EGF.
Conclusion Topical application of EGF showed therapeutic effects on BAC-induced mouse dry eye by stabilizing the tear film, maintaining the integrity of epithelium, promoting proliferation, preventing apoptosis, increasing the number of goblet cells, up-regulating MUC1 expression. Our study demonstrated the great potential of EGF in the clinical treatment of dry eye.