Purpose: To investigate the protective effect of rapamycin against alkali burn-induced corneal damage in mice.
Methods: BALB/c mice were treated with 0.1 N NaOH to the cornea for 30 seconds. Corneal neovascularization and opacity were clinically evaluated at 1, 2, and 4 weeks after chemical burn injury. Rapamycin was delivered topically to right eyes (1 mg/mL) and injected intraperitoneally (0.2 mg/kg) once a day. Concentrations of interleukin-6 (IL-6) and transforming growth factor-beta1 (TGF-β1) in the cornea were measured by enzyme-linked immunosorbent assay (ELISA). In vitro-cultured human corneal stromal cells were treated with 0 to 500 nM rapamycin for 3 days and then assessed by immunofluorescence staining of vimentin and alpha-smooth muscle actin (α-SMA). Western blotting assays for α-SMA, phosphorylated extracellular signal-regulated kinase (ρ-ERK 1/2), and total ERK 1/2 were also performed.
Results: Corneal neovascularization and corneal opacity scores measured 4 weeks after the chemical burn corneal injury were lower in the rapamycin group than in the control group. Two weeks after the chemical burn injury, a significant elevation in the corneal IL-6 levels of the positive control group was observed, compared to the levels in the negative control group or the rapamycin group (P < 0.05). Corneal TGF-β1 levels were lower in the rapamycin-treated group than in the control group at 4 weeks after chemical burn injury (P < 0.05). Moreover, rapamycin inhibited TGF-β1-induced α-SMA expression and augmented ERK 1/2 phosphorylation.
Conclusions: Rapamycin treatment reduced corneal opacity and corneal neovascularization in BALB/c mice. Rapamycin protected the cornea from chemical damage via reduction of IL-6 and TGF-β1 expression. Rapamycin reduced α-SMA expression through the ERK 1/2 pathway.
Keywords: alpha-smooth muscle actin; chemical burn; corneal stromal cell; extracellular signal-regulated kinase; interleukin-6; rapamycin; transforming growth factor-beta1.