Corneal damage induced in adult mice by a single intraperitoneal injection of N-ethyl-N-nitrosourea

Aim: The morphological response and cell kinetics of the mouse cornea to various doses of N-ethyl-N-nitrosourea (ENU) was examined. Materials and Methods: ENU at a dose of 50, 100, 200, 400, or 600 mg/kg was injected intraperitoneally into female BALBIc mice at seven weeks of age. Sequential morphological features and cell kinetics (TUNEL assay as apoptosis marker, PCNA immunostaining as proliferative activity marker, and p63 immunostaining as corneal stem cell marker) of corneal damage caused by 600 mg/kg of ENU were also analyzed 6, 12, 24 and 72 h, and 7 days after exposure. Moreover, older mice (25 to 34 weeks of age) received the same dosage and were sacrificed 7 days later. Both eyes of all mice were analyzed histopathologically and morphometrically, by using the parameters of corneal epithelial thickness. Results: All ENU-treated mice in the 600 mg/kg group developed corneal damage characterized by desquamation and loss of epithelial cells within 7 days. Corneal epithelial thickness was significantly reduced in the 600 mg/kg group as compared to the control group and decreased to approximately half of the normal thickness. Although the number of TUNEL-positive epithelial cells in the ENU-treated mice was similar to that of the control mice, ENU inhibited the proliferative activity of epithelial cells showing PCNA-positivity 72 h after treatment. The p63-positivity of epithelial cells decreased in the central cornea of mice treated with 600 mg/kg of ENU. Older mice did not develop corneal damage from exposure to ENU. Conclusion: ENU induced corneal damage in adult mice, and epithelial cell loss was caused by the inhibition of corneal epithelial proliferation. This is the first report to describe ENU-induced corneal injury in adult mice.