Apoptosis in UV-exposed Rabbit Corneas

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Abstract
Apoptosis was studied in rabbit corneas as a possible mechanism of cell death after photokeratitis induced by different UV wavelengths. Fourteen albino rabbit corneas were exposed to 280-and 310-nm UV radiation (UVR) in 10-nm full wavebands at doses that cause biomicroscopically significant keratitis (0.12 J/cm2 for 280 nm and 0.47 J/cm2 for 310 nm). Animals were killed 24 and 76 h after exposure. Corneas were processed for light and transmission electron microscopy and in situ end labeling of fragmented DNA by using a modification of the TUNEL technique. Corneas exposed to 280-nm UVR showed TUNEL-positive staining only in epithelial cells and superficial keratocytes at 24 and 76 h after irradiation. Twenty-four hours after 310-nm UVR exposure, TUNEL-positive staining was present in the epithelial cells, keratocytes throughout the entire thickness of the central stroma, and in endothelial cells. Seventy-six hours after exposure to 310-nm UVR, keratocytes disappeared throughout the whole thickness of the damaged stroma. Only a few epithelial cells were TUNEL positive at that time. Transmission electron microscopy (TEM) verified the occurrence of apoptotic nuclei and cells. Apoptosis appears to be a mechanism of corneal cell death after UVR. The 310-nm UVR caused more extensive damage to the corneal stroma and endothelium than did the 280-nm UVR.