A comparison of corneal wound healing after UVB and nitrogen mustard exposure

Vesicants such as nitrogen mustard (NM) cause blistering of skin, similar to that caused by ultraviolet B (UVB) exposure from the sun. In the cornea, such injury occurs as microbullae at the basal surface of the basal epithelial cells, where the cells sit on their basement membrane. We hypothesize that the steps in healing are not identical after exposure to these two blistering agents, since UV injury heals well, but mustards often cause injuries that can induce chronic complications. Twenty five years after a mustard exposure recurrent erosions can still develop (Javadi et al., 2005). In an effort to understand the pathogenesis of mustard exposure we investigated whether a NM injury heals more slowly than an equivalent UVB injury. To accomplish this, corneal organ cultures were exposed to different levels of UVB to determine conditions that would produce a 24 hour post-UVB phenotype equivalent to the 24 hour post-exposure phenotype of a 60 minute exposure to 100 nmol NM. Corneal organ cultures were irradiated for various times to produce different UVB exposures: 5 minutes exposure resulted in 100 mJ/cm2; 20 minutes, 400 mJ/cm2; 40 minutes, 800 mJ/cm2; 60 minutes, 1200 mJ/cm2; 80 minutes, 1600 mJ/cm2; and 100 minutes, 2000 mJ/cm2. Corneas were embedded in O.C.T compound, frozen, and then sectioned for H&E staining. Micrographs of sections were overlapped to make composites covering the entire diameter of the cornea. From the composites, the degree of epithelial-stromal separation was calculated as a percentage of the entire width of the cornea. Our results demonstrated that, at 24 hour after a 60 minutes exposure to 100 nmol NM, the epithelial-stromal separation was 58 ± 13 % of the corneal diameter. Of the UVB exposures, a nearly equivalent phenotype, 60 ± 11 % separation between the cell layers, was produced by the 2000 mJ/cm2 UVB exposure. The time needed for healing (i.e., a return to epithelial-stromal structural integrity) was found to be 7 days for NM exposure. In contrast, the equivalently damaged UVB-exposed corneas recovered in only 5 days. Immunofluorescence analysis showed that the provisional matrix components SPARC, hevin, tenascin-C, thrombospondin-1, and fibrillin-1 persisted at least 1 day longer in the NM-exposed corneas than in UVB-exposed corneas.M.S.Includes bibliographical referencesby Iris P. P