Insights into mustard gas keratopathy: Characterizing corneal layer-specific changes in mice exposed to nitrogen mustard

Exposure to mustard agents, such as sulfur mustard (SM) and nitrogen mustard (NM), often results in ocular surface damage. This can lead to the emergence of various corneal disorders that are collectively referred to as mustard gas keratopathy (MGK). In this study, we aimed to develop a mouse model of MGK by using ocular NM exposure, and describe the subsequent structural changes analyzed across the different layers of the cornea. A 3 μL solution of 0.25 mg/mL NM was applied to the center of the cornea via a 2-mm filter paper for 5 min. Mice were evaluated prior to and after exposure on days 1 and 3, and weekly for 4 weeks using slit lamp examination with fluorescein staining. Anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscopy (IVCM) tracked changes in the epithelium, stroma, and endothelium of the cornea. Histologic evaluation and immunostaining were used to examine corneal cross-sections collected at the completion of follow-up. A biphasic ocular injury was observed in mice exposed to NM, most prominent in the corneal epithelium and anterior stroma. Following exposure, mice experienced central corneal epithelial erosions and thinning, accompanied by a decreased number of nerve branches in the subbasal plexus and increased activated keratocytes in the stroma. The epithelium was recovered by day 3, followed by exacerbated punctuate erosions alongside persistent stromal edema that arose and continued onward to four weeks post-exposure. The endothelial cell density was reduced on the first day after NM exposure, which persisted until the end of follow-up, along with increased polymegethism and pleomorphism. Microstructural changes in the central cornea at this time included dysmorphic basal epithelial cells, and in the limbal cornea included decreased cellular layers and p63⁺ area, along with increased DNA oxidization. We present a mouse model of MGK using NM that successfully replicates ocular injury caused by SM in humans who have been exposed to mustard gas. Our research suggests DNA oxidation contributes to the long-term effects of nitrogen mustard on limbal stem cells.