Dexamethasone mitigates sulfur mustard-induced stem cell deficiency in vivo in rabbit limbal tissue by reducing inflammation and oxidative stress

Abstract

Sulfur mustard (SM) exposure induces ocular injury primarily to the cornea, limbus, and sclera. Although corneal injuries have been studied in detail, there is a dearth of literature on the effects of SM on limbus, particularly mechanisms underlying its compromised functioning, causing limbal stem cell deficiency (LSCD). LSCD causes impaired corneal repair leading to persistent epithelial defects, mustard gas keratopathy, and prolonged inflammation, resulting in total blindness in case of severe damage. Notably, dexamethasone (Dex) has been reported to treat SM-induced corneal injuries effectively; however, its efficacy for SM-induced limbus injury has not been studied. Hence, delayed/persistent structural damage (H&E and trichrome staining) and loss of LSCs [ΔNp63; immunofluorescence (IF)] in the limbus at day 28 post-SM exposure were assessed. Thereafter, in-depth proteomic analysis (LC–MS/MS) of SM exposed, Dex treated, and control limbal tissues (New Zealand white male rabbits) was performed. SM exposure significantly modulated the expression profile of 66 proteins, of which 62 were significantly reversed with Dex; thus, markedly inhibiting/hindering SM-induced limbal injury. Ingenuity Pathway Analysis predicted the primary involvement of (1) inflammation and immune response-associated pathways via dysregulation of defensin-5, eosinophil peroxidase, corticostatin-6, myeloperoxidase, and cathepsin C; and (2) drug/toxin metabolism and oxidative stress via GSTs, and ALDH1As modulations. IF analysis confirmed that Dex treatment significantly reversed SM-induced increases in human neutrophil peptides, defensin-5, and cathepsin C expression by 68%, 77%, and 90%, respectively. Thus, Dex markedly mitigated SM-induced limbal tissue injuries and prevented LSCD, via SM-induced inflammatory and oxidative stress inhibition, in our studies.