Decreased expression of antioxidant enzymes in the conjunctival epithelium of dry eye (Sjögren's syndrome) and its possible contribution to the development of ocular surface oxidative injuries.

Previous studies have described elevated lipid peroxidase, myeloperoxidase and xanthine oxidoreductase/xanthine oxidase levels on the ocular surface of patients suffering from autoimmune dry eye (Sjögren's syndrome, SS). Reactive oxygen species generated by various enzymatic systems may be dangerous to the eye if they are not sufficiently cleaved by antioxidants. Because antioxidants have not been investigated in dry eye, the aim of this study was to examine the expression of antioxidant enzymes that cleave reactive oxygen species and play a key role in antioxidant protection. Conjunctival epithelial cells of dry eye (SS) patients were obtained by the method of impression cytology using Millicell membranes. Normal eyes served as controls. In the conjunctival epithelium superoxide dismutase, catalase and glutathione peroxidase were examined immunohistochemically. The enzyme expression levels were determined by image analysis and statistical evaluation. In contrast to normal eyes, where antioxidant enzymes were highly expressed in the conjunctival epithelium, in dry eye their expression was much less pronounced in correlation with the increasing severity of dry eye symptoms. Our study suggests that the decreased expression of antioxidant enzymes in dry eye disease (SS) contributes to the development of anterior eye surface oxidative injuries.