Short-Time Exposure of Hyperosmolarity Triggers Interleukin-6 Expression in Corneal Epithelial Cells

PURPOSE: Although tear hyperosmolarity is assumed to play a major role in dry eye disease, correlation between the level of hyperosmolarity and inflammation remains unclear. The purpose of this study was to examine the effect of short-time hyperosmolarity exposure in the production of inflammatory cytokines in corneal epithelial cells in vitro. METHODS: Human corneal epithelial (HCE) cells were cultured under different osmotic conditions [310 (control), and 400-1000 mOsm]. Lactate dehydrogenase (LDH) release after short-term (10 minutes) or long-term (24 hours) hyperosmotic stress exposure was evaluated to determine HCE cell cytotoxicity. Production of inflammatory cytokines, including IL-6, IL-1β, IL-8, IL-23, and TGF-β1, due to hyperosmotic stress was also measured by enzyme-linked immunosorbent assay and semiquantitative real-time polymerase chain reaction. RESULTS: After a 24-hour culture, exposures above 700 mOsm caused all HCE cells to die, 500 and 600 mOsm damaged the cells, whereas 400 mOsm caused no morphological changes. However, there was a significant increase in the release of LDH after 24-hour cultures, even in 400 mOsm. In contrast, LDH examination showed that there was no cytotoxicity for the 10-minute exposures, even at above 800 mOsm. The significant increases in IL-6 production and mRNA expression at 700 mOsm during the short-time exposures were both dependent on the osmolarity. Other cytokines such as IL-1β, IL-8, IL-23, and TGF-β1 were not detected. CONCLUSIONS: Short-time hyperosmolarity exposure may activate IL-6 expression and production in HCE cells without cytotoxicity. These observations suggest that hyperosmolarity could cause inflammation on the ocular surface in dry eye disease.