The Antioxidant N-Acetylcysteine Inhibits Inflammatory and Apoptotic Processes in Human Conjunctival Epithelial Cells in a High-Glucose Environment.

OBJECTIVE

We evaluated the effects of N-acetylcysteine (NAC), which is known to inhibit reactive oxygen species (ROS)-dependent apoptosis, on high glucose-induced ROS, apoptosis, inflammation, and delayed-wounding closure in primary cultured human conjunctival epithelial cells (pHCECs), and the regulatory effects of cleaved caspase-3, BAX, nuclear factor κB (NF-κB), IL-6, and TNF-α on these processes.

METHODS

High glucose-induced ROS generation was measured using 2',7'-dichlorofluorescein diacetate (DCFH-DA). The effects of NAC on high glucose-induced apoptosis were investigated in pHCECs using Annexin-V and PI staining, and cleaved caspase-3 and BAX expression levels using immunoblotting. To evaluate the inflammatory response, IL-6 and TNF-α expression levels were quantified by multiplex cytokine analysis, and NF-κB activation and IkB-α degradation were assessed by Western blot analysis. The effects of NAC on high glucose-delayed conjunctival epithelial wound healing were assessed by a scratch-induced directional wounding assay.

RESULTS

Compared to the untreated control and normal glucose (5 mM), high glucose at 25 mM stimulated ROS generation, apoptosis, and release of inflammatory cytokines, and delayed wound healing in pHCECs. The addition of NAC markedly reduced the high glucose-induced ROS activation, Annexin-PI-positive cells, and levels of cleaved caspase-3, BAX, IL-6, and TNF-α. N-acetylcysteine also prevented high glucose-delayed wound healing.

CONCLUSIONS

High glucose levels promote apoptosis by affecting mitochondria-dependent caspase activity through elevation of ROS production, a process that can be reversed by the antioxidant NAC. These findings demonstrate that NAC has a beneficial effect on conjunctival epithelial cell wound healing, antiapoptosis, and anti-inflammation in the conjunctival epithelial cell.