Inhibition effect of curcumin on UVB-induced secretion of pro-inflammatory cytokines from corneal limbus epithelial cells.

Abstract

To study the effects of curcumin on the secretion of interleukin (IL)-6 and IL-8 by corneal limbus epithelial cells. Human corneal limbus epithelial cells were isolated and cultured from donor eyes and irradiated by UVB at different dosages with or without curcumin. MTT test was used for studying the effects of UVB and curcumin on the cell viability. The role of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) pathways on the UVB-induced secretion of IL-6 and IL-8 were tested by addition of their inhibitors to the culture with or without UVB-radiation. Levels of various signal pathways, IL-6 and IL-8 in the cells and in the conditioned culture medium were measured by ELISA analysis. UVB at 20 mJ/cm2 or less and curcumin at 20 µmol/L or less did not affect the cell viability of cultured limbus epithelial cells (P>0.05). UVB irradiation at 10 and 20 mJ/cm2 induced a significant increase of secretion of IL-6 and IL-8 and upregulated NF-κB and phosphorylated MAPK pathways of cultured limbus epithelial cells (P<0.05). Various signal pathway inhibitors, including SP600125 (JNK inhibitor), SB203580 (p38 MAPK inhibitor) and BAY11-7082 (NF-κB inhibitor) significantly decreased the UVB-induced secretion of IL-6 and IL-8 secretion (P<0.05). Curcumin at 5-20 µmol/L significantly inhibited UVB-induced secretion of IL-6 and IL-8 by limbus epithelial cells in a dose-dependent manner; while curcumin alone did not affect the secretion of IL-6 and IL-8. The upregulation of NF-κB and MAPK pathways induced by UVB treatment was significantly inhibited by curcumin, suggesting that NF-κB and MAPK pathways are involved in the inhibitory effect of curcumin on UVB-induced production of IL-6 and IL-8. Curcumin may be a promising agent to be explored for the prevention and treatment of pterygium.