Green tea polyphenol epigallocatechin-3-gallate attenuates TNF-α-induced intercellular adhesion molecule-1 expression and monocyte adhesion to retinal pigment epithelial cells.

Epigallocatechin-3-gallate (EGCG) is a major polyphenol component of green tea (Camellia sinensis) and demonstrates anti-oxidant, anticancer and anti-inflammatory properties. EGCG has been shown to protect retinal pigment epithelium (RPE) against oxidative stress-induced cell death. The pathogenesis of diseases in the retina is usually initiated by local inflammation at the RPE cell layer, and inflammation is mostly associated with leukocyte migration and the secretion of pro-inflammatory cytokines. Whether EGCG can modulate the cytokine-induced inflammatory response of RPE, particularly leukocyte migration, has not been clearly elucidated, and was therefore the objective of this study. ARPE-19 cells were cultured with different concentrations of TNF-α in the presence or absence of EGCG to different time points. Intracellular reactive oxygen species (ROS) levels were determined. Intercellular adhesion molecule (ICAM)-1 and phosphor-NF-κB and IκB expression were determined by Western blot analysis. Phosphor-NF-κB nuclear translocation and monocyte-RPE adhesion were investigated using immunofluorescence confocal laser scanning microscopy. Scanning electron microscopy (SEM) was carried out to further determine the ultrastructure of monocyte-RPE adhesion. The results demonstrated that TNF-α modulated inflammatory effects in ARPE-19 by induction of ROS and up-regulation of ICAM-1 expression. Moreover, TNF-α-induced phosphor-NF-κB nuclear translocation, increased phosphor-NF-κB expression and IκB degradation, and increased the degree of monocyte-RPE adhesion. Pretreating the cells with EGCG ameliorated the inflammatory effects of TNF-α. The results indicated that EGCG significantly exerts anti-inflammatory effects in ARPE-19 cells, partly as a suppressor of TNF-α signaling and that the inhibition was mediated via the NF-κB pathway.

TNF-α-induced ICAM-1 expression and monocyte adhesion in human RPE cells is mediated in part through autocrine VEGF stimulation.

PURPOSE: Local inflammation at the RPE cell layer is associated with inflammatory cell migration and secretion of proinflammatory cytokines such as tumor necrosis factor (TNF)-α. TNF-α upregulates intercellular adhesion molecule (ICAM)-1 expression on the RPE, which allows lymphocyte function-associated antigen-1 (LFA-1) to bind on leukocytes that contribute to leukocyte adhesion at sites of inflammation. Vascular endothelial growth factor (VEGF)-A(165)b is generated by alternative splicing of VEGF-A in the terminal exon, exon 8. VEGF-A(165)b is cytoprotective and antiangiogenic, but its effects on inflammation have not yet been elucidated. Therefore, we tested the hypothesis that VEGF-A(165)b regulates TNF-α-induced ICAM-1 expression and monocyte adhesion in RPE cells. METHODS: Primary RPE cells were pretreated with TNF-α alone, VEGF-A(165)b alone, VEGF-A(165)b with anti-VEGF-A(165)b, or the VEGFR-2 inhibitor ZM323881 before exposure to TNF-α for 24 h. Western blotting and monocyte adhesion assays were performed. RESULTS: VEGF-A(165)b and ZM323881 inhibited TNF-α-induced upregulation of ICAM-1 in RPE cells. The effect of VEGF-A(165)b was neutralized by an antibody to VEGF-A(165)b. VEGF-A(165)b ameliorated TNF-α-induced monocyte-RPE adhesion. CONCLUSIONS: These findings indicate that VEGF-A(165)b inhibits TNF-α-mediated upregulation of ICAM-1 expression and increases monocyte-RPE cell adhesion, suggesting an anti-inflammatory property of VEGF-A(165)b in the eye.