Inhibition by Epigallocatechin Gallate of IL-1-Induced Urokinase-Type Plasminogen Activator Expression and Collagen Degradation by Corneal Fibroblasts

The proinflammatory cytokine interleukin (IL)-1 is implicated in corneal ulceration and promotes collagen degradation by corneal fibroblasts cultured in a three-dimensional (3D) collagen gel. Epigallocatechin-3-gallate (EGCG), the principal polyphenol in extracts of green tea, has various beneficial health effects, some of which appear to be mediated through direct or indirect inhibition of protease activity. We therefore examined the effect of EGCG on IL-1β-induced collagen degradation by corneal fibroblasts embedded in a collagen gel. Human corneal fibroblasts were cultured in a type I collagen gel. Collagen degradation was assessed by measurement of hydroxyproline in acid hydrolysates of culture supernatants. The expression of urokinase-type plasminogen activator (uPA) was examined by real-time and RT-PCR analysis and by fibrin zymography, and that of the collagenase matrix metalloproteinase 1 (MMP1) was detected by immunoblot analysis. EGCG inhibited IL-1β-induced, plasminogen-dependent collagen degradation by corneal fibroblasts in a concentration-dependent manner. It also attenuated the IL-1β-induced expression of uPA at both mRNA and protein levels. EGCG inhibited the IL-1β-induced conversion of exogenous plasminogen to plasmin as well as the plasminogen-dependent activation of pro-MMP1 in the 3D cultures without a substantial effect on pro-MMP1 abundance. EGCG inhibits IL-1β-induced collagen degradation by corneal fibroblasts, with this effect likely being mediated by suppression of the upregulation of uPA, the uPA-mediated conversion of plasminogen to plasmin, and the plasmin-mediated activation of pro-MMP1. EGCG thus warrants further investigation as a potential treatment for corneal ulcer.