Abstract
Introduction The major risk factor for osteoarthritis (OA) is aging, but the mechanisms underlying this risk are only partly understood. Age-related accumulation of advanced glycation end products (AGEs) can activate chondrocytes and induce the production of proinflammatory cytokines and matrix metalloproteinases (MMPs). In the present study, we examined the effect of epigallocatechin-3-gallate (EGCG) on AGE-modified-BSA (AGE-BSA)-induced activation and production of TNF alpha and MMP-13 in human OA chondrocytes.
Methods Human chondrocytes were derived from OA cartilage by enzymatic digestion and stimulated with in vitro-generated AGE-BSA. Gene expression of TNF alpha and MMP-13 was measured by quantitative RT-PCR. TNF alpha protein in culture medium was determined using cytokine-specific ELISA. Western immunoblotting was used to analyze the MMP-13 production in the culture medium, phosphorylation of mitogen-activated protein kinases (MAPKs), and the activation of NF-kappa B. DNA binding activity of NF-kappa B p65 was determined using a highly sensitive and specific ELISA. I kappa B kinase (IKK) activity was determined using an in vitro kinase activity assay. MMP-13 activity in the culture medium was assayed by gelatin zymography.
Results EGCG significantly decreased AGE-stimulated gene expression and production of TNF alpha and MMP-13 in human chondrocytes. The inhibitory effect of EGCG on the AGE-BSA-induced expression of TNF alpha and MMP-13 was mediated at least in part via suppression of p38-MAPK and JNK activation. In addition, EGCG inhibited the phosphorylating activity of IKK beta kinase in an in vitro activity assay and EGCG inhibited the AGE-mediated activation and DNA binding activity of NF-kappa B by suppressing the degradation of its inhibitory protein I kappa B alpha in the cytoplasm.
Conclusions These novel pharmacological actions of EGCG on AGE-BSA-stimulated human OA chondrocytes provide new suggestions that EGCG or EGCG-derived compounds may inhibit cartilage degradation by suppressing AGE-mediated activation and the catabolic response in human chondrocytes.