Tea polyphenols protect gingival keratinocytes against TNF-α-induced tight junction barrier dysfunction and attenuate the inflammatory response of monocytes/macrophages

Abstract

Tea, an aromatic beverage prepared with the leaves of the Camellia sinensis plant, is well known to contain bioactive polyphenols. Green tea contains mainly catechins such as epigallocatechin-3-gallate (EGCG), while black tea is characterized by the presence of theaflavins. TNF-α, which is a pro-inflammatory cytokine that activates the endogenous inflammatory cascade, plays a key role in periodontitis. In the present study, we investigated the ability of tea compounds to attenuate TNF-α-mediated activation of the host inflammatory response in monocytes/macrophages as well as the protective effect of green and black tea polyphenols on gingival keratinocyte barrier dysfunction induced by TNF-α. Tea compounds inhibited both the activation of NF-κB and caspase-1 as well as IL-1β secretion by monocytes/macrophages. TNF-α time-dependently damaged keratinocyte tight junction barrier integrity, as determined by changes in transepithelial electrical resistance and FITC-dextran transport. Green tea extract, EGCG, theaflavins, and to a lesser extent, black tea extract protected keratinocytes against the TNF-α-mediated breakdown of barrier integrity. The treatment of keratinocytes with tea polyphenols markedly mitigated the morphological changes of tight junction proteins such as zonula occludens-1 and occludin compared to cells exposed only to TNF-α, as determined by immunofluorescence. Tea polyphenols also time-dependently decreased the paracellular flux of TNF-α-treated keratinocytes. In conclusion, the ability of tea polyphenols to exert an anti-inflammatory effect and to attenuate the gingival epithelial barrier dysfunction induced by TNF-α supports their potential for the prevention and treatment of periodontal disease.