Epigallocatechin-3-gallate prevents TNF-α-induced NF-κB activation thereby upregulating ABCA1 via the Nrf2/Keap1 pathway in macrophage foam cells

The ATP-binding membrane cassette transporter A1 (ABCA1) plays a protective role in the development of atherosclerosis for the reverse cholesterol transport process. Epigallocatechin-3-gallate (EGCG), which exists abundantly in green tea, exerts an anti-atherosclerotic effect via anti-inflammatory and metabolic regulation activities. Many genes and proteins related to lipid metabolism are involved in the lowering cholesterol effects of EGCG. However, effects of EGCG on ABCA1 have rarely been described. In the study presented here, we found that exposure of macrophage foam cells to TNF-α results in a downregulation of ABCA1 and a decrease in cholesterol efflux to apoA1, which is attenuated by pretreatment with EGCG. Moreover, rather than activating the Liver X receptor (LXR) pathway, inhibition of the TNF-α-induced nuclear factor-κB (NF-κB) activity is detected with EGCG treatment in cells. In order to inhibit the NF-κB activity, EGCG can promote the dissociation of the nuclear factor E2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) complex; when the released Nrf2 translocates to the nucleus and activates the transcription of genes containing an ARE element inhibition of NF-κB occurs and Keap1 is separated from the complex to directly interact with IKKβ and thus represses NF-κB function. These results provide novel insight into the anti-inflammatory effects of EGCG, as well as the identification of a novel potential therapeutic role for the prevention of atherosclerosis.