Epigallocatechin-3-gallate Prevents TNF-α-induced NF-κB Activation Thereby Up-regulating ABCA1via Nrf2/keap1Pathway In Macrophage Foam Cells

Background and objective:ATP-binding membrane cassette transporter A1(ABCA1)plays a protective role in the development of atherosclerosis for the reversecholesterol transport process. Epigallocatechin-3-gallate (EGCG), which existsabundantly in green tea, exerts an anti-atherosclerotic effect via anti-inflammatoryand metabolic regulation activities. Many genes and proteins related to lipidmetabolism are involved in the lowering cholesterol effects of EGCG. However,effects of EGCG on ABCA1have rarely been described. To demonstrate the effect ofEGCG on ABCA1and possible mechanism, THP-1macrophage derived foam cellswere exposed to TNF-α and establishing an inflammation cells condition.Methods:We first induced THP-1cells to become macrophages by PMA. ThenTHP-1macrophages were induced to be foam cells by ox-LDL. Before exposure toTNF-α (10ng/ml), the foam cells were pretreated by EGCG with differentconcentrations (0,10,20,40,80μg/mL) and then collected for experiments. Cellularcholesterol efflux experiments and were conducted to determine the cellular lipidaccumulation. MTT were determine the cells toxicity. mRNA levels of ABCA1andLXRα/β were determined by real time quantitative RT-PCR. Luciferase reporter assaywere conducted to determine ABCA1promoter levels. Western bolt were used todetermine the protein levels of ABCA1, LXRα/β, NF-κB p65, Nrf2, Keap1and IKKβ.The DNA-combining activity of NF-κB and Nrf2were investigated by EMSA. Nrf2and Keap1were knocked down by Small interfering RNA transfection. Results: In present studies, we have found that exposure of macrophage foam cells toTNF-α results in a down-regulation of ABCA1and a decrease in cholesterol efflux toapoA1, which is attenuated by pretreatment with EGCG. Moreover, rather thanactivating the LXR pathway, inhibiting the TNF-α-induced NF-κB activities isdetected with EGCG in cells. For inhibiting the NF-κB activities, EGCG can promotethe dissociation of the Nrf2-Keap1complex; when the released Nrf2translocates tothe nucleus and activates the transcription of genes containing an ARE elementthereby inhibiting NF-κB activities, the keap1is separated from the complex todirectly interact with IKKβ and thus represses NF-κB function.Conclusions: EGCG prevents TNF-α-induced NF-κB activation therebyup-regulating ABCA1via Nrf2/Keap1pathway in macrophage foam cells.