Abstract
It is known that the ATP-binding cassette transporter A1 (ABCA1) plays a major role in cholesterol homeostasis and high density lipoprotein (HDL) metabolism. Several laboratories have demonstrated that ABCA1 binding to lipid-poor apolipoprotein A-I (apoA-I) will mediate the assembly of nascent HDL and cellular cholesterol efflux, which suggests a possible receptor-ligand interaction between ABCA1 and apoA-I. In this study, a cell-based-ELISA-like high-throughput screening (HTS) method was developed to identify the synthetic and natural compounds that can regulate binding activity of ABCA1 to apoA-I. The cell-based-ELISA-like high-throughput screen was conducted in a 96-well format using Chinese hamster ovary (CHO) cells stably transfected with ABCA1 pIRE2-EGFP (Enhanced Green Fluorecence Protein) expression vector and the known ABCA1 inhibitor glibenclamide as the antagonist control. From 2,600 compounds, a xanthone compound (IMB 2026791) was selected using this HTS assay, and it was proved as an apoA-I binding agonist to ABCA1 by a flow cytometry assay and western blot analysis. The 3H cholesterol efflux assay of IMB2026791 treated ABCA1-CHO cells and PMA induced THP-1 macrophages (human acute monocytic leukemia cell) further confirmed the compound as an accelerator of cholesterol efflux in a dose-dependent manner with an EC50 of 25.23 μM.
Highlights
ATP-binding cassette transporter A1 (ABCA1) is a membrane transporter that directly contributes to high density lipoprotein (HDL) biogenesis by mediating the cellular efflux of cholesterol and phospholipids to lipid-poor apolipoprotein A-I (apoA-I) [1,2,3]
ABCA1 is a membrane transporter that directly contributes to HDL biogenesis by mediating the cellular efflux of cholesterol and phospholipids to lipid-poor apoA-I [1,2,3]
[9] most of the ABCA1 upregulators are based on the Liver X receptors (LXRs)/retinoid X receptors (RXRs) system or the peroxisome proliferator-activated receptors (PPARs) pathway which results in an extensive pharmacological effect that may not be limited to ABCA1 [9]
Summary
ABCA1 is a membrane transporter that directly contributes to HDL biogenesis by mediating the cellular efflux of cholesterol and phospholipids to lipid-poor apoA-I [1,2,3]. This membrane protein has been shown to play a rate-limiting role in controlling the efflux of the excess cholesterol from cells [4,5,6,7,8]. LXR/RXR heterodimers induce expression of genes (ABCA1) that mediate cholesterol efflux from cells and its ultimate excretion into bile by recognizing specific LXR-response elements consisting of two direct hexanucleotide repeats separated by four nucleotides. Small molecules such as BLT-4 and glibenclamide can modulate
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