Two Types of PPARγ Ligands Identified in the Extract of <i>Artemisia campestris</i>

Abstract

The 70% ethanol extract of Artemisia campestris was screened to find PPARγ ligands using the PPARγ ligand-responsive chimera luciferase reporter system. Capillartemisin B was identified as a PPARγ ligand that stimulated lipid accumulation in 3T3-L1 cells. By further purification of PPARγ ligands from a large-scale preparation of the methanol extract of Artemisia campestris, we isolated and identified eupatilin and santaflavone as PPARγ ligands. Weak PPARγ ligand activity of eupatilin or santaflavone in reporter assay was enhanced by a PPARγ antagonist, GW9662, suggesting that santaflavone or eupatilin and GW9662 bound simultaneously to the multiple sub-pockets of the PPARγ ligand-binding domain (LBD) and cooperatively activated PPARγ. Docking simulation suggested that eupatilin binds to the Ω-pocket but not to the AF-2 pocket of Y-shaped PPARγ LBD where artepillin C that differs from capillartemisin B at the C-5′ position without hydroxy group binds. Eupatilin or santaflavone with or without GW9662 did not stimulate lipid accumulation in differentiated 3T3-L1 cells, suggesting that binding of each compound alone or with GW9662 to the Ω-pocket which stimulated the PPARγ-responsive reporter expression was not enough to stimulate lipid accumulation. The PPARγ ligands found in this study have a potential to design the fragment-based drug design of a novel PPARγ ligand that cover the Y-shaped PPARγ LBD.

Keywords

• PPARγ ligand
• lipid accumulation
• cooperative activation
• ligand binding pocket
• docking simulation