Ursolic Acid Inhibited Cholesterol Esterase and Pancreatic Lipase Activities and Decreased Micellar Cholesterol Solubility In Vitro

Ursolic acid (UA) is a natural triterpene carboxylic acid with an underlying anti-hyperlipidemia effect. This study examined the mechanism of interactions of UA with cholesterol esterase (CEase), pancreatic lipase (PL), and micellar cholesterol solubility in vitro. The half-maximal inhibitory concentration (IC50) of CEase, PL, and micellar cholesterol solubility was determined to be 0.07 ± 0.01 mg/mL, 1.81 ± 0.13 mg/mL, and 1.73 ± 0.08 mg/mL, respectively. Multispectral combination revealed that UA changed the secondary structure and quenched the intrinsic fluorescence by static quenching of the two enzymes. The interactions were exothermic reaction as determined by enthalpy. Furthermore, molecular docking confirmed that UA was bound to amino acids of two enzymes at active site through hydrophobic interaction and van der Waals forces. Molecular dynamics (MD) simulation found that CEase and PL rearranged with UA to form stable complexes. The strong inhibition effect of CEase and PL mediated by UA might provide additional insight into understanding the role of UA in the hypolipidemic effect.