Phytosterols Inhibit ACAT2-Catalyzed Cholesteryl Esterification in Caco-2 Cells without Affecting Cholesterol Transporter Genes

Phytosterols have long been used to prevent hypercholesterolemia-related diseases, although their effects on intestinal cholesterol metabolism remain elusive. This study applied comparative proteomics to investigate the effects of various sterols on proteomic changes in differentiated Caco-2 cells. A total of 206, 231, 180, and 197 differentially expressed proteins were identified following treatment with cholesterol, β-sitosterol, stigmasterol, and campesterol, respectively. Functional enrichment analysis revealed that phytosterols significantly altered the proteome of Caco-2 cells, though their effect on cholesterol transport protein expression was negligible. Notably, while phytosterols did not regulate the expression of acyl-CoA:cholesterol acyltransferase 2 (ACAT2), β-sitosterol and stigmasterol significantly lowered the level of cholesterol oleate in Caco-2 cells by 57.1 ± 0.8% and 51.4 ± 3.9%, respectively, demonstrating that they inhibited ACAT2-catalyzed cholesteryl esterification activity. In view of the fact that cholesterol needs to be converted to cholesteryl esters before incorporation into chylomicrons, it was concluded that phytosterols primarily reduce intestinal cholesterol absorption by inhibiting ACAT2 enzyme activity rather than its gene expression. This study provides new insights into the regulation of cholesterol homeostasis by phytosterols in the small intestine.