Abstract
It is essential for cholesterol absorption to be solubilized in bile salt micelles in intestinal lumen. It is believed that the bile salt micelles can reach to the surface of intestinal epithelial cells through unstirred water layer covering on the apical side of the cells. Since the bile salt micelles cannot be directly incorporated into the cells, cholesterol is believed to be released as a monomer and then to be incorporated into the cells through brush border membrane. Comparative studies of cholesterol and poorly absorbable plant sterols suggest that both solubility in and affinity for the micelles can be major determinants of sterol absorption. The process mediated by NPC1L1 on the brush border membrane is thought to be the major route of the incorporation of cholesterol and plant sterols into the cells. It is thought that a part of incorporated cholesterol and plant sterols is excreted through ABCG5/ABCG8. Mutation in ABCG5 or ABCG8 causes an increase in sterol absorption and therefore, induces deposition of plant sterols. A large part of cholesterol incorporated into the intestinal cells is esterified by ACAT2 and incorporated into chylomicrons and then they are secreted to the lymph.
