Nutritional and clinical aspects of cholesterol

With regard to cholesterol metabolism, it is known that 400 mg of cholesterol is synthesized in the liver every day, while 400-500 mg/day of cholesterol is absorbed through the small intestine and 800-2,000 mg/day of cholesterol circulates in the bile. Recently, NPC1L1 protein, a membrane protein in the brush border of epithelial cells in the small intestine that plays an important role in cholesterol absorption has been discovered in 2004. In the circulation, cholesterol is carried mainly by LDL and HDL. In 1976, Goldstein and Brown discovered LDL-receptor, which is the major determinant of plasma LDL-cholesterol level. Moreover, ABC-A1, a membrane protein in the peripheral cells, which plays a role in cholesterol transfer from peripheral cells to HDL, has been discovered. CETP is a plasma protein which transfers cholesterol from HDL to VLDL and LDL, and so plays a pivotal role to determine the plasma level of HDL. Thus reverse cholesterol transfer system is regulated by these two molecules. Human is not able to hydrolyze the cholesterol molecule but is able to catabolise into bile acid in the liver and secrete in the bile along with cholesterol. However, about 90 % of bile acid and 50 % of cholesterol are reabsorbed at the end of ileum. From the point of view of such cholesterol metabolism, we realize that cholesterol is a very important molecule for human. Recently, however, plasma cholesterol level increased by the change of life-style very quickly in Japan, leading that atherosclerotic diseases increase in Japan as well as Asian countries. But we should not forget that plasma cholesterol is an important marker of nutrition.