食品成分および生体異物によるコレステロール代謝制御に関する研究

Abstract

Dietary protein, xenobiotics or excess amino acids affect cholesterol metabolism. Whey protein exhibited a greater hypocholesterolemic effect in comparison with casein or soybean protein. The effect of soy protein peptic hydrolyzate or β-lactoglobulin tryptic hydrolyzate in suppressing the increase in the serum cholesterol level exceeded that of soy protein. In the case of high cholesterol feeding, dietary proteins affected serum cholesterol levels and inhibited cholesterol absorption through changes of micellar cholesterol solubility in the intestine, accompanied by an increase of fecal steroid excretion. Dietary peptides derived from β-lactoglobulin or soy protein inhibited cholesterol absorption in CaCo-2 cells. Dietary proteins affect the nature of bile acid micelles in the intestine, confirming observations by freeze-fracture transmission electron microscopy. Dietary proteins regulates the expression of the hepatic apolipoprotein gene. Dietary excess tyrosine or xenobiotics caused hypercholesterolemia characterized by an increase of both HDLcholesterol and LDL+VLDL-cholesterol. The stimulated synthesis of cholesterol in the liver is the main reason for this. The causal interrelationship between the hypercholesterolemia induced by dietary xenobiotics and the secretion of catecholamines or thyroid hormones was observed. These results indicate that the changes in cholesterol metabolism induced by dietary proteins, xenobiotics or excess tyrosine are expressed through intestinal and hepatic events.