Studies On Regulatory Key Factors Involved In Cholesterol Metabolism By Rice Protein

Rice protein is an important plant protein, whiich has high nutritional values.Particularly, the function that rice protein can reduce cholesterol levels has been focusedon increasedly. However, less evidence to elucidate how rice protein affects thecholesterol metabolism up to now.Thus, the major aim of this study is to elucidate how rice protein regulates thecholesterol metabolism in adult rats under cholesterol-free and enriched dietarycondition. The cholesterol levels in plasma and liver, cholesterol related enzymes(HMG-CoA R、CYP7A1、ACAT2、LCAT、CETP) activities, cholesterol metabolizingfactors’(SREBP2、LXRα、PPARα、SR-BI、ABCA1、LDLR) gene and protein expressionwere investigated in this study. Results suggest that the cholesterol-loweringmechanisms exerted by rice protein are very complicated and are in part attributed to theregulation of cholesterol synthesis, cholesterol degradation, cholesterol absorption andcholesterol reverse transport. The study will also provides a theoretical basis for furtherstudy on cholesterol metabolism.The major conclusions will be drawn as below:(1) Rice protein can significantly reduce plasma and liver cholesterol levels undercholesterol-free and-enriched dietary conditions, accompanying with a decrease of bileacids. As a result, AIs have been decreased in adult rats.(2) With or without cholesterol in diets, rice protein can inhibit cholesterolsynthesis in adult rats through the decrease of HMG-CoA R activity and geneexpression in comparision with casein.(3) Under cholesterol-free and-enriched dietary conditions, rice protein can activatethe activity and gene expression of the CYP7A1to stimulate the degradation ofcholesterol and result in an increase of fecal excretion of bile acids, accompanying withthe regulation of the gene and protein expression of LXRα and PPARα in adult rats..(4) Rice protein can stimulate the cholesterol reverse transport to reduce plasmacholesterol level, which is due to the inhibition of CETP activity, regulatory effect onplasma LCAT activity and the modification of cholesterol reverse transport relatedregulatory factors (SR-BI、ABCA1、LDLR) gene and protein expressions, regardless ofdiets with or without cholesterol.(5) Compared with casein, rice protein can inhibit cholesterol absorption through increasing the fecal cholesterol excretion and decreasing ACAT2activity and gene level,causing the cholesterol-lowering action in adult period.