Abstract
It is well known that dietary xenobiotics and protein nutrition affect cholesterol and serum lipoprotein metabolism, although these precise mechanism has not been fully clarified. Treatment of rats with xenobiotics such as polychlorinated biphenyls (PCB) resulted in hyper-α-lipoproteinemia, characterized by an increase of apolipoprotein A-I (apo A-I) and replacement of apo E by apo A-I. Dietary PCB increased the hepatic levels of mRNA for apo A-I and HMG-CoA reductase. In hepatocyte culture, a direct effect of PCB on hepatocytes was revealed. The dietary level of protein regulated the expression of the liver apo A-I gene transcriptionally in a liver-specific manner. Soy protein isolate (SPI) decreased the cholesterol level of very-low-density lipoproteins and of high-density lipoproteins in comparison with casein. SPI lowered the level of apo E-rich lipoproteins, and then decreased that of apo A-I-rich lipoproteins. The hepatic apo A-I mRNA level was decreased by SPI, and elevated by addition of methionine. These results demonstrate that dietary xenobiotics and protein are regulators of apo A-I gene expression and the serum level of high-density lipoproteins.
