Apolipoprotein metabolism: a stable-isotope approach.

Lipids are the major fuel of the body. Efficient functioning as an energy source dictates that lipids must be transportable in the plasma from the point of synthesis and assembly to the storage depots and finally to the tissues to provide energy through oxidative metabolism. Complex lipid forms are transported through the plasma as lipoprotein particles. These particles, secreted from the intestine and liver, have nonpolar outer surface composed of cholesterol, phospholipids, and apolipoproteins. Apolipoproteins are essential for the production, secretion, and continued structural integrity of the various lipoprotein particles and thus play a pivotal role in the control mechanisms of lipid transport. Apolipoproteins regulate specific enzyme activities and modulate plasma lipoprotein clearance through receptor-mediated processes. Quantitative information regarding the rates of synthesis and catabolism of apolipoproteins is vital to an understanding of their metabolism in health and disease. General considerations are followed by a specific use of stable-isotope methodology to quantitative the rate of synthesis of very-low-density-lipoprotein apolipoprotein B-100 (VLDL apo B-100) in control and familial-combined-hyperlipidemic (FCHL) patients.