Chylomicron remnants: hepatic receptors and metabolism.

Recent studies support a sequential model for hepatic processing and catabolism of chylomicron remnants. Removal of chylomicron remnants by the liver involves interaction with several macromolecules on the cell surface, including the LDL receptor and heparan-sulfate-bound hepatic lipase and apolipoprotein E. Endocytosis of chylomicron remnants into hepatocytes is mediated by apolipoprotein E and normally occurs through the LDL receptor. Interaction of chylomicron remnants with the LDL receptor-related protein, or another endocytic receptor with similar properties, occurs slowly, requiring modification of surface-bound chylomicron remnants, and serves as a backup mechanism that is utilized primarily when LDL receptors are deficient or down-regulated.