Specific high affinity binding and degradation of high density lipoproteins by isolated epithelial cells of human small intestine.

The interaction of high density lipoproteins (HDL) with isolated epithelial cells of human small intestine (enterocytes) was studied. 125I-HDL3 (density = 1,125 to 1,126 g/cm3) exhibit a high-affinity (Kd = 8.3 X 10(-8). Bmax = 886 ng/mg cell protein), saturable and reversible binding to isolated enterocytes. In the presence of excess unlabeled HDL3, the cell surface-bound 125I-HDL3 are released into the medium nondegraded. Treatment of cells with pronase does not affect 125I-HDL3 binding. The binding is accompanied with internalization and degradation of 125I-HDL3. Chloroquine inhibits the degradation and increases 125I-HDL3 uptake. A threefold excess of HDL3 and HDL2 inhibits the binding and degradation of 125I-HDL3 by 60%, whereas a 20-fold excess of low density lipoproteins (LDL), only by 20%. HDL3 (20 to 1,000 micrograms/mL) stimulates the synthesis of sterols and inhibits sterol ester synthesis in enterocytes. The obtained results make it possible to assume that epithelial cells of the small intestine may participate in the catabolism of HDL in human organism.