A target for cholesterol absorption inhibitors in the enterocyte brush border membrane

Uptake of cholesterol by the intestinal absorptive epithelium can be selectively blocked by specific small molecules, like the sterol glycoside, L-166,143. Furthermore, 3H-labeled L-166,143 administered orally to hamsters binds specifically to the intestinal mucosa, suggesting the existence of a cholesterol transporter. Using autoradiography, the binding site of 3H-L-166,143 in the hamster small intestine was localized to the very apical aspect of the absorptive epithelial cells. Label was competed by non-radioactive L-166,143 and two structurally distinct cholesterol absorption inhibitors, suggesting a common site of action for these compounds. L-166,143 blocked uptake of 3H-cholesterol into enterocytes in vivo, as demonstrated by autoradiography, suggesting that it inhibits a very early step of cholesterol absorption, incorporation into the brush border membrane. This conclusion was confirmed by studies in which intestinal brush borders were isolated from hamsters dosed with 3H-cholesterol in the presence or absence of L-166,143. Uptake of 3H-cholesterol into the membranes was substantially inhibited by the compound. In contrast, an inhibitor of acyl CoA:cholesterol acyltransferase, did not affect uptake of 3H-cholesterol into the brush border membranes. These results strongly support the existence of a specific transporter that facilitates the movement of cholesterol from bile acid micelles into the brush border membranes of enterocytes.