Intestinal mucins and cholesterol uptake in vitro

A mucus material, secreted by intestinal segments, with a high affinity for cholesterol, has been isolated and chemically characterized. The mucin contained 11% carbohydrate, largely as glucosamine, galactose and N-acetylneuraminic acid, and 19% lipid, of which 86% was unesterified fatty acid. The isolated material readily bound cholesterol in a stoichiometric manner. Conditions known to enhance cholesterol absorption in vivo also decreased mucin complexing to cholesterol in vitro. This association of cholesterol and intestinal surface mucin also occurred during incubations of intestinal segments with dispersed cholesterol, resulting in a high level of intestinal adsorption, with little or no cellular absorption of the sterol. However, when cholesterol was solubilized in simple or complex micelles containing bile salts, surface adsorption of cholesterol was reduced and net absorption was increased. The results suggest that surface mucin binding of cholesterol may represent at least one major diffusion limitation to cholesterol absorption in the intestine.