Direct Intestinal Cholesterol Secretion Contributes Significantly to Total Fecal Neutral Sterol Excretion in Mice

Abstract

Hepatobiliary secretion is generally believed to be an integral step in the pathway of cholesterol excretion from the body. Here we have investigated the validity of this paradigm in mice. Cholesterol balance was assessed by measuring intake, excretion, and biliary output in different mouse models. Direct secretion of cholesterol from the luminal side of enterocytes was studied by perfusion of isolated segments of the small intestine in mice. Cholesterol input and output measurements in different mouse models revealed that fecal neutral sterol excretion was higher than the sum of dietary cholesterol intake and biliary cholesterol secretion indicating the existence of an alternative pathway. Here we show that substantial amounts of cholesterol can be secreted directly by enterocytes. Transintestinal cholesterol secretion is a specific process observed throughout the small intestine (proximal > medial > distal). Secretion depended on the presence of a cholesterol acceptor and was strongly stimulated by bile salts and phospholipids. The capacity of the pathway was sufficient to account for the missing cholesterol in the balance studies. The contribution of this pathway to cholesterol excretion in mice is approximately twice that of the biliary pathway. In mice, the intestine plays a significant role in removal of cholesterol from the body.