[Regulation of intestinal cholesterol metabolism]

The small bowel epithelium is of major importance in the cholesterol homeostasis of the organism. The morphological and functional heterogeneity of the gut, complicates studies on intestinal cholesterol metabolism. Cholesterol from diet, de novo synthesis and lipoproteins is strictly compartmentalized intracellularly and supports different metabolic needs. Interactions of cholesterol and lipoproteins were studied in cultured intestinal cells (IEC-6, CaCo-2). Newly synthesized cholesterol is mainly utilized for local purposes like membrane synthesis and is essential for cell growth. In contrast to other cell systems it cannot be replaced by LDL cholesterol in case of blocked synthesis. LDL is specifically bound, internalized and degraded. HDL3 also displays specific binding, internalisation and retroendocytosis, but is not degraded. The observed induction of HMG-CoA reductase, suppression of ACAT, as well as cholesterol efflux after contact of HDL3 with lipid droplets argue for intracellular cholesterol transfer to intact HDL3 and finally resecretion into the medium. HDL3 therefore appears as a mediator of reverse cholesterol transport also in the small intestinal epithelial cell.