Mixed micelle properties and intestinal cholesterol uptake.

The solubilizing powers of taurocholate, taurochenodeoxycholate and tauroursodeoxycholate for monoolein and cholesterol, and the size of the bile salt-monoolein-cholesterol micelles have been determined. For the three bile salt species, the micellar size depends on the saturation with monoolein. As a result, for a given bile salt to monoolein ratio, the taurochenodeoxycholate micelles are smaller than those of taurocholate and both are smaller than those of tauroursodeoxycholate. Intestinal cholesterol uptake has been studied in vitro as a function of the micellar size and the saturation degree with cholesterol. For a given bile salt to monoolein ration and 1) for low cholesterol concentrations, taurocholate leads to the greatest rates of uptake ; 2) for high cholesterol content, taurochenodeoxycholate induces the largest uptake. The specific micellar characteristics of the tauroursodeoxycholate micelles clearly demonstrate why this bile salt is of so little help in the intestinal uptake of cholesterol.