Quaternized colestipol, an improved bile salt adsorbent: in vitro studies

Colestipol.HCl (col-HCl) was quaternized with methyl iodide to form col-CH3l. The in vitro binding capacities of the quaternized and protonated resins in water and in Tris-HCl buffer (0.0015 and 0.0025 M, pH 7.0) at approximately 22 degrees C for sodium glycocholate (NaGC) was determined by reversed-phase HPLC. The binding capacities were found to depend on the adsorption medium. In water, the binding capacity of col-CH3l was 30% greater than that of its protonated form. In Tris-HCl buffer at pH 7.0, the binding capacities of the resins were similar. When the quaternized colestipol was converted to its chloride form, the binding capacity for NaGC in Tris-HCl increased significantly and was 30% greater than that for its protonated analogue. In Cotazym 65B-water, a medium used to test the binding capacity of the resins in the presence of various agents (to try to simulate intestinal conditions), the binding capacity of the quaternized resin was again greater than that of its protonated form. Quaternization thus increases the in vitro binding capacity of colestipol for the glycocholate anion.