MUCINS AND CALCIUM-PHOSPHATE PRECIPITATES ADDITIVELY STIMULATE CHOLESTEROL CRYSTALLIZATION

Human biliary mucin and calcium binding protein (CBP) influence format ion of both calcium salt precipitates and cholesterol crystals and col ocalize in the center of cholesterol gallstones. We investigated how p hysiological concentrations of these proteins regulate cholesterol cry stallization in model biles, supersaturated with cholesterol and calci um salts, mimicking pathological human bile. Using polarizing light mi croscopy and nephelometry to assess cholesterol crystallization, the i nfluence of calcium ions and calcium phosphate precipitates in the abs ence and presence of mucin, CBP, and human serum albumin was determine d. Calcium phosphate precipitates stimulated cholesterol crystallizati on more strongly than soluble calcium, Mucin also stimulated, and with soluble calcium or calcium phosphate precipitates additively increase d, the cholesterol crystal mass. In the absence of mucin, only human s erum albumin plus CBP, not these proteins individually, decreased the stimulating effect of calcium phosphate precipitates but not of solubl e calcium. However, seeding of calcium phosphate precipitates in biles with mucins resulted in near complete cholesterol crystallization wit hin one day whether CBP and HSA were or were not also present. In conc lusion, calcium salt precipitates plus human biliary mucins induce rap id and complete crystallization of cholesterol from model biles, littl e influenced by human biliary calcium binding proteins.