THE DISTRIBUTION OF THE BILIARY-ANIONIC POLYPEPTIDE FRACTION BETWEEN CHOLESTEROL CARRIERS IN BILE AND ITS EFFECT ON NUCLEATION

The small (7 kD) biliary phospholipid and calcium binding polypeptide (anionic polypeptide fraction/calcium binding protein) has been found in higher concentrations in the bile of patients with pigment stones t han in controls. In different model systems it was variously found to promote or retard cholesteral crystalization. In the present study we investigated its distribution between cholesterol carriers in bile and its effect on cholesterol crystalization in native and model biles. O n gel chromatography anionic polypeptide fraction/calcium binding prot ein was found predominantly in three areas: in the vesicular fraction, in the non-vesicular lipid fraction and in another fraction unassocia ted with biliary lipids. It was much more concentrated in the vesicula r than in the non-vesicular fraction, the mean anionic polypeptide fra ction/phospholipid molar ratio being 219 +/- 181 vs. 30.4 +/- 16, resp ectively. Anionic polypeptide fraction/calcium binding protein was add ed at three dose levels, 0.14, 0.28, 0.42 mg/ml (representing approxim ately 18%-55% of the physiologic biliary concentration), to 19 human a nd five model biles. This did not produce any significant changes in t he nucleation time. The addition of anionic polypeptide fraction/calci um binding protein at a dose level of 0.42 mg/ml to 13 different human biles did not induce changes in the distribution of cholesterol among its carriers. The present experiments do not support a role for anion ic polypeptide fraction/calcium binding protein in the process of chol esterol nucleation in bile. Qualitative changes in the protein molecul e, as demonstrated in other human secretions, cannot be excluded. (C) Journal of Hepatology.