Critical tables for calculating the cholesterol saturation of native bile

Abstract

A simple method for the rigorous derivation of lithogenic index or percent cholesterol saturation, embodying both relative and total lipid concentrations, is described. We recently demonstrated that under physiological conditions only two key physical-chemical variables, the bile salt-lecithin ratio and the total lipid (bile salts + lecithin + cholesterol) concentration determine the equilibrium cholesterol solubility of bile. Of relevance to gallstone formation and dissolution in man is that the influence of variations in total lipid concentration on cholesterol solubility is quantitatively more important but has essentially been ignored. Using model biliary lipid systems, we experimentally determined a family of cholesterol solubility curves to encompass a wide range of bile salt-lecithin ratios for physiological variations in total lipid concentration (0.3--30 g/dl) at 37 degrees C (pH 7.0, 0.15 M NaCl) and accurately fitted these with fifth degree polynomial equations. We have now solved these equations for moles percent cholesterol, i.e., [cholesterol] X 100/[bile salt] + [lecithin] + [cholesterol] employing physiological values (0.085--0.425) for molar [lecithini]/[bile salt] + [lecithin] ratios. The resulting tables provide precise values for the maximal amount of cholesterol that would be soluble in bile at any total lipid concentration and bile salt-lecithin ratio and allow for rapid and accurate calculation of lithogenic index or percent cholesterol saturation from the moles percent cholesterol actually present in hepatic, gallbladder, and duodenal biles.