Bile is secreted by the liver and contains bile salts, which are needed for digestion of lipids, plus the phospholipid lecithin, a primary constituent of cell membranes. The gallbladder stores bile between meals, and gallstones result when cholesterol precipitates from bile during this storage period.
Cholesterol is insoluble in water, and precipitation from bile at first appears unavoidable.
For example, lecithin vesicles enhance the solubility of cholesterol in bile nearly one million fold. Such vesicles are thermodynamically metastable so that cholesterol crystals will ultimately prevail at equilibrium. Attainment of equilibrium is typically slow enough that cholesterol passes through the gallbladder without consequence, but diseased individuals are not so fortunate. Kinetic factors, presumably proteins, influence the rate at which vesicles yield crystals, and the question of who develops gallstones is a matter of chemical kinetics, not thermodynamics. Our gallstone research aims at prevention of gallstones in humans by determining the mechanisms by which various proteins influence the rate of gallstone formation.