A study on the influence of bile acid chemical structure on dissolution of insoluble calcium salts: an in vitro study of the use of bile acid-phosphatidylcholine-cholesterol model bile solution.

The influence of bile acid chemical structure on dissolution of insoluble calcium salts and the reducing effect of ionized calcium was studied. Various bile acids were used to compound model bile acid-phosphatidylcholine-cholesterol model bile solutions. After CaCO3 was added to these solutions, both total calcium solubility and ionized calcium concentration in the solutions were measured. Dihydroxy bile acid is more effective than trihydroxy bile acid and 7 alpha-hydroxy bile acid is more effective than 7 beta-hydroxy bile acid, with regard to calcium solubility and the reducing effect of ionized calcium in model bile solution. Glutamic or asparaginic acid conjugates are more effective than glycine or taurine conjugates. Therefore, calcium solubility and the reducing effect of ionized calcium in model bile solutions are dependent on the number and orientation of hydroxy groups on the steroid nucleus as well as electrical charge of conjugating amino acid of bile acid. Chenodeoxycholic acid conjugated with glutamic or asparginic acid possesses high calcium solubility and large binding capacity with ionized calcium.