title: Glycochenodeoxycholic acid inhibits calcium phosphate precipitation in vitro by preventing the transformation of amorphous calcium phosphate to calcium hydroxyapatite.
abstract: Calcium hydroxyapatite can be a significant component of black pigment gallstones. Diverse molecules that bind calcium phosphate inhibit hydroxyapatite precipitation. Because glycine-conjugated bile acids, but not their taurine counterparts, bind calcium phosphate, we studied whether glycochenodeoxycholic acid inhibits calcium hydroxyapatite formation. Glycochenodeoxycholic acid (2 mM) totally inhibited transformation of amorphous calcium phosphate microprecipitates to macroscopic crystalline calcium hydroxyapatite. This inhibition was not mediated by decreased Ca2+ activity. Taurocholic acid (2-12 mM) did not affect hydroxyapatite formation, but antagonized glycochenodeoxycholic acid. Both amorphous and crystalline precipitates contained a surface fraction relatively rich in phosphate. The surface phosphate content was diminish by increasing glycochenodeoxycholic acid concentrations, and this relationship was interpreted as competition between bile acid and HPO4(-4) for binding sites on the calcium phosphate surface. A phosphate-rich crystal surface was associated with rapid transition from amorphous to crystalline states. These results indicate that glycochenodeoxycholic acid prevents transformation of amorphous calcium phosphate to crystalline hydroxyapatite by competitively inhibiting the accumulation of phosphate on the crystal embryo surface.
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.
authors.forename: S M
authors.initials: SM
authors.lastname: Qiu
authors.forename: G
authors.initials: G
authors.lastname: Wen
authors.forename: N
authors.initials: N
authors.lastname: Hirakawa
authors.forename: R D
authors.initials: RD
authors.lastname: Soloway
authors.forename: N K
authors.initials: NK
authors.lastname: Hong
authors.forename: R S
authors.initials: RS
authors.lastname: Crowther
mesh_terms: D002118:Calcium / Q000032:analysis; D002130:Calcium Phosphates / Q000737:chemistry*; D011232:Chemical Precipitation; D017886:Durapatite; D005583:Fourier Analysis; D005999:Glycochenodeoxycholic Acid / Q000494:pharmacology*; D006882:Hydroxyapatites / Q000737:chemistry*; D008823:Micelles; D013656:Taurocholic Acid / Q000494:pharmacology
chemical_list: D002130:Calcium Phosphates; D006882:Hydroxyapatites; D008823:Micelles; C485828:alpha-tricalcium phosphate; C519480:amorphous calcium phosphate; C485830:tetracalcium phosphate; D013656:Taurocholic Acid; D005999:Glycochenodeoxycholic Acid; C485838:calcium phosphate, monobasic, anhydrous; D017886:Durapatite; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous; D002118:Calcium