THE EFFECT OF BILE-ACID HYDROPHOBICITY ON NUCLEATION OF SEVERAL TYPESOF CHOLESTEROL CRYSTALS FROM MODEL BILE VESICLES

Nucleation of cholesterol crystals is thought to occur from cholestero l-phospholipid vesicles. We tested the hypothesis that bile acids are necessary for nucleation of cholesterol crystals. Model bile vesicles were prepared by KBr density ultracentrifugation of supersaturated mod el bile and mixed with one of the following bile acids: ursodeoxychola te, taurocholate, cholate, chenodeoxycholate or deoxycholate in final concentrations of 3, 30 and 100 mM. Vesicles were also mixed with vari ous combinations of ursodeoxycholate and deoxycholate. Nucleation was assessed semi-quantitatively with polarizing microscopy. After 5 days, samples were again subjected to ultracentrifugation. Addition of 3 an d 30 mM taurocholate, cholate, chenodeoxycholate and deoxycholate to v esicles induced nucleation. The extent of nucleation increased signifi cantly with increasing bile acid hydrophobicity: eoxycholate>chenodeox ycholate>cholate>taurocholate (p<0.05). At 100 mM bile acid this order was reversed (p<0.05) because most of the cholesterol was solubilized in micelles as shown by ultracentrifugation after 5 days. Percentages of vesicular cholesterol decreased with increasing hydrophobicity: eo xycholate<chenodeoxycholate<cholate<taurocholate (p<0.05). Ursodeoxych olate did not induce nucleation. At least seven cholesterol crystal sh apes could be distinguished and all crystal types could be found after addition of various combinations of ursodeoxycholate+deoxycholate. We conclude that in this model: (a) bile acid species play an important role in the precipitation of cholesterol crystals from model bile vesi cles; (b) the more hydrophobic bile acids induce more cholesterol crys tal precipitation; and (c) the hydrophobicity of bile acids influences cholesterol crystal morphology. (C) Journal of Hepatology.