Objective: To explore the effect of monoconjugated bilirubin (MCB) on gallstone formation of both categories.
Methods: Using a newly established high performance liquid chromatography (HPLC) technique. MCB was extracted, prepared and purified from gallstone patients bile, and its solubility and pro-nucleative activity were observed.
Results: In a near physiological environment of biliary tract (pH 7.9 and temperature 37 degrees C), the aqueous solubility of MCB (558.25 +/- 5.96 microns) was only 1/7 of that of disconjugated bilirubin (DCB) (3410.9 +/- 2.42 microns), but 44 times higher than that of unconjugated bilirubin (UCB) (2.43 +/- 0.31 microns) (P < 0.01, between and two of them). Moreover, the solubility of MCB changed curvilineally with the alteration of pH, being highest at pH 7.9, zero at pH 4.5 and even lower than that of ionized UCB at pH above 9. In 3 groups of model bile systems made from Kibe's formula, the nucleation time (NT) was examined by polarized microscopy after 170 microns and 340 microns of MCB was added in group 1 and 2 respectively (group 3 was the control, with no MCB added). The NT was 3.33 +/- 0.52. 2.17 +/- 0.41 and 5.83 +/- 0.75 days respectively in the 3 groups (P < 0.05, between any 2 of the 3 groups) and the nucleative activity (NA) was 0.57 and 0.37 in group 1 and 2 respectively, which confirmed that MCB possessed a dose-related NA which was even stronger than that of glycoprotein (0.56) at the dose of 340 microns.
Conclusions: MCB might play an essential role in the formation and nucleation of gallstones with its poor aqueous solubility and strong pro-nucleative activity via certain lithogenic mechanism.