DECONJUGATION OF BILIRUBIN ACCELERATES COPRECIPITATION OF CHOLESTEROL, FATTY-ACIDS, AND MUCIN IN HUMAN BILE - IN-VITRO STUDY

To examine the initial step of brown pigment gallstone formation, ster ile human gallbladder bile samples were incubated with or without beta -glucuronidase in vitro. Enhanced bilirubin deconjugation achieved by adding beta-glucuronidase significantly accelerated the formation of a precipitate that contained bilirubin (28.2 +/- 3.8% of dry weight), c holesterol (14.3 +/- 5.2%), free fatty acids (12.0 +/- 1.3%), and glyc oprotein (10.0 +/- 6.7%). Both the composition and scanning electron m icroscopic appearance of the precipitate were similar to these feature s in brown pigment gallstones. The cholesterol saturation index and nu cleation time in the supernatant did not change with various incubatio n periods. The weight ratios of bilirubin to cholesterol in the precip itates correlated with those in bile (r = 0.76; P = 0.017). Gel chroma tography of the precipitate showed high molecular weight glycoprotein to be the major constituent. Bilirubin, cholesterol, fatty acids, and mucin were found to coprecipitate in accordance with bilirubin deconju gation, which process-may play an important role in an early stage of the formation of brown pigment gallstones.