Significance of different conjugate forms of bilirubin in the formation of pigment gallstones

The aim of the present study was to analyse bile samples from cases with gallstones by high performance liquid chromatography according to the type of stones present, with special reference to the glucoside and xyloside conjugates of bilirubin, and to investigate their deconjugation. The composition of bilirubin conjugates in bile was similar between cholesterol and black pigment stones except that the total bilirubin concentration was about 5 times higher in black pigment stone cases with haemolysis. Unconjugated bilirubin was higher in brown pigment stone cases than in cholesterol stone cases, although total bilirubin concentration was lower in the former. In addition, in brown pigment stone cases, bile contained statistically less bilirubin diglucuronide and more bilirubin diglucoside and monoglucoside than in bile with cholesterol stones (P<0.05). Glucoside and xyloside conjugates are also major components, regardless of the types of gallstones present, accounting for as much as 18 to 25%. Incubation experiment revealed that bilirubin diglucuronide was more readily deconjugated than bilirubin diglucoside or bilirubin monoglucoside monoxyloside. Therefore, glucuronide conjugates were likely to be the main source of unconjugated bilirubin in the formation of pigment gallstones.