Unconjugated bilirubin in hepatic bile with brown pigment gallstones and cholangitis

To investigate the role of cholangitis in hydrolysis of bilirubin in bile with brown pigment gallstones, bilirubin composition and bacterial growth in hepatic bile with and without cholangitis were studied. The study included 38 brown pigment gallstone cases (28 without cholangitis and 10 with cholangitis). The proportion of unconjugated bilirubin in hepatic bile with cholangitis (16.9±8.5%, mean ± SD) was significantly higher than that without cholangitis (3.7±1.8%, P<0.001. A positive correlation was found between bacterial population with β -glucuronidase activity and the proportion of unconjugated bilirubin in bile in cases of brown pigment stones with cholangitis P<0.05) but not in those without cholangitis despite the fact that bacterial species and population are similar regardless of the presence of cholangitis. In cholangitis, pH of bile becomes lower toward the optimal pH of bacterial β-glucuronidase. Together the lower concentration of bile acid and the lower pH in bile result in lower solubility of unconjugated bilirubin, promoting its precipitation. Thus occasional bouts of cholangitis may result in periodic deposition of bilirubinate on brown pigment stones with layered structures by inducing cyclic changes of bile composition in situ.