Origin of oxysterols in hepatic bile of patients with biliary infection

Abstract

Objectives Oxysterols are ubiquitous in the body and are potential cytotoxic agents in addition to being metabolic regulators. Although bile contains high concentrations of cholesterol, oxysterol concentrations in bile and the effect of infection on oxysterol levels have not been measured, nor has their origin been studied. The purpose of this study was to determine if infection of the biliary tract was associated with increased concentrations of oxysterols in the bile and, if so, which oxysterols showed a significant change. Methods Hepatic bile was obtained from eight patients with biliary tract disease by means of a naso-biliary catheter. Oxysterols were extracted and purified by solid-phase extraction, derivatized and measured by gas chromatography–mass spectrometry. Results The following were quantified in hepatic bile: 7-α-hydroxycholesterol, 7-β-hydroxycholesterol, cholestan-3-beta,5-alpha,6-β-triol, 25-hydroxycholesterol, 26-hydroxycholesterol, 7-ketocholesterol, and 7-α-hydroxy-4-cholesten-3-one. Total oxysterols in hepatic bile ranged from 0.133 μmol/L to 7.748 μmol/L (1.47 ± 2.55 μmol/L). Levels of 7-α-hydroxycholesterol and 7-β-hydroxycholesterol were increased in infected bile (14.2 ± 15.1 × 10 −3% of cholesterol vs 1.9 ± 0.5 × 10 −3% of cholesterol, p < 0.05, and 22.0 ± 25.0 × 10 −3% of cholesterol vs 1.6 ± 1.2 × 10 −3% of cholesterol, p < 0.05, respectively). Serum C-reactive protein levels correlated positively with biliary levels of 7-α-hydroxycholesterol ( R = 0.948), 7-β-hydroxycholesterol ( R = 0.976), cholestan-3-beta,5-alpha,6-β-triol ( R = 0.823), 7-α-hydroxy-4-cholesten-3-one ( R = 0.846,) and 7-ketocholesterol ( R = 0.973). Different oxysterols were found in gallstones, chiefly 3-keto-cholest-4-ene (624 ± 316 parts per million [ppm] of dry weight), 3-keto-cholesta-4,6-diene (240 ± 329 ppm) and 7-keto-cholesterol (77 ± 81 ppm). Incubation of human leukocytes with model bile in the presence of bacterial lipopolysaccharide resulted in changes in sterol composition, including increases in oxysterols. Conclusions We have identified and quantified oxysterols from uninfected and infected human hepatic bile and from gallstones and gallbladder bile. Biliary infection may be involved in the biogenesis of oxysterols in bile through the production of reactive oxygen species from activated leukocytes.