beta-Glucuronidase in common duct bile, methodological aspects, variation of pH optima and relation to gallstones

Beneficial changes in gut microbiota after phototherapy for neonatal hyperbilirubinemia

Phototherapy is the most commonly used treatment for neonatal hyperbilirubinemia (NH). Gut microbiota is involved in bilirubin metabolism; however, it is uncertain whether this is affected by phototherapy. The present study included 43 newborns with hyperbilirubinemia and collected fecal samples for high-throughput sequencing before and after phototherapy. Selection α diversity analysis was used to determine the differences in diversity and abundance between the two groups, whereas similarity was determined using β diversity analysis. Linear discriminant analysis effect size analysis was used to screen for markedly different bacteria. The structure of the gut microbiota in newborns with hyperbilirubinemia changed after phototherapy, with a significant decrease in abundance and diversity. The changes in the key bacterial species were characterized by an increase in the abundance of Streptococcus salivarius and a decrease in the abundance of Escherichia, Klebsiella pneumoniae, Rothia mucilaginosa and Streptococcus oralis. These changes mainly manifested as an increase in beneficial bacteria and a decrease in opportunistic bacteria, which may not be related to the side effects of phototherapy. These results can provide theoretical assistance for microbiological research on the later stages of NH.

Bile proteome in health and disease

The study of bile proteins could improve the understanding of physiological processes involved in the regulation of the hepato-biliary system. Researchers have tried for years to investigate the bile proteome but, until recently, only a few tens of proteins were known. The advent of proteomics, availing of large-scale analytical devices paired with potent bioinformatic resources, lately allowed the identification of thousands of proteins in bile. Nevertheless, the knowledge of their role in the hepato-biliary system still represents almost a "blank page in the book of physiology." In this review, we first guide the reader through the historical phases of the analysis of bile protein content, emphasizing the recent progresses achieved through the use of proteomic techniques. Thereafter, we deeply explore the involvement of bile proteins in health and disease, with a particular focus on the discovery of biomarkers for biliary tract malignancies.

Hydrolysis of 3,4-methylenedioxymethamphetamine (MDMA) metabolite conjugates in human, squirrel monkey, and rat plasma

Characterizing the formation of metabolites of 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") in different species (rat, squirrel monkey, and human) may provide insight into mechanisms of MDMA neurotoxicity. Two prominent MDMA metabolites, 3,4-dihydroxymethamphetamine (HHMA) and 4-hydroxy-3-methoxymethamphetamine (HMMA), are conjugated with glucuronic or sulfuric acid, but reference standards are not available; therefore, quantification is only possible after conjugate cleavage. Different concentrations of HHMA and HMMA were obtained in human, squirrel monkey, and rat plasma specimens when acid or enzymatic cleavage was performed. Our data document that these differences are due to species-specific influences on conjugate cleavage. Acidic hydrolysis should be used for analyzing free HHMA and HMMA in human or squirrel monkey plasma, while enzymatic hydrolysis with glucuronidase or sulfatase maximizes recovery of free HHMA and HMMA in rat plasma. Optimization of cleavage conditions showed that sulfate conjugates were more readily cleaved by acid hydrolysis and glucuronides by glucuronidase.

Influence of intestinal barrier function on pigment gallstone formation in guinea pig model

AIM: To investigate the possible action and mechanism of the intestinal barrier function in the pathogenesis of pigment gallstone.

METHODS: Eighty guinea pigs were randomly divided into three groups: normal group (CON), pigment gallstone group (PS) and intestinal mucosa protection group (GLN). Normal forage, pigment gallstone-forming forage and pigment gallstone-forming forage with supplemental intestinal mucosa protector (glutamine) were given to the animals of corresponding groups, respectively. The gallstone-forming rate, morphological changes of intestinal mucosa, intestinal permeability, serum endotoxin and biliary β-glucuronidase were detected after 8 wk.

RESULTS: The gallstone-forming rate was 73.9% in PS. In comparison with those in CON, the intestinal mucosa damage, serum endotoxin level [(1367±525)×10^-6 EU/L vs (77±43) ×10^-6 EU/L, P < 0.01] and activity of biliary β-glucuronidase (endogenous: from 209.8±47.5 vs 122.1±39.5 Fishman Unit, P < 0.01; exogenous: from 2206.6±983.9 vs 573.5±476.9 Fishman Unit, P < 0.01) were significantly increased in PS. In GLN, the gallstone-forming rate was decreased to 44.4%, which was markedly higher than that in PS (P < 0.05). The morphological changes of intestinal mucosa, intestinal permeability and serum endotoxin [(156±97)×10^-6 EU/L vs (1367±525)×10^-6 EU/L, P < 0.05] were notably decreased in GLN as compared with those in PS, and there was no significant difference in β-glucuronidase activity.

CONCLUSION: Intestinal barrier function is correlated with pigment gallstone formation. Intestinal barrier function disorder may promote pigment gallstone formation through bacteria translocation, endotoxemia and change of biliary β-glucuronidase activity.

Relationship between bilirubin free radical and formation of pigment gallstone

In this paper, we summarize the main progresses made in our group in the field of the mechanism of pigment gallstone formation. It was found that after treatment with free radicals, bilirubin (BR) was changed into free radical itself, and a semiquinone free radical and a superoxide free radical bound with metal were recognized, which was detected by ESR (electron spin resonance). By the means of NMR (nuclear magnetic resonance) and IR (Infra-red spectra), it was postulated that bilirubin polymerized through the reaction between the vinyl group and the hydroxyl group under the attack of free radicals. It was also found that bilirubin free radical were liable to calcify in a kinetic study. Because of its chemical properties, bilirubin free radical was shown to be cytotoxic to hepatocyte, which was demonstrated based on the following facts: induction of phospholipid peroxidation (LPO), leakage of lactate dehydrogenase (LDH) and decrease of glutathione. As to the mechanism of bilirubin-induced cytotoxicity, it was postulated that the main target of bilirubin free radical was the cell membrane, including phospholipid and membrane bound proteins, especially spectrin, a content of cytoskeleton. Based on the results mentioned above, it was deduced that bilirubin free radical is the key factor that initiates and promotes the formation of pigment gallstone, which is consistent with other researches in recent years.

Pigment gallstone pathogenesis: slime production by biliary bacteria is more important than beta-glucuronidase production

Pigment stones are thought to form as a result of deconjugation of bilirubin by bacterial beta-glucuronidase, which results in precipitation of calcium bilirubinate. Calcium bilirubinate is then aggregated into stones by an anionic glycoprotein. Slime (glycocalyx), an anionic glycoprotein produced by bacteria causing foreign body infections, has been implicated in the formation of the precipitate that blocks biliary stents. We previously showed that bacteria are present within the pigment portions of gallstones and postulated a bacterial role in pigment stone formation through beta-glucuronidase or slime production. Ninety-one biliary bacterial isolates from 61 patients and 12 control stool organisms were tested for their production of beta-glucuronidase and slime. The average slime production was 42 for biliary bacteria and 2.5 for stool bacteria (P <0.001). Overall, 73% of biliary bacteria and 8% of stool bacteria produced slime (optical density >3). In contrast, only 38% of biliary bacteria produced beta-glucuronidase. Eighty-two percent of all patients, 90% of patients with common bile duct (CBD) stones, 100% of patients with primary CBD stones, and 93% of patients with biliary tubes had one or more bacterial species in their stones that produced slime. By comparison, only 47% of all patients, 60% of patients with CBD stones, 62% of patients with primary CBD stones, and 50% of patients with biliary tubes had one or more bacteria that produced beta-glucuronidase. Most biliary bacteria produced slime, and slime production correlated better than beta-glucuronidase production did with stone formation and the presence of biliary tubes or stents. Patients with primary CBD stones and biliary tubes had the highest incidence of slime production. These findings suggest that bacterial slime is important in gallstone formation and the blockage of biliary tubes.

Brown pigment stones in the common bile duct: reduced bilirubinate diconjugate in bile

BACKGROUND

Bilirubin is the main component of most common bile duct stones. Normally, almost all bilirubin in bile is conjugated to glucuronic acid or some other sugar moiety. These conjugates are unstable and liable to deconjugation. Unconjugated bilirubin is insoluble and may precipitate as the calcium salt found in brown pigment stones. The pattern of bilirubin conjugates in common duct bile of patients with choledocholithiasis has been unknown.

METHODS

In a clinical series of 55 patients with choledocholithiasis common-duct bile was aspirated, and the bilirubin conjugates analyzed with high-performance liquid chromatography. One stone from each patient was analyzed for cholesterol and bilirubin content to determine stone type.

RESULTS

Sixteen patients had cholesterol stones, 38 patients had brown pigment stones, and 1 patient had a black stone. Patients with pigment stones had a lower percentage of bilirubin diglucuronide (median, 60.3%; interquartile range, 49.7%-67.3%) than patients with cholesterol stones (64.0%; 60.2%-73.3%) (Mann-Whitney, P=0.015). No significant difference was found for the other bilirubin conjugates, total bilirubin, or biliary pH when pigment and cholesterol stone patients were compared. The time of bile sampling in relation to papillotomy and treatment of cholestasis was not associated with the low percentage of bilirubin diglucuronide. The observation of reduced values for bilirubin diglucuronide could not be ascribed to duodenal diverticula or Billroth-II gastric resection.

CONCLUSION

The percentage of the main bilirubinate conjugate, bilirubin diglucuronide, is decreased in the common duct bile of patients with pigmented compared with cholesterol stones.