Methods for determination of conjugated bilirubin in rat faeces

HPLC separation and quantification of bilirubin and its glucuronide conjugates in faeces and intestinal contents of germ-free rats

We describe an accurate reverse-phase high-performance liquid chromatography (HPLC) method for the separation and quantification of unconjugated bilirubin (UCB) and its monoglucuronide (BMG) and diglucuronide (BDG) conjugates in faeces and intestinal contents from germ-free (GF) rats. We demonstrated that female GF rats excreted predominantly BMG and that the percentage of this conjugate was at most 71.7% of the total bilirubin excreted with the faeces. The highest percentages for BDG and the UCB were 27.9% and 6.0%, respectively. The bile pigment composition in duodenal contents was 59.8% BDG and 40.2% BMG (median percentage) and was 47.7% BDG, 50.1% BMG and 2.2% UCB in ileal contents. Deconjugation of BDG to BMG was profound in caecal contents with 26.0% BDG, 67.4% BMG and 6.6% UCB. Endogenous (mammalian) beta-glucuronidase activity was present in intestinal contents throughout the entire length of the intestine and in faeces of the GF rats. The results indicated that it is very likely that endogenous beta-glucuronidase plays a role in the deconjugation of bilirubin glucuronides as well as of other glucuronides in the intestine of the GF rat.

High-performance liquid chromatography of bilirubin conjugates in bile: effect of beta-glucuronidase on the bile pigments

A simple, specific, and technically easy high-performance liquid chromatography (HPLC) method for the separation and quantification of unconjugated bilirubin, bilirubin monoglucoside-monoglucuronide, bilirubin diglucuronide, and bilirubin monoglucuronide has been developed. The method was used to determine the bilirubin compounds of bile obtained endoscopically from the common bile duct in 43 patients with gallstone disease and in 6 subjects without gallstones or liver disease. The bile samples were also assessed for the presence of beta-glucuronidase-producing bacteria. The amount of unconjugated bilirubin was significantly higher (p less than 0.01) in bile containing bacteria producing beta-glucuronidase than in bile without such bacterial strains. In six 'normal' bile samples the following quantities of bilirubin conjugates and unconjugated bilirubin were found (median and range): bilirubin monoglucoside-monoglucuronide (mixed conjugate), 61 (27-80) mumol/l; bilirubin diglucuronide, 632 (512-861) mumol/l; bilirubin monoglucuronide, 113 (70-175) mumol/l; and unconjugated bilirubin, 3 (1-7) mumol/l. These results are in good agreement with those obtained with other HPLC methods. The concentrations of unconjugated bilirubin were lower than those found when using conventional diazo methods and thin-layer chromatography. HPLC proved to be a useful tool in gallstone pathogenesis studies. Our results support bacterial glucuronidase as a possible pathogenic factor in pigment gallstone disease.

Influence of antibiotics on the faecal excretion of bile pigments in healthy subjects

We have evaluated the effects of 10 antibiotics, given orally for 6 days to healthy subjects, on faecal excretion of urobilinogen. Intake of bacitracin, vancomycin, clindamycin, erythromycin, and ampicillin resulted in a pronounced suppression of the faecal excretion of urobilinogen (p less than 0.05). Intake of doxycycline, metronidazole, nalidixic acid, ofloxacin, and trimethoprim/sulphamethoxazole had no significant effect. The effects of three antibiotics-ampicillin, clindamycin, and metronidazole--on faecal excretion of conjugated bilirubin were similarly evaluated. Intake of clindamycin led to a marked increase of conjugated bilirubin (p less than 0.05) in the faeces, and the pattern of separated azopigment derivatives of the bilirubin conjugates became altered. Intake of ampicillin and metronidazole resulted in far less alterations in faecal conjugated bilirubin, although a significant change was observed in the subjects receiving metronidazole (p less than 0.05). The differences between the antibiotics with regard to altered intestinal bile pigment metabolism may be due to differences in antimicrobial spectra and/or intestinal concentrations of the drugs. Our findings indicate that orally taken antibiotics may cause a suppression of the microbial deconjugation of conjugated bilirubin and urobilinogen formation, respectively. This may reflect a pronounced disturbance of the intestinal microflora.

Intestinal deconjugation of bilirubin in germfree and conventional rats

The content of conjugated bilirubin (CB) was about the same in small intestinal contents from germfree (GF) and conventional (CONV) rats. Caecal contents from GF rats contained considerably more CB than from CONV rats. The results indicated that the caecum is the major site of microbial deconjugation of CB in the CONV rat. Separation of azopigments prepared from small intestinal contents of GF and CONV rats revealed similar patterns. Similar separation patterns were also observed with azopigments prepared from caecal contents and faeces of GF rats. Some chemical properties of CB prepared from GF rat faeces were studied.

Influence of peroral antibiotics upon the biotransformatory activity of the intestinal microflora in healthy subjects

The effects of ampicillin, clindamycin or metronidazole, given perorally for 6 days to eighteen healthy volunteers, upon the following intestinal microflora-associated characteristics (MACs) were evaluated: breakdown of mucin, formation of coprostanol, hydrolysis of bilirubin conjugates, formation of urobilinogen, and of some short chain fatty acids (SCFAs), presence of beta-aspartylglycine and inactivation of trypsin. Clindamycin markedly influenced the expression of all characteristics, but trypsin and beta-aspartylglycine, resulting in a pattern very much alike what has been found in germ-free animals. Ampicillin caused a significant reduction in total amount of SCFAs (P less than 0.05) and urobilinogen (P less than 0.05) present in the faecal samples. Metronidazole caused a significant reduction in the formation of coprostanol and the deconjugation of bilirubin (P less than 0.05). We conclude that orally given antibiotics may cause major alterations in several parameters reflecting the normal biotransformatory activity of the intestinal microflora, probably caused by severe disturbances in the intestinal ecosystem.

Deconjugation of bilirubin conjugates and urobilin formation by conventionalized germ-free rats

The amounts of conjugated bilirubin and urobilins/urobilinogen were determined semiquantitatively in faeces of germ-free (GF) rats during GF condition and after conventionalization by oral administration of faeces suspension from conventional (CONV) rats. The amount of bilirubin conjugates, detected as their ethyl anthranilate azopigments, decreased rapidly 1 day after conventionalization. Thin-layer chromatography analysis of the corresponding faecal azopigment preparations showed that some azopigments started to disappear a few days after the conventionalization, indicating that their corresponding bilirubin conjugates were deconjugated by the bacteria in the intestine. On day 21 after conventionalization, only two azopigments were detected, namely the unconjugated and glucuronic acid conjugated dipyrroles of bilirubin, respectively, thus indicating the presence of only one bilirubin conjugate, the monoglucuronide. After 69 days no azopigments could be detected, indicating the total absence of conjugated bilirubin in these faeces samples. No urobilins were detected in faeces of the rats during their GF state, but these metabolites appeared in faeces one day after conventionalization and increased during a few days to a CONV level.