Pattern of bile acid regurgitation and metabolism during perfusion of the bile duct obstructed rat liver

Quantitative bile acid profiling in healthy adult dogs and pups from serum, plasma, urine, and feces using LC-MS/MS

Synthesis and secretion of bile acids (BA) is a key physiological function of the liver. In pathological conditions like portosystemic shunt, hepatic insufficiency, hepatitis, or cirrhosis BA metabolism and secretion are disturbed. Quantification of total serum BA is an established diagnostic method to assess the general liver function and allows early detection of abnormalities, liver disease progression and guidance of treatment decisions. To date, data on comparative BA profiles in dogs are limited. However, BA profiles might be even better diagnostic parameters than total BA concentrations. On this background, the present study analyzed and compared individual BA profiles in serum, plasma, urine, and feces of 10 healthy pups and 40 adult healthy dogs using ultra-high performance liquid chromatography coupled to electrospray ionization mass spectrometry. Sample preparation was performed by solid-phase extraction for serum, plasma, and urine samples or by protein precipitation with methanol for the feces samples. For each dog, 22 different BA, including unconjugated BA and their glycine and taurine conjugates, were analyzed. In general, there was a great interindividual variation for the concentrations of single BA, mostly exemplified by the fact that cholic acid (CA) was by far the most prominent BA in blood and urine samples of some of the dogs (adults and pups), while in others, CA was under the detection limit. There were no significant age-related differences in the BA profiles, but pups showed generally lower absolute BA concentrations in serum, plasma, and urine. Taurine-conjugated BA were predominant in the serum and plasma of both pups (68%) and adults (74-75%), while unconjugated BA were predominant in the urine and feces of pups (64 and 95%, respectively) and adults (68 and 99%, respectively). The primary BA chenodeoxycholic acid and taurocholic acid and the secondary BA deoxycholic acid and lithocholic acid were the most robust analytes for potential diagnostic purpose. In conclusion, this study reports simultaneous BA profiling in dog serum, plasma, urine, and feces and provides valuable diagnostic data for subsequent clinical studies in dogs with different kinds of liver diseases.

TGR5 agonists induce peripheral and central hypersensitivity to bladder distension

The mechanisms underlying chronic bladder conditions such as interstitial cystitis/bladder pain syndrome (IC/BPS) and overactive bladder syndrome (OAB) are incompletely understood. However, targeting specific receptors mediating neuronal sensitivity to specific stimuli is an emerging treatment strategy. Recently, irritant-sensing receptors including the bile acid receptor TGR5, have been identified within the viscera and are thought to play a key role in neuronal hypersensitivity. Here, in mice, we identify mRNA expression of TGR5 (Gpbar1) in all layers of the bladder as well as in the lumbosacral dorsal root ganglia (DRG) and in isolated bladder-innervating DRG neurons. In bladder-innervating DRG neurons Gpbar1 mRNA was 100% co-expressed with Trpv1 and 30% co-expressed with Trpa1. In vitro live-cell calcium imaging of bladder-innervating DRG neurons showed direct activation of a sub-population of bladder-innervating DRG neurons with the synthetic TGR5 agonist CCDC, which was diminished in Trpv1-/- but not Trpa1-/- DRG neurons. CCDC also activated a small percentage of non-neuronal cells. Using an ex vivo mouse bladder afferent recording preparation we show intravesical application of endogenous (5α-pregnan-3β-ol-20-one sulphate, Pg5α) and synthetic (CCDC) TGR5 agonists enhanced afferent mechanosensitivity to bladder distension. Correspondingly, in vivo intravesical administration of CCDC increased the number of spinal dorsal horn neurons that were activated by bladder distension. The enhanced mechanosensitivity induced by CCDC ex vivo and in vivo was absent using Gpbar1-/- mice. Together, these results indicate a role for the TGR5 receptor in mediating bladder afferent hypersensitivity to distension and thus may be important to the symptoms associated with IC/BPS and OAB.

Bile Acid sulfation: a pathway of bile acid elimination and detoxification

Sulfotransferase-2A1 catalyzes the formation of bile acid-sulfates (BA-sulfates). Sulfation of BAs increases their solubility, decreases their intestinal absorption, and enhances their fecal and urinary excretion. BA-sulfates are also less toxic than their unsulfated counterparts. Therefore, sulfation is an important detoxification pathway of BAs. Major species differences in BA sulfation exist. In humans, only a small proportion of BAs in bile and serum are sulfated, whereas more than 70% of BAs in urine are sulfated, indicating their efficient elimination in urine. The formation of BA-sulfates increases during cholestatic diseases. Therefore, sulfation may play an important role in maintaining BA homeostasis under pathologic conditions. Farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor are potential nuclear receptors that may be involved in the regulation of BA sulfation. This review highlights current knowledge about the enzymes and transporters involved in the formation and elimination of BA-sulfates, the effect of sulfation on the pharmacologic and toxicologic properties of BAs, the role of BA sulfation in cholestatic diseases, and the regulation of BA sulfation.

Repetitive short-term bile duct obstruction and relief causes reproducible and reversible bile acid regurgitation

BACKGROUND

Long-term bile duct obstruction causes sinusoidal regurgitation of bile acids, a shift in bile acid metabolism, and alterations of liver histology. In this study we investigated the regurgitation of bile acids during short-term bile duct obstruction and its reversibility and reproducibility. In addition, the biotransformation of taurodeoxycholate and its appearance in bile and perfusate effluent were studied as well as liver histology.

METHODS

Rat livers (n = 5) were perfused in vitro with 32 nmol/min/g liver taurodeoxycholate over 85 min with the bile duct being intermittently closed for 30 and 20 min, respectively.

RESULTS

Within the first 5 min after bile duct obstruction bile acids started to regurgitate to the perfusate effluent amounting to approximately 15% of hepatic uptake until the end of the perfusion period. After relief of obstruction, bile flow and biliary bile acid excretion showed an overshoot phenomenon and were almost doubled compared to preobstruction. In contrast, sinusoidal bile acid regurgitation declined. The same phenomenon was observed during the second closure/opening cycle of the bile duct. Regurgitated bile acids consisted of significantly more taurodeoxycholate metabolites (approximately 70%) than did biliary bile acids (approximately 30%). Histology of liver parenchyma was preserved.

CONCLUSIONS

During repetitive short-term bile duct obstruction bile acid regurgitation is reversible and reproducible. The absence of altered mechanical barriers suggests that specific pathways are involved in the regurgitation process of bile acids.

Presence of white bile associated with lower survival in malignant biliary obstruction

OBJECTIVE

The chemical composition and clinical significance of white bile in patients with malignant biliary obstruction were evaluated in a prospective study.

METHODS

Consecutive patients (January 1996 through December 1997) with inoperable malignant biliary obstruction underwent endoscopic placement of 10F straight, plastic biliary stents. Bile was aspirated during the endoscopic procedure. Patients were divided into 2 groups: those with white and those with yellow bile. The chemical composition of bile was analyzed. Levels of bile acids in the serum and bile (11 samples) were estimated by high-performance thin-layer chromatography. The groups were compared for decremental fall in bilirubin (b value), cholangitis after stent insertion, and survival.

RESULTS

Thirty-five patients (15 men, 20 women; mean age 54 years) underwent endoscopic drainage for malignant obstruction (29 hilar, 6 distal bile duct). Eighteen patients had white bile. Refractory jaundice (b > -0.025) was seen in 9 (50%) patients with white bile compared with 3 (17.6%) with yellow bile; mean difference -42.2 (95% CI [-62.4, -22.0]) and -45.7 (95% CI [-72.0, -19.4]), respectively. The bilirubin (0.48 mg/L) and bile acid (15.6 mmol/L) concentrations in white bile were significantly less than bilirubin (42.7 mg/L) and bile acid (61.3 mmol/L) concentrations in yellow bile; mean difference -42.2 (95% CI [-62.4, -22.0]) and mean difference -45.7 (95% CI [-72.0, -19.4]), respectively. Cholangitis developed in 66.6% of patients with white bile compared with 35% of those with yellow bile (OR 3.67: 95% CI [0.74, 19.25]). Kaplan-Meier curves showed that median survival (interquartile range) was shorter in patients with white bile (35 [23-60] versus 77 [35-220] days) (p = 0.004, log rank test), which was significant even after adjusting for potential confounders with Cox proportional hazards regression.

CONCLUSION

White bile is largely devoid of bilirubin and bile acids. The presence of white bile was associated with significantly worse survival in patients with malignant biliary obstruction.

Bile duct ligation in rats induces biliary expression of cytokine-induced neutrophil chemoattractant

BACKGROUND & AIMS

Bile duct obstruction causes neutrophilic inflammation of the liver and leads to hepatic fibrosis. In obstructive liver disease, the localization of neutrophils in portal tracts suggests that cells within this region produce neutrophil chemoattractants. In this study, we investigated whether bile duct obstruction in rats induces portal expression of cytokine-induced neutrophil chemoattractant (CINC).

METHODS

Rats underwent bile duct ligation for 3 hours to 8 days. CINC regulation was examined in vivo at various intervals by immunohistochemistry, ribonuclease protection, and in situ hybridization. CINC production was also investigated in cell culture, in response to putative stimuli from obstructed liver.

RESULTS

Bile duct ligation caused neutrophilic infiltration of the liver within 3 hours. CINC was also rapidly induced, with specific expression identified in biliary cells. Rat intrahepatic biliary cells produced CINC constitutively in culture; when exposed to cholestatic bile, they showed a 12-fold increase in CINC secretion. The effect of bile was not attributable to toxicity or to dissolved cytokines or endotoxin. Mechanical strain, designed to mimic the stretching of biliary cells during obstruction, did not induce CINC.

CONCLUSIONS

Biliary cells contribute to hepatic inflammation during cholestasis by producing neutrophil chemoattractants. A major stimulus to biliary chemoattractant production in vivo may be bile itself.