Effect of taurohyodeoxycholic acid, a hydrophilic bile salt, on bile salt and biliary lipid secretion in the rat

Taurohyodeoxycholic acid alleviates trinitrobenzene sulfonic acid induced ulcerative colitis via regulating Th1/Th2 and Th17/Treg cells balance

AIMS

Taurohyodeoxycholic acid (THDCA), a natural 6α-hydroxylated bile acid, exhibits intestinal anti-inflammatory effects. This study aimed to explore the efficacy of THDCA on ulcerative colitis and to reveal its mechanisms of action.

MAIN METHODS

Colitis was induced by intrarectal administration of trinitrobenzene sulfonic acid (TNBS) to mice. Mice in the treatment group were gavage THDCA (20, 40, and 80 mg/kg/day) or sulfasalazine (500 mg/kg/day) or azathioprine (10 mg/kg/day). The pathologic markers of colitis were comprehensively assessed. The levels of Th1-/Th2-/Th17-/Treg-related inflammatory cytokines and transcription factors were detected by ELISA, RT-PCR, and Western blotting. The balance of Th1/Th2 and Th17/Treg cells was analyzed by Flow cytometry.

KEY FINDINGS

THDCA significantly alleviated colitis by improving the body weight, colon length, spleen weight, histological characteristics, and MPO activity of colitis mice. THDCA reduced the secretion of Th1-/Th17-related cytokines (IFN-γ, IL-12p70, IL-6, IL-17A, IL-21, IL-22, and TNF-α) and the expressions of transcription factors (T-bet, STAT4, RORγt, and STAT3), but increase the production of Th2-/Treg-related cytokines (IL-4, IL-10, and TGF-β1) and the expressions of transcription factors (GATA3, STAT6, Foxp3, and Smad3) in the colon. Meanwhile, THDCA inhibited the expressions of IFN-γ, IL-17A, T-bet, and RORγt, but improved the expression of IL-4, IL-10, GATA3, and Foxp3 in the spleen. Furthermore, THDCA restored the proportion of Th1, Th2, Th17, and Treg cells, and balanced the Th1/Th2 and Th17/Treg immune response of colitis mice.

SIGNIFICANCE

THDCA can alleviate TNBS-induced colitis via regulating Th1/Th2 and Th17/Treg balance, which may represent a promising treatment for patients with colitis.

Hypothyroidism Increases Cholesterol Gallstone Prevalence in Mice by Elevated Hydrophobicity of Primary Bile Acids

Background: Thyroid hormone (TH) deficiency has been associated with increased cholesterol gallstone prevalence. Hypothyroidism impacts hepatic lipid homeostasis, biliary secretion, gallbladder motility, and gallstone (LITH) gene expression, all potential factors contributing to cholesterol gallstone disease (CGD). However, how TH deficiency may lead to gallstone formation is still poorly understood. Therefore, we performed molecular studies in a CGD mouse model under lithogenic conditions and modulation of TH status. Methods: Male, three-month-old C57BL/6 mice were randomly divided into a control (euthyroid) group, a hypothyroid (hypo) group, a gallstone (litho) group, and a gallstone+hypothyroid (litho+hypo) group and were treated for 2, 4, and 6 weeks (n = 8/treatment period). Gallstone prevalence, biliary composition and cholesterol crystals, hepatic expression of genes participating in cholesterol, bile acid (BA), and phosphatidylcholine synthesis (Hmgcr, Cyp7a1, Pcyt1a), and canalicular transport (Abcg5, Bsep, Abcb4) were investigated. Results: Increased cholesterol gallstone prevalence was observed in hypothyroid mice under lithogenic diet after 4 and 6 weeks of treatment (4 weeks: 25% vs. 0%; 6 weeks: 75% vs. 37.5%). Interestingly, neither the composition of the three main biliary components, cholesterol, BAs, and phosphatidylcholine, nor the hepatic expression of genes involved in synthesis and transport could explain the differences in cholesterol gallstone formation in the mice. However, TH deficiency resulted in significantly increased hydrophobicity of primary BAs in bile. Furthermore, downregulation of hepatic sulfonation enzymes Papss2 and Sult2a8 as well as diminished biliary BA sulfate concentrations in mice were observed under hypothyroid conditions all contributing to a lithogenic biliary milieu as evidenced by microscopic cholesterol crystals and macroscopic gallstone formation. Conclusions: We describe a novel pathogenic link between TH deficiency and CGD and suggest that the increased hydrophobic character of biliary BAs due to the diminished expression of hepatic detoxification enzymes promotes cholesterol crystal precipitation and enhances cholesterol gallstone formation in the bile of hypothyroid mice.

Enhancing effect of taurohyodeoxycholate on ABCB4-mediated phospholipid efflux

Hydrophilic bile salts, ursodeoxycholate and hyodeoxycholate, have choleretic effects. ABCB4, a member of the ABC transporter family, is essential for the secretion of phospholipids from hepatocytes into bile. In this study, we assessed the effects of taurine- or glycine-conjugated cholate, ursodeoxycholate and hyodeoxycholate on the ABCB4-mediated phosphatidylcholine (PC) efflux using Abcb4 knockout mice and HEK293 cells stably expressing ABCB4. To evaluate the effects of bile salts on bile formation in Abcb4+/+ or Abcb4-/- mice, the bile was collected during intravenous infusion of saline or bile salts. The biliary PC secretion in Abcb4+/+ mice was significantly increased by the infusions of all tested bile salts, especially taurohyodeoxycholate. On the other hand, Abcb4-/- mice exhibited extremely low secretion of PC into bile, which was not altered by bile salt infusions. We also showed that the PC efflux from ABCB4-expressing HEK293 cells was stimulated by taurohyodeoxycholate much more strongly than the other tested bile salts. However, taurohyodeoxycholate did not restore the activities of ABCB4 mutants. Furthermore, light scattering measurements demonstrated a remarkable ability of taurohyodeoxycholate to form mixed micelles with PC. Therefore, the enhancing effect of taurohyodeoxycholate on the ABCB4-mediated PC efflux may be due to the strong mixed micelle formation ability.

Nonclinical toxicology studies with sodium taurodeoxycholate: acute and subacute toxicity in dogs

Sodium taurodeoxycholate (TDCA) has been investigated for various inflammatory disorders such as sepsis. We recently evaluated nonclinical safety profile of TDCA using rats infused intravenously. As a series of preclinical safety investigations, we further conducted toxicity studies with TDCA delivered to dogs via intravenous administration under Good Laboratory Practice regulation in this study. In dose range-finding study (dose escalation study), dogs given with TDCA at a dose of 150 mg/kg showed marked changes in clinical signs, hematology, and serum biochemistry. And biochemical markers of liver damage and local skin lesions were observed following intravenous infusion of 100 mg/kg TDCA, suggesting that 100 mg/kg was chosen as the highest dose of TDCA for 4-week repeated-dose toxicity study using dogs. Despite no treatment-related significant changes in body weight, food consumption, ophthalmoscopy, and urinalysis, skin lesions were observed at the injection site of animals administered with higher than 50 mg/kg of TDCA along with biochemical and histopathological changes associated with liver injury. However, most of off-target effects were found to be reversible since these were recovered after stopping TDCA infusion. These findings indicate that the no-observed-adverse-effect-level (NOAEL) for TDCA in dogs was considered to be 5 mg/kg/d. Taken together, our results provide important toxicological profiles regarding the safe dose of TDCA for drug development or clinical application.

A phylogenetic survey of biliary lipids in vertebrates ,

Biliary lipids (bile salts, phospholipids, cholesterol, plant sterols) were determined in 89 vertebrate species (cartilaginous and bony fish, reptiles, birds, and mammals), and individual phospholipid classes were measured in 35 species. All samples contained conjugated bile salts (C(27) bile alcohol sulfates and/or N-acyl amidates of C(27) and/or C(24) bile acids). Phospholipids were generally absent in the bile of cartilaginous fish and reptiles and were present in low amounts relative to bile salts in bony fish and most birds. In mammals, the phospholipid-bile salt ratio varied widely. The bile from species with low biliary phospholipid-bile salt ratios often contained a high proportion of sphingomyelin, confirmed by HPLC-MS. In species with a high phospholipid-bile salt ratio, the predominant biliary phospholipid was phosphatidylcholine (PC). The phospholipid-bile salt ratio correlated weakly with the calculated weighted hydrophobic index value. Cholesterol was present in the bile of virtually all species, with plant sterols uniformly being present in only trace amounts. The cholesterol-bile salt ratio tended to be higher in mammals than in non-mammals, but bile of all species was unsaturated. Thus, most nonmammalian vertebrates have relatively low levels of biliary phospholipid and cholesterol, suggesting that cholesterol is eliminated predominantly as bile salts. Mammals have a higher phospholipid and cholesterol to bile salt ratio, with the dominant phospholipid being PC.

Ursodeoxycholic acid induced activation of the glucocorticoid receptor in primary rat hepatocytes

BACKGROUND AND AIMS

Ursodeoxycholic acid (UDCA), a hydrophilic bile acid, improves biochemical, immunopathological and histological parameters in chronic cholestatic liver diseases. The immunomodulatory properties of UDCA show interesting similarities with the effects of glucocorticoids. We investigated the activation of the glucocorticoid receptor by UDCA and the glucocorticoid receptor dependent gene expression in primary rat hepatocytes as well as binding of radiolabelled UDCA to the glucocorticoid receptor ligand binding site expressed in a glucocorticoid receptor fusion protein.

METHODS

Primary rat hepatocytes in culture were co-transfected with a luciferase reporter gene construct (GRE-luc) containing a glucocorticoid receptor responsive element (GRE) and a glucocorticoid receptor expression vector (6RGR) followed by stimulation with dexamethasone or UDCA. Luciferase activity was determined and specific binding of glucocorticoid receptor to the GRE was confirmed by an electrophoretic mobility shift assay (EMSA). The glucocorticoid receptor binding site was expressed in a GR-myc fusion protein and binding of radiolabelled UDCA to the fusion protein was determined.

RESULTS

Incubation of co-transfected hepatocytes with 0.1-1.000 microM dexamethasone or 0.1-1.000 microM UDCA led to an 11.9- to 20.85-fold (dexamethasone) and 2.6- to 4.3-fold (UDC) increase of luciferase activity. Mobility shift assays using nuclear extracts from transfected and stimulated hepatocytes also showed a dose dependent increase of DNA binding after stimulation with UDCA. However, incubation of the GR-myc fusion protein with radiolabelled UDCA yielded no specific binding of UDCA to the glucocorticoid receptor binding site, whereas dexamethasone showed specific binding of the fusion protein.

CONCLUSIONS

UDCA activates the intracellular glucocorticoid receptor in a dose-dependent manner. Direct binding of the glucocorticoid receptor by radiolabelled UDCA at the glucocorticoid receptor binding site could be excluded as the mechanism of activation. The mechanisms involved in UDCA-mediated glucocorticoid receptor activation and possible targeted glucocorticoid receptor activation due to partial UDCA tissue specificity warrant further elucidation.

Taurohyodeoxycholate- and tauroursodeoxycholate-induced hypercholeresis is augmented in bile duct ligated rats

BACKGROUND/AIMS

Taurohyodeoxycholate (THDCA) and tauroursodeoxycholate (TUDCA) induce more bile flow per molecule excreted compared to endogenous bile acids. The aim of this study is to determine if the hypercholeretic effect of tauroursodeoxycholate or taurohyodeoxycholate in normal and bile duct ligated (BDL) rats is due to increased ductal secretion.

METHODS

Normal or BDL rats were infused with tauroursodeoxycholate or taurohyodeoxycholate and bile flow, bicarbonate, bile salt, cholesterol, and phospholipid secretion were measured. Cholangiocytes were stimulated with taurohyodeoxycholate or tauroursodeoxycholate, and secretin-stimulated secretion was measured.

RESULTS

Taurohyodeoxycholate and tauroursodeoxycholate increased bile flow more in BDL than normal rats. Tauroursodeoxycholate increased bicarbonate secretion more in BDL compared to normal rats. Taurohyodeoxycholate when infused with taurocholate increased bile flow (but not phospholipid excretion) to a greater degree in BDL compared to normal rats. Taurohyodeoxycholate and tauroursodeoxycholate decreased secretin-stimulated cholangiocyte secretion.

CONCLUSIONS

Consistent with a ductal origin for bile acid-induced hypercholeresis, taurohyodeoxycholate and tauroursodeoxycholate produced a greater hypercholeresis in BDL than normal rats. Tauroursodeoxycholate- (but not taurohyodeoxycholate-) stimulated hypercholeresis is associated with increased HCO(3)(-) secretion. Tauroursodeoxycholate increases biliary HCO(3)(-) secretion by a mechanism unrelated to secretin-stimulated cholangiocyte secretion. Taurohyodeoxycholate-induced hypercholeresis in BDL rats is unrelated to enhanced phospholipid excretion.

Effects of hydrophobic and hydrophilic bile salt mixtures on cholesterol crystallization in model biles

The hydrophilic bile salt ursodeoxycholate is frequently used to dissolve cholesterol gallstones. We have now quantitated crystallization as a function of bile salt hydrophobicity, phospholipid content, cholesterol saturation and total lipid concentration (TLCo).

METHODS

Crystallization in supersaturated model biles with low phospholipid contents (left two-phase-micelles and crystal-containing-zone) was assessed during 21 days by microscopy and chemical measurement of crystal mass. For model biles with higher phospholipid contents (central three-phase-micelles, vesicles and crystal-containing-zone), lipid distribution into various phases was determined by combined ultracentrifugation-filtration-dialysis methodology (Biochim. Biophys. Acta 1532 (2001) 15-27).

RESULTS

In the left two-phase zone, crystal numbers and masses were highest in case of more hydrophilic bile salt composition (TUDC 100%>TC/TUDC 70%/30%>TC 100%>TC/TDC 70%/30%>TDC 100%) and decreased with increasing phospholipid contents, lower TLCo and lower cholesterol saturation index (CSI). In contrast, in the presence of vesicles (three-phase zone), crystallization decreased at increasing bile salt hydrophilicity, with concomitant increased vesicular cholesterol solubilization.

CONCLUSIONS

Presence of vesicular phases is a prerequisite for inhibition of cholesterol crystallization by tauroursodeoxycholate.

Comparative cytotoxic and cytoprotective effects of taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA) in HepG2 cell line

This study was performed to compare the effects of two hydrophilic bile acids, taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA), on HepG2 cells. Cytotoxicity was evaluated at different times of exposure by incubating cells with increasing concentrations (50-800 micromol/l) of either bile acid, while their cytoprotective effect was tested in comparison with deoxycholic acid (DCA) (350 micromol/l and 750 micromol/l)-induced cytotoxicity. Culture media, harvested at the end of each incubation period, were analyzed to evaluate aspartate transaminase (AST), alanine transaminase and gamma-glutamyltranspeptidase release. In addition, the hemolytic effect of THDCA and TUDCA on human red blood cells was also determined. At 24 h of incubation neither THDCA nor TUDCA was cytotoxic at concentrations up to 200 and 400 micromol/l. At 800 micromol/l both THDCA and TUDCA induced a slight increase in AST release. At this concentration and with time of exposure prolonged up to 72 h, THDCA and TUDCA induced a progressive increase of AST release significantly (P<0.05) higher than that of controls being AST values for THDCA (2.97+/-0.88 time control value (tcv) at 48 h and 4.50+/-1.13 tcv at 72 h) significantly greater than those of TUDCA (1.50+/-0.20 tcv at 48 h and 1.80+/-0.43 tcv at 72 h) (P<0.01). In cytoprotection experiments, the addition of 50 micromol/l THDCA decreased only slightly (-5%) AST release induced by 350 micromol/l DCA, while the addition of 50 micromol/l TUDCA was significantly effective (-23%; P<0.05). Higher doses of THDCA or TUDCA did not reduce toxicity induced by 350 micromol/l DCA, but were much less toxic than an equimolar dose of DCA alone. At the concentration used in this experimental model neither THDCA nor TUDCA was hemolytic; however at a very high concentration (6 mmol/l) both bile acids induced 5-8% hemolysis. We conclude that bile acid molecules with a similar degree of hydrophilicity may show different cytotoxic and cytoprotective properties.

Hydrophilic bile salts enhance differential distribution of sphingomyelin and phosphatidylcholine between micellar and vesicular phases: potential implications for their effects in vivo

BACKGROUND/AIMS

The hepatocyte canalicular membrane outer leaflet contains both phosphatidylcholine (PC) and sphingomyelin (SM). Normally, PC is the exclusive phospholipid in bile. We examined effects of bile salt hydrophobicity on cytotoxicity and on differential SM and PC distribution between detergent-resistant aggregated vesicles (model for detergent-resistant canalicular membrane) and mixed micelles or small unilamellar vesicles (representing lipid phases in bile).

METHODS

Aggregated vesicles were obtained by ultracentrifugation of cholesterol-supersaturated model systems containing SM, PC and various bile salts, micelles by ultrafiltration and unilamellar vesicles by dialysis of the supernatant. Erythrocyte hemolysis and lactate dehydrogenase release from CaCo-2 cells upon incubation with various micelles were quantified.

RESULTS

Preferential SM distribution and lipid solubilization in aggregated vesicles increased in rank order taurodeoxycholate < taurocholate < tauroursodeoxycholate < taurohyodeoxycholate, with reciprocal PC enrichment in micelles and small unilamellar vesicles. Including small amounts of PC within taurohyodeoxycholate micelles increased cytotoxicity with more erythrocyte hemolysis and LDH release from CaCo-2 cells upon incubation, but decreased cytotoxicity in case of tauroursodeoxycholate micelles.

CONCLUSIONS

Hydrophilic but not hydrophobic bile salts preserve integrity of pathophysiologically relevant phosphatidylcholine plus sphingomyelin-containing bilayers. Enhanced biliary phospholipid secretion during taurohyodeoxycholate but not during tauroursodeoxycholate therapy (Hepatology 25 (1997) 1306) may relate to different interactions of these bile salts with phospholipids.

Taurohyodeoxycholic acid protects against taurochenodeoxycholic acid-induced cholestasis in the rat

The prevention of the hepatotoxic effects produced by intravenous infusion of taurochenodeoxycholic acid (TCDCA) by coinfusion with taurohyodeoxycholic acid (THDCA) was evaluated in bile fistula rats; the hepatoprotective effects of the latter were also compared with those of tauroursodeoxycholic acid (TUDCA). Rats infused with TCDCA at a dose of 8 micromol/min/kg showed reduced bile flow and calcium secretion, as well as increased biliary release of alkaline phosphatase (AP) and lactate dehydrogenase (LDH). This was associated with a very low biliary secretion rate of TCDCA (approximately 1 micromol/min/kg). Simultaneous infusion of THDCA or TUDCA at the same dose preserved bile flow and almost totally abolished the pathological leakage of the two enzymes into bile. The effect was slightly more potent for THDCA. The maximum secretion rate of TCDCA increased to the highest value (8 micromol/min/kg) when coinfused with either of the two hepatoprotective bile acids (BA), which were efficiently and completely secreted in the bile, without metabolism. Calcium output was also restored and phospholipid (PL) secretion increased with respect to the control saline infusion. This increase was higher in the THDCA study. These data show that THDCA is highly effective in the prevention of hepatotoxicity induced by intravenous infusion of TCDCA by facilitating its biliary secretion and reducing its hepatic residence time; this was associated with selective stimulation of PL biliary secretion.

Dissolution of human cholesterol gallstones in bile salt/lecithin mixtures: effect of bile salt hydrophobicity and various pHs

BACKGROUND

Unconjugated bile salts currently available for gallstone dissolution are poorly effective. We evaluated in vitro the litholytic potency of taurine-amidated bile salts against human cholesterol gallstones.

METHODS

Seventy radiolucent gallstones with similar size and composition (cholesterol content, 70.1 +/- 0.9%) from a single patient were incubated in model biles composed of 100 mM of either taurochenodeoxycholate (TCDC), taurocholate (TC), taurohyodeoxycholate (THDC) or tauroursodeoxycholate (TUDC) and of 45 mM egg yolk lecithin in saline buffered with tris/HCl (at pHs 7 and 8) or phosphate (at pHs 4 and 6). Biles (total lipids, 10 g/dl; cholesterol saturation, 99%) were incubated at 37 degrees C for 40 days. Gallstones were periodically weighed and returned to the dissolution vials, and the biliary cholesterol concentration was monitored.

RESULTS

Model biles remained optically clear during the initial 48 h of incubation. Then, biles containing THDC and TUDC, but not those with TC and TCDC, became progressively turbid until, after several days, a white precipitate surrounded the residual stone. Abundant liquid crytalline droplets were observed at polarizing microscopy in biles containing TUDC and THDC. Gallstone dissolution was closely related to cholesterol solubilization and decreased in the order TCDC > THDC > or = TC > TUDC, being highest at pH 8. At the physiologic pH of 7 THDC was more litholythic than TC.

CONCLUSIONS

In vitro, the litholytic potency of bile salts on cholesterol gallstones primarily depends on their hydrophobicity. THDC is a new potential gallstone-dissolving agent, deserving in vivo studies.