Ileal Bile Acid Absorption Research Articles

Activation of Nrf2 decreases bile acid concentrations in livers of female mice

1. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of oxidative/electrophilic stress. Studies suggest a role of Nrf2 in regulating bile acid (BA) metabolism in male mice. However, whether Nrf2 is important for BA homeostasis in female mice remains undefined. In this study, we systematically investigated the effect of Nrf2 activation, either through CDDO-imidazolide (CDDO-Im) treatment or genetic modulation of Kelch-like ECH associating protein 1 (Keap1), on BA homeostasis in female mice. 2. Both pharmacological and genetic Nrf2 activation increased mRNA levels of multidrug resistance‐associated protein 2 and 3 (Mrp2 and Mrp3), two Nrf2 target genes, in livers and ilea of female mice. Both pharmacological and genetic activation of Nrf2 decreased BA concentrations in the liver, which did not appear to be due to increased biliary BA excretion or decreased ileal BA absorption. Importantly, both pharmacological and genetic activation of Nrf2 downregulated hepatic Cyp7a1 mRNA, which might be attributable to the upregulation of the Fxr-Fgf15 signalling in the ileum. 3. To conclude, Nrf2 activation lowers BA concentrations in livers of female mice, which appears to be attributable to the decreased hepatic BA synthesis.

Elobixibat, the first-in-class Ileal Bile Acid Transporter inhibitor, for the treatment of Chronic Idiopathic Constipation

ABSTRACTIntroduction: Elobixibat is the first in class ileal bile acid transporter (IBAT) inhibitor. IBAT inhibitors block ileal absorption of bile acids by: (1) interrupting the enterohepatic circulation of bile resulting in a fall in serum cholesterol and (2) increasing the delivery of bile acids into the colon. Increasing colonic bile acids causes mucosal fluid secretion and enhances colonic motor activity. Changes in colonic physiology may be useful in treating constipation.Areas covered: In this review, the author reviews the prevalence and medical cost of Chronic Idiopathic Constipation (CIC) and the heterogeneity of the CIC patient population as a complicating factor in drug development and clinical care. He also reviews the history of Bile Acid cathartics and the complex pharmacophysiology of bile therapy with fluid and electrolyte shifts, colonic motor function changes and mucosal immunologic activation. Finally, the author reviews elobixabat development and the clinical trials that demonstrate improvement in constipation.Expert opinion: The early phases of elobixibat development provide confirmation of high IBAT binding affinity which translates into the expected inhibition of enterohepatic bile acid circulation and enhanced delivery of ileal bile acids to the colon associated with expected physiological changes. Elobixibat as a treatment of CIC appears promising.

A Novel Agent for Pruritus in Primary Biliary Cholangitis

In cholestatic liver disease such as primary biliary cholangitis (PBC), ileal bile acid absorption is increased and might lead to pruritus. Therefore,

Microbiota Modification with Probiotics Induces Hepatic Bile Acid Synthesis via Downregulation of the Fxr-Fgf15 Axis in Mice

Gut microbiota influences host health status by providing trophic, protective, and metabolic functions, including bile acid (BA) biotransformation. Microbial imprinting on BA signature modifies pool size and hydrophobicity, thus contributing to BA enterohepatic circulation. Microbiota-targeted therapies are now emerging as effective strategies for preventing and/or treating gut-related diseases. Here, we show that gut microbiota modulation induced by VSL#3 probiotics enhances BA deconjugation and fecal excretion in mice. These events are associated with changes in ileal BA absorption, repression of the enterohepatic farnesoid X receptor-fibroblast growth factor 15 (FXR-FGF15) axis, and increased hepatic BA neosynthesis. Treatment with a FXR agonist normalized fecal BA levels in probiotic-administered mice, whereas probiotic-induced alterations in BA metabolism are abolished upon FXR and FGF15 deficiency. Our data provide clear in vivo evidence that VSL#3 probiotics promote ileal BA deconjugation with subsequent fecal BA excretion and induce hepatic BA neosynthesis via downregulation of the gut-liver FXR-FGF15 axis.

Intestine-Specific Deletion of SIRT1 in Mice Impairs DCoH2–HNF-1α–FXR Signaling and Alters Systemic Bile Acid Homeostasis

Sirtuin 1 (SIRT1), the most conserved mammalian oxidized nicotinamide adenine dinucleotide-dependent protein deacetylase, is an important metabolic sensor in many tissues. However, little is known about its role in the small intestine, which absorbs and senses nutrients. We investigated the functions of intestinal SIRT1 in systemic bile acid and cholesterol metabolism in mice. SIRT1 was specifically deleted from the intestines of mice using the flox-Villin-Cre system (SIRT1 iKO mice). Intestinal and hepatic tissues were collected, and bile acid absorption was analyzed using the everted gut sac experiment. Systemic bile acid metabolism was studied in SIRT1 iKO and flox control mice placed on standard diets, diets containing 0.5% cholic acid or 1.25% cholesterol, or lithogenic diets. SIRT1 iKO mice had reduced intestinal farnesoid X receptor (FXR) signaling via hepatocyte nuclear factor 1α (HNF-1α) compared with controls, which reduced expression of the bile acid transporter genes Asbt and Mcf2l (encodes Ost) and absorption of ileal bile acids. SIRT1 regulated HNF-1α/FXR signaling partially through dimerization cofactor of HNF-1a (Dcoh2) Dcoh2, which increases dimerization of HNF-1α. SIRT1 was found to deacetylate Dcoh2, promoting its interaction with HNF-1α and inducing DNA binding by HNF-1α. Intestine-specific deletion of SIRT1 increased hepatic bile acid biosynthesis, reduced hepatic accumulation of bile acids, and protected animals from liver damage from a diet high in levels of bile acids. Intestinal SIRT1, a key nutrient sensor, is required for ileal bile acid absorption and systemic bile acid homeostasis in mice. We delineated the mechanism of metabolic regulation of HNF-1α/FXR signaling. Reagents designed to inhibit intestinal SIRT1 might be developed to treat bile acid-related diseases such as cholestasis.

Administration of ampicillin increases ileal Asbt protein amounts resulting in reduction of fecal bile acid excretion in mice

Administration of the antibacterial drug ampicillin (ABPC) significantly decreased fecal bile acid excretion although it increased hepatic cholesterol 7α‐hydroxylation as well as CYP7A1 mRNA level. In the present study, we have investigated the mechanisms for the reduction of fecal bile acid excretion in ABPC‐treated mice. Bile acid amounts in small intestinal lumen and portal blood concentrations of bile acids were increased 1.6‐fold and 2.0‐fold, respectively, in ABPC‐treated mice. Ileal apical sodium‐dependent bile salt transporter (Asbt) mRNA levels were significantly increased in ABPC‐treated mice whereas ileal bile acid binding protein and organic solute transporter alpha and beta mRNA levels were reduced. Ileal Asbt protein amounts in brush border membranes were increased 2.5‐fold in ABPC‐treated mice. These results suggest that enhancement of ileal Asbt‐mediated bile acid absorption contributes to the reduction of fecal bile acid excretion in ABPC‐treated mice.

1α,25‐dihydroxyvitamin D3 triggered vitamin D receptor and farnesoid X receptor‐like effects in rat intestine and liver in vivo

1alpha,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), a natural ligand of the vitamin D receptor (VDR), was found to increase the rat ileal Asbt and bile acid absorption. The effects of VDR, whose expression is low in liver, on hepatic transporters and enzymes are unknown. Protein and mRNA levels of target genes in the small intestine, colon and liver after intraperitoneal dosing of 1,25(OH)(2)D(3) (0-2.56 nmol/kg/day for 4 days) to the rat were determined by Western blotting and qPCR, respectively. The 1,25(OH)(2)D(3) treatment increased total Cyp3a protein and Cyp3a1 mRNA expressions in the proximal small intestine, and the short heterodimer partner (SHP), the fibroblast growth factor 15 (FGF15), organic solute transporter (Ostalpha and Ostbeta) mRNA and Asbt protein expressions in the ileum. About 50% higher portal bile acid concentration (65.1+/-14.9 vs 41.9+/-7.8 microm, p<0.05) and elevated expressions of the hepatic farnesoid X receptor (FXR) and SHP mRNA resulted with 1,25(OH)(2)D(3) treatment. Increased Bsep and Ostalpha mRNA expressions in liver and a>50% reduction in the Cyp7a1 protein level (p<0.05) and cholesterol metabolism in rat liver microsomes (p=0.002), likely consequences of the bile acid-FXR-SHP cascade and activation of the signaling pathway for Cyp7a1 inhibition by FGF15, were found. Increased hepatic multidrug resistance-associated protein (Mrp3) and multidrug resistance protein 1a (Mdr1a) mRNA and P-gp protein were also observed. It was concluded that the changes in hepatic transporters and enzymes in the rat were indirect, secondary effects of the liver FXR-SHP cascade due to increased intestinal absorption of bile acids and elevated levels of FGF15, events that led to the activation of FXR.

Cholesterol Feeding Prevents Hepatic Accumulation of Bile Acids in Cholic Acid-Fed Farnesoid X Receptor (FXR)-Null Mice: FXR-Independent Suppression of Intestinal Bile Acid Absorption

Cholic acid (CA) feeding of farnesoid X receptor (Fxr)-null mice results in markedly elevated hepatic bile acid levels and liver injury. In contrast, Fxr-null mice fed cholesterol plus CA (CA+Chol) do not exhibit liver injury, and hepatic bile acid levels and bile acid pool size are reduced 51 and 40%, respectively, compared with CA-treated Fxr-null mice. These decreases were not observed in wild-type mice. Despite a reduced bile acid pool size, hepatic Cyp7a1 mRNA expression was increased in Fxr-null mice fed the CA+Chol diet, and biliary bile acid output was not changed. Analysis of other potential protective mechanisms revealed significant decreases in portal blood bile acid concentrations and a reduced ileal bile acid absorption capacity, as estimated using an in situ loop method. Fecal bile acid excretion was also increased in Fxr-null mice fed the CA+Chol versus CA diet. The decreased ileal bile acid absorption correlated with decreased ileal apical sodium-dependent bile salt transporter (ASBT) protein expression in brush-border membranes. These results suggest a critical role for ileal bile acid absorption in regulation of hepatic bile acid levels in Fxr-null mice fed CA+Chol. Furthermore, experiments with Fxr-null mice suggest that cholesterol feeding can down-regulate ASBT expression through a pathway independent of FXR.

Inhibitory effects of choleretic hydroxyacetophenones on ileal bile acid transport in rats

The effects of the choleretic and cholesterol lowering compound, 2,4,6-trihydroxyacetophenone (THA) and its analog, 2,6-dihydroxyacetophenone (DHA), on ileal bile acid absorption were investigated in rats. THA inhibited taurocholate (TC) uptake into ileal brush-border membrane vesicles (BBMV), showing a maximum inhibition of 50%, whereas DHA completely inhibited TC uptake into ileal BBMV. THA exhibited competitive inhibition with a K i of 9.88 mM, while DHA showed non-competitive inhibition with a K i of 7.65 mM. Both total and ouabain-sensitive basolateral membrane (BLM) Na +–K +–ATPase activities, which are essential for maintenance of the Na +-gradient for bile acid transport, were inhibited by THA and DHA in a dose-dependent manner. The inhibition of BLM ATPase was uncompetitive with a K i of 10.1 and 5.0 mM for THA and DHA, respectively. Administration of THA or DHA (400 μmol/kg) twice a day, to hypercholesterolemic rats for 3 weeks caused similar and marked reductions in plasma cholesterol to 60% of the cholesterol-fed controls. The data suggest that the inhibitory actions of THA and DHA on two essential components of ileal bile acid recycling to liver could, in part, contribute to the cholesterol lowering effect of the hydroxyacetophenone compounds. These effects on decreasing bile acid recycling, in combination with their potent choleretic effect, accelerating biliary excretion of bile acids, are responsible for the effective cholesterol lowering capacities of these compounds.

Steroids in the management of PBC: Why do we need them?

Steroids in the management of PBC: Why do we need them?

Inhibition of ileal bile acid transport lowers plasma cholesterol levels by inactivating hepatic farnesoid X receptor and stimulating cholesterol 7α-hydroxylase

We investigated the effect of SC-435, a competitive inhibitor of ileal apical sodium-dependent bile acid cotransporter (ASBT) on ileal bile acid absorption and the hepatic nuclear receptor FXR (farnesoid X receptor), which regulates cholesterol 7α-hydroxylase (CYP7A1) activity and mRNA levels. Eighteen New Zealand White (NZW) rabbits were divided into 2 groups: controls (n = 10) and fed SC-435 125 mg/kg/d for 1 week (n = 8). In rabbits treated with SC-435, fecal bile acid outputs increased by more than 8 times, reflecting substantial bile acid malabsorption. Plasma cholesterol levels decreased 26%, while bile acid pool sizes and biliary bile acid outputs did not change after treatment. CYP7A1 activity increased 64% and mRNA rose by 4 times after treatment. The expression of FXR target genes in the liver, short heterodimer partner (SHP) and bile salt export pump (BSEP), decreased 11.6 and 2.6 times, respectively, after treatment, which indicates inactivation of hepatic FXR. However, the mRNA levels of ileal bile acid binding protein (IBABP) did not change significantly, while ileal ASBT mRNA expression increased by 2.4 times after treatment. Rabbits treated with SC-435 developed ileal bile acid malabsorption, which decreased the return of bile acids (FXR ligands) to the liver to inactivate hepatic FXR, which upregulated CYP7A1 and lowered plasma cholesterol levels. Although fecal bile acid malabsorption was substantial, increased bile acid production from hepatic cholesterol kept biliary bile acid outputs intact. Thus, a new balance was reached in the liver, where increased bile acid synthesis compensated for diminished ileal bile acid absorption to maintain the circulating enterohepatic bile acid pool.

Analysis of the Ileal Bile Acid Transporter Gene, SLC10A2 , in Subjects With Familial Hypertriglyceridemia

Familial hypertriglyceridemia (FHTG), a disease characterized by elevated plasma very low density lipoprotein triglyceride levels, has been associated with impaired intestinal absorption of bile acids. The aim of this study was to test the hypothesis that defects in the active ileal absorption of bile acids are a primary cause of FHTG. Single-stranded conformation polymorphism analysis was used to screen the ileal Na(+)/bile acid cotransporter gene (SLC10A2) for FHTG-associated mutations. Analysis of 20 hypertriglyceridemic patients with abnormal bile acid metabolism revealed 3 missense mutations (V98I, V159I, and A171S), a frame-shift mutation (646insG) at codon 216, and 4 polymorphisms in the 5' flanking sequence of SLC10A2. The SLC10A2 missense mutations and 5' flanking sequence polymorphisms were not correlated with bile acid production or turnover in the hypertriglyceridemic patients and were equally prevalent in the unaffected control subjects. In transfected COS cells, the V98I, V159I, and A171S isoforms all transported bile acids similar to the wild-type SLC10A2. The 646insG frame-shift mutation abolished bile acid transport activity in transfected COS cells but was found in only a single FHTG patient. These findings indicate that the decreased intestinal bile acid absorption in FHTG patients is not commonly associated with inherited defects in SLC10A2.

Ileal mucosal bile acid absorption is increased in Cftr knockout mice

Ileal mucosal bile acid absorption is increased in Cftr knockout mice

Ontogenic regulation of components of ileal bile acid absorption.

The apical sodium-dependent bile acid cotransporter (ASBT) and the ileal bile acid binding protein (IBABP) are two components of ileal bile acid absorption. During the third postnatal week of the rat, there is a dramatic increase in ASBT and IBABP expression. The goals of this study were to examine the role of hormones on the ontogenic expression of ASBT mRNA and the role of weaning for both ASBT and IBABP mRNA. Administration of various doses of dexamethasone during the second postnatal week induced ASBT mRNA levels, and this effect was significantly increased with concomitant thyroxine treatment. Early weaning and weaning prevention were utilized to investigate the influence of dietary factors. ASBT and IBABP mRNA levels were significantly elevated by early weaning and were decreased by weaning prevention compared with littermate controls. Thus, glucocorticoids and thyroxine appear to play a role in the ontogenic expression of ASBT mRNA and weaning appears to participate in both ASBT and IBABP expression.

Downregulation of ileal bile acid absorption in bile-duct-ligated rats

Background/Aims: Accumulation of toxic bile acids in cholestasis contributes to liver injury and depends on their synthesis, secretion and intestinal absorption. In the present study, we investigated the effect of cholestasis on the active ileal absorption of bile acids in vivo and the adaptation of transporters involved in ileal bile acid absorption. Methods: Male Wistar rats underwent ligation of the common bile duct or biliary diversion. Sham-operated rats served as controls. Active ileal bile acid absorption of taurocholate was measured by an intestinal perfusion technique. Transporter mRNA levels of the Na +/bile acid cotransporting protein (IBAT), ileal lipid binding protein (ILBP) and organic anion transporter subtype 3 (Oatp3) and protein expression of IBAT and ILBP were determined in the distal ileum. Results: After bile duct ligation the intestinal absorption rates of taurocholate were lower ( p<0.05) and after biliary diversion absorption rates were higher compared to sham-operated animals ( p<0.05). The absorption rates were inversely correlated to serum bile acid concentrations. Levels of IBAT-, ILBP- and Oatp3- mRNA were not different between the groups. However, in cholestatic rats, the expression of the 99-kDa dimer of IBAT was decreased compared to controls ( p<0.05), whereas the 46-kDa monomeric protein of IBAT and the expression of ILBP was unchanged. After biliary diversion a similar pattern of protein expression was observed, despite an increased absorption rate. Conclusions: Cholestasis leads to a decreased active ileal absorption of taurocholate. The changes in protein expression may not account for the different absorption rates. The intestinal absorption of bile acids seems to be regulated by their systemic concentration.

Effect of cholestasis on ileal absorption of bile acids and on ileal bile acid transporter in rat

Effect of cholestasis on ileal absorption of bile acids and on ileal bile acid transporter in rat

Inhibition of ileal bile acid transport by cyclosporin A in rat

Chronic administration of cyclosporin A may induce cholestasis and this effect has been attributed to impaired hepatic bile salt synthesis, metabolism and transport. We investigated the effect of cyclosporin A on intestinal absorption of bile acids in the ileum of rat. Ileal bile acid absorption was measured by in vivo intestinal perfusion with cyclosporin A and the solvent Cremophor EL. During ileal perfusion with 25 microM glycocholic acid, the concentration of 2.8 mM cyclosporin A inhibited intestinal bile acid absorption on average by 34%. Additional experiments were performed with everted gut sacs of the distal ileum to evaluate active absorption. A dose and time dependent inhibition of the active intestinal absorption of bile acids was found, with a 50% transport inhibition at an average cyclosporin A concentration of 2.69 mmol L-1. Thus, cyclosporin A inhibits the active intestinal absorption of bile acids which may influence bile acid synthesis, turnover and secretion and may contribute to cyclosporin A induced cholestasis.

Effects of 2164U90 on ileal bile acid absorption and serum cholesterol in rats and mice.

2164U90, [(3R,5R)-trans-3-butyl-3-ethyl-2,3,4,5-tetrahydro-5-phenyl-1,4- benzothiazepine 1,1-dioxide], was found to be a potent inhibitor of the ileal bile acid active transport system. In vitro, 2164U90 decreased uptake and active transport of taurocholic acid by rat everted ileal sacs with IC50s of 4.0 microM and 1.5 microM, respectively. In vivo, 2164U90 produced dose-dependent increases in 23,25-75Se-labeled homocholic acid taurine (SeHCAT) fecal excretion in rats and mice at doses of 3-30 mg/kg and 1-10 mg/kg, respectively. In rats, 30 mg/kg 2164U90 was equivalent to 500 mg/kg cholestyramine. Two days oral administration of 10 mg/kg 2164U90 to rats decreased the bile concentrations of total bile acids 42%, orally administered [3H]taurocholic acid ([3H]TC) 82%, and cholesterol 35%. Cholestyramine (500 mg/kg) had effects similar to 2164U90 on total bile acid and orally administered [3H]TC concentrations but had no effect on biliary cholesterol. The hypocholesterolemic activity of 2164U90 was determined in cholesterol-cholic acid-fed rats and cholesterol-cholic acid-coconut oil-fed mice. 2164U90 inhibited the dietary-induced increase in dextran sulfate-precipitable lipoprotein cholesterol (VLDL+LDL) at doses comparable to doses needed to increase the fecal excretion of bile acids. These data indicate that 2164U90 decreases bile acid absorption by inhibiting the ileal bile acid active transport system, resulting in hypocholesterolemic activity.

Intestinal bile acid malabsorption in cystic fibrosis.

This study aimed at examining the mechanisms participating in excessive faecal bile acid loss in cystic fibrosis. The study was designed to define the relation between faecal fat and faecal bile acid loss in patients with and without cystic fibrosis related liver disease; to assess terminal ileal bile acid absorption by a seven day whole body retention of selenium labelled homotaurocholic acid (SeHCAT); and to determine if small intestinal bacterial overgrowth contributes to faecal bile acid loss. The study population comprised 40 patients (27 men; median age 18 years) with cystic fibrosis (n = 8) and without (n = 32) liver disease and eight control subjects. Faecal bile acid excretion was significantly higher in cystic fibrosis patients without liver disease compared with control subjects (mean (SEM) 21.5 (2.4) and 7.3 (1.2) micromoles/kg/24 hours respectively; p < 0.01) and patients with liver disease (7.9 (1.3) micromoles/kg/24 hours; p < 0.01). No correlation was found between faecal fat (g fat/24 hours) and faecal bile acid (micromoles 24 hours) excretion. Eight (33%) of cystic fibrosis patients had seven day SeHCAT retention < 10% (normal retention > 20%). SeHCAT retention in cystic fibrosis patients with liver disease was comparable with control subjects (30.0 (SEM) 8.3% v 36.8 (5.9)%; p = NS) while SeHCAT retention in cystic fibrosis patients who did not have liver disease was significantly reduced (19.9 (3.8); p < 0.05). Although evidence of small bowel bacterial overgrowth was present in 40% of patients no relation was found between breath hydrogen excretion, faecal fat, and faecal bile acid loss. The results are consistent with the presence of an abnormality in terminal ideal function in patients with cystic fibrosis who do not have liver disease and that a defect in the ileal absorption of bile acids may be a contributory factor to excessive faecal bile acid loss. Faecal bile acid loss in cystic fibrosis is unrelated to the presence of intraluminal fat or intestinal bacterial overgrowth.

Reduced Ileal Taurocholate Absorption with Total Parenteral Nutrition

Total parenteral nutrition is associated with decreased primary bile acid output. This may result from reduced synthesis or decreased absorption of primary bile acids in the enterohepatic circulation. Ileal atrophy occurs with total parenteral nutrition, and we postulated that absorption of primary bile acids is reduced. Ileal absorption of taurocholate was investigated in miniswine on total parenteral nutrition and this was compared to orally fed animals. Following cholecystectomy and bile duct cannulation, 20 cm, of lieum was perfused with taurocholate. Since miniswine have no significant endogenous taurocholate secretion, the measured taurocholate output reflected ileal absorption. To examine uptake and secretion of taurocholate by the liver, pigs on total parenteral nutrition and controls were infused with intravenous taurocholate (0.5 to 2.5 μmole/kg/min), and bile acid output was determined. Baseline bile acid output was decreased in animals on total parenteral nutrition, yet the response to intravenous taurocholate was similar to controls. When taurocholate was perfused in the ileum, taurocholate output was markedly different. Taurocholate output (pmole/cm ileum/min) at the taurocholate perfusate concentrations of 3 and 20 mM was, respectively, 65 ± 14 and 183 ± 63 for controls and 18 ± 3 and 63 ± 17 for miniswine on total parenteral nutrition. The latter group's output was significantly lower, at P < 0.05. Both groups of pigs had equal increases in bile acid output with intravenous infusion of taurocholate, suggesting normal hepatic uptake and secretion. Ileal perfusion with taurocholate, however, resulted in decreased taurocholate output with total parenteral nutrition due to decreased ileal absorption of bile acids. This may contribute to the reduction in primary bile acid secretion that occurs with total parenteral nutrition.